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Sample records for tensile crack tips

  1. Neutron diffraction studies on lattice strain evolution around a crack-tip during tensile loading and unloading cycles

    Energy Technology Data Exchange (ETDEWEB)

    Sun Yinan [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States)]. E-mail: ysun1@utk.edu; Choo, Hahn [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Liaw, Peter K. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Lu Yulin [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Yang Bing [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Brown, Donald W. [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Bourke, Mark A.M. [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2005-10-15

    Elastic lattice-strain profiles ahead of a fatigue-crack-tip were measured during tensile loading and unloading cycles using neutron diffraction. The crack-closure phenomenon after an overload was observed. Furthermore, the plastic-zone size in front of the crack-tip was estimated from the diffraction-peak broadening, which showed good agreement with the calculated result.

  2. On fatigue crack growth in ductile materials by crack-tip blunting

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

    One of the basic mechanisms for fatigue crack growth in ductile metals is that depending on crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading. In a standard numerical analysis accounting for finite strains it is not possible to follow this process during...

  3. A study on fatigue crack growth behavior subjected to a single tensile overload

    International Nuclear Information System (INIS)

    Lee, S.Y.; Liaw, P.K.; Choo, H.; Rogge, R.B.

    2011-01-01

    Neutron diffraction and electric potential experiments were carried out to investigate the growth behavior of a fatigue crack subjected to a single tensile overload. The specific objectives were to (i) probe the crack tip deformation and fracture behaviors under applied loads; (ii) examine the overload-induced transient crack growth micromechanism; (iii) validate the effective stress intensity factor range based on the crack closure approach as the fatigue crack tip driving force; and (iv) establish a quantitative relationship between the crack tip driving force and crack growth behavior. Immediately after a single tensile overload was introduced and then unloaded, the crack tip became blunt and enlarged compressive residual stresses in both magnitude and zone size were observed around the crack tip. The results show that the combined contributions of the overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are responsible for the observed changes in the crack opening load and the resultant post-overload transient crack growth behavior.

  4. The effect of a single tensile overload on stress corrosion cracking growth of stainless steel in a light water reactor environment

    International Nuclear Information System (INIS)

    Xue He; Li Zhijun; Lu Zhanpeng; Shoji, Tetsuo

    2011-01-01

    Research highlights: → The affect of a single tensile overload on SCC growth rate is investigated. → A single tensile overload would produce a residual plastic strain in the SCC tip. → The residual plastic strain would decrease the plastic strain rate in the SCC tip. → A single tensile overload would cause crack growth rate retardation in the SCC tip. → SCC growth rate in the quasi-stationary crack tip is relatively lower. - Abstract: It has been found that a single tensile overload applied during constant load amplitude might cause crack growth rate retardation in various crack propagating experiments which include fatigue test and stress corrosion cracking (SCC) test. To understand the affecting mechanism of a single tensile overload on SCC growth rate of stainless steel or nickel base alloy in light water reactor environment, based on elastic-plastic finite element method (EPFEM), the residual plastic strain in both tips of stationary and growing crack of contoured double cantilever beam (CDCB) specimen was simulated and analyzed in this study. The results of this investigation demonstrate that a residual plastic strain in the region immediately ahead of the crack tips will be produced when a single tensile overload is applied, and the residual plastic strain will decrease the plastic strain rate level in the growing crack tip, which will causes crack growth rate retardation in the tip of SCC.

  5. Improved method for determining the stress relaxation at the crack tip

    Science.gov (United States)

    Grinevich, A. V.; Erasov, V. S.; Avtaev, V. V.

    2017-10-01

    A technique is suggested to determine the stress relaxation at the crack tip during tests of a specimen of a new type at a constant crack opening fixed by a stay bolt. The shape and geometry of the specimen make it possible to set the load and to determine the crack closure force after long-term exposure using the force transducer of a tensile-testing machine. The stress relaxation at the crack tip is determined in a V95pchT2 alloy specimen at elevated temperatures.

  6. Effect of tensile overloads on fatigue crack growth of high strength steel wires

    International Nuclear Information System (INIS)

    Haag, J.; Reguly, A.; Strohaecker, T.R.

    2013-01-01

    Highlights: • A proof load process may be an option to increase the fatigue life of flexible pipelines. • There is possibility to produce plastic deformation at crack tip of tensile armor wires. • Controlled overloads provide effective crack growth retardation. • Crack growth retardation is also evident at higher stress ratios. - Abstract: Fatigue of the tensile armor wires is the main failure mode of flexible risers. Techniques to increase the life of these components are required to improve the processes safety on oil exploration. This work evaluates the crack growth retardation of high strength steel wires used in flexible pipelines. Fracture toughness tests were performed to establish the level of stress intensity factor wherein the wires present significant plastic deformation at the crack tip. The effect of tensile overload on fatigue behavior was assessed by fatigue crack growth testing under constant ΔK control and different overload ratios with two different load ratios. The outcomes show that the application of controlled overloads provides crack retardation and increases the fatigue life of the wires more than 31%. This behavior is also evident at stress ratio of 0.5, in spite of the crack closure effect being minimized by increasing the applied mean stress

  7. Tensile cracks in creeping solids

    International Nuclear Information System (INIS)

    Riedel, H.; Rice, J.R.

    1979-02-01

    The loading parameter determining the stress and strain fields near a crack tip, and thereby the growth of the crack, under creep conditions is discussed. Relevant loading parameters considered are the stress intensity factor K/sub I/, the path-independent integral C*, and the net section stress sigma/sub net/. The material behavior is modelled as elastic-nonlinear viscous where the nonlinear term describes power law creep. At the time t = 0 load is applied to the cracked specimen, and in the first instant the stress distribution is elastic. Subsequently, creep deformation relaxes the initial stress concentration at the crack tip, and creep strains develop rapidly near the crack tip. These processes may be analytically described by self-similar solutions for short times t. Small scale yielding may be defined. In creep problems, this means that elastic strains dominate almost everywhere except in a small creep zone which grows around the crack tip. If crack growth ensues while the creep zone is still small compared with the crack length and the specimen size, the stress intensity factor governs crack growth behavior. If the calculated creep zone becomes larger than the specimen size, the stresses become finally time-independent and the elastic strain rates can be neglected. In this case, the stress field is the same as in the fully-plastic limit of power law hardening plasticity. The loading parameter which determines the near tip fields uniquely is then the path-independent integral C*.K/sub I/ and C* characterize opposite limiting cases. The case applied in a given situation is decided by comparing the creep zone size with the specimen size and the crack length. Besides several methods of estimating the creep zone size, a convenient expression for a characteristic time is derived, which characterizes the transition from small scale yielding to extensive creep of the whole specimen

  8. Stress induced martensite at the crack tip in NiTi alloys during fatigue loading

    Directory of Open Access Journals (Sweden)

    E. Sgambitterra

    2014-10-01

    Full Text Available Crack tip stress-induced phase transformation mechanisms in nickel-titanium alloys (NiTi were analyzed by Digital Image Correlation (DIC, under fatigue loads. In particular, Single Edge Crack (SEC specimens, obtained from a commercial pseudoelastic NiTi sheet, and an ad-hoc experimental setup were used, for direct measurements of the near crack tip displacement field by the DIC technique. Furthermore, a fitting procedure was developed to calculate the mode I Stress Intensity Factor (SIF, starting from the measured displacement field. Finally, cyclic tensile tests were performed at different operating temperature, in the range 298-338 K, and the evolution of the SIF was studied, which revealed a marked temperature dependence.

  9. Static Tensile and Transient Dynamic Response of Cracked Aluminum Plate Repaired with Composite Patch - Numerical Study

    Science.gov (United States)

    Khalili, S. M. R.; Shariyat, M.; Mokhtari, M.

    2014-06-01

    In this study, the central cracked aluminum plates repaired with two sided composite patches are investigated numerically for their response to static tensile and transient dynamic loadings. Contour integral method is used to define and evaluate the stress intensity factors at the crack tips. The reinforcement for the composite patches is carbon fibers. The effect of adhesive thickness and patch thickness and configuration in tensile loading case and pre-tension, pre-compression and crack length effect on the evolution of the mode I stress intensity factor (SIF) (KI) of the repaired structure under transient dynamic loading case are examined. The results indicated that KI of the central cracked plate is reduced by 1/10 to 1/2 as a result of the bonded composite patch repair in tensile loading case. The crack length and the pre-loads are more effective in repaired structure in transient dynamic loading case in which, the 100 N pre-compression reduces the maximum KI for about 40 %, and the 100 N pre-tension reduces the maximum KI after loading period, by about 196 %.

  10. Crack tip stress and strain

    International Nuclear Information System (INIS)

    Francois, D.

    1975-01-01

    The study of potential energy variations in a loaded elastic solid containing a crack leads to determination of the crack driving force G. Generalization of this concept to cases other than linear elasticity leads to definition of the integral J. In a linear solid, the crack tip stress field is characterized by a single parameter: the stress-intensity factor K. When the crack tip plastic zone size is confined to the elastic singularity J=G, it is possible to establish relationship between these parameters and plastic strain (and in particular the crack tip opening displacement delta). The stress increases because of the triaxiality effect. This overload rises with increasing strain hardening. When the plastic zone size expands, using certain hypotheses, delta can be calculated. The plastic strain intensity is exclusively dependent on parameter J [fr

  11. Continuum damage mechanics analysis of crack tip zone

    International Nuclear Information System (INIS)

    Yinchu, L.; Jianping, Z.

    1989-01-01

    The crack tip field and its intensity factor play an important role in fracture mechanics. Generally, the damage such as microcracks, microvoids etc. will initiate and grow in materials as the cracked body is subjected to external loadings, especially in the crack tip zone. The damage evolution will load to the crack tip damage field and the change of the stress, strain and displacement fields of cracks tip zone. In this paper, on the basis of continuum damage mechanics, the authors have derived the equations which the crack tip field and its intensity factor must satisfy in a loading process, calculated the angle distribution curves of stress, strain and displacement fields in a crack tip zone and have compared them with the corresponding curves of HRR field and linear elastic field in undamaged materials. The equations of crack tip field intensity factors have been solved and its solutions give the variation of the field intensity factors with the loading parameter

  12. Fatigue crack growth in 2024-T3 aluminum under tensile and transverse shear stresses

    Science.gov (United States)

    Viz, Mark J.; Zehnder, Alan T.

    1994-01-01

    The influence of transverse shear stresses on the fatigue crack growth rate in thin 2024-T3 aluminum alloy sheets is investigated experimentally. The tests are performed on double-edge cracked sheets in cyclic tensile and torsional loading. This loading generates crack tip stress intensity factors in the same ratio as the values computed for a crack lying along a lap joint in a pressurized aircraft fuselage. The relevant fracture mechanics of cracks in thin plates along with the details of the geometrically nonlinear finite element analyses used for the test specimen calibration are developed and discussed. Preliminary fatigue crack growth data correlated using the fully coupled stress intensity factor calibration are presented and compared with fatigue crack growth data from pure delta K(sub I)fatigue tests.

  13. Effects of plastic anisotropy on crack-tip behaviour

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Tvergaard, Viggo; Kuroda, Mitsutoshi

    2002-01-01

    For a crack in a homogeneous material the effect of plastic anisotropy on crack-tip blunting and on the near-tip stress and strain fields is analyzed numerically. The full finite strain analyses are carried out for plane strain under small scale yielding conditions, with purely symmetric mode I...... loading remote from the crack-tip. In cases where the principal axes of the anisotropy are inclined to the plane of the crack it is found that the plastic zones as well as the stress and strain fields just around the blunted tip of the crack become non-symmetric. In these cases the peak strain...... on the blunted tip occurs off the center line of the crack, thus indicating that the crack may want to grow in a different direction. When the anisotropic axes are parallel to the crack symmetry is retained, but the plastic zones and the near-tip fields still differ from those predicted by standard isotropic...

  14. Some aspects of forces and fields in atomic models of crack tips

    International Nuclear Information System (INIS)

    Hoagland, R.G.; Daw, M.S.; Hirth, J.P.

    1991-01-01

    This paper examines the stresses and displacement gradients in atomistic models of cracks based on an EAM potential devised for aluminum. Methods for computing these quantities are described. Results are presented for two models differing in terms of the orientations of the crack relative to the crystal, a [100](010) orientation that behaves in a brittle fashion and a [111](110) orientation which emits partial dislocations prior to extending. Both models display lattice trapping. The stresses in the brittle crack model are compared with the linear elastic prediction and found to be in remarkably good agreement to within distances of about one lattice parameter of the crack tip and at the free surface where contributions from sources other than strain energy (e.g., surface tension) influence the results. Similar results are observed for the ductile model until dislocation emission occurs. The largest stresses that develop just prior to crack extension or dislocation emission are used to estimate the ratio of theoretical tensile strength to shear strength in this material. Eshelby's conservation integrals, F and M, are also computed. F is found to be essentially contour independent and in agreement with the linear elastic prediction in both models until dislocation emission occurs, at which point a large screening contribution arises from the emitted partials. The contour size dependence of M reveals some interesting features of the crack tip including a slight wobble of the crack tip inside its potential well with changing applied K and the existence of forces acting to move the crack faces apart as blunting occurs

  15. Ductile crack growth simulation from near crack tip dissipated energy

    International Nuclear Information System (INIS)

    Marie, S.; Chapuliot, S.

    2000-01-01

    A method to calculate ductile tearing in both small scale fracture mechanics specimens and cracked components is presented. This method is based on an estimation of the dissipated energy calculated near the crack tip. Firstly, the method is presented. It is shown that a characteristic parameter G fr can be obtained, relevant to the dissipated energy in the fracture process. The application of the method to the calculation of side grooved crack tip (CT) specimens of different sizes is examined. The value of G fr is identified by comparing the calculated and experimental load line displacement versus crack extension curve for the smallest CT specimen. With this identified value, it is possible to calculate the global behaviour of the largest specimen. The method is then applied to the calculation of a pipe containing a through-wall thickness crack subjected to a bending moment. This pipe is made of the same material as the CT specimens. It is shown that it is possible to simulate the global behaviour of the structure including the prediction of up to 90-mm crack extension. Local terms such as the equivalent stress or the crack tip opening angle are found to be constant during the crack extension process. This supports the view that G fr controls the fields in the vicinity near the crack tip. (orig.)

  16. Investigation on the Crack Initiation of V-Shaped Notch Tip in Precision Cropping

    Directory of Open Access Journals (Sweden)

    Lijun Zhang

    2014-01-01

    Full Text Available The crack initiation of V-shaped notch tip has a very important influence on the cross-section quality and the cropping time for every segment of metal bar in course of low stress precision cropping. By the finite element method, the influence of machining precision of V-shaped notch bottom corner on the crack initiation location is analyzed and it is pointed out that the crack initiation point locates in the place at the maximal equivalent stress change rate on V-shaped notch surface. The judgment criterion of the crack initiation direction is presented and the corresponding crack initiation angle can be calculated by means of the displacement extrapolation method. The factual crack initiation angle of the metal bar has been measured by using the microscopic measurement system. The formula of the crack initiation life of V-shaped notch tip is built, which mainly includes the stress concentration factor of V-shaped notch, the tensile properties of metal material, and the cyclic loading conditions. The experimental results show that the obtained theoretical analyses about the crack initiation location, the crack initiation direction, and the crack initiation time in this paper are correct. It is also shown that the crack initiation time accounts for about 80% of the cropping time for every segment of the metal bar.

  17. A numerical study of non-linear crack tip parameters

    Directory of Open Access Journals (Sweden)

    F.V. Antunes

    2015-07-01

    Full Text Available Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, different authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle, were investigated. It was demonstrated that: i LEFM concepts are applicable to the problem under study; ii the crack closure phenomenon has a great influence on crack tip parameters decreasing their values; iii the Keff concept is able to explain the variations of crack tip parameters produced by the contact of crack flanks; iv the analysis of remote compliance is the best numerical parameter to quantify the crack opening level; v without contact there is no effect of stress ratio on crack tip parameters. Therefore it is proved that the crack closure concept is valid.

  18. TEM observations of crack tip: cavity interactions

    International Nuclear Information System (INIS)

    Horton, J.A.; Ohr, S.M.; Jesser, W.A.

    1981-01-01

    Crack tip-cavity interactions have been studied by performing room temperature deformation experiments in a transmission electron microscope on ion-irradiated type 316 stainless steel with small helium containing cavities. Slip dislocations emitted from a crack tip cut, sheared, and thereby elongated cavities without a volume enlargement. As the crack tip approached, a cavity volume enlargement occurred. Instead of the cavities continuing to enlarge until they touch, the walls between the cavities fractured. Fracture surface dimples do not correlate in size or density with these enlarged cavities

  19. Stress corrosion crack tip microstructure in nickel-based alloys

    International Nuclear Information System (INIS)

    Shei, S.A.; Yang, W.J.

    1994-04-01

    Stress corrosion cracking behavior of several nickel-base alloys in high temperature caustic environments has been evaluated. The crack tip and fracture surfaces were examined using Auger/ESCA and Analytical Electron Microscopy (AEM) to determine the near crack tip microstructure and microchemistry. Results showed formation of chromium-rich oxides at or near the crack tip and nickel-rich de-alloying layers away from the crack tip. The stress corrosion resistance of different nickel-base alloys in caustic may be explained by the preferential oxidation and dissolution of different alloying elements at the crack tip. Alloy 600 (UNS N06600) shows good general corrosion and intergranular attack resistance in caustic because of its high nickel content. Thermally treated Alloy 690 (UNS N06690) and Alloy 600 provide good stress corrosion cracking resistance because of high chromium contents along grain boundaries. Alloy 625 (UNS N06625) does not show as good stress corrosion cracking resistance as Alloy 690 or Alloy 600 because of its high molybdenum content

  20. The generalized fracture criteria based on the multi-parameter representation of the crack tip stress field

    Science.gov (United States)

    Stepanova, L. V.

    2017-12-01

    The paper is devoted to the multi-parameter asymptotic description of the stress field near the crack tip of a finite crack in an infinite isotropic elastic plane medium subject to 1) tensile stress; 2) in-plane shear; 3) mixed mode loading for a wide range of mode-mixity situations (Mode I and Mode II). The multi-parameter series expansion of stress tensor components containing higher-order terms is obtained. All the coefficients of the multiparameter series expansion of the stress field are given. The main focus is on the discussion of the influence of considering the higher-order terms of the Williams expansion. The analysis of the higher-order terms in the stress field is performed. It is shown that the larger the distance from the crack tip, the more terms it is necessary to keep in the asymptotic series expansion. Therefore, it can be concluded that several more higher-order terms of the Williams expansion should be used for the stress field description when the distance from the crack tip is not small enough. The crack propagation direction angle is calculated. Two fracture criteria, the maximum tangential stress criterion and the strain energy density criterion, are used. The multi-parameter form of the two commonly used fracture criteria is introduced and tested. Thirty and more terms of the Williams series expansion for the near-crack-tip stress field enable the angle to be calculated more precisely.

  1. Crack Tip Mechanics in Distortion Gradient Plasticity

    DEFF Research Database (Denmark)

    Fuentes-Alonso, Sandra; Martínez Pañeda, Emilio

    2017-01-01

    Gradient Plasticity (DGP), the influence on crack tip mechanics of DGP's distinguishing features that entail superior modelling capabilities has not been investigated yet. In this work crack tip fields are thoroughly examined by implementing the higher order theory of DGP in an implicit finite element...

  2. Effect of Crack Tip Stresses on Delayed Hydride Cracking in Zr-2.5Nb Tubes

    International Nuclear Information System (INIS)

    Kim, Young Suk; Cheong, Yong Moo

    2007-01-01

    Delayed hydride cracking (DHC) tests have shown that the DHC velocity becomes faster in zirconium alloys with a higher yield stress. To account for this yield stress effect on the DHC velocity, they suggested a simple hypothesis that increased crack tip stresses due to a higher yield stress would raise the difference in hydrogen concentration between the crack tip and the bulk region and accordingly the DHC velocity. This hypothesis is also applied to account for a big leap in the DHC velocity of zirconium alloys after neutron irradiation. It should be noted that this is based on the old DHC models that the driving force for DHC is the stress gradient. Puls predicted that an increase in the yield stress of a cold worked Zr-2.5Nb tube due to neutron irradiation by about 300 MPa causes an increase of its DHC velocity by an order of magnitude or 2 to 3 times depending on the accommodation energy values. Recently, we proposed a new DHC model that a driving force for DHC is not the stress gradient but the concentration gradient arising from the stress-induced precipitation of hydrides at the crack tip. Our new DHC model and the supporting experimental results have demonstrated that the DHC velocity is governed primarily by hydrogen diffusion at below 300 .deg. C. Since hydrogen diffusion in Zr-2.5Nb tubes is dictated primarily by the distribution of the β-phase, the DHC velocity of the irradiated Zr-2.5Nb tube must be determined mainly by the distribution of the β-phase, not by the increased yield stress, which is in contrast with the hypothesis of the previous DHC models. In short, a controversy exists as to the effect on the DHC velocity of zirconium alloys of a change in the crack tip stresses by irradiation hardening or cold working or annealing. The aim of this study is to resolve this controversy and furthermore to prove the validity of our DHC model. To this end, we cited Pan et al.'s experiment where the delayed hydride cracking velocity, the tensile strengths

  3. Deformation localization at the tips of shear fractures: An analytical approach

    Science.gov (United States)

    Misra, Santanu

    2011-04-01

    Mechanical heterogeneities are important features in rocks which trigger deformation localization in brittle, ductile or brittle-ductile modes during deformation. In a recent study Misra et al. (2009) have investigated these different processes of deformation localization at the tips of pre-existing planar shear fractures. The authors identified four mechanisms of deformation, ranging from brittle to ductile, operating at the crack tips. Mechanism A: brittle deformation is the dominant process that forms a pair of long tensile fractures at the two crack tips. Mechanism B: nature of deformation is mixed where the tensile fractures grow to a finite length with incipient plastic deformation at the tips. Mechanism C: mixed mode deformation characterized by dominating macro-scale shear bands, and short, opened-out tensile fissures. Mechanism D: localization of plastic bands in the form of a pair of shear bands at each tip without any discernible brittle fracturing. The transition of the mechanisms is a function of orientation ( α) of the crack with respect to the bulk compression direction and the finite length ( l) of the crack. The aim of this study is to present a theoretical analysis to account for the variability of deformation localization in the vicinity of pre-existing shear cracks considering an elastic-plastic rheological model. The analysis calculates the principal tensile stress ( σ1) and the second stress invariant ( I2) of the stress field at the fracture tip to explain the transition from Mechanism A (tensile fracturing) to Mechanism D (ductile strain). The results show that σ1 at the fracture tip increases non-linearly with increasing α and Ar (aspect ratio of the shear crack), and assumes a large value when α > 50 o, promoting tensile fractures. On the other hand, I2 is a maximum at α < 45°, resulting in nucleation of ductile shear bands.

  4. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy.

    Science.gov (United States)

    Withers, P J

    2015-03-06

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored.

  5. On short cracks that depart from elastoplastic notch tips

    Directory of Open Access Journals (Sweden)

    Verônica Miquelin Machado

    2017-07-01

    Full Text Available The behavior of short cracks that depart from elastoplastic notch tips is modeled to estimate the stresses required to initiate and to propagate cracks in notched structural components, and to evaluate the size of tolerable crack-like defects under general loading conditions. This analysis can model both fatigue and environmentally assisted cracking problems; can evaluate notch sensitivity in both cases; and can as well be used to establish design or acceptance criteria for tolerable non-propagating crack-like defects in such cases. The growth of short cracks is assumed driven by the applied stresses and by the stress gradient ahead the notch tip, and supported by the material resistances to crack initiation and to long crack propagation by fatigue or EAC. In the elastoplastic case, the stress gradient ahead of the notch tip is quantified by a J-field to consider the short crack behavior. The tolerable short crack predictions made by this model are evaluated by suitable fatigue and EAC tests of notched specimens specially designed to start nonpropagating cracks from the notch tips, both under elastic and elastoplastic conditions.

  6. Characterization of SCC crack tip and hydrogen distribution in alloy 600

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, Katsuhiko; Nakajima, Nobuo; Fukuya, Koji [Institute of Nuclear Safety System Inc., Mihama, Fukui (Japan); Hatano, Yuji [Toyama Univ. (Japan)

    2001-09-01

    In order to identify the mechanism of primary water stress corrosion cracking (SCC), direct observations of SCC crack tip microstructure and hydrogen distribution in alloy 600 were carried out. A new technique has been developed to prepare electron transparent foils including the crack tip using focused-ion beam (FIB) micro-processing technique. Cr-rich oxide and metal-Ni phase were identified in the crack tip and grain boundary ahead of the crack. >From the fact that similar microstructure was observed in the surface oxide layer, it is suggested that the oxidation mechanism is identical at the crack tip region and the surface. It became clear that the crack tip region and the oxidized grain boundary don't work as strong trapping sites of solute hydrogen under unloaded condition, because a homogeneous hydrogen distribution around the crack tip region was detected by tritium microautoradiography. (author)

  7. Sub-10-micrometer toughening and crack tip toughness of dental enamel

    OpenAIRE

    Ang, Siang Fung; Schulz, Anja; Pacher Fernandes, Rodrigo; Schneider, Gerold A.

    2011-01-01

    In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip toughness (KI0, KIII0), the crack closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine en...

  8. Effects of δ-hydride precipitation at a crack tip on crack propagation in delayed hydride cracking of Zircaloy-2

    Energy Technology Data Exchange (ETDEWEB)

    Kubo, T., E-mail: kubo@nfd.co.jp [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan); Kobayashi, Y. [M.O.X. Co., Ltd., 1828-520 Hirasu-cho, Mito, Ibaraki 311-0853 (Japan)

    2013-08-15

    Highlights: • Steady state crack velocity of delayed hydride cracking in Zircaloy-2 was analyzed. • A large stress peak is induced at an end of hydride by volume expansion of hydride. • Hydrogen diffuses to the stress peak, thereby accelerating steady hydride growth. • Crack velocity was estimated from the calculated hydrogen flux into the stress peak. • There was good agreement between calculation results and experimental data. -- Abstract: Delayed hydride cracking (DHC) of Zircaloy-2 is one possible mechanism for the failure of boiling water reactor fuel rods in ramp tests at high burnup. Analyses were made for hydrogen diffusion around a crack tip to estimate the crack velocity of DHC in zirconium alloys, placing importance on effects of precipitation of δ-hydride. The stress distribution around the crack tip is significantly altered by precipitation of hydride, which was strictly analyzed using a finite element computer code. Then, stress-driven hydrogen diffusion under the altered stress distribution was analyzed by a differential method. Overlapping of external stress and hydride precipitation at a crack tip induces two stress peaks; one at a crack tip and the other at the front end of the hydride precipitate. Since the latter is larger than the former, more hydrogen diffuses to the front end of the hydride precipitate, thereby accelerating hydride growth compared with that in the absence of the hydride. These results indicated that, after hydride was formed in front of the crack tip, it grew almost steadily accompanying the interaction of hydrogen diffusion, hydride growth and the stress alteration by hydride precipitation. Finally, crack velocity was estimated from the calculated hydrogen flux into the crack tip as a function of temperature, stress intensity factor and material strength. There was qualitatively good agreement between calculation results and experimental data.

  9. Observations on Hydride Structures at the Tip of Arrested Cracks Grown under Conditions of Delayed Hydride Cracking

    International Nuclear Information System (INIS)

    Pettersson, Kjell; Oskarsson, Magnus; Bergqvist, Hans

    2003-04-01

    One sample of Zr2.5%Nb and one sample of cold worked and stress relieved Zircaloy-4 which have been tested for hydrogen induced crack growth have been examined in the crack tip region with the aim of determining the mechanism behind the growth of cracks. The proposed mechanisms are brittle failure of a crack tip hydride and hydrogen enhanced localized shear. The examinations were done by TEM and SEM. However attempts to produce a TEM specimen with a thinned region at the tip of the crack were unsuccessful in both samples. One feature observed in the Zr2.5%Nb material may however be an indication of intense shear deformation at the tip of the crack. On the other hand all observations on the Zircaloy-4 sample indicate precipitation of hydrides ahead of the crack tip and the presence of hydrides on the crack flanks

  10. Semi-empirical crack tip analysis

    Science.gov (United States)

    Chudnovsky, A.; Ben Ouezdon, M.

    1988-01-01

    Experimentally observed crack opening displacements are employed as the solution of the multiple crack interaction problem. Then the near and far fields are reconstructed analytically by means of the double layer potential technqiue. Evaluation of the effective stress intensity factor resulting from the interaction of the main crack and its surrounding crazes in addition to the remotely applied load is presented as an illustrative example. It is shown that crazing (as well as microcracking) may constitute an alternative mechanism to Dugdale-Berenblatt models responsible for the cancellation of the singularity at the crack tip.

  11. Crack tip fracture toughness of base glasses for dental restoration glass-ceramics using crack opening displacements.

    Science.gov (United States)

    Deubener, J; Höland, M; Höland, W; Janakiraman, N; Rheinberger, V M

    2011-10-01

    The critical stress intensity factor, also known as the crack tip toughness K(tip), was determined for three base glasses, which are used in the manufacture of glass-ceramics. The glasses included the base glass for a lithium disilicate glass-ceramic, the base glass for a fluoroapatite glass-ceramic and the base glass for a leucite glass-ceramic. These glass-ceramic are extensively used in the form of biomaterials in restorative dental medicine. The crack tip toughness was established by using crack opening displacement profiles under experimental conditions. The crack was produced by Vickers indentation. The crack tip toughness parameters determined for the three glass-ceramics differed quite significantly. The crack tip parameters of the lithium disilicate base glass and the leucite base glass were higher than that of the fluoroapatite base glass. This last material showed glass-in-glass phase separation. The discussion of the results clearly shows that the droplet glass phase is softer than the glass matrix. Therefore, the authors conclude that a direct relationship exists between the chemical nature of the glasses and the crack tip parameter. Copyright © 2011 Elsevier Ltd. All rights reserved.

  12. Analysis on the stress corrosion crack inception based on pit shape and size of the FV520B tensile specimen

    Science.gov (United States)

    Xiang, Longhao; Pan, Juyi; Chen, Songying

    2018-06-01

    The influence of pit shape and size on local stress concentration in the tensile specimen and the stress corrosion cracks inception was studied by employing the element remove technique. The maximum stress located in the bottom of pit on FV520B tensile specimen. The location of maximum strain was near the mouth of the pit or the shoulder and plastic strain existed in this region. Stress concentration factor and plastic deformation on four different geometrical shape pits of hemisphere, semi-ellipsoid, bullet and butterfly were numerically investigated, respectively. The simulation results showed that butterfly pit got the biggest stress concentration factor. The plastic strain rate during pit growth was in the sensitivity range of stress corrosion cracks inception, indicating that stress corrosion cracks were more likely to nucleate near the pit tip or the shoulder.

  13. Behavior of Fatigue Crack Tip Opening in Air and Corrosive Atmosphere

    Science.gov (United States)

    Hayashi, Morihito; Toeda, Kazunori

    In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

  14. Sub-10-micrometer toughening and crack tip toughness of dental enamel.

    Science.gov (United States)

    Ang, Siang Fung; Schulz, Anja; Pacher Fernandes, Rodrigo; Schneider, Gerold A

    2011-04-01

    In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip's toughness (K(I0),K(III0)), the crack's closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystallite. The crack-opening-displacement (COD) profile of cracks induced by Vickers indents on mature bovine enamel was studied using atomic force microscopy (AFM). The mode I crack tip toughness K(I0) of cracks along enamel rod boundaries and across enamel rods exhibit a similar range of values: K(I0,Ir)=0.5-1.6MPa m(0.5) (based on Irwin's 'near-field' solution) and K(I0,cz)=0.8-1.5MPa m(0.5) (based on the cohesive zone solution of the Dugdale-Muskhelishvili (DM) crack model). The mode III crack tip toughness K(III0,Ir) was computed as 0.02-0.15MPa m(0.5). The crack-closure stress at the crack tip was computed as 163-770 MPa with a cohesive zone length and width 1.6-10.1μm and 24-44 nm utilizing the cohesive zone solution. Toughening elements were observed under AFM and SEM: crack bridging due to protein ligament and hydroxyapatite fibres (micro- and nanometer scale) as well as microcracks were identified. Crown Copyright © 2010. Published by Elsevier Ltd. All rights reserved.

  15. Characterization of SCC crack tips and surface oxide layers in alloy 600

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, Katsuhiko; Fukuya, Koji [Inst. of Nuclear Safety System Inc., Mihama, Fukui (Japan)

    2002-09-01

    In order to investigate the mechanism of primary water stress corrosion cracking (SCC), direct observation of microstructures of SCC crack tips and surface oxide layers in alloy 600 were carried out. A focused-ion beam (FIB) micro-processing technique was applied to prepare electron transparent foils including the crack tip and the surface oxide layer without any damage to those microstructures. Transmission electron microscopy and analysis were used to characterize the crack tips and surface oxide layers. Cr-rich oxides and a metal-Ni phase were identified in the crack tips and grain boundaries ahead of the crack tips independent of dissolved hydrogen concentrations. >From the fact that the Cr-rich oxides and metal-Ni phase were observed in the inner surface oxide layer, the same oxidation mechanism as the surface is proposed for the crack tip region and internal oxidation accompanying selective Cr oxidation is suggested as the mechanism. (author)

  16. Effect of plastic prestrain on the crack tip constraint of pipeline steels

    International Nuclear Information System (INIS)

    Eikrem, P.A.; Zhang, Z.L.; Nyhus, B.

    2007-01-01

    Before and during operation, pipelines may suffer from plastic pre-deformation due to accidental loading, cold bending and ground movement. Plastic prestrain not only modifies steel's yield and flow properties but also influences its fracture performance. This paper focuses on the effect of prestrain history on crack driving force and crack tip constraint. A single-edge notched tension specimen has been selected for the study and the crack is assumed to exist before a prestrain history was applied. The results show that prestrain history has a strong effect on the crack tip stress field. A new parameter has been proposed to characterize the prestrain-induced crack tip constraint. For the same crack tip opening displacement level, prestrain history will elevate the crack tip stress field. The prestrain-induced constraint decreases with the increase of loading

  17. A demonstration of mitigation of environmentally-assisted cracking by the application of a tensile overload

    International Nuclear Information System (INIS)

    James, L.A.

    1997-01-01

    Environmentally-assisted cracking (EAC) of low-alloy steels in high-temperature aqueous environments typical of those employed in light-water reactor (LWR) systems has been a subject of considerable interest since the pioneering work of Kondo et al demonstrated significantly higher fatigue crack propagation (FCP) rates in water than would be expected in an air environment under similar conditions. Here, environmentally-assisted cracking (EAC) of low-alloy steels in elevated temperature aqueous environments is readily observed in many laboratory experiments conducted in autoclaves, yet the observation of EAC in actual components operating in the same environments is quite rare. Mass transport of sulfides from the crack enclave by diffusion and convection occurring in operating components provides one plausible explanation to this apparent paradox. Another contribution to EAC mitigation may also arise from the non-constant stress amplitudes typical for many operating components. This paper provides a demonstration of how a single tensile overload to 40% above a steady-state maximum fatigue stress can retard subsequent crack growth at the steady-state level for a sufficient period of time that diffusion mass transport can reduce the crack-tip sulfide concentration to a level below that necessary to sustain EAC

  18. A demonstration of mitigation of environmentally-assisted cracking by the application of a tensile overload

    Energy Technology Data Exchange (ETDEWEB)

    James, L.A.

    1997-02-01

    Environmentally-assisted cracking (EAC) of low-alloy steels in high-temperature aqueous environments typical of those employed in light-water reactor (LWR) systems has been a subject of considerable interest since the pioneering work of Kondo et al demonstrated significantly higher fatigue crack propagation (FCP) rates in water than would be expected in an air environment under similar conditions. Here, environmentally-assisted cracking (EAC) of low-alloy steels in elevated temperature aqueous environments is readily observed in many laboratory experiments conducted in autoclaves, yet the observation of EAC in actual components operating in the same environments is quite rare. Mass transport of sulfides from the crack enclave by diffusion and convection occurring in operating components provides one plausible explanation to this apparent paradox. Another contribution to EAC mitigation may also arise from the non-constant stress amplitudes typical for many operating components. This paper provides a demonstration of how a single tensile overload to 40% above a steady-state maximum fatigue stress can retard subsequent crack growth at the steady-state level for a sufficient period of time that diffusion mass transport can reduce the crack-tip sulfide concentration to a level below that necessary to sustain EAC.

  19. 2D mapping of plane stress crack-tip fields following an overload

    Directory of Open Access Journals (Sweden)

    P. J. Withers

    2015-07-01

    Full Text Available The evolution of crack-tip strain fields in a thin (plane stress compact tension sample following an overload (OL event has been studied using two different experimental techniques. Surface behaviour has been characterised by Digital Image Correlation (DIC, while the bulk behaviour has been characterised by means of synchrotron X-ray diffraction (XRD. The combination of both surface and bulk information allowed us to visualise the through-thickness evolution of the strain fields before the OL event, during the overload event, just after OL and at various stages after it. Unlike previous work, complete 2D maps of strains around the crack-tip were acquired at 60m spatial resolution by XRD. The DIC shows less crack opening after overload and the XRD a lower crack-tip peak stress after OL until the crack has grown past the compressive crack-tip residual stress introduced by the overload after which the behaviour returned to that for the baseline fatigue response. While the peak crack-tip stress is supressed by the compressive residual stress, the crack-tip stress field changes over each cycle are nevertheless the same for all Kmax cycles except at OL.

  20. Effect of CT Specimen Thickness on the Mechanical Characteristics at the Crack Tip of Stress Corrosion Cracking in Ni-based Alloys

    Science.gov (United States)

    Yinghao, Cui; He, Xue; Lingyan, Zhao

    2017-12-01

    It’s important to obtain accurate stress corrosion crack(SCC) growth rate for quantitative life prediction of components in nuclear power plants. However, the engineering practice shows that the crack tip constraint effect has a great influence on the mechanical properties and crack growth rate of SCC at crack tip. To study the influence of the specimen thickness on the crack tip mechanical properties of SCC, the stress, strain and C integral at creep crack tip are analyzed under different specimens thickness. Results show that the cracked specimen is less likely to crack due to effect of crack tip constraint. When the thickness ratio B/W is larger than 0.1, the crack tip constraint is almost ineffective. Value of C integral is the largest when B/W is 0.25. Then specimen thickness has little effect on the value of C integral. The effect of specimen thickness on the value of C integral is less significant at higher thickness ratio.

  1. Numerical investigation of J-characterization of growing crack tips

    International Nuclear Information System (INIS)

    Nilsson, F.

    1992-01-01

    Two different geometries, a centrally cracked panel and a three-point bend bar, are modelled with aid of the finite element program ABAQUS. Elastic-plastic behaviour with a realistic linear hardening modulus is assumed. By simulation of the growth with the aid of nodal relaxation, the J-value for a remote path around the growing tip is obtained for some different local-crack growth histories. The J F -value is compared to the J D -value that results if the crack tip is assumed to be stationary at the current length. It is found that the J C - and J F -values agree well for crack growth histories satisfying the criteria for J-characterization. However, after examination of the crack surface displacements it was found that the results for the bend geometry and the tension geometry, respectively, did not coincide for corresponding J-values, except at low load levels. This raises doubt about the abilities of J to characterize the state at a growing tip. (orig.)

  2. New theory for crack-tip twinning in fcc metals

    Science.gov (United States)

    Andric, Predrag; Curtin, W. A.

    2018-04-01

    Dislocation emission from a crack tip is a necessary mechanism for crack tip blunting and toughening. In fcc metals under Mode I loading, a first partial dislocation is emitted, followed either by a trailing partial dislocation ("ductile" behaviour) or a twinning partial dislocation ("quasi-brittle"). The twinning tendency is usually estimated using the Tadmor and Hai extension of the Rice theory. Extensive molecular statics simulations reveal that the predictions of the critical stress intensity factor for crack tip twinning are always systematically lower (20-35%) than observed. Analyses of the energy change during nucleation reveal that twin partial emission is not accompanied by creation of a surface step while emission of the trailing partial creates a step. The absence of the step during twinning motivates a modified model for twinning nucleation that accounts for the fact that nucleation does not occur directly at the crack tip. Predictions of the modified theory are in excellent agreement with all simulations that show twinning. Emission of the trailing partial dislocation, including the step creation, is predicted using a model recently introduced to accurately predict the first partial emission and shows why twinning is preferred. A second mode of twinning is found wherein the crack first advances by cleavage and then emits the twinning partial at the new crack tip; this mode dominates for emission beyond the first twinning partial. These new theories resolve all the discrepancies between the Tadmor twinning analysis and simulations, and have various implications for fracture behaviour and transitions.

  3. Effects of absorbed hydrogen on crack-tip ductility in the welded A516 steel

    International Nuclear Information System (INIS)

    Khattak, M.A.; Haslan, M.H.; Tamin, M.N.

    2007-01-01

    Effects of absorbed hydrogen on structure and properties of welded A516 Grade-70 steel are investigated. Emphasis is placed on ductility measure of the crack-tip plastic zone under Mode I loading. Specimens are cathodically charged in a cell with dilute sulphuric acid and corrosion inhibitor with uniform charging current density of 20 mA/ cm 2 and at different exposure time. Results indicate a change from coarse- to fine-grained microstructures in the weld region and heat affected zone (HAZ) of hydrogen-charged specimen. Well-defined ferrite-pearlite bands in the base metal are transformed into coarse-grain structure. Hardness variation along radial distance indicates higher values towards the center of the bar, possibly due to faster diffusion rate but limited solubility of hydrogen. Load-COD responses indicate that slow, stable crack propagation occurred in both base metal and HAZ. The measured provisional fracture toughness, K Q is higher for HAZ than that for the base metal. The toughness values decreases significantly for the initial three hours of hydrogen charging. The tensile fracture region in the immediate fatigue pre-crack tip forms a triangular (rough) zone due to limited constraint to free surface deformation in the thin specimen. Fracture surface of HAZ is dominated by intergranular fracture with localized cleavage facets. (author)

  4. A numerical study of crack tip constraint in ductile single crystals

    Science.gov (United States)

    Patil, Swapnil D.; Narasimhan, R.; Mishra, R. K.

    In this work, the effect of crack tip constraint on near-tip stress and deformation fields in a ductile FCC single crystal is studied under mode I, plane strain conditions. To this end, modified boundary layer simulations within crystal plasticity framework are performed, neglecting elastic anisotropy. The first and second terms of the isotropic elastic crack tip field, which are governed by the stress intensity factor K and T-stress, are prescribed as remote boundary conditions and solutions pertaining to different levels of T-stress are generated. It is found that the near-tip deformation field, especially, the development of kink or slip shear bands, is sensitive to the constraint level. The stress distribution and the size and shape of the plastic zone near the crack tip are also strongly influenced by the level of T-stress, with progressive loss of crack tip constraint occurring as T-stress becomes more negative. A family of near-tip fields is obtained which are characterized by two terms (such as K and T or J and a constraint parameter Q) as in isotropic plastic solids.

  5. Crack Tip Creep Deformation Behavior in Transversely Isotropic Materials

    International Nuclear Information System (INIS)

    Ma, Young Wha; Yoon, Kee Bong

    2009-01-01

    Theoretical mechanics analysis and finite element simulation were performed to investigate creep deformation behavior at the crack tip of transversely isotropic materials under small scale creep (SCC) conditions. Mechanical behavior of material was assumed as an elastic-2 nd creep, which elastic modulus ( E ), Poisson's ratio (v ) and creep stress exponent ( n ) were isotropic and creep coefficient was only transversely isotropic. Based on the mechanics analysis for material behavior, a constitutive equation for transversely isotropic creep behavior was formulated and an equivalent creep coefficient was proposed under plain strain conditions. Creep deformation behavior at the crack tip was investigated through the finite element analysis. The results of the finite element analysis showed that creep deformation in transversely isotropic materials is dominant at the rear of the crack-tip. This result was more obvious when a load was applied to principal axis of anisotropy. Based on the results of the mechanics analysis and the finite element simulation, a corrected estimation scheme of the creep zone size was proposed in order to evaluate the creep deformation behavior at the crack tip of transversely isotropic creeping materials

  6. Assisted crack tip flipping under Mode I thin sheet tearing

    DEFF Research Database (Denmark)

    Felter, Christian Lotz; Nielsen, Kim Lau

    2017-01-01

    Crack tip flipping, where the fracture surface alternates from side to side in roughly 45° shear bands, seems to be an overlooked propagation mode in Mode I thin sheet tearing. In fact, observations of crack tip flipping is rarely found in the literature. Unlike the already established modes...

  7. Crack Tip Parameters for Growing Cracks in Linear Viscoelastic Materials

    DEFF Research Database (Denmark)

    Brincker, Rune

    In this paper the problem of describing the asymptotic fields around a slowly growing crack in a linearly viscoelastic material is considered. It is shown that for plane mixed mode problems the asymptotic fields must be described by 6 parameters: 2 stress intensity factors and 4 deformation...... intensity factors. In the special case of a constant Poisson ratio only 2 deformation intensity factors are needed. Closed form solutions are given both for a slowly growing crack and for a crack that is suddenly arrested at a point at the crack extension path. Two examples are studied; a stress boundary...... value problem, and a displacement boundary value problem. The results show that the stress intensity factors and the displacement intensity factors do not depend explicitly upon the velocity of the crack tip....

  8. Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth

    Science.gov (United States)

    Telesman, Jack; Gabb, Tim; Ghosn, Louis J.

    2016-01-01

    Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress intensity parameter, Kmax, was developed by incorporating into the formulation the remaining stress level concept as measured by simple stress relaxation tests. The newly proposed parameter, Ksrf, did an excellent job in correlating the dwell crack growth rates for the four heat treatments which were shown to have similar intrinsic environmental cyclic fatigue crack growth resistance.

  9. Analysis of short and long crack behavior and single overload effect by crack opening stress

    International Nuclear Information System (INIS)

    Song, Sam Hong; Lee, Kyeong Ro

    1999-01-01

    The study analyzed the behaviors of short and long crack as well as the effect of single tensile overload on the crack behaviors by using fatigue crack opening behavior. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many data using strain gages during experiment. The unusual growth behaviors of short crack and crack after the single tensile overload applied, was explained by the variations of crack opening stress. In addition, fatigue crack growth rate was expressed as a linear form for short crack as for long crack by using effective stress intensity factor range as fracture mechanical parameter, which is based on crack closure concept. And investigation is performed with respect to the relation between plastic zone size formed at the crack tip and crack retardation, crack length and the number of cycles promoted or retarded, and the overload effect on the fatigue life

  10. Cracking and Deformation Modelling of Tensile RC Members Using Stress Transfer Approach

    Directory of Open Access Journals (Sweden)

    Ronaldas Jakubovskis

    2016-12-01

    Full Text Available The paper presents a modeling technique for bond, cracking and deformation analysis of RC members. The proposed mod-eling technique is not restricted by the geometrical dimensions of the analyzed member and may be applied for various load-ing conditions. Tensile as well as bending RC members may be analyzed using the proposed technique. Adequacy of the modeling strategy was evaluated by the developed numerical discrete crack algorithm, which allows modeling deformation and cracking behavior of tensile RC members. Comparison of experimental and numerical results proved the applicability of the proposed modeling strategy.

  11. Noncontact fatigue crack evaluation using thermoelastic

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji Min; An, Yun Kyu; Sohn, Hoon [KAIST, Daejeon (Korea, Republic of)

    2012-12-15

    This paper proposes a noncontact thermography technique for fatigue crack evaluation under a cyclic tensile loading. The proposed technique identifies and localizes an invisible fatigue crack without scanning, thus making it possible to instantaneously evaluate an incipient fatigue crack. Based on a thermoelastic theory, a new fatigue crack evaluation algorithm is proposed for the fatigue crack tip localization. The performance of the proposed algorithm is experimentally validated. To achieve this, the cyclic tensile loading is applied to a dog bone shape aluminum specimen using a universal testing machine, and the corresponding thermal responses induced by thermoelastic effects are captured by an infrared camera. The test results confirm that the fatigue crack is well identified and localized by comparing with its microscopic images.

  12. Unstable propagation behavior of a ductile crack in SUS-304 stainless steel under high compliance tensile loading

    International Nuclear Information System (INIS)

    Tomoda, Yoshio

    1981-01-01

    In relation to the safe maintenance of nuclear power plants, it is necessary to prevent reactor coolant pipings from burst type failure caused by the unstable propagation of defects and cracks, such as stress corrosion cracking and fatigue cracks. In ductile materials, crack propagation is stable in tensile loading under fixed grip condition, when a specimen is controlled to deform in proportion to the increase of tensile load. However, it has been known that the instability of ductile cracks occurs after tensile load reached the maximum, especially under constant loading condition arising in the loading devices with high compliance or low tensile rigidity. In order to confirm the reliability of SUS 304 stainless pipes subjected to SCC, the crack propagation behavior was examined with the specimens having center cracks, using both testing machines with high compliance and low compliance. The instability of ductile cracks and the propagation velocity of unstable cracks were analyzed, and the calculated results were compated with the experimental results. Not only the compliance of testing machines but also the conditions of specimens affected the propagation of cracks. (Kako, I.)

  13. High-voltage electron-microscopical observation of crack-tip dislocations in silicon crystals

    International Nuclear Information System (INIS)

    Tanaka, Masaki; Higashida, Kenji

    2005-01-01

    Crack-tip dislocations in silicon single crystals were observed by high-voltage electron microscopy. Cracks were introduced into silicon wafers at room temperature by a Vickers indenter. The indented specimens were annealed at 823 K in order to activate dislocation emission from the crack tip under the residual stress due to the indentation. In the specimen without annealing, no dislocations were observed around the crack. On the other hand, in the specimen after the annealing, the aspect of the early stage of dislocation emission was observed, where dislocations were emitted not as a perfect dislocation but as a partial dislocation in the hinge-type plastic zone. Prominent dislocation arrays that were emitted from a crack tip were also observed, and they were found to be of shielding type, which increases the fracture toughness of those crystals

  14. Characterization of cracking in Strain-Hardening Cementitious Composites using the compact tension test

    DEFF Research Database (Denmark)

    Pereira, Eduardo B.; Fischer, Gregor; Barros, Joaquim A. O.

    The characterization of the tensile behavior of strain hardening cementitious composites (SHCC) is of significant importance to the material design. In a previous work the tensile stress-crack opening response of different types of SHCC was characterized using notched specimens tested in direct...... tension, where a single crack was obtained and mechanically characterized by performing Single Crack Tension Test (SCTT). In this study the tensile behavior of SHCC materials is characterized under eccentric tensile load using the Compact Tension Test (CTT). The long edge notch placed in the rectangular...... plate specimens and the eccentrically applied tensile load create the local conditions necessary to the initiation of a single crack at the tip of the notch. Further propagation and opening of the crack in Mode I allow the assessment of the tensile load-displacement relationship. The experimental...

  15. A study on fatigue crack growth behavior subjected to a single tensile overload: Part II. Transfer of stress concentration and its role in overload-induced transient crack growth

    International Nuclear Information System (INIS)

    Lee, S.Y.; Choo, H.; Liaw, P.K.; An, K.; Hubbard, C.R.

    2011-01-01

    The combined effects of overload-induced enlarged compressive residual stresses and crack tip blunting with secondary cracks are suggested to be responsible for the observed changes in the crack opening load and resultant post-overload transient crack growth behavior [Lee SY, Liaw PK, Choo H, Rogge RB, Acta Mater 2010;59:485-94]. In this article, in situ neutron diffraction experiments were performed to quantify the influence of the combined effects by investigating the internal-stress evolution at various locations away from the crack tip. In the overload-retardation period, stress concentration occurs in the crack blunting region (an overload point) until a maximum crack arrest load is reached. The stress concentration is then transferred from the blunting region to the propagating crack tip (following the overload), requiring a higher applied load, as the closed crack is gradually opened. The transfer phenomena of the stress concentration associated with a crack opening process account for the nonlinearity of strain response in the vicinity of the crack tip. The delaying action of stress concentration at the crack tip is understood in conjunction with the concept of a critical stress (i.e. the stress required to open the closed crack behind the crack tip). A linear relationship between Δε eff and ΔK eff provides experimental support for the hypothesis that ΔK eff can be considered as the fatigue crack tip driving force.

  16. Role of hydrogen on the incipient crack tip deformation behavior in α-Fe: An atomistic perspective

    Science.gov (United States)

    Adlakha, I.; Solanki, K. N.

    2018-01-01

    A crack tip in α-Fe presents a preferential trap site for hydrogen, and sufficient concentration of hydrogen can change the incipient crack tip deformation response, causing a transition from a ductile to a brittle failure mechanism for inherently ductile alloys. In this work, the effect of hydrogen segregation around the crack tip on deformation in α-Fe was examined using atomistic simulations and the continuum based Rice-Thompson criterion for various modes of fracture (I, II, and III). The presence of a hydrogen rich region ahead of the crack tip was found to cause a decrease in the critical stress intensity factor required for incipient deformation for various crack orientations and modes of fracture examined here. Furthermore, the triaxial stress state ahead of the crack tip was found to play a crucial role in determining the effect of hydrogen on the deformation behavior. Overall, the segregation of hydrogen atoms around the crack tip enhanced both dislocation emission and cleavage behavior suggesting that hydrogen has a dual role during the deformation in α-Fe.

  17. Mode I and mixed mode crack-tip fields in strain gradient plasticity

    DEFF Research Database (Denmark)

    Goutianos, Stergios

    2011-01-01

    Strain gradients develop near the crack-tip of Mode I or mixed mode cracks. A finite strain version of the phenomenological strain gradient plasticity theory of Fleck–Hutchinson (2001) is used here to quantify the effect of the material length scales on the crack-tip stress field for a sharp...... stationary crack under Mode I and mixed mode loading. It is found that for material length scales much smaller than the scale of the deformation gradients, the predictions converge to conventional elastic–plastic solutions. For length scales sufficiently large, the predictions converge to elastic solutions....... Thus, the range of length scales over which a strain gradient plasticity model is necessary is identified. The role of each of the three material length scales, incorporated in the multiple length scale theory, in altering the near-tip stress field is systematically studied in order to quantify...

  18. Direct observation of microtwin formation at crack tips in InP

    International Nuclear Information System (INIS)

    Vanderschaeve, G.; Caillard, D.; Peyrade, J.P.

    1992-01-01

    This paper reports that in brittle materials which contain cracks, stress concentrations arise at crack tips. At low temperatures, when the load is increased, brittle fracture happens for a critical stress intensity factor, which is an intrinsic material property, depending on the loading mode and on the cleavage plane. At higher temperatures dislocations may be emitted at the crack tip: a plastic zone is formed, which releases the stresses and increases the critical load for crack propagation. It is generally accepted that the brittle-to ductile transition is controlled directly or indirectly by dislocation mobility. During the course of an in situ transmission electron microscopy, study of dislocation mobility in the III-V compound InP, we have observed the nucleation at a crack tip and the propagation of partial dislocations of same Burgers vectors, resulting in a microtwinning of the crystal. Such an observation provides information on both the way stress relaxation occurs and the relative mobilities of the partial dislocations in this material. In spite of the importance of twin formation on the quality of the material used as substrate in semiconducting devices, this last point is rather poorly documented

  19. The effect of residual thermal stresses on the fatigue crack growth of laser-surface-annealed AISI 304 stainless steel Part I: computer simulation

    International Nuclear Information System (INIS)

    Shiue, R.K.; Chang, C.T.; Young, M.C.; Tsay, L.W.

    2004-01-01

    The effect of residual thermal stresses on the fatigue crack growth of the laser-surface-annealed AISI 304 stainless steel, especially the effect of stress redistribution ahead of the crack tip was extensively evaluated in the study. Based on the finite element simulation, the longitudinal residual tensile stress field has a width of roughly 20 mm on the laser-irradiated surface and was symmetric with respect to the centerline of the laser-annealed zone (LAZ). Meanwhile, residual compressive stresses distributed over a wide region away from the LAZ. After introducing a notch perpendicular to the LAZ, the distribution of longitudinal residual stresses became unsymmetrical about the centerline of LAZ. High residual compressive stresses exist within a narrow range ahead of notch tip. The improved crack growth resistance of the laser-annealed specimen might be attributed to those induced compressive stresses. As the notch tip passed through the centerline of the LAZ, the residual stress ahead of the notch tip was completely reverted into residual tensile stresses. The existence of unanimous residual tensile stresses ahead of the notch tip was maintained, even if the notch tip extended deeply into the LAZ. Additionally, the presence of the residual tensile stress ahead of the notch tip did not accelerate the fatigue crack growth rate in the compact tension specimen

  20. Crack-tip constraint analyses and constraint-dependent LBB curves for circumferential through-wall cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y.L.; Wang, G.Z., E-mail: gzwang@ecust.edu.cn; Xuan, F.Z.; Tu, S.T.

    2015-04-15

    Highlights: • Solution of constraint parameter τ* for through-wall cracked pipes has been obtained. • Constraint increases with increasing crack length and radius–thickness ratio of pipes. • Constraint-dependent LBB curve for through-wall cracked pipes has been constructed. • For increasing accuracy of LBB assessments, constraint effect should be considered. - Abstract: The leak-before-break (LBB) concept has been widely applied in the structural integrity assessments of pressured pipes in nuclear power plants. However, the crack-tip constraint effects in LBB analyses and designs cannot be incorporated. In this paper, by using three-dimensional finite element calculations, the modified load-independent T-stress constraint parameter τ* for circumferential through-wall cracked pipes with different geometries and crack sizes has been analyzed under different loading conditions, and the solutions of the crack-tip constraint parameter τ* have been obtained. Based on the τ* solutions and constraint-dependent J–R curves of a steel, the constraint-dependent LBB (leak-before-break) curves have been constructed. The results show that the constraint τ* increases with increasing crack length θ, mean radius R{sub m} and radius–thickness ratio R{sub m}/t of the pipes. In LBB analyses, the critical crack length calculated by the J–R curve of the standard high constraint specimen for pipes with shorter cracks is over-conservative, and the degree of conservatism increases with decreasing crack length θ, R{sub m} and R{sub m}/t. Therefore, the constraint-dependent LBB curves should be constructed to modify the over-conservatism and increase accuracy of LBB assessments.

  1. The dislocation distribution function near a crack tip generated by external sources

    International Nuclear Information System (INIS)

    Lung, C.W.; Deng, K.M.

    1988-06-01

    The dislocation distribution function near a crack tip generated by external sources is calculated. It is similar to the shape of curves calculated for the crack tip emission case but the quantative difference is quite large. The image forces enlarges the negative dislocation zone but does not change the form of the curve. (author). 10 refs, 3 figs

  2. Mixed-mode crack tip loading and crack deflection in 1D quasicrystals

    Science.gov (United States)

    Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas

    2016-12-01

    Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J1, J2 and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

  3. Effects of External Hydrogen on Hydrogen Transportation and Distribution Around the Fatigue Crack Tip in Type 304 Stainless Steel

    Science.gov (United States)

    Chen, Xingyang; Zhou, Chengshuang; Cai, Xiao; Zheng, Jinyang; Zhang, Lin

    2017-10-01

    The effects of external hydrogen on hydrogen transportation and distribution around the fatigue crack tip in type 304 stainless steel were investigated by using hydrogen microprint technique (HMT) and thermal desorption spectrometry. HMT results show that some silver particles induced by hydrogen release are located near the fatigue crack and more silver particles are concentrated around the crack tip, which indicates that hydrogen accumulates in the vicinity of the crack tip during the crack growth in hydrogen gas environment. Along with the crack propagation, strain-induced α' martensite forms around the crack tip and promotes hydrogen invasion into the matrix, which will cause the crack initiation and propagation at the austenite/ α' martensite interface. In addition, the hydrogen content in the vicinity of the crack tip is higher than that at the crack edge far away from the crack tip, which is related to the stress state and strain-induced α' martensite.

  4. The tensile effect on crack formation in single crystal silicon irradiated by intense pulsed ion beam

    Science.gov (United States)

    Liang, Guoying; Shen, Jie; Zhang, Jie; Zhong, Haowen; Cui, Xiaojun; Yan, Sha; Zhang, Xiaofu; Yu, Xiao; Le, Xiaoyun

    2017-10-01

    Improving antifatigue performance of silicon substrate is very important for the development of semiconductor industry. The cracking behavior of silicon under intense pulsed ion beam irradiation was studied by numerical simulation in order to understand the mechanism of induced surface peeling observed by experimental means. Using molecular dynamics simulation based on Stillinger Weber potential, tensile effect on crack growth and propagation in single crystal silicon was investigated. Simulation results reveal that stress-strain curves of single crystal silicon at a constant strain rate can be divided into three stages, which are not similar to metal stress-strain curves; different tensile load velocities induce difference of single silicon crack formation speed; the layered stress results in crack formation in single crystal silicon. It is concluded that the crack growth and propagation is more sensitive to strain rate, tensile load velocity, stress distribution in single crystal silicon.

  5. Size-effects at a crack-tip interacting with a number of voids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo; Niordson, Christian Frithiof

    2008-01-01

    A strain gradient plasticity theory is used to analyse the growth of discretely represented voids in front of a blunting crack tip, in order to study the influence of size effects on two competing mechanisms of crack growth. For a very small void volume fraction the crack tip tends to interact...... of the characteristic material length relative to the initial void radius. For a case showing the multiple void mechanism, it is found that the effect of the material length can change the behaviour towards the void by void mechanism. A material model with three characteristic length scales is compared with a one...

  6. Water radiolysis in a crack tip under gamma ray irradiation

    International Nuclear Information System (INIS)

    Satoh, Tomonori; Uchida, Shunsuke; Satoh, Yoshiyuki

    2002-01-01

    Under a non-irradiation condition, oxidant, e.g., O 2 and H 2 O 2 , in a crack tip is supplied from the bulk water. But under irradiation conditions, even if the diffusion of radiolytic species is not sufficient, direct radiolysis in the crack tip causes high concentrations of radiolytic species. As a result of measurements and Monte Carlo calculation of gamma ray energy deposition, it has been confirmed that the energy deposition rate in the gap water is larger than that in the bulk water. The energy absorption rate increases as the gap width decreases and reaches 1.3 times that in the bulk water. In order to evaluate crack propagation rate for irradiation assisted stress corrosion cracking (IASCC) of stainless steel, a water radiolysis model in a crevice is proposed. A larger energy deposition rate in the crevice water produces many more radiolytic species, which causes high oxidant concentrations in spite of enhanced recombination of the species at the crevice inner surface. So, for IASCC evaluation, crevice water chemistry plays an important role to determine the crack propagation rate under irradiation. (authors)

  7. Multi-parameter approximation of the stress field in a cracked body in the more distant surroundings of the crack tip

    Czech Academy of Sciences Publication Activity Database

    Veselý, V.; Sobek, J.; Frantík, P.; Seitl, Stanislav

    2016-01-01

    Roč. 89, AUG (2016), s. 20-35 ISSN 0142-1123. [International Conference on Characterisation of Crack Tip Fields /3./. Urbino, 20.04.2015-22.04.2015] Institutional support: RVO:68081723 Keywords : Crack-tip fields * Williams power series * Higher order terms * Stress field reconstruction * Multi-parameter approximation accuracy Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.899, year: 2016

  8. Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth in a Nickel-Base Disk Alloy

    Science.gov (United States)

    Telesman, J.; Gabb, T. P.; Ghosn, L. J.

    2016-01-01

    Both environmental embrittlement and crack tip visco-plastic stress relaxation play a significant role in determining the dwell fatigue crack growth (DFCG) resistance of nickel-based disk superalloys. In the current study performed on the Low Solvus High Refractory (LSHR) disk alloy, the influence of these two mechanisms were separated so that the effects of each could be quantified and modeled. Seven different microstructural variations of LSHR were produced by controlling the cooling rate and the subsequent aging and thermal exposure heat treatments. Through cyclic fatigue crack growth testing performed both in air and vacuum, it was established that four out of the seven LSHR heat treatments evaluated, possessed similar intrinsic environmental resistance to cyclic crack growth. For these four heat treatments, it was further shown that the large differences in dwell crack growth behavior which still persisted, were related to their measured stress relaxation behavior. The apparent differences in their dwell crack growth resistance were attributed to the inability of the standard linear elastic fracture mechanics (LEFM) stress intensity parameter to account for visco-plastic behavior. Crack tip stress relaxation controls the magnitude of the remaining local tensile stresses which are directly related to the measured dwell crack growth rates. It was hypothesized that the environmentally weakened grain boundary crack tip regions fail during the dwells when their strength is exceeded by the remaining local crack tip tensile stresses. It was shown that the classical creep crack growth mechanisms such as grain boundary sliding did not contribute to crack growth, but the local visco-plastic behavior still plays a very significant role by determining the crack tip tensile stress field which controls the dwell crack growth behavior. To account for the influence of the visco-plastic behavior on the crack tip stress field, an empirical modification to the LEFM stress

  9. Transport of lead to crack tips in steam generator tubes

    International Nuclear Information System (INIS)

    Adler, G.D.; Marks, C.R.; Fruzzetti, K.

    2009-01-01

    The mechanisms by which lead is transported from its ultimate source to steam generator tubes and into cracks are not well understood and, to date, a comprehensive evaluation of possible mechanisms has not previously been performed. Specifically, local lead concentrations up to 20 wt. percent have been measured at crack tips, and it is not fully understood how lead concentrations of this magnitude occur, since lead concentrations in SG feedwater are typically quite low (on the order of a few parts per trillion). Additionally, there is evidence that at secondary side conditions, lead is essentially entirely adsorbed onto solid surfaces. Furthermore, if lead were present in the liquid phase, it would not be expected to be in a form that would facilitate concentration in a crevice (crack) by electrochemical means. There has previously been some speculation that lead transport to crack tips may occur through surface diffusion of adsorbed species. It has also been postulated that lead transport may occur via diffusion through the oxide layer along crack walls or via diffusion of lead out of the bulk Alloy 600 to grain boundaries exposed to secondary water by advancing cracks. However, there have been no critical evaluations of these hypotheses. With the current state of knowledge, it is difficult for utilities to determine whether additional efforts to further reduce the inventory of lead in the secondary system are justified. Furthermore, specific sources of lead that are especially likely to accelerate SCC cannot be identified (e.g., significant masses of lead are present in SG deposits, but it is not known if this lead can be transported to crack tips). The work presented in this paper quantitatively evaluates (based on the published literature, not new experimental work) a number of hypothesized lead transport mechanisms, including: Liquid phase diffusion; Electrochemically influenced diffusion of cations and anions; Bulk alloy diffusion; Surface diffusion; Solid

  10. Numerical Analysis of Joule Heating Behavior and Residual Compressive Stress around Crack Tip under High Electric Load

    Directory of Open Access Journals (Sweden)

    Thomas Jin-Chee Liu

    2017-01-01

    Full Text Available This paper discusses the Joule heating effect and residual compressive stress near the crack tip under the electro-thermo-structural coupling state. For the crack tip field, the compressive condition is important for retarding or stopping the crack growth.

  11. Dislocation structures around crack tips of fatigued polycrystalline copper

    International Nuclear Information System (INIS)

    Kaneko, Yoshihisa; Ishikawa, Masao; Hashimoto, Satoshi

    2005-01-01

    Dislocation structures near fatigue cracks of polycrystalline copper specimens were analyzed using the electron channelling contrast imaging (ECCI) technique. Prior to the ECCI observations, optical microscopy was conducted to classify the fatigue crack morphologies into several kinds. It was found that the dislocation structures were correlated with the slip morphologies observed using the optical microscope. The cell structure almost corresponded to the severely deformed plastic zone where the individual slip bands could not be identified. The labyrinth dislocation structure was detected at the double-slip region. Ladder-like dislocation structure was detected ahead of the Stage I type fatigue crack. Hence, it can be said that the persistent slip band (PSB) was a favorable crack path. However, the microscopic route of the crack growth was not along the PSB but along the cell structure, which was developed locally in the vicinity of the crack tip

  12. Low temperature tensile properties and stress corrosion cracking resistance in the super duplex stainless steels weldments

    International Nuclear Information System (INIS)

    Lee, Jeung Woo; Sung, Jang Hyun; Lee, Sung Keun

    1998-01-01

    Low temperature tensile properties and SCC resistances of super duplex stainless steels and their weldments are investigated. Tensile strengths increase remarkably with decreasing test temperature, while elongations decrease steeply at -196 .deg. C after showing peak or constant value down to -100 .deg. C. Owing to the low tensile deformation of weld region, elongations of welded specimen decrease in comparison to those of unwelded specimen. The welded tensile specimen is fractured through weld region at -196 .deg. C due to the fact that the finely dispersed ferrite phase in the austenite matrix increases an opportunity to supply the crack propagation path through the brittle ferrite phase at low temperature. The stress corrosion cracking initiates preferentially at the surface ferrite phase of base metal region and propagates through ferrite phase. When the corrosion crack meets with the fibrously aligned austenite phase to the tensile direction, the ferrite phase around austenite continues to corrode. Eventually, fracture of the austenite phase begins without enduring the tensile load. The addition of Cu+W to the super duplex stainless steel deteriorates the SCC resistance in boiling MgCl 2 solution, possibly due to the increment of pits in the ferrite phase and reduction of N content in the austenite phase

  13. Analytical description of brittle-to-ductile transition in bcc metals. Nucleation of dislocation loop at the crack tip

    International Nuclear Information System (INIS)

    Voskoboinikov, R.E.

    2002-03-01

    Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Dependence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc) in the crack tip vicinity. (orig.)

  14. Crack growth prediction method considering interaction between multiple cracks. Growth of surface cracks of dissimilar size under cyclic tensile and bending load

    International Nuclear Information System (INIS)

    Kamaya, Masayuki; Miyokawa, Eiichi; Kikuchi, Masanori

    2011-01-01

    When multiple cracks approach one another, the stress intensity factor is likely to change due to the interaction of the stress field. This causes change in growth rate and shape of cracks. In particular, when cracks are in parallel position to the loading direction, the shape of cracks becomes non-planar. In this study, the complex growth of interacting cracks is evaluated by using the S-Version finite element method, in which local detailed finite element mesh (local mesh) is superposed on coarse finite element model (global mesh) representing the global structure. In order to investigate the effect of interaction on the growth behavior, two parallel surface cracks are subjected to cyclic tensile or bending load. It is shown that the smaller crack is shielded by larger crack due to the interaction and stops growing when the difference in size of two cracks is significant. Based on simulations of various conditions, a procedure and criteria for evaluating crack growth for fitness-for-service assessment is proposed. According to the procedure, the interaction is not necessary to be considered in the crack growth prediction when the difference in size of two cracks exceeds the criterion. (author)

  15. The evolution of crack-tip stresses during a fatigue overload event

    International Nuclear Information System (INIS)

    Steuwer, A.; Rahman, M.; Shterenlikht, A.; Fitzpatrick, M.E.; Edwards, L.; Withers, P.J.

    2010-01-01

    The mechanisms responsible for the transient retardation or acceleration of fatigue crack growth subsequent to overloading are a matter of intense debate. Plasticity-induced closure and residual stresses have often been invoked to explain these phenomena, but closure mechanisms are disputed, especially under conditions approximating to generalised plane strain. In this paper we exploit synchrotron radiation to report very high spatial resolution two-dimensional elastic strain and stress maps at maximum and minimum loading measured under plane strain during a normal fatigue cycle, as well as during and after a 100% overload event, in ultra-fine grained AA5091 aluminium alloy. These observations provide direct evidence of the material stress state in the vicinity of the crack-tip in thick samples. Significant compressive residual stresses were found both in front of and behind the crack-tip immediately following the overload event. The effective stress intensity at the crack-tip was determined directly from the local stress field measured deep within the bulk (plane strain) by comparison with linear elastic fracture mechanical theory. This agrees well with that nominally applied at maximum load and 100% overload. After overload, however, the stress fields were not well described by classical K fields due to closure-related residual stresses. Little evidence of overload closure was observed sometime after the overload event, in our case possibly because the overload plastic zone was very small.

  16. Crack Tip Flipping Under Mode I/III Tearing

    DEFF Research Database (Denmark)

    Felter, Christian Lotz; Specht Jensen, Lasse; Nielsen, Kim Lau

    Crack tip flipping, where the fracture surface alternates from side to side in 45° shear bands, seems to be an overlooked propagation mode in Mode I sheet tearing often disregarded as  “transitional” or tied to randomness in the material. In fact, such observations rarely make it to the literature...

  17. The crack propagating behavior of composite coatings prepared by PEO on aluminized steel during in situ tensile processing

    International Nuclear Information System (INIS)

    Chen Zhitong; Li Guang; Wu Zhenqiang; Xia Yuan

    2011-01-01

    Research highlights: → Composite coatings on the aluminized steel were prepared by the plasma electrolytic oxidation (PEO) technique, which comprised of Fe-Al layer, Al layer and Al 2 O 3 layer. → The evaluation method of the crack critical opening displacement δ c was introduced to describe quantitatively the resistance of Al layer to the propagation behavior of cracks and evaluate the fracture behavior of composite coatings. → The crack propagating model was established. - Abstract: This paper investigates the in situ tensile cracks propagating behavior of composite coatings on the aluminized steel generated using the plasma electrolytic oxidation (PEO) technique. Cross-sectional micrographs and elemental compositions were investigated by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The composite coatings were shown to consist of Fe-Al, Al and Al 2 O 3 layers. The cracks propagating behavior was observed in real-time in situ SEM tensile test. In tensile process, the cracks were temporarily stopped when cracks propagated from Fe-Al layer to Al layer. The critical crack opening displacement δ c was introduced to quantitatively describe the resistance of the Al layer. There was a functional relation among the thickness ratio t Al /t Al 2 O 3 , the δ c of composite coatings and tensile cracks' spacing. The δ c increased with the increasing of the thickness ratio (t Al /t Al 2 O 3 ). The high δ c value means high fracture resistance. Therefore, a control of the thickness ratio t Al /t Al 2 O 3 was concerned as a key to improve the toughness and strength of the aluminized steel.

  18. Biaxial loading and shallow-flaw effects on crack-tip constraint and fracture toughness

    International Nuclear Information System (INIS)

    Bass, B.R.; Bryson, J.W.; Theiss, T.J.; Rao, M.C.

    1994-01-01

    A program to develop and evaluate fracture methodologies for the assessment of crack-tip constraint effects on fracture toughness of reactor pressure vessel (RPV) steels has been initiated in the Heavy-Section Steel Technology (HSST) Program. Crack-tip constraint is an issue that significantly impacts fracture mechanics technologies employed in safety assessment procedures for commercially licensed nuclear RPVs. The focus of studies described herein is on the evaluation of two stressed-based methodologies for quantifying crack-tip constraint (i.e., J-Q theory and a micromechanical scaling model based on critical stressed volumes) through applications to experimental and fractographic data. Data were utilized from single-edge notch bend (SENB) specimens and HSST-developed cruciform beam specimens that were tested in HSST shallow-crack and biaxial testing programs. Results from applications indicate that both the J-Q methodology and the micromechanical scaling model can be used successfully to interpret experimental data from the shallow- and deep-crack SENB specimen tests. When applied to the uniaxially and biaxially loaded cruciform specimens, the two methodologies showed some promising features, but also raised several questions concerning the interpretation of constraint conditions in the specimen based on near-tip stress fields. Fractographic data taken from the fracture surfaces of the SENB and cruciform specimens are used to assess the relevance of stress-based fracture characterizations to conditions at cleavage initiation sites. Unresolved issues identified from these analyses require resolution as part of a validation process for biaxial loading applications. This report is designated as HSST Report No. 142

  19. The characteristics of ultra-high performance concrete and cracking behavior of reinforced concrete tensile specimens

    Directory of Open Access Journals (Sweden)

    H.A. Rahdar

    2016-09-01

    Full Text Available The tensile behavior of concrete depends on some factors such as member dimensions, reinforcement ratio, diameter of rebar, strength and elasticity modulus of material. In this research the experimental method is used to examine the characteristics and the behavior of ultra-high performance concrete on the tensile behavior of concrete members reinforced by steel rebar. The results show that increasing the rebar cover on diameter rebar ratio (C/d increases the initial stiffening before the cracking stage in concrete. Also, by increasing of reinforcement ratio the cracking space decreased.

  20. Linear least squares approach for evaluating crack tip fracture parameters using isochromatic and isoclinic data from digital photoelasticity

    Science.gov (United States)

    Patil, Prataprao; Vyasarayani, C. P.; Ramji, M.

    2017-06-01

    In this work, digital photoelasticity technique is used to estimate the crack tip fracture parameters for different crack configurations. Conventionally, only isochromatic data surrounding the crack tip is used for SIF estimation, but with the advent of digital photoelasticity, pixel-wise availability of both isoclinic and isochromatic data could be exploited for SIF estimation in a novel way. A linear least square approach is proposed to estimate the mixed-mode crack tip fracture parameters by solving the multi-parameter stress field equation. The stress intensity factor (SIF) is extracted from those estimated fracture parameters. The isochromatic and isoclinic data around the crack tip is estimated using the ten-step phase shifting technique. To get the unwrapped data, the adaptive quality guided phase unwrapping algorithm (AQGPU) has been used. The mixed mode fracture parameters, especially SIF are estimated for specimen configurations like single edge notch (SEN), center crack and straight crack ahead of inclusion using the proposed algorithm. The experimental SIF values estimated using the proposed method are compared with analytical/finite element analysis (FEA) results, and are found to be in good agreement.

  1. Biaxial loading and shallow-flaw effects on crack-tip constraint and fracture-toughness

    International Nuclear Information System (INIS)

    Pennell, W.E.; Bass, B.R.; Bryson, J.W.; McAfee, W.J.; Theiss, T.J.; Rao, M.C.

    1993-01-01

    Uniaxial tests of single-edged notched bend (SENB) specimens with both deep- and shallow-flaws have shown elevated fracture-toughness for the shallow flaws. The elevation in fracture-toughness for shallow flaws has been shown to be the result of reduced constraint at the crack-tip. Biaxial loading has the potential to increase constraint at the crack-tip and thereby reduce some of the shallow-flaw, fracture-toughness elevation. Biaxial fracture-toughness tests have shown that the shallow-flaw, fracture-toughness elevation is reduced but not eliminated by biaxial loading. Dual-parameter, fracture-toughness correlations have been proposed to reflect the effect of crack-tip constraint on fracture-toughness. Test results from the uniaxial and biaxial tests were analyzed using the dual-parameter technology. Discrepancies between analysis results and cleavage initiation site data from fractographic examinations indicate that the analysis models are in need of further refinement. Addition of a precleavage, ductile-tearing element to the analysis model has the potential to resolve the noted discrepancies

  2. [Mechanism of the dentino-enamel junction on the resist-crack propagation of human teeth by the finite element method].

    Science.gov (United States)

    Jingjing, Zheng; Tiezhou, Hou; Hong, Tao; Xueyan, Guo; Cui, Wu

    2014-10-01

    This study aims to identify the crack tip stress intensity factor of the propagation process, crack propagation path, and the changes in the shape of the crack tip by the finite element method. The finite element model of dentino-enamel junction was established with ANSYS software, and the length of the initial crack in the single edge was set to 0.1 mm. The lower end of the sample was fixed. The tensile load of 1 MPa with frequency of 5 Hz was applied to the upper end. The stress intensity factor, deflection angle, and changes in the shape of the crack tip in the crack propagation were calculated by ANSYS. The stress intensity factor suddenly and continuously decreased in dentino-enamel junction as the crack extended. A large skewed angle appeared, and the stress on crack tip was reduced. The dentino-enamel junction on human teeth may resist crack propagation through stress reduction.

  3. Multi-scale analysis of deformation behavior at SCC crack tip (2). (Contract research)

    International Nuclear Information System (INIS)

    Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Hayakawa, Masao; Nagashima, Nobuo

    2007-03-01

    This report describes a result of the research conducted by the Japan Atomic Energy Agency and the National Institute for Materials Science under contract with Japan Nuclear Energy Safety Organization (JNES) that was concerned with a multi-scale analysis of plastic deformation behavior at the crack tip of stress corrosion cracking (SCC). The research was carried out to evaluate the validity of the SCC growth data acquired in the intergranular SCC (IGSCC) project based on a mechanistic understanding of SCC. For the purpose, in this research, analyses of the plastic deformation behavior and microstructure around the crack tip were performed in a nano-order scale. The hardness measured in nano, meso and macro scales was employed as a common index of the strength, and the essential data necessary to understand the SCC propagation behavior were acquired and analyzed that are mainly a size of plastic deformation region and a microstructural information in the region, e.g. data of crystallografy, microscopic deformation and dislocations at the inside of grains and grain boundaries. In this year, we analyzed the state of plastic deformation region at the crack tip of IGSCC under various conditions and investigated relationship between crack growth behavior and stress intensity factor. Especially, we investigated in detail about two different hardened specimens used in the SCC growth tests in the IGSCC project. (J.P.N.)

  4. Cleavage crack growth resistance due to plastic flow around a near-tip dislocation-free region

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    1997-01-01

    ; but plastic yielding far from the tip still adds to the fracture toughness. The model employed makes use of a dislocation-free strip of elastic material, inside which the crack propagates, while the material outside the strip is described by continuum plasticity. The approximation involved in assuming......Crack growth resistance curves are computed numerically for cases where fracture occurs by atomic separation, so that the length scale of the fracture process is typically much smaller than the dislocation spacing. Here, continuum plasticity would not give realistic stress levels near the crack tip...

  5. Influence of tip mass on dynamic behavior of cracked cantilever pipe conveying fluid with moving mass

    International Nuclear Information System (INIS)

    Yoon, Han Ik; Son, In Soo

    2005-01-01

    In this paper, we studied about the effect of the open crack and a tip mass on the dynamic behavior of a cantilever pipe conveying fluid with a moving mass. The equation of motion is derived by using Lagrange's equation and analyzed by numerical method. The cantilever pipe is modelled by the Euler-Bernoulli beam theory. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The influences of the crack, the moving mass, the tip mass and its moment of inertia, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the tip-displacement of the cantilever pipe are analytically clarified

  6. Tensile flow stress of ceramic particle-reinforced metal in the presence of particle cracking

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, R. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory for Mechanical Metallurgy, CH-1015 Lausanne (Switzerland); Rossoll, A. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory for Mechanical Metallurgy, CH-1015 Lausanne (Switzerland)], E-mail: andreas.rossoll@epfl.ch; Weber, L. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory for Mechanical Metallurgy, CH-1015 Lausanne (Switzerland); Bourke, M.A.M. [Los Alamos National Laboratory (LANL), LANSCE-12, P.O. Box 1663, MS H805, Los Alamos, NM 87545 (United States); Dunand, D.C. [Northwestern University, Department of Materials Science and Engineering, Evanston, IL 60208 (United States); Mortensen, A. [Ecole Polytechnique Federale de Lausanne (EPFL), Laboratory for Mechanical Metallurgy, CH-1015 Lausanne (Switzerland)

    2008-10-15

    A simplified model is proposed to quantify the effect of damage in the form of particle cracking on the elastic and plastic behaviour of particle-reinforced metal matrix composites under uniaxial tensile loading: cracked particles are simply replaced, in a mean-field model, with as much matrix. Pure aluminium reinforced with 44 vol.% alumina particles, tested in tension and unloaded at periodic plastic deformations, is analysed by neutron diffraction during each reloading elastic step, at 30%, 50%, 70% and 90% of the tensile flow stress. The data give the evolution of the elastic matrix strains in the composite and also measure the progress of internal damage by particle cracking. The test gives (i) the evolution of the in situ matrix flow stress, and (ii) the evolution of load partitioning during elastic deformation with increasing composite damage. Predictions of the present model compare favourably with relevant results in the literature, and with results from the present neutron diffraction experiments.

  7. Tensile flow stress of ceramic particle-reinforced metal in the presence of particle cracking

    International Nuclear Information System (INIS)

    Mueller, R.; Rossoll, A.; Weber, L.; Bourke, M.A.M.; Dunand, D.C.; Mortensen, A.

    2008-01-01

    A simplified model is proposed to quantify the effect of damage in the form of particle cracking on the elastic and plastic behaviour of particle-reinforced metal matrix composites under uniaxial tensile loading: cracked particles are simply replaced, in a mean-field model, with as much matrix. Pure aluminium reinforced with 44 vol.% alumina particles, tested in tension and unloaded at periodic plastic deformations, is analysed by neutron diffraction during each reloading elastic step, at 30%, 50%, 70% and 90% of the tensile flow stress. The data give the evolution of the elastic matrix strains in the composite and also measure the progress of internal damage by particle cracking. The test gives (i) the evolution of the in situ matrix flow stress, and (ii) the evolution of load partitioning during elastic deformation with increasing composite damage. Predictions of the present model compare favourably with relevant results in the literature, and with results from the present neutron diffraction experiments

  8. Effect of temperature on the rate of fatigue crack propagation in some steels during low cycle fatigue

    International Nuclear Information System (INIS)

    Taira, S.; Fujino, M.; Maruyama, S.

    Temperature dependence of the rate of fatigue crack propagation in steels was examined, and compared with the temperature dependence of tensile ductility. Microcracks initiate and affect the propagation behavior of the main crack at elevated temperatures. Factors found to be elucidated include initiation rate of microcracks, reduction of ductility of the material in the vicinity of the main crack tip, and relaxation of concentrated strain by multi-cracks. It was found that during a strain controlled low cycle fatigue test at 1 cpm, the rate of crack propagation is largest at the blue-brittleness temperature range (200 to 300 0 C) in a low carbon steel. On the other hand, it is largest at above 700 0 C in austenite stainless steels. The temperature dependence of the rate of fatigue crack propagation is opposite to that of tensile ductility. Microcracks formed in the vicinity of the main crack tip were calculated, by considering the strain concentration and strain cycles imposed. Then, the local fracture strain was evaluated. Good correlation was found between the rate of crack propagation and the local fracture strain. (U.S.)

  9. Crack Propagation Calculations for Optical Fibers under Static Bending and Tensile Loads Using Continuum Damage Mechanics

    Science.gov (United States)

    Chen, Yunxia; Cui, Yuxuan; Gong, Wenjun

    2017-01-01

    Static fatigue behavior is the main failure mode of optical fibers applied in sensors. In this paper, a computational framework based on continuum damage mechanics (CDM) is presented to calculate the crack propagation process and failure time of optical fibers subjected to static bending and tensile loads. For this purpose, the static fatigue crack propagation in the glass core of the optical fiber is studied. Combining a finite element method (FEM), we use the continuum damage mechanics for the glass core to calculate the crack propagation path and corresponding failure time. In addition, three factors including bending radius, tensile force and optical fiber diameter are investigated to find their impacts on the crack propagation process and failure time of the optical fiber under concerned situations. Finally, experiments are conducted and the results verify the correctness of the simulation calculation. It is believed that the proposed method could give a straightforward description of the crack propagation path in the inner glass core. Additionally, the predicted crack propagation time of the optical fiber with different factors can provide effective suggestions for improving the long-term usage of optical fibers. PMID:29140284

  10. Multi-scale analysis of deformation behavior at SCC crack tip (3) (Contract research)

    International Nuclear Information System (INIS)

    Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Hayakawa, Masao; Nagashima, Nobuo

    2008-08-01

    In recent years, incidents of the stress corrosion cracking (SCC) were frequently reported that occurred to the various components of domestic boiling water reactors (BWR), and the cause investigation and measure become the present important issue. By the Japan nuclear energy safety organization (JNES), a research project on the intergranular SCC (IGSCC) in nuclear grade stainless steels (henceforth, IGSCC project) is under enforcement from a point of view to secure safety and reliability of BWR, and SCC growth data of low carbon stainless steels are being accumulated for the weld part or the work-hardened region adjacent to the weld metal. In the project, it has been an important subject to guarantee the validity of accumulated SCC data. At a crack tip of SCC in compact tension (CT) type specimen used for the SCC propagation test, a macroscopic plastic region is formed where heterogeneity of microstructure developed by microscopic sliding and dislocations is observed. However, there is little quantitative information on the plastic region, and therefore, to assess the data of macroscopic SCC growth rate and the validity of propagation test method, it is essentially required to investigate the plastic region at the crack tip in detail from a microscopic viewpoint. This report describes a result of the research conducted by the Japan Atomic Energy Agency and the National Institute for Materials Science under contract with JNES that was concerned with a multi-scale analysis of plastic deformation behavior at the crack tip of SCC. The research was carried out to evaluate the validity of the SCC growth data acquired in the IGSCC project based on a mechanistic understanding of SCC. For the purpose, in this research, analyses of the plastic deformation behavior and microstructure around the crack tip were performed in a nano-order scale. The hardness measured in nano, meso and macro scales was employed as a common index of the strength, and the essential data necessary

  11. An experimental and analytical study of ductile fracture and stable crack-growth

    International Nuclear Information System (INIS)

    Rousselier, G.

    1978-01-01

    A study is described, the objectives of which were to define a numerical model for stable crack growth, to calibrate the model by tensile tests, and to obtain agreement between corresponding numerical calculations and experiments on cracked specimens. The model was based on a finite element program with a critical state at the crack tip defined by a ductility curve: equivalent plastic strain versus stress triaxiality. The curve was determined by tests on notched tensile specimens of a low alloy rotor steel. The critical states corresponded to the initiation of a crack at the centre of the specimens. Three point bend tests were also performed and experimental and numerical load displacement curves and crack growth versus displacement curves were compared. Agreement with experiments on cracked specimens was obtained by simple fittings of the 'ductility' curve in the high triaxiality area. Results are discussed and it is indicated where future progress might be made in numerical modelling of cracked bodies. (author)

  12. Crack tip field in circumferentially-cracked round bar (CCRB in tension affected by loss of axial symmetry

    Directory of Open Access Journals (Sweden)

    J. Toribio

    2017-07-01

    Full Text Available In this paper, the stress intensity factor (SIF is computed in a circumferentially-cracked round bar (CCRB subjected to tensile loading, considering that the resistant ligament is circular and exhibits certain eccentricity in relation to the cylinder axis. The computation was performed by means of the finite element method (FEM using a three dimensional (3D model and the J-integral, the analyzed variable being the eccentricity of the circular ligament. Results show that the SIF is higher at the deepest point of the crack and that an increase of eccentricity (in relation to the bar axis raises the difference between the SIF values along the crack front. From a certain value of the misalignment a bending effect appears, so that the crack remains closed in the area near the point of lower depth.

  13. Enhancement of J estimation for typical nuclear pipes with a circumferential surface crack under tensile load

    International Nuclear Information System (INIS)

    Cho, Doo Ho; Woo, Seung Wan; Choi, Jae Boong; Kim, Young Jin; Chang, Yoon Suk; Jhung, Myung Jo; Choi, Young Hwan

    2010-01-01

    This paper is to report enhancement of engineering J estimation for semi-elliptical surface cracks under tensile load. Firstly, limitation of the sole solution suggested by Zahoor is shown for reliable structural integrity assessment of thin-walled nuclear pipes. An improved solution is then developed based on extensive 3D FE analyses employing deformation plasticity theory for typical nuclear piping materials. It takes over the structure of the existing solution but provides new tabulated plastic influence functions to cover a wide range of pipe geometry and crack shape. Furthermore, to facilitate easy prediction of the plastic influence function, an alternative simple equation is also developed by using a statistical response surface method. The proposed H 1 values can be used for elastic-plastic fracture analyses of thin-walled pipes with a circumferential surface crack subjected to tensile loading

  14. Enhancement of J estimation for typical nuclear pipes with a circumferential surface crack under tensile load

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Doo Ho; Woo, Seung Wan; Choi, Jae Boong; Kim, Young Jin [Sungkyunkwan University, Suwon (Korea, Republic of); Chang, Yoon Suk [Kyung Hee University, Yongin (Korea, Republic of); Jhung, Myung Jo; Choi, Young Hwan [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

    2010-03-15

    This paper is to report enhancement of engineering J estimation for semi-elliptical surface cracks under tensile load. Firstly, limitation of the sole solution suggested by Zahoor is shown for reliable structural integrity assessment of thin-walled nuclear pipes. An improved solution is then developed based on extensive 3D FE analyses employing deformation plasticity theory for typical nuclear piping materials. It takes over the structure of the existing solution but provides new tabulated plastic influence functions to cover a wide range of pipe geometry and crack shape. Furthermore, to facilitate easy prediction of the plastic influence function, an alternative simple equation is also developed by using a statistical response surface method. The proposed H{sub 1} values can be used for elastic-plastic fracture analyses of thin-walled pipes with a circumferential surface crack subjected to tensile loading

  15. Strain gradient plasticity modeling of hydrogen diffusion to the crack tip

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; del Busto, S.; Niordson, Christian Frithiof

    2016-01-01

    to characterize the gradient-enhanced stress elevation and subsequent diffusion of hydrogen towards the crack tip. Results reveal that GNDs, absent in conventional plasticity predictions, play a fundamental role on hydrogen transport ahead of a crack. SGP estimations provide a good agreement with experimental......In this work hydrogen diffusion towards the fracture process zone is examined accounting for local hardening due to geometrically necessary dislocations (GNDs) by means of strain gradient plasticity (SGP). Finite element computations are performed within the finite deformation theory...

  16. Prediction of crack density and electrical resistance changes in indium tin oxide/polymer thin films under tensile loading

    KAUST Repository

    Mora Cordova, Angel; Khan, Kamran; El Sayed, Tamer

    2014-01-01

    We present unified predictions for the crack onset strain, evolution of crack density, and changes in electrical resistance in indium tin oxide/polymer thin films under tensile loading. We propose a damage mechanics model to quantify and predict

  17. Dynamical observations on the crack tip zone and stress corrosion of two-dimensional MoS2

    KAUST Repository

    Ly, Thuc Hue

    2017-01-18

    Whether and how fracture mechanics needs to be modified for small length scales and in systems of reduced dimensionality remains an open debate. Here, employing in situ transmission electron microscopy, atomic structures and dislocation dynamics in the crack tip zone of a propagating crack in two-dimensional (2D) monolayer MoS2 membrane are observed, and atom-to-atom displacement mapping is obtained. The electron beam is used to initiate the crack; during in situ observation of crack propagation the electron beam effect is minimized. The observed high-frequency emission of dislocations is beyond previous understanding of the fracture of brittle MoS2. Strain analysis reveals dislocation emission to be closely associated with the crack propagation path in nanoscale. The critical crack tip plastic zone size of nearly perfect 2D MoS2 is between 2 and 5 nm, although it can grow to 10 nm under corrosive conditions such as ultraviolet light exposure, showing enhanced dislocation activity via defect generation.

  18. A quantitative prediction model of SCC rate for nuclear structure materials in high temperature water based on crack tip creep strain rate

    International Nuclear Information System (INIS)

    Yang, F.Q.; Xue, H.; Zhao, L.Y.; Fang, X.R.

    2014-01-01

    Highlights: • Creep is considered to be the primary mechanical factor of crack tip film degradation. • The prediction model of SCC rate is based on crack tip creep strain rate. • The SCC rate calculated at the secondary stage of creep is recommended. • The effect of stress intensity factor on SCC growth rate is discussed. - Abstract: The quantitative prediction of stress corrosion cracking (SCC) of structure materials is essential in safety assessment of nuclear power plants. A new quantitative prediction model is proposed by combining the Ford–Andresen model, a crack tip creep model and an elastic–plastic finite element method. The creep at the crack tip is considered to be the primary mechanical factor of protective film degradation, and the creep strain rate at the crack tip is suggested as primary mechanical factor in predicting the SCC rate. The SCC rates at secondary stage of creep are recommended when using the approach introduced in this study to predict the SCC rates of materials in high temperature water. The proposed approach can be used to understand the SCC crack growth in structural materials of light water reactors

  19. Nonlocal Effects of Crack Curving.

    Science.gov (United States)

    1982-07-01

    close vTcinity of the crack tip. Supported by the Office of Naval Research. 2 For brittle solids, a fracture criterion based on the maximum tensile...Reidel Pubi. Co. Dordrecht. Holland. pp. 271-318, 1978. [13] A.S. Jayatilaka, Fracture of Engineering Brittle Materials, Appl. Sci. Publishers, London...Crescent leach Road, Glen Cove * Long Island, New Tork 11542 Commanding Officer (2) U.s Amy Research Office PO, Sax 12211 Research Triangle Park. C 27709 8

  20. Mechanisms of fatigue crack retardation following single tensile overloads in powder metallurgy aluminum alloys

    Science.gov (United States)

    Bray, G. H.; Reynolds, A. P.; Starke, E. A., Jr.

    1992-01-01

    In ingot metallurgy (IM) alloys, the number of delay cycles following a single tensile overload typically increases from a minimum at an intermediate baseline stress intensity range, Delta-K(B), with decreasing Delta-K(B) approaching threshold and increasing Delta-K(B) approaching unstable fracture to produce a characteristic 'U' shaped curve. Two models have been proposed to explain this behavior. One model is based on the interaction between roughness and plasticity-induced closure, while the other model only utilizes plasticity-induced closure. This article examines these models, using experimental results from constant amplitude and single overload fatigue tests performed on two powder metallurgy (PM) aluminum alloys, AL-905XL and AA 8009. The results indicate that the 'U'-shaped curve is primarily due to plasticity-induced closure, and that the plasticity-induced retardation effect is through-thickness in nature, occurring in both the surface and interior regions. However, the retardation effect is greater at the surface, because the increase in plastic strain at the crack tip and overload plastic zone size are larger in the plane-stress surface regions than in the plane-strain interior regions. These results are not entirely consistent with either of the proposed models.

  1. Fringe Analysis around an Inclined Crack Tip of Finite-Width Plate under Tensile Load by Photoelastic Phase-Shifting Method

    International Nuclear Information System (INIS)

    Li, Weizheng; Baek, Tae Hyun; Lee, Byung Hee; Seo, Jin; Hong, Dong Pyo

    2012-01-01

    Photoelasticity is a technique of experimental methods and has been widely used in various domains of engineering to determine the stress distribution of structures. Without complicated mathematical formulation, this technique can conveniently provide a fairly accurate whole-field stress analysis for a mechanical structure. Here, stress distribution around an inclined crack tip of finite-width plate is studied by 8-step phase-shifting method. This method is a kind of photoelastic phase-shifting techniques and can be used for the determination of the phase values of isochromatics and isoclinics. According to stress-optic law, the stress distribution could be obtained from fringe patterns. The results obtained by polariscope arrangement combined with 8-step method and ABAQUS FEM simulations are compared with each other. Good agreement between them shows that 8-step phase-shifting method is reliable and can be used for determination of stress by experiment

  2. Crack-tips enriched platinum-copper superlattice nanoflakes as highly efficient anode electrocatalysts for direct methanol fuel cells.

    Science.gov (United States)

    Zheng, Lijun; Yang, Dachi; Chang, Rong; Wang, Chengwen; Zhang, Gaixia; Sun, Shuhui

    2017-07-06

    We have developed "crack-tips" and "superlattice" enriched Pt-Cu nanoflakes (NFs), benefiting from the synergetic effects of "crack-tips" and "superlattice crystals"; the Pt-Cu NFs exhibit 4 times higher mass activity, 6 times higher specific activity and 6 times higher stability than those of the commercial Pt/C catalyst, respectively. Meanwhile, the Pt-Cu NFs show more enhanced CO tolerance than the commercial Pt/C catalyst.

  3. Motion of Defect Clusters and Dislocations at a Crack Tip of Irradiated Material

    International Nuclear Information System (INIS)

    Moon, Won Jin; Kwon, Sang Chul; Kim, Whung Whoe

    2007-01-01

    Effects of defect clusters on mechanical properties of irradiated materials have not been clarified until now. Two radiation hardening models have been proposed. One is a dispersed barrier hardening mechanism based on the Orowan hardening model. This explains defect clusters as barriers to a dislocation motion. Generally the dislocation would rather shear or remove the defect clusters than make so-called Orowan loops. And the other is a cascade induced source hardening mechanism, which explains defect clusters as a Cottrell atmosphere for dislocation motions. However, the above mechanisms can not explain the microstructure of deformed material after irradiation and the phenomenon of yield softening. These mechanisms are based on an immobility of clusters. But we observed defect clusters could move into a specific crystallographic direction easily. Through 3 times of High Voltage Electron Microscope analysis, defect clusters have been observed to make one dimensional motion without applied external stress. If very small defect clusters could move under a stress gradient due to interactions between clusters, we can suggest that the clusters will move more actively when a stress gradient is applied externally. In-situ tensile test at TEM, we confirmed that kind of motion. We suggest defect clusters can move into crack tip, a stress-concentrated area due to tensile stress gradient and dislocations move out from the area by shear stress. Therefore radiation hardening can be explained agglomeration of defect clusters at stress concentrated area prohibits a generation of dislocation and make an increase of yield point

  4. A linear least squares approach for evaluation of crack tip stress field parameters using DIC

    Science.gov (United States)

    Harilal, R.; Vyasarayani, C. P.; Ramji, M.

    2015-12-01

    In the present work, an experimental study is carried out to estimate the mixed-mode stress intensity factors (SIF) for different cracked specimen configurations using digital image correlation (DIC) technique. For the estimation of mixed-mode SIF's using DIC, a new algorithm is proposed for the extraction of crack tip location and coefficients in the multi-parameter displacement field equations. From those estimated coefficients, SIF could be extracted. The required displacement data surrounding the crack tip has been obtained using 2D-DIC technique. An open source 2D DIC software Ncorr is used for the displacement field extraction. The presented methodology has been used to extract mixed-mode SIF's for specimen configurations like single edge notch (SEN) specimen and centre slant crack (CSC) specimens made out of Al 2014-T6 alloy. The experimental results have been compared with the analytical values and they are found to be in good agreement, thereby confirming the accuracy of the algorithm being proposed.

  5. Cross-validated detection of crack initiation in aerospace materials

    Science.gov (United States)

    Vanniamparambil, Prashanth A.; Cuadra, Jefferson; Guclu, Utku; Bartoli, Ivan; Kontsos, Antonios

    2014-03-01

    A cross-validated nondestructive evaluation approach was employed to in situ detect the onset of damage in an Aluminum alloy compact tension specimen. The approach consisted of the coordinated use primarily the acoustic emission, combined with the infrared thermography and digital image correlation methods. Both tensile loads were applied and the specimen was continuously monitored using the nondestructive approach. Crack initiation was witnessed visually and was confirmed by the characteristic load drop accompanying the ductile fracture process. The full field deformation map provided by the nondestructive approach validated the formation of a pronounced plasticity zone near the crack tip. At the time of crack initiation, a burst in the temperature field ahead of the crack tip as well as a sudden increase of the acoustic recordings were observed. Although such experiments have been attempted and reported before in the literature, the presented approach provides for the first time a cross-validated nondestructive dataset that can be used for quantitative analyses of the crack initiation information content. It further allows future development of automated procedures for real-time identification of damage precursors including the rarely explored crack incubation stage in fatigue conditions.

  6. Hydrogen induced crack propagation in metal under plain-strain deformation

    International Nuclear Information System (INIS)

    Fishgojt, A.V.; Kolachev, B.A.

    1981-01-01

    A model of subcritical crack propagation conditioned by the effect of dissolved hydrogen in the case of plane-strain deformation of high-strength materials, is suggested. It is supposed that diffusion takes place in the isotropic material and hydrogen diffuses in the region of tensile stress maximum before crack tip under the effect of the stress gradient. When hydrogen achieves the critical concentration, microcrack growth takes place. Values of crack growth rates experimentally obtained agree with values calculated according to the suggested formula. Calculation and experimental data on the Ti-6Al-4V alloy, are presented [ru

  7. Hydrogen Induced Crack and Phase Transformation in Hydrogen Pressured Tensile Test of 316L Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Un Bong; Nam, Sung Hoon [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Choe, Byung Hak; Shim, Jong Hun [Gangneung-Wonju National University, Gangneung (Korea, Republic of); Kim, Young Uk [Hanyang University, Ansan (Korea, Republic of); Kim, Young Suk; Kim, Sung Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Hong, Keyyong [Korea Research Institute of Ship and Ocean Engineering, Deajeon (Korea, Republic of)

    2015-02-15

    The aim of this investigation is to prove the mechanism of hydrogen induced crack (HIC) of 316L stainless steels in hydrogen pressured tensile test. Microstructures like twin, planar slip, and abnormal phase transformation around the HIC were analyzed by transmission electron microscopy. Deformation twin accompanied by planar slip could be related to the main cause of HIC in the hydrogen pressured tensile condition, because intragranular HICs were mainly observed along the boundaries of twins and planar slip lines. An abnormal forbidden diffraction was also accompanied by HIC in the hydrogen attacked area. Examination of the HIC mechanism in austenitic stainless steel can be applied to the fitness of use for alloys with the possibility of various susceptible cracks in a hydrogen and stress atmosphere.

  8. Determination of Fracture Parameters for Multiple Cracks of Laminated Composite Finite Plate

    Science.gov (United States)

    Srivastava, Amit Kumar; Arora, P. K.; Srivastava, Sharad Chandra; Kumar, Harish; Lohumi, M. K.

    2018-04-01

    A predictive method for estimation of stress state at zone of crack tip and assessment of remaining component lifetime depend on the stress intensity factor (SIF). This paper discusses the numerical approach for prediction of first ply failure load (FL), progressive failure load, SIF and critical SIF for multiple cracks configurations of laminated composite finite plate using finite element method (FEM). The Hashin and Chang failure criterion are incorporated in ABAQUS using subroutine approach user defined field variables (USDFLD) for prediction of progressive fracture response of laminated composite finite plate, which is not directly available in the software. A tensile experiment on laminated composite finite plate with stress concentration is performed to validate the numerically predicted subroutine results, shows excellent agreement. The typical results are presented to examine effect of changing the crack tip distance (S), crack offset distance (H), and stacking fiber angle (θ) on FL, and SIF .

  9. Extended timescale atomistic modeling of crack tip behavior in aluminum

    International Nuclear Information System (INIS)

    Baker, K L; Warner, D H

    2012-01-01

    Traditional molecular dynamics (MD) simulations are limited not only by their spatial domain, but also by the time domain that they can examine. Considering that many of the events associated with plasticity are thermally activated, and thus rare at atomic timescales, the limited time domain of traditional MD simulations can present a significant challenge when trying to realistically model the mechanical behavior of materials. A wide variety of approaches have been developed to address the timescale challenge, each having their own strengths and weaknesses dependent upon the specific application. Here, we have simultaneously applied three distinct approaches to model crack tip behavior in aluminum at timescales well beyond those accessible to traditional MD simulation. Specifically, we combine concurrent multiscale modeling (to reduce the degrees of freedom in the system), parallel replica dynamics (to parallelize the simulations in time) and hyperdynamics (to accelerate the exploration of phase space). Overall, the simulations (1) provide new insight into atomic-scale crack tip behavior at more typical timescales and (2) illuminate the potential of common extended timescale techniques to enable atomic-scale modeling of fracture processes at typical experimental timescales. (paper)

  10. Quasi-static crack tip fields in rate-sensitive FCC single crystals

    Indian Academy of Sciences (India)

    In this work, the effects of loading rate, material rate sensitivity and constraint level on quasi-static crack tip fields in a FCC single crystal are studied. ... Global General Motors R&D, India Science Lab, GM Technical Centre (India), Bangalore 560 066, India; Department of Mechanical Engineering, Indian Institute of Science, ...

  11. Mechano-electrochemical study of stress corrosion crack tip area: Case of Zircaloy-4 in halide solution

    International Nuclear Information System (INIS)

    Durif, E.

    2012-01-01

    Stress corrosion cracking (SCC) is a damage phenomenon which results from the synergy between corrosion process (dissolution, adsorption) and mechanical fracture (crack propagation). Although this phenomenon is well known, its modelling is still a challenging issue, especially concerning mechano-electrochemical coupling mechanisms at crack tip, because it depends on model system (metal/aggressive media) and large number of mechanical and electrochemical factors. In this thesis, mutual interactions between dissolution and the stress state around the crack tip (stress intensity factor) are studied in the case of Zircaloy-4 in aqueous halide solution. Samples are first pre-cracked in air by using fatigue load-shedding procedure to control the stress intensity factor. Then, pre-oxidation is used to produce a thin protective passive layer on their surface. The electro-chemical reactions are thus concentrated at the crack tip which also induces a concentration of the mechanical effect. During the test, digital images of the sample surface are acquired. Digital Image Correlation is performed a posteriori in order to obtain the evolution of the crack length and the stress intensity factors. Further, a specific procedure is developed in order to perform the DIC analysis while the test is running. This allows to control the load so that a given value of the stress intensity factor is prescribed. With this innovative experimental technique, we perform experimental tests that allow to discriminate the effects between different stress corrosion cracking mechanisms. It is suggested that once a critical anodic polarization is exceeded, the crack growth rate depends on the stress intensity factor but also on its time derivative. Indeed, a threshold effect is obtained on the stress intensity factor, meaning that plasticity must increase for the dissolution reaction to occur, but also on its rate meaning that time for plasticity to produce new dislocations must not exceed the

  12. Models for ductile crack initiation and tearing resistance under mode 1 loading in pressure vessel steels

    International Nuclear Information System (INIS)

    Jones, M.R.

    1988-06-01

    Micromechanistic models are presented which aim to predict plane strain ductile initiation toughness, tearing resistance and notched bar fracture strains in pressure vessel steels under monotonically increasing tensile (mode 1) loading. The models for initiation toughness and tearing resistance recognize that ductile fracture proceeds by the growth and linkage of voids with the crack-tip. The models are shown to predict the trend of initiation toughness with inclusion spacing/size ratio and can bound the available experimental data. The model for crack growth can reproduce the tearing resistance of a pressure vessel steel up to and just beyond crack growth initiation. The fracture strains of notched bars pulled in tension are shown to correspond to the achievement of a critical volume fraction of voids. This criterion is combined with the true stress - true strain history of a material point ahead of a blunting crack-tip to predict the initiation toughness. An attempt was made to predict the fracture strains of notched tensile bars by adopting a model which predicts the onset of a shear localization phenomenon. Fracture strains of the correct order are computed only if a ''secondary'' void nucleation event at carbide precipitates is taken into account. (author)

  13. Crack Tip Flipping under Mode I Tearing: Investigated by X-Ray Tomography

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau; Gundlach, Carsten

    2017-01-01

    The fracture surface morphology that results from mode I tearing of ductile plate metals depends heavily on both the elastic-plastic material properties and the microstructure. Severe tunneling of the advancing crack tip (resulting in cup-cup, or bath-tub like fracture surfaces) can take place...... in a range of materials, often of low strength, while tearing of high strength metals typically progress by the shear band failure mechanism (slanting). In reality, however, most fracture surfaces display a mixture of morphologies. For example, slant crack propagation can be accompanied by large shear lips...... near the outer free plate surface or a complete shear band switch - seemingly distributed randomly on the fracture surface. The occasionally observed shear band switch of mode I slant cracks, related to ductile plate tearing, is far from random as the crack can flip systematically from one side...

  14. Heat-affected zone liquation crack on resistance spot welded TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Dulal Chandra [Department of Advanced Materials Engineering, Dong-Eui University, 995 Eomgwangno, Busanjin-gu, Busan 614-714 (Korea, Republic of); Chang, InSung [Automotive Production Development Division, Hyundai Motor Company (Korea, Republic of); Park, Yeong-Do, E-mail: ypark@deu.ac.kr [Department of Advanced Materials Engineering, Dong-Eui University, 995 Eomgwangno, Busanjin-gu, Busan 614-714 (Korea, Republic of)

    2014-07-01

    In this study, the heat affected zone (HAZ) liquation crack and segregation behavior of the resistance spot welded twinning induced plasticity (TWIP) steel have been reported. Cracks appeared in the post-welded joints that originated at the partially melted zone (PMZ) and propagated from the PMZ through the heat affected zone (HAZ) to the base metal (BM). The crack length and crack opening widths were observed increasing with heat input; and the welding current was identified to be the most influencing parameter for crack formation. Cracks appeared at the PMZ when nugget diameter reached at 4.50 mm or above; and the liquation cracks were found to occur along two sides of the notch tip in the sheet direction rather than in the electrode direction. Cracks were backfilled with the liquid films which has lamellar structure and supposed to be the eutectic constituent. Co-segregation of alloy elements such as, C and Mn were detected on the liquid films by electron-probe microanalysis (EPMA) line scanning and element map which suggests that the liquid film was enrich of Mn and C. The eutectic constituent was identified by analyzing the calculated phase diagram along with thermal temperature history of finite element simulation. Preliminary experimental results showed that cracks have less/no significant effect on the static cross-tensile strength (CTS) and the tensile-shear strength (TSS). In addition, possible ways to avoid cracking were discussed. - Highlights: • The HAZ liquation crack during resistance spot welding of TWIP steel was examined. • Cracks were completely backfilled and healed with divorced eutectic secondary phase. • Co-segregation of C and Mn was detected in the cracked zone. • Heat input was the most influencing factor to initiate liquation crack. • Cracks have less/no significant effect on static tensile properties.

  15. Heat-affected zone liquation crack on resistance spot welded TWIP steels

    International Nuclear Information System (INIS)

    Saha, Dulal Chandra; Chang, InSung; Park, Yeong-Do

    2014-01-01

    In this study, the heat affected zone (HAZ) liquation crack and segregation behavior of the resistance spot welded twinning induced plasticity (TWIP) steel have been reported. Cracks appeared in the post-welded joints that originated at the partially melted zone (PMZ) and propagated from the PMZ through the heat affected zone (HAZ) to the base metal (BM). The crack length and crack opening widths were observed increasing with heat input; and the welding current was identified to be the most influencing parameter for crack formation. Cracks appeared at the PMZ when nugget diameter reached at 4.50 mm or above; and the liquation cracks were found to occur along two sides of the notch tip in the sheet direction rather than in the electrode direction. Cracks were backfilled with the liquid films which has lamellar structure and supposed to be the eutectic constituent. Co-segregation of alloy elements such as, C and Mn were detected on the liquid films by electron-probe microanalysis (EPMA) line scanning and element map which suggests that the liquid film was enrich of Mn and C. The eutectic constituent was identified by analyzing the calculated phase diagram along with thermal temperature history of finite element simulation. Preliminary experimental results showed that cracks have less/no significant effect on the static cross-tensile strength (CTS) and the tensile-shear strength (TSS). In addition, possible ways to avoid cracking were discussed. - Highlights: • The HAZ liquation crack during resistance spot welding of TWIP steel was examined. • Cracks were completely backfilled and healed with divorced eutectic secondary phase. • Co-segregation of C and Mn was detected in the cracked zone. • Heat input was the most influencing factor to initiate liquation crack. • Cracks have less/no significant effect on static tensile properties

  16. Investigation and microstructural analyses of massive LSP impacts with coverage area on crack initiation location and tensile properties of AM50 magnesium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Luo, K.Y.; Wang, C.Y. [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); Sun, G.F. [School of Mechanical Engineering, Southeast University, Nanjing 211189 (China); Cui, C.Y.; Sheng, J. [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China); Lu, J.Z., E-mail: blueesky2005@163.com [School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013 (China)

    2016-01-05

    The influence of massive laser shock peening (LSP) impacts with coverage area on tensile properties of AM50 magnesium alloy was investigated using MTS880-10 servo-hydraulic material testing machine system. Microstructure in the surface layer and fracture morphologies of as-machined and LSPed tensile specimens were also characterized and analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cross-sectional optical microscopy (OM). Special attention is paid to the crack initiation location as a function of LSPed coverage area in the gauge part of tensile specimen. Experimental results and analysis indicate that coverage area significantly influenced tensile properties of the tensile specimen. In addition, the grain refinement process in the top surface layer of AM50 magnesium alloy caused by massive LSP impacts is presented. Furthermore, the underlying influence mechanism of LSPed coverage area on tensile properties and crack initiation location of tensile specimen was clearly revealed.

  17. Investigation and microstructural analyses of massive LSP impacts with coverage area on crack initiation location and tensile properties of AM50 magnesium alloy

    International Nuclear Information System (INIS)

    Luo, K.Y.; Wang, C.Y.; Sun, G.F.; Cui, C.Y.; Sheng, J.; Lu, J.Z.

    2016-01-01

    The influence of massive laser shock peening (LSP) impacts with coverage area on tensile properties of AM50 magnesium alloy was investigated using MTS880-10 servo-hydraulic material testing machine system. Microstructure in the surface layer and fracture morphologies of as-machined and LSPed tensile specimens were also characterized and analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cross-sectional optical microscopy (OM). Special attention is paid to the crack initiation location as a function of LSPed coverage area in the gauge part of tensile specimen. Experimental results and analysis indicate that coverage area significantly influenced tensile properties of the tensile specimen. In addition, the grain refinement process in the top surface layer of AM50 magnesium alloy caused by massive LSP impacts is presented. Furthermore, the underlying influence mechanism of LSPed coverage area on tensile properties and crack initiation location of tensile specimen was clearly revealed.

  18. Transient hydrogen diffusion analyses coupled with crack-tip plasticity under cyclic loading

    International Nuclear Information System (INIS)

    Kotake, Hirokazu; Matsumoto, Ryosuke; Taketomi, Shinya; Miyazaki, Noriyuki

    2008-01-01

    The effect of hydrogen on the material strengths of metals is known as the hydrogen embrittlement, which affects the structural integrity of a hydrogen energy system. In the present paper, we developed a computer program for a transient hydrogen diffusion-elastoplastic coupling analysis by combining an in-house finite element program with a general purpose finite element computer program to analyze hydrogen diffusion. In this program, we use a hypothesis that the hydrogen absorbed in the metal affects the yield stress of the metal. In the present paper, we discuss the effects of the cyclic loading on the hydrogen concentration near the crack tip. An important finding we obtained here is the fact that the hydrogen concentration near the crack tip greatly depends on the loading frequency. This result indicates that the fatigue lives of the components in a hydrogen system depend not only on the number of loading cycles but also on the loading frequency

  19. Actual light deflections in regions of crack tips and their influence on measurements in photomechanics

    Science.gov (United States)

    Hecker, Friedrich W.; Pindera, Jerzy T.; Wen, Baicheng

    Crack-tip photomechanics procedures are based on certain simplifying assumptions that are seldom discussed. In a recent paper the theoretical bases of the shadow optical methods of caustics have been analysed and tested using the results obtained by three analytical-experimental procedures, namely classical strain gage techniques, isodynes, and strain-gradient index method. It has been concluded that the straing-radient index method appears to be a suitable tool for analysis of stress states near crack tips and notches and, in particular, for testing the predictive power of the pertinent singular solutions of the linear elastic fracture mechanics and the ranges of their applicability. In the present paper, a more detailed analysis of all results obtained in light deflection experiments allows to quantify the contribution of both involved effects and to determine the distortion of the faces of the investigated plates along their crack planes. The ability of the strain-gradient light bending method to analyse some features of the three-dimensional stress-state is reported. Finally, the presented experimental evidence allows to draw conclusions related to limits of applicability of certain photomechanical measurements near crack tips. An extensive summary of this paper is published in the Proceedings of the Second International Conference on Photomechanics and Speckle Metrology, Vol. 1554A, part of SPIE's 1991 International Symposium on Optical Applied Science and Engineering, 22-26 July 1991, San Diego, CA, USA. 1

  20. Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD

    Energy Technology Data Exchange (ETDEWEB)

    Laureys, A., E-mail: Aurelie.Laureys@UGent.be [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Depover, T. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Petrov, R. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Verbeken, K. [Department of Materials Science and Engineering, Ghent University (UGent), Technologiepark 903, B-9052 Ghent (Belgium)

    2016-02-15

    The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses just after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of

  1. Microstructural characterization of hydrogen induced cracking in TRIP-assisted steel by EBSD

    International Nuclear Information System (INIS)

    Laureys, A.; Depover, T.; Petrov, R.; Verbeken, K.

    2016-01-01

    The present work evaluates hydrogen induced cracking by performing an elaborate EBSD (Electron BackScatter Diffraction) study in a steel with transformation induced plasticity (TRIP-assisted steel). This type of steel exhibits a multiphase microstructure which undergoes a deformation induced phase transformation. Additionally, each microstructural constituent displays a different behavior in the presence of hydrogen. The aim of this study is to obtain a better understanding on the mechanisms governing hydrogen induced crack initiation and propagation in the hydrogen saturated multiphase structure. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The tests were interrupted at stresses just after reaching the tensile strength, i.e. before macroscopic failure of the material. This allowed to study hydrogen induced crack initiation and propagation by SEM (Scanning Electron Microscopy) and EBSD. A correlation was found between the presence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. Initiation seems to occur mostly by martensite decohesion. High strain regions surrounding the hydrogen induced crack tips indicate that further crack propagation may have occurred by the HELP (hydrogen-enhanced localized plasticity) mechanism. Small hydrogen induced cracks located nearby the notch are typically S-shaped and crack propagation was dominantly transgranularly. The second stage of crack propagation consists of stepwise cracking by coalescence of small hydrogen induced cracks. - Highlights: • Hydrogen induced cracking in TRIP-assisted steel is evaluated by EBSD. • Tensile tests were conducted on notched hydrogen saturated samples. • Crack initiation occurs by a H-Enhanced Interface DEcohesion (HEIDE) mechanism. • Crack propagation involves growth and coalescence of small cracks. • Propagation is governed by the characteristics of

  2. Observation and simulation of crack growth in Zry-4

    International Nuclear Information System (INIS)

    Bertolino, Graciela; Meyer, Gabriel; Perez Ipina, J

    2003-01-01

    Security and life extension of components of nuclear reactors are the most motivating aspects that encourage to study embrittlement processes of zirconium alloys by reaction with hydrogen.Here, the use of fracture mechanics tests are suitable to monitor the material resistance of components under service.Because many times is difficult to obtain normalized probes from real size components, researchers look for alternative experimental techniques or crack growth simulation from the knowledge of particular material properties.In this work we present the results obtained after experimental observation and computer simulation of crack growth in Zry-4 probes.Experimental observation were obtained by performing flexion tests in three point probes SSEN(B) of 3 x 7 x 32 mm 3 located in the chamber of a scanning electron microscope, measuring in situ the crack length and opening when an external load is applied.Using the information obtained from stress-displacement measurements after tensile tests and the empiric relationship between crack opening and crack length, the crack growth process was simulated.Displacement field in the zone close to the crack tip was obtained by finite elements technique (Castem, DMT, CEA) assuming plain stress, a plastic bilinear homogeneous material and neglecting texture or directional anisotropy.To compare experimental observation and simulation, a grid (10 x 10 μm 2 each square) was drawn in the zone close to the crack tip by selective sputtering.Following the movement of two (three) points of the surface allows to compare uni (bi) dimensional deformation.A good agreement between observation and simulation was observed: after the crack opening grew 28 times (from 1.5 to 42 μm) the base-height relationship of a triangle involving the crack tip change 40% (35%) in the experimental observation (simulation)

  3. Pearlitic ductile cast iron: damaging micromechanisms at crack tip

    Directory of Open Access Journals (Sweden)

    F. Iacoviello

    2013-07-01

    Full Text Available Ductile cast irons (DCIs are characterized by a wide range of mechanical properties, mainly depending on microstructural factors, as matrix microstructure (characterized by phases volume fraction, grains size and grain distribution, graphite nodules (characterized by size, shape, density and distribution and defects presence (e.g., porosity, inclusions, etc.. Versatility and higher performances at lower cost if compared to steels with analogous performances are the main DCIs advantages. In the last years, the role played by graphite nodules was deeply investigated by means of tensile and fatigue tests, performing scanning electron microscope (SEM observations of specimens lateral surfaces during the tests (“in situ” tests and identifying different damaging micromechanisms.In this work, a pearlitic DCIs fatigue resistance is investigated considering both fatigue crack propagation (by means of Compact Type specimens and according to ASTM E399 standard and overload effects, focusing the interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules. On the basis of experimental results, and considering loading conditions and damaging micromechanisms, the applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in ferritic DCIs is critically analyzed, mainly focusing the stress intensity factor amplitude role.

  4. Experimental estimation of the heat energy dissipated in a volume surrounding the tip of a fatigue crack

    Directory of Open Access Journals (Sweden)

    G. Meneghetti

    2016-01-01

    Full Text Available Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, when combined with the Neuber’s structural volume concept, it might be used as an experimentally measurable parameter to assess the fatigue damage accumulation rate of cracked components. On the basis of a theoretical model published previously, in this work the heat energy dissipated in a volume surrounding the crack tip is estimated experimentally on the basis of the radial temperature profiles measured by means of an infrared camera. The definition of the structural volume in a fatigue sense is beyond the scope of the present paper. The experimental crack propagation tests were carried out on hot-rolled, 6-mm-thick AISI 304L stainless steel specimens subject to completely reversed axial fatigue loading.

  5. Hydrogen Absorption Induced Slow Crack Growth in Austenitic Stainless Steels for Petrochemical Pressure Vessel Industries

    Directory of Open Access Journals (Sweden)

    Ronnie Rusli

    2011-05-01

    Full Text Available Type 304Land type 309 austenitic stainless steels were tested either by exposed to gaseous hydrogen or undergoing polarized cathodic charging. Slow crack growth by straining was observed in type 304L, and the formation of α‘ martensite was indicated to be precursor for such cracking. Gross plastic deformation was observed at the tip of the notch, and a single crack grew slowly from this region in a direction approximately perpendicular to the tensile axis. Martensite formation is not a necessary condition for hydrogen embrittlement in the austenitic phase.

  6. Standard test method for crack-tip opening displacement (CTOD) fracture toughness measurement

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2008-01-01

    1.1 This test method covers the determination of critical crack-tip opening displacement (CTOD) values at one or more of several crack extension events, and may be used to measure cleavage crack initiation toughness for materials that exhibit a change from ductile to brittle behavior with decreasing temperature, such as ferritic steels. This test method applies specifically to notched specimens sharpened by fatigue cracking. The recommended specimens are three-point bend [SE(B)], compact [C(T)], or arc-shaped bend [A(B)] specimens. The loading rate is slow and influences of environment (other than temperature) are not covered. The specimens are tested under crosshead or clip gage displacement controlled loading. 1.1.1 The recommended specimen thickness, B, for the SE(B) and C(T) specimens is that of the material in thicknesses intended for an application. For the A(B) specimen, the recommended depth, W, is the wall thickness of the tube or pipe from which the specimen is obtained. Superficial surface machini...

  7. Measurements of radiated elastic wave energy from dynamic tensile cracks

    Science.gov (United States)

    Boler, Frances M.

    1990-01-01

    The role of fracture-velocity, microstructure, and fracture-energy barriers in elastic wave radiation during a dynamic fracture was investigated in experiments in which dynamic tensile cracks of two fracture cofigurations of double cantilever beam geometry were propagating in glass samples. The first, referred to as primary fracture, consisted of fractures of intact glass specimens; the second configuration, referred to as secondary fracture, consisted of a refracture of primary fracture specimens which were rebonded with an intermittent pattern of adhesive to produce variations in fracture surface energy along the crack path. For primary fracture cases, measurable elastic waves were generated in 31 percent of the 16 fracture events observed; the condition for radiation of measurable waves appears to be a local abrupt change in the fracture path direction, such as occurs when the fracture intersects a surface flaw. For secondary fractures, 100 percent of events showed measurable elastic waves; in these fractures, the ratio of radiated elastic wave energy in the measured component to fracture surface energy was 10 times greater than for primary fracture.

  8. Numerical modeling of hydrogen diffusion in structural steels under cathodic overprotection and its effects on fatigue crack propagation

    Energy Technology Data Exchange (ETDEWEB)

    Silva Diniz, D.; Almeida Silva, A. [Federal University of Campina Grande, Campina Grande-PB (Brazil); Andrade Barbosa, J.M. [Federal University of Pernambuco, Recife-PE (Brazil); Palma Carrasco, J.

    2012-05-15

    This paper presents a numerical simulation of the effect of hydrogen atomic diffusion on fatigue crack propagation on structural steels. The simulation was performed with a specimen type CT of API 5CT P110 steel, loaded in the tensile opening mode, in plane strain state and under the effects of a cyclic mechanical load and the hydrogen concentration at the crack tip. As hydrogen source, a cathodic protection system was considered, commonly used in subsea pipelines. The equations of evolution of variables at the crack tip form a non-linear system of ordinary differential equations that was solved by means of the 4th order Runge-Kutta method. The solid-solid diffusion through the lattice ahead of the crack tip was simulated using the finite difference method. The simulations results show that under these conditions, the fatigue crack evolution process is enhanced by the hydrogen presence in the material, and that the start time of the crack propagation decreases as its concentration increases. These results show good correlation and consistency with macroscopic observations, providing a better understanding of hydrogen embrittlement in fatigue crack propagation processes in structural steels. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Facts and views on the role of anionic impurities, crack tip chemistry and oxide films in environmentally assisted cracking

    International Nuclear Information System (INIS)

    Aaltonen, P.; Bojinov, M.; Helin, M.

    2002-01-01

    The aim of this literature study has been to evaluate the level of understanding of the role of anionic impurities in environmentally assisted cracking (EAC) of iron- and nickel-based alloys in the coolant conditions of a boiling water reactor (BWR) - type nuclear power plant, mainly under normal water chemistry (NWC). The study has been motivated by a need to find the most relevant experimental approaches that can be applied when looking for correlations between crack growth rate and measurable electrochemical and chemical parameters. Special crack tip chemistry conditions are established, when trace amounts are present in the BWR coolant and become enriched within a crack. Anions may influence both the conductivity and the pH of the coolant within the crack. In addition, they may influence the composition, structure and properties of the oxide films formed on crack walls either directly via adsorption or incorporation or indirectly via the effect of changes in pH within the crack. Based on the proposed mechanisms for EAC, oxide films formed on crack wall surfaces are likely to play a key role in determing the crack growth rate of structural materials. The prediction of the influence of anionic impurities is thus likely to be facilitated by means of understanding their effect on the films on crack walls. One of the most promising approaches to experimentally clarify this influence is based on investigating the electrochemical behaviour of oxide films Fe- and Ni-based materials in high-temperature conditions simulating the special chemistry within a stress corrosion crack. Results from such studies should be compared and combined with ex situ analytical results obtained using modern electron microscopic techniques. In addition to crack growth, currently available electro-chemical techniques should also be applied to find out whether crack initiation can be explained and modelled on the basis of the electrochemical behaviour of oxide films. (orig.)

  10. Crack Tip Flipping: A New Phenomenon yet to be Resolved in Ductile Plate Tearing

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau

    2017-01-01

    Conclusive insight to the mechanics that govern so-called “crack tip flipping”remains to be revealed, but details continue to fall into place as researcher dig deeper. The work presents an overview of the latest findings and the next steps to be made....

  11. The role of crack tip opening in corrosion fatigue for the ductile ferritic steel-water system

    International Nuclear Information System (INIS)

    Tomkins, B.

    1977-01-01

    Water vapour or a water environment can dramatically reduce the fatigue strength of structural alloys, including aluminium and steel, and this reduction can be often related to the effect of the environment on crack initiation. More recently, however, under certain circumstances, it has become clear that fatigue crack growth rates can also be increased. A limited examination of crack tip openings in ductile steels under corrosion fatigue conditions, indicates that it may be possible to develop more physically based design rules for components which operate in some aqueous environments (author)

  12. Influence of sample geometry and microstructure on the hydrogen induced cracking characteristics under uniaxial load

    Energy Technology Data Exchange (ETDEWEB)

    Laureys, A., E-mail: aurelie.laureys@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium); Depover, T., E-mail: tom.depover@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium); Petrov, R., E-mail: roumen.petrov@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Verbeken, K., E-mail: kim.verbeken@ugent.be [Department of Materials, Textiles and Chemical Engineering, Ghent University (UGent), Tech Lane Ghent Science Park - Campus A, Technologie park 903, B-9052 Gent (Belgium)

    2017-04-06

    The present work evaluates hydrogen induced cracking in a TRIP (transformation induced plasticity) assisted steel and pure iron. The goal of this work is to understand the effect of the macroscopic stress distribution in the material on the hydrogen induced cracking phenomenon. Additionally, the effect of a complex multiphase microstructure on the characteristics of hydrogen induced cracking was investigated by comparing results for TRIP-assisted steel and pure iron as reference material. Tensile tests on notched and unnotched samples combined with in-situ electrochemical hydrogen charging were conducted. Tests were performed until the tensile strength was reached and until fracture. The resulting hydrogen induced cracks were studied by optical microscopy and scanning electron microscopy (SEM). Hydrogen induced cracks showed a typical S-shape and crack propagation was mainly transgranular, independently of the presence of a notch or the material's microstructure. This was also the case for the V-shaped secondary crack network and resulting stepped crack morphology characteristic for hydrogen induced damage. These observations indicate that the stress state surrounding the crack tip has a very large impact on the hydrogen induced cracking characteristics. The use of a notch or the presence of a different microstructure did not influence the overall hydrogen induced cracking features, but did change the kinetics of the hydrogen induced cracking process.

  13. Influence of sample geometry and microstructure on the hydrogen induced cracking characteristics under uniaxial load

    International Nuclear Information System (INIS)

    Laureys, A.; Depover, T.; Petrov, R.; Verbeken, K.

    2017-01-01

    The present work evaluates hydrogen induced cracking in a TRIP (transformation induced plasticity) assisted steel and pure iron. The goal of this work is to understand the effect of the macroscopic stress distribution in the material on the hydrogen induced cracking phenomenon. Additionally, the effect of a complex multiphase microstructure on the characteristics of hydrogen induced cracking was investigated by comparing results for TRIP-assisted steel and pure iron as reference material. Tensile tests on notched and unnotched samples combined with in-situ electrochemical hydrogen charging were conducted. Tests were performed until the tensile strength was reached and until fracture. The resulting hydrogen induced cracks were studied by optical microscopy and scanning electron microscopy (SEM). Hydrogen induced cracks showed a typical S-shape and crack propagation was mainly transgranular, independently of the presence of a notch or the material's microstructure. This was also the case for the V-shaped secondary crack network and resulting stepped crack morphology characteristic for hydrogen induced damage. These observations indicate that the stress state surrounding the crack tip has a very large impact on the hydrogen induced cracking characteristics. The use of a notch or the presence of a different microstructure did not influence the overall hydrogen induced cracking features, but did change the kinetics of the hydrogen induced cracking process.

  14. Fracture Anisotropy and Toughness in the Mancos Shale: Implications for crack-growth geometry

    Science.gov (United States)

    Chandler, M. R.; Meredith, P. G.; Brantut, N.; Crawford, B. R.

    2013-12-01

    The hydraulic fracturing of gas-shales has drawn attention to the fundamental fracture properties of shales. Fracture propagation is dependent on a combination of the in-situ stress field, the fracturing fluid and pressure, and the mechanical properties of the shale. However, shales are strongly anisotropic, and there is a general paucity of available experimental data on the anisotropic mechanical properties of shales in the scientific literature. The mode-I stress intensity factor, KI, quantifies the concentration of stress at crack tips. The Fracture Toughness of a linear elastic material is then defined as the critical value of this stress intensity factor; KIc, beyond which rapid catastrophic crack growth occurs. However, shales display significant non-linearity, which produces hysteresis during experimental cyclic loading. This allows for the calculation of a ductility coefficient using the residual displacement after successive loading cycles. From this coefficient, a ductility corrected Fracture Toughness value, KIcc can be determined. In the Mancos Shale this ductility correction can be as large as 60%, giving a Divider orientation KIcc value of 0.8 MPa.m0.5. Tensile strength and mode-I Fracture Toughness have been experimentally determined for the Mancos Shale using the Brazil Disk and Short-Rod methodologies respectively. The three principal fracture orientations; Arrester, Divider and Short-Transverse were all analysed. A significant anisotropy is observed in the tensile strength, with the Arrester value being 1.5 times higher than the Short-Transverse value. Even larger anisotropy is observed in the Fracture Toughness, with KIcc in the Divider and Arrester orientations being around 1.8 times that in the Short-Transverse orientation. For both tensile strength and fracture toughness, the Short-Transverse orientation, where the fracture propagates in the bedding plane in a direction parallel to the bedding, is found to have significantly lower values than

  15. On the constitutive criteria for the fault: influence of size and tensile cracks generation during rupture

    International Nuclear Information System (INIS)

    Riera, J.D.; Miguel, L.F.F.; Gudiel, L.A.D.

    2005-01-01

    In recent studies the authors consider the possibility of occurrence of tensile crack generation near the free surface during faulting. The main assumption is that the dynamic tensile stress created during the shear rupture process would be dominant over the background stress near the free-surface. The proposed model was able to simulate the mechanism of cracks developed as a flower like-structure surrounding the shear fault in the vicinity of the free surface and explain some aspects of the fracture zones found after the 2000 Tottori earthquake. The applicability of various constitutive laws for the fault employed in numerical analysis of the near source motion, such as the slip-weakening, velocity-weakening or rate- and state-dependent friction laws, were also recently discussed by the authors in connection with results of laboratory experiments on friction. In this paper, the most important conclusions of the studies outlined above are summarized by way of introduction to the numerical modeling of the region adjacent to the fault surface, which includes material nonhomogeneities as well as the possibility of generation of new tensile cracks. In the presence of fracture, both factors exert important influence on the macro constitutive laws for the fault, which relate the static (mean normal and shear stresses) with kinetic (displacements) variables, as well as with their time derivatives. By means of simulation, it is shown that the coefficients in the equation that relate the relevant variables depend on size, that is, they vary with the contact area over which stresses, displacements and velocities are averaged. Any variability in Young's modulus or mass density of the surround rock may however be neglected, the only significant random fields being those that describe friction at the interface and the specific fracture energy. (authors)

  16. Application of computer assisted moire to the study of a crack tip

    Science.gov (United States)

    Sciammarella, C. A.; Albertazzi, A., Jr.; Mourikes, J.

    The basic principles of computer assisted moire are discussed. The influence of the image sensor and its finite dimensions on the sampling theorem requirements is discussed. Criteria for the selection of grating pitch on the basis of the spatial bandwidth of the pattern to be observed and the requirements arising from sensitivity considerations are given. The method is used to analyze the strain field in the neighborhood of the crack tip of a standard ASTM compact tension specimen. From the displacements the strains are computed, and from the strains the stresses are obtained using the generalized Ramberg-Osgood stress strain relationship. The stresses are used to compute the values for the J-integral in several circuits surrounding the crack. Good agreement is obtained between the values of the stress intensity factors obtained by different methods. The plastic region surrounding the crack does not show a HRR field and thus the usual rationale to justify the J-integral methods must be re-evaluated.

  17. Role of plasticity-induced crack closure in fatigue crack growth

    Directory of Open Access Journals (Sweden)

    Jesús Toribio

    2013-07-01

    Full Text Available The premature contact of crack surfaces attributable to the near-tip plastic deformations under cyclic loading, which is commonly referred to as plasticity induced crack closure (PICC, has long been focused as supposedly controlling factor of fatigue crack growth (FCG. Nevertheless, when the plane-strain near-tip constraint is approached, PICC lacks of straightforward evidence, so that its significance in FCG, and even the very existence, remain debatable. To add insights into this matter, large-deformation elastoplastic simulations of plane-strain crack under constant amplitude load cycling at different load ranges and ratios, as well as with an overload, have been performed. Modeling visualizes the Laird-Smith conceptual mechanism of FCG by plastic blunting and re-sharpening. Simulation reproduces the experimental trends of FCG concerning the roles of stress intensity factor range and overload, but PICC has never been detected. Near-tip deformation patterns discard the filling-in a crack with material stretched out of the crack plane in the wake behind the tip as supposed PICC origin. Despite the absence of closure, load-deformation curves appear bent, which raises doubts about the trustworthiness of closure assessment from the compliance variation. This demonstrates ambiguities of PICC as a supposedly intrinsic factor of FCG and, by implication, favors the stresses and strains in front of the crack tip as genuine fatigue drivers.

  18. Molecular dynamics simulation of effect of hydrogen atoms on crack propagation behavior of α-Fe

    Energy Technology Data Exchange (ETDEWEB)

    Song, H.Y., E-mail: gsfshy@sohu.com; Zhang, L.; Xiao, M.X.

    2016-12-16

    The effect of the hydrogen concentration and hydrogen distribution on the mechanical properties of α-Fe with a pre-existing unilateral crack under tensile loading is investigated by molecular dynamics simulation. The results reveal that the models present good ductility when the front region of crack tip has high local hydrogen concentration. The peak stress of α-Fe decreases with increasing hydrogen concentration. The studies also indicate that for the samples with hydrogen atoms, the crack propagation behavior is independent of the model size and boundaries. In addition, the crack propagation behavior is significantly influenced by the distribution of hydrogen atoms. - Highlights: • The distribution of hydrogen plays a critical role in the crack propagation. • The peak stress decrease with the hydrogen concentration increasing. • The crack deformation behavior is disclosed and analyzed.

  19. An investigation into the change of shape of fatigue cracks initiated at surface flaws

    International Nuclear Information System (INIS)

    Portch, D.J.

    1979-09-01

    Surface fatigue cracks found in plant can often be closely approximated in shape by a semi-ellipse. The stress intensity factor range at the deepest part of the surface crack is dependent upon a number of variables, including the crack aspect ratio. In fatigue life analysis, the aspect ratio of a propagating crack is frequently assumed to remain constant, possibly due to the complexity of estimating aspect ratio change on the basis of linear elastic fracture mechanics. This report describes the results of an experimental programme to examine the change of shape of fatigue cracks subjected to uniaxial tensile or bending stresses. The data obtained has been used to modify equations proposed by the author in a previous report to predict the change of aspect ratio of a crack propagating from a known defect. These modified equations, although not including terms to account for the effects of varying mean stress levels or material properties, generally give a good agreement with published experimental results. Crack propagation rate data obtained from the tensile fatigue tests has been used to estimate crack tip stress intensity factors. These are compared with values calculated from published solutions using both the constant geometry assumption and also the shape change equations proposed in this report. Use of these equations gives improved agreement with experiment in most cases. (author)

  20. Effect of overloading types on fatigue crack growth threshold for stainless steel SUS316

    International Nuclear Information System (INIS)

    Osada, Toshio; Sano, Hayato; Takahashi, Koji

    2013-01-01

    Effect of overloading types on the fatigue crack growth threshold of SUS316 was studied. Three types of overloading: tensile (type I), tensile+compression (type II), and tensile+compression+tensile (type III) were applied to compact tension specimens, then the fatigue tests were carried out to determine the apparent threshold stress intensity factor range Δ N K th . The results showed that the Δ N K th values increased with increasing the single tensile overload stress intensity factor K ov above the K ov > ΔK th . Additional compressive loading (type II) led to decrease in Δ N K th to the ΔK th =6MPa×m 1/2 within the all tested K ov values ranging from -45MPa×m 1/2 ≤K ov 1/2 . This is due to the fact that the compressive residual stress field at crack tip changed to the tensile stress field by the compressive loading. Furthermore, the Δ N K th values increased again by additional tensile overloading (type III) from ΔK th to the almost same Δ N K th values as that by Type I loading. This means that the almost same compressive residual stress field formed by type III overloading as the type I overloading. The experimental Δ N K th increasing behaviors were discussed by Finite Element Method (FEM). (author)

  1. Numerical simulations of material mismatch and ductile crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Oestby, Erling

    2002-07-01

    Both the global geometry and inhomogeneities in material properties will influence the fracture behaviour of structures in presence of cracks. In this thesis numerical simulations have been used to investigate how some aspects of both these issues affect the conditions at the crack-tip. The thesis is organised in an introduction chapter, summarising the major findings and conclusions, a review chapter, presenting the main aspects of the developments in the field of fracture mechanics, and three research papers. Paper I considers the effect of mismatch in hardening exponent on the local near-tip stress field for stationary interface cracks in bi-materials under small scale yielding conditions. It is demonstrated that the stress level in the weaker material increases compared to what is found in the homogeneous material for the same globally applied load level, with the effect being of increasing importance as the crack-tip is approached. Although a coupling between the radial and angular dependence of the stress fields exists, the evolving stress field can still be normalised with the applied J. The effect on the increase in stress level can closely be characterised by the difference in hardening exponent, {delta}n, termed the hardening mismatch, and is more or less independent of the absolute level of hardening in the two materials. Paper II and Ill deal with the effects of geometry, specimen size, hardening level and yield stress mismatch in relation to ductile crack growth. The ductile crack growth is simulated through use of the Gurson model. In Paper H the effect of specimen size on the crack growth resistance is investigated for deep cracked bend and shallow cracked tensile specimens. At small amounts of crack growth the effect of specimen size on the crack growth resistance is small, but a more significant effect is found for larger amounts of crack growth. The crack growth resistance decreases in smaller specimens loaded in tension, whereas the opposite is

  2. Stress corrosion cracking of X80 pipeline steel exposed to high pH solutions with different concentrations of bicarbonate

    Science.gov (United States)

    Fan, Lin; Du, Cui-wei; Liu, Zhi-yong; Li, Xiao-gang

    2013-07-01

    Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in high pH solutions with various concentrations of HCO{3/-} at a passive potential of -0.2 V vs. SCE were investigated by slow strain rate tensile (SSRT) test. The SCC mechanism and the effect of HCO{3/-} were discussed with the aid of electrochemical techniques. It is indicated that X80 steel shows enhanced susceptibility to SCC with the concentration of HCO{3/-} increasing from 0.15 to 1.00 mol/L, and the susceptibility can be evaluated in terms of current density at -0.2 V vs. SCE. The SCC behavior is controlled by the dissolution-based mechanism in these circumstances. Increasing the concentration of HCO{3/-} not only increases the risk of rupture of passive films but also promotes the anodic dissolution of crack tips. Besides, little susceptibility to SCC is found in dilute solution containing 0.05 mol/L HCO{3/-} for X80 steel. This can be attributed to the inhibited repassivation of passive films, manifesting as a more intensive dissolution in the non-crack tip areas than at the crack tips.

  3. Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads

    International Nuclear Information System (INIS)

    Han, Jeong Woo; Woo, Eun Taek; Han, Seung Ho

    2015-01-01

    To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%

  4. Estimation of Fatigue Crack Growth Behavior of Cracked Specimen Under Mixed-mode Loads

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jeong Woo [KIMM, Daejeon (Korea, Republic of); Woo, Eun Taek; Han, Seung Ho [Dong-A University, Busan (Korea, Republic of)

    2015-07-15

    To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka’s equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka’s equation, and the Paris’ equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.

  5. Subsurface metals fatigue cracking without and with crack tip

    Directory of Open Access Journals (Sweden)

    Andrey Shanyavskiy

    2013-07-01

    Full Text Available Very-High-Cycle-Fatigue regime for metals was considered and mechanisms of the subsurface crack origination were introduced. In many metals first step of crack origination takes place with specific area formation because of material pressing and rotation that directed to transition in any volume to material ultra-high-plasticity with nano-structure appearing. Then by the border of the nano-structure takes place volume rotation and fracture surface creates with spherical particles which usually named Fine-Granular-Area. In another case there takes place First-Smooth-Facet occurring in area of origin due to whirls appearing by the one of the slip systems under discussed the same stress-state conditions. Around Fine-Granular-Area or First-Smooth-Facet there plastic zone appeared and, then, subsurface cracking develops by the same manner as for through cracks. In was discussed quantum-mechanical nature of fatigue crack growth in accordance with Yang’s modulus quantization for low level of deformations. New simply equation was considered for describing subsurface cracking in metals out of Fine-Granular-Area or Fist-Smooth-Facet.

  6. A small angle X-ray scattering method to investigate the crack tip in metals. Final report of the Marie Curie individual fellowship project

    International Nuclear Information System (INIS)

    Ouytsel, K. van; Boehmert, J.; Mueller, G.

    2003-08-01

    Structural materials, such as ferritic and austenitic steels or aluminium alloys used in the nuclear and aircraft industry, are subjected to external operational loads in different environments. Adopting a damage tolerant design principle, understanding the growth of preexisting or newly formed cracks under these conditions is of prime relevance to prevent extensive crack propagation and failure of the component. Within this framework, the characterization of early stages of the damage processes, as nucleation, growth and coalescence of micro-voids and the evolution of the spatial dislocation distribution (dislocation patterning) is a particularly challenging aspect. It was the objective of the work performed to investigate the damage structure near a crack tip by means of small angle X-ray scattering (SAXS). Pre-cracked fracture mechanics standard specimens from different aluminium alloys and steels were loaded up to different amounts of crack growth. From the crack tip range samples of 100 to 200 μm thickness were prepared and a small region around the crack tip was scanned using a microfocused Synchrotron beam. The SAXS experiments were performed at different Synchrotron sources and equipments with different beam cross section, scan step width and X-ray energy. Additionally, the investigation was completed by other methods like X-ray diffraction, X-ray imaging diffraction technique (MAXIM), transmission electron microscopy, scanning electron microscopy, and positron annihilation spectroscopy. The SAXS intensity pattern shows location-related effects. Potential SAXS parameters to characterize the damage are the integral intensity, a fractal dimension parameter and a value determined from the ratio of the intensity vertical and horizontal to the direction of crack growth. Above all, the last parameter is suitable to depict the damage zone around the crack tip. It is robust and applicable even for a material which exhibits an anisotropic SAXS pattern in the

  7. Plugging wellbore fractures : limit equilibrium of a Bingham drilling mud cake in a tensile crack

    Energy Technology Data Exchange (ETDEWEB)

    Garagash, D.I. [Dalhousie Univ., Halifax, NS (Canada). Dept. of Civil and Resource Engineering

    2009-07-01

    The proper selection of drilling muds is important in order to successfully drill hydrocarbon wells in which wellbore mud pressure remains low enough to prevent circulation loss and high enough to support the uncased wellbore against the shear failure. This paper presented a mathematical model to study invasion of mud cake into a drilling-induced planar fracture at the edge of a wellbore perpendicular to the minimum in situ principal stress. The model assumed a planar edge-crack geometry loaded by the wellbore hoop stress, variable mud pressure along the invaded region adjacent to the wellbore, and uniform pore-fluid pressure along the rest of the crack. The invading mud was assumed to freely displaces the pore-fluid in the crack without mixing with it. The case corresponding to a sufficiently permeable formation was considered. This solution provides a means to evaluate whether or not the mud cake could effectively plug the fracture, thereby prevent fracture propagation and associated uncontrollable loss of wellbore drilling mud. The toughness or tensile strength is evaluated based on criterion for initiation of crack propagation, which may lead to uncontrollable loss of mud circulation in a well. The study provided information on the breakdown pressure as a function of the rock ambient stress, ambient pore pressure, pre-existing crack length, and mud cake properties. 12 refs., 6 figs.

  8. Effect of micromorphology at the fatigue crack tip on the crack growth in electron beam welded Ti-6Al-4V joint

    International Nuclear Information System (INIS)

    Tao, Junhui; Hu, Shubing; Ji, Longbo

    2016-01-01

    In this paper, we describe experiments on welded joints of Ti-6Al-4V alloy specimens exhibiting fatigue characteristics in the base metal (BM), hot affected zone (HAZ) and fuse zone (FZ). The effect of micromorphology on crack propagation at the tip of the fatigue crack in joints formed by electron beam welding was investigated using an optical microscope, transmission electron microscope and other methodologies. The results demonstrated that the fatigue crack originated in and propagated along α/β boundaries in the BM. In the HAZ, the fatigue crack occurred at the boundary between martensite laths, and propagated through most irregular-equiaxed α phases and a few martensite laths. In the FZ, the fatigue crack originated at the boundaries between the fine crushing phases among martensite laths, and propagated along a majority of α/β boundaries and several narrow martensite laths. The electron beam welded joint of Ti-6Al-4V alloy showed instances of zigzag fatigue cracks that increased in degree from lowest in the HAZ, moderate in the FZ to greatest in the BM. Conversely, fatigue crack growth rate (FCGR) was greatest in the HAZ, less in the FZ and slowest in the BM. - Highlights: •Ti-6Al-4V welded joint exhibits different fatigue characteristics. •The fatigue crack propagates along α/β boundaries in the BM. •The fatigue crack propagates through α phases and martensite laths in the HAZ. •The fatigue crack propagates along α/β boundaries and martensite laths in the FZ. •Fatigue crack growth rate is fastest in the HAZ, less in the FZ, slowest in the BM.

  9. Prediction of crack density and electrical resistance changes in indium tin oxide/polymer thin films under tensile loading

    KAUST Repository

    Mora Cordova, Angel

    2014-06-11

    We present unified predictions for the crack onset strain, evolution of crack density, and changes in electrical resistance in indium tin oxide/polymer thin films under tensile loading. We propose a damage mechanics model to quantify and predict such changes as an alternative to fracture mechanics formulations. Our predictions are obtained by assuming that there are no flaws at the onset of loading as opposed to the assumptions of fracture mechanics approaches. We calibrate the crack onset strain and the damage model based on experimental data reported in the literature. We predict crack density and changes in electrical resistance as a function of the damage induced in the films. We implement our model in the commercial finite element software ABAQUS using a user subroutine UMAT. We obtain fair to good agreement with experiments. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

  10. Development of chloride-induced corrosion in pre-cracked RC beams under sustained loading: Effect of load-induced cracks, concrete cover, and exposure conditions

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Linwen [Université de Toulouse, UPS, INSA, LMDC, Toulouse (France); Université de Sherbrooke, Quebec (Canada); François, Raoul, E-mail: raoul.francois@insa-toulouse.fr [Université de Toulouse, UPS, INSA, LMDC, Toulouse (France); Dang, Vu Hiep [Hanoi Architectural University, Faculty of Civil Engineering, Hanoi (Viet Nam); L' Hostis, Valérie [CEA Saclay, CEA, DEN, DPC, SECR, Laboratoire d' Etude du Comportement des Bétons et des Argiles, Gif-sur-Yvette (France); Gagné, Richard [Université de Sherbrooke, Quebec (Canada)

    2015-01-15

    This paper deals with corrosion initiation and propagation in pre-cracked reinforced concrete beams under sustained loading during exposure to a chloride environment. Specimen beams that were cast in 2010 were compared to specimens cast in 1984. The only differences between the two sets of beams were the casting direction in relation to tensile reinforcement and the exposure conditions in the salt-fog chamber. The cracking maps, corrosion maps, chloride profiles, and cross-sectional loss of one group of two beams cast in 2010 were studied and their calculated corrosion rates were compared to that of beams cast in 1984 in order to investigate the factors influencing the natural corrosion process. Experimental results show that, after rapid initiation of corrosion at the crack tip, the corrosion process practically halted and the time elapsing before corrosion resumed depended on the exposure conditions and cover depth.

  11. On the measurement of the crack tip stress field as a means of determining Delta K(sub eff) under conditions of fatigue crack closure

    Science.gov (United States)

    Wallhead, Ian R.; Edwards, Lyndon; Poole, Peter

    1994-01-01

    The optical method of caustics has been successfully extended to enable stress intensity factors as low as 1MPa square root of m to be determined accurately for central fatigue cracks in 2024-T3 aluminium alloy test panels. The feasibility of using this technique to study crack closure, and to determine the effective stress intensity factor range, Delta K(sub eff), has been investigated. Comparisons have been made between the measured values of stress intensity factor, K(sub caus), and corresponding theoretical values, K(sub theo), for a range of fatigue cracks grown under different loading conditions. The values of K(sub caus) and K(sub theo) were in good agreement at maximum stress, where the cracks are fully open, while K(sub caus) exceeded K(sub theo) at minimum stress, due to crack closure. However, the levels of crack closure and values of Delta K(sub eff) obtained could not account for the variations of crack growth rate with loading conditions. It is concluded that the values of Delta K(sub eff), based on caustic measurements in a 1/square root of r stress field well outside the plastic zone, do not fully reflect local conditions which control crack tip behavior.

  12. The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

    International Nuclear Information System (INIS)

    Ulaganathan, Jaganathan; Newman, Roger C.

    2014-01-01

    The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved

  13. Measuring the stress field around an evolving crack in tensile deformed Mg AZ31 using three-dimensional X-ray diffraction

    International Nuclear Information System (INIS)

    Oddershede, Jette; Camin, Bettina; Schmidt, Søren; Mikkelsen, Lars P.; Sørensen, Henning Osholm; Lienert, Ulrich; Poulsen, Henning Friis; Reimers, Walter

    2012-01-01

    The stress field around a notch in a coarse grained Mg AZ31 sample has been measured under tensile load using the individual grains as probes in an in situ high energy synchrotron diffraction experiment. The experimental set-up, a variant of three-dimensional X-ray diffraction microscopy, allows the position, orientation and full stress tensor of each illuminated grain to be determined and, hence, enables the study of evolving stress fields in coarse grained materials with a spatial resolution equal to the grain size. Grain resolved information like this is vital for understanding what happens when the traditional continuum mechanics approach breaks down and fracture is governed by local heterogeneities (e.g. phase or stress differences) between grains. As a first approximation the results obtained were averaged through the thickness of the sample and compared with an elastic–plastic continuum finite element simulation. It was found that a full three-dimensional simulation was required to account for the measured transition from the overall plane stress case away from the notch to the essentially plane strain case observed near the notch tip. The measured and simulated stress contours were shown to be in good agreement except at the highest applied load, at which stress relaxation at the notch tip was observed in the experimental data. This stress relaxation is attributed to the initiation and propagation of a crack. Finally, it was demonstrated that the measured lattice rotations could be used as a qualitative measure of the shape and extent of the plastic deformation zone.

  14. Effects of surface cracks and strain rate on the tensile behavior of Balmoral Red granite

    Directory of Open Access Journals (Sweden)

    Mardoukhi Ahmad

    2015-01-01

    Full Text Available This paper presents an experimental procedure for studying the effects of surface cracks on the mechanical behavior of Balmoral Red granite under dynamic and quasi-static loading. Three different thermal shocks were applied on the surface of the Brazilian Disc test samples by keeping a flame torch at a fixed distance from the sample surface for 10, 30, and 60 seconds. Microscopy clearly shows that the number of the surface cracks increases with the duration of the thermal shock. After the thermal shock, the Brazilian Disc tests were performed using a servohydraulic materials testing machine and a compression Split Hopkinson Pressure Bar (SHPB device. The results show that the tensile strength of the rock decreases and the rate sensitivity of the rock increases as more cracks are introduced to the structure. The DIC analysis of the Brazilian disc tests shows that the fracture of the sample initiates at the center of the samples or slightly closer to the incident bar contact point. This is followed by crushing of the samples at both contact points with the stress bars.

  15. A consistent partly cracked XFEM element for cohesive crack growth

    DEFF Research Database (Denmark)

    Asferg, Jesper L.; Poulsen, Peter Noe; Nielsen, Leif Otto

    2007-01-01

    Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra...... enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-triangle of the cracked element. With the extra enrichments, the crack-tip element becomes...... capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node constant strain triangle (CST) and a standard algorithm...

  16. Sub-critical cohesive crack propagation with hydro-mechanical coupling and friction

    Directory of Open Access Journals (Sweden)

    S. Valente

    2016-01-01

    Full Text Available Looking at the long-time behaviour of a dam, it is necessary to assume that the water can penetrate a possible crack washing away some components of the concrete. This type of corrosion reduces the tensile strength and fracture energy of the concrete compared to the same parameters measured during a short-time laboratory test. This phenomenon causes the so called sub-critical crack propagation. That is the reason why the International Commission of Large Dams recommends to neglect the tensile strength of the joint between the dam and the foundation, which is the weakest point of a gravity dam. In these conditions a shear displacement discontinuity starts growing in a point, called Fictitious Crack Tip (shortened FCT, which is still subjected to a compression stress. In order to manage this problem, in this paper the cohesive crack model is re-formulated with the focus on the shear stress component. In this context, the classical Newton-Raphson method fails to converge to an equilibrium state. Therefore the approach used is based on two stages: (a a global one in which the FCT is moved ahead of one increment; (b a local one in which the non-linear conditions occurring in the Fracture Process Zone are taken into account. This two-stage approach, which is known in the literature as a Large Time Increment method, is able to model three different mechanical regimes occurring during the crack propagation between a dam and the foundation rock.

  17. Analysis of crack opening stresses for center- and edge-crack tension specimens

    Directory of Open Access Journals (Sweden)

    Tong Di-Hua

    2014-04-01

    Full Text Available Accurate determination of crack opening stress is of central importance to fatigue crack growth analysis and life prediction based on the crack-closure model. This paper studies the crack opening behavior for center- and edge-crack tension specimens. It is found that the crack opening stress is affected by the crack tip element. By taking the crack tip element into account, a modified crack opening stress equation is given for the center-crack tension specimen. Crack surface displacement equations for an edge crack in a semi-infinite plate under remote uniform tension and partially distributed pressure are derived by using the weight function method. Based on these displacements, a crack opening stress equation for an edge crack in a semi-infinite plate under uniform tension has been developed. The study shows that the crack opening stress is geometry-dependent, and the weight function method provides an effective and reliable tool to deal with such geometry dependence.

  18. Unloading Effect on Delayed Hydride Cracking in Zirconium Alloys

    International Nuclear Information System (INIS)

    Kim, Young Suk; Kim, Sung Soo

    2010-01-01

    It is well-known that a tensile overload retards not only the crack growth rate (CGR) in zirconium alloys during the delayed hydride cracking (DHC) tests but also the fatigue crack growth rate in metals, the cause of which is unclear to date. A considerable decrease in the fatigue crack growth rate due to overload is suggested to occur due either to the crack closure or to compressive stresses or strains arising from unloading of the overload. However, the role of the crack closure or the compressive stress in the crack growth rate remains yet to be understood because of incomplete understanding of crack growth kinetics. The aim of this study is to resolve the effect of unloading on the CGR of zirconium alloys, which comes in last among the unresolved issues as listed above. To this end, the CGRs of the Zr-2.5Nb tubes were determined at a constant temperature under the cyclic load with the load ratio, R changing from 0.13 to 0.66 where the extent of unloading became higher at the lower R. More direct evidence for the effect of unloading after an overload is provided using Simpson's experiment investigating the effect on the CGR of a Zr-2.5Nb tube of the stress states of the prefatigue crack tip by unloading or annealing after the formation of a pre-fatigue crack

  19. Stress corrosion cracking resistance of aluminum alloy 7000 series after two-step aging

    Directory of Open Access Journals (Sweden)

    Jegdić Bore V.

    2015-01-01

    Full Text Available The effect of one step-and a new (short two-step aging on the resistance to stress corrosion cracking of an aluminum alloy 7000 series was investigated, using slow strain rate test and fracture mechanics method. Aging level in the tested alloy was evaluated by means of scanning electron microscopy and measurements of electrical resistivity. It was shown that the alloy after the new two-step aging is significantly more resistant to stress corrosion cracking. Values of tensile properties and fracture toughness are similar for both thermal states. Processes that take place at the crack tip have been considered. The effect of the testing solution temperature on the crack growth rate on the plateau was determined. Two values of the apparent activation energy were obtained. These values correspond to different processes that control crack growth rate on the plateau at higher and lower temperatures. [Projekat Ministarstva nauke Republike Srbije, br. TR 34028 i br. TR 34016

  20. Role of hydrogen in stress corrosion cracking

    International Nuclear Information System (INIS)

    Mehta, M.L.

    1981-01-01

    Electrochemical basis for differentiation between hydrogen embrittlement and active path corrosion or anodic dissolution crack growth mechanisms is examined. The consequences of recently demonstrated acidification in crack tip region irrespective of electrochemical conditions at the bulk surface of the sample are that the hydrogen can evolve within the crack and may be involved in the cracking process. There are basically three aspects of hydrogen involvement in stress corrosion cracking. In dissolution models crack propagation is assumed to be caused by anodic dissolution on the crack tip sustained by cathodic reduction of hydrogen from electrolyte within the crack. In hydrogen induced structural transformation models it is postulated that hydrogen is absorbed locally at the crack tip producing structural changes which facilitate crack propagation. In hydrogen embrittlement models hydrogen is absorbed by stressed metal from proton reduction from the electrolyte within the crack and there is interaction between lattice and hydrogen resulting in embrittlement of material at crack tip facilitating crack propagation. In the present paper, the role of hydrogen in stress corrosion crack growth in high strength steels, austenitic stainless steels, titanium alloys and high strength aluminium alloys is discussed. (author)

  1. The determination of the local conditions for void initiation in front of a crack tip for materials with second-phase particles

    Energy Technology Data Exchange (ETDEWEB)

    Sabirov, I. [Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstrasse 12, A-8700 Leoben (Austria)]. E-mail: sabirov@unileoben.ac.at; Duschlbauer, D. [Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gusshausstrasse 27-29, A-1040 Vienna (Austria); Pettermann, H.E. [Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gusshausstrasse 27-29, A-1040 Vienna (Austria); Kolednik, O. [Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstrasse 12, A-8700 Leoben (Austria)

    2005-02-25

    A procedure is proposed to determine, for second-phase particles near a crack tip, the maximum particle stresses at the moment of void initiation by either particle fracture or particle/matrix interface separation. A digital image analysis system is applied to perform a quantitative analysis of corresponding fracture surface regions from stereo image pairs taken in the scanning electron microscope. The fracture surface analysis is used to measure, for individual particles, the crack tip opening displacement at the moment of void initiation and the particle location with respect to the crack tip. From these data, the stress tensor at the moment of void initiation is calculated from the Hutchinson-Rice-Rosengren (HRR) field theory. The corresponding average local stresses within the particle are evaluated by a non-linear Mori-Tanaka-type approach. These stresses are compared to estimates according to the models by Argon et al. [A.S. Argon, J. Im, R. Safoglu, Metall. Trans. 6 (1975) 825] and Beremin [F.M. Beremin, Metall. Trans. 12 (1981) 723]. The procedure is demonstrated on an Al6061-10% Al{sub 2}O{sub 3} metal matrix composite.

  2. Analysis of accuracy of Williams series approximation of stress field in cracked body – influence of area of interest around crack-tip on multi-parameter regression performance

    Directory of Open Access Journals (Sweden)

    J. Sobek

    2017-01-01

    Full Text Available A study on the accuracy of an approximation of the stress field in a cracked body is presented. Crack-tip stress tensor is expressed using the linear elastic fracture mechanics (LEFM theory in this work, more precisely via its multi-parameter formulation, i.e. by Williams power series (WPS. Determination of coefficients of terms of this series is performed using a least squares-based regression technique known as over-deterministic method (ODM for which results from finite element (FE method computation are usually taken as inputs. Main attention is paid to a detailed analysis of a suitable selection of FE nodes whose results serve as the inputs to the employed method. Two different ways of FE nodal selection are compared – nodes selected from the crack tip vicinity lying at a ring of a certain radius versus nodes selected more or less uniformly from a specified part of the test specimen body. Comparison of these approaches is made with the help of procedures developed by the authors which enable both the determination of the coefficients of terms of the analytical WPS approximation of the stress field based on the FE results and the backward reconstruction of the field (again using WPS from those determined terms’ coefficients/functions. The wedge-splitting test (WST specimen with a crack is taken as example for the study.

  3. Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels

    Directory of Open Access Journals (Sweden)

    Suvi Papula

    2017-06-01

    Full Text Available Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility.

  4. Crack-tip chemistry modeling of stage I stress corrosion cracking

    International Nuclear Information System (INIS)

    Jones, R.H.; Simonen, E.P.

    1991-10-01

    Stage I stress corrosion cracking usually exhibits a very strong K dependence with Paris law exponents of up to 30. 2 Model calculations indicate that the crack velocity in this regime is controlled by transport through a salt film and that the K dependence results from crack opening controlled salt film dissolution. An ionic transport model that accounts for both electromigration through the resistive salt film and Fickian diffusion through the aqueous solution was used for these predictions. Predicted crack growth rates are in excellent agreement with measured values for Ni with P segregated to the grain boundaries and tested in IN H 2 SO 4 at +900 mV. This salt film dissolution may be applicable to stage I cracking of other materials

  5. Ultrasonic sizing of fatigue cracks

    International Nuclear Information System (INIS)

    Burns, D.J.

    1983-12-01

    Surface and buried fatigue cracks in steel plates have been sized using immersion probes as transmitters-receivers, angled to produce shear waves in the steel. Sizes have been estimated by identifying the ultrasonic waves diffracted from the crack tip and by measuring the time taken for a signal to travel to and from the crack tip. The effects of compression normal to a fatigue crack and of crack front curvature are discussed. Another diffraction technique, developed by UKAEA, Harwell, is reviewed

  6. Fatigue crack tip damaging micromechanisms in a ferritic-pearlitic ductile cast iron

    Directory of Open Access Journals (Sweden)

    Francesco Iacoviello

    2015-07-01

    Full Text Available Due to the peculiar graphite elements shape, obtained by means of a chemical composition control (mainly small addition of elements like Mg, Ca or Ce, Ductile Cast Irons (DCIs are able to offer the good castability of gray irons with the high mechanical properties of irons (first of all, toughness. This interesting properties combination can be improved both by means of the chemical composition control and by means of different heat treatments(e.g. annealing, normalizing, quenching, austempering etc. In this work, fatigue crack tip damaging micromechanisms in a ferritic-pearlitic DCI were investigated by means of scanning electron microscope observations performed on a lateral surface of Compact Type (CT specimens during the fatigue crack propagation test (step by step procedure, performed according to the “load shedding procedure”. On the basis of the experimental results, different fatigue damaging micromechanisms were identified, both in the graphite nodules and in the ferritic – pearlitic matrix.

  7. The effect of a curvature-dependent surface tension on the singularities at the tips of a straight interface crack

    KAUST Repository

    Zemlyanova, A. Y.

    2013-01-01

    A problem of an interface crack between two semi-planes made out of different materials under an action of an in-plane loading of general tensile-shear type is treated in a semi-analytical manner with the help of Dirichlet-to-Neumann mappings

  8. Creep crack extension by grain-boundary cavitation

    International Nuclear Information System (INIS)

    Bassani, J.L.

    1981-01-01

    Recent work by Riedel and coworkers has led to various descriptions of stationary and moving crack tip fields under creep conditions. For stationary and growing cracks, several flow mechanisms (e.g., elastic, time-independent plastic, primary creep, and secondary creep) can dictate the analytical form of the crack tip field. In this paper, relationship between overall loading and crack velocities are modelled based upon grain-boundary cavity growth and coalescence within the zone of concentrated strain in the crack tip field. Coupled diffusion and creep growth of the cavities is considered. Overall crack extension is taken to be intermittent on a size scale equivalent to the size of a grain. Numerical results are presented for a center-cracked panel of 304 stainless steel. (author)

  9. Crack turning in integrally stiffened aircraft structures

    Science.gov (United States)

    Pettit, Richard Glen

    Current emphasis in the aircraft industry toward reducing manufacturing cost has created a renewed interest in integrally stiffened structures. Crack turning has been identified as an approach to improve the damage tolerance and fail-safety of this class of structures. A desired behavior is for skin cracks to turn before reaching a stiffener, instead of growing straight through. A crack in a pressurized fuselage encounters high T-stress as it nears the stiffener---a condition favorable to crack turning. Also, the tear resistance of aluminum alloys typically varies with crack orientation, a form of anisotropy that can influence the crack path. The present work addresses these issues with a study of crack turning in two-dimensions, including the effects of both T-stress and fracture anisotropy. Both effects are shown to have relation to the process zone size, an interaction that is central to this study. Following an introduction to the problem, the T-stress effect is studied for a slightly curved semi-infinite crack with a cohesive process zone, yielding a closed form expression for the future crack path in an infinite medium. For a given initial crack tip curvature and tensile T-stress, the crack path instability is found to increase with process zone size. Fracture orthotropy is treated using a simple function to interpolate between the two principal fracture resistance values in two-dimensions. An extension to three-dimensions interpolates between the six principal values of fracture resistance. Also discussed is the transition between mode I and mode II fracture in metals. For isotropic materials, there is evidence that the crack seeks out a direction of either local symmetry (pure mode I) or local asymmetry (pure mode II) growth. For orthotropic materials the favored states are not pure modal, and have mode mixity that is a function of crack orientation. Drawing upon these principles, two crack turning prediction approaches are extended to include fracture

  10. Recent advances in modelling creep crack growth

    International Nuclear Information System (INIS)

    Riedel, H.

    1988-08-01

    At the time of the previous International Conference on Fracture, the C* integral had long been recognized as a promising load parameter for correlating crack growth rates in creep-ductile materials. The measured crack growth rates as a function of C* and of the temperature could be understood on the basis of micromechanical models. The distinction between C*-controlled and K I -controlled creep crack growth had been clarified and first attempts had been made to describe creep crack growth in the transient regime between elastic behavior and steady-state creep. This paper describes the progress in describing transient crack growth including the effect of primary creep. The effect of crack-tip geometry changes by blunting and by crack growth on the crack-tip fields and on the validity of C* is analyzed by idealizing the growing-crack geometry by a sharp notch and using recent solutions for the notch-tip fields. A few new three-dimensional calculations of C* are cited and important theoretical points are emphasized regarding the three-dimensional fields at crack tips. Finally, creep crack growth is described by continuum-damage models for which similarity solutions can be obtained. Crack growth under small-scale creep conditions turns out to be difficult to understand. Slightly different models yield very different crack growth rates. (orig.) With 4 figs

  11. Biaxial loading effects on the growth of cracks

    International Nuclear Information System (INIS)

    Brown, M.W.; Miller, K.J.; Walker, T.J.

    1983-01-01

    Fatigue crack growth under different biaxial stress states is considered for both small scale yielding and high bulk stress conditions. Analytical and elastic finite element results are compared favourably alongside experimental results on a AISI 316 stainless steel at both room and elevated temperatures. Differences in crack growth rates are compared against different crack tip cyclic plastic zone sizes for various degrees of mixed mode loading, thereby overcoming the limitations of the Paris Law and LEFM. The usefulness of the approach is indicated for studies in the behaviour of materials subjected to thermal shock. Where steep temperature gradients are introduced due to rapid thermal transients, high strains are produced which propagate fatigue cracks under cyclic conditions. Since stress gradients are generally associated with thermal shock situations, the cracks grow through a plastically deformed region near the surface into an elastic region. A unified approach to fatigue behaviour, encompassing both linear elastic and elastic-plastic fracture mechanics, will enable analysis of thermal shock situations. The approach to crack propagation developed here shows that cyclic growth rates are a function of a severe strain zone size in which local stresses exceed the tensile strength, i.e. monotonic instability. The effects of stress biaxiality and mixed mode loading are included in the analysis, which may be extended to general yielding situations. (orig.)

  12. Evaluation and Observation of Autogenous Healing Ability of Bond Cracks along Rebar

    Directory of Open Access Journals (Sweden)

    Choonghyun Kang

    2014-04-01

    Full Text Available Micro cracks occurring in concrete around tensile rebar is well known latent damage phenomenon. These micro cracks develop, and can be detected after reaching the surface of the concrete. Detection of these cracks before they are fully formed is preferable, but observing the whole crack structure is difficult. Another problem is repairing micro cracks under the concrete surface. The autogenous ability of bond cracks along rebar was evaluated using the air permeability test. Air permeability coefficients were measured before and after tensile loading, and experimental air permeability coefficients became larger near cracks along rebar as a result of tensile loading. Recuring for 28 days after tensile loading made the air permeability coefficients smaller, but this restriction only occurred during water recuring. Observation of crack patterns helped the understanding of change in the air permeability coefficients. Several small cracks along rebar were observed after tensile loading, and most cracks along rebar were not found after water recuring. On the other hand, the crack pattern did not change after air recuring. These results indicate that bond cracks along rebar can be closed by autogenous healing, and cause the air permeability coefficients.

  13. The effect of crack branching on the residual lifetime of machine components containing stress corrosion cracks

    International Nuclear Information System (INIS)

    Magdowski, R.M.; Uggowitzer, P.J.; Speidel, M.O.

    1985-01-01

    A comparison is presented of theoretical, numerical and experimental investigations concerning the effect of crack branching on the reduction of stress intensity at the tip of single cracks. The results indicate that the division of a single crack into n branches reduces the stress intensity at the branch tips by a factor of about 1/√n. This permits branched cracks to grow to larger depths before becoming critical. The implication is that longer residual lifetimes and longer operating times between inspections can be calculated for machine components with growing branched stress corrosion cracks. (author)

  14. Microstructural modelling of creep crack growth from a blunted crack

    NARCIS (Netherlands)

    Onck, P.R.; Giessen, E. van der

    1998-01-01

    The effect of crack tip blunting on the initial stages of creep crack growth is investigated by means of a planar microstructural model in which grains are represented discretely. The actual linking-up process of discrete microcracks with the macroscopic crack is simulated, with full account of the

  15. Mathematical modeling of the crack growth in linear elastic isotropic materials by conventional fracture mechanics approaches and by molecular dynamics method: crack propagation direction angle under mixed mode loading

    Science.gov (United States)

    Stepanova, Larisa; Bronnikov, Sergej

    2018-03-01

    The crack growth directional angles in the isotropic linear elastic plane with the central crack under mixed-mode loading conditions for the full range of the mixity parameter are found. Two fracture criteria of traditional linear fracture mechanics (maximum tangential stress and minimum strain energy density criteria) are used. Atomistic simulations of the central crack growth process in an infinite plane medium under mixed-mode loading using Large-scale Molecular Massively Parallel Simulator (LAMMPS), a classical molecular dynamics code, are performed. The inter-atomic potential used in this investigation is Embedded Atom Method (EAM) potential. The plane specimens with initial central crack were subjected to Mixed-Mode loadings. The simulation cell contains 400000 atoms. The crack propagation direction angles under different values of the mixity parameter in a wide range of values from pure tensile loading to pure shear loading in a wide diapason of temperatures (from 0.1 К to 800 К) are obtained and analyzed. It is shown that the crack propagation direction angles obtained by molecular dynamics method coincide with the crack propagation direction angles given by the multi-parameter fracture criteria based on the strain energy density and the multi-parameter description of the crack-tip fields.

  16. On the mechanism of crack propagation resistance of fully lamellar TiAl alloy

    International Nuclear Information System (INIS)

    Cao, R.; Yao, H.J.; Chen, J.H.; Zhang, J.

    2006-01-01

    The study was done using notched two-colony thick tensile specimens of a directionally solidified cast fully lamellar TiAl alloy. In-situ observations of fracture processes in scanning electron microscope (SEM) were combined with section-to-section related observations of fracture surfaces to investigate the crack growth process. Finite element method (FEM) calculations are carried out to evaluate the stresses for propagating cracks. The results reveal that: (1) the reason why enhancement of applied load is required to propagate the main crack, was attributed to that the main crack observed at the surface did not extend all the way through the specimen's thickness thus the stress field was still controlled by the notch, in which a definite stress required for extending a crack tip should be kept by increasing the applied load. (2) Crack propagation resistance is enhanced at colony boundaries, only when a change occurs from an inter-lamellar propagation to a trans-lamellar propagation (3) Ligament bridging toughening phenomena can be integrated into aforementioned mechanism. As a whole the processes of new crack nucleation with bridging ligament formation decreases the crack propagation resistance rather than increasing it. (4) In case the majority of microcracks are surface cracks, the effect of microcrack shielding is not obvious

  17. Molecular dynamics simulations of quasi-brittle crack development in iron

    Energy Technology Data Exchange (ETDEWEB)

    Borodin, V.A., E-mail: borodin@dni.polin.kiae.su [Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany); NRC Kurchatov Institute, Kurchatov Sq. 1, 123182 Moscow (Russian Federation); Vladimirov, P.V., E-mail: Pavel.Vladimirov@kit.edu [Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany)

    2011-08-31

    The paper presents the results of molecular dynamics (MD) simulations of three-dimensional kinetics of micro-crack propagation in alpha-iron and the accompanying lattice transformations at the crack tips. We show that crack initiation on {l_brace}0 0 1{r_brace} planes in iron is preceded with the emission of compact slip bands from the pre-crack tips, in agreement with the predictions of the earlier quasi-two-dimensional simulations. The application of Voronoi decomposition technique for atomic short-range order processing has allowed us to clarify the kinetics of structural transformations at the tips of nucleating and propagating cracks for three most common systems of crack propagation in iron. It is demonstrated that the compact slip bands emanating from the crack tips not only accompany crack nucleation, but remain an essential feature of the crack propagation on {l_brace}0 0 1{r_brace} planes. Due to the strong coupling between the crack tip and slip band propagation, the crack propagation can be limited by slip band interaction with microstructural obstacles, abundantly created in ferritic-martensitic steels in radiation environment of nuclear facilities.

  18. Ratcheting Strain and Microstructure Evolution of AZ31B Magnesium Alloy under a Tensile-Tensile Cyclic Loading.

    Science.gov (United States)

    Yan, Zhifeng; Wang, Denghui; Wang, Wenxian; Zhou, Jun; He, Xiuli; Dong, Peng; Zhang, Hongxia; Sun, Liyong

    2018-03-28

    In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material's fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11-20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11-20} tensile twins.

  19. A comparison of conventional local approach and the short crack approach to fatigue crack initiation at a notch

    Energy Technology Data Exchange (ETDEWEB)

    Ranganathan, Narayanaswami; Leroy, Rene; Tougui, Abdellah [Laboratoire de Mecanique et Rheologie, Universite Francois Rabelais de Tours, Polytech Tours, Departement Mecanique et Conception de Systemes, Tours (France)

    2009-09-15

    Methods to estimate fatigue crack initiation life at a notch tip are compared. The methods used determine the strain amplitudes at the notch tip using Neuber's or Glinka's approximation. In conventional approaches, equivalent-damage levels are determined, using appropriate strain-life relationships coupled with damage-summation models. In the short-crack approach, a crack-like defect is assumed to exist at the notch tip. It is shown that the short-crack concept can be successfully applied to predict crack-initiation behavior at a notch. Model predictions are compared with carefully designed experiments. It is shown that model predictions are very close to experimentally measured lives under an aircraft-wing loading spectrum. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  20. Prediction of pure water stress corrosion cracking (PWSCC) in nickel base alloys using crack growth rate models

    International Nuclear Information System (INIS)

    Thompson, C.D.; Krasodomski, H.T.; Lewis, N.; Makar, G.L.

    1995-01-01

    The Ford/Andresen slip dissolution SCC model, originally developed for stainless steel components in BWR environments, has been applied to Alloy 600 and Alloy X-750 tested in deaerated pure water chemistry. A method is described whereby the crack growth rates measured in compact tension specimens can be used to estimate crack growth in a component. Good agreement was found between model prediction and measured SCC in X-750 threaded fasteners over a wide range of temperatures, stresses, and material condition. Most data support the basic assumption of this model that cracks initiate early in life. The evidence supporting a particular SCC mechanism is mixed. Electrochemical repassivation data and estimates of oxide fracture strain indicate that the slip dissolution model can account for the observed crack growth rates, provided primary rather than secondary creep rates are used. However, approximately 100 cross-sectional TEM foils of SCC cracks including crack tips reveal no evidence of enhanced plasticity or unique dislocation patterns at the crack tip or along the crack to support a classic slip dissolution mechanism. No voids, hydrides, or microcracks are found in the vicinity of the crack tips creating doubt about classic hydrogen related mechanisms. The bulk oxide films exhibit a surface oxide which is often different than the oxides found within a crack. Although bulk chromium concentration affects the rate of SCC, analytical data indicates the mechanism does not result from chromium depletion at the grain boundaries. The overall findings support a corrosion/dissolution mechanism but not one necessarily related to slip at the crack tip

  1. Strain gradient plasticity-based modeling of hydrogen environment assisted cracking

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Niordson, Christian Frithiof; P. Gangloff, Richard

    2016-01-01

    Finite element analysis of stress about a blunt crack tip, emphasizing finite strain and phenomenologicaland mechanism-based strain gradient plasticity (SGP) formulations, is integrated with electrochemical assessment of occluded-crack tip hydrogen (H) solubility and two H-decohesion models...... to predict hydrogen environment assisted crack growth properties. SGP elevates crack tip geometrically necessary dislocation density and flow stress, with enhancement declining with increasing alloy strength. Elevated hydrostatic stress promotes high-trapped H concentration for crack tip damage......; it is imperative to account for SGP in H cracking models. Predictions of the threshold stress intensity factor and H-diffusion limited Stage II crack growth rate agree with experimental data for a high strength austenitic Ni-Cusuperalloy (Monel®K-500) and two modern ultra-high strength martensitic steels (Aer...

  2. Shear-tensile crack as a tool for reliable estimates of the non-double-couple mechanism: West Bohemia-Vogtland earthquake 1997 swarm

    Czech Academy of Sciences Publication Activity Database

    Šílený, Jan; Horálek, Josef

    2016-01-01

    Roč. 95, October (2016), s. 113-124 ISSN 1474-7065 R&D Projects: GA ČR GAP210/12/2235; GA ČR(CZ) GA16-03950S Institutional support: RVO:67985530 Keywords : earthquake mechanism * moment tensor * shear-tensile crack * confidence regions Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.426, year: 2016

  3. Modelling of liquid sodium induced crack propagation in T91 martensitic steel: Competition with ductile fracture

    Energy Technology Data Exchange (ETDEWEB)

    Hemery, Samuel [Institut PPRIME, CNRS, Université de Poitiers, ISAE ENSMA, UPR 3346, Téléport 2, 1 Avenue Clément Ader, BP 40109, 86961 Futuroscope Chasseneuil Cedex (France); Berdin, Clotilde, E-mail: clotilde.berdin@u-psud.fr [Univ Paris-Sud, SP2M-ICMMO, CNRS UMR 8182, F-91405 Orsay Cedex (France); Auger, Thierry; Bourhi, Mariem [Ecole Centrale-Supelec, MSSMat CNRS UMR 8579, F-92295 Chatenay Malabry Cedex (France)

    2016-12-01

    Liquid metal embrittlement (LME) of T91 steel is numerically modeled by the finite element method to analyse experimental results in an axisymmetric notched geometry. The behavior of the material is identified from tensile tests then a crack with a constant crack velocity is introduced using the node release technique in order to simulate the brittle crack induced by LME. A good agreement between the simulated and the experimental macroscopic behavior is found: this suggests that the assumption of a constant crack velocity is correct. Mechanical fields during the embrittlement process are then extracted from the results of the finite element model. An analysis of the crack initiation and propagation stages: the ductile fracture probably breaks off the LME induced brittle fracture. - Highlights: • T91 martensitic steel is embrittled by liquid sodium depending on the loading rate at 573 K. • The mechanical behavior is modeled by a von Mises elastic-plastic law. • The LME induced crack propagates at a constant velocity. • The mechanical state at the crack tip does not explain a brittle crack arrest. • The occurrence of the ductile fracture breaks off the brittle fracture.

  4. Experimental study of the crack depth ratio threshold to analyze the slow crack growth by creep of high density polyethylene pipes

    International Nuclear Information System (INIS)

    Laiarinandrasana, Lucien; Devilliers, Clémence; Lucatelli, Jean Marc; Gaudichet-Maurin, Emmanuelle; Brossard, Jean Michel

    2014-01-01

    To assess the durability of drinking water connection pipes subjected to oxidation and slow crack growth, a comprehensive database was constructed on a novel specimen geometry: the pre-cracked NOL ring. 135 tests were carried out consisting of initial crack depth ratio ranging from 0.08 to 0.6; single or double longitudinal cracks: tensile with steady strain rate and creep loading. A threshold value of the crack depth ratio of 0.2, induced by the oxidation was determined by analyzing several mechanical parameters. This threshold value was shown to be independent on the strain rate effects, single or double crack configuration and the kind of loading: tensile or creep. Creep test results with crack depth ratio larger than 0.2 were then utilized to establish a failure assessment diagram. A methodology allowing the prediction of residual lifetime of in-service pipes was proposed, using this diagram. - Highlights: • Experimental data on pre-cracked rings featuring a longitudinally cracked HDPE pipe. • Crack depth ratio threshold for slow crack growth study consecutive to oxidation. • Investigation of the effects of the single/double notch(es) and of the strain rate. • Original results obtained from tests performed with tensile and creep loadings. • Correlation between creep initiation time and C* with DENT and ring specimens

  5. Post-uniform elongation and tensile fracture mechanisms of Fe-18Mn-0.6C-xAl twinning-induced plasticity steels

    International Nuclear Information System (INIS)

    Yu, Ha-Young; Lee, Sang-Min; Nam, Jae-Hoon; Lee, Seung-Joon; Fabrègue, Damien; Park, Myeong-heom; Tsuji, Nobuhiro; Lee, Young-Kook

    2017-01-01

    The objective of the present study was to elucidate the complicated interrelationship between necking, post-uniform elongation (e_p_u), strain rate sensitivity (SRS), fracture mechanism and Al concentration in Fe-18Mn-0.6C-xAl twinning-induced plasticity steels. Many tensile tests were conducted for in- and ex-situ observations of necking, fracture surfaces, crack propagation and the density and size of micro-voids with the assistance of a high-speed camera and X-ray tomographic equipment. The addition of Al increased e_p_u, SRS and reduction ratios in dimension of the neck part of tensile specimens, and also changed fracture mode from quasi-cleavage to ductile fracture at the edge part. The quasi-cleavage surface of Al-free specimen was induced by edge and side cracks occurring along grain boundary junctions and twin boundaries within the edges and side surfaces where local deformation bands meet. The ductile-fracture surface of 1.5 %Al-added specimen was formed by the coalescence of micro-voids. While the side-to-middle crack propagation occurred in Al-free and 1 %Al-added specimens due to side cracks, the middle-to-side crack propagation was observed in 1.5 %Al-added specimen. The Al-free specimen had the larger size of the 20 largest voids compared to the 1.5 %Al-added specimen despite its lower void density and local strain due to the accelerated growth of voids near the tips of side cracks. Evaluating the negligible e_p_u of Al-free specimen by SRS is not deemed to be reasonable due to its inappreciable necking and side cracks. The improvement of e_p_u in 1.5 %Al-added specimen is primarily due to disappearance of edge and side cracks.

  6. Effect of nitrogen in austenitic stainless steel on deformation behavior and stress corrosion cracking susceptibility in BWR simulated environment

    International Nuclear Information System (INIS)

    Roychowdhury, S.; Kain, V.; Dey, G.K.

    2012-01-01

    Intergranular stress corrosion cracking (IGSCC) of austenitic stainless steel (SS) components in boiling water reactor (BWR has been a serious issue and is generic in nature. Initial cracking incidences were attributed to weld induced sensitisation and low temperature sensitisation which was mitigated by the use of low carbon grade of SS and molybdenum and nitrogen containing nuclear grade SS. However, IGSCC has occurred in these SS in the non-sensitised condition which was attributed to residual weld induced strain. Strain hardening in SS has been identified as a major cause for enhanced IGSCC susceptibility in BWR environment. Nitrogen in SS has a significant effect on the strain hardening characteristics and has potential to affect the IGSCC susceptibility in BWR environment. Type 304LN stainless steel is a candidate material for use in future reactors with long design life like the Advanced Heavy Water Reactor (AHWR), in which the operating conditions are similar to BWR. This study reports the effect of nitrogen in type 304LN stainless steel on the strain hardening behaviour and deformation characteristics and its effect on the IGSCC susceptibility in BWR/AHWR environment. Two heats of type 304LN stainless steel were used containing different levels of nitrogen, 0.08 and 0.16 wt % (SS alloys A and B, respectively). Both the SS was strain hardened by cross rolling at 200℃ to simulate the strain hardened regions having higher IGSCC susceptibility in BWRs. Tensile testing was done at both room temperature and 288℃(temperature simulating operating BWR conditions) and the effect of nitrogen on the tensile properties were established. Tensile testing was done at strain rates similar to the crack tip strain rates associated with a growing IGSCC in SS. Detailed transmission electron microscopic (TEM) studies were done to establish the effect of nitrogen on the deformation modes. Results indicated twinning was the major mode of deformation during cross rolling while

  7. Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

    Energy Technology Data Exchange (ETDEWEB)

    Beushausen, Hans, E-mail: hans.beushausen@uct.ac.za; Chilwesa, Masuzyo

    2013-11-15

    Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus. -- Highlights: •Parameter study on material characteristics influencing overlay cracking. •Analytical model gives good quantitative indication of overlay cracking. •Ring test presents good qualitative indication of overlay cracking. •Curing duration has little effect on overlay cracking.

  8. Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

    International Nuclear Information System (INIS)

    Beushausen, Hans; Chilwesa, Masuzyo

    2013-01-01

    Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus. -- Highlights: •Parameter study on material characteristics influencing overlay cracking. •Analytical model gives good quantitative indication of overlay cracking. •Ring test presents good qualitative indication of overlay cracking. •Curing duration has little effect on overlay cracking

  9. Tensile stress corrosion cracking of type 304 stainless steel irradiated to very high dose

    Energy Technology Data Exchange (ETDEWEB)

    Chung, H. M.; Ruther, W. E.; Strain, R. V.; Shack, W. J.

    2001-09-01

    Certain safety-related core internal structural components of light water reactors, usually fabricated from Type 304 or 316 austenitic stainless steels (SSs), accumulate very high levels of irradiation damage (20--100 displacement per atom or dpa) by the end of life. The data bases and mechanistic understanding of, the degradation of such highly irradiated components, however, are not well established. A key question is the nature of irradiation-assisted intergranular cracking at very high dose, i.e., is it purely mechanical failure or is it stress-commotion cracking? In this work, hot-cell tests and microstructural characterization were performed on Type 304 SS from the hexagonal fuel can of the decommissioned EBR-11 reactor after irradiation to {approximately}50 dpa at {approximately}370 C. Slow-strain-rate tensile tests were conducted at 289 C in air and in water at several levels of electrochemical potential (ECP), and microstructural characteristics were analyzed by scanning and transmission electron microcopies. The material deformed significantly by twinning and exhibited surprisingly high ductility in air, but was susceptible to severe intergranular stress corrosion cracking (IGSCC) at high ECP. Low levels of dissolved O and ECP were effective in suppressing the susceptibility of the heavily irradiated material to IGSCC, indicating that the stress corrosion process associated with irradiation-induced grain-boundary Cr depletion, rather than purely mechanical separation of grain boundaries, plays the dominant role. However, although IGSCC was suppressed, the material was susceptible to dislocation channeling at low ECP, and this susceptibility led to poor work-hardening capability and low ductility.

  10. Modified Dugdale crack models - some easy crack relations

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1997-01-01

    the same strength as a plain Dugdale model. The critical energy release rates Gamma_CR, however, become different. Expressions (with easy computer algorithms) are presented in the paper which relate critical energy release rates and crack geometry to arbitrary cohesive stress distributions.For future...... lifetime analysis of viscoelastic materials strain energy release rates, crack geometries, and cohesive stress distributions are considered as related to sub-critical loads sigma stress-deformation tests......The Dugdale crack model is widely used in materials science to predict strength of defective (cracked) materials. A stable Dugdale crack in an elasto-plastic material is prevented from spreading by uniformly distributed cohesive stresses acting in narrow areas at the crack tips. These stresses...

  11. On the dynamic fracture toughness and crack tip strain behavior of nuclear pressure vessel steel: Application of electromagnetic force

    International Nuclear Information System (INIS)

    Yagawa, G.; Yoshimura, S.

    1986-01-01

    This paper is concerned with the application of the electromagnetic force to the determination of the dynamic fracture toughness of materials. Taken is an edge-cracked specimen which carries a transient electric current and is simply supported in a steady magnetic field. As a result of their interaction, the dynamic electromagnetic force occurs in the whole body of the specimen, which is then deformed to fracture in the opening mode of cracking. Using the electric potential and the J-R curve methods to determine the dynamic crack initiation point in the experiment, together with the finite element method to calculate the extended J-integral with the effects of the electromagnetic force and inertia, the dynamic fracture toughness values of nuclear pressure vessel steel A508 class 3 are evaluated over a wide temperature range from lower to upper shelves. The strain distribution near the crack tip in the dynamic process of fracture is also obtained by applying a computer picture processing. (orig.)

  12. Dynamic ductile fracture of a central crack

    Science.gov (United States)

    Tsai, Y. M.

    1976-01-01

    A central crack, symmetrically growing at a constant speed in a two dimensional ductile material subject to uniform tension at infinity, is investigated using the integral transform methods. The crack is assumed to be the Dugdale crack, and the finite stress condition at the crack tip is satisfied during the propagation of the crack. Exact expressions of solution are obtained for the finite stress condition at the crack tip, the crack shape, the crack opening displacement, and the energy release rate. All those expressions are written as the product of explicit dimensional quantities and a nondimensional dynamic correction function. The expressions reduce to the associated static results when the crack speed tends to zero, and the nondimensional dynamic correction functions were calculated for various values of the parameter involved.

  13. Mechanisms of hydrogen induced delayed cracking in hydride forming materials

    International Nuclear Information System (INIS)

    Dutton, R.; Nuttall, K.; Puls, M.P.; Simpson, L.A.

    1977-01-01

    Mechanisms which have been formulated to describe delayed hydrogen cracking in hydride-forming metals are reviewed and discussed. Particular emphasis is placed on the commercial alloy Zr--2.5% Nb (Cb) which is extensively used in nuclear reactor core components. A quantitative model for hydrogen cracking in this material is presented and compared with available experimental data. The kinetics of crack propagation are controlled by the growth of hydrides at the stressed crack tip by the diffusive ingress of hydrogen into this region. The driving force for the diffusion flux is provided by the local stress gradient which interacts with both hydrogen atoms in solution and hydrogen atoms being dissolved and reprecipitated at the crack tip. The model is developed using concepts of elastoplastic fracture mechanics. Stage I crack growth is controlled by hydrides growing in the elastic stress gradient, while Stage II is controlled by hydride growth in the plastic zone at the crack tip. Recent experimental observations are presented which indicate that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles

  14. Mechanisms of hydrogen induced delayed cracking in hydride forming materials

    International Nuclear Information System (INIS)

    Dutton, R.; Nuttall, K.; Puls, M.P.; Simpson, L.A.

    1977-01-01

    Mechanisms which have been formulated to describe delayed hydrogen cracking in hydride-forming metals are reviewed and discussed. Particular emphasis is placed on the commercial alloy Zr-2.5 pct Nb which is extensively used in nuclear reactor core components. A quantitative model for hydrogen cracking in this material is presented and compared with available experimental data. The kinetics of crack propagation are controlled by the growth of hydrides at the stressed crack tip by the diffusive ingress of hydrogen into this region. The driving force for the diffusion flux is provided by the local stress gradient which interacts with both hydrogen atoms in solution and hydrogen atoms being dissolved and reprecipitated at the crack tip. The model is developed using concepts of elastoplastic fracture mechanics. Stage I crack growth is controlled by hydrides growing in the elastic stress gradient, while Stage II is controlled by hydride growth in the plastic zone at the crack tip. Recent experimental observations are presented which indicate that the process occurs in an intermittent fashion; hydride clusters accumulate at the crack tip followed by unstable crack advance and subsequent crack arrest in repeated cycles. 55 refs., 6 figs

  15. A Crack Closure Model and Its Application to Vibrothermography Nondestructive Evaluation

    Science.gov (United States)

    Schiefelbein, Bryan Edward

    Vibrothermography nondestructive evaluation (NDE) is in the early stages of research and development, and there exists uncertainty in the fundamental mechanisms and processes by which heat generation occurs. Holland et al. have developed a set of tools which simulate and predict the outcome of a vibrothermography inspection by breaking the inspection into three distinct processes: vibrational excitation, heat generation, and thermal imaging. The stage of vibrothermography which is not well understood is the process by which vibrations are converted to heat at the crack surface. It has been shown that crack closure and closure state impact the resulting heat generation. Despite this, research into the link between partial crack closure and vibrothermography is limited. This work seeks to rectify this gap in knowledge by modeling the behavior of a partially closed crack in response to static external loading and a dynamic vibration. The residual strains left by the plastic wake during fatigue crack growth manifest themselves as contact stresses acting at the crack surface interface. In response to an applied load below the crack opening stress, the crack closure state will evolve, but the crack will remain partially closed. The crack closure model developed in this work is based in linear elastic fracture mechanics (LEFM) and describes the behavior of a partially closed crack in response to a tensile external load and non-uniform closure stress distribution. The model builds on work by Fleck to describe the effective length, crack opening displacement, and crack tip stress field for a partially closed crack. These quantities are solved for by first establishing an equilibrium condition which governs the effective or apparent length of the partially closed crack. The equilibrium condition states that, under any external or crack surface loading, the effective crack tip will be located where the effective stress intensity factor is zero. In LEFM, this is equivalent to

  16. Dislocation model of a subsurface crack

    International Nuclear Information System (INIS)

    Yang, F.; Li, J.C.

    1997-01-01

    A dislocation model of a subsurface crack parallel to the surface is presented. For tensile loading, the results agree with those of previous workers except that we studied the crack very close to the surface and found that K II (mode II stress intensity factor) approaches K I (mode I stress intensity factor) to within about 22% (K II =0.78K I ). (Note that K II is zero when the crack is far away from the surface). Using bending theory for such situations, it is found that both stress intensity factors are inversely proportional to the 3/2 power of the distance between the subsurface crack and the free surface. For shear loading, the crack faces overlap each other for the free traction condition. This indicates the failure of the model. However, there was no overlap for tensile loading even though the stresses in front of the crack oscillate somewhat when the crack is very close to the surface. copyright 1997 American Institute of Physics

  17. Post-cracking tensile behaviour of steel-fibre-reinforced roller-compacted-concrete for FE modelling and design purposes

    International Nuclear Information System (INIS)

    Jafarifar, N.; Pilakoutas, K.; Angelakopoulos, H.; Bennett, T.

    2017-01-01

    Fracture of steel-fibre-reinforced-concrete occurs mostly in the form of a smeared crack band undergoing progressive microcracking. For FE modelling and design purposes, this crack band could be characterised by a stress-strain (σ-ε) relationship. For industrially-produced steel fibres, existing methodologies such as RILEM TC 162-TDF (2003) propose empirical equations to predict a trilinear σ-ε relationship directly from bending test results. This paper evaluates the accuracy of these methodologies and their applicability for roller-compacted-concrete and concrete incorporating steel fibres recycled from post-consumer tyres. It is shown that the energy absorption capacity is generally overestimated by these methodologies, sometimes up to 60%, for both conventional and roller-compacted concrete. Tensile behaviour of fibre-reinforced-concrete is estimated in this paper by inverse analysis of bending test results, examining a variety of concrete mixes and steel fibres. A multilinear relationship is proposed which largely eliminates the overestimation problem and can lead to safer designs. [es

  18. The relative stress-corrosion-cracking susceptibility of candidate aluminum-lithium alloys for aerospace applications

    Science.gov (United States)

    Pizzo, P. P.

    1982-01-01

    Stress corrosion tests of Al-Li-Cu powder metallurgy alloys are described. Alloys investigated were Al-2.6% Li-1.4% and Al-2.6% Li-1.4% Cu-1.6% Mg. The base properties of the alloys were characterized. Process, heat treatment, and size/orientational effects on the tensile and fracture behavior were investigated. Metallurgical and electrochemical conditions are identified which provide reproducible and controlled parameters for stress corrosion evaluation. Preliminary stress corrosion test results are reported. Both Al-Li-Cu alloys appear more susceptible to stress corrosion crack initiation than 7075-T6 aluminum, with the magnesium bearing alloy being the most susceptible. Tests to determine the threshold stress intensity for the base and magnesium bearing alloys are underway. Twelve each, bolt loaded DCB type specimens are under test (120 days) and limited crack growth in these precracked specimens has been observed. General corrosion in the aqueous sodium chloride environment is thought to be obscuring results through crack tip blunting.

  19. Method of measurement of near tip field of fast propagating cracks by means of interferometry; Hikari kansho ni yoru kosoku shinten kiretsu sentanbu no oryokuba keisokuho

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, s.; Miyazaki, F. [Toyohashi University of Technology, Aichi (Japan); Nakane, K. [Nitto Denko Corp., Osaka (Japan)

    1994-12-15

    The measurement by an interference method at the tip of fast propagating cracks was investigated. To clarify the direction-dependent problem of dynamic cracks in a higher-order term, a high-precision stress field must be measured in every direction. In this method, the propagated interference fringes near the crack tip are shot at a speed of some hundreds of m/sec, and the coefficient of dynamic stress extension is obtained from the expression given when the number of fringes (`m`) in the interferences fringes is differentiated partially. The information below was obtained. The stress field in every direction can be analyzed by the interference method. However, the interference fringes in an area of absolute {theta} < 120{degree} are radially spread from the crack tip, so the precision of the interference fringes in the {gamma} direction deteriorates. In this area, the above partial differential is higher in precision when {alpha}m/{alpha}{theta} is used instead of {alpha}m/{alpha}{gamma}. The stress extension coefficient obtained by a caustic method can be verified if a stress field of {theta} = {plus_minus}72{degree} is analyzed by the interference method. By shooting in this optical system, the COD measurement, the K-value measurement of caustic light, and the stress field measurement by an interference method can be done simultaneously. 17 refs., 11 figs.

  20. A Continuum-Atomistic Analysis of Transgranular Crack Propagation in Aluminum

    Science.gov (United States)

    Yamakov, V.; Saether, E.; Glaessgen, E.

    2009-01-01

    A concurrent multiscale modeling methodology that embeds a molecular dynamics (MD) region within a finite element (FEM) domain is used to study plastic processes at a crack tip in a single crystal of aluminum. The case of mode I loading is studied. A transition from deformation twinning to full dislocation emission from the crack tip is found when the crack plane is rotated around the [111] crystallographic axis. When the crack plane normal coincides with the [112] twinning direction, the crack propagates through a twinning mechanism. When the crack plane normal coincides with the [011] slip direction, the crack propagates through the emission of full dislocations. In intermediate orientations, a transition from full dislocation emission to twinning is found to occur with an increase in the stress intensity at the crack tip. This finding confirms the suggestion that the very high strain rates, inherently present in MD simulations, which produce higher stress intensities at the crack tip, over-predict the tendency for deformation twinning compared to experiments. The present study, therefore, aims to develop a more realistic and accurate predictive modeling of fracture processes.

  1. Propagation of stress corrosion cracks in alpha-brasses

    Energy Technology Data Exchange (ETDEWEB)

    Beggs, Dennis Vinton [Univ. of Illinois, Urbana-Champaign, IL (United States)

    1981-01-01

    Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, Δt greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, Δx, decreased linearly with Δt. With Δt less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, Δx = Δx* which approached a limiting value of 1 μm. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.

  2. Influence of pores on crack initiation in monotonic tensile and cyclic loadings in lost foam casting A319 alloy by using 3D in-situ analysis

    International Nuclear Information System (INIS)

    Wang, Long; Limodin, Nathalie; El Bartali, Ahmed; Witz, Jean-François; Seghir, Rian; Buffiere, Jean-Yves; Charkaluk, Eric

    2016-01-01

    Lost Foam Casting (LFC) process is replacing the conventional gravity Die Casting (DC) process in automotive industry for the purpose of geometry optimization, cost reduction and consumption control. However, due to lower cooling rate, LFC produces in a coarser microstructure that reduces fatigue life. In order to study the influence of the casting microstructure of LFC Al-Si alloy on damage micromechanisms under monotonic tensile loading and Low Cycle Fatigue (LCF) at room temperature, an experimental protocol based on the three dimensional (3D) in-situ analysis has been set up and validated. This paper focuses on the influence of pores on crack initiation in monotonic and cyclic tensile loadings. X-ray Computed Tomography (CT) allowed the microstructure of material being characterized in 3D and damage evolution being followed in-situ also in 3D. Experimental and numerical mechanical fields were obtained by using Digital Volume Correlation (DVC) technique and Finite Element Method (FEM) simulation respectively. Pores were shown to have an important influence on strain localization as large pores generate enough strain localization zones for crack initiation both in monotonic tensile and cyclic loadings.

  3. Influence of pores on crack initiation in monotonic tensile and cyclic loadings in lost foam casting A319 alloy by using 3D in-situ analysis

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Long, E-mail: longwang_calt@163.com [Univ. Lille, CNRS, Centrale Lille, Arts et Metiers Paris tech, FRE 3723 – LML – Laboratoire de Mecanique de Lille, F-59000 Lille (France); Limodin, Nathalie; El Bartali, Ahmed; Witz, Jean-François; Seghir, Rian [Univ. Lille, CNRS, Centrale Lille, Arts et Metiers Paris tech, FRE 3723 – LML – Laboratoire de Mecanique de Lille, F-59000 Lille (France); Buffiere, Jean-Yves [Laboratoire Matériaux, Ingénierie et Sciences (MATEIS), CNRS UMR5510, INSA-Lyon, 20 Av. Albert Einstein, 69621 Villeurbanne (France); Charkaluk, Eric [Univ. Lille, CNRS, Centrale Lille, Arts et Metiers Paris tech, FRE 3723 – LML – Laboratoire de Mecanique de Lille, F-59000 Lille (France)

    2016-09-15

    Lost Foam Casting (LFC) process is replacing the conventional gravity Die Casting (DC) process in automotive industry for the purpose of geometry optimization, cost reduction and consumption control. However, due to lower cooling rate, LFC produces in a coarser microstructure that reduces fatigue life. In order to study the influence of the casting microstructure of LFC Al-Si alloy on damage micromechanisms under monotonic tensile loading and Low Cycle Fatigue (LCF) at room temperature, an experimental protocol based on the three dimensional (3D) in-situ analysis has been set up and validated. This paper focuses on the influence of pores on crack initiation in monotonic and cyclic tensile loadings. X-ray Computed Tomography (CT) allowed the microstructure of material being characterized in 3D and damage evolution being followed in-situ also in 3D. Experimental and numerical mechanical fields were obtained by using Digital Volume Correlation (DVC) technique and Finite Element Method (FEM) simulation respectively. Pores were shown to have an important influence on strain localization as large pores generate enough strain localization zones for crack initiation both in monotonic tensile and cyclic loadings.

  4. Retarding effect of prior-overloading on stress corrosion cracking of cold rolled 316L SS in simulated PWR water environment

    Science.gov (United States)

    Chen, Junjie; Lu, Zhanpeng; Xiao, Qian; Ru, Xiangkun; Ma, Jiarong; Shoji, Tetsuo

    2017-12-01

    The effect of prior single tensile overloading on the stress corrosion cracking behavior of cold rolled 316L in a simulated PWR water environment at 310 °C was investigated. SCC growth retardation by overloading was observed in cold rolled 316L specimens in both the T-L and L-T orientations. The stretch zone observed on the fracture surfaces of the overloaded specimens affected SCC propagation. The compressive residual stress induced by overloading process reduced the effective driving force of SCC propagation. The negative dK/da effect ahead of the crack tip likely contributes to the retardation of SCC growth. The duration of overloading is dependent on water chemistry and the local stress conditions.

  5. Multi-parameter crack tip stress state description for estimation of fracture process zone extent in silicate composite WST specimens

    Czech Academy of Sciences Publication Activity Database

    Veselý, V.; Sobek, J.; Šestáková, L.; Frantík, P.; Seitl, Stanislav

    2013-01-01

    Roč. 7, č. 25 (2013), s. 69-78 ISSN 1971-8993 R&D Projects: GA ČR(CZ) GAP104/11/0833; GA ČR(CZ) GAP105/11/1551 Institutional support: RVO:68081723 Keywords : Near-crack tip fields * Williams series * higher-order terms * stress field approximation * wedge splitting test * fracture process zone Subject RIV: JL - Materials Fatigue, Friction Mechanics

  6. Attractive and repulsive cracks in a heterogeneous material

    International Nuclear Information System (INIS)

    Cortet, Pierre-Philippe; Huillard, Guillaume; Vanel, Loïc; Ciliberto, Sergio

    2008-01-01

    We study experimentally the paths of an assembly of cracks growing in interaction in a heterogeneous two-dimensional elastic brittle material submitted to uniaxial stress. For a given initial crack assembly geometry, we observe two types of crack path. The first one corresponds to a repulsion followed by an attraction on one end of the crack and a tip-to-tip attraction on the other end. The second one corresponds to a pure attraction. Only one of the crack path types is observed in a given sample. Thus, selection between the two types appears as a statistical collective process

  7. Threshold intensity factors as lower boundaries for crack propagation in ceramics

    Directory of Open Access Journals (Sweden)

    Walter Per-Ole

    2004-11-01

    Full Text Available Abstract Background Slow crack growth can be described in a v (crack velocity versus KI (stress intensity factor diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. Methods We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly disappeared. Results We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. Conclusion The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness, which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials

  8. Modelling probabilistic fatigue crack propagation rates for a mild structural steel

    OpenAIRE

    Correia, J.A.F.O.; de Jesus, A.M.P.; Fernández-Canteli, A.

    2014-01-01

    A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force asse...

  9. Fracture Mechanics Analyses for Interface Crack Problems - A Review

    Science.gov (United States)

    Krueger, Ronald; Shivakumar, Kunigal; Raju, Ivatury S.

    2013-01-01

    Recent developments in fracture mechanics analyses of the interfacial crack problem are reviewed. The intent of the review is to renew the awareness of the oscillatory singularity at the crack tip of a bimaterial interface and the problems that occur when calculating mode mixity using numerical methods such as the finite element method in conjunction with the virtual crack closure technique. Established approaches to overcome the nonconvergence issue of the individual mode strain energy release rates are reviewed. In the recent literature many attempts to overcome the nonconvergence issue have been developed. Among the many approaches found only a few methods hold the promise of providing practical solutions. These are the resin interlayer method, the method that chooses the crack tip element size greater than the oscillation zone, the crack tip element method that is based on plate theory and the crack surface displacement extrapolation method. Each of the methods is validated on a very limited set of simple interface crack problems. However, their utility for a wide range of interfacial crack problems is yet to be established.

  10. Crack growth and development of fracture zones in plain concrete and similar materials

    International Nuclear Information System (INIS)

    Petersson, P.-E.

    1981-12-01

    A calculation model (the Fictitious Crack Model), based on fracture mechanics and the finite element method, is presented. In the model the fracture zone in front of a crack is represented by a fictitious crack that is able to transfer stress. The stress transferring capability of the fictitious crack normally decreases when the crack width increases. The applicability of linear elastic fracture mechanics to concrete and similar materials is analysed by use of the Fictitious Crack Model. The complete tensile stress-strain curve is introduced as a fracture mechanical parameter. The curve can be approximately determined if the tensile strength, the Young's modulus and the fracture energy are known. Suitable test methods for determining these properties are presented and test results are reported for a number of concrete qualities. A new type of very stiff tensile testing machine is presented by which it is possible to carry out stable tensile tests on concrete. The complete tensile stress-strain curves have been determined for a number of concrete qualities. A complete system for analysing crack propagation in concrete is covered, as a realistic material model, a functional calculation model and methods for determining the material properties necessary for the calculations are included. (Auth.)

  11. The effect of crack blunting on the competition between dislocation nucleation and cleavage

    Science.gov (United States)

    Fischer, Lisa L.; Beltz, Glenn E.

    2001-03-01

    To better understand the ductile versus brittle fracture behavior of crystalline materials, attention should be directed towards physically realistic crack geometries. Currently, continuum models of ductile versus brittle behavior are typically based on the analysis of a pre-existing sharp crack in order to use analytical solutions for the stress fields around the crack tip. This paper examines the effects of crack blunting on the competition between dislocation nucleation and atomic decohesion using continuum methods. We accomplish this by assuming that the crack geometry is elliptical, which has the primary advantage that the stress fields are available in closed form. These stress field solutions are then used to calculate the thresholds for dislocation nucleation and atomic decohesion. A Peierls-type framework is used to obtain the thresholds for dislocation nucleation, in which the region of the slip plane ahead of the crack develops a distribution of slip discontinuity prior to nucleation. This slip distribution increases as the applied load is increased until an instability is reached and the governing integral equation can no longer be solved. These calculations are carried out for various crack tip geometries to ascertain the effects of crack tip blunting. The thresholds for atomic decohesion are calculated using a cohesive zone model, in which the region of the crack front develops a distribution of opening displacement prior to atomic decohesion. Again, loading of the elliptical crack tip eventually results in an instability, which marks the onset of crack advance. These calculations are carried out for various crack tip geometries. The results of these separate calculations are presented as the critical energy release rates versus the crack tip radius of curvature for a given crack length. The two threshold curves are compared simultaneously to determine which failure mode is energetically more likely at various crack tip curvatures. From these

  12. Creep, Fatigue and Environmental Interactions and Their Effect on Crack Growth in Superalloys

    Science.gov (United States)

    Telesman, J.; Gabb, T. P.; Ghosn, L. J.; Smith, T.

    2017-01-01

    Complex interactions of creep/fatigue/environment control dwell fatigue crack growth (DFCG) in superalloys. Crack tip stress relaxation during dwells significantly changes the crack driving force and influence DFCG. Linear Elastic Fracture Mechanics, Kmax, parameter unsuitable for correlating DFCG behavior due to extensive visco-plastic deformation. Magnitude of remaining crack tip axial stresses controls DFCG resistance due to the brittle-intergranular nature of the crack growth process. Proposed a new empirical parameter, Ksrf, which incorporates visco-plastic evolution of the magnitude of remaining crack tip stresses. Previous work performed at 704C, extend the work to 760C.

  13. Creep crack growth in phosphorus alloyed oxygen free copper

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Rui; Seitisleam, Facredin (Swerea KIMAB (Sweden)); Sandstroem, Rolf; Jin, Lai-Zhe (Materials Science and Engineering, Royal Inst. of Technology (Sweden))

    2011-01-15

    Using standard compact tension (CT) specimens taken from a pierce and draw cylinder, creep crack growth (CCG) has been studied in phosphorus-alloyed oxygen-free copper (Cu-OFP) parent metal at 22, 75, 175, and 215 deg C. Pre- and post-test metallography are performed. At higher temperatures the rupture time of CCG is shorter by a factor up of 65 than that of uniaxial at same stress/reference stress. At 175 and 215 deg C, crack does grow by creep about 10 mm before final instantaneous failure. In contrast, there is hardly any visible crack growth at 22 and 75 deg C. The tests were interrupted after 5000 to 13000 hours. For ruptured tests at 175 and 215 deg C, strongly elongated and deformed grains are observed adjacent to crack. Extensive and intergranular creep cavities and microcracks are found several mm around crack. For interrupted tests at 22 and 75 deg C, strongly elongated and deformed grains, creep cavities, as well as microcracks are observed close to crack tip. Surface cracks from both sides have initiated and grown about 45 deg to the load direction towards inside. For the interrupted tests, hardness adjacent to crack tip has more than doubled because of work hardening, or heavy deformation. This is consistent with large crack tip opening. The true strain at the crack tip is estimated to 10 and 4 for the tests at 22 and 75 deg C, respectively. The stress state behind the crack tip has been modelled with FEM. Stress relaxation after loading has also been taken into account. A model for the creep damage based on the creep strain rate has been formulated that can describe the uniaxial creep rupture data without fitting parameters. Based on the formulation for the creep damage, a model for the crack propagation has been set up. When the creep damage has reached the value unity in front of the crack tip, the crack is assumed to propagate. Taking multiaxial effects into account the observed life times of the CT specimens can be well described. The multiaxial

  14. Creep crack growth in phosphorus alloyed oxygen free copper

    International Nuclear Information System (INIS)

    Wu, Rui; Seitisleam, Facredin; Sandstroem, Rolf; Jin, Lai-Zhe

    2011-01-01

    Using standard compact tension (CT) specimens taken from a pierce and draw cylinder, creep crack growth (CCG) has been studied in phosphorus-alloyed oxygen-free copper (Cu-OFP) parent metal at 22, 75, 175, and 215 deg C. Pre- and post-test metallography are performed. At higher temperatures the rupture time of CCG is shorter by a factor up of 65 than that of uniaxial at same stress/reference stress. At 175 and 215 deg C, crack does grow by creep about 10 mm before final instantaneous failure. In contrast, there is hardly any visible crack growth at 22 and 75 deg C. The tests were interrupted after 5000 to 13000 hours. For ruptured tests at 175 and 215 deg C, strongly elongated and deformed grains are observed adjacent to crack. Extensive and intergranular creep cavities and microcracks are found several mm around crack. For interrupted tests at 22 and 75 deg C, strongly elongated and deformed grains, creep cavities, as well as microcracks are observed close to crack tip. Surface cracks from both sides have initiated and grown about 45 deg to the load direction towards inside. For the interrupted tests, hardness adjacent to crack tip has more than doubled because of work hardening, or heavy deformation. This is consistent with large crack tip opening. The true strain at the crack tip is estimated to 10 and 4 for the tests at 22 and 75 deg C, respectively. The stress state behind the crack tip has been modelled with FEM. Stress relaxation after loading has also been taken into account. A model for the creep damage based on the creep strain rate has been formulated that can describe the uniaxial creep rupture data without fitting parameters. Based on the formulation for the creep damage, a model for the crack propagation has been set up. When the creep damage has reached the value unity in front of the crack tip, the crack is assumed to propagate. Taking multiaxial effects into account the observed life times of the CT specimens can be well described. The multiaxial

  15. Numerical Simulation on the Dynamic Splitting Tensile Test of reinforced concrete

    Science.gov (United States)

    Zhao, Zhuan; Jia, Haokai; Jing, Lin

    2018-03-01

    The research for crack resistance was of RC was based on the split Hopkinson bar and numerical simulate software LS-DYNA3D. In the research, the difference of dynamic splitting failure modes between plane concrete and reinforced concrete were completed, and the change rule of tensile stress distribution with reinforcement ratio was studied; also the effect rule with the strain rate and the crack resistance was also discussed by the radial tensile stress time history curve of RC specimen under different loading speeds. The results shows that the reinforcement in the concrete can impede the crack extension, defer the failure time of concrete, increase the tension intensity of concrete; with strain rate of concrete increased, the crack resistance of RC increased.

  16. On the Fracture Response of Shape Memory Alloy Actuators

    Science.gov (United States)

    Jape, Sameer; Parrinello, Antonino; Baxevanis, Theocharis; Lagoudas, Dimitris C.

    In this paper, the effect of global thermo-mechanically-induced phase transformation on the driving force for crack growth in polycrystalline shape memory alloys is analyzed in an infinite center-cracked plate subjected to thermal actuation under isobaric, plane strain, mode I loading. Finite element calculations are carried out to determine the mechanical fields near the static crack and the crack-tip energy release rate using the virtual crack closure technique. Analysis of the static crack shows that, as compared to constant mechanical loading, the energy release rate during cooling increases by approximately an order of magnitude. This increase is attributed to the stress redistribution at the crack-tip induced by global phase transformation during cooling. Crack growth during actuation is assumed to occur when the crack-tip energy release rate reaches a material specific critical value. Fracture toughening behavior is observed during crack growth and is mainly associated with the energy dissipated by the progressively occurring phase transformation close to the moving crack tip. Lastly, the effect of crack configuration on fracture toughness enhancement in the large-scale transformation problem is studied. Numerical results for static cracks in compact tensile and three-point bending SMA specimens are reported and a comparison of fracture toughening during thermal actuation in the semi-infinite crack configuration with the compact tensile and three-point bending geometries is presented.

  17. Infrared thermography study of the fatigue crack propagation

    Directory of Open Access Journals (Sweden)

    O.A. Plekhov

    2012-07-01

    Full Text Available The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone.

  18. The combined effect of gamma radiation and stress cracking in polycarbonate;Efeito combinado da radiacao gama e stress cracking no policarbonato

    Energy Technology Data Exchange (ETDEWEB)

    Melo, Raphaela N. de; Rabello, Marcelo S., E-mail: marcelo@dema.ufcg.edu.b [Universidade Federal de Campina Grande (DEMa/UFCG), PB (Brazil). Dept. de Engenharia de Materiais; Silva, Leonardo G.A. [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2009-07-01

    In this work the combined effect of gamma irradiation and stress cracking was studied in polycarbonate (PC). Tensile test bars were produced by injection moulding and then exposed to different doses of gamma radiation. After that they were submitted to the contact with isopropanol, the stress cracking agent used in this work. The specimens were tested for mechanical properties, viscosity molecular weight and fractography. The results indicated that the previous radiation intensified the stress cracking effects, as evidenced by the reduction in tensile properties and surface damage caused to the samples. (author)

  19. Fast fracture: an adiabatic restriction on thermally activated crack propagation

    Energy Technology Data Exchange (ETDEWEB)

    Burns, S.J.

    1978-01-01

    Slow, isothermal, crack propagation is widely suspected to be rate controlled by thermally activated plastic deformation in the crack tip region. Adiabatic conditions are generally established in the fracture modified material at the tip of a crack during fast fracture. The temperature of this material is not the temperature of the specimen and is generally not measured during fast fracture. Thus, a complete thermodynamic description of adiabatic crack propagation data can not be made. When the slow, isothermal, crack propagation mechanisms are assumed to be operative during adiabatic crack propagation then certain predictions can be made. For example: the changes in the driving force due to temperature and rate are always in the opposite sense; there is no minimum in the driving force versus crack velocity without a change in mechanism; the temperature rise in the crack tip fracture modified material is determined mainly by the activation enthalpy for crack propagation; the interpretation of fast fracture structural steel data from simple plastic models is suspect since these materials have dissimilar isothermal temperature dependencies.

  20. Dislocations, the elastic energy momentum tensor and crack propagation

    International Nuclear Information System (INIS)

    Lung, Chi-wei

    1979-07-01

    Based upon dislocation theory, some stress intensity factors can be calculated for practical cases. The results obtained by this method have been found to agree fairly well with the results obtained by the conventional fracture mechanics. The elastic energy momentum tensor has been used to calculate the force acting on the crack tip. A discussion on the kinetics of migration of impurities to the crack tip was given. It seems that the crack tip sometimes may be considered as a singularity in an elastic field and the fundamental law of classical field theory is applicable on the problem in fracture of materials. (author)

  1. Fracture mechanics of piezoelectric solids with interface cracks

    CERN Document Server

    Govorukha, Volodymyr; Loboda, Volodymyr; Lapusta, Yuri

    2017-01-01

    This book provides a comprehensive study of cracks situated at the interface of two piezoelectric materials. It discusses different electric boundary conditions along the crack faces, in particular the cases of electrically permeable, impermeable, partially permeable, and conducting cracks. The book also elaborates on a new technique for the determination of electromechanical fields at the tips of interface cracks in finite sized piezoceramic bodies of arbitrary shape under different load types. It solves scientific problems of solid mechanics in connection with the investigation of electromechanical fields in piezoceramic bodies with interface cracks, and develops calculation models and solution methods for plane fracture mechanical problems for piecewise homogeneous piezoceramic bodies with cracks at the interfaces. It discusses the “open” crack model, which leads to a physically unrealistic oscillating singularity at the crack tips, and the contact zone model for in-plane straight interface cracks betw...

  2. SOLID BURNT BRICKS’ TENSILE STRENGTH

    Directory of Open Access Journals (Sweden)

    Aneta Maroušková

    2017-11-01

    Full Text Available This paper deals with experimental testing of solid burnt bricks and mortar in pure (axial tension. The obtained working diagrams will be further use for a detailed numerical analysis of whole brick masonry column under concentric compressive load. Failure mechanism of compressed brick masonry column is characterized by the appearance and development of vertical tensile cracks in masonry units (bricks passing in the direction of principal stresses and is accompanied by progressive growth of horizontal deformations. These cracks are caused by contraction and interaction between two materials with different mechanical characteristics (brick and mortar. The aim of this paper is more precisely describe the response of quasi-brittle materials to uniaxial loading in tension (for now only the results from three point bending test are available. For these reasons, bricks and mortar tensile behavior is experimentally tested and the obtained results are discussed.

  3. Multiscale model of short cracks in a random polycrystalline aggregate

    International Nuclear Information System (INIS)

    Simonovski, I.; Cizelj, L.; Petric, Z.

    2006-01-01

    A plane-strain finite element crystal plasticity model of microstructurally small stationary crack emanating at a surface grain in a 316L stainless steel is proposed. The model consisting of 212 randomly shaped, sized and oriented grains is loaded monotonically in uniaxial tension to a maximum load of 1.12Rp0.2 (280MPa). The influence that a random grain structure imposes on a Stage I crack is assessed by calculating the crack tip opening (CTOD) and sliding displacements (CTSD) for single crystal as well as for polycrystal models, considering also different crystallographic orientations. In the single crystal case the CTOD and CTSD may differ by more than one order of magnitude. Near the crack tip slip is activated on all the slip planes whereby only two are active in the rest of the model. The maximum CTOD is directly related to the maximal Schmid factors. For the more complex polycrystal cases it is shown that certain crystallographic orientations result in a cluster of soft grains around the crack-containing grain. In these cases the crack tip can become a part of the localized strain, resulting in a large CTOD value. This effect, resulting from the overall grain orientations and sizes, can have a greater impact on the CTOD than the local grain orientation. On the other hand, when a localized soft response is formed away from the crack, the localized strain does not affect the crack tip directly, resulting in a small CTOD value. The resulting difference in CTOD can be up to a factor of 4, depending upon the crystallographic set. Grains as far as 6 times the value of crack length significantly influence that crack tip parameters. It was also found that a larger crack containing grain tends to increase the CTOD. Finally, smaller than expected drop in the CTOD (12.7%) was obtained as the crack approached the grain boundary. This could be due to the assumption of the unchanged crack direction, only monotonic loading and simplified grain boundary modelling. (author)

  4. Analysis of steady-state ductile crack growth

    DEFF Research Database (Denmark)

    Niordson, Christian

    1999-01-01

    The fracture strength under quasi-static steady-state crack growth in an elastic-plastic material joined by a laser weld is analyzed. Laser welding gives high mismatch between the yield stress within the weld and the yield stress in the base material. This is due to the fast termic cycle, which...... the finite element mesh remains fixed relative to the tip of the growing crack. Fracture is modelled using two different local crack growth criteria. One is a crack opening displacement criterion, while the other is a model in which a cohesive zone is imposed in front of the crack tip along the fracture zone....... Both models predict that in general a thinner laser weld gives higher interface strength. Furthermore, both fracture criteria show, that the preferred path of the crack is close outside the weld material; a phenomenon also observed in experiments....

  5. Design of a cruciform bend specimen for determination of out-of- plane biaxial tensile stress effects on fracture toughness for shallow cracks

    International Nuclear Information System (INIS)

    Bass, B.R.; Bryson, J.W.; Mcafee, W.J.; Pennell, W.E.; Theiss, T.J.

    1993-01-01

    Pressurized-thermal-shock loading in a reactor pressure vessel produces significant positive out-of-plane stresses along the crack front for both circumferential and axial cracks. Experimental evidence, while very limited, seems to indicate that a reduction in toughness is associated with out-of-plane biaxial loading when compared with toughness values obtained under uniaxial conditions. A testing program is described that seeks to determine the effects of out-of-plane biaxial tensile loading on fracture toughness of RPV steels. A cruciform bend specimen that meets specified criteria for the testing pregam is analyzed using three-dimensional elastic-plastic finite-element techniques. These analysis results provide the basis for proposed test conditions that are judged likely to produce a biaxial loading effect in the cruciform bend specimen

  6. Towards a quantification of stress corrosion mechanisms: numerical simulations of hydrogen-dislocations at the very crack tip

    International Nuclear Information System (INIS)

    Chateau, J.P.

    1999-01-01

    We discuss the respective roles played by anodic dissolution and hydrogen in SCC mechanisms of f.c.c. materials, by studying the fracture of copper in nitrite for which we compare the results with that previously obtained in 316L steel in hot chloride. It is surprising to note that even the crystallographies at the scale of the micron are different, the macroscopic inclination of the fracture surfaces are the same. In the case of 316L steel, the formation of strong pile-ups in the presence of hydrogen leads to a zigzag fracture along alternated slip planes in the most general case. In the absence of hydrogen, as in copper, this mechanism effectively disappears. Furthermore, numerical simulations of crack shielding by dislocations emitted on one plane predict the macroscopic inclination. It shows that it is due to the mere dissolution which confines slip activity at the very crack tip in f.c.c. materials. In order to quantify the mechanism involved in 316L steel, we developed simulations which numerically solve the coupled diffusion and elasticity equations for hydrogen in the presence of a crack and shielding dislocations. They reproduce the mechanisms of hydrogen segregation on edge dislocations and of a localised softening effect by decreasing pair interactions. These mechanisms lead to i) a localisation of hydrogen embrittlement along the activated slip planes, ii) an increase of the dislocation density in pile-ups, and iii) a decrease of the cross slip probability. These three factors enhance micro-fracture at the head of a pile-up, which is responsible of the zigzag fracture. Introducing the free surface effects for hydrogen, we point out a new mechanism: the inhibition of dislocation sources at the crack tip, which is relevant with the brittle fracture surfaces observed in some cases in 316L steel. The quantification of these different mechanisms allows to give a relation between the local fracture possibility and the macroscopic parameters. A general law for

  7. Stress intensity factor at the tip of cladding incipient crack in RIA-simulating experiments for high-burnup PWR fuels

    International Nuclear Information System (INIS)

    Udagawa, Yutaka; Suzuki, Motoe; Sugiyama, Tomoyuki; Fuketa, Toyoshi

    2009-01-01

    RIA-simulating experiments for high-burnup PWR fuels have been performed in the NSRR, and the stress intensity factor K 1 at the tip of cladding incipient crack has been evaluated in order to investigate its validity as a PCMI failure threshold under RIA conditions. An incipient crack depth was determined by observation of metallographs. The maximum hydride-rim thickness in the cladding of the test fuel rod was regarded as the incipient crack depth in each test case. Hoop stress in the cladding periphery during the pulse power transient was calculated by the RANNS code. K 1 was calculated based on crack depth and hoop stress. According to the RANNS calculation, PCMI failure cases can be divided into two groups: failure in the elastic phase and failure in the plastic phase. In the former case, elastic deformation was predominant around the incipient crack at failure time. K 1 is available only in this case. In the latter, plastic deformation was predominant around the incipient crack at failure time. Failure in the elastic phase never occurred when K 1 was less than 17 MPa m 1/2 . For failure in the plastic phase, the plastic hoop strain of the cladding periphery at failure time clearly showed a tendency to decrease with incipient crack depth. The combination of K 1 , for failure in the elastic phase, and plastic hoop strain at failure, for failure in the plastic phase, can be an effective index of PCMI failure under RIA conditions. (author)

  8. Fracture resistance of welded panel specimen with perpendicular crack in tensile

    International Nuclear Information System (INIS)

    Gochev, Todor; Adziev, Todor

    1998-01-01

    Defects caused by natural crack in welded joints of high-strength low-alloy (HSLA) steels are very often. Perpendicular crack in welded joints and its heat treatment after the welding has also an influence on the fracture resistance. The fracture resistance of welded joints by crack in tense panel specimens was investigated by crack mouse opening displesment (CMOD), the parameter of fracture mechanic. Crack propagation was analysed by using a metallographic analysis of fractured specimens after the test. (Author)

  9. Cessation of environmentally-assisted cracking in a low-alloy steel: Theoretical analysis

    International Nuclear Information System (INIS)

    Wire, G.L.

    1997-01-01

    Environmentally Assisted Cracking (EAC) can cause increases in fatigue crack growth rates of 40 to 100 times the rate in air for low alloy steels. The increased rates can lead to very large predicted crack growth. EAC is activated by a critical level of dissolved sulfides at the crack tip. Sulfide inclusions (MnS) in the steel produce corrosive sulfides in solution following exposure by a growing crack. In stagnant, low oxygen water conditions considered here, diffusion is the dominant mass transport mechanism acting to change the sulfide concentration within the crack. The average crack tip velocity is below the level required to produce the critical crack tip sulfide ion concentration required for EAC. Crack extension analyses also consider the breakthrough of large, hypothetical embedded defects with the attendant large freshly exposed sulfide inventory. Combrade et al. noted that a large inventory of undissolved metallurgical sulfides on crack flanks could trigger EAC, but did not quantify the effects. Diffusion analysis is extended herein to cover breakthrough of embedded defects with large sulfide inventories. The mass transport via diffusion is limited by the sulfide solubility. As a result, deep cracks in high sulfur steels are predicted to retain undissolved sulfides for extended but finite periods of time t diss which increase with the crack length and the metallurgical sulfide content in the steel. The analysis shows that the duration of EAC is limited to t diss providing V eac , the crack tip velocity associated with EAC is less than V In , the crack tip velocity below which EAC will not occur in an initially sulfide free crack. This condition on V eac need only be met for a short time following crack cleanup to turn off EAC. The predicted crack extension due to limited duration of EAC is a small fraction of the initial embedded defect size and would not greatly change calculated crack depths

  10. The reinitiation of fracture at the tip of an arrested crack in a reactor pressure vessel: The effect of ligaments on the reinitiation K value

    International Nuclear Information System (INIS)

    Smith, E.

    1986-01-01

    During a hypothetical thermal shock event involving a water-cooled nuclear reactor steel pressure vessel, it is possible for a crack to propagate deep into the reactor vessel thickness by a series of run-arrest-reinitiation events. Furthermore, within the transition temperature regime, crack propagation and arrest are associated with a combination of cleavage and ductile rupture processes, the latter being manifested by ligaments that are normal to the crack plane and parallel to the direction of crack propagation. Earlier work by the author has modelled the effect of ligaments on the reinitiation of fracture at the tip of an arrested crack. Proceeding from the basis that the ligaments fail by a ductile rupture process, reinitiation K values were calculated. These values were appreciably higher than the experimental reinitiation K values for cracks in model vessels subject to thermal shock; it was therefore argued that the ligaments, which are present at arrest, are unlikely to fail entirely by ductile rupture prior to the reinitiation of fracture at an arrested crack tip. Instead it was suggested that the ligaments fail by cleavage, and consequently do not markedly affect the reinitiation K value, which therefore correlates with Ksub(IC). This paper's theoretical analysis extends the earlier work by relaxing a key assumption in the earlier work that, when calculating the reinitiation K value on the basis that the ligaments fail by ductile rupture, they should disappear completely prior to reinitiation. The new results, however, show that the predicted reinitiation K values are still so much greater than the model test reinitiation K values, that it is unlikely that the ligaments fail solely by ductile rupture prior to reinitiation. The view that the ligaments can fail by cleavage is therefore reinforced. (orig.)

  11. The effect of a curvature-dependent surface tension on the singularities at the tips of a straight interface crack

    KAUST Repository

    Zemlyanova, A. Y.

    2013-03-08

    A problem of an interface crack between two semi-planes made out of different materials under an action of an in-plane loading of general tensile-shear type is treated in a semi-analytical manner with the help of Dirichlet-to-Neumann mappings. The boundaries of the crack and the interface between semi-planes are subjected to a curvature-dependent surface tension. The resulting system of six singular integro-differential equations is reduced to the system of three Fredholm equations. It is shown that the introduction of the curvature-dependent surface tension eliminates both classical integrable power singularity of the order 1/2 and an oscillating singularity present in a classical linear elasticity solutions. The numerical results are obtained by solving the original system of singular integro-differential equations by approximating unknown functions with Taylor polynomials. © 2013 The Author.

  12. Sizing of cracks by ultrasonic testing - Diffraction methods

    International Nuclear Information System (INIS)

    Hoegberg, K.; Sattari-Far, I.; Pers-Anderson, E.B.

    1989-01-01

    The work has been concentrated on manual ultrasonic testing of plates in carbon and austenitic steel with thicknesses of 10-40 mm. Evaluation of data was performed by studying the amplitude, accuracy (crack depth) and visibility. The experience from the project showed that identification of the weak signals from the crack tips requires well-trained personnel. Besides that, the following can be recommended: Estimate if the crack has compressive stresses. Especially shallow cracks are exposed for compressive stresses. Chose a refraction angle ≥ 60 degrees if the crack is deep. Try both low (approx equivalent to 2MHz) and high (approx equivalent to 4-5MHz) frequency. Lower frequencies often increase amplitude response. Avoid the combination of refraction angle greater than 60 degrees and low frequency. Inspect with half as well as full skip. Sometimes a stronger signal is received for full skip, because the amplitude of the diffracted signal is higher from the cracked side. Use complementary measurements with mode conversion techniques. Focused probes can improve the results, especially for complicated geometries. Do not use reference reflectors of EDM-notch type for verification of signal amplitude. No correlation between amplitude from an EDM-notch tip and a crack tip exists. Reference reflectors of EDM-notch type can be used to verify the resolution of the system. A shallow EDM-notch can show if the probe can separate the tip and corner. It is our experience that general solutions does not exist, and each case needs an individual solution

  13. Prediction of Crack Growth Aqueous Environments.

    Science.gov (United States)

    1983-06-01

    ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK AREA & WORK UNIT NUMBERS SRI International 333 Ravenswood Avenue Menlo Park, CA 94025 II...34no crack" has at least a vestigial rupture, associated with cyclic loading of the oxide film at the crack tip. The curve labeled "crack" was obtained...be an effect of crack opening. For the data set labeled "crack", the vestigial crack, although short, is very tight and the impedance is large. Under

  14. Modelling and Simulation of Tensile Fracture in High Velocity Compacted Metal Powder

    International Nuclear Information System (INIS)

    Jonsen, P.; Haeggblad, H.-A.

    2007-01-01

    In cold uniaxial powder compaction, powder is formed into a desired shape with rigid tools and a die. After pressing, but before sintering, the compacted powder is called green body. A critical property in the metal powder pressing process is the mechanical properties of the green body. Beyond a green body free from defects, desired properties are high strength and uniform density. High velocity compaction (HVC) using a hydraulic operated hammer is a production method to form powder utilizing a shock wave. Pre-alloyed water atomised iron powder has been HVC-formed into circular discs with high densities. The diametral compression test also called the Brazilian disc test is an established method to measure tensile strength in low strength material like e.g. rock, concrete, polymers and ceramics. During the test a thin disc is compressed across the diameter to failure. The compression induces a tensile stress perpendicular to the compressed diameter. In this study the test have been used to study crack initiation and the tensile fracture process of HVC-formed metal powder discs with a relative density of 99%. A fictitious crack model controlled by a stress versus crack-width relationship is utilized to model green body cracking. Tensile strength is used as a failure condition and limits the stress in the fracture interface. The softening rate of the model is obtained from the corresponding rate of the dissipated energy. The deformation of the powder material is modelled with an elastic-plastic Cap model. The characteristics of the tensile fracture development of the central crack in a diametrically loaded specimen is numerically studied with a three dimensional finite element simulation. Results from the finite element simulation of the diametral compression test shows that it is possible to simulate fracturing of HVC-formed powder. Results from the simulation agree reasonably with experiments

  15. Cessation of environmentally-assisted cracking in a low-alloy steel: Experimental results

    International Nuclear Information System (INIS)

    Li, Y.Y.

    1997-01-01

    The presence of dissolved metallurgical sulfides in pressure vessel and piping steels has been linked to Environmentally-Assisted Cracking (EAC), a phenomenon observed in laboratory tests that results in fatigue crack growth rates as high as 100 times that in air. Previous experimental and analytical work based on diffusion as the mass transport process has shown that surface cracks that are initially clean of sulfides will not initiate EAC in most applications. This is because the average crack tip velocity would not be sufficiently high to expose enough metallurgical sulfides per unit time and produce the sulfide concentration required for EAC. However, there is a potential concern for the case of a relatively large embedded crack breaking through to the wetted surface. Such a crack would not be initially clean of sulfides, and EAC could initiate. This paper presents the results of a series of experiments conducted on two heats of an EAC susceptible, high-sulfur, low-alloy steel in 243 degrees C low-oxygen water to further study the phenomenon of EAC persistence at low crack tip velocities. A load cycle profile that incorporated a significant load dwell period at minimum load was used. In one experiment, the fatigue cycling history was such that relatively high crack tip velocities at the start of the experiment produced a persistent case of EAC even when crack tip velocities were later reduced to levels below the EAC initiation velocity. The other series of experiments used initial crack tip velocities that were much lower and probably more realistic. Air precracking of the compact tension specimens produced an initial inventory of undissolved sulfides on the crack flanks that directly simulates the array of sulfides expected from the breakthrough of an embedded crack. In all cases, results showed EAC ceased after several hundred hours of cycling

  16. Critique of the Ford-Andresen film rupture model for aqueous stress corrosion cracking

    International Nuclear Information System (INIS)

    Hall, M.M.

    2009-01-01

    The Ford-Andresen film rupture model for aqueous stress corrosion cracking has obtained a prominent position in the nuclear reactor industry. The model is said to have superior predictive capabilities because it is derived from a fundamental understanding of the film rupture-repassivation mechanism of crack advance. However, a critical review shows that there are conceptual and mathematical problems with the Ford-Andresen model development; there are inconsistencies among the stated and implied assumptions, the crack tip current density expression lacks the necessary dependence on crack tip strain rate and the fundamental proportionality that exists between crack tip strain rate and crack growth rate is overlooked and omitted from the model development. Consequently, the Ford-Andresen model must be considered neither phenomenologically nor fundamentally supported.

  17. Uncertainty quantification methodologies development for stress corrosion cracking of canister welds

    Energy Technology Data Exchange (ETDEWEB)

    Dingreville, Remi Philippe Michel [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Bryan, Charles R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2016-09-30

    This letter report presents a probabilistic performance assessment model to evaluate the probability of canister failure (through-wall penetration) by SCC. The model first assesses whether environmental conditions for SCC – the presence of an aqueous film – are present at canister weld locations (where tensile stresses are likely to occur) on the canister surface. Geometry-specific storage system thermal models and weather data sets representative of U.S. spent nuclear fuel (SNF) storage sites are implemented to evaluate location-specific canister surface temperature and relative humidity (RH). As the canister cools and aqueous conditions become possible, the occurrence of corrosion is evaluated. Corrosion is modeled as a two-step process: first, pitting is initiated, and the extent and depth of pitting is a function of the chloride surface load and the environmental conditions (temperature and RH). Second, as corrosion penetration increases, the pit eventually transitions to a SCC crack, with crack initiation becoming more likely with increasing pit depth. Once pits convert to cracks, a crack growth model is implemented. The SCC growth model includes rate dependencies on both temperature and crack tip stress intensity factor, and crack growth only occurs in time steps when aqueous conditions are predicted. The model suggests that SCC is likely to occur over potential SNF interim storage intervals; however, this result is based on many modeling assumptions. Sensitivity analyses provide information on the model assumptions and parameter values that have the greatest impact on predicted storage canister performance, and provide guidance for further research to reduce uncertainties.

  18. Modelling probabilistic fatigue crack propagation rates for a mild structural steel

    Directory of Open Access Journals (Sweden)

    J.A.F.O. Correia

    2015-01-01

    Full Text Available A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force assessment, allowing mean stresses and loading sequential effects to be modelled. An extension of the fatigue crack propagation model originally proposed by Noroozi et al. (2005 to derive probabilistic fatigue crack propagation data is proposed, in particular concerning the derivation of probabilistic da/dN-ΔK-R fields. The elastic-plastic stresses at the vicinity of the crack tip, computed using simplified formulae, are compared with the stresses computed using an elasticplastic finite element analyses for specimens considered in the experimental program proposed to derive the fatigue crack propagation data. Using probabilistic strain-life data available for the S355 structural mild steel, probabilistic crack propagation fields are generated, for several stress ratios, and compared with experimental fatigue crack propagation data. A satisfactory agreement between the predicted probabilistic fields and experimental data is observed.

  19. FEM Modeling of Crack Propagation in a Model Multiphase Alloy

    Institute of Scientific and Technical Information of China (English)

    Lihe QIAN; Seishi NISHIDO; Hiroyuki TODA; Tosliro KOBAYASHI

    2006-01-01

    In this paper, several widely applied fracture criteria were first numerically examined and the crack-tip-region Jintegral criterion was confirmed to be more applicable to predict fracture angle in an elastic-plastic multiphase material. Then, the crack propagation in an idealized dendritic two-phase Al-7%Si alloy was modeled using an elastic-plastic finite element method. The variation of crack growth driving force with crack extension was also demonstrated. It is found that the crack path is significantly influenced by the presence of α-phase near the crack tip, and the crack growth driving force varies drastically from place to place. Lastly, the simulated fracture path in the two-phase model alloy was compared with the experimentally observed fracture path.

  20. Short intergranular cracks in the piecewise anisotropic continuum model of the microstructure

    International Nuclear Information System (INIS)

    Cizelj, L.; Kovse, I.

    2001-01-01

    Computational algorithms aiming at modeling and visualization of the initiation and growth of intergranular stress corrosion cracks (e.g., in the steam generator tubes) on the grain-size scale have already been proposed [6]. The main focus of the paper is given to the influence of randomly oriented neighboring grains on the microscopic stress fields at crack tips. The incompatibility strains, which develop along the boundaries of randomly oriented anisotropic grains, are shown to influence the local stress fields at crack tips significantly. Special attention has been paid to the implementation and comparison of different numerical methods estimating the local stress fields at crack tips, aiming at optimizing the computational time and the numerical accuracy of the results. The limited number of calculations indicate that the anisotropic arrangement of grains with local incompatibility strains causes on average about 10% (plane strain) and 26% (plane stress) higher J-integral values at the crack tips than expected from the calculations in the isotropic case.(author)

  1. Microscopic Characterization of Tensile and Shear Fracturing in Progressive Failure in Marble

    Science.gov (United States)

    Cheng, Yi; Wong, Louis Ngai Yuen

    2018-01-01

    Compression-induced tensile and shear fractures were reported to be the two fundamental fracture types in rock fracturing tests. This study investigates such tensile and shear fracturing process in marble specimens containing two different flaw configurations. Observations first reveal that the development of a tensile fracture is distinct from shear fracture with respect to their nucleation, propagation, and eventual formation in macroscale. Second, transgranular cracks and grain-scale spallings become increasingly abundant in shear fractures as loading increases, which is almost not observed in tensile fractures. Third, one or some dominant extensional microcracks are commonly observed in the center of tensile fractures, while such development of microcracks is almost absent in shear fractures. Microcracks are generally of a length comparable to grain size and distribute uniformly within the damage zone of the shear fracture. Fourth, the width of densely damaged zone in the shear fracture is nearly 10 times of that in the tensile fracture. Quantitative measurement on microcrack density suggests that (1) microcrack density in tensile and shear fractures display distinct characteristics with increasing loading, (2) transgranular crack density in the shear fracture decreases logarithmically with the distance away from the shear fracture center, and (3) whatever the fracture type, the anisotropy can only be observed for transgranular cracks with a large density, which partially explains why microcrack anisotropy usually tends to be unobvious until approaching peak stress in specimens undergoing brittle failure. Microcracking characteristics observed in this work likely shed light to some phenomena and conclusions generalized in seismological studies.

  2. Fatigue crack retardation of high strength steel in saltwater

    International Nuclear Information System (INIS)

    Tokaji, K.; Ando, Z.; Imai, T.; Kojima, T.

    1983-01-01

    A high strength steel was studied in 3 percent saltwater to investigate the effects of a corrosive environment and sheer thickness on fatigue crack propagation behavior following the application of a single tensile overload. Experiments were carried out under sinusoidally varying loads at a load ratio of 0 and frequency of 10 H /SUB z/ . A single tensile overload was found to cause delayed retardation, and the crack propagation rate at first increased, followed by fairly rapid decrease to a minimum value and then increased gradually to its steady-state value, just as it did in air. The overload affected zone size and the retardation cycles increased with decreasing sheet thickness, just as they did in air. However, the zone size and the cycles were larger in 3 percent saltwater than in air. Since the crack propagation rates through the overload affected zone were not affected by the test environment, the longer retardation cycles in 3 percent saltwater were attributed to an enlargement of the overload affected zone size. The crack propagation behavior following the application of a single tensile overload in 3 percent saltwater was well explained by the crack closure concept

  3. Curvilinear crack layer propagation

    Science.gov (United States)

    Chudnovsky, Alexander; Chaoui, Kamel; Moet, Abdelsamie

    1987-01-01

    An account is given of an experiment designed to allow observation of the effect of damage orientation on the direction of crack growth in the case of crack layer propagation, using polystyrene as the model material. The direction of crack advance under a given loading condition is noted to be determined by a competition between the tendency of the crack to maintain its current direction and the tendency to follow the orientation of the crazes at its tip. The orientation of the crazes is, on the other hand, determined by the stress field due to the interaction of the crack, the crazes, and the hole. The changes in craze rotation relative to the crack define the active zone rotation.

  4. Crack Coalescence in Molded Gypsum and Carrara Marble

    Science.gov (United States)

    Wong, N.; Einstein, H. H.

    2007-12-01

    This research investigates the fracturing and coalescence behavior in prismatic laboratory-molded gypsum and Carrara marble specimens, which consist of either one or two pre-existing open flaws, under uniaxial compression. The tests are monitored by a high speed video system with a frame rate up to 24,000 frames/second. It allows one to precisely observe the cracking mechanisms, in particular if shear or tensile fracturing takes place. Seven crack types and nine crack coalescence categories are identified. The flaw inclination angle, the ligament length and the bridging angle between two flaws have different extents of influence on the coalescence patterns. For coplanar flaws, as the flaw inclination angle increases, there is a general trend of variation from shear coalescence to tensile coalescence. For stepped flaws, as the bridging angle changes from negative to small positive, and further up to large positive values, the coalescence generally progresses from categories of no coalescence, indirect coalescence to direct coalescence. For direct coalescence, it generally progresses from shear, mixed shear-tensile to tensile as the bridging angle increases. Some differences in fracturing and coalescence processes are observed in gypsum and marble, particularly the crack initiation in marble is preceded by the development of macroscopic white patches, but not in gypsum. Scanning Electron Microprobe (SEM) study reveals that the white patches consist of zones of microcracks (process zones).

  5. Innovative Approach to Establish Root Causes for Cracking in Aggressive Reactor Environments

    International Nuclear Information System (INIS)

    Bruemmer, Stephen M.; Thomas, Larry E.; Vetrano, John S.; Simonen, Edward P.

    2003-01-01

    The research focuses on the high-resolution characterization of degradation microstructures and microchemistries in specimens tested under controlled conditions for the environment and for the material where in-service complexities can be minimized. Thermodynamic and kinetic modeling of crack-tip processes is employed to analyze corrosion-induced structures and gain insights into degradation mechanisms. Novel mechanistic ''fingerprinting'' of crack-tip structures is used to isolate causes of environmental cracking in tandem with quantitative measurements of crack growth. Sample preparation methods and advanced analytical techniques are used to characterize corrosion/oxidation reactions and crack-tip structures at near atomic dimensions in order to gain insight into fundamental environmental cracking mechanisms. Reactions at buried interfaces, not accessible by conventional approaches, are being systematically interrogated. Crack-growth experiments in high-temperature water environments are evaluating and isolating the effects of material condition (matrix strength, grain boundary composition and precipitation) on stress corrosion cracking (SCC). The fundamental understanding of crack advance mechanisms will establish the basis to design new corrosion-resistant alloys for current light-water reactors and advanced reactor systems

  6. Evaluation of the presence of constraint in crack run/arrest events

    International Nuclear Information System (INIS)

    Schwartz, C.W.; Bass, B.R.

    1988-01-01

    Crack arrest studies currently being conducted by the Heavy-Section Steel Technology Program are designed to improve our understanding of the conditions contributing to the arrest of a propagating fracture in a pressure vessel. These studies are generating data spanning a wide temperature range for a variety of experimental configurations. Dynamic crack arrest parameters are back-figured from these experiments through 'generation mode' dynamic viscoplastic finite element calculations driven by the measured crack tip history input. A major approximation in these analyses, which is dictated by the practical limitations of current supercomputer hardware, is the assumption of two-dimensional plane stress conditions. Although this approximation is reasonable over most of the problem domain for many test specimen geometries, it deteriorates at locations near the crack tip due to triaxial constraint effects. This paper describes plans for a fine-grained three-dimensional computational study to investigate the importance of these near-tip triaxial constraint effects on crack tip yielding and to develop appropriate algorithms for incorporating these effects into conventional two-dimensional plane stress approximations. (author)

  7. Simulation of fatigue crack growth under large scale yielding conditions

    Science.gov (United States)

    Schweizer, Christoph; Seifert, Thomas; Riedel, Hermann

    2010-07-01

    A simple mechanism based model for fatigue crack growth assumes a linear correlation between the cyclic crack-tip opening displacement (ΔCTOD) and the crack growth increment (da/dN). The objective of this work is to compare analytical estimates of ΔCTOD with results of numerical calculations under large scale yielding conditions and to verify the physical basis of the model by comparing the predicted and the measured evolution of the crack length in a 10%-chromium-steel. The material is described by a rate independent cyclic plasticity model with power-law hardening and Masing behavior. During the tension-going part of the cycle, nodes at the crack-tip are released such that the crack growth increment corresponds approximately to the crack-tip opening. The finite element analysis performed in ABAQUS is continued for so many cycles until a stabilized value of ΔCTOD is reached. The analytical model contains an interpolation formula for the J-integral, which is generalized to account for cyclic loading and crack closure. Both simulated and estimated ΔCTOD are reasonably consistent. The predicted crack length evolution is found to be in good agreement with the behavior of microcracks observed in a 10%-chromium steel.

  8. Microstructural features of environmentally assisted cracking in pipeline steel

    International Nuclear Information System (INIS)

    Williams, B.W.; Lambert, S.B.; Zhang, X.; Plumtree, A.; Sutherby, R.

    2003-01-01

    A number of small-scale pipeline specimens containing edge or surface cracks were tested in simulated groundwater (NS4 solution) in an anaerobic environment under cyclic loading conditions. Micrographs of the crack surface showed corrosion fatigue at high frequencies and low R-ratios. Following large amounts of growth (∼200 μm) for those specimens tested at low frequencies, evidence of transgranular quasi-cleavage was detected. Green rust was found to be present at the crack tips and along their flanks. Iron sulfide, resulting from anaerobic sulfate-reducing bacteria and iron carbonate were also present in the NS4 solution during testing. These corrosion products retarded crack growth in the depth direction of surface cracks. Under variable amplitude loadings conditions, the accompanying increased surface crack growth rate can be accounted for by rupture of the green rust film at the crack tip. (author)

  9. Mechanism of crack healing at room temperature revealed by atomistic simulations

    International Nuclear Information System (INIS)

    Li, J.; Fang, Q.H.; Liu, B.; Liu, Y.; Liu, Y.W.; Wen, P.H.

    2015-01-01

    Three dimensional molecular dynamics (MD) simulations are systematically carried out to reveal the mechanism of the crack healing at room temperature, in terms of the dislocation shielding and the atomic diffusion to control the crack closure, in a copper (Cu) plate suffering from a shear loading. The results show that the process of the crack healing is actualized through the dislocation emission at a crack tip accompanied with intrinsic stacking faults ribbon forming in the crack tip wake, the dislocation slipping in the matrix and the dislocation annihilation in the free surface. Dislocation included stress compressing the crack tip is examined from the MD simulations and the analytical models, and then the crack closes rapidly due to the assistance of the atomic diffusion induced by the thermal activation when the crack opening displacement is less than a threshold value. This phenomenon is very different from the previous results for the crack propagation under the external load applied because of the crack healing (advancing) largely dependent on the crystallographic orientations of crack and the directions of external loading. Furthermore, based on the energy characteristic and considering the crack size effect, a theoretical model is established to predict the relationships between the crack size and the shear stress which qualitatively agree well with that obtained in the MD simulations

  10. Susceptibility of cold-worked zirconium-2.5 wt% niobium alloy to delayed hydrogen cracking

    International Nuclear Information System (INIS)

    Coleman, C.E.

    1976-01-01

    Notched tensile specimens of cold-worked zirconium-2.5 wt% niobium alloy have been stressed at 350 K and 520 K. At 350 K, above a possible threshold stress of 200 MPa, specimens exhibited delayed failure which was attributed to hydride cracking. Metallography showed that hydrides accumulated at notches and tips of growing cracks. The time to failure appeared to be independent of hydrogen content over the range 7 to 100 ppm hydrogen. Crack growth rates of about 10 -10 m/s deduced from fractography were in the same range as those necessary to fracture pressure tubes. The asymptotic stress intensity for delayed failure, Ksub(1H), appeared to be about 5 MPa√m. With this low value of Ksub(1H) small surface flaws may propagate in pressure tubes which contain large residual stresses. Stress relieving and modified rolling procedures will reduce the residual stresses to such an extent that only flaws 12% of the wall thickness or greater will grow. At 520 K no failures were observed at times a factor of three greater than times to failure at 350 K. Zirconium-2.5 wt% niobium appears to be safe from delayed hydrogen cracking at the reactor operating temperature. (author)

  11. Tensile and stress corrosion cracking properties of type 304 stainless steel irradiated to a very high dose

    International Nuclear Information System (INIS)

    Chung, H.M.; Strain, R.V.; Shack, W.J.

    2001-01-01

    Certain safety-related core internal structural components of light water reactors, usually fabricated from Type 304 or 316 austenitic stainless steels (SSs), accumulate very high levels of irradiation damage (20-100 displacement per atom or dpa) by the end of life. Our databases and mechanistic understanding of the degradation of such highly irradiated components, however, are not well established. A key question is the nature of irradiation-assisted intergranular cracking at very high doses, i.e. is it purely mechanical failure or is it stress-corrosion cracking? In this work, hot-cell tests and microstructural characterization were performed on Type 304 SS from the hexagonal fuel can of the decommissioned EBR-II reactor after irradiation to ∼50 dpa at ∼370 deg. C. Slow-strain-rate tensile tests were conducted at 289 degree sign C in air and in water at several levels of electrochemical potential (ECP), and microstructural characteristics were analyzed by scanning and transmission electron microscopies. The material deformed significantly by twinning and exhibited surprisingly high ductility in air, but was susceptible to severe intergranular stress corrosion cracking (IGSCC) at high ECP. Low levels of dissolved O and ECP were effective in suppressing the susceptibility of the heavily irradiated material to IGSCC, indicating that the stress corrosion process associated with irradiation-induced grain-boundary Cr depletion, rather than purely mechanical separation of grain boundaries, plays the dominant role. However, although IGSCC was suppressed, the material was susceptible to dislocation channeling at a low ECP, and this susceptibility led to a poor work-hardening capability and low ductility

  12. Problems of procedure for studying crack resistance

    International Nuclear Information System (INIS)

    Babak, A.V.; Uskov, E.I.

    1984-01-01

    Procedures are developed for studying crack resistance in sintered hot-worked tungsten within 20-2200 deg C. Certain structural properties of the installation for studying high-temperature crack resistance of tungsten are considered. Technological peculiarities of eccentric tensile strength of tungsten specimens and methodical peculiarities of initjation and fixation of initial cracks in specimens of different tungsten alloys are studied

  13. Micromechanical Analyses of Debonding and Matrix Cracking in Dual-Phase Materials

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Yang, Qingda

    2016-01-01

    Failure in elastic dual-phase materials under transverse tension is studied numerically. Cohesive zones represent failure along the interface and the augmented finite element method (A-FEM) is used for matrix cracking. Matrix cracks are formed at an angle of 55 deg - 60 deg relative to the loading...... direction, which is in good agreement with experiments. Matrix cracks initiate at the tip of the debond, and for equi-biaxial loading cracks are formed at both tips. For elliptical reinforcement the matrix cracks initiate at the narrow end of the ellipse. The load carrying capacity is highest for ligaments...

  14. Subcritical crack growth in a phosphate laser glass

    Energy Technology Data Exchange (ETDEWEB)

    Crichton, S.N.; Tomozawa, M.; Hayden, J.S.; Suratwala, T.I.; Campbell, J.H.

    1999-11-01

    The rate of subcritical crack growth in a metaphosphate Nd-doped laser glass was measured using the double-cleavage-drilled compression (DCDC) method. The crack velocity is reported as a function of stress intensity at temperatures ranging from 296 to 573 K and in nitrogen with water vapor pressures ranging from 40 Pa (0.3 mmHg) to 4.7 x 10{sup 4} Pa (355 mmHg). The measured crack velocities follow region I, II, and III behavior similar to that reported for silicate glasses. A chemical and mass-transport-limited reaction rate model explains the behavior of the data except at high temperatures and high water vapor pressures where crack tip blunting is observed. Blunting is characterized to reinitiate slow crack growth at higher stresses. A dynamic crack tip blunting mechanism is proposed to explain the deviation from the reaction rate model.

  15. Quarter elliptical crack growth using three dimensional finite element method and crack closure technique

    Energy Technology Data Exchange (ETDEWEB)

    Gozin, Mohammad-Hosein; Aghaie-Khafri, Mehrdad [K. N. Toosi University of Technology, Tehran (Korea, Republic of)

    2014-06-15

    Shape evolution of a quarter-elliptical crack emanating from a hole is studied. Three dimensional elastic-plastic finite element analysis of the fatigue crack closure was considered and the stress intensity factor was calculated based on the duplicated elastic model at each crack tip node. The crack front node was advanced proportional to the imposed effective stress intensity factor. Remeshing was applied at each step of the crack growth and solution mapping algorithm was considered. Crack growth retardation at free surfaces was successfully observed. A MATLAB-ABAQUS interference code was developed for the first time to perform crack growth on the basis of crack closure. Simulation results indicated that crack shape is sensitive to the remeshing strategy. Predictions based on the proposed models were in good agreement with Carlson's experiments results.

  16. Investigation of plastic zones near SCC tips in a pipeline after hydrostatic testing

    International Nuclear Information System (INIS)

    Li Jian; Elboujdaini, M.; Gao, M.; Revie, R.W.

    2008-01-01

    Stress corrosion cracking (SCC) is an important failure mechanism for oil and gas pipelines. In the past, hydrostatic testing has been frequently used to assess and mitigate stress corrosion cracking. It is commonly agreed that an effective hydrostatic test not only eliminates critical crack-like flaws, but also blunts the sub-critical crack tip thereby suppressing further SCC propagation. However, little study has been done on the plastic deformation that results from the high stress intensity at the crack tip due to hydrostatic testing pressure and its possible role in subsequent SCC propagation. In this study, microstructural details were examined of an API 5L X52 SCC-containing pipe removed from field service. Plastic deformation generated by the hydrostatic testing pressure was revealed by using high-resolution imaging of a focused ion beam (FIB) microscope. The existence of the microscopic plastic zones around some crack tips suggests that caution should be taken when setting up pipeline hydrostatic tests

  17. Investigation of plastic zones near SCC tips in a pipeline after hydrostatic testing

    Energy Technology Data Exchange (ETDEWEB)

    Li Jian [Materials Technology Laboratory, Natural Resources Canada, 568 Booth Street, Ottawa, Ont., K1A 0G1 (Canada)], E-mail: jili@nrcan.gc.ca; Elboujdaini, M [Materials Technology Laboratory, Natural Resources Canada, 568 Booth Street, Ottawa, Ont., K1A 0G1 (Canada); Gao, M [Blade Energy Partners, 16225 Park Ten Place, Suite 450, Houston, TX 77084 (United States); Revie, R W [Materials Technology Laboratory, Natural Resources Canada, 568 Booth Street, Ottawa, Ont., K1A 0G1 (Canada)

    2008-07-15

    Stress corrosion cracking (SCC) is an important failure mechanism for oil and gas pipelines. In the past, hydrostatic testing has been frequently used to assess and mitigate stress corrosion cracking. It is commonly agreed that an effective hydrostatic test not only eliminates critical crack-like flaws, but also blunts the sub-critical crack tip thereby suppressing further SCC propagation. However, little study has been done on the plastic deformation that results from the high stress intensity at the crack tip due to hydrostatic testing pressure and its possible role in subsequent SCC propagation. In this study, microstructural details were examined of an API 5L X52 SCC-containing pipe removed from field service. Plastic deformation generated by the hydrostatic testing pressure was revealed by using high-resolution imaging of a focused ion beam (FIB) microscope. The existence of the microscopic plastic zones around some crack tips suggests that caution should be taken when setting up pipeline hydrostatic tests.

  18. Crack growth threshold under hold time conditions in DA Inconel 718 – A transition in the crack growth mechanism

    Directory of Open Access Journals (Sweden)

    E. Fessler

    2016-01-01

    Full Text Available Aeroengine manufacturers have to demonstrate that critical components such as turbine disks, made of DA Inconel 718, meet the certification requirements in term of fatigue crack growth. In order to be more representative of the in service loading conditions, crack growth under hold time conditions is studied. Modelling crack growth under these conditions is challenging due to the combined effect of fatigue, creep and environment. Under these conditions, established models are often conservative but the degree of conservatism can be reduced by introducing the crack growth threshold in models. Here, the emphasis is laid on the characterization of crack growth rates in the low ΔK regime under hold time conditions and in particular, on the involved crack growth mechanism. Crack growth tests were carried out at high temperature (550 °C to 650 °C under hold time conditions (up to 1200 s in the low ΔK regime using a K-decreasing procedure. Scanning electron microscopy was used to identify the fracture mode involved in the low ΔK regime. EBSD analyses and BSE imaging were also carried out along the crack path for a more accurate identification of the fracture mode. A transition from intergranular to transgranular fracture was evidenced in the low ΔK regime and slip bands have also been observed at the tip of an arrested crack at low ΔK. Transgranular fracture and slip bands are usually observed under pure fatigue loading conditions. At low ΔK, hold time cycles are believed to act as equivalent pure fatigue cycles. This change in the crack growth mechanism under hold time conditions at low ΔK is discussed regarding results related to intergranular crack tip oxidation and its effect on the crack growth behaviour of Inconel 718 alloy. A concept based on an “effective oxygen partial pressure” at the crack tip is proposed to explain the transition from transgranular to intergranular fracture in the low ΔK regime.

  19. Effect of short-term overloads on crack propagation under creep

    International Nuclear Information System (INIS)

    Sushok, V.V.; Sobolev, N.D.; Zolotukhin, S.Yu.

    1986-01-01

    Kinetics of crack propagation after overload has been studied using plane samples of Kh18N10T steel. Tests of samples with a notch have been carried out in the air at 293 K. Observation of the crack growth has been carried out by the microscope and the method of electric potential difference. It is established that during overload besides crack tip blunting, decrease of creep rate of the material stregthened near it, that leads to crack retardation, decrease of plasticity and formation of microcracks in front of the tip of the main-line crack occurs. It is marked that, estimating serviceability of a member, it is necessary to take into account the decrease of crack propagation rate after short term overloads

  20. Development of nondestructive method for prediction of crack instability

    International Nuclear Information System (INIS)

    Schroeder, J.L.; Eylon, D.; Shell, E.B.; Matikas, T.E.

    2000-01-01

    A method to characterize the deformation zone at a crack tip and predict upcoming fracture under load using white light interference microscopy was developed and studied. Cracks were initiated in notched Ti-6Al-4V specimens through fatigue loading. Following crack initiation, specimens were subjected to static loading during in-situ observation of the deformation area ahead of the crack. Nondestructive in-situ observations were performed using white light interference microscopy. Profilometer measurements quantified the area, volume, and shape of the deformation ahead of the crack front. Results showed an exponential relationship between the area and volume of deformation and the stress intensity factor of the cracked alloy. These findings also indicate that it is possible to determine a critical rate of change in deformation versus the stress intensity factor that can predict oncoming catastrophic failure. In addition, crack front deformation zones were measured as a function of time under sustained load, and crack tip deformation zone enlargement over time was observed

  1. Prediction of PWSCC in nickel base alloys using crack growth rate models

    International Nuclear Information System (INIS)

    Thompson, C.D.

    1995-01-01

    The Ford/Andresen slip dissolution SCC model, originally developed for stainless steel components in BWR environments, has been applied to Alloy 600 and Alloy X-750 tested in deaerated pure water chemistry. A method is described whereby the crack growth rates measured in compact tension specimens can be used to estimate crack growth in a component. Good agreement was found between model prediction and measured SCC in X-750 threaded fasteners over a wide range of temperatures, stresses, and material condition. Most data support the basic assumption of this model that cracks initiate early in life. The evidence supporting a particular SCC mechanism is mixed. Electrochemical repassivation data and estimates of oxide fracture strain indicate that the slip dissolution model can account for the observed crack growth rates, provided primary rather than secondary creep rates are used. However, approximately 100 cross-sectional TEM foils of SCC cracks including crack tips reveal no evidence of enhanced plasticity or unique dislocation patterns at the crack tip or along the crack to support a classic slip dissolution mechanism. No voids, hydrides,, or microcracks are found in the vicinity of the crack tips creating doubt about classic hydrogen related mechanisms. The bulk oxide films exhibit a surface oxide which is often different than the oxide found within a crack. Although bulk chromium concentration affects the rate of SCC, analytical data indicates the mechanism does not result from chromium depletion at the grain boundaries. The overall findings support a corrosion/dissolution mechanism but not one necessarily related to slip at the crack tip. (author). 12 refs, 27 figs

  2. Transient cracks and triple junctions induced by Cocos-Nazca propagating rift

    Science.gov (United States)

    Schouten, H.; Smith, D. K.; Zhu, W.; Montesi, L. G.; Mitchell, G. A.; Cann, J. R.

    2009-12-01

    The Galapagos triple junction is a ridge-ridge-ridge triple junction where the Cocos, Nazca, and Pacific plates meet around the Galapagos microplate (GMP). On the Cocos plate, north of the large gore that marks the propagating Cocos-Nazca (C-N) Rift, a 250-km-long and 50-km-wide band of NW-SE-trending cracks crosscuts the N-S-trending abyssal hills of the East Pacific Rise (EPR). These appear as a succession of minor rifts, accommodating some NE-SW extension of EPR-generated seafloor. The rifts successively intersected the EPR in triple junctions at distances of 50-100 km north of the tip of the C-N Rift. We proposed a simple crack interaction model to explain the location of the transient rifts and their junction with the EPR. The model predicts that crack locations are controlled by the stress perturbation along the EPR, induced by the dominant C-N Rift, and scaled by the distance of its tip to the EPR (Schouten et al., 2008). The model also predicts that tensile stresses are symmetric about the C-N Rift and thus, similar cracks should have occurred south of the C-N Rift prior to formation of the GMP about 1 Ma. There were no data at the time to test this prediction. In early 2009 (AT 15-41), we mapped an area on the Nazca plate south of the C-N rift out to 4 Ma. The new bathymetric data confirm the existence of a distinctive pattern of cracks south of the southern C-N gore that mirrors the pattern on the Cocos plate until about 1 Ma, and lends support to the crack interaction model. The envelope of the symmetric cracking pattern indicates that the distance between the C-N Rift tip and the EPR varied between 40 and 65 km during this time (1-4 Ma). The breakdown of the symmetry at 1 Ma accurately dates the onset of a southern plate boundary of the GMP, now Dietz Deep Rift. At present, the southern rift boundary of the GMP joins the EPR with a steep-sided, 80 km long ridge. This ridge releases the stress perturbation otherwise induced along the EPR by elastic

  3. Flexural Cracking Behavior Of Steel Fiber Reinforced Concrete Beams

    Directory of Open Access Journals (Sweden)

    Ashraf Abdalkader

    2017-08-01

    Full Text Available Steel fibers are added to concrete due to its ability to improve the tensile strength and control propagation of cracks in reinforced concrete members. Steel fiber reinforced concrete is made of cement fine water and coarse aggregate in addition to steel fibers. In this experimental work flexural cracking behavior of reinforced concrete beams contains different percentage of hooked-end steel fibers with length of 50 mm and equivalent diameter of 0.5 mm was studied. The beams were tested under third-point loading test at 28 days. First cracking load maximum crack width cracks number and load-deflection relations were investigated to evaluate the flexural cracking behavior of concrete beams with 34 MPa target mean strength. Workability wet density compressive and splitting tensile strength were also investigated. The results showed that the flexural crack width is significantly reduced with the addition of steel fibers. Fiber contents of 1.0 resulted in 81 reduction in maximum crack width compared to control concrete without fiber. The results also showed that the first cracking load and maximum load are increased with the addition of steel fibers.

  4. Compressive failure with interacting cracks

    International Nuclear Information System (INIS)

    Yang Guoping; Liu Xila

    1993-01-01

    The failure processes in concrete and other brittle materials are just the results of the propagation, coalescence and interaction of many preexisting microcracks or voids. To understand the real behaviour of the brittle materials, it is necessary to bridge the gap from the relatively matured one crack behaviour to the stochastically distributed imperfections, that is, to concern the crack propagation and interaction of microscopic mechanism with macroscopic parameters of brittle materials. Brittle failure in compression has been studied theoretically by Horii and Nemat-Nasser (1986), in which a closed solution was obtained for a preexisting flaw or some special regular flaws. Zaitsev and Wittmann (1981) published a paper on crack propagation in compression, which is so-called numerical concrete, but they did not take account of the interaction among the microcracks. As for the modelling of the influence of crack interaction on fracture parameters, many studies have also been reported. Up till now, some researcher are working on crack interaction considering the ratios of SIFs with and without consideration of the interaction influences, there exist amplifying or shielding effects of crack interaction which are depending on the relative positions of these microcracks. The present paper attempts to simulate the whole failure process of brittle specimen in compression, which includes the complicated coupling effects between the interaction and propagation of randomly distributed or other typical microcrack configurations step by step. The lengths, orientations and positions of microcracks are all taken as random variables. The crack interaction among many preexisting random microcracks is evaluated with the help of a simple interaction matrix (Yang and Liu, 1991). For the subcritically stable propagation of microcracks in mixed mode fracture, fairly known maximum hoop stress criterion is adopted to compute branching lengths and directions at each tip of the crack

  5. Creep Behavior and Durability of Cracked CMC

    Science.gov (United States)

    Bhatt, R. T.; Fox, Dennis; Smith, Craig

    2015-01-01

    To understand failure mechanisms and durability of cracked Ceramic matrix composites (CMCs), Melt Infiltration (MI) SiCSiC composites with Sylramic-iBN fibers and full Chemical vapour infiltration SiCSiC composites with Sylramic-ion bombarded BN (iBN) and Hi-Nicalon -S fibers were pre-cracked between 150 to 200 megapascal and then creep and Sustained Peak Low Cycle Fatigue (SPLCF) tested at 13150 C at stress levels from 35 to 103 megapascal for up to 200 hours under furnace and burner rig conditions. In addition creep testing was also conducted on pre-cracked full Chemical vapour infiltration SiCSiC composites at 14500 C between 35 and 103 megapascal for up to 200 hours under furnace conditions. If the specimens survived the 200 hour durability tests, then they were tensile tested at room temperature to determine their residual tensile properties. The failed specimens were examined by Scanning electron microscope (SEM) to determine the failure modes and mechanisms. The influence of crack healing matrix, fiber types, crack density, testing modes and interface oxidation on durability of cracked Ceramic matrix composites (CMCs) will be discussed.

  6. Tensile and high cycle fatigue behaviors of high-Mn steels at 298 and 110 K

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Wongyu; Jeong, Daeho; Sung, Hyokyung; Kim, Sangshik, E-mail: sang@gnu.ac.kr

    2017-02-15

    Tensile and high cycle fatigue behaviors of high-Mn austenitic steels, including 25Mn, 25Mn0.2Al, 25Mn0.5Cu, 24Mn4Cr, 22Mn3Cr and 16Mn2Al specimens, were investigated at 298 and 110 K. Depending on the alloying elements, tensile ductility of high-Mn steels either increased or decreased with decreasing temperature from 298 to 110 K. Reasonable correlation between the tendency for martensitic tranformation, the critical twinning stress and the percent change in tensile elongation suggested that tensile deformation of high-Mn steels was strongly influenced by SFE determining TRIP and TWIP effects. Tensile strength was the most important parameter in determining the resistance to high cycle fatigue of high-Mn steels with an exceptional work hardening capability at room and cryogenic temperatures. The fatigue crack nucleation mechanism in high-Mn steels did not vary with decreasing tempertature, except Cr-added specimens with grain boundary cracking at 298 K and slip band cracking at 110 K. The EBSD (electron backscatter diffraction) analyses suggested that the deformation mechanism under fatigue loading was significantly different from tensile deformation which could be affected by TRIP and TWIP effects. - Highlights: •The resistances to HCF of various high-Mn steels were measured. •The variables affecting tensile and HCF behaviors of high-Mn steels were assessed. •The relationship between tensile and the HCF behaviors of high-Mn steels was established.

  7. Fatigue crack growth behavior of RAFM steel in Paris and threshold regimes at different temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Babu, M. Nani; Sasikala, G., E-mail: gsasi@igcar.gov.in; Dutt, B. Shashank; Venugopal, S.; Bhaduri, A.K.; Jayakumar, T.

    2014-04-01

    Fatigue crack growth (FCG) behavior of a reduced activation ferritic martensitic (indigenous RAFM) steel has been evaluated at 300, 653 and 823 K in Paris and threshold regimes. The effect of temperature on threshold stress intensity factor range and associated crack closure mechanisms is highlighted. The FCG results were compared with those for EUROFER 97. Further, crack tip effective stress intensity factor ranges (ΔK{sub tip,eff}) have been evaluated by taking crack tip shielding into account in order to examine the effect of temperature on true intrinsic FCG behavior.

  8. Evaluation of delayed hydride cracking and fracture toughness in zirconium alloys

    International Nuclear Information System (INIS)

    Oh, Je Yong

    2000-02-01

    The tensile, fracture toughness, and delayed hydride cracking (DHC) test were carried at various temperatures to understand the effect of hydrides on zirconium alloys. And the effects of yield stress and texture on the DHC velocity were discussed. The tensile properties of alloy A were the highest, and the difference between directions in alloy C was small due to texture. The fracture toughness at room temperature decreased sharply when hydrided. Although the alignment of hydride plates was parallel to loading direction, the hydrides were fractured due to the triaxiality at the crack tip region. The fracture toughness over 200 .deg. C was similar regardless of the hydride existence, because the triaxiality region was lost due to the decrease of yield stress with temperature. As the yield stress decreased, the threshold stress intensity factor and the striation spacing increased in alloy A, and the fracture surfaces and striations were affected by microstructures in all alloys. To evaluate the effect of the yield stress on DHC velocity, a normalization method was proposed. When the DHC velocity was normalized with dividing by the terminal solid solubility and the diffusion coefficient of hydrogen, the relationship between the yield stress and the DHC velocity was representable on one master curve. The equation from the master curve was able to explain the difference between the theoretical activation energy and the experimental activation energy in DHC. The difference was found to be ascribed to the decrease of yield stress with temperature. texture affected the delayed hydride cracking velocity by yield stress and by hydride reprecipitation. The relationship between the yield stress and the DHC velocity was expressed as an exponential function, and the relationship between the reprecipitation of hydride and the DHC velocity was expressed as a linear function

  9. Fully plastic crack opening analyses of complex-cracked pipes for Ramberg-Osgood materials

    International Nuclear Information System (INIS)

    Jeong, Jae Uk; Choi, Jae Boong; Huh, Nam Su; Kim, Yun Jae

    2016-01-01

    The plastic influence functions for calculating fully plastic Crack opening displacement (COD) of complex-cracked pipes were newly proposed based on systematic 3-dimensional (3-D) elastic-plastic Finite element (FE) analyses using Ramberg-Osgood (R-O) relation, where global bending moment, axial tension and internal pressure are considered separately as a loading condition. Then, crack opening analyses were performed based on GE/EPRI concept by using the new plastic influence functions for complex-cracked pipes made of SA376 TP304 stainless steel, and the predicted CODs were compared with FE results based on deformation plasticity theory of tensile material behavior. From the comparison, the confidence of the proposed fully plastic crack opening solutions for complex-cracked pipes was gained. Therefore, the proposed engineering scheme for COD estimation using the new plastic influence functions can be utilized to estimate leak rate of a complex-cracked pipe for R-O material.

  10. The combined effect of gamma radiation and stress cracking in polycarbonate

    International Nuclear Information System (INIS)

    Melo, Raphaela N. de; Rabello, Marcelo S.

    2009-01-01

    In this work the combined effect of gamma irradiation and stress cracking was studied in polycarbonate (PC). Tensile test bars were produced by injection moulding and then exposed to different doses of gamma radiation. After that they were submitted to the contact with isopropanol, the stress cracking agent used in this work. The specimens were tested for mechanical properties, viscosity molecular weight and fractography. The results indicated that the previous radiation intensified the stress cracking effects, as evidenced by the reduction in tensile properties and surface damage caused to the samples. (author)

  11. The pipeline fracture behavior and pressure assessment under HIC (Hydrogen induced cracking) environment

    Energy Technology Data Exchange (ETDEWEB)

    Shaohua, Dong [China National Petroleum Corporation (CNPC), Beijing (China); Lianwei, Wang [University of Science and Technology Beijing (USTB), Beijing (China)

    2009-07-01

    As Hydrogen's transmit and diffuse, after gestating for a while, the density of hydrogen around crack tip of pipeline will get to the critical density, and the pipeline material will descend, make critical stress factor, the reason of pipeline Hydrogen Induced Cracking is Hydrogen's transmit and diffuse. The stress factor of Hydrogen Induced Cracking under surroundings-condition of stress is the key that estimate material's rupture behavior. The paper study the relationship among hydrogen concentrate, crack tip stress, stain field, hydrogen diffusion and inner pressure for crack tip process zone, then determined the length of HIC (hydrogen induced cracking) process zone. Based on the theory of propagation which reason micro-crack making core, dislocation model is produced for fracture criteria of HIC, the influence between material and environments under the HIC is analyzed, step by step pipeline maximum load pressure and threshold of J-integrity ( J{sub ISCC} ) is calculated, which is very significant for pipeline safety operation. (author)

  12. Influence of surrounding environment on subcritical crack growth in marble

    Science.gov (United States)

    Nara, Yoshitaka; Kashiwaya, Koki; Nishida, Yuki; , Toshinori, Ii

    2017-06-01

    Understanding subcritical crack growth in rock is essential for determining appropriate measures to ensure the long-term integrity of rock masses surrounding structures and for construction from rock material. In this study, subcritical crack growth in marble was investigated experimentally, focusing on the influence of the surrounding environment on the relationship between the crack velocity and stress intensity factor. The crack velocity increased with increasing temperature and/or relative humidity. In all cases, the crack velocity increased with increasing stress intensity factor. However, for Carrara marble (CM) in air, we observed a region in which the crack velocity still increased with temperature, but the increase in the crack velocity with increasing stress intensity factor was not significant. This is similar to Region II of subcritical crack growth observed in glass in air. Region II in glass is controlled by mass transport to the crack tip. In the case of rock, the transport of water to the crack tip is important. In general, Region II is not observed for subcritical crack growth in rock materials, because rocks contain water. Because the porosity of CM is very low, the amount of water contained in the marble is also very small. Therefore, our results imply that we observed Region II in CM. Because the crack velocity increased in both water and air with increasing temperature and humidity, we concluded that dry conditions at low temperature are desirable for the long-term integrity of a carbonate rock mass. Additionally, mass transport to the crack tip is an important process for subcritical crack growth in rock with low porosity.

  13. Ductile failure simulation of tensile plates with multiple through-wall cracks

    International Nuclear Information System (INIS)

    Kim, Nak Hyun; Oh, Chang Sik; Kim, Yun Jae

    2009-01-01

    In this paper, failure behaviors of ductile plates with multiple cracks are simulated, finite element analyses using ABAQUS. To simulate crack coalescence or propagation of multiple cracks, a technique to reduce stresses within an finite element is proposed and implemented using user-defined subroutines provided in ABAQUS. In the proposed method, all stress components reduce to almost zero when the effective strain reaches critical values which are a function of the stress triaxiality. A main benefit of the proposed numerical scheme is its simplicity. The proposed scheme is applied to simulate multiple-cracked plate tests by Japanese researchers. Simulated maximum loads are compared with experimental ones, showing overall good agreements.

  14. Study of overload effects in bainitic steel by synchrotron X-ray diffraction

    Directory of Open Access Journals (Sweden)

    P. Lopez-Crespo

    2013-07-01

    Full Text Available This work presents an in-situ characterisation of crack-tip strain fields following an overload by means of synchrotron X-ray diffraction. The study is made on very fine grained bainitic steel, thus allowing a very high resolution so that small changes occurring around the crack-tip were captured along the crack plane at the mid-thickness of the specimen. We have followed the crack as it grew through the overload location. Once the crack-tip has progressed past the overload event there is strong evidence that the crack faces contact in the region of the overload event (though not in the immediate vicinity of the current locations of the crack tip at Kmin even when the crack has travelled 1mm beyond the overload location. It was also found that at Kmax the peak tensile strain ahead of the crack-tip decreases soon after the overload is applied and then gradually recovers as the crack grows past the compressive region created by the overload.

  15. Crack behavior of oxidation resistant coating layer on Zircaloy-4 for accident tolerant fuel claddings

    International Nuclear Information System (INIS)

    Park, Jung Hwan; Kim, Eui Jung; Jung, Yang Il; Park, Dong Jun; Kim, Hyun Gil; Park, Jeong Yong; Yang, Jae Ho

    2016-01-01

    Terrani et al. reported the oxidation resistance of Fe-based alloys for protecting zirconium alloys from the rapid oxidation in a high-temperature steam environment. Kim and co-workers also reported the corrosion behavior of Cr coated zirconium alloy using a plasma spray and laser beam scanning. Cracks are developed by tensile stress, and this significantly deteriorates the oxidation resistance. This tensile stress is possibly generated by the thermal cycle or bending or the irradiation growth of zirconium. In this study, Cr was deposited by AIP on to Zircaloy-4 plate, and the crack behavior of Cr coated Zircaloy-4 under uni-axial tensile strain was observed. In addition, the strain of the as-deposited state was calculated by iso-inclination method. Coating began to crack at 8% of applied strain. It is assumed that a well-densified structure by AIP tends to be resistant to cracking under tensile strain.

  16. Crack behavior of oxidation resistant coating layer on Zircaloy-4 for accident tolerant fuel claddings

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jung Hwan; Kim, Eui Jung; Jung, Yang Il; Park, Dong Jun; Kim, Hyun Gil; Park, Jeong Yong; Yang, Jae Ho [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    Terrani et al. reported the oxidation resistance of Fe-based alloys for protecting zirconium alloys from the rapid oxidation in a high-temperature steam environment. Kim and co-workers also reported the corrosion behavior of Cr coated zirconium alloy using a plasma spray and laser beam scanning. Cracks are developed by tensile stress, and this significantly deteriorates the oxidation resistance. This tensile stress is possibly generated by the thermal cycle or bending or the irradiation growth of zirconium. In this study, Cr was deposited by AIP on to Zircaloy-4 plate, and the crack behavior of Cr coated Zircaloy-4 under uni-axial tensile strain was observed. In addition, the strain of the as-deposited state was calculated by iso-inclination method. Coating began to crack at 8% of applied strain. It is assumed that a well-densified structure by AIP tends to be resistant to cracking under tensile strain.

  17. Coolant compatibility studies. The effect of irradiation on tensile properties and stress corrosion cracking sensitivity of martensitic steels. MANET 4 - complementary studies

    International Nuclear Information System (INIS)

    Nystrand, A.C.

    1994-02-01

    Tensile and stress corrosion cracking tests have been carried out on MANET-type (1.4914 and FV448) and reduced activation (LA12TaLC) high-chromium martensitic steels. The materials had previously been exposed up to 5000 h at ∼275 degrees C in the core, above the core and remote from the core of a high pressure water loop in the Studsvik R2 reactor. After the mechanical testing the materials were examined visually and metallographically. The steel samples exposed in the core section showed large increases in tensile yield strengths when tested at 250 degrees C. However, the magnitude of the radiation hardening was considerably smaller in the reduced activation steel compared to the commercial steels; this observation is consistent with published data on other high-chromium martensitic steels and is associated with the lower chromium content of the LA12TaLC steel (8.9%) compared with those of the commercial steels (10.6 and 11.3%). Irradiation assisted stress corrosion cracking (IASCC) was not detected in any of the stressed steel samples after autoclave testing for times up to 1500 h at 250 degrees C in air-saturated high purity water. This apparent resistance to IASCC may be due to the high chromium martensitic steels not being sensitized by the irradiation in a comparable manner to that shown by the austenitic steels. However, additional studies are required to clarify some of the existing uncertainties with respect to IASCC of these martensitic steels

  18. Stress corrosion cracking of titanium alloys

    Science.gov (United States)

    May, R. C.; Beck, F. H.; Fontana, M. G.

    1971-01-01

    Experiments were conducted to study (1) the basic electrochemical behavior of titanium in acid chloride solutions and (2) the response of the metal to dynamic straining in the same evironment. The aim of this group of experiments was to simulate, as nearly as possible, the actual conditions which exist at the tip of a crack. One of the foremost theories proposed to explain the propagation of stress corrosion cracks is a hydrogen embrittlement theory involving the precipitation of embrittling titanium hydrides inside the metal near the crack tip. An initial survey of the basic electrochemical literature indicated that surface hydrides play a critical role in the electrochemistry of titanium in acid solutions. A comprehensive analysis of the effect of surface films, particularly hydrides, on the electrochemical behavior of titanium in these solution is presented.

  19. Multi-parameter crack tip stress state description for evaluation of nonlinear zone width in silicate composite specimens in component splitting/bending test geometry

    Czech Academy of Sciences Publication Activity Database

    Veselý, V.; Frantík, P.; Sopek, J.; Malíková, L.; Seitl, Stanislav

    2015-01-01

    Roč. 38, č. 2 (2015), s. 200-214 ISSN 8756-758X R&D Projects: GA ČR(CZ) GAP104/11/0833 Institutional support: RVO:68081723 Keywords : near-crack tip fields * Williams series * higher-order terms * stress field * failure criterion * nonlinear zone * quasi-brittle fracture * splitting-bending geometry Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.838, year: 2015

  20. Crack initiation under generalized plane strain conditions

    International Nuclear Information System (INIS)

    Shum, D.K.M.; Merkle, J.G.

    1991-01-01

    A method for estimating the decrease in crack-initiation toughness, from a reference plane strain value, due to positive straining along the crack front of a circumferential flaw in a reactor pressure vessel is presented in this study. This method relates crack initiation under generalized plane strain conditions with material failure at points within a distance of a few crack-tip-opening displacements ahead of a crack front, and involves the formulation of a micromechanical crack-initiation model. While this study is intended to address concerns regarding the effects of positive out-of- plane straining on ductile crack initiation, the approach adopted in this work can be extended in a straightforward fashion to examine conditions of macroscopic cleavage crack initiation. Provided single- parameter dominance of near-tip fields exists in the flawed structure, results from this study could be used to examine the appropriateness of applying plane strain fracture toughness to the evaluation of circumferential flaws, in particular to those in ring-forged vessels which have no longitudinal welds. In addition, results from this study could also be applied toward the analysis of the effects of thermal streaming on the fracture resistance of circumferentially oriented flaws in a pressure vessel. 37 refs., 8 figs., 1 tab

  1. Variation of the energy release rate as a crack approaches and passes through an elastic inclusion

    Science.gov (United States)

    Li, Rongshun; Chudnovsky, A.

    1993-01-01

    The variation of the energy release rate (ERP) at the tip of a crack penetrating an elastic inclusion is analyzed using an approach involving modeling the random array of microcracks or other defects by an elastic inclusion with effective elastic properties. Computations are carried out using a finite element procedure. The eight-noded isoparametric serendipity element with the shift of the midpoint to the quarter-point is used to simulate the singularity at the crack tip, and the crack growth is accommodated by implementing a mesh regeneration technique. The ERP values were calculated for various crack tip positions which simulate the process of the crack approaching and penetrating the inclusion.

  2. Oxidation-induced crack healing in Ti3AlC2 ceramics

    NARCIS (Netherlands)

    Song, G.M.; Pei, Y.T.; Sloof, W.G.; Li, S.B.; Hosson, J.Th.M. De; Zwaag, S. van der

    Crack healing of Ti3AlC2 was investigated by oxidizing a partially pre-cracked sample. A crack near a notch was introduced into the sample by tensile deformation. After oxidation at 1100 degrees C in air for 2 h, the crack was completely healed, with oxidation products consisting primarily of

  3. Time-dependent crack growth and fracture in concrete

    International Nuclear Information System (INIS)

    Zhou Fan Ping.

    1992-02-01

    The objectives of this thesis are to study time-dependent fracture behaviour in concrete. The thesis consists of an experimental study, costitutive modelling and numerical analysis. The experimental study was undertaken to investigate the influences of time on material properties for the fracture process zone and on crack growth and fracture in plain concrete structures. The experiments include tensile relaxation tests, bending tests on notched beams to determine fracture energy at varying deflection rates, and sustained bending and compact tensile tests. From the tensile relaxation tests, the envelope of the σ-w relation does not seem to be influenced by holding periods, though some local detrimental effect does occur. Fracture energy seems to decrease as rates become slower. In the sustained loading tests, deformation (deflection or CMOD) growth curves display three stages, as usually observed in a creep rupture test. The secondary stage dominates the whole failure lifetime, and the secondary deformation rate appears to have good correlation with the failure lifetime. A crack model for time-dependent fracture is proposed, by applying the idea of the Fictitious Crack Model. In this model, a modified Maxwell model is introduced for the fracture process zone incorporated with the static σ-w curve as a failure criterion, based on the observation of the tensile relaxation tests. The time-dependent σ-w curve is expressed in an incremental law. The proposed model has been implemented in a finite element program and applied to simulating sustained flexural and compact tensile tests. Numerical analysis includes simulations of crack growth, load-CMOD curves, stress-failure lifetime curves, size effects on failure life etc. The numerical results indicate that the model seems to be able to properly predict the main features of time-dependent fracture behaviour in concrete, as compared with the experimental results. 97 refs

  4. A new procedure for investigating three-dimensional stress fields in a thin plate with a through-the-thickness crack

    Science.gov (United States)

    Yi, Dake; Wang, TzuChiang

    2018-06-01

    In the paper, a new procedure is proposed to investigate three-dimensional fracture problems of a thin elastic plate with a long through-the-thickness crack under remote uniform tensile loading. The new procedure includes a new analytical method and high accurate finite element simulations. In the part of theoretical analysis, three-dimensional Maxwell stress functions are employed in order to derive three-dimensional crack tip fields. Based on the theoretical analysis, an equation which can describe the relationship among the three-dimensional J-integral J( z), the stress intensity factor K( z) and the tri-axial stress constraint level T z ( z) is derived first. In the part of finite element simulations, a fine mesh including 153360 elements is constructed to compute the stress field near the crack front, J( z) and T z ( z). Numerical results show that in the plane very close to the free surface, the K field solution is still valid for in-plane stresses. Comparison with the numerical results shows that the analytical results are valid.

  5. Crack propagation direction in a mixed mode geometry estimated via multi-parameter fracture criteria

    Czech Academy of Sciences Publication Activity Database

    Malíková, L.; Veselý, V.; Seitl, Stanislav

    2016-01-01

    Roč. 89, AUG (2016), s. 99-107 ISSN 0142-1123. [International Conference on Characterisation of Crack Tip Fields /3./. Urbino, 20.04.2015-22.04.2015] Institutional support: RVO:68081723 Keywords : Near-crack-tip fields * Mixed mode * Crack propagation direction * Multi-parameter fracture criteria * Finite element analysis Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.899, year: 2016

  6. Evaluation and Study the Effect of Additives and Other Factors on Tensile Strength of Asphalt Paving Mixtures

    Directory of Open Access Journals (Sweden)

    Hanaa Khaleel A. Al-Baiti

    2012-03-01

    Full Text Available The resistance of asphaltic concrete to cracking is dependent upon its tensile strength and flexibility characteristics. Also the low tensile strength has recognized as a major contributor to other performance problems. The fatigue life of mixtures decreases exponentially with decreasing of tensile strength. This trend is justified by the loss in stiffness and thereby initiating cracks and stripping. The main objective of this research is intended to study the effect of different variables related with the used materials and the external conditions on the tensile strength and predict a model of indirect tensile strength in asphalt concrete paving materials under the local prevailing conditions and investigate the effect of percent of additives of (Polyestrene resins and Hydrated Lime to enhance the resistance ability of asphalt concrete mixture against distresses. The main affected factors; soaking, asphalt content, compaction, aggregate maximum size and temperature, influence on the indirect tensile strength and presented through a statistics analysis model for tensile strength in asphalt mixture

  7. Hydride effect on crack instability of Zircaloy cladding

    Energy Technology Data Exchange (ETDEWEB)

    Tseng, Che-Chung, E-mail: cctseng@iner.gov.tw [Institute of Nuclear Energy Research, No. 1000, Wunhua Road, Jiaan Village, Lungtan, Township, Taoyuan County 32546, Taiwan (China); Sun, Ming-Hung [Institute of Nuclear Energy Research, No. 1000, Wunhua Road, Jiaan Village, Lungtan, Township, Taoyuan County 32546, Taiwan (China); Chao, Ching-Kong [Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 106, Taiwan (China)

    2014-04-01

    Highlights: • Radial hydrides near the crack tip had a significant effect on crack propagation. • For radial hydrides off the crack line vertically, the effect on crack propagation was notably reduced. • The longer hydride platelet resulted in a remarkable effect on crack propagation. • A long split in the radial hydride precipitate would enhance crack propagation. • The presence of circumferential hydride among radial hydrides may play an important role in crack propagation. - Abstract: A methodology was proposed to investigate the effect of hydride on the crack propagation in fuel cladding. The analysis was modeled based on an outside-in crack with radial hydrides located near its crack tip. The finite element method was used in the calculation; both stress intensity factor K{sub I} and J integral were applied to evaluate the crack stability. The parameters employed in the analysis included the location of radial hydride, hydride dimensions, number of hydrides, and the presence of circumferential hydride, etc. According to our study, the effective distance between a radial hydride and the assumed cladding surface crack for the enhancement of crack propagation proved to be no greater than 0.06 mm. For a hydride not on the crack line, it would induce a relatively minor effect on crack propagation if the vertical distance was beyond 0.05 mm. However, a longer hydride precipitate as well as double radial hydrides could have a remarkable effect on crack propagation. A combined effect of radial and circumferential hydrides was also discussed.

  8. Comparison of experiment and theory for elastic-plastic plane strain crack growth

    International Nuclear Information System (INIS)

    Hermann, L.; Rice, J.R.

    1980-02-01

    Recent theoretical results on elastic-plastic plane strain crack growth, and experimental results for crack growth in a 4140 steel in terms of the theoretical concepts are reviewed. The theory is based on a recent asymptotic analysis of crack surface opening and strain distributions at a quasi-statically advancing crack tip in an ideally-plastic solid. The analysis is incomplete in that some of the parameters which appear in it are known only approximately, especially at large scale yielding. Nevertheless, it suffices to derive a relation between the imposed loading and amount of crack growth, prior to general yielding, based on the assumption that a geometrically similar near-tip crack profile is maintained during growth. The resulting predictions for the variation of J with crack growth are found to fit well to the experimental results obtained on deeply cracked compact specimens

  9. Fracture Testing with Surface Crack Specimens. [especially the residual tensile strength test

    Science.gov (United States)

    Orange, T. W.

    1974-01-01

    Recommendations are given for the design, preparation, and static fracture testing of surface crack specimens. The recommendations are preceded by background information including discussions of stress intensity factors, crack opening displacements, and fracture toughness values associated with surface crack specimens. Cyclic load and sustained load tests are discussed briefly.

  10. Environmentally assisted cracking in light water reactors

    International Nuclear Information System (INIS)

    Chopra, O.K.; Chung, H.M.; Gruber, E.E.

    1996-07-01

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from April 1995 to December 1995. Topics that have been investigated include fatigue of carbon and low-alloy steel used in reactor piping and pressure vessels, EAC of Alloy 600 and 690, and irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS. Fatigue tests were conducted on ferritic steels in water that contained various concentrations of dissolved oxygen (DO) to determine whether a slow strain rate applied during different portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Crack-growth-rate tests were conducted on compact-tension specimens from several heats of Alloys 600 and 690 in simulated LWR environments. Effects of fluoride-ion contamination on susceptibility to intergranular cracking of high- and commercial- purity Type 304 SS specimens from control-tensile tests at 288 degrees Centigrade. Microchemical changes in the specimens were studied by Auger electron spectroscopy and scanning electron microscopy to determine whether trace impurity elements may contribute to IASCC of these materials

  11. EFAM GTP-CREEP 02 - the GKSS test procedure for determining the creep crack extension of materials

    International Nuclear Information System (INIS)

    Schwalbe, K.H.

    2002-01-01

    This document describes a fracture mechanics method in procedural form for determining the creep crack extension of materials. It is based on the unified fracture mechanics test method EFAM GTP 02, the ASTM standard E 1457-98, activities of VAMAS TWA 19, and GKSS experience in creep crack extension testing. It introduces novel features such as the rate of the δ 5 crack tip opening displacement, the crack tip opening angle, and the middle cracked tension specimen. (orig.) [de

  12. In situ TEM observation of microcrack nucleation and propagation in pure tin solder

    International Nuclear Information System (INIS)

    Ding Ying; Wang Chunqing; Li, Mingyu; Wang Weiqiang

    2006-01-01

    Microcrack nucleation and propagation behavior in pure tin solder was investigated by using transmission electron microscopy (TEM) through in situ tensile test. Observation results showed that fracture process was completed in this visco-plastic material by connecting discontinuous cracks or voids. Depending on remarkable vacancy diffusion ability, microvoids were nucleated and developed in the dislocation free zone (DFZ) or super thinned area ahead of crack tip under local high stress concentration. The cracks were linked with each other by mutual dislocation emission which expedites the propagation of crack tips effectively

  13. Non-self-similar cracking in unidirectional metal-matrix composites

    International Nuclear Information System (INIS)

    Rajesh, G.; Dharani, L.R.

    1993-01-01

    Experimental investigations on the fracture behavior of unidirectional Metal Matrix Composites (MMC) show the presence of extensive matrix damage and non-self-similar cracking of fibers near the notch tip. These failures are primarily observed in the interior layers of an MMC, presenting experimental difficulties in studying them. Hence an investigation of the matrix damage and fiber fracture near the notch tip is necessary to determine the stress concentration at the notch tip. The classical shear lag (CLSL) assumption has been used in the present study to investigate longitudinal matrix damage and nonself-similar cracking of fibers at the notch tip of an MMC. It is seen that non-self-similar cracking of fibers reduces the stress concentration at the notch tip considerably and the effect of matrix damage is negligible after a large number of fibers have broken beyond the notch tip in a non-self-similar manner. Finally, an effort has been made to include non-self-similar fiber fracture and matrix damage to model the fracture behavior of a unidirectional boron/aluminum composite for two different matrices viz. a 6061-0 fully annealed aluminum matrix and a heat treated 6061-T6 aluminum matrix. Results have been drawn for several characteristics pertaining to the shear stiffnesses and the shear yield stresses of the two matrices and compared with the available experimental results

  14. Factors controlling nitrate cracking of mild steel

    International Nuclear Information System (INIS)

    Donovan, J.A.

    1977-01-01

    Nitrite and hydroxide ions inhibit the growth of nitrate stress corrosion cracks in mild steel. Crack growth measurements showed that sufficient concentrations of nitrite and hydroxide ions can prevent crack growth; however, insufficient concentrations of these ions did not influence the Stage II growth rate or the threshold stress intensity, but extended the initiation time. Stage III growth was discontinuous. Oxide formed in the grain boundaries ahead of the crack tip and oxide dissolution (Stage II) and fracture (Stage III) are the proposed mechanisms of nitrate stress corrosion crack growth

  15. Crack propagation in teeth: a comparison of perimortem and postmortem behavior of dental materials and cracks.

    Science.gov (United States)

    Hughes, Cris E; White, Crystal A

    2009-03-01

    This study presents a new method for understanding postmortem heat-induced crack propagation patterns in teeth. The results demonstrate that patterns of postmortem heat-induced crack propagation differ from perimortem and antemortem trauma-induced crack propagation patterns. Dental material of the postmortem tooth undergoes dehydration leading to a shrinking and more brittle dentin material and a weaker dentin-enamel junction. Dentin intertubule tensile stresses are amplified by the presence of the pulp cavity, and initiates crack propagation from the internal dentin, through the dentin-enamel junction and lastly the enamel. In contrast, in vivo perimortem and antemortem trauma-induced crack propagation initiates cracking from the external surface of the enamel toward the dentin-enamel junction where the majority of the energy of the crack is dissipated, eliminating the crack's progress into the dentin. These unique patterns of crack propagation can be used to differentiate postmortem taphonomy-induced damage from antemortem and perimortem trauma in teeth.

  16. Tensile Properties of Under-Matched Weld Joints for 950 MPa Steel.

    Science.gov (United States)

    Yamamoto, Kouji; Arakawa, Toshiaki; Akazawa, Nobuki; Yamamoto, Kousei; Matsuo, Hiroki; Nakagara, Kiyoyuki; Suita, Yoshikazu

    In welding of 950 MPa-class high tensile strength steel, preheating is crucial in order to avoid cold cracks, which, however, eventually increases welding deformations. One way to decrease welding deformations is lowering preheating temperature by using under-matched weld metal. Toyota and others clarify that although breaking elongation can decrease due to plastic constraint effect under certain conditions, static tensile of under-matched weld joints is comparable to that of base metal. However, there has still been no report about joint static tensile of under-matched weld joints applied to 950 MPa-class high tensile strength steel. In this study, we aim to research tensile strength and fatigue strength of under-matched weld joints applied to 950 MPa-class high tensile steel.

  17. A partly and fully cracked triangular XFEM element for modeling cohesive fracture

    DEFF Research Database (Denmark)

    Mougaard, Jens Falkenskov; Poulsen, Peter Noe; Nielsen, Leif Otto

    2011-01-01

    This paper discusses the build‐up of a partly cracked cohesive crack tip element. The crack tip element is based on the principles of the eXtended Finite Element Method (XFEM) and is of Linear Strain Triangle (LST) type. The composition of the enrichment has been in focus to achieve as complete...... as a fully cracked element with a few restrictions in the displacement field. The performance of the developed element has been tested in three examples. One example is an infinite sheet with an initial flaw in pure tension, where a semianalytical solution exists. The two other examples are the two benchmark...

  18. A crack opening stress equation for fatigue crack growth

    Science.gov (United States)

    Newman, J. C., Jr.

    1984-01-01

    A general crack opening stress equation is presented which may be used to correlate crack growth rate data for various materials and thicknesses, under constant amplitude loading, once the proper constraint factor has been determined. The constraint factor, alpha, is a constraint on tensile yielding; the material yields when the stress is equal to the product of alpha and sigma. Delta-K (LEFM) is plotted against rate for 2024-T3 aluminum alloy specimens 2.3 mm thick at various stress ratios. Delta-K sub eff was plotted against rate for the same data with alpha = 1.8; the rates correlate well within a factor of two.

  19. Stress corrosion cracking of iron-nickel-chromium alloys in primary circuit environment of PWR-type reactors

    International Nuclear Information System (INIS)

    Boursier, Jean-Marie

    1993-01-01

    Stress corrosion cracking of Alloy 600 steam generator tubing is a great concern for pressurized water reactors. The mechanism that controls intergranular stress corrosion cracking of Alloy 600 in primary water (lithiated-borated water) has yet to be clearly identified. A study of stress corrosion cracking behaviour, which can identify the main parameters that control the cracking phenomenon, was so necessary to understand the stress corrosion cracking process. Constant extension rate tests, and constant load tests have evidenced that Alloy 600 stress corrosion cracking involves firstly an initiation period, then a slow propagation stage with crack less than 50 to 80 micrometers, and finally a rapid propagation stage leading to failure. The influence of mechanical parameters have shown the next points: - superficial strain hardening and cold work have a strong effect of stress corrosion cracking resistance (decrease of initiation time and increase of crack growth rate), - strain rate was the most suitable parameter for describing the different stage of propagation. The creep behaviour of alloy 600 has shown an increase of creep rate in primary water compared to air, which implies a local interaction plasticity/corrosion. An assessment of the durations of the initiation and the propagation stages was attempted for the whole uniaxial tensile tests, using the macroscopic strain rate: - the initiation time is less than 100 hours and seems to be an electrochemical process, - the durations of the propagation stage are strongly dependent on the strain rate. The behaviour in high primary water temperature of Alloys 690 and 800, which replace Alloy 600, was studied to appraise their margin, and validate their choice. Then the last chapter has to objective to evaluate the crack tip strain rate, in order to better describe the evolution of the different stages of cracking. (author) [fr

  20. Crack path predictions and experiments in plane structures considering anisotropic properties and material interfaces

    Directory of Open Access Journals (Sweden)

    P.O. Judt

    2015-10-01

    Full Text Available In many engineering applications special requirements are directed to a material's fracture behavior and the prediction of crack paths. Especially if the material exhibits anisotropic elastic properties or fracture toughnesses, e.g. in textured or composite materials, the simulation of crack paths is challenging. Here, the application of path independent interaction integrals (I-integrals, J-, L- and M-integrals is beneficial for an accurate crack tip loading analysis. Numerical tools for the calculation of loading quantities using these path-invariant integrals are implemented into the commercial finite element (FE-code ABAQUS. Global approaches of the integrals are convenient considering crack tips approaching other crack faces, internal boundaries or material interfaces. Curved crack faces require special treatment with respect to integration contours. Numerical crack paths are predicted based on FE calculations of the boundary value problem in connection with an intelligent adaptive re-meshing algorithm. Considering fracture toughness anisotropy and accounting for inelastic effects due to small plastic zones in the crack tip region, the numerically predicted crack paths of different types of specimens with material interfaces and internal boundaries are compared to subcritically grown paths obtained from experiments.

  1. Acquisition of Inertia by a Moving Crack

    Science.gov (United States)

    Goldman, Tamar; Livne, Ariel; Fineberg, Jay

    2010-03-01

    We experimentally investigate the dynamics of “simple” tensile cracks. Within an effectively infinite medium, a crack’s dynamics perfectly correspond to inertialess behavior predicted by linear elastic fracture mechanics. Once a crack interacts with waves that it generated at earlier times, this description breaks down. Cracks then acquire inertia and sluggishly accelerate. Crack inertia increases with crack speed v and diverges as v approaches its limiting value. We show that these dynamics are in excellent accord with an equation of motion derived in the limit of an infinite strip [M. Marder, Phys. Rev. Lett. 66, 2484 (1991)PRLTAO0031-900710.1103/PhysRevLett.66.2484].

  2. The Reflective Cracking in Flexible Pavements

    Directory of Open Access Journals (Sweden)

    Pais Jorge

    2013-07-01

    Full Text Available Reflective cracking is a major concern for engineers facing the problem of road maintenance and rehabilitation. The problem appears due to the presence of cracks in the old pavement layers that propagate into the pavement overlay layer when traffic load passes over the cracks and due to the temperature variation. The stress concentration in the overlay just above the existing cracks is responsible for the appearance and crack propagation throughout the overlay. The analysis of the reflective cracking phenomenon is usually made by numerical modeling simulating the presence of cracks in the existing pavement and the stress concentration in the crack tip is assessed to predict either the cracking propagation rate or the expected fatigue life of the overlay. Numerical modeling to study reflective cracking is made by simulating one crack in the existing pavement and the loading is usually applied considering the shear mode of crack opening. Sometimes the simulation considers the mode I of crack opening, mainly when temperature effects are predominant.

  3. Investigation of fatigue crack growth rate of Al 5484 ultrafine grained alloy after ECAP process

    Energy Technology Data Exchange (ETDEWEB)

    Brynk, Tomasz; Rasinski, Marcin; Pakiela, Zbigniew; Kurzydlowski, Krzysztof J. [Faculty of Materials Science and Engineering, Warsaw University of Technology (Poland); Olejnik, Lech [Faculty of Production Engineering, Warsaw University of Technology (Poland)

    2010-05-15

    During the last decade equal-channel angular pressing (ECAP) has emerged as a widely used fabrication route of ultrafine-grained (UFG) metals and alloys. Enhanced mechanical properties of UFG materials produced by severe plastic deformation, with a grain size smaller than 1 {mu}m, have been reported in a large number of publications. However, the higher strength does not imply higher resistance to fatigue both high- and low-cyclic. In fact, due to reduced plasticity, higher fatigue crack propagation rates are reported for UFG materials, particularly in low-amplitude range. The aim of this work was to investigate fatigue crack propagation in samples of Al 5483 alloy subjected to ECAP treatment. Because of small dimensions of the coupons processed by ECAP, non-standard, mini-samples were used in a crack propagation tests. Two test procedures were used to estimate stress intensity factor (K). The first was based on optical measurements of crack length from images recorded during the test. The second method was based on digital image correlation (DIC), which was used to determine K value directly from displacement field near the crack tip. Comparison of these two methods is made and the relationship between the intensity of ECAP process (measured in terms of the number of ECAP passes) and fatigue crack propagation rates proposed. In addition to fatigue resistance, the results of tensile tests carried out with mini-samples are presented. Applicability of such samples in the investigations of the mechanical properties of UFG materials is discussed. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  4. Fatigue crack growth retardation in spot heated mild steel sheet

    Indian Academy of Sciences (India)

    A fatigue crack can be effectively retarded by heating a spot near the crack tip under nil remote stress condition. The subcritical spot heating at a proper position modifies the crack growth behaviour in a way, more or less, similar to specimen subjected to overload spike. It is observed that the extent of crack growth retardation ...

  5. Minimizing hydride cracking in zirconium alloys

    International Nuclear Information System (INIS)

    Coleman, C.E.; Cheadle, B.A.; Ambler, J.F.R.; Eadie, R.L.

    1985-01-01

    Zirconium alloy components can fail by hydride cracking if they contain large flaws and are highly stressed. If cracking in such components is suspected, crack growth can be minimized by following two simple operating rules: components should be heated up from at least 30K below any operating temperature above 450K, and when the component requires cooling to room temperature from a high temperature, any tensile stress should be reduced as much and as quickly as is practical during cooling. This paper describes the physical basis for these rules

  6. Tensile behavior and tension stiffening of reinforced concrete

    International Nuclear Information System (INIS)

    Choun, Young Sun; Seo, Jeong Moon

    2001-03-01

    For the ultimate behavior analysis of containment buildings under severe accident conditions, a clear understanding of tensile behaviors of plain and reinforced concrete is necessary. Nonlinear models for tensile behaviors of concrete are also needed. This report describe following items: tensile behaviors of plain concrete, test results of reinforced concrete panels in uniaxial and biaxial tension, tension stiffening. The tensile behaviors of reinforced concrete are significantly influenced by the properties of concrete and reinforcing steel. Thus, for a more reliable evaluation of tensile behavior and ultimate pressure capacity of a reinforced or prestressed concrete containment building, an advanced concrete model which can be considered rebar-concrete interaction effects should be developed. In additions, a crack behavior analysis method and tension stiffening models, which are based on fracture mechanics, should be developed. The model should be based on the various test data from specimens considering material and sectional properties of the containment building

  7. On the controlling parameters for fatigue-crack threshold at low homologous temperatures

    International Nuclear Information System (INIS)

    Yu, W.; Gerberich, W.W.

    1983-01-01

    Fatigue crack propagation phenomena near the threshold stress intensity level ΔK /SUB TH/ , has been a vigorously studied topic in recent years. Near threshold the crack propagates rather slowly, thus giving enough time for various physical and chemical reactions to take place. Room air, which is the most commonly encountered environment, can still supply various ingredients such as oxygen, water vapor (and thus hydrogen) to support these reactions. Much effort had been directed toward the environmental aspects of near threshold fatigue crack growth. By conducting tests under vacuum, Suresh and coworkers found that the crack propagation rate in a 2-1/4 Cr-1Mo steel was higher in vacuum than in air. An oxide induced closure, which served to reduce the effective stress intensity at the crack tip, seems to furnish a good explanation. Neumann and coworkers proposed that during the fatigue process, extrusion-intrusion pairs can develop as a consequence of reversed slip around the crack tip when the crack was propagated near threshold stress intensity. Beevers demonstrated that fatigue fracture surfaces contact each other during unloading even under tension-tension cycling. Kanninen and Atkinson also reached the conclusion that the compressive stress acting at the crack tip due to residual plasticity can induce closure. Microstructural effects have also been cited as important factors in near threshold crack growth. It is generally accepted that coarser grains have a beneficial effect on the resistance to the near threshold crack propagation

  8. A short summary on finite element modelling of fatigue crack closure

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Konjengbam Darunkumar [Indian Institute of Technology, Guwahati (India); Parry, Matthew Roger [Airbus Operations Ltd, Bristol(United Kingdom); Sinclair, Ian [University of Southampton, Southampton (United Kingdom)

    2011-12-15

    This paper presents a short summary pertaining to the finite element modelling of fatigue crack closure. Several key issues related to finite element modelling of fatigue crack closure are highlighted: element type, mesh refinement, stabilization of crack closure, crack-tip node release scheme, constitutive model, specimen geometry, stress-states (i.e., plane stress, plane strain), crack closure monitoring. Reviews are presented for both straight and deflected cracks.

  9. FEM Modelling of the Evolution of Corrosion Cracks in Reinforced Concrete Structures

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Corrosion cracks are caused by the increasing volume of corrosion products during the corrosion of the reinforcement. After corrosion initiation the rust products from the corroded reinforcement will initially fill the porous zone near the reinforcement and the result in an expansion of the concr......Corrosion cracks are caused by the increasing volume of corrosion products during the corrosion of the reinforcement. After corrosion initiation the rust products from the corroded reinforcement will initially fill the porous zone near the reinforcement and the result in an expansion...... of the concrete near the reinforcement. Tensile stresses are then initiated in the concrete. With increasing corrosion, the tensile stresses will at a certain time reach a critical value and cracks will be developed. The increase of the crack with after formation of the initial crack is the subject of this paper...

  10. Strain energy density-distance criterion for the initiation of stress corrosion cracking of alloy X-750

    Energy Technology Data Exchange (ETDEWEB)

    Hall, M.M. Jr.; Symons, D.M.

    1996-05-01

    A strain energy density-distance criterion was previously developed and used to correlate rising-load K{sub c} initiation data for notched and fatigue precracked specimens of hydrogen precharged Alloy X-750. This criterion, which was developed for hydrogen embrittlement (HE) cracking, is used here to correlate static-load stress corrosion cracking (SCC) initiation times obtained for smooth geometry, notched and fatigue precracked specimens. The onset of SCC crack growth is hypothesized to occur when a critical strain, which is due to environment-enhanced creep, is attained within the specimen interior. For notched and precracked specimens, initiation is shown by analysis to occur at a variable distance from notch and crack tips. The initiation site varies from very near the crack tip, for highly loaded sharp cracks, to a site that is one grain diameter from the notch, for lower loaded, blunt notches. The existence of hydrogen gradients, which are due to strain-induced hydrogen trapping in the strain fields of notch and crack tips, is argued to be controlling the site for initiation of cracking. By considering the sources of the hydrogen, these observations are shown to be consistent with those from the previous HE study, in which the characteristic distance for crack initiation was found to be one grain diameter from the notch tip, independent of notch radius, applied stress intensity factor and hydrogen level.

  11. Mesh sensitivity effects on fatigue crack growth by crack-tip blunting and re-sharpening

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2007-01-01

    remeshing at several stages of the plastic deformation, with studies of the effect of overloads or compressive underloads. Recent published analyses for the first two cycles have shown folding of the crack surface in compression, leading to something that looks like striations. The influence of mesh...... refinement is used to study the possibility of this type of behaviour within the present method. Even with much refined meshes no indication of crack surface folding is found here....

  12. Stress-intensity factor equations for cracks in three-dimensional finite bodies

    Science.gov (United States)

    Newman, J. C., Jr.; Raju, I. S.

    1981-01-01

    Empirical stress intensity factor equations are presented for embedded elliptical cracks, semi-elliptical surface cracks, quarter-elliptical corner cracks, semi-elliptical surface cracks at a hole, and quarter-elliptical corner cracks at a hole in finite plates. The plates were subjected to remote tensile loading. Equations give stress intensity factors as a function of parametric angle, crack depth, crack length, plate thickness, and where applicable, hole radius. The stress intensity factors used to develop the equations were obtained from three dimensional finite element analyses of these crack configurations.

  13. On the anomalous temperature dependency of fatigue crack growth of SS 316(N) weld

    Energy Technology Data Exchange (ETDEWEB)

    Babu, M. Nani; Dutt, B. Shashank; Venugopal, S. [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Sasikala, G., E-mail: gsasi@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India); Bhaduri, A.K.; Jayakumar, T.; Raj, Baldev [Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102 (India)

    2010-07-25

    Fatigue crack growth behaviour of a nuclear grade SS 316(N) weld metal was examined in the Paris and threshold regimes in the as-welded condition, at 300, 573 and 823 K. The {Delta}K{sub th} values were 11.2, 7.5, and 9.5 MPa {radical}m, respectively. These values were corrected for closure effects and the corresponding {Delta}K{sub th,eff} were found to be 7.7, 5.8 and 3.5 MPa {radical}m, respectively. The anomalous behaviour, i.e., the high value of {Delta}K{sub th} at 823 K has been explained based on crack closure effect which is roughness induced at 300 K and oxide induced at 823 K, with both these insignificant at 573 K. The effect of temperature on crack growth mechanism and the associated closure mechanisms are discussed. The stress shielding at the crack tip due to closure is accounted for and the effective stress intensity factor experienced by the crack tip, {Delta}K{sub eff,tip} is determined. It is demonstrated that {Delta}K{sub eff,tip} qualifies as a more appropriate parameter as the driving force for the temperature-dependent crack growth in the near-threshold and Paris regimes.

  14. Hybrid fiber reinforcement and crack formation in Cementitious Composite Materials

    DEFF Research Database (Denmark)

    Pereira, E.B.; Fischer, Gregor; Barros, J.A.O.

    2011-01-01

    reinforcement systems. The research described in this paper shows that the multi-scale conception of cracking and the use of hybrid fiber reinforcements do not necessarily result in an improved tensile behavior of the composite. Particular material design requirements may nevertheless justify the use of hybrid......- to the macroscale. In this study, the performance of different fiber reinforced cementitious composites is assessed in terms of their tensile stress-crack opening behavior. The results obtained from this investigation allow a direct quantitative comparison of the behavior obtained from the different fiber...

  15. Combined effect of gamma radiation and stress cracking in polystyrene

    International Nuclear Information System (INIS)

    Amorim, Fernando A.; Rabello, Marcelo S.; Silva, Leonardo G.A.

    2011-01-01

    This study aimed to evaluate the combined effect of gamma radiation and stress cracking in polystyrene. Three different grades of polystyrene were analysed. The material was submitted to tensile tests and relaxation, analysis of molecular weight and determination of crosslinking. The results showed an increase in tensile strength in the specimens that had been exposed to radiation. The higher the molecular weight polystyrene showed better mechanical properties and after suffering the effects of gamma radiation there was an increase of 5.67% in the resistance to stress cracking effects. (author)

  16. T-stresses for internally cracked components

    International Nuclear Information System (INIS)

    Fett, T.

    1997-12-01

    The failure of cracked components is governed by the stresses in the vicinity of the crack tip. The singular stress contribution is characterised by the stress intensity factor K, the first regular stress term is represented by the so-called T-stress. T-stress solutions for components containing an internal crack were computed by application of the Bundary Collocation Method (BCM). The results are compiled in form of tables or approximative relations. In addition a Green's function of T-stresses is proposed for internal cracks which enables to compute T-stress terms for any given stress distribution in the uncracked body. (orig.) [de

  17. Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.

    Science.gov (United States)

    Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard

    2017-01-01

    Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

  18. The interaction of two collinear cracks in a rectangular superconductor slab under an electromagnetic force

    International Nuclear Information System (INIS)

    Gao Zhiwen; Zhou Youhe; Lee, Kang Yong

    2010-01-01

    The interaction of two collinear cracks is obtained for a type-II superconducting under electromagnetic force. Fracture analysis is performed by means of finite element method and the magnetic behavior of superconductor is described by the critical-state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. It is revealed that the stress intensity factor decreases as applied field increases. The crack-tip stress intensity factors decrease when the distance between the two collinear cracks increases and the superconductors with smaller crack has more remarkable shielding effect than those with larger cracks.

  19. Analysis of internal crack in a six-ton P91 ingot

    Directory of Open Access Journals (Sweden)

    Jing-an Yang

    2016-05-01

    Full Text Available P91 is a new kind of heat-resistant and high-tensile steel. It can be extruded after ingot casting and can be widely used for different pipes in power plants. However, due to its mushy freezing characteristics, a lack of feeding in the ingot center often generates many defects, such as porosity and crack. A six-ton P91 ingot was cast and sliced, and a representative part of the longitudinal section was inspected in more detail. The morphology of crack-like defects was examined by X-ray high energy industrial CT and reconstructed by 3D software. There are five main portions of defects larger than 200 mm3, four of which are interconnected. These initiated from continuous liquid film, and then were torn apart by excessive tensile stress within the brittle temperature range (BTR. The 3D FEM analysis of thermo-mechanical simulation was carried out to analyze the formation of porosity and internal crack defects. The results of shrinkage porosity and Niyama values revealed that the center of the ingot suffers from inadequate feeding. Several criteria based on thermal and mechanical models were used to evaluate the susceptibility of hot crack formation. The Clyne and Davies’ criterion and Katgerman’s criterion successfully predicted the high hot crack susceptibility in the ingot center. Six typical locations in the longitudinal section had been chosen for analysis of the stresses and strains evolution during the BTR. Locations in the defects region showed the highest tensile stresses and relative high strain values, while other locations showed either low tensile stresses or low strain values. In conclusion, hot crack develops only when stress and strain exceed a threshold value at the same time during the BTR.

  20. Fractographic Observations on the Mechanism of Fatigue Crack Growth in Aluminium Alloys

    Science.gov (United States)

    Alderliesten, R. C.; Schijve, J.; Krkoska, M.

    Special load histories are adopted to obtain information about the behavior of the moving crack tip during the increasing and decreasing part of a load cycle. It is associated with the crack opening and closure of the crack tip. Secondly, modern SEM techniques are applied for observations on the morphology of the fractures surfaces of a fatigue crack. Information about the cross section profiles of striations are obtained. Corresponding locations of the upper and the lower fracture surface are also explored in view of the crack extension mechanism. Most experiments are carried out on sheet specimens of aluminum alloys 2024-T3, but 7050-T7451 specimens are also tested in view of a different ductility of the two alloys.

  1. A phenomenological model for iodine stress corrosion cracking of zircaloy

    International Nuclear Information System (INIS)

    Miller, A.K.; Tasooji, A.

    1981-01-01

    To predict the response of Zircaloy tubing in iodine environments under conditions where either crack initiation or crack propagation predominates, a unified model of the SCC process has been developed based on the local conditions (the local stress, local strain, and local iodine concentration) within a small volume of material at the cladding inner surface or the crack tip. The methodology used permits computation of these values from simple equations. A nonuniform distribution of local stress and strain results once a crack has initiated. The local stress can be increased due to plastic constraint and triaxiality at the crack tip. Iodine penetration is assumed to be a surface diffusion-controlled process. Experimental data are used to derive criteria for intergranular failure, transgranular failure, and ductile rupture in terms of the local conditions. The same failure criteria are used for both crack initiation and crack propagation. Irradiation effects are included in the model by changing the value of constants in the equation governing iodine penetration and by changing the values used to represent the mechanical properties of the Zircaloy. (orig./HP)

  2. Diffusion model of delayed hydride cracking in zirconium alloys

    NARCIS (Netherlands)

    Shmakov, AA; Kalin, BA; Matvienko, YG; Singh, RN; De, PK

    2004-01-01

    We develop a method for the evaluation of the rate of delayed hydride cracking in zirconium alloys. The model is based on the stationary solution of the phenomenological diffusion equation and the detailed analysis of the distribution of hydrostatic stresses in the plane of a sharp tensile crack.

  3. Crack propagation rate modelling for 316SS exposed to PWR-relevant conditions

    International Nuclear Information System (INIS)

    Vankeerberghen, M.; Weyns, G.; Gavrilov, S.; Martens, B.; Deconinck, J.

    2009-01-01

    The crack propagation rate of Type 316 stainless steel in boric acid-lithium hydroxide solutions under PWR-relevant conditions was modelled. A film rupture/dissolution/repassivation mechanism is assumed and extended to cold worked materials by including a stress-dependent bare metal dissolution current density. The chemical and electrochemical conditions within the crack are calculated by finite element calculations, an analytical expression is used for the crack-tip strain rate and the crack-tip stress is assumed equal to 2.5 times the yield stress (plane-strain). First the model was calibrated against a literature published data set. Afterwards, the influence of various variables - dissolved hydrogen, boric acid and lithium hydroxide content, stress intensity, crack length, temperature, flow rate - was studied. Finally, other published crack growth rate tests were modelled and the calculated crack growth rates were found to be in reasonable agreement with the reported ones

  4. Tensile strength of structural concrete repaired with hi-bond polymer modified mortar

    International Nuclear Information System (INIS)

    Khaskheli, G.B.

    2009-01-01

    Repair of cracks in concrete is often required to save the concrete structures. Appearance of crack in concrete is bound with the tensile strength of concrete. Recently a cement factory in Sindh has launched a HBPMM (Hi-Bond Polymer Modified Mortar) that can be used as a concrete repairing material instead of normal OPC (Ordinary Portland Cement). It is needed to investigate its performance compared to that of OPC. In total 144 concrete cylinders (150x300mm) having strength of 3000 and 5000 psi were manufactured. These cylinders were then splitted by using a UTM (Universal Testing Machine) and their actual tensile strength was obtained. The concrete cylinders were then repaired with different applications of HBPMM and arc. The repaired samples were again splitted at different curing ages (3, 7 and 28 days) and their tensile strength after repair was obtained. The results show that the concrete cylinders repaired with HBPMM could give better tensile strength than that repaired with arc, the tensile strength of concrete cylinders after repair could increase with increase in the application of repairing material i.e. HBPMM or OPC and with curing time, and HBPMM could remain more effective in case of rich mix concrete than that of normal mix concrete. (author)

  5. Cracking and Failure in Rock Specimen Containing Combined Flaw and Hole under Uniaxial Compression

    Directory of Open Access Journals (Sweden)

    Xiang Fan

    2018-01-01

    Full Text Available Flaw is a key factor influencing failure behavior of a fractured specimen. In the present study, rectangular-flawed specimens were prepared using sandstone to investigate the effect of flaw on failure behavior of rock. Open flaw and cylindrical hole were simultaneously precut within rock specimens using high-pressure water jet cutting technology. Five series of specimens including intact, single-hole-alone, two-hole-alone, single-hole and two-flaw, and two-hole and single-flaw blocks were prepared. Uniaxial compressive tests using a rigid servo control instrument were carried out to investigate the fracture processes of these flawed specimens. It is observed that during loading, internal stress always intensively distributed at both sidewalls of open hole, especially at midpoint of sidewalls, so rock crumb flaking was firstly observed among all sandstone specimens containing single hole or two holes. Cracking around open hole is associated with the flaw inclination angle which was observed in Series III and V. Crack easily initiated at the tips of flaw with inclination angles of 0°, 30°, and 60° but hard for 90° in Series III and V. Rock burst was the major failure mode among most tested specimens, which generally induced new cracks and finally created crater shape. Additionally, due to extrusion between blocks, new shear or tensile cracks were generated and the rock specimen surface spalled. Eventually, four typical failure processes including rock crumb flaking, crack initiation and propagation, rock burst, and second rupture, were summarized.

  6. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    Energy Technology Data Exchange (ETDEWEB)

    Utz, S.; Soppa, E.; Silcher, H.; Kohler, C. [Stuttgart Univ. (Germany). Materials Testing Inst.

    2013-07-01

    measurements the deformation induced transformation of an fcc-austenite into a bcc α'-martensite was observed in different stages of the specimen lifetime. Plastic zones develop at the crack tips, in which stress and strain amplitudes are much higher than the nominal loading, and enable martensitic transformation in the surrounding of the crack tip. The consequence of this is that cracks grow in the ''martensitic tunnels''. The short and long crack growth behaviours of the steel X6CrNiNb18-10 under mechanical loading at room temperature and T = 288 C were studied for different loading parameters. Moreover, the R-ratio was modified in order to study the effect of crack closure at the crack tip for long cracks. Several FE models of specimens with different geometries and microstructures were created and cyclically loaded according to the experimental boundary conditions. A plastic constitutive law based on a Chaboche type model was implemented as a user subroutine in the FE software ABAQUS. The corresponding material parameters were identified using uniaxial LCF tests of X6CrNiNb18-10 with different strain amplitudes and at different temperatures. These calculations delivered the estimation of stress and strain distributions in the critical areas in which the crack initiation was expected.

  7. Mechanism of crack initiation and crack growth under thermal and mechanical fatigue loading

    International Nuclear Information System (INIS)

    Utz, S.; Soppa, E.; Silcher, H.; Kohler, C.

    2013-01-01

    measurements the deformation induced transformation of an fcc-austenite into a bcc α'-martensite was observed in different stages of the specimen lifetime. Plastic zones develop at the crack tips, in which stress and strain amplitudes are much higher than the nominal loading, and enable martensitic transformation in the surrounding of the crack tip. The consequence of this is that cracks grow in the ''martensitic tunnels''. The short and long crack growth behaviours of the steel X6CrNiNb18-10 under mechanical loading at room temperature and T = 288 C were studied for different loading parameters. Moreover, the R-ratio was modified in order to study the effect of crack closure at the crack tip for long cracks. Several FE models of specimens with different geometries and microstructures were created and cyclically loaded according to the experimental boundary conditions. A plastic constitutive law based on a Chaboche type model was implemented as a user subroutine in the FE software ABAQUS. The corresponding material parameters were identified using uniaxial LCF tests of X6CrNiNb18-10 with different strain amplitudes and at different temperatures. These calculations delivered the estimation of stress and strain distributions in the critical areas in which the crack initiation was expected.

  8. Dynamic steady-state analysis of crack propagation in rubber-like solids using an extended finite element method

    Science.gov (United States)

    Kroon, Martin

    2012-01-01

    In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of plane stress and steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to examine the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The computational framework builds upon a previous work by the present author (Kroon in Int J Fract 169:49-60, 2011). The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. The predicted distributions of stress and dissipation around the propagating crack tip are presented. The predicted crack tip profiles also agree qualitatively with experimental findings.

  9. Modeling of a Curvilinear Planar Crack with a Curvature-Dependent Surface Tension

    KAUST Repository

    Zemlyanova, A. Y.; Walton, J. R.

    2012-01-01

    An approach to modeling fracture incorporating interfacial mechanics is applied to the example of a curvilinear plane strain crack. The classical Neumann boundary condition is augmented with curvature-dependent surface tension. It is shown that the considered model eliminates the integrable crack-tip stress and strain singularities of order 1/2 present in the classical linear fracture mechanics solutions, and also leads to the sharp crack opening that is consistent with empirical observations. Unlike for the case of a straight crack, for a general curvilinear crack some components of the stresses and the derivatives of the displacements may still possess weaker singularities of a logarithmic type. Generalizations of the present study that lead to complete removal of all crack-tip singularities, including logarithmic, are the subject of a future paper. © 2012 Society for Industrial and Applied Mathematics.

  10. Variable amplitude fatigue crack growth behavior - a short overview

    International Nuclear Information System (INIS)

    Singh, Konjengbam Darunkumar; Parry, Matthew Roger; Sinclair, Ian

    2011-01-01

    A short overview concerning variable amplitude (VA) fatigue crack growth behavior is presented in this paper. The topics covered in this review encompass important issues pertaining to both single and repeated overload transients. Reviews on transient post overload effects such as plasticity induced crack closure, crack tip blunting, residual stresses, crack deflection and branching, activation of near threshold mechanisms, strain hardening are highlighted. A brief summary on experimental trends and finite element modelling of overload induced crack closure is also presented

  11. Variable amplitude fatigue crack growth behavior - a short overview

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Konjengbam Darunkumar [Indian Institute of Technology, Guwahati (India); Parry, Matthew Roger [Airbus Operations Ltd, Bristol (United Kingdom); Sinclair, Ian [University of Southampton, Southampton (United Kingdom)

    2011-03-15

    A short overview concerning variable amplitude (VA) fatigue crack growth behavior is presented in this paper. The topics covered in this review encompass important issues pertaining to both single and repeated overload transients. Reviews on transient post overload effects such as plasticity induced crack closure, crack tip blunting, residual stresses, crack deflection and branching, activation of near threshold mechanisms, strain hardening are highlighted. A brief summary on experimental trends and finite element modelling of overload induced crack closure is also presented.

  12. Toward a better understanding of strain incompatibilities at grain boundaries in the analysis of fatigue crack initiation at low temperature in the UdimetTM 720 Li superalloy

    Directory of Open Access Journals (Sweden)

    Larrouy Baptiste

    2014-01-01

    Full Text Available Low cycle fatigue properties of polycrystalline γ-γ′ Ni-based superalloys are dependent on many factors such as temperature, environment, grain size and distribution of the strengthening phases. Under LCF conditions at intermediate temperatures, an intergranular crack initiation could be observed. In this paper we propose to analyze the local conditions favouring such an intergranular cracking mode considering the high strength C&W UdimetTM720 Li alloy, widely used for manufacturing high pressure turbine disk for aeroengine applications. Tensile and fatigue tests were performed in air in the 20–465 ∘C range of temperature on micro-samples in order to focus on plasticity and damage processes developed near grain boundaries. A special attention was paid on the slip transfer between neighbouring grains taking into account their local crystallographic orientations. In some specific crystallographic configurations, small zones were detected at the tip of slip bands presenting an intense elastic/plastic activity. Although they are limited in size, they are associated to local crystalline rotations. High levels of local strain/stress were also evaluated in these volumes using an EBSD pattern cross correlation technique. The development of such specific zones was investigated at different stages of the tensile and LCF behaviour and was identified as leading to micro-cracks initiation for both solicitation modes.

  13. On the driving force for crack growth during thermal actuation of shape memory alloys

    Science.gov (United States)

    Baxevanis, T.; Parrinello, A. F.; Lagoudas, D. C.

    2016-04-01

    The effect of thermomechanically induced phase transformation on the driving force for crack growth in polycrystalline shape memory alloys is analyzed in an infinite center-cracked plate subjected to a thermal actuation cycle under mechanical load in plain strain. Finite element calculations are carried out to determine the mechanical fields near the static crack and the crack-tip energy release rate using the virtual crack closure technique. A substantial increase of the energy release rate - an order of magnitude for some material systems - is observed during the thermal cycle due to the stress redistribution induced by large scale phase transformation. Thus, phase transformation occurring due to thermal variations under mechanical load may result in crack growth if the crack-tip energy release rate reaches a material specific critical value.

  14. Numerical analysis of interacting cracks in biaxial stress field

    International Nuclear Information System (INIS)

    Kovac, M.; Cizelj, L.

    1999-01-01

    The stress corrosion cracks as seen for example in PWR steam generator tubing made of Inconel 600 usually produce highly irregular kinked and branched crack patterns. Crack initialization and propagation depends on stress state underlying the crack pattern. Numerical analysis (such as finite element method) of interacting kinked and branched cracks can provide accurate solutions. This paper discusses the use of general-purpose finite element code ABAQUS for evaluating stress fields at crack tips of interacting complex cracks. The results obtained showed reasonable agreement with the reference solutions and confirmed use of finite elements in such class of problems.(author)

  15. Effects of cyclic tensile loading on stress corrosion cracking susceptibility for sensitized Type 304 stainless steel in 290 C high purity water

    International Nuclear Information System (INIS)

    Takaku, H.; Tokiwai, M.; Hirano, H.

    1979-01-01

    The effects of load waveform on intergranular stress corrosion cracking (IGSCC) susceptibility have been examined for sensitized Type 304 stainless steels in a 290 C high purity water loop. Concerning the strain rate in the trapezoidal stress waveform, it was found that IGSCC susceptibility was higher for smaller values of the strain rate. It was also shown that IGSCC susceptibility became higher when the holding time at the upper stress was prolonged, and when the upper stress was high. The occurrence of IGSCC for sensitized Type 304 stainless steel became easy due to the application of cyclic tensile stress in 290 C high purity water

  16. The fatigue life and fatigue-crack-through-thickness behavior of a surface-cracked plate, 3

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Matsui, Kentaro; Ando, Kotoji; Ogura, Nobukazu

    1989-01-01

    The LBB (leak-before-break) design is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LNG carriers and various other structures. In the LBB design, it is necessary to evaluate precisely the lifetime of steel plate. Furthermore, the change in crack shape that occurs during the propagation after through thickness is of paramount importance. For this reason, in a previous report, the authors proposed a simplified evaluation model for the stress intensity factor after cracking through thickness. Using this model, the crack propagation behavior, crack-opening displacement and crack shape change of surface-cracked smooth specimens and surface-cracked specimens with a stress concentration were evaluated quantitatively. The present study was also done to investigate the fatigue crack propagation behavior of surface cracks subjected to combined tensile and bending stress. Estimation of fatigue crack growth was done using the Newman-Raju formula before through thickness, and using formula (7) and (8) after through thickness. Crack length a r at just through thickness increases with increasing a bending stress. Calculated fatigue crack shape showed very good agreement with experimental one. It was also found that particular crack growth behavior and change in crack shape after cracking through thickness can be explained quantitatively using the K value based on Eqs. (7) and (8). (author)

  17. Stress Intensity Factor for Interface Cracks in Bimaterials Using Complex Variable Meshless Manifold Method

    Directory of Open Access Journals (Sweden)

    Hongfen Gao

    2014-01-01

    Full Text Available This paper describes the application of the complex variable meshless manifold method (CVMMM to stress intensity factor analyses of structures containing interface cracks between dissimilar materials. A discontinuous function and the near-tip asymptotic displacement functions are added to the CVMMM approximation using the framework of complex variable moving least-squares (CVMLS approximation. This enables the domain to be modeled by CVMMM without explicitly meshing the crack surfaces. The enriched crack-tip functions are chosen as those that span the asymptotic displacement fields for an interfacial crack. The complex stress intensity factors for bimaterial interfacial cracks were numerically evaluated using the method. Good agreement between the numerical results and the reference solutions for benchmark interfacial crack problems is realized.

  18. Crack path and fracture surface modifications in cement composites

    Directory of Open Access Journals (Sweden)

    Sajjad Ahmad

    2015-10-01

    Full Text Available There is a tremendous increase in the use of high strength and high performance self-consolidating cementitious composites due to their superior workability and mechanical strengths. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to the low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses etc. These cracks developed at the nanoscale may grow rapidly due to the applied stresses and join together to form micro and macro cracks. The growth of cracks from nanoscale to micro and macro scale is very rapid and may lead to sudden failure of the cement composites. The present paper reports the modifications in the crack growth pattern of the high performance cement composites to achieve enhanced ductility and toughness. The objective was accomplished by the incorporation of the micro sized inert particulates in the cement composite matrix. The results indicate that the incorporation of micro sized inert particles acted as the obstacles in the growth of the cracks thus improving the ductility and the energy absorption capacity of the self-consolidating cementitious composites.

  19. Seismic characteristics of tensile fracture growth induced by hydraulic fracturing

    Science.gov (United States)

    Eaton, D. W. S.; Van der Baan, M.; Boroumand, N.

    2014-12-01

    Hydraulic fracturing is a process of injecting high-pressure slurry into a rockmass to enhance its permeability. Variants of this process are used for unconventional oil and gas development, engineered geothermal systems and block-cave mining; similar processes occur within volcanic systems. Opening of hydraulic fractures is well documented by mineback trials and tiltmeter monitoring and is a physical requirement to accommodate the volume of injected fluid. Numerous microseismic monitoring investigations acquired in the audio-frequency band are interpreted to show a prevalence of shear-dominated failure mechanisms surrounding the tensile fracture. Moreover, the radiated seismic energy in the audio-frequency band appears to be a miniscule fraction (<< 1%) of the net injected energy, i.e., the integral of the product of fluid pressure and injection rate. We use a simple penny-shaped crack model as a predictive framework to describe seismic characteristics of tensile opening during hydraulic fracturing. This model provides a useful scaling relation that links seismic moment to effective fluid pressure within the crack. Based on downhole recordings corrected for attenuation, a significant fraction of observed microseismic events are characterized by S/P amplitude ratio < 5. Despite the relatively small aperture of the monitoring arrays, which precludes both full moment-tensor analysis and definitive identification of nodal planes or axes, this ratio provides a strong indication that observed microseismic source mechanisms have a component of tensile failure. In addition, we find some instances of periodic spectral notches that can be explained by an opening/closing failure mechanism, in which fracture propagation outpaces fluid velocity within the crack. Finally, aseismic growth of tensile fractures may be indicative of a scenario in which injected energy is consumed to create new fracture surfaces. Taken together, our observations and modeling provide evidence that

  20. Evaluation of crack interaction effect for in-plane surface cracks using elastic finite element analyses

    International Nuclear Information System (INIS)

    Huh, Nam Su; Choi, Suhn; Park, Keun Bae; Kim, Jong Min; Choi, Jae Boong; Kim, Young Jin

    2008-01-01

    The crack-tip stress fields and fracture mechanics assessment parameters, such as the elastic stress intensity factor and the elastic-plastic J-integral, for a surface crack can be significantly affected by adjacent cracks. Such a crack interaction effect due to multiple cracks can magnify the fracture mechanics assessment parameters. There are many factors to be considered, for instance the relative distance between adjacent cracks, crack shape and loading condition, to quantify a crack interaction effect on the fracture mechanics assessment parameters. Thus, the current guidance on a crack interaction effect (crack combination rule), including ASME Sec. XI, BS7910, British Energy R6 and API RP579, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates a crack interaction effect by evaluating the elastic stress intensity factor of adjacent surface cracks in a plate along the crack front through detailed 3-dimensional elastic finite element analyses. The effects of the geometric parameters, the relative distance between cracks and the crack shape, on the stress intensity factor are systematically investigated. As for the loading condition, only axial tension is considered. Based on the elastic finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks in a plate were discussed

  1. Effects of microstructure and residual stress on fatigue crack growth of stainless steel narrow gap welds

    International Nuclear Information System (INIS)

    Jang, Changheui; Cho, Pyung-Yeon; Kim, Minu; Oh, Seung-Jin; Yang, Jun-Seog

    2010-01-01

    The effects of weld microstructure and residual stress distribution on the fatigue crack growth rate of stainless steel narrow gap welds were investigated. Stainless steel pipes were joined by the automated narrow gap welding process typical to nuclear piping systems. The weld fusion zone showed cellular-dendritic structures with ferrite islands in an austenitic matrix. Residual stress analysis showed large tensile stress in the inner-weld region and compressive stress in the middle of the weld. Tensile properties and the fatigue crack growth rate were measured along and across the weld thickness direction. Tensile tests showed higher strength in the weld fusion zone and the heat affected zone compared to the base metal. Within the weld fusion zone, strength was greater in the inner weld than outer weld region. Fatigue crack growth rates were several times greater in the inner weld than the outer weld region. The spatial variation of the mechanical properties is discussed in view of weld microstructure, especially dendrite orientation, and in view of the residual stress variation within the weld fusion zone. It is thought that the higher crack growth rate in the inner-weld region could be related to the large tensile residual stress despite the tortuous fatigue crack growth path.

  2. Cause of Damage. Hot cracking; Schadensursache Heissrissigkeit

    Energy Technology Data Exchange (ETDEWEB)

    Wader, Therese [BENTELER Steel/Tube GmbH, Paderborn (Germany). Vorentwicklung Werkstoffe

    2016-10-15

    Under certain conditions, Nb-containing stainless steels are susceptible to hot cracking. Such conditions include low melting phases on the grain boundaries, a coarse-grained microstructure such as cast structures, microstructure orientations towards the main tensile direction and high processing temperatures. The case of damage was characterized using metallographic and microanalytical methods. In the laboratory, the critical temperature range for the formation of hot cracks could furthermore specifically be localized under mechanical stresses by means of a dilatometer aiming at clearly verifying the cause of the damage, namely ''hot cracks''.

  3. A Fourth Order Formulation of DDM for Crack Analysis in Brittle Solids

    Directory of Open Access Journals (Sweden)

    Abolfazl Abdollahipour

    2017-01-01

    Full Text Available A fourth order formulation of the displacement discontinuity method (DDM is proposed for the crack analysis of brittle solids such as rocks, glasses, concretes and ceramics. A fourth order boundary collocation scheme is used for the discretization of each boundary element (the source element. In this approach, the source boundary element is divided into five sub-elements each recognized by a central node where the displacement discontinuity components are to be numerically evaluated. Three different formulating procedures are presented and their corresponding discretization schemes are discussed. A new discretization scheme is also proposed to use the fourth order formulation for the special crack tip elements which may be used to increase the accuracy of the stress and displacement fields near the crack ends. Therefore, these new crack tips discretizing schemes are also improved by using the proposed fourth order displacement discontinuity formulation and the corresponding shape functions for a bunch of five special crack tip elements. Some example problems in brittle fracture mechanics are solved for estimating the Mode I and Mode II stress intensity factors near the crack ends. These semi-analytical results are compared to those cited in the fracture mechanics literature whereby the high accuracy of the fourth order DDM formulation is demonstrated.

  4. The Numerical Simulation of the Crack Elastoplastic Extension Based on the Extended Finite Element Method

    Directory of Open Access Journals (Sweden)

    Xia Xiaozhou

    2013-01-01

    Full Text Available In the frame of the extended finite element method, the exponent disconnected function is introduced to reflect the discontinuous characteristic of crack and the crack tip enrichment function which is made of triangular basis function, and the linear polar radius function is adopted to describe the displacement field distribution of elastoplastic crack tip. Where, the linear polar radius function form is chosen to decrease the singularity characteristic induced by the plastic yield zone of crack tip, and the triangle basis function form is adopted to describe the displacement distribution character with the polar angle of crack tip. Based on the displacement model containing the above enrichment displacement function, the increment iterative form of elastoplastic extended finite element method is deduced by virtual work principle. For nonuniform hardening material such as concrete, in order to avoid the nonsymmetry characteristic of stiffness matrix induced by the non-associate flowing of plastic strain, the plastic flowing rule containing cross item based on the least energy dissipation principle is adopted. Finally, some numerical examples show that the elastoplastic X-FEM constructed in this paper is of validity.

  5. Fatigue Crack Propagation Under Variable Amplitude Loading Analyses Based on Plastic Energy Approach

    Directory of Open Access Journals (Sweden)

    Sofiane Maachou

    2014-04-01

    Full Text Available Plasticity effects at the crack tip had been recognized as “motor” of crack propagation, the growth of cracks is related to the existence of a crack tip plastic zone, whose formation and intensification is accompanied by energy dissipation. In the actual state of knowledge fatigue crack propagation is modeled using crack closure concept. The fatigue crack growth behavior under constant amplitude and variable amplitude loading of the aluminum alloy 2024 T351 are analyzed using in terms energy parameters. In the case of VAL (variable amplitude loading tests, the evolution of the hysteretic energy dissipated per block is shown similar with that observed under constant amplitude loading. A linear relationship between the crack growth rate and the hysteretic energy dissipated per block is obtained at high growth rates. For lower growth rates values, the relationship between crack growth rate and hysteretic energy dissipated per block can represented by a power law. In this paper, an analysis of fatigue crack propagation under variable amplitude loading based on energetic approach is proposed.

  6. On Early Age Crack Formation in FRC Slabs

    DEFF Research Database (Denmark)

    Olesen, John Forbes; Stang, Henrik

    1997-01-01

    The problem of early age crack formation in FRC slabs due to restrained temperature and shrinkage deformations, is given an analytical treatment. A model taking into account the ageing properties of the tensile softening curve and the continued development in the temperature and shrinkage...... deformations after crack initiation, is presented. Based on this model a design strategy for FRC slabs is outlined....

  7. Influence of the non-singular stress on the crack extension and fatigue life

    International Nuclear Information System (INIS)

    Cheng, C.Z.; Recho, N.; Niu, Z.R.

    2012-01-01

    Highlights: ► BEM is combined by characteristic analysis to calculate the singular stress field. ► A new method is proposed to evaluate the full stress field at crack tip region. ► Effect of non-singular stress on the propagation direction of the fatigue crack is analyzed. ► The influence of non-singular stress on the fatigue crack life is evaluated. - Abstract: The complete elasticity stress field at a crack tip region can be presented by the sum of the singular stress and several non-singular stress terms according to the Williams asymptotic expansion theory. The non-singular stress has a non-negligible influence on the prediction of the crack extension direction and crack growth rate under the fatigue loading. A novel method combining the boundary element method and the singularity characteristic analysis is proposed here to evaluate the complete stress field at a crack tip region. In this new method, any non-singular stress term in the Williams series expansion can be evaluated according to the computational accuracy requirement. Then, a modified Paris law is introduced to predict the crack propagation under the mixed-mode loading for exploring the influence of the non-singular stress on the fatigue life duration. By comparing with the existed experimental results, the predicted crack fatigue life when the non-singular stress is taken into consideration is more accurate than the predicted ones only considering the singular stress.

  8. Characterization of the failure behavior of zinc coating on dual phase steel under tensile deformation

    International Nuclear Information System (INIS)

    Song Guiming; Sloof, Willem G.

    2011-01-01

    Highlights: → The microcracks and voids at the zinc grain boundaries are the initial sites for the coating cracking. → The crack spacing of the fragmentally fractured zinc coating is mainly determined by the zinc grain size. → Small zinc grain size and the c-axis direction of zinc grain parallel to the zinc surface are beneficial to the mitigation of the zinc coating delamination. - Abstract: The failure behavior of hot-dip galvanized zinc coatings on dual phase steels under tensile deformation is characterized with in situ scanning electron microscopy (SEM). Under tension, the pre-existed microcracks and voids at the zinc grain boundaries propagate along the zinc grain boundaries to form crack nets within the coating, leading to a segmented fracture of the zinc coating with the crack spacing approximately equal to the zinc grain size. With further loading, the coating segments partially delaminated along the interface between the top zinc layer and the inhibition layer instead of the interface between the inhibition layer and steel substrate. As the c-axis of zinc grains trends to be normal to the tensile loading direction, the twinning deformation became more noticeable, and meanwhile the coating delamination was diminished. The transverse and incline tunneling cracks occurred in the inhibition layer with tensile deformation. The existence of the brittle FeZn 13 particles on top of the inhibition layer was unfavorable to the coating adhesion.

  9. Complete Tangent Stiffness for eXtended Finite Element Method by including crack growth parameters

    DEFF Research Database (Denmark)

    Mougaard, J.F.; Poulsen, P.N.; Nielsen, L.O.

    2013-01-01

    the crack geometry parameters, such as the crack length and the crack direction directly in the virtual work formulation. For efficiency, it is essential to obtain a complete tangent stiffness. A new method in this work is presented to include an incremental form the crack growth parameters on equal terms......The eXtended Finite Element Method (XFEM) is a useful tool for modeling the growth of discrete cracks in structures made of concrete and other quasi‐brittle and brittle materials. However, in a standard application of XFEM, the tangent stiffness is not complete. This is a result of not including...... with the degrees of freedom in the FEM‐equations. The complete tangential stiffness matrix is based on the virtual work together with the constitutive conditions at the crack tip. Introducing the crack growth parameters as direct unknowns, both equilibrium equations and the crack tip criterion can be handled...

  10. Surface, structural and tensile properties of proton beam irradiated zirconium

    Energy Technology Data Exchange (ETDEWEB)

    Rafique, Mohsin; Chae, San; Kim, Yong-Soo, E-mail: yongskim@hanyang.ac.kr

    2016-02-01

    This paper reports the surface, structural and tensile properties of proton beam irradiated pure zirconium (99.8%). The Zr samples were irradiated by 3.5 MeV protons using MC-50 cyclotron accelerator at different doses ranging from 1 × 10{sup 13} to 1 × 10{sup 16} protons/cm{sup 2}. Both un-irradiated and irradiated samples were characterized using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD) and Universal Testing Machine (UTM). The average surface roughness of the specimens was determined by using Nanotech WSxM 5.0 develop 7.0 software. The FESEM results revealed the formation of bubbles, cracks and black spots on the samples’ surface at different doses whereas the XRD results indicated the presence of residual stresses in the irradiated specimens. Williamson–Hall analysis of the diffraction peaks was carried out to investigate changes in crystallite size and lattice strain in the irradiated specimens. The tensile properties such as the yield stress, ultimate tensile stress and percentage elongation exhibited a decreasing trend after irradiation in general, however, an inconsistent behavior was observed in their dependence on proton dose. The changes in tensile properties of Zr were associated with the production of radiation-induced defects including bubbles, cracks, precipitates and simultaneous recovery by the thermal energy generated with the increase of irradiation dose.

  11. Surface, structural and tensile properties of proton beam irradiated zirconium

    Science.gov (United States)

    Rafique, Mohsin; Chae, San; Kim, Yong-Soo

    2016-02-01

    This paper reports the surface, structural and tensile properties of proton beam irradiated pure zirconium (99.8%). The Zr samples were irradiated by 3.5 MeV protons using MC-50 cyclotron accelerator at different doses ranging from 1 × 1013 to 1 × 1016 protons/cm2. Both un-irradiated and irradiated samples were characterized using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD) and Universal Testing Machine (UTM). The average surface roughness of the specimens was determined by using Nanotech WSxM 5.0 develop 7.0 software. The FESEM results revealed the formation of bubbles, cracks and black spots on the samples' surface at different doses whereas the XRD results indicated the presence of residual stresses in the irradiated specimens. Williamson-Hall analysis of the diffraction peaks was carried out to investigate changes in crystallite size and lattice strain in the irradiated specimens. The tensile properties such as the yield stress, ultimate tensile stress and percentage elongation exhibited a decreasing trend after irradiation in general, however, an inconsistent behavior was observed in their dependence on proton dose. The changes in tensile properties of Zr were associated with the production of radiation-induced defects including bubbles, cracks, precipitates and simultaneous recovery by the thermal energy generated with the increase of irradiation dose.

  12. Numerical investigation on the prefabricated crack propagation of FV520B stainless steel

    Directory of Open Access Journals (Sweden)

    Juyi Pan

    Full Text Available FV520B is a common stainless steel for manufacturing centrifugal compressor impeller and shaft. The internal metal flaw destroys the continuity of the material matrix, resulting in the crack propagation fracture of the component, which seriously reduces the service life of the equipment. In this paper, Abaqus software was used to simulate the prefabricated crack propagation of FV520B specimen with unilateral gap. The results of static crack propagation simulation results show that the maximum value of stress–strain located at the tip of the crack and symmetrical distributed like a butterfly along the prefabricated crack direction, the maximum stress is 1990 MPa and the maximum strain is 9.489 × 10−3. The Mises stress and stress intensity factor KI increases with the increase of the expansion step, the critical value of crack initiation is reached at the 6th extension step. The dynamic crack propagation simulation shows that the crack propagation path is perpendicular to the load loading direction. Similarly, the maximum Mises stress located at the crack tip and is symmetrically distributed along the crack propagation direction. The critical stress range of the crack propagation is 23.3–43.4 MPa. The maximum value of stress–strain curve located at the 8th extension step, that is, the crack initiation point, the maximum stress is 55.22 MPa, and the maximum strain is 2.26 × 10−4. On the crack tip, the stress changed as 32.24–40.16 MPa, the strain is at 1.292 × 10−4–1.897 × 10−4. Keywords: FV520B, Crack propagation, Mises stress, Stress–strain, Numerical investigation

  13. Crack propagation in dynamic thermoelasticity

    International Nuclear Information System (INIS)

    Bui, H.D.

    1980-01-01

    We study the singular thermoelastic fields near the crack tip, in the linear strain assumption. The equations are coupled and non linear. The asymptotic expansions of the displacement and the temperature are given for the first and the second order. It is shown that the temperature is singular when the crack propagates. However, this field does not change the dominant singularity of the mechanical field which is the same as that obtained in the theory of isothermal elasticity [fr

  14. Development of Tensile Softening Model for Plain Concrete

    Energy Technology Data Exchange (ETDEWEB)

    Lee, S.K.; Song, Y.C. [Korea Electric Power Research Institute, Taejon (Korea)

    2002-07-01

    Large-scale direct tensile softenng tests using plate concrete specimens(4000, 5000psi) with notch were performed under uniaxial stress. There were presented the basic physical properties and the complete load-CMOD(Crack Mouth Opening Displacement) curves for them And them the fracture energy was evaluated using the complete load-CMOD curves respectively, and there was presents optimal tensile softening model which is modified by a little revision of an existing one. Therefore, here provided the real verification data through the tests for developing other nonlinear concrete finite element models. (author). 32 refs., 38 figs., 4 tabs.

  15. Crack initiation life analysis in notched pipe under cyclic bending loads

    International Nuclear Information System (INIS)

    Lee, Joon Seong; Kwak, Sang Log; Kim, Young Jin; Park, Youn Won

    2001-01-01

    In order to improve leak-before-break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but crack initiation cycle was higher than the experimental result

  16. On the variation in crack-opening stresses at different locations in a three-dimensional body

    Science.gov (United States)

    Chermahini, R. G.; Blom, Anders F.

    1990-01-01

    Crack propagation and closure behavior of thin, and thick middle crack tension specimens under constant amplitude loading were investigated using a three dimensional elastic plastic finite element analysis of fatigue crack propagation and closure. In the thin specimens the crack front closed first on the exterior (free) surface and closed last in the interior during the unloading portion of cyclic loading; a load reduced displacement technique was used to determine crack opening stresses at specified locations in the plate from the displacements calculated after the seven cycle. All the locations were on the plate external surface and were located near the crack tip, behind the crack tip, at the centerline of the crack. With this technique, the opening stresses at the specified points were found to be 0.52, 0.42, and 0.39 times the maximum applied stress.

  17. Resolved shear stress intensity coefficient and fatigue crack growth in large crystals

    Science.gov (United States)

    Chen, QI; Liu, Hao-Wen

    1988-01-01

    Fatigue crack growth in large grain Al alloy was studied. Fatigue crack growth is caused primarily by shear decohesion due to dislocation motion in the crack tip region. The crack paths in the large crystals are very irregular and zigzag. The crack planes are often inclined to the loading axis both in the inplane direction and the thickness direction. The stress intensity factors of such inclined cracks are approximated from the two dimensional finite element calculations. The plastic deformation in a large crystal is highly anisotropic, and dislocation motion in such crystals are driven by the resolved shear stress. The resolved shear stress intensity coefficient in a crack solid, RSSIC, is defined, and the coefficients for the slip systems at a crack tip are evaluated from the calculated stress intensity factors. The orientations of the crack planes are closely related to the slip planes with the high RSSIC values. If a single slip system has a much higher RSSIC than all the others, the crack will follow the slip plane, and the slip plane becomes the crack plane. If two or more slip systems have a high RSSIC, the crack plane is the result of the decohesion processes on these active slip planes.

  18. Analysis of Crack Propagation Path on the Anisotropic Bi-Material Rock

    Directory of Open Access Journals (Sweden)

    Chao-Shi Chen

    2010-01-01

    Full Text Available This paper presents a single-domain boundary element method (SDBEM for linear elastic fracture mechanics analysis in the 2D anisotropic bimaterial. In this formulation, the displacement integral equation is collocated on the uncracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. The complete fundamental solution (Green's function for anisotropic bi-materials was also derived and implemented into the boundary integral formulation so the discretization along the interface can be avoided except for the interfacial crack part. A special crack-tip element was introduced to capture exactly the crack-tip behavior. A computer program with the FORTRAN code has been developed to effectively calculate the stress intensity factors, crack initiation angle, and propagation path of an anisotropic bi-material. This SDBEM program has been verified having a good accuracy with the previous researches. In addition, a rock of type (1/(2 disk specimen with a central crack was made to conduct the Brazilian test under diametrical loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation.

  19. Friction stress effects on mode I crack growth predictions

    NARCIS (Netherlands)

    Chen, Q.; Deshpande, V.S.; Giessen, E. van der; Needleman, A.

    2003-01-01

    The effect of a lattice friction stress on the monotonic growth of a plane strain mode I crack under small-scale yielding conditions is analyzed using discrete dislocation plasticity. When the friction stress is increased from zero to half the dislocation nucleation stress, the crack tip stress

  20. The effect of pre-stress cycles on fatigue crack growth - An analysis of crack growth mechanism. [in Al alloy plates

    Science.gov (United States)

    Kang, T. S.; Liu, H. W.

    1974-01-01

    Cyclic prestress increases subsequent fatigue crack growth rate in 2024-T351 aluminum alloy. This increase in growth rate, caused by the prestress, and the increased rate, caused by temper embrittlement as observed by Ritchie and Knott (1973), cannot be explained by the crack tip blunting model alone. Each fatigue crack increment consists of two components, a brittle and a ductile component. They are controlled by the ductility of the material and its cyclic yield strength, respectively.

  1. Influence of corrosion environment composition on crack propagation in high-strength martensitic steel

    International Nuclear Information System (INIS)

    Romaniv, O.N.; Nikiforchin, G.N.; Tsirul'nik, A.T.

    1984-01-01

    The 40 Kh steel is taken as an example to investigate the dependence of electrochemical parameters in the crack tip and characteristics of corrosion static cracking resistance of martensitic steel on the composition of environment. The tests are performed in acidic and alkaline solutions prepared by adding HC or NaOH in distilled water. It is established that growth of pH value of initial solutions trom 0 to 13 brings about linear increase of a threshold stress intensity factor. It is found that acidic medium in the crack tip preserves up to pH 13 of initial medium. The possibility of corrosion crack propagation in alkaline solutions according to the mechanism of hydrogen embrittlement is proved

  2. Steady-State Crack Growth in Rate-Sensitive Single Crystals

    DEFF Research Database (Denmark)

    Juul, Kristian Jørgensen; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2016-01-01

    The characteristics of the active plastic zone surrounding a crack growingin a single crystal (FCC, BCC, and HCP) at constant velocity is investigated for ModeI loading under plane strain assumptions. The framework builds upon a steady-state relation bringing the desired solution out in a frame...... translating with the crack tip. In the study, the shielding of the crack tip that follows from plastic slip is investigated by adopting the SSV-model. High resolution plots of the plastic zones are obtained and a detailed study confirms the existence of analytically determined velocity discontinuities from...... the literature. The plastic zone is found to be smallest for the FCC structure andlargest for the HCP structure, which is also reected in the shielding ratio, where FCC crystals show the smallest shielding and HCP the largest shielding....

  3. Thermal fatigue cracking in T-fittings of feed water systems

    International Nuclear Information System (INIS)

    Oesterberg, J.

    1983-03-01

    The existence of thermal fatigue cracks can be determined by ultrasonic methods. The depth of the cracks will be of importance for evaluation of the seriousness of the situation. Currently, no method is available for determining depth of cracks without cutting and grinding. Methods for gaining information of crack depth have been discussed with leading European materials testing institutes. More elaborate ultrasonic methods have been tested with negative results. On testing signals from crack corners flood possible signals from the crack tips. At present no reliable technique based on ultrasonics exist (in Europe, that will give information of crack depth.(P.Aa.)

  4. On the application of cohesive crack modeling in cementitious materials

    DEFF Research Database (Denmark)

    Stang, Henrik; Olesen, John Forbes; Poulsen, Peter Noe

    2007-01-01

    typically for multi scale problems such as crack propagation in fiber reinforced composites. Mortar and concrete, however, are multi-scale materials and the question naturally arises, if bridged crack models in fact are more suitable for concrete and mortar as well? In trying to answer this question a model......Cohesive crack models-in particular the Fictitious Crack Model - are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models-where cohesive stresses are assumed to exist together with a stress singularity at the crack tip-on the other hand, are used...

  5. Effect of grain boundary microcracks on crack resistance of annealed tungsten

    International Nuclear Information System (INIS)

    Babak, A.V.; Uskov, E.I.

    1984-01-01

    Effect of grain boundary microcracks in tungsten, produced by the method of powder sintering, on its crack resistance after annealing at T=2200 deg C, has been considered. On the basis of complex physncomechanical study of tungsten crack resistance it is shown, that the value of ultimate tensile stress does not depend on temperature. The presence of grain boundary cracks in such material (in the limits from 2 to 8%) does not produce effect on its crack resistance

  6. Internal shear cracking in bulk metal forming

    DEFF Research Database (Denmark)

    Christiansen, Peter; Nielsen, Chris Valentin; Bay, Niels Oluf

    2017-01-01

    This paper presents an uncoupled ductile damage criterion for modelling the opening and propagation of internal shear cracks in bulk metal forming. The criterion is built upon the original work on the motion of a hole subjected to shear with superimposed tensile stress triaxiality and its overall...... performance is evaluated by means of side-pressing formability tests in Aluminium AA2007-T6 subjected to different levels of pre-strain. Results show that the new proposed criterionis able to combine simplicity with efficiency for predicting the onset of fracture and the crack propagation path for the entire...... cracking to internal cracks formed undert hree-dimensional states of stress that are typical of bulk metal forming....

  7. Evaluation of fatigue crack growth and fracture resistance of SA350 LF2 material

    International Nuclear Information System (INIS)

    Singh, P.K.; Dubey, J.S.; Chakrabarty, J.K.; Vaze, K.K.; Kushwaha, H.S.

    2003-01-01

    The aim of the present paper is to evaluate the tensile and fracture mechanics properties of the SA350 LF2 carbon steel material used as the Header material in the primary heat transport (PHT) system piping of the Indian pressurized heavy water reactors (PHWR). Tensile, fatigue crack growth rate and fracture toughness tests have been carried out on specimens machined from the Header of the actual PHT pipes. The effect of temperature on tensile properties has been discussed. The effect of temperature and notch orientation on fracture resistance behavior of the material and fatigue crack growth rate dependence on the notch orientation and stress ratio has also been discussed. (author)

  8. Crack initiation life analysis in notched pipe under cyclic bending loads

    International Nuclear Information System (INIS)

    Goak, S. R.; Kim, Y. J.; Lee, J. S.; Park, Y. W.

    2000-01-01

    In order to improve LBB(Leak-Before-Break) methodology, more precisely the crack growth evaluation, a benchmark problem was proposed by the CEA Saclay. The aim of this benchmark analysis was to evaluate the crack growth in a notched pipe under cyclic bending loads. The proposed benchmark analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result

  9. H2S cracking resistance of type 420 stainless steel tubulars

    International Nuclear Information System (INIS)

    Klein, L.J.

    1984-01-01

    Type 420 stainless steel (13Cr) production tubing is being used successfully in deep sour gas wells in the Tuscaloosa Trend. Despite their reputation for poor H 2 S cracking resistance in laboratory tests, 12-13% Cr steels continue to perform well in sour environments. NACE Tensile Test and Shell bent beam test results indicate Type 420 is more resistant to H 2 S cracking than Type 410, but is not as resistant as carbon steel, at to 586-690 MPa (85-100 ksi) yield strength level. In addition to evaluating Type 420 stainless steel in the standard NACE Tensile and Shell bent beam tests, the effects on cracking tendency of chloride concentration, pH, and H 2 S gas concentration in the NACE Test solution were also examined. Type 420 appears to be more resistant to H 2 S cracking than is indicated by standard laboratory tests, at least in low H 2 S level sour environments

  10. Crack propagation under conditions of low cycle fatigue

    International Nuclear Information System (INIS)

    Hellmann, D.

    1988-01-01

    A literature review is given of convenient concepts describing the mechanical behaviour of a cracked body under cyclic loading. Only the range of high growth rates is considered. However, caused by large scale yielding in this range, the application of linear elastic fracture mechanics is no longer possible. Mechanical parameters which control fatigue crack growth are a modified stress intensity factor, the J-integral, the crack tip opening displacement and a suitable strain amplitude. (orig.) With 20 figs [de

  11. Comparison of theory and experiment for elastic-plastic plane-strain crack growth. [AISI 4140 steel

    Energy Technology Data Exchange (ETDEWEB)

    Hermann, L.; Rice, J.R.

    1980-08-01

    Recent theoretical results on elastic-plastic plane-strain crack growth are reviewed and experimental results for crack growth in a 4140 steel are discussed in terms of the theoretical concepts. The theory is based on a recent asymptotic analysis of crack surface opening and strain distributions at a quasistatically advancing crack tip in an ideally plastic solid. The analysis is incomplete in that some of the parameters which appear in it are known only approximately, especially at large-scale yielding. Nevertheless, it is sufficient for the derivation of a relation between the imposed loading and amount of crack growth prior to general yielding, based on the assumption that a geometrically similar near-tip crack profile is maintained during growth. The resulting predictions for the variation of J with crack growth are found to fit well to the experimental results obtained on deeply cracked compact specimens.

  12. Ultrasonic testing of fatigue cracks under various conditions

    International Nuclear Information System (INIS)

    Jessop, T.J.; Cameron, A.G.B.

    1983-01-01

    Reliable detection of the fatigue cracks was possible under all conditions studied. Applied load affected the ultrasonic response in a variety of ways but never more than by 20dB and generally considerably less. Material variations affected the response under applied load by up to 20dB. Oxide in the crack and crack morphology affected the response by up to 9dB (12dB under load). Crack size variations and presence of water had little effect. Sizing accuracy was generally within 2mm although there was a tendency to undersize. The time of flight sizing technique gave the best accuracy if a tensile load was applied

  13. The influence of surface stress on dislocation emission from sharp and blunt cracks in f.c.c. metals

    DEFF Research Database (Denmark)

    Schiøtz, Jakob

    2000-01-01

    We use computer simulations to study the behaviour of atomically sharp and blunted cracks in various fee metals. The simulations use effective medium potentials which contain many-body interactions. We find that when using potentials representing platinum and gold a sharp crack is stable with res......We use computer simulations to study the behaviour of atomically sharp and blunted cracks in various fee metals. The simulations use effective medium potentials which contain many-body interactions. We find that when using potentials representing platinum and gold a sharp crack is stable...... with respect to the emission of a dislocation from the crack tip, whereas for all other metals studied the sharp crack is unstable. This result cannot be explained by existing criteria for the intrinsic ductile/brittle behaviour of crack tips, but is probably caused by surface stresses. When the crack...... is no longer atomically sharp dislocation emission becomes easier in all the studied metals. The effect is relatively strong; the critical stress intensity factor for emission to occur is reduced by up to 20%. This behaviour appears to be caused by the surface stress near the crack tip. The surface stress...

  14. Analytical model for time to cover cracking in RC structures due to rebar corrosion

    International Nuclear Information System (INIS)

    Bhargava, Kapilesh; Ghosh, A.K.; Mori, Yasuhiro; Ramanujam, S.

    2006-01-01

    The structural degradation of concrete structures due to reinforcement corrosion is a major worldwide problem. Reinforcement corrosion causes a volume increase due to the oxidation of metallic iron, which is mainly responsible for exerting the expansive radial pressure at the steel-concrete interface and development of hoop tensile stresses in the surrounding concrete. Cracking occurs, once the maximum hoop tensile stress exceeds the tensile strength of the concrete. The cracking begins at the steel-concrete interface and propagates outwards and eventually results in the thorough cracking of the cover concrete and this would indicate the loss of service life for the corrosion affected structures. An analytical model is proposed to predict the time required for cover cracking and the weight loss of reinforcing bar in corrosion affected reinforced concrete structures. The modelling aspects of the residual strength of cracked concrete and the stiffness contribution from the combination of reinforcement and expansive corrosion products have also been incorporated in the model. The problem is modeled as a boundary value problem and the governing equations are expressed in terms of the radial displacement. The analytical solutions are presented considering a simple two-zone model for the cover concrete, viz. cracked or uncracked. Reasonable estimation of the various parameters in the model related to the composition and properties of expansive corrosion products based on the available published experimental data has also been discussed. The performance of the proposed corrosion cracking model is then investigated through its ability to reproduce available experimental trends. Reasonably good agreement between experimental results and the analytical predictions has been obtained. It has also been found that tensile strength and initial tangent modulus of cover concrete, annual mean corrosion rate and modulus of elasticity of reinforcement plus corrosion products combined

  15. The cracking of pressure tubes in the Pickering reactor

    International Nuclear Information System (INIS)

    Ross-Ross, P.A.

    1978-01-01

    Small cracks in 17 of the 390 pressure tubes in Unit 3 of the 2056 MW (electrical) Pickering Generating Station and of 52 tubes in Unit 4, resulted in each of these units being out of service for many months. The cracks originated at areas of extremely high residual tensile stress produced by improper positioning of the rolling tool used during construction to join the pressure tube to its end-fitting. The mechanism of failure was delayed hydrogen cracking. (author)

  16. The application of an atomistic J-integral to a ductile crack.

    Science.gov (United States)

    Zimmerman, Jonathan A; Jones, Reese E

    2013-04-17

    In this work we apply a Lagrangian kernel-based estimator of continuum fields to atomic data to estimate the J-integral for the emission dislocations from a crack tip. Face-centered cubic (fcc) gold and body-centered cubic (bcc) iron modeled with embedded atom method (EAM) potentials are used as example systems. The results of a single crack with a K-loading compare well to an analytical solution from anisotropic linear elastic fracture mechanics. We also discovered that in the post-emission of dislocations from the crack tip there is a loop size-dependent contribution to the J-integral. For a system with a finite width crack loaded in simple tension, the finite size effects for the systems that were feasible to compute prevented precise agreement with theory. However, our results indicate that there is a trend towards convergence.

  17. In-vitro characterization of stress corrosion cracking of aluminium-free magnesium alloys for temporary bio-implant applications.

    Science.gov (United States)

    Choudhary, Lokesh; Singh Raman, R K; Hofstetter, Joelle; Uggowitzer, Peter J

    2014-09-01

    The complex interaction between physiological stresses and corrosive human body fluid may cause premature failure of metallic biomaterials due to the phenomenon of stress corrosion cracking. In this study, the susceptibility to stress corrosion cracking of biodegradable and aluminium-free magnesium alloys ZX50, WZ21 and WE43 was investigated by slow strain rate tensile testing in a simulated human body fluid. Slow strain rate tensile testing results indicated that each alloy was susceptible to stress corrosion cracking, and this was confirmed by fractographic features of transgranular and/or intergranular cracking. However, the variation in alloy susceptibility to stress corrosion cracking is explained on the basis of their electrochemical and microstructural characteristics. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Tensile creep behavior in an advanced silicon nitride

    International Nuclear Information System (INIS)

    Lofaj, F.

    2000-01-01

    Tensile creep behavior and changes in the microstructure of the advanced silicon nitride, SN 88M, were studied at temperatures from 1250 to 1400 C to reveal the creep resistance and lifetime-controlling processes. Assuming power law dependence of the minimum strain rate on stress, stress exponents from 6 to 8 and an apparent activation energy of 780 kJ/mol were obtained. Extensive electron microscopy observations revealed significant changes in the crystalline secondary phases and creep damage development. Creep damage was classified in two groups: 'inter-granular' defects in the amorphous boundary phases, and 'intra-granular' defects in silicon nitride grains. The inter-granular defects involved multigrain junction cavities, two-grain junction cavities, microcracks and cracks. The intra-granular defects included broken large grains, small symmetrical and asymmetrical cavities, and crack-like intragranular cavities. Cavities are generated continuously during the whole deformation starting from the threshold strain of ∝0.1%, and they contribute linearly to the tensile strain. Cavities produce more than 90% of the total tensile strain, and it is concluded that cavitation is the main creep mechanism in silicon nitride ceramics. The multigrain junction cavities are considered to be the most important for generating new volume and producing tensile strain. The Luecke and Wiederhorn (L and W) creep model, based on cavitation at multigrain junctions according to an exponential law, was proven to correspond to the stress dependence of the minimum strain rate. A qualitative model based on the L and W model was suggested and expanded to include intragranular cavitation. The basic mechanisms involve a repeating of the sequence grain boundary sliding (GBS) => cavitation at multigrain junctions => viscous flow and dissolution-precipitation. (orig.)

  19. ORMGEN3D, 3-D Crack Geometry FEM Mesh Generator

    International Nuclear Information System (INIS)

    Bass, B.R.; Bryson, J.W.

    1994-01-01

    1 - Description of program or function: ORMGEN3D is a finite element mesh generator for computational fracture mechanics analysis. The program automatically generates a three-dimensional finite element model for six different crack geometries. These geometries include flat plates with straight or curved surface cracks and cylinders with part-through cracks on the outer or inner surface. Mathematical or user-defined crack shapes may be considered. The curved cracks may be semicircular, semi-elliptical, or user-defined. A cladding option is available that allows for either an embedded or penetrating crack in the clad material. 2 - Method of solution: In general, one eighth or one-quarter of the structure is modelled depending on the configuration or option selected. The program generates a core of special wedge or collapsed prism elements at the crack front to introduce the appropriate stress singularity at the crack tip. The remainder of the structure is modelled with conventional 20-node iso-parametric brick elements. Element group I of the finite element model consists of an inner core of special crack tip elements surrounding the crack front enclosed by a single layer of conventional brick elements. Eight element divisions are used in a plane orthogonal to the crack front, while the number of element divisions along the arc length of the crack front is user-specified. The remaining conventional brick elements of the model constitute element group II. 3 - Restrictions on the complexity of the problem: Maxima of 5,500 nodes, 4 layers of clad elements

  20. Effect of hybrid fiber reinforcement on the cracking process in fiber reinforced cementitious composites

    DEFF Research Database (Denmark)

    Pereira, Eduardo B.; Fischer, Gregor; Barros, Joaquim A.O.

    2012-01-01

    The simultaneous use of different types of fibers as reinforcement in cementitious matrix composites is typically motivated by the underlying principle of a multi-scale nature of the cracking processes in fiber reinforced cementitious composites. It has been hypothesized that while undergoing...... tensile deformations in the composite, the fibers with different geometrical and mechanical properties restrain the propagation and further development of cracking at different scales from the micro- to the macro-scale. The optimized design of the fiber reinforcing systems requires the objective...... materials is carried out by assessing directly their tensile stress-crack opening behavior. The efficiency of hybrid fiber reinforcements and the multi-scale nature of cracking processes are discussed based on the experimental results obtained, as well as the micro-mechanisms underlying the contribution...

  1. A unified model of hydride cracking based on elasto-plastic energy release rate over a finite crack extension

    International Nuclear Information System (INIS)

    Zheng, X.J.; Metzger, D.R.; Sauve, R.G.

    1995-01-01

    A fracture criterion based on energy balance is proposed for elasto-plastic cracking at hydrides in zirconium, assuming a finite length of crack advance. The proposed elasto-plastic energy release rate is applied to the crack initiation at hydrides in smooth and notched surfaces, as well as the subsequent delayed hydride cracking (DHC) considering limited crack-tip plasticity. For a smooth or notched surface of an elastic body, the fracture parameter is related to the stress intensity factor for the initiated crack. For DHC, a unique curve relates the non-dimensionalized elasto-plastic energy release rate with the length of crack extension relative to the plastic zone size. This fracture criterion explains experimental observations concerning DHC in a qualitative manner. Quantitative comparison with experiments is made for fracture toughness and DHC tests on specimens containing certain hydride structures; very good agreement is obtained. ((orig.))

  2. Application of cyclic J-integral to low cycle fatigue crack growth of Japanese carbon steel pipe

    Energy Technology Data Exchange (ETDEWEB)

    Miura, N.; Fujioka, T.; Kashima, K. [and others

    1997-04-01

    Piping for LWR power plants is required to satisfy the LBB concept for postulated (not actual) defects. With this in mind, research has so far been conducted on the fatigue crack growth under cyclic loading, and on the ductile crack growth under excessive loading. It is important, however, for the evaluation of the piping structural integrity under seismic loading condition, to understand the fracture behavior under dynamic and cyclic loading conditions, that accompanies large-scale yielding. CRIEPI together with Hitachi have started a collaborative research program on dynamic and/or cyclic fracture of Japanese carbon steel (STS410) pipes in 1991. Fundamental tensile property tests were conducted to examine the effect of strain rate on tensile properties. Cracked pipe fracture tests under some loading conditions were also performed to investigate the effect of dynamic and/or cyclic loading on fracture behavior. Based on the analytical considerations for the above tests, the method to evaluate the failure life for a cracked pipe under cyclic loading was developed and verified. Cyclic J-integral was introduced to predict cyclic crack growth up to failure. This report presents the results of tensile property tests, cracked pipe fracture tests, and failure life analysis. The proposed method was applied to the cracked pipe fracture tests. The effect of dynamic and/or cyclic loading on pipe fracture was also investigated.

  3. On the strong crack-microcrack interaction problem

    Science.gov (United States)

    Gorelik, M.; Chudnovsky, A.

    1992-07-01

    The problem of the crack-microcrack interaction is examined with special attention given to the iterative procedure described by Chudnovsky and Kachanov (1983), Chudnovsky et al. (1984), and Horii and Nemat-Nasser (1983), which yields erroneous results as the crack tips become closer (i.e., for strong crack interaction). To understand the source of error, the traction distributions along the microcrack line on the n-th step of iteration representing the exact and asymptotic stress fields are compared. It is shown that the asymptotic solution gives a gross overestimation of the actual traction.

  4. The COD concept and its application to fracture mechanical evaluation of cracked components

    International Nuclear Information System (INIS)

    Kockelmann, H.

    1984-01-01

    Based on a comprehensive literature study, this report critically evaluates the current state of experiences with the COD concept in fracture mechanics. First the concept is explained and the procedure of materials testing with a view to fracture mechanics is discussed in detail with emphasis on: The definition of crack shape modification; the procedure to detect crack modification, with subsequent comparison; the determination of material characteristics; the impact on the characteristics of the crack tip opening and the dispersion of results. The correlation between crack tip opening characteristics and notch impact strength is explained, and the methods applied for analysis of the streses affecting the structural components are shown. The design-based and failure threshold curves and the treatment of real crack geometries are also discussed. Problems still to be solved are shown. (orig./HP) [de

  5. Static and free-vibration analyses of cracks in thin-shell structures based on an isogeometric-meshfree coupling approach

    Science.gov (United States)

    Nguyen-Thanh, Nhon; Li, Weidong; Zhou, Kun

    2018-03-01

    This paper develops a coupling approach which integrates the meshfree method and isogeometric analysis (IGA) for static and free-vibration analyses of cracks in thin-shell structures. In this approach, the domain surrounding the cracks is represented by the meshfree method while the rest domain is meshed by IGA. The present approach is capable of preserving geometry exactness and high continuity of IGA. The local refinement is achieved by adding the nodes along the background cells in the meshfree domain. Moreover, the equivalent domain integral technique for three-dimensional problems is derived from the additional Kirchhoff-Love theory to compute the J-integral for the thin-shell model. The proposed approach is able to address the problems involving through-the-thickness cracks without using additional rotational degrees of freedom, which facilitates the enrichment strategy for crack tips. The crack tip enrichment effects and the stress distribution and displacements around the crack tips are investigated. Free vibrations of cracks in thin shells are also analyzed. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the coupling approach.

  6. A Prediction Method of Tensile Young's Modulus of Concrete at Early Age

    Directory of Open Access Journals (Sweden)

    Isamu Yoshitake

    2012-01-01

    Full Text Available Knowledge of the tensile Young's modulus of concrete at early ages is important for estimating the risk of cracking due to restrained shrinkage and thermal contraction. However, most often, the tensile modulus is considered equal to the compressive modulus and is estimated empirically based on the measurements of compressive strength. To evaluate the validity of this approach, the tensile Young's moduli of 6 concrete and mortar mixtures are measured using a direct tension test. The results show that the tensile moduli are approximately 1.0–1.3-times larger than the compressive moduli within the material's first week of age. To enable a direct estimation of the tensile modulus of concrete, a simple three-phase composite model is developed based on random distributions of coarse aggregate, mortar, and air void phases. The model predictions show good agreement with experimental measurements of tensile modulus at early age.

  7. Strength of tensed and compressed concrete segments in crack spacing under short-term dynamic load

    Directory of Open Access Journals (Sweden)

    Galyautdinov Zaur

    2018-01-01

    Full Text Available Formation of model describing dynamic straining of reinforced concrete requires taking into account the basic aspects influencing the stress-strain state of structures. Strength of concrete segments in crack spacing is one of the crucial aspects that affect general strain behavior of reinforced concrete. Experimental results demonstrate significant change in strength of tensed and compressed concrete segments in crack spacing both under static and under dynamic loading. In this case, strength depends on tensile strain level and the slope angle of rebars towards the cracks direction. Existing theoretical and experimental studies estimate strength of concrete segments in crack spacing under static loading. The present work presents results of experimental and theoretical studies of dynamic strength of plates between cracks subjected to compression-tension. Experimental data was analyzed statistically; the dependences were suggested to describe dynamic strength of concrete segments depending on tensile strain level and slope angle of rebars to cracks direction.

  8. Delayed hydrogen cracking test design for pressure tubes

    International Nuclear Information System (INIS)

    Haddad, Roberto; Loberse, Antonio N.; Yawny, Alejandro A.; Riquelme, Pablo

    1999-01-01

    CANDU nuclear power stations pressure tubes of alloy Zr-2,5 % Nb present a cracking phenomenon known as delayed hydrogen cracking (DHC). This is a brittle fracture of zirconium hydrides that are developed by hydrogen due to aqueous corrosion on the metal surface. This hydrogen diffuses to the crack tip where brittle zirconium hydrides develops and promotes the crack propagation. A direct current potential decay (DCPD) technique has been developed to measure crack propagation rates on compact test (CT) samples machined from a non irradiated pressure tube. Those test samples were hydrogen charged by cathodic polarization in an acid solution and then pre cracked in a fatigue machine. This technique proved to be useful to measure crack propagation rates with at least 1% accuracy for DHC in pressure tubes. (author)

  9. The diffusional growth of a grain boundary crack

    International Nuclear Information System (INIS)

    Puls, M.P.; Dutton, R.

    1977-10-01

    This report considers the possibility of high temperature rupture occurring by a grain boundary diffusional mechanism. It is assumed that a pre-existing, intergranular crack grows by loss of atoms from the crack tip to the grain boundary. Rupture occurs when the crack has grown to a critical length. A theoretical treatment of the kinetics of crack growth is presented and equations are derived for the crack velocity and time to rupture. A comparison is made with a previous theoretical model developed by Charles, together with rupture data obtained experimentally for the nickel-based alloy, Nimonic 80A. We conclude that experimental verification of the theoretical models requires a comparison with crack velocity data rather than time to rupture data. (author)

  10. Crack Front Segmentation and Facet Coarsening in Mixed-Mode Fracture

    Science.gov (United States)

    Chen, Chih-Hung; Cambonie, Tristan; Lazarus, Veronique; Nicoli, Matteo; Pons, Antonio J.; Karma, Alain

    2015-12-01

    A planar crack generically segments into an array of "daughter cracks" shaped as tilted facets when loaded with both a tensile stress normal to the crack plane (mode I) and a shear stress parallel to the crack front (mode III). We investigate facet propagation and coarsening using in situ microscopy observations of fracture surfaces at different stages of quasistatic mixed-mode crack propagation and phase-field simulations. The results demonstrate that the bifurcation from propagating a planar to segmented crack front is strongly subcritical, reconciling previous theoretical predictions of linear stability analysis with experimental observations. They further show that facet coarsening is a self-similar process driven by a spatial period-doubling instability of facet arrays.

  11. Influence of a gaseous atmosphere on fatigue crack propagation

    International Nuclear Information System (INIS)

    Henaff, G.

    2002-01-01

    The paper presents a review of the current knowledge on the influence of gaseous atmospheres, and primarily ambient air, on fatigue crack propagation in metallic alloys. Experimental evidence of the effect of exposure to ambient air or any moist environment on fatigue crack propagation in steels is first proposed. The different interacting processes are analyzed so as to clearly uncouple the influence of the various factors on crack growth resistance. Two distinct mechanisms are identified: the adsorption of vapour molecules and hydrogen assisted fracture at crack tip. (author)

  12. Thermal analysis of cracked bodies using finite element techniques

    International Nuclear Information System (INIS)

    Hellen, T.K.; Price, R.H.; Harrison, R.P.

    1975-01-01

    The paper develops the potential energy equation in terms of finite element theory including thermal loads. Following this, the energy release rate and consequently the stress intensity factors are derived. Considerations of the classical near crack tip equations are made and deficiencies with the popular substitution methods are highlighted. A method of removing these deficiencies is described. Various energy methods are reconsidered in terms of the role of the thermal energy contribution to the potential energy. These methods include work of crack closure, energy compliance and virtual crack extensions with no other change in nodal geometry, and therefore only requires the recalculation of the stiffness matrices of the crack tip elements. An example of a quadratic temperature gradient parallel to the crack plane in an edge cracked plate is described. Comparisons of the various finite element methods are made and generally show good agreement. A second application compares the virtual crack extension method with an approximate analytical solution in determining stress intensity factors for a thick hollow cylinder with an axial crack for various depths through the wall thickness and for different times. Initially the cylinder is at a uniform high temperature and is then subjected to a sustained cooling shock. Analytical solutions are available for temperature and stress distributions in the uncracked pipe. The stress intensity for a shallow crack in the early stages of the transient has been determined using a superposition procedure. Comparison of the analytical and computed results shows good agreement between the methods

  13. Influence of crack depth on the fracture toughness of reactor pressure vessel steel

    International Nuclear Information System (INIS)

    Theiss, T.J.; Bryson, J.W.

    1991-01-01

    The Heavy Section Steel Technology Program (HSST) at Oak Ridge National Laboratory (ORNL) is investigating the influence of flaw depth on the fracture toughness of reactor pressure vessel (RPV) steel. Recently, it has been shown that, in notched beam testing, shallow cracks tend to exhibit an elevated toughness as a result of a loss of constraint at the crack tip. The loss of constraint takes place when interaction occurs between the elastic-plastic crack-tip stress field and the specimen surface nearest the crack tip. An increased shallow-crack fracture toughness is of interest to the nuclear industry because probabilistic fracture-mechanics evaluations show that shallow flaws play a dominant role in the probability of vessel failure during postulated pressurized-thermal-shock (PTS) events. Tests have been performed on beam specimens loaded in 3-point bending using unirradiated reactor pressure vessel material (A533 B). Testing has been conducted using specimens with a constant beam depth (W = 94 mm) and within the lower transition region of the toughness curve for A533 B. Test results indicate a significantly higher fracture toughness associated with the shallow flaw specimens compared to the fracture toughness determined using deep-crack (a/W = 0.5) specimens. Test data also show little influence of thickness on the fracture toughness for the current test temperature (-60 degree C). 21 refs., 5 figs., 3 tabs

  14. Identifying and Understanding Environment-Induced Crack propagation Behavior in Ni-based Superalloy INCONEL 617

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Longzhou

    2012-11-30

    The nickel-based superalloy INCONEL 617 is a candidate material for heat exchanger applications in the next-generation nuclear plant (NGNP) system. This project will study the crack propagation process of alloy 617 at temperatures of 650°C-950°C in air under static/cyclic loading conditions. The goal is to identify the environmental and mechanical damage components and to understand in-depth the failure mechanism. Researchers will measure the fatigue crack propagation (FCP) rate (da/dn) under cyclic and hold-time fatigue conditions, and sustained crack growth rates (da/dt) at elevated temperatures. The independent FCP process will be identified and the rate-controlled sustained loading crack process will be correlated with the thermal activation equation to estimate the oxygen thermal activation energy. The FCP-dependent model indicates that if the sustained loading crack growth rate, da/dt, can be correlated with the FCP rate, da/dn, at the full time dependent stage, researchers can confirm stress-accelerated grain-boundary oxygen embrittlement (SAGBOE) as a predominate effect. Following the crack propagation tests, the research team will examine the fracture surface of materials in various cracking stages using a scanning electron microscope (SEM) and an optical microscope. In particular, the microstructure of the crack tip region will be analyzed in depth using high resolution transmission electron microscopy (TEM) and electron energy loss spectrum (EELS) mapping techniques to identify oxygen penetration along the grain boundary and to examine the diffused oxygen distribution profile around the crack tip. The cracked sample will be prepared by focused ion beam nanofabrication technology, allowing researchers to accurately fabricate the TEM samples from the crack tip while minimizing artifacts. Researchers will use these microscopic and spectroscopic results to interpret the crack propagation process, as well as distinguish and understand the environment or

  15. Measurements of delayed hydride cracking propagation rate in the radial direction of Zircaloy-2 cladding tubes

    Energy Technology Data Exchange (ETDEWEB)

    Kubo, T., E-mail: kubo@nfd.co.jp [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan); Kobayashi, Y. [M.O.X. Co., Ltd., 1828-520 Hirasu-cho, Mito, Ibaraki 311-0853 (Japan); Uchikoshi, H. [Nippon Nuclear Fuel Development Co., Ltd., 2163 Narita-cho, Oarai-machi, Ibaraki 311-1313 (Japan)

    2012-08-15

    Highlights: Black-Right-Pointing-Pointer The delayed hydride cracking (DHC) velocity of Zircaloy-2 was measured. Black-Right-Pointing-Pointer The velocity followed the Arrhenius law up to 270 Degree-Sign C. Activation energy was 49 kJ/mol. Black-Right-Pointing-Pointer The threshold stress intensity factor for the DHC was from 4 to 6 MPa m{sup 1/2}. Black-Right-Pointing-Pointer An increase in material strength accelerated the DHC. Black-Right-Pointing-Pointer Precipitation and fracture of hydrides at a crack tip is responsible for the DHC. - Abstract: Delayed hydride cracking (DHC) tests of Zircaloy-2 cladding tubes were performed in the chamber of a scanning electron microscope (SEM) to directly observe the crack propagation and measure the crack velocity in the radial direction of the tubes. Pre-cracks were produced at the outer surfaces of the tubes. Hydrogen contents of the tubes were from 90 ppm to 130 ppm and test temperatures were from 225 Degree-Sign C to 300 Degree-Sign C. The crack velocity followed the Arrhenius law at temperatures lower than about 270 Degree-Sign C with apparent activation energy of about 49 kJ/mol. The upper temperature limit for DHC, above which DHC did not occur, was about 280 Degree-Sign C. The threshold stress intensity factor for the initiation of the crack propagation, K{sub IH}, was from about 4 MPa m{sup 1/2} to 6 MPa m{sup 1/2}, almost independent of temperature. An increase in 0.2% offset yield stress of the material accelerated the crack velocity and slightly decreased K{sub IH}. Detailed observations of crack tip movement showed that cracks propagated in an intermittent fashion and the propagation gradually approached the steady state as the crack depth increased. The SEM observations also showed that hydrides were formed at a crack tip and a number of micro-cracks were found in the hydrides. It was presumed from these observations that the repetition of precipitation and fracture of hydrides at the crack tip would be

  16. Thermographic Inspection of Fatigue Crack by Using Contact Thermal Resistance

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Seung Yong; Kim, No Hyu [Korean University of Technology and Education, Cheonan (Korea, Republic of)

    2013-04-15

    Fatigue crack was detected from a temperature change around surface crack using the thermographic technique. Thermal gradient across the crack decreased very much due to thermal resistance of contact surface in the crack. Heat diffusion flow passing through the discontinuity was visualized in temperature by infrared camera to find and locate the crack. A fatigue crack specimen(SM-45C), which was prepared according to KS specification and notched in its center to initiate fatigue crack from the notch tip, was heated by halogen lamp at the end of one side to generate a heat diffusion flow in lateral direction. A abrupt jump in temperature across the fatigue crack was observed in thermographic image, by which the crack could be located and sized from temperature distribution.

  17. Thermographic Inspection of Fatigue Crack by Using Contact Thermal Resistance

    International Nuclear Information System (INIS)

    Yang, Seung Yong; Kim, No Hyu

    2013-01-01

    Fatigue crack was detected from a temperature change around surface crack using the thermographic technique. Thermal gradient across the crack decreased very much due to thermal resistance of contact surface in the crack. Heat diffusion flow passing through the discontinuity was visualized in temperature by infrared camera to find and locate the crack. A fatigue crack specimen(SM-45C), which was prepared according to KS specification and notched in its center to initiate fatigue crack from the notch tip, was heated by halogen lamp at the end of one side to generate a heat diffusion flow in lateral direction. A abrupt jump in temperature across the fatigue crack was observed in thermographic image, by which the crack could be located and sized from temperature distribution.

  18. Fatigue crack Behaviour in a High Strength Tool Steel

    DEFF Research Database (Denmark)

    Højerslev, Christian; Carstensen, Jesper V.; Brøndsted, Povl

    2002-01-01

    The influence of microstructure on fatigue crack initiation and crack growth of a hardened and tempered high speed steel was investigated. The evolution of fatigue cracks was followed in four point bending at room temperature. It was found that a carbide damage zone exists above a threshold load...... value of maximally 80% of the yield strength of the steel. The size of this carbide damage zone increases with increasing load amplitude, and the zone is apparently associated with crack nucleation. On fatigue crack propagation plastic deformation of the matrix occurs in a radius of approximately 4...... microns in front of the fatigue crack tip, which is comparable with the relevant mean free carbide spacing....

  19. Crack growth of throughwall flaw in Alloy 600 tube during leak testing

    International Nuclear Information System (INIS)

    Bahn, Chi Bum; Majumdar, Saurin

    2015-01-01

    Graphical abstract: - Highlights: • A series of leak testing was conducted at a constant pressure and room temperature. • The time-dependent increase in the leak rate was observed. • The fractography revealed slip offsets and crystallographic facets. • Time-dependent plasticity at the crack tip caused the slip offsets. • Fatigue by jet/structure interaction caused the crystallographic facets. - Abstract: We examined the issue of whether crack growth in a full thickness material can occur in a leaking crack. A series of leak tests was conducted at a room temperature and constant pressure (17.3 MPa) with Alloy 600 tube specimens containing a tight rectangular throughwall axial fatigue crack. To exclude a potential pulsation effect by a high pressure pump, the test water was pressurized by using high pressure nitrogen gas. Fractography showed that crack growth in the full thickness material can occur in the leaking crack by two mechanisms: time-dependent plasticity at the crack tip and fatigue induced by jet/structure interaction. The threshold leak rate at which the jet/structure interaction was triggered was between 1.3 and 3.3 L/min for the specific heat of the Alloy 600 tube tested

  20. Effect of interaction of embedded crack and free surface on remaining fatigue life

    Directory of Open Access Journals (Sweden)

    Genshichiro Katsumata

    2016-12-01

    Full Text Available Embedded crack located near free surface of a component interacts with the free surface. When the distance between the free surface and the embedded crack is short, stress at the crack tip ligament is higher than that at the other area of the cracked section. It can be easily expected that fatigue crack growth is fast, when the embedded crack locates near the free surface. To avoid catastrophic failures caused by fast fatigue crack growth at the crack tip ligament, fitness-for-service (FFS codes provide crack-to-surface proximity rules. The proximity rules are used to determine whether the cracks should be treated as embedded cracks as-is, or transformed to surface cracks. Although the concepts of the proximity rules are the same, the specific criteria and the rules to transform embedded cracks into surface cracks differ amongst FFS codes. This paper focuses on the interaction between an embedded crack and a free surface of a component as well as on its effects on the remaining fatigue lives of embedded cracks using the proximity rules provided by the FFS codes. It is shown that the remaining fatigue lives for the embedded cracks strongly depend on the crack aspect ratio and location from the component free surface. In addition, it can be said that the proximity criteria defined by the API and RSE-M codes give overly conservative remaining lives. On the contrary, the WES and AME codes always give long remaining lives and non-conservative estimations. When the crack aspect ratio is small, ASME code gives non-conservative estimation.

  1. Discrete fracture in quasi-brittle materials under compressive and tensile stress states

    CSIR Research Space (South Africa)

    Klerck, PA

    2004-01-01

    Full Text Available A method for modelling discrete fracture in geomaterials under tensile and compressive stress fields has been developed based on a Mohr-Coulomb failure surface in compression and three independent anisotropic rotating crack models in tension...

  2. Molecular dynamics simulation of mode-I-crack propagation and dislocation generation processes in α-Fe

    International Nuclear Information System (INIS)

    Wang Jianwei; Lu Guocai; Shang Xinchun

    2011-01-01

    The process of I-mode crack propagations in α-Fe for uniaxial tension experiments are simulated by molecular dynamics (MD) methods. The formation process of dislocation and fracture mechanisms in the crack growing under various temperatures were studied. The results show that the crack propagation is a process of successive emission of dislocation. The dislocation-free zone and the stacking faults were initially formed at crack tip. When the stress K I increased into 0. 566 MPam 1/2 , one layer of atoms near crack tip would be separated into two layers which produced a dislocation. The first dislocation was emitted when stress K I reached 0.669 MPam 1/2 . With the temperature increasing, the critical stress intensity factor decreased gradually and the dislocation emission correspondingly became faster as well. (authors)

  3. Chloride Ingress in Concrete Cracks under Cyclic Loading

    DEFF Research Database (Denmark)

    Küter, André; Geiker, Mette Rica; Olesen, John Forbes

    2005-01-01

    was similar for both sets and the maximum crack width was kept constant throughout the exposure period by means of precracking and an external prestressed reinforcement. Chloride profiles after 40 days revealed a considerable increase in ingress towards the crack tip in contrast to data from the literature....... Preliminary investigations have been undertaken to quantify the effect of dynamic load application on the chloride ingress into concrete cracks. Specimens were designed allowing ingress of a chloride solution into a single crack of a saturated unreinforced mortar beam. One set of specimens was subjected...... to a load frequency of ten applications per minute and a second set to one application per hour simulating static cracks, however limiting the ingress hampering effects of autogenous healing and a possible dense precipitation on the crack faces. The averaged chloride exposure interval of the crack faces...

  4. Crack embryo formation before crack initiation and growth in high temperature water

    International Nuclear Information System (INIS)

    Arioka, Koji; Yamada, Takuyo; Terachi, Takumi; Miyamoto, Tomoki

    2008-01-01

    Crack growth measurements were performed in high temperature water and in air to examine the role of creep on IGSCC growth using cold rolled non-sensitized Type316(UNS S31600), TT690 alloy, MA600 alloy, and Carbon steel (STPT42). In addition, crack initiation tests were performed also in high temperature water and in air using specially designed CT specimen. The obtained major results are as follows: (1) TT690 did crack in intergranularly in hydrogenated high temperature water if material is cold worked in heavily. (2) Cold worked carbon steel also cracked in intergranularly in dearated high temperature water. (3) Intergranular crack growth was recognized on cold worked 316, TT690, MA600, and carbon steel even in air which might be crack embryo of IGSCC. (4) Simple Arrhenius type temperature dependence was observed on IGSCC in high temperature water and creep crack growth in air. This suggested that intergranular crack growth rate was determined by some thermal activated reaction. (5) Vacancy condensation was recognized at just ahead of the crack tips of IGSCC and creep crack of cold worked steel. This showed that IGSCC and creep crack growth was controlled by same mechanism. (6) Clear evidence of vacancies condensation was recognized at just beneath the surface before crack initiation. This proved that crack did initiate as the result of diffusion of vacancies in the solid. And the incubation time seems to be controlled by the required time for the condensation of vacancies to the stress concentrated zone. (7) Diffusion of subsituational atoms was also driven by stress gradient. This is the important knowledge to evaluate the SCC initiation after long term operation in LWR's. Based on the observed results, IGSCC initiation and growth mechanism were proposed considering the diffusion process of cold worked induced vacancies. (author)

  5. On-line monitoring of crack propagation by the acoustic emission method

    International Nuclear Information System (INIS)

    Chung, M.K.; Park, D.Y.; Choi, S.P.; Kim, H.J.; Moon, Y.S.; Shon, G.H.; Kim, T.S.

    1983-01-01

    Stress corrosion cracking experiment was carried out to find out the acoustic emission (AE) characteristics of Al 5052 and SCM-4 steel in 3.5% NaCl-H 2 O solution. In advance of the above test, some mechanical properties of these materials were investigated through the tensile test with standard round tensile specimens and WOL specimens which were originaly designed for the stress corrosion cracking experiment. About 5mm fatigue crack was given to WOL specimen by MTS system. We measure the relationship between stress intensity factor and AE count rate under various temperature of the solution such as 15degC, 33 degC, 45 degC and compared their AE characteristics of two materials. While AE count rate of Al 5052 is even higher than that of SCM-4 steel by one order or two, velocity of corrosion crack is much slow. The AE generation rate of SCM-4 steel is discrete and about 0.25 mm corrosion growth corresponds to 10 3 counts. Also location of defects in linear specimen was studied. (Author)

  6. Exploring How Weathering Related Stresses and Subcritical Crack Growth May Influence the Size of Sediment Produced From Different Rock Types.

    Science.gov (United States)

    Eppes, M. C.; Hallet, B.; Hancock, G. S.; Mackenzie-Helnwein, P.; Keanini, R.

    2016-12-01

    The formation and diminution of rock debris, sediment and soil at and near Earth's surface is driven in large part by in situ, non-transport related, rock cracking. Given the relatively low magnitude stresses that arise in surface and near-surface settings, this production and diminution of granular material is likely strongly influenced and/or driven by subcritical crack growth (Eppes et al., 2016), cracking that occurs under stress loading conditions much lower than a rock's strength as typically measured in the laboratory under rapid loading. Despite a relatively sound understanding of subcritical crack growth through engineering and geophysical studies, its geomorphic and sedimentologic implications have only been minimally explored. Here, based on existing studies, we formulate several hypotheses to predict how weathering-induced stresses combined with the subcritical crack growth properties of rock may influence sediment size distribution. For example, subcritical crack growth velocity (v) can be described by v = CKIn where KI is the mode I (simple opening mode) stress intensity factor, a function of tensile stress at the crack tip and crack length; C is a rock- and environment-dependent constant; and n is material constant, the subcritical crack growth index. Fracture length and spacing in rock is strongly dependent on n, where higher n values result in fewer, more distally spaced cracks (e.g. Olsen, 1993). Thus, coarser sediment might be expected from rocks with higher n values. Weathering-related stresses such as thermal stresses and mineral hydration, however, can disproportionally stress boundaries between minerals with contrasting thermal or chemical properties and orientation, resulting in granular disintegration. Thus, rocks with properties favorable to inducing these stresses might produce sediment whose size is reflective of its constituent grains. We begin to test these hypotheses through a detailed examination of crack and rock characteristics in

  7. Development of a computer code 'CRACK' for elastic and elastoplastic fracture mechanics analysis of 2-D structures by finite element technique

    International Nuclear Information System (INIS)

    Dutta, B.K.; Kakodkar, A.; Maiti, S.K.

    1986-01-01

    The fracture mechanics analysis of nuclear components is required to ensure prevention of sudden failure due to dynamic loadings. The linear elastic analysis near to a crack tip shows presence of stress singularity at the crack tip. The simulation of this singularity in numerical methods enhance covergence capability. In finite element technique this can be achieved by placing mid nodes of 8 noded or 6 noded isoparametric elements, at one fourth ditance from crack tip. Present report details this characteristic of finite element, implementation of this element in a code 'CRACK', implementation of J-integral to compute stress intensity factor and solution of number of cases for elastic and elastoplastic fracture mechanics analysis. 6 refs., 6 figures. (author)

  8. Direct assessment of tensile stress-crack opening behavior of Strain Hardening Cementitious Composites (SHCC)

    DEFF Research Database (Denmark)

    Pereira, Eduardo B.; Fischer, Gregor; Barros, Joaquim A.O.

    2012-01-01

    -deformation behavior of these materials is therefore of great importance and is frequently carried out by characterizing the material tensile stress–strain behavior. In this paper an alternative approach to evaluate the tensile performance of SHCC is investigated. The behavior of the material in tension is studied...

  9. Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history

    International Nuclear Information System (INIS)

    Stout, R.B.

    2001-01-01

    An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)

  10. Hydride precipitation crack propagation in zircaloy cladding during a decreasing temperature history

    Energy Technology Data Exchange (ETDEWEB)

    Stout, R.B. [California Univ., Livermore, CA (United States). Lawrence Livermore National Lab

    2001-07-01

    An assessment of safety, design, and cost tradeoff issues for short (ten to fifty years) and longer (fifty to hundreds of years) interim dry storage of spent nuclear fuel in Zircaloy rods shall address potential failures of the Zircaloy cladding caused by the precipitation response of zirconium hydride platelets. To perform such assessment analyses rigorously and conservatively will be necessarily complex and difficult. For Zircaloy cladding, a model for zirconium hydride induced crack propagation velocity was developed for a decreasing temperature field and for hydrogen, temperature, and stress dependent diffusive transport of hydrogen to a generic hydride platelet at a crack tip. The development of the quasi-steady model is based on extensions of existing models for hydride precipitation kinetics for an isolated hydride platelet at a crack tip. An instability analysis model of hydride-crack growth was developed using existing concepts in a kinematic equation for crack propagation at a constant thermodynamic crack potential subject to brittle fracture conditions. At the time an instability is initiated, the crack propagation is no longer limited by hydride growth rate kinetics, but is then limited by stress rates. The model for slow hydride-crack growth will be further evaluated using existing available data. (authors)

  11. Nonlinear crack mechanics

    International Nuclear Information System (INIS)

    Khoroshun, L.P.

    1995-01-01

    The characteristic features of the deformation and failure of actual materials in the vicinity of a crack tip are due to their physical nonlinearity in the stress-concentration zone, which is a result of plasticity, microfailure, or a nonlinear dependence of the interatomic forces on the distance. Therefore, adequate models of the failure mechanics must be nonlinear, in principle, although linear failure mechanics is applicable if the zone of nonlinear deformation is small in comparison with the crack length. Models of crack mechanics are based on analytical solutions of the problem of the stress-strain state in the vicinity of the crack. On account of the complexity of the problem, nonlinear models are bason on approximate schematic solutions. In the Leonov-Panasyuk-Dugdale nonlinear model, one of the best known, the actual two-dimensional plastic zone (the nonlinearity zone) is replaced by a narrow one-dimensional zone, which is then modeled by extending the crack with a specified normal load equal to the yield point. The condition of finite stress is applied here, and hence the length of the plastic zone is determined. As a result of this approximation, the displacement in the plastic zone at the abscissa is nonzero

  12. Interface fatigue crack propagation in sandwich X-joints – Part I: Experiments

    DEFF Research Database (Denmark)

    Moslemian, Ramin; Berggreen, Christian

    2013-01-01

    Correlation technique was used to locate the crack tip and monitor the crack growth. For the specimens with H45 core, unstable crack growth took place initially. Following the unstable propagation, the crack propagated in the core underneath the resin-rich cell layer approaching the interface. However......, the crack did not kink into the interface. For the specimens with H100 core, the crack propagated initially in the core and then returned into the interface and continued to propagate in the interface. For the specimens with H250 core, the crack initially propagated in the core and then kinked...

  13. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    International Nuclear Information System (INIS)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong; Lee, Changhee; Woo, WanChuck; Park, Sunhong

    2015-01-01

    Highlights: • Major problem, clad cracking in laser cladding process, was researched. • Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. • Relationship between the residual stress and crack initiation was showed clearly. • Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. • Initiation sites of generating clad cracks were specifically studied in MMC coatings. - Abstract: Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures

  14. Residual stress and crack initiation in laser clad composite layer with Co-based alloy and WC + NiCr

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Changmin; Park, Hyungkwon; Yoo, Jaehong [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Lee, Changhee, E-mail: chlee@hanyang.ac.kr [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Woo, WanChuck [Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon 305-353 (Korea, Republic of); Park, Sunhong [Research Institute of Industrial Science & Technology, Hyo-ja-dong, Po-Hang, Kyoung-buk, San 32 (Korea, Republic of)

    2015-08-01

    Highlights: • Major problem, clad cracking in laser cladding process, was researched. • Residual stress measurements were performed quantitatively by neutron diffraction method along the surface of specimens. • Relationship between the residual stress and crack initiation was showed clearly. • Ceramic particle effect in the metal matrix was showed from the results of residual stress measurements. • Initiation sites of generating clad cracks were specifically studied in MMC coatings. - Abstract: Although laser cladding process has been widely used to improve the wear and corrosion resistance, there are unwanted cracking issues during and/or after laser cladding. This study investigates the tendency of Co-based WC + NiCr composite layers to cracking during the laser cladding process. Residual stress distributions of the specimen are measured using neutron diffraction and elucidate the correlation between the residual stress and the cracking in three types of cylindrical specimens; (i) no cladding substrate only, (ii) cladding with 100% stellite#6, and (iii) cladding with 55% stellite#6 and 45% technolase40s. The microstructure of the clad layer was composed of Co-based dendrite and brittle eutectic phases at the dendritic boundaries. And WC particles were distributed on the matrix forming intermediate composition region by partial melting of the surface of particles. The overlaid specimen exhibited tensile residual stress, which was accumulated through the beads due to contraction of the coating layer generated by rapid solidification, while the non-clad specimen showed compressive. Also, the specimen overlaid with 55 wt% stellite#6 and 45 wt% technolase40s showed a tensile stress higher than the specimen overlaid with 100% stellite#6 possibly, due to the difference between thermal expansion coefficients of the matrix and WC particles. Such tensile stresses can be potential driving force to provide an easy crack path ways for large brittle fractures

  15. Influence of scan strategy and molten pool configuration on microstructures and tensile properties of selective laser melting additive manufactured aluminum based parts

    Science.gov (United States)

    Dai, Donghua; Gu, Dongdong; Zhang, Han; Xiong, Jiapeng; Ma, Chenglong; Hong, Chen; Poprawe, Reinhart

    2018-02-01

    Selective laser melting additive manufacturing of the AlSi12 material parts through the re-melting of the previously solidified layer using the continuous two layers 90° rotate scan strategy was conducted. The influence of the re-melting behavior and scan strategy on the formation of the ;track-track; and ;layer-layer; molten pool boundaries (MPBs), dimensional accuracy, microstructure feature, tensile properties, microscopic sliding behavior and the fracture mechanism as loaded a tensile force has been studied. It showed that the defects, such as the part distortion, delamination and cracks, were significantly eliminated with the deformation rate less than 1%. The microstructure of a homogeneous distribution of the Si phase, no apparent grain orientation on both sides of the MPBs, was produced in the as-fabricated part, promoting the efficient transition of the load stress. Cracks preferentially initiate at the ;track-track; MPBs when the tensile stress increases to a certain value, resulting in the formation of the cleavage steps along the tensile loading direction. The cracks propagate along the ;layer-layer; MPBs, generating the fine dimples. The mechanical behavior of the SLM-processed AlSi12 parts can be significantly enhanced with the ultimate tensile strength, yield strength and elongation of 476.3 MPa, 315.5 MPa and 6.7%, respectively.

  16. Main factors causing intergranular and quasi-cleavage fractures at hydrogen-induced cracking in tempered martensitic steels

    Science.gov (United States)

    Kurokawa, Ami; Doshida, Tomoki; Hagihara, Yukito; Suzuki, Hiroshi; Takai, Kenichi

    2018-05-01

    Though intergranular (IG) and quasi-cleavage (QC) fractures have been widely recognized as typical fracture modes of the hydrogen-induced cracking in high-strength steels, the main factor has been unclarified yet. In the present study, the hydrogen content dependence on the main factor causing hydrogen-induced cracking has been examined through the fracture mode transition from QC to IG at the crack initiation site in the tempered martensitic steels. Two kinds of tempered martensitic steels were prepared to change the cohesive force due to the different precipitation states of Fe3C on the prior γ grain boundaries. A high amount of Si (H-Si) steel has a small amount of Fe3C on the prior austenite grain boundaries. Whereas, a low amount of Si (L-Si) steel has a large amount of Fe3C sheets on the grain boundaries. The fracture modes and initiations were observed using FE-SEM (Field Emission-Scanning Electron Microscope). The crack initiation sites of the H-Si steel were QC fracture at the notch tip under various hydrogen contents. While the crack initiation of the L-Si steel change from QC fracture at the notch tip to QC and IG fractures from approximately 10 µm ahead of the notch tip as increasing in hydrogen content. For L-Si steels, two possibilities are considered that the QC or IG fracture occurred firstly, or the QC and IG fractures occurred simultaneously. Furthermore, the principal stress and equivalent plastic strain distributions near the notch tip were calculated with FEM (Finite Element Method) analysis. The plastic strain was the maximum at the notch tip and the principle stress was the maximum at approximately 10 µm from the notch tip. The position of the initiation of QC and IG fracture observed using FE-SEM corresponds to the position of maximum strain and stress obtained with FEM, respectively. These findings indicate that the main factors causing hydrogen-induced cracking are different between QC and IG fractures.

  17. Prediction of crack propagation and arrest in X100 natural gas transmission pipelines with a strain rate dependent damage model (SRDD). Part 2: Large scale pipe models with gas depressurisation

    International Nuclear Information System (INIS)

    Oikonomidis, F.; Shterenlikht, A.; Truman, C.E.

    2014-01-01

    Part 1 of this paper described a specimen for the measurement of high strain rate flow and fracture properties of pipe material and for tuning a strain rate dependent damage model (SRDD). In part 2 the tuned SRDD model is used for the simulation of axial crack propagation and arrest in X100 natural gas pipelines. Linear pressure drop model was adopted behind the crack tip, and an exponential gas depressurisation model was used ahead of the crack tip. The model correctly predicted the crack initiation (burst) pressure, the crack speed and the crack arrest length. Strain rates between 1000 s −1 and 3000 s −1 immediately ahead of the crack tip are predicted, giving a strong indication that a strain rate material model is required for the structural integrity assessment of the natural gas pipelines. The models predict the stress triaxiality of about 0.65 for at least 1 m ahead of the crack tip, gradually dropping to 0.5 at distances of about 5–7 m ahead of the crack tip. Finally, the models predicted a linear drop in crack tip opening angle (CTOA) from about 11−12° at the onset of crack propagation down to 7−8° at crack arrest. Only the lower of these values agree with those reported in the literature for quasi-static measurements. This discrepancy might indicate substantial strain rate dependence in CTOA. - Highlights: • Finite element simulations of 3 burst tests of X100 pipes are detailed. • Strain rate dependent damage model, tuned on small scale X100 samples, was used. • The models correctly predict burst pressure, crack speed and crack arrest length. • The model predicts a crack length dependent critical CTOA. • The strain rate dependent damage model is verified as mesh independent

  18. Evaluation method for ductile crack propagation in pre-strained plates; Yohizumizai no ensei kiretsu denpa hyokaho

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Y.; Murakawa, H. [Osaka Univ., Osaka (Japan). Welding Research Inst.; Tanigawa, M. [Hitachi Zosen Corp., Osaka (Japan)

    1996-12-31

    In order to investigate an effect of the plastic deformation, which was generated on ship side outer platings subjected to collision load before crack initiation, on the crack propagation behavior, crack propagation experiments using pre-strained specimens and simulation analysis by means of FEM method were carried out, to discuss about the practical simulation analysis method. As a result of the crack propagation experiments using pre-strained center notched plate specimens, a phenomenon where the crack is apt to propagate due to the pre-strains was confirmed, and measured data of crack tip opening angles were obtained. A method was proposed, in which the critical crack tip opening angle values are corrected by considering the difference between the crack shapes obtained from the FEM analysis model and actually measured, and its effectiveness was confirmed. The finite element size effect was also examined. A method using an equivalent plastic strain as the crack propagation condition was shown to determine the relationship between the element size and the critical value of equivalent plastic strain. 5 refs., 21 figs., 4 tabs.

  19. Evaluation method for ductile crack propagation in pre-strained plates; Yohizumizai no ensei kiretsu denpa hyokaho

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Y; Murakawa, H [Osaka Univ., Osaka (Japan). Welding Research Inst.; Tanigawa, M [Hitachi Zosen Corp., Osaka (Japan)

    1997-12-31

    In order to investigate an effect of the plastic deformation, which was generated on ship side outer platings subjected to collision load before crack initiation, on the crack propagation behavior, crack propagation experiments using pre-strained specimens and simulation analysis by means of FEM method were carried out, to discuss about the practical simulation analysis method. As a result of the crack propagation experiments using pre-strained center notched plate specimens, a phenomenon where the crack is apt to propagate due to the pre-strains was confirmed, and measured data of crack tip opening angles were obtained. A method was proposed, in which the critical crack tip opening angle values are corrected by considering the difference between the crack shapes obtained from the FEM analysis model and actually measured, and its effectiveness was confirmed. The finite element size effect was also examined. A method using an equivalent plastic strain as the crack propagation condition was shown to determine the relationship between the element size and the critical value of equivalent plastic strain. 5 refs., 21 figs., 4 tabs.

  20. Modelling the tearing crack growth in a ductile ferritic steel using X-FEM elements

    International Nuclear Information System (INIS)

    Simatos, A.; Prabel, B.; Marie, S.; Nedelec, M.; Combescure, A.

    2012-01-01

    Extended Finite Element Method (X-FEM) is used to model a cracked structure without meshing explicitly the crack. Indeed, the crack is represented by a discontinuity of the displacement field through additional degrees of freedom using Heaviside type function or derived from the Irwin's singular fields. Initially, the stress integration in the XFEM framework supposed to divide the cut elements into sub-triangles that are conform to the crack. This was motivated in order to integrate the behaviour accurately on both sides of the crack in particular at proximity of the crack tip where singular enrichments are present. This strategy induces field projections from the usual Gauss point configuration to a variable new one that depends on the crack position in the element. For ductile fracture modelization, this approach is not applicable, because in presence of large scale yield, the projection of internal variable fields is not conservative, in particular at proximity of the crack tip. In order to circumvent this problem, a new integration strategy was proposed by B. Prabel. It consists in using 64 Gauss points that are placed without regards to the crack position. This simple integration scheme permits to take implicitly into account the crack position and the fields in the element in an accurate and consistent way. This strategy was used in problem calculation for which the plastic radius remained small. It allowed introducing the over integrated elements in the probable propagation zone, just before plastification. In the case of ductile tearing, the plasticity is not confined near the crack tip and an improvement of the proposed strategy is made. This is then used to model large ductile crack growth in a ductile ferritic steel. To validate the predictions, the modelization is compared to a second F.E. calculation using the node release technique for the crack propagation. It is then shown that the two predictions are strictly equivalents. (authors)

  1. Characterization and modeling of tensile behavior of ceramic woven fabric composites

    Science.gov (United States)

    Kuo, Wen-Shyong; Chen, Wennei Y.; Parvizi-Majidi, Azar; Chou, Tsu-Wei

    1991-01-01

    This paper examines the tensile behavior of SiC/SiC fabric composites. In the characterization effort, the stress-strain relation and damage evolution are studied with a series of loading and unloading tensile test experiments. The stress-strain relation is linear in response to the initial loading and becomes nonlinear when loading exceeds the proportional limit. Transverse cracking has been observed to be a dominant damage mode governing the nonlinear deformation. The damage is initiated at the inter-tow pores where fiber yarns cross over each other. In the modeling work, the analysis is based upon a fiber bundle model, in which fiber undulation in the warp and fill directions and gaps among fiber yarns have been taken into account. Two limiting cases of fabric stacking arrangements are studied. Closed form solutions are obtained for the composite stiffness and Poisson's ratio. Transverse cracking in the composite is discussed by applying a constant failure strain criterion.

  2. Specific features of corrosion processes in a crack tip in chloride solution

    International Nuclear Information System (INIS)

    Kurov, O.V.; Vasilenko, I.I.

    1981-01-01

    Electrode potentials of metal and pH solution are measured by means of microelectrodes on structural materials-45 and 12Kh18N10T steels, AT3 titanium alloy and D16 aluminium alloy in the vertex of corrosion crack formed during corrosion cracking in 3% NaCl solution. Metal corrosion is shown to be followed by hydrogen liberation on all the investigated materials at corrosion potentials. The effects of chemical composition of alloys as well as external polarization on the solution pH in the crack vertex are determined

  3. Photoelastic Analysis of Cracked Thick Walled Cylinders

    Science.gov (United States)

    Pastramă, Ştefan Dan

    2017-12-01

    In this paper, the experimental determination of the stress intensity factor in thick walled cylinders subject to uniform internal pressure and having longitudinal non-penetrating cracks is presented. Photoelastic measurements were used together with the expressions of the stress field near the crack tip for Mode I crack extension and a specific methodology for stress intensity factor determination. Two types of longitudinal cracks - internal and external - were considered. Four plane models were manufactured and analyzed in a plane polariscope at different values of the applied internal pressure. The values of the normalized stress intensity factor were calculated and the results were compared to those reported by other authors. A good accuracy was noticed, showing the reliability of the experimental procedure.

  4. Application of acoustic emission to hydride cracking

    International Nuclear Information System (INIS)

    Sagat, S.; Ambler, J.F.R.; Coleman, C.E.

    1986-07-01

    Acoustic emission has been used for over a decade to study delayed hydride cracking (DHC) in zirconium alloys. At first acoustic emission was used primarily to detect the onset of DHC. This was possible because DHC was accompanied by very little plastic deformation of the material and furthermore the amplitudes of the acoustic pulses produced during cracking of the brittle hydride phase were much larger than those from dislocation motion and twinning. Acoustic emission was also used for measuring crack growth when it was found that for a suitable amplitude threshold, the total number of acoustic emission counts was linearly related to the cracked area. Once the proportionality constant was established, the acoustic counts could be converted to the crack length. Now the proportionality between the count rate and the crack growth rate is used to provide feedback between the crack length and the applied load, using computer technology. In such a system, the stress at the crack tip can be maintained constant during the test by adjusting the applied load as the crack progresses, or it can be changed in a predetermined manner, for example, to measure the threshold stress for cracking

  5. On the path of a crack near a graded interface under large scale yielding

    DEFF Research Database (Denmark)

    Rashid, M. M.; Tvergaard, Viggo

    2003-01-01

    The trajectory of a crack lying parallel to a thin graded layer between two plastically dissimilar materials is studied using the exclusion region (ER) theory of fracture. The ER theory is a theoretical framework for surface separation within which a broad range of fracture phenomenologies can...... be represented. In the present study, the direction of crack advance is determined by maximizing the resolved normal-opening force on the near-tip region, whereas separation itself is governed by the intensity of plastic deformation near the tip. A computational study was undertaken using the ER theory....... The special-purpose finite element analysis platform accommodates arbitrary-and a priori unknown-crack trajectories. The model problem considered herein involves two plastically dissimilar, but elastically identical, materials joined by a thin, graded interface layer. The initial crack lies parallel...

  6. Investigation of the microcrack evolution in a Ti-based bulk metallic glass matrix composite

    Directory of Open Access Journals (Sweden)

    Yongsheng Wang

    2014-04-01

    Full Text Available The initiation and evolution behavior of the shear-bands and microcracks in a Ti-based metallic-glass–matrix composite (MGMC were investigated by using an in-situ tensile test under transmission electron microscopy (TEM. It was found that the plastic deformation of the Ti-based MGMC related with the generation of the plastic deformation zone in crystalline and shear deformation zone in glass phase near the crack tip. The dendrites can suppress the propagation of the shear band effectively. Before the rapid propagation of cracks, the extending of plastic deformation zone and shear deformation zone ahead of crack tip is the main pattern in the composite.

  7. In situ investigation of the tensile deformation of laser welded Ti{sub 2}AlNb joints

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Kezhao; Ni, Longchang; Lei, Zhenglong, E-mail: leizhenglong@hit.edu.cn; Chen, Yanbin; Hu, Xue

    2017-01-15

    The tensile deformation behavior of laser welded Ti{sub 2}AlNb joints was investigated using in situ analysis methods. The fracture mode of the single-B2-phase fusion zone was quasi-cleavage at room temperature and intergranular at 650 °C, while that of base metal was microvoid coalescence at both room temperature and 650 °C. Tensile deformation at room temperature was observed using in situ SEM tensile testing. In base metal, microcracks nucleated and propagated mainly within the O phase or along O/B2 phase boundaries. While both the cross- and multi-slips were found in the single-B2-phase fusion zone, a confocal laser scanning microscopy was used to observe the crack initiation and propagation process in situ at 650 °C. Cracks mainly formed along the B2/O phase boundaries in base metal, along the fragile grain boundaries of B2 phase in the fusion zone. The thermal simulation experiment and following TEM analysis indicated that the precipitation of continuous O-phase films along the B2 grain boundaries resulted in the high temperature brittleness of laser welded Ti{sub 2}AlNb joints. - Highlights: •Cracks formed within O phase or along B2/O boundaries in the base metal. •Cross- and multi-slips relieved stress in the fusion zone at room temperature. •Cracks mainly formed along the B2/O boundaries at 650 °C. •In the fusion zone, intergranular cracks were in situ observed at 650 °C. •O-phase films along B2 grain boundaries caused the high temperature brittleness.

  8. Elastic crack-tip stress field in a semi-strip

    Directory of Open Access Journals (Sweden)

    Victor Reut

    2018-04-01

    Full Text Available In this article the plain elasticity problem for a semi-strip with a transverse crack is investigated in the different cases of the boundary conditions at the semi-strips end. Unlike many works dedicated to this subject, the fixed singularities in the singular integral equation�s kernel are considered. The integral transformations� method is applied by the generalized scheme to reduce the initial problem to a one-dimensional problem. The one-dimensional problem is formulated as the vector boundary value problem which is solved with the help of matrix differential calculations and Green�s matrix apparatus. The solution of the problem is reduced to the solving of the system of three singular integral equations. Depending on the conditions given on the short edge of the semi-strip, the constructed singular integral equation can have one, or two fixed singularities. A special method is applied to solve this equation in regard of the singularities existence. Hence the system of the singular integral equations (SSIE is solved with the help of the generalized method. The stress intensity factors (SIF are investigated for different lengths of crack. The novelty of this work is in the application of new approach allowing the consideration of the fixed singularities in the problem about a transverse crack in the elastic semi-strip. The comparison of the numerical results� accuracy during the usage of the different approaches to the solving of SSIE is worked out

  9. Delayed hydrogen cracking of zirconium alloy pressure tubes

    International Nuclear Information System (INIS)

    Jackman, A.H.; Dunn, J.T.

    1976-10-01

    After several years of almost continuous service, Pickering Units 3 and 4 have both experienced long outages to replace cracked pressure tubes. This report summarizes the status of the investigation into the cause of the cracks as of May 1976. The basic cause of the cracking was the presence of very high residual tensile stresses in the pressure tubes due to improper rolling procedures. These residual stresses are being reduced to acceptable levels by local stress relieving techniques at Bruce G.S. and in future reactors improvements in rolling procedures and changes in pressure tube specifications will prevent a recurrence of this problem. (author)

  10. Effect of residual stresses on interface crack growth by void expansion mechanism

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2006-01-01

    Crack growth along an interface between two adjacent elastic-plastic materials in a layered solid is analysed, using special interface elements to represent the fracture process ahead of the crack-tip. These interface elements account for ductile failure by the nucleation and growth of voids to c....... The results show that the value of the T-stress component in the softer material adjacent to the interface crack plays the dominant role, such that a negative value of this stress component gives a significant increase of the interface fracture toughness.......Crack growth along an interface between two adjacent elastic-plastic materials in a layered solid is analysed, using special interface elements to represent the fracture process ahead of the crack-tip. These interface elements account for ductile failure by the nucleation and growth of voids...... to coalescence. In these elements the stress components normal to the interface and the shear stresses are given by equilibrium with the surrounding material, and the stress component tangential to the interface is determined by the requirement of compatibility with the surrounding material in the tangential...

  11. Thermomechanical Behavior of Amorphous Polymers During High-Speed Crack Propagation

    National Research Council Canada - National Science Library

    Bjerke, Todd

    2002-01-01

    .... Experiments were performed using two materials, nominally brittle polymethyl methacrylate and nominally ductile polycarbonate to quantify crack tip heating and identify dominant dissipative mechanisms...

  12. The effect of potential on the high-temperature fatigue crack growth response of low alloy steels: Part II, electrochemical results

    International Nuclear Information System (INIS)

    Moshier, W.C.; James, L.A.

    1997-01-01

    Environmentally assisted cracking (EAC) in low alloy steels was found to be dependent on externally applied potential in low sulfur steels in high temperature water. EAC could be turned on when the specimen was polarized anodically above a critical potential. However, hydrogen (H) additions inhibited the ability of potential to affect EAC. The behavior was related to formation of H ions during H oxidation at the crack mouth. A mechanism based on formation of H sulfide at the crack tip and H ions at the crack mouth is presented to describe the process by which sulfides and H ions affect the critical sulfide concentration at the crack tip

  13. On crack interaction effects of in-plane surface cracks using elastic and elastic-plastic finite element analyses

    International Nuclear Information System (INIS)

    Kim, Jong Min; Huh, Nam Su

    2010-01-01

    The crack-tip stress fields and fracture mechanics assessment parameters for a surface crack, such as the elastic stress intensity factor or the elastic-plastic J-integral, can be affected significantly by the adjacent cracks. Such a crack interaction effect due to multiple cracks can alter the fracture mechanics assessment parameters significantly. There are many factors to be considered, for instance the relative distance between adjacent cracks, the crack shape, and the loading condition, to quantify the crack interaction effect on the fracture mechanics assessment parameters. Thus, the current assessment codes on crack interaction effects (crack combination rules), including ASME Sec. XI, BS7910, British Energy R6 and API 579-1/ASME FFS-1, provide different rules for combining multiple surface cracks into a single surface crack. The present paper investigates crack interaction effects by evaluating the elastic stress intensity factor and the elastic-plastic J-integral of adjacent in-plane surface cracks in a plate through detailed 3-dimensional elastic and elastic-plastic finite element analyses. The effects on the fracture mechanics assessment parameters of the geometric parameters, the relative distance between two cracks, and the crack shape are investigated systematically. As for the loading condition, an axial tension is considered. Based on the finite element results, the acceptability of the crack combination rules provided in the existing guidance was investigated, and the relevant recommendations on a crack interaction for in-plane surface cracks are discussed. The present results can be used to develop more concrete guidance on crack interaction effects for crack shape characterization to evaluate the integrity of defective components

  14. A theoretical model of semi-elliptic surface crack growth

    Directory of Open Access Journals (Sweden)

    Shi Kaikai

    2014-06-01

    Full Text Available A theoretical model of semi-elliptic surface crack growth based on the low cycle strain damage accumulation near the crack tip along the cracking direction and the Newman–Raju formula is developed. The crack is regarded as a sharp notch with a small curvature radius and the process zone is assumed to be the size of cyclic plastic zone. The modified Hutchinson, Rice and Rosengren (HRR formulations are used in the presented study. Assuming that the shape of surface crack front is controlled by two critical points: the deepest point and the surface point. The theoretical model is applied to semi-elliptic surface cracked Al 7075-T6 alloy plate under cyclic loading, and five different initial crack shapes are discussed in present study. Good agreement between experimental and theoretical results is obtained.

  15. Transient subcritical crack-growth behavior in transformation-toughened ceramics

    International Nuclear Information System (INIS)

    Dauskardt, R.H.; Ritchie, R.O.; Carter, W.C.; Veirs, D.K.

    1990-01-01

    Transient subcritical crack-growth behavior following abrupt changes in the applied load are studied in transformation-toughened ceramics. A mechanics analysis is developed to model the transient nature of transformation shielding of the crack tip, K s , with subcritical crack extension following the applied load change. conditions for continued crack growth, crack growth followed by arrest, and no crack growth after the load change, are considered and related to the magnitude and sign of the applied load change and to materials properties such as the critical transformation stress. The analysis is found to provide similar trends in K s compared to values calculated from experimentally measured transformation zones in a transformation-toughened Mg-PSZ. In addition, accurate prediction of the post load-change transient crack-growth behavior is obtained using experimentally derived steady-state subcritical crack-growth relationships for cyclic fatigue in the same material

  16. Fatigue crack growth from blunt notches

    International Nuclear Information System (INIS)

    Rhodes, D.

    1982-01-01

    A number of methods have been proposed, by which the formation and early growth of fatigue cracks at blunt notches may be predicted. In this report, four methods are compared - i.e. analysis of the crack tip plastic deformation, the cyclic contour integral, δJ, the strain in a critical volume of material, and the notch root plastic strain range. It is shown that these approaches have fundamental elements in common, and that all are compatable with linear elastic fracture mechanics. Early results from a continuing experimental programme are reported. (orig.) [de

  17. Experimental and analytical comparison of constraint effects due to biaxial loading and shallow-flaws

    International Nuclear Information System (INIS)

    Theiss, T.J.; Bass, B.R.; Bryson, J.W.

    1993-01-01

    A program to develop and evaluate fracture methodologies for the assessment of crack-tip constraint effects on fracture toughness of reactor pressure vessel (RPV) steels has been initiated in the Heavy-Section Steel Technology (HSST) Program. The focus of studies described herein is on the evaluation of a micromechanical scaling model based on critical stressed volumes for quantifying crack-tip constraint through applications to experimental data. Data were utilized from single-edge notch bend (SENB) specimens and HSST-developed cruciform beam specimens that were tested in HSST shallow-crack and biaxial testing programs. Shallow-crack effects and far-field tensile out-of-plane biaxial loading have been identified as constraint issues that influence both fracture toughness and the extent of the toughness scatter band. Results from applications indicate that the micromechanical scaling model can be used successfully to interpret experimental data from the shallow- and deep-crack SENB specimen tests. When applied to the uniaxially and biaxially loaded cruciform specimens, the two methodologies showed some promising features, but also raised several questions concerning the interpretation of constraint conditions in the specimen based on near-tip stress fields. Crack-tip constraint analyses of the shallow-crack cruciform specimen based on near-tip stress fields. Crack-tip constraint analyses of the shallow-crack cruciform specimen subjected to uniaxial or biaxial loading conditions are shown to represent a significant challenge for these methodologies. Unresolved issued identified from these analyses require resolution as part of a validation process for biaxial loading applications

  18. Steady-state crack growth in single crystals under Mode I loading

    DEFF Research Database (Denmark)

    Juul, Kristian Jørgensen; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2017-01-01

    The active plastic zone that surrounds the tip of a sharp crack growing under plane strain Mode I loading conditions at a constant velocity in a single crystal is studied. Both the characteristics of the plastic zone and its effect on the macroscopic toughness is investigated in terms of crack tip...... that the largest shielding effect develops in HCP crystals, while the lowest shielding exists for FCC crystals. Rate-sensitivity is found to affect the plastic zone size, but the characteristics overall remain similar for each individual crystal structure. An increasing rate-sensitivity at low crack velocities...... shielding due to plasticity (quantified by employing the Suo, Shih, and Varias set-up). Three single crystals (FCC, BCC, HCP) are modelled in a steady-state elastic visco-plastic framework, with emphasis on the influence of rate-sensitivity and crystal structures. Distinct velocity discontinuities...

  19. Ductile fracture evaluation of ductile cast iron and forged steel by nonlinear-fracture-mechanics. Pt. 1. Tensile test by large scaled test pieces with surface crack

    International Nuclear Information System (INIS)

    Kosaki, Akio; Ajima, Tatsuro; Inohara, Yasuto

    1999-01-01

    The ductile fracture tests of Ductile Cast Iron and Forged Steel under a tensile stress condition were conducted using large-scaled flat test specimens with a surface crack and were evaluated by the J-integral values, in order to propose an evaluation method of initiation of ductile fracture of a cask body with crack by nonlinear-fracture-mechanics. Following results were obtained. 1) 1 -strain relations of Ductile Cast Iron and Forged Steel under the tensile stress condition were obtained, which is necessary for the development of J-integral design curves for evaluating the initiation of ductile fracture of the cask body. 2) In case of Ductile Cast Iron, the experimental J-integral values obtained from strain-gauges showed a good agreement with the linear-elastic-theory by Raju and Newman at room temperature, in both elastic and plastic regions. But, at 70degC in plastic region, the experimental i-integral values showed middle values between those predicted by the linear-elastic-theory and by the non- linear-elastic- theory (based on the fully plastic solution by Yagawa et al.). 3) In case of Forged Steel at both -25degC and room temperature, the experimental i-integral values obtained from strain-gauges showed a good agreement with those predicted by the linear-elastic-theory by Raju and Newman, in the elastic region. In the plastic region, however, the experimental i-integral values fell apart from the curve predicted by the linear-elastic-theory by Raju and Newman, and also approached to those by the non-linear-elastic-theory with increasing strain.(author)

  20. Finite element simulation for creep crack growth

    International Nuclear Information System (INIS)

    Miyazaki, Noriyuki; Sasaki, Toru; Nakagaki, Michihiko; Brust, F.W.

    1992-01-01

    A finite element method was applied to a generation phase simulation of creep crack growth. Experimental data on creep crack growth in a 1Cr-1Mo-1/4V steel compact tension specimen were numerically simulated using a node-release technique and the variations of various fracture mechanics parameters such as CTOA, J, C * and T * during creep crack growth were calculated. The path-dependencies of the integral parameters J, C * and T * were also obtained to examine whether or not they could characterize the stress field near the tip of a crack propagating under creep condition. The following conclusions were obtained from the present analysis. (1) The J integral shows strong path-dependency during creep crack growth, so that it is does not characterize creep crack growth. (2) The C * integral shows path-dependency to some extent during creep crack growth even in the case of Norton type steady state creep law. Strictly speaking, we cannot use it as a fracture mechanics parameter characterizing creep crack growth. It is, however, useful from the practical viewpoint because it correlates well the rate of creep crack growth. (3) The T * integral shows good path-independency during creep crack growth. Therefore, it is a candidate for a fracture mechanics parameter characterizing creep crack growth. (author)

  1. Numerical analysis of macro-crack formation behavior within the lump coke; Cokes sonai kiretsu shinten kiko no kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, H; Sato, H; Miura, T [Tohoku University, Sendai (Japan). Faculty of Engineering

    1995-03-15

    The thermal stress analysis within lump coke was studied in order to investigate macro-crack formation and deformation behavior which strongly influence heat and mass transfer in a coke oven chamber. The dilatation of plastic layer, heating rate dependence of thermophysical and mechanical properties of coal/coke, creep in the plastic and semi-coke layers, macro-crack propagation and radiative heat transfer within the macro-crack were considered in an analytical model. The macro-crack propagation was determined from the estimated crack tip stress intensity factor, K{sub I}, at the macro-crack tip compared with the plane strain fracture toughness, K{sub IC}, through the unsteady-state calculation. Calculated results on crack formation and deformation behavior of lump coke were in good agreement with experimental observations in a laboratory-scale oven chamber. The analytical model could predict micro-crack formation within the lump coke normal to the heated wall and the coke surface close to the heated wall. 12 refs., 13 figs.

  2. Stress corrosion cracking of stainless steel under deaerated high-temperature water. Influence of cold work and processing orientation

    International Nuclear Information System (INIS)

    Terachi, Takumi; Yamada, Takuyo; Chiba, Goro; Arioka, Koji

    2006-01-01

    The influence of cold work and processing orientation on the propagation of stress corrosion cracking (SCC) of stainless steel under hydrogenated high-temperature water was examined. It was shown that (1) the crack growth rates increased with heaviness of cold work, and (2) processing orientation affected crack growth rate with cracking direction. Crack growth rates showed anisotropy of T-L>>T-S>L-S, with T-S and L-S branches representing high shear stress direction. Geometric deformation of crystal grains due to cold work caused the anisotropy and shear stress also assisted the SCC propagation. (3) The step intervals of slip like patterns observed on intergranular facets increased cold work. (4) Nano-indentation hardness of the crack tip together with EBSD measurement indicated that the change of hardness due to crack propagation was less than 5% cold-work, even though the distance from the crack tip was 10μm. (author)

  3. Fatigue Crack Behavior of Stainless Steel 304 by the Addition of Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Rizwanulhaque Syed

    2014-01-01

    Full Text Available Fatigue is the main source of almost half of whole mechanical failures. This research investigated the effect on cyclic fatigue behavior of stainless steel 304 (SS304 when including carbon nanotubes (CNTs at the crack tip. The cyclic fatigue tests were conducted on compact tension (CT specimens to establish the relationship between crack growth and the number of cycles (a-N. It is found that the incorporation of a small amount of CNTs increased the fatigue life of the SS304/metal. Micrographs showed that the enhancement in fatigue life is caused by CNTs dense arrangement around the crack tip, entangled with each other, and finer grain size. Smooth bonding at the interface of the CNTs and SS304 grains is also observed.

  4. The manufacturing of Stress Corrosion Crack (SCC) on Inconel 600 tube

    International Nuclear Information System (INIS)

    Bae, Seunggi; Bak, Jaewoong; Kim, Seongcheol; Lee, Sangyul; Lee, Boyoung

    2014-01-01

    The Stress Corrosion Crack (SCC), taken a center stage in recently accidents about nuclear power plants, is one of the environmentally induced cracking occurred when a metallic structure under tensile stress is exposed to corrosive environment. In this study, the SCC was manufactured in the simulated corrosive environmental conditions on Inconel 600 tube that widely applied in the nuclear power plants. The tensile stress which is one of the main factors to induce SCC was given by GTAW welding in the inner surface of the specimen. The corrosive environment was simulated by using the sodium hydroxide (NaOH) and sodium sulfide (Na 2 S). In this study, SCC was manufactured in the simulated corrosive environmental conditions with Inconel 600 tube that widely applied in the nuclear power plants. 1) The SCC was manufactured on Inconel 600 tube in simulated operational environments of nuclear power plants. In the experiment, the welding heat input which is enough to induce the cracking generated the SCC near the welding bead. So, in order to prevent the SCC, the residual stress on structure should be relaxed. 2) The branch-type cracking was detected

  5. Continuum damage mechanics method for fatigue growth of surface cracks

    International Nuclear Information System (INIS)

    Feng Xiqiao; He Shuyan

    1997-01-01

    With the background of leak-before-break (LBB) analysis of pressurized vessels and pipes in nuclear plants, the fatigue growth problem of either circumferential or longitudinal semi-elliptical surface cracks subjected to cyclic loading is studied by using a continuum damage mechanics method. The fatigue damage is described by a scalar damage variable. From the damage evolution equation at the crack tip, a crack growth equation similar to famous Paris' formula is derived, which shows the physical meaning of Paris' formula. Thereby, a continuum damage mechanics approach is developed to analyze the configuration evolution of surface cracks during fatigue growth

  6. Effects of the Crack Tip Constraint on the Fracture Assessment of an Al 5083-O Weldment for Low Temperature Applications

    Directory of Open Access Journals (Sweden)

    Dong Hyun Moon

    2017-07-01

    Full Text Available The constraint effect is the key issue in structural integrity assessments based on two parameter fracture mechanics (TPFM to make a precise prediction of the load-bearing capacity of cracked structural components. In this study, a constraint-based failure assessment diagram (FAD was used to assess the fracture behavior of an Al 5083-O weldment with various flaws at cryogenic temperature. The results were compared with those of BS 7910 Option 1 FAD, in terms of the maximum allowable stress. A series of fracture toughness tests were conducted with compact tension (CT specimens at room and cryogenic temperatures. The Q parameter for the Al 5083-O weldment was evaluated to quantify the constraint level, which is the difference between the actual stress, and the Hutchinson-Rice-Rosengren (HRR stress field near the crack tip. Nonlinear 3D finite element analysis was carried out to calculate the Q parameter at cryogenic temperature. Based on the experimental and numerical results, the influence of the constraint level correction on the allowable applied stress was investigated using a FAD methodology. The results showed that the constraint-based FAD procedure is essential to avoid an overly conservative allowable stress prediction in an Al 5083-O weldment with flaws.

  7. Analytical Tem Comparisons of Stress-Corrosion-Crack Microstructures in Alloy 600 under Steam-Generator Service and Laboratory Test Conditions

    International Nuclear Information System (INIS)

    Thomas, L.E.; Bruemmer, S.M.; Scott, P.M.

    2002-01-01

    High-resolution analytical transmission electron microscopy (ATEM) has been used to characterize stress-corrosion cracks (SCC) in Alloy 600 steam-generator (SG) tubing from tests with caustic and acid-sulfate solutions. The aim of this work was to identify the microstructural and microchemical signatures of intergranular attack and cracking produced under well-controlled test conditions in order to determine the local environments promoting degradation in service. Cross-sectioned cracks and crack tips were examined in samples of mill-annealed alloy 600 tested in concentrated caustic and acid-sulfate solutions at 320 C. Characteristic microstructures observed in the caustic (10% NaOH) test sample included deeply penetrative attack along crack-intersected grain boundaries, with Cr-rich spinel and NiO structure oxides ranging from random nanocrystalline to oriented epitaxial films filling cracks up to the tips. Sodium was readily detectable in the oxides (up to 5 wt.% in the spinel corrosion product) along with S and Cu enrichment at crack-wall metal/oxide interfaces and local attack of the metal matrix around IG carbide particles. In the sulfate (Na 2 SO 4 + FeSO 4 ) test sample, the grain boundaries were also deeply attacked/cracked. Epitaxial NiO-structure oxide formed on the crack walls and S, sometimes with Cu, was concentrated between the oriented oxide layers rather than along the metal/oxide interfaces. Carbides were attacked and partially converted to fine-grained oxide containing up to several percent S. Observations of crack tips in the acid sulfate sample also revealed nm-wide cracks preceding the oxide along grain boundaries. The SCC structures produced in the laboratory tests differed in most details from the secondary-side SCC structures observed in pulled SG tubes. Important differences included the oxide morphologies, the presence of easily detectable Na and absence of sulfides in the test samples, different types of attack on IG carbide particles

  8. Analytical Solution for Stress Field and Intensity Factor in CSTBD under Mixed Mode Conditions

    Directory of Open Access Journals (Sweden)

    Najaf Ali Ghavidel

    2014-06-01

    Full Text Available Considering the fact that rocks fail faster under tensile stress, rock tensile strength is of greatimportance in applications such as blasting, rock fragmentation, slope stability, hydraulic fracturing,caprock integrity, and geothermal energy extraction. There are two direct and indirect methods tomeasure tensile strength. Since direct methods always encompass difficulties in test setup, indirectmethods, specifically the Brazilian test, have often been employed for tensile strength measurement.Tensile failure is technically attributed to crack propagation in rock. Fracture mechanics hassignificant potential for the determination of crack behaviour as well as propagation pattern. To applyBrazilian tests, cracked disc geometry has been suggested by the International Society for RockMechanics ISRM. Accordingly, a comprehensive study is necessary to evaluate stress field and stressintensity factor (SIF around the crack in the centre of the specimen. In this paper, superpositionprinciple is employed to solve the problem of cracked straight-through Brazilian disc (CSTBD, usingtwo methods of dislocation and complex stress function. Stress field and SIF in the vicinity of thecrack tip are then calculated. With the proposed method, the magnitude of critical load for crackinitiation in structures can be predicted. This method is valid for any crack of any arbitrary length andangle. In addition, numerical modelling has been carried out for the Brazilian disc. Finally, theanalytical solution has been compared with numerical modelling results showing the same outcomefor both methods.

  9. Quasi-static and dynamic experimental studies on the tensile strength and failure pattern of concrete and mortar discs.

    Science.gov (United States)

    Jin, Xiaochao; Hou, Cheng; Fan, Xueling; Lu, Chunsheng; Yang, Huawei; Shu, Xuefeng; Wang, Zhihua

    2017-11-10

    As concrete and mortar materials widely used in structural engineering may suffer dynamic loadings, studies on their mechanical properties under different strain rates are of great importance. In this paper, based on splitting tests of Brazilian discs, the tensile strength and failure pattern of concrete and mortar were investigated under quasi-static and dynamic loadings with a strain rate of 1-200 s -1 . It is shown that the quasi-static tensile strength of mortar is higher than that of concrete since coarse aggregates weaken the interface bonding strength of the latter. Numerical results confirmed that the plane stress hypothesis lead to a lower value tensile strength for the cylindrical specimens. With the increase of strain rates, dynamic tensile strengths of concrete and mortar significantly increase, and their failure patterns change form a single crack to multiple cracks and even fragment. Furthermore, a relationship between the dynamic increase factor and strain rate was established by using a linear fitting algorithm, which can be conveniently used to calculate the dynamic increase factor of concrete-like materials in engineering applications.

  10. Epitaxial Growth and Cracking Mechanisms of Thermally Sprayed Ceramic Splats

    Science.gov (United States)

    Chen, Lin; Yang, Guan-jun

    2018-02-01

    In the present study, the epitaxial growth and cracking mechanisms of thermally sprayed ceramic splats were explored. We report, for the first time, the epitaxial growth of various splat/substrate combinations at low substrate temperatures (100 °C) and large lattice mismatch (- 11.26%). Our results suggest that thermal spray deposition was essentially a liquid-phase epitaxy, readily forming chemical bonding. The interface temperature was also estimated. The results convincingly demonstrated that atoms only need to diffuse and rearrange over a sufficiently short range during extremely rapid solidification. Concurrently, severe cracking occurred in the epitaxial splat/substrate systems, which indicated high tensile stress was produced during splat deposition. The origin of the tensile stress was attributed to the strong constraint of the locally heated substrate by its cold surroundings.

  11. Delayed Hydride Cracking in Zr-2.5Nb Tubes with the Direction of An Approach to Temperature

    International Nuclear Information System (INIS)

    Kim, Young Suk; Im, Kyung Soo; Kim, Kang Soo; Ahn, Sang Bok; Cheong, Yong Moo

    2006-01-01

    One of the unique features of delayed hydride cracking (DHC) of zirconium alloys is that the DHC velocity (DHCV) of zirconium alloys strongly depends on the path to the test temperature. Ambler reported that the DHCV of Zr-2.5Nb tubes at temperatures above 180 .deg. C depended upon the direction of an approach to the test temperatures, and reported on a presence of the DHC arrest temperature or TDAT above which the DHCV decreased upon an approach to the test temperature by a heating. Ambler proposed a hydrogen transfer from the bulk to the crack tip assuming that the hydrides formed at the crack tip and in the bulk region are fully constrained and partially constrained at the crack tip, respectively. In other words, the terminal solid solubility (TSS) of hydrogen would be governed by elastic strain energy induced by the precipitating hydrides, leading to a higher TSS in the bulk region than that at the crack tip. In a sense, his assumption that the hydrogen concentration is higher in the bulk region than that at the crack tip due to a higher TSS in the bulk region is, in a way, similar to Kim's DHC model. Even though Ambler assumed a different strain energy of the matrix hydrides with the direction of an approach to the test temperature, the peak temperature, hydrogen concentration and the hydride phase, a feasible rationale for this assumption is yet to be given. In this study, a path dependence of DHC velocity of Zr-2.5Nb tubes will be investigated using Kim's DHC model where a driving force for DHC is the supersaturated hydrogen concentration between the crack tip and the bulk region. To this ends, the furnace cooled and water-quenched Zr-2.5Nb specimens were subjected to DHC tests at different test temperatures that were approached by a heating or by a cooling. Kim's DHC model predicts that the water-quenched Zr- 2.5Nb will have DHC crack growth even at temperatures above 180 .deg. C where the furnace-cooled Zr-2.5Nb will not. This experiment will provide

  12. Delayed Hydride Cracking in Zr-2.5Nb Tubes with the Direction of An Approach to Temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Im, Kyung Soo; Kim, Kang Soo; Ahn, Sang Bok; Cheong, Yong Moo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    2006-07-01

    One of the unique features of delayed hydride cracking (DHC) of zirconium alloys is that the DHC velocity (DHCV) of zirconium alloys strongly depends on the path to the test temperature. Ambler reported that the DHCV of Zr-2.5Nb tubes at temperatures above 180 .deg. C depended upon the direction of an approach to the test temperatures, and reported on a presence of the DHC arrest temperature or TDAT above which the DHCV decreased upon an approach to the test temperature by a heating. Ambler proposed a hydrogen transfer from the bulk to the crack tip assuming that the hydrides formed at the crack tip and in the bulk region are fully constrained and partially constrained at the crack tip, respectively. In other words, the terminal solid solubility (TSS) of hydrogen would be governed by elastic strain energy induced by the precipitating hydrides, leading to a higher TSS in the bulk region than that at the crack tip. In a sense, his assumption that the hydrogen concentration is higher in the bulk region than that at the crack tip due to a higher TSS in the bulk region is, in a way, similar to Kim's DHC model. Even though Ambler assumed a different strain energy of the matrix hydrides with the direction of an approach to the test temperature, the peak temperature, hydrogen concentration and the hydride phase, a feasible rationale for this assumption is yet to be given. In this study, a path dependence of DHC velocity of Zr-2.5Nb tubes will be investigated using Kim's DHC model where a driving force for DHC is the supersaturated hydrogen concentration between the crack tip and the bulk region. To this ends, the furnace cooled and water-quenched Zr-2.5Nb specimens were subjected to DHC tests at different test temperatures that were approached by a heating or by a cooling. Kim's DHC model predicts that the water-quenched Zr- 2.5Nb will have DHC crack growth even at temperatures above 180 .deg. C where the furnace-cooled Zr-2.5Nb will not. This experiment

  13. Contribution to the study of the mechanism of crack in amorphous silica: study by the molecular dynamics of crack in amorphous silica

    International Nuclear Information System (INIS)

    Van Brutzel, L.

    2000-01-01

    The aim of this thesis was to understand the mechanism which occurs during the crack at the atomic scale in amorphous silica. The difficulties of the experimental observations at this length scale lead us to use numerical studies by molecular dynamics to access to the dynamical and the thermodynamical informations. We have carried out large simulations with 500000 atoms and studied the structure of the amorphous silica before to studying their behaviours under an imposed strain. The structure of this simulated amorphous silica settled in three length scales. In small length scale between 0 and 5 angstrom glass is composed of tetrahedra, this is close to the crystalline structure. In intermediate length scale between 3 and 10 angstrom tetrahedra are connected together and build rings of different sizes composed in majority between 5 and 7 tetrahedra. In bigger length scale between 15 and 60 angstrom, areas with high density of rings are surrounded by areas with low density of rings. These structural considerations play an important role in initiation and propagation of a crack. Indeed. in this length scale. crack propagates by growth and coalescence of some small cavities which appear in area with low density of rings behind the crack tip. The cavities dissipate the stress with carries away a delay to propagation of the crack. This phenomenons seems ductile and leads to non linear elastic behaviour near the crack tip. We have also shown that the addition of alkali in the amorphous silica changes the structure by creation of nano-porosities and leads to enhance the ductility during the crack propagation. (author)

  14. Tensile and fracture behavior of polymer foams

    International Nuclear Information System (INIS)

    Kabir, Md. E.; Saha, M.C.; Jeelani, S.

    2006-01-01

    Tensile and mode-I fracture behavior of cross-linked polyvinyl chloride (PVC) and rigid polyurethane (PUR) foams are examined. Tension tests are performed using prismatic bar specimens and mode-I fracture tests are performed using single edge notched bend (SENB) specimens under three-point bending. Test specimens are prepared from PVC foams with three densities and two different levels of cross-linking, and PUR foam with one density. Tension and quasi-static fracture tests are performed using a Zwick/Rowell test machine. Dynamic fracture tests are performed using a DYNATUP model 8210 instrumented drop-tower test set up at three different impact energy levels. Various parameters such as specimen size, loading rate, foam density, cross-linking, crack length, cell orientation (flow and rise-direction) and solid polymer material are studied. It is found that foam density and solid polymer material have a significant effect on tensile strength, modulus, and fracture toughness of polymer foams. Level of polymer cross-linking is also found to have a significant effect on fracture toughness. The presence of cracks in the rise- and flow direction as well as loading rate has minimal effect. Dynamic fracture behavior is found to be different as compared to quasi-static fracture behavior. Dynamic fracture toughness (K d ) increases with impact energy. Examination of fracture surfaces reveals that the fracture occurs in fairly brittle manner for all foam materials

  15. Low Temperature (320 deg C and 340 deg C) Creep Crack Growth in Low Alloy Reactor Pressure Vessel Steel

    International Nuclear Information System (INIS)

    Rui Wu; Sandstroem, Rolf; Seitisleam, Facredin

    2004-02-01

    Uni-axial creep and creep crack growth (CCG) tests at 320 deg C and 340 deg C as well as post test metallography have been carried out in a low alloy reactor pressure vessel steel (ASTM A508 class 2) having simulated coarse grained heat affected zone microstructure. The CCG behaviour is studied in terms of steady crack growth rate, creep fracture parameter C*, stress intensity factor and reference stress at given testing conditions. It has been found that CCG does occur at both tested temperatures. The lifetimes for the CCG tests are considerably shorter than those for the uni-axial creep tests. This is more pronounced at longer lifetimes or lower stresses. Increasing temperature from 320 deg C to 340 deg C causes a reduction of lifetime by approximately a factor of five and a corresponding increase of steady crack growth rate. For the CCG tests, there are three regions when the crack length is plotted against time. After incubation, the crack grows steadily until it accelerates when rupture is approached. Notable crack growth takes place at later stage of the tests. No creep cavitation is observed and transgranular fracture is dominant for the uni-axial creep specimens. In the CT specimens the cracks propagate intergranularly, independent of temperature and time. Some relations between time to failure, reference stress and steady crack growth rate are found for the CCG tests. A linear extrapolation based on the stress-time results indicates that the reference stress causing failure due to CCG at a given lifetime of 350,000 hours at 320 deg C is clearly lower than both yield and tensile strengths, on which the design stress may have based. Therefore, caution must be taken to prevent premature failure due to low temperature CCG. Both uni-axial and CCG tests on real welded joint at 320 deg C, study of creep damage zone at crack tip as well as numerical simulation are recommended for future work

  16. Analysis of cracks in stainless steel TIG [tungsten inert gas] welds

    International Nuclear Information System (INIS)

    Nakagaki, M.; Marschall, C.; Brust, F.

    1986-12-01

    This report contains the results of a combined experimental and analytical study of ductile crack growth in tungsten inert gas (TIG) weldments of austenitic stainless steel specimens. The substantially greater yield strength of the weld metal relative to the base metal causes more plastic deformation in the base metal adjacent to the weld than in the weld metal. Accordingly, the analytical studies focused on the stress-strain interaction between the crack tip and the weld/base-metal interface. Experimental work involved tests using compact (tension) specimens of three different sizes and pipe bend experiments. The compact specimens were machined from a TIG weldment in Type 304 stainless steel plate. The pipe specimens were also TIG welded using the same welding procedures. Elastic-plastic finite element methods were used to model the experiments. In addition to the J-integral, different crack-tip integral parameters such as ΔT/sub p/* and J were evaluated. Also, engineering J-estimation methods were employed to predict the load-carrying capacity of the welded pipe with a circumferential through-wall crack under bending

  17. Thermal Stress Cracking of Slide-Gate Plates in Steel Continuous Casting

    Science.gov (United States)

    Lee, Hyoung-Jun; Thomas, Brian G.; Kim, Seon-Hyo

    2016-04-01

    The slide-gate plates in a cassette assembly control the steel flow through the tundish nozzle, and may experience through-thickness cracks, caused by thermal expansion and/or mechanical constraint, leading to air aspiration and safety concerns. Different mechanisms for common and rare crack formation are investigated with the aid of a three-dimensional finite-element model of thermal mechanical behavior of the slide-gate plate assembly during bolt pretensioning, preheating, tundish filling, casting, and cooling stages. The model was validated with previous plant temperature measurements of a ladle plate during preheating and casting, and then applied to a typical tundish-nozzle slide-gate assembly. The formation mechanisms of different types of cracks in the slide-gate plates are investigated using the model and evaluated with actual slide-gate plates at POSCO. Common through-thickness radial cracks, found in every plate, are caused during casting by high tensile stress on the outside surfaces of the plates, due to internal thermal expansion. In the upper plate, these cracks may also arise during preheating or tundish filling. Excessive bolt tightening, combined with thermal expansion during casting may cause rare radial cracks in the upper and lower plates. Rare radial and transverse cracks in middle plate appear to be caused during tundish filling by impingement of molten steel on the middle of the middle plate that generates tensile stress in the surrounding refractory. The mechanical properties of the refractory, the bolt tightening conditions, and the cassette/plate design are all important to service life.

  18. Methodology to evaluate the crack growth rate by stress corrosion cracking in dissimilar metals weld in simulated environment of PWR nuclear reactor

    International Nuclear Information System (INIS)

    Paula, Raphael G.; Figueiredo, Celia A.; Rabelo, Emerson G.

    2013-01-01

    Inconel alloys weld metal is widely used to join dissimilar metals in nuclear reactors applications. It was recently observed failures of weld components in plants, which have triggered an international effort to determine reliable data on the stress corrosion cracking behavior of this material in reactor environment. The objective of this work is to develop a methodology to determine the crack growth rate caused by stress corrosion in Inconel alloy 182, using the specimen (Compact Tensile) in simulated PWR environment. (author)

  19. Causes of the cracks in the pipeline made of the 15HM steel

    Directory of Open Access Journals (Sweden)

    Słania J.

    2017-03-01

    Full Text Available Issues referring to cracks in the pipelines made of the 15HM steel are described. Metallographic specimen of welded joints are provided. The results of impact strength tests, hardness tests and static tensile tests are given. Tests results as well as direct and indirect causes of the pipeline cracks are shown.

  20. Tensile, Creep, and Fatigue Behaviors of 3D-Printed Acrylonitrile Butadiene Styrene

    Science.gov (United States)

    Zhang, Hanyin; Cai, Linlin; Golub, Michael; Zhang, Yi; Yang, Xuehui; Schlarman, Kate; Zhang, Jing

    2018-01-01

    Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastics in 3D printing. However, there is a lack of thorough investigation of the mechanical properties of 3D-printed ABS components, including orientation-dependent tensile strength and creep fatigue properties. In this work, a systematic characterization is conducted on the mechanical properties of 3D-printed ABS components. Specifically, the effect of printing orientation on the tensile and creep properties is investigated. The results show that, in tensile tests, the 0° printing orientation has the highest Young's modulus of 1.81 GPa, and ultimate strength of 224 MPa. In the creep test, the 90° printing orientation has the lowest k value of 0.2 in the plastics creep model, suggesting 90° is the most creep resistant direction. In the fatigue test, the average cycle number under load of 30 N is 3796 cycles. The average cycle number decreases to 128 cycles when the load is 60 N. Using the Paris law, with an estimated crack size of 0.75 mm, and stress intensity factor is varied from 352 to 700 N√ m, the derived fatigue crack growth rate is 0.0341 mm/cycle. This study provides important mechanical property data that is useful for applying 3D-printed ABS in engineering applications.

  1. Fracture mechanical investigations about crack resistance behaviour in non-transforming ceramics in particular aluminum oxide

    International Nuclear Information System (INIS)

    Baer, K.K.O.; Kleist, G.; Nickel, H.

    1991-03-01

    The aim of this work is the clearification of R-curve behaviour of non-transforming ceramics, in particular aluminum oxide exhibiting incrystalline fracture. Investigations of crack growth in controlled bending experiments were performed using 3-Pt- and 4-Pt-bending samples of differing sizes under inert conditions. The fracture experiments were realized using several loading techniques, for example constant and varying displacement rates, load rupture (P = 0) and relaxation tests (v = 0). In addition unloading and reloading experiments were performed to investigate hysteresis curves and residual displacements in accordance with R-curve behaviour. During the crack-growth experiments, the crack extension was measured in situ using a high resolution immersion microscope. With this technique, the fracture processes near the crack tip (crack activity zone) was observed as well. The crack resistance as a function of crack extension (R-curve) was determined using differing calculation methods. All of the methods used resulted in approximately identical R-curves, within the statistical error band. The crack resistance at initiation R 0 was 20 N/m. The crack resistance increased during approximately 3 mm of growth to a maximum of 90 N/m. A decrease in the crack resistance was determined for large a/W (crack length normalized with sample height) values, independant of the calculation methods. The R-curve behaviour was interpreted as due to a functional resistance behind the observed crack tip, which arises from a volume dilatation in the crack activity zone while the crack proceeds. (orig.) [de

  2. Influences of semiconductor morphology on the mechanical fatigue behavior of flexible organic electronics

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young-Joo; Yeon, Han-Wool; Shin, Hae-A-Seul; Joo, Young-Chang, E-mail: ycjoo@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, 151-744 Seoul (Korea, Republic of); Uk Lee, Yong; Evans, Louise A. [Center for Process Innovation Limited, Thomas Wright Way, NETPark, Sedgefield, TS21 3FG County Durham (United Kingdom)

    2013-12-09

    The influence of crystalline morphology on the mechanical fatigue of organic semiconductors (OSCs) was investigated using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as a crystalline OSC and poly(triarylamine) (PTAA) as an amorphous OSC. During cyclic bending, resistances of the OSCs were monitored using the transmission-line method on a metal-semiconductor-metal structure. The resistance of the TIPS-pentacene increased under fatigue damage in tensile-stress mode, but no such degradation was observed in the PTAA. Both OSCs were stable under compressive bending fatigue. The formation of intergranular cracks at the domain boundaries of the TIPS-pentacene was responsible for the degradation of its electrical properties under tensile bending fatigue.

  3. Failure prediction for Crack-in-Corrosion defects in natural gas transmission pipelines

    International Nuclear Information System (INIS)

    Bedairi, B.; Cronin, D.; Hosseini, A.; Plumtree, A.

    2012-01-01

    Cracks occurring coincidentally with corrosion (Crack-in-Corrosion or CIC), represent a new hybrid defect in pipelines that are not directly addressed in the current codes or assessment methods. To understand the failure response of these defects, the finite element method using an elastic–plastic fracture mechanics approach was applied to predict the failure pressures of comparable crack, corrosion and CIC defects in 508 mm diameter pipe with 5.7 mm wall thickness. Failure pressure predictions were made based on measured tensile, Charpy impact and J testing data, and validated using experimental rupture tests. Plastic collapse was predicted for corrosion and crack defects using the critical strength based on the material tensile strength, whereas fracture was predicted using the measured J 0.2 value. The model predictions were found to be conservative for the CIC defects (17.4% on average), 12.4% conservative for crack-only defects, and 3.2% conservative for corrosion defects compared to the experimental tests, demonstrating the applicability of the material-based failure criteria. For the defects considered in this study, all were predicted to fail by plastic collapse. The finite element method provided less conservative predictions than existing corrosion or crack-based analytical methods. Highlights: ► Cracks occurring coincidentally with corrosion represent a new hybrid defect in pipelines. ► Existing methods for prediction corrosion and crack defect failure pressures are conservative. ► The FE method can provide improved prediction of rupture pressure using actual material properties. ► Failure was predicted using FE with a critical stress for plastic collapse and J value for fracture. ► FE failure pressure predictions for crack in corrosion defects were 17% conservative on average.

  4. Simulation of cracks in tungsten under ITER specific heat loads

    International Nuclear Information System (INIS)

    Peschany, S.

    2006-01-01

    The problem of high tritium retention in co-deposited carbon layers on the walls of ITER vacuum chamber motivates investigation of materials for the divertor armour others than carbon fibre composite (CFC). Tungsten is most probable material for CFC replacement as the divertor armour because of high vaporisation temperature and heat conductivity. In the modern ITER design tungsten is a reference material for the divertor cover, except for the separatrix strike point armoured with CFC. As divertor armour, tungsten should withstand severe heat loads at off-normal ITER events like disruptions, ELMs and vertical displacement events. Experiments on tungsten heating with plasma streams and e-beams have shown an intense crack formation at the surface of irradiated sample [ V.I. Tereshin, A.N. Bandura, O.V. Byrka et al. Repetitive plasma loads typical for ITER type-I ELMs: Simulation at QSPA Kh-50.PLASMA 2005. ed. By Sadowski M.J., AIP Conference Proceedings, American Institute of Physics, 2006, V 812, p. 128-135., J. Linke. Private communications.]. The reason for tungsten cracking under severe heat loads is thermo stress. It appears as due to temperature gradient in solid tungsten as in resolidified layer after cooling down. Both thermo stresses are of the same value, but the gradiental stress is compressive and the stress in the resolidified layer is tensile. The last one is most dangerous for crack formation and it was investigated in this work. The thermo stress in tungsten that develops during cooling from the melting temperature down to room temperature is ∼ 8-16 GPa. Tensile strength of tungsten is much lower, < 1 GPa at room temperature, and at high temperatures it drops at least for one order of magnitude. As a consequence, various cracks of different characteristic scales appear at the heated surface of the resolidified layer. For simulation of the cracks in tungsten the numeric code PEGASUS-3D [Pestchanyi and I. Landman. Improvement of the CFC structure to

  5. Stress intensity factors of three parallel edge cracks under bending moments

    International Nuclear Information System (INIS)

    Ismail, A E

    2013-01-01

    This paper reports the study of stress intensity factors (SIF) of three edge cracks in a finite plate under bending moments. The goal of this paper was to analyze the three edge crack interactions under such loading. Several studies can be found in literature discussing on mode I SIF. However, most of these studies obtained the SIFs using tensile force. Lack of SIF reported discussing on the SIFs obtained under bending moments. ANSYS finite element program was used to develop the finite element model where singular elements were used to model the cracks. Different crack geometries and parameters were utilized in order to characterize the SIFs. According to the present results, crack geometries played a significant role in determining the SIFs and consequently induced the crack interaction mechanisms

  6. Fatigue crack closure behavior at high stress ratios

    Science.gov (United States)

    Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

    1988-01-01

    Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

  7. A surface flaw sizing study by time-of-flight ultrasonic technique

    International Nuclear Information System (INIS)

    Lamy, C.A.

    1990-07-01

    In this work, sizing of inclined slits and surface cracks in ferritic steel using the ultrasonic time-of-flight technique was studied. The surface cracks were vertical and inclined, nut the slits were only inclined. It was surface Rayleigh wave that was converted to shear wave mode in the material. The specimens with surface crack were submitted to a three four point loading fracture mechanics tests, so that the region of the crack tip became under an increasing tensile stress. Thus, the ultrasonic crack sizing could be compared to the material stress intensity factor (K) of the material for different loadings. Results show that the greater the slope and/or lenght of the slits the greater its subsizing. Vertical cracks int he parent metal are reliably and accuratly sized; in the weld the same remark held if one increases the gain of ultrasonic flaw detector to compensate for the weld attenuation phenomenon. Sizing of inclined cracks in the parent metal shows the same trends of the inclined slits, differing only in slopes over 30 sup(0) where the sizing in surface cracks is no longer reliable. A new appraisal procedure here proposed made reliable these results. The techniques employed in this work lead to reliable and accurate results for sizing of different slits and cracks. It should be noted however that good results are only obtained if a tensile stress state exists in the neighbourhood of the c rack tip. (author)

  8. Stress-intensity factors for a thick-walled cylinder containing an annular imbedded or external or internal surface crack

    Science.gov (United States)

    Erdol, R.; Erdogan, F.

    1976-01-01

    The elastostatic axisymmetric problem for a long thick-walled cylinder containing a ring-shaped internal or edge crack is considered. Using the standard transform technique the problem is formulated in terms of an integral equation which has a simple Cauchy kernel for the internal crack and a generalized Cauchy kernel for the edge crack as the dominant part. As examples the uniform axial load and the steady-state thermal stress problems have been solved and the related stress intensity factors have been calculated. Among other findings the results show that in the cylinder under uniform axial stress containing an internal crack the stress intensity factor at the inner tip is always greater than that at the outer tip for equal net ligament thicknesses and in the cylinder with an edge crack which is under a state of thermal stress the stress intensity factor is a decreasing function of the crack depth, tending to zero as the crack depth approaches the wall thickness.

  9. Dependency of Delayed Hydride Crack Velocity on the Direction of an Approach to Test Temperatures in Zirconium Alloys

    International Nuclear Information System (INIS)

    Kim, Young Suk; Kim, Kang Soo; Im, Kyung Soo; Ahn, Sang Bok; Cheong, Yong Moo

    2005-01-01

    Recently, Kim proposed a new DHC model where a driving force for the DHC is a supersaturated hydrogen concentration as a result of a hysteresis of the terminal solid solubility (TSS) of hydrogen in zirconium alloys upon a heating and a cooling. This model was demonstrated to be valid through a model experiment where the prior plastic deformation facilitated nucleation of the reoriented hydrides, thus reducing the supersaturated hydrogen concentration at the plastic zone ahead of the crack tip and causing hydrogen to move to the crack tip from the bulk region. Thus, an approach to the test temperature by a cooling is required to create a supersaturation of hydrogen, which is a driving force for the DHC of zirconium alloys. However, despite the absence of the supersaturation of hydrogen due to an approach to the test temperature by a heating, DHC is observed to occur in zirconium alloys at the test temperatures below 180 .deg. C. As to this DHC phenomenon, Kim proposed that stress-induced transformation from γ-hydrides to δ-hydrides is likely to be a cause of this, based on Root's observation that the γ-hydride is a stable phase at temperatures lower than 180 .deg. C. In other words, the hydrides formed at the crack tip would be δ-hydrides due to the stressinduced transformation while the bulk region still maintains the initial hydride phase or γ-hydrides. It should be noted that Ambler has also assumed the crack tip hydrides to be δ-hydrides. When the δ-hydrides or ZrH1.66 are precipitated at the crack tip due to the transformation of the γ-hydrides or ZrH, the crack tip will have a decreased concentration of dissolved hydrogen in zirconium, considering the atomic ratio of hydrogen and zirconium in the γ- and δ-hydrides. In contrast, due to no stress-induced transformation of hydrides, the bulk region maintains the initial concentration of dissolved hydrogen. Hence, there develops a difference in the hydrogen concentration or .C between the bulk and the

  10. Dependency of Delayed Hydride Crack Velocity on the Direction of an Approach to Test Temperatures in Zirconium Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young Suk; Kim, Kang Soo; Im, Kyung Soo; Ahn, Sang Bok; Cheong, Yong Moo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)

    2005-07-01

    Recently, Kim proposed a new DHC model where a driving force for the DHC is a supersaturated hydrogen concentration as a result of a hysteresis of the terminal solid solubility (TSS) of hydrogen in zirconium alloys upon a heating and a cooling. This model was demonstrated to be valid through a model experiment where the prior plastic deformation facilitated nucleation of the reoriented hydrides, thus reducing the supersaturated hydrogen concentration at the plastic zone ahead of the crack tip and causing hydrogen to move to the crack tip from the bulk region. Thus, an approach to the test temperature by a cooling is required to create a supersaturation of hydrogen, which is a driving force for the DHC of zirconium alloys. However, despite the absence of the supersaturation of hydrogen due to an approach to the test temperature by a heating, DHC is observed to occur in zirconium alloys at the test temperatures below 180 .deg. C. As to this DHC phenomenon, Kim proposed that stress-induced transformation from {gamma}-hydrides to {delta}-hydrides is likely to be a cause of this, based on Root's observation that the {gamma}-hydride is a stable phase at temperatures lower than 180 .deg. C. In other words, the hydrides formed at the crack tip would be {delta}-hydrides due to the stressinduced transformation while the bulk region still maintains the initial hydride phase or {gamma}-hydrides. It should be noted that Ambler has also assumed the crack tip hydrides to be {delta}-hydrides. When the {delta}-hydrides or ZrH1.66 are precipitated at the crack tip due to the transformation of the {gamma}-hydrides or ZrH, the crack tip will have a decreased concentration of dissolved hydrogen in zirconium, considering the atomic ratio of hydrogen and zirconium in the {gamma}- and {delta}-hydrides. In contrast, due to no stress-induced transformation of hydrides, the bulk region maintains the initial concentration of dissolved hydrogen. Hence, there develops a difference in the

  11. Slow Growth of a Crack with Contacting Faces in a Viscoelastic Body

    Science.gov (United States)

    Selivanov, M. F.

    2017-11-01

    An algorithm for solving the problem of slow growth of a mode I crack with a zone of partial contact of the faces is proposed. The algorithm is based on a crack model with a cohesive zone, an iterative method of finding a solution for the elastic opening displacement, and elasto-viscoelastic analogy, which makes it possible to describe the time-dependent opening displacement in Boltzmann-Volterra form. A deformation criterion with a constant critical opening displacement and cohesive strength during quasistatic crack growth is used. The algorithm was numerically illustrated for tensile loading at infinity and two concentrated forces symmetric about the crack line that cause the crack faces to contact. When the crack propagates, the contact zone disappears and its dynamic growth begins.

  12. Studies on the disbonding initiation of interfacial cracks.

    Energy Technology Data Exchange (ETDEWEB)

    McAdams, Brian J. (Lehigh University, Bethlehem, PA); Pearson, Raymond A. (Lehigh University, Bethlehem, PA)

    2005-08-01

    With the continuing trend of decreasing feature sizes in flip-chip assemblies, the reliability tolerance to interfacial flaws is also decreasing. Small-scale disbonds will become more of a concern, pointing to the need for a better understanding of the initiation stage of interfacial delamination. With most accepted adhesion metric methodologies tailored to predict failure under the prior existence of a disbond, the study of the initiation phenomenon is open to development and standardization of new testing procedures. Traditional fracture mechanics approaches are not suitable, as the mathematics assume failure to originate at a disbond or crack tip. Disbond initiation is believed to first occur at free edges and corners, which act as high stress concentration sites and exhibit singular stresses similar to a crack tip, though less severe in intensity. As such, a 'fracture mechanics-like' approach may be employed which defines a material parameter--a critical stress intensity factor (K{sub c})--that can be used to predict when initiation of a disbond at an interface will occur. The factors affecting the adhesion of underfill/polyimide interfaces relevant to flip-chip assemblies were investigated in this study. The study consisted of two distinct parts: a comparison of the initiation and propagation phenomena and a comparison of the relationship between sub-critical and critical initiation of interfacial failure. The initiation of underfill interfacial failure was studied by characterizing failure at a free-edge with a critical stress intensity factor. In comparison with the interfacial fracture toughness testing, it was shown that a good correlation exists between the initiation and propagation of interfacial failures. Such a correlation justifies the continuing use of fracture mechanics to predict the reliability of flip-chip packages. The second aspect of the research involved fatigue testing of tensile butt joint specimens to determine lifetimes at sub

  13. Threshold velocity for environmentally-assisted cracking in low alloy steels

    International Nuclear Information System (INIS)

    Wire, G.L.; Kandra, J.T.

    1997-01-01

    Environmentally Assisted Cracking (EAC) in low alloy steels is generally believed to be activated by dissolution of MnS inclusions at the crack tip in high temperature LWR environments. EAC is the increase of fatigue crack growth rate of up to 40 to 100 times the rate in air that occurs in high temperature LWR environments. A steady state theory developed by Combrade, suggested that EAC will initiate only above a critical crack velocity and cease below this same velocity. A range of about twenty in critical crack tip velocities was invoked by Combrade, et al., to describe data available at that time. This range was attributed to exposure of additional sulfides above and below the crack plane. However, direct measurements of exposed sulfide densities on cracked specimens were performed herein and the results rule out significant additional sulfide exposure as a plausible explanation. Alternatively, it is proposed herein that localized EAC starting at large sulfide clusters reduces the calculated threshold velocity from the value predicted for a uniform distribution of sulfides. Calculations are compared with experimental results where the threshold velocity has been measured, and the predicted wide range of threshold values for steels of similar sulfur content but varying sulfide morphology is observed. The threshold velocity decreases with the increasing maximum sulfide particle size, qualitatively consistent with the theory. The calculation provides a basis for a conservative minimum velocity threshold tied directly to the steel sulfur level, in cases where no details of sulfide distribution are known

  14. Analysis of cracking potential and micro-elongation of linerboard

    Directory of Open Access Journals (Sweden)

    Supattra Panthai

    2016-11-01

    Full Text Available Folding cracks of linerboards in relation to their micro-elongation and the forming conditions were studied using an industrial linerboard machine with a top former. The experiments consisted of the study of various forming conditions by manipulating the jet/wire speed ratio to produce linerboard with differences in fiber structures that were related to the cracked and uncracked products. The results showed that changes to the jet/wire speed ratio of about 0.01–0.02 to improve the tested folding endurance in the machine direction potentially produced folding cracks in the linerboard, which indicated an ambiguous interpretation of the foldability tests. The delaminated cracked layers were found to have a high folding endurance and tensile strength, while the decrease in the micro-elongation formulated in this study was found to be related to cracking. A lower micro-elongation of about 350–500 μm/N·g was found in a range of products with folding cracks.

  15. Impacts of bedding directions of shale gas reservoirs on hydraulically induced crack propagation

    Directory of Open Access Journals (Sweden)

    Keming Sun

    2016-03-01

    Full Text Available Shale gas reservoirs are different from conventional ones in terms of their bedding architectures, so their hydraulic fracturing rules are somewhat different. In this paper, shale hydraulic fracturing tests were carried out by using the triaxial hydraulic fracturing test system to identify the effects of natural bedding directions on the crack propagation in the process of hydraulic fracturing. Then, the fracture initiation criterion of hydraulic fracturing was prepared using the extended finite element method. On this basis, a 3D hydraulic fracturing computation model was established for shale gas reservoirs. And finally, a series of studies were performed about the effects of bedding directions on the crack propagation created by hydraulic fracturing in shale reservoirs. It is shown that the propagation rules of hydraulically induced fractures in shale gas reservoirs are jointly controlled by the in-situ stress and the bedding plane architecture and strength, with the bedding direction as the main factor controlling the crack propagation directions. If the normal tensile stress of bedding surface reaches its tensile strength after the fracturing, cracks will propagate along the bedding direction, and otherwise vertical to the minimum in-situ stress direction. With the propagating of cracks along bedding surfaces, the included angle between the bedding normal direction and the minimum in-situ stress direction increases, the fracture initiation and propagation pressures increase and the crack areas decrease. Generally, cracks propagate in the form of non-plane ellipsoids. With the injection of fracturing fluids, crack areas and total formation filtration increase and crack propagation velocity decreases. The test results agree well with the calculated crack propagation rules, which demonstrate the validity of the above-mentioned model.

  16. Study of stress corrosion cracking initiation of high alloy materials

    Energy Technology Data Exchange (ETDEWEB)

    Blahetova, Marie; Cihal, Vladimir; Lasek, Stanislav [Department of Materials Engineering, VSB - Technical University of Ostrava, tr. 17. listopadu 15, 708 33 Ostrava - Poruba (Czech Republic)

    2004-07-01

    The stainless steels and related alloys with sufficient resistance to a general corrosion can be susceptible to a localized corrosion (pitting, cracking, intergranular corrosion) in certain environment under specific conditions. The Drop Evaporation Test (DET) was developed for study of stainless materials resistance to stress corrosion cracking (SCC) at elevated temperatures 100 - 300 deg. C under constant external load using a chloride containing water solution. In the contribution the initiation and propagation of short cracks as well as pits were observed during the test. The crack initiation and/or propagation can be influenced by the cyclic thermal stresses, when the diluted water solution drops cool down the hot sample. The coordinates measurement of microscopic pits and sharp corrosion crack tips by the travelling microscope method allowed to derive the crack growth lengths and rates of short cracks. (authors)

  17. Study of stress corrosion cracking initiation of high alloy materials

    International Nuclear Information System (INIS)

    Blahetova, Marie; Cihal, Vladimir; Lasek, Stanislav

    2004-01-01

    The stainless steels and related alloys with sufficient resistance to a general corrosion can be susceptible to a localized corrosion (pitting, cracking, intergranular corrosion) in certain environment under specific conditions. The Drop Evaporation Test (DET) was developed for study of stainless materials resistance to stress corrosion cracking (SCC) at elevated temperatures 100 - 300 deg. C under constant external load using a chloride containing water solution. In the contribution the initiation and propagation of short cracks as well as pits were observed during the test. The crack initiation and/or propagation can be influenced by the cyclic thermal stresses, when the diluted water solution drops cool down the hot sample. The coordinates measurement of microscopic pits and sharp corrosion crack tips by the travelling microscope method allowed to derive the crack growth lengths and rates of short cracks. (authors)

  18. Tension stiffening in partially prestressed concrete flexural members

    International Nuclear Information System (INIS)

    Oukaili, K. N.

    2000-01-01

    Concrete tensile strength is not being zero, cracking does not extend to the neutral axis as assumed in standard cracked section analysis. In addition, un cracked concrete, which exists above the crack tip in the tension zone, contributes to the stiffness of the member. This paper discusses the influence of concrete tensile stress below the neut ural axis position at the cracked section on the tension stiffening phenomenon and deflection of progressively cracking partially prestressed concrete flexural members. The computation of the neutral axis location, which takes into consideration the effect of concrete in tension, can be achieved by solving iteratively tow simultaneous equation derived from forces and moments equilibrium, strain compatibility and linear stress - strain relationship in concrete across the section depth. Once the section depth after cracking is known, it can be used to calculate the effective moment of inertia for deflection analysis. (author). 13 refs., 3 figs., 1 table

  19. Damage Tolerant Analysis of Cracked Al 2024-T3 Panels repaired with Single Boron/Epoxy Patch

    Science.gov (United States)

    Mahajan, Akshay D.; Murthy, A. Ramachandra; Nanda Kumar, M. R.; Gopinath, Smitha

    2018-06-01

    It is known that damage tolerant analysis has two objectives, namely, remaining life prediction and residual strength evaluation. To achieve the these objectives, determination of accurate and reliable fracture parameter is very important. XFEM methodologies for fatigue and fracture analysis of cracked aluminium panels repaired with different patch shapes made of single boron/epoxy have been developed. Heaviside and asymptotic crack tip enrichment functions are employed to model the crack. XFEM formulations such as displacement field formulation and element stiffness matrix formulation are presented. Domain form of interaction integral is employed to determine Stress Intensity Factor of repaired cracked panels. Computed SIFs are incorporated in Paris crack growth model to predict the remaining fatigue life. The residual strength has been computed by using the remaining life approach, which accounts for both crack growth constants and no. of cycles to failure. From the various studies conducted, it is observed that repaired panels have significant effect on reduction of the SIF at the crack tip and hence residual strength as well as remaining life of the patched cracked panels are improved significantly. The predicted remaining life and residual strength will be useful for design of structures/components under fatigue loading.

  20. Validity limits in J-resistance curve determination: A computational approach to ductile crack growth under large-scale yielding conditions. Volume 2

    International Nuclear Information System (INIS)

    Shih, C.F.; Xia, L.; Hutchinson, J.W.

    1995-02-01

    In this report, Volume 2, Mode I crack initiation and growth under plane strain conditions in tough metals are computed using an elastic/plastic continuum model which accounts for void growth and coalescence ahead of the crack tip. The material parameters include the stress-strain properties, along with the parameters characterizing the spacing and volume fraction of voids in material elements lying in the plane of the crack. For a given set of these parameters and a specific specimen, or component, subject to a specific loading, relationships among load, load-line displacement and crack advance can be computed with no restrictions on the extent of plastic deformation. Similarly, there is no limit on crack advance, except that it must take place on the symmetry plane ahead of the initial crack. Suitably defined measures of crack tip loading intensity, such as those based on the J-integral, can also be computed, thereby directly generating crack growth resistance curves. In this report, the model is applied to five specimen geometries which are known to give rise to significantly different crack tip constraints and crack growth resistance behaviors. Computed results are compared with sets of experimental data for two tough steels for four of the specimen types. Details of the load, displacement and crack growth histories are accurately reproduced, even when extensive crack growth takes place under conditions of fully plastic yielding. A description of material resistance to crack initiation and subsequent growth is essential for assessing structural integrity such as nuclear pressure vessels and piping

  1. Simulation and experiment for depth sizing of cracks in anchor bolts by ultrasonic phased array technology

    Science.gov (United States)

    Lin, Shan

    2018-04-01

    There have been lots of reports about the occurrence of cracks in bolts in aging nuclear and thermal power plants. Sizing of such cracks is crucial for assessing the integrity of bolts. Currently, hammering and visual tests are used to detect cracks in bolts. However, they are not applicable for sizing cracks. Although the tip diffraction method is well known as a crack sizing technique, reflection echoes from threads make it difficult to apply this technique to bolts. This paper addresses a method for depth sizing of cracks in bolts by means of ultrasonic phased array technology. Numerical results of wave propagation in bolts by the finite element method (FEM) shows that a peak associated within the vicinity of a crack tip can be observed in the curve of echo intensity versus refraction angle for deep cracks. The refraction angle with respect to this peak decreases as crack depth increases. Such numerical results are verified by experiments on bolt specimens that have electrical discharge machining notches or fatigue cracks with different depths. In the experiment, a 10-MHz linear array probe is used. Depth of cracks in bolts using the refraction angle associated with the peak is determined and compared to actual depths. The comparison shows that accurately determining a crack depth from the inspection results is possible.

  2. Evaluation of cracking in steam generator feedwater piping in pressurized water reactor plants

    International Nuclear Information System (INIS)

    Goldberg, A.; Streit, R.D.

    1981-05-01

    Cracking in feedwater piping was detected near the inlet to steam generators in 15 pressurized water reactor plants. Sections with cracks from nine plants are examined with the objective of identifying the cracking mechanism and assessing various factors that might contribute to this cracking. Using transmission electron microscopy, fatigue striations are observed on replicas of cleaned crack surfaces. Calculations based on the observed striation spacings gave a cyclic stress value of 150 MPa (22 ksi) for one of the major cracks. The direction of crack propagation was invariably related to the piping surface and not to the piping axis. These two factors are consistent with the proposed concept of thermally induced, cyclic, tensile surface stresses and it is concluded that the overriding factor in the cracking problem was the presence of such undocumented cyclic loads

  3. 3D finite element analysis on crack-tip plastic zone

    African Journals Online (AJOL)

    user

    International Journal of Engineering, Science and Technology ... directed in this investigation to achieve a few numerical estimations of 3D plastic zone shape ..... crack front, using domain integral method the software (ABAQUS) automatically.

  4. Criterion of cleavage crack propagation and arrest in a nuclear PWR vessel steel

    International Nuclear Information System (INIS)

    Bousquet, Amaury

    2013-01-01

    The purpose of this PhD thesis is to understand physical mechanisms of cleavage crack propagation and arrest in the 16MND5 PWR vessel steel and to propose a robust predicting model based on a brittle fracture experimental campaign of finely instrumented laboratory specimens associated with numerical computations. First, experiments were carried out on thin CT25 specimens at five temperatures (-150 C, -125 C, -100 C, -7 C, -50 C). Two kinds of crack path, straight or branching path, have been observed. To characterize crack propagation and to measure crack speed, a high-speed framing camera system was used, combined with the development of an experimental protocol which allowed to observe CT surface without icing inside the thermal chamber and on the specimen. The framing camera (520 000 fps) has allowed to have a very accurate estimation of crack speed on the complete ligament of CT (∼ 25 mm). Besides, to analyse experiments and to study the impact of viscosity on the mechanical response around the crack tip, the elastic-viscoplastic behavior of the ferritic steel has been studied up to a strain rate of 104 s -1 for the tested temperatures.The extended Finite Element Method (X-FEM) was used in CAST3M FE software to model crack propagation. Numerical computations combine a local non linear dynamic approach with a RKR type fracture stress criterion to a characteristic distance. The work carried out has confirmed the form of the criterion proposed by Prabel at -125 C, and has identified the dependencies of the criterion on temperature and strain rate. From numerical analyzes in 2D and 3D, a multi-temperature fracture stress criterion, increasing function of the strain rate, was proposed. Predictive modeling were used to confirm the identified criterion on two specimen geometries (CT and compressive ring) in mode I at different temperatures. SEM observations and 3D analyzes made with optical microscope showed that the fracture mechanism was the cleavage associated

  5. Zircaloy-4 stress corrosion by iodine: crack kinetics and influence of irradiation on the crack initiation

    International Nuclear Information System (INIS)

    Serres, A.

    2008-01-01

    During the PWR power transients, iodine-induced stress corrosion cracking (I-SCC) is one of the potential failure modes of Zircaloy-4 fuel claddings under Pellet-Cladding Interaction conditions. The primary objective of this study is to distinguish the parameters that contribute to the I-SCC phenomenon in iodized methanol solutions at ambient temperature, on notched tensile specimens, using crack growth rate measurements provided by Direct Current Potential Drop. The results show that for a KI lower than 20 MPa.m 1/2 , the IG and mixed IG/TG velocity of propagation is a linear function of KI, regardless of the propagation mode. Between 20 and 25 MPa.m 1/2 , the TG crack growth rate also depends linearly on KI, but increases at a faster rate with respect to KI than during the IG and mixed IG/TG propagation steps. The crack propagation direction and plane (LT and TL) have an impact on the propagation modes, but no impact on the kinetics. The increase of iodine content induces an increase of the crack growth rate for a given KI, and a decrease of the KI, threshold, allowing the crack propagation. This work enables us to quantify the effect of iodine content and of KI on the crack propagation step, propose a propagation law taking into accounts these parameters, and improve the I-SCC description for models. During operation, a zirconium cladding is neutron-irradiated, modifying its microstructure and deformation modes. The second objective of the study is therefore to investigate the impact of these modifications on I-SCC. For that purpose, smooth specimens in recrystallized Zircaloy-4 are proton-irradiated to 2 dpa at 305 C, the microstructure and deformation modes of unirradiated and irradiated Zircaloy-4 are characterized by TEM and SEM, and the influence of these radiation-induced modifications on the I-SCC susceptibility is studied. The Laves phases precipitates are slightly modified by irradiation. The formation of P -type dislocation loops correlated with

  6. Standard test method for creep-fatigue crack growth testing

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This test method covers the determination of creep-fatigue crack growth properties of nominally homogeneous materials by use of pre-cracked compact type, C(T), test specimens subjected to uniaxial cyclic forces. It concerns fatigue cycling with sufficiently long loading/unloading rates or hold-times, or both, to cause creep deformation at the crack tip and the creep deformation be responsible for enhanced crack growth per loading cycle. It is intended as a guide for creep-fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. Therefore, this method requires testing of at least two specimens that yield overlapping crack growth rate data. The cyclic conditions responsible for creep-fatigue deformation and enhanced crack growth vary with material and with temperature for a given material. The effects of environment such as time-dependent oxidation in enhancing the crack growth ra...

  7. Crack diffusion coefficient - A candidate fracture toughness parameter for short fiber composites

    Science.gov (United States)

    Mull, M. A.; Chudnovsky, A.; Moet, A.

    1987-01-01

    In brittle matrix composites, crack propagation occurs along random trajectories reflecting the heterogeneous nature of the strength field. Considering the crack trajectory as a diffusive process, the 'crack diffusion coefficient' is introduced. From fatigue crack propagation experiments on a set of identical SEN polyester composite specimens, the variance of the crack tip position along the loading axis is found to be a linear function of the effective 'time'. The latter is taken as the effective crack length. The coefficient of proportionality between variance of the crack trajectory and the effective crack length defines the crack diffusion coefficient D which is found in the present study to be 0.165 mm. This parameter reflects the ability of the composite to deviate the crack from the energetically most efficient path and thus links fracture toughness to the microstructure.

  8. Dynamic crack growth in a nonlocal progressively cavitating solid

    DEFF Research Database (Denmark)

    Needleman, A.; Tvergaard, Viggo

    1998-01-01

    Dynamic crack growth is analyzed numerically using a nonlocal constitutive formulation for a porous ductile material. The delocalization relates to the void growth and coalescence mechanism and is incorporated in terms of an integral condition on the rate of increase of the void volume fraction....... The material is modeled as elastic-viscoplastic with the thermal softening due to adiabatic heating accounted for. Finite element computations are carried our for edge cracked specimens subject to tensile impact loading. Two values of the material characteristic length and two finite-element discretizations...... are used in most computations. The effect of the material characteristic length on the crack growth behavior and on the mesh sensitivity of the results is considered. For comparison purposes, results are also obtained For the corresponding local constitutive relation. The crack growth resistance is found...

  9. An application of the J-integral to an incremental analysis of blunting crack behavior

    International Nuclear Information System (INIS)

    Merkle, J.G.

    1989-01-01

    This paper describes an analytical approach to estimating the elastic-plastic stresses and strains near the tip of a blunting crack with a finite root radius. Rice's original derivation of the path independent J-integral considered the possibility of a finite crack tip root radius. For this problem Creager's elastic analysis gives the relation between the stress intensity factor K I and the near tip stresses. It can be shown that the relation K I 2 = E'J holds when the root radius is finite. Recognizing that elastic-plastic behavior is incrementally linear then allows a derivation to be performed for a bielastic specimen having a crack tip region of reduced modulus, and the result differentiated to estimate elastic-plastic behavior. The result is the incremental form of Neuber's equation. This result does not require the assumption of any particular stress-strain relation. However by assuming a pure power law stress-strain relation and using Ilyushin's principle, the ordinary deformation theory form of Neuber's equation, K σ K var epsilon = K t 2 , is obtained. Applications of the incremental form of Neuber's equation have already been made to fatigue and fracture analysis. This paper helps to provide a theoretical basis for these methods previously considered semiempirical. 26 refs., 4 figs

  10. Study of the inhomogeneity of critical current under in-situ tensile stress for YBCO tape

    Science.gov (United States)

    Zhu, Y. P.; Chen, W.; Zhang, H. Y.; Liu, L. Y.; Pan, X. F.; Yang, X. S.; Zhao, Y.

    2018-07-01

    A Hall sensor system was used to measure the local critical current of YBCO tape with high spatial resolution under in-situ tensile stress. The hot spot generation and minimum quench energy of YBCO tape, which depended on the local critical current, was calculated through the thermoelectric coupling model. With the increase in tensile stress, the cracks which have different dimensions and critical current degradation arose more frequently and lowered the thermal stability of the YBCO tape.

  11. Monitoring of pre-release cracks in prestressed concrete using fiber optic sensors

    Science.gov (United States)

    Abdel-Jaber, Hiba; Glisic, Branko

    2015-04-01

    Prestressed concrete experiences low to no tensile stresses, which results in limiting the occurrence of cracks in prestressed concrete structures. However, the nature of construction of these structures requires the concrete not to be subjected to the compressive force from the prestressing tendons until after it has gained sufficient compressive strength. Although the structure is not subjected to any dead or live load during this period, it is influenced by shrinkage and thermal variations. Thus, the concrete can experience tensile stresses before the required compressive strength has been attained, which can result in the occurrence of "pre-release" cracks. Such cracks are visually closed after the transfer of the prestressing force. However, structural capacity and behavior can be impacted if cracks are not sufficiently closed. This paper researches a method for the verification of the status of pre-release cracks after transfer of the prestressing force, and it is oriented towards achievement of Level IV Structural Health Monitoring (SHM). The method relies on measurements from parallel long-gauge fiber optic sensors embedded in the concrete prior to pouring. The same sensor network is used for the detection and characterization of cracks, as well as the monitoring of the prestressing force transfer and the determination of the extent of closure of pre-release cracks. This paper outlines the researched method and presents its application to a real-life structure, the southeast leg of Streicker Bridge on the Princeton University campus. The application structure is a curved continuous girder that was constructed in 2009. Its deck experienced four pre-release cracks that were closed beyond the critical limits based on the results of this study.

  12. Some Aspects of Formation of Cracks in FRC with Main Reinforcement

    DEFF Research Database (Denmark)

    Brincker, Rune; Simonsen, J.; Hansen, W.

    1997-01-01

    In this paper the response of fibre reinforced concrete (FRC) with main reinforcement in pure tension is considered. Test results are presented showing three distinct regimes: a regime og linear elasticity, a regime of yielding at approximately constant stress, and finally, a regime of strain...... hardening. a simple model is presented which takes into account the debonding between the reinforcement and the fiber reinforced matrix as well as the crack opening relation of the fiber reinforced matrix. The fracture process is described from the un-cracked state and formation of the first crack till......, and a more ductile contribution from the fiber bridging, a plastic regime will be present in the tensile response. The case of a parabolic crack opening relation defines a brittleness number that describes the transition from formation of unstable discrete cracks to smaller cracks controlled by the softening...

  13. The tensile properties and high cyclic fatigue characteristics of Mg-5Li-3Al-1.5Zn-2RE alloy

    International Nuclear Information System (INIS)

    Li Tingqu; Liu Yongbing; Cao Zhanyi; Jiang Dongmei; Cheng Liren

    2010-01-01

    Research highlights: → The PLC phenomenon was observed during tensile deformation in LAZ531-2RE alloy. → The negative SRS in high strain rate regime can be explained by the DSA mechanism. → The higher ductility may be associated with finer-grained microstructure and Li addition. → Fatigue crack propagation was characterized by striation-like features. - Abstract: The tensile and fatigue properties of the Mg-5Li-3Al-1.5Zn-2RE (LAZ531-2RE) alloy were presented. The alloy was prepared by hot extrusion after vacuum casting. The Portevin-Le Chatelier (PLC) phenomenon was observed during tensile deformation. The PLC effect was attributed to the dynamic interaction between solute atoms (Li) and dislocation movement. The abnormal negative strain rate sensitivity (SRS) in high strain rate regime can be explained by the dynamic strain ageing (DSA) mechanism. The higher ductility may be associated with finer-grained microstructure and Li addition. Fatigue crack propagation was characterized by striation-like features. The smaller spacing of fatigue striations and larger fatigue crack propagation zone at the lower total strain amplitude gave rise to a longer fatigue life.

  14. Crack classification in concrete beams using AE parameters

    Science.gov (United States)

    Bahari, N. A. A. S.; Shahidan, S.; Abdullah, S. R.; Ali, N.; Zuki, S. S. Mohd; Ibrahim, M. H. W.; Rahim, M. A.

    2017-11-01

    The acoustic emission (AE) technique is an effective tool for the evaluation of crack growth. The aim of this study is to evaluate crack classification in reinforced concrete beams using statistical analysis. AE has been applied for the early monitoring of reinforced concrete structures using AE parameters such as average frequency, rise time, amplitude counts and duration. This experimental study focuses on the utilisation of this method in evaluating reinforced concrete beams. Beam specimens measuring 150 mm × 250 mm × 1200 mm were tested using a three-point load flexural test using Universal Testing Machines (UTM) together with an AE monitoring system. The results indicated that RA value can be used to determine the relationship between tensile crack and shear movement in reinforced concrete beams.

  15. Comparative Study on Crack Initiation and Propagation of Glass under Thermal Loading

    Directory of Open Access Journals (Sweden)

    Yu Wang

    2016-09-01

    Full Text Available This paper explores the fracture process based on finite element simulation. Both probabilistic and deterministic methods are employed to model crack initiation, and several commonly used criteria are utilized to predict crack growth. It is concluded that the criteria of maximum tensile stress, maximum normal stress, and maximum Mises stress, as well as the Coulomb-Mohr criterion are able to predict the initiation of the first crack. The mixed-mode criteria based on the stress intensity factor (SIF, energy release rate, and the maximum principal stress, as well as the SIF-based maximum circumferential stress criterion are suitable to predict the crack propagation.

  16. Finite element analysis of crack growth from rectangular notch in mixed mode loading

    International Nuclear Information System (INIS)

    Mohd Rawi Mohd Zin

    2002-01-01

    The direction of crack growth from rectangular notch for ductile material is determined in this paper. The ductile material is assumed to exhibit the elastic-plastic behaviour. In the model, the crack is assumed to start when the J-integral fracture criterion exceeded the critical value during the application of load and the crack tip propagated to a priori. The direction of the crack is characterised by maximum principles stress criterion and the mechanism of crack propagation is simulated by deleted element technique. The model is validated with experimental results and it shows good agreement. (Author)

  17. Growth behavior of fatigue cracks in ultrafine grained Cu smooth specimens with a small hole

    Directory of Open Access Journals (Sweden)

    Masahiro Goto

    2015-10-01

    Full Text Available In order to study the growth mechanism of fatigue cracks in ultrafine grained copper, stresscontrolled fatigue tests of round-bar specimens with a small blind hole as a crack starter were conducted. The hole was drilled on the surface where an intersection between the shear plane of the final ECAP processing and the specimen surface makes an angle of 45° or 90° with respect to the loading axis. At a low stress (  a = 90 MPa, the direction of crack paths was nearly perpendicular to the loading direction regardless of the location of the hole. Profile of crack face was examined, showing the aspect ratio (b/a of b/a = 0.82. At a high stress (  a = 240 MPa, although the growth directions inclined 45° and 90° to the loading-axis were observed depending on the location of the drilling hole, crack faces in these cracks were extended along one set of maximum shear stress planes, corresponding to the final ECAP shear plane. The value of aspect ratios was b/a = 0.38 and 1.10 for the cracks with 45° and 90° inclined path directions, respectively. The role of deformation mode at the crack tip areas on crack growth behavior were discussed in terms of the mixed-mode stress intensity factor. The crack path formation at high stress amplitudes was affected by the in-plane shear-mode deformation at the crack tip.

  18. The elastic T-stress for slightly curved or kinked cracks

    DEFF Research Database (Denmark)

    Li, Dong-Feng; Li, Chen-Feng; Qing, Hai

    2010-01-01

    This work presents a solution for the elastic T-stress at the tip of a slightly curved or kinked crack based on a perturbation approach. Compared to other exact or numerical solutions the present solution is accurate for considerable deviations from straightness. The T-stress variation as crack...... extends along a curved trajectory is subsequently examined. It is predicted that T-stress always keeps negative during crack extension when the crack has an initial negative T-stress. In the case of a positive T-stress and non-zero first and second stress intensity factors initially accompanying the crack......, the T-stress is not positive with increasing the extension length until a threshold is exceeded. Based on directional stability criterion with respect to the sign of the T-stress, this result implies that for a straight crack with a positive T-stress, the crack extension path will not turn immediately...

  19. Multi-parameter approximation of stress field in a cracked specimen using purpose-built Java applications

    Czech Academy of Sciences Publication Activity Database

    Veselý, V.; Sopek, J.; Tesař, D.; Frantík, P.; Pail, T.; Seitl, Stanislav

    2015-01-01

    Roč. 9, č. 33 (2015), s. 120-133 ISSN 1971-8993 Institutional support: RVO:68081723 Keywords : Cracked specimen * Near-crack-tip fields * Williams expansion * Higher order terms * Stress field reconstruction * Finite element analysis * Java application Subject RIV: JL - Materials Fatigue, Friction Mechanics

  20. On the behavior of crack surface ligaments

    International Nuclear Information System (INIS)

    Nilsson, P.; Staahle, P.; Sundin, K.G.

    1998-01-01

    Small ligaments connecting the fracture surfaces just behind a moving crack front are assumed to exist under certain conditions. The ligaments are rapidly torn as the crack advances. Inelastic straining of such ligaments influences the energy balance in the fracture process. The rapid tearing of a single ligament is studied both numerically and experimentally. An elastic visco-plastic material model is adopted for finite-element calculations. The results show that relatively large amounts of energy are dissipated during the tearing process. Further, the energy needed to tear a ligament increases rapidly with increasing tearing rate. The computed behavior is partly verified in a few preliminary experiments. The implications for slow stable crack tip speeds during dynamic fracture are discussed. (orig.)