Monitoring crack growth using thermography
International Nuclear Information System (INIS)
Djedjiga, Ait Aouita; Abdeldjalil, Ouahabi
2008-01-01
The purpose of this work is to present a novel strategy for real-time monitoring crack growth of materials. The process is based on the use of thermal data extracted along the horizontal axis of symmetry of single edge notch tension (SENT) specimens, during fatigue tests. These data are exploited using an implemented program to detect in situ the growth of fatigue crack, with the critical size and propagation speed of the crack. This technique has the advantage to be applicable to a wide range of materials regardless of their electrical conductivity and their surface texture. (authors)
A crack growth evaluation method for interacting multiple cracks
International Nuclear Information System (INIS)
Kamaya, Masayuki
2003-01-01
When stress corrosion cracking or corrosion fatigue occurs, multiple cracks are frequently initiated in the same area. According to section XI of the ASME Boiler and Pressure Vessel Code, multiple cracks are considered as a single combined crack in crack growth analysis, if the specified conditions are satisfied. In crack growth processes, however, no prescription for the interference between multiple cracks is given in this code. The JSME Post-Construction Code, issued in May 2000, prescribes the conditions of crack coalescence in the crack growth process. This study aimed to extend this prescription to more general cases. A simulation model was applied, to simulate the crack growth process, taking into account the interference between two cracks. This model made it possible to analyze multiple crack growth behaviors for many cases (e.g. different relative position and length) that could not be studied by experiment only. Based on these analyses, a new crack growth analysis method was suggested for taking into account the interference between multiple cracks. (author)
The crack growth mechanism in asphaltic mixes
Jacobs, M.M.J.; Hopman, P.C.; Molenaar, A.A.A.
1995-01-01
The crack growth mechanism in asphalt concrete (Ac) mixes is studied. In cyclic tests on several asphaltic mixes crack growth is measured, both with crack foils and with cOD-gauges. It is found that crack growth in asphaltic mixes is described by three processes which are parallel in time: cohesive
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...
Microstructural modelling of creep crack growth from a blunted crack
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
Fatigue crack growth in fiber reinforced plastics
Mandell, J. F.
1979-01-01
Fatigue crack growth in fiber composites occurs by such complex modes as to frustrate efforts at developing comprehensive theories and models. Under certain loading conditions and with certain types of reinforcement, simpler modes of fatigue crack growth are observed. These modes are more amenable to modeling efforts, and the fatigue crack growth rate can be predicted in some cases. Thus, a formula for prediction of ligamented mode fatigue crack growth rate is available.
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
Mechanics of quasi-static crack growth
Energy Technology Data Exchange (ETDEWEB)
Rice, J R
1978-10-01
Results on the mechanics of quasi-static crack growth are reviewed. These include recent studies on the geometry and stability of crack paths in elastic-brittle solids, and on the thermodynamics of Griffith cracking, including environmental effects. The relation of crack growth criteria to non-elastic rheological models is considered and paradoxes with energy balance approaches, based on singular crack models, are discussed for visco-elastic, diffuso-elastic, and elastic-plastic materials. Also, recent approaches to prediction of stable crack growth in ductile, elastic-plastic solids are discussed.
International Nuclear Information System (INIS)
Hariprasad, S.; Sastry, S.M.L.; Jerina, K.L.
1994-01-01
The room-temperature fatigue crack growth rates (FCGR) and fracture toughness were evaluated for different crack plane Orientations of an Al-8.5 pct Fe-1.2 pct V-1.7 pct Si alloy produced by planar flow casting (PFC) and atomized melt deposition (AMD) processes. For the alloy produced by the PFC process, properties were determined in six different orientations, including the short transverse directions S-T and S-L. Diffusion bonding and adhesive bonding methods were used to prepare specimens for determining FCGR and fracture toughness in the short transverse direction. Interparticle boundaries control fracture properties in the alloy produced by PFC. Fracture toughness of the PFC alloy varies from 13.4 MPa√ bar m to 30.8 MPa√ bar m, depending on the orientation of the crack plane relative to the interparticle boundaries. Fatigue crack growth resistance and fracture toughness are greater in the L-T, L-S, and T-S directions than in the T-L, S-T, and S-L orientations. The alloy produced by AMD does not exhibit anisotropy in fracture toughness and fatigue crack growth resistance in the as-deposited condition or in the extruded condition. The fracture toughness varies from 17.2 MPa√ bar m to 18.5 MPa√ bar m for the as-deposited condition and from 19.8 MPa√ bar m to 21.0 MPa√ bar m for the extruded condition. Fracture properties are controlled by intrinsic factors in the alloy produced by AMD. Fatigue crack growth rates of the AMD alloy are comparable to those of the PFC alloy in the L-T orientation. The crack propagation modes were studied by optical metallographic examination of crack-microstructure interactions and scanning electron microscopy of the fracture surfaces
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)
A crack opening stress equation for fatigue crack growth
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.
The Growth of Small Corrosion Fatigue Cracks in Alloy 7075
Piascik, Robert S.
2015-01-01
The corrosion fatigue crack growth characteristics of small (greater than 35 micrometers) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500×) crack length measurements in laboratory air and 1% sodium chloride (NaCl) environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.
Stress corrosion crack growth in unirradiated zircaloy
International Nuclear Information System (INIS)
Pettersson, K.
1978-10-01
Experimental techniques suitable for the determination of stress corrosion crack growth rates in irradiated Zircaloy tube have been developed. The techniques have been tested on unirradiated. Zircaloy and it was found that the results were in good agreement with the results of other investigations. Some of the results were obtained at very low stress intensities and the crack growth rates observed, gave no indication of the existance of a K sub(ISCC) for iodine induced stress corrosion cracking in Zircaloy. This is of importance both for fuel rod behavior after a power ramp and for long term storage of spent Zircaloy-clad fuel. (author)
Crack Growth Properties of Sealing Glasses
Salem, Jonathan A.; Tandon, R.
2008-01-01
The crack growth properties of several sealing glasses were measured using constant stress rate testing in 2% and 95% RH (relative humidity). Crack growth parameters measured in high humidity are systematically smaller (n and B) than those measured in low humidity, and velocities for dry environments are approx. 100x lower than for wet environments. The crack velocity is very sensitivity to small changes in RH at low RH. Confidence intervals on parameters that were estimated from propagation of errors were comparable to those from Monte Carlo simulation.
Improvement of elastic-plastic fatigue crack growth evaluation method. 2. Crack opening behavior
Energy Technology Data Exchange (ETDEWEB)
Takahashi, Yukio [Central Research Inst. of Electric Power Industry, Tokyo (Japan)
2001-05-01
Evaluation of crack growth behavior under cyclic loading is often required in the structural integrity assessment of cracked components. Closing and re-opening of the crack give large influence on crack growth rate through the change of fracture mechanics parameters. Based on the finite element analysis for a center-cracked plate, dependency of crack opening ratio on applied stress range and mean stress was examined. Simple formulae for representing the results were derived for plane stress and plane strain conditions. (author)
Fatigue crack initiation and growth life prediction with statistical consideration
International Nuclear Information System (INIS)
Kwon, J.D.; Choi, S.H.; Kwak, S.G.; Chun, K.O.
1991-01-01
Life prediction or residual life prediction of structures or machines is one of the most strongly world wide needed problems as requirement in the stage of slowly developing economy which comes after rapidly and highly developing stage. For the purpose of statistical life prediction, fatigue test was conducted under the 3 stress levels, and for each stress level, 20 specimens are used. The statistical properties of the crack growth parameter m and C in the fatigue crack growth law of da/dN = C(ΔK) m , and the relationship between m and C, and the statistical distribution pattern of fatigue crack initiation, growth and fracture lives can be obtained by experimental results
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.)
Fatigue crack growth from a cracked elastic particle into a ductile matrix
Groh, S.; Olarnrithinun, S.; Curtin, W. A.; Needleman, A.; Deshpande, V. S.; Van der Giessen, E.
2008-01-01
The monotonic and cyclic crack growth rate of cracks is strongly influenced by the microstructure. Here, the growth of cracks emanating from pre-cracked micron-scale elastic particles and growing into single crystals is investigated, with a focus on the effects of (i) plastic confinement due to the
Parametric analysis of fatigue crack growth
International Nuclear Information System (INIS)
Carden, A.E.
1975-01-01
The effect of temperature and frequency on fatigue crack growth were empirically observed and treated as a coefficient on a stress intensity factor term. The stress intensity factor term is a function of Ksub(max), Ksub(min) (or stress ratio) and a threshold K term. The apparent threshold values were selected in order to linearize the data. At 1000 0 F a constant da/dt (creep crack growth rate) is approached for cycle periods approaching 2000 s indicating a limiting and linear-inverse frequency effect. (author)
International Nuclear Information System (INIS)
Lee, Shin Young; Song, Ji Ho
2000-01-01
Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow-and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks
Crack growth by micropore coalescence at high temperatures
International Nuclear Information System (INIS)
Beere, W.
1981-01-01
At high temperatures in the creep regime the stress distribution around a crack is different from the low temperature elastically generated distribution. The stress distribution ahead of the crack is calculated for a crack preceded by an array of growing cavities. The cavities maintain a displacement wedge ahead of the crack. When the displacement wedge is less than one-tenth the crack length the driving force for crack growth is similar to an all elastically loaded crack. When the deforming wedge exceeds the crack length the net section stress controls crack growth. An expression is derived for a crack growing by the growth and coalescence of cavities situated in the crack plane. It is predicted that at high temperatures above a critical stress intensity, the crack propagates in a brittle fashion. (author)
Numerical treatment of creep crack growth
International Nuclear Information System (INIS)
Kienzler, R.; Hollstein, T.
1990-06-01
To accomplish the safety analysis and to predict the lifetime of high-termpature components with flaws, several concepts have been proposed to correlate creep-crack initiation and growth with fracture mechanics parameters. The concepts of stress-intensity factor K, reference stress σ ref , line integral C * , and others will be discussed. Among them, the C * -integral concept seems to have the widest range of applicability, if large creep zones develop and steady state creep conditions can be assumed. The numerical evaluation of C * by the virtual crack extension method is described. The methods are demonstrated by two- and three-dimensional finite element simulations including creep crack growth. As for ductile fracture experiments, plane stress and plane strain simulations are bounds to the three-dimensional simulations which agree well with corresponding experiments. (orig.)
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 ...
1972-01-01
At the current rate of population growth, world population by 2000 is expected to reach 7 billion or more, with developing countries accounting for some 5.4 billion, and economically advanced nations accounting for 1.6 billion. 'Population explosion' is the result of falling mortality rates and continuing high birth rates. Many European countries, and Japan, have already completed what is termed as demographic transition, that is, birth rates have fallen to below 20 births per 1000 population, death rates to 10/1000 population, and annual growth rates are 1% or less; annual growth rates for less developed countries ranged from 2 to 3.5%. Less developed countries can be divided into 3 groups: 1) countries with both high birth and death rates; 2) countries with high birth rates and low death rates; and 3) countries with intermediate and declining birth rates and low death rates. Rapid population growth has serious economic consequences. It encourages inequities in income distribution; it limits rate of growth of gross national product by holding down level of savings and capital investments; it exerts pressure on agricultural production and land; and it creates unemployment problems. In addition, the quality of education for increasing number of chidren is adversely affected, as high proportions of children reduce the amount that can be spent for the education of each child out of the educational budget; the cost and adequacy of health and welfare services are affected in a similar way. Other serious consequences of rapid population growth are maternal death and illness, and physical and mental retardation of children of very poor families. It is very urgent that over a billion births be prevented in the next 30 years to reduce annual population growth rate from the current 2% to 1% per year.
Crack initiation and growth in welded structures
International Nuclear Information System (INIS)
Assire, A.
2000-01-01
This work concerns the remaining life assessment of a structure containing initial defects of manufacturing. High temperature crack initiation and growth are studied for austenitic stainless steels, and defect assessment methods are improved in order to take into account welded structures. For these one, the probability to have a defect is significant. Two kinds of approaches are commonly used for defect assessment analysis. Fracture mechanics global approach with an energetic criterion, and local approach with a model taking into account the physical damage mechanism. For both approaches mechanical fields (stress and strain) have to be computed everywhere within the structure. Then, Finite Element computation is needed. The first part of the thesis concerns the identification of non linear kinematic and isotropic constitutive models. A pseudo-analytical method is proposed for a 'Two Inelastic Strain' model. This method provides a strategy of identification with a mechanical meaning, and this enables to associate each parameter to a physical phenomenon. Existing identifications are improved for cyclic plasticity and creep on a large range of stress levels. The second part concerns high temperature crack initiation and growth in welded structures. Finite Element analysis on plate and tube experimental configuration enable to understand the phenomenons of interaction between base metal and weld metal under mechanical and thermal loading. Concerning global approach, criteria based on C* parameter (Rice integral for visco-plasticity) are used. Finite Element computations underline the fact that for a defect located in the weld metal, C* values strongly depend on the base metal creep strain rate, because widespread visco-plasticity is located in both metals. A simplified method, based on the reference stress approach, is proposed and validated with Finite Element results. Creep crack growth simplified assessment is a quite good validation of the experimental results
Formation of thermal fatigue cracks in periodic rapid quenching of metal
Energy Technology Data Exchange (ETDEWEB)
Ots, A. [Tallinn Technical University, Thermal Engineering Department, Tallinn (Estonia)
1998-12-31
Water lancing is an effective technique for cleaning boiler heating surfaces from ash deposits by burning low-grade fuels with complicated composition of mineral matter. In water cleaning cycles of boiler`s heat transfer surfaces due to rapid quenching destruction of corrosion protective oxide film and formation of thermal fatigue cracks on the outer surface of the tube`s metal occur. The criterion of the thermal fatigue cracks` formation and their growth intensity depend on the character of temperature field in the tube`s metal outer layer. The solution of non-stationary heat conductivity equation for metal rapid quenching conditions is given. The convective heat transfer coefficients from hot metal surface to water jet were established experimentally. Thermal fatigue crack growth intensity was investigated in real boilers` heat transfer surfaces` tubes as well as in laboratory conditions. The formula for predicting thermal fatigue cracks` depth depending on the number of cleaning cycles. (orig.) 5 refs.
Formation of thermal fatigue cracks in periodic rapid quenching of metal
Energy Technology Data Exchange (ETDEWEB)
Ots, A [Tallinn Technical University, Thermal Engineering Department, Tallinn (Estonia)
1999-12-31
Water lancing is an effective technique for cleaning boiler heating surfaces from ash deposits by burning low-grade fuels with complicated composition of mineral matter. In water cleaning cycles of boiler`s heat transfer surfaces due to rapid quenching destruction of corrosion protective oxide film and formation of thermal fatigue cracks on the outer surface of the tube`s metal occur. The criterion of the thermal fatigue cracks` formation and their growth intensity depend on the character of temperature field in the tube`s metal outer layer. The solution of non-stationary heat conductivity equation for metal rapid quenching conditions is given. The convective heat transfer coefficients from hot metal surface to water jet were established experimentally. Thermal fatigue crack growth intensity was investigated in real boilers` heat transfer surfaces` tubes as well as in laboratory conditions. The formula for predicting thermal fatigue cracks` depth depending on the number of cleaning cycles. (orig.) 5 refs.
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
On Subsurface Crack Growth in Fibre Metal Laminate Materials
National Research Council Canada - National Science Library
Randall, Christian
2003-01-01
Fatigue crack growth in fibre metal laminates (FMLs) is significantly more complex than in monolithic materials due to the interaction of various physical mechanisms that govern the growth of cracks in laminates...
Crack Growth along Interfaces in Porous Ceramic Layers
DEFF Research Database (Denmark)
Sørensen, Bent F.; Horsewell, Andy
2001-01-01
Crack growth along porous ceramic layers was studied experimentally. Double cantilever beam sandwich specimens were loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope enabling in situ observations...
Some considerations regarding the creep crack growth threshold
International Nuclear Information System (INIS)
Thouless, M.D.; Evans, A.G.
1984-01-01
The preceding analysis reveals that the existence of a threshold determined by the sintering stress does not influence the post threshold crack velocity. Considerations of the sintering stress can thus be conveniently excluded from analysis of the post threshold crack velocity. The presence of a crack growth threshold has been predicted, based on the existence of cavity nucleation controlled crack growth. A preliminary analysis of cavity nucleation rates within the damage zone reveals that this threshold is relatively abrupt, in accord with experimental observations. Consequently, at stress intensities below K /SUB th/ growth becomes nucleation limited and crack blunting occurs in preference to crack growth
Modeling of multibranched crosslike crack growth
International Nuclear Information System (INIS)
Canessa, E.; Tanatar, B.
1991-06-01
Multibranched crosslike crack patterns formed in concentrically loaded square plates are studied in terms of fractal geometry, where the associated fractal dimension d f is calculated for their characterization. We apply simplest deterministic and stochastic approaches at a phenomenological level in an attempt to find generic features as guidelines for future experimental and theoretical work. The deterministic model for fracture propagation we apply, which is a variant of the discretized Laplace approach for randomly ramified fractal cracks proposed by Takayasu, reproduces the basic ingredients of observed complex fracture patters. The stochastic model, although is not strictly a model for crack propagation, is based on diffusion-limited aggregation (DLA) for fractal growth and produces slightly more realistic assessment of the crosslike growth of the cracks in asymmetric multibranches. Nevertheless, this simple ad-hoc DLA-version for modeling the present phenomena as well as the deterministic approach for fracture propagation give fractal dimensionality for the fracture pattern in accord with our estimations made from recent experimental data. It is found that there is a crossover of two fractal dimensions, corresponding to the core (higher d f ) and multibranched crosslike (lower D f ) regions, that contains loops, that are interpreted as representing different symmetry regions within the square plates of finite size. (author). 26 refs, 5 figs
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.
Mixed-Mode Crack Growth in Wood
Directory of Open Access Journals (Sweden)
Octavian POP
2012-09-01
Full Text Available In timber elements the mixed mode dependsessentially of wood anatomy and load configuration.In these conditions, in order to evaluate the materialbehavior and the fracture process, it’s necessary toseparate the part of each mode. The mixed modeseparation allows evaluating the amplitude offracture mode. In the present paper, using a mixedmodecrack growth specimen made in Douglas fir,the mixed mode crack growth process is studythanks to marks tracking method. Using the markstracking method the characteristic displacementsassociated to opening and shear mode aremeasured. From the experimental measurements,the energy release rate associated to opening andshear modes is calculated into to account the crackadvancement during the test.
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
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.
Epitaxial Growth and Cracking Mechanisms of Thermally Sprayed Ceramic Splats
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.
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.)
Smart Patches for Monitoring Fatigue Crack Growth in Aircraft Structures
National Research Council Canada - National Science Library
Ihn, Jeong-Beom
2001-01-01
A built-in cost-effective diagnostic system for monitoring crack growth in aircraft structures was developed, particularly for riveted fuselage joints and cracked aircraft parts with composite bonded patches...
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...
Prediction of Crack Growth Aqueous Environments.
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
Miniaturized fatigue crack growth specimen technology and results
International Nuclear Information System (INIS)
Puigh, R.J.; Bauer, R.E.; Ermi, A.M.; Chin, B.A.
1981-01-01
The miniature fatigue crack propagation technology has been extended to in-cell fabrication of irradiated specimens. Baseline testing of selected titanium alloys has been performed at 25 0 C in air. At relatively small values for the stress intensity factor, ΔK, the crack growth rates for all titanium alloys investigated are within a factor of three. The crack growth rates for these titanium alloys are a factor of three greater than the crack growth rates of either 316SS (20% CW) or HT-9. Each of the titanium alloys has observable crack propagation for stress intensity factors as small as 4.2 MPa√m
Fatigue crack growth in additive manufactured products
Directory of Open Access Journals (Sweden)
A. Riemer
2015-10-01
Full Text Available Additive Manufacturing (AM is a new innovative technique that allows the direct fabrication of complex, individual, delicate and high-strength products, based on their 3D data. Selective Laser Melting (SLM is one of the AM processes that generates metallic components layer by layer using powder-bed technique. The irradiation and consequent melting of metallic powder is realised by the laser source. Employing SLM, especially complex and individual products, such as implants or aerospace parts, are well suited for economic production in small batches. The first important issue in this work was to analyse the fatigue crack growth (FCG in titanium alloy Ti-6-4 and stainless steel 316L processed by SLM. As a first step, stress intensity range decreasing tests were performed on SLM samples in their “as-built” condition. The next step was to adopt measures for optimisation of fatigue crack growth performance of SLM parts. For this purpose various heat treatments such as stress relief annealing and hot isostatic pressing (HIP were applied to the CT specimens. Finally, the strong impact of heat treatment on the residual lifetime was demonstrated by numerical fatigue crack growth simulations. For this purpose, the hip joint implant consisting of Ti-6-4 and processed by SLM was taken into account. It was found that residual stresses have a strong influence on the crack growth in Ti-6-4, while the influence of the micro-pores on the threshold values remains low. In contrast the results for 316L show that its fracturemechanical behaviour is not affected by residual stresses, whereas the microstructural features lead to modification in the da/dN-K-data. The second fundamental aim of this work was to demonstrate the possibilities of the SLM process. For that reason, the individually tailored bicycle crank was optimised regarding its weight and local stresses and finally manufactured using the SLM system. The iterative optimisation procedure was based on
Time-dependent crack growth in steam generator tube leakage
International Nuclear Information System (INIS)
Chung, H.D.; Lee, J.H.; Park, Y.W.; Choi, Y.H.
2006-01-01
In general, cracks found in steam generator tubes have semi-elliptical shapes and it is assumed to be rectangular shape for conservatism after crack penetration. Hence, the leak and crack growth behavior has not been clearly understood after the elliptical crack penetrates the tube wall. Several experimental results performed by Argonne Nation Laboratory exhibited time-dependent crack growth behavior of rectangular flaws as well as trapezoidal flaws under constant pressure. The crack growth faster than expected was observed in both cases, which is likely attributed to time-dependent crack growth accompanied by fatigue sources such as the interaction between active jet and crack. The stress intensity factor, K 1 , is necessary for the prediction of the observed fatigue crack growth behavior. However, no K 1 solution is available for a trapezoidal flaw. The objective of this study is to develop the stress intensity factor which can be used for the fatigue analysis of a trapezoidal crack. To simplify the analysis, the crack is assumed to be a symmetric trapezoidal shape. A new K 1 formula for axial trapezoidal through-wall cracks was proposed based on the FEM results. (author)
Subcritical crack growth along polymer interfaces
Gurumurthy, Charavana Kumara
2000-10-01
The adhesion characteristics have been investigated for a polyimide (PI)/model epoxy (ME) interface that is important for microelectronic applications. The fracture toughness (G*c) of this interface has been measured using an asymmetric double cantilever beam (ADCB) technique. The G*c is low, 10-25 J/m 2, and is sensitive to the mechanical phase angle psi. A modified ADCB setup has been used to measure the subcritical crack growth velocity v due to the stress-assisted water attack (SAWA) at various relative humidities (RH) and temperatures (T) as a function of its driving force (the strain energy release rate) G*. The threshold G* decreases remarkably. Above the threshold log v rises linearly with √ G* (a hydrolysis controlled regime) but then enters a regime where the crack velocity is almost independent of √G*, i.e., v = v* (a transport controlled regime). A model for SAWA has been developed based on thermally-activated kinetics for hydrolysis of the ester covalent bonds that bridge from one side to the other of the interface. A new technique has been developed for the determination of the fatigue crack growth under thermal (T) and hydro-thermal (HT) conditions as a function of the range in the strain energy release rate (DeltaG). Under T-fatigue, the fatigue crack growth per unit temperature cycle (da/dN) increases as a power of DeltaG, i.e., a Paris law relationship holds. The HT da/dN measured is higher than da/dN under T-fatigue conditions and has been successfully modeled as a summation of two components: (a) the da/dN due to T-fatigue and (b) the da/dN due to the SAWA along the interface for a given T-cycle. A surface modification procedure that converts a thin interpenetrated by a solvent cast ME is used to strengthen ME/PI interface. The G* c increases with the interpenetration distance w. Increasing w also improves the resistance of the PI/ME interface to SAWA with the threshold G* increasing and the water transport controlled velocity (v
Predominantly elastic crack growth under combined creep-fatigue cycling
International Nuclear Information System (INIS)
Lloyd, G.J.
1979-01-01
A rationalization of the various observed effects of combined creep-fatigue cycling upon predominantly elastic fatigue-crack propagation in austenitic steel is presented. Existing and new evidence is used to show two main groups of behaviour: (i) material and cycling conditions which lead to modest increases (6-8 times) in the rate of crack growth are associated with relaxation-induced changes in the material deformation characteristics, and (ii) material and cycling conditions severe enough to generate internal fracture damage lead to significant (up to a factor of 30) increases in crack growth rate when compared with fast-cycling crack propagation rates at the same temperature. A working hypothesis is presented to show that the boundary between the two groups occurs when the scale of the nucleated creep damage is of the same magnitude as the crack tip opening displacement. This leads to the possibility of unstable crack advance. Creep crack growth rates are shown to provide an upper bound to creep-fatigue crack growth rates when crack advance is unstable. If the deformation properties only are affected by the creep-fatigue cycling then creep crack growth rates provide a lower bound. The role of intergranular oxygen corrosion in very low frequency crack growth tests is also briefly discussed. (author)
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)
The crack growth resistance of thin steel sheets under eccentric ...
Indian Academy of Sciences (India)
Ľ AMBRIŠKO
2018-03-10
Mar 10, 2018 ... Abstract. The stable crack growth in thin steel sheets is the topic of this paper. The crack opening was observed using a videoextensometry system, allowing the crack extension determination. JR-curve and dR-curve were established from obtained data. The ductile tearing properties of different thin sheets ...
Stress corrosion and corrosion fatigue crack growth monitoring in metals
International Nuclear Information System (INIS)
Senadheera, T.; Shipilov, S.A.
2003-01-01
Environmentally assisted cracking (including stress corrosion cracking and corrosion fatigue) is one of the major causes for materials failure in a wide variety of industries. It is extremely important to understand the mechanism(s) of environmentally assisted crack propagation in structural materials so as to choose correctly from among the various possibilities-alloying elements, heat treatment of steels, parameters of cathodic protection, and inhibitors-to prevent in-service failures due to stress corrosion cracking and corrosion fatigue. An important step towards understanding the mechanism of environmentally assisted crack propagation is designing a testing machine for crack growth monitoring and that simultaneously provides measurement of electrochemical parameters. In the present paper, a direct current (DC) potential drop method for monitoring crack propagation in metals and a testing machine that uses this method and allows for measuring electrochemical parameters during stress corrosion and corrosion fatigue crack growth are described. (author)
Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth
Czech Academy of Sciences Publication Activity Database
Kruml, Tomáš; Hutař, Pavel; Náhlík, Luboš; Seitl, Stanislav; Polák, Jaroslav
2011-01-01
Roč. 412, 1 (2011), s. 7-12 ISSN 0022-3115 R&D Projects: GA ČR GA106/09/1954; GA ČR GA101/09/0867 Institutional research plan: CEZ:AV0Z20410507 Keywords : ferritic-martensitic steel * long crack growth * small crack growth * crack closure Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.052, year: 2011
Fatigue crack growth in an aluminum alloy-fractographic study
Salam, I.; Muhammad, W.; Ejaz, N.
2016-08-01
A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.
Fatigue crack growth and fracture behavior of bainitic rail steels.
2011-09-01
"The microstructuremechanical properties relationships, fracture toughness, fatigue crack growth and fracture surface morphology of J6 bainitic, manganese, and pearlitic rail steels were studied. Microstructuremechanical properties correlation ...
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
Fatigue crack growth behavior under cyclic thermal transient stress
International Nuclear Information System (INIS)
Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.
1986-01-01
Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)
Fatigue crack growth behavior under cyclic transient thermal stress
International Nuclear Information System (INIS)
Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.
1987-01-01
Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)
Hydrogen induced crack growth in Grade-12 titanium
International Nuclear Information System (INIS)
Ahn, T.M.; Lee, K.S.
1984-01-01
Internal hydrogen induced crack growth rates were measured in Grade-12 titanium which is a candidate material for high-level nuclear waste containers. As-received and hydrogen charged samples (5 ppM to 330 ppM hydrogen) were used for slow crack growth measurements at constant loads using a Krak Gauge. The testing temperature ranged from room temperature to 148 0 C. The crack growth kinetics under low to moderate loads are linear, but this linear rate is interrupted by discrete fast crack jump segments with parabolic or cubic type kinetics. These fast jump segments are thought to be associated with the passage of the crack front through the alpha-beta interface phase or with the initial loading sequence. By measuring striation spacings on the fracture surface, most crack growth rates observed are found to be in stage II. The striations are considered to be associated with hydride fracture. The crack path is either transgranular in the alpha phase or interfacial in the alpha phase adjacent to the beta phase. For transgranular growth, crack growth rates are constant and slower than those for interfacial growth which is associated with fast crack growth through a high hydrogen concentration region. Most stage II crack growth rates depend slightly on the stress intensity suggesting the contribution of plastic tearing process to stage II kinetics. The activation energies for crack growth are much lower than the activation energy of hydrogen diffusion through the alpha phase, implying that hydrogen is transported along dislocations, grain boundaries or interfaces. When the temperature is increased, the crack velocity first reaches a maximum and then decreases at higher temperatures. These temperature effects come from lower hydrogen concentration trapped at dislocations or from slower hydride nucleation kinetics, both at higher temperatures
Stochastic modeling of thermal fatigue crack growth
Radu, Vasile
2015-01-01
The book describes a systematic stochastic modeling approach for assessing thermal-fatigue crack-growth in mixing tees, based on the power spectral density of temperature fluctuation at the inner pipe surface. It shows the development of a frequency-temperature response function in the framework of single-input, single-output (SISO) methodology from random noise/signal theory under sinusoidal input. The frequency response of stress intensity factor (SIF) is obtained by a polynomial fitting procedure of thermal stress profiles at various instants of time. The method, which takes into account the variability of material properties, and has been implemented in a real-world application, estimates the probabilities of failure by considering a limit state function and Monte Carlo analysis, which are based on the proposed stochastic model. Written in a comprehensive and accessible style, this book presents a new and effective method for assessing thermal fatigue crack, and it is intended as a concise and practice-or...
Crack growth rate of PWR piping
International Nuclear Information System (INIS)
Bethmont, M.; Doyen, J.J.; Lebey, J.
1979-01-01
The Aquitaine 1 program, carried out jointly by FRAMATOME and the CEA is intended to improve knowledge about cracking mechanisms in AISI 316 L austenitic stainless steel under conditions similar to those of the PWR environment (irradiation excluded). Experiments of fatigue crack growth are performed on piping elements, scale 1/4 of primary pipings, by means of internal hydraulic cyclic pressure. Interpretation of results requires a knowledge of the stress intensity factor Ksub(I) at the front of the crack. Results of a series of calculations of Ksub(I) obtained by different methods for defects of finite and infinite length (three dimensional calculations) are given in the paper. The following have been used: calculations by finite elements, calculations by weight function. Notches are machined on the test pipes, which are subjected to internal hydraulic pressure cycles, under cold conditions, to initiate a crack at the tip of the notch. They are then cycled at a frequency of 4 cycles/hour on on water demineralised loop at a temperature of 280 0 C, the pressure varying at each cycle between approximately 160 bars and 3 bars. After each test, a specimen containing the defect is taken from the pipe for micrographic analysis. For the first test the length of the longitudinal external defect is assumed infinite. The number of cycles carried out is 5880 cycles. Two defects are machined in the tube for the second test. The number of cycles carried out is N = 440. The tests are performed under hot conditions (T = 280 0 C). For the third test two defects are analysed under cold and hot conditions. The number of cycles carried out for the external defect is 7000 when hot and 90000 when cold. The number of cycles for the internal defect is 1650 when hot and 68000 when cold. In order to interpret the results, the data da/dN are plotted on a diagram versus ΔK. Comparisons are made between these results and the curves from laboratory tests
Mechanism of Fatigue Crack Growth of Bridge Steel Structures
Directory of Open Access Journals (Sweden)
Zhu H.
2016-12-01
Full Text Available This study was carried out on the background of Sutong Bridge project based on fracture mechanics, aiming at analyzing the growth mechanism of fatigue cracks of a bridge under the load of vehicles. Stress intensity factor (SIF can be calculated by various methods. Three steel plates with different kinds of cracks were taken as the samples in this study. With the combination of finite element analysis software ABAQUS and the J integral method, SIF values of the samples were calculated. After that, the extended finite element method in the simulation of fatigue crack growth was introduced, and the simulation of crack growth paths under different external loads was analyzed. At last, we took a partial model from the Sutong Bridge and supposed its two dangerous parts already had fine cracks; then simulative vehicle load was added onto the U-rib to predict crack growth paths using the extended finite element method.
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)
Mechanism of electric fatigue crack growth in lead zirconate titanate
International Nuclear Information System (INIS)
Westram, Ilona; Oates, William S.; Lupascu, Doru C.; Roedel, Juergen; Lynch, Christopher S.
2007-01-01
A series of experiments was performed with through-thickness cracks in ferroelectric double cantilever beam (DCB) specimens. Cyclic electric fields of different amplitudes were applied which resulted in cyclic crack propagation perpendicular to the electric field direction. Crack propagation was observed optically and three regimes were identified: a pop-in from a notch, steady-state crack growth and a decrease of the crack growth rate with increasing cycle number. Crack growth only occurred if the applied field exceeded the coercive field strength of the material. Furthermore, the crack extended during each field reversal and the crack growth rate increased with increasing field. Based on the experimental observations, a mechanistic understanding was developed and contrasted with a nonlinear finite element analysis which quantified the stress intensity in the DCB specimens. The driving forces for crack formation at the notch and subsequent fatigue crack growth were computed based on the distribution of residual stresses due to ferroelectric switching. The finite element results are in good agreement with the experimental observations and support the proposed mechanism
Influence of surrounding environment on subcritical crack growth in marble
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.
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
Thermo-Mechanical Fatigue Crack Growth of RR1000.
Pretty, Christopher John; Whitaker, Mark Thomas; Williams, Steve John
2017-01-04
Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.
Thermo-Mechanical Fatigue Crack Growth of RR1000
Directory of Open Access Journals (Sweden)
Christopher John Pretty
2017-01-01
Full Text Available Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP testing produces accelerated crack growth rates compared with out-of-phase (OOP due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.
Fatigue crack growth due to overloads in plain concrete using ...
Indian Academy of Sciences (India)
cation of overload on concrete structures, acceleration in the crack growth process .... study by the same authors, Ray & Chandra Kishen (2010), they have employed the population growth ...... Institute of Technology, University of Trondheim.
SCC crack growth rate of cold worked 316L stainless steel in PWR environment
Du, Donghai; Chen, Kai; Yu, Lun; lu, Hui; Zhang, Lefu; Shi, Xiuqiang; Xu, Xuelian
2015-01-01
Many component failures in nuclear power plants were found to be caused by stress corrosion cracking (SCC) of cold worked austenitic steels. Some of the pressure boundary component materials are even cold worked up to 35% plastic deformation, leaving high residual stress and inducing high growth rate of corrosion crack. Controlling water chemistry is one of the best counter measure to mitigate this problem. In this work, the effects of temperature (200 up to 325 °C) and dissolved oxygen (0 up to 2000 μg/L) on SCC crack growth rates of cold worked austenitic stainless steel type 316L have been tested by using direct current potential drop (DCPD) method. The results showed that temperature affected SCC crack growth rates more significantly in oxygenated water than in deaerated water. In argon deaerated water, the crack growth rate exhibited a peak at about 250 °C, which needs further verification. At 325 °C, the SCC crack growth rate increased rapidly with the increase of dissolved oxygen concentration within the range from 0 up to 200 μg/L, while when dissolved oxygen was above 200 μg/L, the crack growth rate followed a shallower dependence on dissolved oxygen concentration.
International Nuclear Information System (INIS)
Hendry, S.
1993-01-01
This time last year China's paramount leader, Deng Xiaoping, launched the country on another bout of fast-paced economic growth and restructuring. After three years of riding out political and economic clampdown, foreign chemical companies were jerked awake by major changes in China's chemical industry. As the state becomes less involved with managing the economy, unleashing 12% gross national product growth, closer involvement with domestic factories has become attractive and essential. MCI officials say government funds will now be channeled toward clearing energy and transport bottlenecks, and chemical enterprises will be given more chance to turn a profit. They will be allowed to issue shares, seek foreign investment partners themselves, and bypass trading companies like China National Import-Export Corp. (Sinochem), the former state monopoly. Foreign analysts question whether China's finances and oil resources can support expansion. Even if they can, Cai estimates that ethylene imports will remain around the present level of 1 million tons. To further guarantee chemical supplies, China has invested in urea and polypropylene plants in the US and polystyrene plant in Hong Kong
Crack growth prediction for low-cycle fatigue regime
International Nuclear Information System (INIS)
Kamaya, Masayuki
2017-01-01
The objective of this study is to show a crack growth prediction procedure for the low-cycle fatigue regime. First, fatigue crack growth tests using Type 316 stainless steel specimens at room temperature were reviewed. It was seen that the crack growth rates correlated well with the equivalent stress intensify factor, which was derived using strain range instead of stress range. Furthermore, the effective equivalent stress intensify factor derived using the effective strain range exhibited excellent correlation with the crack growth rates obtained under various specimen geometries and loading conditions including high and low-cycle regimens. The obtained crack growth rates were also compared with the growth rate prescribed in the fitness-for-service code of the Japan Society of Mechanical Engineers (JSME). The test results agreed with the growth rate of JSME code. Finally, the procedure for predicting the low-cycle fatigue crack growth was shown. Although the JSME code is aimed at predicting fatigue crack growth for the so-called small scale yielding condition (high-cycle fatigue regime), the material constants determined for the high-cycle fatigue regime can be used even for the low-cycle fatigue regime. (author)
International Nuclear Information System (INIS)
Hayes, D.
2000-01-01
The Indian government has published (in Hydrocarbon Vision 2025) its ideas for a long term strategy for its oil industry which is currently growing at an unprecedented rate. Increasing domestic production and investment in oil exploration and production overseas figure strongly in the plan. At present, India has a refining surplus but with an annual growth of 8-10%, this will disappear in the next 2-3 years. The report recommends that India should maintain 90% self-sufficiency in refining. The report sees development of the domestic oil industry as globally competitive and helping safeguard India's assets. The capability of India's refineries, current upgrading, the newer refineries and plans for new projects are all mentioned
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.
Crack growth determination on laboratory components
International Nuclear Information System (INIS)
Hurst, R.C.
1993-01-01
In order to aid design and support remanent life assessment of plant components operating at elevated temperatures, the reliability of the analytical methods, which translate materials data procured from the laboratory to the behaviour of actual components, requires validation. Such a validation can of course be interpreted from operating plant, however the potential risks involved encourage the development of out of plant techniques for the validation of representative components. For meaningful validation, these techniques need careful control and high accuracy which can best be achieved in a laboratory environment. As the laboratory component test should be designed to simulate actual plant conditions as closely as possible, the direct extension of the results to the plant component case requires scaling up. Consequently the successful development of such a test may even lead to the advantageous situation where it could form an alternative to the conventional route where, for example, it may not be possible to obtain the plant component's metallurgical structure in a conventional specimen or, alternatively, when too many assumptions are required in the analysis when translating to different geometries and stress systems. Under these conditions, in spite of the more sophisticated test requirements, it may prove more reasonable to opt for the more representative laboratory component data for use in design or lifetime prediction. The present work describes the application of the component validation test philosophy to the problem of crack growth under two rather different loading conditions. In both cases, crack growth is measured using the direct current potential drop (PD) technique on tubular metallic components containing artificial defects, however the plant conditions to be simulated lead to either creep or thermal fatigue. The creep studies on Alloy 800H support heat exchanger design for nuclear plant, solar towers and chemical plant, whereas the work on the
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....
Thermal fatigue crack growth analysis in a nozzle corner
International Nuclear Information System (INIS)
Blauel, J.G.; Hodulak, L.
1983-01-01
Calculations of the crack growth under local thermal shock fatigue are performed. Estimates of crack growth are based on stress distributions obtained by a finite element analysis for thermal transients in the structure without crack. Stress intensity factors are calculated using interpolation formulae derived from known basic solutions for part-through cracks under constant and linearly varying load. The crack propagation at selected parts of the crack front is calculated stepwise by integration of the Paris law with material constants C and n interpolated from test results on compact specimens at constant temperatures. Experimental results for the model vessel test MB1 at an internal pressure of 14 N/mm 2 and a temperature of 320 0 C exposed to a repeated local spraying with cold water are presented and compared to predictions
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.
Fatigue crack growth behavior in equine cortical bone
Shelton, Debbie Renee
2001-07-01
Objectives for this research were to experimentally determine crack growth rates, da/dN, as a function of alternating stress intensity factor, DeltaK, for specimens from lateral and dorsal regions of equine third metacarpal cortical bone tissue, and to determine if the results were described by the Paris law. In one set of experiments, specimens were oriented for crack propagation in the circumferential direction with the crack plane transverse to the long axis of the bone. In the second set of experiments, specimens were oriented for radial crack growth with the crack plane parallel to the long axis of the bone. Results of fatigue tests from the latter specimens were used to evaluate the hypothesis that crack growth rates differ regionally. The final experiments were designed to determine if crack resistance was dependent on region, proportion of hooped osteons (those with circumferentially oriented collagen fibers in the outer lamellae) or number of osteons penetrated by the crack, and to address the hypothesis that hooped osteons resist invasion by cracks better than other osteonal types. The transverse crack growth data for dorsal specimens were described by the Paris law with an exponent of 10.4 and suggested a threshold stress intensity factor, DeltaKth, of 2.0 MPa·m1/2 and fracture toughness of 4.38 MPa·m 1/2. Similar results were not obtained for lateral specimens because the crack always deviated from the intended path and ran parallel to the loading direction. Crack growth for the dorsal and lateral specimens in the radial orientation was described by the Paris law with exponents of 8.7 and 10.2, respectively, and there were no regional differences in the apparent DeltaK th (0.5 MPa·m1/2) or fracture toughness (1.2 MPa·m 1/2). Crack resistance was not associated with cortical region, proportion of hooped osteons or the number of osteons penetrated by the crack. The extent to which cracks penetrate osteons was influenced by whether the collagen fiber
Simulation of fatigue crack growth under large scale yielding conditions
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.
Miniature specimen technology for postirradiation fatigue crack growth testing
International Nuclear Information System (INIS)
Mervyn, D.A.; Ermi, A.M.
1979-01-01
Current magnetic fusion reactor design concepts require that the fatigue behavior of candidate first wall materials be characterized. Fatigue crack growth may, in fact, be the design limiting factor in these cyclic reactor concepts given the inevitable presence of crack-like flaws in fabricated sheet structures. Miniature specimen technology has been developed to provide the large data base necessary to characterize irradiation effects on the fatigue crack growth behavior. An electrical potential method of measuring crack growth rates is employed on miniature center-cracked-tension specimens (1.27 cm x 2.54 cm x 0.061 cm). Results of a baseline study on 20% cold-worked 316 stainless steel, which was tested in an in-cell prototypic fatigue machine, are presented. The miniature fatigue machine is designed for low cost, on-line, real time testing of irradiated fusion candidate alloys. It will enable large scale characterization and development of candidate first wall alloys
Automatic measurement for monitoring crack growth with electric potential technique
International Nuclear Information System (INIS)
Nakajima, Nobuya; Kikuchi, Masaaki; Shima, Seishi
1981-10-01
In the study of fracture mechanics, it is one of the most important problems to monitor the crack growth phenomena. Recently, many experimental methods have been developed. In this report, the Direct Current (DC) potential method is employed for measuring the crack growth length in the pressuried high temperature water. The objective of the current investigation is to develop an experimental method to quantify the sensitivity of this method in the air environment using the Compact Tension (CT) specimen. The main results obtained are as follows: 1) It is ignored that the electrical potential changes with plastic deformation at the crack tip of the specimen. 2) Using the Reversible Direct Current (RDC) Method, the measurement system gives no effect on the electrical stability for a long time. 3) For the fatigue and statical crack growth length, good relation is observed between the crack length-to-specimen width ratio (a/W) and potential ratio (Va/Vo). (author)
Friction stress effects on mode I crack growth predictions
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
The assessment of creep-fatigue initiation and crack growth
International Nuclear Information System (INIS)
Priest, R.H.; Miller, D.A.
1991-01-01
An outline of Nuclear Electric's Assessment Procedure for the High Temperature Response of Structures ('R5') for creep-fatigue initiation and crack growth is given. A unified approach is adopted for both regimes. For initiation, total damage is described in terms of separate creep and fatigue components. Ductility exhaustion is used for estimating creep damage whilst continuous cycling endurance data are used to evaluate the fatigue damage term. Evidence supporting this approach is given through the successful prediction of creep-fatigue endurances for a range of materials, cycle types, dwell period times, etc. Creep-fatigue crack growth is similarly described in terms of separated creep and fatigue components. Crack growth rates for each component are characterised in terms of fracture mechanics parameters. It is shown that creep crack growth rates can be rationalised on a ductility basis. Creep-fatigue interactions are accommodated in the cyclic growth component through the use of materials coefficients which depend on dwell time. (orig.)
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)
Standard test method for creep-fatigue crack growth testing
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...
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...
Cyclic inelastic deformation aspects of fatigue-crack-growth analysis
Energy Technology Data Exchange (ETDEWEB)
Leis, B.N.; Zahoor, A.
1980-01-01
This paper concentrates on a J-integral analysis of fatigue crack growth. Data on cyclic plasticity are analyzed showing that there are limitations to the usefulness of the deformation theory in applications to cyclic plasticity. 56 refs.
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.
High temperature cracking of steels: effect of geometry on creep crack growth laws
International Nuclear Information System (INIS)
Kabiri, M.R.
2003-12-01
This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C * and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C * parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C * parameter, a second non singular term, denoted here as Q * , is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C * parameter (da/dt - C * ), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C * type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C * ), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical expressions utilised for the experimental
Stainless steels: general considerations and rates of crack growth
International Nuclear Information System (INIS)
Chator, T.
1992-05-01
This report describes the different types of stainless steels, and presents the laws governing the rates of crack growth for several stainless steels extensively used for the manufacture of structures in nuclear power plants. The laws are not discussed in detail in the report. After a brief review of the development of stainless steels, the main categories of stainless steels, their mechanical characteristics and corrosion resistance, are presented. Finally, the rates of crack growth are presented for various stainless steels, mainly austenitic. The study overall aim is an investigation of the cracking in the 900 MWe primary pump thermal barriers and shafts
Fatigue crack growth thresholds measurements in structural materials
International Nuclear Information System (INIS)
Lindstroem, R.; Lidar, P.; Rosborg, B.
1999-05-01
Fatigue crack growth thresholds and da/dN-data at low Δk I -values ( 1/2 ) have been determined for type 304 stainless steel, nickel-base weld metal Alloy 182, nickel-base metal Alloy 600, and low-alloy steel in air at ambient temperature and in high-temperature water and steam. The stainless alloys have been tested in water with 0.2 ppm O 2 at 288 deg C and the low-alloy steel in steam at 286 deg C. The fatigue crack growth threshold was defined as the ΔK I -value resulting in a crack growth rate of 10 -7 mm per cycle. The measured fatigue crack growth thresholds (at frequencies from 0.5 to 20 Hz) are quite similar independent of the material and the environment. A relatively inexpensive and time-saving method for measuring fatigue crack growth thresholds, and fatigue crack growth rates at low ΔK I -values, has been used in the tests. The method is a ΔK I -decreasing test with constant K I Max
International Nuclear Information System (INIS)
Shibata, Katsuyuki; Yokoyama, Norio; Ohba, Toshihiro; Kawamura, Takaichi; Miyazono, Shohachiro
1982-12-01
Part-through surface cracks are most frequently observed in the inspection of structural components, and it is one of the important subjects in the assessment of safety to evaluate appropriately the growth of such cracks during the service life of structural components. Due to the complexity of the stress at the front free surface, the crack growth at the surface shows a different behavior from the other part. Besides, an effect of interaction is caused in the growth of multiple surface cracks. These effects should be included in the growth analysis of surface part-through cracks. Authors have carried out a series of fatigue tests on some kinds of pipes with multiple cracks in the inner surface, and subsequently the fatigue test of flat plate specimens, made of Type 304L stainless steel, with a single or double surface cracks was carried out to study the basic characteristics in the growth of multiple surface cracks. Based on the results of the flat plate test. the correction factors for the front free surface (Cs) and interaction (Ci) of surface cracks were derived quantitatively by the following empirical expressions; Cs = 0.824. Ci = (0.227(a/b) 2 (sec(PI X/2) - 1) + 1)sup(1/m). Using these two correction factors, a procedure to predict the growth of surface cracks was developed by applying the crack growth formula to both the thickness and surface directions. Besides, the crack growth predictions based on the procedure of ASME Code Sex. XI, and the above procedure without the correction of the free surface and interactions on the crack growth behaviors were compared with the test results of flat plate specimens. The crack growth behavior predicted by the procedure described in this report showed the best agreement with the test results in respects of the crack growth life and the change in the crack shape. The criteria of the ASME Code did not agree with the test results. (author)
Crack growth in an austenitic stainless steel at high temperature
International Nuclear Information System (INIS)
Polvora, J.P.
1998-01-01
This study deals with crack propagation at 650 deg C on an austenitic stainless steel referenced by Z2 CND 17-12 (316L(NN)). It is based on an experimental work concerning two different cracked specimens: CT specimens tested at 650 deg C in fatigue, creep and creep-fatigue with load controlled conditions (27 tests), tube specimens containing an internal circumferential crack tested in four points bending with displacement controlled conditions (10 tests). Using the fracture mechanics tools (K, J and C* parameters), the purpose here is to construct a methodology of calculation in order to predict the evolution of a crack with time for each loading condition using a fracture mechanics global approach. For both specimen types, crack growth is monitored by using a specific potential drop technique. In continuous fatigue, a material Paris law at 650 deg C is used to correlate crack growth rate with the stress intensity factor range corrected with a factor U(R) in order to take into account the effects of crack closure and loading ratio R. In pure creep on CT specimens, crack growth rate is correlated to the evolution of the C* parameter (evaluated experimentally) which can be estimated numerically with FEM calculations and analytically by using a simplified method based on a reference stress approach. A modeling of creep fatigue growth rate is obtained from a simple summation of the fatigue contribution and the creep contribution to the total crack growth. Good results are obtained when C* parameter is evaluated from the simplified expression C* s . Concerning the tube specimens tested in 4 point bending conditions, a simulation based on the actual A 16 French guide procedure proposed at CEA. (authors)
Directory of Open Access Journals (Sweden)
Elenice Maria Rodrigues
2005-09-01
Full Text Available Aluminum-lithium alloys are candidate materials for many aerospace applications because of their high specific strength and elastic modulus. These alloys have several unique characteristics such as excellent fatigue crack growth resistance when compared with that of the conventional 2000 and 7000 series alloys. In this study, fatigue crack propagation behavior has been examined in a commercial thin plate of Al-Li-Cu-Mg alloy (8090, with specific emphasis at the fatigue threshold. The results are compared with those of the traditional Al-Cu-Mg alloy (2024. Fatigue crack closure is used to explain the different behavior of the compared alloys.
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)
Simplified method of computation for fatigue crack growth
International Nuclear Information System (INIS)
Stahlberg, R.
1978-01-01
A procedure is described for drastically reducing the computation time in calculating crack growth for variable-amplitude fatigue loading when the loading sequence is periodic. By the proposed procedure, the crack growth, r, per loading is approximated as a smooth function and its reciprocal is integrated, rather than summing crack growth cycle by cycle. The savings in computation time results since only a few pointwise values of r must be computed to generate an accurate interpolation function for numerical integration. Further time savings can be achieved by selecting the stress intensity coefficient (stress intensity divided by load) as the argument of r. Once r has been obtained as a function of stress intensity coefficient for a given material, environment, and loading sequence, it applies to any configuration of cracked structure. (orig.) [de
Fatigue crack growth in austenitic stainless steel piping
International Nuclear Information System (INIS)
Bethmont, M.; Cheissoux, J.L.; Lebey, J.
1981-04-01
The study presented in this paper is being carried out with a view to substantiating the calculations of the fatigue crack growth in pipes made of 316 L stainless steel. The results obtained may be applied to P.W.R. primary piping. It is divided into two parts. First, fatigue tests (cyclic pressure) are carried out under hot and cold conditions with straight pipes machined with notches of various dimensions. The crack propagation and the fatigue crack growth rate are measured here. Second, calculations are made in order to interpret experimental results. From elastic calculations the stress intensity factor is assessed to predict the crack growth rate. The results obtained until now and presented in this paper relate to longitudinal notches
A numerical analysis of crack growth in brittle microcracking composites
International Nuclear Information System (INIS)
Biner, S.B.
1993-01-01
A set of numerical analyses of crack growth was performed to elucidate the mechanism of microcracking on the observed fracture behavior of brittle solids and composites. The random nucleation, orientation and size effects of discrete microcracks and resulting interactions are fully accounted for in a hybrid finite element model. The results indicate that the energy expenditure due the microcrack nucleation seems not to contribute significantly to the resistance to crack growth. The main controlling parameter appears to be elastic interaction of the microcracks with the main crack in the absence of a reinforcing phase; therefore, the microcrack density plays an important role. In the case of the composites, the interaction of the main crack with the stress fields of the reinforcing phase, rather than interaction of microcracks, is the controlling parameter for the resistance to the crack growth even in the presence of a large population of microcracks. It will be also shown that the crack branching and crack kinking can readily develop as a result of microcracking
Fatigue Crack Growth Rate and Stress-Intensity Factor Corrections for Out-of-Plane Crack Growth
Forth, Scott C.; Herman, Dave J.; James, Mark A.
2003-01-01
Fatigue crack growth rate testing is performed by automated data collection systems that assume straight crack growth in the plane of symmetry and use standard polynomial solutions to compute crack length and stress-intensity factors from compliance or potential drop measurements. Visual measurements used to correct the collected data typically include only the horizontal crack length, which for cracks that propagate out-of-plane, under-estimates the crack growth rates and over-estimates the stress-intensity factors. The authors have devised an approach for correcting both the crack growth rates and stress-intensity factors based on two-dimensional mixed mode-I/II finite element analysis (FEA). The approach is used to correct out-of-plane data for 7050-T7451 and 2025-T6 aluminum alloys. Results indicate the correction process works well for high DeltaK levels but fails to capture the mixed-mode effects at DeltaK levels approaching threshold (da/dN approximately 10(exp -10) meter/cycle).
Crack growth in thermally sprayed ceramic coatings
Czech Academy of Sciences Publication Activity Database
Kroupa, František; Náhlík, Luboš; Knésl, Zdeněk
2004-01-01
Roč. 49, č. 2 (2004), s. 149-168 ISSN 0001-7043 R&D Projects: GA ČR GP106/04/P084; GA ČR GA101/03/0331 Institutional research plan: CEZ:AV0Z2043910 Keywords : ceramic coatings, fracture mechanics, crack extension Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass
Fatigue crack growth in Aluminium Alloys
Van Kranenburg, C.
2010-01-01
Fatigue is a gradual process of local strength reduction. It is a phenomenon of damage accumulation at stress concentrations caused by fluctuating stresses and/or strains. In metals this results in microscopic cracks. These will start to grow under continued cyclic loading until final failure
FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (UNIX VERSION)
Newman, J. C.
1994-01-01
Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied
FASTRAN II - FATIGUE CRACK GROWTH STRUCTURAL ANALYSIS (IBM PC VERSION)
Newman, J. C.
1994-01-01
Predictions of fatigue crack growth behavior can be made with the Fatigue Crack Growth Structural Analysis (FASTRAN II) computer program. As cyclic loads are applied to a selected crack configuration with an initial crack size, FASTRAN II predicts crack growth as a function of cyclic load history until either a desired crack size is reached or failure occurs. FASTRAN II is based on plasticity-induced crack-closure behavior of cracks in metallic materials and accounts for load-interaction effects, such as retardation and acceleration, under variable-amplitude loading. The closure model is based on the Dugdale model with modifications to allow plastically deformed material to be left along the crack surfaces as the crack grows. Plane stress and plane strain conditions, as well as conditions between these two, can be simulated in FASTRAN II by using a constraint factor on tensile yielding at the crack front to approximately account for three-dimensional stress states. FASTRAN II contains seventeen predefined crack configurations (standard laboratory fatigue crack growth rate specimens and many common crack configurations found in structures); and the user can define one additional crack configuration. The baseline crack growth rate properties (effective stress-intensity factor against crack growth rate) may be given in either equation or tabular form. For three-dimensional crack configurations, such as surface cracks or corner cracks at holes or notches, the fatigue crack growth rate properties may be different in the crack depth and crack length directions. Final failure of the cracked structure can be modelled with fracture toughness properties using either linear-elastic fracture mechanics (brittle materials), a two-parameter fracture criterion (brittle to ductile materials), or plastic collapse (extremely ductile materials). The crack configurations in FASTRAN II can be subjected to either constant-amplitude, variable-amplitude or spectrum loading. The applied
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.
International Nuclear Information System (INIS)
Taheri, Said; Julan, Emricka; Tran, Xuan-Van; Robert, Nicolas
2017-01-01
Highlights: • For crack growth analysis, weld residual stress field must be considered through its SIF in presence of a crack. • Presence of cracks of same depth proves their arrest, where equal depth is because mean stress acts only on crack opening. • Not considering amplitudes under a fatigue crack growth threshold (FCGT) does not compensate the lack of FGCT in Paris law. • Propagation rates are close for axisymmetric and circumferential semi-elliptical cracks. - Abstract: High cycle thermal crazing has been observed in some residual heat removal (RHR) systems made of 304 stainless steel in PWR nuclear plants. This paper deals with two types of analyses including logical argumentation and simulation. Crack arrest in networks is demonstrated due to the presence of two cracks of the same depth in the network. This identical depth may be proved assuming that mean stress acts only on crack opening and that cracks are fully open during the load cycle before arrest. Weld residual stresses (WRS) are obtained by an axisymmetric simulation of welding on a tube with a chamfer. Axisymmetric and 3D parametric studies of crack growth on: representative sequences for variable amplitude thermal loading, fatigue crack growth threshold (FCGT), permanent mean stress, cyclic counting methods and WRS, are performed with Code-Aster software using XFEM methodology. The following results are obtained on crack depth versus time: the effect of WRS on crack growth cannot be determined by the initial WRS field in absence of crack, but by the associated stress intensity factor. Moreover the relation between crack arrest depth and WRS is analyzed. In the absence of FCGT Paris’s law may give a significant over-estimation of crack depth even if amplitudes of loading smaller than FCGT have not been considered. Appropriate depth versus time may be obtained using different values of FCGT, but axisymmetric simulations do not really show a possibility of arrest for shallow cracks in
Energy Technology Data Exchange (ETDEWEB)
Taheri, Said, E-mail: Said.taheri@edf.fr [EDF-LAB, IMSIA, 7 Boulevard Gaspard Monge, 91120 Palaiseau Cedex (France); Julan, Emricka [EDF-LAB, AMA, 7 Boulevard Gaspard Monge, 91120 Palaiseau Cedex (France); Tran, Xuan-Van [EDF Energy R& D UK Centre/School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom); Robert, Nicolas [EDF-DPN, UNIE, Strategic Center, Saint Denis (France)
2017-01-15
Highlights: • For crack growth analysis, weld residual stress field must be considered through its SIF in presence of a crack. • Presence of cracks of same depth proves their arrest, where equal depth is because mean stress acts only on crack opening. • Not considering amplitudes under a fatigue crack growth threshold (FCGT) does not compensate the lack of FGCT in Paris law. • Propagation rates are close for axisymmetric and circumferential semi-elliptical cracks. - Abstract: High cycle thermal crazing has been observed in some residual heat removal (RHR) systems made of 304 stainless steel in PWR nuclear plants. This paper deals with two types of analyses including logical argumentation and simulation. Crack arrest in networks is demonstrated due to the presence of two cracks of the same depth in the network. This identical depth may be proved assuming that mean stress acts only on crack opening and that cracks are fully open during the load cycle before arrest. Weld residual stresses (WRS) are obtained by an axisymmetric simulation of welding on a tube with a chamfer. Axisymmetric and 3D parametric studies of crack growth on: representative sequences for variable amplitude thermal loading, fatigue crack growth threshold (FCGT), permanent mean stress, cyclic counting methods and WRS, are performed with Code-Aster software using XFEM methodology. The following results are obtained on crack depth versus time: the effect of WRS on crack growth cannot be determined by the initial WRS field in absence of crack, but by the associated stress intensity factor. Moreover the relation between crack arrest depth and WRS is analyzed. In the absence of FCGT Paris’s law may give a significant over-estimation of crack depth even if amplitudes of loading smaller than FCGT have not been considered. Appropriate depth versus time may be obtained using different values of FCGT, but axisymmetric simulations do not really show a possibility of arrest for shallow cracks in
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
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
Fatigue crack growth analysis of a 450 PWR - lateral
International Nuclear Information System (INIS)
Taupin, P.; Flamand, F.
1988-01-01
Fatigue Crack Growth analysis of a 5 mm deep surface crack in the crotch region of a 45 0 Lateral (12 inch diameter) was performed on a 3-Loop 900 MWe PWR Plant under Normal and upset loading conditions. Stress Intensity factors were computed using the weight-function technique. The latter were obtained for a polynomial stress distribution at the corner of the lateral under contract with the Pressure Vessel Research Committee of the WRC. The study shows that after 40 years of normal operation the size of the end of life crack is limited to about 25 mm for the chosen lateral with a thickness of 300 mm
Fatigue-crack growth behavior in dissimilar metal weldments
International Nuclear Information System (INIS)
James, L.A.
1977-03-01
The techniques of linear-elastic fracture mechanics were used to characterize fatigue-crack propagation behavior in three dissimilar metal weldments at test temperatures of 800 0 F (427 0 C) and 1000 0 F (538 0 C). The weldments studied included Inconel 718/Type 316, all using Inconel 82 as the filler metal. In general, fatigue-crack growth rates in the weldments were equal to, or less than, those observed in the base metals. Crack deviation from the expected path perpendicular to the loading axis was noted in some cases, and is discussed
Methods of forecasting crack growth rate under creep conditions
International Nuclear Information System (INIS)
Ol'kin, S.I.
1979-01-01
Using construction aluminium alloy application possibility of linear mechanics of the destruction for quantitative description of crack development process under creepage conditions is investigated. It is shown, that the grade dependence between the stress intensity coefficient and the crack growth rate takes place only at certain combination of the sample geometry and creepage parameters, and consequently, its applicability in every given case must necessarily be tested experimentally
Crack growth simulation for plural crack using hexahedral mesh generation technique
International Nuclear Information System (INIS)
Orita, Y; Wada, Y; Kikuchi, M
2010-01-01
This paper describes a surface crack growth simulation using a new mesh generation technique. The generated mesh is constituted of all hexahedral elements. Hexahedral elements are suitable for an analysis of fracture mechanics parameters, i.e. stress intensity factor. The advantage of a hexahedral mesh is good accuracy of an analysis and less number of degrees of freedoms than a tetrahedral mesh. In this study, a plural crack growth simulation is computed using the hexahedral mesh and its distribution of stress intensity factor is investigated.
A grain boundary sliding model for cavitation, crack growth and ...
African Journals Online (AJOL)
A model is presented for cavity growth, crack propagation and fracture resulting from grain boundary sliding (GBS) during high temperature creep deformation. The theory of cavity growth by GBS was based on energy balance criteria on the assumption that the matrix is sufficiently plastic to accommodate misfit strains ...
Effects of microscale inertia on dynamic ductile crack growth
Jacques, N.; Mercier, S.; Molinari, A.
2012-04-01
The aim of this paper is to investigate the role of microscale inertia in dynamic ductile crack growth. A constitutive model for porous solids that accounts for dynamic effects due to void growth is proposed. The model has been implemented in a finite element code and simulations of crack growth in a notched bar and in an edge cracked specimen have been performed. Results are compared to predictions obtained via the Gurson-Tvergaard-Needleman (GTN) model where micro-inertia effects are not accounted for. It is found that microscale inertia has a significant influence on the crack growth. In particular, it is shown that micro-inertia plays an important role during the strain localisation process by impeding void growth. Therefore, the resulting damage accumulation occurs in a more progressive manner. For this reason, simulations based on the proposed modelling exhibit much less mesh sensitivity than those based on the viscoplastic GTN model. Microscale inertia is also found to lead to lower crack speeds. Effects of micro-inertia on fracture toughness are evaluated.
Temperature and loading frequency effects of fatigue crack growth in HDPE pipe material
International Nuclear Information System (INIS)
Merah, N.; Khan, Z.; Bazoune, A.; Saghir, F.
2006-01-01
High density polyethylene (HDPE) pipes are being extensively used for gas, water, sewage and waste water distribution systems. Laboratory tests appear to show that HDPE is more able to suppress rapid crack propagation, while remaining somehow resistant to slow crack growth failures observed in service. Procedures for estimating pipe life in service have been established by making use of fatigue crack growth (FCG) results. These procedures are concerned mainly with room temperature. Applications with some safety factor to include the temperature effect. Use of HDPE pipes in water and gas distribution in the Gulf area has seen a net increase. This study addresses the combined effects of temperature and frequency on FCG properties of commercial HDPE pipe material. FCG accelerated tests were conducted on single-etch notch (SEN) specimens in the temperature range of -10 to 70C at frequencies ranging from 0.1 to 50 Hz. The FCG tests are conducted at a stress amplitude level approximately 1/4 of room temperature yield stress and crack growth behavior was investigated using linear elastic fracture mechanics concepts. The stress intensity range delta K gave satisfactory correlation of crack, growth rate (da/dN) at the temperatures of -10, 0, 23 and 40C and at frequencies of 0.1, 1, and 50 Hz. The crack growth resistance was found to decrease with increase in test temperature and decrease growth resistance was found to decrease with increase in test temperature and decrease with frequency. For 70C no crack propagation was observed, the failure was observed to occur by collapse or generalized yielding. Fractographic analyses results are used to explain temperature and frequency effects on FCG. The effect of temperature on da/dN for HDPE material was investigated by considering the variation of mechanical properties with temperature. Master curves were developed by normalizing delta K yield stress. (author)
Outline and current status of crack growth evaluation
International Nuclear Information System (INIS)
Arai, Taku
2017-01-01
This paper explains the outline of crack growth evaluation against stress corrosion cracking (SCC), knowledge obtained from actual equipment failure cases, and the latest trends of technology development concerning crack growth evaluation. As for the reactor integrity evaluation system, the use of the maintenance standards for the nuclear power generation of the Japan Society of Mechanical Engineers (hereinafter referred to as maintenance standards') is specified for its evaluation. Based on whether or not the result satisfies the evaluation criteria for the SCC soundness assessment, it is judged whether continuous operation within the evaluation period is allowed or repair/replacement is required. According to main findings obtained from the cases of actual equipment failure, the following have been recognized. (1) The SCC generated and developed in the nickel base alloy welded metal stayed at the boundary between low alloy steel and stainless steel. (2) The progress of SCC strongly depends on the growth direction of dendrite, which is the welded solidified structure, and preferentially develops in the direction parallel to the growth direction. The latest development of crack propagation evaluation includes (1) development of solution for stress intensity factor, and (2) crack propagation evaluation by means of FEM analysis. With regard to the SCC of stainless steel in recirculation system piping under BWR environment, if the defect depth and surface length are sized, the progress of cracks in the actual equipment can be reproduced to some extent by crack growth according to maintenance standards. The sizing results of the defect based on non-destructive test are the starting point. (A.O.)
Evaluation of stress corrosion crack growth in BWR piping systems
International Nuclear Information System (INIS)
Kassir, M.; Sharma, S.; Reich, M.; Chang, M.T.
1985-05-01
This report presents the results of a study conducted to evaluate the effects of stress intensity factor and environment on the growth behavior of intergranular stress corrosion cracks in type 304 stainless steel piping systems. Most of the detected cracks are known to be circumferential in shape, and initially started at the inside surface in the heat affected zone near girth welds. These cracks grow both radially in-depth and circumferentially in length and, in extreme cases, may cause leakage in the installation. The propagation of the crack is essentially due to the influence of the following simultaneous factors: (1) the action of applied and residual stress; (2) sensitization of the base metal in the heat affected zone adjacent to girth weld; and (3) the continuous exposure of the material to an aggressive environment of high temperature water containing dissolved oxygen and some levels of impurities. Each of these factors and their effects on the piping systems is discussed in detail in the report. The report also evaluates the time required for hypothetical cracks in BWR pipes to propagate to their critical size. The pertinent times are computed and displayed graphically. Finally, parametric study is performed in order to assess the relative influence and sensitivity of the various input parameters (residual stress, crack growth law, diameter of pipe, initial size of defect, etc.) which have bearing on the growth behavior of the intergranular stress corrosion cracks in type 304 stainless steel. Cracks in large-diameter as well as in small-diameter pipes are considered and analyzed. 27 refs., 25 figs., 10 tabs
Crack growth in non-homogeneous transformable ceramics. Part II : Crack deflection
Stam, Geert; Giessen, Erik van der
1996-01-01
Crack growth in transformation toughened ceramics is studied using a micromechanics based continuum model which accounts for both dilatant and shear transformation strain components. In the computations, the transformable phase is taken to be distributed non-homogeneously in order to model Zirconia
Crack under biaxial loading: Two-parameter description and prediction of crack growth direction
Czech Academy of Sciences Publication Activity Database
Seitl, Stanislav
2014-01-01
Roč. 31, APR (2014), s. 44-49 ISSN 0213-3725 R&D Projects: GA MŠk(CZ) 7AMB14AT012 Institutional support: RVO:68081723 Keywords : Concrete * T-stress * cracks growth prediction * numerical calculation * biaxial loading Subject RIV: JL - Materials Fatigue, Friction Mechanics
Elevated temperature crack growth in advanced powder metallurgy aluminum alloys
Porr, William C., Jr.; Gangloff, Richard P.
1990-01-01
Rapidly solidified Al-Fe-V-Si powder metallurgy alloy FVS0812 is among the most promising of the elevated temperature aluminum alloys developed in recent years. The ultra fine grain size and high volume fraction of thermally stable dispersoids enable the alloy to maintain tensile properties at elevated temperatures. In contrast, this alloy displays complex and potentially deleterious damage tolerant and time dependent fracture behavior that varies with temperature. J-Integral fracture mechanics were used to determine fracture toughness (K sub IC) and crack growth resistance (tearing modulus, T) of extruded FVS0812 as a function of temperature. The alloy exhibits high fracture properties at room temperature when tested in the LT orientation, due to extensive delamination of prior ribbon particle boundaries perpendicular to the crack front. Delamination results in a loss of through thickness constraint along the crack front, raising the critical stress intensity necessary for precrack initiation. The fracture toughness and tensile ductility of this alloy decrease with increasing temperature, with minima observed at 200 C. This behavior results from minima in the intrinsic toughness of the material, due to dynamic strain aging, and in the extent of prior particle boundary delaminations. At 200 C FVS0812 fails at K levels that are insufficient to cause through thickness delamination. As temperature increases beyond the minimum, strain aging is reduced and delamination returns. For the TL orientation, K (sub IC) decreased and T increased slightly with increasing temperature from 25 to 316 C. Fracture in the TL orientation is governed by prior particle boundary toughness; increased strain localization at these boundaries may result in lower toughness with increasing temperature. Preliminary results demonstrate a complex effect of loading rate on K (sub IC) and T at 175 C, and indicate that the combined effects of time dependent deformation, environment, and strain aging
Potential drop technique for monitoring stress corrosion cracking growth
International Nuclear Information System (INIS)
Neves, Celia F.C.; Schvartzman, Monica M.A.M.; Moreira, Pedro A.L.D.P.L.P.
2002-01-01
Stress corrosion cracking is one of most severe damage mechanisms influencing the lifetime of components in the operation of nuclear power plants. To assess the initiation stages and kinetics of crack growth as the main parameters coming to residual lifetime determination, the testing facility should allow active loading of specimens in the environment which is close to the real operation conditions of assessed component. Under cooperation of CDTN/CNEN and International Atomic Energy Agency a testing system has been developed by Nuclear Research Institute, Czech Republic, that will be used for the environmentally assisted cracking testing at CDTN/CNEN. The facility allows high temperature autoclave corrosion mechanical testing in well-defined LWR water chemistry using constant load, slow strain rate and rising displacement techniques. The facility consists of autoclave and refreshing water loop enabling testing at temperatures up to 330 deg C. Active loading system allows the maximum load on a specimen as high as 60 kN. The potential drop measurement is used to determine the instant crack length and its growth rate. The paper presents the facility and describes the potential drop technique, that is one of the most used techniques to monitor crack growth in specimens under corrosive environments. (author)
Microscopic examination of crack growth in a pressure vessel steel
Energy Technology Data Exchange (ETDEWEB)
Isacsson, M.; Narstroem, T. [Royal Inst. of Tech., Stockholm (Sweden)
1997-01-01
A fairly systematic microscopic study concerning ductile and ductile-brittle crack growth in the A508B pressure vessel steel has been performed. The main method of investigation was to subject fracture mechanics specimens (sub-sized three point bend specimens) to predetermined load levels corresponding to different amounts of ductile crack extension. The specimens were then cut perpendicularly to the plane of the crack and the area in front of the crack was examined in a SEM. The object of these examinations was to determine if newly encountered computational results could be correlated to crack extension characteristics and to study whether the mechanism of ductile growth was of the void growth type or of the fast shear mechanism. This is important for further numerical modelling of the process. Both the original material and a specially heat treated piece were investigated. The heat treatment was performed in order to raise the transition temperature to about 60 deg C with the object to provide a more convenient testing situation. Charpy V tests were performed for the specially heat treated material to obtain the temperature dependence of the toughness. This was also studied by performing fracture toughness determination on the same type of specimens as were used for the microscopic study. The heat treatment used fulfilled the above purpose and the microscopic studies provide a good understanding of the micro mechanisms operating in the ductile fracture process for this material. 19 refs, 8 figs, 3 tabs.
Microscopic examination of crack growth in a pressure vessel steel
International Nuclear Information System (INIS)
Isacsson, M.; Narstroem, T.
1997-01-01
A fairly systematic microscopic study concerning ductile and ductile-brittle crack growth in the A508B pressure vessel steel has been performed. The main method of investigation was to subject fracture mechanics specimens (sub-sized three point bend specimens) to predetermined load levels corresponding to different amounts of ductile crack extension. The specimens were then cut perpendicularly to the plane of the crack and the area in front of the crack was examined in a SEM. The object of these examinations was to determine if newly encountered computational results could be correlated to crack extension characteristics and to study whether the mechanism of ductile growth was of the void growth type or of the fast shear mechanism. This is important for further numerical modelling of the process. Both the original material and a specially heat treated piece were investigated. The heat treatment was performed in order to raise the transition temperature to about 60 deg C with the object to provide a more convenient testing situation. Charpy V tests were performed for the specially heat treated material to obtain the temperature dependence of the toughness. This was also studied by performing fracture toughness determination on the same type of specimens as were used for the microscopic study. The heat treatment used fulfilled the above purpose and the microscopic studies provide a good understanding of the micro mechanisms operating in the ductile fracture process for this material
Probabilistic Prognosis of Non-Planar Fatigue Crack Growth
Leser, Patrick E.; Newman, John A.; Warner, James E.; Leser, William P.; Hochhalter, Jacob D.; Yuan, Fuh-Gwo
2016-01-01
Quantifying the uncertainty in model parameters for the purpose of damage prognosis can be accomplished utilizing Bayesian inference and damage diagnosis data from sources such as non-destructive evaluation or structural health monitoring. The number of samples required to solve the Bayesian inverse problem through common sampling techniques (e.g., Markov chain Monte Carlo) renders high-fidelity finite element-based damage growth models unusable due to prohibitive computation times. However, these types of models are often the only option when attempting to model complex damage growth in real-world structures. Here, a recently developed high-fidelity crack growth model is used which, when compared to finite element-based modeling, has demonstrated reductions in computation times of three orders of magnitude through the use of surrogate models and machine learning. The model is flexible in that only the expensive computation of the crack driving forces is replaced by the surrogate models, leaving the remaining parameters accessible for uncertainty quantification. A probabilistic prognosis framework incorporating this model is developed and demonstrated for non-planar crack growth in a modified, edge-notched, aluminum tensile specimen. Predictions of remaining useful life are made over time for five updates of the damage diagnosis data, and prognostic metrics are utilized to evaluate the performance of the prognostic framework. Challenges specific to the probabilistic prognosis of non-planar fatigue crack growth are highlighted and discussed in the context of the experimental results.
Nanoscale and submicron fatigue crack growth in nickel microbeams
International Nuclear Information System (INIS)
Yang, Y.; Yao, N.; Imasogie, B.; Soboyejo, W.O.
2007-01-01
This paper presents a novel edge-notched microbeam technique for the study of short fatigue crack growth. The technique is used to study submicron and nanoscale fatigue in LIGA Ni thin films with columnar microstructures. The edge-notched microbeams were fabricated within LIGA Ni thin films, using focused ion beam (FIB) techniques. The microbeams were then cyclically deformed to failure at a stress ratio of 0.1. Different slip-band structures were observed below the nanoscale notches. Cyclic deformation resulted in the formation of primary slip bands below the notch. Subsequent crack growth then occurred by the unzipping of fatigue cracks along intersecting slip bands. The effects of the primary slip bands were idealized using dislocation-based models. These were used to estimate the intrinsic fatigue threshold and the fatigue endurance limit. The estimates from the model are shown to be consistent with experimental data from prior stress-life experiments and current/prior fatigue threshold estimates
Stress corrosion crack growth rate in dissimilar metal welds
International Nuclear Information System (INIS)
Fernandez, M. P.; Lapena, J.; Lancha, A. M.; Perosanz, F. J.; Navas, M.
2000-01-01
Dissimilar welds, used to join different sections in light water reactors, are potentially susceptible to stress corrosion cracking (SCC) in aqueous mediums characteristic of nuclear plants. However, the study of these The ma has been limited to evaluating the weld material susceptibility in these mediums. Little scarce data are available on crack growth rates due, fundamentally, to inadequate testing techniques. In order to address this lack of information the crack growth rate at the interface of ferritic SA 533 B-1 alloy and alloy I-82, in a dissimilar weld (SA533B-1/I-82/316L), was studied. Experiments were conducted in water at 288 degree centigrade, 8 ppm of O 2 and 1 μS/cm conductivity. (Author) 33 refs
Analysis of Fatigue Crack Growth in Ship Structural Details
Directory of Open Access Journals (Sweden)
Leheta Heba W.
2016-04-01
Full Text Available Fatigue failure avoidance is a goal that can be achieved only if the fatigue design is an integral part of the original design program. The purpose of fatigue design is to ensure that the structure has adequate fatigue life. Calculated fatigue life can form the basis for meaningful and efficient inspection programs during fabrication and throughout the life of the ship. The main objective of this paper is to develop an add-on program for the analysis of fatigue crack growth in ship structural details. The developed program will be an add-on script in a pre-existing package. A crack propagation in a tanker side connection is analyzed by using the developed program based on linear elastic fracture mechanics (LEFM and finite element method (FEM. The basic idea of the developed application is that a finite element model of this side connection will be first analyzed by using ABAQUS and from the results of this analysis the location of the highest stresses will be revealed. At this location, an initial crack will be introduced to the finite element model and from the results of the new crack model the direction of the crack propagation and the values of the stress intensity factors, will be known. By using the calculated direction of propagation a new segment will be added to the crack and then the model is analyzed again. The last step will be repeated until the calculated stress intensity factors reach the critical value.
Fatigue crack growth in welded joints in seawater
Energy Technology Data Exchange (ETDEWEB)
Lambert, S.B.
1988-01-01
A pipe-to-plate specimen has been developed to study the influence of seawater on the fatigue behaviour of welded tubular joints. DC potential drop techniques have been used to detect fatigue crack initiation, and to monitor the subsequent growth of fatigue cracks. Results for three specimens, tested in air are compared with similar data for tubular and T-plate joints. These comparisons indicate that the pipe/plate is a reasonable model of a tubular joint. Testing was performed on a further six specimens in artificial seawater; two each with free corrosion, optimum cathodic protection, and cathodic overprotection. Fatigue life reduction factors compared with corresponding tests in air were 1.8 and 2.8 for free corrosion, 1.7 and 1.1 with cathodic protection, and 4.2 and 3.3 with cathodic over-protection. These fatigue life reduction factors were comparable to results on T-plate specimens, and were strongly dependent on crack shape development. Linear elastic fracture mechanics techniques appear suitable for the calculation of fatigue crack propagation life. Three approximate solution techniques for crack tip stress intensity factors show reasonable agreement with experimentally derived values. It is recommended that forcing functions be used to model crack aspect ratio development in welded joints. Such forcing functions are influenced by the initial stress distribution and the environment. 207 refs., 192 figs., 22 tabs.
Thermal fatigue crack growth on a thick wall tube containing a semi elliptical circumferential crack
International Nuclear Information System (INIS)
Deschanels, H.; Wakai, T.; Lacire, M.H.; Michel, B.
2001-01-01
In order to check the ability of the simplified assessment procedure (A16 guide) to predict fatigue crack growth, a benchmark problem was conducted. This work is carried out under the project ''agreement on the Exchange of Information and Collaboration in the field of Research and Development of Fast Breeder Reactor (FBR) between Europe (EU) and Japan''. Experimental work is conducted by PNC using Air cooled Thermal transient Test Facility (ATTF). Specimen is a thick wall tube containing a semi elliptical (3-D) circumferential crack and subjected to cyclic thermal transients. The constitutive material is the 304 austenitic stainless steel type SUS304. Due to thermal shock (650 C-300 C) the stress distribution through the wall is non-linear and well approximated using a 3 rd order polynomial. When comparing computations and tests data we observe a good agreement for the crack propagation in length. In crack depth, accurate results are obtained in the first part of the test, but on the later stage of the experiment the computations slightly underestimate the propagation (deep crack). In addition, we notice the importance of good evaluation of fracture mechanics parameters for non-linear stress distribution through the wall. At present A16 guide handbook gives stress intensity factor solutions for non-linear stress distribution through the wall. (author)
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
The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD
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
The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD
Relations among the crack growth modes resulting from tensor splitting
Czech Academy of Sciences Publication Activity Database
Kafka, Vratislav
2015-01-01
Roč. 60, č. 4 (2015), s. 319-335 ISSN 0001-7043 Institutional support: RVO:68378297 Keywords : fracture mechanics * combination of crack-growth modes * non-local effect * tensor splitting Subject RIV: JL - Materials Fatigue, Friction Mechanics http://journal.it.cas.cz/60(15)4-Contents/60(15)4a.pdf
Fatigue crack propagation and delamination growth in Glare
Alderliesten, R.C.
2005-01-01
Fibre Metal Laminate Glare consists of thin aluminium layers bonded together with pre-impregnated glass fibre layers and shows an excellent fatigue crack growth behaviour compared to monolithic aluminium. The fibres are insensitive to the occurring fatigue loads and remain intact while the fatigue
Improving subcritical crack growth resistance for alumina glass dental composite
Zhu, Q.; With, de G.
2005-01-01
The improvement of subcritical crack growth (SCG) resistance for alumina glass dental composites was explored in this study. The addition of nitrogen to the glass phases in the composite was found to increase the SCG resistance, where the SCG exponent n increases from 22 for the oxide glass
Analysis of hygral induced crack growth in multiphase materials
Sadouki, H.; Van Mier, J.G.M.
1996-01-01
In this paper a numerical model for simulating crack growth processes caused by moisture movement in a porous multiphase material like concrete is proposed. In the model, the material is schematized as a regular triangular network of beam elements. The meso-material structure of the material is
Hybrid discrete dislocation models for fatigue crack growth
Curtin, W. A.; Deshpande, V. S.; Needleman, A.; Van der Giessen, E.; Wallin, M.
A framework for accurately modeling fatigue crack growth in ductile crystalline solids is necessarily multiscale The creation of new free surface occurs at the atomistic scale, where the material's cohesive strength is controlled by the local chemistry On the other hand, significant dissipation
Study of creep crack growth behavior of 316LN welds
International Nuclear Information System (INIS)
Venugopal, S.; Kumar, Yatindra; Sasikala, G.
2016-01-01
Creep crack growth (CCG) behavior plays an important role in the assessment of structural integrity of components operating at elevated temperature under load/stress condition. Integrity of the welded components is decided primarily by that of the weld. Creep crack growth behavior of 316LN welds prepared using consumables developed indigenously for welding the 316L(N) SS components for the Prototype Fast Breeder Reactor has been studied. The composition of the consumable is tailored to ensure about 5 FN (ferrite number) of δ ferrite in the weld deposit. Constant load CCG tests were carried out as per ASTM E1457 at different applied loads at temperatures in the range 823-923 K on CT specimens fabricated from 'V-type' weld joints with notch in the weld centre. The creep crack growth rate (α) is commonly correlated to a time dependent fracture mechanics parameter known as C*. The α3-C* correlations (α=D(C*) φ ) were established in the temperature range 823-923 K. The crack growth rates at different temperature have been compared with that given in RCC-MR. Extensive microstructural and fractographic studies using optical and scanning electron microscopy were carried out on the CCG tested specimens to understand the effect of transformation of delta ferrite on the creep damage and fracture mechanisms associated with CCG in the weld metal at different test conditions. (author)
Creep crack growth investigations for elevated temperature material application
International Nuclear Information System (INIS)
Krompholz, K.; Pierick, J.B.; Grosser, E.D.
1981-01-01
Creep crack growth data for the cast alloys IN-519 at 1123 K, Manaurite 36 X at 1123 K and 1173 K, and for the wrought alloys Incoloy 800 H and Inconel 617 at 1123 K, 1173 K, 1223 K, and 1273 K are reported. Up to 1273 K the crack lengths were measured by means of the potential drop technique. The data are plotted da/dt vs. net section stress. These results are compared with data on Inconel 617 analyzed according to stress intensity. (orig.)
Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth
Dawicke, D. S.; Newman, J. C., Jr.
1992-08-01
A technique was developed to calculate the stress intensity factor for multiple interacting cracks. The analysis was verified through comparison with accepted methods of calculating stress intensity factors. The technique was incorporated into a fatigue crack growth prediction model and used to predict the fatigue crack growth life for multiple-site damage (MSD). The analysis was verified through comparison with experiments conducted on uniaxially loaded flat panels with multiple cracks. Configuration with nearly equal and unequal crack distribution were examined. The fatigue crack growth predictions agreed within 20 percent of the experimental lives for all crack configurations considered.
Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth
Dawicke, D. S.; Newman, J. C., Jr.
1992-01-01
A technique was developed to calculate the stress intensity factor for multiple interacting cracks. The analysis was verified through comparison with accepted methods of calculating stress intensity factors. The technique was incorporated into a fatigue crack growth prediction model and used to predict the fatigue crack growth life for multiple-site damage (MSD). The analysis was verified through comparison with experiments conducted on uniaxially loaded flat panels with multiple cracks. Configuration with nearly equal and unequal crack distribution were examined. The fatigue crack growth predictions agreed within 20 percent of the experimental lives for all crack configurations considered.
Silitonga, S.; Maljaars, J.; Soetens, F.; Snijder, H.H.
2014-01-01
In this work, a numerical method is pursued based on a cohesive zone model (CZM). The method is aimed at simulating fatigue crack growth as well as crack growth retardation due to an overload. In this cohesive zone model, the degradation of the material strength is represented by a variation of the
A proposal for unification of fatigue crack growth law
Kobelev, V.
2017-05-01
In the present paper, the new fractional-differential dependences of cycles to failure for a given initial crack length upon the stress amplitude in the linear fracture approach are proposed. The anticipated unified propagation function describes the infinitesimal crack length growths per increasing number of load cycles, supposing that the load ratio remains constant over the load history. Two unification fractional-differential functions with different number of fitting parameters are proposed. An alternative, threshold formulations for the fractional-differential propagation functions are suggested. The mean stress dependence is the immediate consequence from the considered laws. The corresponding formulas for crack length over the number of cycles are derived in closed form.
Fatigue cracks in Eurofer 97 steel: Part I. Nucleation and small crack growth kinetics
Czech Academy of Sciences Publication Activity Database
Kruml, Tomáš; Polák, Jaroslav
2011-01-01
Roč. 412, 1 (2011), s. 2-6 ISSN 0022-3115 R&D Projects: GA ČR GA106/09/1954; GA ČR GA101/09/0867 Institutional research plan: CEZ:AV0Z20410507 Keywords : ferritic-martensitic steel * low cycle fatigue * small crack growth * fatigue life prediction Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.052, year: 2011
Underclad cracks growth under fatigue loading in stainless steel cladding
International Nuclear Information System (INIS)
Bernard, J.L.; Bodson, F.; Doule, A.; Slama, G.; Bramat, M.; Doucet, J.P.; Maltrud, F.
1981-01-01
Hydrogen induced cracks have been found in HAZ of PWR vessel nozzles under stainless steel cladding. Fatigue tests were performed to collect a large amount of data on the possible propagation of this type of flaws. Tests were conducted in two steps. The aim of the first step was to set up the experimental equipment and to device an adequate method for following cracks during fatigue loading. Clad plates with electroerosion machined slots were used for this purpose. The second step was then undertaken with material taken out of an actual nozzle containing hydrogen induced cracks in the HAZ under stainless steel cladding or flaws simulated by electroerosion machined slots. The test loadings were comparable to in service loadings of the nozzles. Special attention was taken to get representative R ratios. Again for the sake of representativity, the tests were performed at 300 0 C (In service temperature) and the hydrotest was simulated. The main results are: It was possible to follow the whole failure process by combining non-destructive examinations during fatigue testing and fractographic observations of broken specimens. Different striation patterns, before and after air has penetrated the actual embedded cracks were observed. Numerical simulation of fatigue crack growth of actual or simulated defects were consistent with experimental data, provided mainly that defect shape, effect of R ratio and of environment were taken into account. (orig.)
Crack growth through low-cycle fatigue loading of material ARMOX 500T
Directory of Open Access Journals (Sweden)
V. Pepel
2016-10-01
Full Text Available This paper presents microstructure analysis of the creation and growth of cracks in uniaxial load. Analyse were done for steel Armox 500T (armour sheet. Results show that cracks are present quit early in steel lifetime. First micro cracks occur before the 200th cycles, whereby crack growth is progressive during further loading. Also it can be seen that after a certain number of cycles there are more longer cracks then shorter ones.
Zhang, Yuwei; Guo, Zhansheng
2018-03-01
Mechanical degradation, especially fractures in active particles in an electrode, is a major reason why the capacity of lithium-ion batteries fades. This paper proposes a model that couples Li-ion diffusion, stress evolution, and damage mechanics to simulate the growth of central cracks in cathode particles (LiMn2O4) by an extended finite element method by considering the influence of multiple factors. The simulation shows that particles are likely to crack at a high discharge rate, when the particle radius is large, or when the initial central crack is longer. It also shows that the maximum principal tensile stress decreases and cracking becomes more difficult when the influence of crack surface diffusion is considered. The fracturing process occurs according to the following stages: no crack growth, stable crack growth, and unstable crack growth. Changing the charge/discharge strategy before unstable crack growth sets in is beneficial to prevent further capacity fading during electrochemical cycling.
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
On the influence of the environment on modeling the fatigue crack growth process
International Nuclear Information System (INIS)
Mc Evily, A.J.
1987-01-01
The effect of the environment at room and elevated temperature were considered with respect to the influence exerted on the basic mechanical aspects of the fatigue crack growth process. An experimental assessment of this influence was obtained by conducting fatigue crack growth tests both in air and vacuum and the results of such experiments are given. Topics considered include crack closure, short crack growth in notched and unnotched specimens, Mode II crack growth, and the effects of oxidation at elevated temperatures. It is shown that the basic mechanisms of fatigue crack growth can be greatly altered by the presence of oxide films at the fatigue crack tip. Modeling the mechanical aspects of the crack growth process is by itself a challenging task. In addition, the environmental considerations adds to the complexity of the modeling process. (Author)
Thermo-Mechanical Fatigue Crack Growth of RR1000
Christopher John Pretty; Mark Thomas Whitaker; Steve John Williams
2017-01-01
Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechan...
Constraint effect on the slow crack growth in polyethylene
Czech Academy of Sciences Publication Activity Database
Hutař, Pavel; Zouhar, Michal; Nezbedová, E.; Sadílek, J.; Žídek, J.; Náhlík, Luboš; Knésl, Zdeněk
2012-01-01
Roč. 2, č. 3 (2012), s. 118-126 ISSN 1757-9864 R&D Projects: GA ČR GD106/09/H035; GA ČR GA106/09/0279; GA ČR GC101/09/J027 Institutional support: RVO:68081723 Keywords : slow crack growth * polyethylene * constraint Subject RIV: JL - Materials Fatigue, Friction Mechanics
NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software
Forman, Royce; Shivakumar, V.; Mettu, Sambi; Beek, Joachim; Williams, Leonard; Yeh, Feng; McClung, Craig; Cardinal, Joe
2004-01-01
This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.
Fatigue crack growth in fiber-metal laminates
Ma, YuE; Xia, ZhongChun; Xiong, XiaoFeng
2014-01-01
Fiber-metal laminates (FMLs) consist of three layers of aluminum alloy 2024-T3 and two layers of glass/epoxy prepreg, and it (it means FMLs) is laminated by Al alloy and fiber alternatively. Fatigue crack growth rates in notched fiber-metal laminates under constant amplitude fatigue loading were studied experimentally and numerically and were compared with them in monolithic 2024-T3 Al alloy plates. It is shown that the fatigue life of FMLs is about 17 times longer than monolithic 2024-T3 Al alloy plate; and crack growth rates in FMLs panels remain constant mostly even when the crack is long, unlike in the monolithic 2024-T3 Al alloy plates. The formula to calculate bridge stress profiles of FMLs was derived based on the fracture theory. A program by Matlab was developed to calculate the distribution of bridge stress in FMLs, and then fatigue growth lives were obtained. Finite element models of FMLs were built and meshed finely to analyze the stress distributions. Both results were compared with the experimental results. They agree well with each other.
Measurement of fatigue crack growth rate of reactor structural material in air based on DCPD method
International Nuclear Information System (INIS)
Du Donghai; Chen Kai; Yu Lun; Zhang Lefu; Shi Xiuqiang; Xu Xuelian
2014-01-01
The principles and details of direct current potential drop (DCPD) in monitoring the crack growth of reactor structural materials was introduced in this paper. Based on this method, the fatigue crack growth rate (CGR) of typical structural materials in nuclear power systems was measured. The effects of applied load, load ratio and loading frequency on the fatigue crack growth rate of reactor structural materials were discussed. The result shows that the fatigue crack growth rate of reactor structural materials depends on the hardness of materials, and the harder the material is, the higher the rate of crack growth is. (authors)
The effects of loading history on fatigue crack growth threshold
International Nuclear Information System (INIS)
Ogawa, Takeshi; Tokaji, Keiro; Ochi, Satoshi; Kobayashi, Hideo.
1987-01-01
The effects of loading history on threshold stress intensity range (ΔK th ) were investigated in a low alloy steel SFVQ1A (A508 - 3) and a low carbon steel S10C. A single overload and multiple overloads were chosen as loading history. Crack growth and crack closure following the loading histories were measured at load ratios of 0.05 and 0.70. Threshold values were determined as a fatigue limit of preloaded specimens. The ΔK th values increased with increasing overload stress intensity factor (K h ). For a given K h value, multiple overloads produced much larger increase in ΔK th than a single overload and threshold values expressed by maximum stress intensity factor (K max,th ) were almost constant, independent of stress ratio. The results obtained were discussed in terms of crack closure behaviour, and a method was proposed to evaluate the threshold value based on plasticity-induced crack closure. (author)
A comparison of fatigue crack growth in human enamel and hydroxyapatite.
Bajaj, Devendra; Nazari, Ahmad; Eidelman, Naomi; Arola, Dwayne D
2008-12-01
Cracks and craze lines are often observed in the enamel of human teeth, but they rarely cause tooth fracture. The present study evaluates fatigue crack growth in human enamel, and compares that to the fatigue response of sintered hydroxyapatite (HAp) with similar crystallinity, chemistry and density. Miniature inset compact tension (CT) specimens were prepared that embodied a small piece of enamel (N=8) or HAp (N=6). The specimens were subjected to mode I cyclic loads and the steady state crack growth responses were modeled using the Paris Law. Results showed that the fatigue crack growth exponent (m) for enamel (m=7.7+/-1.0) was similar to that for HAp (m=7.9+/-1.4), whereas the crack growth coefficient (C) for enamel (C=8.7 E-04 (mm/cycle)x(MPa m(0.5))(-m)) was significantly lower (pcrack growth in the enamel occurred primarily along the prism boundaries. In regions of decussation, the microstructure promoted microcracking, crack bridging, crack deflection and crack bifurcation. Working in concert, these mechanisms increased the crack growth resistance and resulted in a sensitivity to crack growth (m) similar to bone and lower than that of human dentin. These mechanisms of toughening were not observed in the crack growth response of the sintered HAp. While enamel is the most highly mineralized tissue of the human body, the microstructural arrangement of the prisms promotes exceptional resistance to crack growth.
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
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
... spending time in a rehab facility or getting cognitive-behavioral therapy or other treatments. Right now, there are no medicines to treat a crack addiction. If you smoke crack, talking with a counselor ...
An effective FEM-based approach for discrete 3D crack growth
DEFF Research Database (Denmark)
Nielsen, Morten Eggert; Lambertsen, Søren Heide; Pedersen, Erik B.
2015-01-01
A new geometric approach for discrete crack growth modeling is proposed and implemented in a commercial FEM software. The basic idea is to model the crack growth by removing volumes of material as the crack front advances. Thereby, adaptive meshing techniques, found in commercial software, is wel...
Standard test method for measurement of fatigue crack growth rates
American Society for Testing and Materials. Philadelphia
2015-01-01
1.1 This test method covers the determination of fatigue crack growth rates from near-threshold to Kmax controlled instability. Results are expressed in terms of the crack-tip stress-intensity factor range (ΔK), defined by the theory of linear elasticity. 1.2 Several different test procedures are provided, the optimum test procedure being primarily dependent on the magnitude of the fatigue crack growth rate to be measured. 1.3 Materials that can be tested by this test method are not limited by thickness or by strength so long as specimens are of sufficient thickness to preclude buckling and of sufficient planar size to remain predominantly elastic during testing. 1.4 A range of specimen sizes with proportional planar dimensions is provided, but size is variable to be adjusted for yield strength and applied force. Specimen thickness may be varied independent of planar size. 1.5 The details of the various specimens and test configurations are shown in Annex A1-Annex A3. Specimen configurations other than t...
Fatigue crack growth behavior in niobium-hydrogen alloys
International Nuclear Information System (INIS)
Lin, M.C.C.; Salama, K.
1997-01-01
Near-threshold fatigue crack growth behavior has been investigated in niobium-hydrogen alloys. Compact tension specimens (CTS) with three hydrogen conditions are used: hydrogen-free, hydrogen in solid solution, and hydride alloy. The specimens are fatigued at a temperature of 296 K and load ratios of 0.05, 0.4, and 0.75. The results at load ratios of 0.05 and 0.4 show that the threshold stress intensity range (ΔK th ) decreases as hydrogen is added to niobium. It reaches a minimum at the critical hydrogen concentration (C cr ), where maximum embrittlement occurs. The critical hydrogen concentration is approximately equal to the solubility limit of hydrogen in niobium. As the hydrogen concentration exceeds C cr , ΔK th increases slowly as more hydrogen is added to the specimen. At load ratio 0.75, ΔK th decreases continuously as the hydrogen concentration is increased. The results provide evidence that two mechanisms are responsible for fatigue crack growth behavior in niobium-hydrogen alloys. First, embrittlement is retarded by hydride transformation--induced and plasticity-induced crack closures. Second, embrittlement is enhanced by the presence of hydrogen and hydride
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.
International Nuclear Information System (INIS)
James, L.A.
1985-08-01
Section XI of the ASME Boiler and Pressure Vessel Code provides rules for the analysis of structures for which cracks or crack-like flaws have been discovered during inservice inspection. The Code provides rules for the analysis of both surface flaws as well as flaws that are embedded within the wall of the pressure vessel. In the case of surface flaws, the Code provides fatigue crack growth rate relationships for typical nuclear pressure vessel steels (e.g., ASTM A508-2 and A533-B) cycled in water environments typical of those in light-water reactors (LWR). However, for the case of embedded cracks, the Code provides crack growth relationships based on results from specimens that were cycled in an elevated temperature air environment. Although these latter relationships are often referred to as applying to ''inert'' environments, the results of this paper will show that an elevated temperature air environment is anything but inert, and that use of such relationships can result in overly pessimistic estimates of fatigue-crack growth lifetimes of embedded cracks. The reason, of course, is that embedded cracks grow in an environment that is probably much closer to a vacuum than an air environment
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
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
Creep, Fatigue and Environmental Interactions and Their Effect on Crack Growth in Superalloys
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.
Separating the Influence of Environment from Stress Relaxation Effects on Dwell Fatigue Crack Growth
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.
Fatigue crack growth studies on a tee junction using ultrasonic non-destructive methods
International Nuclear Information System (INIS)
Subramanian, C.V.; Thavasimuthu, M.; Ramesh, A.S.; Jayakumar, T.; Kalyanasundaram, P.; Baldev Raj
1996-01-01
Fatigue cracks need to be detected and sized to maintain structural integrity. The significance of cracks detected in service must also be assessed. This paper describes the on-line ultrasonic testing carried out on a Tee joint subjected to fatigue loading. The initiation and growth of the cracks were monitored for every 5,000 cycles up to 40,000 cycles. The study demonstrated the use of ultrasonic testing for fatigue crack growth detection and sizing. (author)
Crack growth behavior of low-alloy bainitic 51CrV4 steel
Canadinç, Demircan; Lambers, H. G.; Gorny B.; Tschumak, S.; Maier, H.J.
2010-01-01
The crack growth behavior of low-alloy bainitic 51CrV4 steel was investigated. The current results indicate that the stress state present during the isothermal bainitic transformation has a strong influence on the crack propagation behavior in the near threshold regime, when the crack growth direction is perpendicular to the loading axis of the original sample undergoing phase transformation. However, the influence of stresses superimposed during the bainitic transformation on the crack growt...
Role of prism decussation on fatigue crack growth and fracture of human enamel.
Bajaj, Devendra; Arola, Dwayne
2009-10-01
The role of prism decussation on the crack growth resistance of human enamel is evaluated. Miniature inset compact tension (CT) specimens embodying a section of cuspal enamel were subjected to Mode I cyclic or monotonic loads. Cracks were grown in either the forward (from outer enamel inwards) or reverse (from inner enamel outwards) direction and the responses were compared quantitatively. Results showed that the outer enamel exhibits lower resistance to the inception and growth of cracks. Regardless of the growth direction, the near-threshold region of cyclic extension was typical of "short crack" behavior (i.e. deceleration of growth with an increase in crack length). Cyclic crack growth was more stable in the forward direction and occurred over twice the spatial distance achieved in the reverse direction. In response to the monotonic loads, a rising R-curve response was exhibited by growth in the forward direction only. The total energy absorbed in fracture for the forward direction was more than three times that in the reverse. The rise in crack growth resistance was largely attributed to a combination of mechanisms that included crack bridging, crack bifurcation and crack curving, which were induced by decussation in the inner enamel. An analysis of the responses distinguished that the microstructure of enamel appears optimized for resisting crack growth initiating from damage at the tooth's surface.
Fracture processes and mechanisms of crack growth resistance in human enamel
Bajaj, Devendra; Park, Saejin; Quinn, George D.; Arola, Dwayne
2010-07-01
Human enamel has a complex micro-structure that varies with distance from the tooth’s outer surface. But contributions from the microstructure to the fracture toughness and the mechanisms of crack growth resistance have not been explored in detail. In this investigation the apparent fracture toughness of human enamel and the mechanisms of crack growth resistance were evaluated using the indentation fracture approach and an incremental crack growth technique. Indentation cracks were introduced on polished surfaces of enamel at selected distances from the occlusal surface. In addition, an incremental crack growth approach using compact tension specimens was used to quantify the crack growth resistance as a Junction of distance from the occlusal surface. There were significant differences in the apparent toughness estimated using the two approaches, which was attributed to the active crack length and corresponding scale of the toughening mechanisms.
Automated corrosion fatigue crack growth testing in pressurized water environments
International Nuclear Information System (INIS)
Ceschini, L.J.; Liaw, P.K.; Rudd, G.E.; Logsdon, W.A.
1984-01-01
This paper describes in detail a novel approach to construct a test facility for developing corrosion fatigue crack growth rate (FCGR) properties in aggressive environments. The environment studied is that of a pressurized water reactor (PWR) at 288 0 C (550 0 F) and 13.8 MPa (200 psig). To expedite data generation, each chamber was designed to accommodate two test specimens. A common water recirculation and pressurization system was employed to service two test chambers. Thus, four fatigue crack propagation rate tests could be conducted simultaneously in the pressurized water environment. The data analysis was automated to minimize the typically high labor costs associated with corrosion fatigue crack propagation testing. Verification FCGR tests conducted on an ASTM A469 rotor steel in a room temperature air environment as well as actual PWR environment FCGR tests performed on an ASTM A533 Grade B Class 2 pressure vessel steel demonstrated that the dual specimen test facility is an excellent system for developing the FCGR properties of materials in adverse environments
Crack Growth Monitoring in Harsh Environments by Electric Potential Measurements
International Nuclear Information System (INIS)
Lloyd, Wilson Randolph; Reuter, Walter Graham; Weinberg, David Michael
1999-01-01
Electric potential measurement (EPM) technology offers an attractive alternative to conventional nondestructive evaluation (NDE) for monitoring crack growth in harsh environments. Where conventional NDE methods typically require localized human interaction, the EPM technique developed at the Idaho National Engineering and Environmental Laboratory (INEEL) can be operated remotely and automatically. Once a crack-like defect is discovered via conventional means, EPM can be applied to monitor local crack size changes. This is of particular interest in situations where an identified structural defect is not immediately rejectable from a fitness-for-service viewpoint, but due to operational and environmental conditions may grow to an unsafe size with continuing operation. If the location is in a harsh environment where periodic monitoring by normal means is either too costly or not possible, a very expensive repair may be immediately mandated. However, the proposed EPM methodology may offer a unique monitoring capability that would allow for continuing service. INEEL has developed this methodology, supporting equipment, and calibration information to apply EPM in a field environment for just this purpose. Laboratory and pilot scale tests on full-size engineering structures (pressure vessels and piping) have been successfully performed. The technique applicable is many severe environments because the sensitive equipment (electronics, operators) can be situated in a remote location, with only current and voltage probe electrical leads entering into the harsh environment. Experimental results showing the utility of the methodology are presented, and unique application concepts that have been examined by multiple experiments are discussed
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.
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...
International Nuclear Information System (INIS)
Kim, Sung Jin; Kwon, Oh Yang
2004-01-01
The fatigue crack growth behavior of a fatigue-cracked and patch-repaired AA2024-T3 plate has been monitored. It was found that the overall crack growth rate was reduced and the crack propagation into the adjacent hole was also retarded. Signals due to crack growth after patch-repair and those due to debonding of the plate-patch interface were discriminated each other by using principal component analysis. The former showed higher center frequency and lower amplitude, whereas the latter showed longer rise time, lower frequency and higher amplitude.
Numerical Simulation of Fatigue Crack Growth in Hip Implants
Czech Academy of Sciences Publication Activity Database
Colic, K.; Sedmak, A.; Grbovic, A.; Burzić, M.; Hloch, Sergej; Sedmak, S.
2016-01-01
Roč. 149, č. 149 (2016), s. 229-235 E-ISSN 1877-7058. [International Conference on Manufacturing Engineering and Materials, ICMEM 2016. Nový Smokovec, 06.06.2016-10.06.2016] R&D Projects: GA MŠk ED2.1.00/03.0082; GA MŠk(CZ) LO1406 Institutional support: RVO:68145535 Keywords : biomedical application design * extended finite element method (XFEM) * Ti-6Al-4V alloy * stress intensity factor (SIF) * fatigue crack growth Subject RIV: JQ - Machines ; Tools http://www.sciencedirect.com/science/article/pii/S1877705816311699
Probabilistic Model for Fatigue Crack Growth in Welded Bridge Details
DEFF Research Database (Denmark)
Toft, Henrik Stensgaard; Sørensen, John Dalsgaard; Yalamas, Thierry
2013-01-01
In the present paper a probabilistic model for fatigue crack growth in welded steel details in road bridges is presented. The probabilistic model takes the influence of bending stresses in the joints into account. The bending stresses can either be introduced by e.g. misalignment or redistribution...... of stresses in the structure. The fatigue stress ranges are estimated from traffic measurements and a generic bridge model. Based on the probabilistic models for the resistance and load the reliability is estimated for a typical welded steel detail. The results show that large misalignments in the joints can...
Fatigue Crack Growth in Bodies with Thermally Sprayed Coating
Czech Academy of Sciences Publication Activity Database
Kovářík, O.; Haušild, P.; Medřický, Jan; Tomek, L.; Siegl, J.; Mušálek, Radek; Curry, N.; Björklund, S.
2016-01-01
Roč. 25, 1-2 (2016), s. 311-320 ISSN 1059-9630. [ITSC 2015: International Thermal Spray Conference and Exposition. Long Beach, California, 11.05.2015-14.05.2015] R&D Projects: GA ČR GB14-36566G Institutional support: RVO:61389021 Keywords : Thermal barrier coating * fatigue * crack growth * digital image correlation * digital image correlation Subject RIV: JK - Corrosion ; Surface Treatment of Materials Impact factor: 1.488, year: 2016 http://link.springer.com/article/10.1007%2Fs11666-015-0329-9
Crack growth under combined creep and fatigue conditions in alloy 800
International Nuclear Information System (INIS)
Pfaffelhuber, M.; Roedig, M.; Schubert, F.; Nickel, H.
1989-08-01
To investigate the crack growth behaviour under combined creep-fatigue loading, CT 25 mm-specimens of X10NiCrAlTi 32 20 (Alloy 800) have been tested in experiments with cyclic loadings and hold times, with static loadings and short stress rekief interrupts, with ramp type loadings and with sequences of separate fatigue and creep crack growth periods. The test temperature of 700deg C was selected because only in this temperature range this alloy provides similar amounts of crack growth under creep and fatigue conditions due to equivalent stress levels. For the estimation of crack growth under combined loading conditions a linear accumulation of increase in crack length was proved using the crack growth laws of pure creep and fatigue crack growth. Hold time and ramp loadings lead to a higher crack growth rate compared with pure creep or pure fatigue crack growth tests. In hold time experiments the crack growth rate is higher than ramp tests of the same period time. The results of hold time tests can be fairly enough predicted by linear damage accumulation rules. (orig.) [de
International Nuclear Information System (INIS)
Lee, S. G.; Kim, I. S.; Park, Y. S.; Kim, J. W.; Park, C. Y.
2001-01-01
Fatigue tests in air and in room temperature water were performed to obtain comparable data and stable crack measuring conditions. In air environment, fatigue crack growth rate was increased with increasing temperature due to an increase in crack tip oxidation rate. In room temperature water, the fatigue crack growth rate was faster than in air and crack path varied on loading conditions. In simulated light water reactor (LWR) conditions, there was little environmental effect on the fatigue crack growth rate (FCGR) at low dissolved oxygen or at high loading frequency conditions. While the FCGR was enhanced at high oxygen condition, and the enhancement of crack growth rate increased as loading frequency decreased to a critical value. In fractography, environmentally assisted cracks, such as semi-cleavage and secondary intergranular crack, were found near sulfide inclusions only at high dissolved oxygen and low loading frequency condition. The high crack growth rate was related to environmentally assisted crack. These results indicated that environmentally assisted crack could be formed by the Electrochemical effect in specific loading condition
Evaluation of creep-fatigue crack growth for large-scale FBR reactor vessel and NDE assessment
Energy Technology Data Exchange (ETDEWEB)
Joo, Young Sang; Kim, Jong Bum; Kim, Seok Hun; Yoo, Bong
2001-03-01
Creep fatigue crack growth contributes to the failure of FRB reactor vessels in high temperature condition. In the design stage of reactor vessel, crack growth evaluation is very important to ensure the structural safety and setup the in-service inspection strategy. In this study, creep-fatigue crack growth evaluation has been performed for the semi-elliptical surface cracks subjected to thermal loading. The thermal stress analysis of a large-scale FBR reactor vessel has been carried out for the load conditions. The distributions of axial, radial, hoop, and Von Mises stresses were obtained for the loading conditions. At the maximum point of the axial and hoop stress, the longitudinal and circumferential surface cracks (i.e. PTS crack, NDE short crack and shallow long crack) were postulated. Using the maximum and minimum values of stresses, the creep-fatigue crack growth of the proposed cracks was simulated. The crack growth rate of circumferential cracks becomes greater than that of longitudinal cracks. The total crack growth of the largest PTS crack is very small after 427 cycles. The structural integrity of a large-scale reactor can be maintained for the plant life. The crack depth growth of the shallow long crack is faster than that of the NDE short crack. In the ISI of the large-scale FBR reactor vessel, the ultrasonic inspection is beneficial to detect the shallow circumferential cracks.
TGO growth and crack propagation in a thermal barrier coating
Energy Technology Data Exchange (ETDEWEB)
Chen, W.R.; Archer, R.; Huang, X. [National Research Council of Canada, Ottawa, ON (Canada); Marple, B.R. [National Research Council of Canada, Boucherville, PQ (Canada)
2008-07-01
In thermal barrier coating (TBC) systems, a continuous alumina layer developed at the ceramic topcoat/bond coat interface helps to protect the metallic bond coat from further oxidation and improve the durability of the TBC system under service conditions. However, other oxides such as spinel and nickel oxide, formed in the oxidizing environment, are believed to be detrimental to TBC durability during service at high temperatures. It was shown that in an air-plasma-sprayed (APS) TBC system, post-spraying heat treatments in low-pressure oxygen environments could suppress the formation of the detrimental oxides by promoting the formation of an alumina layer at the ceramic topcoat/bond coat interface, leading to an improved TBC durability. This work presents the influence of post-spraying heat treatments in low-pressure oxygen environments on the oxidation behaviour and durability of a thermally sprayed TBC system with high-velocity oxy-fuel (HVOF)-produced Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat. Oxidation behaviour of the TBCs is evaluated by examining their microstructural evolution, growth kinetics of the thermally grown oxide (TGO) layers, as well as crack propagation during low frequency thermal cycling at 1050 C. The relationship between the TGO growth and crack propagation will also be discussed. (orig.)
Model for predicting non-linear crack growth considering load sequence effects (LOSEQ)
International Nuclear Information System (INIS)
Fuehring, H.
1982-01-01
A new analytical model for predicting non-linear crack growth is presented which takes into account the retardation as well as the acceleration effects due to irregular loading. It considers not only the maximum peak of a load sequence to effect crack growth but also all other loads of the history according to a generalised memory criterion. Comparisons between crack growth predicted by using the LOSEQ-programme and experimentally observed data are presented. (orig.) [de
Economic analyses of rapid population growth.
Birdsall, N
1989-01-01
"Discussion of the macroeconomic consequences of rapid population growth is organized into three schools: pessimists, optimists, and the recent revisionists. For the revisionists, differing views are presented about the pervasiveness and relevance of market failures, such as the negative externalities of childbearing, and about the ability of families and institutions to adjust rapidly to changes brought on by rapid population growth. A welfare economics approach is used to review the merits of various public policies to reduce fertility, including public financing of family planning services and taxes and incentives associated with childbearing." The focus is on developing countries. excerpt
Modification of the FRI crack growth model formulation from a mathematical viewpoint
International Nuclear Information System (INIS)
Hashimoto, Tsuneyuki; Koshiishi, Masato
2009-01-01
The FRI model of crack growth, which incorporates mechanical properties into the slip oxidation mechanism of crack advance, is an extension of the well-known Ford-Andresen model. When the exponent of the oxidation current decay curve is set close to 1, however, the FRI model gives an infinite crack growth rate. Here, the oxidation decay curve integral is revised to eliminate this divergence, and modified crack growth rate equations are derived. Also presented here is a procedure for determining the oxidation current parameters from the curve-fitting to measurements of crack growth rate. Parameter value determination and crack growth calculations are illustrated for cold-worked Type 316L stainless steel. (author)
Fatigue crack growth in 2024-T3 aluminum under tensile and transverse shear stresses
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.
Fatigue crack growth in mode II of adhesively joined composites
DEFF Research Database (Denmark)
Biel, Anders; Toftegaard, Helmuth Langmaack
2017-01-01
, experiments are performed to derive material data for a crack propagation in shear i.e. in mode II. The shear loading of the crack is achieved by use of double cantilever beam specimens loaded with uneven bending moments. The experiments are performed under a constant cyclic displacement. An initial mode I...... loading is used to make the crack start in the adhesive. The crack length is measured using a load synchronized camera. Due to the shear loading the crack deviates from the adhesive layer into the laminate. A stable crack propagation is detected in the laminate. No influence have been detected due...... to an increasing crack length. It is also observed that the crack is trapped in the laminate; if the loading is changed to mode I the crack continues to propagate in the laminate....
Thresholds of time dependent intergranular crack growth in a nickel disc alloy Alloy 720Li
Directory of Open Access Journals (Sweden)
Li Hangyue
2014-01-01
Full Text Available At high temperatures in air, introducing a dwell period at the peak stress of fatigue cycles promotes time dependent intergranular crack growth which can increase crack growth rates by upto a few orders of magnitude from the rates of transgranular fatigue crack growth in superalloys. It is expected that time dependent intergranular crack growth in nickel-based superalloys may not occur below a critical mechanical driving force, ΔKth−IG, analogous to a fatigue threshold (ΔKth and a critical temperature, Tth. In this study, dwell fatigue crack growth tests have been carefully designed and conducted on Alloy 720Li to examine such thresholds. Unlike a fatigue threshold, the threshold stress intensity factor range for intergranular crack growth is observed to be highly sensitive to microstructure, dwell time and test procedure. The near threshold crack growth behaviour is made complex by the interactions between grain boundary oxidation embrittlement and crack tip stress relaxation. In general, lower ΔKth−IG values are associated with finer grain size and/or shorter dwell times. Often a load increasing procedure promotes stress relaxation and tends to lead to higher ΔKth−IG. When there is limited stress relaxation at the crack tip, similar ΔKth−IG values are measured with load increasing and load shedding procedures. They are generally higher than the fatigue threshold (ΔKth despite faster crack growth rates (da/dN in the stable crack growth regime. Time dependent intergranular crack growth cannot be activated below a temperature of 500 ∘C.
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%
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%.
Crack Growth Behaviour of P92 Steel Under Creep-fatigue Interaction Conditions
Directory of Open Access Journals (Sweden)
JING Hong-yang
2017-05-01
Full Text Available Creep-fatigue interaction tests of P92 steel at 630℃ under stress-controlled were carried out, and the crack propagation behaviour of P92 steel was studied. The fracture mechanism of crack growth under creep-fatigue interaction and the transition points in a-N curves were analyzed based on the fracture morphology. The results show that the fracture of P92 steel under creep-fatigue interaction is creep ductile fracture and the (Ctavg parameter is employed to demonstrate the crack growth behaviour; in addition, the fracture morphology shows that the crack growth for P92 steel under creep-fatigue interaction is mainly caused by the nucleation and growth of the creep voids and micro-cracks. Furthermore, the transition point of a-lg(Ni/Nf curve corresponds to the turning point of initial crack growth changed into steady crack growth while the transition point of (da/dN-N curve exhibits the turning point of steady creep crack growth changed into the accelerated crack growth.
Test Method Variability in Slow Crack Growth Properties of Sealing Glasses
Salem, J. A.; Tandon, R.
2010-01-01
The crack growth properties of several sealing glasses were measured by using constant stress rate testing in 2 and 95 percent RH (relative humidity). Crack growth parameters measured in high humidity are systematically smaller (n and B) than those measured in low humidity, and crack velocities for dry environments are 100x lower than for wet environments. The crack velocity is very sensitive to small changes in RH at low RH. Biaxial and uniaxial stress states produced similar parameters. Confidence intervals on crack growth parameters that were estimated from propagation of errors solutions were comparable to those from Monte Carlo simulation. Use of scratch-like and indentation flaws produced similar crack growth parameters when residual stresses were considered.
Modes of long crack growth under non-stationary temperature fields
International Nuclear Information System (INIS)
Tereshin, D.A.
2012-01-01
Highlights: ► Moving thermal stresses can result in much lengthier cracks than usually expected. ► Codirectional crack grows gradually along with thermal zone movement. ► Oppositely directed crack grows stepwise towards thermal tension movement. ► The total crack increment can be up to the whole region of thermal tension travel. - Abstract: The exploitation practice of structures under thermal loads evidences that the final length of a quasistatic crack can be considerably greater than the thermal tension zone, sometimes causing that the structure approaches complete fracture. This occurs in one or several cycles of a gradual crack growth due to the evolution of thermal field in time resulting in that fracture zone follows the moving tension zone. By the extreme example of quasistationary thermal stress field the set of quasistatic crack growth modes and their peculiarities for the case of moving thermal stresses are described here. These are modes developing both in the direction of the thermal stress field propagation and in the opposite direction. The critical condition of each mode is described, and the crack growth rates are estimated. The rational crack growth evaluation procedure is also proposed. The theoretical conclusions are supported by the experiment, which demonstrates the growth of long thermal cracks.
Accelerated Near-Threshold Fatigue Crack Growth Behavior of an Aluminum Powder Metallurgy Alloy
Piascik, Robert S.; Newman, John A.
2002-01-01
Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low DK, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = Kmin/Kmax). The near threshold accelerated FCG rates are exacerbated by increased levels of Kmax (Kmax less than 0.4 KIC). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and Kmax influenced accelerated crack growth is time and temperature dependent.
Resolved shear stress intensity coefficient and fatigue crack growth in large crystals
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.
Crack Initiation and Growth Behavior at Corrosion Pit in 2024-T3 Aluminum Alloy
2014-09-01
concepts of fracture mechanics. Corrosion crack initiation or growth can develop when exposed to continuous or intermittent humid environment during...act as nucleation sites. For many materials of the structure such as Al, steel the growth of fatigue cracks from corrosion pit stands legitimate...critical or rather threshold values below which the nucleation of fatigue crack is not possible [6]. Under certain conditions that prevail on
Role of Prism Decussation on Fatigue Crack Growth and Fracture of Human Enamel
Bajaj, Devendra; Arola, Dwayne
2009-01-01
The role of prism decussation on the crack growth resistance of human enamel is evaluated. Miniature inset Compact Tension (CT) specimens embodying a section of cuspal enamel were subjected to Mode I cyclic or monotonic loads. Cracks were grown in either the forward (from outer enamel inwards) or reverse (from inner enamel outwards) direction and the responses were compared quantitatively. Results showed that the outer enamel exhibits lower resistance to the inception and growth of cracks. Re...
On the driving force for crack growth during thermal actuation of shape memory alloys
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.
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)
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.
Standard test method for measurement of creep crack growth times in metals
American Society for Testing and Materials. Philadelphia
2007-01-01
1.1 This test method covers the determination of creep crack growth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loading conditions. The time (CCI), t0.2 to an initial crack extension δai = 0.2 mm from the onset of first applied force and creep crack growth rate, ˙a or da/dt is expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and Ct (1-14). The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods (15-25). 1.1.1 The choice of the crack growth correlating parameter C*, C*(t), Ct, or K depends on the material creep properties, geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile (1-14) and creep-brittle (26-37). In creep ductile materials, where cr...
Effect of T-stress on crack growth along an interface between ductile and elastic solids
DEFF Research Database (Denmark)
Tvergaard, Viggo
2003-01-01
For crack growth along an interface joining an elastic-plastic solid to an elastic substrate the effect of a non-singular stress component in the crack growth direction in the elastic-plastic solid is investigated. Conditions of small scale yielding are assumed, and due to the mismatch of elastic...
International Nuclear Information System (INIS)
Kamaya, Masayuki; Kawakubo, Masahiro
2012-01-01
In this study, the fatigue damage was assumed to be equivalent to the crack initiation and its growth, and fatigue life was assessed by predicting the crack growth. First, a low-cycle fatigue test was conducted in air at room temperature under constant cyclic strain range of 1.2%. The crack initiation and change in crack size during the test were examined by replica investigation. It was found that a crack of 41.2 μm length was initiated almost at the beginning of the test. The identified crack growth rate was shown to correlate well with the strain intensity factor, whose physical meaning was discussed in this study. The fatigue life prediction model (equation) under constant strain range was derived by integrating the crack growth equation defined using the strain intensity factor, and the predicted fatigue lives were almost identical to those obtained by low-cycle fatigue tests. The change in crack depth predicted by the equation also agreed well with the experimental results. Based on the crack growth prediction model, it was shown that the crack size would be less than 0.1 mm even when the estimated fatigue damage exceeded the critical value of the design fatigue curve, in which a twenty-fold safety margin was used for the assessment. It was revealed that the effect of component size and surface roughness, which have been investigated empirically by fatigue tests, could be reasonably explained by considering the crack initiation and growth. Furthermore, the environmental effect on the fatigue life was shown to be brought about by the acceleration of crack growth. (author)
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)
Design of four-point SENB specimens with stable crack growth
DEFF Research Database (Denmark)
Jørgensen, Jeppe Bjørn; Kildegaard, Casper; Sørensen, Bent F.
2018-01-01
A four-point single-edge-notch-beam (SENB) test specimen loaded in displacement control (fixed grip) is proposed for studying crack deflection at bi-material interfaces. In order to ensure stable crack growth, a novel analytical model of the four-point SENB specimen in fixed grip is derived...... and compared with numerical models. Model results show that the specimen should be short and thick, and the start-crack length should be deep for the crack to propagate stable towards the bi-material interface. Observations from experimental tests of four-point SENB specimens with different start-crack lengths...
Effect of T-stress on the cleavage crack growth resistance resulting from plastic flow
DEFF Research Database (Denmark)
Tvergaard, Viggo
1998-01-01
Crack growth is studied numerically for cases where fracture occurs by atomic separation, sc that the length scale of the fracture process is typically much smaller than the dislocation spacing. Thus, the crack growth mechanism is brittle, but due to plastic flow at some distance from the crack tip......, the materials show crack growth resistance. It is shown here that the resistance is strongly dependent on the value of the non-singular T-stress, acting parallel to the crack plane. The numerical technique employed makes use of a thin dislocation-free strip of elastic material inside which the crack propagates......, with the material outside described by continuum plasticity. Thus the width of the strip is a material length scale comparable to the dislocation spacing or the dislocation cell size....
The influence of loading frequency on near-threshold fatigue crack growth
International Nuclear Information System (INIS)
Ogawa, Takeshi; Tokaji, Keiro; Ochi, Satoshi
1986-01-01
Fatigue crack growth and crack closure in the near-threshold region were investigated under different loading frequencies for three types of steel. The results show that the loading frequency influences the near-threshold characteristics in fatigue crack growth, through the different contributions of the fretting oxide induced crack closure. This behaviour is attributed to condensation of moisture between crack faces, which is influenced by the loading frequency. The formation of the fretting oxide debris promoted by the condensation of moisture becomes marked at a higher frequency. However, it is an unstable and complicating phenomenon, since the condensation is also influenced by relative humidity, test temperature and sheet thickness. Therefore, it is concluded that non-oxide controlled crack growth characteristics should be used for the life prediction of structures. (author)
Slow Growth of a Crack with Contacting Faces in a Viscoelastic Body
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.
International Nuclear Information System (INIS)
Kim, Jong Sung; Kim, Cheol; Jin, Tae Eun; Dong, P.
2004-01-01
The mesh-insensitive structural stress procedure by Dong is modified to apply to the welded joints with local thickness variation and inarguable shear/normal stresses along local discontinuity surface. In order to make use of the structural stress based K solution for fatigue correlation of welded joints, a proper crack growth model needs to be developed. There exist some significant discrepancies in inferring the slope or crack growth exponent in the conventional Paris law regime. Two-stage crack growth model was not considered since its applications are focused upon the fatigue behavior in welded joints in which the load ratio effects are considered negligible. In this paper, a two-stage crack growth law considering high mean loading is proposed and proven to be effective in unifying the so-called anomalous short crack growth data
DEFF Research Database (Denmark)
Pereira, Gilmar Ferreira; Mikkelsen, Lars Pilgaard; McGugan, Malcolm
2015-01-01
This article presents a novel method to asses a crack growing/damage event in fibre reinforced plastic, or adhesive using Fibre Bragg Grating (FBG) sensors embedded in a host material. Different features of the crack mechanism that induce a change in the FBG response were identified. Double Canti...
Crack growth analysis in a weld-heat-affected zone using S-version FEM
International Nuclear Information System (INIS)
Kikuchi, Masanori; Wada, Yoshitaka; Shimizu, Yuto; Li, Yulong
2012-01-01
The objective of this study is the prediction of crack propagation under thermal, residual stress fields using S-Version FEM (S-FEM). By using the S-FEM technique, only the local mesh should be re-meshed and it becomes easy to simulate crack growth. By combining with an auto-meshing technique, the local mesh is re-meshed automatically, and a curved crack path is modeled easily. Virtual crack closure integral method (VCCM) is used to evaluate energy release rate at the crack tip. For crack growth analyses, crack growth rate and growth direction are determined using criteria for mixed mode loading condition. In order to confirm the validity of this analysis, some comparisons with previously reported analyses were done, and good agreement obtained. In this study, residual stress data were provided by JAEA, Japan Atomic Energy Agency, based on their numerical simulation. Stress corrosion crack (SCC) growth analyses in a pipe are conducted in two-dimensional and three-dimensional fields. Two cases, for an axi-symmetric distribution of residual stress in the pipe wall and a non-axisymmetric one are assumed. Effects of residual stress distribution patterns on SCC cracking are evaluated and discussed.
Statistical analysis of fatigue crack growth behavior for grade B cast steel
International Nuclear Information System (INIS)
Li, W.; Sakai, T.; Li, Q.; Wang, P.
2011-01-01
Tests for fatigue crack growth rate (FCGR) and crack-tip opening displacement (CTOD) were performed to clarify the fatigue crack growth behavior of a railway grade B cast steel. The threshold values of this steel with specific survival probabilities are evaluated, in which the mean value is 8.3516 MPa m 1/2 , very similar to the experimental value, about 8.7279 MPa m 1/2 . Under the conditions of plane strain and small-scale yielding, the values of fracture toughness for this steel with specific survival probabilities are converted from the corresponding critical CTOD values, in which the mean value is about 138.4256 MPa m 1/2 . In consideration of the inherent variability of crack growth rates, six statistical models are proposed to represent the probabilistic FCGR curves of this steel in entire crack propagation region from the viewpoints of statistical evaluation on the number of cycles at a given crack size and the crack growth rate at a given stress intensity factor range, stochastic characteristic of crack growth as well as statistical analysis of coefficient and exponent in FCGR power law equation. Based on the model adequacy checking, result shows that all models are basically in good agreement with test data. Although the probabilistic damage-tolerant design based on some models may involve a certain amount of risk in stable crack propagation region, they just accord with the fact that the dispersion degree of test data in this region is relatively smaller.
Preloading To Accelerate Slow-Crack-Growth Testing
Gyekenyesi, John P.; Choi, Sung R.; Pawlik, Ralph J.
2004-01-01
An accelerated-testing methodology has been developed for measuring the slow-crack-growth (SCG) behavior of brittle materials. Like the prior methodology, the accelerated-testing methodology involves dynamic fatigue ( constant stress-rate) testing, in which a load or a displacement is applied to a specimen at a constant rate. SCG parameters or life prediction parameters needed for designing components made of the same material as that of the specimen are calculated from the relationship between (1) the strength of the material as measured in the test and (2) the applied stress rate used in the test. Despite its simplicity and convenience, dynamic fatigue testing as practiced heretofore has one major drawback: it is extremely time-consuming, especially at low stress rates. The present accelerated methodology reduces the time needed to test a specimen at a given rate of applied load, stress, or displacement. Instead of starting the test from zero applied load or displacement as in the prior methodology, one preloads the specimen and increases the applied load at the specified rate (see Figure 1). One might expect the preload to alter the results of the test and indeed it does, but fortunately, it is possible to account for the effect of the preload in interpreting the results. The accounting is done by calculating the normalized strength (defined as the strength in the presence of preload the strength in the absence of preload) as a function of (1) the preloading factor (defined as the preload stress the strength in the absence of preload) and (2) a SCG parameter, denoted n, that is used in a power-law crack-speed formulation. Figure 2 presents numerical results from this theoretical calculation.
Ford, Audrey C; Gramling, Hannah; Li, Samuel C; Sov, Jessica V; Srinivasan, Amrita; Pruitt, Lisa A
2018-03-01
Polycarbonate polyurethane has cartilage-like, hygroscopic, and elastomeric properties that make it an attractive material for orthopedic joint replacement application. However, little data exists on the cyclic loading and fracture behavior of polycarbonate polyurethane. This study investigates the mechanisms of fatigue crack growth in polycarbonate polyurethane with respect to time dependent effects and conditioning. We studied two commercially available polycarbonate polyurethanes, Bionate® 75D and 80A. Tension testing was performed on specimens at variable time points after being removed from hydration and variable strain rates. Fatigue crack propagation characterized three aspects of loading. Study 1 investigated the impact of continuous loading (24h/day) versus intermittent loading (8-10h/day) allowing for relaxation overnight. Study 2 evaluated the effect of frequency and study 3 examined the impact of hydration on the fatigue crack propagation in polycarbonate polyurethane. Samples loaded intermittently failed instantaneously and prematurely upon reloading while samples loaded continuously sustained longer stable cracks. Crack growth for samples tested at 2 and 5Hz was largely planar with little crack deflection. However, samples tested at 10Hz showed high degrees of crack tip deflection and multiple crack fronts. Crack growth in hydrated samples proceeded with much greater ductile crack mouth opening displacement than dry samples. An understanding of the failure mechanisms of this polymer is important to assess the long-term structural integrity of this material for use in load-bearing orthopedic implant applications. Copyright © 2018 Elsevier Ltd. All rights reserved.
Creep crack growth behaviour of an AISI 316 steel plate for fast reactor structures
International Nuclear Information System (INIS)
D'Angelo, D.; Regis, V.
1985-01-01
The paper presents and analyses creep crack growth data obtained at 550, 600 and 650 0 C in air with SENT and CT specimens on type 316 stainless steel plate for LMFBR applications. Crack initiation and crack growth are tentatively correlated to K, sigmasub(net) and J* taking into account the constraint conditions due to specimen geometry. The validity of these parameters is discussed following the concept of transition time from small scale creep at the crack tip to extensive creep within the ligament. Post exposure microstructural and fractographic investigations do evidence that grain deformation processes are mainly responsible for cavity evolution. (orig.)
International Nuclear Information System (INIS)
Ekobori, T.; Konosu, S.; Ekobori, A.
1980-01-01
Classified are models of the crack growth mechanism, and in the framework of the fracture mechanics suggested are combined micro- and macroapproaches to interpreting the criterion of the brittle fracture and fatigue crack growth as fracture typical examples, when temporal processes are important or unimportant. Under the brittle fracture conditions the crack propagation criterion is shown to be brought with the high accuracy to a form analogous to one of the crack propagation in a linear fracture mechanics although it is expressed with micro- and macrostructures. Obtained is a good agreement between theoretical and experimental data
International Nuclear Information System (INIS)
Bertolino, G.; Sauzay, M.; Bertolino, G.; Doquet, V.
2003-01-01
An attempt to model the variability of short cracks development in high-cycle fatigue is made by coupling finite element calculations of the stresses ahead of a microcrack in a polycrystal with simulations of crack growth along slip planes based on discrete dislocations dynamics. The model predicts a large scatter in growth rates related to the roughness of the crack path. It also describes the influence of the mean grain size and the fact that overloads may suppress the endurance limit by allowing arrested cracks to cross the grain boundaries. (authors)
Crack growth rates in vessel head penetration materials
International Nuclear Information System (INIS)
Gomez Briceno, D.; Lapena, J.; Blazquez, F.
1994-01-01
The cracks detected in reactor vessel head penetrations in certain European plants have been attributed to Primary Water Stress Corrosion Cracking (PWSCC). The penetrations in question are made from Inconel 600. The susceptibility of this alloy to PWSCC has been widely studied in relation to use of this material for steam generator tubes. When the first reactor vessel head penetration cracks were detected, most of the available data on crack propagation rates were from test specimens made from steam generator tubes and tested under conditions that questioned the validity of these data for assessment of the evolution of cracks in penetrations. For this reason, the scope of the Spanish Research Project on the Inspection and Repair of PWR reactor vessel head penetrations included the acquisition of data on crack propagation rates in Inconel 600, representative of the materials used for vessel head penetrations. (authors). 1 fig., 2 tabs., 6 refs
2014-09-18
Fatigue crack growth ..................................................................................................25 Probability of detection...32 Figure 5: Fatigue crack growth simulation results for 10 runs .............................................. 35 Figure 6...43 Figure 10: Linear regression fit of ln() vs. ln( ) data for SHM using PZT sensors (Kuhn, 2009
The reduction in fatigue crack growth resistance of dentin with depth.
Ivancik, J; Neerchal, N K; Romberg, E; Arola, D
2011-08-01
The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.
The creep-fatigue crack growth behaviour of a 1CrMoV rotor steel
International Nuclear Information System (INIS)
Priest, R.H.; Miller, D.A.; Gladwin, D.N.; Maguire, J.
1989-01-01
Crack growth rates under simultaneous creep-fatigue conditions have been quantified for a 1CrMoV rotor steel. Measured growth rates were partitioned into cyclic and hold period contributions and these characterized by the relevant fracture mechanics parameters K and C. Cyclic growth rates measured in the creep-fatigue tests were enhanced compared with pure fatigue rates. This observation is compared with the behaviour of other steels and explained by quantitative metallography. The resulting crack growth equation can be used during integrity assessments for plant components containing cracks which are subject to thermal fatigue
Fatigue Crack Growth Behavior of Gas Metal Arc Welded AISI 409 Grade Ferritic Stainless Steel Joints
Lakshminarayanan, A. K.; Shanmugam, K.; Balasubramanian, V.
2009-10-01
The effect of filler metals such as austenitic stainless steel, ferritic stainless steel, and duplex stainless steel on fatigue crack growth behavior of the gas metal arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Center cracked tensile specimens were prepared to evaluate fatigue crack growth behavior. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN was used to evaluate the fatigue crack growth behavior of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.
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....
Application of the cracked pipe element to creep crack growth prediction
Energy Technology Data Exchange (ETDEWEB)
Brochard, J.; Charras, T.
1997-04-01
The modification of a computer code for leak before break analysis is very briefly described. The CASTEM2000 code was developed for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading. The modification extends the capabilities of the cracked pipe element to the determination of fracture parameters under creep conditions (C*, {phi}c and {Delta}c). The model has the advantage of evaluating significant secondary effects, such as those from thermal loading.
Towards a European draft code of practice in creep crack growth testing
International Nuclear Information System (INIS)
Nikbin, K.M.
2003-01-01
Crack growth and initiation models as well as defect assessment codes need reliable and verifiable material properties data for use in their predictive methodologies. These data consist of uniaxial, multiaxial and crack initiation and growth data under static and cyclic loading at the relevant temperatures. International collaboration for developing standards in this field started in 1987 under the auspices of the VAMAS (Versailles Agreement for MAterials and Standards). Two technical Working Areas TWA11 and TWA19 committees ending 1998 have made substantial progress in unifying and standardising the methods for obtaining the relevant data. This collaboration has resulted in the development of ASTM E1457 creep crack growth testing standard. The European collaborative programme CRETE (see Acknowledgements), which began in 1999, is following up this valuable research in order to develop a European Code of Practice for elevated temperature crack growth which is planned to have a wider field of application. A Round Robin experimental, analytical and verification programme in CRETE will include testing a type 316 LN stainless steel at 550 degC and a Carbon-Manganese steel at 400 degC consisting of seven different geometries. The paper reviews the methods of analysis used for laboratory creep crack growth data and their relevance to long term crack initiation and growth in components. In addition, since design and life assessment and material properties under creep are an integral part of this project a short review of the models available for predicting creep and fatigue crack growth is presented. (author)
International Nuclear Information System (INIS)
Singh, R.N.; Kishore, R.; Roychaudhury, S.; Unnikrishnan, M.; Sinha, T.K.; De, P.K.; Banerjee, S.; Kumar, Santosh
2000-12-01
Nuclear structural materials have to perform under most demanding and exotic environmental conditions. Due to its unique properties dilute zirconium alloys are the only choice for in-core structural materials in water cooled nuclear reactors. Hydrogen related problems have been recognized as the life-limiting factor for the core components of Pressurized Heavy Water Reactors (PHWR). Delayed Hydride Cracking (Dhc) is one of them. In this study, Dhc crack growth has been monitored using Direct Current Potential Drop (Dcp) technique. Calibration curve between normalized Dcp output and normalized crack length was established at different test temperatures. Dhc velocity was measured along the axial direction of the Zirconium-2.5Niobium pressure tube material at 203 and 250 degree C. (author)
Shaari, M. S.; Akramin, M. R. M.; Ariffin, A. K.; Abdullah, S.; Kikuchi, M.
2018-02-01
The paper is presenting the fatigue crack growth (FCG) behavior of semi-elliptical surface cracks for API X65 gas pipeline using S-version FEM. A method known as global-local overlay technique was used in this study to predict the fatigue behavior that involve of two separate meshes each specifically for global (geometry) and local (crack). The pre-post program was used to model the global geometry (coarser mesh) known as FAST including the material and boundary conditions. Hence, the local crack (finer mesh) will be defined the exact location and the mesh control accordingly. The local mesh was overlaid along with the global before the numerical computation taken place to solve the engineering problem. The stress intensity factors were computed using the virtual crack closure-integral method (VCCM). The most important results is the behavior of the fatigue crack growth, which contains the crack depth (a), crack length (c) and stress intensity factors (SIF). The correlation between the fatigue crack growth and the SIF shows a good growth for the crack depth (a) and dissimilar for the crack length (c) where stunned behavior was resulted. The S-version FEM will benefiting the user due to the overlay technique where it will shorten the computation process.
Effects of root radius, stress, crack growth and rate on fracture instability
Energy Technology Data Exchange (ETDEWEB)
McClintock, F A
1965-01-01
Of various criteria for fracture at the root of a notch, the energy, local stress, and displacement criteria have limited validity. More appropriate is the history of both stress and strain over a small region ahead of the crack, as required for fracture by the coalescence of holes. Expressions are given for crack initiation, growth, and subsequent instability in anti-plane strain of a nonhardening material. Instability is shown to depend primarily on those strain increments arising from crack growth at constant load rather than on those from increasing load at constant crack length. Thus final instability conditions are similar for single and double- ended cracks, round notches, and cracks cut under constant load. Round notches may give instability, restabilization and final instability. The growth and coalescence of holes in front of a crack in a linearly viscous material is studied for both tensile and anti-plant-strain cracks. The absence of residual strain eliminates instability, but the crack continually accelerates. (26 refs.)
Study on fatigue life evaluation of structural component based on crack growth criterion
International Nuclear Information System (INIS)
Shibata, Katsuyuki
1984-07-01
As one of the practical application of fracture mechanics, fatigue life evaluation method based on crack growth criterion has been diffusing in various field of technology in order to determine the rational and reliable life of structural components. The fatigue life by this method is evaluated based on the fatigue crack growth analysis from defects, while many problems, such as the influence of residual stress on the crack growth behavior, the effect of overloading, and evaluation method for multiple surface cracks, are not sufficiently solved yet. In this paper, the above problems are treated, and based on some exprimental data some simple mehtods for fatigue life evaluation are proposed regarding the above problems. Verification of the proposed methods are shown in the paper by comparing with some experimental results, and the applicability of the proposed method is also examined by the fatigue test of pipes with cracks in the inner surface. (author)
Crack growth retardation due to micro-roughness: a mechanism for overload effects in fatigue
International Nuclear Information System (INIS)
Suresh, S.
1982-01-01
A new mechanism for fatigue crack growth retardation following an overload is presented in this paper, based on a micro-roughness model. It is reasoned, with the aid of extensive experimental evidence available in the literature, that retardation following an overload is governed by the micromechanisms of near-threshold crack growth. This model is found to rationalize a number of hitherto unexplained experimental observations. Moreover, the present arguments, which suggest that plasticity-induced crack closure is not likely to be the primary mechanism for retardation following single overloads, do not exclude the role of residual stresses or blunting, but provide further mechanistic basis to account for the inconsistencies in the previous models. Additional sources of prolonged retardation, in terms of crack closure due to corrosion debris formed in moist environments, are suggested. It is pointed out that such environmental effects could play an important role in post-overload crack growth in certain alloy systems
International Nuclear Information System (INIS)
Yagawa, Genki; Yoshimura, Shinobu; Aoki, Shigeru; Kikuchi, Masanori; Arai, Yoshio; Kashima, Koichi; Watanabe, Takayuki; Shimakawa, Takashi
1993-01-01
The paper describes stable crack growth behaviors in welded CT specimens made of nuclear pressure vessel A533B class 1 steel, in which initial cracks are placed to be normal to fusion line. At first, using the relations between the load-line displacement (δ) and the crack extension amount (Δa) measured in experiments, the generation phase finite element crack growth analyses are performed, calculating the applied load (P) and various kinds of J-integrals. Next, the simplified crack growth analyses based on the GE/EPRI method and the reference stress method are performed using the same experimental results. Some modification procedures of the two simplified assessment schemes are discussed to make them applicable to inhomogeneous materials. Finally, a neural network approach is proposed to optimize the above modification procedures. 20 refs., 13 figs., 1 tab
International Nuclear Information System (INIS)
Iida, Satoshi; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki
2014-01-01
For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)
The Effects of Salt Water on the Slow Crack Growth of Soda Lime Silicate Glass
Hausmann, Bronson D.; Salem, Jonathan A.
2016-01-01
The slow crack growth parameters of soda-lime silicate were measured in distilled and salt water of various concentrations in order to determine if stress corrosion susceptibility is affected by the presence of salt and the contaminate formation of a weak sodium film. Past research indicates that solvents effect the rate of crack growth, however, the effects of salt have not been studied. The results indicate a small but statistically significant effect on the slow crack growth parameters A and n. However, for typical engineering purposes, the effect can be ignored.
Slow crack growth in post-consumer recycled high-density polyethylene
Sciammarella, Cesar A.; Yang, Y.
2015-01-01
An experimental study of slow crack growth behavior of post-consumer recycled high-density polyethylene blended with virgin high-density polyethylene copolymer has been done. The study has been performed under constant load and in baths of distilled water at 40, 60, 80°C. The specimen used is notched with side grooves. The test results of crack growth have been analyzed using linear fracture mechanics and the rate process theory. The results show that the resistance to crack growth increases ...
Long fatigue crack growth in Inconel 718 produced by selective laser melting
Czech Academy of Sciences Publication Activity Database
Konečná, R.; Kunz, Ludvík; Nicoletto, G.; Bača, A.
2016-01-01
Roč. 92, NOV (2016), s. 499-506 ISSN 0142-1123. [CP 2015 - International Conference on Crack Paths /5./. Ferrara, 16.09.2015-18.09.2015] Institutional support: RVO:68081723 Keywords : Inconel 718 * Selective laser melting * Microstructure * Fatigue crack growth * Fractography Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.899, year: 2016
Effect of stress ratio and frequency on fatigue crack growth rate of ...
Indian Academy of Sciences (India)
Effect of stress ratio and frequency on the fatigue crack propagation of 2618 aluminium alloy–silicon carbide composite were investigated at ambient temperature. With the first set of specimens, the fatigue crack growth rates were studied at three frequencies of 1 Hz, 5 Hz and 10 Hz at a stress ratio of 0.1 whereas the effects ...
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
Nonlinear response arising from non self-similar crack growth in finite thickness plates
International Nuclear Information System (INIS)
Sih, G.C.; Chen, C.
1982-07-01
Described in this report is a three-dimensional finite element procedure for finding the stresses in a finite thickness plate with a through crack. The Mode I loading is increased incrementally such that crack growth occurs in segments. The individual crack profiles are assumed to coincide with the locations of minimum strain energy density, (dW/dV)/sub min/. Its shape is found to change during growth. Each successive crack growth increment will increase even though the rising load increment is kept constant. Three different plate thickness to half crack length ratios were analyzed. An average critical crack ligament distance r/sub c/ = 0.172 in (0.437 cm) being independent of crack and specimen size was obtained. This corresponds to an analytically predicted fracture toughness S/sub c/ = r/sub c/ (dW/dV)/sub c/ = 15.489 lb/in (2708.825 N/m) for A533B steel at -10 0 F. Data at low temperature were used in order to confine crack growth within the linear elastic range
International Nuclear Information System (INIS)
Peyrat, Christine
1997-01-01
A phenomenological study of Stress Corrosion Cracking (SCC) cracks initiation and growth was carried out on a Z 2 CN 18.10 stainless steel in a boiling aqueous magnesium chloride solution at 153 deg. C. The characterization method exploits the morphological information (cracks shape and size distribution) available on a specimen after SCC test. This method, independent of any mechanistic hypothesis, led to the analytical representation of the growth rate of a given crack as a function of its depth and of the density of deeper cracks. The presence of this last parameter could be the expression of a 'shielding effect' of mechanical origin, exerted by the cracks of large size. A 'true initiation' rate was calculated by an extrapolation based on the analytical expression of the growth rate. This analytical representation of cracks initiation and growth accounts for the saturation observed in the experimental determination of the 'apparent initiation'. As time goes, the number of cracks deeper than a given threshold depth tends towards a limit which depends very strongly on the chosen threshold. This saturation effect can be interpreted as exclusively due to the way the small cracks propagate, as the 'true initiation' rate can be expressed versus time by a simple power law. In the case of slow strain rate tests, it is shown that the kinetic parameters characteristic of initiation and growth depend on the applied elongation rate. In particular, the initial crack growth rate increases with elongation rate. The validity domains of the proposed expressions have been specified by means of SCC tests carried out under different types of mechanical loading. (author) [fr
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.
DEFF Research Database (Denmark)
Manca, Marcello; Quispitupa, Amilcar; Berggreen, Christian
2012-01-01
Face/core fatigue crack growth in foam-cored sandwich composites is examined using the mixed mode bending (MMB) test method. The mixed mode loading at the debond crack tip is controlled by changing the load application point in the MMB test fixture. Sandwich specimens were manufactured using H45...... and H100 PVC foam cores and E-glass/polyester face sheets. All specimens were pre-cracked in order to define a sharp crack front. The static debond fracture toughness for each material configuration was measured at different mode-mixity phase angles. Fatigue tests were performed at 80% of the static...
International Nuclear Information System (INIS)
Marci, G.; Bazant, E.; Kautz, H.R.
1978-01-01
A fracture mechanics fatigue analysis is made for an assumed crack emanating from the bore of an instrumentation rod. This assumed crack has partially penetrated the Inconel buttering of the 22 Ni Mo Cr 37 on which the structural Inconel welds are laid. Our analysis shows that the assumed crack could only penetrate 26% of the remaining ligament of the Inconel structural weld as a result of the fatigue crack growth during the entire operating life of the pressure vessel. Therefore a leak caused by a flaw missed during pre-service and in-service non-destructive testing can be excluded. (author)
Surface crack growth in cylindrical hollow specimen subject to tension and torsion
Directory of Open Access Journals (Sweden)
V. Shlyannikov
2015-07-01
Full Text Available The subject for studies is an aluminium cylindrical hollow specimen with external axial and part circumferential semi-elliptical surface crack undergoing fatigue loads. Both the optical microscope measurements and the crack opening displacement (COD method are used to monitor and calculate both crack depth and crack length during the tests. The variation of crack growth behaviour is studied under cyclic axial tension, pure torsion and combined tension+torsion fatigue loading. For the particular surface flaw geometries considered, the elastic and plastic in-plane and out-of-plane constraint parameters, as well as the governing parameter for stress fields in the form of In-integral and plastic stress intensity factor, are obtained as a function of the aspect ratio, dimensionless crack length and crack depth. The combined effect of tension and torsion loading and initial surface flaw orientation on the crack growth for two type of aluminium alloys is made explicit. The experimental and numerical results of the present study provided the opportunity to explore the suggestion that fatigue crack propagation may be governed more strongly by the plastic stress intensity factor rather than the magnitude of the elastic SIFs alone. One advantage of the plastic SIF is its sensitivity to combined loading due to accounting for the plastic properties of the material.
Crack growth behaviour of aluminium wrought alloys in the Very High Cycle Fatigue regime
Directory of Open Access Journals (Sweden)
Bülbül Fatih
2018-01-01
Full Text Available Investigations have shown that in the regime of Very High Cycle Fatigue (VHCF “natural” crack initiation often takes place underneath the material surface leading to crack propagation without contact to atmospheric components. In order to elucidate the environmental damage contribution and its effect on the VHCF long crack propagation, fatigue experiments with alternating environment (vacuum and laboratory air were performed. An ultrasonic fatigue testing system (USFT equipped with a small vacuum chamber was applied that enables the in-situ examination of the long fatigue crack propagation at a resonance frequency of about 20 kHz by using a long distance microscope. By means of the Focused-Ion-Beam technique, micro-notches were prepared in the USFT specimens. The tests were carried out on the aluminium alloys EN-AW 6082 and 5083 in different conditions. It has been found that the atmosphere has a significant influence on the VHCF long crack propagation which manifests itself in the crack path as well as in the crack growth rates. Because of pronounced single sliding in vacuum, shear-stress-controlled crack propagation was detected whereas in laboratory air normal-stress-controlled crack propagation occurred. Furthermore, it has been proven that the secondary precipitation state of the aluminium alloy significantly influences the VHCF long crack propagation in vacuum.
Application of the cracked pipe element to creep crack growth prediction
Energy Technology Data Exchange (ETDEWEB)
Brochard, J.; Charras, T. [C.E.A.-C.E.-Saclay DRN/DMT, Gif Sur Yvette (France); Ghoudi, M. [C.E.A.-C.E.-Saclay, Gif Sur Yvette (France)
1997-04-01
Modifications to a computer code for ductile fracture assessment of piping systems with postulated circumferential through-wall cracks under static or dynamic loading are very briefly described. The modifications extend the capabilities of the CASTEM2000 code to the determination of fracture parameters under creep conditions. The main advantage of the approach is that thermal loads can be evaluated as secondary stresses. The code is applicable to piping systems for which crack propagation predictions differ significantly depending on whether thermal stresses are considered as primary or secondary stresses.
Influence of hydride microstructure on through-thickness crack growth in zircaloy-4 sheet
International Nuclear Information System (INIS)
Raynaud, P.A.; Meholic, M.J.; Koss, D.A.; Motta, A.T.; Chan, K.S.
2007-01-01
The fracture toughness of cold-worked and stress-relieved Zircaloy-4 sheet subject to through-thickness crack growth within a 'sunburst' hydride microstructure was determined at 25 o C. The results were obtained utilizing a novel testing procedure in which a narrow linear strip of hydride blister was fractured at small loads under bending to create a well-defined sharp pre-crack that arrested at the blister-substrate interface. The hydriding procedure also forms 'sunburst' hydrides emanating from the blister that were aligned both in the plane of the crack and in the crack growth direction. Subsequent tensile loading caused crack growth initiation into the field of 'sunburst' hydrides. Specimen failure occurred under near-linear elastic behavior, and the fracture toughness for crack growth initiation into sunburst hydrides was in the range K Q ∼10-15 MPa√m. These results, when combined with those of a previous study, indicate that the through-thickness crack growth initiation toughness at 25 o C is very sensitive to the hydride microstructure. (author)
New evaluation method of crack growth in SiC/SiC composites using interface elements
International Nuclear Information System (INIS)
Serizawa, H.; Ando, M.; Lewinsohn, C.A.; Murakawa, H.
2000-01-01
Crack propagation behavior in SiC/SiC composites was analyzed using a new computer simulation method that included time-dependent interface elements. The simulation method was used to describe the time-dependent crack growth in SiC/SiC composites under four-point bending of single-edge-notched beam bend-bars. Two methods were used to simulate time-dependent crack growth in SiC/SiC composites due to fiber creep. In one method, the creep property was introduced into the interface elements by the general method of finite element method (FEM) analysis. In the second method, a new technique making the best use of the potential function was used to represent crack closure tractions due to creeping fibers. The stage-II slow crack growth of a general creep deformation was simulated by both methods. Additionally, stage-III crack growth and the transition from stage-II to stage-III could be simulated by the new method. The new method has the potential to completely simulate time-dependent crack growth behavior in SiC/SiC composites due to fiber creep
International Nuclear Information System (INIS)
Radu, V.
2016-01-01
The problem of thermal fatigue in mixing areas arises in nuclear piping where a turbulent mixing or vortices produce rapid fluid temperature fluctuations with random frequencies. The assessment of fatigue crack growth due to cyclic thermal loads arising from turbulent mixing presents significant challenges, principally due to the difficulty of establishing the actual loading spectrum. To apply the Stochastic approach of thermal fatigue, a frequency temperature response function is proposed. For the elastic thermal stresses distribution solutions, the magnitude of the frequency response function is first derived and checked against the prediction by FEA. The connection between SIF.s power spectral density (PSD) and temperature.s PSD is assured with SIF frequency response function modulus. The frequency of the peaks of each magnitude for KI is supposed to be a stationary narrow-band Gaussian process. The probabilities of failure are estimated by means of the Monte Carlo methods considering a limit state function. (authors)
Creep crack growth by grain boundary cavitation under monotonic and cyclic loading
Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan
2017-11-01
Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.
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.
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
Probabilistic modeling of fatigue crack growth in Ti-6Al-4V
International Nuclear Information System (INIS)
Soboyejo, W.O.; Shen, W.; Soboyejo, A.B.O.
2001-01-01
This paper presents the results of a combined experimental and analytical study of the probabilistic nature of fatigue crack growth in Ti-6Al-4V. A simple experimental fracture mechanics framework is presented for the determination of statistical fatigue crack growth parameters from two fatigue tests. The experimental studies show that the variabilities in long fatigue crack growth rate data and the Paris coefficient are well described by the log-normal distributions. The variabilities in the Paris exponent are also shown to be well characterized by a normal distribution. The measured statistical distributions are incorporated into a probabilistic fracture mechanics framework for the estimation of material reliability. The implications of the results are discussed for the probabilistic analysis of fatigue crack growth in engineering components and structures. (orig.)
A test procedure for determining the influence of stress ratio on fatigue crack growth
Fitzgerald, J. H.; Wei, R. P.
1974-01-01
A test procedure is outlined by which the rate of fatigue crack growth over a range of stress ratios and stress intensities can be determined expeditiously using a small number of specimens. This procedure was developed to avoid or circumvent the effects of load interactions on fatigue crack growth, and was used to develop data on a mill annealed Ti-6Al-4V alloy plate. Experimental data suggest that the rates of fatigue crack growth among the various stress ratios may be correlated in terms of an effective stress intensity range at given values of K max. This procedure is not to be used, however, for determining the corrosion fatigue crack growth characteristics of alloys when nonsteady-state effects are significant.
Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments
International Nuclear Information System (INIS)
James, L.A.; Mills, W.J.
1981-05-01
Gas-tungsten-arc weldments in Alloy 718 were studied in fatigue-crack growth test conducted at five temperatures over the range 24--649 degree C. In general, crack growth rates increased with increasing temperature, and weldments given the ''conventional'' post-weld heat-treatment generally exhibited crack growth rates that were higher than for weldments given the ''modified'' (INEL) heat-treatment. Limited testing in the as-welded condition revealed crack growth rates significantly lower than observed for the heat-treated cases, and this was attributed to residual stresses. Three different heats of filler wire were utilized, and no heat-to-heat variations were noted. 23 refs., 9 figs., 6 tabs
Fatigue crack growth behavior of Inconel 718 produced by selective laser melting
Czech Academy of Sciences Publication Activity Database
Konečná, R.; Kunz, Ludvík; Nicoletto, G.; Bača, A.
2016-01-01
Roč. 35, č. 10 (2016), s. 31-40 ISSN 1971-8993 Institutional support: RVO:68081723 Keywords : Inconel 718 * Selective laser melting * Microstructure * Fatigue crack growth * Fractography Subject RIV: JL - Materials Fatigue, Friction Mechanics
National Research Council Canada - National Science Library
Choi, Sung R; Kowalik, Robert W; Alexander, Donald J
2007-01-01
...) including three gas-turbine grade melt-infiltrated SiC/SiC composites. Modes I and II crack growth resistances, GI and GII, were evaluated at ambient temperature using double cantilever beam and end notched flexure methods, respectively...
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)
Application of a Cycle Jump Technique for Acceleration of Fatigue Crack Growth Simulation
DEFF Research Database (Denmark)
Moslemian, Ramin; Berggreen, Christian; Karlsson, A.M.
2010-01-01
A method for accelerated simulation of fatigue crack growth in a bimaterial interface is proposed. To simulate fatigue crack growth in a bimaterial interface a routine is developed in the commercial finite element code ANSYS and a method to accelerate the simulation is implemented. The proposed m...... of the simulation show that with fair accuracy, using the cycle jump method, more than 70% reduction in computation time can be achieved....
Short fatigue cracks growth and closure behavior in an austenitic stainless steel at 600 C and 650 C
International Nuclear Information System (INIS)
Polvora, J.P.; Laiarinandrasana, L.; Drubay, B.; Piques, R.; Martelet, B.
1995-01-01
In this work, following fatigue crack growth tests carried out at the CEN-SACLAY (AMORFIS program) by Laiarinandrasana (1994) on 316 L(N) CT specimens at 650 0 C and 600 0 C, short crack behavior of cracks emanating from machined notches is investigated. Experimental results are presented and discussions are directed to notch plasticity effect in relation with variations in crack opening stress intensity factor, K op , with crack lenght (author). 12 refs., 5 figs., 2 tab
International Nuclear Information System (INIS)
Izumo, Hironobu; Ishida, Takuya; Kawamata, Kazuo; Inoue, Shuichi; Ide, Hiroshi; Saito, Takashi; Ishitsuka, Etsuo; Chimi, Yasuhiro; Ise, Hideo; Miwa, Yukio; Ugachi, Hirokazu; Nakano, Junichi; Kaji, Yoshiyuki; Tsukada, Takashi
2009-04-01
To evaluate integrity of irradiation-assisted stress corrosion cracking (IASCC) on in-core structural materials used in light water reactors (LWRs), useful knowledge regarding IASCC has been obtained mainly by post-irradiation examinations (PIEs). In the core of commercial LWRs, however, the actual IASCC occurs under the effects of irradiation on both materials and high-temperature water environment. Therefore, it is necessary to confirm the suitability of the knowledge by PIE with comparison to IASCC behaviors during in-core SCC tests. Fundamental techniques for in-core crack growth and crack initiation tests have been developed already at the Japan Materials Testing Reactor (JMTR) of the Japan Atomic Energy Agency (JAEA). For the in-core crack growth test technique, to evaluate the effects of neutron irradiation on stainless steels irradiated to low neutron fluences, it is indispensable to develop new loading technique which is applicable to compact tension (CT) specimens with thickness of 0.5 inch (0.5T), from the viewpoint of validity based on the fracture mechanics. Based on the present technical investigation for the in-core loading technique, it is expected that a target load of 7.6 kN approximately can apply to a 0.5T-CT specimen by adopting a loading unit of a lever type instead of the previous uni-axial tension type. For the in-core crack initiation test technique, moreover, construction of a loading unit adopting linear variable differential transformers (LVDTs) has been investigated and technical issues have examined. (author)
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
A finite element analysis of stable crack growth in inhomogeneous materials
International Nuclear Information System (INIS)
Miyazaki, N.; Sakai, T.; Nakagaki, M.; Sasaki, T.
1993-01-01
The finite element method was applied to generation phase analyses for stable crack growth in inhomogeneous materials. Experimental data on stable crack growth in bimaterial CT specimens, which were composed of a base metal and a weld metal, were numerically simulated using the node-release technique, and the variations of the fracture mechanics parameters such as J-integral. T*-integral. J-circumflex-integral and CTOA were calculated. The effects of the fusion line and the weld on the near crack fracture mechanics parameters were discussed. (author)
Interface crack growth for anisotropic plasticity with non-normality effects
DEFF Research Database (Denmark)
Tvergaard, Viggo; Legarth, Brian Nyvang
2007-01-01
A plasticity model with a non-normality plastic flow rule is used to analyze crack growth along an interface between a solid with plastic anisotropy and an elastic substrate. The fracture process is represented in terms of a traction-separation law specified on the crack plane. A phenomenological...... an oscillating stress singularity, and with conditions of small scale yielding this solution is applied as boundary conditions on the outer edge of the region analyzed. Crack growth resistance curves are calculated numerically, and the effect of the near-tip mode mixity on the steady-state fracture toughness...
Online fatigue crack growth monitoring with clip gauge and direct current potential drop
De Tender, Steven; Micone, Nahuel; De Waele, Wim
2016-01-01
Fatigue is a well-known failure phenomenon which has been and still is extensively studied. Often structures are designed according to the safe-life principle so no crack initiation occurs. Nowadays there is a high emphasis on cost-efficiency, and one might rather opt for a fail-safe design. Therefore a certain amount of crack growth can be allowed in structures, but then a good knowledge of stresses and related crack growth rates is needed. To this end, extensive studies are done to obtain a...
Stable and unstable crack growth in Type 304 stainless steel plate
International Nuclear Information System (INIS)
Yagawa, G.
1984-01-01
Experimental and theoretical results on stable as well as unstable fractures for Type 304 stainless steel plates with a central crack subjected to tension force are given. In the experiment using a testing machine with a special spring for high compliance, the transition points from the stable to the unstable crack growth are observed and comparisons are made between the test results and the finite element solutions. A round robin calculation for the elastic-plastic stable crack growth using one of the specimens mentioned above is also given. (orig.)
Fracture toughness and crack growth resistance of pressure vessel plate and weld metal steels
International Nuclear Information System (INIS)
Moskovic, R.
1988-01-01
Compact tension specimens were used to measure the initiation fracture toughness and crack growth resistance of pressure vessel steel plates and submerged arc weld metal. Plate test specimens were manufactured from four different casts of steel comprising: aluminium killed C-Mn-Mo-Cu and C-Mn steel and two silicon killed C-Mn steels. Unionmelt No. 2 weld metal test specimens were extracted from welds of double V butt geometry having either the C-Mn-Mo-Cu steel (three weld joints) or one particular silicon killed C-Mn steel (two weld joints) as parent plate. A multiple specimen test technique was used to obtain crack growth data which were analysed by simple linear regression to determine the crack growth resistance lines and to derive the initiation fracture toughness values for each test temperature. These regression lines were highly scattered with respect to temperature and it was very difficult to determine precisely the temperature dependence of the initiation fracture toughness and crack growth resistance. The data were re-analysed, using a multiple linear regression method, to obtain a relationship between the materials' crack growth resistance and toughness, and the principal independent variables (temperature, crack growth, weld joint code and strain ageing). (author)
The frequency effect on the fatigue crack growth rate of 304 stainless steel
International Nuclear Information System (INIS)
Shih, Y.-S.; Chen, J.-J.
1999-01-01
Under cyclic loading condition, the fatigue crack growth (FCG) rate governed by stress intensity factor and stress ratio is well known; Walker's equation, Forman's equation and Elber's equation are typical formulae to describe the fatigue crack growth rate. However, the loading frequency effect on the fatigue crack growth rate has yet to be explored. Recently, studies have focused on the loading frequency effect on some visco-elastic materials, and have provided a clearer understanding of the frequency effect on the fatigue crack growth rate. In a physical sense, knowledge about the loading frequency effect on the fatigue crack growth rate for 304 stainless steel is still lacking. James conducted a lot of experiments, and through data analysis, he concluded an evaluation equation which is based upon the experimental illustration. In this study, the physical properties of the material are used to illustrate the modification of fatigue crack growth rate, and a new formula which is based upon the modified Forman's equation, is provided. (orig.)
Sub-critical crack growth and clad integrity in a PWR reactor pressure vessel
International Nuclear Information System (INIS)
Tice, D.R.; Foreman, A.J.E.; Sharples, J.K.
1987-10-01
The possibility of in-service growth of sub-critical defects in a PWR reactor pressure vessel to a critical size which could result in vessel failure was addressed in both the 1976 and 1982 reports of the Light Water Reactor Study Group (LWRSG), under the Chairmanship of Dr W Marshall (now Lord Marshall). An addendum to this report was published by UKAEA in April 1987. The section of the addendum dealing with subcritical crack growth and the related issue of integrity of the stainless steel cladding on the inner vessel surface is reproduced in this report. This section of the LWRSG addendum provides a review of the current status of fatigue crack growth and environmentally assisted cracking research for pressure vessel steels in light water reactor environments, as well as a review of developments in crack growth assessment methods. The review concludes that the alternative assessment procedures now being developed give a more realistic prediction of in service crack growth than the ASME Section XI Appendix A fatigue crack growth curves. (author)
Directory of Open Access Journals (Sweden)
G. Lesiuk
2015-10-01
Full Text Available The goal of the authors’ investigations was determination of the fatigue crack growth in fragments of steel structures (of the puddled steel and its cyclic behavior. Tested steel elements coming from the turn of the 19th and 20th were gained from still operating ancient steel construction (a main hall of Railway Station, bridges etc.. This work is a part of investigations devoted to the phenomenon of microstructural degradation and its potential influence on their strength properties. The analysis of the obtained results indicated that those long operating steels subject to microstructure degradation processes consisting mainly in precipitation of carbides and nitrides inside ferrite grains, precipitation of carbides at ferrite grain boundaries and degeneration of pearlite areas [1, 2]. It is worth noticing that resistance of the puddled steel to fatigue crack propagation in the normalized state was higher. The authors proposed the new kinetic equation of fatigue crack growth rate in such a steel. Thus the relationship between the kinetics of degradation processes and the fatigue crack growth rate also have been shown. It is also confirmed by the materials research of the viaduct from 1885, which has not shown any significant changes in microstructure. The non-classical kinetic fatigue fracture diagrams (KFFD based on deformation ( or energy (W approach was also considered. In conjunction with the results of low- and high-cycle fatigue and gradual loss of ductility as a consequence (due to the microstructural degradation processes - it seems to be a promising construction of the new kinetics fatigue fracture diagrams with the energy approach.
Effect of Microstructure on Time Dependent Fatigue Crack Growth Behavior In a P/M Turbine Disk Alloy
Telesman, Ignacy J.; Gabb, T. P.; Bonacuse, P.; Gayda, J.
2008-01-01
A study was conducted to determine the processes which govern hold time crack growth behavior in the LSHR disk P/M superalloy. Nineteen different heat treatments of this alloy were evaluated by systematically controlling the cooling rate from the supersolvus solutioning step and applying various single and double step aging treatments. The resulting hold time crack growth rates varied by more than two orders of magnitude. It was shown that the associated stress relaxation behavior for these heat treatments was closely correlated with the crack growth behavior. As stress relaxation increased, the hold time crack growth resistance was also increased. The size of the tertiary gamma' in the general microstructure was found to be the key microstructural variable controlling both the hold time crack growth behavior and stress relaxation. No relationship between the presence of grain boundary M23C6 carbides and hold time crack growth was identified which further brings into question the importance of the grain boundary phases in determining hold time crack growth behavior. The linear elastic fracture mechanics parameter, Kmax, is unable to account for visco-plastic redistribution of the crack tip stress field during hold times and thus is inadequate for correlating time dependent crack growth data. A novel methodology was developed which captures the intrinsic crack driving force and was able to collapse hold time crack growth data onto a single curve.
Creep crack growth in a reactor pressure vessel steel at 360 deg C
Energy Technology Data Exchange (ETDEWEB)
Rui Wu; Seitisleam, F.; Sandstroem, R. [Swedish Institute for Metals Research, Stockholm (Sweden)
1998-12-31
Plain creep (PC) and creep crack growth (CCG) tests at 360 deg C and post metallography were carried out on a low alloy reactor pressure vessel steel (ASTM A508 class 2) with different microstructures. Lives for the CCG tests were shorter than those for the PC tests and this is more pronounced for simulated heat affected zone microstructure than for the parent metal at longer lives. For the CCG tests, after initiation, the cracks grew constantly and intergranularly before they accelerated to approach rupture. The creep crack growth rate is well described by C*. The relations between reference stress, failure time and steady crack growth rate are presented for the CCG tests. It is demonstrated that the failure stress due to CCG is considerably lower than the yield stress at 360 deg C. Consequently, the CCG will control the static strength of a reactor vessel. (orig.) 17 refs.
Material size effects on crack growth along patterned wafer-level Cu–Cu bonds
DEFF Research Database (Denmark)
Tvergaard, Viggo; Niordson, Christian Frithiof; Hutchinson, John W.
2013-01-01
together. Crack growth along the bond interface is here studied numerically using finite element analyses. The experiments have shown that plasticity in the Cu films makes a major contribution to the macroscopic interface toughness. To account for the size dependence of the plastic flow a strain gradient...... plasticity model is applied here for the metal. A cohesive zone model is applied to represent the crack growth along the bond between the two Cu films. This cohesive zone model incorporates the effect of higher order stresses in the continuum, such that the higher order tractions on the crack faces decay...... the toughness peak and the subsequent plateau level are highly sensitive to the value of the characteristic material length. A small material length, relative to the thickness of the Cu film, gives high toughness whereas a length comparable to the film thickness gives much reduced crack growth resistance...
Creep crack growth in a reactor pressure vessel steel at 360 deg C
Energy Technology Data Exchange (ETDEWEB)
Wu, Rui; Seitisleam, F; Sandstroem, R [Swedish Institute for Metals Research, Stockholm (Sweden)
1999-12-31
Plain creep (PC) and creep crack growth (CCG) tests at 360 deg C and post metallography were carried out on a low alloy reactor pressure vessel steel (ASTM A508 class 2) with different microstructures. Lives for the CCG tests were shorter than those for the PC tests and this is more pronounced for simulated heat affected zone microstructure than for the parent metal at longer lives. For the CCG tests, after initiation, the cracks grew constantly and intergranularly before they accelerated to approach rupture. The creep crack growth rate is well described by C*. The relations between reference stress, failure time and steady crack growth rate are presented for the CCG tests. It is demonstrated that the failure stress due to CCG is considerably lower than the yield stress at 360 deg C. Consequently, the CCG will control the static strength of a reactor vessel. (orig.) 17 refs.
Time-dependent crack growth in Alloy 718: An interim assessment
International Nuclear Information System (INIS)
James, L.A.
1982-08-01
Previous results on the time-dependent nature of fatigue-crack propagation (FCP) in Alloy 718 at elevated temperatures were reviewed. Additional experiments were conducted to further define certain aspects of the time-dependent crack growth behavior. it was found that loading waveform influenced FCP behavior, with tensile hold-times producing higher growth rates than continuous cycling at the same frequency. Crack growth rates under hold-time conditions tended to increase with decreasing grain size. Finally, experiments were conducted which tended to cast some doubt upon the ability of linear-elastic fracture mechanics (LEFM) techniques to characterize cracking behavior in this alloy under hold-time conditions. However, since a superior correlating parameter has not yet been proven, it is suggested that LEFM methods be used in the interim with appropriate safety factors to account for the potential errors. 34 refs., 10 figs., 4 tabs
Accelerated Threshold Fatigue Crack Growth Effect-Powder Metallurgy Aluminum Alloy
Piascik, R. S.; Newman, J. A.
2002-01-01
Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low (Delta) K, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = K(sub min)/K(sub max)). The near threshold accelerated FCG rates are exacerbated by increased levels of K(sub max) (K(sub max) = 0.4 K(sub IC)). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and K(sub max) influenced accelerated crack growth is time and temperature dependent.
Fatigue crack growth in ferritic steels as influence by elevated temperature and environment
International Nuclear Information System (INIS)
Nakamura, H.; Minakawa, K.; Murali, K.; Mc Evily, A.J.
1987-01-01
Fatigue crack growth studies have been carried out at room temperature and at 538 deg C in air as well as in vacuum in order to assess the influence of both temperature and environment on the growth process. The materials investigated were 2 1/4Cr-1Mo steel, a modified 9Cr-1Mo steel and a 9Cr-2Mo steel, as well as weldments of the 9Cr-2Mo steel. Crack opening levels were determined for all test conditions. The R-dependency of the crack growth rate could be accounted for by crack closure, both at room and elevated temperature. Closure in air at 538 deg C was due to oxidation, whereas at room temperature closure was due to microstructurally related roughness and the influence of oxygen. (Author)
Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys
Sarkar, Bhaskar; Lisagor, W. B.
1992-01-01
The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.
International Nuclear Information System (INIS)
Wakai, T.; Horikiri, M.; Poussard, C.; Drubay, B.
2005-01-01
This paper presents the results of a benchmark on thermal fatigue crack growth evaluation for a thick-wall cylinder subjected to cyclic thermal transients. The simplified crack growth evaluation methods of both JNC in JAPAN and A16 procedures proposed by CEA in France are presented. The predictions obtained using both methods are compared with the experimental data. The JNC method, which accounts for the non-linear stress component provides predictions of crack advance in a good agreement with the experimental data. In contrast, significant differences are observed between the A16 predictions and the experimental data. The discrepancies are mainly due to the non-linear stress component which is not accounted for in the A16 method. When using the JNC stress intensity factor solution determined by finite element analysis to account for the non-linear stress component, the A16 method well predicts the thermal fatigue crack growth behavior
Development of European creep crack growth testing code of practice for industrial specimens
International Nuclear Information System (INIS)
Dogan, B.; Nikbin, K.; Petrovski, B.
2004-01-01
The integrity and residual life assessment of high temperature components require defects, detected or assumed to exist, through minimum allowable limits of detectable flaws using nondestructive testing methods. It relies on information obtained from the material's mechanical, uniaxial creep, creep crack initiation and growth properties. The information derived from experiments needs to be validated and harmonised following a Code of Practice that data variability between different institutions can be reduced to a minimum. The present paper reports on a Code of Practice (CoP) being prepared within the framework of the partially European Commission funded project CRETE. The novel aspect of the presented CoP is the inclusion of component relevant industrial specimen geometries. It covers testing and analysis of Creep Crack growth (CCG) in metallic materials at elevated temperature using six different cracked geometries that have been validated in. It aims to give advice on testing, measurements and analysis of creep crack growth data for a range of creep brittle to creep ductile materials using component service relevant specimen geometries and sizes. The CoP may be used for material selection criteria and inspection requirements for damage tolerant applications. In quantitative terms, these types of tests can be used to assess the individual and combined effects of metallurgical, fabrication, operating temperature, and loading conditions on creep crack growth life. Further issues will be addressed including material properties, damage and crack growth related constraint effect, stress relaxation and stress-strain fields, residual stresses, partitioning displacement, analysis of elastic creep, elastic compliance measurements
International Nuclear Information System (INIS)
Brocks, W.; Krafka, H.; Mueller, W.; Wobst, K.
1988-01-01
In connection with the problem of the transferability of parameters obtained experimentally with the help of fracture-mechanical test specimens and used for the initiation and the stable propagation of cracks in cases of pulsating stress and of the elasto-plastic behaviour of construction components, a pressure vessel with an inside diameter of 1500 mm, a cylindrical length of 3000 mm and a wall thickness of 40 mm was hydraulically loaded with the help of internal pressure in the first stage, to attain an average crack growth of 1 mm at Δ a ≅, the loading taking place at about 21deg C. This stress-free annealed vessel exhibited an axial semielliptical vibration-induced surface crack about 181 mm long and 20 mm deep, as a test defect, in a welded circular blank made of the steel 20MnMoNi 55. The fractographic analysis of the first stable crack revealed that its growth rate of Δa was highest in the area of transition from the weak to the strong bend of the crack front (55deg m /σ v (average principal stress: σ m , Mises' reference stress: σ v v). A comparison of the experimental with the numerical results from the first stable crack shows that the local stable crack growth Δa cannot be calculated solely with reference to J, because Δa appears to depend essentially on the quotient σ m /σ v . (orig./MM) [de
Fatigue crack growth monitoring: fracture mechanics and non-destructive testing requirements
International Nuclear Information System (INIS)
Williams, S.; Mudge, P.J.
1982-01-01
If a fatigue crack is found in a component in service, two options exist if plant integrity is to be maintained: first, the plant can be removed from service and repairs effected or replacements fitted; second, the growth of the crack can be monitored non-destructively until it is either considered to be too large to tolerate, in which case it must be repaired, or until a convenient down time when repair can be effected. The second option has obvious benefits for plant operators, but in such a situation it is essential that errors of the non-destructive estimate of defect size, which will undoubtedly exist, and uncertainties in the fatigue crack growth laws in operation must both be allowed for if a safe extension of service life is to be obtained; i.e. without failure by leakage or fast fracture arising from the fatigue crack. This paper analyses the accuracy required of non-destructive crack measurement techniques to permit the safe monitoring of crack growth by periodic inspection. It then demonstrates that it is possible to achieve adequate crack monitoring using conventional ultrasonic techniques. (author)
Energy Technology Data Exchange (ETDEWEB)
Soppa, Ewa Anna; Silcher, Horst
2015-01-31
Fatigue crack growth of short and long cracks was investigated for both materials: the Nb-stabilized austenitic stainless steel X6 CrNiNb 18-10 and the ferritic-bainitic steel 22 NiMoCr 3-7. These both steels belong to the materials in the primary circuit of german power plants. For a reliable estimation of the lifetime of components subject to cyclic fatigue a detailed knowledge of the phenomena accompanying fatigue processes and which cause both - initiation and growth of fatigue cracks is essential. The deformation induced transformation of austenite into α'-martensite at room temperature is thus very important in the initiation and growth of fatigue cracks. Because these processes are manifest at first at the microlevel, the use of methods which reveal information at high resolution is of significant importance. In order to study the initiation and growth of short cracks, cylindrical smooth specimens, compact tension C(T)- and modified C(T)-specimens have been used. Cyclic crack propagation of long cracks was investigated on compact tension C(T)-specimens with W=50 mm and B=10 mm. The SEM, TEM and EBSD technique are powerful methods for determining crystallographic orientation, for the identification of individual phases and for recealing plastic deformation. They were used for analyses of microcracks in combination with interrupted cyclic tests. The impact of crack closure on the threshold parameter ΔK{sub th} and the crack growth rate da/dN was investigated experimentally for the growth of long cracks under cyclic loading for different R-values at room temperature. Additional tests were performed at T=288 C in order to investigate the role of temperature on crack growth rates. The effect of overloads in tension and compression as another factor influencing the crack growth was also studied. Measured crack growth curves were fitted using Paris and Erdogan-Ratwani law as well as the NASGRO-equation. Fracture surfaces of selected specimens for both steels
Predictions of mixed mode interface crack growth using a cohesive zone model for ductile fracture
DEFF Research Database (Denmark)
Tvergaard, Viggo
2004-01-01
Special interface elements that account for ductile failure by the nucleation and growth of voids to coalescence are used to analyse crack growth. In these elements the stress component tangential to the interface is accounted for, as determined by the requirement of compatibility with the surrou......Special interface elements that account for ductile failure by the nucleation and growth of voids to coalescence are used to analyse crack growth. In these elements the stress component tangential to the interface is accounted for, as determined by the requirement of compatibility...
Short fatigue cracks nucleation and growth in lean duplex stainless steel LDX 2101
Energy Technology Data Exchange (ETDEWEB)
Strubbia, R., E-mail: strubbia@ifir-conicet.gov.ar [Instituto de Física Rosario – CONICET, Universidad Nacional de Rosario (Argentina); Hereñú, S.; Alvarez-Armas, I. [Instituto de Física Rosario – CONICET, Universidad Nacional de Rosario (Argentina); Krupp, U. [Faculty of Engineering and Computer Science, University of Applied Sciences Osnabrück (Germany)
2014-10-06
This work is focused on the fatigue damage of lean duplex stainless steels (LDSSs) LDX 2101. Special interest is placed on analyzing short fatigue crack behavior. In this sense, short crack initiation and growth during low cycle fatigue (LCF) and short crack nucleation during high cycle fatigue (HCF) of this LDSS have been studied. The active slip systems and their associated Schmid factors (SF) are determined using electron backscattered diffraction (EBSD). Additionally, the dislocation structure developed during cycling is observed by transmission electron microscopy (TEM). Regardless of the fatigue regime, LCF and HCF, short cracks nucleate along intrusion/extrusions in ferritic grains. Moreover, during the LCF phase boundaries decelerate short crack propagation. These results are rationalized by the hardness of the constitutive phases and the dependence of screw dislocation mobility in the ferrite phase on strain rate and stress amplitude.
Fatigue Crack Growth Behavior of Nickel-base Superalloy Haynes 282 at 550-750 °C
Rozman, K. A.; Kruzic, J. J.; Hawk, J. A.
2015-08-01
The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at temperatures of 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 Hz and 0.25 Hz. Increasing the temperature from 550 to 750 °C caused the fatigue crack growth rates to increase from ~20 to 60% depending upon the applied stress intensity level. The effect of reducing the applied loading frequency increased the fatigue crack growth rates from ~20 to 70%, also depending upon the applied stress intensity range. The crack path was observed to be transgranular for the temperatures and frequencies used during fatigue crack growth rate testing. At 750 °C, there were some indications of limited intergranular cracking excursions at both loading frequencies; however, the extent of intergranular crack growth was limited and the cause is not understood at this time.
The crack growth resistance of thin steel sheets under eccentric ...
Indian Academy of Sciences (India)
Ľ AMBRIŠKO
2018-03-10
Mar 10, 2018 ... of zinc-coated automotive steel sheets (IF – deep drawing interstitial free steel ..... to determine; therefore, the Ji was determined for observ- able crack initiation .... M R S, da Silva L F M and de Castro P M S T 2011. Analysis of ...
Monitoring crack growth by a potential drop method
International Nuclear Information System (INIS)
Tomlinson, J.R.
1978-01-01
A theoretical model has been developed for the surface current flow and potential distribution around a surface breaking crack. This model's predictions have been confirmed in the laboratory and the method applied on site. It proved possible by careful design and rigorous testing to overcome the problems of interference in an electrically noisy environment. The principal weaknesses of the technique are that it is only capable of detecting cracks that break the accessible surface of the component, and that there may be problems with conductive bridging across the crack. On the other hand, the lack of any sophisticated probe in contact with the component makes the method suitable for high temperature use, and, being an electrical method, it is capable of continuous use. The use of a.c., as opposed to d.c., enables lower currents to be used. Given good access to the crack tip, a high sensitivity can be obtained, which enables noise rejection to be achieved with the use of a high threshold. (orig.) [de
International Nuclear Information System (INIS)
James, L.A.; Moshier, W.C.
1997-01-01
Corrosion-fatigue crack propagation experiments were conducted on several low-alloy steels in elevated temperature aqueous environments, and experimental parameters included temperature, sulfur content of the steel, applied potential level, and dissolved hydrogen (and in one case, dissolved oxygen) concentration in the water. Specimen potentials were controlled potentiostatically, and the observation (or non-observation) of accelerated fatigue crack growth rates was a complex function of the above parameters. Electrochemical results and the postulated explanation for the complex behavior are given in Part II
International Nuclear Information System (INIS)
Bruckner-Foit, A.; Munz, D.
1989-10-01
A deterministic and a probabilistic crack growth analysis is presented for the major defects found in the welds during ultrasonic pre-service inspection. The deterministic analysis includes first a determination of the number of load cycles until crack initiation, then a cycle-by-cycle calculation of the growth of the embedded elliptical cracks, followed by an evaluation of the growth of the semi-elliptical surface crack formed after the crack considered has broken through the wall and, finally, a determination of the critical crack size and shape. In the probabilistic analysis, a Monte-Carlo simulation is performed with a sample of cracks where the statistical distributions of the crack dimensions describe the uncertainty in sizing of the ultrasonic inspection. The distributions of crack depth, crack length and location are evaluated as a function of the number of load cycles. In the simulation, the fracture mechanics model of the deterministic analysis is employed for each random crack. The results of the deterministic and probabilistic crack growth analysis are compared with the results of the second in-service inspection where stable extension of some of the cracks had been observed. It is found that the prediction and the experiment agree only with a probability of the order of 5% or less
Round Robin/collaborative programme [cyclic crack growth in low alloy steel
International Nuclear Information System (INIS)
Jones, R.L.; Hurst, P.; Scott, P.M.
1989-01-01
During the 10 years of its existence International Cooperative Group on Cyclic Crack Growth the (ICCGR) has undertaken five collaborative efforts related to cyclic crack growth and stress corrosion susceptibility in reactor pressure vessel steels. The initial collaborative effort, a data reduction exercise, identified and reconciled several important procedural differences and led to confidence that, given the same crack length versus cycles data, the Group members could all derive similar plots of da/dN versus δK. Subsequently, a low-R testing round robin highlighted the importance of a number of comparatively subtle aspects of the methods used for cyclic crack growth testing in water environments and led to confidence that the various laboratories could generate similar test data, given the same test material and a sufficiently precise and detailed test specification. The results of a high-R test programme support the conclusion that the state of the art of cyclic crack growth testing has now advanced to a point at which coordinated, multilaboratory test programmes are feasible and indeed, such a programme covering the influence of temperature is currently under way. The slow strain rate round robin has highlighted important test variables, notably the electrochemical potential, which must be carefully controlled in assessing the conditions under which pressure vessel steels may suffer from stress corrosion cracking. (author)
An engineering approach for examining crack growth and stability in flawed structures
International Nuclear Information System (INIS)
Shih, C.F.; German, M.D.; Kumar, V.
1981-01-01
Progress made in two research programmes, sponsored by the Electric Power Research Institute (EPRI), to identify viable parameters for characterising crack initiation and continued extension are summarised. An engineering/design methodology, based on these parameters, for the assessment of crack growth and instability in engineering structures which are stressed beyond the regime of applicability of linear elastic fracture mechanics is developed. The ultimate goal in the development of such a methodology is to establish an improved basis for analysing the effect of flaws (postulated or detected) on the safety margins of pressure boundary components of light water-cooled type nuclear steam supply systems. The methodology can also be employed for structural integrity analyses of other engineering components. Extensive experimental and analytical investigations undertaken to evaluate potential criteria for crack initiation and growth and the selection of the final criteria for analysing crack growth and stability in flawed structures are summarised. The experimental and analytical results obtained to date suggest that parameters based on the J-integral and the crack tip opening displacement, delta, are the most promising. This is not surprising since, from a theoretical basis, the two approaches are similar if certain conditions are met. An engineering/design approach for the assessment of crack growth and instability in flawed structures is outlined. (author)
Growth model for large branched three-dimensional hydraulic crack system in gas or oil shale
Chau, Viet T.
2016-01-01
Recent analysis of gas outflow histories at wellheads shows that the hydraulic crack spacing must be of the order of 0.1 m (rather than 1 m or 10 m). Consequently, the existing models, limited to one or several cracks, are unrealistic. The reality is 105–106 almost vertical hydraulic cracks per fracking stage. Here, we study the growth of two intersecting near-orthogonal systems of parallel hydraulic cracks spaced at 0.1 m, preferably following pre-existing rock joints. One key idea is that, to model lateral cracks branching from a primary crack wall, crack pressurization, by viscous Poiseuille-type flow, of compressible (proppant-laden) frac water must be complemented with the pressurization of a sufficient volume of micropores and microcracks by Darcy-type water diffusion into the shale, to generate tension along existing crack walls, overcoming the strength limit of the cohesive-crack or crack-band model. A second key idea is that enforcing the equilibrium of stresses in cracks, pores and water, with the generation of tension in the solid phase, requires a new three-phase medium concept, which is transitional between Biot’s two-phase medium and Terzaghi’s effective stress and introduces the loading of the solid by pressure gradients of diffusing pore water. A computer program, combining finite elements for deformation and fracture with volume elements for water flow, is developed to validate the new model. This article is part of the themed issue ‘Energy and the subsurface’. PMID:27597791
International Nuclear Information System (INIS)
Smith, E.
1987-01-01
Tada, Paris and Gamble have used the tearing modulus approach to examine the stability of growth of a through-wall circumferential crack in a 304 stainless steel circular cylindrical pipe subject to bending deformation. They showed that crack growth is stable, in the sense that growth requires the rotation imposed at the pipe-ends to be increased, provided the pipe length is less than a critical length Lsub(c), which is given by their analysis. The Tada-Paris-Gamble analysis focuses on the question of the stability, or otherwise, of crack growth at the onset of crack extension. The analysis does not consider the possibilities that (a) instability might occur after some stable crack growth, and (b) arrest might occur after some unstable growth. A study of these aspects of the circumferential crack growth problem using the tearing modulus approach is precluded by the geometry dependence of the J-crack growth resistance curve. Consequently the present paper uses a crack tip opening angle criterion to describe crack growth, and thereby demonstrates that possibilities (a) and (b) should both occur, depending on the initial crack length and pipe length. In terms of relevance to the technologically important problem of cracking in Boiling Water Reactor piping, the important conclusion stemming from the paper's analysis is that stability of crack growth after the onset of crack extension is assured if the pipe length is less than a critical length L'sub(c). L'sub(c) is less than Lsub(c), the critical length relevant to the onset of crack extension, but it is still appreciably greater than the pipe run lengths in actual reactor piping systems, and safety against guillotine failure of a pipe is therefore generally assured. (author)
Influence of overloads on dwell time fatigue crack growth in Inconel 718
Energy Technology Data Exchange (ETDEWEB)
Saarimäki, Jonas, E-mail: jonas.saarimaki@liu.se [Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping (Sweden); Moverare, Johan [Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping (Sweden); Siemens Industrial Turbomachinery AB, Materials Technology, SE-61283 Finspång (Sweden); Eriksson, Robert; Johansson, Sten [Division of Engineering Materials, Department of Management and Engineering, Linköping University, SE-58183 Linköping (Sweden)
2014-08-26
Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ∼700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate.
Influence of overloads on dwell time fatigue crack growth in Inconel 718
International Nuclear Information System (INIS)
Saarimäki, Jonas; Moverare, Johan; Eriksson, Robert; Johansson, Sten
2014-01-01
Inconel 718 is one of the most commonly used superalloys for high temperature applications in gasturbines and aeroengines and is for example used for components such as turbine discs. Turbine discs can be subjected to temperatures up to ∼700 °C towards the outer radius of the disc. During service, the discs might start to develop cracks due to fatigue and long dwell times. Additionally, temperature variations during use can lead to large thermal transients during start-up and shutdown which can lead to overload peaks in the normal dwell time cycle. In this study, tests at 550 °C with an overload prior to the start of each dwell time, have been performed. The aim of the investigation was to get a better understanding of the effects of overloads on the microstructure and crack mechanisms. The microstructure was studied using electron channelling contrast imaging (ECCI). The image analysis toolbox in Matlab was used on cross sections of the cracks to quantify: crack length, branch length, and the number of branches in each crack. It was found that the amount of crack branching increases with an increasing overload and that the branch length decreases with an increasing overload. When the higher overloads were applied, the dwell time effect was almost cancelled out. There is a strong tendency for an increased roughness of the crack path with an increasing crack growth rate
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
Growth optimization for thick crack-free GaN layers on sapphire with HVPE
Energy Technology Data Exchange (ETDEWEB)
Richter, E.; Hennig, Ch.; Kissel, H.; Sonia, G.; Zeimer, U.; Weyers, M. [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, 12489 Berlin (Germany)
2005-05-01
Conditions for optimized growth of thick GaN layers with crack-free surfaces by HVPE are reported. It was found that a 1:1 mixture of H{sub 2}/N{sub 2} as carrier gas leads to the lowest density of cracks in the surface. Crack formation also depends on the properties of the GaN/sapphire templates used. Best results have been obtained for 5 {mu}m thick GaN/sapphire templates grown by MOVPE with medium compressive strain {epsilon}{sub zz} of about 0.05%. But there is no simple dependence of the crack formation on the strain status of the starting layer indicating that the HVPE growth of GaN can itself introduce strong tensile strain. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Fatigue crack growth of 316NG austenitic stainless steel welds at 325 °C
Li, Y. F.; Xiao, J.; Chen, Y.; Zhou, J.; Qiu, S. Y.; Xu, Q.
2018-02-01
316NG austenitic stainless steel is a commonly-used material for primary coolant pipes of pressurized water reactor systems. These pipes are usually joined together by automated narrow gap welding process. In this study, welds were prepared by narrow gap welding on 316NG austenitic stainless steel pipes, and its microstructure of the welds was characterized. Then, fatigue crack growth tests were conducted at 325 °C. Precipitates enriched with Mn and Si were found in the fusion zone. The fatigue crack path was out of plane and secondary cracks initiated from the precipitate/matrix interface. A moderate acceleration of crack growth was also observed at 325°Cair and water (DO = ∼10 ppb) with f = 2 Hz.
A fracture- mechanics calculation of crack growth rate for a gas turbine blade
International Nuclear Information System (INIS)
Mirzaei, M.; Karimi, R.
2002-01-01
The existence of thermo-mechanical stresses, due to the frequent start-ups and shutdowns of gas turbines. Combined with high working temperatures may cause creep and fatigue failure of the blades. This paper describes a fracture-mechanics life assessment of a gas turbine blade. Initially, the distributions of thermal and mechanical stresses were obtained by using the finite element method. Accordingly; the crack modeling was performed in a high stress region at the suction side surface of the blade. Several crack growth increments were observed and the related crack tip parameters were calculated. Finally; the creep-fatigue crack growth in each cycle was calculated and the total number of start-stop cycles was determined
Fatigue crack growth of the MA12 magnesium alloy in vacuum and air
International Nuclear Information System (INIS)
Grinberg, N.M.; Serdyuk, V.A.; Zmeevets, S.G.; Ostapenko, I.Z.; Malinkina, T.I.; Kamyshkov, A.S.
1978-01-01
The growth of a crack and the failure mechanism have been examined in the specimens prepared from magnesium alloy sheets containing 2.9% Nd and 0.44% Zr,the specimens being subjected to the cyclic bending in the open air and in vacuum of 1x10 -6 mm Hg. Examination of the plastic zone around a crack was carried out by the methods of optical microscopy and X-ray structure analysis of fractures. It has been shown that when tested in vacuum, the growth rate of a fatigue crac in vacuum is essentially slower than being tested in the open air. The fatigue failure mechanism is the same in the open air and in vacuum; during the slow growing of a crack, that mechanism is essentially a brittle intragrain cleavage. The plastic zone forming around the crack is greater in vacuum than in the open air
Fatigue crack growth prediction in 2xxx AA with friction stir weld HAZ properties
Directory of Open Access Journals (Sweden)
A. Tzamtzis
2016-02-01
Full Text Available An analytical model is developed to predict fatigue crack propagation rate under mode I loading in 2024 aluminum alloy with FSW HAZ material characteristics. Simulation of the HAZ local properties in parent 2024 AA was performed with overaging using specific heat treatment conditions. The model considers local cyclic hardening behavior in the HAZ to analyze crack growth. For the evaluation of the model, the analytical results have been compared with experimental fatigue crack growth on overaged 2024 alloy simulating material behavior at different positions within the HAZ. The analytical results showed that cyclic hardening at the crack tip can be used successfully with the model to predict FCG in a material at overaged condition associated with a location in the FSW HAZ.
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.
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.
International Nuclear Information System (INIS)
Kuna, M.; Guth, W.; Nguyen Huy, T.
1990-01-01
Cracks in nozzles are failures with a 3D geometry and therefore are a very complicated task for modelling and calculation. A very much simplified 2D model was established of nozzle cracking, which allows less different preliminary examination and a conservative (safe) assessement. The lecture explains the testing and verification of this 2D model with regard to its applicability, analysing the model's suitability for determining the thermo-elastic-plastic loads by means of FE calculations, or the J-dependent crack growth in the nozzle. (orig.) [de
Multiple gingival pregnancy tumors with rapid growth
Directory of Open Access Journals (Sweden)
Wei-Lian Sun
2014-09-01
Full Text Available Pregnancy gingivitis is an acute form of gingivitis that affects pregnant women, with a prevalence of 30%, possibly ranging up to 100%. Sometimes, pregnancy gingivitis shows a tendency toward a localized hyperplasia called gingival pyogenic granuloma. Pregnancy tumor is a benign gingival hyperplasia with the gingiva as the most commonly involved site, but rarely it involves almost the entire gingiva. A 22-year-old woman was referred to our clinic with a chief complaint of gingival swelling that had lasted for 2 days. The lesions progressed rapidly and extensively, and almost all the gingiva was involved a week later. Generalized erythema, edema, hyperplasia, a hemorrhagic tendency, and several typical hemangiomatous masses were noted. Pregnancy was denied by the patient at the first and second visits, but was confirmed 2 weeks after the primary visit. The patient was given oral hygiene instructions. She recovered well, and the mass gradually regressed and had disappeared completely at the end of 12 weeks of pregnancy, without recurrence. The gingival lesions were finally diagnosed as multiple gingival pregnancy tumors. The patient delivered a healthy infant. An extensive and rapid growth of gingival pregnancy tumors during the early first month of pregnancy is a rare occurrence that is not familiar to dentists, gynecologists, and obstetricians. Those practitioners engaged in oral medicine and periodontology, primary care obstetrics, and gynecology should be aware of such gingival lesions to avoid misdiagnosis and overtreatment.
A Comparison of Fatigue Crack Growth in Human Enamel and Hydroxyapatite
Bajaj, Devendra; Nazari, Ahmad; Eidelman, Naomi; Arola, Dwayne
2008-01-01
Cracks and craze lines are often observed in the enamel of human teeth, but they rarely cause tooth fracture. The present study evaluates fatigue crack growth in human enamel, and compares that to the fatigue response of sintered hydroxyapatite (HAp) with similar crystallinity, chemistry and density. Miniature inset compact tension (CT) specimens were prepared that embodied a small piece of enamel (N=8) or HAp (N=6). The specimens were subjected to mode I cyclic loads and the steady state cra...
Study on the PWSCC Crack Growth Rate for Steam Generator Tubing
International Nuclear Information System (INIS)
Kang, Shin Hoo; Hwang, Il Soon; Lim, Jun; Lee, Seung Gi; Ryu, Kyung Ha
2008-03-01
Using in-situ Raman spectroscopy and crack growth rate lest system in simulated PWR primary water environment, the relationship between the oxide film chemistry and the PWSCC growth rate has been studied. We used I/2T compact tension specimen and disk specimen made of Alloy 182 and Alloy 600 for crack growth rate test and in-situ Raman spectroscopy measurement. Test was made in a refreshed autoclave with 30 cc STP / kg of dissolved hydrogen concentration. Conductivity, pH, dissolved hydrogen and oxygen concentration were continuously monitored at the outlet. The crack growth rate was measured by using switching DCPD technique under cyclinc triangular loading and at the same time oxide phase was determined by using in-situ Raman spectra at the elevation of the temperature. Additionally Raman spectroscopy was achieved for oxide phase transition of Alloy 600 according to the temperature and dissolved hydrogen concentration, 2 and 30cc STP / kg
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.
International Nuclear Information System (INIS)
Nogami, Shuhei; Sato, Yuki; Hasegawa, Akira
2010-01-01
Crack growth behavior under low cycle fatigue in reduced activation ferritic/martensitic steel, F82H IEA-heat (Fe-8Cr-2W-0.2V-0.02Ta), was investigated to improve the fatigue life assessment method of fusion reactor structural material. Low cycle fatigue test was carried out at room temperature in air at a total strain range of 0.4-1.5% using an hourglass-type miniature fatigue specimen. The relationship between the surface crack length and life fraction was described using one equation independent of the total strain range. Therefore, the fatigue life and residual life could be estimated using the surface crack length. Moreover, the microcrack initiation life could be estimated using the total strain range if there was a one-to-one correspondence between the total strain range and number of cycles to failure. The crack growth rate could be estimated using the total strain range and surface crack length by introducing the concept of the normalized crack growth rate. (author)
Analytical prediction model for non-symmetric fatigue crack growth in Fibre Metal Laminates
Wang, W.; Rans, C.D.; Benedictus, R.
2017-01-01
This paper proposes an analytical model for predicting the non-symmetric crack growth and accompanying delamination growth in FMLs. The general approach of this model applies Linear Elastic Fracture Mechanics, the principle of superposition, and displacement compatibility based on the
A Comparison Study of Machine Learning Based Algorithms for Fatigue Crack Growth Calculation.
Wang, Hongxun; Zhang, Weifang; Sun, Fuqiang; Zhang, Wei
2017-05-18
The relationships between the fatigue crack growth rate ( d a / d N ) and stress intensity factor range ( Δ K ) are not always linear even in the Paris region. The stress ratio effects on fatigue crack growth rate are diverse in different materials. However, most existing fatigue crack growth models cannot handle these nonlinearities appropriately. The machine learning method provides a flexible approach to the modeling of fatigue crack growth because of its excellent nonlinear approximation and multivariable learning ability. In this paper, a fatigue crack growth calculation method is proposed based on three different machine learning algorithms (MLAs): extreme learning machine (ELM), radial basis function network (RBFN) and genetic algorithms optimized back propagation network (GABP). The MLA based method is validated using testing data of different materials. The three MLAs are compared with each other as well as the classical two-parameter model ( K * approach). The results show that the predictions of MLAs are superior to those of K * approach in accuracy and effectiveness, and the ELM based algorithms show overall the best agreement with the experimental data out of the three MLAs, for its global optimization and extrapolation ability.
An Eulerian-Lagrangian finite-element method for modeling crack growth in creeping materials
International Nuclear Information System (INIS)
Lee Hae Sung.
1991-01-01
This study is concerned with the development of finite-element-solution methods for analysis of quasi-static, ductile crack growth in history-dependent materials. The mixed Eulerian-Langrangian description (ELD) kinematic model is shown to have several desirable properties for modeling inelastic crack growth. Accordingly, a variational statement based on the ELD for history-dependent materials is developed, and a new moving-grid finite-element method based on the variational statement is presented. The moving-grid finite-element method based on the variational statement is presented. The moving-grid finite-element method is applied to the analysis of transient, quasi-static, mode-III crack growth in creeping materials. A generalized Petrov-Galerkin method (GPG) is developed that simultaneously stabilizes the statement to admit L 2 basis functions for the nonlinear strain field. Quasi-static, model-III crack growth in creeping materials under small-scale-yielding (SSY) conditions is considered. The GPG/ELD moving-grid finite-element formulation is used to model a transient crack-growth problem. The GPG/ELD results compare favorably with previously-published numerical results and the asymptotic solutions
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.
Fracture Anisotropy and Toughness in the Mancos Shale: Implications for crack-growth geometry
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
Hall, L. R.; Finger, R. W.
1972-01-01
This experimental program was divided into two parts. The first part evaluated stress corrosion cracking in 2219-T87 aluminum and 5Al-2.5Sn (ELI) titanium alloy plate and weld metal. Both uniform height double cantilever beam and surface flawed specimens were tested in environments normally encountered during the fabrication and operation of pressure vessels in spacecraft and booster systems. The second part studied compatibility of material-environment combinations suitable for high energy upper stage propulsion systems. Surface flawed specimens having thicknesses representative of minimum gage fuel and oxidizer tanks were tested. Titanium alloys 5Al-2.5Sn (ELI), 6Al-4V annealed, and 6Al-4V STA were tested in both liquid and gaseous methane. Aluminum alloy 2219 in the T87 and T6E46 condition was tested in fluorine, a fluorine-oxygen mixture, and methane. Results were evaluated using modified linear elastic fracture mechanics parameters.
An evaluation on fatigue crack growth in a fine-grained isotropic graphite
Energy Technology Data Exchange (ETDEWEB)
Wang Hongtao; Sun Libin [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Li Chenfeng [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom); Shi Li [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Wang Haitao, E-mail: wanght@tsinghua.edu.cn [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China)
2012-09-15
Highlights: Black-Right-Pointing-Pointer The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. Black-Right-Pointing-Pointer The curves of the fatigue crack growth rate versus the SIF range show three stages. Black-Right-Pointing-Pointer The fatigue microcrack propagation is very sensitive to graphite's microstructures. Black-Right-Pointing-Pointer Graphite's microstructures have no significant impact on fatigue macrocrack growth. Black-Right-Pointing-Pointer The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45 Degree-Sign , showing the
An evaluation on fatigue crack growth in a fine-grained isotropic graphite
International Nuclear Information System (INIS)
Wang Hongtao; Sun Libin; Li Chenfeng; Shi Li; Wang Haitao
2012-01-01
Highlights: ► The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. ► The curves of the fatigue crack growth rate versus the SIF range show three stages. ► The fatigue microcrack propagation is very sensitive to graphite's microstructures. ► Graphite's microstructures have no significant impact on fatigue macrocrack growth. ► The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45°, showing the main cause of the fatigue fracture is the shear stress. There are also a large amount of secondary cracks inside unit cells and on cell walls
Directory of Open Access Journals (Sweden)
Kim S.-W.
2017-06-01
Full Text Available This work aims to study the stress corrosion crack growth behavior of cold-rolled Alloy 690 in the primary water of a pressurized water reactor. Compared with Alloy 600, which shows typical intergranular cracking along high angle grain boundaries, the cold-rolled Alloy 690, with its heterogeneous microstructure, revealed an abnormal crack growth behavior in mixed mode, that is, in transgranular cracking near a banded region, and in intergranular cracking in a matrix region. From local strain distribution analysis based on local mis-orientation, measured along the crack path using the electron back scattered diffraction method, it was suggested that the abnormal behavior was attributable to a heterogeneity of local strain distribution. In the cold-rolled Alloy 690, the stress corrosion crack grew through a highly strained area formed by a prior cold-rolling process in a direction perpendicular to the maximum principal stress applied during a subsequent stress corrosion cracking test.
Internal hydrogen-induced subcritical crack growth in austenitic stainless steels
Huang, J. H.; Altstetter, C. J.
1991-11-01
The effects of small amounts of dissolved hydrogen on crack propagation were determined for two austenitic stainless steel alloys, AISI 301 and 310S. In order to have a uniform distribution of hydrogen in the alloys, they were cathodically charged at high temperature in a molten salt electrolyte. Sustained load tests were performed on fatigue precracked specimens in air at 0 ‡C, 25 ‡C, and 50 ‡C with hydrogen contents up to 41 wt ppm. The electrical potential drop method with optical calibration was used to continuously monitor the crack position. Log crack velocity vs stress intensity curves had definite thresholds for subcritical crack growth (SCG), but stage II was not always clearly delineated. In the unstable austenitic steel, AISI 301, the threshold stress intensity decreased with increasing hydrogen content or increasing temperature, but beyond about 10 wt ppm, it became insensitive to hydrogen concentration. At higher concentrations, stage II became less distinct. In the stable stainless steel, subcritical crack growth was observed only for a specimen containing 41 wt ppm hydrogen. Fractographic features were correlated with stress intensity, hydrogen content, and temperature. The fracture mode changed with temperature and hydrogen content. For unstable austenitic steel, low temperature and high hydrogen content favored intergranular fracture while microvoid coalescence dominated at a low hydrogen content. The interpretation of these phenomena is based on the tendency for stress-induced phase transformation, the different hydrogen diffusivity and solubility in ferrite and austenite, and outgassing from the crack tip. After comparing the embrittlement due to internal hydrogen with that in external hydrogen, it is concluded that the critical hydrogen distribution for the onset of subcritical crack growth is reached at a location that is very near the crack tip.
Micromechanisms of ductile stable crack growth in nuclear pressure vessel steels
Energy Technology Data Exchange (ETDEWEB)
Belcher, W.P.A.; Druce, S.G.
1981-10-01
The objective of this work was to investigate the relationship between the micromechanisms of ductile crack growth, the microstructural constituent phases present in nuclear pressure vessel steel, and the observed fracture behavior as determined by impact and fracture mechanics tests. Results from a microstructural and mechanical property comparison of an A508 Class 3 pressurized water reactor nozzle forging cutout and a 150-mm-thick A533B Class 1 plate are reported. The variation of upper-shelf toughness between the two steels and its orientation sensitivity are discussed on the basis of inclusion and precipitate distributions. Inclusion clusters in A533B, deformed to elongated disks in the rolling plane, have a profound effect on short transverse fracture properties. Data derived using the multi-specimen J-integral method to characterize the initiation of ductile crack extension and resistance to stable crack growth are compared with equivalent Charpy results. Results of the J /SUB R/ -curve analyses indicate (1) that the A533B short transverse crack growth resistance is approximately half that observed from transverse and longitudinal specimen orientations, and (2) that the A508 initiation toughness and resistance to stable crack growth are insensitive to position through the forging wall, and are higher than exhibited by A533B at any orientation in the midthickness position.
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...
77 K Fatigue Crack Growth Rate of Modified CF8M Stainless Steel Castings
International Nuclear Information System (INIS)
Walsh, R. P.; Toplosky, V. J.; Han, K.; Heitzenroeder, P. J.; Nelson, B. E.
2006-01-01
The National Compact Stellerator Experiment (NCSX) is the first of a new class of stellarators. The modular superconducting coils in the NCSX have complex geometry that are manufactured on cast stainless steel (modified CF8M) winding forms. Although CF8M castings have been used before at cryogenic temperature there is limited data available for their mechanical properties at low temperatures. The fatigue life behavior of the cast material is vital thus a test program to generate data on representative material has been conducted. Fatigue test specimens have been obtained from key locations within prototype winding forms to determine the 77 K fatigue crack growth rate. The testing has successfully developed a representative database that ensures confident design. The measured crack growth rates are analyzed in terms of the Paris law parameters and the crack growth properties are related to the materials microstructure
Creep crack growth verification testing in alloy 800H tubular components
International Nuclear Information System (INIS)
Hunter, C.P.; Hurst, R.C.
1992-01-01
A method for determining the creep crack growth, CCG, and stress rupture behaviour of Alloy 800H tubular components containing longitudinal notches at 800deg C is described. The presence of the notch is found to systematically weaken the tube, the degree of weaking dependent upon the notch length and depth. The creep crack growth rates, determined from a specially adapted potential drop technique are compared with those obtained from conventional compact tension type specimens. Using the stress intensity factor, K 1 , and the C * parameter as the basis of comparison it is found that the latter gives excellent correlation between the specimen and component behaviour. Finally attention is drawn to the potential dangers of predicting the component creep crack growth behaviour from the data obtained using conventional specimens for a structure sensitive material such as Alloy 800H and conversely to the advantages of the component type CCG tests developed in the present work. (orig.)
Fatigue crack growth and endurance data on 9% Cr 1% Mo steels for AGR applications
International Nuclear Information System (INIS)
Priddle, E.K.
1987-01-01
Experimental investigations have been carried out on 9%Cr 1%Mo steels to examine: (1) The significance of carburisation on the fatigue endurance of plain and welded boiler tubes, and tube spacer strip; (2) the high cycle fatigue endurance of spacer strip and spacer weld metal; (3) fatigue crack growth rates in spacer strip and spacer weld metal. This report summarises the results of these investigations and where necessary compares the data to that in current data sheets. The effects of carburisation are variable depending on the structure and type of carburisation. The fatigue endurance properties of spacer strip and spacer weld metal are also similar and need not be considered separately for assessment or design purposes. Fatigue crack growth rates in spacer strip and space weld metal are similar and are influenced by both stress ratio and temperature. A design curve from a fast reactor data sheet may be used as an upper bound to these fatigue crack growth results. (author)
Crack growth modeling in a specimen with polymer weld
Czech Academy of Sciences Publication Activity Database
Ševčík, Martin; Hutař, Pavel; Náhlík, Luboš; Lach, R.; Knésl, Zdeněk; Grellmann, W.
488-489, č. 1 (2012), s. 158-161 ISSN 1013-9826. [International Conference on Fracture and Damage Mechanics - FDM 2011 /10./. Dubrovník, 19.09.2011-21.09.2011] R&D Projects: GA ČR GC101/09/J027; GA ČR GD106/09/H035 Institutional research plan: CEZ:AV0Z20410507 Keywords : polymer weld * crack propagation * graded structure * fracture mechanics Subject RIV: JL - Materials Fatigue, Friction Mechanics
Crack growth rate in the HAZ of alloy 690TT/152
International Nuclear Information System (INIS)
Gomez-Briceno, D.; Lapena, J.; Garcia-Redondo, M.; Castro, L.; Perosanz, F.J.; Ahluwalia, K.; Hickling, J.
2011-01-01
Crack growth rate (CGR) experiments to obtain data for the HAZ of nickel base alloys using fracture mechanics specimens are a challenge, primarily due to the difficulties of positioning the tip of the notch (or pre-crack) in the desired location within the complex region adjacent to the fusion line that is altered in several ways by the welding process. This paper describes an experimental program carried out to determine the CGR in the HAZ of an Alloy 690 test weld made using Alloy 152. Compact tension (CT) specimens have been tested in simulated PWR primary water at temperatures of 340 and 360 C under cyclic and constant loading (both with and without periodic partial unloading). For the Alloy 690 HAZ tested here, transgranular crack propagation (primarily due to environmentally assisted fatigue) with isolated intergranular secondary cracks was observed and there was no increase of the crack growth rate in comparison with that for Alloy 690 base metal. In both cases, the CGR values at constant load were very low (4*10 -9 mm/s down to effectively zero) and generally comparable with the data found in the literature for intergranular cracking of thermally treated or solution annealed Alloy 690 in simulated primary water. The scarce CGR data for the HAZ of Alloy 690 available to date do not suggest a significant increase in the PWSCC susceptibility of this resistant alloy, but further testing is still required given the expected variability in actual production welds. (authors)
Coupled FEM-DBEM method to assess crack growth in magnet system of Wendelstein 7-X
Directory of Open Access Journals (Sweden)
R. Citarella
2013-10-01
Full Text Available The fivefold symmetric modular stellarator Wendelstein 7-X (W7-X is currently under construction in Greifswald, Germany. The superconducting coils of the magnet system are bolted onto a central support ring and interconnected with five so-called lateral support elements (LSEs per half module. After welding of the LSE hollow boxes to the coil cases, cracks were found in the vicinity of the welds that could potentially limit the allowed number N of electromagnetic (EM load cycles of the machine. In response to the appearance of first cracks during assembly, the Stress Intensity Factors (SIFs were calculated and corresponding crack growth rates of theoretical semi-circular cracks of measured sizes in potentially critical position and orientation were predicted using Paris’ law, whose parameters were calibrated in fatigue tests at cryogenic temperature. In this paper the Dual Boundary Element Method (DBEM is applied in a coupled FEM-DBEM approach to analyze the propagation of multiple cracks with different shapes. For this purpose, the crack path is assessed with the Minimum Strain Energy density criterion and SIFs are calculated by the J-integral approach. The Finite Element Method (FEM is adopted to model, using the commercial codes Ansys or Abaqus;, the overall component whereas the submodel analysis, in the volume surrounding the cracked area, is performed by FEM (“FEM-FEM approach” or alternatively by DBEM (“FEM-DBEM approach”. The “FEM-FEM approach” considers a FEM submodel, that is extracted from the FEM global model; the latter provide the boundary conditions for the submodel. Such approach is affected by some restrictions in the crack propagation phase, whereas, with the “FEM-DBEM approach”, the crack propagation simulation is straightforward. In this case the submodel is created in a DBEM environment with boundary conditions provided by the global FEM analysis; then the crack is introduced and a crack propagation analysis
Effects of temperature on corrosion fatigue crack growth of pressure vessel steels in PWR coolant
International Nuclear Information System (INIS)
Tice, D.R.; Bramwell, I.L.; Fairbrother, H.; Worswick, D.
1994-01-01
This paper presents experimental results concerning crack propagation rates in A508-III pressure vessel steel (medium sulphur content) exposed to PWR primary water at temperatures between 130 and 290 C. The results indicate that the greatest increase in corrosion fatigue crack growth rate occurs at temperatures in the range 150 to 200 C. Under these conditions, there was a marked change in the appearance of the fracture surface, with extensive micro-branching of the crack front and occasional bifurcation of the whole crack path. In contrast, at 290 C, the fracture surface is smoother, similar to that due to inert fatigue. The implication of these observations for assessment of the pressure vessel integrity, is examined. 14 refs., 15 figs., 3 tabs
Crack growth resistance for anisotropic plasticity with non-normality effects
DEFF Research Database (Denmark)
Tvergaard, Viggo; Legarth, Brian Nyvang
2006-01-01
For a plastically anisotropic solid a plasticity model using a plastic flow rule with non-normality is applied to predict crack growth. The fracture process is modelled in terms of a traction–separation law specified on the crack plane. A phenomenological elastic–viscoplastic material model...... is applied, using one of two different anisotropic yield criteria to account for the plastic anisotropy, and in each case the effect of the normality flow rule is compared with the effect of non-normality. Conditions of small scale yielding are assumed, with mode I loading conditions far from the crack......-tip, and various directions of the crack plane relative to the principal axes of the anisotropy are considered. It is found that the steady-state fracture toughness is significantly reduced when the non-normality flow rule is used. Furthermore, it is shown that the predictions are quite sensitive to the value...
Role of damage tolerance and fatigue crack growth in the power generation industry
International Nuclear Information System (INIS)
Coffin, L.F.
1988-01-01
The problem of intergranular stress-corrosion cracking (IGSCC) in boiling water reactor (BWR) piping is discussed and the body of work undertaken in the author's laboratory to solve that problem is described. Particular attention is given to the development of electrical potential crack monitoring techniques and their application to surface crack growth, particularly under conditions approaching those found in service. The important role of water chemistry and its control is described in this context. The concept and description of sensors to monitor in situ the degree of damage containment from intergranular stress-corrosion cracking is then described, with reference to use in piping components and other types of monitoring. Finally, a concept for the life management of structures is described where damage processes are identified and monitored in situ using appropriate sensors to measure the damage rate continuously
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.
Effects of Aqueous Solutions on the Slow Crack Growth of Soda-Lime-Silicate Glass
Hausmann, Bronson D.; Salem, Jonathan A.
2016-01-01
The slow crack growth (SCG) parameters of soda-lime-silicate were measured in distilled and saltwater of various concentrations in order to determine if the presence of salt and the contaminate formation of a weak sodium film affects stress corrosion susceptibility. Past research indicates that solvents affect the rate of crack growth; however, the effects of salt have not been studied. The results indicate a small but statistically significant effect on the SCG parameters A and n at high concentrations; however, for typical engineering purposes, the effect can be ignored.
Probabilistic Modeling of the Fatigue Crack Growth Rate for Ni-base Alloy X-750
International Nuclear Information System (INIS)
Yoon, Jae Young; Nam, Hyo On; Hwang, Il Soon; Tae Hyun Lee
2012-01-01
The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model(FCGR) was developed by fitting into Paris' Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode. From fitting the data to Paris' Law, the parameters C and m of Paris' Law model were assumed to obey the Gaussian distribution. These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were updated to reduce the uncertainty in the model by using the Bayesian inference method. (author)
Ductile-phase toughening and fatigue crack growth in Nb3Al base alloys
International Nuclear Information System (INIS)
Gnanamoorthy, R.; Hanada, S.
1996-01-01
Niobium aluminide (Nb 3 Al) base intermetallic compounds exhibit good high-temperature strength and creep properties and potential for applications above 1,200 C provided their inadequately low room-temperature ductility, fracture toughness and fatigue crack growth behavior are improved. Addition of tantalum to Nb 3 Al base materials improves the high-temperature strength significantly and seems to be a potential alloying element. In the present study, room temperature fracture toughness and fatigue crack growth behavior of tantalum alloyed Nb 3 Al base alloy prepared by ingot metallurgy are investigated
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)
Sub-surface Fatigue Crack Growth at Alumina Inclusions in AISI 52100 Roller Bearings
DEFF Research Database (Denmark)
Cerullo, Michele
2014-01-01
Sub-surface fatigue crack growth at non metallic inclusions is studied in AISI 52100 bearing steel under typical rolling contact loads. A first 2D plane strain finite element analysis is carried out to compute the stress history in the innner race at a characteristic depth, where the Dang Van...... damage factor is highest. Subsequently the stress history is imposed as boundary conditions in a periodic unit cell model, where an alumina inclusion is embedded in a AISI 52100 matrix. Cracks are assumed to grow radially from the inclusion under cyclic loading. The growth is predicted by means...
Fatigue crack growth and life prediction under mixed-mode loading
Sajith, S.; Murthy, K. S. R. K.; Robi, P. S.
2018-04-01
Fatigue crack growth life as a function of crack length is essential for the prevention of catastrophic failures from damage tolerance perspective. In damage tolerance design approach, principles of fracture mechanics are usually applied to predict the fatigue life of structural components. Numerical prediction of crack growth versus number of cycles is essential in damage tolerance design. For cracks under mixed mode I/II loading, modified Paris law (d/a d N =C (ΔKe q ) m ) along with different equivalent stress intensity factor (ΔKeq) model is used for fatigue crack growth rate prediction. There are a large number of ΔKeq models available for the mixed mode I/II loading, the selection of proper ΔKeq model has significant impact on fatigue life prediction. In the present investigation, the performance of ΔKeq models in fatigue life prediction is compared with respect to the experimental findings as there are no guidelines/suggestions available on the selection of these models for accurate and/or conservative predictions of fatigue life. Within the limitations of availability of experimental data and currently available numerical simulation techniques, the results of present study attempt to outline models that would provide accurate and conservative life predictions. Such a study aid the numerical analysts or engineers in the proper selection of the model for numerical simulation of the fatigue life. Moreover, the present investigation also suggests a procedure to enhance the accuracy of life prediction using Paris law.
On the inter relationship between fatigue crack growth parameters in Paris regime
International Nuclear Information System (INIS)
Sasikala, G.
2016-01-01
Studies on fatigue crack growth behaviour of several steels and their welds for nuclear applications have been characterized in the author's laboratory in the past decade as a part of (i) creating the required database for integrity assessment of components, (ii) providing inputs for materials development, and (iii) understanding the crack growth behaviour in the light of basic mechanisms of cyclic deformation and damage. These include, effects of test variables (such as temperature, load ratio R) and material conditions (such as base and weld materials in as received, as welded or after subjecting to different ageing conditions). Different steels investigated include the ferritic grades modified 9Cr-1Mo steel (P91) and reduced activation ferritic martensitic steel, and austenitic grade SS 316L(N) and its weld. A common observation in the FCG literature is the inverse relationship between the Paris constant (log C) and exponent m, which has attracted considerable attention of the researchers in the field. The present paper attempts a fresh look at the inter relationship between Paris parameters obtained in the FCG studies on the above materials including the effect of crack closure and crack tip shielding. Further, some observed deviations from the inter relationship will be discussed in the light of changes in material properties and crack growth mechanisms. (author)
Equation of short fatigue crack growth law of 1Cr18Ni9Ti weld metal
International Nuclear Information System (INIS)
Zhao Yongxiang; Yang Bing; Gao Qing
2005-01-01
The method is investigated for characterizing the short fatigue crack (SFC) behaviour of 1Cr18Ni9Ti weld metal by the 'effective short fatigue crack criterion'. Three considerations are given. Firstly, the dominant effective short fatigue crack (DESFC) behaviour is a result of the interaction and evolution of the collective SFCs and, therefore, it is deemed suitable to describe their collective behaviour. Secondly, the significant character of microstructural short crack (MSC) regime and physical short crack (PSC) regime for the behaviour of SFCs indicates that it should be well exhibited in the characterization. Thirdly, the stronger irregular behaviour of SFCs indicates the single parameter of cyclic stress or strain amplitude for representing driving force of DESFC growth may be not appropriated. A new growth law for the collective SFCs is derived from a consideration of the local cyclic strain energy density driving the DESFC initiation in the initial zone and, then, driving the DESFC growth in the zones around its tips. The final form of this law is relative to the total cyclic strain energy density of remote fields, which circle the initial zone and, then, the zones around the DESFC tips. Availability has been indicated by an analysis of the test data of present material. (authors)
Nucleation and growth of fatigue cracks in magnesium alloys of different structure
International Nuclear Information System (INIS)
Grinberg, N.M.; Serdyuk, V.A.; Malinkina, T.I.; Kamyshkov, A.S.
1982-01-01
Duration of the fatigue crack nucleation and growth rate have been in a wide range of stress intensity factor variations for MA2-1, MA2-1 hp (higher purity), MA12, (T2, T6 and T8), MA15, IMB6, MA21 magnesium alloys of different composition and structural state. The threshold and criti- cal values of stress intensity factors, Ksub(th) and Ksub(fc) are determined for those alloys, and morphology of fracture is studied at different stages of crack growth. Duration of the nucleation stage of a fatigue crack, the rate and micromechanisms of its growth are found to depedend on alloying and structural state of magnesium alloys. The best crack resistance characteristics has the MA2-1 alloy, the poorest - MA12 (T2) alloy. It is stated that thermal treatment by hardening and ageing increases the resistance of the MA12 alloy to fatigue fracture and the MA2-1 alloy of higher purity gives poorer parameters of crack resistance [ru
Development of European creep crack growth testing code of practice for industrial specimens
Energy Technology Data Exchange (ETDEWEB)
Dogan, B.; Nikbin, K. [Imperial College, London (United Kingdom); Petrovski, B. [Technische Univ. Darmstadt (DE). Inst. fuer Werkstoffkunde (IFW)
2004-07-01
The integrity and residual life assessment of high temperature components require defects, detected or assumed to exist, through minimum allowable limits of detectable flaws using nondestructive testing methods. It relies on information obtained from the material's mechanical, uniaxial creep, creep crack initiation and growth properties. The information derived from experiments needs to be validated and harmonised following a Code of Practice that data variability between different institutions can be reduced to a minimum. The present paper reports on a Code of Practice (CoP) being prepared within the framework of the partially European Commission funded project CRETE. The novel aspect of the presented CoP is the inclusion of component relevant industrial specimen geometries. It covers testing and analysis of Creep Crack growth (CCG) in metallic materials at elevated temperature using six different cracked geometries that have been validated in. It aims to give advice on testing, measurements and analysis of creep crack growth data for a range of creep brittle to creep ductile materials using component service relevant specimen geometries and sizes. The CoP may be used for material selection criteria and inspection requirements for damage tolerant applications. In quantitative terms, these types of tests can be used to assess the individual and combined effects of metallurgical, fabrication, operating temperature, and loading conditions on creep crack growth life. Further issues will be addressed including material properties, damage and crack growth related constraint effect, stress relaxation and stress-strain fields, residual stresses, partitioning displacement, analysis of elasticcreep, elastic compliance measurements.
Further Development of Crack Growth Detection Techniques for US Test and Research Reactors
International Nuclear Information System (INIS)
Kohse, Gordon; Carpenter, David M.; Ostrovsky, Yakov; Joseph Palmer, A.; Teysseyre, Sebastien P.; Davis, Kurt L.; Rempe, Joy L.
2015-01-01
One of the key issues facing Light Water Reactors (LWRs) in extending lifetimes beyond 60 years is characterizing the combined effect of irradiation and water chemistry on material degradation and failure. Irradiation Assisted Stress Corrosion Cracking (IASCC), in which a crack propagates in a susceptible material under stress in an aggressive environment, is a mechanism of particular concern. Full understanding of IASCC depends on real time crack growth data acquired under relevant irradiation conditions. Techniques to measure crack growth in actively loaded samples under irradiation have been developed outside the US - at the Halden Boiling Water Reactor, for example. Several types of IASCC tests have also been deployed at the MITR, including passively loaded crack growth measurements and actively loaded slow strain rate tests. However, there is not currently a facility available in the US to measure crack growth on actively loaded, pre-cracked specimens in LWR irradiation environments. A joint program between the Idaho National Laboratory (INL) and the Massachusetts Institute of Technology (MIT) Nuclear Reactor Laboratory (NRL) is currently underway to develop and demonstrate such a capability for US test and research reactors. Based on the Halden design, the samples will be loaded using miniature high pressure bellows and a compact loading mechanism, with crack length measured in real time using the switched Direct Current Potential Drop (DCPD) method. The basic design and initial mechanical testing of the load system and implementation of the DCPD method have been previously reported. This paper presents the results of initial autoclave testing at INL and the adaptation of the design for use in the high pressure, high temperature water loop at the MITR 6 MW research reactor, where an initial demonstration is planned in mid-2015. Materials considerations for the high pressure bellows are addressed. Design modifications to the loading mechanism required by the
International Nuclear Information System (INIS)
Kim, Sung Jin; Kwon, Oh Yang; Jang, Yong Joon
2007-01-01
The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by using the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location
International Nuclear Information System (INIS)
Arora, Punit; Singh, P.K.; Bhasin, Vivek; Vaze, K.K.; Pukazhendhi, D.M.; Gandhi, P.; Raghava, G.
2011-01-01
The objective of the present study is to understand the fatigue crack growth behavior in austenitic stainless steel and carbon steel pipes and pipe welds by carrying out analysis/predictions and experiments. The Paris law has been used for the prediction of fatigue crack growth life. To carry out the analysis, Paris constants have been determined for pipe (base) and pipe weld materials by using Compact Tension (CT)/Three Point Bend (TPB) specimens machined from the actual pipe/pipe weld. Analyses have been carried out to predict the fatigue crack growth life of pipes/pipe welds having part through cracks on the outer surface. In the analyses, Stress Intensity Factors (K) have been evaluated through two different schemes. The first scheme considers the 'K' evaluations at two points of the crack front i.e. maximum crack depth and crack tip at the outer surface. The second scheme accounts for the area averaged root mean square stress intensity factor (K RMS ) at deepest and surface points. In order to validate the analytical procedure/results, experiments have been carried out on full scale pipe and pipe welds with part through circumferential crack. Fatigue crack growth life evaluated using both schemes have been compared with experimental results. Use of stress intensity factor (K RMS ) evaluated using second scheme gives better fatigue crack growth life prediction compared to that of first scheme. (author)
Evaluation of the MMCLIFE 3.0 code in predicting crack growth in titanium aluminide composites
International Nuclear Information System (INIS)
Harmon, D.; Larsen, J.M.
1999-01-01
Crack growth and fatigue life predictions made with the MMCLIFE 3.0 code are compared to test data for unidirectional, continuously reinforced SCS-6/Ti-14Al-21Nb (wt pct) composite laminates. The MMCLIFE 3.0 analysis package is a design tool capable of predicting strength and fatigue performance in metal matrix composite (MMC) laminates. The code uses a combination of micromechanic lamina and macromechanic laminate analyses to predict stresses and uses linear elastic fracture mechanics to predict crack growth. The crack growth analysis includes a fiber bridging model to predict the growth of matrix flaws in 0 degree laminates and is capable of predicting the effects of interfacial shear stress and thermal residual stresses. The code has also been modified to include edge-notch flaws in addition to center-notch flaws. The model was correlated with constant amplitude, isothermal data from crack growth tests conducted on 0- and 90 degree SCS-6/Ti-14-21 laminates. Spectrum fatigue tests were conducted, which included dwell times and frequency effects. Strengths and areas for improvement for the analysis are discussed
International Nuclear Information System (INIS)
Baumjohann, F.; Kroening, J.
1999-01-01
The present paper originates from a contribution to the safety assessment of a reactor pressure vessel (RPV). Investigations evaluating the safety against brittle fracture (exclosure of crack initiation and arrest assessments) are completed by calculations concerning ductile crack extension. Crack geometries including the expected crack extension are generated parametrically by a computer code and are used for further calculations with finite element programs. J-integrals of ductile growing cracks located between two comparative contours are determined by interpolation. The comparative contours are loaded by instationary temperature and pressure fields and are evaluated in advance. Taking the stability condition into consideration, the ductile crack extension is determined by pursuing the equilibrium between loading and crack resistance. The automatic modelling and a mathematical program processing the finite element results evaluate the crack growth of the finite element results very effectively. (orig.)
Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.
1998-01-01
The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.
DEFF Research Database (Denmark)
Carlone, Pierpaolo; Citarella, Roberto; Sonne, Mads Rostgaard
2016-01-01
A great deal of attention is currently paid by several industries toward the friction stir welding process to realize lightweight structures. Within this aim, the realistic prediction of fatigue behavior of welded assemblies is a key factor. In this work an integrated finite element method - dual...... boundary element method (FEM-DBEM) procedure, coupling the welding process simulation to the subsequent crack growth assessment, is proposed and applied to simulate multiple crack propagation, with allowance for manufacturing effects. The friction stir butt welding process of the precipitation hardened AA...... on a notched specimen. The whole procedure was finally tested comparing simulation outcomes with experimental data. The good agreement obtained highlights the predictive capability of the method. The influence of the residual stress distribution on crack growth and the mutual interaction between propagating...
Observations of the severity of notch-root radius in initiation of subcritical crack growth
International Nuclear Information System (INIS)
Reuter, W.G.; Eiholzer, C.R.; Tupper, M.A.
1981-01-01
Slow bend tests were conducted on Charpy specimens containing precracks or machined notches of 0.10 or 0.25 mm radius. The test specimens were fabricated from three heats of annealed Type 304 stainless steel. The purpose of these tests was to examine the effects of notch root radius, in very ductile materials, on initiation of subcritical crack growth. In addition, it was intended to establish the critical values of J, COD, etc. for the single-edge notch specimen for comparison with results obtained from specimens containing surface flaws. This paper will briefly describe only those results of the calculation for J. The tests were monitored by acoustic emission to identify the load corresponding to initiation of subcritical crack growth, by a crack-opening displacement gage (COD), by cross-head displacement, and by stop-action photography
Potential drop crack growth monitoring in high temperature biaxial fatigue tests
International Nuclear Information System (INIS)
Fitzgerald, B.P.; Krempl, E.
1993-01-01
The present work describes a procedure for monitoring crack growth in high temperature, biaxial, low cycle fatigue tests. The reversing DC potential drop equipment monitors smooth, tubular type 304 stainless steel specimens during fatigue testing. Electrical interference from an induction heater is filtered out by an analog filter and by using a long integration time. A Fourier smoothing algorithm and two spline interpolations process the large data set. The experimentally determined electrical potential drop is compared with the theoretical electrostatic potential that is found by solving Laplace's equation for an elliptical crack in a semi-infinite conducting medium. Since agreement between theory and experiment is good, the method can be used to measure crack growth to failure from the threshold of detectability
Evaluation of stable crack growth by using the finite element method
International Nuclear Information System (INIS)
Saarenheimo, A.
1996-01-01
In the study the analysis of stable crack growth by using the finite element method is considered. The results of numerical analyses are compared with the corresponding experimental results. The applications are reported in three separate papers enclosed at the end of the work. The first paper deals with the numerical analysis of a full scale pressure vessel test. The second and the third paper concern numerical analyses of fracture mechanical test specimens. In the literature study section of the work basic theories of fracture mechanics and common crack growth criteria are presented. The balance equations needed are written based on thermodynamical considerations. Physical interpretations of the energy release rate are briefly considered. Numerical calculation methods for determining the J-integral values are presented. The virtual crack extension method is used in the numerical examples. Also the Domain integral method and its implementation in the finite element method are described. (orig.) (70 refs.)
Directory of Open Access Journals (Sweden)
Tong Di Hua
2016-01-01
Full Text Available KR crack growth resistance curve can be used to predict crack propagation behavior, estimate the crack component bearing capacity after the crack, so KR curve research occupies very important position in the fracture mechanics. Based on crack growth resistance KR test curve of 2060 - T8E30 lithium aluminum alloy under the same thickness for different width, studies have shown that under the same thickness, the influence of the width on the resistance curve of crack propagation can be neglected. Empirical equation of resistance curve of crack extension of the smaller width specimen is given. Extending the fitting equation to that of larger width, it can be found that it is highly coincided with the experimental results.
Directory of Open Access Journals (Sweden)
Gourdin Stéphane
2014-01-01
Full Text Available Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensitive areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduces a certain degree of conservatism when calculating the fatigue life of surface flaws. Preliminary studies have shown that the first stages of crack propagation from surface anomalies are responsible for the conservative results. Thus, the aim of the study is to characterize the crack propagation from typical surface anomalies and to establish a new crack growth model, which can account for the micro-propagation stage. To separate the effects of the geometry of the anomalies and the residual stress state after introduction of the surface flaws, two V-type anomalies are studied: scratches and dents. Different studies have shown that the residual stresses beneath the anomalies seem to control the fatigue life of samples exhibiting scratches and dents. In order to monitor the crack micro-propagation, a direct current potential drop technique, coupled with heat tints is used during fatigue tests at elevated temperature. Thermal treatments releasing the residual stresses are also used to decouple the effect of crack morphology and residual stresses.
Restraint of fatigue crack growth by wedge effects of fine particles
Takahashi, I; Kotani, N
2000-01-01
Presents some experimental results which demonstrate restraint of fatigue crack growth in an Al-Mg alloy by wedge effects of fine particles. Fatigue test specimens were machined from a JIS A5083P-O Al-Mg alloy plate of 5 mm thickness and an EDM starter notch was introduced to each specimen. Three kinds of fine particles were prepared as the materials to be wedged into the fatigue cracks, i.e. magnetic particles and two kinds of alumina particles having different mean particle sizes of 47.3 mu m and 15.2 mu m. Particles of each kind were suspended in an oil to form a paste, which was applied on the specimen surface covering the notch zone prior to the fatigue tests. In order to make some fracture mechanics approaches, in situ observations of fatigue cracks were performed for the two cases using a CCD microscope, with a magnification of *1000. The crack length and the crack opening displacement (COD) at the notch root, delta , were measured. The crack retardation effect continues almost through the entire lifet...
Effect of laser shock processing on fatigue crack growth of duplex stainless steel
International Nuclear Information System (INIS)
Rubio-Gonzalez, C.; Felix-Martinez, C.; Gomez-Rosas, G.; Ocana, J.L.; Morales, M.; Porro, J.A.
2011-01-01
Research highlights: → LSP is an effective surface treatment to improve fatigue properties of duplex stainless steel. → Increasing pulse density, fatigue crack growth rate is reduced. → Microstructure is not affected by LSP. → Compressive residual stresses increases increasing pulse density. - Abstract: Duplex stainless steels have wide application in different fields like the ship, petrochemical and chemical industries that is due to their high strength and excellent toughness properties as well as their high corrosion resistance. In this work an investigation is performed to evaluate the effect of laser shock processing on some mechanical properties of 2205 duplex stainless steel. Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. A convergent lens is used to deliver 2.5 J, 8 ns laser pulses by a Q-switched Nd:YAG laser, operating at 10 Hz with infrared (1064 nm) radiation. The pulses are focused to a diameter of 1.5 mm. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is determined by the contour method. It is observed that the higher the pulse density the greater the compressive residual stress. Pulse densities of 900, 1600 and 2500 pul/cm 2 are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness if this steel.
International Nuclear Information System (INIS)
Castano, M.L.; Garcia, M.S.; Diego, G. de; Gomez-Briceno, D.; Francia, L.
2002-01-01
Intergranular cracking of non-sensitized materials, found in light water reactor (LWR) components exposed to neutron radiation, has been attributed to Irradiation Assisted Stress Corrosion Cracking (IASCC). Cracking of baffle former bolts, fabricated of AISI-316L and AISI-347, have been reported in some Europeans and US PWR plants. Examinations of removed bolts indicate the intergranular cracking characteristics can be associated with IASCC phenomena. Neutron radiation produce critical modifications of the microstructure and microchemical of stainless steels such hardening due to irradiation and Radiation Induce Segregation (RIS) at grain boundaries, among others. Chromium depletion at grain boundary due to RIS seems to justify the intergranular cracking of irradiated materials, both in plant and in lab tests, at high electrochemical corrosion potential (BWR-NWC environments), but it is not enough to explain cracking at low corrosion potential (BWR-HWC and PWR environments). In these latter conditions, hardening is considered a possible additional mechanism to explain the behavior of irradiated material. Radiation Hardening can be simulated in non irradiated material by mechanical deformation. Although some differences exists in the types of defects produced by radiation and mechanical deformation, it is accepted that the study of the stress corrosion behavior of unirradiated austenitic steels with different hardening levels would contribute to the understanding of IASCC mechanism. In order to evaluate the influence of hardening on the stress corrosion susceptibility of austenitic steels, crack growth rate tests with 316L and 347 stainless steels with nominal yield strengths from 500 to 900 MPa, produced by cold work are being carried out at 340 deg C in PWR conditions. Preliminary results indicate that crack propagation was obtained in the 316Lss and 347ss cold worked, even with a yield strength of 550 MPa. (authors)
Yahyazadehfar, Mobin
The enamel of human teeth is generally regarded as a brittle material with low fracture toughness. Consequently, the contributions of this tissue in resisting tooth fracture and the importance of its complex microstructure have been largely overlooked. The primary objective of this dissertation is to characterize the role of enamel's microstructure and degree of decussation on the fracture behavior of human enamel. The importance of the protein content and aging on the fracture toughness of enamel were also explored. Incremental crack growth in sections of human enamel was achieved using a special inset Compact Tension (CT) specimen configuration. Crack extension was achieved in two orthogonal directions, i.e. longitudinal and transverse to the prism axes. Fracture surfaces and the path of crack growth path were evaluated using scanning electron microscopy (SEM) to understand the fundamental mechanisms of crack growth extension. Furthermore, a hybrid approach was adopted to quantify the contribution of toughening mechanisms to the overall toughness. Results of this investigations showed that human enamel exhibits rising R-curve for both directions of crack extension. Cracks extending transverse to the rods in the outer enamel achieved lower rise in toughness with crack extension, and significantly lower toughness (1.23 +/- 0.20 MPa·m 0.5) than in the inner enamel (1.96 +/- 0.28 MPa· 0.5) and in the longitudinal direction (2.01 +/- 0.21 MPa· 0.5). The crack growth resistance exhibited both anisotropy and inhomogeneity, which arise from the complex hierarchical microstructure and the decussated prism structure. Decussation causes deflection of cracks extending from the enamel surface inwards, and facilitates a continuation of transverse crack extension within the outer enamel. This process dissipates fracture energy and averts cracks from extending toward the dentin and vital pulp. This study is the first to investigate the importance of proteins and the effect of
Short fatigue cracks growth and closure behavior in an austenitic stainless steel at 600 C and 650 C
Energy Technology Data Exchange (ETDEWEB)
Polvora, J.P.; Laiarinandrasana, L.; Drubay, B.; Piques, R.; Martelet, B. [Instituto de Pesquisas Energeticas e Nucleares (IPEN), Sao Paulo, SP (Brazil)
1995-12-31
In this work, following fatigue crack growth tests carried out at the CEN-SACLAY (AMORFIS program) by Laiarinandrasana (1994) on 316 L(N) CT specimens at 650{sup 0}C and 600{sup 0}C, short crack behavior of cracks emanating from machined notches is investigated. Experimental results are presented and discussions are directed to notch plasticity effect in relation with variations in crack opening stress intensity factor, K{sub op}, with crack lenght (author). 12 refs., 5 figs., 2 tab.
Crack growth in the creep region: criteria based on material forces
International Nuclear Information System (INIS)
Roche, R.L.
1984-12-01
Meaning of C* concept is discussed. It is shown that this concept is only a global approach of material force rate concept. The field of Csub(i)sup(*) (material force rate densities) is more representative of creep crack growth than C* integral. As application corrected expressions of C* are proposed for non isothermal cases, strain hardening creep and effect of material elasticity
A study on fatigue crack growth in dual phase martensitic steel in air
Indian Academy of Sciences (India)
Dual phase (DP) steel was intercritically annealed at different temperatures from fully martensitic state to achieve martensite plus ferrite, microstructures with martensite contents in the range of 32 to 76%. Fatigue crack growth (FCG) and fracture toughness tests were carried out as per ASTM standards E 647 and E 399, ...
Multiple-site damage crack growth behaviour in Fibre Metal Laminate structures
Wang, W.
2017-01-01
Fibre metal laminates (FMLs)were developed and refined for their superior crack growth resistance and critical damage size that complimented the damage tolerance design philosophy utilized in the aerospace sector. Robust damage tolerance tools have been developed for FMLs. However, they tend to
Probabilistic evaluation of fatigue crack growth in SA 508 and SA 533 B steel
International Nuclear Information System (INIS)
Dufresne, J.; Rieunier, J.B.
1982-07-01
This paper describes the method used to select the best representative law of fatigue crack growth in view of its introduction in a probabilist computer code). A modelling of the selected law (Paris law) and the statistical distribution of the corresponding numerical coefficients are presented. Results of computation are given in the case of a PWR pressure vessel with defects in belt line weld
Small fatigue crack growth in aluminium alloy EN-AW 6082/T6
Czech Academy of Sciences Publication Activity Database
Jíša, D.; Liškutín, P.; Kruml, Tomáš; Polák, Jaroslav
2010-01-01
Roč. 32, č. 12 (2010), s. 1913-1920 ISSN 0142-1123 R&D Projects: GA ČR GA101/07/1500 Institutional research plan: CEZ:AV0Z20410507 Keywords : Aluminium alloys * small cracks * grack growth rate Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.799, year: 2010
Effects of loading variables on fatigue-crack growth in liquid-metal environments
CSIR Research Space (South Africa)
Fernandes, PJL
1995-10-01
Full Text Available Liquid-metal-induced embrittlement (LMIE) refers to the loss of ductility in normally ductile metals and alloys when stressed while in contact with a liquid metal. In this study, the fatigue crack growth behaviour of brass in molten gallium...
Three-dimensional microstructural effects on plane strain ductile crack growth
DEFF Research Database (Denmark)
Tvergaard, Viggo; Needleman, Alan
2006-01-01
Ductile crack growth under mode 1, plane strain, small scale yielding conditions is analyzed. Overall plane strain loading is prescribed, but a full 3D analysis is carried out to model three dimensional microstructural effects. An elastic-viscoplastic constitutive relation for a porous plastic...
Corrosion fatigue crack growth of pressure vessel welds in PWR environment
International Nuclear Information System (INIS)
Bamford, W.H.; Ceschini, L.J.; Moon, D.M.
1983-01-01
The fatigue crack growth rate behavior of several pressure vessel steel welds in PWR environment is discussed. The behavior is compared with associated heat-affected zone behavior, and with comparable base metal results. The welds show different degrees of susceptibility to the environmental influence, and this is discussed in some detail, along with fractographic observations on the tested specimens
Subcritical crack growth behavior of AI2O3-Glass dental composites
Zhu, Q.; With, G. de; Dortmans, L.J.M.G.; Feenstra, F.
2003-01-01
The purpose of this study is to investigate the subcritical crack growth (SCG) behavior of alumina-glass dental composites. Alumina-glass composites were fabricated by infiltrating molten glass to porous alumina preforms. Rectangular bars of the composite were subject to dynamic loading in air, with
Development of a crack growth analysis is program for reactor head penetration
Energy Technology Data Exchange (ETDEWEB)
Hong, Sung Yull; Choi, Kwang Hee; Park, Jeong Il [Korea Electric Power Research Institute, Taejon (Korea, Republic of); Kang, Young Hwan; Park, Sung Ho; Kim, Il; Kim, Young Jong; Yoo, Young Joon; Yoo, Wan; Maeng, Wan Young; Choi, Suk Nam; Kim, Kee Suk; Yoon, Sung Won; Kim, Jee Ho; Park, Myung Kyu [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1996-12-31
Crack growth analysis program for Reactor Head Penetration is being developed for applying to plants such as, Kori 1, Kori 2, Kori 3,4 YoungKwang 1,2 and Uljin 1,2 (1) Stress Evaluation - The stress analysis is required to evaluate the structure integrity for the RVH penetration tubes. The RVH penetration tubes are geometrically non-symmetry except center one. Thus, 3D finite element analysis should be employed for the stress analysis. The magnitude and distribution of residual stress resulted from welding can be determined analytically by simulation welding procedure. (2) Flaw Evaluation - There are two objectives of the penetration tube flaw evaluation to predict the time required for a crack to propagate to the acceptance criteria. The first objective is to perform the parametric evaluation for a postulated crack. The second objective is to develop the flaw evaluation program for the crack detected during the inspection. (3) Characterization of Material Properties of Alloy 600 - These study is to provide data which similarly represent the properties of PWR power plants in Korea. The data is used for analyzing of the stress distribution around penetration tubes. And the PWSCC data will be used for the crack growth rate of the penetration tubes. (author). 92 refs., 121 figs.
Measurement of fatigue crack growth using low-profile eddy-current sensors
International Nuclear Information System (INIS)
Ditchburn, R.J.; Ibrahim, M.E.; Burke, S.K.
2011-01-01
Conformable spiral coils show promise as permanently mounted eddy-current sensors for the detection and monitoring of surface-breaking cracks in electrically conductive structures. Flexibility and a low profile (typically less than 0.5 mm) are key advantages that allow the sensors to be unobtrusively mounted on curved surfaces and beneath surface coatings. Furthermore, these sensors can be permanently mounted in areas that would otherwise be difficult or impossible to reach without significant disassembly. The sensors can be activated and interrogated using the same well-established electromagnetic measurement principles in eddy-current nondestructive inspection. A material test machine was used to grow through-thickness fatigue crack in a compact-tension specimen made from the aerospace-grade aluminium alloy AA2014. The growth of the crack was examined by measuring the small impedance changes of planar spiral-coil sensors attached to the specimen. The results indicate that permanently attached conformable spiral coils can be used to detect a deep crack once it has grown beneath the sensor, and then to monitor subsequent crack growth.
A structural health monitoring fastener for tracking fatigue crack growth in bolted metallic joints
Rakow, Alexi Schroder
Fatigue cracks initiating at fastener hole locations in metallic components are among the most common form of airframe damage. The fastener hole site has been surveyed as the second leading initiation site for fatigue related accidents of fixed wing aircraft. Current methods for inspecting airframes for these cracks are manual, whereby inspectors rely on non-destructive inspection equipment or hand-held probes to scan over areas of a structure. Use of this equipment often demands disassembly of the vehicle to search appropriate hole locations for cracks, which elevates the complexity and cost of these maintenance inspections. Improved reliability, safety, and reduced cost of such maintenance can be realized by the permanent integration of sensors with a structure to detect this damage. Such an integrated system of sensors would form a structural health monitoring (SHM) system. In this study, an Additive, Interleaved, Multi-layer Electromagnetic (AIME) sensor was developed and integrated with the shank of a fastener to form a SHM Fastener, a new SHM technology targeted at detection of fastener hole cracks. The major advantages of the SHM Fastener are its installation, which does not require joint layer disassembly, its capability to detect inner layer cracks, and its capability to operate in a continuous autonomous mode. Two methods for fabricating the proposed SHM Fastener were studied. The first option consisted of a thin flexible printed circuit film that was bonded around a thin metallic sleeve placed around the fastener shank. The second option consisted of coating sensor materials directly to the shank of a part in an effort to increase the durability of the sensor under severe loading conditions. Both analytical and numerical models were developed to characterize the capability of the sensors and provide a design tool for the sensor layout. A diagnostic technique for crack growth monitoring was developed to complete the SHM system, which consists of the
Fatigue crack growth retardation in spot heated mild steel sheet
Indian Academy of Sciences (India)
Unknown
Department of Metallurgical Engineering, *Department of Applied Mechanics and Hydraulics, ... growth retardation increases with increasing level of overload as well as with ..... Suresh S 1996 Fatigue of materials (Cambridge: Cambridge.
Detection and monitoring of shear crack growth using S-P conversion of seismic waves
Modiriasari, A.; Bobet, A.; Pyrak-Nolte, L. J.
2017-12-01
, which causes energy partitioning into P, S, and P-to-S or S-to-P waves. This finding provides a diagnostic method for detecting shear crack initiation and growth using seismic wave conversions. Acknowledgments: This material is based upon work supported by the National Science Foundation, Geomechanics and Geotechnical Systems Program (award No. CMMI-1162082).
Fatigue Crack Growth Behavior of Austempered AISI 4140 Steel with Dissolved Hydrogen
Directory of Open Access Journals (Sweden)
Varun Ramasagara Nagarajan
2017-11-01
Full Text Available The focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behavior of an austempered low-alloy AISI 4140 steel. The investigation also examined the influence of dissolved hydrogen on the fatigue threshold in this material. The material was tested in two conditions, as-received (cold rolled and annealed and austempered (austenitized at 882 °C for 1 h and austempered at 332 °C for 1 h. The microstructure of the annealed specimens consisted of a mix of ferrite and fine pearlite; the microstructure of the austempered specimens was lower bainite. Tensile and Compact Tension specimens were prepared. To examine the influence of dissolved hydrogen, two subsets of the CT specimens were charged with hydrogen for three different time periods between 150 and 250 h. All of the CT samples were then subjected to fatigue crack growth tests in the threshold and linear regions at room temperature. The test results indicate that austempering resulted in significant improvement in the yield and tensile strength as well as the fracture toughness of the material. The test results also show that, in the absence of dissolved hydrogen, the crack growth rate in the threshold and linear regions was lower in austempered samples compared to the as-received (annealed samples. The fatigue threshold was also slightly greater in the austempered samples. In presence of dissolved hydrogen, the crack growth rate was dependent upon the ∆K value. In the low ∆K region (<30 MPa√m, the presence of dissolved hydrogen caused the crack growth rate to be higher in the austempered samples as compared to annealed samples. Above this value, the crack growth rate was increasingly greater in the annealed specimens when compared to the austempered specimens in presence of dissolved hydrogen. It is concluded that austempering of 4140 steel appears to provide a processing route by which the strength, hardness, and fracture toughness of
Influence of dissolved hydrogen on the fatigue crack growth behaviour of AISI 4140 steel
Ramasagara Nagarajan, Varun
Many metallic structural components come into contact with hydrogen during manufacturing processes or forming operations such as hot stamping of auto body frames and while in service. This interaction of metallic parts with hydrogen can occur due to various reasons such as water molecule dissociation during plating operations, interaction with atmospheric hydrogen due to the moisture present in air during stamping operations or due to prevailing conditions in service (e.g.: acidic or marine environments). Hydrogen, being much smaller in size compared to other metallic elements such as Iron in steels, can enter the material and become dissolved in the matrix. It can lodge itself in interstitials locations of the metal atoms, at vacancies or dislocations in the metallic matrix or at grain boundaries or inclusions (impurities) in the alloy. This dissolved hydrogen can affect the functional life of these structural components leading to catastrophic failures in mission critical applications resulting in loss of lives and structural component. Therefore, it is very important to understand the influence of the dissolved hydrogen on the failure of these structural materials due to cyclic loading (fatigue). For the next generation of hydrogen based fuel cell vehicles and energy systems, it is very crucial to develop structural materials for hydrogen storage and containment which are highly resistant to hydrogen embrittlement. These materials should also be able to provide good long term life in cyclic loading, without undergoing degradation, even when exposed to hydrogen rich environments for extended periods of time. The primary focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behaviour of a commercially available high strength medium carbon low alloy (AISI 4140) steel. The secondary objective was to examine the influence of microstructure on the fatigue crack growth behaviour of this material and to determine the
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)
Rovinelli, Andrea; Guilhem, Yoann; Proudhon, Henry; Lebensohn, Ricardo A.; Ludwig, Wolfgang; Sangid, Michael D.
2017-06-01
Microstructurally small cracks exhibit large variability in their fatigue crack growth rate. It is accepted that the inherent variability in microstructural features is related to the uncertainty in the growth rate. However, due to (i) the lack of cycle-by-cycle experimental data, (ii) the complexity of the short crack growth phenomenon, and (iii) the incomplete physics of constitutive relationships, only empirical damage metrics have been postulated to describe the short crack driving force metric (SCDFM) at the mesoscale level. The identification of the SCDFM of polycrystalline engineering alloys is a critical need, in order to achieve more reliable fatigue life prediction and improve material design. In this work, the first steps in the development of a general probabilistic framework are presented, which uses experimental result as an input, retrieves missing experimental data through crystal plasticity (CP) simulations, and extracts correlations utilizing machine learning and Bayesian networks (BNs). More precisely, experimental results representing cycle-by-cycle data of a short crack growing through a beta-metastable titanium alloy, VST-55531, have been acquired via phase and diffraction contrast tomography. These results serve as an input for FFT-based CP simulations, which provide the micromechanical fields influenced by the presence of the crack, complementing the information available from the experiment. In order to assess the correlation between postulated SCDFM and experimental observations, the data is mined and analyzed utilizing BNs. Results show the ability of the framework to autonomously capture relevant correlations and the equivalence in the prediction capability of different postulated SCDFMs for the high cycle fatigue regime.
Creep and Creep-Fatigue Crack Growth at Structural Discontinuities and Welds
Energy Technology Data Exchange (ETDEWEB)
Dr. F. W. Brust; Dr. G. M. Wilkowski; Dr. P. Krishnaswamy; Mr. Keith Wichman
2010-01-27
The subsection ASME NH high temperature design procedure does not admit crack-like defects into the structural components. The US NRC identified the lack of treatment of crack growth within NH as a limitation of the code and thus this effort was undertaken. This effort is broken into two parts. Part 1, summarized here, involved examining all high temperature creep-fatigue crack growth codes being used today and from these, the task objective was to choose a methodology that is appropriate for possible implementation within NH. The second part of this task, which has just started, is to develop design rules for possible implementation within NH. This second part is a challenge since all codes require step-by-step analysis procedures to be undertaken in order to assess the crack growth and life of the component. Simple rules for design do not exist in any code at present. The codes examined in this effort included R5, RCC-MR (A16), BS 7910, API 579, and ATK (and some lesser known codes). There are several reasons that the capability for assessing cracks in high temperature nuclear components is desirable. These include: (1) Some components that are part of GEN IV reactors may have geometries that have sharp corners - which are essentially cracks. Design of these components within the traditional ASME NH procedure is quite challenging. It is natural to ensure adequate life design by modeling these features as cracks within a creep-fatigue crack growth procedure. (2) Workmanship flaws in welds sometimes occur and are accepted in some ASME code sections. It can be convenient to consider these as flaws when making a design life assessment. (3) Non-destructive Evaluation (NDE) and inspection methods after fabrication are limited in the size of the crack or flaw that can be detected. It is often convenient to perform a life assessment using a flaw of a size that represents the maximum size that can elude detection. (4) Flaws that are observed using in-service detection
Creep and Creep-Fatigue Crack Growth at Structural Discontinuities and Welds
International Nuclear Information System (INIS)
Brust, F.W.; Wilkowski, G.M.; Krishnaswamy, P.; Wichman, Keith
2010-01-01
The subsection ASME NH high temperature design procedure does not admit crack-like defects into the structural components. The US NRC identified the lack of treatment of crack growth within NH as a limitation of the code and thus this effort was undertaken. This effort is broken into two parts. Part 1, summarized here, involved examining all high temperature creep-fatigue crack growth codes being used today and from these, the task objective was to choose a methodology that is appropriate for possible implementation within NH. The second part of this task, which has just started, is to develop design rules for possible implementation within NH. This second part is a challenge since all codes require step-by-step analysis procedures to be undertaken in order to assess the crack growth and life of the component. Simple rules for design do not exist in any code at present. The codes examined in this effort included R5, RCC-MR (A16), BS 7910, API 579, and ATK (and some lesser known codes). There are several reasons that the capability for assessing cracks in high temperature nuclear components is desirable. These include: (1) Some components that are part of GEN IV reactors may have geometries that have sharp corners - which are essentially cracks. Design of these components within the traditional ASME NH procedure is quite challenging. It is natural to ensure adequate life design by modeling these features as cracks within a creep-fatigue crack growth procedure. (2) Workmanship flaws in welds sometimes occur and are accepted in some ASME code sections. It can be convenient to consider these as flaws when making a design life assessment. (3) Non-destructive Evaluation (NDE) and inspection methods after fabrication are limited in the size of the crack or flaw that can be detected. It is often convenient to perform a life assessment using a flaw of a size that represents the maximum size that can elude detection. (4) Flaws that are observed using in-service detection
Development of detailed analysis program for high-temperature crack growth evaluation
Energy Technology Data Exchange (ETDEWEB)
Takahashi, Yukio; Nakayama, Yasunari [Central Research Inst. of Electric Power Industry, Komae, Tokyo (Japan). Komae Research Lab
2001-04-01
Evaluation of crack growth as well as crack initiation is necessary to make realistic evaluation of structural integrity and life management of high-temperature plant components. Domain integral formulae for three kinds of nonlinear fracture mechanics parameters, i.e. J-integral, fatigue J-integral range and creep J-integral were derived for two-dimensional, three-dimensional and axi-symmetrical structures. Furthermore, methods for applying them to finite element results were derived and a computer program was developed for the general-purpose finite element program, MARC. The program was applied to various problems and its effectiveness was demonstrated. (author)
Fatigue crack growth behaviour of 21/4Cr1Mo steel tube at elevated temperature
International Nuclear Information System (INIS)
Bulloch, J.H.; Buchanan, L.W.
1987-01-01
The fatigue crack growth characteristics of 21/4Cr1Mo steel tube have been examined at 588 0 C over the frequency range 0.02-20 Hz and dwell time range 10-960 min. All tests were conducted under load control in laboratory air at an R-ratio of 0.5. The elevated temperature fatigue crack growth characteristics were adequately described in terms of the stress intensity range ΔKAPPA. The continuous cyclic test data exhibited a significant effect of frequency that agreed well with predicted effects using a simple mathematical model of the high temperature fatigue process. With the dwell time range of 10-100 min there was a significant dwell time effect on the critical ΔKAPPA level for creep-fatigue interactive growth. At dwell times > 100 min the dwell time effect saturates. When creep-fatigue interactive growth occurs, growth rates reside above the maximum for continuum-controlled fatigue crack growth, and exhibit a da/dN varies as ΔKAPPA 10 dependence; failure is then intergranular in nature. (author)
Finite element analysis of three dimensional crack growth by the use of a boundary element sub model
DEFF Research Database (Denmark)
Lucht, Tore
2009-01-01
A new automated method to model non-planar three dimensional crack growth is proposed which combines the advantages of both the boundary element method and the finite element method. The proposed method links the two methods by a submodelling strategy in which the solution of a global finite...... element model containing an approximation of the crack is interpolated to a much smaller boundary element model containing a fine discretization of the real crack. The method is validated through several numerical comparisons and by comparison to crack growth measured in a test specimen for an engineering...
Creep deformation and crack growth in a low alloy steel welded pressure vessel containing defects
International Nuclear Information System (INIS)
Coleman, M.C.
1982-01-01
A full-size pressure vessel was tested for effects of welding residual stresses on creep deformation and crack growth. The vessel, based on 1/2 Cr 1/2 Mo 1/4 V main steam pipe, contained four 2CrMo manual metal arc welds, two in the as-welded condition and two stress-relieved. All the welds contained pre-existing defects machined in the heat affected zones. Testing was carried out at two internal steam pressures, 250 and 350 bar, and 565 0 C. Cracked and uncracked areas of the vessel were monitored continuously. Results are presented for the continuous creep deformation observed in both the hoop and axial directions of the welds throughout the 11,400 h of testing, as well as the intermittent strain data obtained during inspections. Crack growth observations are described based on nondestructive examination. The residual stresses measured are also given for both the as-welded and stress relieved weldments. Results obtained are discussed in terms of the effects of welding residual stress on the hoop and axial deformations observed in the welds. Similarly, the effects of residual stress on creep crack growth are considered together with compositional and microstructural implications. 9 figures, 5 tables
Creep Crack Initiation and Growth Behavior for Ni-Base Superalloys
Nagumo, Yoshiko; Yokobori, A. Toshimitsu, Jr.; Sugiura, Ryuji; Ozeki, Go; Matsuzaki, Takashi
The structural components which are used in high temperature gas turbines have various shapes which may cause the notch effect. Moreover, the site of stress concentration might have the heterogeneous microstructural distribution. Therefore, it is necessary to clarify the creep fracture mechanism for these materials in order to predict the life of creep fracture with high degree of accuracy. In this study, the creep crack growth tests were performed using in-situ observational testing machine with microscope to observe the creep damage formation and creep crack growth behavior. The materials used are polycrystalline Ni-base superalloy IN100 and directionally solidified Ni-base superalloy CM247LC which were developed for jet engine turbine blades and gas turbine blades in electric power plants, respectively. The microstructural observation of the test specimens was also conducted using FE-SEM/EBSD. Additionally, the analyses of two-dimensional elastic-plastic creep finite element using designed methods were conducted to understand the effect of microstructural distribution on creep damage formation. The experimental and analytical results showed that it is important to determine the creep crack initiation and early crack growth to predict the life of creep fracture and it is indicated that the highly accurate prediction of creep fracture life could be realized by measuring notch opening displacement proposed as the RNOD characteristic.
Fatigue-crack growth behavior of Type 347 stainless steels under simulated PWR water conditions
Energy Technology Data Exchange (ETDEWEB)
Hong, Seokmin; Min, Ki-Deuk; Yoon, Ji-Hyun; Kim, Min-Chul; Lee, Bong-Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)
2015-10-15
Fatigue crack growth rate (FCGR) curve of stainless steel exists in ASME code section XI, but it is still not considering the environmental effects. The longer time nuclear power plant is operated, the more the environmental degradation issues of materials pop up. There are some researches on fatigue crack growth rate of S304 and S316, but researches of FCGR of S347 used in Korea nuclear power plant are insufficient. In this study, the FCGR of S347 stainless steel was evaluated in the PWR high temperature water conditions. The FCGRs of S347 stainless steel under pressurized-water conditions were measured by using compact-tension (CT) specimens at different levels of dissolved oxygen (DO) and frequency. 1. FCGRs of SS347 were slower than that in ASME XI and environmental effect did not occur when frequency was higher than 1Hz. 2. Fatigue crack growth is accelerated by corrosion fatigue and it is more severe when frequency is slower than 0.1Hz. 3. Increase of crack tip opening time increased corrosion fatigue and it deteriorated environmental fatigue properties.
Analysis of crack initiation and growth in the high level vibration test at Tadotsu
International Nuclear Information System (INIS)
Kassir, M.K.; Park, Y.J.; Hofmayer, C.H.; Bandyopadhyay, K.K.; Shteyngart, S.
1993-08-01
The High Level Vibration Test data are used to assess the accuracy and usefulness of current engineering methodologies for predicting crack initiation and growth in a cast stainless steel pipe elbow under complex, large amplitude loading. The data were obtained by testing at room temperature a large scale modified model of one loop of a PWR primary coolant system at the Tadotsu Engineering Laboratory in Japan. Fatigue crack initiation time is reasonably predicted by applying a modified local strain approach (Coffin-Mason-Goodman equation) in conjunction with Miner's rule of cumulative damage. Three fracture mechanics methodologies are applied to investigate the crack growth behavior observed in the hot leg of the model. These are: the ΔK methodology (Paris law), ΔJ concepts and a recently developed limit load stress-range criterion. The report includes a discussion on the pros and cons of the analysis involved in each of the methods, the role played by the key parameters influencing the formulation and a comparison of the results with the actual crack growth behavior observed in the vibration test program. Some conclusions and recommendations for improvement of the methodologies are also provided
Fatigue crack growth behaviour of the aluminium-lithium alloy 2090
International Nuclear Information System (INIS)
Tabrett, C.P.; McKeighan, P.C.; Smith, D.J.
1993-01-01
The fatigue crack growth (FCG) behavior of the aluminum lithium (Al-Li) alloy 2090-T84 has been investigated from a series of constant amplitude FCG tests. The influence of in plane orientation (L-T, T-L+45) and sheet thickness (1.6 and 6 mm) on the FCG rates for the rolled product has been examined. In general, the T-L orientation possess superior FCG resistance for both thicknesses and the 6 mm thick sheet material showed improved FCG resistance when compared to the 1.6 mm thick material for all orientations. It is believed this trend is related to the greater roughness and larger asperities found on the fatigue crack surfaces for the 6 mm thick material. Closure corrected FCG data suggests that much of the difference between the L-T and T-L orientation for the 6 mm thick sheet arise from variations in crack closure levels. (author)
International Nuclear Information System (INIS)
Arora, Punit; Tripathi, R.; Singh, P.K.; Bhasin, V.; Vijayan, P.K.
2016-01-01
The objective of the present study is to understand the Fatigue Crack Growth Rate (FCGR) behaviour after single over-load/ under-load event on carbon steel piping material. The tests have been carried out on standard Compact Tension (CT) specimens. The effect of different crack length to width ratio (a/W) of specimen and overload/under-load ratios on FCGR have been studied. The studies have shown significant reduction in FCG rate after overload event. The strain field has been measured using Digital Image Correlation (DIC) technique ahead of the crack tip to quantify the plastic zone size due to overload and constant amplitude load. In addition, plastic zone calculations have also been carried out using 3D finite element analyses for the prediction of post overload FCGR/ life. The predicted FCGR are in agreement with experimentally determined FCGR. (author)
On a separating method for mixed-modes crack growth in wood material using image analysis
Moutou Pitti, R.; Dubois, F.; Pop, O.
2010-06-01
Due to the complex wood anatomy and the loading orientation, the timber elements are subjected to a mixed-mode fracture. In these conditions, the crack tip advance is characterized by mixed-mode kinematics. In order to characterize the fracture process function versus the loading orientation, a new mixed-mode crack growth timber specimen is proposed. In the present paper, the design process and the experimental validation of this specimen are proposed. Using experimental results, the energy release rate is calculated for several modes. The calculi consist on the separation of each fracture mode. The design of the specimen is based on the analytical approach and numerical simulation by finite element method. The specimen particularity is the stability of the crack propagation under a force control.
Growth of 2D and 3D plane cracks under thermo-mechanical loading with varying amplitudes
International Nuclear Information System (INIS)
Sbitti, Amine
2009-01-01
After a presentation of the phenomenon of thermal fatigue (in industrial applications and nuclear plants), this research thesis reports the investigation of the growth and arrest of a 2D crack under thermal fatigue (temperature and stress distribution over thickness, calculation of stress intensity factors, laws of fatigue crack growth, growth under varying amplitude), and the investigation of 3D crack growth under cyclic loading with varying amplitudes (analytic and numerical calculation of stress intensity factors, variational formulation in failure mechanics, 3D crack propagation under fatigue, use of the Aster code, use of the extended finite element method or X-FEM). The author discusses the origin and influence of the 3D crack network under thermal fatigue
Directory of Open Access Journals (Sweden)
Tai-Cheng Chen
2018-03-01
Full Text Available Austenitic stainless steels are often considered candidate materials for use in hydrogen-containing environments because of their low hydrogen embrittlement susceptibility. In this study, the fatigue crack growth behavior of the solution-annealed and cold-rolled 301, 304L, and 310S austenitic stainless steels was characterized in 0.2 MPa gaseous hydrogen to evaluate the hydrogen-assisted fatigue crack growth and correlate the fatigue crack growth rates with the fracture feature or fracture surface roughness. Regardless of the testing conditions, higher fracture surface roughness could be obtained in a higher stress intensity factor (∆K range and for the counterpart cold-rolled specimen in hydrogen. The accelerated fatigue crack growth of 301 and 304L in hydrogen was accompanied by high fracture surface roughness and was associated with strain-induced martensitic transformation in the plastic zone ahead of the fatigue crack tip.
Parametric calculations of fatigue-crack growth in piping
International Nuclear Information System (INIS)
Simonen, F.A.; Goodrich, C.W.
1983-06-01
This study presents calculations of the growth of piping flaws produced by fatigue. Flaw growth was predicted as a function of the initial flaw size, the level and number of stress cycles, the piping material, and environmental factors. The results indicate that the present flaw acceptance standards of ASME Section XI provide a relatively consistent set of allowable flaw sizes because the predicted life of flawed piping is relatively insensitive to pipe wall thickness, flaw aspect ratio, and piping material (ferritic versus austenitic). On the other hand, the results show that flaws that are acceptable under ASME Section XI can grow at unacceptable rates if the cyclic stresses are at the maximum level permitted by the design rules of ASME Section III. However, a review of the conservatisms inherent to the ASME code rules is presented to explain the low occurrence of piping fatigue failures in service. It is concluded that decreases in the allowable flaw sizes are not justified
International Nuclear Information System (INIS)
Yasuoka, Tetsuo; Mizutani, Yoshihiro; Todoroki, Akira
2014-01-01
High-temperature water stress corrosion cracking has high tensile stress sensitivity, and its growth rate has been evaluated using the stress intensity factor, which is a linear fracture mechanics parameter. Stress corrosion cracking mainly occurs and propagates around welded metals or heat-affected zones. These regions have complex residual stress distributions and yield strength distributions because of input heat effects. The authors previously reported that the stress intensity factor becomes inapplicable when steep residual stress distributions or yield strength distributions occur along the crack propagation path, because small-scale yielding conditions deviate around those distributions. Here, when the stress intensity factor is modified by considering these distributions, the modified stress intensity factor may be used for crack growth evaluation for large-scale yielding. The authors previously proposed a modified stress intensity factor incorporating the stress distribution or yield strength distribution in front of the crack using the rate of change of stress intensity factor and yield strength. However, the applicable range of modified stress intensity factor for large-scale yielding was not clarified. In this study, the range was analytically investigated by comparison with the J-integral solution. A three-point bending specimen with parallel surface crack was adopted as the analytical model and the stress intensity factor, modified stress intensity factor and equivalent stress intensity factor derived from the J-integral were calculated and compared under large-scale yielding conditions. The modified stress intensity was closer to the equivalent stress intensity factor when compared with the stress intensity factor. If deviation from the J-integral solution is acceptable up to 2%, the modified stress intensity factor is applicable up to 30% of the J-integral limit, while the stress intensity factor is applicable up to 10%. These results showed that
Effect of Microstructure and Environment on Static Crack Growth Resistance in Alloy 706
Yang, Ling; Hawk, Jeffrey A.; Duquette, David J.; Schwant, Robin C.
2009-06-01
The relationship between thermo-mechanical processing, resultant microstructure, and mechanical properties has been of interest in the field of metallurgy for centuries. In this work, the effect of heat treatment on microstructure and key mechanical properties important for turbine rotor design has been investigated. Specifically, the tensile yield strength and crack growth resistance for a nickel-iron based superalloy 706 has been examined. Through a systematic study, a correlation was found between the processing parameters and the microstructure. Specifically, differences in grain boundary and grain interior precipitates were identified and correlated with processing conditions. Further, a strong relationship between microstructure and mechanical properties was identified. The type and orientation of grain boundary precipitates affect time-dependent crack propagation resistance, and the size and volume fraction of grain interior precipitates were correlated with tensile yield strength. It was also found that there is a strong environmental effect on time-dependent crack propagation resistance, and the sensitivity to environmental damage is microstructure dependent. Microstructures with η decorated grain boundaries were more resistant to environmental damage through oxygen embrittlement than microstructures with no η phase on the grain boundaries. An effort was made to explore the mechanisms of improving the time-dependent crack propagation resistance through thermo-mechanical processing, and several mechanisms were identified in both the environment-dependent and the environment-independent category. These mechanisms were ranked based on their contributions to crack propagation resistance.
Analysis of crack initiation and growth in the high level vibration test at Tadotsu
International Nuclear Information System (INIS)
Kassir, M.K.; Hofmayer, C.H.; Bandyopadhyay, K.K.
1991-01-01
A High Level Vibration Test (HLVT) Program was carried out recently on the seismic table at the Tadotsu Engineering Laboratory of Nuclear Power Engineering Center (NUPEC) in Japan. The objective of the study being performed at Brookhaven National Laboratory is to use the HLVT data to assess the accuracy and usefulness of existing methods for predicting crack initiation and growth under complex, large amplitude loading. The work to be performed as part of this effort involves: (1) analysis of the stress/strain distribution in the vicinity of the crack, including the potential for residual stresses due to the weld repair; (2) analysis of the number of load cycles required for crack initiation, including estimates of the impact of the weld repair on the crack initiation behavior; (3) analysis of crack advance as a function of applied loading (classic fatigue versus cyclic tearing) taking into account the variable amplitude loading and the possible influence of the repair; and (4) material property testing to supplement the work performed as part of the HLVT, providing the materials data necessary to perform the analysis efforts. A summary of research progress for FY 1990 is presented. 2 refs
International Nuclear Information System (INIS)
Sansoz, F.; Ghonem, H.
2003-01-01
This paper deals with crack tip/microstructure interactions at 520 deg. C in lamellar Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242) alloy under different fatigue loading frequencies. A series of heat treatments were performed in order to produce large colony microstructures that vary in their lamellar and colony size. Fatigue crack growth (FCG) experiments were conducted on these microstructures at loading frequencies of 10 and 0.05 Hz. The lower frequency was explored with and without imposing a 5 min hold-time at the peak stress level during each loading cycle. Results show that the crack growth behavior is sensitive to the loading frequency. For the same microstructure, the crack growth rate is found to be lower at 10 than at 0.05 Hz. The addition of a hold-time, however, did not alter the FCG rate indicating that creep strain during one loading cycle does not contribute significantly in the crack growth process. It is also shown that variations in lamella and colony size have no effects on the FCG rate except for the early stage of crack propagation. Scanning Electron Microscope examinations are performed on the fracture surface in order to identify the relevant crack growth mechanisms with respect to the loading frequency and the microstructure details. Quasi-cleavage of the α/β colonies along strong planar shear bands is shown to be a major mode of failure under all test condition. At a loading frequency of 10 Hz, the crack path proceeds arbitrary along planes either perpendicular or parallel to the long axis of α lamellae, while at 0.05 Hz, parallel-to-lamellae crack paths become favored. Corresponding differences of crack growth behavior are examined in terms of slip emission at the crack tip and interactions with the microstructure details
Crack growth from defects in tee intersections and nkzzles
International Nuclear Information System (INIS)
Burns, D.J.
The general objective of the research summarized in this report was to investigate the application of the continuous monitoring immersion technique to curved surfaces. In particular, experiments were carried out on pipe sections to assess the accuracy of the immersion technique for curved surfaces, followed by a design study of its application to monitoring defects in the crotch of tee pipe intersections. It was concluded that an immersion ultrasonic technique based on the measurement of echo amplitude can be used to monitor the growth of a sawcut in a pipe at 260 0 C, but more effort is needed in time-domain studies
International Nuclear Information System (INIS)
Marsh, D.; Green, D.; Parker, R.
1984-01-01
This paper reports the results of an experiment in which a severe thermal cycle comprising of alternate upshocks and downshocks has been applied to an axisymmetric feature with an internal, partial penetration weld and crevice. The direction of cracking and crack growth rate were observed experimentally and detailed records made of the thermal cycle. A second part to the paper, reported separately, compares a linear elastic fracture mechanics assessment of the cracking to the experimental observations
International Nuclear Information System (INIS)
Tice, D.R.; Stairmand, J.W.; Fairbrother, H.J.; Stock, A.
2007-01-01
Although austenitic stainless steels do not show a high degree of susceptibility to stress corrosion cracking (SCC) in PWR primary environments, there is limited evidence from laboratory testing that crack propagation may occur under some conditions for materials in a cold-worked condition. A test program is therefore underway to examine the factors influencing SCC propagation in good quality PWR primary coolant. Type 304 stainless steel was subjected to cold working by either rolling (at ambient or elevated temperature) or fatigue cycling, to produce a range of yield strengths. Compact tension specimens were fabricated from these materials and tested in simulated high temperature (250-300 o C) PWR primary coolant. It was observed that the degree of crack propagation was influenced by the degree of cold work, the crack growth orientation relative to the rolling direction and the method of working. (author)
Micromechanisms of Crack Growth in Ceramics and Glasses in Corrosive Environments.
1980-05-01
Resistance Mecanique du Verre et les Moyens de l’Amelioree, Union Scientifique Continentale du Verre , Charleroix, Belgium, (1962). 8. B. A. Proctor, I...exhibit similar types of delayed failure curves. Failure occurs most rapidly at high loads. Below a critical value of the load known as the stress...fracture for the three types of materials differ greatly. Polymers and metals have plastic zones at their crack tips, so that stress corrosion
Technical report on the fatigue crack Growth Benchmark based on CEA pipe bending tests
International Nuclear Information System (INIS)
2001-07-01
In order to improve the estimation methods of surface crack propagation through the thickness of components, CEA has proposed a benchmark to members of the IAGE WG, sub-group on Integrity of metal components and structures. The subject is a simple configuration of a pipe containing an axisymmetric notch and submitted to a cyclic bending load. An experimental data-set form CEA was used to validate three issues in the topic of Leak Before Break. - Crack initiation, - Crack propagation through the thickness, - Crack penetration. All material and geometrical data which are necessary for the simulation were given in the proposal, including experimental results. Due to the peculiar complexity of the problem, it was decided to focus the work on methodologies comparison so as to allow participants to tune up parameters and adjust their models and tools. This report presents all estimations performed by the participants and collected by CEA. They are compared to the experimental results. An analysis of the used procedures is also proposed. This, associated with the study of the accuracy of different methodologies, leads to comments and recommendations on the analysis of fatigue crack growth. The participation in the first step was important: nine participants have proposed analyses, sometimes parametric analysis to estimate crack growth. Results sorted out three estimation methods groups that give results in accordance with experimental ones (these three groups are based on a strain range evaluation and the fatigue curve of the material): - The use of an elastic stress at the notch tip and a fatigue notch concentration factor to determine the strain range. - The use of a KI (or elastic F.E. calculation) and a Neuber rule for the estimation of the strain range at a characteristic distance from the crack tip. - The direct calculation of the strain range at the characteristic distance by an elastic plastic F.E. calculation. Only 4 participants have proposed an estimate of the
Ductile crack growth resistance of PWR components. Application for structural integrity assessment
International Nuclear Information System (INIS)
Bethmont, M.; Eripret, C.; Le Delliou, P.; Frund, J.M.
1995-01-01
Structural integrity assessment of PWR components, as pressure vessel and piping, needs to evaluate the ductile crack growth resistance which is generally characterized by J resistance curves (or J-R curves) based on the path-independent J Integral. These curves are more often obtained from laboratory tests with small specimens as CT-specimens and their application to large component safety analysis could be questionable Indeed, it is well known that J-R curves could depend on the specimen size and on the loading mode (i.e. bending stress versus tensile stress) but this dependency could be different from one material to another. This means that it would depend not only on the stress-strain state but also on the actual local fracture mechanisms (i. e. the damage) occurring before the crack initiation or during the crack propagation. The purpose of this paper is to gather some results of crack growth resistance measurement studied at EDF with different materials in order to show how the effect of the parameters, as specimen geometry and mode of loading, is directly related to the local fracture mechanisms or the microstructure of the materials. For that a number of results are analysed by means of the local approach of fracture which is a very useful tool to predict quantitatively the J-R curve dependency, related to fracture mechanisms (authors). 12 refs., 9 figs
Effect of heat treatment upon the fatigue-crack growth behavior of Alloy 718 weldments
International Nuclear Information System (INIS)
Mills, W.J.; James, L.A.
1981-05-01
The microstructural features that influenced the room and elevated temperature fatigue-crack growth behavior of as-welded, conventional heat-treated, and modified heat-treated Alloy 718 GTA weldments were studied. Electron fractographic examination of fatigue fracture surfaces revealed that operative fatigue mechanisms were dependent on microstructure, temperatures and stress intensity factor. All specimens exhibited three basic fracture surface appearances at temperatures up to 538 degrees C: crystallographic faceting at low stress intensity range (ΔK) levels, striation, formation at intermediate values, and dimples coupled with striations in the highest (ΔK) regime. At 649 degrees C, the heat-treated welds exhibited extensive intergranular cracking. Laves and δ particles in the conventional heat-treated material nucleated microvoids ahead of the advancing crack front and caused on overall acceleration in crack growth rates at intermediate and high ΔK levels. The modified heat treatment removed many of these particles from the weld zone, thereby improving its fatigue resistance. The dramatically improved fatigue properties exhibited by the as-welded material was attributed to compressive residual stresses introduced by the welding process. 19 refs., 16 figs
Rovinelli, Andrea; Sangid, Michael D.; Proudhon, Henry; Guilhem, Yoann; Lebensohn, Ricardo A.; Ludwig, Wolfgang
2018-06-01
Small crack propagation accounts for most of the fatigue life of engineering structures subject to high cycle fatigue loading conditions. Determining the fatigue crack growth rate of small cracks propagating into polycrystalline engineering alloys is critical to improving fatigue life predictions, thus lowering cost and increasing safety. In this work, cycle-by-cycle data of a small crack propagating in a beta metastable titanium alloy is available via phase and diffraction contrast tomography. Crystal plasticity simulations are used to supplement experimental data regarding the micromechanical fields ahead of the crack tip. Experimental and numerical results are combined into a multimodal dataset and sampled utilizing a non-local data mining procedure. Furthermore, to capture the propensity of body-centered cubic metals to deform according to the pencil-glide model, a non-local driving force is postulated. The proposed driving force serves as the basis to construct a data-driven probabilistic crack propagation framework using Bayesian networks as building blocks. The spatial correlation between the postulated driving force and experimental observations is obtained by analyzing the results of the proposed framework. Results show that the above correlation increases proportionally to the distance from the crack front until the edge of the plastic zone. Moreover, the predictions of the propagation framework show good agreement with experimental observations. Finally, we studied the interaction of a small crack with grain boundaries (GBs) utilizing various slip transmission criteria, revealing the tendency of a crack to cross a GB by propagating along the slip directions minimizing the residual Burgers vector within the GB.
International Nuclear Information System (INIS)
Tomkins, B.
1989-01-01
The formation and development of the International Cooperative Group on Cyclic Crack Growth Rate (ICCGR) is outlined. By 1976, it had become apparent that the number of variables that affected the cyclic crack growth rate in reactor water was large and that the rate of data generation was very slow, because it was the low frequency regime that was of major practical importance. A clear need was recognised for a forum to exchange ideas and data, but most important of all to explore collaborative testing to minimise duplication and achieve economies. It was from the outset recognised as a complex and therefore very expensive materials testing area. In response to this situation, it was agreed to set up a group which was formally chartered as the ICCGR in 1978. What had begun as a sharing of views rapidly became an active collaborative group concerned to resolve three issues: 1. development of a consistent method for data reduction; 2. the practice of consistent testing methods; 3. a physical understanding of the underlying mechanisms involved in the process. Three Task Groups were eventually formed to address these issues; Test Methods, Mechanisms, Data Collection and Evaluation. (author)
Mills, Thomas Brian
1997-11-01
Exfoliation corrosion is a potentially severe form of corrosion that frequently affects high-strength aluminum, particularly 2xxx- and 7xxx-series alloys. Exfoliation degrades components such as sheets, plates, and extrusions that have highly elongated grain structures. Few attempts have been made to investigate the effects of this form of corrosion on the fatigue performance of these materials, so a preliminary study was conducted to determine the effects of exfoliation corrosion on the fatigue response of quarter-inch 7075-T651 aluminum alloy plate. This was accomplished by subjecting aluminum panels to an ASTM standard corrosive solution known as EXCO then fatiguing the panels in corrosion fatigue environments of dry air, humid air, and artificial acid rain. Statistical analyses of the fatigue crack growth data suggest that prior-corrosion and corrosion fatigue are competing mechanisms that both have the potential of accelerating crack growth rates. In the dry air cases, exfoliation accelerated crack growth rates a maximum of 4.75 times over the uncorroded material at lower stress intensities such as 5 ksi surdinch. This accelerated behavior dropped off rapidly, however, and was nonexistent at higher stress intensities. Humid air increased crack velocities considerably as compared to the dry air uncorroded case, but the addition of exfoliation corrosion to the humid cases did not have a significant effect on crack growth behavior. On the other hand, specimens containing exfoliation corrosion and then exposed to artificial acid rain had significantly higher crack growth rates than their uncorroded counterparts. Finally, fractographic examinations of the specimens revealed evidence of lower energy, quasi-cleavage fracture persisting near to the exfoliated edge of specimens tested in the dry air, humid air, and artificial acid rain environments. The implications of this research are that prior-corrosion damage has the ability to significantly increase crack growth
International Nuclear Information System (INIS)
Kwon, H.S.; Wuensche, A.; Macdonald, D.D.
2000-01-01
Intergranular stress corrosion cracking (IGSCC) in weld-sensitized, Type 304 (UNS S30400) (1) stainless steel (SS) remains a major threat to the integrity of heat transport circuits (HTC) in boiling water reactors (BWR), in spite of extensive research over the last 30 years. Effects of flow rate on intergranular crack growth in sensitized Type 304 stainless steel (UNS S30400) in distilled water containing 15 ppm or 25 ppm (2.59 x 10 -4 or 4.31 x 10 -4 m) sodium chloride (NaCl) at 250 C were examined using compact tension (CT) specimens under constant loading conditions. On increasing the flow rate, the crack growth rate (CGR) drastically increased, but later decreased to a level that was lower than the initial value. The initial increase in CGR was attributed to an enhanced rate of mass transfer of oxygen to the external surface, where it consumed the current emanating from the crack mouth. However, the subsequent decrease in CGR was attributed to crack flushing, which is a delayed process because of the time required to destroy the aggressive conditions that exist within the crack. Once flushing destroyed the aggressive crack environment, CGR decreased with increasing flow rate. The time over which CGR increased after an increase in the flow rate depended on how fast crack flushing occurred by fluid flow; the higher the flow rate and the greater the crack opening, the faster the crack flushing and the shorter the transition time. Finally, intergranular cracks propagated faster in regions nearer both sides of the Ct specimens, where the oxygen supply to the external surface was enhanced under stirring conditions and where minimal resistance existed to current flow from the crack tip to the external surfaces. This observation provided evidence that the crack's internal and external environments were coupled electrochemically
Directory of Open Access Journals (Sweden)
Ivo Černý
2009-11-01
Full Text Available Results of an investigation of effect of shot peening on development of physically short fatigue crack in an aircraft V-95 Al-alloy, which is of a similar type as 7075 alloy, are described and discussed in the paper. The first part deals with adaptation and verification of direct current potential drop method for detection and measurement of short crack initiation and growth. The specific material and quite large dimensions of flat specimens with side necking of a low stress concentration factor had to be considered when position of electrodes was specified and the measurement method verified. The specimen type and dimensions were proposed taking account of the investigation of shot peening effects. Physically short fatigue cracks of the length from 0.2 mm to more than 3 mm, most of them between 0.8 – 1.5 mm, were prepared under high cycle fatigue loading of a constant nominal stress amplitude plus/minus 160 MPa. Specimens with existing short fatigue cracks were shot peened using two different groups of parameters. Development of crack growth after shot peening was measured and compared with crack growth in specimens without shot peening. Retardation of crack growth was significant particularly with cracks shorter than 2 mm. For the specific stress amplitude, evaluated results enable to estimate threshold length of defects, which after the application of shot peening will be reliably arrested.
Jeevan Kumar, N.; Ramesh Babu, P.
2018-04-01
This paper presents the numerical study of the mode I and mode II interlaminar crack growth arrest in hybrid laminated curved composite stiffened joint with Z-fibre reinforcement. A FE model of hybrid laminated skin-stiffener joint reinforced with Z-pins is developed to investigate the effect of Z- fibre pins on mode I and mode II crack growth where the delamination is embedded inbetween the skin and stiffener interface. A finite element model was developed using S4R element of a 4-node doubly curved thick shell elements to model the composite laminates and non linear interface elements to simulate the reinforcements. The numerical analyses revealed that Z-fibre pinning were effective in suppressing the delamination growth when propagated due to applied loads. Therefore, the Z-fibre technique effectively improves the crack growth resistance and hence arrests or delays crack growth extension.
Fatigue Crack Growth Behavior of 2099-T83 Extrusions in two Different Environments
Goma, Franck Armel Tchitembo; Larouche, Daniel; Bois-Brochu, Alexandre; Blais, Carls; Boselli, Julien; Brochu, Mathieu
Aluminum-lithium alloy 2099-T83 is an advanced material with superior mechanical properties, as compared to traditional alloys used in structural applications, and has been selected for use in the latest generation of airplanes. While this alloy exhibits improved fatigue crack growth (FCG) performance over non-Li alloys, it is of interest to simulate the impact of fluctuating loads under variable temperature during airplane service, particularly in terms of the potential effects of material processing history. In the present paper, the FCG behavior in an Integrally Stiffened Panel (ISP) has been investigated both at room temperature and at 243 K. It has been shown that the resistance to crack growth in a cold environment was higher than in ambient laboratory air. Results of this investigation are discussed from the microfractographic point of view, with regard to the variation of the local extrusion aspect ratio, a parameter which correlates with both the crystallographic texture and the grain structure.
A Review of Fatigue Crack Growth for Pipeline Steels Exposed to Hydrogen.
Nanninga, N; Slifka, A; Levy, Y; White, C
2010-01-01
Hydrogen pipeline systems offer an economical means of storing and transporting energy in the form of hydrogen gas. Pipelines can be used to transport hydrogen that has been generated at solar and wind farms to and from salt cavern storage locations. In addition, pipeline transportation systems will be essential before widespread hydrogen fuel cell vehicle technology becomes a reality. Since hydrogen pipeline use is expected to grow, the mechanical integrity of these pipelines will need to be validated under the presence of pressurized hydrogen. This paper focuses on a review of the fatigue crack growth response of pipeline steels when exposed to gaseous hydrogen environments. Because of defect-tolerant design principles in pipeline structures, it is essential that designers consider hydrogen-assisted fatigue crack growth behavior in these applications.
Effect of chloride contamination in MON-1 propellant on crack growth properties of metals
Moran, C. M.; Toth, L. R.
1981-01-01
The effect of a high level of chloride content (800 ppm) in MON-1 propellant on the crack growth properties of seven materials was investigated. Sustained load tests were conducted at 49 C (120 F) temperature with thin gauge tensile specimens having a semi-elliptical surface flaw. Alloys included aluminum 1100, 3003, 5086 and 6061; corrosion resistant steel types A286 and 347; and titanium 6Al-4V. The configurations tested with precracked flaws exposed to MON-1 were: parent or base metal, center weld, and heat affected zone. It was concluded that this chloride level in MON-1 does not affect the stress corrosion, crack growth properties of these alloys after 1000 hour exposure duration under high stresses.
Thermal fatigue crack growth in mixing tees nuclear piping - An analytical approach
International Nuclear Information System (INIS)
Radu, V.
2009-01-01
The assessment of fatigue crack growth due to cyclic thermal loads arising from turbulent mixing presents significant challenges, principally due to the difficulty of establishing the actual loading spectrum. So-called sinusoidal methods represent a simplified approach in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface. The need for multiple calculations in this process has lead to the development of analytical solutions for thermal stresses in a pipe subject to sinusoidal thermal loading, described in previous work performed at JRC IE Petten, The Netherlands, during the author's stage as seconded national expert. Based on these stress distributions solutions, the paper presents a methodology for assessment of thermal fatigue crack growth life in mixing tees nuclear piping. (author)
The effect of environment on the creep crack growth behavior of several structural alloys
International Nuclear Information System (INIS)
Sadananda, K.; Shahinian, P.
1980-01-01
The creep crack growth behaviors of alloy 718, Inconel X-750, Udimet 700 and cold-worked type 304 and annealed and cold-worked type 316 austenitic stainless steels were determined in vacuum at elevated temperatures and the results were compared with those previously obtained in air. Alloy 718 and Inconel X-750 were found to be significantly sensitive to air with crack growth rates one to two orders of magnitude greater than those in vacuum. Udimet 700 is less sensitive to the environment and it is more sensitive to small changes in microstructure than to the environment per se. The austenitic stainless steels are least sensitive of all. Since the environmental sensitivity varies significantly for different materials, the service environment should be considered in the selection of materials for high temperature components. (Auth.)
Effect of a new specimen size on fatigue crack growth behavior in thick-walled pressure vessels
International Nuclear Information System (INIS)
Shariati, Mahmoud; Mohammadi, Ehsan; Masoudi Nejad, Reza
2017-01-01
Fatigue crack growth in thick-walled pressure vessels is an important factor affecting their fracture. Predicting the path of fatigue crack growth in a pressure vessel is the main issue discussed in fracture mechanics. The objective of this paper is to design a new geometrical specimen in fatigue to define the behavior of semi-elliptical crack growth in thick-walled pressure vessels. In the present work, the importance of the behavior of fatigue crack in test specimen and real conditions in thick-walled pressure vessels is investigated. The results of fatigue loading on the new specimen are compared with the results of fatigue loading in a cylindrical pressure vessel and a standard specimen. Numerical and experimental methods are used to investigate the behavior of fatigue crack growth in the new specimen. For this purpose, a three-dimensional boundary element method is used for fatigue crack growth under stress field. The modified Paris model is used to estimate fatigue crack growth rates. In order to verify the numerical results, fatigue test is carried out on a couple of specimens with a new geometry made of ck45. A comparison between experimental and numerical results has shown good agreement. - Highlights: • This paper provides a new specimen to define the behavior of fatigue crack growth. • We estimate the behavior of fatigue crack growth in specimen and pressure vessel. • A 3D finite element model has been applied to estimate the fatigue life. • We compare the results of fatigue loading for cylindrical vessel and specimens. • Comparison between experimental and numerical results has shown a good agreement.
Stress Intensity Factors for Cracked Metallic Structures Under Rapid Thermal Loading
1987-10-01
solution algorithm was developed based on the influence function method, and numerical results were generated to show the variation of K with flaw size and...numerical algorithms developed can be executed on a desktop microcomputer illustrating the efficient and powerful characteristic of the influence function method... Function Method 3-6 Superposition and Crack Face Loading Equivalence 3-7 Influence Function Generation 3-10 Influence Functions For Two Cracked Body
International Nuclear Information System (INIS)
Brickstad, B.
1984-01-01
Predictions of crack arrest behaviour are performed for a cracked reactor pressure vessel under both thermal and pressure loading. The object is to compare static and dynamic calculations. The dynamic calculations are made using an explicit finite element technique where crack growth is simulated by gradual nodal release. Three different load cases and the effect of different velocity dependence on the crack propagation toughness are studied. It is found that for the analysed cases the static analysis is slightly conservative, thus justifying its use for these problems. (orig.)
On the Importance of Aging to the Crack Growth Resistance of Human Enamel
Yahyazadehfar, Mobin; Zhang, Dongsheng; Arola, Dwayne
2015-01-01
With improvements in oral health and an overall increase in quality of life, the percentage of fully or largely dentate seniors is increasing. Understanding the effects of aging on the mechanical properties of teeth is essential to the maintenance of lifelong oral health. In this investigation the effects of aging on the fracture toughness of human enamel were evaluated from incremental crack growth experiments performed on tissue of donor teeth representing ?young? (17? age ? 25) and ?old? (...
Sensitivity Analysis of Fatigue Crack Growth Model for API Steels in Gaseous Hydrogen.
Amaro, Robert L; Rustagi, Neha; Drexler, Elizabeth S; Slifka, Andrew J
2014-01-01
A model to predict fatigue crack growth of API pipeline steels in high pressure gaseous hydrogen has been developed and is presented elsewhere. The model currently has several parameters that must be calibrated for each pipeline steel of interest. This work provides a sensitivity analysis of the model parameters in order to provide (a) insight to the underlying mathematical and mechanistic aspects of the model, and (b) guidance for model calibration of other API steels.
Fatigue and fatigue crack growth properties of 316LN and Incoloy 908 below 10 K
International Nuclear Information System (INIS)
Nyilas, A.; Zhang, J.; Obst, B.; Ulbricht, A.
1992-01-01
The cyclic loading characteristics of Tokamak type thermonuclear machines demand study of the fatigue response of the materials used in critical components. The large superconducting magnets and their superconductors will operate under cyclic mechanical stress conditions. The present paper is biased towards the current superconductor design of the NET (Next European Torus) model coil concept. The superconductor of this coil will be a cable-in-conduit Nb 3 Sn type with an enveloped stiff external jacket structure. The wall thickness of the jacket structure is within the range of 4-5 mm. The manufacturing of the jacket lengths for several hundred meters require an appropriate joining process due to the prefabricated section pieces available only in short lengths of 5-7 meters. The recently anticipated solution favors the flash butt welding technique. The performance of the superconductors jacket will depend on the material selection and the proper structural design according to the existing low temperature structural materials data base. The wind and react Nb 3 Sn-manufacturing process must also account the materials properties after ageing. A program was set up to elucidate the fatigue-life behavior and fatigue crack growth rate (FCGR) of the selected two candidate materials. These materials were the AISI 316LN with a specified low carbon content to avoid the embrittlement after the ageing process and the Incoloy 908. The 316LN material in the as received condition was tested with respect to its fatigue-life for specimens bearing predefined flaws and cracks. The propagation of surface cracks at 12 K and at 295 K was characterized with non standard specimens. The tests were performed in a cryogenic dynamic test facility under helium gas environment between 7 K and 20 K. Using the reference growth laws obtained from these measurements the total crack propagation starting with the initial crack length of the specimen could be predicted by numerical computation
Fatigue crack growth threshold of austenitic stainless steels in simulated PWR primary water
International Nuclear Information System (INIS)
Tsutsumi, Kazuya; Yamamoto, Kenji; Nitta, Yoshikazu
2007-01-01
Many studies have revealed that fatigue crack growth (FCG) rate of austenitic stainless steels is accelerated in light water reactor environment compared to that in air at room temperature. Major driving factors in the acceleration of FCG rate are stress ratio, temperature and stress rise time. Based on this knowledge, FCG curves have been developed considering these factors as parameters. However, there are few data of FCG threshold ΔK th in light water reactor environment. Hence it is necessary to clarify FCG rate under near-threshold condition for more accurate evaluation of fatigue crack growth behavior under cyclic stress with relatively low ΔK. In the present study, therefore, ΔK th was determined for austenitic stainless steels in simulated PWR primary water, and FCG behavior under near-threshold condition was revealed by collecting fatigue crack propagation data. The results are summarized as follows: No propagation of fatigue crack was found in high temperature water, and there was a definite ΔK th . Average ΔK eff,th was 4.3 MPa·m 0.5 at 325degC, 3.3 MPa·m 0.5 at 100degC, and there was no considerable reduction compared to currently known ΔK eff,th in air. Thus, it was revealed tha ambient conditions had minimal effect, on ΔK eff,th , ΔK th increases with increasing temperature and decreasing frequency. As a result of fracture surface observation, oxide-induced-crack-closure was considered to be a cause of the dependency described above. In addition, it was suggested that changes in material properties also had influence on ΔK th, since ΔK eff,th itself increased at elevated temperature. (author)
Shishvan, Siamak Soleymani; Van der Giessen, Erik
Analyses of monotonic loading of a plane-strain mode I crack in an fcc single crystal under small-scale yielding are carried out using discrete dislocation plasticity (DDP) incorporating anisotropic elasticity. Two crystallographically symmetric crack orientations are considered where plane-strain
International Nuclear Information System (INIS)
Wang, L.H.; Hsu, T.Y.; Huang, C.S.
2000-01-01
Increasing pH of reactor water to mildly alkaline is considered as one of the mitigating water chemistry strategies to reduce the activity release of radioactive oxides and suppress the growth rate of stress corrosion cracking. However, only limited experimental data are currently available in the published literature, it is imperative to perform additional tests to verify the effectiveness of slightly alkaline reactor water. Because the electrochemical behavior and SCC are intricately related, this study will attempt to investigates the electrochemical properties and measures the crack growth rates (CGRs) of type 304 stainless steel (SS) in both normal water chemistry (200 ppb O 2 , neutral pH 25 ) and alkaline chemistry (200 ppb O 2 , pH 25 = 8.0). The additive for pH control is potassium hydroxide (KOH). The crack growth rate was monitored by reversing DC potential drop technique. The electrochemical measurements include AC impedance measurement and potential pulsing test to measure the repassivation behavior. The characteristics of electrochemical properties and its effect on stress corrosion crocking in BWR alkaline environments have been further examined. (author)
Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading
Forman, R. G.; Zanganeh, M.
2014-01-01
This paper describes the results of a research program conducted to improve the understanding of fatigue crack growth rate behavior in the threshold growth rate region and to answer a question on the validity of threshold region test data. The validity question relates to the view held by some experimentalists that using the ASTM load shedding test method does not produce valid threshold test results and material properties. The question involves the fanning behavior observed in threshold region of da/dN plots for some materials in which the low R-ratio data fans out from the high R-ratio data. This fanning behavior or elevation of threshold values in the low R-ratio tests is generally assumed to be caused by an increase in crack closure in the low R-ratio tests. Also, the increase in crack closure is assumed by some experimentalists to result from using the ASTM load shedding test procedure. The belief is that this procedure induces load history effects which cause remote closure from plasticity and/or roughness changes in the surface morphology. However, experimental studies performed by the authors have shown that the increase in crack closure is a result of extensive crack tip bifurcations that can occur in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the fanning behavior which occurs in aluminum alloys is a function of intrinsic dislocation property of the alloy, and therefore, the fanned data does represent the true threshold properties of the material. However, for the corrosion sensitive steel alloys tested in laboratory air, the occurrence of fanning results from fretting corrosion at the crack tips, and these results should not be considered to be representative of valid threshold properties because the fanning is
Newman, John A.; Smith, Stephen W.; Seshadri, Banavara R.; James, Mark A.; Brazill, Richard L.; Schultz, Robert W.; Donald, J. Keith; Blair, Amy
2015-01-01
An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.
Deterministic estimation of crack growth rates in steels in LWR coolant environments
International Nuclear Information System (INIS)
Macdonald, D.D.; Lu, P.C.; Urquidi-Macdonald, M.
1995-01-01
In this paper, the authors extend the coupled environment fracture model (CEFM) for intergranular stress corrosion cracking (IGSCC) of sensitized Type 304SS in light water reactor heat transport circuits by incorporating steel corrosion, the oxidation of hydrogen, and the reduction of hydrogen peroxide, in addition to the reduction of oxygen (as in the original CEFM), as charge transfer reactions occurring on the external surfaces. Additionally, the authors have incorporated a theoretical approach for estimating the crack tip strain rate, and the authors have included a void nucleation model to account for ductile failure at very negative potentials. The key concept of the CEFM is that coupling between the internal and external environments, and the need to conserve charge, are the physical and mathematical constraints that determine the rate of crack advance. The model provides rational explanations for the effects of oxygen, hydrogen peroxide, hydrogen, conductivity, stress intensity, and flow velocity on the rate of crack growth in sensitized Type 304 in simulated LWR in-vessel environments. They propose that the CEFM can serve as the basis of a deterministic method for estimating component life times
International Nuclear Information System (INIS)
Jones, D.P.; Hoppe, R.G.; James, B.A.
1993-01-01
A series of fatigue crack growth rate tests was conducted in order to study effects of negative stress ratio on fatigue crack growth rate of low-alloy steel in air. Four-point bend specimens were used to simulate linear stress distributions typical of pressure vessel applications. This type of testing adds to knowledge on negative stress ratio effects for low-alloy steels obtained in the past from uniform tension-compression tests. Applied bending stress range was varied over twice the yield strength. Load control was used for tests for which the stress range was less than twice the yield strength and deflection control was used for the higher stress range tests. Crack geometries were both short and long fatigue cracks started at notches and tight fatigue cracks for which crack closure could occur over the full crack face. Results are presented in terms of the stress intensity factor ratio R = K MIN /K MAX . The negative R-ratio test results were correlated to an equation of the form da/dN = C[ΔK/(A-R)] n , where A, C, and n are curve fitting parameters. It was found that effects of negative R-ratio on fatigue crack growth rates for even the high stress range tests could be bounded by correlating the above equation to only positive R-ratio test results and extending the resulting equation into the negative R-ratio regime
National Research Council Canada - National Science Library
Chan, Kwai
2004-01-01
... of aerospace structural alloys. In this three-year program, physics-based fatigue crack initiation and growth models were developed and integrated into a probabilistic micromechanical code for treating fatigue life variability...
International Nuclear Information System (INIS)
Yoo, Yeon-Sik
2003-11-01
This study clarified the effect of a membrane and a through-wall bending stresses on fatigue crack growth behavior and coolant leakage velocity due to irregularity of crack surface. Each stress component relates to fatigue crack growth behavior directly in general and thus the wild-used K I solutions are anticipated to give good evaluation results on it. Meanwhile, it is necessary to notify that surface irregularity for coolant leakage assessment is made by stress history in nature. Surface irregularity is known to be largely classified into the following two aspects: surface roughness due to continuous crack opening and closure behavior and surface turnover due to cyclic bending stress dominance. Therefore, the deterministic parameters on resistance of coolant leakage by surface irregularity are considered to be not only stress history but crack opening behavior. (author)
On the importance of aging to the crack growth resistance of human enamel.
Yahyazadehfar, Mobin; Zhang, Dongsheng; Arola, Dwayne
2016-03-01
With improvements in oral health and an overall increase in quality of life, the percentage of fully or largely dentate seniors is increasing. Understanding the effects of aging on the mechanical properties of teeth is essential to the maintenance of lifelong oral health. In this investigation the effects of aging on the fracture toughness of human enamel were evaluated from incremental crack growth experiments performed on tissue of donor teeth representing "young" (17 ⩽ age ⩽ 25) and "old" (age ⩾ 55) age groups. Results showed that the old enamel exhibited significantly lower resistance to fracture than that of the young tissue in two orthogonal directions of crack growth. For crack growth transverse to the enamel rods, the fracture toughness of the old enamel (0.37 ± 0.15 MPa m(0.5)) was nearly 70% lower than that of tissue from the young teeth (1.23 ± 0.20 MPa m(0.5)). Based on results from a mechanistic analysis of crack growth, the reduction in fracture resistance is attributed to a decrease in the degree of extrinsic toughening. The practice of restorative dentistry should account for these changes in tooth tissues in the treatment of senior patients. The mechanical behavior of enamel has been studied for over 3 decades. Due to the limited volume of tissue available for evaluation, past work has been largely based on indentation methods. In this investigation we have evaluated the resistance to fracture of human enamel using a conventional fracture mechanics approach and incremental crack growth. We compared the fracture resistance of cuspal enamel obtained from the teeth of representative "young" and "old" donor groups. Our results show that there is a substantial reduction in the resistance to fracture with age, that it is anisotropic, and that the degradation is more severe than that which occurs to dentin. As such, we feel this work is a significant contribution to the field. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All
Organisational Factors of Rapid Growth of Slovenian Dynamic Enterprises
Directory of Open Access Journals (Sweden)
Pšeničny Viljem
2013-01-01
Full Text Available The authors provide key findings on the internal and external environmental factors of growth that affect the rapid growth of dynamic enterprises in relation to individual key organisational factors or functions. The key organisational relationships in a growing enterprise are upgraded with previous research findings and identified key factors of rapid growth through qualitative and quantitative analysis based on the analysis of 4,511 dynamic Slovenian enterprises exhibiting growth potential. More than 250 descriptive attributes of a sample of firms from 2011 were also used for further qualitative analysis and verification of key growth factors. On the basis of the sample (the study was conducted with 131 Slovenian dynamic enterprises, the authors verify whether these factors are the same as the factors that were studied in previous researches. They also provide empirical findings on rapid growth factors in relation to individual organisational functions: administration - management - implementation (entrepreneur - manager - employees. Through factor analysis they look for the correlation strength between individual variables (attributes that best describe each factor of rapid growth and that relate to the aforementioned organisational functions in dynamic enterprises. The research findings on rapid growth factors offer companies the opportunity to consider these factors during the planning and implementation phases of their business, to choose appropriate instruments for the transition from a small fast growing firm to a professionally managed growing company, to stimulate growth and to choose an appropriate growth strategy and organisational factors in order to remain, or become, dynamic enterprises that can further contribute to the preservation, growth and development of the Slovenian economy
Fatigue crack growth behavior of a new single crystal nickel-based superalloy (CMSX-4) at 650 C
International Nuclear Information System (INIS)
Sengupta, A.; Putatunda, S.K.
1994-01-01
CMSX-4 is a recently developed rhenium containing single crystal nickel-based superalloy. This alloy has potential applications in many critical high-temperature applications such as turbine blades, rotors, nuclear reactors, etc. The fatigue crack growth rate and the fatigue threshold data of this material is extremely important for accurate life prediction, as well as failure safe design, at elevated temperatures. In this paper, the fatigue crack growth behavior of CMSX-4 has been studied at 650 C. The investigation also examined the influence of γ' precipitates (size and distribution) on the near-threshold fatigue crack growth rate and the fatigue threshold. The influence of load ratio on the fatigue crack growth rate and the fatigue threshold was also examined. Detailed fractographic studies were carried out to determine the crack growth mechanism in fatigue in the threshold region. Compact tension specimens were prepared from the single crystal nickel-based superalloy CMSX-4 with [001] orientation as the tensile loading axis direction. These specimens were given three different heat treatments to produce three different γ' precipitate sizes and distributions. Fatigue crack growth behavior of these specimens was studied at 650 C in air. The results of the present investigation indicate that the near-threshold fatigue crack growth rate decreases and that the fatigue threshold increases with an increase in the γ' precipitate size at 650 C. The fatigue threshold decreased linearly with an increase in load ratio. Fractographs at 650 C show a stage 2 type of crack growth along {100} type of crystal planes in the threshold region, and along {111} type of crystal planes in the high ΔK region
Application of stable crack growth in fracture assessment of defects in ductile materials
International Nuclear Information System (INIS)
Dillstroem, Peter
2009-06-01
This report goes through the use of methods/standards, which consider stable (J-controlled) crack growth. We have demonstrated the following: - ASME XI, App. C, App. H, which deals with analysis of stainless steel and ferritic piping, take account of stable growth. In App. C, this corresponds to the inclusion of stable growth up to Δa ∼ 10 mm. - R6-method, BS 7910:1999 and ASME XI, Code Case N-494, contains an established formalism to take account of stable growth. A prerequisite is that you have access to relevant and authentic material data in the form of fracture resistance K k /J k and J r curves. - All of the above methods/standards are applicable in the nuclear context. We reported also that required to produce relevant and valid data (fracture resistance K k /J k and J r curves) to be used for the analysis of stable growth. This report does not specify how much stable crack that can be counted at a Safety Assessment
World pipeline work set for rapid growth
International Nuclear Information System (INIS)
Anon.
1992-01-01
This paper reports on international pipeline construction which has entered a fast-growth period, accelerated by the new political and economic realities around the world and increasing demand for natural gas, crude oil and refined petroleum products. Many projects are under way or in planning for completion in the mid- to late 1990s in Europe, South America, Asia and the Middle East. Pipeline And Gas Journal's projection calls for construction or other work on 30,700 miles of new natural gas, crude oil and refined products pipelines in the 1992-93 period outside Canada and the U.S. These projects will cost an estimated $30 billion-plus. Natural gas pipelines will comprise most of the mileage, accounting for almost 23,000 miles at an estimated cost of $26.3 billion. Products pipelines, planned or under construction, will add another 5,800 miles at a cost of $2.8 billion. Crude oil pipelines, at a minimum, will total 1,900 new miles at a cost of slightly under $1 billion
International Nuclear Information System (INIS)
Troshchenko, V.T.; Pokrovskij, V.V.; Yarusevich, V.L.; Mikhajlov, V.I.; Sher, V.A.
1990-01-01
Resistance to fatigue crack growth (FCG) has been studied in welded joints of structural titanium alloys contaminated by embrittling impurities. Besides, effect of crack closing has been taken into account what makes it possible to determine the effective coefficient of the stress intensity. The rate of fatigue crack growth is proved to considerably depend on the value and direction of residual stresses. The rate dependence of FCG in welded joints of structural titanium alloys on the swing of effective coefficient of stress intensity is invariant to the value and direction of weld residual stresses
Evaluation of neutron irradiation effect on SCC crack growth behaviour of austenitic stainless steel
Energy Technology Data Exchange (ETDEWEB)
NONE
2012-08-15
Austenitic stainless steels are widely used as structural materials alloy in reactor pressure vessel internal components because of their high strength, ductility and fracture toughness. However, exposure due to neutron irradiation results in changes in microstructure, mechanical properties and microchemistry of the material. Irradiation assisted stress corrosion cracking (IASCC) caused by the effect of neutron irradiation during long term operation in high temperature water environments in nuclear power plants is considered to take the form of intergranular stress corrosion cracking (IGSCC) and the critical fluence level has been reported to be about 5x10{sup 24}n/m{sup 2} (E>1MeV) for Type 304 SS in BWR environment. JNES had been conducting IASCC project during from JFY 2000 to JFY 2008, and prepared an engineering database on IASCC. However, the data of crack growth rate (CGR) below the critical fluence level are not sufficient. Therefore, evaluation of neutron irradiation effect project (ENI) was initiated to obtain the CGR data below the critical fluence level, and prepare the SCC growth rate diagram for life time evaluation of core shroud. Test specimens have been irradiated in the OECD/Halden reactor, and the post irradiation experiments (PIE) have been conducting during from JFY 2011 to JFY 2013, finally the modified IASCC guide will be prepared in JFY 2013. (author)
Fatigue crack growth rate of API X70 steel pipelines under spectrum loading
International Nuclear Information System (INIS)
Beden, S.M.; Abdullah, S.; Ariffin, A.K.
2012-01-01
Pipelines offer the most efficient way to transport bulk quantities of gas and oil, either from points of production to storage locations or from storage locations to distributed points of end use. As one of the main materials of west–east gas transmission pipes, X70 pipelines usually serve under variable amplitude loading (VAL). Base on the importance of in-service API X70 pipelines, it is important for the safe operation of this system to know its behaviour under VAL. This paper focuses on the ability of using the NASGRO model to predict the fatigue crack growth (FCG), based on investigation with the modified Wheeler model and experimental data. The results show that the NASGRO model give a fatigue life near by to that published in literatures and also showed the FCG rate response of X70 pipeline steels when exposed to VAL with different overload values. Extra modification to the NASGRO model may lead to better representing of FCG rate. Highlights: ► The assessment of fatigue crack propagation under different load histories are proposed and presented in this paper. ► Due to lack of knowledge in the related area, as yet no universal model exists. ► The output was based on both simulation and experiments. The simulation part was carried out based on the NASGRO model. ► This work focus on fatigue crack growth (FCG) and fatigue life based on the comparison with the previous work.
Fatigue crack growth-Microstructure relationships in a high-manganese austenitic TWIP steel
Energy Technology Data Exchange (ETDEWEB)
Niendorf, T., E-mail: niendorf@mail.uni-paderborn.de [University of Paderborn, Lehrstuhl fuer Werkstoffkunde (Materials Science), 33095 Paderborn (Germany); Rubitschek, F.; Maier, H.J. [University of Paderborn, Lehrstuhl fuer Werkstoffkunde (Materials Science), 33095 Paderborn (Germany); Niendorf, J.; Richard, H.A. [University of Paderborn, Fachgruppe Angewandte Mechanik (Applied Mechanics), 33095 Paderborn (Germany); Frehn, A. [Benteler Automotive, Product Group Chassis Systems, An der Talle 27-31, 33102 Paderborn (Germany)
2010-04-15
The crack growth behavior of a high-manganese austenitic steel, which exhibits the twinning-induced plasticity (TWIP) effect, was investigated under positive stress ratios. An experimental study making use of miniature compact tension (CT) specimens and thorough microstructural analyses including transmission electron microscopy and fracture analyses demonstrated that the microstructural evolution in the plastic zone of the fatigued TWIP CT specimens is substantially different as compared to the monotonic plastic deformation case. Specifically, the twin density in the plastic zone of the CT specimens is very low, leading to the conclusion that the deformation mechanisms depend drastically on the loading conditions. The absence of twinning under cyclic loading in the plastic zone of the CT specimens indicates that even large accumulated plastic strains are not sufficient to cause substantial twinning in the TWIP steel. This lack of hardening preserves the ductile character of the TWIP steel in the plastic zone ahead of the crack tip and provides for a crack growth rate in the Paris regime lower than reported for other high strength steels.
Investigation into fatigue crack growth and kinetic diagrams of fatigue failure
International Nuclear Information System (INIS)
Yarema, S.Ya.
1977-01-01
Studies on fatigue failure are discussed in terms of fatigue failure kinetic diagrams (FFKD), in which the fatigue crack growth rate is plotted against the stress intensity coefficient (SIC). The physical sense of the crack growth rate and SIC is discussed and their applicability for description of the material in the destruction zone, particularly in presence of various media. Variation of experimental parameters (loading and environment) is followed by a transition period during which the results of the experiment may depend on its history, so that FFKD would remain invariant. Advantages of tests under constant experimental conditions are shown. The ways to stabilize SIC are indicated and requirements to the samples are given. As an example, the tests of disc samples made of plate materials are given, where SIC does not depend on the crack length. The question of controlling the experimental conditions such as asymmetry and shape of the loading cycle, loading frequency, fluctuations of temperature and air composition is considered. The analytical functions describing FFKD are discussed. It is shown, that in appropriate dimensionless coordinates the FFKD of different materials merge into one curve
The role of organic proteins on the crack growth resistance of human enamel.
Yahyazadehfar, Mobin; Arola, Dwayne
2015-06-01
With only 1% protein by weight, tooth enamel is the most highly mineralized tissue in mammals. The focus of this study was to evaluate contributions of the proteins on the fracture resistance of this unique structural material. Sections of enamel were obtained from the cusps of human molars and the crack growth resistance was quantified using a conventional fracture mechanics approach with complementary finite element analysis. In selected specimens the proteins were extracted using a potassium hydroxide treatment. Removal of the proteins resulted in approximately 40% decrease in the fracture toughness with respect to the fully proteinized control. The loss of organic content was most detrimental to the extrinsic toughening mechanisms, causing over 80% reduction in their contribution to the total energy to fracture. This degradation occurred by embrittlement of the unbroken bridging ligaments and consequent reduction in the crack closure stress. Although the organic content of tooth enamel is very small, it is essential to crack growth toughening by facilitating the formation of unbroken ligaments and in fortifying their potency. Replicating functions of the organic content will be critical to the successful development of bio-inspired materials that are designed for fracture resistance. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Discrete modelling of ductile crack growth by void growth to coalescence
DEFF Research Database (Denmark)
Tvergaard, Viggo
2007-01-01
of the ligaments between the crack-tip and a void or between voids involves the development of very large strains, which are included in the model by using remeshing at several stages of the plastic deformation. The material is here described by standard isotropic hardening Mises theory. For a very small void...
Energy Technology Data Exchange (ETDEWEB)
Lee, Hyeong-Yeon; Kim, Woo-Gon; Kim, Nak-Hyun [Korea Atomic Energy Reserach Institute, Daejeon (Korea, Republic of)
2015-01-15
The material properties of crack growth models at an elevated temperature were derived from the results of numerous crack growth tests for Mod.9Cr-1Mo (ASME Grade 91) steel specimens under fatigue loading and creep loading at an elevated temperature. These crack growth models were needed for defect assessment under creep-fatigue loading. The mathematical crack growth rate models for fatigue crack growth (FCG) and creep crack growth (CCG) were determined based on the test results, and the models were compared with those of the French design code RCCMRx to investigate the conservatism of the code. The French design code RCC-MRx provides an FCG model and a CCG model for Grade 91 steel in Section III Tome 6. It was shown that the FCG model of RCC-MRx is conservative, while the CCG model is non-conservative compared with the present test data. Thus, it was shown that further validation of the property was required. Mechanical strength tests and creep tests were also conducted, and the test results were compared with those of RCC-MRx.
Proposal of fatigue crack growth rate curve in air for nickel-base alloys used in BWR
International Nuclear Information System (INIS)
Ogawa, Takuya; Itatani, Masao; Nagase, Hiroshi; Aoike, Satoru; Yoneda, Hideki
2013-01-01
When the defects are detected in the nuclear components in Japan, structural integrity assessment should be performed for the technical judgment on continuous service based on the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers Code (JSME FFS Code). Fatigue crack growth analysis is required when the cyclic loading would be applied for the components. Recently, fatigue crack growth rate curve in air environment for Nickel-base alloys weld metal used in BWR was proposed by the authors and it was adopted as a code case of JSME FFS Code to evaluate the embedded flaw. In this study, fatigue crack growth behavior for heat-affected zone (HAZ) of Nickel-base alloys in air was investigated. And a unified fatigue crack growth rate curve in air for HAZ and weld metal of Nickel-base alloys used in BWR was evaluated. As a result, it was found that the curve for weld metal could be applied as a curve for both HAZ and weld metal since moderately conservative assessment of fatigue crack growth rate of HAZ is possible by the curve for weld metal in the Paris region. And the threshold value of stress intensity far range (ΔK th ) is determined to 3.0 MPa√m based on the fatigue crack growth rate of HAZ. (author)
Engineering approach for examining crack growth and stability in flawed structures
International Nuclear Information System (INIS)
Shih, C.F.
1980-01-01
Progress made in two research programs sponsored by the Electric Power Research Institute (EPRI), to identify viable parameters for characterizing crack initiation and continued extension, and to develop an engineering/design methodology, based on these parameters, for the assessment of crack growth and instability in engineering structures which are stressed beyond the regime of applicability of linear elastic fracture mechanics is reported. The goal in the development of such methodology is to establish an improved basis for analyzing the effect of flaws (postulated or detected) on the safety margins of pressure boundary components of light water-cooled type nuclear steam supply systems. The methodology can also be employed for structural integrity analyses of other engineering structures
Jeevan Kumar, N.; Ramesh Babu, P.
2018-02-01
In recent years carbon fibre-reinforced polymers (CFRP) emerged its increasing demand in aerospace engineering. Due to their high specific strength to weight ratio, these composites offer more characteristics and considerable advantages compared to metals. Metals, unlike composites, offer plasticity effects to evade high stress concentrations during postbuckling. Under compressive load, composite structures show a wide range of damage mechanisms where a set of damage modes combined together might lead to the eventual structural collapse. Crack is one of the most critical damages in fiber composites, which are being employed in primary aircraft structures. A parametric study is conducted to investigate the arrest mechanism of the delamination or crack growth with installation of multiple fasteners when the delamination is embedded in between the skin and stiffener interface.
Prediction of Accurate Mixed Mode Fatigue Crack Growth Curves using the Paris' Law
Sajith, S.; Krishna Murthy, K. S. R.; Robi, P. S.
2017-12-01
Accurate information regarding crack growth times and structural strength as a function of the crack size is mandatory in damage tolerance analysis. Various equivalent stress intensity factor (SIF) models are available for prediction of mixed mode fatigue life using the Paris' law. In the present investigation these models have been compared to assess their efficacy in prediction of the life close to the experimental findings as there are no guidelines/suggestions available on selection of these models for accurate and/or conservative predictions of fatigue life. Within the limitations of availability of experimental data and currently available numerical simulation techniques, the results of present study attempts to outline models that would provide accurate and conservative life predictions.
Fatigue Crack Growth Characteristics of Cold Stretched STS 304 Welded Joint
Energy Technology Data Exchange (ETDEWEB)
Lee, Jeong Won; Na, Seong Hyeon; Yoon, Dong Hyun; Kim, Jae Hoon [Chungnam Nat’l Univ., Daejeon (Korea, Republic of); Kim, Young Kyun; Kim, Ki Dong [Korea Gas Coporation R& D Division, Daejeon (Korea, Republic of)
2017-09-15
STS 304 steel is used as pressure vessel material, and although it exhibits excellent mechanical characteristics at a low temperature, it is heavier than other materials. To address this issue, a method using cold-stretching techniques for STS 304 can be applied. In this study, a cold-stretching part and welded joint specimen were directly obtained from a cold-stretching pressure vessel manufactured according to ASME code. Fatigue crack propagation tests were carried out at room temperature and -170℃ using the compliance method for stress ratios of 0.1 and 0.5. The results indicate that crack growth rate of the welded joint is higher than that of the cold-stretching part within the same stress intensity factor range. The outcome of this work is expected to serve as a basis for the development of a cold-stretched STS 304 pressure vessel.
Investigation on crack growth parameters in the elastic plastic region (interim report)
International Nuclear Information System (INIS)
Prij, J.
1982-03-01
Some theoretical as well as numerical results are presented with respect to the 2D and 3D application of linear elastic fracture mechanics. The application of the finite element method to calculate the stress and strain field in cracked bodies has been discussed with special attention to: singularity representation, parameter extraction and mesh refinement. Detailed 3D stress analyses of fracture mechanics test specimen are presented showing that: the stress intensity concept cannot be extended simply into a 3D concept, the energy release concept is more promising within this aspect and the plastic region along the crackfront will not have a dogbone shape. The 3D elastic fracture mechanics concept is applied to evaluate the consequences of the thermal stresses due to γ-heating in an in-pile crack growth experiment
The role of microcracking on the crack growth resistance of brittle solids and composites
International Nuclear Information System (INIS)
Biner, S.B.
1994-01-01
A set of numerical analyses of crack growth was preformed to elucidate the influence of microcracking on the fracture behavior of microcracking brittle solids and composites. The random nucleation, orientation and size effects of discrete nucleating microcracks and resulting interactions are fully accounted for in a hybrid finite element model. The results obtained from the finite element analysis are compared with the continuum description of the microcracking. Although continuum description can provide a reasonable estimation of shielding, it fails to resolve the details of micromechanism of toughening resulting from microcracking, since not every shielding event during the course of crack extension corresponds to an increase in the R-curve. Moreover, as seen in the composite cases, the local events leading to toughening behavior may not be associated with the microcracking even in the presence of a large population of microcracks
Device for investigating subcritical crack growth of RPV steel specimens under BWR conditions
International Nuclear Information System (INIS)
Anders, D.; Ahlf, J.
1983-01-01
An experiment is being prepared to investigate the subcritical crack growth of RPV steel specimens under cyclic load and under the environmental conditions of a BWR with regard to primary water and irradiation. The experiment will be carried out in the VAK reactor Kahl which is a boiling water reactor operating at 71 bar, 286 0 C and generating 16 MW/sub e/. The experimental setup is composed of an open frame to which a string consisting of five compact tension speciments (40 mm thickness) and connecting links is fixed. The specimen chain is set under cyclic load by a pneumatically actuated bellows unit which is attached to the frame top. Specimen strain and crack opening are measured by linear differential transformers; for temperature distribution measurements in the specimens thermocouples are applied
Microstructure-based approach for predicting crack initiation and early growth in metals.
Energy Technology Data Exchange (ETDEWEB)
Cox, James V.; Emery, John M.; Brewer, Luke N.; Reedy, Earl David, Jr.; Puskar, Joseph David; Bartel, Timothy James; Dingreville, Remi P. M.; Foulk, James W., III; Battaile, Corbett Chandler; Boyce, Brad Lee
2009-09-01
Fatigue cracking in metals has been and is an area of great importance to the science and technology of structural materials for quite some time. The earliest stages of fatigue crack nucleation and growth are dominated by the microstructure and yet few models are able to predict the fatigue behavior during these stages because of a lack of microstructural physics in the models. This program has developed several new simulation tools to increase the microstructural physics available for fatigue prediction. In addition, this program has extended and developed microscale experimental methods to allow the validation of new microstructural models for deformation in metals. We have applied these developments to fatigue experiments in metals where the microstructure has been intentionally varied.
Hydrogen-assisted fatigue crack growth in ferritic steels – a fractographic study
Directory of Open Access Journals (Sweden)
Wan Di
2018-01-01
Full Text Available Fatigue crack growth (FCG behavior of a Fe-3wt.%Si ferritic alloy under different environmental conditions using in-situ electrochemical (cathodic hydrogen (H charging has been investigated. Three frequencies have been applied. Results clearly show that the FCG rate increased by a factor spanning from 20 to 1000 times, depending on the loading frequencies, when compared to the reference test in air. Lower frequency leads to higher FCG rate. A comprehensive fractographic analysis was carried out: the area fraction of different fracture surface features was measured and taken into statistical analysis. Based on these investigations, the possible mechanisms of H-enhanced FCG are discussed. Similar tests in high-pressure H gas from other studies were also compared and discussed. These results give a preliminary understanding of H effect in fatigue crack propagation procedure in ferritic alloys.
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
Thermal fatigue crack growth tests and analyses of thick wall cylinder made of Mod.9Cr–1Mo steel
Energy Technology Data Exchange (ETDEWEB)
Wakai, Takashi, E-mail: wakai.takashi@jaea.go.jp [Japan Atomic Energy Agency, 4002 Narita-cho Oarai, Ibaraki 3111393 (Japan); Inoue, Osamu [IX Knowledge Inc., 3-22-23 MSC Center Bldg, Kaigan Minato-ku, Tokyo 1080022 Japan (Japan); Ando, Masanori; Kobayashi, Sumio [Japan Atomic Energy Agency, 4002 Narita-cho Oarai, Ibaraki 3111393 (Japan)
2015-12-15
Highlights: • A thermal fatigue crack growth test was performed using Mod.9Cr–1Mo steel cylinder. • Axial/circumferential notches were machined on the inner surface of the cylinder. • Simplified analytical results were compared to the test data. • Crack length could not be predicted by the analyses because of crack conjunctions. • If there are no surface cracks, the calculations might agree with the observations. - Abstract: In Japan, the basic designing works for a demonstration plant of Japan Sodium cooled Fast Reactor (JSFR) are now conducted. JSFR is an advanced loop type reactor concept. To enhance the safety and the economic competitiveness, JSFR employs modified 9% chromium–1% molybdenum (Mod.9Cr–1Mo) steel as a material for coolant pipes and components, because the steel has both excellent high temperature strength and thermal properties. The steel has been standardized as a nuclear material in Japan Society of Mechanical Engineers (JSME) code in 2012. In JSFR pipes, demonstration of Leak Before Break (LBB) aspect is strongly expected because the safety assessment may be performed on the premise of leak rate where the LBB aspect is assured. Although the authors have already performed a series of thermal fatigue crack growth tests of austenitic stainless steel cylinders (Wakai et al., 2005), crack growth behavior in the structures made of Mod.9Cr–1Mo steel has not been investigated yet. Especially for the welded joints of Mod.9Cr–1Mo steel, “Type-IV” cracking may occur at heat affected zone (HAZ). Therefore, this study performed a series of thermal fatigue crack growth tests of thick wall cylinders made of Mod.9Cr–1Mo steel including welds, to obtain the crack growth data under cyclic thermal transients. The test results were compared to the analytical results obtained from JAEA's simplified methods (Wakai et al., 2005).
Fatigue behaviour and crack growth of ferritic steel under environmental conditions
International Nuclear Information System (INIS)
Herter, K.H.; Schuler, X.; Weissenberg, T.
2012-01-01
The assessment of fatigue and cyclic crack growth behaviour of safety relevant components is of importance for the ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as a limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way. Fatigue tests were performed in the low cycle fatigue (LCF) und high cycle fatigue (HCF) regime with low alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in air and high temperature (HT) boiling water reactor environment to extend the state of knowledge of environmentally assisted fatigue (EAF) as it can occur in boiling water reactor (BWR) plants. Using the reactor pressure vessel (RPV) steel 22NiMoCr3-7 experimental data were developed to verify the influence of BWR coolant environment (high purity water as well as sulphate containing water with 90 ppb SO 4 at a test temperature of 240 C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor F en accounting for the environment. The experimental results are compared with international available mean data curves, the new design curves and on the basis of the environmental factor F en . Furthermore the behaviour of steel 22NiMoCr3-7 in oxygenated high temperature water under transient loading conditions was investigated with respect to crack initiation and cyclic crack growth. In this process the stress state of the specimen and the chemical composition of the high
International Nuclear Information System (INIS)
Mills, W.J.; James, L.A.
1978-05-01
The room temperature and elevated temperature fatigue-crack growth behavior of two heats of Alloy 718 was characterized within a linear-elastic fracture mechanics framework. Two different heat-treatments were used: the ''conventional'' (ASTM A637) treatment, and a ''modified'' heat-treatment designed to improve the toughness of Alloy 718 base metal and weldments. Heat-to-heat variations in the fatigue-crack propagation behavior were observed in the conventionally-treated material. On the other hand, no heat-to-heat variations were observed in the modified condition. Furthermore, both heats of Alloy 718 exhibited superior fatigue-crack growth resistance when given the modified heat-treatment. Electron fractographic examination of Alloy 718 fatigue fracture surfaces revealed that the operative crack growth mechanisms were dependent on heat-treatment, temperature, and ΔK level
Glass fabrics self-cracking catalytic growth of boron nitride nanotubes
Wang, Jilin; Peng, Daijang; Long, Fei; Wang, Weimin; Gu, Yunle; Mo, Shuyi; Zou, Zhengguang; Fu, Zhengyi
2017-02-01
Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.
Fatigue Crack Growth Mechanisms for Nickel-based Superalloy Haynes 282 at 550-750 °C
Rozman, Kyle A.; Kruzic, Jamie J.; Sears, John S.; Hawk, Jeffrey A.
2015-10-01
The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 and 0.25 Hz. The crack path was observed to be primarily transgranular for all temperatures, and the observed effect of increasing temperature was to increase the fatigue crack growth rates. The activation energy associated with the increasing crack growth rates over these three temperatures was calculated less than 60 kJ/mol, which is significantly lower than typical creep or oxidation mechanisms; therefore, creep and oxidation cannot explain the increase in fatigue crack growth rates. Transmission electron microscopy was done on selected samples removed from the cyclic plastic zone, and a trend of decreasing dislocation density was observed with increasing temperature. Accordingly, the trend of increasing crack growth rates with increasing temperature was attributed to softening associated with thermally assisted cross slip and dislocation annihilation.
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.
International Nuclear Information System (INIS)
Honda, T.; Kudo, Y.; Hatano, T.; Kikuchi, K.; Nishimura, T.; Saito, M.
2003-01-01
The long pulse operation is assumed in ITER and future reactor. If the first wall has a defect, the crack may be propagated by cyclic thermal loads. In addition, flattop of more than 300 s during plasma burning is expected in ITER, so the crack propagation behavior will depend on the operation duration period. This study deals with the crack propagation behavior on F82H under high thermal load cycles. The high heat flux tests were performed under three types of duration periods to investigate creep fatigue behavior. To clarify the crack growth mechanism and the effects of transient creep, three-dimensional analyses were performed. It was concluded that the creep effect during the operation duration period enlarges stress intensity factor K in the cooling period and that consequently, the crack propagation length was increased
Energy Technology Data Exchange (ETDEWEB)
NONE
2013-08-15
Austenitic stainless steels are widely used as structural components in reactor pressure vessel internals because of their high strength, ductility, and fracture toughness. However, exposure to neutron irradiation results in changes in microstructure, mechanical properties and microchemistry of the steels. Irradiation assisted stress corrosion cracking (IASCC) caused by the effect of neutron irradiation during long term plant operation in high temperature water environments is considered to take the form of intergranular stress corrosion cracking (IGSCC) and the critical fluence level has been reported to be about 5x10{sup 24}n/m{sup 2} (E>1MeV) in Type 304 stainless steel in BWR environment. JNES had been conducting IASCC project during the JFY (2000) - JFY (2008) period, and prepared an engineering database on IASCC. However, the data of Crack Growth Rate (CGR) below the critical fluence level are not sufficient. So, this project was initiated to obtain the CGR data below the critical fluence level. Test specimens have been irradiated in the Halden reactor, operating by the OECD Halden Reactor Project, and the post irradiation examination (PIE) will be conducted from JFY (2011) to JFY (2013), finally the modified IASCC guide will be prepared in JFY (2013). (author)
Creep and Creep Crack Growth Behaviors for SMAW Weldments of Gr. 91 Steel
International Nuclear Information System (INIS)
Kim, Woo Gon; Yin, Song Nan; Park, Ji Yeon; Hong, Sung Deok; Kim, Yong Wan; Park, Jae Young
2010-01-01
High Cr ferritic resistance steels with tempered martensite microstructures posses enhanced creep strength at the elevated temperatures. Those steels as represented by a modified 9Cr-1Mo steel (ASME Grade 91, hereafter Gr.91) are regarded as main structural materials of sodium-cooled fast reactors (SFR) and reactor pressure vessel materials of very high temperature reactors (VHTR). The SFR and VHTR systems are designed during long-term duration reaching 60 years at elevated temperatures and often subjected to non-uniform stress and temperature distribution during service. These conditions may generate localized creep damage and propagate the cracks and ultimately may cause a fracture. A significant portion of its life is spent in crack propagation. Therefore, a creep crack growth rate (CCGR) due to creep damage should be assessed for both the base metal (BM) and welded metal (WM). Enough CCGR data for them should be provided for assessing their structural integrities. However, their CCGR data for the Gr. 91 steels is still insufficient. In this study, the CCGR for the BM and the WM of the Gr. 91 steel was comparatively investigated. A series of the CCG tests were conducted under different applied loads for the BM and the WM at 600 .deg. C. The CCGR was characterized in terms of the C parameter, and their CCG behavior were compared, respectively
Acoustic emission studies for characterization of fatigue crack growth behavior in HSLA steel
Kumar, Jalaj; Ahmad, S.; Mukhopadhyay, C. K.; Jayakumar, T.; Kumar, Vikas
2016-01-01
High strength low alloy (HSLA) steels are a group of low carbon steels and used in oil and gas pipelines, automotive components, offshore structures and shipbuilding. Fatigue crack growth (FCG) characteristics of a HSLA steel have been studied at two different stress ratios (R = 0.3 and 0.5). Acoustic emission (AE) signals generated during the FCG tests have been used to understand the FCG processes. The AE signals were captured by mounting two piezoelectric sensors on compact tension specimens in liner location configuration. The AE generated in stage II of the linear Paris region of FCG has been attributed to the presence of two sub-stages with two different slopes. The AE generated at higher values of stress intensity factor is found to be useful to identify the transition from stage II to stage III of the FCG. AE location analysis has provided support for increased damage at the crack tip for higher stress ratio. The peak stress intensity (Kmax) values at the crack tip have shown good correlation with the transitions from stage IIa to stage IIb and stage II to stage III of the FCG for the two stress ratios.
Formation of stress/strain cycles for analytical assessment of fatigue crack initiation and growth
International Nuclear Information System (INIS)
Tashkinov, A.V.
2005-01-01
This paper discusses standard techniques for setting up cycles of stresses, strains and stress intensity factors (SIF) for use in analysing the fatigue characteristics of crack-free components or the fatigue crack growth if crack-like flaws are present. A number of improved techniques are proposed. An enhanced procedure for analytical description of true metal stress-strain curves, covering plastic effects, is presented. This procedure involves standard physical and mechanical properties of the metal in question, such as ultimate stress, yield stress and elasticity modulus. It is emphasized that the currently practiced rain-flow method of design cycle formation, which is effective for an actual (truly known) cyclic loading history, is not suitable for a projected (anticipated) history, as it leaves out of account possible variations in the sequence of operating conditions. Improved techniques for establishing design stress/strain and SIF cycles are described, which make allowance for the most unfavourable sequence of events in the projected loading history. The paper points to a basic difference in the methods of design cycle formation, employed in assessment of the current condition of a component (with the actual history accounted for) and in estimation of the residual lifetime or life extension (for a projected history). (authors)
Coupling of water radiolysis and crack growth in sensitized stainless steels
International Nuclear Information System (INIS)
Macdonald, D.D.
1991-01-01
The electrochemical potential from exchange reactions on an inert metal surface such as platinum is equivalent to the redox potential. Equivalents of oxidant (i.e., oxygen) reduced are equal to the equivalents of reductant (i.e., hydrogen) oxidized. Electrons flow through the metal. An equivalent ionic current completing the circuit, flows in the solution. Cations migrate in the opposite direction to anions. When a metal corrodes in a localized surface area or crack, the metal-solution potential at that location, as probed by a reference electrode, changes due to the metal dissolution. The amount of change in the mixed potential system depends on the magnitude of the previously controlling exchange reactions. It is usually significant and easily measured. Thus, the potential difference between the redox potential and the potential of the corroding metal gives at least an indication and perhaps a measure of corrosion. Calculations showed that an increasing conductivity in the external solution up to a concentration of about 10E-10 mol/cm 3 (5.8 ppm) of NaCl sharply increased the crack growth rate. Stress intensity also increased the cracking rate but not so sharply
Effect of helium on fatigue crack growth and life of reduced activation ferritic/martensitic steel
International Nuclear Information System (INIS)
Nogami, Shuhei; Takahashi, Manabu; Hasegawa, Akira; Yamazaki, Masanori
2013-01-01
The effects of helium on the fatigue life, micro-crack growth behavior up to final fatigue failure, and fracture mode under fatigue in the reduced activation ferritic/martensitic steel, F82H IEA-heat, were investigated by low cycle fatigue tests at room temperature in air at a total strain range of 0.6–1.5%. Significant reduction of the fatigue life due to helium implantation was observed for a total strain range of 1.0–1.5%, which might be attributable to an increase in the micro-crack propagation rate. However, the reduction of fatigue life due to helium implantation was not significant for a total strain range of 0.6–0.8%. A brittle fracture surface (an original point of micro-crack initiation) and a cleavage fracture surface were observed in the helium-implanted region of fracture surface. A striation pattern was observed in the non-implanted region. These fracture modes of the helium-implanted specimen were independent of the strain range
Comparison of Fatigue Properties and Fatigue Crack Growth Rates of Various Implantable Metals
Okazaki, Yoshimitsu
2012-01-01
The fatigue strength, effects of a notch on the fatigue strength, and fatigue crack growth rate of Ti-15Zr-4Nb-4Ta alloy were compared with those of other implantable metals. Zr, Nb, and Ta are important alloying elements for Ti alloys for attaining superior long-term corrosion resistance and biocompatibility. The highly biocompatible Ti-15Zr-4Nb-4Ta alloy exhibited an excellent balance between strength and ductility. Its notched tensile strength was much higher than that of a smooth specimen. The strength of 20% cold-worked commercially pure (C.P.) grade 4 Ti was close to that of Ti alloy. The tension-to-tension fatigue strength of an annealed Ti-15Zr-4Nb-4Ta rod at 107 cycles was approximately 740 MPa. The fatigue strength of this alloy was much improved by aging treatment after solution treatment. The fatigue strengths of C.P. grade 4 Ti and stainless steel were markedly improved by 20% cold working. The fatigue strength of Co-Cr-Mo alloy was markedly increased by hot forging. The notch fatigue strengths of 20% cold-worked C.P. grade 4 Ti, and annealed and aged Ti-15Zr-4Nb-4Ta, and annealed Ti-6Al-4V alloys were less than those of the smooth specimens. The fatigue crack growth rate of Ti-15Zr-4Nb-4Ta was the same as that of Ti-6Al-4V. The fatigue crack growth rate in 0.9% NaCl was the same as that in air. Stainless steel and Co-Cr-Mo-Ni-Fe alloy had a larger stress-intensity factor range (ΔK) than Ti alloy.
International Nuclear Information System (INIS)
Ihara, Ryohei; Katsuyama, JInya; Onizawa, Kunio; Hashimoto, Tadafumi; Mikami, Yoshiki; Mochizuki, Masahito
2011-01-01
Research highlights: → Residual stress distributions due to welding and machining are evaluated by XRD and FEM. → Residual stress due to machining shows higher tensile stress than welding near the surface. → Crack growth analysis is performed using calculated residual stress. → Crack growth result is affected machining rather than welding. → Machining is an important factor for crack growth. - Abstract: In nuclear power plants, stress corrosion cracking (SCC) has been observed near the weld zone of the core shroud and primary loop recirculation (PLR) pipes made of low-carbon austenitic stainless steel Type 316L. The joining process of pipes usually includes surface machining and welding. Both processes induce residual stresses, and residual stresses are thus important factors in the occurrence and propagation of SCC. In this study, the finite element method (FEM) was used to estimate residual stress distributions generated by butt welding and surface machining. The thermoelastic-plastic analysis was performed for the welding simulation, and the thermo-mechanical coupled analysis based on the Johnson-Cook material model was performed for the surface machining simulation. In addition, a crack growth analysis based on the stress intensity factor (SIF) calculation was performed using the calculated residual stress distributions that are generated by welding and surface machining. The surface machining analysis showed that tensile residual stress due to surface machining only exists approximately 0.2 mm from the machined surface, and the surface residual stress increases with cutting speed. The crack growth analysis showed that the crack depth is affected by both surface machining and welding, and the crack length is more affected by surface machining than by welding.
International Nuclear Information System (INIS)
Rubio-Gonzalez, C.; Ocana, J.L.; Gomez-Rosas, G.; Molpeceres, C.; Paredes, M.; Banderas, A.; Porro, J.; Morales, M.
2004-01-01
Laser shock processing (LSP) or laser shock peening is a new technique for strengthening metals. This process induces a compressive residual stress field which increases fatigue crack initiation life and reduces fatigue crack growth rate. Specimens of 6061-T6 aluminum alloy are used in this investigation. A convergent lens is used to deliver 1.2 J, 8 ns laser pulses by a Q-switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 1.5 mm onto a water-immersed type aluminum samples. Effect of pulse density in the residual stress field is evaluated. Residual stress distribution as a function of depth is assessed by the hole drilling method. It is observed that the higher the pulse density the larger the zone size with compressive residual stress. Densities of 900, 1350 and 2500 pulses/cm 2 with infrared (1064 nm) radiation are used. Pre-cracked compact tension specimens were subjected to LSP process and then tested under cyclic loading with R = 0.1. Fatigue crack growth rate is determined and the effect of LSP process parameters is evaluated. Fatigue crack growth rate is compared in specimens with and without LSP process. In addition fracture toughness is determined in specimens with and without LSP treatment. It is observed that LSP reduces fatigue crack growth and increases fracture toughness in the 6061-T6 aluminum alloy
Fatigue crack growth spectrum simplification: Facilitation of on-board damage prognosis systems
Adler, Matthew Adam
2009-12-01
Better lifetime predictions of systems subjected to fatigue loading are needed in support of the optimization of the costs of life-cycle engineering. In particular, the climate is especially encouraging for the development of safer aircraft. One issue is that aircraft experience complex fatigue loading and current methods for the prediction of fatigue damage accumulation rely on intensive computational tools that are not currently carried onboard during flight. These tools rely on complex models that are made more difficult by the complicated load spectra themselves. This presents an overhead burden as offline analysis must be performed at an offsite facility. This architecture is thus unable to provide online, timely information for on-board use. The direct objective of this research was to facilitate the real-time fatigue damage assessments of on-board systems with a particular emphasis on aging aircraft. To achieve the objective, the goal of this research was to simplify flight spectra. Variable-amplitude spectra, in which the load changes on a cycle-by-cycle basis, cannot readily be supported by an onboard system because the models required to predict fatigue crack growth during variable-amplitude loading are too complicated. They are too complicated because variable-amplitude fatigue crack growth analysis must be performed on a cycle-by-cycle basis as no closed-form solution exists. This makes these calculations too time-consuming and requires impractical, heavy onboard systems or offsite facilities. The hypothesis is to replace a variable-amplitude spectrum with an equivalent constant-amplitude spectrum. The advantage is a dramatic reduction in the complexity of the problem so that damage predictions can be made onboard by simple, fast calculations in real-time without the need to add additional weight to the aircraft. The intent is to reduce the computational burden and facilitate on-board projection of damage evolution and prediction for the accurate
Probabilistic Modeling of the Fatigue Crack Growth Rate for Ni-base Alloy X-750
International Nuclear Information System (INIS)
Yoon, J.Y.; Nam, H.O.; Hwang, I.S.; Lee, T.H.
2012-01-01
Extending the operating life of existing nuclear power plants (NPP's) beyond 60 years. Many aging problems of passive components such as PWSCC, IASCC, FAC and Corrosion Fatigue; Safety analysis: Deterministic analysis + Probabilistic analysis; Many uncertainties of parameters or relationship in general probabilistic analysis such as probabilistic safety assessment (PSA); Bayesian inference: Decreasing uncertainties by updating unknown parameter; Ensuring the reliability of passive components (e.g. pipes) as well as active components (e.g. valve, pump) in NPP's; Developing probabilistic model for failures; Updating the fatigue crack growth rate (FCGR)
The increase in fatigue crack growth rates observed for Zircaloy-4 in a PWR environment
Cockeram, B. V.; Kammenzind, B. F.
2018-02-01
Cyclic stresses produced during the operation of nuclear reactors can result in the extension of cracks by processes of fatigue. Although fatigue crack growth rate (FCGR) data for Zircaloy-4 in air are available, little testing has been performed in a PWR primary water environment. Test programs have been performed by Gee et al., in 1989 and Picker and Pickles in 1984 by the UK Atomic Energy Authority, and by Wisner et al., in 1994, that have shown an enhancement in FCGR for Zircaloy-2 and Zircaloy-4 in high-temperature water. In this work, FCGR testing is performed on Zircaloy-4 in a PWR environment in the hydrided and non-hydrided condition over a range of stress-intensity. Measurements of crack extension are performed using a direct current potential drop (DCPD) method. The cyclic rate in the PWR primary water environment is varied between 1 cycle per minute to 0.1 cycle per minute. Faster FCGR rates are observed in water in comparison to FCGR testing performed in air for the hydrided material. Hydrided and non-hydrided materials had similar FCGR values in air, but the non-hydrided material exhibited much lower rates of FCGR in a PWR primary water environment than for hydrided material. Hydrides are shown to exhibit an increased tendency for cracking or decohesion in a PWR primary water environment that results in an enhancement in FCGR values. The FCGR in the PWR primary water only increased slightly with decreasing cycle frequency in the range of 1 cycle per minute to 0.1 cycle per minute. Comparisons between the FCGR in water and air show the enhancement from the PWR environment is affected by the applied stress intensity.
Ali, Mohammed Ali Nasser
The research project presents a fundamental understanding of the fatigue crack growth mechanisms of AISI 420 martensitic stainless steel, based on the comparison analysis between the theoretical and numerical modelling, incorporating research findings under isothermal fatigue loading for solid cylindrical specimen and the theoretical modelling with the numerical simulation for tubular specimen when subjected to cyclic mechanical loading superimposed by cyclic thermal shock.The experimental part of this research programme studied the fatigue stress-life data for three types of surface conditions specimen and the isothermal stress-controlled fatigue testing at 300 °C - 600 °C temperature range. It is observed that the highest strength is obtained for the polished specimen, while the machined specimen shows lower strength, and the lowest strength is the notched specimen due to the high effect of the stress concentration. The material behaviour at room and high temperatures shows an initial hardening, followed by slow extension until fully plastic saturation then followed by crack initiation and growth eventually reaching the failure of the specimen, resulting from the dynamic strain ageing occurred from the transformation of austenitic microstructure to martensite and also, the nucleation of precipitation at grain boundaries and the incremental temperature increase the fatigue crack growth rate with stress intensity factor however, the crack growth rate at 600 °C test temperature is less than 500 °C because of the creep-fatigue taking place.The theoretical modelling presents the crack growth analysis and stress and strain intensity factor approaches analysed in two case studies based on the addition of thermo-elastic-plastic stresses to the experimental fatigue applied loading. Case study one estimates the thermal stresses superimposed sinusoidal cyclic mechanical stress results in solid cylinder under isothermal fatigue simulation. Case study two estimates the
International Nuclear Information System (INIS)
Andersson, Peder; Segle, Peter; Samuelson, Lars Aa.
1999-04-01
A 3D finite element study of creep crack growth in cross-weld CT specimens with material properties of 2.25Cr1Mo at 550 deg C is carried out, where large strain and displacement theory is used. The creep crack growth rate is calculated using a creep ductility based damage model, in which the creep strain rate perpendicular to the crack plane ahead of the crack tip is integrated, considering the multiaxial stress state. The influence of specimen size on creep crack growth rate under constant load is given special attention, but the possibility to transfer results from cross-weld CT specimens to welded high temperature components is also investigated. The creep crack growth rate of a crack in a circumferentially welded pipe is compared with the creep crack growth rate of cross-weld CT specimens of three different sizes, cut out from the pipe. Although the constraint ahead of the crack tip is higher for a larger CT specimen, the creep crack growth rate is higher for a smaller specimen than for a larger one if they are loaded to attain the same stress intensity factor. If the specimens are loaded to the same C* value, however, a more complicated pattern occurs; depending on the material properties of the weldment constituents, the CT specimen with the intermediate size will either yield the highest or the lowest creep crack growth rate
International Nuclear Information System (INIS)
Ide, Hiroshi; Matsui, Yoshinori; Kawamata, Kazuo; Taguchi, Taketoshi; Kanazawa, Yoshiharu; Onuma, Yuichi; Watanabe, Hiroyuki; Inoue, Shuichi; Izumo, Hironobu; Ishida, Takuya; Saito, Takashi; Ishitsuka, Etsuo; Kawamura, Hiroshi; Kaji, Yoshiyuki; Ugachi, Hirokazu; Tsukada, Takashi
2008-03-01
It is known that Irradiation Assisted Stress Corrosion Cracking (IASCC) occurs when austenitic stainless steel components used for light water reactor (LWR) are irradiated for a long period. In order to evaluate the high aging of the nuclear power plant, the study of IASCC becomes the important problem. The specimens irradiated in the reactor were evaluated by post irradiation examination in the past study. For the appropriate evaluation of IASCC, it is necessary to test it under the simulated LWR conditions; temperature, water chemistry and irradiation conditions. In order to perform in-pile SCC test, saturated temperature capsule (SATCAP) was developed. There are crack growth test, crack propagation test and so on for in-pile SCC test. In this report, SATCAP for crack growth test is reported. (author)
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...
Ivo Černý
2009-01-01
Results of an investigation of effect of shot peening on development of physically short fatigue crack in an aircraft V-95 Al-alloy, which is of a similar type as 7075 alloy, are described and discussed in the paper. The first part deals with adaptation and verification of direct current potential drop method for detection and measurement of short crack initiation and growth. The specific material and quite large dimensions of flat specimens with side necking of a low stress concentration fac...
Fracture and subcritical crack-growth behavior of Y-Si-Al-O-N glasses and Si3N4 ceramics
International Nuclear Information System (INIS)
Bhatnagar, A.; Hoffman, M.J.; Dauskardt, R.H.
2000-01-01
Fracture and environmentally assisted subcritical crack-growth processes are examined in bulk Y-Si-Al-O-N oxynitride glasses with compositions typical of the grain boundary phase of silicon nitride ceramics. Both long-crack (in compact tension specimens) as well as short-crack behavior (using indentation techniques) were investigated to establish a reliable fracture toughness and to elucidate the anomalous densification behavior of the oxynitride glass. Environmentally assisted subcritical crack-growth processes were studied in inert, moist, and wet environments under both cyclic and static loading conditions. Behavior is discussed in terms of the interaction of the environment with the crack tip. Likely mechanisms for environmentally assisted crack growth are discussed and related to the subcritical crack-growth behavior of silicon nitride ceramics
Crack growth rate in the HAZ of alloy 600/182
Energy Technology Data Exchange (ETDEWEB)
Gomez-Briceno, D.; Lapena, J.; Garcia-Redondo, M.; Castro, L.; Perosanz, F.J. [CIEMAT (Spain); Ahluwalia, K. [EPRI, (United States); Hickling, J. [EPRI Consultant (Cyprus)
2011-07-01
CGR (Crack Growth Rate) experiments to obtain data for the HAZ (Heat Affected Zone) of nickel base alloys using fracture mechanics specimens are a challenge, primarily due to the difficulties of positioning the tip of the notch (or pre-crack) in the desired location within the complex region adjacent to the fusion line. This paper presents some results obtained in an experimental program carried out to the CGR in the HAZ of several welded Alloy 600 plates. Compact tension (CT) specimens have been tested in simulated PWR primary water at temperatures of 340 and 360 C degrees under cyclic and constant loading (both with and without periodic partial unloading). Satisfactory CGR data were obtained for the HAZ in an Alloy 600 plate (mill annealed at high temperature) welded with Alloy 182 under both environmentally assisted fatigue test conditions (cyclic loading at different frequencies) and during stress corrosion testing (i.e. at predominantly constant load). The CGR values were generally similar to those obtained for the corresponding base metal (with tentative evidence for slightly faster growth in the HAZ under pure constant load). The HAZ specimens showed a higher tendency to crack inter-granularly under cyclic loading. CGR values under predominantly SCC conditions corresponded well (after temperature correction) with the MRP - 55 75. percentile disposition curve for PWSCC in Alloy 600 materials. This contrasts with the behavior observed by other investigators, where the HAZ material was found to exhibit markedly higher CGRs. A possible explanation for this discrepancy is the higher PWSCC susceptibility of the Alloy 600 base metal used to prepare the HAZ specimens in this program. It appears that the strong increase in the HAZ CGR observed elsewhere may take place if the base metal is a heat with inherently low PWSCC susceptibility (i.e. with good microstructure, adequate carbide distribution, etc.). However, if the Alloy 600 base metal already has a susceptible
Crack growth rate in the HAZ of alloy 600/182
International Nuclear Information System (INIS)
Gomez-Briceno, D.; Lapena, J.; Garcia-Redondo, M.; Castro, L.; Perosanz, F.J.; Ahluwalia, K.; Hickling, J.
2011-01-01
CGR (Crack Growth Rate) experiments to obtain data for the HAZ (Heat Affected Zone) of nickel base alloys using fracture mechanics specimens are a challenge, primarily due to the difficulties of positioning the tip of the notch (or pre-crack) in the desired location within the complex region adjacent to the fusion line. This paper presents some results obtained in an experimental program carried out to the CGR in the HAZ of several welded Alloy 600 plates. Compact tension (CT) specimens have been tested in simulated PWR primary water at temperatures of 340 and 360 C degrees under cyclic and constant loading (both with and without periodic partial unloading). Satisfactory CGR data were obtained for the HAZ in an Alloy 600 plate (mill annealed at high temperature) welded with Alloy 182 under both environmentally assisted fatigue test conditions (cyclic loading at different frequencies) and during stress corrosion testing (i.e. at predominantly constant load). The CGR values were generally similar to those obtained for the corresponding base metal (with tentative evidence for slightly faster growth in the HAZ under pure constant load). The HAZ specimens showed a higher tendency to crack inter-granularly under cyclic loading. CGR values under predominantly SCC conditions corresponded well (after temperature correction) with the MRP - 55 75. percentile disposition curve for PWSCC in Alloy 600 materials. This contrasts with the behavior observed by other investigators, where the HAZ material was found to exhibit markedly higher CGRs. A possible explanation for this discrepancy is the higher PWSCC susceptibility of the Alloy 600 base metal used to prepare the HAZ specimens in this program. It appears that the strong increase in the HAZ CGR observed elsewhere may take place if the base metal is a heat with inherently low PWSCC susceptibility (i.e. with good microstructure, adequate carbide distribution, etc.). However, if the Alloy 600 base metal already has a susceptible
International Nuclear Information System (INIS)
Mager, T.R.; Moon, D.M.; Landes, J.D.
1976-01-01
To characterize the effect of environment on crack growth rate properties of reactor pressure vessel materials, a program was initiated as part of the Heavy Section Steel Technology Program (HSST) to evaluate the effect of Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) primary grade coolant environments. The experiments included such variables as frequency, temperature and R ratio. This paper describes the investigation and presents the results of a fracture mechanics evaluation of the fatigue crack growth rate tests of A533 Grade B Class 1 steel plate material in an environment of primary reactor grade water at 550 0 F (288 0 C). A compliance crack growth monitoring technique was utilized to measure the crack growth. The compliance crack length monitor uses a linear variable differential transformer (LVDT) to measure the specimen front face displacement which is converted to crack length by the appropriate compliance calibration curve. The crack growth rate tests were conducted on constant load universal fatigue machines, under sinusoidal tension to tension loading conditions. Tests showed an increase in growth rates at a frequency of 1 cpm over previous results obtained at frequencies of 60 cpm and higher. This increase, the general character of the crack growth rate versus the $DELTA$K curve, and the results from fractographic studies, all indicated that stress corrosion cracking might have occurred for this material and environment. However, a specimen loaded statically in a PWR environment showed no static load crack growth. 13 refs
Telesman, J.; Smith, T. M.; Gabb, T. P.; Ring, A. J.
2017-01-01
An investigation of high temperature cyclic fatigue crack growth (FCG) threshold behavior of two advanced nickel disk alloys was conducted. The focus of the study was the unusual crossover effect in the near-threshold region of these type of alloys where conditions which produce higher crack growth rates in the Paris regime, produce higher resistance to crack growth in the near threshold regime. It was shown that this crossover effect is associated with a sudden change in the fatigue failure mode from a predominant transgranular mode in the Paris regime to fully intergranular mode in the threshold fatigue crack growth region. This type of a sudden change in the fracture mechanisms has not been previously reported and is surprising considering that intergranular failure is typically associated with faster crack growth rates and not the slow FCG rates of the near-threshold regime. By characterizing this behavior as a function of test temperature, environment and cyclic frequency, it was determined that both the crossover effect and the onset of intergranular failure are caused by environmentally driven mechanisms which have not as yet been fully identified. A plausible explanation for the observed behavior is proposed.
Persistent Environmental Toxicants in Breast Milk and Rapid Infant Growth.
Criswell, Rachel; Lenters, Virissa; Mandal, Siddhartha; Stigum, Hein; Iszatt, Nina; Eggesbø, Merete
2017-01-01
Many environmental toxicants are passed to infants in utero and through breast milk. Exposure to toxicants during the perinatal period can alter growth patterns, impairing growth or increasing obesity risk. Previous studies have focused on only a few toxicants at a time, which may confound results. We investigated levels of 26 toxicants in breast milk and their associations with rapid infant growth, a risk factor for later obesity. We used data from the Norwegian HUMIS study, a multi-center cohort of 2,606 mothers and newborns enrolled between 2002 and 2008. Milk samples collected 1 month after delivery from a subset of 789 women oversampled by overweight were analyzed for toxicants including polychlorinated biphenyls (PCBs), heavy metals, and pesticides. Growth was defined as change in weight-for-age z-score between 0 and 6 months among the HUMIS population, and rapid growth was defined as change in z-score above 0.67. We used a Bayesian variable selection method to determine the exposures that most explained variation in the outcome. Identified toxicants were included in logistic and linear regression models to estimate associations with growth, adjusting for maternal age, smoking, education, pre-pregnancy body mass index (BMI), gestational weight gain, parity, child sex, cumulative breastfeeding, birth weight, gestational age, and preterm status. Of 789 infants, 19.2% displayed rapid growth. The median maternal age was 29.6 years, and the median pre-pregnancy BMI was 24.0 kg/m2, with 45.3% of mothers overweight or obese. Rapid growers were more likely to be firstborn. Hexachlorobenzene, β-hexachlorocyclohexane (β-HCH), and PCB-74 were identified in the variable selection method. An interquartile range (IQR) increase in β-HCH exposure was associated with a lower odds of rapid growth (OR 0.63, 95% CI 0.42-0.94). Newborns exposed to high levels of β-HCH showed reduced infant growth (β = -0.03, 95% CI -0.05 to -0.01 for IQR increase in breast milk concentration
Effect of specimen geometry on the variability in fatigue crack growth rate
International Nuclear Information System (INIS)
Tsuji, Hirokazu; Nakajima, Hajime; Kondo, Tatsuo
1982-02-01
Fatigue crack growth tests on SA 533 grade B class 1 steel were conducted in air with both contoured double cantilever beam (CDCB) specimens and compact-tension (CT) specimens for comparison, which corresponded to the ΔK constant and ΔK increasing fatigue tests respectively. The variability of the measured values was examined statistically, and possible sources of the determined variability were discussed. The variability in the ΔK increasing fatigue tests with the CT specimens was found to be substantially greater than that in the ΔK constant fatigue tests with the CDCB specimens employed in the present study. In addition, the width of the scatter as well as in the degree of deviation from the expected linearity in da/dN versus ΔK plots were found to be varied depending on the level of ΔK in the CT specimen. Based on the results, a conclusion was drawn that constant ΔK type tests should be preferred in the tests where accuracy and reproducibility of crack growth rate measurement was of particular importance. (author)
Bayesian Model on Fatigue Crack Growth Rate of Type 304 Stainless Steel
Energy Technology Data Exchange (ETDEWEB)
Choi, Sanhae; Yoon, Jae Young; Hwang, Il Soon [Nuclear Materials Laboratory, Seoul National University, Seoul (Korea, Republic of)
2015-10-15
The fatigue crack growth rate curve is typically estimated by deterministic methods in accordance with the ASME Boiler and Pressure Vessel Code Sec. XI. The reliability of nuclear materials must also consider the environmental effect. This can be overcome by probabilistic methods that estimate the degradation of materials. In this study, fatigue tests were carried out on Type 304 stainless steel (STS 304) to obtain a fatigue crack growth rate curve and Paris' law constants. Tests were conducted on a constant load and a constant delta K, respectively. The unknown constants of Paris' law were updated probabilistically by Bayesian inference and the method can be used for the probabilistic structural integrity assessment of other nuclear materials. In this paper, Paris' law constants including C and m for Type 304 stainless steel were determined by probabilistic approach with Bayesian Inference. The Bayesian update process is limited in accuracy, because this method should assume initial data distribution. If we select an appropriate distribution, this updating method is powerful enough to get data results considering the environment and materials. Until now, remaining lives of NPPs are estimated by deterministic methods using a priori model to finally assess structural integrity. Bayesian approach can utilize in-service inspection data derived from aged properties.
Accelerated Testing Methodology for the Determination of Slow Crack Growth of Advanced Ceramics
Choi, Sung R.; Salem, Jonathan A.; Gyekenyesi, John P.
1997-01-01
Constant stress-rate (dynamic fatigue) testing has been used for several decades to characterize slow crack growth behavior of glass and ceramics at both ambient and elevated temperatures. The advantage of constant stress-rate testing over other methods lies in its simplicity: Strengths are measured in a routine manner at four or more stress rates by applying a constant crosshead speed or constant loading rate. The slow crack growth parameters (n and A) required for design can be estimated from a relationship between strength and stress rate. With the proper use of preloading in constant stress-rate testing, an appreciable saving of test time can be achieved. If a preload corresponding to 50 % of the strength is applied to the specimen prior to testing, 50 % of the test time can be saved as long as the strength remains unchanged regardless of the applied preload. In fact, it has been a common, empirical practice in strength testing of ceramics or optical fibers to apply some preloading (less then 40%). The purpose of this work is to study the effect of preloading on the strength to lay a theoretical foundation on such an empirical practice. For this purpose, analytical and numerical solutions of strength as a function of preloading were developed. To verify the solution, constant stress-rate testing using glass and alumina at room temperature and alumina silicon nitride, and silicon carbide at elevated temperatures was conducted in a range of preloadings from O to 90 %.
Accelerated Testing Methodology Developed for Determining the Slow Crack Growth of Advanced Ceramics
Choi, Sung R.; Gyekenyesi, John P.
1998-01-01
Constant stress-rate ("dynamic fatigue") testing has been used for several decades to characterize the slow crack growth behavior of glass and structural ceramics at both ambient and elevated temperatures. The advantage of such testing over other methods lies in its simplicity: strengths are measured in a routine manner at four or more stress rates by applying a constant displacement or loading rate. The slow crack growth parameters required for component design can be estimated from a relationship between strength and stress rate. With the proper use of preloading in constant stress-rate testing, test time can be reduced appreciably. If a preload corresponding to 50 percent of the strength is applied to the specimen prior to testing, 50 percent of the test time can be saved as long as the applied preload does not change the strength. In fact, it has been a common, empirical practice in the strength testing of ceramics or optical fibers to apply some preloading (<40 percent). The purpose of this work at the NASA Lewis Research Center is to study the effect of preloading on measured strength in order to add a theoretical foundation to the empirical practice.
Fracture Toughness and Fatigue Crack Growth Behavior of As-Cast High-Entropy Alloys
Seifi, Mohsen; Li, Dongyue; Yong, Zhang; Liaw, Peter K.; Lewandowski, John J.
2015-08-01
The fracture toughness and fatigue crack growth behavior of two as-vacuum arc cast high-entropy alloys (HEAs) (Al0.2CrFeNiTi0.2 and AlCrFeNi2Cu) were determined. A microstructure examination of both HEA alloys revealed a two-phase structure consisting of body-centered cubic (bcc) and face-centered cubic (fcc) phases. The notched and fatigue precracked toughness values were in the range of those reported in the literature for two-phase alloys but significantly less than recent reports on a single phase fcc-HEA that was deformation processed. Fatigue crack growth experiments revealed high fatigue thresholds that decreased significantly with an increase in load ratio, while Paris law slopes exhibited metallic-like behavior at low R with significant increases at high R. Fracture surface examinations revealed combinations of brittle and ductile/dimpled regions at overload, with some evidence of fatigue striations in the Paris law regime.
An adaptive ARX model to estimate the RUL of aluminum plates based on its crack growth
Barraza-Barraza, Diana; Tercero-Gómez, Víctor G.; Beruvides, Mario G.; Limón-Robles, Jorge
2017-01-01
A wide variety of Condition-Based Maintenance (CBM) techniques deal with the problem of predicting the time for an asset fault. Most statistical approaches rely on historical failure data that might not be available in several practical situations. To address this issue, practitioners might require the use of self-starting approaches that consider only the available knowledge about the current degradation process and the asset operating context to update the prognostic model. Some authors use Autoregressive (AR) models for this purpose that are adequate when the asset operating context is constant, however, if it is variable, the accuracy of the models can be affected. In this paper, three autoregressive models with exogenous variables (ARX) were constructed, and their capability to estimate the remaining useful life (RUL) of a process was evaluated following the case of the aluminum crack growth problem. An existing stochastic model of aluminum crack growth was implemented and used to assess RUL estimation performance of the proposed ARX models through extensive Monte Carlo simulations. Point and interval estimations were made based only on individual history, behavior, operating conditions and failure thresholds. Both analytic and bootstrapping techniques were used in the estimation process. Finally, by including recursive parameter estimation and a forgetting factor, the ARX methodology adapts to changing operating conditions and maintain the focus on the current degradation level of an asset.
Fatigue crack growth monitoring in multi-layered structures using guided ultrasonic waves
International Nuclear Information System (INIS)
Kostson, E; Fromme, P
2009-01-01
This contribution investigates the application of low frequency guided ultrasonic waves for monitoring fatigue crack growth at fastener holes in the 2nd layer of multi-layered plate structures, a common problem in aerospace industry. The model multi-layered structure investigated consists of two aluminum plate-strips adhesively bonded using a structural paste adhesive. Guided ultrasonic waves were excited using multiple piezoelectric discs bonded to the surface of the multi-layered structure. The wave propagation in the tensile specimen was measured using a laser interferometer and compared to numerical simulations. Thickness and width mode shapes of the excited flexural waves were identified from Semi-Analytical Finite Element (SAFE) calculations. Experiments and 3D Finite Element (FE) simulations show a change in the scattered field around fastener holes caused by a defect in the 2nd layer. The amplitude of the guided ultrasonic wave was monitored during fatigue experiments at a single point. The measured changes in the amplitude of the ultrasonic signal due to fatigue crack growth agree well with FE simulations.
Influence of hydrogen on crack growth rate of alloy 690 CW in PWR conditions
International Nuclear Information System (INIS)
Garcia Redondo, M.S.; Perosanz, F.J.; Lapena, J.; Gomez-Briceno, D.
2015-01-01
The influence of hydrogen concentration is well established for Alloy 600 and other nickel base alloys as Alloy 182/ 82 weld metals and X-750. It is accepted that for these materials maximum crack growth rate peaks close to Ni/NiO phase boundary. The influence of the hydrogen on the CGR of Alloy 690 is not well established. Available results for Alloy 690 are scarce and not conclusive. Results obtained by CIEMAT, in conditions representative of the PWR operating plants, indicated an apparent crack growth rate increase by a 3 factor when the hydrogen concentration increased from 35 to 81 cm -3 of H 2 /kg H 2 O. In order to gain some insight into the influence of the hydrogen, a new test has been performed with 20 cm -3 H 2 /kg H 2 O at 360 Celsius degrees, concentration close to Ni/NiO phase boundary. The material used was extruded control rod drive mechanism (CRDM) tubes with homogeneous microstructure. Rolling and tensile straining was applied to the CRDM material to obtain 20% of cold work in order to simulate the strain condition expected in the Heat Affected Zone (HAZ). (authors)
Bayesian Model on Fatigue Crack Growth Rate of Type 304 Stainless Steel
International Nuclear Information System (INIS)
Choi, Sanhae; Yoon, Jae Young; Hwang, Il Soon
2015-01-01
The fatigue crack growth rate curve is typically estimated by deterministic methods in accordance with the ASME Boiler and Pressure Vessel Code Sec. XI. The reliability of nuclear materials must also consider the environmental effect. This can be overcome by probabilistic methods that estimate the degradation of materials. In this study, fatigue tests were carried out on Type 304 stainless steel (STS 304) to obtain a fatigue crack growth rate curve and Paris' law constants. Tests were conducted on a constant load and a constant delta K, respectively. The unknown constants of Paris' law were updated probabilistically by Bayesian inference and the method can be used for the probabilistic structural integrity assessment of other nuclear materials. In this paper, Paris' law constants including C and m for Type 304 stainless steel were determined by probabilistic approach with Bayesian Inference. The Bayesian update process is limited in accuracy, because this method should assume initial data distribution. If we select an appropriate distribution, this updating method is powerful enough to get data results considering the environment and materials. Until now, remaining lives of NPPs are estimated by deterministic methods using a priori model to finally assess structural integrity. Bayesian approach can utilize in-service inspection data derived from aged properties
International Nuclear Information System (INIS)
Ritter, S.; Seifert, H.P.
2008-01-01
The low-frequency corrosion fatigue (CF) crack growth behaviour of different low-alloy reactor pressure vessel steels was characterized under simulated boiling water reactor conditions by cyclic fatigue tests with pre-cracked fracture mechanics specimens. The experiments were performed in the temperature range of 240-288 deg. C with different loading parameters at different electrochemical corrosion potentials (ECPs). Modern high-temperature water loops, on-line crack growth monitoring (DCPD) and fractographical analysis by SEM were used to quantify the cracking response. In this paper the effect of ECP on the CF crack growth behaviour is discussed and compared with the crack growth model of General Electric (GE). The ECP mainly affected the transition from fast ('high-sulphur') to slow ('low-sulphur') CF crack growth, which appeared as critical frequencies ν crit = f(ΔK, R, ECP) and ΔK-thresholds ΔK EAC f(ν, R, ECP) in the cycle-based form and as a critical air fatigue crack growth rate da/dt Air,crit in the time-domain form. The critical crack growth rates, frequencies, and ΔK EAC -thresholds were shifted to lower values with increasing ECP. The CF crack growth rates of all materials were conservatively covered by the 'high-sulphur' CF line of the GE-model for all investigated temperatures and frequencies. Under most system conditions, the model seems to reasonably well predict the experimentally observed parameter trends. Only under highly oxidizing conditions (ECP ≥ 0 mV SHE ) and slow strain rates/low loading frequencies the GE-model does not conservatively cover the experimentally gathered crack growth rate data. Based on the GE-model and the observed cracking behaviour a simple time-domain superposition-model could be used to develop improved reference CF crack growth curves for codes
National Research Council Canada - National Science Library
Barron, Michael
1999-01-01
.... Specifically, the FAA's goal was to develop "Crack Growth-Based Predictive Methodologies for the Maintenance of the Structural Integrity of Repaired and Nonrepaired Aging Engine Stationary Components...
International Nuclear Information System (INIS)
Heerens, J.
1990-01-01
A procedure is developed which allows to estimate crack tip blunting using the stress-strain curve of the material and the J-integral. The second part deals with cleavage fracture in a quenched and tempered pressure vessel steel. It was found that within the ductile to brittle transition regime the fracture toughness is controlled by cleavage initiated at 'weak spots of the material' and by the normal stresses at the weak spots. In the last part of the paper the influence of specimen size on J-, Jm- and δ 5 -R-curves for side grooved CT-specimens under fully plastic condition is investigated. In order to characterize constraint-effects the necking of the specimens was measured. For specimens having similar constraint the parameters Jm and δ 5 yielded size independent R-curves over substantial larger amounts of crack extension than the J-integral. (orig.) With 114 figs., 10 tabs [de
In Search of a Time Efficient Approach to Crack and Delamination Growth Predictions in Composites
Krueger, Ronald; Carvalho, Nelson
2016-01-01
Analysis benchmarking was used to assess the accuracy and time efficiency of algorithms suitable for automated delamination growth analysis. First, the Floating Node Method (FNM) was introduced and its combination with a simple exponential growth law (Paris Law) and Virtual Crack Closure technique (VCCT) was discussed. Implementation of the method into a user element (UEL) in Abaqus/Standard(Registered TradeMark) was also presented. For the assessment of growth prediction capabilities, an existing benchmark case based on the Double Cantilever Beam (DCB) specimen was briefly summarized. Additionally, the development of new benchmark cases based on the Mixed-Mode Bending (MMB) specimen to assess the growth prediction capabilities under mixed-mode I/II conditions was discussed in detail. A comparison was presented, in which the benchmark cases were used to assess the existing low-cycle fatigue analysis tool in Abaqus/Standard(Registered TradeMark) in comparison to the FNM-VCCT fatigue growth analysis implementation. The low-cycle fatigue analysis tool in Abaqus/Standard(Registered TradeMark) was able to yield results that were in good agreement with the DCB benchmark example. Results for the MMB benchmark cases, however, only captured the trend correctly. The user element (FNM-VCCT) always yielded results that were in excellent agreement with all benchmark cases, at a fraction of the analysis time. The ability to assess the implementation of two methods in one finite element code illustrated the value of establishing benchmark solutions.
International Nuclear Information System (INIS)
Foehl, J.; Weissenberg, T.; Gomez-Briceno, D.; Lapena, J.; Ernestova, M.; Zamboch, M.; Seifert, H.P.; Ritter, S.; Roth, A.; Devrient, B.; Ehrnsten, U.
2004-01-01
The CASTOC project addresses environmentally assisted cracking (EAC) phenomena in low alloy steels used for pressure boundary components in both Western type boiling water reactors (BWR) and Russian type pressurised water reactors (VVER). It comprises the four work packages (WP): inter-laboratory comparison test (WP1); EAC behaviour under static load (WP2), EAC behaviour under cyclic load and load transients (WP3); evaluation of the results with regard to their relevance for components in practice (WP4). The use of sophisticated test facilities and measurement techniques for the on-line detection of crack advances have provided a more detailed understanding of the mechanisms of environmentally assisted cracking and provided quantitative data of crack growth rates as a function of loading events and time, respectively. The effect of several major parameters controlling EAC was investigated with particular emphasis on the transferability of the results to components in service. The obtained crack growth rate data were reflected on literature data and on commonly applied prediction curves as presented in the appropriate Code. At relevant stress intensity factors it could be shown that immediate cessation of growing cracks occurs after changing from cyclic to static load in high purity oxygenated BWR water and oxygen-free VVER water corresponding to steady state operation conditions. Susceptibility to environmentally assisted cracking under static load was observed for a heat affected zone material in oxygenated high purity water and also in base materials during a chloride transient representing BWR water condition below Action Level 1 of the EPRI Water Chemistry Guidelines according to the lectrical conductivity of the water but in the range of Action Level 2 according to the content of chlorides. Time based crack growth was also observed in one Russian type base material in oxygenated VVER water and in one Western type base material in oxygenated high purity BWR
International Nuclear Information System (INIS)
Kim, Seon Jin; Kim, Jong Hoon; Ahn, Seok Hwan
2000-01-01
Constant ΔK fatigue crack growth tests were performed applying an intermediate multiple overload for SM45C steel. The purpose of the present study is to investigate the effects of specimen thickness at various baseline stress intensity levels(ΔK b ), overload application position(a/W) and overload application frequency(OL Hz ) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The amount of retardation for a given ΔK b level is increased with increasing the baseline stress intensity level in all specimen thickness. The normalized minimum crack growth rate is increased with increasing the specimen thickness, except for ΔK=45MPa√m. The retardation cycle is decreased with increasing the overload application position and increased with the overload application frequency
Rate-dependent mode I interlaminar crack growth mechanisms in graphite/epoxy and graphite/PEEK
Gillespie, J. W., Jr.; Carlsson, L. A.; Smiley, A. J.
1987-01-01
In this paper the mode I fracture behavior of graphite/epoxy and graphite/PEEK composites is examined over four decades of crosshead rates (0.25-250 mm/min). Straight-sided double-cantilever-beam specimens consisting of unidirectional laminates were tested at room temperature. For graphite/epoxy the load-deflection response was linear to fracture, and stable slow crack growth initiating at the highest load level was observed for all rates tested. In contrast, mode I crack growth in the graphite/PEEK material was often unstable and showed stick-slip behavior. Subcritical crack growth occurring prior to the onset of fracture was observed at intermediate displacement rates. A mechanism for the fracture behavior of the graphite/PEEK material (based on viscoelastic, plastic, and microcrack coalescence in the process zone) is proposed and related to the observed rate-dependent phenomena.
International Nuclear Information System (INIS)
Aktaa, J.; Lerch, M.
2005-05-01
For the assessment of cracks in First Wall structures built from EUROFER 97 of future fusion reactors the fatigue crack behaviour in EUROFER 97 was investigated at room temperature (RT), 300, 500 and 550 C. For this purpose fatigue crack growth tests were performed using CT specimens with two R-ratios, R=0.1 and R=0.5, respectively. Hence, fatigue crack threshold, fatigue crack growth behaviour in the near-threshold range and their dependences on temperature and R-ratio were determined and described using an analytical formula. The fatigue crack threshold showed a monotonic dependence on temperature which is for insignificantly small. The fatigue crack growth behaviour exhibited for a nonmonotonic dependence on temperature which is explained by the decrease of yield stress and the increase of creep damage when increasing the temperature [de
International Nuclear Information System (INIS)
Simatos, A.
2010-01-01
This work extends the applicability of local models for ductile fracture to large crack growth modelization for ductile tearing. This is done inserting a cohesive zone model whose constitutive law is identified in order to be consistent with the local model. The consistency is obtained through the cohesive law incremental construction which ensures the equivalence of the energy and of the mechanical response of the models. The extension of the applicability domain of the local modelization is enabled via the XFEM framework which allows for maintaining the mechanical energy during the crack extension step. This method permits also to introduce the cohesive zone model during the calculation without regards to the mesh of the structure for its maximal tensile stress. To apply the XFEM to ductile tearing, this method is extended to non linear problems (Updated Lagrangian Formulation, large scale yield plasticity). The cohesive zone model grows when the criterion defined in term of porosity, tested at the front of the cohesive crack front, is verified. The cohesive zone growth criterion is determined in order to model most of the damaging phase with the local model to ensure that the modelization takes into account the triaxiality ratio history accurately. The proposed method is applied to the Rousselier local model for ductile fracture in the XFEM framework of Cast3M, the FE software of the CEA. (author) [fr
Effect of pre-strain history on small crack growth under low cycle fatigue for JIS SFVQ1A steel
International Nuclear Information System (INIS)
Hasunuma, Shota; Miyata, Yohei; Sakaue, Kenichi; Ogawa, Takeshi
2011-01-01
Low cycle fatigue tests were performed for a low alloy steel, JIS SFVQ1A, used for pressure vessels of nuclear power plants. The effect of pre-strain history on the small crack initiation and growth was investigated in detail using cellulose acetate replicas. Under the tests in which the total strain range, Δε, is constant, surface crack length, 2c, was smaller for the tests with larger Δε due to the different numbers of small crack initiation and coalescence. The pre-strain histories were applied at Δε of 8 or 16% with its fatigue usage factor, UF, of less than 0.2, followed by fatigue loading at Δε=2% until fracture. In these tests, the relationships between 2c and UF agreed with each other unless crack coalescence occurred. The scatter in fatigue life was attributed to the coalescences of small cracks. Fracture mechanics approach was applied to predict the fatigue lives and to characterize the growth behavior of small fatigue cracks. (author)