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Sample records for crack arrest methodology

  1. Comparison of crack arrest methodologies

    International Nuclear Information System (INIS)

    Anon.

    1979-01-01

    The ASTM Cooperative Test Program Data were used to compare the static (K/sub Ia/) and dynamic (K/sud ID/, K/sub IDm/) approaches to crack arrest. K/sub Ia/ is not dependent on K/sub Q/. This is consistent with the requirements of the static approach, but not the dynamic one which requires that K/sub Ia/ decrease with K/sub Q/ if K/sub ID/ (= K/sub IDm/) is a constant. K/sub ID/ increases systematically with K/sub Q/ at a rate that is consistent with calculations based on the use of a constant value for K/sub Ia/ which is equal to its measured mean value. Only in the limiting case of very short crack jumps (associated with very low average crack speeds) can K/sub ID/ be identified as a minimum value at which K/sub ID/ = K/sub IDm/. In this case K/sub IDm/ approx. K/sub Ia/ approx. K/sub Im/. The latter is the idealized minimum value of K that will support the continued propagation of a running crack

  2. Critical experiments, measurements, and analyses to establish a crack arrest methodology for nuclear pressure vessel steels

    International Nuclear Information System (INIS)

    Hahn, G.T.

    1977-01-01

    Substantial progress was made in three important areas: crack propagation and arrest theory, two-dimensional dynamic crack propagation analyses, and a laboratory test method for the material property data base. The major findings were as follows: Measurements of run-arrest events lent support to the dynamic, energy conservation theory of crack arrest. A two-dimensional, dynamic, finite-difference analysis, including inertia forces and thermal gradients, was developed. The analysis was successfully applied to run-arrest events in DCB (double-cantilever-beam) and SEN (single-edge notched) test pieces. A simplified procedure for measuring K/sub D/ and K/sub Im/ values with ordinary and duplex DCB specimens was demonstrated. The procedure employs a dynamic analysis of the crack length at arrest and requires no special instrumentation. The new method was applied to ''duplex'' specimens to measure the large K/sub D/ values displayed by A533B steel above the nil-ductility temperature. K/sub D/ crack velocity curves and K/sub Im/ values of two heats of A533B steel and the corresponding values for the plane strain fracture toughness associated with static initiation (K/sub Ic/), dynamic initiation (K/sub Id/), and the static stress intensity at crack arrest (K/sub Ia/) were measured. Possible relations among these toughness indices are identified. During the past year the principal investigators of the participating groups reached agreement on a crack arrest theory appropriate for the pressure vessel problem. 7 figures

  3. An evaluation of analysis methodologies for predicting cleavage arrest of a deep crack in an RPV subjected to PTS loading conditions

    International Nuclear Information System (INIS)

    Keeney-Walker, J.; Bass, B.R.

    1992-01-01

    Several calculational procedures are compared for predicting cleavage arrest of a deep crack in the wall of a prototypical reactor pressure vessel (RPV) subjected to pressurized-thermal-shock (PTS) types of loading conditions. Three procedures examined in this study utilized the following models: (1) a static finite-element model (full bending); (2) a radially constrained static model; and (3) a thermoelastic dynamic finite-element model. A PTS transient loading condition was selected that produced a deep arrest of an axially-oriented initially shallow crack according to calculational results obtained from the static (full-bending) model. Results from the two static models were compared with those generated from the detailed thermoelastic dynamic finite-element analysis. The dynamic analyses modeled cleavage-crack propagation using node-release technique and an application-mode methodology based on dynamic fracture toughness curves generated from measured data. Comparisons presented here indicate that the degree to which dynamic solutions can be approximated by static models is highly dependent on several factors, including the material dynamic fracture curves and the propensity for cleavage reinitiation of the arrested crack under PTS loading conditions. Additional work is required to develop and validate a satisfactory dynamic fracture toughness model applicable to postcleavage arrest conditions in an RPV

  4. Dynamic photoelastic investigation of crack arrest

    International Nuclear Information System (INIS)

    Irwin, G.R.; Dally, J.W.; Kobayashi, T.; Fourney, W.L.

    1977-01-01

    Crack arrest and crack arrest toughness are of great interest, particularly for studies pertaining to safety of nuclear reactor pressure vessels. Investigations are needed in which the instantaneous values of stress intensity factor (K) can be observed during crack propagation and arrest. Such observations are possible if the test specimens are made from plates of a transparent photoelastic sensitive material. Values of K as a function of crack speed are shown for Homalite 100 and various epoxy blends. 9 figures

  5. Critical experiments, measurements and analyses to establish a crack arrest methodology for nuclear pressure vessel steels. First annual progress report

    International Nuclear Information System (INIS)

    Hahn, G.T.; Gehlen, P.C.; Hoagland, R.G.; Kanninen, M.F.; Popelar, C.; Rosenfield, A.R.; deCampos, V.S.

    1975-08-01

    The one-dimensional, Timoshenko beam-on-a-generalized elastic foundation treatment has been extended to contoured-DCB specimens and to the conditions attending tensile loading in an ordinary testing machine. Preliminary calculations show that the crack propagation and arrest events in contoured DCB specimens are very similar to those calculated for regular DCB-specimens for comparable initiation conditions. In both cases the calculated K/sub Ia/-values are between 44 and 100 percent of K/sub ID,min/ and show a systematic variation with the initiation K/sub Q/-level. In contrast with stiff wedge loading, which favors a continuous event, the calculations for rectangular and contoured DCB specimens in series with an idealized testing machine load train display one or more halts and restarts before the final arrest. A series of experiments designed to distinguish between the K/sub D/ and K/sub a/ approaches to predicting crack arrest are described. Studies of the effect of side grooves in rectangular DCB specimens confirm that grooves with depths representing up to 60 percent of the cross section have no significant effect on either K/sub ID/ or K/sub Ia/ measurements. (auth)

  6. Critical experiments, measurements and analyses to establish a crack arrest methodology for nuclear pressure vessel steels. Sixth quarterly progress report, January--March 1976

    International Nuclear Information System (INIS)

    Hahn, G.T.; Gehlen, P.C.; Hoagland, R.G.; Kanninen, M.F.; Popelar, C.; Rosenfield, A.R.

    1976-07-01

    Governing equations for a complete two-dimensional analysis of fast fracture and crack arrest (including inertia and thermal gradients) are derived. Strain energy and compliance values calculated for an SEN specimen agree with experiment. In the case of a nonstationary crack, the strain energy release rate is computed from the nodal displacements in the immediate vicinity of the crack tip. This value of G is sensitive to the spacings between nodes in the x and y direction. Results of two-dimensional analyses of propagation and arrest in the SEN test piece are also described; they are in general accord with one propagation event measured in an SEN A533B steel test piece. Compliance measurements were carried out on the rectangular DCB specimen to test the accuracy of the compliance values calculated with the one-dimensional beam-on-elastic-foundation model. These compliance values and the derivatives of compliance with crack length are used to relate the loads or displacements at fracture onset and at arrest to K/sub Q/, K/sub D/, and K/sub a/. Efforts were also made to test the assumption that energy losses arising from damping remote from the crack tip can be neglected. Measurements of damped oscillations in an A533B DCB specimen with a stationary crack indicate that total damping rates are relatively low, and that oscillations of the load pins in the pinhole account for the bulk of the damping. Finally, a new procedure for measuring K/sub D/ and K/sub m/ values is described; it is based on a dynamic analysis of the crack length at arrest and dynamically stiff wedge loading (the tie-down device) and eliminates the need for crack velocity measurements. It can also be applied to both small and large crack jumps and to ordinary and duplex-DCB specimens. Results for A533B steel agree with K/sub D/-values obtained from velocity measurements. The new procedure is also used to analyze results for a series of ship steels

  7. HSST crack-arrest studies overview

    International Nuclear Information System (INIS)

    Pugh, C.E.; Whitman, G.D.

    1985-01-01

    An overview is given of the efforts underway in the Heavy-Section Steel Technology (HSST) Program to better understand and model crack-arrest behavior in reactor pressure vessel steels. The efforts are both experimental and analytical. The experimental work provides K/sub Ia/ data from laboratory-sized specimens, from thick-wall cylinders which exhibit essentially-full restraint and from nonisothermal wide-plate specimens. These data serve to define toughness-temperature trends and to provide validation data under prototypical reactor conditions. The analytical efforts interpret and correlate the data, plus provide LEFM, elastodynamic and viscoplastic methods for analyzing crack run-arrest behavior in reactor vessels. The analysis methods are incorporated into finite element computer programs which are under development at three separate laboratories. 22 refs., 10 figs

  8. Impacts of weld residual stresses and fatigue crack growth threshold on crack arrest under high-cycle thermal fluctuations

    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

  9. Impacts of weld residual stresses and fatigue crack growth threshold on crack arrest under high-cycle thermal fluctuations

    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

  10. Crack arrest concepts for failure prevention and life extension. Proceedings

    International Nuclear Information System (INIS)

    Wiesner, C.S.

    1996-01-01

    These proceedings contain the thirteen papers presented at a seminar on crack arrest concepts for failure prevention and life extension. They provide a picture of the current position of crack arrest testing, models and applications, discussion of the relevance of recent research to industrial problems, and an assessment of whether the application of crack arrest models provides additional safety. Separate abstracts have been prepared for seven papers of relevance to the nuclear industry and, in particular, reactor pressure vessels. (UK)

  11. Critical experiments, measurements and analyses to establish a crack arrest methodology for nuclear pressure vessel steels. Task 62. Second annual progress report, 1 July 1975 to 30 June 1976

    International Nuclear Information System (INIS)

    Hahn, G.T.; Gehlen, P.C.; Hoagland, R.G.; Marschall, C.W.; Kanninen, M.F.; Popelar, C.; Rosenfield, A.R.

    1976-10-01

    Developments of the theory, the analyses and the materials characterization for assessments of crack arrest in heavy walled nuclear pressure vessels are described. A two-dimensional, dynamic, finite difference analysis of crack propagation and arrest, including inertia forces and thermal stresses is derived. The analysis is used to treat run-arrest events in DCB- and SEN-specimens. Calculations based on the one-dimensional analysis are compared with detailed measurements of run-arrest in two polymeric materials. The agreements between calculations and experiments support the dynamic, energy conservation theory of crack arrest. Implications of a K/sub ID/-crack velocity curve with a negative slope are examined. The quantity K/sub Im/, the minimum propagating crack toughness, is identified as the crack arrest material property for engineering applications. Considerations entering the design of a crack arrest property measuring procedure, including specimen shape, size, thickness and the crack jump are discussed. The influence of side grooves on the propensity for crack branching is examined. Compliance measurements for rectangular DCB-specimens are presented and analyzed. Energy losses arising from damping remote from the crack tip in an A533B steel DCB specimen are described, and classed as negligible. Interactions between test pieces and the loading system are examined. A simplified procedure for measuring K/sub D/-, K/sub m/-, and K/sub a/-values, based on the dynamic analysis of the crack length at arrest is demonstrated. Measurements of K/sub D/ at temperatures in the range (NDT-66)C to (NDT +34)C and for crack velocities in the range 200 ms -1 to 1000 ms -1 are presented. The connection between propagating crack toughness values and the rapidly loaded stationary crack toughness K/sub Id/ is examined

  12. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    DEFF Research Database (Denmark)

    Martakos, G.; Andreasen, J. H.; Berggreen, Christian

    2017-01-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect o...

  13. Dynamic propagation and cleavage crack arrest in bainitic steel

    International Nuclear Information System (INIS)

    Hajjaj, M.

    2006-06-01

    In complement of the studies of harmfulness of defects, generally realized in term of initiation, the concept of crack arrest could be used as complementary analyses to the studies of safety. The stop occurs when the stress intensity factor becomes lower than crack arrest toughness (KIa) calculated in elasto-statics (KI ≤ KIa). The aim of this thesis is to understand and predict the stop of a crack propagating at high speed in a 18MND5 steel used in the pressure water reactor (PWR). The test chosen to study crack arrest is the disc thermal shock test. The observations under the scanning electron microscope of the fracture surface showed that the crack arrest always occurs in cleavage mode and that the critical microstructural entity with respect to the propagation and crack arrest corresponds to at least the size of the prior austenitic grain. The numerical analyses in elasto-statics confirm the conservatism of the codified curve of the RCC-M with respect to the values of KIa. The dynamic numerical analyses show that the deceleration of the crack measured at the end of the propagation is related to the global dynamic of the structure (vibrations). The transferability to components of crack arrest toughness obtained from tests analysed in static is thus not assured. The disc thermal shock tests were also modelled by considering a criterion of propagation and arrest of the type 'RKR' characterized by a critical stress sc which depends on the temperature. The results obtained account well for the crack jump measured in experiments as well as the shape of the crack arrest front. (author)

  14. Experimental investigation of interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device

    DEFF Research Database (Denmark)

    Martakos, G.; Andreasen, J.H.; Berggreen, Christian

    2017-01-01

    A recently proposed face-sheet–core interface crack arresting device is implemented in sandwich beams and tested using the Sandwich Tear Test configuration. Fatigue loading conditions are applied to propagate the crack and determine the effect of the crack stopper on the fatigue growth rate and a...

  15. A crack arrest test using a toughness gradient steel plate

    International Nuclear Information System (INIS)

    Okamura, H.; Yagawa, G.; Urabe, Y.; Satoh, M.; Sano, J.

    1995-01-01

    Pressurized thermal shock (PTS) is a phenomenon that can occur in the reactor pressure vessels (RPVs) with internal pressure and is one of the most severe stress conditions that can be applied to the vessel. Preliminary research has shown that no PTS concern is likely to exist on Japanese RPVs during their design service lives. However, public acceptance of vessel integrity requires analyses and experiment in order to establish an analytical method and a database for life extension of Japanese RPVs. The Japanese PTS integrity study was carried out from FY 1983 to FY 1991 as a national project by Japan Power Engineering and Inspection Corporation (JAPEIC) under contract with Ministry of International Trade and Industry (MITI) in cooperation with LWR utilities and vendors. Here, a crack arrest test was carried out using a toughness gradient steel plate with three layers to study the concept of crack arrest toughness. Four-point bending load with thermal shock was applied to the large flat plate specimen with a surface crack. Five crack initiations and arrests were observed during the test and the propagated crack bifurcated. Finally, cracks were arrested at the boundary of the first and the second layer, except for a small segment of the crack. The first crack initiation took place slightly higher than the lower bound of K Ic data obtained by ITCT specimens. That is, the K IC concept for brittle crack initiation was verified for heavy section steel plates. The first crack arrest took place within the scatter band of K Ia and K Id data for the first layer. That is, the K Ia concept appears applicable for crack arrest of a short crack jump

  16. Interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device – Numerical modelling

    DEFF Research Database (Denmark)

    Martakos, G.; Andreasen, J.H.; Berggreen, Christian

    2017-01-01

    A novel crack arresting device is implemented in foam-cored composite sandwich beams and tested using the Sandwich Tear Test (STT) configuration. A finite element model of the setup is developed, and the predictions are correlated with observations and results from a recently conducted experiment...... concept, as well as a design tool that can be used for the implementation of crack arresting devises in engineering applications of sandwich components and structures....

  17. Crack propagation and arrest simulation of X90 gas pipe

    International Nuclear Information System (INIS)

    Yang, Fengping; Huo, Chunyong; Luo, Jinheng; Li, He; Li, Yang

    2017-01-01

    To determine whether X90 steel pipe has enough crack arrest toughness or not, a damage model was suggested as crack arrest criterion with material parameters of plastic uniform percentage elongation and damage strain energy per volume. Fracture characteristic length which characterizes fracture zone size was suggested to be the largest mesh size on expected cracking path. Plastic uniform percentage elongation, damage strain energy per volume and fracture characteristic length of X90 were obtained by five kinds of tensile tests. Based on this criterion, a length of 24 m, Φ1219 × 16.3 mm pipe segment model with 12 MPa internal gas pressure was built and computed with fluid-structure coupling method in ABAQUS. Ideal gas state equation was used to describe lean gas behavior. Euler grid was used to mesh gas zone inside the pipe while Lagrangian shell element was used to mesh pipe. Crack propagation speed and gas decompression speed were got after computation. The result shows that, when plastic uniform percentage elongation is equal to 0.054 and damage strain energy per volume is equal to 0.64 J/mm"3, crack propagation speed is less than gas decompression speed, which means the simulated X90 gas pipe with 12 MPa internal pressure can arrest cracking itself. - Highlights: • A damage model was suggested as crack arrest criterion. • Plastic uniform elongation and damage strain energy density are material parameters. • Fracture characteristic length is suggested to be largest mesh size in cracking path. • Crack propagating simulation with coupling of pipe and gas was realized in ABAQUS. • A Chinese X90 steel pipe with 12 MPa internal pressure can arrest cracking itself.

  18. An engineering interpretation of pop-in arrest and tearing arrest in terms of static crack arrest, Ksub(Ia)

    International Nuclear Information System (INIS)

    Witt, F.J.

    1983-01-01

    When fracture toughness specimens are tested under displacement controlled conditions, they are often observed to exhibit unstable cleavage fracture followed by arrest of the cleavage mode wherein a significant load remains on the specimen (pop-in arrest). This behavior carries over into the ductile tearing regime wherein tearing may occur rapidly identified by load reduction and then proceeds at a discernible less rate (tearing arrest). Both these behaviors represent an initiation condition followed by an arrest condition. In this paper it is demonstrated that from either of the arrest conditions an arrest value may be determined which, for available experimental data, is shown to be an engineering estimate for the static crack arrest toughness, Ksub(Ia). A data analysis procedure is outlined and Ksub(Ic) and Ksub(Ia) estimates from sixty-eight 1/2, 1 and 2 in. thick compact specimens from two steels (A533 Grade B Class 1 and AISI 1018) tested between -40 deg F and 200 deg F are summarized. The crack arrest estimates are seen to compare favorably with Ksub(Ia) results obtained by other investigators using 2 in. thick specimens. Also it is demonstrated that when failure is by fully ductile tearing, the crack arrest toughness is at least equal to the estimate for Ksub(Ic) for the specimen. (author)

  19. Crack arrest toughness measurements with A533B steel

    International Nuclear Information System (INIS)

    Salonen, Seppo.

    1979-11-01

    This work covers crack arrest toughness measurements on A533B steel done at the Technical Research Centre of Finland. These measurements are one part of a multinational effort, involving 30 laboratories. The aim of the cooperative test program is to examine two test procedures for measuring the crack arrest toughness, to give information about their reproducibility, and to identify the factors affecting the interpretation. The principles given for the testing were easy to apply in general and the results were satisfactory. Some factors in the test runs and in the specimen's behaviour are indicated which can cause error in the results or make implementation of the test more difficult. By comparing the results from our laboratory with average values from the test program a good agreement can be seen. Crack arrest toughness values derived from the compared procedures with a static analysis agree closely, but values calculated using a dynamic analysis differ considerably. (author)

  20. Crack arrest toughness of structural steels evaluated by compact test

    International Nuclear Information System (INIS)

    Nakano, Yoshifumi; Tanaka, Michihiro

    1982-01-01

    Crack arrest tests such as compact, ESSO and DCB tests were made on SA533B Cl. 1, HT80 and KD32 steels to evaluate the crack arrest toughness. The main results obtained are as follows: (1) The crack arrest toughness could be evaluated by K sub(Ia) which was obtained by the static analysis of compact test. (2) K sub(ID) determined by the dynamic analysis of compact test was greater than K sub(Ia), though K sub(ID) became close to K sub(Ia)/K sub(Q) became a unity where K sub(Q) is the stress intensity factor at the crack initiation. (3) No significant difference was observed between K sub(Ia) and K sub(ca) obtained by ESSO and DCB tests, though K sub(ca) obtained by DCB test tended to be smaller than K sub(Ia) at lower temperatures. (4) K sub(Ia) was smaller than K sub(Ic) in the transition temperature range, while it was greater than K sub(Id). In the temperature range where K sub(Ic), which was determined from J sub(Ic), decreased with temperature increase, however, it was smaller than K sub(Ia). (5) The fracture appearance transition temperature and the absorbed energy obtained by 2 mm V-notch Charpy test were appropriate parameters for representing the crack arrest toughness, while the NDT temperature was not. (author)

  1. Nuclear reactor pressure vessel integrity insurance by crack arrestability evaluation using load from CVN tests

    International Nuclear Information System (INIS)

    Fabry, A.

    1997-01-01

    The present work is undertaken in the framework of nuclear reactor pressure vessel (RPV) surveillance and aims at revisiting the crack arrest approach to structural integrity insurance. This approach, performed under normal plant operation conditions, can also offer an attractive alternative to the crack initiation philosophy promoted for accidental analysis. To this end, an accidental conservative, cost effective and robust methodology is forwarded and demonstrated: it makes use of the crack arrest information contained in the instrumented Charpy V-notch impact test and/or in the shear fracture appearance of broken samples. Particular attention is paid to the appraisal of uncertainties and the related safety margin. The resulting capability is placed in perspective with the state-of-the-art crack initiation methodology based on the slow bend testing of recracked specimens, presently under standardization world-wide. The investigation leads to highlight three conceptual weaknesses of current enfgineering and regulatory practices. Improved crack arrestability evaluation emerges as an optimal approach to insure safe PWR operation up to design end-of-life and beyond

  2. Nuclear reactor pressure vessel integrity insurance by crack arrestability evaluation using load from CVN tests

    Energy Technology Data Exchange (ETDEWEB)

    Fabry, A.

    1997-10-15

    The present work is undertaken in the framework of nuclear reactor pressure vessel (RPV) surveillance and aims at revisiting the crack arrest approach to structural integrity insurance. This approach, performed under normal plant operation conditions, can also offer an attractive alternative to the crack initiation philosophy promoted for accidental analysis. To this end, an accidental conservative, cost effective and robust methodology is forwarded and demonstrated: it makes use of the crack arrest information contained in the instrumented Charpy V-notch impact test and/or in the shear fracture appearance of broken samples. Particular attention is paid to the appraisal of uncertainties and the related safety margin. The resulting capability is placed in perspective with the state-of-the-art crack initiation methodology based on the slow bend testing of recracked specimens, presently under standardization world-wide. The investigation leads to highlight three conceptual weaknesses of current enfgineering and regulatory practices. Improved crack arrestability evaluation emerges as an optimal approach to insure safe PWR operation up to design end-of-life and beyond.

  3. Advances in crack-arrest technology for reactor pressure vessels

    International Nuclear Information System (INIS)

    Bass, B.R.; Pugh, C.E.

    1988-01-01

    The Heavy-Section Steel Technology (HSST) Program at the Oak Ridge National Laboratory (ORNL) under the sponsorship of the US Nuclear Regulatory Commission is continuing to improve the understanding of conditions that govern the initiation, rapid propagation, arrest, and ductile tearing of cracks in reactor pressure vessel (RPV) steels. This paper describes recent advances in a coordinated effort being conducted under the HSST Program by ORNL and several subcontracting groups to develop the crack-arrest data base and the analytical tools required to construct inelastic dynamic fracture models for RPV steels. Large-scale tests are being carried out to generate crack-arrest toughness data at temperatures approaching and above the onset of Charpy upper-shelf behavior. Small- and intermediate-size specimens subjected to static and dynamic loading are being developed and tested to provide additional fracture data for RPV steels. Viscoplastic effects are being included in dynamic fracture models and computer programs and their utility validated through analyses of data from carefully controlled experiments. Recent studies are described that examine convergence problems associated with energy-based fracture parameters in viscoplastic-dynamic fracture applications. Alternative techniques that have potential for achieving convergent solutions for fracture parameters in the context of viscoplastic-dynamic models are discussed. 46 refs., 15 figs., 3 tabs

  4. The relevance of crack arrest phenomena for pressure vessel structural integrity assessment

    International Nuclear Information System (INIS)

    Connors, D.C.; Dowling, A.R.; Flewitt, P.E.J.

    1996-01-01

    The potential role of a crack arrest argument for the structural integrity assessments of steel pressure vessels and the relationship between crack initiation and crack arrest philosophies are described. A typical structural integrity assessment using crack initiation fracture mechanics is illustrated by means of a case study based on assessment of the steel pressure vessels for Magnox power stations. Evidence of the occurrence of crack arrest in structures is presented and reviewed, and the applications to pressure vessels which are subjected to similar conditions are considered. An outline is given of the material characterisation that would be required to undertake a crack arrest integrity assessment. It is concluded that crack arrest arguments could be significant in the structural integrity assessment of PWR reactor pressure vessels under thermal shock conditions, whereas for Magnox steel pressure vessels it would be limited in its potential to supporting existing arguments. (author)

  5. Crack arrest: some comments on microscopic and macroscopic aspects in relation to the assurance of structural integrity

    Energy Technology Data Exchange (ETDEWEB)

    Lidbury, D.P.G.; Druce, S.G.; Tomkins, B. [AEA Technology, Risley (United Kingdom)

    1996-12-31

    Fracture prevention in high integrity structures in general, and steel nuclear reactor pressure vessels (RPVs) in particular, is based upon the avoidance of crack initiation, with due regard to real or postulated defects, material toughness and anticipated normal and off-normal loading conditions. However, avoidance of crack initiation can never be guaranteed in any absolute sense. Thus, in cases where there is the possibility of an initiated crack propagating by brittle, cleavage fracture, the crack arrest concept may be usefully applied to provide some additional assurance of structural integrity. Within this context, the mechanical processes operative during the initiation and arrest of cleavage cracks are briefly compared and contrasted. The empirical evidence for indexing and onset-of-upper-shelf temperature for initiation (OUST) and the crack arrest temperature (CAT) relative to the Pellini drop-weight nil-ductility transition temperature (NDTT) is examined, and estimates of the parameter (OUST-CAT) are made for a range of steels. In the light of this, correlations between small-scale tests and more structurally relevant, large-scale tests are examined in relation to both initiation- and arrest-based failure avoidance methodologies. (author).

  6. Comparison of analysis and experimental data for a unique crack arrest specimen

    International Nuclear Information System (INIS)

    Ayres, D.J.; Fabi, R.J.; Schonenberg, R.Y.; Norris, D.M.

    1988-01-01

    A new fracture test specimen has been developed to study crack extension and arrest in nuclear reactor vessel steels subject to stress-intensity factor and toughness gradients similar to those in postulated pressurized thermal shock situations. A summary of the results of all the tests performed is presented to illustrate the range of crack arrest and crack reinitiation conditions observed. One test of this specimen with the corresponding stress analysis is described in detail. During this test the crack initiated, extended, arrested, reinitiated, extended again, and reached a final arrest. Comparison of detailed dynamic elastic-plastic finite-element analyses and dynamic strain and displacement measurements of the crack extension, arrest, and reinitiation events, combined with topographic analysis of the future surfaces, has led to a new understanding of the crack extension and arrest process. The results of the tests demonstrate crack arrest in rising stress-intensity field at near-upper-shelf temperature conditions and show that the toughness required for arrest is lower than would be predicted by the analysis procedures usually employed for pressurized thermal shock evaluations

  7. Crack arrest within teeth at the dentinoenamel junction caused by elastic modulus mismatch

    OpenAIRE

    Bechtle, Sabine

    2010-01-01

    Enamel and dentin compose the crowns of human teeth. They are joined at the dentinoenamel junction (DEJ) which is a very strong and well-bonded interface unlikely to fail within healthy teeth despite the formation of multiple cracks within enamel during a lifetime of exposure to masticatory forces. These cracks commonly are arrested when reaching the DEJ. The phenomenon of crack arrest at the DEJ is described in many publications but there is little consensus on the underlying cause and mecha...

  8. Finite-Element Analysis of Crack Arrest Properties of Fiber Reinforced Composites Application in Semi-Elliptical Cracked Pipelines

    Science.gov (United States)

    Wang, Linyuan; Song, Shulei; Deng, Hongbo; Zhong, Kai

    2018-04-01

    In nowadays, repair method using fiber reinforced composites as the mainstream pipe repair technology, it can provide security for X100 high-grade steel energy long-distance pipelines in engineering. In this paper, analysis of cracked X100 high-grade steel pipe was conducted, simulation analysis was made on structure of pipes and crack arresters (CAs) to obtain the J-integral value in virtue of ANSYS Workbench finite element software and evaluation on crack arrest effects was done through measured elastic-plastic fracture mechanics parameter J-integral and the crack arrest coefficient K, in a bid to summarize effect laws of composite CAs and size of pipes and cracks for repairing CAs. The results indicate that the K value is correlated with laying angle λ, laying length L2/D1, laying thickness T1/T2of CAs, crack depth c/T1 and crack length a/c, and calculate recommended parameters for repairing fiber reinforced composite CAs in terms of two different crack forms.

  9. Crack-arrest behavior in SEN wide plates of low-upper-shelf base metal tested under nonisothermal conditions: WP-2 series

    International Nuclear Information System (INIS)

    Naus, D.J.; Keeney-Walker, J.; Bass, B.R.; Robinson, G.C. Jr.; Iskander, S.K.; Alexander, D.J.; Fields, R.J.; deWit, R.; Low, S.R.; Schwartz, C.W.

    1990-08-01

    The Heavy-Section Steel Technology (HSST) Program at the Oak Ridge National Laboratory under the sponsorship of the Nuclear Regulatory Commission is conducting analytical and experimental studies aimed at understanding the circumstances that would initiate the growth of an existing crack in a reactor pressure vessel (RPV) and the conditions leading to arrest of a propagating crack. Objectives of these studies are to determine (1) if the material will exhibit crack-arrest behavior when the driving force on a crack exceeds the ASME limit, (2) the relationship between K Ia and temperature, and (3) the interaction of fracture modes (arrest, stable crack growth, unstable crack growth, and tensile instability) when arrest occurs at high temperatures. In meeting these objectives, crack-arrest data are being developed over an expanded temperature range through tests involving large thermally shocked cylinders, pressurized thermally shocked vessels, and wide-plate specimens. The wide-plate specimens provide the opportunity for a significant number of data points to be obtained at relatively affordable costs. These tests are designed to provide fracture-toughness measurements approaching or above the onset of the Charpy upper-shelf regime in a rising toughness region and with an increasing driving force. This document discusses test methodology and results. 23 refs., 92 figs., 25 tabs

  10. Master curve based correlation between static initiation toughness KIC and crack arrest toughness KIa

    International Nuclear Information System (INIS)

    Wallin, K.; Rintamaa, R.

    1999-01-01

    Historically the ASME reference curve concept assumes a constant relation between static fracture toughness initiation toughness and crack arrest toughness. In reality, this is not the case. Experimental results show that the difference between K IC and K Ia is material specific. For some materials there is a big difference while for others they nearly coincide. So far, however, no systematic study regarding a possible correlation between the two parameters has been performed. The recent Master curve method, developed for brittle fracture initiation estimation, has enabled a consistent analysis of fracture initiation toughness data. The Master curve method has been modified to be able to describe also crack arrest toughness. Here, this modified 'crack arrest master curve' is further validated and used to develop a simple, but yet (for safety assessment purpose) adequately accurate correlation between the two fracture toughness parameters. The correlation enables the estimation of crack arrest toughness from small Charpy-sized static fracture toughness tests. The correlation is valid for low Nickel steels ≤ (1.2% Ni). If a more accurate description of the crack arrest toughness is required, it can either be measured experimentally or estimated from instrumented Charpy-V crack arrest load information. (orig.)

  11. Crack arrest within teeth at the dentinoenamel junction caused by elastic modulus mismatch.

    Science.gov (United States)

    Bechtle, Sabine; Fett, Theo; Rizzi, Gabriele; Habelitz, Stefan; Klocke, Arndt; Schneider, Gerold A

    2010-05-01

    Enamel and dentin compose the crowns of human teeth. They are joined at the dentinoenamel junction (DEJ) which is a very strong and well-bonded interface unlikely to fail within healthy teeth despite the formation of multiple cracks within enamel during a lifetime of exposure to masticatory forces. These cracks commonly are arrested when reaching the DEJ. The phenomenon of crack arrest at the DEJ is described in many publications but there is little consensus on the underlying cause and mechanism. Explanations range from the DEJ having a larger toughness than both enamel and dentin up to the assumption that not the DEJ itself causes crack arrest but the so-called mantle dentin, a thin material layer close to the DEJ that is somewhat softer than the bulk dentin. In this study we conducted 3-point bending experiments with bending bars consisting of the DEJ and surrounding enamel and dentin to investigate crack propagation and arrest within the DEJ region. Calculated stress intensities around crack tips were found to be highly influenced by the elastic modulus mismatch between enamel and dentin and hence, the phenomenon of crack arrest at the DEJ could be explained accordingly via this elastic modulus mismatch. Copyright 2010 Elsevier Ltd. All rights reserved.

  12. A dynamic analysis of crack propagation and arrest of pressurized thermal shock experiments (PTSE)

    International Nuclear Information System (INIS)

    Brickstad, B.; Nilsson, F.

    1984-01-01

    The PTS-experiments performed at ORNL are dynamically analysed by aid ot a two-dimensional FEM-code with capability of simulating rapid crack growth.It is found that both a quasistatic and a dynamic treatment agree well with the experimentally obtained crack arrest lengths. (author)

  13. Use of forces from instrumented Charpy V-notch testing to determine crack-arrest toughness

    International Nuclear Information System (INIS)

    Iskander, S.K.; Nanstad, R.K.; Sokolov, M.A.; McCabe, D.E.; Hutton, J.T.

    1996-06-01

    The objective of this investigation is an estimation of the crack-arrest toughness, particularly of irradiated materials, from voltage versus time output of an instrumented setup during a test on a Charpy V-notch (CVN) specimen. This voltage versus time trace (which can be converted to force versus displacement) displays events during fracture of the specimen. Various stages of the fracture process can be identified on the trace, including an arrest point indicating arrest of brittle fracture. The force at arrest, F a , versus test temperature, T, relationship is examined to explore possible relationships to other experimental measures of crack-arrest toughness such as the drop-weight nil-ductility temperature (NDT), or crack-arrest toughness, K a . For a wide range of weld and plate materials, the temperature at which F a = 2.45 kN correlates with NDT with a standard deviation, sigma, of about 11 K. Excluding the so-called low upper-shelf energy (USE) welds from the analysis resulted in F a = 4.12 kN and σ = 6.6 K. The estimates of the correlation of the temperature for F a = 7.4 kN with the temperature at 100-MPa√m level for a mean American Society of Mechanical Engineers (ASME) type K Ia curve through crack-arrest toughness values show that prediction of conservative values of K a are possible

  14. Conservatism of ASME KIR-reference curve with respect to crack arrest

    International Nuclear Information System (INIS)

    Wallin, K.; Rintamaa, R.; Nagel, G.

    1999-01-01

    The conservatism of the RT NDT temperature indexing parameter and the ASME K IR -reference curve with respect to crack arrest toughness, has been evaluated. Based on an analysis of the original ASME K Ia data, it was established that inherently, the ASME K IR -reference curve corresponds to an overall 5% lower bound curve with respect to crack arrest. It was shown that the scatter of crack arrest toughness is essentially material independent and has a standard deviation of 18% and the temperature dependence of K Ia has the same form as predicted by the master curve for crack initiation toughness. The 'built in' offset between the mean 100 MPa√(m) crack arrest temperature, TK Ia , and RT NDT is 38 C (TK Ia =RT NDT +38 C) and the experimental relation between TK Ia and NDT is, TK Ia =NDT+28 C. The K IR -reference curve using NDT as reference temperature will be conservative with respect to the general 5% lower bound K Ia(5%) -curve, with a 75% confidence. The use of RT NDT , instead of NDT, will generally increase the degree of conservatism, both for non-irradiated as well as irradiated materials, close to a 95% confidence level. This trend is pronounced for materials with Charpy-V upper shelf energies below 100 J. It is shown that the K IR -curve effectively constitutes a deterministic lower bound curve for crack arrest. The findings are valid both for nuclear pressure vessel plates, forgings and welds. (orig.)

  15. An energy analysis of crack-initiation and arrest in epoxy

    Science.gov (United States)

    Chudnovsky, A.; Kim, A.; Bosnyak, C. P.

    1992-01-01

    The objective of this work is to study fracture processes such as crack initiation and arrest in epoxy. A compact tension specimen with displacement-controlled loading is employed to observe multiple crack initiations and arrests. The energy release rate at crack initiation is significantly higher than that at crack arrest, as has been observed elsewhere. In this study, the difference between these energy release rates is found to depend on specimen size (scale effect), and is quantitatively related to the fracture surface morphology. The scale effect, similar to that in strength theory, is conventionally attributed to the statistics of defects which control the fracture process. Triangular shaped ripples, deltoids, are formed on the fracture surface of the epoxy during the slow sub-critical crack growth, prior to the smooth mirrorlike surface characteristic of fast cracks. The deltoids are complimentary on the two crack faces which excludes any inelastic deformation from consideration. The deltoids are analogous to the ripples created on a river surface downstream from a small obstacle. However, in spite of the expectation based on this analogy and the observed scale effect, there are no 'defects' at the apex of the deltoids detectable down to the 0.1 micron level. This suggests that the formation of deltoids during the slow process of subcritical crack growth is an intrinsic feature of the fracture process itself, triggered by inhomogeneity of material on a submicron scale. This inhomogeneity may be related to a fluctuation in the cross-link density of the epoxy.

  16. In situ observations of crack arrest and bridging by nanoscale twins in copper thin films

    International Nuclear Information System (INIS)

    Kim, Seong-Woong; Li Xiaoyan; Gao Huajian; Kumar, Sharvan

    2012-01-01

    In situ tensile experiments in a transmission electron microscope revealed that micro-cracks in ultrafine grained, free-standing, thin copper foils containing nanoscale twins initiated in matrix domains separated by the twins and then arrested at twin boundaries as twin boundary sliding proceeded. The adjacent microcracks eventually coalesced through shear failure of the bridging twins. To investigate the atomic mechanism of this rarely seen nanoscale crack bridging behavior, molecular dynamics simulations were performed to show that during crack propagation twin boundaries are impinged upon by numerous dislocations from the plastically deforming matrix. These dislocations react at the interface and evolve into substantially impenetrable dislocation walls that strongly confine crack nucleation and resist crack propagation, leading to the experimentally observed crack bridging behavior. The present results raise an approach to significantly toughening polycrystalline thin films by incorporating nanoscale twin structures into individual grains that serve as crack bridging ligaments.

  17. Full thickness crack arrest investigations on compact specimens and a heavy wide-plate

    International Nuclear Information System (INIS)

    Kussmaul, K.; Gillot, R.; Elenz, T.

    1993-01-01

    In order to determine the influence of specimen size and testing procedure on the crack arrest toughness K Ia at various temperatures, investigations were carried out on a wide-plate and compact specimens using a highly brittle material. Test interpretation included static as well as dynamic methods. The comparison of the measured K Ia -values shows good agreement although there is a distinct difference in specimen size. In general, the (static) ASTM test method yields a lower and thus conservative estimate of the crack arrest toughness K Ia . 14 refs., 27 figs., 3 tabs

  18. Conservatism of ASME KIR-reference curve with respect to crack arrest

    International Nuclear Information System (INIS)

    Wallin, K.; Rintamaa, R.; Nagel, G.

    2001-01-01

    The conservatism of the RT NDT temperature indexing parameter and the ASME K IR -reference curve with respect to crack arrest toughness, has been evaluated. Based on an analysis of the original ASME K Ia data, it was established that inherently, the ASME K IR -reference curve corresponds to an overall 5% lower bound curve with respect to crack arrest. It was shown that the scatter of crack arrest toughness is essentially material independent and has a standard deviation (S.D.) of 18% and the temperature dependence of K Ia has the same form as predicted by the master curve for crack initiation toughness. The 'built in' offset between the mean 100 MPa√m crack arrest temperature, TK Ia , and RT NDT is 38 deg. C (TK Ia =RT NDT +38 deg. C) and the experimental relation between TK Ia and NDT is, TK Ia =NDT+28 deg. C. The K IR -reference curve using NDT as reference temperature will be conservative with respect to the general 5% lower bound K Ia(5%) -curve, with a 75% confidence. The use of RT NDT , instead of NDT, will generally increase the degree of conservatism, both for non-irradiated as well as irradiated materials, close to a 95% confidence level. This trend is pronounced for materials with Charpy-V upper shelf energies below 100 J. It is shown that the K IR -curve effectively constitutes a deterministic lower bound curve for crack arrest The findings are valid both for nuclear pressure vessel plates, forgings and welds

  19. European experiences of the proposed ASTM test method for crack arrest toughness of ferritic materials

    International Nuclear Information System (INIS)

    Jutla, T.; Lidbury, D.P.G.; Ziebs, J.; Zimmermann, C.

    1986-01-01

    The proposed ASTM test method for measuring the crack arrest toughness of ferritic materials using wedge-loaded, side-grooved, compact specimens was applied to three steels: A514 bridge steel, A588 bridge steel, and A533B pressure vessel steel. Five sets of results from different laboratories are discussed here. Notches were prepared by spark erosion, although root radii varied from ∝0.1-1.5 mm. Although fast fractures were successfully initiated, arrest did not occur in a significant number of cases. The results showed no obvious dependence of crack arrest toughness, K a , (determined by a static analysis) on crack initiation toughness, K 0 . It was found that K a decreases markedly with increasing crack jump distance. A limited amount of further work on smaller specimens of the A533B steel showed that lower K a values tended to be recorded. It is concluded that a number of points relating to the proposed test method and notch preparation are worthy of further consideration. It is pointed out that the proposed validity criteria may screen out lower bound data. Nevertheless, for present practical purposes, K a values may be regarded as useful in providing an estimate of arrest toughness - although not necessarily a conservative estimate. (orig./HP)

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

    International Nuclear Information System (INIS)

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

    1988-01-01

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

  1. Crack-arrest tests on two irradiated high-copper welds

    International Nuclear Information System (INIS)

    Iskander, S.K.; Corwin, W.R.; Nanstad, R.K.

    1994-03-01

    The objective of the Heavy-Section Steel Irradiation Program Sixth Irradiation Series is to determine the effect of neutron irradiation on the shift and shape of the lower-bound curve to crack-arrest toughness data. Two submerged-arc welds with copper contents of 0.23 and 0.31 wt % were commercially fabricated in 220-mm-thick plate. Crack-arrest specimens fabricated from these welds were irradiated at a nominal temperature of 288 degrees C to an average fluence of 1.9 x 10 19 neutrons/cm 2 (>1 MeV). This is the second report giving the results of the tests on irradiated duplex-type crack-arrest specimens. A previous report gave results of tests on irradiated weld-embrittled-type specimens. Charpy V-notch (CVN) specimens irradiated in the same capsules as the crack-arrest specimens were also tested, and a 41-J transition temperature shift was determined from these specimens. open-quotes Mean close-quote curves of the same form as the American Society of Mechanical Engineers (ASME) K la curve were fit to the data with only the open-quotes reference temperatureclose quotes as a parameter. The shift between the mean curves agrees well with the 41-J transition temperature shift obtained from the CVN specimen tests. Moreover, the four data points resulting from tests on the duplex crack-arrest specimens of the present study did not make a significant change to mean curve fits to either the previously obtained data or all the data combined

  2. Elastodynamic fracture analyses of large crack-arrest experiments

    International Nuclear Information System (INIS)

    Bass, B.R.; Pugh, C.E.; Walker, J.K.

    1985-01-01

    Results obtained to date show that the essence of the run-arrest events, including dynamic behavior, is being modeled. Refined meshes and optimum solution algorithms are important parameters in elastodynamic analysis programs to give sufficient resolution to the geometric and time-dependent aspects of fracture analyses. Further refinements in quantitative representation of material parameters and the inclusion of rate dependence through viscoplastic modeling is expected to give an even more accurate basis for assessing the fracture behavior of reactor pressure vessels under PTS and other off-normal loading conditions

  3. Results of crack-arrest tests on irradiated a 508 class 3 steel

    International Nuclear Information System (INIS)

    Iskander, S.K.; Milella, P.P.; Pini, M.A.

    1998-02-01

    Ten crack-arrest toughness values for irradiated specimens of A 508 class 3 forging steel have been obtained. The tests were performed according to the American Society for Testing and Materials (ASTM) Standard Test Method for Determining Plane-Strain Crack-Arrest Fracture Toughness, K la of Ferritic Steels, E 1221-88. None of these values are strictly valid in all five ASTM E 1221-88 validity criteria. However, they are useful when compared to unirradiated crack-arrest specimen toughness values since they show the small (averaging approximately 10 degrees C) shifts in the mean and lower-bound crack-arrest toughness curves. This confirms that a low copper content in ASTM A 508 class 3 forging material can be expected to result in small shifts of the transition toughness curve. The shifts due to neutron irradiation of the lower bound and mean toughness curves are approximately the same as the Charpy V-notch (CVN) 41-J temperature shift. The nine crack-arrest specimens were irradiated at temperatures varying from 243 to 280 degrees C, and to a fluence varying from 1.7 to 2.7 x 10 19 neutrons/cm 2 (> 1 MeV). The test results were normalized to reference values that correspond to those of CVN specimens irradiated at 284 degrees C to a fluence of 3.2 x 10 19 neutrons/cm 2 (> 1 MeV) in the same capsule as the crack-arrest specimens. This adjustment resulted in a shift to lower temperatures of all the data, and in particular moved two data points that appeared to lie close to or lower than the American Society of Mechanical Engineers K la curve to positions that seemed more reasonable with respect to the remaining data. A special fixture was designed, fabricated, and successfully used in the testing. For reasons explained in the text, special blocks to receive the Oak Ridge National Laboratory clip gage were designed, and greater-than-standard crack-mouth opening displacements measured were accounted for. 24 refs., 13 figs., 12 tabs

  4. Development of a viscoplastic dynamic fracture mechanics treatment for crack arrest predictions in a PTS event

    International Nuclear Information System (INIS)

    Kanninen, M.F.; Hudak, S.J. Jr.; Reed, K.W.; Dexter, R.J.; Polch, E.Z.; Cardinal, J.W.; Achenbach, J.D.; Popelar, C.H.

    1986-01-01

    The objective of this research is to develop a fundamentally correct methodology for the prediction of crack arrest at the high upper shelf conditions occurring in a postulated pressurized thermal shock (PTS) event. The effort is aimed at the development of a versatile finite-element method for the solution of time-dependent boundary value problems that admit inertia effects, a prescribed spatial temperature distribution, and viscoplastic constitutive and fracture behavior. Supporting this development are (1) material characterization and fracture experimentation, (2) detailed mathematical analyses of the near-tip region, (3) elastodynamic fracture analysis, and (4) elastic-plastic tearing instability analyses. As a first step, dynamic-viscoplastic analyses are currently being made of the wide plate tests being performed by the National Bureau of Standards in a companion HSST program. Some preliminary conclusions drawn from this work and from the supporting research activities are offered in this paper. The outstanding critical issues that subsequent research must focus on are also described

  5. The use of COD and plastic instability in crack propagation and arrest in shells

    Science.gov (United States)

    Erdogan, F.; Ratwani, M.

    1974-01-01

    The initiation, growth, and possible arrest of fracture in cylindrical shells containing initial defects are dealt with. For those defects which may be approximated by a part-through semi-elliptic surface crack which is sufficiently shallow so that part of the net ligament in the plane of the crack is still elastic, the existing flat plate solution is modified to take into account the shell curvature effect as well as the effect of the thickness and the small scale plastic deformations. The problem of large defects is then considered under the assumptions that the defect may be approximated by a relatively deep meridional part-through surface crack and the net ligament through the shell wall is fully yielded. The results given are based on an 8th order bending theory of shallow shells using a conventional plastic strip model to account for the plastic deformations around the crack border.

  6. Heavy-Section Steel Technology Program: Recent developments in crack initiation and arrest research

    International Nuclear Information System (INIS)

    Pennell, W.E.

    1991-01-01

    Technology for the analysis of crack initiation and arrest is central to the reactor pressure vessel fracture-margin-assessment process. Regulatory procedures for nuclear plants utilize this technology to assure the retention of adequate fracture-prevention margins throughout the plant operating license period. As nuclear plants age and regulatory procedures dictate that fracture-margin assessments be performed, interest in the fracture-mechanics technology incorporated into those procedures has heightened. This has led to proposals from a number of sources for development and refinement of the underlying crack-initiation and arrest-analysis technology. This paper presents an overview of ongoing Heavy-Section Steel Technology (HSST) Program research aimed at refining the fracture toughness data used in the analysis of fracture margins under pressurized-thermal-shock loading conditions. 33 refs., 13 figs

  7. Development of crack shape: LBB methodology for cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Moulin, D.; Chapuliot, S.; Drubay, B. [Commissariat a l Energie Atomique, Gif sur Yvette (France)

    1997-04-01

    For structures like vessels or pipes containing a fluid, the Leak-Before-Break (LBB) assessment requires to demonstrate that it is possible, during the lifetime of the component, to detect a rate of leakage due to a possible defect, the growth of which would result in a leak before-break of the component. This LBB assessment could be an important contribution to the overall structural integrity argument for many components. The aim of this paper is to review some practices used for LBB assessment and to describe how some new R & D results have been used to provide a simplified approach of fracture mechanics analysis and especially the evaluation of crack shape and size during the lifetime of the component.

  8. Criterion of cleavage crack propagation and arrest in a nuclear PWR vessel steel

    International Nuclear Information System (INIS)

    Bousquet, Amaury

    2013-01-01

    The purpose of this PhD thesis is to understand physical mechanisms of cleavage crack propagation and arrest in the 16MND5 PWR vessel steel and to propose a robust predicting model based on a brittle fracture experimental campaign of finely instrumented laboratory specimens associated with numerical computations. First, experiments were carried out on thin CT25 specimens at five temperatures (-150 C, -125 C, -100 C, -7 C, -50 C). Two kinds of crack path, straight or branching path, have been observed. To characterize crack propagation and to measure crack speed, a high-speed framing camera system was used, combined with the development of an experimental protocol which allowed to observe CT surface without icing inside the thermal chamber and on the specimen. The framing camera (520 000 fps) has allowed to have a very accurate estimation of crack speed on the complete ligament of CT (∼ 25 mm). Besides, to analyse experiments and to study the impact of viscosity on the mechanical response around the crack tip, the elastic-viscoplastic behavior of the ferritic steel has been studied up to a strain rate of 104 s -1 for the tested temperatures.The extended Finite Element Method (X-FEM) was used in CAST3M FE software to model crack propagation. Numerical computations combine a local non linear dynamic approach with a RKR type fracture stress criterion to a characteristic distance. The work carried out has confirmed the form of the criterion proposed by Prabel at -125 C, and has identified the dependencies of the criterion on temperature and strain rate. From numerical analyzes in 2D and 3D, a multi-temperature fracture stress criterion, increasing function of the strain rate, was proposed. Predictive modeling were used to confirm the identified criterion on two specimen geometries (CT and compressive ring) in mode I at different temperatures. SEM observations and 3D analyzes made with optical microscope showed that the fracture mechanism was the cleavage associated

  9. Effects of irradiation on crack-arrest toughness of two high-copper welds

    International Nuclear Information System (INIS)

    Iskander, S.K.; Corwin, W.R.; Nanstad, R.K.

    1990-01-01

    The objective of this study is to determine the effect of neutron irradiation on the shift and shape of the lower-bound curve to crack-arrest data. Two submerged-arc welds with copper contents of 0.23 and 0.31 wt % were commercially fabricated in 220-mm-thick plate. Crack-arrest specimens fabricated from these welds were irradiated at a nominal temperature of 288 degree C to an average fluence of 1.9 x 10 19 neutrons/cm 2 (>1 MeV). A preliminary evaluation of the results shows that the neutron-irradiation induced crack-arrest toughness temperature shift is about the same as the Charpy V-notch impact temperature shift at the 41-J energy level. The shape of the lower-bound curves, (for the range of test temperatures covered), compared to those of the ASME K Ia -curve did not seem to have been altered by irradiation. 10 refs., 9 figs., 7 tabs

  10. Heavy-Section Steel Technology Program: Recent developments in crack initiation and arrest research

    International Nuclear Information System (INIS)

    Pennell, W.E.

    1991-01-01

    Technology for the analysis of crack initiation and arrest is central to the reactor pressure vessel fracture-margin-assessment process. Regulatory procedures for nuclear plants utilize this technology to assure the retention of adequate fracture-prevention margins throughout the plant operating license period. As nuclear plants age and regulatory procedures dictate that fracture-margin assessments be performed, interest in the fracture-mechanics technology incorporated into those procedures has heightened. This has led to proposals from a number of sources for development and refinement of the underlying crack-initiation and arrest-analysis technology. An important element of the Heavy-Section Steel Technology (HSST) Program is devoted to the investigation and evaluation of these proposals. This paper presents the technological bases and fracture-margin assessment objectives for some of the recently proposed crack-initiation and arrest-technology developments. The HSST Program approach to the evaluation of the proposals is described and the results and conclusions obtained to date are presented

  11. Results of crack-arrest tests on two irradiated high-copper welds

    International Nuclear Information System (INIS)

    Iskander, S.K.; Corwin, W.R.; Nanstead, R.K.

    1990-12-01

    The objective of this study was to determine the effect of neutron irradiation on the shift and shape of the lower-bound curve to crack-arrest data. Two submerged-arc welds with copper contents of 0.23 and 0.31 wt % were commercially fabricated in 220-mm-thick plate. Crack-arrest specimens fabricated from these welds were irradiated at a nominal temperature of 288 degree C to an average fluence of 1.9 x 10 19 neutrons/cm 2 (>1 MeV). Evaluation of the results shows that the neutron-irradiation-induced crack-arrest toughness temperature shift is about the same as the Charpy V-notch impact temperature shift at the 41-J energy level. The shape of the lower-bound curves (for the range of test temperatures covered) did not seem to have been altered by irradiation compared to those of the ASME K Ia curve. 9 refs., 21 figs., 10 tabs

  12. Brutal crack propagation in dynamic fracture: industrial application to the length of the crack arrest

    International Nuclear Information System (INIS)

    Dumouchel, P.E.

    2008-03-01

    This research thesis aims at understanding and analysing some mechanisms involved in the dynamic failure under various loadings which are notably present in industrial environment, and more particularly in some parts of EDF's plants where networks of micro-cracks may steadily grow: heterogeneous zones, defects under coating. The author presents a simplified model based on the de-bonding of a film to understand the mechanisms of a sudden failure under a quasi-static loading. He develops a similar model to explore the influence of a defect on crack propagation under a quasi-static loading, and then under a sudden loading. This model is then generalized to the case of several defects, and more particularly very small defects. Finally, the author gives a numerical interpretation of a sudden propagation under quasi-static loading

  13. Summary of HSST wide-plate crack-arrest tests and analyses

    International Nuclear Information System (INIS)

    Naus, D.J.; Bass, B.R.; Keeney-Walker, J.; Fields, R.J.; DeWit, R.; Low, S.R. III

    1988-01-01

    Eleven wide-plate crack-arrest tests have been completed to date, seven utilizing specimens fabricated from A533B class 1 material (WP-1 series), and four fabricated from a low upper-shelf base material (WP-2 series). With the exception of one test in the WP-1 series and two tests in the WP-2 series which utilized 152-mm-thick specimens, each test utilized a single-edge notched (SEN) plate specimen 1 by 1 by 0.1 m that was subjected to a linear thermal gradient along the plane of crack propagation. Test results exhibit an increase in crack-arrest toughness with temperature, with the rate of increase becoming greater as the temperature increases. When the wide-place test results are combined with other large-specimen results (Japanese ESSO, thermal-shock experiments and pressurized-thermal-shock experiments) the data show a consistent trend in which the K Ia data extends above the limit provided in ASME Section XI. (author)

  14. Crack Arrest Toughness of Two High Strength Steels (AISI 4140 and AISI 4340)

    Science.gov (United States)

    Ripling, E. J.; Mulherin, J. H.; Crosley, P. B.

    1982-04-01

    The crack initiation toughness ( K c ) and crack arrest toughness ( K a ) of AISI 4140 and AISI 4340 steel were measured over a range of yield strengths from 965 to 1240 MPa, and a range of test temperatures from -53 to +74°C. Emphasis was placed on K a testing since these values are thought to represent the minimum toughness of the steel as a function of loading rate. At the same yield strengths and test temperatures, K a for the AISI 4340 was about twice as high as it was for the AISI 4140. In addition, the K a values showed a more pronounced transition temperature than the K c values, when the data were plotted as a function of test temperature. The transition appeared to be associated with a change in fracture mechanism from cleavage to dimpled rupture as the test temperature was increased. The occurrence of a “pop-in” behavior at supertransition temperatures has not been found in lower strength steels, and its evaluation in these high strength steels was possible only because they are not especially tough at their supertransition temperatures. There is an upper toughness limit at which pop-in will not occur, and this was found for the AISI 4340 steel when it was tempered to its lowest yield strength (965 MPa). All the crack arrest data were identified as plane strain values, while only about one-half of the initiation values could be classified this way.

  15. Investigation Analysis of Crack Growth Arresting with Fasteners in Hybrid Laminated Skin-Stiffener Joint

    Science.gov (United States)

    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.

  16. Dynamic analysis of crack growth and arrest in a pressure vessel subjected to thermal and pressure loading

    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.)

  17. Use of the Master Curve methodology for real three dimensional cracks

    International Nuclear Information System (INIS)

    Wallin, Kim

    2007-01-01

    At VTT, development work has been in progress for 15 years to develop and validate testing and analysis methods applicable for fracture resistance determination from small material samples. The VTT approach is a holistic approach by which to determine static, dynamic and crack arrest fracture toughness properties either directly or by correlations from small material samples. The development work has evolved a testing standard for fracture toughness testing in the transition region. The standard, known as the Master Curve standard is in a way 'first of a kind', since it includes guidelines on how to properly treat the test data for use in structural integrity assessment. No standard, so far, has done this. The standard is based on the VTT approach, but presently, the VTT approach goes beyond the standard. Key components in the standard are statistical expressions for describing the data scatter, and for predicting a specimens size (crack front length) effect and an expression (Master Curve) for the fracture toughness temperature dependence. The standard and the approach, it is based upon, can be considered to represent the state of the art of small specimen fracture toughness characterization. Normally, the Master Curve parameters are determined using test specimens with 'straight' crack fronts and comparatively uniform stress state along the crack front. This enables the use of a single K I value and single constraint value to describe the whole specimen. For a real crack in a structure, this is usually not the case. Normally, both K I and constraint vary along the crack front and in the case of a thermal shock, even the temperature will vary along the crack front. A proper means of applying the Master Curve methodology for such cases is presented here

  18. Use of the master curve methodology for real three dimensional cracks

    International Nuclear Information System (INIS)

    Wallin, K.; Rintamaa, R.

    2005-01-01

    At VTT, development work has been in progress for 15 years to develop and validate testing and analysis methods applicable for fracture resistance determination from small material samples. The VTT approach is a holistic approach by which to determine static, dynamic and crack arrest fracture toughness properties either directly or by correlations from small material samples. The development work has evolved a testing standard for fracture toughness testing in the transition region. The standard, known as the Master Curve standard is in a way 'first of a kind', since it includes guidelines on how to properly treat the test data for use in structural integrity assessment. No standard, so far, has done this. The standard is based on the VTT approach, but presently, the VTT approach goes beyond the standard. Key components in the standard are statistical expressions for describing the data scatter, and for predicting a specimen's size (crack front length) effect and an expression (Master Curve) for the fracture toughness temperature dependence. The standard and the approach it is based upon can be considered to represent the state of the art of small specimen fracture toughness characterization. Normally, the Master Curve parameters are determined using test specimens with 'straight' crack fronts and comparatively uniform stress state along the crack front. This enables the use of a single KI value and single constraint value to describe the whole specimen. For a real crack in a structure, this is usually not the case. Normally, both KI and constraint varies along the crack front and in the case of a thermal shock, even the temperature will vary along the crack front. A proper means of applying the Master Curve methodology for such cases is presented here. (authors)

  19. Experimental assessment of welded joints brittle fracture on the crack arrest criterion for WWER-1000 RPV

    International Nuclear Information System (INIS)

    Blumin, A.A.; Timofeev, B.T.

    2000-01-01

    The crack arrest fracture toughness in a vessel steel used in WWER-1000 reactor, namely in steel 15Kh2NMFA and its submerged arc welded joints, produced with Sv-08KhGNMTA, Sv-12 Kh2NMFA welding wires and NF-18 M, FZ-16 A welding fluxes, is under study. Experimental studies are carried out using three heats with the chemical composition meeting the specifications. Weld specimens 100-200 mm thick are subjected to tempering according various regimes to induce the embrittlement and simulate mechanical properties (yield strength and ductile-brittle transition temperature) corresponding to those at the end of service life under neutron radiation effect. Base metal and weld properties are compared. The wide scatter is noted for experimental data on fracture toughness temperature dependences. A possibility to use the dependence of K Ia = f (T-T k ) for determining the crack arrest fracture toughness is discussed taking in account that K Ia is a stress intensity factor calculated within the frame of static fracture mechanics [ru

  20. Viscoplastic-dynamic analyses of small-scale fracture tests to obtain crack arrest toughness values for PTS conditions

    International Nuclear Information System (INIS)

    Kanninen, M.F.; Hudak, S.J. Jr; Dexter, R.J.; Couque, H.; O'Donoghue, P.E.; Polch, E.Z.

    1988-01-01

    Reliable predictions of crack arrest at the high upper shelf toughness conditions involved in postulated pressurized thermal shock (PTS) events require procedures beyond those utilized in conventional fracture mechanics treatments. To develop such a procedure, viscoplastic-dynamic fracture mechanics finite element analyses, viscoplastic material characterization testing, and small-scale crack propagation and arrest experimentation are being combines in this research. The approach couples SwRI's viscoplastic-dynamic fracture mechanics finite element code VISCRK with experiments using duplex 4340/A533B steel compact specimens. The experiments are simulated by VISCRK computations employing the Bodner-Partom viscoplastic constitutive relation and the nonlinear fracture mechanics parameter T. The goal is to develop temperature-dependent crack arrest toughness values for A533B steel. While only room temperature K Ia values have been obtained so far, these have been found to agree closely with those obtained from wide plate tests. (author)

  1. Analysis of Mode I and Mode II Crack Growth Arrest Mechanism with Z-Fibre Pins in Composite Laminated Joint

    Science.gov (United States)

    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.

  2. Prediction of cleavage crack propagation and arrest in a nuclear pressure vessel steel (16MND5) under thermal shock

    International Nuclear Information System (INIS)

    Yang, Xiaoyu

    2015-01-01

    The purpose of this PhD study is to predict the propagation and arrest of cleavage cracks in a French PWR vessel steel (16MND5). This is accomplished through use of a local criterion based on the critical stress calculated ahead of crack tip. Previous work has shown that fracture mechanism was cleavage associated with the ductile shear zone between the different planes of cracking. Thus, the critical stress at crack tip depends on stain rate. This thesis consists of numerical optimization, identification and validation of a local criterion based on experiments which have complex thermomechanical loads. The criterion accounts for various crack paths, deepening the knowledge about micro mechanisms during crack propagation in order to justify the established criterion. Criterion identification was carried out by using numerical simulations of tension tests performed on CT (Compact Tension) specimens at four different temperatures (-150 C, -125 C, -100 C and -75 C). The eXtended Finite Element Method (X-FEM) was used in CAST3M FE software to model dynamic crack propagation and arrest. The analysis results in 2D and 3D showed that the critical stress at crack tip increased with the inelastic strain rate. Therefore, a criterion based on the critical stress was established. An analytical model was developed to justify the identified criterion. The critical stress given by the local criterion was considered as the sum of the critical cleavage stress and the stress generated by the deformation of ligaments behind the crack tip. In order to quantify this phenomenon, measurements of ligaments' characteristics have been performed on fracture surfaces and on cross-sections of the specimens. The stress profile of the crack lips generated by ligaments was calculated by modeling of multi-cracks on specimen's cross-section. The contribution of stress generated by ligaments to the critical stress at crack tip was obtained with this method, and then the analytical model of

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

    International Nuclear Information System (INIS)

    Pettersson, Kjell; Oskarsson, Magnus; Bergqvist, Hans

    2003-04-01

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

  4. Methodology for formulating predictions of stress corrosion cracking life

    International Nuclear Information System (INIS)

    Yamauchi, Kiyoshi; Hattori, Shigeo; Shindo, Takenori; Kuniya, Jiro

    1994-01-01

    This paper presents a methodology for formulating predictions to evaluate the stress corrosion cracking (SCC) potential of each light-water reactor component, where an index is introduced as a life index or F index. The index denotes the SCC time ratio of a given SCC system to be evaluated against a reference SCC system. The life index is expressed by the products of several subdivided life indexes, which correspond to each SCC influencing factor. Each subdivided life index is constructed as a function containing the influencing factor variable, obtained by analyzing experimental SCC life data. The methodology was termed the subdivided factor method. Application of the life index to SCC life data and field data showed that it was effective for evaluating the SCC potential, i.e. the SCC life. Accordingly, the proposed methodology can potentially describe a phenomenon expressed by a function which consists of the variables of several influencing factors whether there are formulae which unite as a physical model or not. ((orig.))

  5. Determination of crack arrest toughness in A508 CL.3 forging steel from ASTM E1221-88 procedure. Comparison with the values obtained from thermal loading tests

    International Nuclear Information System (INIS)

    Frund, J.M.; Difant, M.; Bethmont, M.

    1994-01-01

    A crack arrest study is under way at Electricite de France as part of the analysis of the risk of fast fracture of PWR vessels in emergency conditions. The first objective of this study is to evaluate the toughness which characterizes crack arrest through tests on reduced-size specimens. Some of the tests on a forging steel (A508 Cl.3) were conducted in conformity with two experimental methods. One method recommended by the ASTM calls for the use of an imposed-displacement mechanical loading on specimens kept under homogeneous temperature. Since the stress intensity factor K applied to the outside loading decreases along the crack growth, we can observe the arrest of the crack. In order to obtain brittle crack initiations in cleavage in the whole studied range of temperature and crack propagation of a sufficient length, the application of a weld point at the top of the notch is done. The other experimental method is based on a thermal loading. It requires the use of a disk or a cylinder with a longitudinal initial crack of the external surface. We dip this specimen in liquid nitrogen and we heat its internal surface with inducing current. There is a temperature gradient in the thickness of the specimen which produces a stress field which tends to open the crack. When the value of K is reached the crack initiation takes place. Several phenomena act to oppose the crack growth, they even go as far as stopping it. First the value of K, after increasing, gets steady then decreases, then, the rate of energy dissipated by plasticity at the top of the crack increases because the crack meets warmer and warmer areas on its way. The arrest toughness values which were obtained were then analyzed and compared to one another and with values proposed by RCC-m code. (authors). 12 refs., 11 figs., 3 tabs

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

    International Nuclear Information System (INIS)

    Smith, E.

    1986-01-01

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

  7. Comparisons of irradiation-induced shifts in fracture toughness, crack arrest toughness, and Charpy impact energy in high-copper welds

    International Nuclear Information System (INIS)

    Corwin, W.R.; Nanstad, R.K.; Iskander, S.K.

    1991-01-01

    The Heavy-Section Steel Irradiation (HSSI) Program is examining relative shifts and changes in shape of fracture and crack-arrest toughness versus temperature behavior for two high-copper welds. Fracture toughness 100-MPa√m temperature shifts are greater than Charpy 41-J shifts for both welds. Mean curve fits to the fracture toughness data provide mixed results regarding curve shape changes, but curves constructed as lower boundaries indicate lower slopes. Preliminary crack-arrest toughness results indicate that shifts of lower-bound curves are approximately the same as CVN 41-J shifts with no shape changes

  8. An appraisal of crack arrest results and their relevance to the onset of upper shelf temperature issue

    International Nuclear Information System (INIS)

    Smith, E.

    1996-01-01

    The paper appraises experimental results which support the view that a crack can propagate by cleavage mechanism in a ferritic steel as used in a nuclear reactor pressure vessel, at temperatures that are markedly in excess of the onset of upper shelf temperature as estimated using an initiation based criterion. At temperatures in the vicinity of the onset shelf as estimated by such a criterion, cleavage crack propagation can occur at K values that are markedly less than the static fracture toughness values appropriate to the same temperature regime. It is demonstrated how these conclusions are reflected in the ASME Code Section III Appendix G procedure for defining the pressure-temperature limits associated with the normal operation of a PWR reactor pressure vessel in the USA. This procedure defines the onset of upper shelf temperature in relation to the crack arrest toughness curve and not the initiation toughness curve, the difference between the onset of upper shelf temperatures using the two definitions being about 80 o F. (author)

  9. Thermal shock experiment analysis, the use of crack arrest toughness measurements

    International Nuclear Information System (INIS)

    Miannay, D.; Pellissier-Tanon, A.; Chavaillard, J.P.

    1984-06-01

    The main purpose of thermal shock experiment is to assess the procedure codified in the ASME XI appendix 1 or RCC-M-B appendix ZG, and allow comparisons with numerical simulations. The analysis of the integrity of the PWR vessel belt line under accidental transients is based on reference curves. The test-piece is a cylinder of SA 508 cl.3 steel. Arrest toughness measured agrees with reference curve

  10. Fracture mechanical modeling of brittle crack propagation and arrest of steel. 3. Application to duplex-type test; Kozai no zeisei kiretsu denpa teisi no rikigaku model. 3. Konseigata shiken eno tekiyo

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, S.; Tsuchida, Y. [Nippon Steel Corp., Tokyo (Japan); Machida, S.; Yoshinari, H. [The University of Tokyo, Tokyo (Japan). Faculty of Engineering

    1996-12-31

    A proposal was made previously on a model of brittle crack propagation and arrest that considers the effect of crack opening suppression by using unbroken ligaments generated on steel plate surface and the effect that cracks precede in the central part of the plate thickness, based on a local limit stress theory for brittleness fracture. This paper discusses applicability of this model to a mixed type test, and elucidates causes for difference in the arrest tenacity of both types in a double tensile test of the standard size. The brittle crack propagation and arrest model based on the local limit stress theory was found applicable to a simulation of the mixed type test. Experimental crack propagation speed history and behavior of the arrest were reproduced nearly completely by using this model. When load stress is increased, the arrests in the mixed type test may be classified into arrests of both inside the steel plate and near the surface, cracks in the former position or arrest in the latter position, and rush of cracks into both positions. Furthermore, at higher stresses, the propagation speed drops once after cracks rushed into the test plate, but turns to a rise, leading to propagation and piercing. 8 refs., 15 figs., 3 tabs.

  11. Fracture mechanical modeling of brittle crack propagation and arrest of steel. 3. Application to duplex-type test; Kozai no zeisei kiretsu denpa teisi no rikigaku model. 3. Konseigata shiken eno tekiyo

    Energy Technology Data Exchange (ETDEWEB)

    Aihara, S; Tsuchida, Y [Nippon Steel Corp., Tokyo (Japan); Machida, S; Yoshinari, H [The University of Tokyo, Tokyo (Japan). Faculty of Engineering

    1997-12-31

    A proposal was made previously on a model of brittle crack propagation and arrest that considers the effect of crack opening suppression by using unbroken ligaments generated on steel plate surface and the effect that cracks precede in the central part of the plate thickness, based on a local limit stress theory for brittleness fracture. This paper discusses applicability of this model to a mixed type test, and elucidates causes for difference in the arrest tenacity of both types in a double tensile test of the standard size. The brittle crack propagation and arrest model based on the local limit stress theory was found applicable to a simulation of the mixed type test. Experimental crack propagation speed history and behavior of the arrest were reproduced nearly completely by using this model. When load stress is increased, the arrests in the mixed type test may be classified into arrests of both inside the steel plate and near the surface, cracks in the former position or arrest in the latter position, and rush of cracks into both positions. Furthermore, at higher stresses, the propagation speed drops once after cracks rushed into the test plate, but turns to a rise, leading to propagation and piercing. 8 refs., 15 figs., 3 tabs.

  12. Ductile fracture mechanics methodology for complex cracks in nuclear piping

    Energy Technology Data Exchange (ETDEWEB)

    Zahoor, A.

    1988-02-01

    Limit load and J-integral estimation solutions are developed for circumferentially complex-cracked pipes in bending. The limit load solution is developed using thick-walled cylinder analysis which included the effects of flaw depth accurately. J-integral estimation solutions are developed that are suitable for a wide range of loading from linear elastic, elastic-plastic to net-section yielding of the flawed section. Mode I stress intensity factor solution is developed from experimental compliance data. Two types of J solutions are developed. First, J solutions for determining the J-resistance curve from single load-displacement record are presented. Next, elastic-plastic J solution in the format of EPRI J estimation scheme is presented. The latter solution was used to predict the load carrying capacity of complex-cracked pipes made of Type-304 stainless steel, Inconel 600, and A106 GrB materials. Predictions were compared against pipe tests to demonstrate the accuracy of the limit load and J estimation solutions.

  13. Ductile fracture mechanics methodology for complex cracks in nuclear piping

    International Nuclear Information System (INIS)

    Zahoor, A.

    1988-01-01

    Limit load and J-integral estimation solutions are developed for circumferentially complex-cracked pipes in bending. The limit load solution is developed using thick-walled cylinder analysis which included the effects of flaw depth accurately. J-integral estimation solutions are developed that are suitable for a wide range of loading from linear elastic, elastic-plastic to net-section yielding of the flawed section. Mode I stress intensity factor solution is developed from experimental compliance data. Two types of J solutions are developed. First, J solutions for determining the J-resistance curve from single load-displacement record are presented. Next, elastic-plastic J solution in the format of EPRI J estimation scheme is presented. The latter solution was used to predict the load carrying capacity of complex-cracked pipes made of Type-304 stainless steel, Inconel 600, and A106 GrB materials. Predictions were compared against pipe tests to demonstrate the accuracy of the limit load and J estimation solutions. (orig.)

  14. Crack

    Science.gov (United States)

    ... 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 ...

  15. A methodology for the investigation of toughness and crack propagation in mouse bone.

    Science.gov (United States)

    Carriero, Alessandra; Zimmermann, Elizabeth A; Shefelbine, Sandra J; Ritchie, Robert O

    2014-11-01

    Bone fracture is a health concern for those with aged bone and brittle bone diseases. Mouse bone is widely used as a model of human bone, especially to investigate preclinical treatment strategies. However, little is known about the mechanisms of mouse bone fracture and its similarities and differences from fracture in human bone. In this work we present a methodology to investigate the fracture toughness during crack initiation and crack propagation for mouse bone. Mouse femora were dissected, polished on their periosteal surface, notched on the posterior surface at their mid-diaphysis, and tested in three-point bending under displacement control at a rate of 0.1mm/min using an in situ loading stage within an environmental scanning electron microscope. We obtained high-resolution real-time imaging of the crack initiation and propagation in mouse bone. From the images we can measure the crack extension at each step of the crack growth and calculate the toughness of the bone (in terms of stress intensity factor (K) and work to fracture (Wf)) as a function of stable crack length (Δa), thus generating a resistance curve for the mouse bone. The technique presented here provides insight into the evolution of microdamage and the toughening mechanisms that resist crack propagation, which are essential for preclinical development of treatments to enhance bone quality and combat fracture risk. Copyright © 2014 Elsevier Ltd. All rights reserved.

  16. The role of ductile ligaments and warm prestress on the re-initiation of fracture from a crack arrested during thermal shock

    International Nuclear Information System (INIS)

    Smith, E.

    1982-01-01

    The protection offered by warm prestress can be important for preserving a nuclear pressure vessel's integrity during a postulated emergency condition involving a loss of coolant, when the emergency core cooling water subjects the pressure vessel to a thermal shock. There are two aspects to the problem: (a) the initial extension of a defect into the vessel wall, and (b) the subsequent re-initiation of fracture at an arrested crack tip. This note considers the effect of warm prestress on the re-initiation of fracture from an arrested crack, and emphasizes the role of ductile ligaments. It is argued that the warm prestress concept is applicable, thus complementing the limited experimental results provided by the HSST Thermal Shock experimental programme. (orig.)

  17. Prediction of crack propagation and arrest in X100 natural gas transmission pipelines with a strain rate dependent damage model (SRDD). Part 2: Large scale pipe models with gas depressurisation

    International Nuclear Information System (INIS)

    Oikonomidis, F.; Shterenlikht, A.; Truman, C.E.

    2014-01-01

    Part 1 of this paper described a specimen for the measurement of high strain rate flow and fracture properties of pipe material and for tuning a strain rate dependent damage model (SRDD). In part 2 the tuned SRDD model is used for the simulation of axial crack propagation and arrest in X100 natural gas pipelines. Linear pressure drop model was adopted behind the crack tip, and an exponential gas depressurisation model was used ahead of the crack tip. The model correctly predicted the crack initiation (burst) pressure, the crack speed and the crack arrest length. Strain rates between 1000 s −1 and 3000 s −1 immediately ahead of the crack tip are predicted, giving a strong indication that a strain rate material model is required for the structural integrity assessment of the natural gas pipelines. The models predict the stress triaxiality of about 0.65 for at least 1 m ahead of the crack tip, gradually dropping to 0.5 at distances of about 5–7 m ahead of the crack tip. Finally, the models predicted a linear drop in crack tip opening angle (CTOA) from about 11−12° at the onset of crack propagation down to 7−8° at crack arrest. Only the lower of these values agree with those reported in the literature for quasi-static measurements. This discrepancy might indicate substantial strain rate dependence in CTOA. - Highlights: • Finite element simulations of 3 burst tests of X100 pipes are detailed. • Strain rate dependent damage model, tuned on small scale X100 samples, was used. • The models correctly predict burst pressure, crack speed and crack arrest length. • The model predicts a crack length dependent critical CTOA. • The strain rate dependent damage model is verified as mesh independent

  18. An elastic-plastic fracture mechanics based methodology to characterize cracking behavior and its application to environmental assisted processes

    International Nuclear Information System (INIS)

    Alvarez, J.A.; Gutierrez-Solana, F.

    1999-01-01

    Cracking processes suffered by new structural and piping steels when used in petroleum or other energy installations have demonstrated the need for a cracking resistance characterization methodology. This methodology, valid for both elastic and elastoplastic regimes, should be able to define crack propagation kinetics as a function of their controlling local parameters. This work summarizes an experimental and analytical methodology that has been shown to be suitable for characterizing cracking processes using compact tensile specimens, especially subcritical environmentally assisted ones, such as those induced by hydrogen in microalloyed steels. The applied and validated methodology has been shown to offer quantitative results of cracking behavior and to correlate these with the existing fracture micromechanisms. (orig.)

  19. Elastic-Plastic J-Integral Solutions or Surface Cracks in Tension Using an Interpolation Methodology

    Science.gov (United States)

    Allen, P. A.; Wells, D. N.

    2013-01-01

    No closed form solutions exist for the elastic-plastic J-integral for surface cracks due to the nonlinear, three-dimensional nature of the problem. Traditionally, each surface crack must be analyzed with a unique and time-consuming nonlinear finite element analysis. To overcome this shortcoming, the authors have developed and analyzed an array of 600 3D nonlinear finite element models for surface cracks in flat plates under tension loading. The solution space covers a wide range of crack shapes and depths (shape: 0.2 less than or equal to a/c less than or equal to 1, depth: 0.2 less than or equal to a/B less than or equal to 0.8) and material flow properties (elastic modulus-to-yield ratio: 100 less than or equal to E/ys less than or equal to 1,000, and hardening: 3 less than or equal to n less than or equal to 20). The authors have developed a methodology for interpolating between the goemetric and material property variables that allows the user to reliably evaluate the full elastic-plastic J-integral and force versus crack mouth opening displacement solution; thus, a solution can be obtained very rapidly by users without elastic-plastic fracture mechanics modeling experience. Complete solutions for the 600 models and 25 additional benchmark models are provided in tabular format.

  20. Methodology to evaluate the crack growth rate by stress corrosion cracking in dissimilar metals weld in simulated environment of PWR nuclear reactor

    International Nuclear Information System (INIS)

    Paula, Raphael G.; Figueiredo, Celia A.; Rabelo, Emerson G.

    2013-01-01

    Inconel alloys weld metal is widely used to join dissimilar metals in nuclear reactors applications. It was recently observed failures of weld components in plants, which have triggered an international effort to determine reliable data on the stress corrosion cracking behavior of this material in reactor environment. The objective of this work is to develop a methodology to determine the crack growth rate caused by stress corrosion in Inconel alloy 182, using the specimen (Compact Tensile) in simulated PWR environment. (author)

  1. Assessing edge cracking resistance in AHSS automotive parts by the Essential Work of Fracture methodology

    Science.gov (United States)

    Frómeta, D.; Tedesco, M.; Calvo, J.; Lara, A.; Molas, S.; Casellas, D.

    2017-09-01

    Lightweight designs and demanding safety requirements in automotive industry are increasingly promoting the use of Advanced High Strength Steel (AHSS) sheets. Such steels present higher strength (above 800 MPa) but lower ductility than conventional steels. Their great properties allow the reduction of the thickness of automobile structural components without compromising the safety, but also introduce new challenges to parts manufacturers. The fabrication of most cold formed components starts from shear cut blanks and, due to the lower ductility of AHSS, edge cracking problems can appear during forming operations, forcing the stop of the production and slowing down the industrial process. Forming Limit Diagrams (FLD) and FEM simulations are very useful tools to predict fracture problems in zones with high localized strain, but they are not able to predict edge cracking. It has been observed that the fracture toughness, measured through the Essential Work of Fracture (EWF) methodology, is a good indicator of the stretch flangeability in AHSS and can help to foresee this type of fractures. In this work, a serial production automotive component has been studied. The component showed cracks in some flanged edges when using a dual phase steel. It is shown that the conventional approach to explain formability, based on tensile tests and FLD, fails in the prediction of edge cracking. A new approach, based on fracture mechanics, help to solve the problem by selecting steel grades with higher fracture toughness, measured by means of EWF. Results confirmed that fracture toughness, in terms of EWF, can be readily used as a material parameter to rationalize cracking related problems and select AHSS with improved edge cracking resistance.

  2. Optimization of Reactor Temperature and Catalyst Weight for Plastic Cracking to Fuels Using Response Surface Methodology

    Directory of Open Access Journals (Sweden)

    Istadi Istadi

    2011-01-01

    Full Text Available The present study deals with effect of reactor temperature and catalyst weight on performance of plastic waste cracking to fuels over modified catalyst waste as well as their optimization. From optimization study, the most operating parameters affected the performance of the catalytic cracking process is reactor temperature followed by catalyst weight. Increasing the reactor temperature improves significantly the cracking performance due to the increasing catalyst activity. The optimal operating conditions of reactor temperature about 550 oC and catalyst weight about 1.25 gram were produced with respect to maximum liquid fuel product yield of 29.67 %. The liquid fuel product consists of gasoline range hydrocarbons (C4-C13 with favorable heating value (44,768 kJ/kg. ©2010 BCREC UNDIP. All rights reserved(Received: 10th July 2010, Revised: 18th September 2010, Accepted: 19th September 2010[How to Cite: I. Istadi, S. Suherman, L. Buchori. (2010. Optimization of Reactor Temperature and Catalyst Weight for Plastic Cracking to Fuels Using Response Surface Methodology. Bulletin of Chemical Reaction Engineering and Catalysis, 5(2: 103-111. doi:10.9767/bcrec.5.2.797.103-111][DOI: http://dx.doi.org/10.9767/bcrec.5.2.797.103-111 || or local:  http://ejournal.undip.ac.id/index.php/bcrec/article/view/797

  3. Development of methodology for evaluating and monitoring steam generator feedwater nozzle cracking in PWRs

    International Nuclear Information System (INIS)

    Shvarts, S.; Gerber, D.A.; House, K.; Hirschberg, P.

    1994-01-01

    The objective of this paper is to describe a methodology for evaluating and monitoring steam generator feedwater nozzle cracking in PWR plants. This methodology is based in part on plant test data obtained from a recent Diablo Canyon Power Plant (DCPP) Unit 1 heatup. Temperature sensors installed near the nozzle-to-pipe weld were monitored during the heatup, along with operational parameters such as auxiliary feedwater (AFW) flow rate and steam generator temperature. A thermal stratification load definition was developed from this data. Steady state characteristics of this data were used in a finite element analysis to develop relationship between AFW flow and stratification interface level. Fluctuating characteristics of this data were used to determine transient parameters through the application of a Green's Function approach. The thermal stratification load definition from the test data was used in a three-dimensional thermal stress analysis to determine stress cycling and consequent fatigue damage or crack growth during AFW flow fluctuations. The implementation of the developed methodology in the DCPP and Sequoyah Nuclear Plant (SNP) fatigue monitoring systems is described

  4. A novel survival model of cardioplegic arrest and cardiopulmonary bypass in rats: a methodology paper

    Directory of Open Access Journals (Sweden)

    Podgoreanu Mihai V

    2008-08-01

    Full Text Available Abstract Background Given the growing population of cardiac surgery patients with impaired preoperative cardiac function and rapidly expanding surgical techniques, continued efforts to improve myocardial protection strategies are warranted. Prior research is mostly limited to either large animal models or ex vivo preparations. We developed a new in vivo survival model that combines administration of antegrade cardioplegia with endoaortic crossclamping during cardiopulmonary bypass (CPB in the rat. Methods Sprague-Dawley rats were cannulated for CPB (n = 10. With ultrasound guidance, a 3.5 mm balloon angioplasty catheter was positioned via the right common carotid artery with its tip proximal to the aortic valve. To initiate cardioplegic arrest, the balloon was inflated and cardioplegia solution injected. After 30 min of cardioplegic arrest, the balloon was deflated, ventilation resumed, and rats were weaned from CPB and recovered. To rule out any evidence of cerebral ischemia due to right carotid artery ligation, animals were neurologically tested on postoperative day 14, and their brains histologically assessed. Results Thirty minutes of cardioplegic arrest was successfully established in all animals. Functional assessment revealed no neurologic deficits, and histology demonstrated no gross neuronal damage. Conclusion This novel small animal CPB model with cardioplegic arrest allows for both the study of myocardial ischemia-reperfusion injury as well as new cardioprotective strategies. Major advantages of this model include its overall feasibility and cost effectiveness. In future experiments long-term echocardiographic outcomes as well as enzymatic, genetic, and histologic characterization of myocardial injury can be assessed. In the field of myocardial protection, rodent models will be an important avenue of research.

  5. A new methodology for non-contact accurate crack width measurement through photogrammetry for automated structural safety evaluation

    International Nuclear Information System (INIS)

    Jahanshahi, Mohammad R; Masri, Sami F

    2013-01-01

    In mechanical, aerospace and civil structures, cracks are important defects that can cause catastrophes if neglected. Visual inspection is currently the predominant method for crack assessment. This approach is tedious, labor-intensive, subjective and highly qualitative. An inexpensive alternative to current monitoring methods is to use a robotic system that could perform autonomous crack detection and quantification. To reach this goal, several image-based crack detection approaches have been developed; however, the crack thickness quantification, which is an essential element for a reliable structural condition assessment, has not been sufficiently investigated. In this paper, a new contact-less crack quantification methodology, based on computer vision and image processing concepts, is introduced and evaluated against a crack quantification approach which was previously developed by the authors. The proposed approach in this study utilizes depth perception to quantify crack thickness and, as opposed to most previous studies, needs no scale attachment to the region under inspection, which makes this approach ideal for incorporation with autonomous or semi-autonomous mobile inspection systems. Validation tests are performed to evaluate the performance of the proposed approach, and the results show that the new proposed approach outperforms the previously developed one. (paper)

  6. Crack Growth-Based Predictive Methodology for the Maintenance of the Structural Integrity of Repaired and Nonrepaired Aging Engine Stationary Components

    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...

  7. Effects of irradiation on initiation and crack-arrest toughness of two high-copper welds and on stainless steel cladding

    International Nuclear Information System (INIS)

    Nanstad, R.K.; Iskander, S.K.; Haggag, F.M.

    1990-01-01

    The objective of the study on the high-copper welds is to determine the effect of neutron irradiation on the shift and shape of the ASME K Ic and K Ia toughness curves. Two submerged-arc welds with copper contents of 0.23 and 0.31 wt % were commercially fabricated in 220-mm-thick plate. Compact specimens fabricated from these welds were irradiated at a nominal temperature of 288 degree C to fluences from 1.5 to 1.9 x 10 19 neutrons/cm 2 (>1 MeV). The fracture toughness test results show that the irradiation-induced shifts at 100 MPa/m were greater than the Charpy 41-J shifts by about 11 and 18 degree C. Mean curve fits indicate mixed results regarding curve shape changes, but curves constructed as lower boundaries to the data do indicate curves of lower slopes. A preliminary evaluation of the crack-arrest results shows that the neutron-irradiation induced crack-arrest toughness temperature shift is about the same as the Charpy V-notch impact temperature shift at the 41-J energy level. The shape of the lower bound curves (for the range of test temperatures covered), compared to those of the ASME K Ia curve did not appear to have been altered by the irradiation. Three-wire stainless steel weld overlay cladding was irradiated at 288 degree C to fluences of 2 and 5 x 10 19 neutrons/cm 2 (>1 MeV). Charpy 41-J temperature shifts of 13 and 28 degree C were observed, respectively. For the lower fluence only, 12.7-mm thick compact specimens showed decreases in both J Ic and the tearing modulus. Comparison of the fracture toughness results with typical plate and a low upper-shelf weld reveals that the irradiated stainless steel cladding possesses low ductile initiation fracture toughness comparable to the low upper-shelf weld. 8 refs., 12 figs., 2 tabs

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-09-30

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

  9. Incorporating plastic collapse into the linear elastic fracture mechanics methodology in determining crack propagation lifetimes

    International Nuclear Information System (INIS)

    Glasgow, B.B.; Wolfer, W.G.

    1986-01-01

    Crack growth can result in a breech of a pressure boundary causing coolant loss or in total structural failure. This paper discusses brittle and plastic failure in terms of a unified structural model called the Two Criteria model. The model takes into account the flow stress of the material as well as the fracture toughness. Our results indicate that for fusion reactor first wall structures, ferritic steel is better able to resist crack propagation and subsequent structural failure than 316 stainless steel under the same wall loadings and geometry

  10. A FEM based methodology to simulate multiple crack propagation in friction stir welds

    DEFF Research Database (Denmark)

    Lepore, Marcello; Carlone, Pierpaolo; Berto, Filippo

    2017-01-01

    . The residual stress field was inferred by a thermo-mechanical FEM simulation of the process, considering temperature dependent elastic-plastic material properties, material softening and isotropic hardening. Afterwards, cracks introduced in the selected location of FEM computational domain allow stress...

  11. Accelerated Testing Methodology for the Determination of Slow Crack Growth of Advanced Ceramics

    Science.gov (United States)

    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 %.

  12. Accelerated Testing Methodology Developed for Determining the Slow Crack Growth of Advanced Ceramics

    Science.gov (United States)

    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.

  13. Development of a Physically-Based Methodology for Predicting Material Variability in Fatigue Crack Initiation and Growth Response

    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...

  14. Daily Arrests

    Data.gov (United States)

    Montgomery County of Maryland — This dataset provides the public with arrest information from the Montgomery County Central Processing Unit (CPU) systems. The data presented is derived from every...

  15. Cardiac arrest

    Science.gov (United States)

    ... magnesium. These minerals help your heart's electrical system work. Abnormally high or low levels can cause cardiac arrest. Severe physical stress. Anything that causes a severe stress on your ...

  16. An analysis for crack layer stability

    Science.gov (United States)

    Sehanobish, K.; Botsis, J.; Moet, A.; Chudnovsky, A.

    1986-01-01

    The problem of uncontrolled crack propagation and crack arrest is considered with respect to crack layer (CL) translational stability. CL propagation is determined by the difference between the energy release rate and the amount of energy required for material transformation, and necessary and sufficient conditions for CL instability are derived. CL propagation in polystyrene is studied for two cases. For the case of remotely applied fixed load fatigue, the sufficient condition of instability is shown to be met before the necessary condition, and the necessary condition controls the stability. For the fixed displacement case, neither of the instability conditions are met, and CL propagation remains stable, resulting in crack arrest.

  17. Alternative methodology for assessing part-through-wall cracks in carbon steel bends removed from Point Lepreau Generating Station

    Energy Technology Data Exchange (ETDEWEB)

    Duan Xinjian, E-mail: duanx@aecl.c [Senior Engineer, Reactor Engineering Department, Atomic Energy of Canada Ltd., Mississauga, ON (Canada); Kozluk, Michael J., E-mail: kozlukm@aecl.c [Independent Consultant, Oakville, ON (Canada); Gendron, Tracy [Manager-HTS Materials Integrity, Atomic Energy of Canada Ltd., Chalk River, ON (Canada); Slade, John [Senior Technical Advisor, Point Lepreau Generating Station, Lepreau, NB (Canada)

    2011-03-15

    In 2008 April Point Lepreau Generating Station entered an extended refurbishment outage that will involve the replacement of key reactor components (fuel channels and connecting feeder pipes). Prior to the refurbishment outage, New Brunswick Power Nuclear had been successfully managing intergranular, axial cracking of carbon steel feeder piping, that were also experiencing thinning, in the Point Lepreau Generating Station, primarily by an aggressive program of inspection, repair and testing of ex-service material. For the previous three maintenance outages, a probabilistic safety evaluation (PSE) had been used to demonstrate that annual inspection of the highest risk locations maintains the nuclear safety risk from cracking at an acceptably low level. The PSE makes use of the Failure Assessment Diagram (FAD) model to predict the failure of part-through-wall cracks. Burst-pressure testing of two ex-service feeder pipe sections with part-through-wall cracks showed that this FAD model significantly under predicts the failure pressure measured in the component tests. Use of this FAD model introduces undesirable conservatism into PSE assessments that are used to optimize feeder piping inspection and maintenance plans. This paper describes an alternative finite element approach, which could be used to provide more representative structural models for use in PSE assessments. This alternative approach employs the elasto-plastic large strain finite element formulation; uses representative material properties; considers the spatial microstructural distribution; accounts for the effect of work hardening rate; models all deformation processes, i.e., uniform deformation, localized necking, and failure imitation and propagation. Excellent pre-test prediction was shown for the burst-pressure test performed in 2006. Although cold-worked feeder bends have reduced fracture toughness compared to the parent straight pipe, post-test metallurgical examinations showed that failure at the

  18. A survey of attitudes and factors associated with successful cardiopulmonary resuscitation (CPR knowledge transfer in an older population most likely to witness cardiac arrest: design and methodology

    Directory of Open Access Journals (Sweden)

    Brehaut Jamie C

    2008-11-01

    Full Text Available Abstract Background Overall survival rates for out-of-hospital cardiac arrest rarely exceed 5%. While bystander cardiopulmonary resuscitation (CPR can increase survival for cardiac arrest victims by up to four times, bystander CPR rates remain low in Canada (15%. Most cardiac arrest victims are men in their sixties, they usually collapse in their own home (85% and the event is witnessed 50% of the time. These statistics would appear to support a strategy of targeted CPR training for an older population that is most likely to witness a cardiac arrest event. However, interest in CPR training appears to decrease with advancing age. Behaviour surrounding CPR training and performance has never been studied using well validated behavioural theories. Methods/Design The overall goal of this study is to conduct a survey to better understand the behavioural factors influencing CPR training and performance in men and women 55 years of age and older. The study will proceed in three phases. In phase one, semi-structured qualitative interviews will be conducted and recorded to identify common categories and themes regarding seeking CPR training and providing CPR to a cardiac arrest victim. The themes identified in the first phase will be used in phase two to develop, pilot-test, and refine a survey instrument based upon the Theory of Planned Behaviour. In the third phase of the project, the final survey will be administered to a sample of the study population over the telephone. Analyses will include measures of sampling bias, reliability of the measures, construct validity, as well as multiple regression analyses to identify constructs and beliefs most salient to seniors' decisions about whether to attend CPR classes or perform CPR on a cardiac arrest victim. Discussion The results of this survey will provide valuable insight into factors influencing the interest in CPR training and performance among a targeted group of individuals most susceptible to

  19. Resuscitation Outcomes Consortium (ROC) PRIMED cardiac arrest trial methods part 1: rationale and methodology for the impedance threshold device (ITD) protocol.

    Science.gov (United States)

    Aufderheide, Tom P; Kudenchuk, Peter J; Hedges, Jerris R; Nichol, Graham; Kerber, Richard E; Dorian, Paul; Davis, Daniel P; Idris, Ahamed H; Callaway, Clifton W; Emerson, Scott; Stiell, Ian G; Terndrup, Thomas E

    2008-08-01

    The primary aim of this study is to compare survival to hospital discharge with a modified Rankin score (MRS)CPR) plus an active impedance threshold device (ITD) versus standard CPR plus a sham ITD in patients with out-of-hospital cardiac arrest. Secondary aims are to compare functional status and depression at discharge and at 3 and 6 months post-discharge in survivors. Prospective, double-blind, randomized, controlled, clinical trial. Patients with non-traumatic out-of-hospital cardiac arrest treated by emergency medical services (EMS) providers. EMS systems participating in the Resuscitation Outcomes Consortium. Based on a one-sided significance level of 0.025, power=0.90, a survival with MRSCPR and sham ITD, and two interim analyses, a maximum of 14,742 evaluable patients are needed to detect a 6.69% survival with MRSCPR and active ITD (1.36% absolute survival difference). If the ITD demonstrates the hypothesized improvement in survival, it is estimated that 2700 deaths from cardiac arrest per year would be averted in North America alone.

  20. Evaluation of methodologies for the calculation of leak rates for pressure retaining components with crack-like leaks

    International Nuclear Information System (INIS)

    Sievers, Juergen; Heckmann, Klaus; Blaesius, Christoph

    2015-06-01

    For the demonstration of break preclusion for pressure retaining components in nuclear power plants, the nuclear safety standard KTA 3206 determines also the requirements for the leak-before-break verification. For this procedure, it has to be ensured that a wall-penetrating crack is subcritical with respect to instable growth, and that the resulting leakage under stationary operation conditions can be detected by a leak detection system. Within the scope of the project 3613R01332 analyses with respect to conservative estimates of the leak rates in case of detections regarding break preclusion were performed by means of leak rate models being available at GRS. For this purpose, conservative assumptions in the procedure were quantified by comparative calculations concerning selected leak rate experiments and the requirements regarding the determination of leak rates indicated in the KTA 3206 were verified and specified. Moreover, the models were extended and relevant recommendations for the calculation procedure were developed. During the investigations of leak rate tests the calculation methods were validated, qualified by means of both examples indicated in KTA 3206 and applied to a postulated leak accident in the cooling circuit of a PWR. For the calculation of leak rates several simplified solution methods which are included in the GRS program WinLeck were applied, and for the simulation of a leak accident the large-scale programs ANSYS Mechanical and ATHLET (thermohydraulics program developed by GRS) were used. When applying simplified methods for the calculation of leak rates using the limiting curve for the friction factor which has been derived during the project and which is included in the KTA 3206 attention has to be paid to the fact that in case of small flow lengths the entrance loss can dominate compared to the friction loss. However, the available data do not suffice in order to make a quantitative statement with respect to limits of applicability

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

    DEFF Research Database (Denmark)

    Brincker, Rune

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

  2. Corrosion cracking

    International Nuclear Information System (INIS)

    Goel, V.S.

    1985-01-01

    This book presents the papers given at a conference on alloy corrosion cracking. Topics considered at the conference included the effect of niobium addition on intergranular stress corrosion cracking, corrosion-fatigue cracking in fossil-fueled-boilers, fracture toughness, fracture modes, hydrogen-induced thresholds, electrochemical and hydrogen permeation studies, the effect of seawater on fatigue crack propagation of wells for offshore structures, the corrosion fatigue of carbon steels in seawater, and stress corrosion cracking and the mechanical strength of alloy 600

  3. Elastic-Plastic J-Integral Solutions or Surface Cracks in Tension Using an Interpolation Methodology. Appendix C -- Finite Element Models Solution Database File, Appendix D -- Benchmark Finite Element Models Solution Database File

    Science.gov (United States)

    Allen, Phillip A.; Wells, Douglas N.

    2013-01-01

    No closed form solutions exist for the elastic-plastic J-integral for surface cracks due to the nonlinear, three-dimensional nature of the problem. Traditionally, each surface crack must be analyzed with a unique and time-consuming nonlinear finite element analysis. To overcome this shortcoming, the authors have developed and analyzed an array of 600 3D nonlinear finite element models for surface cracks in flat plates under tension loading. The solution space covers a wide range of crack shapes and depths (shape: 0.2 less than or equal to a/c less than or equal to 1, depth: 0.2 less than or equal to a/B less than or equal to 0.8) and material flow properties (elastic modulus-to-yield ratio: 100 less than or equal to E/ys less than or equal to 1,000, and hardening: 3 less than or equal to n less than or equal to 20). The authors have developed a methodology for interpolating between the goemetric and material property variables that allows the user to reliably evaluate the full elastic-plastic J-integral and force versus crack mouth opening displacement solution; thus, a solution can be obtained very rapidly by users without elastic-plastic fracture mechanics modeling experience. Complete solutions for the 600 models and 25 additional benchmark models are provided in tabular format.

  4. Circulatory Arrest, Brain Arrest and Death Determination

    Directory of Open Access Journals (Sweden)

    Sam David Shemie

    2018-03-01

    Full Text Available Technological advances, particularly in the capacity to support, replace or transplant failing organs, continue to challenge and refine our understanding of human death. Given the ability to reanimate organs before and after death, both inside and outside of the body, through reinstitution of oxygenated circulation, concepts related to death of organs (e.g. cardiac death are no longer valid. This paper advances the rationale for a single conceptual determination of death related to permanent brain arrest, resulting from primary brain injury or secondary to circulatory arrest. The clinical characteristics of brain arrest are the permanent loss of capacity for consciousness and loss of all brainstem functions. In the setting of circulatory arrest, death occurs after the arrest of circulation to the brain rather than death of the heart. Correspondingly, any intervention that resumes oxygenated circulation to the brain after circulatory arrest would invalidate the determination of death.

  5. Adaptive numerical modeling of dynamic crack propagation

    International Nuclear Information System (INIS)

    Adouani, H.; Tie, B.; Berdin, C.; Aubry, D.

    2006-01-01

    We propose an adaptive numerical strategy that aims at developing reliable and efficient numerical tools to model dynamic crack propagation and crack arrest. We use the cohesive zone theory as behavior of interface-type elements to model crack. Since the crack path is generally unknown beforehand, adaptive meshing is proposed to model the dynamic crack propagation. The dynamic study requires the development of specific solvers for time integration. As both geometry and finite element mesh of the studied structure evolve in time during transient analysis, the stability behavior of dynamic solver becomes a major concern. For this purpose, we use the space-time discontinuous Galerkin finite element method, well-known to provide a natural framework to manage meshes that evolve in time. As an important result, we prove that the space-time discontinuous Galerkin solver is unconditionally stable, when the dynamic crack propagation is modeled by the cohesive zone theory, which is highly non-linear. (authors)

  6. A probabilistic approach to crack instability

    Science.gov (United States)

    Chudnovsky, A.; Kunin, B.

    1989-01-01

    A probabilistic model of brittle fracture is examined with reference to two-dimensional problems. The model is illustrated by using experimental data obtained for 25 macroscopically identical specimens made of short-fiber-reinforced composites. It is shown that the model proposed here provides a predictive formalism for the probability distributions of critical crack depth, critical loads, and crack arrest depths. It also provides similarity criteria for small-scale testing.

  7. The Dugdale solution for two unequal straight cracks weakening

    Indian Academy of Sciences (India)

    A crack arrest model is proposed for an infinite elastic perfectly-plastic plate weakened by two unequal, quasi-static, collinear straight cracks. The Dugdale model solution is obtained for the above problem when the developed plastic zones are subjected to normal cohesive quadratically varying yield point stress. Employing ...

  8. Probabilistic modeling of crack networks in thermal fatigue

    International Nuclear Information System (INIS)

    Malesys, N.

    2007-11-01

    Thermal superficial crack networks have been detected in mixing zone of cooling system in nuclear power plants. Numerous experimental works have already been led to characterize initiation and propagation of these cracks. The random aspect of initiation led to propose a probabilistic model for the formation and propagation of crack networks in thermal fatigue. In a first part, uniaxial mechanical test were performed on smooth and slightly notched specimens in order to characterize the initiation of multiple cracks, their arrest due to obscuration and the coalescence phenomenon by recovery of amplification stress zones. In a second time, the probabilistic model was established under two assumptions: the continuous cracks initiation on surface, described by a Poisson point process law with threshold, and the shielding phenomenon which prohibits the initiation or the propagation of a crack if this one is in the relaxation stress zone of another existing crack. The crack propagation is assumed to follow a Paris' law based on the computation of stress intensity factors at the top and the bottom of crack. The evolution of multiaxial cracks on the surface can be followed thanks to three quantities: the shielding probability, comparable to a damage variable of the structure, the initiated crack density, representing the total number of cracks per unit surface which can be compared to experimental observations, and the propagating crack density, representing the number per unit surface of active cracks in the network. The crack sizes distribution is also computed by the model allowing an easier comparison with experimental results. (author)

  9. Initiation and arrest - two approaches to pressure vessel safety

    International Nuclear Information System (INIS)

    Brumovsky, M.; Filip, R.; Stepanek, S.

    1976-01-01

    The safety analysis is described of the reactor pressure vessel related to brittle fracture based on the fracture mechanics theory using two different approximations, i.e., the Crack Arrest Temperature (CAT) or Nil Ductility Temperature (NDT), and fracture toughness. The variation of CAT with stress was determined for different steel specimens of 120 to 200 mm in thickness. A diagram is shown of CAT variation with stress allowing the determination of crack arrest temperature for all types of commonly used steels independently of the NDT initial value. The diagram also shows that the difference between fracture transition elastic (FTE) and NDT depends on the type of material and determines the value of the ΔTsub(sigma) factor typical of the safety coefficient. The so-called fracture toughness reference value Ksub(IR) is recommended for the computation of pressure vessel criticality. Also shown is a defect analysis diagram which may be used for the calculation of pressure vessel safety prior to and during operation and which may also be used in making the decision on what crack sizes are critical, what cracks may be arrested and what cracks are likely to expand. The diagram is also important for the fact that it is material-independent and may be employed for the estimates of pre-operational and operational inspections and for pressure vessel life prediction. It is generally applicable to materials of greater thickness in the region where the validity of linear elastic fracture mechanics is guaranteed. (J.P.)

  10. Investigations of Low Temperature Time Dependent Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Van der Sluys, W A; Robitz, E S; Young, B A; Bloom, J

    2002-09-30

    The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity. The resultant data was integrated into current available life prediction tools.

  11. Development of Validated Crack Measurement System for Vibrating Structures

    National Research Council Canada - National Science Library

    Ratwani, Mohan

    2002-01-01

    ...) solutions in AFGROW or other crack growth codes could not be used for accurate prediction of crack growth because of absence of methodology accounting for dynamic stresses and frequency effects...

  12. Pittsburgh Police Arrest Data

    Data.gov (United States)

    Allegheny County / City of Pittsburgh / Western PA Regional Data Center — Arrest data contains information on people taken into custody by City of Pittsburgh police officers. More serious crimes such as felony offenses are more likely to...

  13. Entering a Crack: An Encounter with Gossip

    Science.gov (United States)

    Henderson, Linda

    2014-01-01

    In this paper, I enter a crack to think otherwise about the concept "gossip". Drawing on previous scholarship engaging with Deleuzian concepts to inform research methodologies, this paper builds on this body of work. Following Deleuze and Guattari, the paper undertakes a mapping of gossip, subsequent to an encounter with a crack.…

  14. Influence of MSD crack pattern on the residual strength of flat stiffened sheets

    Science.gov (United States)

    Nilsson, K.-F.

    A parameter study of the residual strength for a multiple site damaged (MSD) stiffened sheet is presented. The analysis is based on an elastic-plastic fracture analysis using the yield-strip model for interaction between a lead crack and the smaller MSD cracks. Two crack growth criteria, one with a pronounced crack growth resistance and one with no crack growth resistance and five different MSD crack patterns, are analysed for different sizes of the lead crack and the smaller MSD cracks. The analysis indicates that the residual strength reduction depends on all these parameters and that MSD may totally erode the crack arrest capability of a tear strap. Another important outcome is that for certain combinations also very small MSD cracks may induce a significant residual strength reduction.

  15. Password cracking

    OpenAIRE

    Χριστοφάκης, Μιχαήλ Κ.

    2014-01-01

    Information security is the next big thing in computers society because of the rapidly growing security incidents and the outcomes of those. Hacking and cracking existed even from the start of the eighties decade when there was the first step of the interconnection through the internet between humans. From then and ever after there was a big explosion of such incidents mostly because of the worldwide web which was introduced in the early nineties. Following the huge steps forward of computers...

  16. On governing equations for crack layer propagation

    Science.gov (United States)

    Chudnovsky, A.; Botsis, J.

    1988-01-01

    Results of analysis on damage distribution of a crack layer, in a model material, supported the self-similarity hypothesis of damage evolution which has been adopted by the crack layer theory. On the basis of measurements of discontinuity density and the double layer potential technique, a solution to the crack damage interaction problem has been developed. Evaluation of the stress intensity factor illustrated the methodology. Analysis of experimental results showed that Arrhenius type constitutive relationship described very well the expansion of the active zone of a crack layer.

  17. Hydride effect on crack instability of Zircaloy cladding

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-01

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

  18. Runway Arrested Landing Site (RALS)

    Data.gov (United States)

    Federal Laboratory Consortium — The Runway Arrested Landing Site includes an underground complex located on a Mod 2, Mod 3, and Mod 3+ arresting gear and are located under the runway and accurately...

  19. Cracking hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Forwood, G F; Lane, M; Taplay, J G

    1921-10-07

    In cracking and hydrogenating hydrocarbon oils by passing their vapors together with steam over heated carbon derived from shale, wood, peat or other vegetable or animal matter, the gases from the condenser are freed from sulfuretted hydrogen, and preferably also from carbon dioxide, and passed together with oil vapors and steam through the retort. Carbon dioxide may be removed by passage through slaked lime, and sulfuretted hydrogen by means of hydrated oxide of iron. Vapors from high-boiling oils and those from low-boiling oils are passed alternately through the retort, so that carbon deposited from the high-boiling oils is used up during treatment of low-boiling oils.

  20. Crack propagation of brittle rock under high geostress

    Science.gov (United States)

    Liu, Ning; Chu, Weijiang; Chen, Pingzhi

    2018-03-01

    Based on fracture mechanics and numerical methods, the characteristics and failure criterions of wall rock cracks including initiation, propagation, and coalescence are analyzed systematically under different conditions. In order to consider the interaction among cracks, adopt the sliding model of multi-cracks to simulate the splitting failure of rock in axial compress. The reinforcement of bolts and shotcrete supporting to rock mass can control the cracks propagation well. Adopt both theory analysis and simulation method to study the mechanism of controlling the propagation. The best fixed angle of bolts is calculated. Then use ansys to simulate the crack arrest function of bolt to crack. Analyze the influence of different factors on stress intensity factor. The method offer more scientific and rational criterion to evaluate the splitting failure of underground engineering under high geostress.

  1. Multiple cracks initiation and propagation behavior of stainless steel in high temperature water environment

    International Nuclear Information System (INIS)

    Kamaya, Masayuki; Chiba, Goro; Nakajima, Nobuo; Totsuka, Nobuo

    2001-01-01

    Environmentally assisted crack initiation behavior is greatly affected by applied stress and environmental factors, such as water temperature, contained impurities and so on. On the other hand, crack initiation behavior also influences crack propagation. A typical example of this influence can be observed as the interference effects of multiple cracks, such as the coalescence of approaching crack tips or the arrest phenomena in the relaxation zone of an adjacent crack. To understand these effects of crack initiation on crack propagation behavior is very important to predict the lifetime of components, in which quite a few cracks tend to occur. This study aimed at revealing the crack initiation behavior and the influence of this behavior on propagation. At first, to evaluate the effect of applied stress on crack initiation behavior, sensitized stainless steel was subjected to a four-point bending test in a high temperature water environment at the constant potentials of ECP +50 mV and ECP +150 mV. Secondly, a crack initiation and growth simulation model was developed, in which the interference effect of multiple cracks is evaluated by the finite element method, based on the experimental results. Using this model, the relationship between crack initiation and propagation was studied. From the model, it was revealed that the increasing number of the cracks accelerates crack propagation and reduces life. (author)

  2. Initiation and propagation of multiple cracks of stainless steel in high temperature water environment

    Energy Technology Data Exchange (ETDEWEB)

    Kamaya, Masayuki; Chiba, Goro; Nakajima, Nobuo; Totsuka, Nobuo [Institute of Nuclear Safety System Inc., Mihama, Fukui (Japan)

    2001-09-01

    Environmentally assisted crack initiation behavior is greatly affected by applied stress and environmental factors, such as water temperature, contained impurities and so on. Crack initiation behavior also influences crack propagation. A typical example of this influence can be observed as the interference effects of multiple cracks, such as the coalescence of approaching crack tips or the arrest phenomena in the relaxation zone of an adjacent crack. To understand these effects of crack initiation on crack propagation behavior is very important to predict the lifetime of components, in which relatively large number of cracks tend to occur. This study aimed at revealing the crack initiation behavior and the influence of this behavior on propagation. At first, to evaluate the effect of applied stress on crack initiation behavior, sensitized stainless steel was subjected to a four-point bending test in high temperature water environment at the constant potentials of +50 mV SHE and +150 mV SHE Secondly, a crack initiation and growth simulation model was developed, in which the interference effect of multiple cracks is evaluated by the finite element method, based on the experimental results. Using this model, the relationship between crack initiation and propagation was investigated, and it was revealed that the increasing number of the cracks accelerates crack propagation and reduces life. (author)

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

    International Nuclear Information System (INIS)

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

    1977-01-01

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

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

    International Nuclear Information System (INIS)

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

    1977-01-01

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

  5. Cohesive zone model for intergranular slow crack growth in ceramics: influence of the process and the microstructure

    International Nuclear Information System (INIS)

    Romero de la Osa, M; Olagnon, C; Chevalier, J; Estevez, R; Tallaron, C

    2011-01-01

    Ceramic polycrystals are prone to slow crack growth (SCG) which is stress and environmentally assisted, similarly to observations reported for silica glasses. The kinetics of fracture are known to be dependent on the load level, the temperature and the relative humidity. In addition, evidence is available on the influence of the microstructure on the SCG rate with an increase in the crack velocity with decreasing the grain size. Crack propagation takes place beyond a load threshold, which is grain size dependent. We present a cohesive zone model for the intergranular failure process. The methodology accounts for an intrinsic opening that governs the length of the cohesive zone and allows the investigation of grain size effects. A rate and temperature-dependent cohesive model is proposed (Romero de la Osa M, Estevez R et al 2009 J. Mech. Adv. Mater. Struct. 16 623–31) to mimic the reaction–rupture mechanism. The formulation is inspired by Michalske and Freiman's picture (Michalske and Freiman 1983 J. Am. Ceram. Soc. 66 284–8) together with a recent study by Zhu et al (2005 J. Mech. Phys. Solids 53 1597–623) of the reaction–rupture mechanism. The present investigation extends a previous work (Romero de la Osa et al 2009 Int. J. Fracture 158 157–67) in which the problem is formulated. Here, we explore the influence of the microstructure in terms of grain size, their elastic properties and residual thermal stresses originating from the cooling from the sintering temperature down to ambient conditions. Their influence on SCG for static loadings is reported and the predictions compared with experimental trends. We show that the initial stress state is responsible for the grain size dependence reported experimentally for SCG. Furthermore, the account for the initial stresses enables the prediction of a load threshold below which no crack growth is observed: a crack arrest takes place when the crack path meets a region in compression

  6. The detectability of cracks using sonic IR

    Science.gov (United States)

    Morbidini, Marco; Cawley, Peter

    2009-05-01

    This paper proposes a methodology to study the detectability of fatigue cracks in metals using sonic IR (also known as thermosonics). The method relies on the validation of simple finite-element thermal models of the cracks and specimens in which the thermal loads have been defined by means of a priori measurement of the additional damping introduced in the specimens by each crack. This estimate of crack damping is used in conjunction with a local measurement of the vibration strain during ultrasonic excitation to retrieve the power released at the crack; these functions are then input to the thermal model of the specimens to find the resulting temperature rises (sonic IR signals). The method was validated on mild steel beams with two-dimensional cracks obtained in the low-cycle fatigue regime as well as nickel-based superalloy beams with three-dimensional "thumbnail" cracks generated in the high-cycle fatigue regime. The equivalent 40kHz strain necessary to obtain a desired temperature rise was calculated for cracks in the nickel superalloy set, and the detectability of cracks as a function of length in the range of 1-5mm was discussed.

  7. 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

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

    Science.gov (United States)

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

    2013-12-01

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

  9. Modified Dugdale cracks and Fictitious cracks

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1998-01-01

    A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local...... areas, so-called fictitious cracks, in front of the crack.The Modified Dugdale theory presented in this paper is also based on the concept of Dugdale cracks. Any cohesive stress distribution, however, can be considered in front of the crack. Formally the strength of a material weakened by a modified...... Dugdale crack is the same as if it has been weakened by the well-known Griffith crack, namely sigma_CR = (EG_CR/phi)^1/2 where E and 1 are Young's modulus and crack half-length respectively, and G_CR is the so-called critical energy release rate. The physical significance of G_CR, however, is different...

  10. Cardiac arrest – cardiopulmonary resuscitation

    Directory of Open Access Journals (Sweden)

    Basri Lenjani

    2014-01-01

    Conclusions: All survivors from cardiac arrest have received appropriate medical assistance within 10 min from attack, which implies that if cardiac arrest occurs near an institution health care (with an opportunity to provide the emergent health care the rate of survival is higher.

  11. Cardiac Arrest: MedlinePlus Health Topic

    Science.gov (United States)

    ... Handouts Cardiac arrest (Medical Encyclopedia) Also in Spanish Topic Image MedlinePlus Email Updates Get Cardiac Arrest updates ... this? GO MEDICAL ENCYCLOPEDIA Cardiac arrest Related Health Topics Arrhythmia CPR Pacemakers and Implantable Defibrillators National Institutes ...

  12. Experimental investigation of flawed pipes with respect to fracture behavior and development of crack opening area

    Energy Technology Data Exchange (ETDEWEB)

    Stoppler, W [Stuttgart Univ. (Germany). Staatliche Materialpruefungsanstalt

    1993-12-31

    The critical length of a longitudinal through-wall flaw, defined as that causing rupture, was first determined hydro-statically on large experimental vessels under internal pressure; the leak before rupture diagram for the base material of the vessel is established by experiment and calculation; it gives a limit between the two modes of failure, leakage or rupture (catastrophic failure), depending on slit length and loading conditions. Tests under pneumatic pressure were then carried out to investigate crack arrest, with notched discs made of a brittle material welded in the cylindrical part of the vessel, and cracks triggered by means of a small charged ignited over the notch. In the case of discs of a diameter smaller than the critical slit length, crack arrest occurred when the crack entered the tough material, while a disc corresponding to the critical crack length of the vessel led to rupture. 5 refs., 16 figs., 2 tabs.

  13. Crack detection using image processing

    International Nuclear Information System (INIS)

    Moustafa, M.A.A

    2010-01-01

    care using Wiener filter. An integrated methodology for the detection and removal of cracks on digitized images is presented in this thesis. The cracks are detected by steepest descent algorithm (SDA) the output of the piping image as cracks are removed using either a gradient Function (GRF) and processed data or a semi-automatic procedure based on region growing. Finally, crack filling using the steepest descent algorithm. The methodology has been shown to perform very well on digitized images suffering from cracks, using Matlab, and Visual Fortran programming. The thesis presents an application of the wavelet transform for damage detection or crack detection based on digital image processing measurements.

  14. "House Arrest" or "Developmental Arrest"? A Study of Youth Under House Arrest.

    Science.gov (United States)

    Chamiel, Elad; Walsh, Sophie D

    2018-06-01

    Studies have examined the potential benefits and risks of alternative forms of detention, such as house arrest, for adults but, despite its growing use, little research has examined the implications of house arrest for juveniles. The current research examined the experience of 14 adolescents under house arrest. Six main themes were identified in the narratives of the participants: the experience of detention, daily schedule and utilization of time, emotions and self-reflection, relationships with peers, relation to parents and supervisor(s), and contact with professionals. Findings emphasized the potential developmental dangers of house arrest at the critical stage of adolescence. Yet, analysis also showed that the period of house arrest has the potential to be a period of positive changes, and can be used for successful rehabilitation.

  15. Cocaine (Coke, Crack) Facts

    Science.gov (United States)

    ... That People Abuse » Cocaine (Coke, Crack) Facts Cocaine (Coke, Crack) Facts Listen Cocaine is a white ... 69 KB) "My life was built around getting cocaine and getting high." ©istock.com/ Marjot Stacey is ...

  16. Metoclopramide-induced cardiac arrest

    Directory of Open Access Journals (Sweden)

    Martha M. Rumore

    2011-11-01

    Full Text Available The authors report a case of cardiac arrest in a patient receiving intravenous (IV metoclopramide and review the pertinent literature. A 62-year-old morbidly obese female admitted for a gastric sleeve procedure, developed cardiac arrest within one minute of receiving metoclopramide 10 mg via slow intravenous (IV injection. Bradycardia at 4 beats/min immediately appeared, progressing rapidly to asystole. Chest compressions restored vital function. Electrocardiogram (ECG revealed ST depression indicative of myocardial injury. Following intubation, the patient was transferred to the intensive care unit. Various cardiac dysrrhythmias including supraventricular tachycardia (SVT associated with hypertension and atrial fibrillation occurred. Following IV esmolol and metoprolol, the patient reverted to normal sinus rhythm. Repeat ECGs revealed ST depression resolution without pre-admission changes. Metoclopramide is a non-specific dopamine receptor antagonist. Seven cases of cardiac arrest and one of sinus arrest with metoclopramide were found in the literature. The metoclopramide prescribing information does not list precautions or adverse drug reactions (ADRs related to cardiac arrest. The reaction is not dose related but may relate to the IV administration route. Coronary artery disease was the sole risk factor identified. According to Naranjo, the association was possible. Other reports of cardiac arrest, severe bradycardia, and SVT were reviewed. In one case, five separate IV doses of 10 mg metoclopramide were immediately followed by asystole repeatedly. The mechanism(s underlying metoclopramide’s cardiac arrest-inducing effects is unknown. Structural similarities to procainamide may play a role. In view of eight previous cases of cardiac arrest from metoclopramide having been reported, further elucidation of this ADR and patient monitoring is needed. Our report should alert clinicians to monitor patients and remain diligent in surveillance and

  17. Crystallographic fatigue crack growth in a polycrystal: simulations based on FEM and discrete dislocation dynamics

    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)

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

    International Nuclear Information System (INIS)

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

    2011-01-01

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

  19. Photoelastic Analysis of Cracked Thick Walled Cylinders

    Science.gov (United States)

    Pastramă, Ştefan Dan

    2017-12-01

    In this paper, the experimental determination of the stress intensity factor in thick walled cylinders subject to uniform internal pressure and having longitudinal non-penetrating cracks is presented. Photoelastic measurements were used together with the expressions of the stress field near the crack tip for Mode I crack extension and a specific methodology for stress intensity factor determination. Two types of longitudinal cracks - internal and external - were considered. Four plane models were manufactured and analyzed in a plane polariscope at different values of the applied internal pressure. The values of the normalized stress intensity factor were calculated and the results were compared to those reported by other authors. A good accuracy was noticed, showing the reliability of the experimental procedure.

  20. Recent evaluations of crack-opening-area in circumferentially cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, S.; Brust, F.; Ghadiali, N.; Wilkowski, G.; Miura, N.

    1997-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. The results from twenty-five full-scale pipe fracture experiments, conducted in the Degraded Piping Program, the International Piping Integrity Research Group Program, and the Short Cracks in Piping and Piping Welds Program, were used to verify the analytical models. Standard statistical analyses were performed to assess used to verify the analytical models. Standard statistical analyses were performed to assess quantitatively the accuracy of the predictive models. The evaluation also involved finite element analyses for determining the crack-opening profile often needed to perform leak-rate calculations.

  1. A practical method for computation of ductile crack growth by means of finite elements and parametric 3D-modelling

    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.)

  2. Investigation of Helicopter Longeron Cracks

    Science.gov (United States)

    Newman, John A.; Baughman, James; Wallace, Terryl A.

    2009-01-01

    Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurgical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

  3. Crack detecting method

    International Nuclear Information System (INIS)

    Narita, Michiko; Aida, Shigekazu

    1998-01-01

    A penetration liquid or a slow drying penetration liquid prepared by mixing a penetration liquid and a slow drying liquid is filled to the inside of an artificial crack formed to a member to be detected such as of boiler power generation facilities and nuclear power facilities. A developing liquid is applied to the periphery of the artificial crack on the surface of a member to be detected. As the slow-drying liquid, an oil having a viscosity of 56 is preferably used. Loads are applied repeatedly to the member to be detected, and when a crack is caused to the artificial crack, the permeation liquid penetrates into the crack. The penetration liquid penetrated into the crack is developed by the developing liquid previously coated to the periphery of the artificial crack of the surface of the member to be detected. When a crack is caused, since the crack is developed clearly even if it is a small opening, the crack can be recognized visually reliably. (I.N.)

  4. Refinement and evaluation of crack-opening-area analyses for circumferential through-wall cracks in pipes

    International Nuclear Information System (INIS)

    Rahman, S.; Brust, F.; Ghadiali, N.; Krishnaswamy, P.; Wilkowski, G.; Choi, Y.H.; Moberg, F.; Brickstad, B.

    1995-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet impingement shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. These leak rates depend on the crack-opening area of a through-wall crack in the pipe. In addition to LBB analyses, which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section 11. This study was requested by the NRC to review, evaluate, and refine current analytical models for crack-opening-area analyses of pipes with circumferential through-wall cracks. Twenty-five pipe experiments were analyzed to determine the accuracy of the predictive models. Several practical aspects of crack-opening such as; crack-face pressure, off-center cracks, restraint of pressure-induced bending, cracks in thickness transition regions, weld residual stresses, crack-morphology models, and thermal-hydraulic analysis, were also investigated. 140 refs., 105 figs., 41 tabs

  5. Curvilinear crack layer propagation

    Science.gov (United States)

    Chudnovsky, Alexander; Chaoui, Kamel; Moet, Abdelsamie

    1987-01-01

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

  6. Reinforcement against crack propagation of PWR absorbers by development of boron-carbon-hafnium composites

    International Nuclear Information System (INIS)

    Provot, B.; Herter, P.

    2000-01-01

    In order to improve the mechanical behaviour of materials used as neutron absorbers in nuclear reactors, we have developed CERCER or CERMET composites with boron and hafnium. Thus a new composite B 4 C/HfB 2 has been especially studied. We have identified three kinds of degradation under irradiation (thermal gradient, swelling due to fission products and accidental corrosion) that induce imposed deformations cracking phenomena. Mechanical behaviour and crack propagation resistance have been studied by ball-on-three-balls and double torsion tests. A special device was developed to enable crack propagation and associated stress intensity factor measurements. Effects of structure and of a second phase are underline. First results show that these materials present crack initiation and propagation resistance much higher than pure boron carbide or hafnium diboride. We observe R-Curves effects, crack bridging or branching, crack arrests, and toughness increases that we can relate respectively to the composite structures. (author)

  7. Study of toughening mechanisms through the observations of crack propagation in nanostructured and layered metallic sheet

    International Nuclear Information System (INIS)

    Chen, A.Y.; Li, D.F.; Zhang, J.B.; Liu, F.; Liu, X.R.; Lu, J.

    2011-01-01

    Highlights: → A nanostructured and layered steel exhibits high strength and large ductility. → The excellent combination originates from a multiple interlaminar cracking. → The initiation and propagation of cracks are controlled by three aspects. → The cracks are deflected by interface and arrested by compressive residual stress. → Finally, the cracks are blunted by the graded grain size distribution. - Abstract: A layered and nanostructured (LN) 304 SS sheet was produced by combination of surface mechanical attrition treatment (SMAT) with warm co-rolling. The microstructure of LN sheet is characterized by a periodic distribution of nanocrystalline layers and micron-grained layers with a graded transition of grain size. Tensile test results show that exceptional properties of high yield strength and large elongation to fracture are achieved. A multiple interlaminar cracking was observed by scanning electron microscopy, which is induced by repeated crack initiation and propagation. The toughening mechanisms of the LN sheet are proposed to be controlling the crack propagation path by several strategies. The main cracks initiating at interface defects are arrested by large compressive residual stress, deflected by weak interface bonding and blunted by the graded grain size distribution.

  8. Effects of off-centered crack and restraint of induced bending due to pressure on the crack-opening-area analysis of pipes

    International Nuclear Information System (INIS)

    Rahman, S.; Ghadiali, N.; Wilkowski, G.; Bonora, N.

    1995-01-01

    Estimation of leak rate is an important element in developing leak-before-break (LBB) methodology for piping integrity and safety analysis of nuclear power plants. Here, current models for the crack-opening-area analysis of pipes with circumferential through-wall cracks are based on various idealizations or assumption which are often necessary to simplify the mathematical formulation and numerical calculation. This paper focuses on the validity of two such assumptions involving off-centered cracks and restraint of induced bending due to pressure and quantifies their effects on the crack-opening analysis of pipes. Both finite element and/or simple estimation methods were employed to compute the center-crack-opening displacement and crack-opening shape for a through-wall-cracked pipe considering off-centered cracks and restrain of induced bending due to pressure. The results of analyses show that for both cases the crack-opening area can be reduced significantly. For pipes with off-centered cracks, the crack-opening area can be evaluated from analyses of symmetrically centered cracks and assuming elliptical profile. For pipes with complete restraint of induced bending due to pressure, the reduction of crack-opening area depends on the crack size. When the crack size is small, the restraint effects can be ignored. However, when the crack size is larger, the restrained crack-opening can be significantly smaller than the unrestrained crack-opening depending on the length of pipe involved, and hence, may be important for the crack-opening-area and leak-rate analyses

  9. Crack layer theory

    Science.gov (United States)

    Chudnovsky, A.

    1987-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  10. Atomistics of crack propagation

    International Nuclear Information System (INIS)

    Sieradzki, K.; Dienes, G.J.; Paskin, A.; Massoumzadeh, B.

    1988-01-01

    The molecular dynamic technique is used to investigate static and dynamic aspects of crack extension. The material chosen for this study was the 2D triangular solid with atoms interacting via the Johnson potential. The 2D Johnson solid was chosen for this study since a sharp crack in this material remains stable against dislocation emission up to the critical Griffith load. This behavior allows for a meaningful comparison between the simulation results and continuum energy theorems for crack extension by appropriately defining an effective modulus which accounts for sample size effects and the non-linear elastic behavior of the Johnson solid. Simulation results are presented for the stress fields of moving cracks and these dynamic results are discussed in terms of the dynamic crack propagation theories, of Mott, Eshelby, and Freund

  11. Sudden Cardiac Arrest (SCA) Risk Assessment

    Science.gov (United States)

    ... HRS Find a Specialist Share Twitter Facebook SCA Risk Assessment Sudden Cardiac Arrest (SCA) occurs abruptly and without ... people of all ages and health conditions. Start Risk Assessment The Sudden Cardiac Arrest (SCA) Risk Assessment Tool ...

  12. Cracked gas generator

    Energy Technology Data Exchange (ETDEWEB)

    Abthoff, J; Schuster, H D; Gabler, R

    1976-11-17

    A small cracked-gas generator in a vehicle driven, in particular, by an air combustion engine has been proposed for the economic production of the gases necessary for low toxicity combustion from diesel fuel. This proceeds via catalytic crack-gasification and exploitation of residual heat from exhaust gases. This patent application foresees the insertion of one of the catalysts supporting the cracked-gas reaction in a container through which the reacting mixture for cracked-gas production flows in longitudinal direction. Further, air ducts are embedded in the catalyst through which exhaust gases and fresh air flow in counter direction to the cracked gas flow in the catalyst. The air vents are connected through heat conduction to the catalyst. A cracked gas constituting H/sub 2//CO/CO/sub 2//CH/sub 4/ and H/sub 2/O can be produced from the air-fuel mixture using appropriate catalysts. By the addition of 5 to 25% of cracked gas to the volume of air drawn in by the combustion engine, a more favourable combustion can be achieved compared to that obtained under normal combustion conditions.

  13. Assessment of surge arrester failure rate and application studies in Hellenic high voltage transmission lines

    Energy Technology Data Exchange (ETDEWEB)

    Christodoulou, C.A.; Fotis, G.P.; Gonos, I.F.; Stathopulos, I.A. [National Technical University of Athens, School of Electrical and Computer Engineering, High Voltage Laboratory, 9 Iroon Politechniou St., Zografou Campus, 157 80 Athens (Greece); Ekonomou, L. [A.S.PE.T.E. - School of Pedagogical and Technological Education, Department of Electrical Engineering Educators, N. Heraklion, 141 21 Athens (Greece)

    2010-02-15

    The use of transmission line surge arresters to improve the lightning performance of transmission lines is becoming more common. Especially in areas with high soil resistivity and ground flash density, surge arresters constitute the most effective protection mean. In this paper a methodology for assessing the surge arrester failure rate based on the electrogeometrical model is presented. Critical currents that exceed arresters rated energy stress were estimated by the use of a simulation tool. The methodology is applied on operating Hellenic transmission lines of 150 kV. Several case studies are analyzed by installing surge arresters on different intervals, in relation to the region's tower footing resistance and the ground flash density. The obtained results are compared with real records of outage rate showing the effectiveness of the surge arresters in the reduction of the recorded failure rate. The presented methodology can be proved valuable to the studies of electric power systems designers intending in a more effective lightning protection, reducing the operational costs and providing continuity of service. (author)

  14. Crack identification for rotating machines based on a nonlinear approach

    Science.gov (United States)

    Cavalini, A. A., Jr.; Sanches, L.; Bachschmid, N.; Steffen, V., Jr.

    2016-10-01

    In a previous contribution, a crack identification methodology based on a nonlinear approach was proposed. The technique uses external applied diagnostic forces at certain frequencies attaining combinational resonances, together with a pseudo-random optimization code, known as Differential Evolution, in order to characterize the signatures of the crack in the spectral responses of the flexible rotor. The conditions under which combinational resonances appear were determined by using the method of multiple scales. In real conditions, the breathing phenomenon arises from the stress and strain distribution on the cross-sectional area of the crack. This mechanism behavior follows the static and dynamic loads acting on the rotor. Therefore, the breathing crack can be simulated according to the Mayes' model, in which the crack transition from fully opened to fully closed is described by a cosine function. However, many contributions try to represent the crack behavior by machining a small notch on the shaft instead of the fatigue process. In this paper, the open and breathing crack models are compared regarding their dynamic behavior and the efficiency of the proposed identification technique. The additional flexibility introduced by the crack is calculated by using the linear fracture mechanics theory (LFM). The open crack model is based on LFM and the breathing crack model corresponds to the Mayes' model, which combines LFM with a given breathing mechanism. For illustration purposes, a rotor composed by a horizontal flexible shaft, two rigid discs, and two self-aligning ball bearings is used to compose a finite element model of the system. Then, numerical simulation is performed to determine the dynamic behavior of the rotor. Finally, the results of the inverse problem conveyed show that the methodology is a reliable tool that is able to estimate satisfactorily the location and depth of the crack.

  15. Crack Cocaine-Induced Cardiac Conduction Abnormalities Are Reversed by Sodium Bicarbonate Infusion

    Directory of Open Access Journals (Sweden)

    Carlos Henrique Miranda

    2013-01-01

    Full Text Available We report a dramatic case of a 19-year-old man with crack cocaine overdose with important clinical complications as cardiac arrest due to ventricular fibrillation and epileptics status. During this intoxication, electrocardiographic abnormalities similar to those found in tricyclic antidepressant poisoning were observed, and they were reversed by intravenous sodium bicarbonate infusion.

  16. Transport Through Cracked Concrete: Literature Review

    International Nuclear Information System (INIS)

    Langton, C.

    2012-01-01

    Concrete containment structures and cement-based fills and waste forms are used at the Savannah River Site to enhance the performance of shallow land disposal systems designed for containment of low-level radioactive waste. Understanding and measuring transport through cracked concrete is important for describing the initial condition of radioactive waste containment structures at the Savannah River Site (SRS) and for predicting performance of these structures over time. This report transmits the results of a literature review on transport through cracked concrete which was performed by Professor Jason Weiss, Purdue University per SRR0000678 (RFP-RQ00001029-WY). This review complements the NRC-sponsored literature review and assessment of factors relevant to performance of grouted systems for radioactive waste disposal. This review was performed by The Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, and The University of Aberdeen, Aberdeen Scotland and was focused on tank closure. The objective of the literature review on transport through cracked concrete was to identify information in the open literature which can be applied to SRS transport models for cementitious containment structures, fills, and waste forms. In addition, the literature review was intended to: (1) Provide a framework for describing and classifying cracks in containment structures and cementitious materials used in radioactive waste disposal, (2) Document the state of knowledge and research related to transport through cracks in concrete for various exposure conditions, (3) Provide information or methodology for answering several specific questions related to cracking and transport in concrete, and (4) Provide information that can be used to design experiments on transport through cracked samples and actual structures.

  17. TRANSPORT THROUGH CRACKED CONCRETE: LITERATURE REVIEW

    Energy Technology Data Exchange (ETDEWEB)

    Langton, C.

    2012-05-11

    Concrete containment structures and cement-based fills and waste forms are used at the Savannah River Site to enhance the performance of shallow land disposal systems designed for containment of low-level radioactive waste. Understanding and measuring transport through cracked concrete is important for describing the initial condition of radioactive waste containment structures at the Savannah River Site (SRS) and for predicting performance of these structures over time. This report transmits the results of a literature review on transport through cracked concrete which was performed by Professor Jason Weiss, Purdue University per SRR0000678 (RFP-RQ00001029-WY). This review complements the NRC-sponsored literature review and assessment of factors relevant to performance of grouted systems for radioactive waste disposal. This review was performed by The Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, and The University of Aberdeen, Aberdeen Scotland and was focused on tank closure. The objective of the literature review on transport through cracked concrete was to identify information in the open literature which can be applied to SRS transport models for cementitious containment structures, fills, and waste forms. In addition, the literature review was intended to: (1) Provide a framework for describing and classifying cracks in containment structures and cementitious materials used in radioactive waste disposal, (2) Document the state of knowledge and research related to transport through cracks in concrete for various exposure conditions, (3) Provide information or methodology for answering several specific questions related to cracking and transport in concrete, and (4) Provide information that can be used to design experiments on transport through cracked samples and actual structures.

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

    Directory of Open Access Journals (Sweden)

    E. Fessler

    2016-01-01

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

  19. Thermal fatigue cracking of austenitic stainless steels

    International Nuclear Information System (INIS)

    Fissolo, A.

    2001-01-01

    This report deals with the thermal fatigue cracking of austenitic stainless steels as AISI 316 LN and 304 L. Such damage has been clearly observed for some components used in Fast Breeder reactors (FBR) and Pressure Water Reactor (PWR). In order to investigate thermal fatigue, quasi-structural specimen have been used. In this frame, facilities enforcing temperature variations similar to those found under the operation conditions have been progressively developed. As for components, loading results from impeded dilatation. In the SPLASH facility, the purpose was to establish accurate crack initiation conditions in order to check the relevance of the usual component design methodology. The tested specimen is continuously heated by the passage of an electrical DC current, and submitted to cyclic thermal down shock (up to 1000 deg C/s) by means of periodical spraying of water on two opposite specimen faces. The number of cycles to crack initiation N i is deduced from periodic examinations of the quenched surfaces, by means of optical microscopy. It is considered that initiation occurs when at least one 50μm to 150□m long crack is observed. Additional SPLASH tests were performed for N >> N i , with a view to investigate the evolution of a surface multiple cracking network with the number of cycles N. The CYTHIA test was mainly developed for the purpose of assessing crack growth dynamics of one isolated crack in thermal fatigue conditions. Specimens consist of thick walled tubes with a 1 mm circular groove is spark-machined at the specimen centre. During the test, the external wall of the tube is periodically heated by using a HF induction coil (1 MHz), while its internal wall is permanently cooled by flowing water. Total crack growth is derived from post-mortem examinations, whereby the thermal fatigue final rupture surface is oxidized at the end of the test. The specimen is broken afterwards under mechanical fatigue at room temperature. All the tests confirm that

  20. Inspecting cracks in foam insulation

    Science.gov (United States)

    Cambell, L. W.; Jung, G. K.

    1979-01-01

    Dye solution indicates extent of cracking by penetrating crack and showing original crack depth clearly. Solution comprised of methylene blue in denatured ethyl alcohol penetrates cracks completely and evaporates quickly and is suitable technique for usage in environmental or structural tests.

  1. Modelling of Corrosion Cracks

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed.......Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed....

  2. Cracking the Gender Codes

    DEFF Research Database (Denmark)

    Rennison, Betina Wolfgang

    2016-01-01

    extensive work to raise the proportion of women. This has helped slightly, but women remain underrepresented at the corporate top. Why is this so? What can be done to solve it? This article presents five different types of answers relating to five discursive codes: nature, talent, business, exclusion...... in leadership management, we must become more aware and take advantage of this complexity. We must crack the codes in order to crack the curve....

  3. SSRI Facilitated Crack Dancing

    Directory of Open Access Journals (Sweden)

    Ravi Doobay

    2017-01-01

    Full Text Available Choreoathetoid movement secondary to cocaine use is a well-documented phenomenon better known as “crack dancing.” It consists of uncontrolled writhing movements secondary to excess dopamine from cocaine use. We present a 32-year-old male who had been using cocaine for many years and was recently started on paroxetine, a selective serotonin reuptake inhibitor (SSRI for worsening depression four weeks before presentation. He had been doing cocaine every 2 weeks for the last three years and had never “crack danced” before this episode. The authors have conducted a thorough literature review and cited studies that suggest “crack dancing” is associated with excess dopamine. There has never been a documented case report of an SSRI being linked with “crack dancing.” The authors propose that the excess dopaminergic effect of the SSRI lowered the dopamine threshold for “crack dancing.” There is a communication with the Raphe Nucleus and the Substantia Nigra, which explains how the SSRI increases dopamine levels. This is the first documented case of an SSRI facilitating the “crack dance.”

  4. Natural zeolite bitumen cracking

    Energy Technology Data Exchange (ETDEWEB)

    Kuznicki, S.M.; McCaffrey, W.C.; Bian, J.; Wangen, E.; Koenig, A. [Alberta Univ., Edmonton, AB (Canada). Dept. of Chemical and Materials Engineering

    2006-07-01

    A study was conducted to demonstrate how low cost heavy oil upgrading in the field could reduce the need for diluents while lowering the cost for pipelining. Low cost field upgrading could also contribute to lowering contaminant levels. The performance of visbreaking processes could be improved by using disposable cracking agents. In turn, the economics of field upgrading of in-situ derived bitumen would be improved. However, in order to be viable, such agents would have to be far less expensive than current commercial cracking catalysts. A platy natural zeolite was selected for modification and testing due to its unique chemical and morphological properties. A catalyst-bearing oil sand was then heat-treated for 1 hour at 400 degrees C in a sealed microreactor. Under these mild cracking conditions, the catalyst-bearing oil sand produced extractable products of much lower viscosity. The products also contained considerably more gas oil and middle distillates than raw oil sand processed under the same conditions as thermal cracking alone. According to model cracking studies using hexadecane, these modified mineral zeolites may be more active cracking agents than undiluted premium commercial FCC catalyst. These materials hold promise for partial upgrading schemes to reduce solvent requirements in the field. tabs., figs.

  5. Ultrasonic sizing of fatigue cracks

    International Nuclear Information System (INIS)

    Burns, D.J.

    1983-12-01

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

  6. 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...

  7. 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)

  8. The real performance of radioactive lightning arrester

    International Nuclear Information System (INIS)

    Leite, D.M.

    1985-01-01

    The study of the performance of radioactive lightning arrester comparing to the performance of conventional one are presented. Measurements of currents between lightning arrester and an energyzed plate with wind simulation were done for radioactive and conventional lightning arresters, separately. The attraction range of radioactive and conventional lightning arresters using atmospheric pulses produced by a generator of 3MV were verified, separately and simultaneously. The influence of ionization produced by radioactive lightning arrester on critical disruptive tension of a spark plate, testing two lightning arresters for differents nominal attraction distances with applications of atmospheric pulses (positive and negative polarity) and tensions of 60 Hz was verified. The radiation emitted by a radioactive lightning had used in a building was retired and handled without special carefullness by a personnel without worthy of credence to evaluate the hazard in handling radioactive lightning arrester was measured. Critical disruptive tensions of radioactive and conventional lightning arrester using a suspensed electrode and external pulse generator of 6MV was measured. The effect of attraction of a radioactive and conventional lightning arresters disposed symmetrically regarding the same suspensed electrode was verified simultaneously. Seven cases on faults of radioactive lightning arrester in external areas are present. (M.C.K.) [pt

  9. Floating Node Method and Virtual Crack Closure Technique for Modeling Matrix Cracking-Delamination Migration

    Science.gov (United States)

    DeCarvalho, Nelson V.; Chen, B. Y.; Pinho, Silvestre T.; Baiz, P. M.; Ratcliffe, James G.; Tay, T. E.

    2013-01-01

    A novel approach is proposed for high-fidelity modeling of progressive damage and failure in composite materials that combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. In this study, the approach is applied to the modeling of delamination migration in cross-ply tape laminates. Delamination, matrix cracking, and migration are all modeled using fracture mechanics based failure and migration criteria. The methodology proposed shows very good qualitative and quantitative agreement with experiments.

  10. Comparative study of direct and inverse problems of cracked beams

    Directory of Open Access Journals (Sweden)

    Mahieddine Chettah

    2018-01-01

    Full Text Available In recent decades, the analysis and evaluation of the cracked structures were hot spots in several engineering fields and has been the subject of great interest with important and comprehensive surveys covering various methodologies and applications, in order to obtain reliable and effective methods to maintain the safety and performance of structures on a proactive basis. The presence of a crack, not only causes a local variation in the structural parameters (e.g., the stiffness of a beam at its location, but it also has a global effect which affects the overall dynamic behavior of the structure (such as the natural frequencies. For this reason, the dynamic characterization of the cracked structures can be used to detect damage from non-destructive testing. The objective of this paper is to compare the accuracy and ability of two methods to correctly predict the results for both direct problem to find natural frequencies and inverse problem to find crack’s locations and depths of a cracked simply supported beam. Several cases of crack depths and crack locations are investigated. The crack is supposed to remain open. The Euler–Bernoulli beam theory is employed to model the cracked beam and the crack is represented as a rotational spring with a sectional flexibility. In the first method, the transfer matrix method is used; the cracked beam is modeled as two uniform sub-segments connected by a rotational spring located at the cracked section. In the second method which is based on the Rayleigh’s method, the mode shape of the cracked beam is constructed by adding a cubic polynomial function to that of the undamaged beam. By applying the compatibility conditions at crack’s location and the corresponding boundary conditions, the general forms of characteristic equations for this cracked system are obtained. The two methods are then utilized to determine the locations and depths by using any two natural frequencies of a cracked simply

  11. 3D ductile crack propagation within a polycrystalline microstructure using XFEM

    Science.gov (United States)

    Beese, Steffen; Loehnert, Stefan; Wriggers, Peter

    2018-02-01

    In this contribution we present a gradient enhanced damage based method to simulate discrete crack propagation in 3D polycrystalline microstructures. Discrete cracks are represented using the eXtended finite element method. The crack propagation criterion and the crack propagation direction for each point along the crack front line is based on the gradient enhanced damage variable. This approach requires the solution of a coupled problem for the balance of momentum and the additional global equation for the gradient enhanced damage field. To capture the discontinuity of the displacements as well as the gradient enhanced damage along the discrete crack, both fields are enriched using the XFEM in combination with level sets. Knowing the crack front velocity, level set methods are used to compute the updated crack geometry after each crack propagation step. The applied material model is a crystal plasticity model often used for polycrystalline microstructures of metals in combination with the gradient enhanced damage model. Due to the inelastic material behaviour after each discrete crack propagation step a projection of the internal variables from the old to the new crack configuration is required. Since for arbitrary crack geometries ill-conditioning of the equation system may occur due to (near) linear dependencies between standard and enriched degrees of freedom, an XFEM stabilisation technique based on a singular value decomposition of the element stiffness matrix is proposed. The performance of the presented methodology to capture crack propagation in polycrystalline microstructures is demonstrated with a number of numerical examples.

  12. Nonlinear crack mechanics

    International Nuclear Information System (INIS)

    Khoroshun, L.P.

    1995-01-01

    The characteristic features of the deformation and failure of actual materials in the vicinity of a crack tip are due to their physical nonlinearity in the stress-concentration zone, which is a result of plasticity, microfailure, or a nonlinear dependence of the interatomic forces on the distance. Therefore, adequate models of the failure mechanics must be nonlinear, in principle, although linear failure mechanics is applicable if the zone of nonlinear deformation is small in comparison with the crack length. Models of crack mechanics are based on analytical solutions of the problem of the stress-strain state in the vicinity of the crack. On account of the complexity of the problem, nonlinear models are bason on approximate schematic solutions. In the Leonov-Panasyuk-Dugdale nonlinear model, one of the best known, the actual two-dimensional plastic zone (the nonlinearity zone) is replaced by a narrow one-dimensional zone, which is then modeled by extending the crack with a specified normal load equal to the yield point. The condition of finite stress is applied here, and hence the length of the plastic zone is determined. As a result of this approximation, the displacement in the plastic zone at the abscissa is nonzero

  13. Statistical crack mechanics

    International Nuclear Information System (INIS)

    Dienes, J.K.

    1993-01-01

    Although it is possible to simulate the ground blast from a single explosive shot with a simple computer algorithm and appropriate constants, the most commonly used modelling methods do not account for major changes in geology or shot energy because mechanical features such as tectonic stresses, fault structure, microcracking, brittle-ductile transition, and water content are not represented in significant detail. An alternative approach for modelling called Statistical Crack Mechanics is presented in this paper. This method, developed in the seventies as a part of the oil shale program, accounts for crack opening, shear, growth, and coalescence. Numerous photographs and micrographs show that shocked materials tend to involve arrays of planar cracks. The approach described here provides a way to account for microstructure and give a representation of the physical behavior of a material at the microscopic level that can account for phenomena such as permeability, fragmentation, shear banding, and hot-spot formation in explosives

  14. A METHOD OF DETERMINING THE ABILITY OF THE ARRESTER TO ABSORB ENERGY WITHOUT BREAKING THE HEAT BALANCE

    Directory of Open Access Journals (Sweden)

    S.Yu. Shevchenko

    2015-08-01

    Full Text Available Purpose.The aim of this study is to obtain a method for determining the capacity surge arrester nonlinear absorb energy without breaking the heat balance in modes of long-term application of operating voltage, which allows for analysis of their work in terms of violations as electricity. Methodology. For values of the energy passing through the arrester must be able to determine the current value for the voltage value in the area of leakage current-voltage characteristics. We have carried out calculations of the energy passing everywhere arrester for certain periods of time based on the current-voltage characteristics obtained experimentally. Analysis of the experimental current-voltage characteristics of resistors and literature led to the important conclusion that the dielectric properties of the ceramic varistor affect the value of active power losses in the arrester only when the active component of the leakage current is very small. This is confirmed by the characteristics of different classes of varistor voltage. This property of varistors and surge arresters shows the need to consider how the dielectric and conductive properties of the varistor ceramics in the analysis of work in the area of the arrester leakage current-voltage characteristic. These results demonstrate the need to clarify the mathematical model and the method for determining the energy dissipates in the area of the arrester leakage current CVC with their account. Results. The study, an improved mathematical model for calculating energy affects surge arrester during its working life. The study obtained the method, of evaluation capacity surge arrester, maintains heat balance throughout working life. Based on experimentally obtained current-voltage characteristic of the varistors is defined voltage at which surge arrester starts conducting active current. This allowed to receive specified mathematical model for calculating energy affects surge arrester and develop a method

  15. Evaluation Model for Restraint Effect of Pressure Induced Bending on the Plastic Crack Opening of Circumferential Through-Wall-Crack

    International Nuclear Information System (INIS)

    Kim, Jin-Weon

    2006-01-01

    Most of the pipe crack evaluation procedures, including leak-before-break (LBB) analysis, assume that the cracked pipe subjected to remote bending or internal pressure is free to rotate. In this case, the pressure induced bending (PIB) enhances crack opening of a through-wall-crack (TWC) in a pipe. In a real piping system, however, the PIB will be restrained because the ends of the pipe are constrained by the rest of the piping system. Hence, the amount of restraint affects the crack opening of a TWC in a pipe, and the restraint effect on crack opening directly affects the results of LBB evaluation. Therefore, it is necessary to investigate the restraint effect of PIB on crack opening displacement (COD) to quantify the uncertainties in current analysis procedures and to ensure the application of LBB concepts to nuclear piping systems. Recently, several researches were conducted to investigate the restraint effect of PIB on COD, and they proposed a simplified model to evaluate COD under restrained conditions. However, these results are quite limited because the restraint effect was evaluated only in terms of linear-elastic crack opening. In practice, the TWC in a pipe behaves plastically under normal operating loads, and the current LBB analysis methodologies require elastic-plastic crack opening evaluation. Therefore, this study evaluates the restraint effect of PIB on the plastic crack opening of a TWC in a pipe using finite element analysis under various influencing parameters. Based on these results, a closed-from model to be able to estimate the restraint effect of PIB on plastic crack opening is proposed

  16. Simulated Cardiopulmonary Arrests in a Hospital Setting.

    Science.gov (United States)

    Mishkin, Barbara H.; And Others

    1982-01-01

    Describes a simulated interdisciplinary role rehearsal for cardiopulmonary arrest to prepare nurses to function effectively. Includes needs analysis, program components, and responses of program participants. (Author)

  17. Cracking the Cipher Challenge

    CERN Document Server

    CERN. Geneva. Audiovisual Unit; Singh, Simon

    2002-01-01

    In the back of 'The Code Book', a history of cryptography, Simon Singh included a series of 10 encoded messages, each from a different period of history. The first person to crack all 10 messages would win a prize of £10,000. Now that the prize has been won, Simon can reveal the story behind the Cipher Challenge. Along the way he will show how mathematics can be used to crack codes, the role it played in World War Two and how it helps to guarantee security in the Information Age.

  18. Arresting relaxation in Pickering Emulsions

    Science.gov (United States)

    Atherton, Tim; Burke, Chris

    2015-03-01

    Pickering emulsions consist of droplets of one fluid dispersed in a host fluid and stabilized by colloidal particles absorbed at the fluid-fluid interface. Everyday materials such as crude oil and food products like salad dressing are examples of these materials. Particles can stabilize non spherical droplet shapes in these emulsions through the following sequence: first, an isolated droplet is deformed, e.g. by an electric field, increasing the surface area above the equilibrium value; additional particles are then adsorbed to the interface reducing the surface tension. The droplet is then allowed to relax toward a sphere. If more particles were adsorbed than can be accommodated by the surface area of the spherical ground state, relaxation of the droplet is arrested at some non-spherical shape. Because the energetic cost of removing adsorbed colloids exceeds the interfacial driving force, these configurations can remain stable over long timescales. In this presentation, we present a computational study of the ordering present in anisotropic droplets produced through the mechanism of arrested relaxation and discuss the interplay between the geometry of the droplet, the dynamical process that produced it, and the structure of the defects observed.

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

    NARCIS (Netherlands)

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

    1998-01-01

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

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  1. Linear Cracking in Bridge Decks

    Science.gov (United States)

    2018-03-01

    Concrete cracking in bridge decks remains an important issue relative to deck durability. Cracks can allow increased penetration of chlorides, which can result in premature corrosion of the reinforcing steel and subsequent spalling of the concrete de...

  2. Evaluation of methodologies for the calculation of leak rates for pressure retaining components with crack-like leaks; Bewertung von Methoden zur Berechnung von Leckraten fuer druckfuehrende Komponenten mit rissartigen Lecks

    Energy Technology Data Exchange (ETDEWEB)

    Sievers, Juergen; Heckmann, Klaus; Blaesius, Christoph

    2015-06-15

    For the demonstration of break preclusion for pressure retaining components in nuclear power plants, the nuclear safety standard KTA 3206 determines also the requirements for the leak-before-break verification. For this procedure, it has to be ensured that a wall-penetrating crack is subcritical with respect to instable growth, and that the resulting leakage under stationary operation conditions can be detected by a leak detection system. Within the scope of the project 3613R01332 analyses with respect to conservative estimates of the leak rates in case of detections regarding break preclusion were performed by means of leak rate models being available at GRS. For this purpose, conservative assumptions in the procedure were quantified by comparative calculations concerning selected leak rate experiments and the requirements regarding the determination of leak rates indicated in the KTA 3206 were verified and specified. Moreover, the models were extended and relevant recommendations for the calculation procedure were developed. During the investigations of leak rate tests the calculation methods were validated, qualified by means of both examples indicated in KTA 3206 and applied to a postulated leak accident in the cooling circuit of a PWR. For the calculation of leak rates several simplified solution methods which are included in the GRS program WinLeck were applied, and for the simulation of a leak accident the large-scale programs ANSYS Mechanical and ATHLET (thermohydraulics program developed by GRS) were used. When applying simplified methods for the calculation of leak rates using the limiting curve for the friction factor which has been derived during the project and which is included in the KTA 3206 attention has to be paid to the fact that in case of small flow lengths the entrance loss can dominate compared to the friction loss. However, the available data do not suffice in order to make a quantitative statement with respect to limits of applicability

  3. Crack detection '86

    International Nuclear Information System (INIS)

    1986-01-01

    The participants of the conference heard 36 papers of which 13 were incorporated in INIS. The incorporated papers deal with the quality control of the equipment of nuclear power plants, with technical specifications and possibilities of diverse crack detection devices, as well as with personnel training for nondestructive materials testing. (E.S.)

  4. Crack closure, a literature study

    Science.gov (United States)

    Holmgren, M.

    1993-08-01

    In this report crack closure is treated. The state of the art is reviewed. Different empirical formulas for determining the crack closure are compared with each other, and their benefits are discussed. Experimental techniques for determining the crack closure stress are discussed, and some results from fatigue tests are also reported. Experimental data from the literature are reported.

  5. The epidemiology of physical attack and rape among crack-using women.

    Science.gov (United States)

    Falck, R S; Wang, J; Carlson, R G; Siegal, H A

    2001-02-01

    This prospective study examines the epidemiology of physical attack and rape among a sample of 171 not-in-treatment, crack-cocaine using women. Since initiating crack use, 62% of the women reported suffering a physical attack. The annual rate of victimization by physical attack was 45%. Overall, more than half of the victims sought medical care subsequent to an attack. The prevalence of rape since crack use was initiated was 32%, and the annual rate was 11%. Among those women having been raped since they initiated crack use, 83% reported they were high on crack when the crime occurred as were an estimated 57% of the perpetrators. Logistic regression analyses showed that duration of crack use, arrest for prostitution, and some college education were predictors of having experienced a physical attack. Duration of crack use and a history of prostitution were predictors of suffering a rape. Drug abuse treatment programs must be sensitive to high levels of violence victimization experienced by crack-cocaine using women. Screening women for victimization, and treating the problems that emanate from it, may help make drug abuse treatment more effective.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-12-01

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

  7. Optimization of ultrasonic array inspections using an efficient hybrid model and real crack shapes

    Energy Technology Data Exchange (ETDEWEB)

    Felice, Maria V., E-mail: maria.felice@bristol.ac.uk [Department of Mechanical Engineering, University of Bristol, Bristol, U.K. and NDE Laboratory, Rolls-Royce plc., Bristol (United Kingdom); Velichko, Alexander, E-mail: p.wilcox@bristol.ac.uk; Wilcox, Paul D., E-mail: p.wilcox@bristol.ac.uk [Department of Mechanical Engineering, University of Bristol, Bristol (United Kingdom); Barden, Tim; Dunhill, Tony [NDE Laboratory, Rolls-Royce plc., Bristol (United Kingdom)

    2015-03-31

    Models which simulate the interaction of ultrasound with cracks can be used to optimize ultrasonic array inspections, but this approach can be time-consuming. To overcome this issue an efficient hybrid model is implemented which includes a finite element method that requires only a single layer of elements around the crack shape. Scattering Matrices are used to capture the scattering behavior of the individual cracks and a discussion on the angular degrees of freedom of elastodynamic scatterers is included. Real crack shapes are obtained from X-ray Computed Tomography images of cracked parts and these shapes are inputted into the hybrid model. The effect of using real crack shapes instead of straight notch shapes is demonstrated. An array optimization methodology which incorporates the hybrid model, an approximate single-scattering relative noise model and the real crack shapes is then described.

  8. Statistical analysis of process parameters to eliminate hot cracking of fiber laser welded aluminum alloy

    Science.gov (United States)

    Wang, Jin; Wang, Hui-Ping; Wang, Xiaojie; Cui, Haichao; Lu, Fenggui

    2015-03-01

    This paper investigates hot cracking rate in Al fiber laser welding under various process conditions and performs corresponding process optimization. First, effects of welding process parameters such as distance between welding center line and its closest trim edge, laser power and welding speed on hot cracking rate were investigated experimentally with response surface methodology (RSM). The hot cracking rate in the paper is defined as ratio of hot cracking length over the total weld seam length. Based on the experimental results following Box-Behnken design, a prediction model for the hot cracking rate was developed using a second order polynomial function considering only two factor interaction. The initial prediction result indicated that the established model could predict the hot cracking rate adequately within the range of welding parameters being used. The model was then used to optimize welding parameters to achieve cracking-free welds.

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

    Directory of Open Access Journals (Sweden)

    Suvi Papula

    2017-06-01

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

  10. Assessment of environmentally assisted cracking in PWR pressure vessel steels

    International Nuclear Information System (INIS)

    Tice, D.R.

    1991-01-01

    There is a possibility that extension of pre-existing flaws in the reactor pressure vessel of a pressurised water reactor (PWR) may occur by environmentally assisted cracking, in particular by corrosion fatigue under cyclic transient loading. Crack growth predictions have usually been carried out using cyclic crack growth rate (da/dN) versus stress intensity range (δK) curves, such as those given in Section XI, Appendix A of the ASME Boiler and Pressure Vessel Code. However, the inherent time dependent nature of environmental cracking processes renders such an approach unrealistic. The present paper describes the development of an alternative time based assessment methodology. Illustrative calculations of expected crack growth of assumed defects made using the cyclic (ASME XIA) and time-based approaches are compared. The results illustrate that crack growth predicted by the time-based approach can be greater or less than that calculated by the traditional method. For a PWR operated with good control of water chemistry, actual crack growth rates are expected to be well below those predicted by the ASME code. (Author)

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

    International Nuclear Information System (INIS)

    Miller, A.K.; Tasooji, A.

    1981-01-01

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

  12. Capillary-induced crack healing between surfaces of nanoscale roughness.

    Science.gov (United States)

    Soylemez, Emrecan; de Boer, Maarten P

    2014-10-07

    Capillary forces are important in nature (granular materials, insect locomotion) and in technology (disk drives, adhesion). Although well studied in equilibrium state, the dynamics of capillary formation merit further investigation. Here, we show that microcantilever crack healing experiments are a viable experimental technique for investigating the influence of capillary nucleation on crack healing between rough surfaces. The average crack healing velocity, v̅, between clean hydrophilic polycrystalline silicon surfaces of nanoscale roughness is measured. A plot of v̅ versus energy release rate, G, reveals log-linear behavior, while the slope |d[log(v̅)]/dG| decreases with increasing relative humidity. A simplified interface model that accounts for the nucleation time of water bridges by an activated process is developed to gain insight into the crack healing trends. This methodology enables us to gain insight into capillary bridge dynamics, with a goal of attaining a predictive capability for this important microelectromechanical systems (MEMS) reliability failure mechanism.

  13. The stability of growth of a through-wall circumferential crack in a cylindrical pipe subjected to bending deformation

    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)

  14. Structural health monitoring in end-of-life prediction for steel bridges subjected to fatigue cracking

    NARCIS (Netherlands)

    Attema, T.; Courage, W.M.G.; Maljaars, J.; Meerveld, H. van; Paulissen, J.H.; Pijpers, R.J.M.; Slobbe, A.T.

    2015-01-01

    This paper presents a monitoring and modelling methodology to assess the current and future conditions of steel bridges subjected to fatigue cracking. Steel bridges are subjected to fatigue cracking as a result of fluctuating stresses caused by the crossing of heavy vehicles. Specifically for

  15. Choked flow through cracks

    International Nuclear Information System (INIS)

    Feburie, V.; Giot, M.; Granger, S.; Seynhaeve, J.M.

    1992-06-01

    The leaks through steam-generator cracks are the subject of a research carried out in cooperation between EDF and UCL. A software called ECREVISSE to predict the mass flow rate has been developed and has been successfully validated. The purpose of the paper is to present the mathematical model used in ECREVISSE as well as some comparison between the results and the presently available data. The model takes into account the persistence of some metastable liquid in the crack and the special flow pattern which appears in such particular geometry. Although the model involves the use of several correlations (friction, heat transfer), no adjustment of parameters against the data has been needed, neither in the single-phase part of the flow, or in the two-phase part. (authors). 8 figs., 1 tab., 20 refs

  16. Delayed hydride cracking: alternative pre-cracking method

    International Nuclear Information System (INIS)

    Mieza, Juan I.; Ponzoni, Lucio M.E.; Vigna, Gustavo L.; Domizzi, Gladys

    2009-01-01

    The internal components of nuclear reactors built-in Zr alloys are prone to a failure mechanism known as Delayed Hydride Cracking (DHC). This situation has triggered numerous scientific studies in order to measure the crack propagation velocity and the threshold stress intensity factor associated to DHC. Tests are carried out on fatigued pre-crack samples to ensure similar test conditions and comparable results. Due to difficulties in implementing the fatigue pre-crack method it would be desirable to replace it with a pre-crack produced by the same process of DHC, for which is necessary to demonstrate equivalence of this two methods. In this work tests on samples extracted from two Zr-2.5 Nb tubes were conducted. Some of the samples were heat treated to obtain a range in their metallurgical properties as well as different DHC velocities. A comparison between velocities measured in test samples pre-cracked by fatigue and RDIH is done, demonstrating that the pre-cracking method does not affect the measured velocity value. In addition, the incubation (t inc ), which is the time between the application of the load and the first signal of crack propagation, in samples pre-cracked by RDIH, was measured. It was found that these times are sufficiently short, even in the worst cases (lower speed) and similar to the ones of fatigued pre-cracked samples. (author)

  17. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    alloys (2). [--I Fig. 6. Fatigue fracture in Nitrile- butadien rubber ( NBR ). Fig. 7. The characteristic features of fatigue fracture in press moulded...in plastics and even in rubber . It follows therefore, that fatigue fractures must also occur in the mineral layers of our earth or in the rock on...effective until the weakest point yields and forms a crack. To get a feeling for this process, you can imagine that the stressed article is made of rubber

  18. Distributed password cracking

    OpenAIRE

    Crumpacker, John R.

    2009-01-01

    Approved for public release, distribution unlimited Password cracking requires significant processing power, which in today's world is located at a workstation or home in the form of a desktop computer. Berkeley Open Infrastructure for Network Computing (BOINC) is the conduit to this significant source of processing power and John the Ripper is the key. BOINC is a distributed data processing system that incorporates client-server relationships to generically process data. The BOINC structu...

  19. Utopia Cracks and Polygons

    Science.gov (United States)

    2003-01-01

    MGS MOC Release No. MOC2-339, 23 April 2003This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a pattern of polygonal cracks and aligned, elliptical pits in western Utopia Planitia. The picture covers an area about 3 km (about 1.9 mi) wide near 44.9oN, 274.7oW. Sunlight illuminates the scene from the left.

  20. Cracking hydrocarbons. [British patent

    Energy Technology Data Exchange (ETDEWEB)

    Heyl, G E

    1926-05-06

    The vapors from a still in which oils, coal tar, pitch, creosote, and c. or solid carbonaccous material such as coal or shale are cracked by being heated to 600/sup 0/ to 1000/sup 0/C. are passed through a fractionating column to remove high-boiling constituents which are passed into a second cracking still. The vapors from this still are treated to separate high-boiling fractions which are passed into a third still. The sills preferably contain removable troughs or liners, which are freed from carbon deposits either after removal from the still or by a scraping disc which is rotated in and moved along the trough. Oil to be cracked is forced by a pump through a preheater to a still. Vapours pass through a carbon separator and dephlegmator to a condenser. The reflux from the dephlegmator is forced by a pump to a still, the vapors from which pass through a carbon separator and a dephlegmator, the reflux from which is passed into a third still fitted with a separate carbon separator, dephlegmator and final condenser.

  1. Extracorporeal membrane oxygenation for refractory cardiac arrest

    Directory of Open Access Journals (Sweden)

    Steven A Conrad

    2017-01-01

    Full Text Available Extracorporeal cardiopulmonary resuscitation (ECPR is the use of rapid deployment venoarterial (VA extracorporeal membrane oxygenation to support systemic circulation and vital organ perfusion in patients in refractory cardiac arrest not responding to conventional cardiopulmonary resuscitation (CPR. Although prospective controlled studies are lacking, observational studies suggest improved outcomes compared with conventional CPR when ECPR is instituted within 30-60 min following cardiac arrest. Adult and pediatric patients with witnessed in-hospital and out-of-hospital cardiac arrest and good quality CPR, failure of at least 15 min of conventional resuscitation, and a potentially reversible cause for arrest are candidates. Percutaneous cannulation where feasible is rapid and can be performed by nonsurgeons (emergency physicians, intensivists, cardiologists, and interventional radiologists. Modern extracorporeal systems are easy to prime and manage and are technically easy to manage with proper training and experience. ECPR can be deployed in the emergency department for out-of-hospital arrest or in various inpatient units for in-hospital arrest. ECPR should be considered for patients with refractory cardiac arrest in hospitals with an existing extracorporeal life support program, able to provide rapid deployment of support, and with resources to provide postresuscitation evaluation and management.

  2. 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

  3. 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)

  4. Investigation of Cracks Found in Helicopter Longerons

    Science.gov (United States)

    Newman, John A.; Baughman, James M.; Wallace, Terryl A.

    2009-01-01

    Four cracked longerons, containing a total of eight cracks, were provided for study. Cracked regions were cut from the longerons. Load was applied to open the cracks, enabling crack surface examination. Examination revealed that crack propagation was driven by fatigue loading in all eight cases. Fatigue crack initiation appears to have occurred on the top edge of the longerons near geometric changes that affect component bending stiffness. Additionally, metallurigical analysis has revealed a local depletion in alloying elements in the crack initiation regions that may be a contributing factor. Fatigue crack propagation appeared to be initially driven by opening-mode loading, but at a crack length of approximately 0.5 inches (12.7 mm), there is evidence of mixed-mode crack loading. For the longest cracks studied, shear-mode displacements destroyed crack-surface features of interest over significant portions of the crack surfaces.

  5. Modified Dugdale crack models - some easy crack relations

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1997-01-01

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

  6. Crack retardation by load reduction during fatigue crack propagation

    International Nuclear Information System (INIS)

    Kim, Hyun Soo; Nam, Ki Woo; Ahn, Seok Hwan; Do, Jae Yoon

    2003-01-01

    Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction

  7. 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.)

  8. 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)

  9. Crisis management during anaesthesia: cardiac arrest.

    Science.gov (United States)

    Runciman, W B; Morris, R W; Watterson, L M; Williamson, J A; Paix, A D

    2005-06-01

    Cardiac arrest attributable to anaesthesia occurs at the rate of between 0.5 and 1 case per 10 000 cases, tends to have a different profile to that of cardiac arrest occurring elsewhere, and has an in-hospital mortality of 20%. However, as individual practitioners encounter cardiac arrest rarely, the rapidity with which the diagnosis is made and the consistency of appropriate management varies considerably. To examine the role of a previously described core algorithm "COVER ABCD-A SWIFT CHECK", supplemented by a sub-algorithm for cardiac arrest, in the management of cardiac arrest occurring in association with anaesthesia. The potential performance of this structured approach for each the relevant incidents among the first 4000 reported to the Australian Incident Monitoring Study (AIMS) was compared with the actual management as reported by the anaesthetists involved. There were 129 reports of cardiac arrest associated with anaesthesia among the first 4000 AIMS incident reports. Identified aetiological factors were grouped into five categories: (1) anaesthetic technique (11 cases with this category alone; 32 with this and one or more of the other categories, representing 25% of all 129 cardiac arrests); (2) drug related (16; 32, 25%); (3) associated with surgical procedure (9; 29, 22%); (4) associated with pre-existing medical or surgical disease (30; 82, 64%); (5) unknown (8; 14, 11%). The "real life" presentation and management of cardiac arrest in association with anaesthesia differs substantially from that detailed in general published guidelines. Cardiac rhythms at the time were sinus bradycardia (23%); asystole (22%); tachycardia/ventricular tachycardia/ventricular fibrillation (14%); and normal (7%), with a further third unknown. Details of treatment were recorded in 110 reports; modalities employed included cardiac compression (72%); adrenaline (61%); 100% oxygen (58%); atropine (38%); intravenous fluids (25%), and electrical defibrillation (17%). There

  10. Dental Calculus Arrest of Dental Caries

    OpenAIRE

    Keyes, Paul H.; Rams, Thomas E.

    2016-01-01

    Background An inverse relationship between dental calculus mineralization and dental caries demineralization on teeth has been noted in some studies. Dental calculus may even form superficial layers over existing dental caries and arrest their progression, but this phenomenon has been only rarely documented and infrequently considered in the field of Cariology. To further assess the occurrence of dental calculus arrest of dental caries, this study evaluated a large number of extracted human t...

  11. Cracking of anisotropic cylindrical polytropes

    Energy Technology Data Exchange (ETDEWEB)

    Mardan, S.A. [University of the Management and Technology, Department of Mathematics, Lahore (Pakistan); Azam, M. [University of Education, Division of Science and Technology, Lahore (Pakistan)

    2017-06-15

    We study the appearance of cracking in charged anisotropic cylindrical polytropes with generalized polytropic equation. We investigate the existence of cracking in two different kinds of polytropes existing in the literature through two different assumptions: (a) local density perturbation with conformally flat condition, and (b) perturbing polytropic index, charge and anisotropy parameters. We conclude that cracking appears in both kinds of polytropes for a specific range of density and model parameters. (orig.)

  12. Sex Disparities in Arrest Outcomes for Domestic Violence

    Science.gov (United States)

    Hamilton, Melissa; Worthen, Meredith G. F.

    2011-01-01

    Domestic violence arrests have been historically focused on protecting women and children from abusive men. Arrest patterns continue to reflect this bias with more men arrested for domestic violence compared to women. Such potential gender variations in arrest patterns pave the way to the investigation of disparities by sex of the offender in…

  13. Cryptography cracking codes

    CERN Document Server

    2014-01-01

    While cracking a code might seem like something few of us would encounter in our daily lives, it is actually far more prevalent than we may realize. Anyone who has had personal information taken because of a hacked email account can understand the need for cryptography and the importance of encryption-essentially the need to code information to keep it safe. This detailed volume examines the logic and science behind various ciphers, their real world uses, how codes can be broken, and the use of technology in this oft-overlooked field.

  14. Stress corrosion cracking

    International Nuclear Information System (INIS)

    Dietzel, W.; Turnbull, A.

    2007-01-01

    Comprehensive Structural Integrity is a reference work which covers all activities involved in the assurance of structural integrity. It provides engineers and scientists with an unparalleled depth of knowledge in the disciplines involved. The new online Volume 11 is dedicated to the mechanical characteristics of materials. This paper contains the chapter 11.03 and is structured as follows: General aspects of SCC testing; Non-precracked specimens; Precracked specimens - the fracture mechanics approach to SCC; Crack growth measurement; Limitations of the LEFM approach to SCC; The use of SCC data; Guide to selection of mechanical scc test method

  15. A new modeling method for natural PWSCC cracking simulation in a dissimilar metal weld

    International Nuclear Information System (INIS)

    Xu, Heqin; Mahmoud, Samer; Nana, Ashok; Killian, Doug

    2014-01-01

    Cracks found in a nuclear power plant reactor coolant system (RCS), such as primary water stress corrosion cracking (PWSCC) and intergranular stress corrosion cracking (IGSCC), usually have natural crack front shapes that can be very different from the idealized semi-elliptical or rectangular shapes considered in engineering handbooks and other analytical solutions based on limited shapes. Simplifications towards semi-elliptical shape or rectangular shape may potentially introduce unnecessary conservatism when the simplified shape has to contain the actual crack shape. On the other hand, it is very time-consuming to create a three-dimensional (3D) finite element (FE) model to simulate crack propagation in a natural shape using existing public-domain software like ABAQUS or ANSYS. In this study, a local deformation-based mesh-mapping (LDMM) method is proposed to model cracks with a natural front shape in any 3D structures. This methodology is first applied to model circumferential surface cracks with a natural crack front shape in the cross-sectional plane of a cylinder. The proposed new method can be applied to simulate both shallow and deep cracks. Also discussed in this paper is a direct method to reproduce welding residual stresses in the crack model using temperature fields combined with other sustained loads to predict crack propagations. With this novel LDMM method, natural crack fronts and non-planar crack faces can be easily modeled. The proposed new method can be used to generate a high-quality finite element model that can be used for both linear-elastic fracture mechanics (LEFM) and elastic–plastic fracture mechanics (EPFM) analyses. The study case illustrates that the proposed LDMM method is easy to implement and more efficient than the existing commercial software

  16. Automated numerical simulation of cracked plates, pipes and elbows

    International Nuclear Information System (INIS)

    Reddy, Babu; Sreehari Kumar, B.; Bhate, S.R.; Kushwaha, H.S.

    2008-01-01

    In the nuclear industry, piping components are one of the key elements participating in its operation. Integrity of structural tubes and pipes plays a major role in nuclear power plants. The ideal procedure to ensure this aspect would be to conduct experimental studies on pilot/test specimens. However, it may not always be feasible to carry out the experimental investigation, as it requires pre-requisite infrastructure which may not be economically viable. This makes it imperative to conduct numerical simulations of the same particularly in the study of presence of cracks in the critical components. While performing the effect of cracks, the quality of the finite element mesh nearer to the crack tip plays a critical role while estimating J-integral value. The designer is often familiar with design methodology only and he obviously requires a convenient and reliable numerical tool to model and perform the analysis. In this context, an effort has been made in NISA, the general purpose finite element software, to automate the generation of FE meshes for a set of pre-defined components with different crack configurations. To simplify the procedure of FE mesh generation, analysis, and post processing, a graphical user interface (GUI) has been developed accordingly. This paper discusses the automated numerical simulation of plates and pipes with different crack configurations. This simulation software is also designed to help parametric study of cracked pipes. (author)

  17. Ductile fracture of circumferentially cracked pipes subjected to bending loads

    International Nuclear Information System (INIS)

    Zahoor, A.; Kanninen, M.F.

    1981-01-01

    A plastic fracture mechanics methodology is presented for part-through cracks in pipes under bending. A previous analysis result on the behavior of part-through cracks in pipes is reviewed. Example quantitative results for the initiation and instability of radial growth of part-through cracks are presented and compared with the experimental data to demonstrate the applicability of the method. The analyses in our previous work are further developed to include the instability of circumferential growth of part-through cracks. Numerical results are then presented for a compliant piping system, under displacement controlled bending, which focus on (1) instability of radial growth (unstable wall breakthrough) and (2) instability of circumferential growth of the resulting throughthe-thickness crack. The combined results of the above two types of analyses are presented on a safety assessment diagram. This diagram defines a curve of critical combination of length and depth of part-through cracks which delineates leak from fracture. The effect of piping compliance on the leak-before-break assessment is discussed

  18. Ductile fracture of circumferentially cracked pipes subjected to bending loads

    Energy Technology Data Exchange (ETDEWEB)

    Zahoor, A.; Kanninen, M.F.

    1981-10-01

    A plastic fracture mechanics methodology is presented for part-through cracks in pipes under bending. A previous analysis result on the behavior of part-through cracks in pipes is reviewed. Example quantitative results for the initiation and instability of radial growth of part-through cracks are presented and compared with the experimental data to demonstrate the applicability of the method. The analyses in our previous work are further developed to include the instability of circumferential growth of part-through cracks. Numerical results are then presented for a compliant piping system, under displacement controlled bending, which focus on (1) instability of radial growth (unstable wall breakthrough) and (2) instability of circumferential growth of the resulting throughthe-thickness crack. The combined results of the above two types of analyses are presented on a safety assessment diagram. This diagram defines a curve of critical combination of length and depth of part-through cracks which delineates leak from fracture. The effect of piping compliance on the leak-before-break assessment is discussed.

  19. Catalytic cracking of lignites

    Energy Technology Data Exchange (ETDEWEB)

    Seitz, M.; Nowak, S.; Naegler, T.; Zimmermann, J. [Hochschule Merseburg (Germany); Welscher, J.; Schwieger, W. [Erlangen-Nuernberg Univ. (Germany); Hahn, T. [Halle-Wittenberg Univ., Halle (Germany)

    2013-11-01

    A most important factor for the chemical industry is the availability of cheap raw materials. As the oil price of crude oil is rising alternative feedstocks like coal are coming into focus. This work, the catalytic cracking of lignite is part of the alliance ibi (innovative Braunkohlenintegration) to use lignite as a raw material to produce chemicals. With this new one step process without an input of external hydrogen, mostly propylene, butenes and aromatics and char are formed. The product yield depends on manifold process parameters. The use of acid catalysts (zeolites like MFI) shows the highest amount of the desired products. Hydrogen rich lignites with a molar H/C ratio of > 1 are to be favoured. Due to primary cracking and secondary reactions the ratio between catalyst and lignite, temperature and residence time are the most important parameter to control the product distribution. Experiments at 500 C in a discontinuous rotary kiln reactor show yields up to 32 wt-% of hydrocarbons per lignite (maf - moisture and ash free) and 43 wt-% char, which can be gasified. Particularly, the yields of propylene and butenes as main products can be enhanced four times to about 8 wt-% by the use of catalysts while the tar yield decreases. In order to develop this innovative process catalyst systems fixed on beads were developed for an easy separation and regeneration of the used catalyst from the formed char. (orig.)

  20. Crack closure and growth behavior of short fatigue cracks under random loading (part I : details of crack closure behavior)

    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

  1. Crack initiation life analysis in notched pipe under cyclic bending loads

    International Nuclear Information System (INIS)

    Lee, Joon Seong; Kwak, Sang Log; Kim, Young Jin; Park, Youn Won

    2001-01-01

    In order to improve leak-before-break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but crack initiation cycle was higher than the experimental result

  2. Combined effect of electric field and residual stress on propagation of indentation cracks in a PZT-5H ferroelectric ceramic

    International Nuclear Information System (INIS)

    Huang, H.Y.; Chu, W.Y.; Su, Y.J.; Qiao, L.J.; Gao, K.W.

    2005-01-01

    The combined effect of electric field and residual stress on propagation of unloaded indentation cracks in a PZT-5 ceramic has been studied. The results show that residual stress itself is too small to induce delayed propagation of the indentation cracks in silicon oil. If applied constant electric field is larger than 0.2 kV/cm, the combined effect of electric field and residual stress can cause delayed propagation of the indentation crack after passing an incubation time in silicon oil, but the crack will arrest after propagating for 10-30 μm because of decrease of the resultant stress intensity factor induced by the field and residual stress with increasing the crack length. The threshold electric field for delayed propagation of the indentation crack in silicon oil is E DP = 0.2 kV/cm. If the applied electric field is larger than 5.25 kV/cm, combined effect of the electric field and residual stress can cause instant propagation of the indentation crack, and under sustained electric field, the crack which has propagated instantly can propagate continuously, until arrest at last. The critical electric field for instant propagation of the indentation crack is E P = 5.25 kV/cm. If the applied electric field is larger than 12.6 kV/cm, the microcracks induced by the electric field initiate everywhere, grow and connect in a smooth specimen, resulting in delayed failure, even without residual stress. The threshold electric field for delayed failure of a smooth specimen in silicon oil is E DF = 12.6 kV/cm and the critical electric field for instant failure is E F = 19.1 kV/cm

  3. Cracking in Drying Colloidal Films

    Science.gov (United States)

    Singh, Karnail B.; Tirumkudulu, Mahesh S.

    2007-05-01

    It has long been known that thick films of colloidal dispersions such as wet clays, paints, and coatings crack under drying. Although capillary stresses generated during drying have been recently identified as the cause for cracking, the existence of a maximum crack-free film thickness that depends on particle size, rigidity, and packing has not been understood. Here, we identify two distinct regimes for crack-free films based on the magnitude of compressive strain at the maximum attainable capillary pressure and show remarkable agreement of measurements with our theory. We anticipate our results to not only form the basis for design of coating formulations for the paints, coatings, and ceramics industry but also assist in the production of crack-free photonic band gap crystals.

  4. Crack tip stress and strain

    International Nuclear Information System (INIS)

    Francois, D.

    1975-01-01

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

  5. Prediction of Crack Growth Aqueous Environments.

    Science.gov (United States)

    1983-06-01

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

  6. Tensile cracks in creeping solids

    International Nuclear Information System (INIS)

    Riedel, H.; Rice, J.R.

    1979-02-01

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

  7. Arrested larval development in cattle nematodes.

    Science.gov (United States)

    Armour, J; Duncan, M

    1987-06-01

    Most economically important cattle nematodes are able to arrest their larval development within the host - entering a period of dormancy or hypobiosis. Arrested larvae have a low death rate, and large numbers can accumulate in infected cattle during the grazing season. Because of this, outbreaks of disease caused by such nematodes can occur at times when recent infection with the parasites could not have occurred, for example during winter in temperature northern climates when cattle are normally housed. The capacity to arrest is a heritable trait. It is seen as an adaptation by the parasite to avoid further development to its free-living stages during times when the climate is unsuitable for free-living survival. But levels of arrestment can vary markedly in different regions, in different cattle, and under different management regimes. Climatic factors, previous conditioning, host immune status, and farm management all seem to affect arrestment levels. In this article, James Armour and Mary Duncan review the biological basis of the phenomenon, and discuss the apparently conflicting views on how it is controlled.

  8. Buckling Analysis of Edge Cracked Sandwich Plate

    Directory of Open Access Journals (Sweden)

    Rasha Mohammed Hussein

    2016-07-01

    Full Text Available This work presents mainly the buckling load of sandwich plates with or without crack for different cases. The buckling loads are analyzed experimentally and numerically by using ANSYS 15. The experimental investigation was to fabricate the cracked sandwich plate from stainless steel and PVC to find mechanical properties of stainless steel and PVC such as young modulus. The buckling load for different aspect ratio, crack length, cracked location and plate without crack found. The experimental results were compared with that found from ANSYS program. Present of crack is decreased the buckling load and that depends on crack size, crack location and aspect ratio.

  9. Measurement and accompanying numerical simulation of fast crack propagation in modified DCB specimens made of Araldit B

    International Nuclear Information System (INIS)

    Stoeckl, H.

    1991-06-01

    Numerical simulations of fracture-mechanical experiments with the aim of determining the stress intensity factor and its relation to the fracture velocity from the measured data of the crack length are problematic with the conventional DCB specimen loaded through wedge and bolt namely because of the not clearly definable limiting conditions. Experiments were therefore carried out with modified DCB specimens made of ARALDIT B, with the loading wedge pressed directly into the crack mouth. In the case of suitable specimen dimensions, K I already in the initial phase of crack propagation before arrival of the first reflected waves covers a great part of the relevant range. Numerical simulations agree well with the shadow-optical measurements in this phase. A specimen variant with T-shaped extension at the counterbearing is suitable especially for crack arrest investigations, since high fracture velocities and brief crack jump lengths can be combined in tests with this specimen. The constant member in the series development of the stress distribution at the crack tip according to Williams determines the directional stability of the crack. The theories established by Cotterell, Schindler, Streit and Finnie are discussed by means of the kinking cracks observed during some experiments. (orig.) [de

  10. AN EFFECT OF SHOT PEENING ON GROWTH AND RETARDATION OF PHYSICALLY SHORT FATIGUE CRACKS IN AN AIRCRAFT Al-ALLOY

    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.

  11. Methodology for plastic fracture. A progress report

    International Nuclear Information System (INIS)

    Wilkinson, J.P.D.; Hahn, G.T.; Smith, R.E.E.

    1977-01-01

    The initiation and growth of flaws in pressure vessels under overload conditions is distinguished by a number of unique features, such as large scale yielding, three-dimensional structural and flaw configurations, and failure instabilities that may be controlled by either toughness or plastic flow. In order to develop a broadly applicable methodology of plastic fracture, these features require the following analytical and experimental studies: development of criteria for crack initiation and growth under large scale yielding; the use of the finite element method to describe elastic-plastic behavior of both the structure and the crack tip region; and extensive experimental studies on laboratory scale and large scale specimens, which attempt to reproduce the pertinent plastic flow and crack growth phenomena. A variety of candidate criteria for crack initiation and growth are examined. For the case of crack initiation, these criteria include the J-integral, crack opening displacement, and strain amplitude. In the case of crack growth, the criteria examined include in addition the strain amplitude at the crack tip, work done in a crack tip process zone, and a generalized energy release-rate approach. Each test specimen configuration is analyzed through the finite element method in order to predict its experimental behavior. Specimens include the compact tension specimen and center cracked panels. The basic materials used in the program are a single heat of reactor grade A533 Grade B Class 1 steel, purchased in the form of a plate of size 4.5 m (178 in.) square and 0.2 m (8 in.) thick, and two alloys with yield strength-to-roughness ratios about five times

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

    International Nuclear Information System (INIS)

    Song, Sam Hong; Lee, Kyeong Ro

    1999-01-01

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

  13. Acoustic emission methodology and application

    CERN Document Server

    Nazarchuk, Zinoviy; Serhiyenko, Oleh

    2017-01-01

    This monograph analyses in detail the physical aspects of the elastic waves radiation during deformation or fracture of materials. I presents the  methodological bases for the practical use of acoustic emission device, and describes the results of theoretical and experimental researches of evaluation of the crack growth resistance of materials, selection of the useful AE signals. The efficiency of this methodology is shown through the diagnostics of various-purpose industrial objects. The authors obtain results of experimental researches with the help of the new methods and facilities.

  14. Probabilistic Analysis of Crack Width

    Directory of Open Access Journals (Sweden)

    J. Marková

    2000-01-01

    Full Text Available Probabilistic analysis of crack width of a reinforced concrete element is based on the formulas accepted in Eurocode 2 and European Model Code 90. Obtained values of reliability index b seem to be satisfactory for the reinforced concrete slab that fulfils requirements for the crack width specified in Eurocode 2. However, the reliability of the slab seems to be insufficient when the European Model Code 90 is considered; reliability index is less than recommended value 1.5 for serviceability limit states indicated in Eurocode 1. Analysis of sensitivity factors of basic variables enables to find out variables significantly affecting the total crack width.

  15. Multispecimen fatigue crack propagation testing

    International Nuclear Information System (INIS)

    Ermi, A.M.; Bauer, R.E.; Chin, B.A.; Straalsund, J.L.

    1981-01-01

    Chains of miniature center-cracked-tension specimens were tested on a conventional testing machine and on a prototypic in-reactor fatigue machine as part of the fusion reactor materials alloy development program. Annealed and 20 percent cold-worked 316 stainless steel specimens were cycled under various conditions of temperature, frequency, stress ratio and chain length. Crack growth rates determined from multispecimen visual measurements and from an electrical potential technique were consistent with those obtained by conventional test methods. Results demonstrate that multispecimen chain testing is a valid method of obtaining fatigue crack propagation information for alloy development. 8 refs

  16. 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)

  17. Password Cracking Using Sony Playstations

    Science.gov (United States)

    Kleinhans, Hugo; Butts, Jonathan; Shenoi, Sujeet

    Law enforcement agencies frequently encounter encrypted digital evidence for which the cryptographic keys are unknown or unavailable. Password cracking - whether it employs brute force or sophisticated cryptanalytic techniques - requires massive computational resources. This paper evaluates the benefits of using the Sony PlayStation 3 (PS3) to crack passwords. The PS3 offers massive computational power at relatively low cost. Moreover, multiple PS3 systems can be introduced easily to expand parallel processing when additional power is needed. This paper also describes a distributed framework designed to enable law enforcement agents to crack encrypted archives and applications in an efficient and cost-effective manner.

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

    International Nuclear Information System (INIS)

    Tao, Junhui; Hu, Shubing; Ji, Longbo

    2016-01-01

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

  19. Subsurface metals fatigue cracking without and with crack tip

    Directory of Open Access Journals (Sweden)

    Andrey Shanyavskiy

    2013-07-01

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

  20. Location of cardiac arrest and impact of pre-arrest chronic disease and medication use on survival

    DEFF Research Database (Denmark)

    Granfeldt, Asger; Wissenberg, Mads; Hansen, Steen Møller

    2017-01-01

    location and a higher mortality can be explained by differences in chronic diseases and medication. METHODS: We identified 27,771 out-of-hospital cardiac arrest patients ≥18 years old from the Danish Cardiac Arrest Registry (2001-2012). Using National Registries, we identified pre-arrest chronic disease......INTRODUCTION: Cardiac arrest in a private location is associated with a higher mortality when compared to public location. Past studies have not accounted for pre-arrest factors such as chronic disease and medication. AIM: To investigate whether the association between cardiac arrest in a private...

  1. Crack initiation life analysis in notched pipe under cyclic bending loads

    International Nuclear Information System (INIS)

    Goak, S. R.; Kim, Y. J.; Lee, J. S.; Park, Y. W.

    2000-01-01

    In order to improve LBB(Leak-Before-Break) methodology, more precisely the crack growth evaluation, a benchmark problem was proposed by the CEA Saclay. The aim of this benchmark analysis was to evaluate the crack growth in a notched pipe under cyclic bending loads. The proposed benchmark analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result

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

    Science.gov (United States)

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

    2009-01-01

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

  3. J-integral elastic plastic fracture mechanics evaluation of the stability of cracks in nuclear reactor pressure vessels

    International Nuclear Information System (INIS)

    Gomez, M.P.; McMeeking, R.M.; Parks, D.M.

    1980-06-01

    Contributions were made toward developing a new methodology to assess the stability of cracks in pressure vessels made from materials that exhibit a significant increase in toughness during the early increments of crack growth. It has a wide range of validity from linear elastic to fully plastic behavior

  4. Cracks in Utopia

    Science.gov (United States)

    1999-01-01

    Many of the craters found on the northern plains of Mars have been partly filled or buried by some material (possibly sediment). The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image presented here (MOC2-136b, above left) shows a high-resolution view of a tiny portion of the floor of one of these northern plains craters. The crater, located in Utopia Planitia at 44oN, 258oW, is shown on the right (MOC2-136a)with a small white box to indicate the location of the MOC image. The MOC image reveals that the material covering the floor of this crater is cracked and pitted. The origin and source of material that has been deposited in this crater is unknown.The MOC image was acquired in June 1999 and covers an area only 1.1 kilometers (0.7 miles) wide at a resolution of 1.8 meters (6 feet) per pixel. The context picture is a mosaic of Viking 2 orbiter images 010B53 and 010B55, taken in 1976. Both images are illuminated from the left. Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  5. Super oil cracking update

    International Nuclear Information System (INIS)

    Mulraney, D.

    1997-01-01

    The conversion of residual fuel oil to usable middle distillates was discussed. The residue conversion processing paths are usually based on separation, carbon rejection, or hydrogen addition principles. Super Oil Cracking (SOC) uses a slurry catalyst system in a new, tubular reactor to achieve high levels of hydrothermal conversion. SOC can upgrade a variety of heavy, high metals residue feedstocks with high yields of middle distillates. The SOC products can also be further treated into feedstocks for FCC or hydrocracking. The SOC process can be incorporated easily into a refinery to obtain incremental residue conversion directly. It can also be integrated with other residue processes, acting as a demetallization and decarbonization step which results in enhanced overall conversion. The relative rate of coke formation and its handling are distinguishing characteristics between residue upgrading technologies. The SOC process operates at higher temperatures that other residue hydrocracking processes resulting in higher rates of thermal decomposition, thus preventing coke formation. SOC process can operate as a stand-alone upgrader or can be integrated with other bottoms processing steps to extend the refiner's range of options for increasing bottoms conversion.3 tabs., 14 figs

  6. Metallurgy of stress corrosion cracking

    International Nuclear Information System (INIS)

    Donovan, J.A.

    1973-01-01

    The susceptibility of metals and alloys to stress corrosion is discussed in terms of the relationship between structural characteristics (crystal structure, grains, and second phases) and defects (vacancies, dislocations, and cracks) that exist in metals and alloys. (U.S.)

  7. Peridynamic model for fatigue cracking.

    Energy Technology Data Exchange (ETDEWEB)

    Silling, Stewart Andrew; Abe Askari (Boeing)

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the "remaining life" of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  8. Shapes formed by interacting cracks

    Science.gov (United States)

    Daniels, Karen

    2012-02-01

    Brittle failure through multiple cracks occurs in a wide variety of contexts, from microscopic failures in dental enamel and cleaved silicon to geological faults and planetary ice crusts. In each of these situations, with complicated stress geometries and different microscopic mechanisms, pairwise interactions between approaching cracks nonetheless produce characteristically curved fracture paths. We investigate the origins of this widely observed ``en passant'' crack pattern by fracturing a rectangular slab which is notched on each long side and subjected to quasi-static uniaxial strain from the short side. The two cracks propagate along approximately straight paths until they pass each other, after which they curve and release a lens-shaped fragment. We find that, for materials with diverse mechanical properties, each curve has an approximately square-root shape, and that the length of each fragment is twice its width. We are able to explain the origins of this universal shape with a simple geometrical model.

  9. The crack growth mechanism in asphaltic mixes

    NARCIS (Netherlands)

    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

  10. Dynamic Crack Branching - A Photoelastic Evaluation,

    Science.gov (United States)

    1982-05-01

    0.41 mPai and a 0.18 MPa, and predicted a theoretical kinking angle of 84°whichagreed well with experimentally measured angle. After crack kinking...Consistent crack branching’at KIb = 2.04 MPaI -i- and r = 1.3 mm verified this crack branching criterion. The crack branching angle predicted by--.’ DD

  11. 21 CFR 137.190 - Cracked wheat.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested by...

  12. Cell cycle arrest induced by radiation

    International Nuclear Information System (INIS)

    Okaichi, Yasuo; Matsumoto, Hideki; Ohnishi, Takeo

    1994-01-01

    It is known that various chemical reactions, such as cell cycle arrest, DNA repair and cell killing, can occur within the cells when exposed to ionizing radiation and ultraviolet radiation. Thus protein dynamics involved in such chemical reactions has received considerable attention. In this article, cell cycle regulation is first discussed in terms of the G2/M-phase and the G1/S-phase. Then, radiation-induced cell cycle arrest is reviewed. Cell cycle regulation mechanism involved in the G2 arrest, which is well known to occur when exposed to radiation, has recently been investigated using yeasts. In addition, recent study has yielded a noticeable finding that the G1 arrest can occur with intracellular accumulation of p53 product following ionization radiation. p53 is also shown to play an extremely important role in both DNA repair and cell killing due to DNA damage. Studies on the role of genes in protein groups induced by radiation will hold promise for the elucidation of cell cycle mechanism. (N.K.) 57 refs

  13. Crack propagation in dynamic thermoelasticity

    International Nuclear Information System (INIS)

    Bui, H.D.

    1980-01-01

    We study the singular thermoelastic fields near the crack tip, in the linear strain assumption. The equations are coupled and non linear. The asymptotic expansions of the displacement and the temperature are given for the first and the second order. It is shown that the temperature is singular when the crack propagates. However, this field does not change the dominant singularity of the mechanical field which is the same as that obtained in the theory of isothermal elasticity [fr

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

    International Nuclear Information System (INIS)

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

    2008-01-01

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

  15. Effect of Microstructure on Time Dependent Fatigue Crack Growth Behavior In a P/M Turbine Disk Alloy

    Science.gov (United States)

    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.

  16. 32 CFR 935.125 - Citation in place of arrest.

    Science.gov (United States)

    2010-07-01

    ... 32 National Defense 6 2010-07-01 2010-07-01 false Citation in place of arrest. 935.125 Section 935... INSULAR REGULATIONS WAKE ISLAND CODE Peace Officers § 935.125 Citation in place of arrest. In any case in which a peace officer may make an arrest without a warrant, he may issue and serve a citation if he...

  17. Transient Central Diabetes Insipidus and Marked Hypernatremia following Cardiorespiratory Arrest

    Directory of Open Access Journals (Sweden)

    Sahar H. Koubar

    2017-01-01

    Full Text Available Central Diabetes Insipidus is often an overlooked complication of cardiopulmonary arrest and anoxic brain injury. We report a case of transient Central Diabetes Insipidus (CDI following cardiopulmonary arrest. It developed 4 days after the arrest resulting in polyuria and marked hypernatremia of 199 mM. The latter was exacerbated by replacing the hypotonic urine by isotonic saline.

  18. An Audit Of Perioperative Cardiac Arrest At Lagos University ...

    African Journals Online (AJOL)

    Objective: Intraoperative cardiac arrests are not uncommon and are related to both surgical and anaesthetic factors. This study aimed to examine the factors which predispose to a periopeartive cardiac arrest, to assess the appropriateness of therapy and the outcome. Materials and Methods: All perioperative cardiac arrests ...

  19. Witnessed arrest, but not delayed bystander cardiopulmonary resuscitation improves prehospital cardiac arrest survival.

    Science.gov (United States)

    Vukmir, R B

    2004-05-01

    This study correlated the effect of witnessing a cardiac arrest and instituting bystander CPR (ByCPR), as a secondary end point in a study evaluating the effect of bicarbonate on survival. This prospective, randomised, double blinded clinical intervention trial enrolled 874 prehospital cardiopulmonary arrest patients encountered in a prehospital urban, suburban, and rural regional emergency medical service (EMS) area. This group underwent conventional advanced cardiac life support intervention followed by empiric early administration of sodium bicarbonate (1 mEq/l), monitoring conventional resuscitation parameters. Survival was measured as presence of vital signs on emergency department (ED) arrival. Data were analysed using chi(2) with Pearson correlation and odds ratio where appropriate. The overall survival rate was 13.9% (110 of 792) of prehospital cardiac arrest patients. The mean (SD) time until provision of bystander cardiopulmonary resuscitation (ByCPR) by laymen was 2.08 (2.77) minutes, and basic life support (BLS) by emergency medical technicians was 6.62 (5.73) minutes. There was improved survival noted with witnessed cardiac arrest-a 2.2-fold increase in survival, 18.9% (76 of 402) versus 8.6% (27 of 315) compared with unwitnessed arrests (ptwo minutes (p = 0.3752). Survival after prehospital cardiac arrest is more likely when witnessed, but not necessarily when ByCPR was performed by laymen.

  20. Stochastic modeling of thermal fatigue crack growth

    CERN Document Server

    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...

  1. Compressive failure with interacting cracks

    International Nuclear Information System (INIS)

    Yang Guoping; Liu Xila

    1993-01-01

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

  2. Influence of microstructure on stress corrosion cracking of mild steel in synthetic caustic-nitrate nuclear waste solution

    International Nuclear Information System (INIS)

    Sarafian, P.G.

    1975-12-01

    The influence of alloy microstructure on stress corrosion cracking of mild steel in caustic-nitrate synthetic nuclear waste solutions was studied. An evaluation was made of the effect of heat treatment on a representative material (ASTM A 516 Grade 70) used in the construction of high activity radioactive waste storage tanks at Savannah River Plant. Several different microstructures were tested for susceptibility to stress corrosion cracking. Precracked fracture specimens loaded in either constant load or constant crack opening displacement were exposed to a variety of caustic-nitrate and nitrate solutions. Results were correlated with the mechanical and corrosion properties of the microstructures. Crack velocity and crack arrest stress intensity were found to be related to the yield strength of the steel microstructures. Fractographic evidence indicated pH depletion and corrosive crack tip chemistry conditions even in highly caustic solutions. Experimental results were compatible with crack growth by a strain-assisted anodic dissolution mechanism; however, hydrogen embrittlement also was considered possible

  3. 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

  4. G-control fatigue testing for cyclic crack propagation in composite structures

    DEFF Research Database (Denmark)

    Manca, Marcello; Berggreen, Christian; Carlsson, Leif A.

    2015-01-01

    This paper presents a computer controlled testing methodology called “The G-control Method” which allows cyclic crack growth testing using real-time control of the cyclic energy release rate. The advantages of using this approach are described and compared with traditional fatigue testing methods...... that the G-control method allows fatigue testing at a constant range of energy release rates leading to a constant crack propagation rate....

  5. Study of the Effect of Swelling on Irradiation Assisted Stress Corrosion Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Teysseyre, Sebastien Paul [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2016-09-01

    This report describes the methodology used to study the effect of swelling on the crack growth rate of an irradiation-assisted stress corrosion crack that is propagating in highly irradiated stainless steel 304 material irradiated to 33 dpa in the Experimental Breeder Reactor-II. The material selection, specimens design, experimental apparatus and processes are described. The results of the current test are presented.

  6. 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)

  7. Reactor pressure vessel failure probability following through-wall cracks due to pressurized thermal shock events

    International Nuclear Information System (INIS)

    Simonen, F.A.; Garnich, M.R.; Simonen, E.P.; Bian, S.H.; Nomura, K.K.; Anderson, W.E.; Pedersen, L.T.

    1986-04-01

    A fracture mechanics model was developed at the Pacific Northwest Laboratory (PNL) to predict the behavior of a reactor pressure vessel following a through-wall crack that occurs during a pressurized thermal shock (PTS) event. This study, which contributed to a US Nuclear Regulatory Commission (NRC) program to study PTS risk, was coordinated with the Integrated Pressurized Thermal Shock (IPTS) Program at Oak Ridge National Laboratory (ORNL). The PNL fracture mechanics model uses the critical transients and probabilities of through-wall cracks from the IPTS Program. The PNL model predicts the arrest, reinitiation, and direction of crack growth for a postulated through-wall crack and thereby predicts the mode of vessel failure. A Monte-Carlo type of computer code was written to predict the probabilities of the alternative failure modes. This code treats the fracture mechanics properties of the various welds and plates of a vessel as random variables. Plant-specific calculations were performed for the Oconee-1, Calvert Cliffs-1, and H.B. Robinson-2 reactor pressure vessels for the conditions of postulated transients. The model predicted that 50% or more of the through-wall axial cracks will turn to follow a circumferential weld. The predicted failure mode is a complete circumferential fracture of the vessel, which results in a potential vertically directed missile consisting of the upper head assembly. Missile arrest calculations for the three nuclear plants predict that such vertical missiles, as well as all potential horizontally directed fragmentation type missiles, will be confined to the vessel enclosre cavity. The PNL failure mode model is recommended for use in future evaluations of other plants, to determine the failure modes that are most probable for postulated PTS events

  8. Cracking in Flexural Reinforced Concrete Members

    DEFF Research Database (Denmark)

    Rasmussen, Annette Beedholm; Fisker, Jakob; Hagsten, Lars German

    2017-01-01

    The system of cracks developing in reinforced concrete is in many aspects essential when modelling structures in both serviceability- and ultimate limit state. This paper discusses the behavior concerning crack development in flexural members observed from tests and associates it with two different...... existing models. From the investigations an approach is proposed on how to predict the crack pattern in flexural members involving two different crack systems; primary flexural cracks and local secondary cracks. The results of the approach is in overall good agreement with the observed tests and captures...... the pronounced size effect associated with flexural cracking in which the crack spacing and crack widths are approximately proportional to the depth of the member....

  9. Dynamic ductile fracture of a central crack

    Science.gov (United States)

    Tsai, Y. M.

    1976-01-01

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

  10. 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)

  11. Fatigue cracking in road pavement

    Science.gov (United States)

    Mackiewicz, P.

    2018-05-01

    The article presents the problem of modelling fatigue phenomena occurring in the road pavement. The example of two selected pavements shows the changes occurring under the influence of the load in different places of the pavement layers. Attention is paid to various values of longitudinal and transverse strains generated at the moment of passing the wheel on the pavement. It was found that the key element in the crack propagation analysis is the method of transferring the load to the pavement by the tire and the strain distribution in the pavement. During the passage of the wheel in the lower layers of the pavement, a complex stress state arises. Then vertical, horizontal and tangent stresses with various values appear. The numerical analyses carried out with the use of finite element methods allowed to assess the strain and stress changes occurring in the process of cracking road pavement. It has been shown that low-thickness pavements are susceptible to fatigue cracks arising "bottom to top", while pavements thicker are susceptible to "top to bottom" cracks. The analysis of the type of stress allowed to determine the cracking mechanism.

  12. Steel weldability. Underbead cold cracking

    International Nuclear Information System (INIS)

    Marquet, F.; Defourny, J.; Bragard, A.

    1977-01-01

    The problem of underbead cold cracking has been studied by the implant technique. This approach allows to take into account in a quantitative manner the different factors acting on the cold cracking phenomenon: structure under the weld bead, level of restraint, hydrogen content in the molten metal. The influence of the metallurgical factors depending from the chemical composition of the steel has been examined. It appeared that carbon equivalent is an important factor to explain cold cracking sensitivity but that it is not sufficient to characterize the steel. The results have shown that vanadium may have a deleterious effect on the resistance to cold cracking when the hydrogen content is high and that small silicon additions are beneficient. The influence of the diffusible hydrogen content has been checked and the important action of pre- and postheating has been shown. These treatments allow the hydrogen to escape from the weld before the metal has been damaged. Some inclusions (sulphides) may also decrease the influence of hydrogen. A method based on the implant tests has been proposed which allows to choose and to control safe welding conditions regarding cold cracking

  13. Role of hydrogen in stress corrosion cracking

    International Nuclear Information System (INIS)

    Mehta, M.L.

    1981-01-01

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

  14. A crack opening stress equation for fatigue crack growth

    Science.gov (United States)

    Newman, J. C., Jr.

    1984-01-01

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

  15. Seismic behaviour of un-cracked and cracked thin pipes

    International Nuclear Information System (INIS)

    Blay, N.; Brunet, G.; Gantenbein, F.; Aguilar, J.

    1995-01-01

    In order to evaluate the seismic behaviour of un-cracked and cracked thin pipes, subjected to high acceleration levels, seismic tests and calculations have been performed on straight thin pipes made of 316L stainless steel, loaded in pure bending by a permanent static and dynamic loading. The seismic tests were carried out on the AZALEE shaking table of the CEA laboratory TAMARIS. The influence of the elasto-plastic model with isotropic or kinematic hardening are studied. 5 refs., 7 figs., 2 tabs

  16. Out-of-hospital cardiac arrest

    DEFF Research Database (Denmark)

    Sondergaard, Kathrine B; Hansen, Steen Moller; Pallisgaard, Jannik L

    2018-01-01

    AIMS: Despite wide dissemination of automated external defibrillators (AEDs), bystander defibrillation rates remain low. We aimed to investigate how route distance to the nearest accessible AED was associated with probability of bystander defibrillation in public and residential locations. METHODS......: We used data from the nationwide Danish Cardiac Arrest Registry and the Danish AED Network to identify out-of-hospital cardiac arrests and route distances to nearest accessible registered AED during 2008-2013. The association between route distance and bystander defibrillation was described using...... in public locations, the probability of bystander defibrillation at 0, 100 and 200meters from the nearest AED was 35.7% (95% confidence interval 28.0%-43.5%), 21.3% (95% confidence interval 17.4%-25.2%), and 13.7% (95% confidence interval 10.1%-16.8%), respectively. The corresponding numbers for cardiac...

  17. Dental Calculus Arrest of Dental Caries.

    Science.gov (United States)

    Keyes, Paul H; Rams, Thomas E

    An inverse relationship between dental calculus mineralization and dental caries demineralization on teeth has been noted in some studies. Dental calculus may even form superficial layers over existing dental caries and arrest their progression, but this phenomenon has been only rarely documented and infrequently considered in the field of Cariology. To further assess the occurrence of dental calculus arrest of dental caries, this study evaluated a large number of extracted human teeth for the presence and location of dental caries, dental calculus, and dental plaque biofilms. A total of 1,200 teeth were preserved in 10% buffered formal saline, and viewed while moist by a single experienced examiner using a research stereomicroscope at 15-25× magnification. Representative teeth were sectioned and photographed, and their dental plaque biofilms subjected to gram-stain examination with light microscopy at 100× magnification. Dental calculus was observed on 1,140 (95%) of the extracted human teeth, and no dental carious lesions were found underlying dental calculus-covered surfaces on 1,139 of these teeth. However, dental calculus arrest of dental caries was found on one (0.54%) of 187 evaluated teeth that presented with unrestored proximal enamel caries. On the distal surface of a maxillary premolar tooth, dental calculus mineralization filled the outer surface cavitation of an incipient dental caries lesion. The dental calculus-covered carious lesion extended only slightly into enamel, and exhibited a brown pigmentation characteristic of inactive or arrested dental caries. In contrast, the tooth's mesial surface, without a superficial layer of dental calculus, had a large carious lesion going through enamel and deep into dentin. These observations further document the potential protective effects of dental calculus mineralization against dental caries.

  18. Dental Calculus Arrest of Dental Caries

    Science.gov (United States)

    Keyes, Paul H.; Rams, Thomas E.

    2016-01-01

    Background An inverse relationship between dental calculus mineralization and dental caries demineralization on teeth has been noted in some studies. Dental calculus may even form superficial layers over existing dental caries and arrest their progression, but this phenomenon has been only rarely documented and infrequently considered in the field of Cariology. To further assess the occurrence of dental calculus arrest of dental caries, this study evaluated a large number of extracted human teeth for the presence and location of dental caries, dental calculus, and dental plaque biofilms. Materials and methods A total of 1,200 teeth were preserved in 10% buffered formal saline, and viewed while moist by a single experienced examiner using a research stereomicroscope at 15-25× magnification. Representative teeth were sectioned and photographed, and their dental plaque biofilms subjected to gram-stain examination with light microscopy at 100× magnification. Results Dental calculus was observed on 1,140 (95%) of the extracted human teeth, and no dental carious lesions were found underlying dental calculus-covered surfaces on 1,139 of these teeth. However, dental calculus arrest of dental caries was found on one (0.54%) of 187 evaluated teeth that presented with unrestored proximal enamel caries. On the distal surface of a maxillary premolar tooth, dental calculus mineralization filled the outer surface cavitation of an incipient dental caries lesion. The dental calculus-covered carious lesion extended only slightly into enamel, and exhibited a brown pigmentation characteristic of inactive or arrested dental caries. In contrast, the tooth's mesial surface, without a superficial layer of dental calculus, had a large carious lesion going through enamel and deep into dentin. Conclusions These observations further document the potential protective effects of dental calculus mineralization against dental caries. PMID:27446993

  19. 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.

  20. Cracking on anisotropic neutron stars

    Science.gov (United States)

    Setiawan, A. M.; Sulaksono, A.

    2017-07-01

    We study the effect of cracking of a local anisotropic neutron star (NS) due to small density fluctuations. It is assumed that the neutron star core consists of leptons, nucleons and hyperons. The relativistic mean field model is used to describe the core of equation of state (EOS). For the crust, we use the EOS introduced by Miyatsu et al. [1]. Furthermore, two models are used to describe pressure anisotropic in neutron star matter. One is proposed by Doneva-Yazadjiev (DY) [2] and the other is proposed by Herrera-Barreto (HB) [3]. The anisotropic parameter of DY and HB models are adjusted in order the predicted maximum mass compatible to the mass of PSR J1614-2230 [4] and PSR J0348+0432 [5]. We have found that cracking can potentially present in the region close to the neutron star surface. The instability due cracking is quite sensitive to the NS mass and anisotropic parameter used.

  1. Dynamic experiments on cracked pipes

    International Nuclear Information System (INIS)

    Petit, M.; Brunet, G.; Buland, P.

    1991-01-01

    In order to apply the leak before break concept to piping systems, the behavior of cracked pipes under dynamic, and especially seismic loading must be studied. In a first phase, an experimental program on cracked stainless steel pipes under quasi-static monotonic loading has been conducted. In this paper, the dynamic tests on the same pipe geometry are described. These tests have been performed on a shaking table with a mono frequency input signal. The main parameter of the tests is the frequency of excitation versus the frequency of the system

  2. Cracking and corrosion recovery boiler

    Energy Technology Data Exchange (ETDEWEB)

    Suik, H. [Tallinn Technical University, Horizon Pulp and Paper, Tallinn (Estonia)

    1998-12-31

    The corrosion of heat surfaces and the cracking the drums are the main problems of the recovery boiler. These phenomena have been appeared during long-term operation of boiler `Mitsubishi - 315` erected at 1964. Depth of the crack is depending on the number of shutdowns and on operation time. Corrosion intensity of different heat surfaces is varying depend on the metal temperature and the conditions at place of positioning of tube. The lowest intensity of corrosion is on the bank tubes and the greatest is on the tubes of the second stage superheater and on the tubes at the openings of air ports. (orig.) 5 refs.

  3. Cracking and corrosion recovery boiler

    Energy Technology Data Exchange (ETDEWEB)

    Suik, H [Tallinn Technical University, Horizon Pulp and Paper, Tallinn (Estonia)

    1999-12-31

    The corrosion of heat surfaces and the cracking the drums are the main problems of the recovery boiler. These phenomena have been appeared during long-term operation of boiler `Mitsubishi - 315` erected at 1964. Depth of the crack is depending on the number of shutdowns and on operation time. Corrosion intensity of different heat surfaces is varying depend on the metal temperature and the conditions at place of positioning of tube. The lowest intensity of corrosion is on the bank tubes and the greatest is on the tubes of the second stage superheater and on the tubes at the openings of air ports. (orig.) 5 refs.

  4. The Reflective Cracking in Flexible Pavements

    Directory of Open Access Journals (Sweden)

    Pais Jorge

    2013-07-01

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

  5. 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

  6. Methodology for plastic fracture - a progress report

    International Nuclear Information System (INIS)

    Wilkinson, J.P.D.; Smith, R.E.E.

    1977-01-01

    This paper describes the progress of a study to develop a methodology for plastic fracture. Such a fracture mechanics methodology, having application in the plastic region, is required to assess the margin of safety inherent in nuclear reactor pressure vessels. The initiation and growth of flaws in pressure vessels under overload conditions is distinguished by a number of unique features, such as large scale yielding, three-dimensional structural and flaw configurations, and failure instabilities that may be controlled by either toughness or plastic flow. In order to develop a broadly applicable methodology of plastic fracture, these features require the following analytical and experimental studies: development of criteria for crack initiation and growth under large scale yielding; the use of the finite element method to describe elastic-plastic behaviour of both the structure and the crack tip region; and extensive experimental studies on laboratory scale and large scale specimens, which attempt to reproduce the pertinent plastic flow and crack growth phenomena. This discussion centers on progress to date on the selection, through analysis and laboratory experiments, of viable criteria for crack initiation and growth during plastic fracture. (Auth.)

  7. Integrated modeling and characterization of local crack chemistry

    International Nuclear Information System (INIS)

    Savchik, J.A.; Burke, M.S.

    1995-01-01

    The MULTEQ computer program has become an industry wide tool which can be used to calculate the chemical composition in a flow occluded region as the solution within concentrates due to a local boiling process. These results can be used to assess corrosion concerns in plant equipment such as steam generators. Corrosion modeling attempts to quantify corrosion assessments by accounting for the mass transport processes involved in the corrosion mechanism. MULTEQ has played an ever increasing role in defining the local chemistry for such corrosion models. This paper will outline how the integration of corrosion modeling with the analysis of corrosion films and deposits can lead to the development of a useful modeling tool, wherein MULTEQ is interactively linked to a diffusion and migration transport process. This would provide a capability to make detailed inferences of the local crack chemistry based on the analyses of the local corrosion films and deposits inside a crack and thus provide guidance for chemical fixes to avoid cracking. This methodology is demonstrated for a simple example of a cracked tube. This application points out the utility of coupling MULTEQ with a mass transport process and the feasibility of an option in a future version of MULTEQ that would permit relating film and deposit analyses to the local chemical environment. This would increase the amount of information obtained from removed tube analyses and laboratory testing that can contribute to an overall program for mitigating tubing and crevice corrosion

  8. Integrated modeling and characterization of local crack chemistry

    International Nuclear Information System (INIS)

    Savchik, J.A.; Burke, M.S.

    1996-01-01

    The MULTEQ computer program has become an industry wide tool which can be used to calculate the chemical composition in a flow occluded region as the solution within concentrates due to a local boiling process. These results can be used to assess corrosion concerns in plant equipment such as steam generators. Corrosion modeling attempts to quantify corrosion assessments by accounting for the mass transport processes involved in the corrosion mechanism. MULTEQ has played an ever increasing role in defining the local chemistry for such corrosion models. This paper will outline how the integration of corrosion modeling with the analysis of corrosion films and deposits can lead to the development of a useful modeling tool, wherein MULTEQ is interactively linked to a diffusion and migration transport process. This would provide a capability to make detailed inferences of the local crack chemistry based on the analyses of the local corrosion films and deposits inside a crack and thus provide guidance for chemical fixes to avoid cracking. This methodology is demonstrated for a simple example of a cracked tube. This application points out the utility of coupling MULTEQ with a mass transport process and the feasibility of an option in a future version of MULTEQ that would permit relating film and deposit analyses to the local chemical environment. This would increase the amount of information obtained from removed tube analyses and laboratory testing that can contribute to an overall program for mitigating tubing and crevice corrosion

  9. Distinct mechanisms act in concert to mediate cell cycle arrest.

    Science.gov (United States)

    Toettcher, Jared E; Loewer, Alexander; Ostheimer, Gerard J; Yaffe, Michael B; Tidor, Bruce; Lahav, Galit

    2009-01-20

    In response to DNA damage, cells arrest at specific stages in the cell cycle. This arrest must fulfill at least 3 requirements: it must be activated promptly; it must be sustained as long as damage is present to prevent loss of genomic information; and after the arrest, cells must re-enter into the appropriate cell cycle phase to ensure proper ploidy. Multiple molecular mechanisms capable of arresting the cell cycle have been identified in mammalian cells; however, it is unknown whether each mechanism meets all 3 requirements or whether they act together to confer specific functions to the arrest. To address this question, we integrated mathematical models describing the cell cycle and the DNA damage signaling networks and tested the contributions of each mechanism to cell cycle arrest and re-entry. Predictions from this model were then tested with quantitative experiments to identify the combined action of arrest mechanisms in irradiated cells. We find that different arrest mechanisms serve indispensable roles in the proper cellular response to DNA damage over time: p53-independent cyclin inactivation confers immediate arrest, whereas p53-dependent cyclin downregulation allows this arrest to be sustained. Additionally, p21-mediated inhibition of cyclin-dependent kinase activity is indispensable for preventing improper cell cycle re-entry and endoreduplication. This work shows that in a complex signaling network, seemingly redundant mechanisms, acting in a concerted fashion, can achieve a specific cellular outcome.

  10. On multiple crack detection in beam structures

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Shapour; Kargozarfard, Mohammad [Shahid Chamran University, Ahvaz (Iran, Islamic Republic of)

    2013-01-15

    This study presents an inverse procedure to identify multiple cracks in beams using an evolutionary algorithm. By considering the crack detection procedure as an optimization problem, an objective function can be constructed based on the change of the eigenfrequencies and some strain energy parameters. Each crack is modeled by a rotational spring. The changes in natural frequencies due to the presence of the cracks are related to a damage index vector. Then, the bees algorithm, a swarm-based evolutionary optimization technique, is used to optimize the objective function and find the damage index vector, whose positive components show the number and position of the cracks. A second objective function is also optimized to find the crack depths. Several experimental studies on cracked cantilever beams are conducted to ensure the integrity of the proposed method. The results show that the number of cracks as well as their sizes and locations can be predicted well through this method.

  11. The analysis of cracked structures

    International Nuclear Information System (INIS)

    Davidson, I.

    1974-01-01

    A brief review of the general problem of stable crack systems in many classes of structures, notably reinforced concrete structures, is made. Very simple methods of analysis are derived and some elaboration is described, as well as methods of optimising the calculations. Analytical methods are compared with experiments

  12. Cracks in functionally graded materials

    International Nuclear Information System (INIS)

    Bahr, H.-A.; Balke, H.; Fett, T.; Hofinger, I.; Kirchhoff, G.; Munz, D.; Neubrand, A.; Semenov, A.S.; Weiss, H.-J.; Yang, Y.Y.

    2003-01-01

    The weight function method is described to analyze the crack growth behavior in functionally graded materials and in particular materials with a rising crack growth resistance curve. Further, failure of graded thermal barrier coatings (TBCs) under cyclic surface heating by laser irradiation is modeled on the basis of fracture mechanics. The damage of both graded and non-graded TBCs is found to develop in several distinct stages: vertical cracking→delamination→blistering→spalling. This sequence can be understood as an effect of progressive shrinkage due to sintering and high-temperature creep during thermal cycling, which increases the energy-release rate for vertical cracks which subsequently turn into delamination cracks. The results of finite element modeling, taking into account the TBC damage mechanisms, are compatible with experimental data. An increase of interface fracture toughness due to grading and a decrease due to ageing have been measured in a four-point bending test modified by a stiffening layer. Correlation with the damage observed in cyclic heating is discussed. It is explained in which way grading is able to reduce the damage

  13. Severity parameters for steam cracking

    NARCIS (Netherlands)

    Golombok, M.; Bijl, J.L.M.; Kornegoor, M.

    2001-01-01

    There are several ways to measure severity in steam cracking which are all a function of residence time, temperature, and pressure. Many measures of severity are not practicable for experimental purposes. Our experimental study shows that methane make is the best measure of severity because it is an

  14. Steam hydrocarbon cracking and reforming

    NARCIS (Netherlands)

    Golombok, M.

    2004-01-01

    Many industrial chemical processes are taught as distinct contrasting reactions when in fact the unifying comparisons are greater than the contrasts. We examine steam hydrocarbon reforming and steam hydrocarbon cracking as an example of two processes that operate under different chemical reactivity

  15. Petrochemical promoters in catalytic cracking

    International Nuclear Information System (INIS)

    Gomez, Maria; Vargas, Clemencia; Lizcano, Javier

    2010-01-01

    This study is based on the current scheme followed by a refinery with available Catalytic Cracking capacity to process new feedstocks such as Straight Run Naphtha and Naphthas from FCC. These feedstocks are of petrochemical interest to produce Ethane, Ethylene, Propylene, i-Butane, Toluene and Xylene. To evaluate the potential of these new streams versus the Cracking-charged Residues, it was performed a detailed chemical analysis on the structural groups in carbons [C1-C12] at the reactor product obtained in pilot plant. A catalyst with and without Propylene Promoter Additive was used. This study analyzes the differences in the chemical composition of the feedstocks, relating them to the yield of each petrochemical product. Straight Run Naphthas with a high content of Naphthenes, and Paraffines n[C5-C12] and i[C7-C12] are selective to the production of i-Butane and Propane, while Naphthas from FCC with a high content of n[C5-C12]Olefins, i-Olefins, and Aromatics are more selective to Propylene, Toluene, and Xylene. Concerning Catalytic Cracking of Naphthas, the Additive has similar selectivity for all the petrochemical products, their yields increase by about one point with 4%wt of Additive, while in cracking of Residues, the Additive increases in three points Propylene yield, corresponding to a selectivity of 50% (?C3= / ?LPG).

  16. Fatigue crack growth in fiber reinforced plastics

    Science.gov (United States)

    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.

  17. Crack Propagation by Finite Element Method

    OpenAIRE

    H. Ricardo, Luiz Carlos

    2017-01-01

    Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FD&E SAE Keyh...

  18. BWR pipe crack remedies evaluation

    International Nuclear Information System (INIS)

    Shack, W.J.; Kassner, T.F.; Maiya, P.S.; Park, J.Y.; Ruther, W.; Kuzay, T.; Rybicki, E.F.; Stonesifer, R.B.

    1988-01-01

    Piping in light-water-reactor power systems has been affected by several types of environmental degradation. This paper presents results from studies of (1) stress corrosion crack growth in fracture mechanics specimens of modified Type 347 SS and Type 304/308L SS weld overlay material, (2) heat-to-heat variations in stress corrosion cracking (SCC) of Types 316NG and 347 SS, (3) SCC of sensitized Type 304 SS in water with cupric ion or organic acid impurities, (4) electrochemical potential (ECP) measurements under gamma irradiation, (5) SCC of ferritic steels, (6) strain-controlled fatigue of Type 316NG SS in air at ambient temperature, and (7) through-wall residual stress measurements and finite-element calculation of residual stresses in weldments treated by a mechanical stress improvement process (MSIP). Fracture-mechanics crack-growth-rate tests on Type 316NG SS have shown that transgranular cracking can occur even in high purity environments, whereas no crack growth was observed in Type 347 SS even in impurity environments. In tests on weld overlay specimens, no cracks penetrated into the overlay even in impurity environments. Instead, the cracks branched when they approached the overlay, and then grew parallel to interface. In SCC tests on sensitized Type 304 SS, cupric ions at concentrations greater than ∼1 ppm were found to be deleterious, whereas organic acids at this concentration were not detrimental. Tests on several ferritic steels indicate a strong correlation between the sulfur content of the steels and susceptibility to SCC. External gamma radiation fields produced a large positive shift in the ECP of Type 304 SS at low dissolved-oxygen concentrations (<5 ppb), whereas in the absence of an external gamma field there was no difference in the ECP values of irradiated and nonirradiated material. Fatigue data for Type 316NG SS are consistent with the ASME code mean curve at high strains, but fall below the curve at low strains. Calculations of the

  19. Correction to the crack extension direction in numerical modelling of mixed mode crack paths

    DEFF Research Database (Denmark)

    Lucht, Tore; Aliabadi, M.H.

    2007-01-01

    In order to avoid introduction of an error when a local crack-growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction...

  20. Fatigue crack growth from a cracked elastic particle into a ductile matrix

    NARCIS (Netherlands)

    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

  1. Catalytic Cracking of Palm Oil Over Zeolite Catalysts: Statistical Approach

    Directory of Open Access Journals (Sweden)

    F. A. A. Twaiq and S. Bhatia

    2012-08-01

    Full Text Available The catalytic cracking of palm oil was conducted in a fixed bed micro-reactor over HZSM-5, zeolite ? and ultrastable Y (USY zeolite catalysts. The objective of the present investigation was to study the effect of cracking reaction variables such as temperature, weight hourly space velocity, catalyst pore size and type of palm oil feed of different molecular weight on the conversion, yield of hydrocarbons in gasoline boiling range and BTX aromatics in the organic liquid product.  Statistical Design of Experiment (DOE with 24 full factorial design was used in experimentation at the first stage.  The nonlinear model and Response Surface Methodology (RSM were utilized in the second stage of experimentation to obtain the optimum values of the variables for maximum yields of hydrocarbons in gasoline boiling range and aromatics.  The HZSM-5 showed the best performance amongst the three catalysts tested.  At 623 K and WHSV of 1 h-1, the highest experimental yields of gasoline and aromatics were 28.3 wt.% and 27 wt.%, respectively over the HZSM-5 catalyst.  For the same catalyst, the statistical model predicted that the optimum yield of gasoline was 28.1 wt.% at WHSV of 1.75 h-1 and 623 K.  The predicted optimum yield of gasoline was 25.5 wt.% at 623 K and WHSV of 1 h-1.KEY WORDS: Catalytic Cracking, Palm Oil, Zeolite, Design Of Experiment, Response Surface Methodology.

  2. Assessment of cracking in dissimilar metal welds

    International Nuclear Information System (INIS)

    Jenssen, Anders; Norrgaard, K.; Lagerstroem, J.; Embring, G.; Tice, D.R.

    2001-08-01

    During the refueling in 2000, indications were observed by non-destructive testing at four locations in the reactor pressure vessel (RPV) nozzle to safe end weld in Ringhals 4. All indications were confined to the outlet nozzle (hotleg) oriented at 25 deg, a nozzle with documented repair welding. Six boat samples were removed from the four locations, and the samples were subsequently subjected to a metallographic examination. The objectives were to establish the fracture morphology, and if possible the root cause for cracking. The examination revealed that cracks were present at all four boat sample locations and that they all were confined to the weld metal, alloy 182. Cracking extended in the axial direction of the safe-end. There was no evidence of any cracks extending into the RPV-steel, or the stainless steel safe-end. All cracking was interdendritic and significantly branched. Among others, these observations strongly suggested crack propagation mainly was caused by interdendritic stress corrosion cracking. In addition, crack type defects and isolated areas on the fracture surfaces suggested the presence of hot cracking, which would have been formed during fabrication. The reason for crack initiation could not be established based on the boat samples examined. However, increased stress levels due to repair welding, cold work from grinding, and defects produced during fabrication, e. g. hot cracks, may alone or in combination have contributed to crack initiation

  3. Solidification cracking in austenitic stainless steel welds

    Indian Academy of Sciences (India)

    M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

    Hot cracking in stainless steel welds is caused by low-melting eutectics containing impurities such as S, ... Total crack length (TCL), used extensively in hot cracking assessment, exhibits greater variability due to ... behaviour appear to be complex and the mechanisms thereof are not completely under- stood. Development of ...

  4. Universal Shapes formed by Interacting Cracks

    Science.gov (United States)

    Fender, Melissa; Lechenault, Frederic; Daniels, Karen

    2011-03-01

    Brittle failure through multiple cracks occurs in a wide variety of contexts, from microscopic failures in dental enamel and cleaved silicon to geological faults and planetary ice crusts. In each of these situations, with complicated curvature and stress geometries, pairwise interactions between approaching cracks nonetheless produce characteristically curved fracture paths known in the geologic literature as en passant cracks. While the fragmentation of solids via many interacting cracks has seen wide investigation, less attention has been paid to the details of individual crack-crack interactions. We investigate the origins of this widely observed crack pattern using a rectangular elastic plate which is notched on each long side and then subjected to quasistatic uniaxial strain from the short side. The two cracks propagate along approximately straight paths until the pass each other, after which they curve and release a lenticular fragment. We find that, for materials with diverse mechanical properties, the shape of this fragment has an aspect ratio of 2:1, with the length scale set by the initial cracks offset s and the time scale set by the ratio of s to the pulling velocity. The cracks have a universal square root shape, which we understand by using a simple geometric model and the crack-crack interaction.

  5. Problems of procedure for studying crack resistance

    International Nuclear Information System (INIS)

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

    1984-01-01

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

  6. Effect of Water Environment on Subcritical Crack Growth of Machinable Ceramics; Kaisakusei seramikkusu no kiretsu shinten tokusei ni oyobosu mizu kankyo no eikyo

    Energy Technology Data Exchange (ETDEWEB)

    Ikeda, K.; Kaizu, K.; Inotani, T. [Miyazaki Univ., Miyazaki (Japan); Yoshikawa, A.; Adachi, K.; Igaki, H. [Osaka Sangyo Univ., Osaka (Japan)

    1997-06-15

    The fatigue behavior of ceramics has been discussed on the basis of the relation between stress intensity facter (KI) and crack velocity (V). In this paper, the effect of environment on the relation between KI and V was studied on machinable ceramics (mica glass ceramics) and two kinds of glass ceramics with different grain sizes. The double torsion (DT) technique was used for the determination of the KI-V characteristics under different environments of air and ion-exchanged water. The characteristics of acoustic emission (AE) during stress corrosion cracking of mica glass ceramics was also examined. In water environment, the region II in the KI-V curve, in which crack velocity varies slowly with KI, disappeared. From this experimental fact, it was considered that at high KI, the crack velocity is encouraged by diffusion of the corrosive species to the crack and thus depended on the amount of water. SEM farc tography revealed that mica single crystals in the material caused crack arrest and deflection to occur. It is also found that AE event rate is quantitatively related to the crack velocity. AE measurement can be used in studying the crack propagation behavior of mica glass ceramics. 11 refs., 12 figs., 3 tabs.

  7. A case of thyroid storm with cardiac arrest

    Directory of Open Access Journals (Sweden)

    Nakashima Y

    2014-05-01

    Full Text Available Yutaka Nakashima,1 Tsuneaki Kenzaka,2 Masanobu Okayama,3 Eiji Kajii31Department for Support of Rural Medicine, Yamaguchi Grand Medical Center, 2Division of General Medicine, Center for Community Medicine, Jichi Medical University School of Medicine, Shimotsuke, Japan; 3Division of Community and Family Medicine, Center for Community Medicine, Jichi Medical University School of Medicine, Shimotsuke, JapanAbstract: A 23-year-old man became unconscious while jogging. He immediately received basic life support from a bystander and was transported to our hospital. On arrival, his spontaneous circulation had returned from a state of ventricular fibrillation and pulseless electrical activity. Following admission, hyperthyroidism led to a suspicion of thyroid storm, which was then diagnosed as a possible cause of the cardiac arrest. Although hyperthyroidism-induced cardiac arrest including ventricular fibrillation is rare, it should be considered when diagnosing the cause of treatable cardiac arrest.Keywords: hyperthyroidism, ventricular fibrillation, treatable cardiac arrest, cardiac arrest, cardiopulmonary arrest

  8. Hydroxylated PBDEs induce developmental arrest in zebrafish

    Energy Technology Data Exchange (ETDEWEB)

    Usenko, Crystal Y., E-mail: Crystal_usenko@baylor.edu; Hopkins, David C.; Trumble, Stephen J., E-mail: Stephen_trumble@baylor.edu; Bruce, Erica D., E-mail: Erica_bruce@baylor.edu

    2012-07-01

    The ubiquitous spread of polybrominated diphenyl ethers (PBDEs) has led to concerns regarding the metabolites of these congeners, in particular hydroxylated PBDEs. There are limited studies regarding the biological interactions of these chemicals, yet there is some concern they may be more toxic than their parent compounds. In this study three hydroxylated PBDEs were assessed for toxicity in embryonic zebrafish: 3-OH-BDE 47, 5-OH-BDE 47, and 6-OH-BDE 47. All three congeners induced developmental arrest in a concentration-dependent manner; however, 6-OH-BDE 47 induced adverse effects at lower concentrations than the other congeners. Furthermore, all three induced cell death; however apoptosis was not observed. In short-term exposures (24–28 hours post fertilization), all hydroxylated PBDEs generated oxidative stress in the region corresponding to the cell death at 5 and 10 ppm. To further investigate the short-term effects that may be responsible for the developmental arrest observed in this study, gene regulation was assessed for embryos exposed to 0.625 ppm 6-OH-BDE 47 from 24 to 28 hpf. Genes involved in stress response, thyroid hormone regulation, and neurodevelopment were significantly upregulated compared to controls; however, genes related to oxidative stress were either unaffected or downregulated. This study suggests that hydroxylated PBDEs disrupt development, and may induce oxidative stress and potentially disrupt the cholinergic system and thyroid hormone homeostasis. -- Highlights: ► OH-PBDEs induce developmental arrest in a concentration-dependent manner. ► Hydroxyl group location influences biological interaction. ► OH-PBDEs induce oxidative stress. ► Thyroid hormone gene regulation was disrupted following exposure. ► To our knowledge, this is the first whole organism study of OH-PBDE toxicity.

  9. Experimental and theoretical investigations on the behaviour of cracks in primary coolant piping

    International Nuclear Information System (INIS)

    Steinbuch, R.; Bartholome, G.; Felski, N.; Kastner, W.

    1981-01-01

    During the investigations of the government-sponsored R+D programs (RS 104 and RS 320) experimental and theoretical work has been performed to describe the leak before break behaviour and the extent of instable crack growth. The test pipes are 300 mm ID pipes made of 20MnMoNi55. Three of them had been welded to a pressure reservoir to simulate the situation of a real system of piping and components as related to hydrodynamics. The instrumentation of the specimen was designed to describe - temperature and pressure during failure - effect of reservoir on depressurisation - motion of the pipe - leakage area as function of time - crack arrest length. At two experiments the pressure dropped to saturation but in others for a short period the pressure was remarkably lower. (orig./GL)

  10. Application of Interfacial Propagation and Kinking Crack Concept to ECC/Concrete Overlay Repair System

    Directory of Open Access Journals (Sweden)

    Yaw ChiaHwan

    2014-01-01

    Full Text Available Research on the application of ultraductile engineered cementitious composite (ECC as overlay in the repair of deteriorated concrete structures is performed in this paper. Also, interfacial crack kinking and trapping mechanism experimentally observed in ECC/concrete overlay repair system are described by comparison of toughness and energy release rate. The mechanism involves cycles of extension, kinking, and arrest of interfacial crack into the overlay. Experimental testing of overlay repair system reveals significant improvements in load carrying capacity and ductility over conventional concrete overlay. The commonly observed overlay system failure mode of delamination or spalling is eliminated when ECC is applied. These failure modes are suppressed when ECC is used as an ideal and durable candidate overlay repair material.

  11. On methodology

    DEFF Research Database (Denmark)

    Cheesman, Robin; Faraone, Roque

    2002-01-01

    This is an English version of the methodology chapter in the authors' book "El caso Berríos: Estudio sobre información errónea, desinformación y manipulación de la opinión pública".......This is an English version of the methodology chapter in the authors' book "El caso Berríos: Estudio sobre información errónea, desinformación y manipulación de la opinión pública"....

  12. Delayed hydride cracking: theoretical model testing to predict cracking velocity

    International Nuclear Information System (INIS)

    Mieza, Juan I.; Vigna, Gustavo L.; Domizzi, Gladys

    2009-01-01

    Pressure tubes from Candu nuclear reactors as any other component manufactured with Zr alloys are prone to delayed hydride cracking. That is why it is important to be able to predict the cracking velocity during the component lifetime from parameters easy to be measured, such as: hydrogen concentration, mechanical and microstructural properties. Two of the theoretical models reported in literature to calculate the DHC velocity were chosen and combined, and using the appropriate variables allowed a comparison with experimental results of samples from Zr-2.5 Nb tubes with different mechanical and structural properties. In addition, velocities measured by other authors in irradiated materials could be reproduced using the model described above. (author)

  13. Comparison of thermal cracking and hydro-cracking yield distributions

    Energy Technology Data Exchange (ETDEWEB)

    Romero, S.; Sayles, S. [KBC Advanced Technologies Inc., Houston, TX (United States)

    2009-07-01

    Operators of bitumen upgraders are faced with the challenge of obtaining maximum performance from existing equipment whose performance is already pushed to the limits. The main constraint is the primary upgrader processes, notably coking and hydrocracking. Under the current economic conditions, funding for new equipment is difficult. However, changes can be made to optimize unit performance by better understanding the basic kinetics in thermal cracking and hydrocracking. This paper reviewed the yield distribution differences between thermal cracking and hydrocracking to provide insight into the basic components of operational changes. The objective was to compare yields, product quality distributions and the elemental balances. The opportunities to increase production and improve performance were then analyzed quantitatively within the existing unit equipment limits. tabs., figs.

  14. Damage Mechanisms and Controlled Crack Propagation in a Hot Pressed Silicon Nitride Ceramic. Ph.D. Thesis - Northwestern Univ., 1993

    Science.gov (United States)

    Calomino, Anthony Martin

    1994-01-01

    The subcritical growth of cracks from pre-existing flaws in ceramics can severely affect the structural reliability of a material. The ability to directly observe subcritical crack growth and rigorously analyze its influence on fracture behavior is important for an accurate assessment of material performance. A Mode I fracture specimen and loading method has been developed which permits the observation of stable, subcritical crack extension in monolithic and toughened ceramics. The test specimen and procedure has demonstrated its ability to generate and stably propagate sharp, through-thickness cracks in brittle high modulus materials. Crack growth for an aluminum oxide ceramic was observed to be continuously stable throughout testing. Conversely, the fracture behavior of a silicon nitride ceramic exhibited crack growth as a series of subcritical extensions which are interrupted by dynamic propagation. Dynamic initiation and arrest fracture resistance measurements for the silicon nitride averaged 67 and 48 J/sq m, respectively. The dynamic initiation event was observed to be sudden and explosive. Increments of subcritical crack growth contributed to a 40 percent increase in fracture resistance before dynamic initiation. Subcritical crack growth visibly marked the fracture surface with an increase in surface roughness. Increments of subcritical crack growth loosen ceramic material near the fracture surface and the fracture debris is easily removed by a replication technique. Fracture debris is viewed as evidence that both crack bridging and subsurface microcracking may be some of the mechanisms contributing to the increase in fracture resistance. A Statistical Fracture Mechanics model specifically developed to address subcritical crack growth and fracture reliability is used together with a damaged zone of material at the crack tip to model experimental results. A Monte Carlo simulation of the actual experiments was used to establish a set of modeling input

  15. Preliminary results on the fracture analysis of multi-site cracking of lap joints in aircraft skins

    Science.gov (United States)

    Beuth, J. L., Jr.; Hutchinson, John W.

    1992-07-01

    Results of a fracture mechanics analysis relevant to fatigue crack growth at rivets in lap joints of aircraft skins are presented. Multi-site damage (MSD) is receiving increased attention within the context of problems of aging aircraft. Fracture analyses previously carried out include small-scale modeling of rivet/skin interactions, larger-scale two-dimensional models of lap joints similar to that developed here, and full scale three-dimensional models of large portions of the aircraft fuselage. Fatigue testing efforts have included flat coupon specimens, two-dimensional lap joint tests, and full scale tests on specimens designed to closely duplicate aircraft sections. Most of this work is documented in the proceedings of previous symposia on the aging aircraft problem. The effect MSD has on the ability of skin stiffeners to arrest the growth of long skin cracks is a particularly important topic that remains to be addressed. One of the most striking features of MSD observed in joints of some test sections and in the joints of some of the older aircraft fuselages is the relative uniformity of the fatigue cracks from rivet to rivet along an extended row of rivets. This regularity suggests that nucleation of the cracks must not be overly difficult. Moreover, it indicates that there is some mechanism which keeps longer cracks from running away from shorter ones, or, equivalently, a mechanism for shorter cracks to catch-up with longer cracks. This basic mechanism has not been identified, and one of the objectives of the work is to see to what extent the mechanism is revealed by a fracture analysis of the MSD cracks. Another related aim is to present accurate stress intensity factor variations with crack length which can be used to estimate fatigue crack growth lifetimes once cracks have been initiated. Results are presented which illustrate the influence of load shedding from rivets with long cracks to neighboring rivets with shorter cracks. Results are also included

  16. Evaluation of throughwall crack pipes under displacement controlled loading

    Energy Technology Data Exchange (ETDEWEB)

    Zahoor, A.

    1987-02-01

    Tearing modulus solutions are developed for flawed throughwall pipes subjected to displacement controlled loading. Two cases of loading were considered: (1) a displacement controlled bending loading, and (2) a displacement controlled axial tension loading. A revised version of the EPRI J-integral estimation scheme is used in the development of the solutions. These solutions can be used for the entire range of elastic-plastic loading, from linear elastic, contained yielding, to large scale yielding of the crack section. Experimental data from pipes in bending were used to assess the accuracy of the compliant loading solutions. The evaluations were performed using elastic plastic J-integral (J) and tearing modulus (T) analysis methods. These solutions are shown to have good accuracy when used to predict the experimental results. The methodology and procedure can also be applied to part-throughwall cracks. These solutions have application to the leak before break fracture mechanics analyses.

  17. Evaluation of throughwall crack pipes under displacement controlled loading

    International Nuclear Information System (INIS)

    Zahoor, A.

    1987-01-01

    Tearing modulus solutions are developed for flawed throughwall pipes subjected to displacement controlled loading. Two cases of loading were considered: (1) a displacement controlled bending loading, and (2) a displacement controlled axial tension loading. A revised version of the EPRI J-integral estimation scheme is used in the development of the solutions. These solutions can be used for the entire range of elastic-plastic loading, from linear elastic, contained yielding, to large scale yielding of the crack section. Experimental data from pipes in bending were used to assess the accuracy of the compliant loading solutions. The evaluations were performed using elastic plastic J-integral (J) and tearing modulus (T) analysis methods. These solutions are shown to have good accuracy when used to predict the experimental results. The methodology and procedure can also be applied to part-throughwall cracks. These solutions have application to the leak before break fracture mechanics analyses. (orig.)

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

    Directory of Open Access Journals (Sweden)

    Tong Di-Hua

    2014-04-01

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

  19. Crack modeling of rotating blades with cracked hexahedral finite element method

    Science.gov (United States)

    Liu, Chao; Jiang, Dongxiang

    2014-06-01

    Dynamic analysis is the basis in investigating vibration features of cracked blades, where the features can be applied to monitor health state of blades, detect cracks in an early stage and prevent failures. This work presents a cracked hexahedral finite element method for dynamic analysis of cracked blades, with the purpose of addressing the contradiction between accuracy and efficiency in crack modeling of blades in rotor system. The cracked hexahedral element is first derived with strain energy release rate method, where correction of stress intensity factors of crack front and formulation of load distribution of crack surface are carried out to improve the modeling accuracy. To consider nonlinear characteristics of time-varying opening and closure effects caused by alternating loads, breathing function is proposed for the cracked hexahedral element. Second, finite element method with contact element is analyzed and used for comparison. Finally, validation of the cracked hexahedral element is carried out in terms of breathing effects of cracked blades and natural frequency in different crack depths. Good consistency is acquired between the results with developed cracked hexahedral element and contact element, while the computation time is significantly reduced in the previous one. Therefore, the developed cracked hexahedral element achieves good accuracy and high efficiency in crack modeling of rotating blades.

  20. Acquisition of Inertia by a Moving Crack

    Science.gov (United States)

    Goldman, Tamar; Livne, Ariel; Fineberg, Jay

    2010-03-01

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

  1. Factors controlling nitrate cracking of mild steel

    International Nuclear Information System (INIS)

    Donovan, J.A.

    1977-01-01

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

  2. Crack Propagation by Finite Element Method

    Directory of Open Access Journals (Sweden)

    Luiz Carlos H. Ricardo

    2018-01-01

    Full Text Available Crack propagation simulation began with the development of the finite element method; the analyses were conducted to obtain a basic understanding of the crack growth. Today structural and materials engineers develop structures and materials properties using this technique. The aim of this paper is to verify the effect of different crack propagation rates in determination of crack opening and closing stress of an ASTM specimen under a standard suspension spectrum loading from FDandE SAE Keyhole Specimen Test Load Histories by finite element analysis. To understand the crack propagation processes under variable amplitude loading, retardation effects are observed

  3. 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)

  4. A method for crack sizing using Bayesian inference arising in eddy current testing

    International Nuclear Information System (INIS)

    Kojima, Fumio; Kikuchi, Mitsuhiro

    2008-01-01

    This paper is concerned with a sizing methodology of crack using Bayesian inference arising in eddy current testing. There is often uncertainty about data through quantitative measurements of nondestructive testing and this can yield misleading inference of crack sizing at on-site monitoring. In this paper, we propose optimal strategies of measurements in eddy current testing using Bayesian prior-to-posteriori analysis. First our likelihood functional is given by Gaussian distribution with the measurement model based on the hybrid use of finite and boundary element methods. Secondly, given a priori distributions of crack sizing, we propose a method for estimating the region of interest for sizing cracks. Finally an optimal sensing method is demonstrated using our idea. (author)

  5. Pathological links between stroke and cardiac arrest

    Institute of Scientific and Technical Information of China (English)

    Shaila Ghanekar; Sydney Corey; Trenton Lippert; Cesar V.Borlongan

    2017-01-01

    There may be a pathological connection between cardiac failure and ischemic stroke.In this article we describe pertinent research that demonstrates subsequent death of cardiac and neural myocytes in the post ischemic stroke brain.Current stroke therapy overlooks the connection between cardiac and cerebrovascular events and fails to address the shared risk factors.Current pre-clinical stroke investigations have provided evidence that suggests the presence of an indirect cell death pathway in which toxic molecules emanate from the stroke brain and trigger cardiac cell death.On the other hand,other studies highlight the presence of a reverse cell death cascade in which toxic molecules from the heart,following cardiac arrest,travel to the brain and induce ischemic cell death.Further examination of these putative cell death pathways between ischemic stroke and cardiac arrest will prompt the advancement of innovative treatments specifically targeting both diseases,leading to ameliorated clinical results of patients diagnosed with heart failure and ischemic stroke.

  6. Cerebral intolerance during flow arrested carotid angioplasty.

    Science.gov (United States)

    St Louis, Myron; Park, Brian D; Dahn, Michael; Bozeman, Patricia

    2012-01-01

    The use of flow arrest as a means of providing cerebral protection during carotid angioplasty offers the advantages of improved efficiency of debris removal and the ability to provide protection under unfavorable (tortuous) anatomic circumstances. However, in contrast to the filtration methods of cerebral protection, this modality requires complete interruption of antegrade carotid artery flow during balloon angioplasty and stent deployment. We report our experience with 9 patients undergoing carotid angioplasty with the Mo.Ma device, which utilizes common and external carotid artery balloon occlusion during the angioplasty procedure. We assessed the clinical outcomes and intraprocedural hemodynamic data. The average duration of carotid occlusion was 8.3 minutes. Of the 9 patients, 2 patients (22%) experienced cerebral intolerance. No stroke occurred in this patient cohort. There appeared to be a poor relationship between procedure intolerance and the presence of significant contralateral stenosis or low carotid back pressure. Furthermore, the incidence of postangioplasty hypotension was not clearly related to cerebral intolerance. Carotid angioplasty with stenting can be safely conducted with flow arrest as an alternative to filter-type cerebral protection devices. However, because cerebral intolerance is not an infrequent occurrence with this approach, clinicians must be cognizant of management strategies for transient cerebral intolerance.

  7. Environmentally assisted cracking of LWR materials

    International Nuclear Information System (INIS)

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Shack, W.J.

    1995-12-01

    Research on environmentally assisted cracking (EAC) of light water reactor materials has focused on (a) fatigue initiation in pressure vessel and piping steels, (b) crack growth in cast duplex and austenitic stainless steels (SSs), (c) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs, and (d) EAC in high- nickel alloys. The effect of strain rate during different portions of the loading cycle on fatigue life of carbon and low-alloy steels in 289 degree C water was determined. Crack growth studies on wrought and cast SSs have been completed. The effect of dissolved-oxygen concentration in high-purity water on IASCC of irradiated Type 304 SS was investigated and trace elements in the steel that increase susceptibility to intergranular cracking were identified. Preliminary results were obtained on crack growth rates of high-nickel alloys in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320 degree C. The program on Environmentally Assisted Cracking of Light Water Reactor Materials is currently focused on four tasks: fatigue initiation in pressure vessel and piping steels, fatigue and environmentally assisted crack growth in cast duplex and austenitic SS, irradiation-assisted stress corrosion cracking of austenitic SSs, and environmentally assisted crack growth in high-nickel alloys. Measurements of corrosion-fatigue crack growth rates (CGRs) of wrought and cast stainless steels has been essentially completed. Recent progress in these areas is outlined in the following sections

  8. 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)

  9. Ductile fracture prediction of an axially cracked pressure vessel under pressurized thermal shock

    International Nuclear Information System (INIS)

    Takahashi, Jun; Okamura, Hiroyuki

    1991-01-01

    In this paper, the J-value of an axially cracked cylinder under several PTS conditions are evaluated using a simple estimation scheme which we proposed. Results obtained are summerized as follow: (1) Under any PTS conditions, the effect of internal pressure is so predominant upon the J-value and dJ/da that it is very important to grasp the transient of internal pressure under any imaginable accident from the viewpoint of structural integrity. (2) Under any IP, TS, and PTS conditions, J - a/W relation shows that the J-value reaches its maximum at a certain crack depth, then drops to zero at a/W ≅ 0.9. Though the effect of inertia is not taken into account, this fact may explain the phenomena of crack arrest qualitatively. (3) The compliance of a cylindrical shell plays an important role in the fracture prediction of a pressure vessel. (4) Under typical PTS conditions, the region at the crack tip dominated by the Hutchinson-Rice-Rosengren singularity is substantially large enough to apply the J-based criterion to predict unstable ductile fracture. (author)

  10. The perception of children of elementary education about cardiorespiratory arrest

    Directory of Open Access Journals (Sweden)

    Mariélli Terassi

    2015-03-01

    Full Text Available Cardiorespiratory arrest (CRA is a serious situation that occurs frequently in public environments, which makes assistance training of the general population of great importance. The objective was to understand the perception of children on CRA. Qualitative research conducted with children 8-10 years old enrolled in a private elementary school with a constructive proposal. Data collection occurred between the months of October and November 2013 in a recorded collective interview. As a criterion for inclusion students should be enrolled in the institution and accept to participate in the research with the consent of a guardian. Thirty children participated in the study. The students were divided into four groups: 5th year, 4th year, 3rd year A and 3rd year B, with an average of 08 students per group. The interviews were analyzed using the Bardin content analysis methodology. From the speeches, two categories emerged: Child's prior knowledge on CRA and how to act on the event of a CRA. Children associate the event of sudden CRA to a condition in which the heart and/or lungs suddenly stop acting. Seeking emergency assistance was reported as one of the main actions to be taken if a person is unconscious. It was observed that the 5th graders had best prior knowledge about the topic CRA when compared to students in the 3rd year. The thematic approach of CRA in schools contributes to the exchange of experiences, awareness of children and building new knowledge-oriented health education.

  11. Nonlocal Effects of Crack Curving.

    Science.gov (United States)

    1982-07-01

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

  12. Aluminum alloy weldability. Identification of weld solidification cracking mechanisms through novel experimental technique and model development

    Energy Technology Data Exchange (ETDEWEB)

    Coniglio, Nicolas

    2008-07-01

    The objective of the present thesis is to make advancements in understanding solidification crack formation in aluminum welds, by investigating in particular the aluminum 6060/4043 system. Alloy 6060 is typical of a family of Al-Mg-Si extrusion alloys, which are considered weldable only when using an appropriate filler alloy such as 4043 (Al-5Si). The effect of 4043 filler dilution (i.e. weld metal silicon content) on cracking sensitivity and solidification path of Alloy 6060 welds are investigated. Afterwards, cracking models are developed to propose mechanisms for solidification crack initiation and growth. Cracking Sensitivity. Building upon the concept that silicon improves weldability and that weldability can be defined by a critical strain rate, strain rate-composition combinations required for solidification crack formation in the Al- 6060/4043 system were determined using the newly developed Controlled Tensile Weldability (CTW) test utilizing local strain extensometer measurements. Results, presented in a critical strain rate - dilution map, show a crack - no crack boundary which reveals that higher local strain rates require higher 4043 filler dilution to avoid solidification cracking when arc welding Alloy 6060. Using the established crack - no crack boundary as a line of reference, additional parameters were examined and their influence on cracking characterized. These parameter influences have included studies of weld travel speed, weld pool contaminants (Fe, O, and H), and grain refiner additions (TiAl{sub 3} + Boron). Each parameter has been independently varied and its effect on cracking susceptibility quantified in terms of strain rate - composition combinations. Solidification Path. Solidification path of the Al-6060/4043 system was characterized using thermal analysis and phase identification. Increasing 4043 filler dilution from 0 to 16% in Alloy 6060 arc welds resulted in little effect on thermal arrests and microstructure, no effect on

  13. Hydrogen-induced cracking: 2

    International Nuclear Information System (INIS)

    Puls, M.P.

    1984-12-01

    There is a strong motivation for understanding the factors controlling zirconium hydride reorientation under stress because of the important role this plays in hydrogen-induced crack growth and/or crack initiation in zirconium and its alloys, particularly under thermal cycling conditions. Following an approach developed by Sauthoff, an analysis of the orienting effect of external stress on the nucleation, growth and coarsening of γ- and delta-zirconium hydride precipitates in zirconium and its alloys is presented. The analysis is based on a previous theoretical study of some of the factors affecting hydride solubility in stressed and unstressed solids. Expressions are derived for the effect of stress on nucleation, growth and coarsening. We conclude, on the basis of these that the preferential orientation of hydride precipitates under stress is most efficient during the nucleation stage. The reason for this is that the overall driving force for nucleation, for the chosen parameters and the usual experimental conditions, is fairly small. Therefore, the driving force for orientating under stress can be a substantial fraction of the overall driving force. The analysis shows that hydride growth is unlikely to play a role in preferential orientation, but coarsening could be important under carefully chosen experimental conditions, which may be relevant to the hydride-cracking process

  14. The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

    Science.gov (United States)

    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.

  15. Hypothermia after cardiac arrest should be further evaluated-A systematic review of randomised trials with meta-analysis and trial sequential analysis

    DEFF Research Database (Denmark)

    Nielsen, Niklas; Friberg, Hans; Gluud, Christian

    2011-01-01

    BACKGROUND: Guidelines recommend mild induced hypothermia (MIH) to reduce mortality and neurological impairment after out-of-hospital cardiac arrest. Our objective was to systematically evaluate the evidence for MIH taking into consideration the risks of systematic and random error and to GRADE...... the evidence. METHODS: Systematic review with meta-analysis and trial sequential analysis of randomised trials evaluating MIH after cardiac arrest in adults. We searched CENTRAL, MEDLINE, and EMBASE databases until May 2009. Retrieved trials were evaluated with Cochrane methodology. Meta-analytic estimates....... The substantial risk of bias and concerns with directness rated down the quality of the evidence to low. CONCLUSIONS: Evidence regarding MIH after out-of-hospital cardiac arrest is still inconclusive and associated with non-negligible risks of systematic and random errors. Using GRADE-methodology, we conclude...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-06-15

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

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

    Science.gov (United States)

    Hughes, Cris E; White, Crystal A

    2009-03-01

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

  18. Vibration based algorithm for crack detection in cantilever beam containing two different types of cracks

    Science.gov (United States)

    Behzad, Mehdi; Ghadami, Amin; Maghsoodi, Ameneh; Michael Hale, Jack

    2013-11-01

    In this paper, a simple method for detection of multiple edge cracks in Euler-Bernoulli beams having two different types of cracks is presented based on energy equations. Each crack is modeled as a massless rotational spring using Linear Elastic Fracture Mechanics (LEFM) theory, and a relationship among natural frequencies, crack locations and stiffness of equivalent springs is demonstrated. In the procedure, for detection of m cracks in a beam, 3m equations and natural frequencies of healthy and cracked beam in two different directions are needed as input to the algorithm. The main accomplishment of the presented algorithm is the capability to detect the location, severity and type of each crack in a multi-cracked beam. Concise and simple calculations along with accuracy are other advantages of this method. A number of numerical examples for cantilever beams including one and two cracks are presented to validate the method.

  19. Methodological guidelines

    International Nuclear Information System (INIS)

    Halsnaes, K.; Callaway, J.M.; Meyer, H.J.

    1999-01-01

    The guideline document establishes a general overview of the main components of climate change mitigation assessment. This includes an outline of key economic concepts, scenario structure, common assumptions, modelling tools and country study assumptions. The guidelines are supported by Handbook Reports that contain more detailed specifications of calculation standards, input assumptions and available tools. The major objectives of the project have been provided a methodology, an implementing framework and a reporting system which countries can follow in meeting their future reporting obligations under the FCCC and for GEF enabling activities. The project builds upon the methodology development and application in the UNEP National Abatement Coasting Studies (UNEP, 1994a). The various elements provide countries with a road map for conducting climate change mitigation studies and submitting national reports as required by the FCCC. (au) 121 refs

  20. Methodological guidelines

    Energy Technology Data Exchange (ETDEWEB)

    Halsnaes, K.; Callaway, J.M.; Meyer, H.J.

    1999-04-01

    The guideline document establishes a general overview of the main components of climate change mitigation assessment. This includes an outline of key economic concepts, scenario structure, common assumptions, modelling tools and country study assumptions. The guidelines are supported by Handbook Reports that contain more detailed specifications of calculation standards, input assumptions and available tools. The major objectives of the project have been provided a methodology, an implementing framework and a reporting system which countries can follow in meeting their future reporting obligations under the FCCC and for GEF enabling activities. The project builds upon the methodology development and application in the UNEP National Abatement Coasting Studies (UNEP, 1994a). The various elements provide countries with a road map for conducting climate change mitigation studies and submitting national reports as required by the FCCC. (au) 121 refs.

  1. Association of National Initiatives to Improve Cardiac Arrest Management With Rates of Bystander Intervention and Patient Survival After Out-of-Hospital Cardiac Arrest

    DEFF Research Database (Denmark)

    Wissenberg, Mads; Lippert, Freddy K; Folke, Fredrik

    2013-01-01

    resuscitation was attempted were identified between 2001 and 2010 in the nationwide Danish Cardiac Arrest Registry. Of 29 111 patients with cardiac arrest, we excluded those with presumed noncardiac cause of arrest (n = 7390) and those with cardiac arrests witnessed by emergency medical services personnel (n...

  2. Performance of Surge Arrester Installation to Enhance Protection

    Directory of Open Access Journals (Sweden)

    Mbunwe Muncho Josephine

    2017-01-01

    Full Text Available The effects of abnormal voltages on power system equipment and appliances in the home have raise concern as most of the equipments are very expensive. Each piece of electrical equipment in an electrical system needs to be protected from surges. To prevent damage to electrical equipment, surge protection considerations are paramount to a well designed electrical system. Lightning discharges are able to damage electric and electronic devices that usually have a low protection level and these are influenced by current or voltage pulses with a relatively low energy, which are induced by lightning currents. This calls for proper designed and configuration of surge arresters for protection on the particular appliances. A more efficient non-linear surge arrester, metal oxide varistor (MOV, should be introduced to handle these surges. This paper shows the selection of arresters laying more emphasis on the arresters for residential areas. In addition, application and installation of the arrester will be determined by the selected arrester. This paper selects the lowest rated surge arrester as it provides insulation when the system is under stress. It also selected station class and distribution class of arresters as they act as an open circuit under normal system operation and to bring the system back to its normal operation mode as the transient voltage is suppressed. Thus, reduces the risk of damage, which the protection measures can be characterized, by the reduction value of the economic loss to an acceptable level.

  3. Cardiac arrest during anesthesia at a University Hospital in Nigeria ...

    African Journals Online (AJOL)

    Background: We assessed the incidence and outcomes of cardiac arrest during anesthesia in the operating room at our university hospital. A previous study on intraoperative cardiac arrests covered a period from 1994-1998 and since then; anesthetic personnel, equipment, and workload have increased remarkably.

  4. Efficacy of silver diamine fluoride for Arresting Caries Treatment.

    NARCIS (Netherlands)

    Yee, R.T.F.; Holmgren, C.J.; Mulder, J.; Lama, D.; Walker, D.; Palenstein Helderman, W.H. van

    2009-01-01

    Arresting Caries Treatment (ACT) has been proposed to manage untreated dental caries in children. This prospective randomized clinical trial investigated the caries-arresting effectiveness of a single spot application of: (1) 38% silver diamine fluoride (SDF) with tannic acid as a reducing agent;

  5. Cooling the crisis: Therapeutic hypothermia after sickle cardiac arrest

    NARCIS (Netherlands)

    Metske, Hennie A.; Postema, Pieter G.; Biemond, Bart J.; Bouman, Catherine S. C.

    2012-01-01

    Objective: The management of patients with sickle-cell disease and cardiac arrest presents special challenges. Mild therapeutic hypothermia may improve survival and neurologic outcome after cardiac arrest, however, it may also precipitate sickling in patients with sickle-cell disease. Rigorous

  6. 29 CFR 1915.159 - Personal fall arrest systems (PFAS).

    Science.gov (United States)

    2010-07-01

    ... 29 Labor 7 2010-07-01 2010-07-01 false Personal fall arrest systems (PFAS). 1915.159 Section 1915... Protective Equipment (PPE) § 1915.159 Personal fall arrest systems (PFAS). The criteria of this section apply to PFAS and their use. Effective January 1, 1998, body belts and non-locking snaphooks are not...

  7. Application of acoustic emission to hydride cracking

    International Nuclear Information System (INIS)

    Sagat, S.; Ambler, J.F.R.; Coleman, C.E.

    1986-07-01

    Acoustic emission has been used for over a decade to study delayed hydride cracking (DHC) in zirconium alloys. At first acoustic emission was used primarily to detect the onset of DHC. This was possible because DHC was accompanied by very little plastic deformation of the material and furthermore the amplitudes of the acoustic pulses produced during cracking of the brittle hydride phase were much larger than those from dislocation motion and twinning. Acoustic emission was also used for measuring crack growth when it was found that for a suitable amplitude threshold, the total number of acoustic emission counts was linearly related to the cracked area. Once the proportionality constant was established, the acoustic counts could be converted to the crack length. Now the proportionality between the count rate and the crack growth rate is used to provide feedback between the crack length and the applied load, using computer technology. In such a system, the stress at the crack tip can be maintained constant during the test by adjusting the applied load as the crack progresses, or it can be changed in a predetermined manner, for example, to measure the threshold stress for cracking

  8. Fatigue crack propagation behavior under creep conditions

    International Nuclear Information System (INIS)

    Ohji, Kiyotsugu; Kubo, Shiro

    1991-01-01

    The crack propagation behavior of the SUS 304 stainless steel under creep-fatigue conditions was reviewed. Cracks propagated either in purely time-dependent mode or in purely cycle-dependent mode, depending on loading conditions. The time-dependent crack propagation rate was correlated with modified J-integral J * and the cycle-dependent crack propagation rate was correlated with J-integral range ΔJ f . Threshold was observed in the cycle-dependent crack propagation, and below this threshold the time-dependent crack propagation appeared. The crack propagation rates were uniquely characterized by taking the effective values of J * and ΔJ f , when crack closure was observed. Change in crack propagation mode occurred reversibly and was predicted by the competitive damage model. The threshold disappeared and the cycle-dependent crack propagation continued in a subthreshold region under variable amplitude conditions, where the threshold was interposed between the maximum and minimum ΔJ f . (orig.)

  9. Cracking and load-deformation behavior of fiber reinforced concrete: Influence of testing method

    DEFF Research Database (Denmark)

    Paegle, Ieva; Minelli, Fausto; Fischer, Gregor

    2016-01-01

    cementitious composites with strain hardening and strain softening behavior. Digital Image Correlation was utilized in the experimental program to detect and quantify the formation of cracks. Results show that the different test methodologies valuate specific aspects of material performance. The outcome...

  10. 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

  11. Maturation arrest of human oocytes at germinal vesicle stage

    Directory of Open Access Journals (Sweden)

    Zhi Qin Chen

    2010-01-01

    Full Text Available Maturation arrest of human oocytes may occur at various stages of the cell cycle. A total failure of human oocytes to complete meiosis is rarely observed during assisted conception cycles. We describe here a case of infertile couples for whom all oocytes repeatedly failed to mature at germinal vesicle (GV stage during in vitro fertilization/Intra cytoplasmic sperm injection (IVF/ICSI. The patient underwent controlled ovarian stimulation followed by oocyte retrieval and IVF/ICSI. The oocytes were stripped off cumulus cells prior to the ICSI procedure and their maturity status was defined. The oocyte maturation was repeatedly arrested at the GV. Oocyte maturation arrest may be the cause of infertility in this couple. The recognition of oocyte maturation arrest as a specific medical condition may contribute to the characterization of the currently known as "oocyte factor." The cellular and genetic mechanisms causing oocyte maturation arrest should be the subject for further investigation.

  12. Growth arrest specific protein (GAS) 6

    DEFF Research Database (Denmark)

    Haase, T N; Rasmussen, Morten; Jaksch, C A M

    2013-01-01

    using RNA microarray and quantitative PCR. The role of a differentially expressed gene, growth arrest specific protein 6 (GAS6), was evaluated in vitro using neonatal rat islets. Results The mRNA level of Gas6, known to be mitogenic in other tissues, was reduced in LP offspring. The mRNA content of Mafa...... was increased in LP offspring suggesting an early maturation of beta cells. When applied in vitro, GAS6 increased proliferation of neonatal pancreatic beta cells, while reducing glucose-stimulated insulin secretion without changing the total insulin content of the islets. In addition, GAS6 decreased the m......RNA content of Mafa. Conclusions/interpretation We propose a role for GAS6 in the regulation of pancreatic beta cells in the critical period around the time of birth. Our results support the hypothesis that the reduced beta cell mass seen in LP offspring is caused by a change in the intra-uterine environment...

  13. Structural arrest in an ideal gas.

    Science.gov (United States)

    van Ketel, Willem; Das, Chinmay; Frenkel, Daan

    2005-04-08

    We report a molecular dynamics study of a simple model system that has the static properties of an ideal gas, yet exhibits nontrivial "glassy" dynamics behavior at high densities. The constituent molecules of this system are constructs of three infinitely thin hard rods of length L, rigidly joined at their midpoints. The crosses have random but fixed orientation. The static properties of this system are those of an ideal gas, and its collision frequency can be computed analytically. For number densities NL(3)/V>1, the single-particle diffusivity goes to zero. As the system is completely structureless, standard mode-coupling theory cannot describe the observed structural arrest. Nevertheless, the system exhibits many dynamical features that appear to be mode-coupling-like. All high-density incoherent intermediate scattering functions collapse onto master curves that depend only on the wave vector.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-08-15

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

  15. ERC initiatives to reduce the burden of cardiac arrest: the European Cardiac Arrest Awareness Day.

    Science.gov (United States)

    Georgiou, Marios; Lockey, Andrew S

    2013-09-01

    The rate of survival from out-of-hospital cardiac arrest in Europe remains unacceptably low and could be increased by better bystander cardiopulmonary resuscitation (CPR) rates. The European Resuscitation Council has announced that there will be a European Cardiac Arrest Awareness Day every year on the 16th of October. This is to coincide with the goals of the Written Declaration passed by the European Parliament in June 2012 that emphasised the importance of equal access to CPR and automated external defibrillator (AED) training. The topic of this year's Awareness Day is 'Children Saving Lives' and it is hoped that all national resuscitation councils will promote awareness of the benefits of training all children in CPR and AED use and lobby for legislative change to ensure that all children receive this training. Children are not just the adults of tomorrow - they are the lifesavers of today and tomorrow. Copyright © 2013 Elsevier Ltd. All rights reserved.

  16. Prehospital cardiac arrest survival and neurologic recovery.

    Science.gov (United States)

    Hillis, M; Sinclair, D; Butler, G; Cain, E

    1993-01-01

    Many studies of prehospital defibrillation have been conducted but the effects of airway intervention are unknown and neurologic follow-up has been incomplete. A non-randomized cohort prospective study was conducted to determine the effectiveness of defibrillation in prehospital cardiac arrest. Two ambulance companies in the study area developed a defibrillation protocol and they formed the experimental group. A subgroup of these patients received airway management with an esophageal obturator airway (EOA) or endotracheal intubation (ETT). The control group was composed of patients who suffered a prehospital cardiac arrest and did not receive prehospital defibrillation. All survivors were assessed for residual deficits using the Sickness Impact Profile (SIP) and the Dementia Rating Scale (DRS). A total of 221 patients were studied over a 32-month period. Both the experimental group (N = 161) and the control group (N = 60) were comparable with respect to age, sex distribution, and ambulance response time. Survival to hospital discharge was 2/60 (3.3%) in the control group and 12/161 (6.3%) in the experimental group. This difference is not statistically significant. Survival in the experimental group by airway management technique was basic airway support (3/76 3.9%), EOA (3/67 4.5%), and ETT (6/48 12.5%). The improved effect on survival by ETT management was statistically significant. Survivors had minor differences in memory, work, and recreation as compared to ischemic heart disease patients as measured by the SIP and DRS. No effect of defibrillation was found on survival to hospital discharge. However, endotracheal intubation improved survival in defibrillated patients. Survivors had a good functional outcome.

  17. Crack turning in integrally stiffened aircraft structures

    Science.gov (United States)

    Pettit, Richard Glen

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

  18. On applicability of crack shape characterization rules for multiple in-plane surface cracks

    International Nuclear Information System (INIS)

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

    2009-01-01

    The fracture mechanics assessment parameters, such as the elastic stress intensity factor and the elastic-plastic J-integral, for a surface crack can be significantly affected by adjacent cracks. Regarding such an interaction effect, the relative distance between adjacent cracks, crack aspect ratio and loading condition were known to be important factors for multiple cracks, which affects the fracture mechanics assessment parameters. Although several guidance (ASME Sec. XI, BS7910, British Energy R6 and API RP579) on a crack interaction effect (crack combination rule) have been proposed and used for assessing the interaction effect, each guidance provides different rules for combining multiple surface cracks into a single surface crack. Based on the systematic elastic and elastic-plastic finite element analyses, the present study investigated the acceptability of the crack combination rules provided in the existing guidance, and the relevant recommendations on a crack interaction for in-plane surface cracks in a plate were discussed. To quantify the interaction effect, the elastic stress intensity factor and elastic-plastic J-integral along the crack front were used. As for the loading condition, only axial tension was considered. As a result, BS7910 seems to provide the most relevant crack combination rule for in-plane dual surface cracks, whereas API RP579 provides the most conservative results. In particular, ASME Sec. XI still seems to have some room for a revision to shorten the critical distance between two adjacent cracks for a crack combination. The overall tendency of the elastic-plastic analyses results is identical to that of the elastic analyses results.

  19. The fatigue life and fatigue crack through thickness behavior of a surface cracked plate, 2

    International Nuclear Information System (INIS)

    Nam, Ki-Woo; Fujibayashi, Shinpei; Ando, Kotoji; Ogura, Nobukazu.

    1987-01-01

    Most structures have a region where stresses concentrate, and the probability of fatigue crack initiation may be higher than in other parts. Therefore, to improve the reliability of an LBB design, it is necessary to evaluate the growth and through thickness behavior of fatigue cracks in the stress concentration part. In this paper, a fatigue crack growth test at a stress concentration region has been made on 3 % NiCrMo and HT 80 steel. Stress concentration is caused by a fillet on the plate. The main results obtained are as follows : (1) Before cracking through the plate thickness, stress concentration has a remarkable effect on the fatigue crack growth behavior and it flatens the shape of a surface crack. The crack growth behavior can be explained quantatively by using the Newman-Raju equation and the stress resolving method proposed by ASME B and P Code SecXI. (2) The da/dN-ΔK relation obtained in a stress concentration specimen shows good agreement with that obtained in a surface cracked smooth specimen. (3) It is shown that stress concentration caused by a fillet has little effect on the crack growth rate after cracking through the plate thickness. (4) By using the K value based on eq. (1), (2), particular crack growth behavior and the change in crack shape after cracking through thickness can be explained quantatively. (author)

  20. Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite–pearlite and ferrite–bainite microstructures

    International Nuclear Information System (INIS)

    Guan, Mingfei; Yu, Hao

    2013-01-01

    The roles of microstructure types in fatigue crack growth behaviors in ferrite–pearlite steel and ferrite–bainite steel were investigated. The ferrite–bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite–pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F–P steel could become unstable more ealier compared with that in F–B steel. The fatigue cracks in ferrite–pearlite were more tortuous and could propagate more freely than that in ferrite–bainite microstructures. However, frequent crack branching were observed in ferrite–bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate (da/dN) with stress intensity factor range (ΔK) for F–P and F–B steels was discussed within the Paris region. It was shown that FCG rate of F–P steel was higher than that of F–B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

  1. Mechanical versus manual chest compressions for cardiac arrest.

    Science.gov (United States)

    Brooks, Steven C; Hassan, Nizar; Bigham, Blair L; Morrison, Laurie J

    2014-02-27

    This is the first update of the Cochrane review on mechanical chest compression devices published in 2011 (Brooks 2011). Mechanical chest compression devices have been proposed to improve the effectiveness of cardiopulmonary resuscitation (CPR). To assess the effectiveness of mechanical chest compressions versus standard manual chest compressions with respect to neurologically intact survival in patients who suffer cardiac arrest. We searched the Cochrane Central Register of Controlled Studies (CENTRAL; 2013, Issue 12), MEDLINE Ovid (1946 to 2013 January Week 1), EMBASE (1980 to 2013 January Week 2), Science Citation abstracts (1960 to 18 November 2009), Science Citation Index-Expanded (SCI-EXPANDED) (1970 to 11 January 2013) on Thomson Reuters Web of Science, biotechnology and bioengineering abstracts (1982 to 18 November 2009), conference proceedings Citation Index-Science (CPCI-S) (1990 to 11 January 2013) and clinicaltrials.gov (2 August 2013). We applied no language restrictions. Experts in the field of mechanical chest compression devices and manufacturers were contacted. We included randomised controlled trials (RCTs), cluster RCTs and quasi-randomised studies comparing mechanical chest compressions versus manual chest compressions during CPR for patients with atraumatic cardiac arrest. Two review authors abstracted data independently; disagreement between review authors was resolved by consensus and by a third review author if consensus could not be reached. The methodologies of selected studies were evaluated by a single author for risk of bias. The primary outcome was survival to hospital discharge with good neurological outcome. We planned to use RevMan 5 (Version 5.2. The Nordic Cochrane Centre) and the DerSimonian & Laird method (random-effects model) to provide a pooled estimate for risk ratio (RR) with 95% confidence intervals (95% CIs), if data allowed. Two new studies were included in this update. Six trials in total, including data from 1166

  2. Preloading To Accelerate Slow-Crack-Growth Testing

    Science.gov (United States)

    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.

  3. Crack formation and prevention in colloidal drops

    Science.gov (United States)

    Kim, Jin Young; Cho, Kun; Ryu, Seul-A.; Kim, So Youn; Weon, Byung Mook

    2015-08-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles.

  4. Online Bridge Crack Monitoring with Smart Film

    Directory of Open Access Journals (Sweden)

    Benniu Zhang

    2013-01-01

    Full Text Available Smart film crack monitoring method, which can be used for detecting initiation, length, width, shape, location, and propagation of cracks on real bridges, is proposed. Firstly, the fabrication of the smart film is developed. Then the feasibility of the method is analyzed and verified by the mechanical sensing character of the smart film under the two conditions of normal strain and crack initiation. Meanwhile, the coupling interference between parallel enameled wires of the smart film is discussed, and then low-frequency detecting signal and the custom communication protocol are used to decrease interference. On this basis, crack monitoring system with smart film is designed, where the collected crack data is sent to the remote monitoring center and the cracks are simulated and recurred. Finally, the monitoring system is applied to six bridges, and the effects are discussed.

  5. Fluid structural response of axially cracked cylinders

    International Nuclear Information System (INIS)

    Garnich, M.R.; Simonen, F.A.

    1985-03-01

    The fluid structural (FS) response of a cylindrical pressure vessel to a suddenly occurring longitudinal through-wall crack is predicted. The effects of vessel internals and depressurization of the compressed water on dynamic crack opening displacements are investigated. A three dimensional (3D) structural finite element model is used as a basis for the development of a two dimensional (2D) FS model. A slice of the vessel taken at the crack midspan and normal to the cylinder axis is modeled. Crack opening displacements are compared between the 2D and 3D models, between the different assumptions about fluid depressurization, and between the static and dynamic solutions. The results show that effects of dynamic amplification associated with the sudden opening of the crack in the cylinder are largely offset by the local depressurization of the fluid adjacent to the crack

  6. A probabilistic model of brittle crack formation

    Science.gov (United States)

    Chudnovsky, A.; Kunin, B.

    1987-01-01

    Probability of a brittle crack formation in an elastic solid with fluctuating strength is considered. A set Omega of all possible crack trajectories reflecting the fluctuation of the strength field is introduced. The probability P(X) that crack penetration depth exceeds X is expressed as a functional integral over Omega of a conditional probability of the same event taking place along a particular path. Various techniques are considered to evaluate the integral. Under rather nonrestrictive assumptions, the integral is reduced to solving a diffusion-type equation. A new characteristic of fracture process, 'crack diffusion coefficient', is introduced. An illustrative example is then considered where the integration is reduced to solving an ordinary differential equation. The effect of the crack diffusion coefficient and of the magnitude of strength fluctuations on probability density of crack penetration depth is presented. Practical implications of the proposed model are discussed.

  7. Noncontact fatigue crack evaluation using thermoelastic

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-12-15

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

  8. Numerical Study of Corrosion Crack Opening

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle; Frandsen, Henrik Lund; Svensson, Staffan

    2008-01-01

    is proportional. More recently, the constant of proportionality, the so-called crack-corrosion index, has been studied further with respect to its dependence on the diameter of the reinforcement and the concrete cover. In the present paper the above-mentioned work is presented and extended with more realistic 3D......-models of the cracked concrete beam. The crack-corrosion index is evaluated for a variation of different parameters, i.e. bar diameter, concrete cover, crack length and type of corrosion product. This paper is an extended version of a paper by Thoft-Christensen et al. (2005) presented at the IFIP WG 7.5 Conference...... for the corrosion crack opening. Experiments and theoretical analysis by a numerical method, FEM, support that the relation between the reduction of the reinforcement bar diameter due to corrosion and the corresponding increase in crack width for a given time interval, measured on the surface of a concrete specimen...

  9. MIRD methodology

    International Nuclear Information System (INIS)

    Rojo, Ana M.; Gomez Parada, Ines

    2004-01-01

    The MIRD (Medical Internal Radiation Dose) system was established by the Society of Nuclear Medicine of USA in 1960 to assist the medical community in the estimation of the dose in organs and tissues due to the incorporation of radioactive materials. Since then, 'MIRD Dose Estimate Report' (from the 1 to 12) and 'Pamphlets', of great utility for the dose calculations, were published. The MIRD system was planned essentially for the calculation of doses received by the patients during nuclear medicine diagnostic procedures. The MIRD methodology for the absorbed doses calculations in different tissues is explained

  10. PSA methodology

    Energy Technology Data Exchange (ETDEWEB)

    Magne, L

    1997-12-31

    The purpose of this text is first to ask a certain number of questions on the methods related to PSAs. Notably we will explore the positioning of the French methodological approach - as applied in the EPS 1300{sup 1} and EPS 900{sup 2} PSAs - compared to other approaches (Part One). This reflection leads to more general reflection: what contents, for what PSA? This is why, in Part Two, we will try to offer a framework for definition of the criteria a PSA should satisfy to meet the clearly identified needs. Finally, Part Three will quickly summarize the questions approached in the first two parts, as an introduction to the debate. 15 refs.

  11. PSA methodology

    International Nuclear Information System (INIS)

    Magne, L.

    1996-01-01

    The purpose of this text is first to ask a certain number of questions on the methods related to PSAs. Notably we will explore the positioning of the French methodological approach - as applied in the EPS 1300 1 and EPS 900 2 PSAs - compared to other approaches (Part One). This reflection leads to more general reflection: what contents, for what PSA? This is why, in Part Two, we will try to offer a framework for definition of the criteria a PSA should satisfy to meet the clearly identified needs. Finally, Part Three will quickly summarize the questions approached in the first two parts, as an introduction to the debate. 15 refs

  12. Energy analysis of crack-damage interaction

    Science.gov (United States)

    Chudnovsky, A.; Wu, Shaofu

    1989-01-01

    The energy release rates associated with a main crack propagating into a surrounding damage zone, and a damage zone translation relative to the main crack, as well as an energy of interaction between the two are analyzed. The displacement and stress fields for the crack-damage interaction problem are reconstructed employing a semi-empirical stress analysis and experimental evaluation of the average craze density in the crazed zone.

  13. Measuring Crack Length in Coarse Grain Ceramics

    Science.gov (United States)

    Salem, Jonathan A.; Ghosn, Louis J.

    2010-01-01

    Due to a coarse grain structure, crack lengths in precracked spinel specimens could not be measured optically, so the crack lengths and fracture toughness were estimated by strain gage measurements. An expression was developed via finite element analysis to correlate the measured strain with crack length in four-point flexure. The fracture toughness estimated by the strain gaged samples and another standardized method were in agreement.

  14. Outcome of Endodontically Treated Cracked Teeth

    Science.gov (United States)

    2016-06-01

    directed by: CAPT Te!Ty Webb, D.D.S., M.S. A " cracked tooth" is defined as a thin surface enamel and dentin disruption of unknown depth, and is often...OUTCOME OF ENDODONTICALL Y TREATED CRACKED TEETH by David Michael Dow II, D.D.S. Lieutenant Commander, Dental Corps United States Navy A thesis...copyrighted material in the thesis manuscript titled: "Outcome ofEndodontically Treated Cracked Teeth" is appropriately acknowledged and, beyond

  15. Crack and fracture behaviour in tough ductile materials

    International Nuclear Information System (INIS)

    Venter, R.D.; Hoeppner, D.W.

    1985-10-01

    The report describes various approaches and developments pertaining to the understanding of crack and fracture behaviour in tough ductile materials. The fundamental elastic fracture mechanics concepts based on the concepts of energy, stress field, and displacement are introduced and their interrelationships demonstrated. The extension of these concepts to include elasto-plastic fracture mechanics considerations is reviewed in the context of the preferred options available for the development of appropriate design methodologies. The recommendations of the authors are directed towards the continued development of the J-integral concept. This energy-based concept, in its fundamental form, has a sound theoretical basis and as such offers the possibility of incorporating elasto-plastic fracture mechanics considerations in the crack and fracture behaviour of tough ductile materials. It must however be emphasized that the concise defintion of J becomes increasingly suspect as the crack length increases. J is not a material property, as is J IC , but emerges as a useful empirical parameter which is dependent upon the particular geometry and the loading imposed on the structure. It is proposed that 'lowest bound' J-resistance curves and the associated J-T curves be experimentally developed and employed in the design process. Improvements to these 'lowest bounds' can be developed through extensive analysis of the twin J-CTOA criteria and validation of this approach through near full scale tests

  16. Sudden Cardiac Arrest during Participation in Competitive Sports.

    Science.gov (United States)

    Landry, Cameron H; Allan, Katherine S; Connelly, Kim A; Cunningham, Kris; Morrison, Laurie J; Dorian, Paul

    2017-11-16

    The incidence of sudden cardiac arrest during participation in sports activities remains unknown. Preparticipation screening programs aimed at preventing sudden cardiac arrest during sports activities are thought to be able to identify at-risk athletes; however, the efficacy of these programs remains controversial. We sought to identify all sudden cardiac arrests that occurred during participation in sports activities within a specific region of Canada and to determine their causes. In this retrospective study, we used the Rescu Epistry cardiac arrest database (which contains records of every cardiac arrest attended by paramedics in the network region) to identify all out-of-hospital cardiac arrests that occurred from 2009 through 2014 in persons 12 to 45 years of age during participation in a sport. Cases were adjudicated as sudden cardiac arrest (i.e., having a cardiac cause) or as an event resulting from a noncardiac cause, on the basis of records from multiple sources, including ambulance call reports, autopsy reports, in-hospital data, and records of direct interviews with patients or family members. Over the course of 18.5 million person-years of observation, 74 sudden cardiac arrests occurred during participation in a sport; of these, 16 occurred during competitive sports and 58 occurred during noncompetitive sports. The incidence of sudden cardiac arrest during competitive sports was 0.76 cases per 100,000 athlete-years, with 43.8% of the athletes surviving until they were discharged from the hospital. Among the competitive athletes, two deaths were attributed to hypertrophic cardiomyopathy and none to arrhythmogenic right ventricular cardiomyopathy. Three cases of sudden cardiac arrest that occurred during participation in competitive sports were determined to have been potentially identifiable if the athletes had undergone preparticipation screening. In our study involving persons who had out-of-hospital cardiac arrest, the incidence of sudden cardiac

  17. Nucleation and arrest of slow slip earthquakes: mechanisms and nonlinear simulations using realistic fault geometries and heterogeneous medium properties

    Science.gov (United States)

    Alves da Silva Junior, J.; Frank, W.; Campillo, M.; Juanes, R.

    2017-12-01

    Current models for slow slip earthquakes (SSE) assume a simplified fault embedded on a homogeneous half-space. In these models SSE events nucleate on the transition from velocity strengthening (VS) to velocity weakening (VW) down dip from the trench and propagate towards the base of the seismogenic zone, where high normal effective stress is assumed to arrest slip. Here, we investigate SSE nucleation and arrest using quasi-static finite element simulations, with rate and state friction, on a domain with heterogeneous properties and realistic fault geometry. We use the fault geometry of the Guerrero Gap in the Cocos subduction zone, where SSE events occurs every 4 years, as a proxy for subduction zone. Our model is calibrated using surface displacements from GPS observations. We apply boundary conditions according to the plate convergence rate and impose a depth-dependent pore pressure on the fault. Our simulations indicate that the fault geometry and elastic properties of the medium play a key role in the arrest of SSE events at the base of the seismogenic zone. SSE arrest occurs due to aseismic deformations of the domain that result in areas with elevated effective stress. SSE nucleation occurs in the transition from VS to VW and propagates as a crack-like expansion with increased nucleation length prior to dynamic instability. Our simulations encompassing multiple seismic cycles indicate SSE interval times between 1 and 10 years and, importantly, a systematic increase of rupture area prior to dynamic instability, followed by a hiatus in the SSE occurrence. We hypothesize that these SSE characteristics, if confirmed by GPS observations in different subduction zones, can add to the understanding of nucleation of large earthquakes in the seismogenic zone.

  18. Catalytic cracking of hydrocarbon oils

    Energy Technology Data Exchange (ETDEWEB)

    1940-09-12

    A process is described for the vapor phase catalytic cracking of hydrocarbon oils boiling substantially in the gas oil range. The reaction takes place in the presence of a solid catalyst between 700 to 900/sup 0/F under pressure between atmospheric and 400 psi. A gas containing between 20 and 90 mol % of free hydrogen is used. The reaction is allowed to proceed until consumption of the free begins. The reaction is discontinued at that point and the catalyst is regenerated for further use.

  19. Modelling of environmentally assisted cracking

    International Nuclear Information System (INIS)

    Aaltonen, P.; Saario, T.; Ehrnsten, U.; Haenninen, H.; Itaeaho, M.; Piippo, J.

    1998-01-01

    During the use of nuclear reactors the properties of the structural materials change. Variations in the operation environment, such as changes in water chemistry, may enhance the development and growth of flaws. Neutron radiation causes embrittlement for in-core vessel materials. Radiation, together with water chemistry, increases the possibility of stress corrosion cracking in stainless steels and superalloys used in the reactor internal parts. Research on structural materials endeavours to study the ageing mechanisms of materials, and the possibilities and methods of preventing or forecasting the damage caused to structures by ageing. (orig.)

  20. SCC crack propagation behavior in 316L weld metal under high temperature water

    International Nuclear Information System (INIS)

    Nakade, Katsuyuki; Hirasaki, Toshifumi; Suzuki, Shunichi; Takamori, Kenro; Kumagai, Katsuhiko; Tanaka, Yoshihiko; Umeoka, Kuniyoshi

    2008-01-01

    Intergranular stress corrosion cracking (SCC) of 316L weld metal is of concern to the BWR plants. PLR pipes in commercial BWR plants have shown SCC in almost HAZ area in high temperature water, whereas, SCC has been arrested around fusion boundary for long time in the actual PLR pipe. The SCC behavior could be characterized in terms of dendrite direction, which was defined as the angle between dendrite growth direction and macro-SCC direction. In this study, the relationship between dendrite growth direction and macro-SCC direction was clearly showed on the fracture surface. The relative large difference of SCC susceptibility of 316L HAZ and weld metal was observed on the fracture surface. In the case of 0 degree, SCC has rapidly propagated into the weld metal parallel to the dendrite structure. In the case of more than 30 degree SCC direction, SCC was arrested around fusion area, and 60 degree SCC was drastically arrested around the fusion area. The large inclined dendrite structure for SCC is highly resistant to SCC. (author)

  1. T-stresses for internally cracked components

    International Nuclear Information System (INIS)

    Fett, T.

    1997-12-01

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

  2. Semi-empirical crack tip analysis

    Science.gov (United States)

    Chudnovsky, A.; Ben Ouezdon, M.

    1988-01-01

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

  3. On cracking of charged anisotropic polytropes

    Energy Technology Data Exchange (ETDEWEB)

    Azam, M. [Division of Science and Technology, University of Education, Township Campus, Lahore-54590 (Pakistan); Mardan, S.A., E-mail: azam.math@ue.edu.pk, E-mail: syedalimardanazmi@yahoo.com [Department of Mathematics, University of the Management and Technology, C-II, Johar Town, Lahore-54590 (Pakistan)

    2017-01-01

    Recently in [1], the role of electromagnetic field on the cracking of spherical polytropes has been investigated without perturbing charge parameter explicitly. In this study, we have examined the occurrence of cracking of anisotropic spherical polytropes through perturbing parameters like anisotropic pressure, energy density and charge. We consider two different types of polytropes in this study. We discuss the occurrence of cracking in two different ways ( i ) by perturbing polytropic constant, anisotropy and charge parameter ( ii ) by perturbing polytropic index, anisotropy and charge parameter for each case. We conclude that cracking appears for a wide range of parameters in both cases. Also, our results are reduced to [2] in the absence of charge.

  4. Cracking of open traffic rigid pavement

    Directory of Open Access Journals (Sweden)

    Niken Chatarina

    2017-01-01

    Full Text Available The research is done by observing the growth of real structure cracking in Natar, Lampung, Indonesia compared to C. Niken’s et al research and literature study. The rigid pavement was done with open traffic system. There are two main crack types on Natar rigid pavement: cracks cross the road, and cracks spreads on rigid pavement surface. The observation of cracks was analyzed by analyzing material, casting, curing, loading and shrinkage mechanism. The relationship between these analysis and shrinkage mechanism was studied in concrete micro structure. Open traffic make hydration process occur under vibration; therefore, fresh concrete was compressed and tensioned alternately since beginning. High temperature together with compression, cement dissociation, the growth of Ca2+ at very early age leads abnormal swelling. No prevention from outside water movement leads hydration process occur with limited water which caused spreads fine cracks. Limited water improves shrinkage and plastic phase becomes shorter; therefore, rigid pavement can’t accommodate the abnormal swelling and shrinking alternately and creates the spread of cracks. Discontinuing casting the concrete makes both mix under different condition, the first is shrink and the second is swell and creates weak line on the border; so, the cracks appear as cracks across the road.

  5. Lateral rigidity of cracked concrete structures

    International Nuclear Information System (INIS)

    Castellani, A.; Chesi, C.

    1979-01-01

    Numerical results are discussed on the lateral rigidity of reinforced concrete structures with a given crack distribution. They have been favourably checked with experimental results for cylindrical shells under the effect of a thermal gradient producing vertical cracking or vertical plus horizontal cracking. The main effects characterizing the concrete behaviour are: (1) The shear transfer across a crack; (2) The shear transfer degradation after cyclic loading; (3) The tension stiffening provided by the concrete between crack and crack, in the normal stress transfer; (4) The temperature effect on the elastic moduli of concrete, when cracks are of thermal origin. Only the 1st effect is discussed on an experimental basis. Two broad cathegories of reinforced concrete structures have been investigated in this respect: shear walls of buildings and cylindrical containment structures. The main conclusions so far reached are: (1) Vertical cracks are unlikely to decrease the lateral rigidity to less than 80% of the original one, and to less than 90% when they do not involve the entire thickness of the wall; (2) The appearence of horizontal cracks can reduce the lateral rigidity by some 30% or more; (3) A noticeable but not yet evaluated influence is shown by cyclic loading. (orig.)

  6. Probabilistic fracture mechanics of nuclear structural components. Consideration of transition from embedded crack to surface crack

    International Nuclear Information System (INIS)

    Yagawa, Genki; Yoshimura, Shinobu; Kanto, Yasuhiro

    1998-01-01

    This paper describes a probabilistic fracture mechanics (PFM) analysis of aged nuclear reactor pressure vessel (RPV) material. New interpolation formulas are first derived for both embedded elliptical surface cracks and semi-elliptical surface cracks. To investigate effects of transition from embedded crack to surface crack in PFM analyses, one of PFM round-robin problems set by JSME-RC111 committee, i.e. 'aged RPV under normal and upset operating conditions' is solved, employing the interpolation formulas. (author)

  7. Statistical distribution of time to crack initiation and initial crack size using service data

    Science.gov (United States)

    Heller, R. A.; Yang, J. N.

    1977-01-01

    Crack growth inspection data gathered during the service life of the C-130 Hercules airplane were used in conjunction with a crack propagation rule to estimate the distribution of crack initiation times and of initial crack sizes. A Bayesian statistical approach was used to calculate the fraction of undetected initiation times as a function of the inspection time and the reliability of the inspection procedure used.

  8. Analysis of events related to cracks and leaks in the reactor coolant pressure boundary

    Energy Technology Data Exchange (ETDEWEB)

    Ballesteros, Antonio, E-mail: Antonio.Ballesteros-Avila@ec.europa.eu [JRC-IET: Institute for Energy and Transport of the Joint Research Centre of the European Commission, Postbus 2, NL-1755 ZG Petten (Netherlands); Sanda, Radian; Peinador, Miguel; Zerger, Benoit [JRC-IET: Institute for Energy and Transport of the Joint Research Centre of the European Commission, Postbus 2, NL-1755 ZG Petten (Netherlands); Negri, Patrice [IRSN: Institut de Radioprotection et de Sûreté Nucléaire (France); Wenke, Rainer [GRS: Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH (Germany)

    2014-08-15

    Highlights: • The important role of Operating Experience Feedback is emphasised. • Events relating to cracks and leaks in the reactor coolant pressure boundary are analysed. • A methodology for event investigation is described. • Some illustrative results of the analysis of events for specific components are presented. - Abstract: The presence of cracks and leaks in the reactor coolant pressure boundary may jeopardise the safe operation of nuclear power plants. Analysis of cracks and leaks related events is an important task for the prevention of their recurrence, which should be performed in the context of activities on Operating Experience Feedback. In response to this concern, the EU Clearinghouse operated by the JRC-IET supports and develops technical and scientific work to disseminate the lessons learned from past operating experience. In particular, concerning cracks and leaks, the studies carried out in collaboration with IRSN and GRS have allowed to identify the most sensitive areas to degradation in the plant primary system and to elaborate recommendations for upgrading the maintenance, ageing management and inspection programmes. An overview of the methodology used in the analysis of cracks and leaks related events is presented in this paper, together with the relevant results obtained in the study.

  9. Damage Tolerant Analysis of Cracked Al 2024-T3 Panels repaired with Single Boron/Epoxy Patch

    Science.gov (United States)

    Mahajan, Akshay D.; Murthy, A. Ramachandra; Nanda Kumar, M. R.; Gopinath, Smitha

    2018-06-01

    It is known that damage tolerant analysis has two objectives, namely, remaining life prediction and residual strength evaluation. To achieve the these objectives, determination of accurate and reliable fracture parameter is very important. XFEM methodologies for fatigue and fracture analysis of cracked aluminium panels repaired with different patch shapes made of single boron/epoxy have been developed. Heaviside and asymptotic crack tip enrichment functions are employed to model the crack. XFEM formulations such as displacement field formulation and element stiffness matrix formulation are presented. Domain form of interaction integral is employed to determine Stress Intensity Factor of repaired cracked panels. Computed SIFs are incorporated in Paris crack growth model to predict the remaining fatigue life. The residual strength has been computed by using the remaining life approach, which accounts for both crack growth constants and no. of cycles to failure. From the various studies conducted, it is observed that repaired panels have significant effect on reduction of the SIF at the crack tip and hence residual strength as well as remaining life of the patched cracked panels are improved significantly. The predicted remaining life and residual strength will be useful for design of structures/components under fatigue loading.

  10. Automatic Crack Detection and Classification Method for Subway Tunnel Safety Monitoring

    Directory of Open Access Journals (Sweden)

    Wenyu Zhang

    2014-10-01

    Full Text Available Cracks are an important indicator reflecting the safety status of infrastructures. This paper presents an automatic crack detection and classification methodology for subway tunnel safety monitoring. With the application of high-speed complementary metal-oxide-semiconductor (CMOS industrial cameras, the tunnel surface can be captured and stored in digital images. In a next step, the local dark regions with potential crack defects are segmented from the original gray-scale images by utilizing morphological image processing techniques and thresholding operations. In the feature extraction process, we present a distance histogram based shape descriptor that effectively describes the spatial shape difference between cracks and other irrelevant objects. Along with other features, the classification results successfully remove over 90% misidentified objects. Also, compared with the original gray-scale images, over 90% of the crack length is preserved in the last output binary images. The proposed approach was tested on the safety monitoring for Beijing Subway Line 1. The experimental results revealed the rules of parameter settings and also proved that the proposed approach is effective and efficient for automatic crack detection and classification.

  11. Automatic crack detection and classification method for subway tunnel safety monitoring.

    Science.gov (United States)

    Zhang, Wenyu; Zhang, Zhenjiang; Qi, Dapeng; Liu, Yun

    2014-10-16

    Cracks are an important indicator reflecting the safety status of infrastructures. This paper presents an automatic crack detection and classification methodology for subway tunnel safety monitoring. With the application of high-speed complementary metal-oxide-semiconductor (CMOS) industrial cameras, the tunnel surface can be captured and stored in digital images. In a next step, the local dark regions with potential crack defects are segmented from the original gray-scale images by utilizing morphological image processing techniques and thresholding operations. In the feature extraction process, we present a distance histogram based shape descriptor that effectively describes the spatial shape difference between cracks and other irrelevant objects. Along with other features, the classification results successfully remove over 90% misidentified objects. Also, compared with the original gray-scale images, over 90% of the crack length is preserved in the last output binary images. The proposed approach was tested on the safety monitoring for Beijing Subway Line 1. The experimental results revealed the rules of parameter settings and also proved that the proposed approach is effective and efficient for automatic crack detection and classification.

  12. Effect of ripple loads on sustained-load cracking in titanium alloys

    International Nuclear Information System (INIS)

    Pao, P.S.; Meyn, D.A.; Bayles, R.A.; Feng, C.R.; Yoder, G.R.

    1995-01-01

    In the present paper, the authors have extended their study on the effect of the ripple loads on the sustained-load cracking (SLC) behavior of two titanium alloys, Ti-6Al-4V (an α-β alloy) and Ti-15V-3Cr-3Al-3Sn (a β-α alloy), in an ambient air environment. The methodology which has been used successfully to treat ripple effects on stress-corrosion cracking (SCC) is employed again to address the influence of ripple loads on sustained-load cracking. Ripple loads can significantly reduce the apparent sustained load cracking resistance of titanium alloys in a relatively benign environment such as ambient air. For a ripple-load amplitude equal to 5% of the sustained load, the ripple-load cracking thresholds (K IRLC ) of beta-annealed Ti-6Al-4V and Ti-15V-3Cr-3al-3Sn are less than half of the respective sustained-load cracking thresholds (K ISLC ). The extent of ripple-load degradation for these alloys in ambient air -- relative to K ISLC , were found comparable to those observed in a much more aggressive 3.5% NaCl aqueous solution

  13. Chloride Penetration through Cracks in High-Performance Concrete and Surface Treatment System for Crack Healing

    Directory of Open Access Journals (Sweden)

    In-Seok Yoon

    2012-01-01

    Full Text Available For enhancing the service life of concrete structures, it is very important to minimize crack at surface. Even if these cracks are very small, the problem is to which extend these cracks may jeopardize the durability of these decks. It was proposed that crack depth corresponding with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It was necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. This study is devoted to examine the effect of high strength concrete and reinforcement of steel fiber on chloride penetration through cracks. High strength concrete is regarded as an excellent barrier to resist chloride penetration. However, durability performance of cracked high strength concrete was reduced seriously up to that of ordinary cracked concrete. Steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly. Meanwhile, surface treatment systems are put on the surface of the concrete in order to seal the concrete. The key-issue is to which extend a sealing is able to ensure that chloride-induced corrosion can be prevented. As a result, penetrant cannot cure cracks, however, coating and combined treatment can prevent chloride from flowing in concrete with maximum crack width of 0.06 mm and 0.08 mm, respectively.

  14. 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...

  15. Crack-opening area calculations for circumferential through-wall pipe cracks

    Energy Technology Data Exchange (ETDEWEB)

    Kishida, K.; Zahoor, A.

    1988-08-01

    This report describes the estimation schemes for crack opening displacement (COD) of a circumferential through-wall crack, then compares the COD predictions with pipe experimental data. Accurate predictions for COD are required to reliably predict the leak rate through a crack in leak-before-break applications.

  16. Crack-opening area calculations for circumferential through-wall pipe cracks

    International Nuclear Information System (INIS)

    Kishida, K.; Zahoor, A.

    1988-08-01

    This report describes the estimation schemes for crack opening displacement (COD) of a circumferential through-wall crack, then compares the COD predictions with pipe experimental data. Accurate predictions for COD are required to reliably predict the leak rate through a crack in leak-before-break applications

  17. Brain stem death as the vital determinant for resumption of spontaneous circulation after cardiac arrest in rats.

    Directory of Open Access Journals (Sweden)

    Alice Y W Chang

    Full Text Available BACKGROUND: Spontaneous circulation returns to less than half of adult cardiac arrest victims who received in-hospital resuscitation. One clue for this disheartening outcome arises from the prognosis that asystole invariably takes place, after a time lag, on diagnosis of brain stem death. The designation of brain stem death as the point of no return further suggests that permanent impairment of the brain stem cardiovascular regulatory machinery precedes death. It follows that a crucial determinant for successful revival of an arrested heart is that spontaneous circulation must resume before brain stem death commences. Here, we evaluated the hypothesis that maintained functional integrity of the rostral ventrolateral medulla (RVLM, a neural substrate that is intimately related to brain stem death and central circulatory regulation, holds the key to the vital time-window between cardiac arrest and resumption of spontaneous circulation. METHODOLOGY/PRINCIPAL FINDINGS: An animal model of brain stem death employing the pesticide mevinphos as the experimental insult in Sprague-Dawley rats was used. Intravenous administration of lethal doses of mevinphos elicited an abrupt cardiac arrest, accompanied by elevated systemic arterial pressure and anoxia, augmented neuronal excitability and enhanced microvascular perfusion in RVLM. This period represents the vital time-window between cardiac arrest and resumption of spontaneous circulation in our experimental model. Animals with restored spontaneous circulation exhibited maintained neuronal functionality in RVLM beyond this critical time-window, alongside resumption of baseline tissue oxygen and enhancement of local blood flow. Intriguingly, animals that subsequently died manifested sustained anoxia, diminished local blood flow, depressed mitochondrial electron transport activities and reduced ATP production, leading to necrotic cell death in RVLM. That amelioration of mitochondrial dysfunction and

  18. Ultrasonic inspection reliability for intergranular stress corrosion cracks

    Energy Technology Data Exchange (ETDEWEB)

    Heasler, P G; Taylor, T T; Spanner, J C; Doctor, S R; Deffenbaugh, J D [Pacific Northwest Lab., Richland, WA (USA)

    1990-07-01

    A pipe inspection round robin entitled Mini-Round Robin'' was conducted at Pacific Northwest Laboratory from May 1985 through October 1985. The research was sponsored by the US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research under a program entitled Evaluation and Improvement of NDE Reliability for Inservice Inspection of Light Water Reactors.'' The Mini-Round Robin (MRR) measured the intergranular stress corrosion (GSC) crack detection and sizing capabilities of inservice inspection (ISI) inspectors that had passed the requirements of IEB 83-02 and the Electric Power Research Institute (EPRI) sizing training course. The MRR data base was compared with an earlier Pipe Inspection Round Robin (PIRR) that had measured the performance of inservice inspection prior to 1982. Comparison of the MRR and PIRR data bases indicates no significant change in the inspection capability for detecting IGSCC. Also, when comparing detection of long and short cracks, no difference in detection capability was measured. An improvement in the ability to differentiate between shallow and deeper IGSCC was found when the MRR sizing capability was compared with an earlier sizing round robin conducted by the EPRI. In addition to the pipe inspection round robin, a human factors study was conducted in conjunction with the Mini-Round Robin. The most important result of the human factors study is that the Relative Operating Characteristics (ROC) curves provide a better methodology for describing inspector performance than only probability of detection (POD) or single-point crack/no crack data. 6 refs., 55 figs., 18 tabs.

  19. Stress corrosion cracking of Alloy 82 in hydrogenated steam at 400 C: influence of microstructural and mechanical parameters on initiation of SCC cracks

    International Nuclear Information System (INIS)

    Chaumun, Elizabeth

    2016-01-01

    In Pressurize Water Reactors (PWR), Stress Corrosion Cracking (SCC) is the mean degradation mode of components pieced together by welding. Nickel based alloys are, among others, used in dissimilar metal welding (DMW). International report showed only 3 cracking cases in Alloy 82 out of 300 cracking cases concerned on nickel based alloys DMW in primary water circuit. The aim of this study is to identify which microstructural and local mechanism parameters at microstructure scale provide the initiation of SCC cracks. Characterizations performed on specimen surface to identify those parameters are composed of chemical composition analysis and EBSD analysis (Electron Back-Scattered Diffraction) to know the morphology and the crystallography of grains for microstructure features on one hand, and experimental strain fields measured by Digital Imaging Correlation (DIC) of gold micro-grids deposed by electronic lithography on U-bend specimen surface and stress fields calculated along grains boundaries by finite element for local mechanical features on the other hand. The correlation between those characterizations and localization of initiation sites of SCC cracks, obtained on U-bend specimens tested in autoclave in hydrogen steam water at 400 C and 188 bar for 3500 hours, confirmed the susceptibility of the Alloy 82 in SCC conditions with intergranular SCC cracks. The perpendicular position to the loading direction (mode I) is the worst conditions for grains boundary in SCC. The others points concern the chemical composition (precipitation, impurities) around grain boundary and the grain boundary type which is more susceptible when it is a High Angle Grain Boundary. It is following by the mechanical characterization (stress and strain gradient) along grain boundary. This methodology can be used to other material and helped to define which microstructural and mechanical parameter can be define the initiation of SCC cracks. (author) [fr

  20. Post-resuscitation care for survivors of cardiac arrest

    Directory of Open Access Journals (Sweden)

    Ashvarya Mangla

    2014-01-01

    Full Text Available Cardiac arrest can occur following a myriad of clinical conditions. With advancement of medical science and improvements in Emergency Medical Services systems, the rate of return of spontaneous circulation for patients who suffer an out-of-hospital cardiac arrest (OHCA continues to increase. Managing these patients is challenging and requires a structured approach including stabilization of cardiopulmonary status, early consideration of neuroprotective strategies, identifying and managing the etiology of arrest and initiating treatment to prevent recurrence. This requires a closely coordinated multidisciplinary team effort. In this article, we will review the initial management of survivors of OHCA, highlighting advances and ongoing controversies.

  1. 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

  2. The application of RBI-concept to ultrasonic measurement of fatigue cracks

    Energy Technology Data Exchange (ETDEWEB)

    Pitkaenen, J.; Saerkiniemi, P.; Kauppinen, P. [VTT Manufacturing Technology, Espoo (Finland)

    1998-12-31

    In many power plants there are problem areas, which are not included in the official inspection programs. Flaws can be induced during service due to the service conditions in components and welded joints. These can lead to failures, which cause unforeseen shutdowns during operation and unscheduled repairs have to be earned out. The basic idea of Risk Based Inspection (RBI) methodology is to include this kind of objects in the inspection program. In this presentation two possible objects for RBI are described - thermal fatigue cracking in process piping and fatigue cracking in spinning fly wheel. (orig.) 4 refs.

  3. The application of RBI-concept to ultrasonic measurement of fatigue cracks

    Energy Technology Data Exchange (ETDEWEB)

    Pitkaenen, J; Saerkiniemi, P; Kauppinen, P [VTT Manufacturing Technology, Espoo (Finland)

    1999-12-31

    In many power plants there are problem areas, which are not included in the official inspection programs. Flaws can be induced during service due to the service conditions in components and welded joints. These can lead to failures, which cause unforeseen shutdowns during operation and unscheduled repairs have to be earned out. The basic idea of Risk Based Inspection (RBI) methodology is to include this kind of objects in the inspection program. In this presentation two possible objects for RBI are described - thermal fatigue cracking in process piping and fatigue cracking in spinning fly wheel. (orig.) 4 refs.

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

    International Nuclear Information System (INIS)

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

    1985-01-01

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

  5. Distributed crack analysis of ceramic inlays

    NARCIS (Netherlands)

    Peters, M.C.R.B.; Vree, de J.H.P.; Brekelmans, W.A.M.

    1993-01-01

    In all-ceramic restorations, crack formation and propagation phenomena are of major concern, since they may result in intra-oral fracture. The objective of this study was calculation of damage in porcelain MOD inlays by utilization of a finite-element (FE) implementation of the distributed crack

  6. In-reactor fatigue crack propagation

    International Nuclear Information System (INIS)

    Ermi, A.M.; Mervyn, D.A.; Straalsund, J.L.

    1979-08-01

    An in-reactor fatigue experiment is being designed to determine the effect of dynamic irradiation on the fatigue crack propagation (FCP) behavior of candidate fusion first wall materials. This investigation has been prompted by studies which show gross differences in crack growth characteristics of creep rupture specimens testing by postirradiation versus dynamic in-reactor methods. The experiment utilizes miniature center-cracked-tension specimens developed specifically for in-reactor studies. In the test, a chain of eight specimens, precracked to various initial crack lengths, is stressed during irradiation to determine crack growth rate as a function of stress intensity. Load levels were chosen which result in small crack growth rates encompassing a regime of the crack growth curve not previously investigated during irradiation studies of FCP. The test will be conducted on 20% cold worked 316 stainless steel at a temperature of 425 0 C, in a sodium environment, and at a frequency of 1 cycle/min. Irradiation will occur in the Oak Ridge Research Reactor, resulting in a He/dpa ratio similar to that expected at the first wall in a fusion reactor. Detailed design of the experiment is presented, along with crack growth data obtained from prototypic testing of the experimental apparatus. These results are compared to data obtained under similar conditions generated by conventional test methods

  7. Crack Tip Mechanics in Distortion Gradient Plasticity

    DEFF Research Database (Denmark)

    Fuentes-Alonso, Sandra; Martínez Pañeda, Emilio

    2017-01-01

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

  8. 46 CFR 59.10-5 - Cracks.

    Science.gov (United States)

    2010-10-01

    ..., DEPARTMENT OF HOMELAND SECURITY (CONTINUED) MARINE ENGINEERING REPAIRS TO BOILERS, PRESSURE VESSELS AND... consecutive cracked ligaments nor more than a total of six cracked ligaments in any one girth joint. (c... ligaments may be repaired by welding. (n) Welding repairs to drums of power boilers, except as otherwise...

  9. Crack velocity measurement by induced electromagnetic radiation

    International Nuclear Information System (INIS)

    Frid, V.; Rabinovitch, A.; Bahat, D.

    2006-01-01

    Our model of electromagnetic radiation (EMR) emanated from fracture implies that EMR amplitude is proportional to crack velocity. Soda lime glass samples were tested under uniaxial tension. Comparison of crack velocity observed by Wallner line analysis and the peak amplitude of EMR signals registered during the test, showed very good correlation, validating this proportionality

  10. Crack velocity measurement by induced electromagnetic radiation

    Energy Technology Data Exchange (ETDEWEB)

    Frid, V. [Deichmann Rock Mechanics Laboratory of the Negev, Geological and Environmental Sciences Department, Ben Gurion University of the Negev, Beer Sheva (Israel)]. E-mail: vfrid@bgu.ac.il; Rabinovitch, A. [Deichmann Rock Mechanics Laboratory of the Negev, Physics Department, Ben Gurion University of the Negev, Beer Sheva (Israel); Bahat, D. [Deichmann Rock Mechanics Laboratory of the Negev, Geological and Environmental Sciences Department, Ben Gurion University of the Negev, Beer Sheva (Israel)

    2006-07-31

    Our model of electromagnetic radiation (EMR) emanated from fracture implies that EMR amplitude is proportional to crack velocity. Soda lime glass samples were tested under uniaxial tension. Comparison of crack velocity observed by Wallner line analysis and the peak amplitude of EMR signals registered during the test, showed very good correlation, validating this proportionality.

  11. Positioning Community Art Practices in Urban Cracks

    Science.gov (United States)

    Verschelden, Griet; Van Eeghem, Elly; Steel, Riet; De Visscher, Sven; Dekeyrel, Carlos

    2012-01-01

    This article addresses the position of community art practices and the role of practitioners in urban cracks. Community art practices raise possibilities for a reconceptualisation of the concept of community and an extension of the concept of art in public space. Urban cracks are conceptualised as spatial, temporal and relational manifestations of…

  12. Corrosion and Cracking of Reinforced Concrete

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of the deterioration of reinforced concrete has in recent years changed from being a deterministic modelling based on experience to be stochastic modelling based on sound and consistent physical, chemical and mechanical principles. In this paper is presented a brief review of modern mod...... for time to initial corrosion, time to initial cracking, and time to a given crack width may be obtained....

  13. Mechanism for iodine cracking of zirconium claddings

    International Nuclear Information System (INIS)

    Novikov, V.V.

    1991-01-01

    The mechanism of iodine cracking of zirconium cladding is analyzed taking into account the effect of stresses on diffusion. A decisive effect of the stress gradiemt on crack propagation in an agressive medium is shown. The experimental data are compared with the proposed model

  14. Crack Formation in Grouted Annular Composite

    DEFF Research Database (Denmark)

    Sørensen, Eigil V.

    The objective of the present analysis is to identify the reason for extensive crack formation which occurred during an annulus grouting performance test, to evaluate possible consequences of the cracking, and to recommend measures to be taken in order to avoid similar problems in the future....

  15. Quenching cracks - formation and possible causes

    International Nuclear Information System (INIS)

    Macherauch, E.; Mueller, H.; Voehringer, O.

    1976-01-01

    The most important principles controlling the martensitic hardening of steels containing carbon are presented, and their effects on the cracks formed by tempering are discussed. Micro-crack formation, influenced by any increase in the carbon content, is dependent on the variations of martensitic morphology; this factor is of decisive importance. Apart from micro residual stresses, macro residual stresses become increasingly involved in the crack development. This is dependent on the given content of carbon and increase in the dimensions of the samples. Based on the empirical values gained from experience about cracks formed by tempering and using a schematic diagram, the constructive influences on the propensity to cracks formed by tempering, with regard to materials and processing, are evaluated. Also the effects of thermic, mechanical and chemical after-treatments upon the propensity to tempering cracks are discussed. In conclusion, the problem of the formation of cracks in hardened parts, i.e. the elongation of the cracks under static stress, is treated briefly. (orig.) [de

  16. Crack Monitoring of Operational Wind Turbine Foundations.

    Science.gov (United States)

    Perry, Marcus; McAlorum, Jack; Fusiek, Grzegorz; Niewczas, Pawel; McKeeman, Iain; Rubert, Tim

    2017-08-21

    The degradation of onshore, reinforced-concrete wind turbine foundations is usually assessed via above-ground inspections, or through lengthy excavation campaigns that suspend wind power generation. Foundation cracks can and do occur below ground level, and while sustained measurements of crack behaviour could be used to quantify the risk of water ingress and reinforcement corrosion, these cracks have not yet been monitored during turbine operation. Here, we outline the design, fabrication and field installation of subterranean fibre-optic sensors for monitoring the opening and lateral displacements of foundation cracks during wind turbine operation. We detail methods for in situ sensor characterisation, verify sensor responses against theoretical tower strains derived from wind speed data, and then show that measured crack displacements correlate with monitored tower strains. Our results show that foundation crack opening displacements respond linearly to tower strain and do not change by more than ±5 μ m. Lateral crack displacements were found to be negligible. We anticipate that the work outlined here will provide a starting point for real-time, long-term and dynamic analyses of crack displacements in future. Our findings could furthermore inform the development of cost-effective monitoring systems for ageing wind turbine foundations.

  17. Crack initiation under generalized plane strain conditions

    International Nuclear Information System (INIS)

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

    1991-01-01

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

  18. Corrosion of steel in cracked concrete: a microscale study

    NARCIS (Netherlands)

    Pacheco, J.; Savija, B.; Schlangen, E.; Polder, R.B.

    2014-01-01

    The influence of concrete cracking upon reinforcement corrosion is complex. Cracks allow fast penetration of chlorides, potentially leading to a shorter initiation period of reinforcement corrosion. Structural regulations control acceptable crack width values based on the exposure class of the

  19. 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)

  20. Analysis of 3D crack propagation by microfocus computed tomography

    International Nuclear Information System (INIS)

    Ao Bo; Chen Fuxing; Deng Cuizhen; Zeng Yabin

    2014-01-01

    The three-point bending test of notched specimens of 2A50 forging aluminum was performed by high frequency fatigue tester, and the surface cracks of different stages were analyzed and contrasted by SEM. The crack was reconstructed by microfocus computed tomography, and its size, position and distribution were visually displayed through 3D visualization. The crack propagation behaviors were researched through gray value and position of crack front of 2D CT images in two adjacent stages, and the results show that crack propagation is irregular. The projection image of crack was obtained if crack of two stages projected onto the reference plane respectively, a significant increase of new crack propagation was observed compared with the previous projection of crack, and the distribution curve of crack front of two stages was displayed. The 3D increment distribution of the crack front propagation was obtained through the 3D crack analysis of two stages. (authors)

  1. Mitigation strategies for reflective cracking in pavements : [research project capsule].

    Science.gov (United States)

    2013-12-01

    Refl ection cracks are caused by discontinuities (cracks or joints) in underlying layers, : which propagate through hot-mix asphalt (HMA) overlay due to continuous movement : at the crack prompted by thermal expansion and traffi c loading. If the new...

  2. Unsaturated Seepage Analysis of Cracked Soil including Development Process of Cracks

    Directory of Open Access Journals (Sweden)

    Ling Cao

    2016-01-01

    Full Text Available Cracks in soil provide preferential pathways for water flow and their morphological parameters significantly affect the hydraulic conductivity of the soil. To study the hydraulic properties of cracks, the dynamic development of cracks in the expansive soil during drying and wetting has been measured in the laboratory. The test results enable the development of the relationships between the cracks morphological parameters and the water content. In this study, the fractal model has been used to predict the soil-water characteristic curve (SWCC of the cracked soil, including the developmental process of the cracks. The cracked expansive soil has been considered as a crack-pore medium. A dual media flow model has been developed to simulate the seepage characteristics of the cracked expansive soil. The variations in pore water pressure at different part of the model are quite different due to the impact of the cracks. This study proves that seepage characteristics can be better predicted if the impact of cracks is taken into account.

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

    International Nuclear Information System (INIS)

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

    2015-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-07-15

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

  5. Process and device for magnetic crack testing

    International Nuclear Information System (INIS)

    Seiler, D.; Meili, E.; Fuchs, E.

    1983-01-01

    There is a problem of sufficient crack depth discrimination to suppress fault signals or pictures due to unevenness not caused by cracks. To solve this, when magnetising in the preferred direction of adhesion, the effect depending on the direction of the crack, before magnetic powder detection, magnetic powder is blown on, showing the fault and for the comparison of the adhesion effect crack direction characteristics it is blown on parallel to the preferred direction, or if one wants to stress the directional characteristic, it is blown on transversely to the preferred direction. In both cases one blows with the same force, without removing the magnetic powder remnants relevant to faults in the intended crack areas. This strong blowing removes the magnetic powder remnants relevant to interference and not relevant to faults. (orig./HP) [de

  6. Strain rate effects in stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Parkins, R.N. (Newcastle upon Tyne Univ. (UK). Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  7. Compliance characteristics of cracked UO2 pellets

    International Nuclear Information System (INIS)

    Williford, R.E.; Mohr, C.L.; Lanning, D.D.

    1981-01-01

    The thermally induced cracking of UO 2 fuel pellets causes simultaneous reductions of the bulk (extrinsic) fuel thermal conductivity and elastic moduli to values significantly less than those for solid pellets. The magnitude of these bulk properly reductions was found to be primarily dependent on the amount of crack area in the transverse plane of the fuel. The model described herein uses a simple description of the crack geometry to couple the fuel rod thermal and mechanical behaviors by relating in-reactor data to Hooke's Law and a crack compliance model. Data from the NRC/PNL Halden experiment IFA-432 show that for a typical helium-filled BWR-design rod at 30 kW/m, the effective thermal conductivity and elastic moduli of the cracked fuel are 4/5 and 1/40 of that for solid pellets, respectively

  8. Crack shape developments and leak rates for circumferential complex-cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Brickstad, B.; Bergman, M. [SAQ Inspection Ltd., Stockholm (Sweden)

    1997-04-01

    A computerized procedure has been developed that predicts the growth of an initial circumferential surface crack through a pipe and further on to failure. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes and for the through-wall cracks, crack opening areas and leak rates are also calculated. The procedure is based on a large number of three-dimensional finite element calculations of cracked pipes. The results from these calculations are stored in a database from which the PC-program, denoted LBBPIPE, reads all necessary information. In this paper, a sensitivity analysis is presented for cracked pipes subjected to both stress corrosion and vibration fatigue.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

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

  10. Prediction of cardiac arrest recurrence using ensemble classifiers

    Indian Academy of Sciences (India)

    Nachiket Tapas

    ECG dataset from PhysioNet, Pima Indian Diabetes dataset from UCI Machine Learning Repository and gene expression ... electrical activity, medically the condition is known as cardiac arrest ... ing, (5) lack of physical exercise, etc. [9]. Using ...

  11. Arrest of cytoplasmic streaming induces algal proliferation in green paramecia.

    Directory of Open Access Journals (Sweden)

    Toshiyuki Takahashi

    Full Text Available A green ciliate Paramecium bursaria, bearing several hundreds of endosymbiotic algae, demonstrates rotational microtubule-based cytoplasmic streaming, in which cytoplasmic granules and endosymbiotic algae flow in a constant direction. However, its physiological significance is still unknown. We investigated physiological roles of cytoplasmic streaming in P. bursaria through host cell cycle using video-microscopy. Here, we found that cytoplasmic streaming was arrested in dividing green paramecia and the endosymbiotic algae proliferated only during the arrest of cytoplasmic streaming. Interestingly, arrest of cytoplasmic streaming with pressure or a microtubule drug also induced proliferation of endosymbiotic algae independently of host cell cycle. Thus, cytoplasmic streaming may control the algal proliferation in P. bursaria. Furthermore, confocal microscopic observation revealed that a division septum was formed in the constricted area of a dividing paramecium, producing arrest of cytoplasmic streaming. This is a first report to suggest that cytoplasmic streaming controls proliferation of eukaryotic cells.

  12. The outcome of anaesthesia related cardiac arrest in a

    Directory of Open Access Journals (Sweden)

    O.O. Adekola

    2016-07-01

    Conclusion: Anaesthesia related cardiac arrest and mortality were linked to cardiovascular depression from halothane overdose in our institution. The burden can be reduced by improving on establishing standard monitoring in the perioperative period, and a team approach to patients care.

  13. Testing methodologies

    Energy Technology Data Exchange (ETDEWEB)

    Bender, M.A.

    1990-01-01

    Several methodologies are available for screening human populations for exposure to ionizing radiation. Of these, aberration frequency determined in peripheral blood lymphocytes is the best developed. Individual exposures to large doses can easily be quantitated, and population exposures to occupational levels can be detected. However, determination of exposures to the very low doses anticipated from a low-level radioactive waste disposal site is more problematical. Aberrations occur spontaneously, without known cause. Exposure to radiation induces no new or novel types, but only increases their frequency. The limitations of chromosomal aberration dosimetry for detecting low level radiation exposures lie mainly in the statistical signal to noise'' problem, the distribution of aberrations among cells and among individuals, and the possible induction of aberrations by other environmental occupational or medical exposures. However, certain features of the human peripheral lymphocyte-chromosomal aberration system make it useful in screening for certain types of exposures. Future technical developments may make chromosomal aberration dosimetry more useful for low-level radiation exposures. Other methods, measuring gene mutations or even minute changes on the DNA level, while presently less will developed techniques, may eventually become even more practical and sensitive assays for human radiation exposure. 15 refs.

  14. Testing methodologies

    International Nuclear Information System (INIS)

    Bender, M.A.

    1990-01-01

    Several methodologies are available for screening human populations for exposure to ionizing radiation. Of these, aberration frequency determined in peripheral blood lymphocytes is the best developed. Individual exposures to large doses can easily be quantitated, and population exposures to occupational levels can be detected. However, determination of exposures to the very low doses anticipated from a low-level radioactive waste disposal site is more problematical. Aberrations occur spontaneously, without known cause. Exposure to radiation induces no new or novel types, but only increases their frequency. The limitations of chromosomal aberration dosimetry for detecting low level radiation exposures lie mainly in the statistical ''signal to noise'' problem, the distribution of aberrations among cells and among individuals, and the possible induction of aberrations by other environmental occupational or medical exposures. However, certain features of the human peripheral lymphocyte-chromosomal aberration system make it useful in screening for certain types of exposures. Future technical developments may make chromosomal aberration dosimetry more useful for low-level radiation exposures. Other methods, measuring gene mutations or even minute changes on the DNA level, while presently less will developed techniques, may eventually become even more practical and sensitive assays for human radiation exposure. 15 refs

  15. Optimisation of the Crack Pattern in Continuously Reinforced Concrete Pavements

    OpenAIRE

    Ren, D.

    2015-01-01

    Recent field investigations on several new Continuously Reinforced Concrete Pavements (CRCP) in Belgium indicate that its crack pattern is characterized by low mean crack spacing along with a high percentage of clusters of closely spaced cracks. Field surveys also indicate that it is difficult to significantly reduce the probability of a non-uniform crack pattern - such as closely spaced cracks, meandering, and Y-cracks - by only slightly adjusting the amount of longitudinal steel. Non-unifor...

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

    International Nuclear Information System (INIS)

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

    1994-01-01

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

  17. Development of a virtual learning environment for cardiorespiratory arrest training.

    Science.gov (United States)

    Silva, Anazilda Carvalho da; Bernardes, Andrea; Évora, Yolanda Dora Martinez; Dalri, Maria Célia Barcellos; Silva, Alexandre Ribeiro da; Sampaio, Camila Santana Justo Cintra

    2016-01-01

    To develop a Virtual Learning Environment (VLE) aiming at the training of nursing team workers and emergency vehicle drivers in Basic Life Support (BLS) to attend Cardiorespiratory arrest, and to evaluate the quality of its contents among specialists in the area of Emergency and Urgent care. Applied research of technological development. The methodology used was based on the Instructional Design Model (ADDIE), which structures the teaching-learning planning in different stages (analysis, design, development, implementation and evaluation). The VLE was composed of texts elaborated from bibliographic research, links, edited video from a simulation scenario in the laboratory and questions to evaluate the fixation of the content, organized in modules. After its development, it was evaluated as adequate to satisfy the needs of the target public, by eight expert judges, which was made available for electronic access. The VLE has potential as a tool for training and qualification in BLS, as it can be easily integrated with other pedagogical approaches and strategies with active methodologies. Desenvolver um Ambiente Virtual de Aprendizagem (AVA) visando à capacitação de trabalhadores da equipe de enfermagem e condutores de veículo de emergência em Suporte Básico de Vida (SBV) no atendimento à Parada Cardiorrespiratória, e avaliar a qualidade do seu conteúdo junto a especialistas na área de Urgência e Emergência. Pesquisa aplicada, de produção tecnológica. A metodologia utilizada foi baseada no Modelo de Design Instrucional (ADDIE), que estrutura o planejamento de ensino-aprendizagem em estágios distintos (analysis, design, development, implementation and evaluation). O AVA foi composto por textos elaborados a partir de pesquisa bibliográfica, links, vídeo construído a partir de um cenário de simulação em laboratório e questões para avaliar a fixação do conteúdo, organizados em módulos. Após a sua construção, foi avaliado como adequado para

  18. Al-Qaeda arrest casts shadow over the LHC

    CERN Multimedia

    Dacey, James

    2010-01-01

    "Cern remains on course for the imminent switch-on of the Large Hadron Collider (LHC) despite the media frenzy following the recent arrest of a physicist who had been working at the facility. The researcher in question is a 32-year-old man of Algerian descent who is expected to face trail in France - the country in which he was arrested" (0.5 page)

  19. Cracks assessment using ultrasonic technology

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, Maria Pia; Tomasella, Marcelo [OLDELVAL S.A. Oleoductos del Valle, Rio Negro (Argentina). Pipeline Integrity Dept.

    2005-07-01

    The goal of Oldelval Integrity Program is to prevent ruptures and leaks, developing strategies for a better handling of the integrity of our pipelines. In order to achieve it we have studied and modeled each process that involved in the integrity pipeline. Those processes are mainly based on defects reported by an internal inspection tool and supplied with field inspection and monitoring data. Years of evaluation, study and the continuous effort overturned towards a phenomenon that worries to the industry, as it is the SCC. Since 1998 up to 2004 SCC was included in the integrity program with some preventive maintenance programs. The accomplishment of the inspection based on ultrasound tools, is the culmination of years of evaluation and investigations supported by field digs and materials susceptibility. This paper describes Oldelval's results with ultrasonic crack detection tool, and how it can be reliably to detect SCC. (author)

  20. Associates of Cardiopulmonary Arrest in the Perihemodialytic Period

    Science.gov (United States)

    Flythe, Jennifer E.; Li, Nien-Chen; Brunelli, Steven M.; Lacson, Eduardo

    2014-01-01

    Cardiopulmonary arrest during and proximate to hemodialysis is rare but highly fatal. Studies have examined peridialytic sudden cardiac event risk factors, but no study has considered associates of cardiopulmonary arrests (fatal and nonfatal events including cardiac and respiratory causes). This study was designed to elucidate patient and procedural factors associated with peridialytic cardiopulmonary arrest. Data for this case-control study were taken from the hemodialysis population at Fresenius Medical Care, North America. 924 in-center cardiopulmonary events (cases) and 75,538 controls were identified. Cases and controls were 1 : 5 matched on age, sex, race, and diabetes. Predictors of cardiopulmonary arrest were considered for logistic model inclusion. Missed treatments due to hospitalization, lower body mass, coronary artery disease, heart failure, lower albumin and hemoglobin, lower dialysate potassium, higher serum calcium, greater erythropoietin stimulating agent dose, and normalized protein catabolic rate (J-shaped) were associated with peridialytic cardiopulmonary arrest. Of these, lower albumin, hemoglobin, and body mass index; higher erythropoietin stimulating agent dose; and greater missed sessions had the strongest associations with outcome. Patient health markers and procedural factors are associated with peridialytic cardiopulmonary arrest. In addition to optimizing nutritional status, it may be prudent to limit exposure to low dialysate potassium (<2 K bath) and to use the lowest effective erythropoietin stimulating agent dose. PMID:25530881

  1. Associates of Cardiopulmonary Arrest in the Perihemodialytic Period

    Directory of Open Access Journals (Sweden)

    Jennifer E. Flythe

    2014-01-01

    Full Text Available Cardiopulmonary arrest during and proximate to hemodialysis is rare but highly fatal. Studies have examined peridialytic sudden cardiac event risk factors, but no study has considered associates of cardiopulmonary arrests (fatal and nonfatal events including cardiac and respiratory causes. This study was designed to elucidate patient and procedural factors associated with peridialytic cardiopulmonary arrest. Data for this case-control study were taken from the hemodialysis population at Fresenius Medical Care, North America. 924 in-center cardiopulmonary events (cases and 75,538 controls were identified. Cases and controls were 1 : 5 matched on age, sex, race, and diabetes. Predictors of cardiopulmonary arrest were considered for logistic model inclusion. Missed treatments due to hospitalization, lower body mass, coronary artery disease, heart failure, lower albumin and hemoglobin, lower dialysate potassium, higher serum calcium, greater erythropoietin stimulating agent dose, and normalized protein catabolic rate (J-shaped were associated with peridialytic cardiopulmonary arrest. Of these, lower albumin, hemoglobin, and body mass index; higher erythropoietin stimulating agent dose; and greater missed sessions had the strongest associations with outcome. Patient health markers and procedural factors are associated with peridialytic cardiopulmonary arrest. In addition to optimizing nutritional status, it may be prudent to limit exposure to low dialysate potassium (<2 K bath and to use the lowest effective erythropoietin stimulating agent dose.

  2. Cardiac arrest due to lymphocytic colitis: a case report

    Directory of Open Access Journals (Sweden)

    Groth Kristian A

    2012-03-01

    Full Text Available Abstract Introduction We present a case of cardiac arrest due to hypokalemia caused by lymphocytic colitis. Case presentation A 69-year-old Caucasian man presented four months prior to a cardiac arrest with watery diarrhea and was diagnosed with lymphocytic colitis. Our patient experienced a witnessed cardiac arrest at his general practitioner's surgery. Two physicians and the emergency medical services resuscitated our patient for one hour and four minutes before arriving at our university hospital. Our patient was defibrillated 16 times due to the recurrence of ventricular tachyarrhythmias. An arterial blood sample revealed a potassium level of 2.0 mmol/L (reference range: 3.5 to 4.6 mmol/L and pH 6.86 (reference range: pH 7.37 to 7.45. As the potassium level was corrected, the propensity for ventricular tachyarrhythmias ceased. Our patient recovered from his cardiac arrest without any neurological deficit. Further tests and examinations revealed no other reason for the cardiac arrest. Conclusion Diarrhea can cause life-threatening situations due to the excretion of potassium, ultimately causing cardiac arrest due to hypokalemia. Physicians treating patients with severe diarrhea should consider monitoring their electrolyte levels.

  3. The neighborhood context of racial and ethnic disparities in arrest.

    Science.gov (United States)

    Kirk, David S

    2008-02-01

    This study assesses the role of social context in explaining racial and ethnic disparities in arrest, with afocus on how distinct neighborhood contexts in which different racial and ethnic groups reside explain variations in criminal outcomes. To do so, I utilize a multilevel, longitudinal research design, combining individual-level data with contextual data from the Project on Human Development in Chicago Neighborhoods (PHDCN). Findings reveal that black youths face multiple layers of disadvantage relative to other racial and ethnic groups, and these layers work to create differences in arrest. At the family level, results show that disadvantages in the form of unstable family structures explain much of the disparities in arrest across race and ethnicity. At the neighborhood level, black youths tend to reside in areas with both significantly higher levels of concentrated poverty than other youths as well as lower levels of collective efficacy than white youths. Variations in neighborhood tolerance of deviance across groups explain little of the arrest disparities, yet tolerance of deviance does influence the frequency with which a crime ultimately ends in an arrest. Even after accounting for relevant demographic, family, and neighborhood-level predictors, substantial residual arrest differences remain between black youths and youths of other racial and ethnic groups.

  4. Fumando la piedra: emerging patterns of crack use among Latino immigrant day laborers in New Orleans.

    Science.gov (United States)

    Valdez, Avelardo; Cepeda, Alice; Negi, Nalini Junko; Kaplan, Charles

    2010-10-01

    The devastating effects of Hurricane Katrina have contributed to a dynamic demographic shift in the Latino composition of New Orleans. This article focuses on a particularly deleterious pattern of crack cocaine smoking associated with numerous social and health consequences. Utilizing a rapid assessment methodology, in-depth qualitative interviews were conducted with 52 Latino immigrant day laborers in New Orleans. Findings reveal that the presence of a flourishing drug market has facilitated and maintained patterns of crack use including initiation and periods of daily use. Moreover, feelings of isolation and constant exposure to victimization due to day laborers' marginal status are described as contributing to this use. This qualitative analysis reveals how social processes and contextual factors contribute to crack use among Latino day laborers in a post-disaster context. This study has important public health implications in the spread of HIV and other blood borne pathogens.

  5. Dislocation model of a subsurface crack

    International Nuclear Information System (INIS)

    Yang, F.; Li, J.C.

    1997-01-01

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

  6. Identification of cracks in thick beams with a cracked beam element model

    Science.gov (United States)

    Hou, Chuanchuan; Lu, Yong

    2016-12-01

    The effect of a crack on the vibration of a beam is a classical problem, and various models have been proposed, ranging from the basic stiffness reduction method to the more sophisticated model involving formulation based on the additional flexibility due to a crack. However, in the damage identification or finite element model updating applications, it is still common practice to employ a simple stiffness reduction factor to represent a crack in the identification process, whereas the use of a more realistic crack model is rather limited. In this paper, the issues with the simple stiffness reduction method, particularly concerning thick beams, are highlighted along with a review of several other crack models. A robust finite element model updating procedure is then presented for the detection of cracks in beams. The description of the crack parameters is based on the cracked beam flexibility formulated by means of the fracture mechanics, and it takes into consideration of shear deformation and coupling between translational and longitudinal vibrations, and thus is particularly suitable for thick beams. The identification procedure employs a global searching technique using Genetic Algorithms, and there is no restriction on the location, severity and the number of cracks to be identified. The procedure is verified to yield satisfactory identification for practically any configurations of cracks in a beam.

  7. A model of survival following pre-hospital cardiac arrest based on the Victorian Ambulance Cardiac Arrest Register.

    Science.gov (United States)

    Fridman, Masha; Barnes, Vanessa; Whyman, Andrew; Currell, Alex; Bernard, Stephen; Walker, Tony; Smith, Karen L

    2007-11-01

    This study describes the epidemiology of sudden cardiac arrest patients in Victoria, Australia, as captured via the Victorian Ambulance Cardiac Arrest Register (VACAR). We used the VACAR data to construct a new model of out-of-hospital cardiac arrest (OHCA), which was specified in accordance with observed trends. All cases of cardiac arrest in Victoria that were attended by Victorian ambulance services during the period of 2002-2005. Overall survival to hospital discharge was 3.8% among 18,827 cases of OHCA. Survival was 15.7% among 1726 bystander witnessed, adult cardiac arrests of presumed cardiac aetiology, presenting in ventricular fibrillation or ventricular tachycardia (VF/VT), where resuscitation was attempted. In multivariate logistic regression analysis, bystander CPR, cardiac arrest (CA) location, response time, age and sex were predictors of VF/VT, which, in turn, was a strong predictor of survival. The same factors that affected VF/VT made an additional contribution to survival. However, for bystander CPR, CA location and response time this additional contribution was limited to VF/VT patients only. There was no detectable association between survival and age younger than 60 years or response time over 15min. The new model accounts for relationships among predictors of survival. These relationships indicate that interventions such as reduced response times and bystander CPR act in multiple ways to improve survival.

  8. Characterization of Mitochondrial Injury after Cardiac Arrest (COMICA)

    Science.gov (United States)

    Donnino, Michael W.; Liu, Xiaowen; Andersen, Lars W.; Rittenberger, Jon C.; Abella, Benjamin S.; Gaieski, David F.; Ornato, Joseph P.; Gazmuri, Raúl J.; Grossestreur, Anne V.; Cocchi, Michaen N.; Abbate, Antonio; Uber, Amy; Clore, John; Peberdy, Mary Anne; Callaway, Clifton

    2017-01-01

    Introduction Mitochondrial injury post-cardiac arrest has been described in pre-clinical settings but the extent to which this injury occurs in humans remains largely unknown. We hypothesized that increased levels of mitochondrial biomarkers would be associated with mortality and neurological morbidity in post-cardiac arrest subjects. Methods We performed a prospective multicenter study of post-cardiac arrest subjects. Inclusion criteria were comatose adults who suffered an out-of-hospital cardiac arrest. Mitochondrial biomarkers were measured at 0, 12, 24, 36 and 48 hours after return of spontaneous circulation as well as in healthy controls. Results Out of 111 subjects enrolled, 102 had evaluable samples at 0 hours. Cardiac arrest subjects had higher baseline cytochrome c levels compared to controls (2.18 ng/mL [0.74, 7.74] vs. 0.16 ng/mL [0.03, 0.91], p<0.001), and subjects who died had higher 0 hours cytochrome c levels compared to survivors (3.66 ng/mL [1.40, 14.9] vs. 1.27 ng/mL [0.16, 2.37], p<0.001). There were significantly higher RNAase P (3.3 [1.2, 5.7] vs. 1.2 [0.8, 1.2], p<0.001) and B2M (12.0 [1.0, 22.9], vs. 0.6 [0.6, 1.3], p<0.001) levels in cardiac arrest subjects at baseline compared to the control subjects. There were no differences between survivors and non-survivors for mitochondrial DNA, nuclear DNA, or cell free DNA. Conclusions Cytochrome C was increased in post-cardiac arrest subjects compared to controls, and in post-cardiac arrest non-survivors compared to survivors. Nuclear DNA and cell free DNA was increased in plasma of post-cardiac arrest subjects. There were no differences in mitochondrial DNA, nuclear DNA, or cell free DNA between survivors and non-survivors. Mitochondrial injury markers showed mixed results in post-arrest period. Future research needs to investigate these differences. PMID:28126408

  9. Characterization of mitochondrial injury after cardiac arrest (COMICA).

    Science.gov (United States)

    Donnino, Michael W; Liu, Xiaowen; Andersen, Lars W; Rittenberger, Jon C; Abella, Benjamin S; Gaieski, David F; Ornato, Joseph P; Gazmuri, Raúl J; Grossestreuer, Anne V; Cocchi, Michael N; Abbate, Antonio; Uber, Amy; Clore, John; Peberdy, Mary Anne; Callaway, Clifton W

    2017-04-01

    Mitochondrial injury post-cardiac arrest has been described in pre-clinical settings but the extent to which this injury occurs in humans remains largely unknown. We hypothesized that increased levels of mitochondrial biomarkers would be associated with mortality and neurological morbidity in post-cardiac arrest subjects. We performed a prospective multicenter study of post-cardiac arrest subjects. Inclusion criteria were comatose adults who suffered an out-of-hospital cardiac arrest. Mitochondrial biomarkers were measured at 0, 12, 24, 36 and 48h after return of spontaneous circulation as well as in healthy controls. Out of 111 subjects enrolled, 102 had evaluable samples at 0h. Cardiac arrest subjects had higher baseline cytochrome c levels compared to controls (2.18ng/mL [0.74, 7.74] vs. 0.16ng/mL [0.03, 0.91], p<0.001), and subjects who died had higher 0h cytochrome c levels compared to survivors (3.66ng/mL [1.40, 14.9] vs. 1.27ng/mL [0.16, 2.37], p<0.001). There were significantly higher Ribonuclease P (RNaseP) (3.3 [1.2, 5.7] vs. 1.2 [0.8, 1.2], p<0.001) and Beta-2microglobulin (B2M) (12.0 [1.0, 22.9], vs. 0.6 [0.6, 1.3], p<0.001) levels in cardiac arrest subjects at baseline compared to the control subjects. There were no differences between survivors and non-survivors for mitochondrial DNA, nuclear DNA, or cell free DNA. Cytochrome c was increased in post- cardiac arrest subjects compared to controls, and in post-cardiac arrest non-survivors compared to survivors. Nuclear DNA and cell free DNA was increased in plasma of post-cardiac arrest subjects. There were no differences in mitochondrial DNA, nuclear DNA, or cell free DNA between survivors and non-survivors. Mitochondrial injury markers showed mixed results in the post-cardiac arrest period. Future research needs to investigate these differences. Copyright © 2017 Elsevier B.V. All rights reserved.

  10. Additive for vanadium and sulfur oxide capture in catalytic cracking

    International Nuclear Information System (INIS)

    Chin, A.A.; Sapre, A.V.; Sarli, M.S.

    1991-01-01

    This patent describes a fluid catalytic cracking process in which a hydrocarbon feedstock. It comprises: a vanadium contaminant in an amount of a least 2 ppmw is cracked under fluid catalytic cracking conditions with a solid, particulate cracking catalyst to produce cracking products of lower molecular weight while depositing carbonaceous material on the particles of cracking catalyst, separating the particles of cracking catalyst from the cracking products in the disengaging zone and oxidatively regenerating the cracking catalyst by burning off the deposited carbonaceous material in a regeneration zone, the improvement comprising reducing the make-up rate of the cracking catalyst by contacting the cracking feed with a particulate additive composition for passivating the vanadium content of the feed, comprising an alkaline earth metal oxide and an alkaline earth metal spinel

  11. 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)

  12. Crack propagation and fracture in silicon carbide

    International Nuclear Information System (INIS)

    Evans, A.G.; Lange, F.F.

    1975-01-01

    Fracture mechanics and strength studies performed on two silicon carbides - a hot-pressed material (with alumina) and a sintered material (with boron) - have shown that both materials exhibit slow crack growth at room temperature in water, but only the hot-pressed material exhibits significant high temperature slow crack growth (1000 to 1400 0 C). A good correlation of the observed fracture behaviour with the crack growth predicted from the fracture mechanics parameters shows that effective failure predictions for this material can be achieved using macro-fracture mechanics data. (author)

  13. Minimizing hydride cracking in zirconium alloys

    International Nuclear Information System (INIS)

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

    1985-01-01

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

  14. Signal processing for underclad crack sizing

    International Nuclear Information System (INIS)

    Shankar, R.; Lane, S.S.; Paradiso, T.J.; Quinn, J.R.

    1985-01-01

    The techniques developed in this work provide a means of sizing underclad cracks and quality control methods for assessing the accuracy of the data. Data were collected with a minicomputer (LSI 11-02), a transient recorder (Biomaton 8100) and anti-aliasing filter. Three techniques were developed: the calibration curve, phase velocity and epicentral. The phase reversal characteristic in the data is a strong indication of the nature of the signal source. That is, cracks are clearly seperable from two isolated inclusions on the basis of observed phase reversal. These methods have been implemented on a computer and appear to provide an accurate rapid method to discriminate and size underclad cracks

  15. 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)

  16. Fatigue cracking on a steam generator tube

    International Nuclear Information System (INIS)

    Boccanfuso, M.; Lothios, J.; Thebault, Y.; Bruyere, B.; Duisabeau, L.; Herms, E.

    2015-01-01

    A circumferential fatigue crack was observed on a steam generator tube of the unit 2 of the Fessenheim plant. The results of destructive testing and the examination of the fracture surface show that the circumferential crack is linked to a large number of cycles with a very low stress intensity factor. Other aggravating factors like inter-granular corrosion have played a role in the initiating phase of fatigue cracking. The damage has been exacerbated by the lack of support of the tube at the level of the anti-vibration bars. (A.C.)

  17. Process and apparatus for cracking petroleum, etc

    Energy Technology Data Exchange (ETDEWEB)

    1931-04-25

    Process for catalytic cracking of petroleum and similar material at normal pressure, characterized by the oil vaporized in a vaporizer being treated in a first catalyst-chamber and in a separator attached to it, light constituents being separated, and then its being run into a second apparatus-group (vaporizer, catalyst-chamber, and separator), further groups following in series, whereby the catalyst works in a separate catalyst apparatus with ever-increasing activity time on the always lesser but always more difficult to crack material, so that in the whole apparatus a methodical cracking process is effected.

  18. Cause of Damage. Hot cracking; Schadensursache Heissrissigkeit

    Energy Technology Data Exchange (ETDEWEB)

    Wader, Therese [BENTELER Steel/Tube GmbH, Paderborn (Germany). Vorentwicklung Werkstoffe

    2016-10-15

    Under certain conditions, Nb-containing stainless steels are susceptible to hot cracking. Such conditions include low melting phases on the grain boundaries, a coarse-grained microstructure such as cast structures, microstructure orientations towards the main tensile direction and high processing temperatures. The case of damage was characterized using metallographic and microanalytical methods. In the laboratory, the critical temperature range for the formation of hot cracks could furthermore specifically be localized under mechanical stresses by means of a dilatometer aiming at clearly verifying the cause of the damage, namely ''hot cracks''.

  19. Eddy current standards - Cracks versus notches

    Science.gov (United States)

    Hagemaier, D. J.; Collingwood, M. R.; Nguyen, K. H.

    1992-10-01

    Eddy current tests aimed at evaluating cracks and electron-discharge machined (EDM) notches in 7075-T6 aluminum specimens are described. A comparison of the shape and amplitude of recordings made from both transverse and longitudinal scans of small EDM notches and fatigue cracks showd almost identical results. The signal amplitude and phase angle increased with an increase of EDM notch and crak size. It is concluded that equivalent eddy current results obtained from similar-size surface cracks and notches in aluminum can be used to establish a desired sensitivity level for inspection.

  20. Crack Growth Properties of Sealing Glasses

    Science.gov (United States)

    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.

  1. TEM observations of crack tip: cavity interactions

    International Nuclear Information System (INIS)

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

    1981-01-01

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

  2. A model-based approach to crack sizing with ultrasonic arrays.

    Science.gov (United States)

    Tant, Katherine M M; Mulholland, Anthony J; Gachagan, Anthony

    2015-05-01

    Ultrasonic phased array systems have become increasingly popular in the last 10 years as tools for flaw detection and characterization within the nondestructive testing industry. The existence and location of flaws can often be deduced via images generated from the data captured by these arrays. A factor common to these imaging techniques is the subjective thresholding required to estimate the size of the flaw. This paper puts forward an objective approach which employs a mathematical model. By exploiting the relationship between the width of the central lobe of the scattering matrix and the crack size, an analytical expression for the crack length is reached via the Born approximation. Conclusions are then drawn on the minimum resolvable crack length of the method and it is thus shown that the formula holds for subwavelength defects. An analytical expression for the error that arises from the discrete nature of the array is then derived and it is observed that the method becomes less sensitive to the discretization of the array as the distance between the flaw and array increases. The methodology is then extended and tested on experimental data collected from welded austenitic plates containing a lack-of-fusion crack of 6 mm length. An objective sizing matrix (OSM) is produced by assessing the similarity between the scattering matrices arising from experimentally collected data with those arising from the Born approximation over a range of crack lengths and frequencies. Initially, the global minimum of the OSM is taken as the objective estimation of the crack size, giving a measurement of 7 mm. This is improved upon by the adoption of a multifrequency averaging approach, with which an improved crack size estimation of 6.4 mm is obtained.

  3. The initiation of environmentally-assisted cracking in semi-elliptical surface cracks

    International Nuclear Information System (INIS)

    James, L.A.

    1997-01-01

    A criterion to predict under what conditions EAC would Initiate In cracks In a high-sulfur steel in contact with low-oxygen water was recently proposed by Wire and U. This EAC Initiation Criterion was developed using transient analyses for the diffusion of sulfides plus experimental test results. The experiments were conducted mainly on compact tension-type specimens with initial crack depths of about 2.54 mm. The present paper expands upon the work of Wire and U by presenting results for significantly deeper initial semi-elliptical surface cracks. In addition, in one specimen, the surface crack penetrated weld-deposited cladding into the high-sulfur steel. The results for the semi-elliptical surface cracks agreed quite well with the EAC Initiation Criterion, and provide confirmation of the applicability of the criterion to crack configurations with more restricted access to water

  4. Synthesis of cracked Calophyllum inophyllum oil using fly ash catalyst for diesel engine application

    KAUST Repository

    Muthukumaran, N.

    2015-04-16

    In this study, production of hydrocarbon fuel from Calophyllum inophyllum oil has been characterized for diesel engine application, by appraising essential fuel processing parameters. As opposed to traditional trans-esterification process, the reported oil was cracked using a catalyst, as the latter improves the fuel properties better than the former. In a bid to make the production process economically viable, a waste and cheap catalyst, RFA (raw fly ash), has been capitalized for the cracking process as against the conventional zeolite catalyst. The fuel production process, which is performed in a fixed bed catalytic reactor, was done methodologically after comprehensively studying the characteristics of fly ash catalyst. Significantly, fly ash characterization was realized using SEM and EDS, which demarcated the surface and internal structures of fly ash particles before and after cracking. After the production of hydrocarbon fuel from C. inophyllum oil, the performed compositional analysis in GC-MS revealed the presence of esters, parfins and olefins. Followed by the characterization of catalytically cracked C. inophyllum oil, suitable blends of it with diesel were tested in a single cylinder diesel engine. From the engine experimental results, BTE (brake thermal efficiency) of the engine for B25 (25% cracked C. inophyllum oil and 75% diesel) was observed to be closer to diesel, while it decreased for higher blends. On the other hand, emissions such as HC (hydrocarbon), CO (carbon monoxide) and smoke were found to be comparable for B25 with diesel. © 2015 Elsevier Ltd. All rights reserved.

  5. Crack propagation in stainless steel AISI 304L in Hydrogen Chemistry conditions (HWC)

    International Nuclear Information System (INIS)

    Diaz S, A.; Fuentes C, P.; Merino C, F.; Castano M, V.

    2006-01-01

    Velocities of crack growth in samples type CT pre cracking of stainless steel AISI 304l solder and sensitized thermally its were obtained by the Rising Displacement method or of growing displacement. It was used a recirculation circuit that simulates the operation conditions of a BWR type reactor (temperature of 280 C and a pressure of 8 MPa) with the chemistry modified by the addition of hydrogen with and without the addition of impurities of a powerful oxidizer like the Cu + ion. In each essay stayed a displacement velocity was constant of 1x10 -9 m/s, making a continuous pursuit of the advance of the crack by the electric potential drop technique. Contrary to the idea of mitigation of the crack propagation velocity by effect of the addition of the hydrogen in the system, the values of the growth velocities obtained by this methodology went similar to the opposing ones under normal operation conditions. To the finish of the rehearsal one carries out the fractographic analysis of the propagation surfaces, which showed cracks growth in trans and intergranular way, evidencing the complexity of the regulator mechanisms of the IGSCC like in mitigation conditions as the alternative Hydrogen Chemistry. (Author)

  6. 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

  7. Cracking the code of change.

    Science.gov (United States)

    Beer, M; Nohria, N

    2000-01-01

    Today's fast-paced economy demands that businesses change or die. But few companies manage corporate transformations as well as they would like. The brutal fact is that about 70% of all change initiatives fail. In this article, authors Michael Beer and Nitin Nohria describe two archetypes--or theories--of corporate transformation that may help executives crack the code of change. Theory E is change based on economic value: shareholder value is the only legitimate measure of success, and change often involves heavy use of economic incentives, layoffs, downsizing, and restructuring. Theory O is change based on organizational capability: the goal is to build and strengthen corporate culture. Most companies focus purely on one theory or the other, or haphazardly use a mix of both, the authors say. Combining E and O is directionally correct, they contend, but it requires a careful, conscious integration plan. Beer and Nohria present the examples of two companies, Scott Paper and Champion International, that used a purely E or purely O strategy to create change--and met with limited levels of success. They contrast those corporate transformations with that of UK-based retailer ASDA, which has successfully embraced the paradox between the opposing theories of change and integrated E and O. The lesson from ASDA? To thrive and adapt in the new economy, companies must make sure the E and O theories of business change are in sync at their own organizations.

  8. Crack imaging by pulsed laser spot thermography

    International Nuclear Information System (INIS)

    Li, T; Almond, D P; Rees, D A S; Weekes, B

    2010-01-01

    A surface crack close to a spot heated by a laser beam impedes lateral heat flow and produces alterations to the shape of the thermal image of the spot that can be monitored by thermography. A full 3D simulation has been developed to simulate heat flow from a laser heated spot in the proximity of a crack. The modelling provided an understanding of the ways that different parameters affect the thermal images of laser heated spots. It also assisted in the development of an efficient image processing strategy for extracting the scanned cracks. Experimental results show that scanning pulsed laser spot thermography has considerable potential as a remote, non-contact crack imaging technique.

  9. Cracking Advanced Encryption Standard-A Review

    Directory of Open Access Journals (Sweden)

    Jashnil Kumar

    2017-07-01

    Full Text Available Password protection is a major security concern the world is facing today. While there are many publications available that discuss ways to protect passwords and data how widely user from around the world adhere to these rules are unknown. The novelty of this study is that this is the first time a review is done on software tools that can be used to crack Advanced Encryption Standards. Firstly the study does a review on top 10 software tools that are available to crack Advanced Encryption Standards. After which an analysis on two software tools was performed to see how long each software tool took to crack a password. The result of the study gives Advanced Encryption Standard researcher Network security researcher and the general public helpful information on how to strengthen advanced encryption standards and strengthen passwords that are hard for the software tools discussed above to crack.

  10. Internal shear cracking in bulk metal forming

    DEFF Research Database (Denmark)

    Christiansen, Peter; Nielsen, Chris Valentin; Bay, Niels Oluf

    2017-01-01

    This paper presents an uncoupled ductile damage criterion for modelling the opening and propagation of internal shear cracks in bulk metal forming. The criterion is built upon the original work on the motion of a hole subjected to shear with superimposed tensile stress triaxiality and its overall...... performance is evaluated by means of side-pressing formability tests in Aluminium AA2007-T6 subjected to different levels of pre-strain. Results show that the new proposed criterionis able to combine simplicity with efficiency for predicting the onset of fracture and the crack propagation path for the entire...... cracking to internal cracks formed undert hree-dimensional states of stress that are typical of bulk metal forming....

  11. Purifying oils, cracking oils, catalysts. [British Patent

    Energy Technology Data Exchange (ETDEWEB)

    1936-02-05

    Hydrocarbon oils are refined by treating while substantially in the liquid phase between 200/sup 0/ and 400/sup 0/C with a phosphoric acid catalyst deposited on metallurgical coke, a suitable blast furnace slag, silica gel or other carrier with similar properties, until the objectionable components are converted into innocuous substances by polymerization cracking, isomerization and/or alkylation. By this treatment the bromine number is reduced, the end-point of the A.S.T.M. distillation is increased, the octane number is raised, mercaptans are converted to hydrogen sulphide and olefines, thioethers and thiophenes are converted to mereaptans, and the initial boiling point is lowered. The process is applicable to gasoline, cracked distillate, kerosine and lubricating oil, obtained by distilling or cracking petroleum, shale and hydrogenated oils; and is particularly applicable for stabilizing cracked distillates.

  12. Crack identification by artificial neural network

    Energy Technology Data Exchange (ETDEWEB)

    Hwu, C.B.; Liang, Y.C. [National Cheng Kung Univ., Tainan (Taiwan, Province of China). Inst. of Aeronaut. and Astronaut.

    1998-04-01

    In this paper, a most popular artificial neural network called the back propagation neural network (BPN) is employed to achieve an ideal on-line identification of the crack embedded in a composite plate. Different from the usual dynamic estimate, the parameters used for the present crack identification are the strains of static deformation. It is known that the crack effects are localized which may not be clearly reflected from the boundary information especially when the data is from static deformation only. To remedy this, we use data from multiple-loading modes in which the loading modes may include the opening, shearing and tearing modes. The results show that our method for crack identification is always stable and accurate no matter how far-away of the test data from its training set. (orig.) 8 refs.

  13. Visualizing Vpr-induced G2 arrest and apoptosis.

    Directory of Open Access Journals (Sweden)

    Tomoyuki Murakami

    Full Text Available Vpr is an accessory protein of human immunodeficiency virus type 1 (HIV-1 with multiple functions. The induction of G2 arrest by Vpr plays a particularly important role in efficient viral replication because the transcriptional activity of the HIV-1 long terminal repeat is most active in G2 phase. The regulation of apoptosis by Vpr is also important for immune suppression and pathogenesis during HIV infection. However, it is not known whether Vpr-induced apoptosis depends on the ability of Vpr to induce G2 arrest, and the dynamics of Vpr-induced G2 arrest and apoptosis have not been visualized. We performed time-lapse imaging to examine the temporal relationship between Vpr-induced G2 arrest and apoptosis using HeLa cells containing the fluorescent ubiquitination-based cell cycle indicator2 (Fucci2. The dynamics of G2 arrest and subsequent long-term mitotic cell rounding in cells transfected with the Vpr-expression vector were visualized. These cells underwent nuclear mis-segregation after prolonged mitotic processes and then entered G1 phase. Some cells subsequently displayed evidence of apoptosis after prolonged mitotic processes and nuclear mis-segregation. Interestingly, Vpr-induced apoptosis was seldom observed in S or G2 phase. Likewise, visualization of synchronized HeLa/Fucci2 cells infected with an adenoviral vector expressing Vpr clearly showed that Vpr arrests the cell cycle at G2 phase, but does not induce apoptosis at S or G2 phase. Furthermore, time-lapse imaging of HeLa/Fucci2 cells expressing SCAT3.1, a caspase-3-sensitive fusion protein, clearly demonstrated that Vpr induces caspase-3-dependent apoptosis. Finally, to examine whether the effects of Vpr on G2 arrest and apoptosis were reversible, we performed live-cell imaging of a destabilizing domain fusion Vpr, which enabled rapid stabilization and destabilization by Shield1. The effects of Vpr on G2 arrest and subsequent apoptosis were reversible. This study is the first to

  14. Thermal fatigue cracking of austenitic stainless steels; Fissuration en fatigue thermique des aciers inoxydables austenitiques

    Energy Technology Data Exchange (ETDEWEB)

    Fissolo, A

    2001-07-01

    This report deals with the thermal fatigue cracking of austenitic stainless steels as AISI 316 LN and 304 L. Such damage has been clearly observed for some components used in Fast Breeder reactors (FBR) and Pressure Water Reactor (PWR). In order to investigate thermal fatigue, quasi-structural specimen have been used. In this frame, facilities enforcing temperature variations similar to those found under the operation conditions have been progressively developed. As for components, loading results from impeded dilatation. In the SPLASH facility, the purpose was to establish accurate crack initiation conditions in order to check the relevance of the usual component design methodology. The tested specimen is continuously heated by the passage of an electrical DC current, and submitted to cyclic thermal down shock (up to 1000 deg C/s) by means of periodical spraying of water on two opposite specimen faces. The number of cycles to crack initiation N{sub i} is deduced from periodic examinations of the quenched surfaces, by means of optical microscopy. It is considered that initiation occurs when at least one 50{mu}m to 150{open_square}m long crack is observed. Additional SPLASH tests were performed for N >> N{sub i}, with a view to investigate the evolution of a surface multiple cracking network with the number of cycles N. The CYTHIA test was mainly developed for the purpose of assessing crack growth dynamics of one isolated crack in thermal fatigue conditions. Specimens consist of thick walled tubes with a 1 mm circular groove is spark-machined at the specimen centre. During the test, the external wall of the tube is periodically heated by using a HF induction coil (1 MHz), while its internal wall is permanently cooled by flowing water. Total crack growth is derived from post-mortem examinations, whereby the thermal fatigue final rupture surface is oxidized at the end of the test. The specimen is broken afterwards under mechanical fatigue at room temperature. All the

  15. 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 ...

  16. Investigation of the fatigue crack opening under low cyclic loading

    International Nuclear Information System (INIS)

    Daunys, M.; Taraskevicius, A.

    2003-01-01

    Low cycle loading crack opening under various load levels were investigated. Analytical method of the fatigue crack opening investigation was described using relations of crack surface displacements. Calculated results of the crack surface displacement were compared with the experimental results. (author)

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

    Directory of Open Access Journals (Sweden)

    F.V. Antunes

    2015-07-01

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

  18. Analysis of cracking in glass molds made of cast iron

    Science.gov (United States)

    Leushin, I. O.; Chistyakov, D. G.

    2014-09-01

    The cracking in the parts of cast iron molds intended for glass is considered, and this cracking substantially affects the operation of glass-blowing equipment, maintainability, and the replacement of mold sets. The processes that cause cracking in the parts of glass molds and initiate crack growth are studied.

  19. Serum tau and neurological outcome in cardiac arrest

    DEFF Research Database (Denmark)

    Mattsson, Niklas; Zetterberg, Henrik; Nielsen, Niklas

    2017-01-01

    OBJECTIVE: To test serum tau as a predictor of neurological outcome after cardiac arrest. METHODS: We measured the neuronal protein tau in serum at 24, 48, and 72 hours after cardiac arrest in 689 patients in the prospective international Target Temperature Management trial. The main outcome...... was poor neurological outcome, defined as Cerebral Performance Categories 3-5 at 6 months. RESULTS: Increased tau was associated with poor outcome at 6 months after cardiac arrest (median = 38.5, interquartile range [IQR] = 5.7-245ng/l in poor vs median = 1.5, IQR = 0.7-2.4ng/l in good outcome, for tau....... The accuracy in predicting outcome by serum tau was equally high for patients randomized to 33 °C and 36 °C targeted temperature after cardiac arrest. INTERPRETATION: Serum tau is a promising novel biomarker for prediction of neurological outcome in patients with cardiac arrest. It may be significantly better...

  20. Major life events as potential triggers of sudden cardiac arrest.

    Science.gov (United States)

    Wicks, April F; Lumley, Thomas; Lemaitre, Rozenn N; Sotoodehnia, Nona; Rea, Thomas D; McKnight, Barbara; Strogatz, David S; Bovbjerg, Viktor E; Siscovick, David S

    2012-05-01

    We investigated the risk of sudden cardiac arrest in association with the recent loss of, or separation from, a family member or friend. Our case-crossover study included 490 apparently healthy married residents of King County, Washington, who suffered sudden cardiac arrest between 1988 and 2005. We compared exposure to spouse-reported family/friend events occurring ≤ 1 month before sudden cardiac arrest with events occurring in the previous 5 months. We evaluated potential effect modification by habitual vigorous physical activity. Recent family/friend events were associated with a higher risk of sudden cardiac arrest (odds ratio [OR] = 1.6; 95% confidence interval [CI] = 1.1-2.4). ORs for cases with and without habitual vigorous physical activity were 1.1 (0.6-2.2) and 2.0 (1.2-3.1), respectively (interaction P = 0.02). These results suggest family/friend events may trigger sudden cardiac arrest and raise the hypothesis that habitual vigorous physical activity may lower susceptibility to these potential triggers.

  1. Current Pharmacological Advances in the Treatment of Cardiac Arrest

    Directory of Open Access Journals (Sweden)

    Andry Papastylianou

    2012-01-01

    Full Text Available Cardiac arrest is defined as the sudden cessation of spontaneous ventilation and circulation. Within 15 seconds of cardiac arrest, the patient loses consciousness, electroencephalogram becomes flat after 30 seconds, pupils dilate fully after 60 seconds, and cerebral damage takes place within 90–300 seconds. It is essential to act immediately as irreversible damage can occur in a short time. Cardiopulmonary resuscitation (CPR is an attempt to restore spontaneous circulation through a broad range of interventions which are early defibrillation, high-quality and uninterrupted chest compressions, advanced airway interventions, and pharmacological interventions. Drugs should be considered only after initial shocks have been delivered (when indicated and chest compressions and ventilation have been started. During cardiopulmonary resuscitation, no specific drug therapy has been shown to improve survival to hospital discharge after cardiac arrest, and only few drugs have a proven benefit for short-term survival. This paper reviews current pharmacological treatment of cardiac arrest. There are three groups of drugs relevant to the management of cardiac arrest: vasopressors, antiarrhythmics, and other drugs such as sodium bicarbonate, calcium, magnesium, atropine, fibrinolytic drugs, and corticosteroids.

  2. The effectiveness of silver diamine fluoride in arresting caries.

    Science.gov (United States)

    Richards, Derek

    2017-10-27

    Data sourcesPubMed, Embase, Scopus, China National Knowledge Infrastructure (CNKI), Ichushi-web, Biblioteca Virtual en Salud Espana (BVSE) and Biblioteca Virtual em Saude (BVS) databases. There were no limits on language or publication dates.Study selectionTwo reviewers selected prospective clinical studies investigating SDF treatment for caries prevention in children.Data extraction and synthesisData was abstracted independently by two reviewers and risk of bias assessed. Meta-analysis was performed on studies in which the caries-arresting rate using 38% SDF solution on primary teeth could be obtained or calculated.ResultsNineteen studies were included; 16 were conducted in the primary dentition and three in permanent dentition. Fourteen studies used 38% SDF, three 30% SDF, and two 10% SDF. Eight studies using 38% SDF contributed to a meta-analysis and the overall proportion of arrested caries was 81% (95% CI; 68-89%). Percentage reductions were also calculated for 6,12,18,24 and >30 months. Arrested carious lesions stained black but no other adverse effects were reported.ConclusionsSDF commonly used at a high concentration (38%, 44,800ppm fluoride) is effective in arresting caries among children. There is no consensus on its number and frequency of application to arrest caries. Further studies are necessary to develop evidence-based guidelines on its use in children.

  3. Fatigue crack threshold relevant to stress ratio, crack wake and loading histories

    International Nuclear Information System (INIS)

    Okazaki, Masakazu; Iwasaki, Akira; Kasahara, Naoto

    2013-01-01

    Fatigue crack propagation behavior was investigated in a low alloy steel which experienced several kind of loading histories. Both the effects of stress ratio, test temperature on the fatigue crack threshold, and the change in the threshold depending on the thermo-mechanical loading histories, were experimentally investigated. It was shown that the thermo-mechanical loading history left its effect along the prior fatigue crack wake resulting in the change of fatigue crack threshold. Some discussions are made on how this type of loading history effect should be treated from engineering point of view. (author)

  4. On the transition of short cracks into long fatigue cracks in reactor pressure vessel steels

    Directory of Open Access Journals (Sweden)

    Singh Rajwinder

    2018-01-01

    Full Text Available Short fatigue cracks, having dimension less than 1 mm, propagate at much faster rates (da/dN even at lower stress intensity factor range (da/dN as compared to the threshold stress intensity factor range obtained from long fatigue crack growth studies. These short cracks originate at the sub-grain level and some of them ultimately transit into critical long cracks over time. Therefore, designing the components subjected to fatigue loading merely on the long crack growth data and neglecting the short crack growth behavior can overestimate the component’s life. This aspect of short fatigue cracks become even more critical for materials used for safety critical applications such as reactor pressure vessel (RPV steel in nuclear plants. In this work, the transition behaviour of short fatigue crack gowth into long fatigue crack is studied in SA508 Grade 3 Class I low alloy steel used in RPVs. In-situ characterization of initiation, propagation and transition of short fatigue cracks is performed using fatigue stage for Scanning Electron Microscope (SEM in addition to digital microscopes fitted over a servo-hydraulic fatigue machine and correlated with the microtructural information obtained using electron backscatter diffraction (EBSD. SA508 steel having an upper bainitic microstructure have several microstructural interfaces such as phase and grain boundaries that play a significant role in controlling the short fatigue crack propagation. Specially designed and prepared short fatigue specimens (eletro-polished with varying initial crack lengths of the order of tens of microns are used in this study. The transition of such short initial cracks into long cracks is then tracked to give detailed insight into the role of each phase and phase/grain boundary with an objective of establishing Kitagawa-Takahashi diagram for the given RPV steel. The behavior of the transited long cracks is then compared with the crack propagation behavior obtained using

  5. Probabilistic fracture mechanics of nuclear structural components: consideration of transition from embedded crack to surface crack

    International Nuclear Information System (INIS)

    Yagawa, G.; Yoshimura, S.

    1999-01-01

    This paper describes a probabilistic fracture mechanics (PFM) analysis of aged nuclear reactor pressure vessel (RPV) material. New interpolation formulas of three-dimensional stress intensity factors are presented for both embedded elliptical surface cracks and semi-elliptical surface cracks. To investigate effects of transition from embedded crack to surface crack in PFM analyses, one of the PFM round-robin problems set by JSME-RC111 committee (i.e. aged RPV under normal and upset operating conditions) is solved, employing the interpolation formulas. (orig.)

  6. Terahertz non-destructive imaging of cracks and cracking in structures of cement-based materials

    Directory of Open Access Journals (Sweden)

    Shujie Fan

    2017-11-01

    Full Text Available Cracks and crack propagation in cement-based materials are key factors leading to failure of structures, affecting safety in construction engineering. This work investigated the application of terahertz (THz non-destructive imaging to inspections on structures of cement-based materials, so as to explore the potential of THz imaging in crack detection. Two kinds of disk specimens made of plain cement mortar and UHMWPE fiber concrete were prepared respectively. A mechanical expansion load device was deployed to generate cracks and control the whole process of cracking. Experimental tests were carried out on cracked specimens by using a commercial THz time domain spectroscopy (THz-TDS during loading. The results show that crack opening and propagation could be examined by THz clearly and the material factors influence the ability of crack resistance significantly. It was found that the THz imaging of crack initiation and propagation agrees with the practical phenomenon and supplies more information about damage of samples. It is demonstrated that the damage behavior of structures of cement-based materials can be successfully detected by THz imaging.

  7. Terahertz non-destructive imaging of cracks and cracking in structures of cement-based materials

    Science.gov (United States)

    Fan, Shujie; Li, Tongchun; Zhou, Jun; Liu, Xiaoqing; Liu, Xiaoming; Qi, Huijun; Mu, Zhiyong

    2017-11-01

    Cracks and crack propagation in cement-based materials are key factors leading to failure of structures, affecting safety in construction engineering. This work investigated the application of terahertz (THz) non-destructive imaging to inspections on structures of cement-based materials, so as to explore the potential of THz imaging in crack detection. Two kinds of disk specimens made of plain cement mortar and UHMWPE fiber concrete were prepared respectively. A mechanical expansion load device was deployed to generate cracks and control the whole process of cracking. Experimental tests were carried out on cracked specimens by using a commercial THz time domain spectroscopy (THz-TDS) during loading. The results show that crack opening and propagation could be examined by THz clearly and the material factors influence the ability of crack resistance significantly. It was found that the THz imaging of crack initiation and propagation agrees with the practical phenomenon and supplies more information about damage of samples. It is demonstrated that the damage behavior of structures of cement-based materials can be successfully detected by THz imaging.

  8. Radioactive tracers and the cracking modelings

    International Nuclear Information System (INIS)

    Bettens, B.

    1982-01-01

    The use of tracers (3H and 14 C) labelled in specific positions is an intensive contribution to the understanding and the revealing of the very often complex cracking modeling. The pyrolytic decay of the phenol and the cresols, of the aniline, of the phenantrene and its hydrogenated derived products were investigated and are presented as examples. The decay mechanisms give a theoretical knowledge of the thermal cracking and allow to handle the results on an industrial scale. (AF)

  9. Molecular dynamics simulation of propagating cracks

    Science.gov (United States)

    Mullins, M.

    1982-01-01

    Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.

  10. Role of hydrogen in stress corrosion cracking

    International Nuclear Information System (INIS)

    Louthan, M.R. Jr.

    1975-01-01

    Hydrogen embrittlement has been postulated as a cause of stress corrosion cracking in numerous alloy systems. Such an interrelationship is useful in design considerations because it permits the designer and working engineer to relate the literature from both fields to a potential environmental compatibility problem. The role of hydrogen in stress corrosion of high strength steels is described along with techniques for minimizing the susceptibility to hydrogen stress cracking. (U.S.)

  11. Reactor vessel nozzle cracks: a photoelastic study

    International Nuclear Information System (INIS)

    Smith, C.W.

    1979-01-01

    A method consisting of a marriage between the ''frozen stress'' photoelastic approach and the local stress field equations of linear elastic fracture mechanics for estimating stress intensity factor distributions in three dimensional, finite cracked body problems is reviewed and extensions of the method are indicated. The method is then applied to the nuclear reactor vessel nozzle corner crack problem for both Intermediate Test Vessel and Boiling Water Reactor geometries. Results are compared with those of other investigators. 35 refs

  12. Problems of tungsten crack resistance optimization

    International Nuclear Information System (INIS)

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

    1986-01-01

    Technically pure and precipitation-hardening tungsten is studied for its crack resistance in the initial and hardened states at the temperatures of 20...2000 deg C. Results of the study are presented. It is shown that hardening of tungsten base alloys in oil from the temperature corresponding to the upper boundary of the temperature region of ductile-brittle transition increases a crack propagation resistance of the studied materias at elevated and high temperatures

  13. Evaluation of flaws or service induced cracks in pressure vessels

    International Nuclear Information System (INIS)

    Riccardella, P.C.; Copeland, J.F.; Gilman, J.

    1987-01-01

    An overview of the ASME flaw evaluation procedures for nuclear pressure vessels is presented, with emphasis on fatigue crack growth evaluations. Environmental and load-rate effects are further considered with respect to new crack growth data and a time-dependent crack growth model. This new crack growth model is applied to evaluate feedwater nozzle cracking in boiling water reactors and is compared to current and past ASME crack growth curves. The time-dependent model bounds the observed cracking and indicates that more detailed consideration of material susceptibility, in terms of sulfur content and product form, is needed

  14. Steady-state propagation of interface corner crack

    DEFF Research Database (Denmark)

    Veluri, Badrinath; Jensen, Henrik Myhre

    2013-01-01

    Steady-state propagation of interface cracks close to three-dimensional corners has been analyzed. Attention was focused on modeling the shape of the interface crack front and calculating the critical stress for steady-state propagation of the crack. The crack propagation was investigated...... on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stresses as a function of the fracture criterion and corner angles. The implication of the results on the delamination is discussed in terms of crack front profiles and the critical stresses...... for propagation and the angle of intersection of the crack front with the free edge....

  15. Numerical analysis of interacting cracks in biaxial stress field

    International Nuclear Information System (INIS)

    Kovac, M.; Cizelj, L.

    1999-01-01

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

  16. Torsion of cracked nanorods using a nonlocal elasticity model

    International Nuclear Information System (INIS)

    Loya, J A; Aranda-Ruiz, J; Fernández-Sáez, J

    2014-01-01

    This paper presents a nonlocal cracked-rod model from which we have analysed the torsional vibrations of a carbon nanotube with a circumferential crack. Several types of boundary conditions, including the consideration of a buckyball at the end of the nanotube, have been studied. The nonlocal Eringen elasticity theory is used to formulate the problem. The cracked rod is modelled by dividing the cracked element into two segments connected by a torsional linear spring whose stiffness is related to the crack severity. The effect of the nonlocal small-scale parameter, crack severity, cracked section position, different boundary conditions and attached mass are examined in this work. (paper)

  17. On the application of cohesive crack modeling in cementitious materials

    DEFF Research Database (Denmark)

    Stang, Henrik; Olesen, John Forbes; Poulsen, Peter Noe

    2007-01-01

    typically for multi scale problems such as crack propagation in fiber reinforced composites. Mortar and concrete, however, are multi-scale materials and the question naturally arises, if bridged crack models in fact are more suitable for concrete and mortar as well? In trying to answer this question a model......Cohesive crack models-in particular the Fictitious Crack Model - are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models-where cohesive stresses are assumed to exist together with a stress singularity at the crack tip-on the other hand, are used...

  18. An engineering methodology for fracture analyses of tough materials

    International Nuclear Information System (INIS)

    Shih, C.F.

    1981-01-01

    The paper summarizes progress made in two research programs sponsored by the Electric Power Research Institute (EPRI), to identify viable parameters for characterizing crack inititation 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. The ultimate goal in the development of such a methodology is to establish a rational 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. (Auth.)

  19. Creep Behavior and Durability of Cracked CMC

    Science.gov (United States)

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

    2015-01-01

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

  20. Electromagnetic pulsed thermography for natural cracks inspection

    Science.gov (United States)

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-01-01

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF). PMID:28169361