Local strain in front of cracks in the case of creep fatigue

International Nuclear Information System (INIS)

Rie Kyongtschong; Olfe, J.

1993-01-01

In-situ measurements of strain fields in front of cracks were performed for high temperature Low Cycle Fatigue (LCF) with different hold times by means of a grid method. The tests were carried out on the austenitic stainless steel 304 L and the ferritic steel X22 CrMoV 12 1. Simultaneous observation of crack growth leads to a correlation between crack growth and local strain. The interaction of creep and fatigue related to strain concentration at the crackk tip and crack growth was discussed. A model is proposed which is based on the formation of cavities on grain boundaries. (orig.) [de

High temperature cracking of steels: effect of geometry on creep crack growth laws

International Nuclear Information System (INIS)

Kabiri, M.R.

2003-12-01

This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C * and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C * parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C * parameter, a second non singular term, denoted here as Q * , is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C * parameter (da/dt - C * ), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C * type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C * ), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical expressions utilised for the experimental

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

Science.gov (United States)

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

2017-01-01

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

Development of nondestructive evaluation of creep-fatigue damage in SUS316 stainless steel

International Nuclear Information System (INIS)

Shoji, Tetsuo; Kawahara, Tetsuji; Awano, Masakazu; Sato, Yasumoto

1999-01-01

Creep-fatigue is a fatal failure mode of high temperature structural materials. It is recognized that the law of linear damage, according to which creep-fatigue damage is expressed by the sum of the creep damage and the fatigue damage, is inadequate to evaluate creep-fatigue damage. This is due to the fact that the law of linear damage does not include the effect of interaction between the creep damage and the fatigue damage. Consequently, development of direct measurement of damage accumulation on the sample of interest is required for plant life evaluation. In this study, the induced current focusing potential drop (ICFPD) technique was used to evaluate the depth of small surface cracks in SUS316FR stainless steel which was subjected to creep-fatigue damage. It is shown that the potential drop increased during the micro-crack initiation and propagation. Correspondingly, the ICFPD technique applied to estimate micro-crack depth changes was used to accurately evaluate the residual life of creep-fatigue damaged structural materials. (author)

Creep-fatigue damage in austenitic stainless steels

International Nuclear Information System (INIS)

Rezgui, Brahim.

1980-06-01

This is a study of hold time effects on the low cycle fatigue (L.C.F.) properties of 316L austenitic stainless steel at 600 0 C in air. Results obtained for different plastic strain levels indicate that a tension hold time at peak strain lead to a reduction in fatigue life. The importance of this effect depend on the length of hold period, and also on the strain amplitude. No saturation had been observed. Metallographic and microstructural analysis of failed specimens indicates mechanisms by which failure is produced. For continuous cycling the fractures occurs by the initiation and the propagation of a trans-granular crack. Creep damage in the bulk of material is formed during periods of tensile stress relaxation; it causes a change in the failure mode which became intergranular. It is the interaction between this creep-damage and fatigue cracks which is partly responsable for the reduction in the fatigue life. Predictions based upon linear cumulative damage method indicate that virgin material properties may be irrelevant in creep-fatigue interactions [fr

Creep-fatigue crack initiation assessment on thick circumferentially notched 316L tubes under cyclic thermal shocks and uniform tension with the σd approach

International Nuclear Information System (INIS)

Michel, B.; Poette, C.

1997-01-01

For crack initiation assessment under creep fatigue loading, in high temperature Fast Reactor's components, specific approaches based on fracture mechanics analysis had to be developed. In the present paper the crack initiation assessment method proposed in the A16 document is presented. The so called ''σ d method'' is also validated on experimental results for tubular specimens with internal axisymmetric surface cracks. Experimental data are extracted from the TERFIS program carried out on a sodium test device at the CEA Cadarache. Metallurgical examinations on TERFIS specimens confirm that the initiation assessment of the ''σ d '' approach is conservative even for a different geometry than the CT specimen on which the method was set up. However, the conservatism is reduced when the creep residual stress field is relaxed during the hold time. An investigation concerning this last point is needed in order to know if relaxing the stress, when using a lower bound of the mechanical properties, always keeps a safety margin. (author). 14 refs, 10 figs, 4 tabs

High-Temperature Creep-Fatigue Behavior of Alloy 617

Directory of Open Access Journals (Sweden)

Rando Tungga Dewa

2018-02-01

Full Text Available This paper presents the high-temperature creep-fatigue testing of a Ni-based superalloy of Alloy 617 base metal and weldments at 900 °C. Creep-fatigue tests were conducted with fully reversed axial strain control at a total strain range of 0.6%, 1.2%, and 1.5%, and peak tensile hold time of 60, 180, and 300 s. The effects of different constituents on the combined creep-fatigue endurance such as hold time, strain range, and stress relaxation behavior are discussed. Under all creep-fatigue tests, weldments’ creep-fatigue life was less than base metal. In comparison with the low-cycle fatigue condition, the introduction of hold time decreased the cycle number of both base metal and weldments. Creep-fatigue lifetime in the base metal was continually decreased by increasing the tension hold time, except for weldments under longer hold time (>180 s. In all creep-fatigue tests, intergranular brittle cracks near the crack tip and thick oxide scales at the surface were formed, which were linked to the mixed-mode creep and fatigue cracks. Creep-fatigue interaction in the damage-diagram (D-Diagram (i.e., linear damage summation was evaluated from the experimental results. The linear damage summation was found to be suitable for the current limited test conditions, and one can enclose all the data points within the proposed scatter band.

Experimental study on creep-fatigue interaction behavior of GH4133B superalloy

International Nuclear Information System (INIS)

Hu Dianyin; Wang Rongqiao

2009-01-01

The creep-fatigue tests have been conducted with nickel-based superalloy GH4133B at 600 deg. C in three cases of type loading to study the creep-fatigue behavior of the alloy and the loading history effect on the creep-fatigue damage. Since the conventional linear cumulative damage rule failed in evaluating the creep-fatigue life based on experimental data, a continuous non-linear model proposed by Mao et al. was employed to describe the creep-fatigue interaction. The creep-fatigue damage in the cases of continuous cyclic creep loading (CF) and prior fatigue followed by creep loading (F + C) was larger than unity and smaller than unity when the type loading was prior creep followed by fatigue loading (C + F). Scanning electron microscope (SEM) analyses of the fracture surface showed that the cracks initiated from the specimen surface and the fracture modes in different loading history were different. The crack mode at CF loading depended on the cyclic period. In the case of F + C loading, the primary fracture mode was transgranular, and in the condition where the type of waveform was C + F, the fracture mode was of mixed transgranular and intergranular type. In addition, the origin of the history effect on creep-fatigue interaction was explained by the SEM observations.

Creep-fatigue propagation of semi-elliptical crack at 650 deg. C in 316L(N) stainless steel plates with or without welded joints

International Nuclear Information System (INIS)

Curtit, F.

2000-01-01

This study realised in LISN Laboratory of CEA Saclay, deals with the creep fatigue propagation of semi elliptical crack at the temperature of 650 deg C in 316L(N) stainless steel plates with or without welded joints. A vast majority of the studies on creep fatigue propagation models are based on specimen (CT) especially designed for crack propagation study. The PLAQFLU program performed in LISN laboratory deals with the application and adaptation of these models to complex crack shape, which are more representative of the cracks observed in industrial components. In this scope, we use propagation tests realised at the temperature of 650 deg C with wide plates containing semi elliptical defects. For some of them, the initial defect is machined in the middle of a welded joint, which constitute a privileged site for the crack initiation. The approach used in this study is based on global parameters of fracture mechanics. At first, tests on CT specimen are used in order to determine the propagation laws correlating the crack growth rate to the global parameters K or C * . These laws are then supposed to be intrinsic to our materials and are used to analysed the semi elliptical crack propagation. The analysis of the comportment of the crack during the hold time demonstrates the possibility to establish a correlation between the crack propagation both in the deepest and the surface point and the local value of C * . These correlations are coherent in the different points of the crack front for the different applied hold times, and they present a reasonably good agreement with the creep propagation law identified on CT specimen. The simulation of test performed on based metal specimen with a model of summation of both creep and pure fatigue crack growth gives acceptable results when the calculus of the simplified expression of C * s considers a continuous evolution of creep deformations rate during the all test. (author)

Stable and unstable fatigue crack propagation during high temperature creep-fatigue in austenitic steels: the role of precipitation

International Nuclear Information System (INIS)

Lloyd, G.J.; Wareing, J.

1979-01-01

The distinction between stable and unstable fatigue crack propagation during high temperature creep-fatigue in austenitic stainless steels is introduced. The transition from one class of behavior to the other is related to the precipitate distribution and to the nature of the prevailing crack path. It is shown by reference to new studies and examples drawn from the literature that this behavior is common to both high strain and predominantly elastic fatigue in austenitic stainless steels. The relevance of this distinction to a mechanistic approach to high temperature plant design is discussed

Probabilistic and microstructural aspects of fatigue cracks initiation in Inconel 718

International Nuclear Information System (INIS)

Alexandre, F.

2004-03-01

Thermomechanical treatments have been recently developed to produce Inconel 718DA (Direct Aged). This alloy optimisation leads to an increase of the fatigue life but also the scatter. The aim of this study is on the one hand the understanding of the fatigue crack initiation mechanisms and on the other hand the modelling of the fatigue life and the scatter. An experimental study showed that the fatigue cracks were initiated from carbide particles in fine grain alloy. Interrupted tensile tests show that the particles cracking occurred at the first quarter of the fatigue cycle. Fatigue behaviour tests were also performed on various grain size 718 alloys. The last experimental part was devoted to measurements of the low cycle fatigue crack growth rates using a high focal distance microscope. For these tests, EDM micro-defects were used for the fatigue crack initiation sites. This method was also used to observe the small fatigue crack coalescence. A fatigue life model is proposed. It is based on the three fatigue crack initiation mechanisms competition: particle crack initiation on the surface, internal particle crack initiation and Stade I crack initiation. The particle fatigue crack initiation is supposed instantaneous at a critical stress level. The Tanaka and Mura model is used for analysing the Stage I crack initiation number of cycles. The fatigue crack growth rate was analysed using the Tomkins model identified on the small fatigue crack growth rate measurements. The proposed fatigue life model decomposed in three levels: a deterministic one and two probabilistic with and without crack coalescence. (author)

Sequential creep-fatigue interaction in austenitic stainless steel type 316L-SPH

International Nuclear Information System (INIS)

Tavassoli, A.A.; Mottot, M.; Petrequin, P.

1986-01-01

Influence of a prior creep or fatigue exposure on subsequent fatigue or creep properties of stainless steel type 316 L SPH has been investigated. The results obtained are used to verify the validity of time and cycle fraction rule and to obtain information on the effect of very long intermittent hold times on low cycle fatigue properties, as well as on transitory loads occurring during normal service of some structural components of LMFBR reactors. Creep and fatigue tests have been carried out at 600 0 C and under conditions yielding equal or different fatigue saturation and creep stresses. Prior creep damage levels introduced range from primary to tertiary creep, whilst those of fatigue span from 20 to 70 percent of fatigue life. In both creep-fatigue and fatigue-creep sequences in the absence of a permanent prior damage (cavitation or cracking) the subsequent resistance of 316 L-SPH to fatigue or creep is unchanged, if not improved. Thin foils prepared from the specimens confirmed these observations and showed that the dislocation substructure developed during the first mode of testing is quickly replaced by that of the second mode. Grain boundary cavitation does not occur in 316 L-SPH during creep exposures to well beyond the apparent end of secondary stage and as a result prior creep exposures up to approximately 80% of rupture life do not affect fatigue properties. Conversely, significant surface cracks were found in the prior fatigue tested specimens after above about 50% life. In the presence of such cracks the subsequent creep damage was localized at the tip of the main crack and the remaining creep life was found to be usually proportional to the effective specimen cross section. Creep and fatigue sequential damage are not necessarily additive and this type of loadings are in general less severe than the repeated creep-fatigue cycling. 17 refs.

Creep Crack Initiation and Growth Behavior for Ni-Base Superalloys

Science.gov (United States)

Nagumo, Yoshiko; Yokobori, A. Toshimitsu, Jr.; Sugiura, Ryuji; Ozeki, Go; Matsuzaki, Takashi

The structural components which are used in high temperature gas turbines have various shapes which may cause the notch effect. Moreover, the site of stress concentration might have the heterogeneous microstructural distribution. Therefore, it is necessary to clarify the creep fracture mechanism for these materials in order to predict the life of creep fracture with high degree of accuracy. In this study, the creep crack growth tests were performed using in-situ observational testing machine with microscope to observe the creep damage formation and creep crack growth behavior. The materials used are polycrystalline Ni-base superalloy IN100 and directionally solidified Ni-base superalloy CM247LC which were developed for jet engine turbine blades and gas turbine blades in electric power plants, respectively. The microstructural observation of the test specimens was also conducted using FE-SEM/EBSD. Additionally, the analyses of two-dimensional elastic-plastic creep finite element using designed methods were conducted to understand the effect of microstructural distribution on creep damage formation. The experimental and analytical results showed that it is important to determine the creep crack initiation and early crack growth to predict the life of creep fracture and it is indicated that the highly accurate prediction of creep fracture life could be realized by measuring notch opening displacement proposed as the RNOD characteristic.

Creep fracture and creep-fatigue fracture in ceramics and ceramic composites

International Nuclear Information System (INIS)

Suresh, S.

1993-01-01

This paper summarizes recent advances in the areas of subcritical crack growth in ceramics subjected to static and cyclic loads at elevated temperatures. Attention is devoted to the specific role of pre-existing and in-situ-formed glass films in influencing creep fracture and creep-fatigue fracture. Experimental results on the effects of cyclic frequency and load ratio, along with detailed transmission electron microscopy of crack-tip and crack-wake damage are highlighted. Some general conclusions are drawn about the dependence of high-temperature damage tolerance on interfacial glass films and about the susceptibility of ceramic materials to cyclic fatigue fracture

Standard test method for creep-fatigue testing

CERN Document Server

American Society for Testing and Materials. Philadelphia

2009-01-01

1.1 This test method covers the determination of mechanical properties pertaining to creep-fatigue deformation or crack formation in nominally homogeneous materials, or both by the use of test specimens subjected to uniaxial forces under isothermal conditions. It concerns fatigue testing at strain rates or with cycles involving sufficiently long hold times to be responsible for the cyclic deformation response and cycles to crack formation to be affected by creep (and oxidation). It is intended as a test method for fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. The cyclic conditions responsible for creep-fatigue deformation and cracking vary with material and with temperature for a given material. 1.2 The use of this test method is limited to specimens and does not cover testing of full-scale components, structures, or consumer products. 1.3 This test method is primarily ...

Crack initiation at high temperature on an austenitic stainless steel; Amorcage de fissure a haute temperature dans un acier inoxydable austenitique

Energy Technology Data Exchange (ETDEWEB)

Laiarinandrasana, L

1994-11-25

The study deals with crack initiation at 600 and 650 degrees Celsius, on an austenitic stainless steel referenced by Z2 CND 17 12. The behaviour laws of the studied plate were update in comparison with existing data. Forty tests were carried out on CT specimens, with continuous fatigue with load or displacement controlled, pure creep, pure relaxation, creep-fatigue and creep-relaxation loadings. The practical initiation definition corresponds to a small crack growth of about the grain size. The time necessary for the crack to initiate is predicted with fracture mechanics global and local approaches, with the helps of microstructural observations and finite elements results. An identification of a `Paris`law` for continuous cyclic loading and of a unique correlation between the initiation time and C{sup *}{sub k} for creep tests was established. For the local approach, crack initiation by creep can be interpreted as the reaching of a critical damage level, by using a damage incremental rule. For creep-fatigue tests, crack growth rates at initiation are greater than those of Paris`law for continuous fatigue. A calculation of a transition time between elastic-plastic and creep domains shows that crack initiation can be interpreted whether by providing Paris`law with an acceleration term when the dwell period is less than the transition time, or by calculating a creep contribution which relies on C{sup *}{sub k} parameter when the dwell period and/or the initiation times are greater than the transition time. Creep relaxation tests present crack growth rates at initiation which are less than those for `equivalent` creep-fatigue tests. These crack growth rates when increasing hold time, but also when temperature decreases. Though, for hold times which are important enough and at lower temperature, there is no effect of the dwell period insofar as crack growth rate is equal to continuous fatigue Paris law predicted ones. (Abstract Truncated)

Creep-fatigue behaviour of the titanium alloy IMI 834 at 600 C

International Nuclear Information System (INIS)

Nowack, H.; Kordisch, T.

1998-01-01

In the present study the creep-fatigue behaviour of the titanium alloy IMI 834 at 600 C was investigated. A comparison of the crack initiation life behaviour and of the crack propagation as caused by different types of complex creep-fatigue cycles (with hold times into tension and/or into compression direction and with different loading rates into tension and/or into compression direction) showed, that a slow increase of the loadings into tension reduced the life and increased the crack velocity more than hold times at the maximum load. Furthermore, there existed environmental influences. On the basis of the experimental investigations the prediction capability of convenient crack initiation life prediction methods was evaluated. It turned out that the prediction capability of the strain range partitioning method could be improved if it was frequency modified. The prediction capability of the frequency modification method could also be improved, if mean stresses in the cycles were explicitely accounted for. In the short and long crack stage the propagation behaviour could be correlated well if the effective cyclic J-integral was used. This is of importance for damage tolerance considerations. Because the strains and the stresses at the crack tip are most important for the crack propagation behaviour, they were analysed on the basis of the finite element method. It was found that the strains and stresses differed for different types of creep-fatigue cycles. (orig.)

Creep-fatigue monitoring system for header ligaments of fossil power plants

International Nuclear Information System (INIS)

Chen, K.L.; Deardorf, A.F.; Copeland, J.F.; Pflasterer, R.; Beckerdite, G.

1993-01-01

The cracking of headers (primary and secondary superheater outlet, and reheater outlet headers) at ligament locations is an important issue for fossil power plants. A model for crack initiation and growth has been developed, based on creep-fatigue damage mechanisms. This cracking model is included in a creep-fatigue monitoring system to assess header structural integrity under high temperature operating conditions. The following principal activities are required to achieve this goal: (1) the development of transfer functions and (2) the development of a ligament cracking model. The first task is to develop stress transfer functions to convert measured (monitored) temperatures, pressures and flow rates into stresses to be used to compute damage. Elastic three-dimensional finite element analyses were performed to study transient thermal stress behavior. The sustained pressure stress redistribution due to high temperature creep was studied by nonlinear finite element analyses. The preceding results are used to derive Green's functions and pressure stress gradient transfer functions for monitoring at the juncture of the tube with the header inner surface, and for crack growth at the ligaments. The virtual crack closure method is applied to derive a stress intensity factor K solution for a corner crack at the tube/header juncture. Similarly, using the reference stress method, the steady state creep crack growth parameter C * is derived for a header corner crack. The C * solution for a small corner crack in a header can be inserted directed into the available C t solution, along with K to provide the complete transient creep solution

Improved methods of creep-fatigue life assessment of components

Energy Technology Data Exchange (ETDEWEB)

Scholz, Alfred; Berger, Christina [Inst. fuer Werkstoffkunde (IfW), Technische Univ. Darmstadt (Germany)

2009-07-01

The improvement of life assessment methods contributes to a reduction of efforts at design and an effective long term operation of high temperature components, reduces technical risk and increases high economical advantages. Creep-fatigue at multi-stage loading, covering cold start, warm start and hot start cycles in typical loading sequences e.g. for medium loaded power plants, was investigated here. At hold times creep and stress relaxation, respectively, lead to an acceleration of crack initiation. Creep fatigue life time can be calculated by a modified damage accumulation rule, which considers the fatigue fraction rule for fatigue damage and the life fraction rule for creep damage. Mean stress effects, internal stress and interaction effects of creep and fatigue are considered. Along with the generation of advanced creep data, fatigue data and creep fatigue data as well scatter band analyses are necessary in order to generate design curves and lower bound properties inclusive. Besides, in order to improve lifing methods the enhancement of modelling activities for deformation and life time are important. For verification purposes, complex experiments at variable creep conditions as well as at creep fatigue interaction under multi-stage loading are of interest. Generally, the development of methods to transfer uniaxial material properties to multiaxial loading situations is a current challenge. For specific design purposes, a constitutive material model is introduced which is implemented as an user subroutine for Finite Element applications due to start-up and shut-down phases of components. Identification of material parameters have been performed by Neural Networks. (orig.)

Creep-fatigue evaluation method for modified 9Cr-1Mo steel

International Nuclear Information System (INIS)

Wada, Y.; Aoto, K.

1997-01-01

As creep-fatigue evaluation methods on normalized and tempered Modified 9Cr-1Mo steel for design use, the time fraction rule and the simplified conventional ductility exhaustion rule are investigated for the prediction of tension strain hold creep-fatigue damage of this material. For the above investigation, stress relaxation behaviour during strain hold has to be analyzed using stress-strain-time relation. The initial value of stress relaxation was determined by cyclic stress-strain curves in continuous cycling fatigue tests. Cyclic stress-strain behaviour of Mod.9Cr-1Mo(NT) steel is different from that of austenitic stainless steels, so this effect was considered. Stress relaxation analysis was performed using static creep strain-time relation and conventional hardening rule. The time fraction by using the above stress relaxation analysis results can give good prediction for creep-fatigue life of Mod.9Cr-1Mo(NT) steel. For design use it is practical to be able to estimate creep damages conservatively by both strain behaviour of cyclic plastic (in continuous cycling fatigue tests) and monotonic creep (in standard creep tests). The life reduction by strain hold at the minimum peak of compressive stress in creep-fatigue tests was examined, and this effects can be evaluated by the relationship between the location of oxidation and the effective deformation at crack tip. In an accelerated oxidation environment, for example in high temperature and high pressure steam, a different approach for life reduction should be developed based on the mechanism of growth of oxide and crack growth with oxidation. However, in the creep damage dominant region, its effect is saturated and the effect of cavity growth along grain boundary becomes dominant for long-term strain hold in the high temperature conditions. (author). 6 refs, 6 figs

Improved methods for prediction of creep-fatigue in next generation conventional and nuclear plant

International Nuclear Information System (INIS)

Payten, Warwick

2012-01-01

Materials technology poses a major challenge in the design and construction of next generation super critical/ultra super critical power plant (SC/USC) and Generation IV (GenIV) nuclear plant. New plant is expected to have in the order of a 60 year life-time, imposing complex design difficulties in areas of creep rupture and creep fatigue damage. For SC/USC plant, the main goal is the enhancement of performance by raising the steam pressure and temperatures. In order to achieve these goals materials with acceptable creep rupture strength at design temperatures and pressures must be used. In GenIV designs, the issue is more complex, with both low and high tempera-ture designs. A key requirement in the majority of the designs, however, will be acceptable resistance to creep rupture, fatigue cracking, creep fatigue interactions, with the additional effects of void swelling and irradiation creep. The accumulation of creep fatigue damage over time in both SC/USC and GenIV plant will be one of the principal damage mechanisms. This will eventually lead to crack initiation in critical high temperature equipment. Hence, improved knowledge of creep and fatigue interactions is a necessary development as components in power-generating plants move to operate at high temperature under cyclic conditions. The key to safe, reliable operation of these high-energy plants will depend on understanding the factors that affect damage initiation and propagation, as well as developing and validating technologies to predict the accumulation of damage in systems and components.

Crack initiation modeling of a directionally-solidified nickel-base superalloy

Science.gov (United States)

Gordon, Ali Page

crystal plasticity model was used to simulate the material behavior in the L and T orientations. The constitutive model was implemented in ABAQUS and a parameter estimation scheme was developed to obtain the material constants. A physically-based model was developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model. Assuming a unique relationship between the damage fraction and cycle fraction with respect to cycles to crack initiation for each damage mode, the total crack initiation life has been represented in terms of the individual damage components (fatigue, creep-fatigue, creep, and oxidation-fatigue) observed at the end state of crack initiation.

Some questions regarding the interaction of creep and fatigue

International Nuclear Information System (INIS)

James, L.A.

1975-04-01

Data are presented from fatigue-crack growth tests conducted on Type 304 S.S. in inert environments at elevated temperatures which show that the thermal-activation noted in similar tests run in air environments is not present in the inert environment. Similar observations from the literature are reviewed, including the observation that the time-dependency noted in tests conducted in elevated temperature air environments is also greatly suppressed in inert environments. These findings suggest that an interaction between the fatigue process and the corrosive air environments is responsible for the thermally activated time-dependent behavior often attributed to creep-fatigue interaction. Data are also presented which show that the fatigue-crack growth behavior of Type 304 S.S. subjected to significant creep damage prior to fatigue testing does not differ appreciably from the behavior of material not subjected to prior creep damage, again indicating minimal interaction between creep and fatigue. It is suggested that in the temperature range where pressure vessels and piping are generally designed to operate (i.e. below about one-half the absolute melting temperature of the alloy), the interaction between creep and fatigue is far less significant than once supposed, and that the major parameter interacting with the fatigue process is that of high-temperature corrosion. (39 references, 12 fig) (auth)

Cumulative fatigue and creep-fatigue damage at 3500C on recrystallized zircaloy 4

International Nuclear Information System (INIS)

Brun, G.; Pelchat, J.; Floze, J.C.; Galimberti, M.

1985-06-01

An experimental programme undertaken by C.E.A., E.D.F. and FRAGEMA with the aim of characterizing the fatigue and creep fatigue behaviour of zircaloy-4 following annealing treatments (recrystallized, stress-delived) is in progress. The results given below concern only recrystallized material. Cyclic properties, low-cycle fatigue curves and creep behaviour laws under stresses have been established. Sequential tests of pure fatigue and creep-fatigue were performed. The cumulative life fractions at fracture depend on the sequence of leading, stress history and number of cycles of prestressing. The MINER's rule appears to be conservative with regard to a low-high loading sequence whereas it is not for the reverse high-low loading sequences. Fatigue and creep damage are not interchangeable. Pre-creep improves the fatigue resistance. Pre-fatigue improves the creep strength as long as the beneficial effect of cyclic hardening overcomes the damaging effect of surface cracking. The introduction of a tension hold time into the fatigue cycle slightly increases cyclic hardening and reduces the number of cycles to failure. For hold times of less than one hour, the sum of fatigue and creep life fractions is closed to one

Multiaxial creep-fatigue rules

International Nuclear Information System (INIS)

Spindler, M.W.; Hales, R.; Ainsworth, R.A.

1997-01-01

Within the UK, a comprehensive procedure, called R5, is used to assess the high temperature response of structures. One part of R5 deals with creep-fatigue initiation, and in this paper we describe developments in this part of R5 to cover multiaxial stress states. To assess creep-fatigue, damage is written as the linear sum of fatigue and creep components. Fatigue is assessed using Miner's law with the total endurance split into initiation and growth cycles. Initiation is assessed by entering the curve of initiation cycles vs strain range using a Tresca equivalent strain range. Growth is assessed by entering the curve of growth cycles vs strain range using a Rankine equivalent strain range. The number of allowable cycles is obtained by summing the initiation and growth cycles. In this way the problem of defining an equivalent strain range applicable over a range of endurance is avoided. Creep damage is calculated using ductility exhaustion methods. In this paper we address two aspects; first, the nature of stress relaxation and, hence, accumulated creep strain in multiaxial stress fields; secondly, the effect of multiaxial stress on creep ductility. The effect of multiaxial stress state on creep ductility has been examined using experimental data and mechanistic models. Good agreement is demonstrated between an empirical description of test data and a cavity growth model, provided a simple nucleation criterion is included. A simple scaling factor is applied to uniaxial creep ductility, defined as a function of stress state. The factor is independent of the cavity growth mechanisms and yields a value of equivalent strain which can be conveniently used in determining creep damage by ductility exhaustion. (author). 14 refs, 4 figs

A metallographic examination of structural degradation during creep-fatigue

International Nuclear Information System (INIS)

Hales, R.

1979-07-01

A series of specimens of T316 stainless steel, which had been tested under creep-fatigue conditions, has been examined by optical and scanning electron microscopy. The development of cavities which are associated with grain-boundary carbide precipitates has been recorded. These cavities increase in size and number with increasing hold time at peak tensile strain and cause the propagating fatigue crack to follow an intergranular path. At a strain range of +- 0.25% the dominant damage mechanism is due to creep damage when the tensile hold time is greater than one minute. The fatigue crack which causes final failure is nucleated at a stress raiser and it is possible that in a smooth specimen failure may occur without the nucleation of a fatigue crack at all but rather by ductile shearing. (author)

Creep-Fatigue Failure Diagnosis

Science.gov (United States)

Holdsworth, Stuart

2015-01-01

Failure diagnosis invariably involves consideration of both associated material condition and the results of a mechanical analysis of prior operating history. This Review focuses on these aspects with particular reference to creep-fatigue failure diagnosis. Creep-fatigue cracking can be due to a spectrum of loading conditions ranging from pure cyclic to mainly steady loading with infrequent off-load transients. These require a range of mechanical analysis approaches, a number of which are reviewed. The microstructural information revealing material condition can vary with alloy class. In practice, the detail of the consequent cracking mechanism(s) can be camouflaged by oxidation at high temperatures, although the presence of oxide on fracture surfaces can be used to date events leading to failure. Routine laboratory specimen post-test examination is strongly recommended to characterise the detail of deformation and damage accumulation under known and well-controlled loading conditions to improve the effectiveness and efficiency of failure diagnosis. PMID:28793676

Creep and fatigue of alloy 800 in helium

International Nuclear Information System (INIS)

Cook, R.H.

1975-01-01

Proposals for use of Alloy 800 as a H.T.R. boiler material have prompted studies of its creep and high temperature fatigue properties in impure helium with comparative tests in air. In impure helium, as expected in a H.T.R., reactions of potential importance are selective oxidation (of chromium, aluminium and titanium) and possibly carburisation from carbon monoxide or methane. In air, general oxidation will occur, possibly accompanied by nitridation. The effects of these reactions will depend on specimen geometry and the nature of the deformation. Two important possibilities are: (i) that environment affects the structure and properties of a surface zone of material undegoing uniform deformation (this may modify creep rate and crack nucleation); and (ii) that environment affects behaviour of a small region (e.g. at the root of a notch or ahead of a crack) in a specimen undergoing non-uniform deformation (this will modify crack growth and hence rupture life or fatigue endurance). This paper summarises experimental work demonstrating an influence of the above reactions on mechanical properties of austenitic steels and nickel-based alloys, drawing examples where possible from the limited data available on Alloy 800. Whilst nitridation and carburisation may simply increase creep resistance at the expense of ductility (and possibly of fatigue resistance), the effects of oxidation are complex. A high oxygen pressures (as in air) oxygen may reduce creep and fatigue resistance by promoting cavitation but formation of oxide in cracks can reduce their propagation rate. At low oxygen pressures, as expected in H.T.R. helium, oxygen enhanced cavitation is less likely, but selective oxidation along grain boundaries can sometimes assist crack nucleation. (author)

Evaluation of long-term creep-fatigue life of stainless steel weldment based on a microstructure degradation model

International Nuclear Information System (INIS)

Asayama, Tai; Hasebe, Shinichi

1997-01-01

This paper describes a newly developed analytical method of evaluation of creep-fatigue strength of stainless weld metals. Based on the observation that creep-fatigue crack initiates adjacent to the interface of sigma-phase/delta-ferrite and matrix, a mechanistic model which allows the evaluation of micro stress/strain concentration adjacent to the interface was developed. Fatigue and creep damage were evaluated using the model which describes the microstructure after exposed to high temperatures for a long time. Thus it was made possible to predict analytically the long-term creep-fatigue life of stainless steel metals whose microstructure is degraded as a result of high temperature service. (author)

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

Effect of microstructure and environment on the crack growth behaviour on Inconel 718 alloy at 650/sup 0/C under fatigue, creep and combined loading

Energy Technology Data Exchange (ETDEWEB)

Pedron, J P; Pineau, A

1982-11-01

The crack growth properties of various microstructures developed in one heat of Inconel 718 alloy were investigated at 650/sup 0/C under air and vacuum environments. The microstructures included fine-grained material (ASTM grain sizes 6-8), coarse-grained material (ASTM grain sizes 3-4) and material of a necklace structure (ASTM grain sizes 3-4 and 8-10). The effect of grain boundary ..beta.. (Ni/sub 3/Nb) phase precipitation was also studied. Continuous fatigue, creep and creep-fatigue conditions were examined. For continuous fatigue the influence of frequency was investigated over the range between 5x10/sup -2/ and 20 Hz. For creep-fatigue conditions, hold times of 10 and 300 s were superimposed on a 5x10/sup -2/ Hz triangular wave shape signal. It was shown that the grain boundary microstructure had a very strong effect when the fatigue crack propagation behaviour was essentially time dependent. This effect is associated with the occurrence of brittle intergranular fracture and dramatic increases in crack growth rate. The microstructure had no effect under vacuum testing.

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)

Modeling of creep-fatigue interaction of zirconium α under cyclic loading at 200 C

International Nuclear Information System (INIS)

Vogel, C.

1996-04-01

The present work deals with mechanical behaviour of zirconium alpha at 200 deg. C and crack initiation prediction methods, particularly when loading conditions lead to interaction of fatigue and creep phenomena. A classical approach used to study interaction between cyclic effects and constant loading effects does not give easy understanding of experimental results. Therefore, a new approach has been developed, which allow to determine a number of cycles for crack initiation for complex structures under large loading conditions. To study influence of fatigue and creep interaction on crack initiation, a model was chosen, using a scalar variable, giving representation of the material deterioration state. The model uses a non linear cumulating effect between the damage corresponding to cyclic loads and the damage correlated to time influence. The model belongs to uncoupled approaches between damage and behaviour, which is described here by a two inelastic deformations model. This mechanical behaviour model is chosen because it allows distinction between a plastic and a viscous part in inelastic flow. Cyclic damage is function of stress amplitude and mean stress. For the peculiar sensitivity of the material to creep, a special parameter bas been defined to be critical toward creep damage. It is the kinematic term associated to state variables describing this type of hardening in the viscous mechanism. (author)

Fatigue and creep-fatigue deformation of an ultra-fine precipitate strengthened advanced austenitic alloy

Energy Technology Data Exchange (ETDEWEB)

Carroll, M.C., E-mail: Mark.Carroll@INL.gov [Idaho National Laboratory, 1955 Fremont, PO Box 1625, Idaho Falls, ID 83415-2218 (United States); Carroll, L.J. [Idaho National Laboratory, 1955 Fremont, PO Box 1625, Idaho Falls, ID 83415-2218 (United States)

2012-10-30

An advanced austenitic alloy, HT-UPS (high-temperature ultrafine-precipitation-strengthened), has been identified as an ideal candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS alloys demonstrate improved creep resistance relative to 316 stainless steel (SS) through additions of Ti and Nb, which precipitate to form a widespread dispersion of stable nanoscale metallic carbide (MC) particles in the austenitic matrix. To investigate the behavior in more representative conditions than are offered by uniaxial creep tests, the low-cycle continuous fatigue and combined creep-fatigue response of an HT-UPS alloy have been investigated at 650 Degree-Sign C and 1.0% total strain, with an R-ratio of -1 and hold times at peak tensile strain of up to 150 min. The cyclic deformation response of HT-UPS is directly compared to that of standard 316 SS. The measured values for total cycles to failure between the two alloys are similar, despite differences in peak stress profiles and in qualitative observations of the deformed microstructures. Crack propagation is primarily transgranular in both fatigue and creep-fatigue of each alloy at the investigated conditions. Internal grain boundary damage in the form of fine cracks resulting from the tensile hold is present following the application of hold times of 60 min and longer, and considerably more internal cracks are quantifiable in 316 SS than in HT-UPS. The dislocation substructures observed in the deformed material differ substantially; an equiaxed cellular structure is observed in the microstructure of 316 SS, whereas HT-UPS exhibits widespread and relatively homogenous tangles of dislocations pinned by the nanoscale MC precipitates. The significant effect of the fine distribution of precipitates on observed fatigue and creep-fatigue response is described in three distinct behavioral regions as the microstructure evolves with continued cycling.

Reduction factors for creep strength and fatigue life of modified 9 Cr-1 Mo steel weldments

International Nuclear Information System (INIS)

Blass, J.J.; Battiste, R.L.; O'Connor, D.G.

1991-01-01

The provisions of ASME B ampersand PV Code Case N-47 currently include reduction factors for creep strength and fatigue life of weldments. To provide experimental confirmation of such factors for modified 9 Cr-1 Mo steel, tests of tubular specimens were conducted at 538 degree C (1000 degree F). Three creep-rupture specimens with longitudinal welds were tested in tension; and, of three with circumferential welds, two were tested in tension and one in torsion. In each specimen with a circumferential weld, a nonuniform axial distribution of strain was easily visible. The test results were compared to an existing empirical model of creep-rupture life. For the torsion test, the comparison was based on a definition of equivalent normal stress recently adopted in Code Case N-47. Some 27 fatigue specimens, with longitudinal, circumferential, or no welds, were tested under axial or torsional strain control. In specimens with welds, fatigue cracking initiated at fusion lines. In axial tests cracks grew in the circumferential direction, and in torsional tests cracks grew along fusion lines. The test results were compared to empirical models of fatigue life based on two definition of equivalent normal strain range. The results have provided some needed confirmation of the reduction factors for creep strength and fatigue life of modified 9 Cr-1 Mo steel weldments currently under consideration by ASME Code committees. 8 refs., 5 figs

Determination and demarcation of fatigue crack initiation phase in rotating bending condition

International Nuclear Information System (INIS)

Pasha, R.A.; Rehman, K.; Shah, M.

2012-01-01

In engineering applications, components often experience cyclic loading and therefore, have crack initiation propagation phase. In this research work experimental demarcation of fatigue crack initiation has been investigated. Initiation phase of fatigue life of Aluminium was determined by using single and two step fatigue loading test on four point rotating bending fatigue testing machine. Experimental data is used to determine the distinction between the initiation and propagation phase. Initiation phase is determined at different stress levels. The obtained results demonstrate the effect of stress level on initiation phase and propagation phase. (author)

A proposal of predictive methods of crack propagation life and remaining life of structural metal under creep-fatigue interacted conditions by use of X-ray profile analysis

International Nuclear Information System (INIS)

Ohnami, M.; Sakane, M.; Nishino, S.

1987-01-01

The following two series of studies are described: One is crack propagation life prediction in high-temperature low-cycle fatigue tests under triangular and trapezoidal strain or stress waves for austenitic stainless steel by X-ray fractography. Another is remaining life prediction of the steel under creep-fatigue interacted conditions by applying the concept of the remaining life diagram and X-ray profile analysis. Particle size and microstrain obtained by X-ray profile analysis were effective nondestructive parameters for estimating crack propagation life and remaining life in creep-fatigue interaction

Benefits of high gradient solidification for creep and low cycle fatigue of AM1 single crystal superalloy

Energy Technology Data Exchange (ETDEWEB)

Steuer, S., E-mail: Susanne.Steuer@ensma.fr [Institut Pprime, CNRS – ENSMA – Université de Poitiers, UPR CNRS 3346, Department of Physics and Mechanics of Materials, ENSMA – Téléport 2, 1 avenue Clément Ader, BP 40109, 86961 Futuroscope Chasseneuil Cedex (France); Villechaise, P. [Institut Pprime, CNRS – ENSMA – Université de Poitiers, UPR CNRS 3346, Department of Physics and Mechanics of Materials, ENSMA – Téléport 2, 1 avenue Clément Ader, BP 40109, 86961 Futuroscope Chasseneuil Cedex (France); Pollock, T.M. [Materials Department, University of California Santa Barbara, Santa Barbara, CA 93106-5050 (United States); Cormier, J. [Institut Pprime, CNRS – ENSMA – Université de Poitiers, UPR CNRS 3346, Department of Physics and Mechanics of Materials, ENSMA – Téléport 2, 1 avenue Clément Ader, BP 40109, 86961 Futuroscope Chasseneuil Cedex (France)

2015-10-01

The influence of high thermal gradient processing on the creep and low cycle fatigue properties of the AM1 Ni-based single crystal superalloy has been studied. Isothermal creep (from 750 °C up to 1200 °C) and low cycle fatigue (750 °C and 950 °C) experiments were performed for AM1 alloy solidified with a conventional radiation cooled (Bridgman) and higher thermal gradient liquid-metal cooled (LMC) casting process to produce coarse and finer-scaled dendritic structures, respectively. There was no significant effect of the casting technique on creep properties, due to the very similar microstructures (γ′-size and γ-channel width) established after full heat treatment of both Bridgman and LMC samples. For low cycle fatigue properties, the benefit of the higher gradient LMC process was dependent on the testing temperature. At 750 °C, cracks primarily initiated at pores created by solidification shrinkage in both Bridgman and LMC samples. Samples produced by the LMC technique demonstrated fatigue lives up to 4 times longer, compared to the Bridgman samples, due to refined porosity. At 950 °C the low cycle fatigue properties of the LMC and conventionally solidified material were not distinguishable due to a shift of crack initiation sites from internal pores to oxidized surface layers or near-surface pores. The benefit of the LMC approach was, however, apparent in fatigue at 950 °C when testing in a vacuum environment. Based on these results, a crack initiation model based on the local slip activity close to casting defect is proposed.

Reduction factors for creep strength and fatigue life of modified 9Cr-1 Mo steel weldments

International Nuclear Information System (INIS)

Blass, J.J.; Battiste, R.L.; O'Connor, D.G.

1991-01-01

This paper reports on the provisions of ASME B and PV code Case N-47 currently include reduction factors for creep strength and fatigue life of weldments. To provide experimental confirmation of such factors for modified 9 Cr-1 Mo steel, tests of tubular specimens were conducted at 538 degrees C (1000 degrees F). Three creep-rupture specimens with longitudinal welds were tested in tension; and, of three with circumferential welds, two were tested in tension and one in torsion. In each specimen with a circumferential weld, a nonuniform axial distribution of strain was easily visible. The test results were compared to an existing empirical model of creep-rupture life. For the torsion test, the comparison was based on a definition of equivalent normal stress recently adopted in code Case N-47. some 27 fatigue specimens, with longitudinal, circumferential, or no welds, were tested under axial or torsional strain control. In specimens with welds, fatigue cracking initiated at fusion lines. In axial tests cracks grew in the circumferential direction, and in torsional tests cracks grew along fusion lines

Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

Energy Technology Data Exchange (ETDEWEB)

Celine Cabet; L. Carroll; R. Wright; R. Madland

2011-05-01

Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which can significantly increase the fatigue crack growth, may be one of the primary IHX damage modes. To address the needs for Alloy 617 codification and licensing, a significant creep-fatigue testing program is underway at Idaho National Laboratory. Strain controlled LCF tests including hold times up to 1800s at maximum tensile strain were conducted at total strain range of 0.3% and 0.6% in air at 950°C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The creep-fatigue tests resulted in failure times up to 1000 hrs. Fatigue resistance was significantly decreased when a hold time was added at peak stress and when the total strain was increased. The fracture mode also changed from transgranular to intergranular with introduction of a tensile hold. Changes in the microstructure were methodically characterized. A combined effect of temperature, cyclic and static loading and environment was evidenced in the targeted operating conditions of the IHX. This paper This paper reviews the data previously published by Carroll and co-workers in references 10 and 11 focusing on the role of inelastic strain accumulation and of oxidation in the initiation and propagation of surface fatigue cracks.

Development of fatigue crack propagation models for engineering applications at elevated temperatures

Energy Technology Data Exchange (ETDEWEB)

Tomkins, B.

1975-05-01

The value of modelling the fatigue crack propagation process is discussed and current models are examined in the light of increasing knowledge of crack tip deformation. Elevated temperature fatigue is examined in detail as an area in which models could contribute significantly to engineering design. A model is developed which examines the role of time-dependent creep cavitation on the failure process in an interactive creep-fatigue situation. (auth)

Creep-fatigue propagation of semi-elliptical crack at 650 deg. C in 316L(N) stainless steel plates with or without welded joints; Propagation de fissures semi-elliptiques en fatigue-fluage a 650 deg. C dans des plaques d'acier 316L(N) avec ou sans joints soudes

Energy Technology Data Exchange (ETDEWEB)

Curtit, F

2000-07-01

This study realised in LISN Laboratory of CEA Saclay, deals with the creep fatigue propagation of semi elliptical crack at the temperature of 650 deg C in 316L(N) stainless steel plates with or without welded joints. A vast majority of the studies on creep fatigue propagation models are based on specimen (CT) especially designed for crack propagation study. The PLAQFLU program performed in LISN laboratory deals with the application and adaptation of these models to complex crack shape, which are more representative of the cracks observed in industrial components. In this scope, we use propagation tests realised at the temperature of 650 deg C with wide plates containing semi elliptical defects. For some of them, the initial defect is machined in the middle of a welded joint, which constitute a privileged site for the crack initiation. The approach used in this study is based on global parameters of fracture mechanics. At first, tests on CT specimen are used in order to determine the propagation laws correlating the crack growth rate to the global parameters K or C{sup *}. These laws are then supposed to be intrinsic to our materials and are used to analysed the semi elliptical crack propagation. The analysis of the comportment of the crack during the hold time demonstrates the possibility to establish a correlation between the crack propagation both in the deepest and the surface point and the local value of C{sup *}. These correlations are coherent in the different points of the crack front for the different applied hold times, and they present a reasonably good agreement with the creep propagation law identified on CT specimen. The simulation of test performed on based metal specimen with a model of summation of both creep and pure fatigue crack growth gives acceptable results when the calculus of the simplified expression of C{sup *}{sub s} considers a continuous evolution of creep deformations rate during the all test. (author)

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

High temperature cracking of steels: effect of geometry on creep crack growth laws; Fissuration des aciers a haute temperature: effet de la geometrie sur la transferabilite des lois de propagation

Energy Technology Data Exchange (ETDEWEB)

Kabiri, M.R

2003-12-01

This study was performed at Centre des Materiaux de l'Ecole des Mines de Paris. It deals with identification and transferability of high temperature creep cracking laws of steels. A global approach, based on C{sup *} and J non-linear fracture mechanics parameters has been used to characterize creep crack initiation and propagation. The studied materials are: the ferritic steels 1Cr-1Mo-1/4V (hot and cold parts working at 540 and 250 C) used in the thermal power stations and the austenitic stainless steel 316 L(N) used in the nuclear power stations. During this thesis a data base was setting up, it regroups several tests of fatigue, creep, creep-fatigue, and relaxation. Its particularity is to contain several creep tests (27 tests), achieved at various temperatures (550 to 650 C) and using three different geometries. The relevance of the C{sup *} parameter to describe the creep crack propagation was analysed by a means of systematic study of elasto-viscoplastic stress singularities under several conditions (different stress triaxiality). It has been shown that, besides the C{sup *} parameter, a second non singular term, denoted here as Q{sup *}, is necessary to describe the local variables in the vicinity of the crack tip. Values of this constraint parameter are always negative. Consequently, application of typical creep crack growth laws linking the creep crack growth rate to the C{sup *} parameter (da/dt - C{sup *}), will be conservative for industrial applications. Furthermore, we showed that for ferritic steels, crack incubation period is important, therefore a correlation of Ti - C{sup *} type has been kept to predict crack initiation time Ti. For the austenitic stainless steel, the relevant stage is the one of the crack propagation, so that a master curve (da/dt - C{sup *}), using a new data analysis method, was established. Finally, the propagation of cracks has been simulated numerically using the node release technique, allowing to validate analytical

Crack initiation and growth in welded structures

International Nuclear Information System (INIS)

Assire, A.

2000-01-01

. Concerning local approach, intergranular creep damage model of the Ecole des Mines de Paris is used for crack initiation and growth under creep and creep fatigue loading. Crack propagations are simulated with an adaptive re-meshing technique and are compared with experimental results for crack located in weld and base metal. A sensibility analysis shows that crack propagation strongly depend on the characteristic distance, which is needed to simulate crack growth with local approach, for the weld metal parameters. (author)

Risk based lifetime assessment of piping under creep-fatigue conditions

International Nuclear Information System (INIS)

Bielak, O.; Bina, V.; Korous, J.

2003-01-01

The analysis of the steam pipeline lifetime is based on: (i) technical procedures supplied by Nuclear Electric R5; (ii) random interpretation of material damage accumulation laws for creep and fatigue; (iii) a stochastic model of the creep process (creep rupture strength, deformation characteristics); (iv) probabilistic description of geometrical quantities of the steam pipeline. The probabilistic procedure results in the calculation of the crack initiation risks both for the critical localities and for the steam pipeline as a whole (its subsystems, if need be). The residual lifetime was calculated from the conditional (a posteriori) probabilities. The risks of crack initiation was calculated for different operating periods (inspection frequency), and the periods were optimised to meet (i) the minimum risk of crack initiation and (2) the operation and economy criteria. The method also involves calculation of the residual lifetime from the updated data (material properties, dimensions). In the standard service-life calculations there is no difference between the weld and BM, the justification being that the weld is exposed to axial stress caused by internal pressure, which is one half of the hoop stress. Thus, the low creep resistant properties of the weld were ignored, as well as the uneven state of stress and its redistribution. In a number of cases it is the welds that are a weak point and therefore should receive considerable attention. The probabilistic method of lifetime and reliability assessment was verified on over 29 piping systems in power and petrochemical plants

Creep fatigue of low-cobalt superalloys: Waspalloy, PM U 700 and wrought U 700

Science.gov (United States)

Leis, B. N.; Rungta, R.; Hopper, A. T.

1983-01-01

The influence of cobalt content on the high temperature creep fatigue crack initiation resistance of three primary alloys was evaluated. These were Waspalloy, Powder U 700, and Cast U 700, with cobalt contents ranging from 0 up to 17 percent. Waspalloy was studied at 538 C whereas the U 700 was studied at 760 C. Constraints of the program required investigation at a single strain range using diametral strain control. The approach was phenomenological, using standard low cycle fatigue tests involving continuous cycling tension hold cycling, compression hold cycling, and symmetric hold cycling. Cycling in the absence of or between holds was done at 0.5 Hz, whereas holds when introduced lasted 1 minute. The plan was to allocate two specimens to the continuous cycling, and one specimen to each of the hold time conditions. Data was taken to document the nature of the cracking process, the deformation response, and the resistance to cyclic loading to the formation of small cracks and to specimen separation. The influence of cobalt content on creep fatigue resistance was not judged to be very significant based on the results generated. Specific conclusions were that the hold time history dependence of the resistance is as significant as the influence of cobalt content and increased cobalt content does not produce increased creep fatigue resistance on a one to one basis.

Fatigue crack initiation in hybrid boron/glass/aluminum fiber metal laminates

International Nuclear Information System (INIS)

Chang, P.-Y.; Yeh, P.-C.; Yang, J.-M.

2008-01-01

The fatigue crack initiation behavior of a high modulus and hybrid boron/glass/aluminum fiber/metal laminate (FML) was investigated experimentally and analytically. Two types of hybrid boron/glass/aluminum FMLs were fabricated and studied, which consisted of aluminum alloy sheets as the metal layers and a mixture of boron fibers and glass fibers as the composite layers. For the first type, the boron fiber/prepreg and the glass fiber/prepreg were used separately in the composite layers, and for the second type, the boron fibers and the glass fibers were mingled together to form a hybrid boron/glass/prepreg composite layer. These hybrid FMLs were consolidated using an autoclave curing process. The incorporation of the boron fibers improved the Young's modulus of the composite layer in FMLs, which in turn, would improve the fatigue crack initiation life of the Al sheet. The experimental results clearly showed that the fatigue crack initiation lives for both types of hybrid boron/glass/aluminum FMLs were superior to the monolithic aluminum alloy under the same loading condition. An analytical approach was proposed to calculate the fatigue crack initiation lives of hybrid boron/glass/aluminum FMLs based on the classical laminate theory and the small-crack theory. A good correlation was obtained between the predictions and the experimental results

Effect of creep and oxidation on reduced fatigue life of Ni-based alloy 617 at 850 °C

Energy Technology Data Exchange (ETDEWEB)

Chen, Xiang, E-mail: chenx@ornl.gov [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States); Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Yang, Zhiqing [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Sokolov, Mikhail A.; Erdman, Donald L. [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Mo, Kun; Stubbins, James F. [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)

2014-01-15

Low cycle fatigue (LCF) and creep–fatigue testing of Ni-based alloy 617 was carried out at 850 °C. Compared with its LCF life, the material’s creep–fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep–fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material’s fatigue life.

An overview of fatigue

International Nuclear Information System (INIS)

Mc Evily, A.J.

1987-01-01

Four topics are briefly discussed in this paper: fatigue crack initiation and growth in a nickel-base superalloy single crystal, the environment effect on near-threshold fatigue crack growth behaviour, the role of crack closure in load-interaction effects in fatigue crack growth, and the nature of creep-fatigue interactions, if any, during fatigue crack growth. (Author)

Some aspects of thermomechanical fatigue of AISI 304L stainless steel: Part I. creep- fatigue damage

Science.gov (United States)

Zauter, R.; Christ, H. J.; Mughrabi, H.

1994-02-01

Thermomechanical fatigue (TMF) tests on the austenitic stainless steel AISI 304L have been conducted under “true≓ plastic-strain control in vacuum. This report considers the damage oc-curring during TMF loading. It is shown how the temperature interval and the phasing (in-phase, out-of-phase) determine the mechanical response and the lifetime of the specimens. If creep-fatigue interaction takes place during in-phase cycling, the damage occurs inside the ma-terial, leading to intergranular cracks which reduce the lifetime considerably. Out-of-phase cy-cling inhibits creep-induced damage, and no lifetime reduction occurs, even if the material is exposed periodically to temperatures in the creep regime. A formula is proposed which allows prediction of the failure mode, depending on whether creep-fatigue damage occurs or not. At a given strain rate, the formula is able to estimate the temperature of transition between pure fatigue and creep-fatigue damage.

Study on the effect of prior fatigue and creep-fatigue damage on the fatigue and creep characteristics of 316 FR stainless steel. 2nd report. The effect of prior creep-fatigue damage on the creep and fatigue characteristics

International Nuclear Information System (INIS)

Yamauchi, Masafumi; Chuman, Yasuharu; Otani, Tomomi; Takahashi, Yukio

2001-01-01

The effect of prior creep-fatigue damage on the creep and the fatigue characteristics was studied to investigate the creep-fatigue life evaluation procedure of 316FR stainless steel. Creep and fatigue tests were conducted at 550degC by using the specimen exposed to prior creep-fatigue cycles at the same temperature and interrupted at 1/4 Nf, 1/2 Nf and 3/4 Nf cycle. The creep and fatigue strength of the pre-damaged material showed monotonic reduction with the prior creep-fatigue damage compared with the virgin material. The creep ductility also showed monotonic reduction with the prior creep-fatigue damage. These results were evaluated by the stress-based Time Fraction Rule and the strain-based Ductility Exhaustion Method. The result showed that the application of the Ductility Exhaustion Method to the creep-fatigue damage evaluation is more promising than the Time Fraction Rule. (author)

Study on creep-fatigue evaluation of chrome-molybdenum steel

International Nuclear Information System (INIS)

Aoto, Kazumi; Wada, Yusaku

1993-01-01

Though chrome-molybdenum steel has quite different basic material properties from austenitic stainless steel, the life fraction rule based on an advanced ductility exhaustion theory proposed for SUS304 is able to give proper prediction for creep-fatigue life of chrome-molybdenum steel. The applicability of the present evaluation method to chrome-molybdenum steel is validated by both mechanical study and micro-structural observation. The mechanism of creep-fatigue failure of Mod.9Cr-1Mo(NT) is one of the most controversial subjects among researchers. However, it is clarified in this report that creep-fatigue damage of this material under actual loading conditions is dominated by creep-cavitation of grain boundaries as same way as that of austenitic stainless steel. Furthermore, for the life reduction of low cycle fatigue of chrome-molybdenum steel with compression-side strain hold, both effects of mean stress and oxide-wedge are denied and it is insisted that the acceleration of fatigue-crack propagation is occurred by oxide-progress location and its thickness. (author)

Mechanism of fatigue crack initiation in austenitic stainless steels in light water reactor environments

International Nuclear Information System (INIS)

Chopra, O.K.; Shack, W.J.; Muscara, J.

2003-01-01

This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. The results indicate that the fatigue lives of these steels are decreased primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. The fracture morphology in the specimens has been characterized. Exploratory fatigue tests were conducted to study the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation. (author)

Numerical treatment of creep crack growth

International Nuclear Information System (INIS)

Kienzler, R.; Hollstein, T.

1990-06-01

To accomplish the safety analysis and to predict the lifetime of high-termpature components with flaws, several concepts have been proposed to correlate creep-crack initiation and growth with fracture mechanics parameters. The concepts of stress-intensity factor K, reference stress σ ref , line integral C * , and others will be discussed. Among them, the C * -integral concept seems to have the widest range of applicability, if large creep zones develop and steady state creep conditions can be assumed. The numerical evaluation of C * by the virtual crack extension method is described. The methods are demonstrated by two- and three-dimensional finite element simulations including creep crack growth. As for ductile fracture experiments, plane stress and plane strain simulations are bounds to the three-dimensional simulations which agree well with corresponding experiments. (orig.)

Fatigue crack initiation and growth life prediction with statistical consideration

International Nuclear Information System (INIS)

Kwon, J.D.; Choi, S.H.; Kwak, S.G.; Chun, K.O.

1991-01-01

Life prediction or residual life prediction of structures or machines is one of the most strongly world wide needed problems as requirement in the stage of slowly developing economy which comes after rapidly and highly developing stage. For the purpose of statistical life prediction, fatigue test was conducted under the 3 stress levels, and for each stress level, 20 specimens are used. The statistical properties of the crack growth parameter m and C in the fatigue crack growth law of da/dN = C(ΔK) m , and the relationship between m and C, and the statistical distribution pattern of fatigue crack initiation, growth and fracture lives can be obtained by experimental results

Evaluations of environmental effect on micro crack initiation and propagation by surface observations of fatigue specimens

International Nuclear Information System (INIS)

Fujikawa, Ryosuke; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki

2014-01-01

Fatigue life of nuclear facilities tends to be decreased by the influence of reactor coolant, which is called environmental effect. The effect accelerates crack growth rate but the influence for crack initiation is not clarified. This study intends to discuss the environmental effect in crack initiation. The crack length and the number of cracks are measured from the investigation of fatigue test specimens in reactor coolant and air. The behavior of crack initiation is revealed from the measurement of number of cracks, crack sizes and fatigue life. From this study, environmental effect of reactor coolant is considered to influence crack initiation and increase the number of micro crack. It is also estimated that the coalescence of cracks influences the acceleration of crack growth. (author)

Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys

Science.gov (United States)

Gupta, Vipul K.

The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of

Multi Resolution In-Situ Testing and Multiscale Simulation for Creep Fatigue Damage Analysis of Alloy 617

Energy Technology Data Exchange (ETDEWEB)

Liu, Yongming [Arizona State Univ., Tempe, AZ (United States). School for Engineering of Matter, Transport and Energy; Oskay, Caglar [Vanderbilt Univ., Nashville, TN (United States). Dept. of Civil and Environmental Engineering

2017-04-30

the grain boundaries. The glide model incorporates a slip resistance evolution model that characterizes the solute-drag creep effects and can capture well the stress-strain and stress time response of fatigue and creep-fatigue tests at various strain ranges and hold times. In order to accurately capture the creep strains that accumulate particularly at relatively low stress levels, a dislocation climb model has been incorporated into the crystal plasticity modeling framework. The dislocation climb model parameters are calibrated and verified through experimental creep tests performed at 950°. In addition, a cohesive zone model has been fully implemented in the context of the crystal plasticity finite element model to capture the intergranular creep damage. The parameters of the cohesive zone model have been calibrated using available experimental data. The numerical simulations illustrate the capability of the proposed model in capturing damage initiation and growth under creep loads as compared to the experimental observations. The microscale analysis sheds light on the crack initiation sites and propagation patterns within the microstructure. The model is also utilized to investigate the hybrid-controlled creep-fatigue tests and has been found to capture reasonably well the stress-strain response with different hold times and hold stress magnitudes.

LCF life prediction for waspaloy in the creep-fatigue interaction regime

International Nuclear Information System (INIS)

Yeom, Jong Taek; Park, Nho Kwang

2001-01-01

This paper describes the empirical rule of strain rate modified linear accumulation of creep damage(SRM rule) for Low-Cycle Fatigue(LCF) life prediction of Waspaloy in the creep-fatigue interaction regime and Chaboche type unified viscoplastic model predicting the stress-strain response in various cyclic loading conditions. The comparison of the experimental data and the predictions for strain controlled LCF tests carried out for various strain ranges at 600 .deg. C and 650 .deg. C was made. Chaboche type unified viscoplastic model described efficiently the inelastic deformation behavior during LCF tests. Crack-initiation lifting method to predict the material life was investigated with Strain Rate Modification(SRM) rule. The application of SRM rule to LCF tests on Waspaloy indicated a good agreement between measured and predicted cycles to failure

Creep-fatigue interactions in an austenitic stainless steel

International Nuclear Information System (INIS)

Majumdar, S.; Maiya, P.S.

1978-01-01

A phenomenological model of the interaction between creep and fatigue in Type 304 stainless steel at elevated temperatures is presented. The model is based on a crack-growth equation and an equation governing cavity growth, expressed in terms of current plastic strain and plastic strain rate. Failure is assumed to occur when a proposed interaction equation is satisfied. Various parameters of the equations can be obtained by correlation with continuously cycling fatigue and monotonic creep-rupture test data, without the use of any hold-time fatigue tests. Effects of various wave shapes such as tensile, compressive, and symmetrical hold on the low-cycle fatigue life can be computed by integrating the damage-rate equations along the appropriate loading path. Microstructural evidence in support of the proposed model is also discussed

Fatigue crack initiation – The role of point defects

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Man, Jiří

2014-01-01

Roč. 65, AUG (2014), s. 18-27 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP108/10/2371; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : Fatigue crack initiation * Point defects * Persistent slip band * Intrusion * Extrusion Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.275, year: 2014

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

Creep-fatigue interaction at high temperature; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991

Science.gov (United States)

Haritos, George K.; Ochoa, O. O.

Various papers on creep-fatigue interaction at high temperature are presented. Individual topics addressed include: analysis of elevated temperature fatigue crack growth mechanisms in Alloy 718, physically based microcrack propagation laws for creep-fatigue-environment interaction, in situ SEM observation of short fatigue crack growth in Waspaloy at 700 C under cyclic and dwell conditions, evolution of creep-fatigue life prediction models, TMF design considerations in turbine airfoils of advanced turbine engines. Also discussed are: high temperature fatigue life prediction computer code based on the total strain version of strainrange partitioning, atomic theory of thermodynamics of internal variables, geometrically nonlinear analysis of interlaminar stresses in unsymmetrically laminated plates subjected to uniform thermal loading, experimental investigation of creep crack tip deformation using moire interferometry. (For individual items see A93-31336 to A93-31344)

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.

Continuous observation of cavity growth and coalescence by creep-fatigue tests in SEM

International Nuclear Information System (INIS)

Arai, Masayuki; Ogata, Takashi; Nitta, Akito

1995-01-01

Structural components operating at high temperatures in power plants are subjected to interaction of thermal fatigue and creep which results in creep-fatigue damage. In evaluating the life of those components, it is important to understand microscopic damage evolution under creep-fatigue conditions. In this study, static creep and creep-fatigue tests with tensile holdtime were conducted on SUS304 stainless steel by using a high-temperature fatigue machine combined with a scanning electron microscope (SEM), and cavity growth and coalescence behaviors on surface grain boundaries were observed continuously by the SEM. Quantitative analysis of creep cavity growth based on the observation was made for comparison with theoretical growth models. As a result, it was found that grain boundary cavities nucleate at random and grow preferentially on grain boundaries in a direction almost normal to the stress axis. Under the creep condition, the cavities grow monotonously on grain boundaries while they remain the elliptical shape. On the other hand, under the creep-fatigue condition the cavities grow with an effect of local strain distribution around the grain boundary due to cyclic loading and the micro cracks of one grain-boundary length were formed by coalescence of the cavities. Also, cavity nucleation and growth rates for creep-fatigue were more rapid than those for static creep and the constrained cavity growth model coincided well with the experimental data for creep. (author)

Probabilistic and microstructural aspects of fatigue cracks initiation in Inconel 718; Aspects probabilistes et microstructuraux de l'amorcage des fissures de fatigue dans l'alliage INCO 718

Energy Technology Data Exchange (ETDEWEB)

Alexandre, F

2004-03-15

Thermomechanical treatments have been recently developed to produce Inconel 718DA (Direct Aged). This alloy optimisation leads to an increase of the fatigue life but also the scatter. The aim of this study is on the one hand the understanding of the fatigue crack initiation mechanisms and on the other hand the modelling of the fatigue life and the scatter. An experimental study showed that the fatigue cracks were initiated from carbide particles in fine grain alloy. Interrupted tensile tests show that the particles cracking occurred at the first quarter of the fatigue cycle. Fatigue behaviour tests were also performed on various grain size 718 alloys. The last experimental part was devoted to measurements of the low cycle fatigue crack growth rates using a high focal distance microscope. For these tests, EDM micro-defects were used for the fatigue crack initiation sites. This method was also used to observe the small fatigue crack coalescence. A fatigue life model is proposed. It is based on the three fatigue crack initiation mechanisms competition: particle crack initiation on the surface, internal particle crack initiation and Stade I crack initiation. The particle fatigue crack initiation is supposed instantaneous at a critical stress level. The Tanaka and Mura model is used for analysing the Stage I crack initiation number of cycles. The fatigue crack growth rate was analysed using the Tomkins model identified on the small fatigue crack growth rate measurements. The proposed fatigue life model decomposed in three levels: a deterministic one and two probabilistic with and without crack coalescence. (author)

Assessment of creep-fatigue damage using the UK strain based procedure

International Nuclear Information System (INIS)

Bate, S.K.

1997-01-01

The UK strain based procedures have been developed for the evaluation of damage in structures, arising from fatigue cycles and creep processes. The fatigue damage is assessed on the basis of modelling crack growth from about one grain depth to an allowable limit which represents an engineering definition of crack formation. Creep damage is based up on the exhaustion of available ductility by creep strain accumulation. The procedures are applicable only when level A and B service conditions apply, as defined in RCC-MR or ASME Code Case N47. The procedures require the components of strain to be evaluated separately, thus they may be used with either full inelastic analysis or simplified methods. To support the development of the UK strain based creep-fatigue procedures an experimental program was undertaken by NNC to study creep-fatigue interaction of structures operating at high temperature. These tests, collectively known as the SALTBATH tests considered solid cylinder and tube-plate specimens, manufactured from Type 316 stainless steel. These specimens were subjected to thermal cycles between 250 deg. C and 600 deg. C. In all the cases the thermal cycle produces tensile residual stresses during dwells at 600 deg. C. One of the tube-plate specimens was used as a benchmark for validating the strain based creep fatigue procedures and subsequently as part of a CEC co-operative study. This benchmark work is described in this paper. A thermal and inelastic stress analysis was carried out using the finite element code ABAQUS. The inelastic behaviour of the material was described using the ORNL constitutive equations. A creep fatigue assessment using the strain based procedures has been compared with an assessment using the RCC-MR inelastic rules. The analyses indicated that both the UK strain based procedures and the RCC-MR rules were conservative, but the conservatism was greater for the RCC-MR rules. (author). 8 refs, 8 figs, 4 tabs

Modeling of creep-fatigue interaction of zirconium {alpha} under cyclic loading at 200 C; Modelisation du comportement et de l`endommagement en fatigue-fluage du zirconium {alpha} a 200C

Energy Technology Data Exchange (ETDEWEB)

Vogel, C.

1996-04-01

The present work deals with mechanical behaviour of zirconium alpha at 200 deg. C and crack initiation prediction methods, particularly when loading conditions lead to interaction of fatigue and creep phenomena. A classical approach used to study interaction between cyclic effects and constant loading effects does not give easy understanding of experimental results. Therefore, a new approach has been developed, which allow to determine a number of cycles for crack initiation for complex structures under large loading conditions. To study influence of fatigue and creep interaction on crack initiation, a model was chosen, using a scalar variable, giving representation of the material deterioration state. The model uses a non linear cumulating effect between the damage corresponding to cyclic loads and the damage correlated to time influence. The model belongs to uncoupled approaches between damage and behaviour, which is described here by a two inelastic deformations model. This mechanical behaviour model is chosen because it allows distinction between a plastic and a viscous part in inelastic flow. Cyclic damage is function of stress amplitude and mean stress. For the peculiar sensitivity of the material to creep, a special parameter bas been defined to be critical toward creep damage. It is the kinematic term associated to state variables describing this type of hardening in the viscous mechanism. (author).

Experimental investigation on low cycle fatigue and creep-fatigue interaction of DZ125 in different dwell time at elevated temperatures

International Nuclear Information System (INIS)

Shi Duoqi; Liu Jinlong; Yang Xiaoguang; Qi Hongyu; Wang Jingke

2010-01-01

Research highlights: → This paper has researched creep-fatigue interaction of directionally solidified superalloy DZ125 with different dwell time at high temperature combined with micro-mechanism by experiment. → The results indicated that the life of creep-fatigue decreases as dwell time increases, but the life of this alloy was almost unchanged when dwell time exceeds a critical value at 850 deg. C. - Abstract: The low cycle fatigue (LCF) and creep-fatigue tests have been conducted with directionally solidified nickel-based superalloy DZ125 at 850 and 980 deg. C to study the creep-fatigue interaction behavior of alloy with different dwell time. On the average, the life of creep-fatigue tests are about 70% less than the life of LCF tests under the same strain range at 850 deg. C. The life of creep-fatigue decreases as dwell time increases, but the life of this alloy was almost unchanged when dwell time exceeds a critical value at 850 deg. C. Scanning electron microscope (SEM) analyses of the fracture revealed that the fracture modes were influenced by different way of loading. In case of LCF, the primary fracture mode was transgranular, while in case of creep-fatigue, the primary fracture mode was mixed with transgranular and intergranular. There were also obvious different morphologies of surface crack between LCF and creep-fatigue.

Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint

Directory of Open Access Journals (Sweden)

Chao He

2017-01-01

Full Text Available Very high cycle fatigue behavior of nugget zone in AA 7075 friction stir welded joint was experimentally investigated using ultrasonic fatigue testing system (20 kHz to clarify the crack initiation mechanism. It was found that the fatigue strength of nugget zone decreased continuously even beyond 107 cycles with no traditional fatigue limits. Fatigue cracks initiated from the welding defects located at the bottom side of the friction stir weld. Moreover, a special semicircular zone could be characterized around the crack initiation site, of which the stress intensity factor approximately equaled the threshold of fatigue crack propagation rate. Finally, a simplified model was proposed to estimate the fatigue life by correlating the welding defect size and applied stress. The predicted results are in good agreement with the experimental results.

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)

High temperature creep-fatigue design

International Nuclear Information System (INIS)

Tavassoli, A. A. F.; Fournier, B.; Sauzay, M.

2010-01-01

Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowable and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed. (authors)

High temperature creep-fatigue design

Energy Technology Data Exchange (ETDEWEB)

Tavassoli, A. A. F.; Fournier, B.; Sauzay, M. [CEA Saclay, DEN DMN, F-91191 Gif Sur Yvette (France)

2010-07-01

Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowable and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed. (authors)

Near-threshold fatigue crack behaviour in EUROFER 97 at different temperatures

Science.gov (United States)

Aktaa, J.; Lerch, M.

2006-07-01

The fatigue crack behaviour in EUROFER 97 was investigated at room temperature (RT), 300, 500 and 550 °C for the assessment of cracks in first wall structures built from EUROFER 97 of future fusion reactors. For this purpose, fatigue crack growth tests were performed using CT specimens with two R-ratios, R = 0.1 and R = 0.5 ( R is the load ratio with R = Fmin/ Fmax where Fmin and Fmax are the minimum and maximum applied loads within a cycle, respectively). Hence, fatigue crack threshold, fatigue crack growth behaviour in the near-threshold range and their dependences on temperature and R-ratio were determined and described using an analytical formula. The fatigue crack threshold showed a monotonous dependence on temperature which is for R = 0.5 insignificantly small. The fatigue crack growth behaviour exhibited for R = 0.1 a non-monotonous dependence on temperature which is explained by the decrease of yield stress and the increase of creep damage with increasing temperature.

Tensile, Creep, and Fatigue Behaviors of 3D-Printed Acrylonitrile Butadiene Styrene

Science.gov (United States)

Zhang, Hanyin; Cai, Linlin; Golub, Michael; Zhang, Yi; Yang, Xuehui; Schlarman, Kate; Zhang, Jing

2018-01-01

Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastics in 3D printing. However, there is a lack of thorough investigation of the mechanical properties of 3D-printed ABS components, including orientation-dependent tensile strength and creep fatigue properties. In this work, a systematic characterization is conducted on the mechanical properties of 3D-printed ABS components. Specifically, the effect of printing orientation on the tensile and creep properties is investigated. The results show that, in tensile tests, the 0° printing orientation has the highest Young's modulus of 1.81 GPa, and ultimate strength of 224 MPa. In the creep test, the 90° printing orientation has the lowest k value of 0.2 in the plastics creep model, suggesting 90° is the most creep resistant direction. In the fatigue test, the average cycle number under load of 30 N is 3796 cycles. The average cycle number decreases to 128 cycles when the load is 60 N. Using the Paris law, with an estimated crack size of 0.75 mm, and stress intensity factor is varied from 352 to 700 N√ m, the derived fatigue crack growth rate is 0.0341 mm/cycle. This study provides important mechanical property data that is useful for applying 3D-printed ABS in engineering applications.

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

Science.gov (United States)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

Factors Influencing Dwell Fatigue Cracking in Notches of Powder Metallurgy Superalloys

Science.gov (United States)

Gabb, T. P.; Telesman, J.; Ghosn, L.; Garg, A.; Gayda, J.

2011-01-01

The influences of heat treatment and cyclic dwells on the notch fatigue resistance of powder metallurgy disk superalloys were investigated for low solvus high refractory (LSHR) and ME3 disk alloys. Disks were processed to produce material conditions with varied microstructures and associated mechanical properties. Notched specimens were first subjected to baseline dwell fatigue cycles having a dwell at maximum load, as well as tensile, stress relaxation, creep rupture, and dwell fatigue crack growth tests at 704 C. Several material heat treatments displayed a bimodal distribution of fatigue life with the lives varying by two orders-of-magnitude, while others had more consistent fatigue lives. This response was compared to other mechanical properties, in search of correlations. The wide scatter in baseline dwell fatigue life was observed only for material conditions resistant to stress relaxation. For selected materials and conditions, additional tests were then performed with the dwells shifted in part or in total to minimum tensile load. The tests performed with dwells at minimum load exhibited lower fatigue lives than max dwell tests, and also exhibited early crack initiation and a substantial increase in the number of initiation sites. These results could be explained in part by modeling evolution of peak stresses in the notch with continued dwell fatigue cycling. Fatigue-environment interactions were determined to limit life for the fatigue cycles with dwells.

Basic Mechanisms Leading to Fatigue Failure of Structural Materials

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Petráš, Roman; Mazánová, Veronika

2016-01-01

Roč. 69, č. 2 (2016), s. 289-294 ISSN 0972-2815. [International Conference on CREEP , FATIGUE and CREEP -FATIGUE INTERACTION /7./. Kalpakkam, 19.01.2016-22.01.2016] R&D Projects: GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : Damage mechanism * Fatigue crack initiation * Austenitic steel * Oxide cracking Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.533, year: 2016

Final Report for Project 13-4791: New Mechanistic Models of Creep-Fatigue Crack Growth Interactions for Advanced High Temperature Reactor Components

Energy Technology Data Exchange (ETDEWEB)

Kruzic, Jamie J [Oregon State Univ., Corvallis, OR (United States); Siegmund, Thomas [Purdue Univ., West Lafayette, IN (United States); Tomar, Vikas [Purdue Univ., West Lafayette, IN (United States)

2018-03-20

This project developed and validated a novel, multi-scale, mechanism-based model to quantitatively predict creep-fatigue crack growth and failure for Ni-based Alloy 617 at 800°C. Alloy 617 is a target material for intermediate heat exchangers in Generation IV very high temperature reactor designs, and it is envisioned that this model will aid in the design of safe, long lasting nuclear power plants. The technical effectiveness of the model was shown by demonstrating that experimentally observed crack growth rates can be predicted under both steady state and overload crack growth conditions. Feasibility was considered by incorporating our model into a commercially available finite element method code, ABAQUS, that is commonly used by design engineers. While the focus of the project was specifically on an alloy targeted for Generation IV nuclear reactors, the benefits to the public are expected to be wide reaching. Indeed, creep-fatigue failure is a design consideration for a wide range of high temperature mechanical systems that rely on Ni-based alloys, including industrial gas power turbines, advanced ultra-super critical steam turbines, and aerospace turbine engines. It is envisioned that this new model can be adapted to a wide range of engineering applications.

Creep-fatigue assessment of a thermina test specimen using the R5 procedure

International Nuclear Information System (INIS)

Booth, P.; Budden, P.J.; Bate, S.K.

1997-01-01

A creep-fatigue life assessment of an axisymmetric 316 stainless steel test specimen under constant mechanical and cyclic thermal shock loading using the R5 Procedure is described in this paper. This test was carried out at CEA, France, and formed part of the 'Thermina' series. Stress analysis has been carried out using both full inelastic finite element analysis and also the simplified shakedown methods, based on elastic calculation, within R5. The estimates of strain range and the stress at the start of the creep dwell have then been used with R5 to estimate creep and fatigue damage per cycle and hence to make predictions of component life. The predicted lives are compared with the lives observed in the tests. The simplified R5 estimate of life, based on development of a crack of depth 200 microns, is 260 cycles using best-estimate material properties. Experimentally, cracks of depth at least 150 microns were observed in between 526 and 650 cycles, for two similar tests. The simplified R5 route therefore leads to an estimate of life which is conservative but not unduly so on this component. Detailed cyclic inelastic analysis using the ORNL constitutive model and the ABAQUS finite element code to estimate the strain range and dwell stress led to a best estimate of 618 cycles to crack initiation using R5. (author). 16 refs, 11 figs, 4 tabs

Study of crack initiation in low-cycle fatigue of an austenitic stainless steel

International Nuclear Information System (INIS)

Mu, P.

2011-03-01

The material studied is an austenitic stainless steel, that is widely used in nuclear equipment for its very high corrosion resistance combined to good mechanical properties. Although crack initiation is proved to play an important role in fatigue, its mechanisms have not been fully understood. Some crack initiation criteria based on physical mechanisms of plastic deformation have been defined. However, these criteria are not easy to use and valid, as they need local variables at the grain scale. The present study aims at establishing a crack initiation criterion in low-cycle fatigue, which should be usable under variable amplitude loading conditions. Tension-compression fatigue tests were first carried out to characterize the mechanical behavior of the stainless steel AISI 316L. The mechanical behavior was simulated using a self-consistent model using a crystalline plastic law based on dislocation densities. The evolution of surface damage was observed during a fatigue test using an in situ optical microscopic device. Cracks were analyzed after 2000 cycles and their crystallographic characteristics calculated. As surface grains exhibit larger strain because they are less constraint by neighbor grains, a specific numerical frame is necessary to determine stress state in surface grains. A localization law specific to surface grains under cyclic loading was identified from finite element simulations. The proposed form needs an intergranular accommodation variable, on the pattern of the localization law of Cailletaud-Pilvin. Stress-strain state in surface grains was simulated. Potential indicators for crack initiation were then compared on a same experimental data base. Indicators based on the equivalent plastic strain were found to be suitable indicators of fatigue damage. (author)

Magnetic characterization of creep-fatigue damage for energy structural materials

International Nuclear Information System (INIS)

Suzuki, Takayuki; Hashidate, Ryuta; Harada, Yoshihisa

2012-01-01

Magnetic characterization of creep-fatigue damage for welded specimens of austenitic stainless steel (SUS316FR) and high-chromium steel (Mod.9Cr-1Mo) steel was performed using magnetic force microscope and Hall sensor. In SUS316FR volume fraction of δ-ferrite at weld metal region decreased by creep or creep-fatigue and the remanent magnetic flux density at weld metal region also decreased. In Mod.9Cr-1Mo steel magnetic characteristics at weld metal region were different from those at base metal initially, however, during creep or creep fatigue the difference of magnetic characteristics between welded metal and base metal became small. It was found that the degradation mechanism for these energy structural materials during creep or creep fatigue could be clarified by magnetic characterization techniques. (author)

Flaw assessment guide for high-temperature reactor components subject to creep-fatigue loading

International Nuclear Information System (INIS)

Ainsworth, R.A.; Takahashi, Y.

1990-10-01

A high-temperature flaw assessment procedure is described. This procedure is a result of a collaborative effort between Electric Power Research Institute in the United States, Central Research Institute of Electric Power Industry in Japan, and Nuclear Electric plc in the United Kingdom. The procedure addresses preexisting defects subject to creep-fatigue loading conditions. Laws employed to calculate the crack growth per cycle are defined in terms of fracture mechanics parameters and constants related to the component material. The crack-growth laws can be integrated to calculate the remaining life of a component or to predict the amount of crack extension in a given period. Fatigue and creep crack growth per cycle are calculated separately, and the total crack extension is taken as the simple sum of the two contributions. An interaction between the two propagation modes is accounted for in the material properties in the separate calculations. In producing the procedure, limitations of the approach have been identified. 25 refs., 1 fig

Image-based creep-fatigue damage mechanism investigation of Alloy 617 at 950 °C

Energy Technology Data Exchange (ETDEWEB)

Tahir, Fraaz; Dahire, Sonam; Liu, Yongming, E-mail: yongming.liu@asu.edu

2017-01-02

Alloy 617 is a primary candidate material to be used in the next generation of nuclear power plants. Structural materials for these plants are expected to undergo creep and fatigue at temperatures as high as 950 °C. This study uses a hybrid-control creep-fatigue loading profile, as opposed to the traditional strain-controlled loading, to generate creep dominated failure. Qualitative and quantitative image analysis through SEM, EDS, and EBSD, is used to show that hybrid control testing is capable of producing creep dominated failure and that time fraction approach is not a valid indicator of creep or fatigue dominated damage. The focus of image analysis is on surface fatigue cracks and internal creep voids. A creep-fatigue damage interaction diagram based on these micro-scale features is plotted. It is shown that the classical time fraction approach suggested by the ASME code does not agree with the experimental findings and has a poor correlation with observed microscale damage features. A new definition of creep damage fraction based on an effective hold time is found to correlate well with the micro-scale image analysis.

Study on the fatigue crack initiation life under spherical contact

Energy Technology Data Exchange (ETDEWEB)

Cho, Yong Joo; Kim, Tae Wan [Busan National Univ., Busan (Korea, Republic of); Lee, Mun Ju [Samsung Electronics Co., Ltd., Suwon (Korea, Republic of)

2001-08-01

In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the prediction of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used.

Study on the fatigue crack initiation life under spherical contact

International Nuclear Information System (INIS)

Cho, Yong Joo; Kim, Tae Wan; Lee, Mun Ju

2001-01-01

In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the prediction of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used

The influence of microstructure on fatigue crack initiation in spheroidal graphite cast irons

International Nuclear Information System (INIS)

Starkey, M.S.; Irving, P.E.

1979-01-01

This paper reports the first stage of this work which concentrates on fatigue crack initiation with particular emphasis on the influence of microstructure. The fatigue lives of three fully ferritic and two fully pearlitic irons, each with different graphite nodule size distributions, have been determined at two strain amplitudes, 0.005 and 0.00018. The tests were carried out in fully reversed strain control on smooth cylindrical specimens in a servohydraulic testing machine. The effects of matrix structure and strength were clearly seen in that the pearlitic irons were superior at both strain levels. Nodule size on the other hand appeared to have no significant effect. The crack initiation sites in the specimens were located by interrupting the tests on detection of a 5% tensile load drop and heat tinting, before continuing. After failure, which was defined as complete separation, the fracture faces were examined on the scanning electron microscope. In the majority of the specimens the major crack origin was found to be a surface micropore with depths ranging from 50 to 250 μm. It is suggested that these micropores and not the graphite modules strongly influence the crack initiation behaviour in SG iron. These findings were confirmed by monitoring the initiation and growth of surface cracks from micropores using surface replica techniques. The influence of microstructure on the percentage of life spent in initiating and propagating a crack was thus determined. Hence the factors contributing to the fatigue behaviour of SG irons can be quantified. Their influence on predictions of cycles to crack initiation using the local approach is discussed. (orig.) 891 RW/orig. 892 RKD [de

Near-threshold fatigue crack behaviour in EUROFER 97 at different temperatures

International Nuclear Information System (INIS)

Aktaa, J.; Lerch, M.

2006-01-01

The fatigue crack behaviour in EUROFER 97 was investigated at room temperature (RT), 300, 500 and 550 deg. C for the assessment of cracks in first wall structures built from EUROFER 97 of future fusion reactors. For this purpose, fatigue crack growth tests were performed using CT specimens with two R-ratios, R = 0.1 and R = 0.5 (R is the load ratio with R = F min /F max where F min and F max are the minimum and maximum applied loads within a cycle, respectively). Hence, fatigue crack threshold, fatigue crack growth behaviour in the near-threshold range and their dependences on temperature and R-ratio were determined and described using an analytical formula. The fatigue crack threshold showed a monotonous dependence on temperature which is for R = 0.5 insignificantly small. The fatigue crack growth behaviour exhibited for R = 0.1 a non-monotonous dependence on temperature which is explained by the decrease of yield stress and the increase of creep damage with increasing temperature

Evaluation of long term creep-fatigue life for type 304 stainless steel

International Nuclear Information System (INIS)

Kawasaki, Hirotsugu; Ueno, Fumiyoshi; Aoto, Kazumi; Ichimiya, Masakazu; Wada, Yusaku

1992-01-01

The long term creep-fatigue life of type 304 stainless steel was evaluated by the creep-fatigue life prediction method based on a linear damage fraction rule. The displacement controlled creep-fatigue tests were carried out, and the time to failure of longer than 10000 hours was obtained. The creep damage of long term creep-fatigue was evaluated by taking into account the stress relaxation behavior with elastic follow-up during the hold period. The relationship between life reduction of creep-fatigue and fracture mode was provided by the creep cavity growth. The results of this study are summarized as follows; (1) The long term creep-fatigue data can be reasonably evaluated by the present method. The predicted lives were within a factor of 3 of the observed ones. (2) The present method provides the capability to predict the long term creep-fatigue life at lower temperatures as well as that at the creep dominant temperature. (3) The value of creep damage for the long term creep-fatigue data increased by elastic follow-up. The creep-fatigue damage diagram intercepted between 0.3 and 1 can represent the observed creep-fatigue damages. (4) The cavity growth depends on the hold time. The fracture of long term creep-fatigue is caused by the intergranular cavity growth. The intergranular fracture of creep-fatigue is initiated by the cavity growth and followed by the microcrack propagation along grain boundaries starting from creep cavities. (author)

Numerical Analysis of Rolling Contact Fatigue Crack Initiation and Fatigue Life Prediction of the Railway Crossing

NARCIS (Netherlands)

Xin, L.; Markine, V.L.; Shevtsov, I.

2015-01-01

The procedure for analysing rolling contact fatigue crack initiation and fatigue life prediction of the railway turnout crossing is developed. A three-dimensional finite element (FE) model is used to obtain stress and strain results, considering the dynamic effects of wheel-crossing rolling contact.

High Temperature Creep-Fatigue-Oxidation Interactions in 9% Cr Martensitic Steels

International Nuclear Information System (INIS)

Fournier, B.; Sauzay, M.; Pineau, A.

2007-01-01

Full text of publication follows: Martensitic steels of the 9-12%Cr family are widely used in the energy industry and were selected as candidate materials for structural components of future fusion reactors [1,2]. Typical in-service conditions require operating temperatures between 673 and 873 K, which means that the creep behaviour of these steels is of primary interest. In addition, some components are anticipated to operate in a pulsed mode, leading to complex time-dependencies of temperature, stress and strain in materials. Therefore, in design procedures, fatigue and creep-fatigue data are required. Furthermore, to meet the need for very long inservice lifetime of components (with very long hold times ∼ one month) reliable cyclic lifetime models are necessary, since complete tests with such long holding periods cannot, of course, be carried out in laboratory. To make these extrapolations safer and more reliable a precise understanding of the damage and interaction mechanisms is required. Fatigue, creep-fatigue and relaxation-fatigue tests were carried out at high temperature (823 K), under three different atmospheres (air, vacuum and He+impurities) and for a large panel of applied fatigue and creep strain. Holding periods are found to decrease the fatigue lifetime. Surprisingly enough compressive holding periods are more deleterious than tensile ones in air. Observations were carried out on fracture surfaces, specimen surfaces and cross sections. No creep cavity is visible, whatever the holding period duration, but a major influence of oxidation is highlighted. Oxidation is all the more predominant for low applied strains. Tests carried out under vacuum and helium show that the formation of a thick oxide layer can lead to a fatigue lifetime 4 times shorter. Crack propagation is mainly transgranular for all applied strains. Both damage observations and a theoretical study of oxide layers fracture mechanisms allow qualitative explanations for recorded fatigue

Parametric analysis of fatigue crack growth

International Nuclear Information System (INIS)

Carden, A.E.

1975-01-01

The effect of temperature and frequency on fatigue crack growth were empirically observed and treated as a coefficient on a stress intensity factor term. The stress intensity factor term is a function of Ksub(max), Ksub(min) (or stress ratio) and a threshold K term. The apparent threshold values were selected in order to linearize the data. At 1000 0 F a constant da/dt (creep crack growth rate) is approached for cycle periods approaching 2000 s indicating a limiting and linear-inverse frequency effect. (author)

Standard test method for measurement of creep crack growth times in metals

CERN Document Server

American Society for Testing and Materials. Philadelphia

2007-01-01

1.1 This test method covers the determination of creep crack growth (CCG) in metals at elevated temperatures using pre-cracked specimens subjected to static or quasi-static loading conditions. The time (CCI), t0.2 to an initial crack extension δai = 0.2 mm from the onset of first applied force and creep crack growth rate, ˙a or da/dt is expressed in terms of the magnitude of creep crack growth relating parameters, C* or K. With C* defined as the steady state determination of the crack tip stresses derived in principal from C*(t) and Ct (1-14). The crack growth derived in this manner is identified as a material property which can be used in modeling and life assessment methods (15-25). 1.1.1 The choice of the crack growth correlating parameter C*, C*(t), Ct, or K depends on the material creep properties, geometry and size of the specimen. Two types of material behavior are generally observed during creep crack growth tests; creep-ductile (1-14) and creep-brittle (26-37). In creep ductile materials, where cr...

Collect Available Creep-Fatigue Data and Study Existing Creep-Fatigue Evaluation Procedures for Grade 91 and Hastelloy XR

International Nuclear Information System (INIS)

Asayama, Tai; Tachibana, Yukio

2007-01-01

This report describes the results of investigation on Task 5 of DOE/ASME Materials Project based on a contract between ASME Standards Technology, LLC (ASME ST-LLC) and Japan Atomic Energy Agency (JAEA). Task 5 is to collect available creep-fatigue data and study existing creep-fatigue evaluation procedures for Grade 91 steel and Hastelloy XR. Part I of this report is devoted to Grade 91 steel. Existing creep-fatigue data were collected (Appendix A) and analyzed from the viewpoints of establishing a creep-fatigue procedure for VHTR design. A fair amount of creep-fatigue data has been obtained and creep-fatigue phenomena have been clarified to develop design standards mainly for fast breeder reactors. Following this, existing creep-fatigue procedures were studied and it was clarified that the creep-fatigue evaluation procedure of the ASME-NH has a lot of conservatisms and they were analyzed in detail from the viewpoints of the evaluation of creep damage of material. Based on the above studies, suggestions to improve the ASME-NH procedure along with necessary research and development items were presented. Part II of this report is devoted to Hastelloy XR. Existing creep-fatigue data used for development of the high temperature structural design guideline for High Temperature Gas-cooled Reactor (HTGR) were collected. Creep-fatigue evaluation procedure in the design guideline and its application to design of the intermediate heat exchanger (IHX) for High Temperature Engineering Test Reactor (HTTR) was described. Finally, some necessary research and development items in relation to creep-fatigue evaluation for Gen IV and VHTR reactors were presented.

Corrosion fatigue initiation and short crack growth behaviour of austenitic stainless steels under light water reactor conditions

International Nuclear Information System (INIS)

Seifert, H.P.; Ritter, S.; Leber, H.J.

2012-01-01

Highlights: ► Corrosion fatigue in austenitic stainless steels under light water reactor conditions. ► Identification of major parameters of influence on initiation and short crack growth. ► Critical system conditions for environmental reduction of fatigue initiation life. ► Comparison with the environmental factor (F env ) approach. - Abstract: The corrosion fatigue initiation and short crack growth behaviour of different wrought low-carbon and stabilised austenitic stainless steels was characterised under simulated boiling water reactor and pressurised water reactor primary water conditions by cyclic fatigue tests with sharply notched fracture mechanics specimens. The special emphasis was placed to the behaviour at low corrosion potentials and, in particular, to hydrogen water chemistry conditions. The major parameter effects and critical conjoint threshold conditions, which result in relevant environmental reduction and acceleration of fatigue initiation life and subsequent short crack growth, respectively, are discussed and summarised. The observed corrosion fatigue behaviour is compared with the fatigue evaluation procedures in codes and regulatory guidelines.

Fatigue Crack Growth Mechanisms for Nickel-based Superalloy Haynes 282 at 550-750 °C

Science.gov (United States)

Rozman, Kyle A.; Kruzic, Jamie J.; Sears, John S.; Hawk, Jeffrey A.

2015-10-01

The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 and 0.25 Hz. The crack path was observed to be primarily transgranular for all temperatures, and the observed effect of increasing temperature was to increase the fatigue crack growth rates. The activation energy associated with the increasing crack growth rates over these three temperatures was calculated less than 60 kJ/mol, which is significantly lower than typical creep or oxidation mechanisms; therefore, creep and oxidation cannot explain the increase in fatigue crack growth rates. Transmission electron microscopy was done on selected samples removed from the cyclic plastic zone, and a trend of decreasing dislocation density was observed with increasing temperature. Accordingly, the trend of increasing crack growth rates with increasing temperature was attributed to softening associated with thermally assisted cross slip and dislocation annihilation.

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

Influence of surface defects on the fatigue crack initiation in pearlitic steel

Directory of Open Access Journals (Sweden)

Toribio Jesús

2014-06-01

Full Text Available Tensile fatigue tests were performed under load control, with constant stress range Δσ on pearlitic steel wires, from the hot rolled bar to the commercial prestressing steel wire (which has undergone seven cold drawing steps. Results show that fatigue cracks in pearlitic steels initiate at the wire surface starting from small defects, whose size decreases with the drawing process. Fatigue cracks created from defects (initiation phase exhibit a fractographic appearance consisting of ductile microtearing events which can be classified as tearing topography surface or TTS, and exhibit a remarkably lower spacing in the prestressing steel wire than in the hot rolled bar. In addition, some S-N tests were performed in both material forms under a stress range of about half the yield strength. In these tests, the main part of the fatigue life corresponds to the propagation stage in the hot rolled bar whereas such a main part of the life is associated with the initiation stage in the case of the prestressing steel wire.

Consistent creep and rupture properties for creep-fatigue evaluation

International Nuclear Information System (INIS)

Schultz, C.C.

1978-01-01

The currently accepted practice of using inconsistent representations of creep and rupture behaviors in the prediction of creep-fatigue life is shown to introduce a factor of safety beyond that specified in current ASME Code design rules for 304 stainless steel Class 1 nuclear components. Accurate predictions of creep-fatigue life for uniaxial tests on a given heat of material are obtained by using creep and rupture properties for that same heat of material. The use of a consistent representation of creep and rupture properties for a mininum strength heat is also shown to provide adequate predictions. The viability of using consistent properties (either actual or those of a minimum heat) to predict creep-fatigue life thus identifies significant design uses for the results of characterization tests and improved creep and rupture correlations

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

International Nuclear Information System (INIS)

Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

2014-01-01

The research built upon a prior investigation to develop a unified constitutive model for design-@by-@analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-@fatigue and creep-@ratcheting tests were conducted on the nickel base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-@controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-@fatigue and creep-@ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-@fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-@ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the

Investigation on effect of laser shock processing on fatigue crack initiation and its growth in aluminum alloy plate

International Nuclear Information System (INIS)

Zhang, X.Q.; Li, H.; Yu, X.L.; Zhou, Y.; Duan, S.W.; Li, S.Z.; Huang, Z.L.; Zuo, L.S.

2015-01-01

Highlights: • LSP can greatly delay crack formation. • The micro-crack growing processes and its fracture are showed clearly. • Surface topographies and crack initiation locations are displayed. - Abstract: A series of contrasting experiments were carried out to examine the effects of laser shock processing (LSP) on fatigue properties of slot in 7075-T6 aluminum alloy plate. Both side surfaces of slot were subjected to LSP. The surface topographies were observed and the residual stresses were tested. The treated and the un-treated specimens were pulled by the fatigue cyclic loading respectively. The fatigue crack propagating processes were recorded, and the fatigue fracture microscopic morphologies were analyzed by scanning electron microscope (SEM). Experimental results and analyses show that LSP induces micro-dent on surface and squeezes the compressive residual stresses into surface layer of specimen. It can remarkably delay the micro-crack formation, and transfer the location of fatigue crack initiation from top surface to sub-surface. The spacing of fatigue striations on the treated specimen fatigue fracture obviously decreases. Therefore, the fatigue life of specimen after LSP treatment significantly increases

Initiation and propagation of fatigue cracks in cast IN713LC superalloy

Czech Academy of Sciences Publication Activity Database

Kunz, Ludvík; Lukáš, Petr; Konečná, R.

2010-01-01

Roč. 77, č. 11 (2010), s. 2008-2015 ISSN 0013-7944 R&D Projects: GA MPO FT-TA4/023; GA AV ČR 1QS200410502 Institutional research plan: CEZ:AV0Z20410507 Keywords : IN 713LC * high temperature fatigue * crystallographic fatigue crack initiation * mean stress effect Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.571, year: 2010

The role of extrusions and intrusions in fatigue crack initiation

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Mazánová, Veronika; Heczko, Milan; Petráš, Roman; Kuběna, Ivo; Casalena, L.; Man, Jiří

2017-01-01

Roč. 185, NOV (2017), s. 46-60 ISSN 0013-7944 R&D Projects: GA MŠk(CZ) LQ1601; GA MŠk LM2015069; GA ČR(CZ) GA13-23652S; GA ČR GA15-08826S Institutional support: RVO:68081723 Keywords : Extrusion * Fatigue crack initiation * Intrusion * Persistent slip marking * Stainless steel Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis Impact factor: 2.151, year: 2016

Consistent creep and rupture properties for creep-fatigue evaluation

International Nuclear Information System (INIS)

Schultz, C.C.

1979-01-01

The currently accepted practice of using inconsistent representations of creep and rupture behaviors in the prediction of creep-fatigue life is shown to introduce a factor of safety beyond that specified in current ASME Code design rules for 304 stainless steel Class 1 nuclear components. Accurate predictions of creep-fatigue life for uniaxial tests on a given heat of material are obtained by using creep and rupture properties for that same heat of material. The use of a consistent representation of creep and rupture properties for a minimum strength heat is also shown to provide reasonable predictions. The viability of using consistent properties (either actual or those of a minimum strength heat) to predict creep-fatigue life thus identifies significant design uses for the results of characterization tests and improved creep and rupture correlations. 12 refs

Creep crack growth in phosphorus alloyed oxygen free copper

Energy Technology Data Exchange (ETDEWEB)

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

2011-01-15

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

Creep crack growth in phosphorus alloyed oxygen free copper

International Nuclear Information System (INIS)

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

2011-01-01

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

Effect of pre-deformation on the fatigue crack initiation life of X60 pipeline steel

International Nuclear Information System (INIS)

Zheng, M.; Luo, J.H.; Zhao, X.W.; Bai, Z.Q.; Wang, R.

2005-01-01

It is impossible to keep petroleum and natural gas transmission pipelines free from defects in the manufacturing, installation and servicing processes. The damage might endanger the safety of pipelines and even shorten their service life; gas or petroleum release due to defects may jeopardise the surrounding ecological environments with associated economic and life costs. Pre-tensile deformation of X60 steel is employed to experimentally simulate the influence of dents on the fatigue crack initiation life. The investigation indicates that the fatigue crack initiation life of pre-deformed X60 pipeline steel can be assessed by a previously proposed energetic approach. The threshold for crack initiation increases with the pre-deformation due to a strain hardening effect, while the fatigue resistant factor exhibits a maximum with pre-deformation owing to its special dependence on fracture strain and fracture strength. The result is expected to be beneficial to the understanding of the effect of damage on the safety of pipelines and fatigue life prediction

Study on deformation behavior and life evaluation method for SUS304 notched plate under bending creep fatigue loading

International Nuclear Information System (INIS)

Fukuda, Yoshio; Satoh, Yoshimi; Nakamura, Kazuhiro; Takahashi, Yukio; Kuwabara, Kazuo.

1990-01-01

Creep-fatigue tests were carried out on notched plates under cyclic bending loads out of plane at 550degC, and the local strain at the notch-root and micro crack propagation behavior were measured. Then, inelastic analysis was performed for the experiment by using three kinds of constitutive models, such as kinematic hardening, ORNL and Ohno models. From the comparison of the experiment with the results of analysis, the following conclusions were obtained. (1) Creep strain caused at the notch-root during load holding was negligibly small compared with plastic strain, so that the neighborhood of the notch-root is subjected to constrained strain type damage. (2) The strain range at the notch-root can be calculated from the results of elastic-plastic analysis for monotonic loading independent of the constitutive models used, where the cyclic stress-strain relationship was used as the material monotonic deformation property. (3) The mean strain calculated was consistent with the experimental value in case of kinematic hardening or ORNL model, while not in case of Ohno model. (4) A method for predicting the crack initiation life of a notched plate has been proposed on the basis of micro-crack propagation behavior obtained by a fundamental creep-fatigue test. (author)

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

Energy Technology Data Exchange (ETDEWEB)

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

2013-07-01

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

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

International Nuclear Information System (INIS)

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

2013-01-01

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and the development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the type of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading - pure thermal and pure mechanical - were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [4]. Interrupted thermal cyclic tests in the temperature range of 150 C to 300 C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM (Scanning Electron Microscope), were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which microcracks arise and evolve to a dominant crack. Finally, these microcracks cause a continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied within the framework of the research project [5], [8]. With a combination of interrupted LCF tests and EBSD

Creep-fatigue life property of FBR high-temperature structural materials under tension-torsion loading and life evaluation method

International Nuclear Information System (INIS)

Ogata, Takashi; Nitta, Akito

1994-01-01

Creep-fatigue damage in high temperature structural components in a FBR progress under multiaxial stress condition depending on their operating conditions and configuration. Therefore, multiaxial stress effects on creep-fatigue damage evolution must be clarified to make precise creep-fatigue damage evaluation of these components. In this study, creep-fatigue tests in FBR high temperature materials such as SUS304, 316FR stainless steels and a modified 9Cr steel were conducted under biaxial stress subjecting tension-compression and torsion loading, in order to examine biaxial stress effects on failure mechanism and life property, and to discuss creep-fatigue life evaluation methods under biaxial stress. Main results obtained in this study are summarized as follows: 1. The main cracks under cyclic torsion loading propagated by shear mode in three materials. But intergranular failure was occurred in SUS304 and 316FR, and transgranular failure was observed in Mod.9Cr steel. 2. Nonlinear damage accumulation model proposed based on uniaxial creep-fatigue test results was extended to apply for creep-fatigue damage evaluation under biaxial stress state by considering the biaxial stress effects on fatigue and creep damage evolution. 3. It was confirmed that creep-fatigue life under biaxial stress could be predicted by the extended evaluation method with higher accuracy than existing methods. (author)

Creep fatigue assessment for EUROFER components

Energy Technology Data Exchange (ETDEWEB)

Özkan, Furkan, E-mail: oezkan.furkan@partner.kit.edu; Aktaa, Jarir

2015-11-15

Highlights: • Design rules for creep fatigue assessment are developed to EUROFER components. • Creep fatigue assessment tool is developed in FORTRAN code with coupling MAPDL. • Durability of the HCPB-TBM design is discussed under typical fusion reactor loads. - Abstract: Creep-fatigue of test blanket module (TBM) components built from EUROFER is evaluated based on the elastic analysis approach in ASME Boiler Pressure Vessel Code (BPVC). The required allowable number of cycles design fatigue curve and stress-to-rupture curve to estimate the creep-fatigue damage are used from the literature. Local stress, strain and temperature inputs for the analysis of creep-fatigue damage are delivered by the finite element code ANSYS utilizing the Mechanical ANSYS Parametric Design Language (MAPDL). A developed external FORTRAN code used as a post processor is coupled with MAPDL. Influences of different pulse durations (hold-times) and irradiation on creep-fatigue damage for the preliminary design of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) are discussed for the First Wall component of the TBM box.

Fatigue micro-crack initiation behavior and effect of irradiation damage on it in austenitic stainless steel

International Nuclear Information System (INIS)

Nakai, Ryosuke; Sato, Yuki; Nogami, Shuhei; Hasegawa, Akira

2012-01-01

The effect of irradiation on slip band formation and growth and micro-crack initiation behavior under low cycle fatigue in SUS316L austenitic stainless steel was investigated using accelerator-based proton irradiation and a low cycle fatigue test at room temperature in air. The micro-crack initiation was observed at slip band, grain boundary, twin boundary, and triple junction regardless of the total strain range and the proton irradiation. In unirradiated specimens, the micro-crack initiation life dropped by 75-90% due to the increase of the plastic strain range. Under the condition the plastic strain range was 0.4%, the micro-crack initiation was observed mainly at the grain boundary. On the other hand, under the condition the plastic strain range was 1.0%, the number fractions of the micro-crack initiation in slip band and twin boundary were increased. In proton-irradiated specimens, the micro-crack initiation life decreased by 50-80% and the micro-crack initiation was observed mainly at slip band and twin boundary. (author)

Crack embryo formation before crack initiation and growth in high temperature water

International Nuclear Information System (INIS)

Arioka, Koji; Yamada, Takuyo; Terachi, Takumi; Miyamoto, Tomoki

2008-01-01

Crack growth measurements were performed in high temperature water and in air to examine the role of creep on IGSCC growth using cold rolled non-sensitized Type316(UNS S31600), TT690 alloy, MA600 alloy, and Carbon steel (STPT42). In addition, crack initiation tests were performed also in high temperature water and in air using specially designed CT specimen. The obtained major results are as follows: (1) TT690 did crack in intergranularly in hydrogenated high temperature water if material is cold worked in heavily. (2) Cold worked carbon steel also cracked in intergranularly in dearated high temperature water. (3) Intergranular crack growth was recognized on cold worked 316, TT690, MA600, and carbon steel even in air which might be crack embryo of IGSCC. (4) Simple Arrhenius type temperature dependence was observed on IGSCC in high temperature water and creep crack growth in air. This suggested that intergranular crack growth rate was determined by some thermal activated reaction. (5) Vacancy condensation was recognized at just ahead of the crack tips of IGSCC and creep crack of cold worked steel. This showed that IGSCC and creep crack growth was controlled by same mechanism. (6) Clear evidence of vacancies condensation was recognized at just beneath the surface before crack initiation. This proved that crack did initiate as the result of diffusion of vacancies in the solid. And the incubation time seems to be controlled by the required time for the condensation of vacancies to the stress concentrated zone. (7) Diffusion of subsituational atoms was also driven by stress gradient. This is the important knowledge to evaluate the SCC initiation after long term operation in LWR's. Based on the observed results, IGSCC initiation and growth mechanism were proposed considering the diffusion process of cold worked induced vacancies. (author)

Study of cyclic strain localization and fatigue crack initiation using FIB technique

Czech Academy of Sciences Publication Activity Database

Man, Jiří; Vystavěl, T.; Weidner, A.; Kuběna, Ivo; Petrenec, Martin; Kruml, Tomáš; Polák, Jaroslav

2012-01-01

Roč. 39, JUN (2012), s. 44-53 ISSN 0142-1123 R&D Projects: GA ČR GAP108/10/2371 Institutional research plan: CEZ:AV0Z20410507 Keywords : fatigue crack initiation * persistent slip band * focused ion beam (FIB) Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.976, year: 2012

Numerical analysis of rolling contact fatigue crack initiation and fatigue life prediction of the railway crossing

OpenAIRE

Xin, L.; Markine, V.L.; Shevtsov, I.

2015-01-01

The procedure for analysing rolling contact fatigue crack initiation and fatigue life prediction of the railway turnout crossing is developed. A three-dimensional finite element (FE) model is used to obtain stress and strain results, considering the dynamic effects of wheel-crossing rolling contact. Material model accounting for elastic- plastic isotropic and kinematic hardening effects is adopted. The results from FE analysis are combined with J-S fatigue model that is based on critical plan...

Creep, fatigue and creep-fatigue damage evaluation and estimation of remaining life of SUS 304 austenitic stainless steel at high temperature

International Nuclear Information System (INIS)

Nishino, Seiichi; Sakane, Masao; Ohnami, Masateru

1986-01-01

Experimental study was made on the damage evaluation and estimation of remaining life of SUS 304 stainless steel in creep, low-cycle fatigue and creep-fatigue at 873 K in air. Creep, fatigue and creep-fatigue damage curves were drawn by the method proposed by D.A. Woodford and the relations between these damages and non-destructive parameters, i.e., microvickers hardness and quantities obtained from X-ray diffraction, were discussed. From these tests, the following conclusions were obtained. (1) Constant damage lines in the diagram of remaining lives in creep and fatigue could be drawn by changing load levels during the tests. Constant damage lines in creep-fatigue were also made by a linear damage rule using both static creep and fatigue damage curves, which agree well with the experimental data in creep-fatigue. (2) Microvickers hardness and half-value breadth in X-ray diffraction are appropriate parameters to evaluate creep damage but are not proper to evaluate fatigue damage. Particle size and microstrain obtained by X-ray profile analysis are good parameters to evaluate both creep and fatigue damages. (author)

Creep crack extension by grain-boundary cavitation

International Nuclear Information System (INIS)

Bassani, J.L.

1981-01-01

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

Fatigue crack growth behaviour of 21/4Cr1Mo steel tube at elevated temperature

International Nuclear Information System (INIS)

Bulloch, J.H.; Buchanan, L.W.

1987-01-01

The fatigue crack growth characteristics of 21/4Cr1Mo steel tube have been examined at 588 0 C over the frequency range 0.02-20 Hz and dwell time range 10-960 min. All tests were conducted under load control in laboratory air at an R-ratio of 0.5. The elevated temperature fatigue crack growth characteristics were adequately described in terms of the stress intensity range ΔKAPPA. The continuous cyclic test data exhibited a significant effect of frequency that agreed well with predicted effects using a simple mathematical model of the high temperature fatigue process. With the dwell time range of 10-100 min there was a significant dwell time effect on the critical ΔKAPPA level for creep-fatigue interactive growth. At dwell times > 100 min the dwell time effect saturates. When creep-fatigue interactive growth occurs, growth rates reside above the maximum for continuum-controlled fatigue crack growth, and exhibit a da/dN varies as ΔKAPPA 10 dependence; failure is then intergranular in nature. (author)

Continuous fatigue crack monitoring of bridges: Long-Term Electrochemical Fatigue Sensor (LTEFS)

Science.gov (United States)

Moshier, Monty A.; Nelson, Levi; Brinkerhoff, Ryan; Miceli, Marybeth

2016-04-01

Fatigue cracks in steel bridges degrade the load-carrying capacity of these structures. Fatigue damage accumulation caused by the repetitive loading of everyday truck traffic can cause small fatigue cracks initiate. Understanding the growth of these fatigue cracks is critical to the safety and reliability of our transportation infrastructure. However, modeling fatigue in bridges is difficult due to the nature of the loading and variations in connection integrity. When fatigue cracks reach critical lengths failures occur causing partial or full closures, emergency repairs, and even full structural failure. Given the aging US highway and the trend towards asset management and life extension, the need for reliable, cost effective sensors and monitoring technologies to alert bridge owners when fatigue cracks are growing is higher than ever. In this study, an innovative Long-Term Electrochemical Fatigue Sensor (LTEFS) has been developed and introduced to meet the growing NDT marketplace demand for sensors that have the ability to continuously monitor fatigue cracks. The performance of the LTEFS has been studied in the laboratory and in the field. Data was collected using machined specimens with different lengths of naturally initiated fatigue cracks, applied stress levels, applied stress ratios, and for both sinusoidal and real-life bridge spectrum type loading. The laboratory data was evaluated and used to develop an empirically based algorithm used for crack detection. Additionally, beta-tests on a real bridge structure has been completed. These studies have conclusively demonstrated that LTEFS holds great potential for long-term monitoring of fatigue cracks in steel structures

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

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

Energy Technology Data Exchange (ETDEWEB)

Lissenden, Cliff [Pennsylvania State Univ., State College, PA (United States); Hassan, Tasnin [North Carolina State Univ., Raleigh, NC (United States); Rangari, Vijaya [Tuskegee Univ., Tuskegee, AL (United States)

2014-10-30

The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched

On fatigue crack growth mechanisms of MMC: Reflection on analysis of 'multi surface initiations'

International Nuclear Information System (INIS)

Mkaddem, A.; El Mansori, M.

2009-01-01

This work attempts to examine the mechanisms of fatigue when cracks synergetically initiate in more than one site at the specimen surface. The metal matrix composites (MMC) i.e. silicon carbide particles reinforced aluminium matrix composites (Al/SiC p -MMC), seem to be good candidates to accelerate fatigue failures following multi surface initiations (MSI). Closure effects of MSI mechanisms on the variation of fatigue behaviour are explored for various stress states. Experiments were carried out using non pre-treated and pre-treated specimens. Using an Equivalent Ellipse Method (EEM), it is shown that the aspect of surface finish of specimen plays an important role on crack growth. Scanning Electron Microscope (SEM) inspections have lead to distinguishing the initiation regions from propagation regions and final separation regions. It is also revealed that the total lifetime of specimens is sensitive to heat treatment. Moreover, it is found that the appearance of MSI in cycled materials is more probable at high level of fatigue loads.

Experimental evidence and physical models of fatigue crack initiation

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Man, Jiří

2016-01-01

Roč. 91, OCT (2016), s. 294-303 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GA13-23652S; GA ČR GA13-32665S; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : Crack initiation * Persistent slip band * Point defects * Extrusions * Intrusions Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.899, year: 2016

In situ observation of fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy at 750 °C

Energy Technology Data Exchange (ETDEWEB)

Min, Zhang [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Xi-ping, Song, E-mail: xpsong@skl.ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Long, Yu; Hong-liang, Li [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Ze-hui, Jiao; Hui-chen, Yu [National Key Laboratory of Science and Technology on Advanced High Temperature Structural Materials, Beijing Institute of Aeronautical Materials, Beijing 100095 (China)

2015-01-12

In this paper, the fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy with nearly lamellar microstructure was studied by in situ scanning electron microscope observation at 750 °C. Dog-bone shaped specimens with a single-edge notch were used in the test. The results showed that the fatigue crack initiated first at the central portion of the notch, and then shifted to the edge portion. As the cycle numbers went on increasing, these cracks joined together and formed a main fatigue crack, which could propagate along the surface of the specimen. During the fatigue crack propagation two or three propagation stages were found depending on the microstructure of the crack tip. When the fatigue crack was parallel to the lamellar laths, it exhibited the rapid, steady and accelerated propagation stages successively, while when the fatigue crack was perpendicular to the lamellar laths, it exhibited only the steady and accelerated propagation stages, with no rapid propagation stage being found. In these different propagation stages the fatigue crack propagation rates were different and depended intensively on the lamellar laths orientation, lamellar colony size, equiaxed gamma grains and peak stress intensity factor K{sub max}. Based on the experimental data it was concluded that the fatigue crack initiation lifetime was much longer than the propagation lifetime for the single-edge notched specimens at 750 °C.

In situ observation of fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy at 750 °C

International Nuclear Information System (INIS)

Min, Zhang; Xi-ping, Song; Long, Yu; Hong-liang, Li; Ze-hui, Jiao; Hui-chen, Yu

2015-01-01

In this paper, the fatigue crack initiation and propagation behavior of a high-Nb TiAl alloy with nearly lamellar microstructure was studied by in situ scanning electron microscope observation at 750 °C. Dog-bone shaped specimens with a single-edge notch were used in the test. The results showed that the fatigue crack initiated first at the central portion of the notch, and then shifted to the edge portion. As the cycle numbers went on increasing, these cracks joined together and formed a main fatigue crack, which could propagate along the surface of the specimen. During the fatigue crack propagation two or three propagation stages were found depending on the microstructure of the crack tip. When the fatigue crack was parallel to the lamellar laths, it exhibited the rapid, steady and accelerated propagation stages successively, while when the fatigue crack was perpendicular to the lamellar laths, it exhibited only the steady and accelerated propagation stages, with no rapid propagation stage being found. In these different propagation stages the fatigue crack propagation rates were different and depended intensively on the lamellar laths orientation, lamellar colony size, equiaxed gamma grains and peak stress intensity factor K max . Based on the experimental data it was concluded that the fatigue crack initiation lifetime was much longer than the propagation lifetime for the single-edge notched specimens at 750 °C

Detection and closure measurement of short fatigue crack initiated at notch root

International Nuclear Information System (INIS)

Lee, Jong-Hyung; Kobayashi, Hideo

1985-01-01

Short fatigue cracks initiated at the notch root were successfully detected at a fairly high accuracy by the ultrasonic amplitude calibration method for the notched compact specimens of an A508-3 steel. Crack closure measurements by the ultrasonic and back-face strain compliance methods were also performed. Crack growth characteristics at the notch root are similar to those of delyed retardation caused by a single peak overload. Also, transitional behavior from short cracks to long cracks was interpreted in terms of effective stress intensity ΔKsub(eff). The relation between crack growth rate da/dN and ΔKsub(eff) for short cracks shows a fairly good agreement with those for long cracks. (author)

Experimental investigation of crack initiation in face-centered cubic materials in the high and very high cycle fatigue regime

Energy Technology Data Exchange (ETDEWEB)

Straub, Thomas

2016-07-01

Materials in many modern small-scale applications are under complex cyclic stress states and undergo up to 10{sup 9} cycles. Fatigue mechanisms limit their lifetime and lead to failure. Therefore, the Very High Cycle Fatigue (VHCF) regime needs to be studied. This thesis investigates the fatigue mechanisms and crack initiation of nickel, aluminum and copper on a small-scale in the VHCF regime by means of innovative fatigue experimentation. Firstly, the development and implementation of a novel custom-built resonant fatigue setup showed that the resonant frequency of bending micro-samples changes with increasing cycle number due to the accumulating fatigue damage. Then, additional insights on early damage formation have been explored. Mechanisms, prior to crack initiation, such as slip band formation at a state where it appears in only a few grains, have been observed. Cyclic hardening, vacancy formation and oxidation formation may be considered as possible explanations for early fatigue mechanisms. In addition, the new experimental setup can be used to define parameters needed for crack initiation models. Finally, these crack initiation processes have been experimentally examined for pure aluminum and pure copper.

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

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)

Creep-fatique interactions in 316 stainless steel under torsional loading

International Nuclear Information System (INIS)

Wei, K.; Dyson, B.F.

1982-01-01

Some fatigue, fatigue with creep dwells and creep tests have been performed in torsion using 316 stainless steel at 600 0 C. As expected from push-pull testing, the introduction of a creep dwell reduced fatigue endurances and changed the fracture from classical transgranular to intergranular. Optical microscopical examination revealed a large number of intergranular cracks concentrated along shear planes, but quantitative assessment identified the importance of creep tensile stresses in crack development. In contrast, little intergranular damage was found after torsion creep, which is consistent with its exhibited buckling mode of failure. It is concluded that reverse plastic strain is the cause of intergranular crack formation in the material and is therefore the primary mechanism of creep-fatigue interaction. (author)

Crack initiation and propagation on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing

Directory of Open Access Journals (Sweden)

G. M. Domínguez Almaraz

2015-10-01

Full Text Available Crack initiation and propagation have been investigated on the polymeric material ABS (Acrylonitrile Butadiene Styrene, under ultrasonic fatigue testing. Three controlled actions were implemented in order to carry out fatigue tests at very high frequency on this material of low thermal conductivity, they are: a The applying load was low to limit heat dissipation at the specimen neck section, b The dimensions of testing specimen were small (but fitting the resonance condition, in order to restraint the temperature gradient at the specimen narrow section, c Temperature at the specimen neck section was restrained by immersion in water or oil during ultrasonic fatigue testing. Experimental results are discussed on the basis of thermo-mechanical behaviour: the tail phenomenon at the initial stage of fatigue, initial shear yielding deformation, crazed development on the later stage, plastic strain on the fracture surface and the transition from low to high crack growth rate. In addition, a numerical analysis is developed to evaluate the J integral of energy dissipation and the stress intensity factor K, with the crack length

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

Energy Technology Data Exchange (ETDEWEB)

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

2009-09-15

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

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

Energy Technology Data Exchange (ETDEWEB)

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

1996-05-01

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

The shape of extrusions and intrusions and initiation of stage I fatigue cracks

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Man, Jiří; Vystavěl, T.; Petrenec, Martin

2009-01-01

Roč. 517, 1-2 (2009), s. 204-211 ISSN 0921-5093 R&D Projects: GA ČR GA106/06/1096; GA ČR GA101/07/1500 Institutional research plan: CEZ:AV0Z20410507 Keywords : Extrusion * Intrusion * Fatigue crack initiation * Stainless steel Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.901, year: 2009

The effect of aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels

International Nuclear Information System (INIS)

James, L.A.

1996-01-01

The effect of elevated temperature aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels is discussed in terms of the several parameters which influence such behavior. These parameters include water chemistry, impurities within the steels themselves, as well as factors such as the water flow rate, loading waveform and loading rates. Some of these parameters have similar effects upon both crack initiation and propagation, while others exhibit different effects in the two stages of cracking. In the case of environmentally-assisted crack (EAC) growth, the most important impurities within the steel are metallurgical sulfide inclusions which dissolve upon contact with the water. A ''critical'' concentration of sulfide ions at the crack tip can then induce environmentally-assisted cracking which proceeds at significantly increased crack growth rates over those observed in air. The occurrence, or non-occurrence, of EAC is governed by the mass-transport of sulfide ions to and from the crack-tip region, and the mass-transport is discussed in terms of diffusion, ion migration, and convection induced within the crack enclave. Examples are given of convective mass-transport within the crack enclave resulting from external free stream flow. The initiation of fatigue cracks in elevated temperature aqueous environments, as measured by the S-N fatigue lifetimes, is also strongly influenced by the parameters identified above. The influence of sulfide inclusions does not appear to be as strong on the crack initiation process as it is on crack propagation. The oxygen content of the environment appears to be the dominant factor, although loading frequency (strain rate) and temperature are also important factors

Averaged strain energy density-based synthesis of crack initiation life in notched steel bars under torsional fatigue

Directory of Open Access Journals (Sweden)

Filippo Berto

2016-10-01

Full Text Available The torsional fatigue behaviour of circumferentially notched specimens made of austenitic stainless steel, SUS316L, and carbon steel, SGV410, characterized by different notch root radii has been recently investigated by Tanaka. In that contribution, it was observed that the total fatigue life of the austenitic stainless steel increases with increasing stress concentration factor for a given applied nominal shear stress amplitude. By using the electrical potential drop method, Tanaka observed that the crack nucleation life was reduced with increasing stress concentration, on the other hand the crack propagation life increased. The experimental fatigue results, originally expressed in terms of nominal shear stress amplitude, have been reanalysed by means of the local strain energy density (SED averaged over a control volume having radius R0 surrounding the notch tip. To exclude all extrinsic effects acting during the fatigue crack propagation phase, such as sliding contact and/or friction between fracture surfaces, crack initiation life has been considered in the present work. In the original paper, initiation life was defined in correspondence of a 0.1÷0.4-mm-deep crack. The control radius R0 for fatigue strength assessment of notched components, thought of as a material property, has been estimated by imposing the constancy of the averaged SED for both smooth and cracked specimens at NA = 2 million loading cycles

Creep-fatigue behavior of turbine disc of superalloy GH720Li at 650 °C and probabilistic creep-fatigue modeling

Energy Technology Data Exchange (ETDEWEB)

Hu, Dianyin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China); Ma, Qihang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Shang, Lihong [Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5 (Canada); Gao, Ye [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Wang, Rongqiao, E-mail: wangrq@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China)

2016-07-18

Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li at an elevated temperature of 650 °C with a stress ratio of 0.1, based on which, different dwell times at the maximum loading were applied to investigate the effect of dwell time on the creep-fatigue behaviors. The tested specimens were cut from the rim region of an actual turbine disc in the hoop direction. The grain size and precipitates of the GH720Li superalloy were examined through scanning electronic microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. Experimental data shows creep-fatigue lifetime decreases as the dwell time prolongs. Further, different scattering was observed in the creep-fatigue lifetime at different dwell times. Then a probabilistic model based on the applied mechanical work density (AMWD), with a linear heteroscedastic function that evaluates the non-constant deviation in the creep-fatigue lifetime, was formulated to describe the dependence of creep-fatigue lifetime on the dwell time. Finally, the possible microscopic mechanism of the creep-fatigue behavior has been discussed by SEM with EDS on the fracture surfaces.

Comparison of fatigue crack initiation behavior in different microstructures of TC21 titanium alloy

Directory of Open Access Journals (Sweden)

Tan Changsheng

2018-01-01

Full Text Available Cyclic heterogeneous deformation, slip characteristics and crack nucleation with different microstructures, such as bimodal microstructure (BM and fine lamellar microstructure (FLM in TC21 alloy (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si, were systematically investigated and analyzed during high cycle fatigue at room temperature. The results demonstrated that the FLM microstructure possesses higher high-cycle fatigue strength than those of the BM one. For BM, the heterogeneous plastic deformation existed within the different large primary α phase, such as equiaxed primary α and primary α lath. The cracks at interfaces and slip bands easily coalesce with each other to form large cracks in BM. However, the α laths with similar morphology and size (nanosize distributed uniformly in FLM and could relatively deform homogeneously in micro-region, which delayed the initiation of the fatigue crack. Based on the electron-backscattered diffraction (EBSD analysis, it found that the strain was nonuniformly distributed in BM, however, it is relatively homogeneous in FLM. Moreover, lots of straight cracks are parallel and along single intrusions within the β grain which delays the coalescence of cracks.

Effect of size of alpha phases on cyclic deformation and fatigue crack initiation during fatigue of an alpha-beta titanium alloy

Directory of Open Access Journals (Sweden)

Sun Qiaoyan

2018-01-01

Full Text Available Alpha phase exhibits equiaxed or lamellar morphologies with size from submicron to microns in an alpha-beta titanium alloy. Cyclic deformation, slip characteristics and crack nucleation during fatigue in different microstructures of TC21 alloy (Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si were systematically investigated and analyzed. During low-cycle fatigue, equiaxed microstructure (EM in TC21 alloy exhibits higher strength, ductility and longer low-cycle fatigue life than those of the lamellar microstructure (LM. There are more voids in the single lamellar alpha than the equiaxed alpha grains. As a result, voids more easily link up to form crack in the lamellar alpha phase than the equiaxed alpha phase. However, during high-cycle fatigue, the fine lamellar microstructure (FLM shows higher fatigue limit than bimodal microstructure (BM. The localized plastic deformation can be induced during high-cycle fatigue. The slip bands or twins are observed in the equiaxed and lamellar alpha phases(>1micron, which tends to form strain concentration and initiate fatigue crack. The localized slip within nanoscale alpha plates is seldom observed and extrusion/intrusion dispersedly distributed on the sample surface in FLM. This indicates that FLM show super resistance to fatigue crack which bring about higher fatigue limit than BM.

FATIGUE CRACK PROPAGATION THROUGH AUSTEMPERED DUCTILE IRON MICROSTRUCTURE

Directory of Open Access Journals (Sweden)

Lukáš Bubenko

2010-10-01

Full Text Available Austempered ductile iron (ADI has a wide range of application, particularly for castings used in automotive and earth moving machinery industries. These components are usually subjected to variable dynamic loading that may promote initiation and propagation of fatigue cracks up to final fracture. Thus, it is important to determine the fatigue crack propagation behavior of ADI. Since fatigue crack growth rate (da/dN vs. stress intensity factor K data describe fatigue crack propagation resistance and fatigue durability of structural materials, da/dN vs. Ka curves of ADI 1050 are reported here. The threshold amplitude of stress intensity factor Kath is also determined. Finally, the influence of stress intensity factor amplitude to the character of fatigue crack propagation through the ADI microstructure is described.

Evaluation procedure of creep-fatigue defect growth in high temperature condition and application

International Nuclear Information System (INIS)

Park, Chang Gyu; Kim, Jong Bum; Lee, Jae Han

2003-12-01

This study proposed the evaluation procedure of creep-fatigue defect growth on the high-temperature cylindrical structure applicable to the KALIMER, which is developed by KAERI. Parameters used in creep defect growth and the evaluation codes with these parameters were analyzed. In UK, the evaluation procedure of defect initiation and growth were proposed with R5/R6 code. In Japan, simple evauation method was proposed by JNC. In France, RCC-MR A16 code which was evaluation procedure of the creep-fatigue defect initiation and growth related to leak before break was developed, and equations related to load conditions were modified lately. As an application example, the creep-fatigue defect growth on circumferential semi-elliptical surface defect in high temperature cylindrical structure was evaluated by RCC-MR A16

Relaxation of Shot-Peened Residual Stresses Under Creep Loading (Preprint)

National Research Council Canada - National Science Library

Buchanan, Dennis J; John, Reji; Brockman, Robert A

2008-01-01

.... Compressive residual stresses retard initiation and growth of fatigue cracks. During the component loading history, loading, or during elevated temperature static loading, such as thermal exposure and creep...

A method for probing the effects of conformal nanoscale coatings on fatigue crack initiation in electroplated Ni films

International Nuclear Information System (INIS)

Straub, T.; Baumert, E.K.; Eberl, C.; Pierron, O.N.

2012-01-01

This paper describes an experimental technique to identify robust nanoscale coatings for improving the long-term reliability of metallic microelectromechanical systems. More specifically, the influence of nanoscale alumina coatings on the fatigue crack initiation process in 20 μm thick electrodeposited Ni films was investigated in a mild (30 °C, 50% RH) and harsh (80 °C, 90% RH) environment. Atomic-layer-deposited alumina layers, with thicknesses of 5 and 25 nm, were coated on Ni fatigue micro-resonators, and the fatigue degradation behavior in the very high cycle fatigue regime was compared to that of uncoated structures. Evidence based on post-test scanning electron microscopy and resonant frequency evolution plots shows that the coatings do not prevent the formation of fatigue extrusions and micro-cracks. However, their formation is likely delayed for the 25 nm thick alumina-coated Ni films. - Highlights: ► Effect of alumina coatings (5 and 25 nm thick) on fatigue initiation in nickel films ► Fatigue tests were performed at 30 °C, 50% relative humidity (RH) and 80 °C, 90% RH. ► Coatings did not prevent fatigue extrusions and micro-cracks. ► 25 nm coatings likely delayed the formation of fatigue extrusions and micro-cracks. ► The technique can be used to identify reliable nanoscale coatings.

Crack initiation and growth in welded structures; Amorcage et propagation de la fissuration dans les jonctions soudees

Energy Technology Data Exchange (ETDEWEB)

Assire, A

2000-10-13

. Concerning local approach, intergranular creep damage model of the Ecole des Mines de Paris is used for crack initiation and growth under creep and creep fatigue loading. Crack propagations are simulated with an adaptive re-meshing technique and are compared with experimental results for crack located in weld and base metal. A sensibility analysis shows that crack propagation strongly depend on the characteristic distance, which is needed to simulate crack growth with local approach, for the weld metal parameters. (author)

Creep crack growth behaviour of an AISI 316 steel plate for fast reactor structures

International Nuclear Information System (INIS)

D'Angelo, D.; Regis, V.

1985-01-01

The paper presents and analyses creep crack growth data obtained at 550, 600 and 650 0 C in air with SENT and CT specimens on type 316 stainless steel plate for LMFBR applications. Crack initiation and crack growth are tentatively correlated to K, sigmasub(net) and J* taking into account the constraint conditions due to specimen geometry. The validity of these parameters is discussed following the concept of transition time from small scale creep at the crack tip to extensive creep within the ligament. Post exposure microstructural and fractographic investigations do evidence that grain deformation processes are mainly responsible for cavity evolution. (orig.)

Crack growth in first wall made of reduced activation ferritic steel by transient creep due to long pulse operation

International Nuclear Information System (INIS)

Honda, T.; Kudo, Y.; Hatano, T.; Kikuchi, K.; Nishimura, T.; Saito, M.

2003-01-01

The long pulse operation is assumed in ITER and future reactor. If the first wall has a defect, the crack may be propagated by cyclic thermal loads. In addition, flattop of more than 300 s during plasma burning is expected in ITER, so the crack propagation behavior will depend on the operation duration period. This study deals with the crack propagation behavior on F82H under high thermal load cycles. The high heat flux tests were performed under three types of duration periods to investigate creep fatigue behavior. To clarify the crack growth mechanism and the effects of transient creep, three-dimensional analyses were performed. It was concluded that the creep effect during the operation duration period enlarges stress intensity factor K in the cooling period and that consequently, the crack propagation length was increased

Effect of HTGR helium on fatigue and creep properties of 2 1/4Cr-1Mo steel

International Nuclear Information System (INIS)

Kurumaji, T.; Yamazaki, H.; Kudo, A.

1982-01-01

Low cycle fatigue and creep tests have been carried out on 2 1/4Cr-1Mo steel (candidate steel for VHTR reactor pressure vessel) in helium environment containing 200 approx. 300 μatm of H 2 , 100 approx. 150 μatm CO, 7 approx. 10 μatm CH 4 , 7 approx. 10 μatm CO 2 and 1 μatm H 2 O (JAERI B Helium). Fatigue life in helium environment was longer than that in air at 450 0 C. This results can be explained by supposing that oxidation at the crack tip causes the wedge effect to promote crack propagation in air. On the otherhand, creep rupture strength showed no significant difference in both helium and air. Equivalent creep rupture strength in both helium and air may be due to the fact that detrimental internal oxidation and carburization or decarburization hardly occur at 400 approx. 450 0 C

Evaluation of micro fatigue crack growth under equi-biaxial stress by membranous pressure fatigue test

International Nuclear Information System (INIS)

Iida, Satoshi; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki

2014-01-01

For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)

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

Science.gov (United States)

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

2017-01-01

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

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...

Crack Tip Creep Deformation Behavior in Transversely Isotropic Materials

International Nuclear Information System (INIS)

Ma, Young Wha; Yoon, Kee Bong

2009-01-01

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

Ductile-phase toughening and fatigue crack growth in Nb3Al base alloys

International Nuclear Information System (INIS)

Gnanamoorthy, R.; Hanada, S.

1996-01-01

Niobium aluminide (Nb 3 Al) base intermetallic compounds exhibit good high-temperature strength and creep properties and potential for applications above 1,200 C provided their inadequately low room-temperature ductility, fracture toughness and fatigue crack growth behavior are improved. Addition of tantalum to Nb 3 Al base materials improves the high-temperature strength significantly and seems to be a potential alloying element. In the present study, room temperature fracture toughness and fatigue crack growth behavior of tantalum alloyed Nb 3 Al base alloy prepared by ingot metallurgy are investigated

The crystallography of fatigue crack initiation in Incoloy-908 and A-286 steel

International Nuclear Information System (INIS)

Krenn, C.R.

1996-12-01

Fatigue crack initiation in the austenitic Fe-Ni superalloys Incoloy-908 and A-286 is examined using local crystallographic orientation measurements. Results are consistent with sharp transgranular initiation and propagation occurring almost exclusively on {111} planes in Incoloy-908 but on a variety of low index planes in A-286. This difference is attributed to the influence of the semicoherent grain boundary η phase in A-286. Initiation in each alloy occurred both intergranularly and transgranularly and was often associated with blocky surface oxide and carbide inclusions. Taylor factor and resolved shear stress and strain crack initiation hypotheses were tested, but despite an inconclusive suggestion of a minimum required {111} shear stress, none of the hypotheses were found to convincingly describe preferred initiation sites, even within the subsets of transgranular cracks apparently free from the influence of surface inclusions. Subsurface inclusions are thought to play a significant role in crack initiation. These materials have applications for use in structural conduit for high field superconducting magnets designed for fusion energy use

AFM and SEM-FEG study on fundamental mechanisms leading to fatigue crack initiation

Czech Academy of Sciences Publication Activity Database

Man, Jiří; Valtr, M.; Petrenec, Martin; Dluhoš, J.; Kuběna, Ivo; Obrtlík, Karel; Polák, Jaroslav

2015-01-01

Roč. 76, JUL (2015), s. 11-18 ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP108/10/2371; GA MŠk(CZ) ED1.1.00/02.0068; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : fatigue crack initiation * 316L austenitic steel * atomic force microscopy * extrusion * intrusion Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.162, year: 2015

Effect of Process Parameters on Fatigue and Fracture Behavior of Al-Cu-Mg Alloy after Creep Aging

Directory of Open Access Journals (Sweden)

Lihua Zhan

2018-04-01

Full Text Available A set of creep aging tests at different aging temperatures and stress levels were carried out for Al-Cu-Mg alloy, and the effects of creep aging on strength and fatigue fracture behavior were studied through tensile tests and fatigue crack propagation tests. The microstructures were further analyzed by using scanning electron microscopy (SEM and transmission electron microscopy (TEM. The results show that temperature and stress can obviously affect the creep behavior, mechanical properties, and fatigue life of Al-Cu-Mg alloy. As the aging temperature increases, the fatigue life of alloy first increases, and then decreases. The microstructure also displays a transition from the Guinier-Preston-Bagaryatsky (GPB zones to the precipitation of S phase in the grain interior. However, the precipitation phases grow up and become coarse at excessive temperatures. Increasing stress can narrow the precipitation-free zone (PFZ at the grain boundary and improve the fatigue life, but overhigh stress can produce the opposite result. In summary, the fatigue life of Al-Cu-Mg alloy can be improved by fine-dispersive precipitation phases and a narrow PFZ in a suitable creep aging process.

Creep-fatigue of low cobalt superalloys

Science.gov (United States)

Halford, G. R.

1982-01-01

Testing for the low cycle fatigue and creep fatigue resistance of superalloys containing reduced amounts of cobalt is described. The test matrix employed involves a single high temperature appropriate for each alloy. A single total strain range, again appropriate to each alloy, is used in conducting strain controlled, low cycle, creep fatigue tests. The total strain range is based upon the level of straining that results in about 10,000 cycles to failure in a high frequency (0.5 Hz) continuous strain-cycling fatigue test. No creep is expected to occur in such a test. To bracket the influence of creep on the cyclic strain resistance, strain hold time tests with ore minute hold periods are introduced. One test per composition is conducted with the hold period in tension only, one in compression only, and one in both tension and compression. The test temperatures, alloys, and their cobalt compositions that are under study are given.

Low cycle fatigue of PM/HIP astroloy

Energy Technology Data Exchange (ETDEWEB)

Choe, S.J.; Stoloff, N.S.; Duquette, D.J. (Rensselaer Polytechnic Institute, Troy, NY (USA))

Low cycle fatigue and creep-fatigue-environment interactions of PM/HIP Astrology were studied at 650 C and 725 C. Total strain range was varied from 1.5% to 2.7% at a frequency of 0.3Hz. Creep-fatigue tests were performed with 2 min. or 5 min. tensile hold times. All tests were run in high purity argon in an attempt to minimize environmental effects. Employing a tensile hold was more damaging than raising temperature by 75 C. Slopes of Coffin-Manson plots were nearly independent of temperature and hold time. Raising temperature from 650 C to 725 C did not change the transgranular (TG) crack propagation mode, whereas employing hold times caused TG+IG propagation. All samples displayed multiple fracture origins associated with inclusions located at the specimen surface; pre-existing pores did not affect fatigue crack initiation. Examination of secondary cracks showed no apparent creep damage. Oxidation in high purity argon appeared to be the major factor in LCF life degradation due to hold times.

An analysis method for fatigue crack initiation on geometrical singularities

International Nuclear Information System (INIS)

Amzallag, C.; Bernard, J.L.; Pellissier-Tanon, A.; Vassal, J.M.

1982-05-01

For studying the significance of defects a promising point of view is to separate fatigue crack initiation and propagation. Comparing the works done on these two stages it appears that relatively few has been done on the first one. This presentation shows how this stage can be evaluated by using appropriate criteria. The validation of a criterion through experimental data obtained on actual and simulated singularities for different specimen geometries is presented

Fatigue crack growth in welded joints in seawater

Energy Technology Data Exchange (ETDEWEB)

Lambert, S.B.

1988-01-01

A pipe-to-plate specimen has been developed to study the influence of seawater on the fatigue behaviour of welded tubular joints. DC potential drop techniques have been used to detect fatigue crack initiation, and to monitor the subsequent growth of fatigue cracks. Results for three specimens, tested in air are compared with similar data for tubular and T-plate joints. These comparisons indicate that the pipe/plate is a reasonable model of a tubular joint. Testing was performed on a further six specimens in artificial seawater; two each with free corrosion, optimum cathodic protection, and cathodic overprotection. Fatigue life reduction factors compared with corresponding tests in air were 1.8 and 2.8 for free corrosion, 1.7 and 1.1 with cathodic protection, and 4.2 and 3.3 with cathodic over-protection. These fatigue life reduction factors were comparable to results on T-plate specimens, and were strongly dependent on crack shape development. Linear elastic fracture mechanics techniques appear suitable for the calculation of fatigue crack propagation life. Three approximate solution techniques for crack tip stress intensity factors show reasonable agreement with experimentally derived values. It is recommended that forcing functions be used to model crack aspect ratio development in welded joints. Such forcing functions are influenced by the initial stress distribution and the environment. 207 refs., 192 figs., 22 tabs.

Feasibility study on ductility exhaustion approach for creep-fatigue damage assessment of FBR 316 stainless steel using published data

International Nuclear Information System (INIS)

Nonaka, Isamu; Kitagawa, Masaki; Torihata, Shoji.

1995-01-01

In order to investigate the applicability of a ductility exhaustion rule to the creep-fatigue life assessment of FBR 316 stainless steel, a feasibility study using the published data was conducted. The assessment method was proposed based on the linear damage summation rule. In the proposed method, fatigue damage was calculated by Minor's rule and creep damage was calculated by a ductility exhaustion rule. The creep-fatigue lives in the published data were predicted by the proposed method. The results obtained are as follows: (1) All the data could be predicted within a factor of two on life by the proposed method. (2) The creep-fatigue lives under 10 minute strain hold at 550degC were overestimated, while those under 60 minute strain hold at 550degC and 600degC were estimated adequately. From the above facts, the proposed method seemed to be effective for the prediction of creep-fatigue life in which the creep damage was dominant and also the intergranular cracking was remarkable. (3) The creep damage was simultaneously calculated by the time fraction rule in order to compare with the ductility exhaustion role. All the data could be also predicted within a factor of two on life by this rule, but it tended to overestimate the life. (author)

Fatigue crack Behaviour in a High Strength Tool Steel

DEFF Research Database (Denmark)

Højerslev, Christian; Carstensen, Jesper V.; Brøndsted, Povl

2002-01-01

The influence of microstructure on fatigue crack initiation and crack growth of a hardened and tempered high speed steel was investigated. The evolution of fatigue cracks was followed in four point bending at room temperature. It was found that a carbide damage zone exists above a threshold load...... value of maximally 80% of the yield strength of the steel. The size of this carbide damage zone increases with increasing load amplitude, and the zone is apparently associated with crack nucleation. On fatigue crack propagation plastic deformation of the matrix occurs in a radius of approximately 4...... microns in front of the fatigue crack tip, which is comparable with the relevant mean free carbide spacing....

Development of European creep crack growth testing code of practice for industrial specimens

International Nuclear Information System (INIS)

Dogan, B.; Nikbin, K.; Petrovski, B.

2004-01-01

The integrity and residual life assessment of high temperature components require defects, detected or assumed to exist, through minimum allowable limits of detectable flaws using nondestructive testing methods. It relies on information obtained from the material's mechanical, uniaxial creep, creep crack initiation and growth properties. The information derived from experiments needs to be validated and harmonised following a Code of Practice that data variability between different institutions can be reduced to a minimum. The present paper reports on a Code of Practice (CoP) being prepared within the framework of the partially European Commission funded project CRETE. The novel aspect of the presented CoP is the inclusion of component relevant industrial specimen geometries. It covers testing and analysis of Creep Crack growth (CCG) in metallic materials at elevated temperature using six different cracked geometries that have been validated in. It aims to give advice on testing, measurements and analysis of creep crack growth data for a range of creep brittle to creep ductile materials using component service relevant specimen geometries and sizes. The CoP may be used for material selection criteria and inspection requirements for damage tolerant applications. In quantitative terms, these types of tests can be used to assess the individual and combined effects of metallurgical, fabrication, operating temperature, and loading conditions on creep crack growth life. Further issues will be addressed including material properties, damage and crack growth related constraint effect, stress relaxation and stress-strain fields, residual stresses, partitioning displacement, analysis of elastic creep, elastic compliance measurements

Crack initiation and propagation paths in small diameter FSW 6082-T6 aluminium tubes under fatigue loading

Directory of Open Access Journals (Sweden)

Roberto Tovo

2016-03-01

Full Text Available This paper reports results of fatigue tests of friction stir welded (FSW aluminium tubes. Relatively small 38 mm diameter tubes were used and hence an automated FSW process using a retracting tool was designed for this project, as the wall thickness of the aluminium tube was similar to the diameter of the FSW tool. This is a more complex joint geometry to weld than the more usual larger diameter tube reported in the literature. S-N fatigue testing was performed using load ratios of R = 0.1 and R = -1. Crack path analysis was performed using both low magnification stereo microscopy and scanning electron microscopy, in order to identify crack initiation sites and to determine the direction of crack propagation. Work is still in progress to follow the crack path through the various microstructural zones associated with the weld. A simple statistical analysis was used to characterize the most typical crack initiation site. This work forms part of a wider project directed at determining multiaxial fatigue design rules for small diameter 6082-T6 aluminium tubes that could be of use in the ground vehicle industry.

Effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue regime

Science.gov (United States)

Gu, Chao; Bao, Yan-ping; Gan, Peng; Wang, Min; He, Jin-shan

2018-06-01

This work aims to investigate the effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue (VHCF) regime. The size and type of inclusions in the steel were quantitatively analyzed, and VHCF tests were performed. Some fatigue cracks were found to be initiated in the gaps between inclusions (Al2O3, MgO-Al2O3) and the matrix, while other cracks originated from the interior of inclusions (TiN, MnS). To explain the related mechanism, the tessellated stresses between inclusions and the matrix were calculated and compared with the yield stress of the matrix. Results revealed that the inclusions could be classified into two types under VHCF; of these two, only one type could be regarded as holes. Findings in this research provide a better understanding of how inclusions affect the high cycle fatigue properties of bearing steel.

Influence of creep ductility on creep-fatigue behaviour of 20%Cr/25%Ni/Nb stainless steel

International Nuclear Information System (INIS)

Gladwin, D.; Miller, D.A.

1985-01-01

The influence of creep ductility on creep-fatigue endurance of 20%Cr/25%Ni/Nb stainless steel has been examined. In order to induce different creep ductilities in the 20/25/Nb stainless steel, three different thermo-mechanical routes were employed. These resulted in a range of ductilities (3-36%) being obtained at the strain rates of interest. Strain controlled slow-fast creep-fatigue cycles were used with strain rates of 10 -6 s -1 , 10 -7 s -1 in tension and 10 -3 s -1 in compression. It was found that creep ductility strongly influenced the creep-fatigue endurance of the 20/25/Nb stainless steel. When failure was creep dominated endurance was found to be directly proportional to the creep ductility. A ductility exhaustion model has been used to successfully predict creep-fatigue endurance when failure was creep dominated. (author)

Prediction of creep-fatigue life by use of creep rupture ductility

International Nuclear Information System (INIS)

Yamaguchi, Koji; Suzuki, Naoyuki; Ijima, Kiyoshi; Kanazawa, Kenji

1985-01-01

It was clarified that tension strain hold reduced creep-fatigue life of many engineering materials in different degrees depending on material, temperature and test duration. However the reduction in the life due to holding for various durations could be correlated to the fraction of intergranular facets on fracture surfaces which was considered to be an index of the damage introduced during strain hold. This fraction of intergranular facets by creep-fatigue failure exhibited a direct relation to the creep rupture ductility of the material tested at the same temperature and for the same creep-fatigue life-time. From these results an empirical equation has been derived as follow; (Δ sub(epsilonsub(i)))/Dsub(c).(N sub(h sup(α))) = C, where Δ sub(epsilonsub(i)) is inelastic strain range, Dsub(c) is the creep rupture ductility for the same duration as creep-fatigue life time, Nsub(h) is the creep-fatigue life under tension strain hold conditions, and α and C are constants depending on the material and testing temperature. From the equation the life prediction is possible for a given inelastic strain range Δ sub(epsilonsub(i)) if the constants α and C, and Dsub(c) are known. The value of α was found to be 0.62 and 0.74 for various austenitic stainless steels and NCF800 at 600 0 C and 700 0 C, respectively, and 0.69 for 1 1/4Cr-1/2Mo steel at 600 0 C. The value of C was found to be 0.50 and 0.59 for various austenitic stainless steels and NCF800 at 600 0 C and 700 0 C, respectively, and 0.49 for 1 1/4Cr-1/2Mo steel at 600 0 C. The creep rupture ductility Dsub(c) is available in the NRIM Creep Data Sheets up to 10 5 h for multi-heats of many kinds of heat resistant alloys. (author)

Multi-cracking in uniaxial and biaxial fatigue of 304L stainless steel

International Nuclear Information System (INIS)

Rupil, J.

2012-01-01

When a mechanical part is subjected to a repeated mechanical stress, it may be damaged after a number of cycles by several cracks initiation and propagation of a main crack. This is the phenomenon of fatigue damage. The thesis deals specifically with possible damage to some components of nuclear plants due to thermal fatigue. Unlike conventional mechanical fatigue damage where a main crack breaks the part, the thermal fatigue damage usually results in the appearance of a surface crack network. Two aspects are discussed in the thesis. The first is the experimental study of fatigue multiple cracking stage also called multi-cracking. Two mechanical test campaigns with multi-cracking detection by digital image correlation were conducted. These campaigns involve uniaxial and equi-biaxial mechanical loads in tension/compression without mean stress. This work allows to monitor and to observe the evolution of different networks of cracks through mechanical solicitations. The second is the numerical simulation of the phenomenon of fatigue damage. Several types of model are used (stochastic, probabilistic, cohesive finite elements). The experimental results have led to identify a multiple crack initiation law in fatigue which is faced with the numerical results. This comparison shows the relevance of the use of an analytical probabilistic model to find statistical results on the density of cracks that can be initiated with thermal and mechanical fatigue loadings. (author) [fr

Accelerated Threshold Fatigue Crack Growth Effect-Powder Metallurgy Aluminum Alloy

Science.gov (United States)

Piascik, R. S.; Newman, J. A.

2002-01-01

Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low (Delta) K, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = K(sub min)/K(sub max)). The near threshold accelerated FCG rates are exacerbated by increased levels of K(sub max) (K(sub max) = 0.4 K(sub IC)). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and K(sub max) influenced accelerated crack growth is time and temperature dependent.

The reduction in fatigue crack growth resistance of dentin with depth.

Science.gov (United States)

Ivancik, J; Neerchal, N K; Romberg, E; Arola, D

2011-08-01

The fatigue crack growth resistance of dentin was characterized as a function of depth from the dentino-enamel junction. Compact tension (CT) specimens were prepared from the crowns of third molars in the deep, middle, and peripheral dentin. The microstructure was quantified in terms of the average tubule dimensions and density. Fatigue cracks were grown in-plane with the tubules and characterized in terms of the initiation and growth responses. Deep dentin exhibited the lowest resistance to the initiation of fatigue crack growth, as indicated by the stress intensity threshold (ΔK(th) ≈ 0.8 MPa•m(0.5)) and the highest incremental fatigue crack growth rate (over 1000 times that in peripheral dentin). Cracks in deep dentin underwent incremental extension under cyclic stresses that were 40% lower than those required in peripheral dentin. The average fatigue crack growth rates increased significantly with tubule density, indicating the importance of microstructure on the potential for tooth fracture. Molars with deep restorations are more likely to suffer from the cracked-tooth syndrome, because of the lower fatigue crack growth resistance of deep dentin.

Crack initiation and growth in welded structures; Amorcage et propagation de la fissuration dans les jonctions soudees

Energy Technology Data Exchange (ETDEWEB)

Assire, A

2000-10-13

results. Concerning local approach, intergranular creep damage model of the Ecole des Mines de Paris is used for crack initiation and growth under creep and creep fatigue loading. Crack propagations are simulated with an adaptive re-meshing technique and are compared with experimental results for crack located in weld and base metal. A sensibility analysis shows that crack propagation strongly depend on the characteristic distance, which is needed to simulate crack growth with local approach, for the weld metal parameters. (author)

Thermographic Inspection of Fatigue Crack by Using Contact Thermal Resistance

Energy Technology Data Exchange (ETDEWEB)

Yang, Seung Yong; Kim, No Hyu [Korean University of Technology and Education, Cheonan (Korea, Republic of)

2013-04-15

Fatigue crack was detected from a temperature change around surface crack using the thermographic technique. Thermal gradient across the crack decreased very much due to thermal resistance of contact surface in the crack. Heat diffusion flow passing through the discontinuity was visualized in temperature by infrared camera to find and locate the crack. A fatigue crack specimen(SM-45C), which was prepared according to KS specification and notched in its center to initiate fatigue crack from the notch tip, was heated by halogen lamp at the end of one side to generate a heat diffusion flow in lateral direction. A abrupt jump in temperature across the fatigue crack was observed in thermographic image, by which the crack could be located and sized from temperature distribution.

Thermographic Inspection of Fatigue Crack by Using Contact Thermal Resistance

International Nuclear Information System (INIS)

Yang, Seung Yong; Kim, No Hyu

2013-01-01

Fatigue crack was detected from a temperature change around surface crack using the thermographic technique. Thermal gradient across the crack decreased very much due to thermal resistance of contact surface in the crack. Heat diffusion flow passing through the discontinuity was visualized in temperature by infrared camera to find and locate the crack. A fatigue crack specimen(SM-45C), which was prepared according to KS specification and notched in its center to initiate fatigue crack from the notch tip, was heated by halogen lamp at the end of one side to generate a heat diffusion flow in lateral direction. A abrupt jump in temperature across the fatigue crack was observed in thermographic image, by which the crack could be located and sized from temperature distribution.

Study on Characteristics of Corrosion Fatigue Crack Propagation for Austenitic Stainless Steel

International Nuclear Information System (INIS)

Lim, Uh Joh; Kim, Bu Ahn

1988-01-01

The characteristics of the corrosion fatigue cracking of both TIG weld heat affected zone and base metal for austenitic stainless steel were investigated under the environments of various specific resistance and the air. The corrosion fatigue crack initiation sensitivity was quantitatively investigated for SUS 304 weldments in the various specific resistances. Also, the characteristics of corrosion fatigue cracking for the weldments were investigated from mechanical, electrochemical, and microstructural point of view. Main results obtained are as follows: (1) The corrosion fatigue crack initiation sensitivity on the base metal and weld hea affected zone increases as the specific resistance of corrosion environment decreases, and the sensitivity of the weld heat affected zone appears increasing more than that of the base metal. (2) The corrosion potentials of various specific resistances are almost constant in initial corrosion fatigue cracking, but the corrosion potential becomes less noble promptly with the corrosion fatigue crack growth as the specific resistances decrease. (3) The corrosion fatigue crack growth of the weld heat affected zone rapid than that of the base metal, because of the softening and the less noble potential caused by welding heat cycle

Development of European creep crack growth testing code of practice for industrial specimens

Energy Technology Data Exchange (ETDEWEB)

Dogan, B.; Nikbin, K. [Imperial College, London (United Kingdom); Petrovski, B. [Technische Univ. Darmstadt (DE). Inst. fuer Werkstoffkunde (IFW)

2004-07-01

The integrity and residual life assessment of high temperature components require defects, detected or assumed to exist, through minimum allowable limits of detectable flaws using nondestructive testing methods. It relies on information obtained from the material's mechanical, uniaxial creep, creep crack initiation and growth properties. The information derived from experiments needs to be validated and harmonised following a Code of Practice that data variability between different institutions can be reduced to a minimum. The present paper reports on a Code of Practice (CoP) being prepared within the framework of the partially European Commission funded project CRETE. The novel aspect of the presented CoP is the inclusion of component relevant industrial specimen geometries. It covers testing and analysis of Creep Crack growth (CCG) in metallic materials at elevated temperature using six different cracked geometries that have been validated in. It aims to give advice on testing, measurements and analysis of creep crack growth data for a range of creep brittle to creep ductile materials using component service relevant specimen geometries and sizes. The CoP may be used for material selection criteria and inspection requirements for damage tolerant applications. In quantitative terms, these types of tests can be used to assess the individual and combined effects of metallurgical, fabrication, operating temperature, and loading conditions on creep crack growth life. Further issues will be addressed including material properties, damage and crack growth related constraint effect, stress relaxation and stress-strain fields, residual stresses, partitioning displacement, analysis of elasticcreep, elastic compliance measurements.

Detection and measurement of fatigue cracks in welded joints

International Nuclear Information System (INIS)

Smith, F.C.

1985-01-01

A direct current potential drop system was developed for the detection and measurement of very small fatigue cracks that grow from the toes of welds. Measurement of crack growth less than 0.01 mm and of crack growth rates less than 10 -10 m/cycle, even for cracks less than 1.0 mm deep, is made possible by using a high stability measurement apparatus and an adjustment based on initial conditions. Thus far, the measurement system has successfully examined several aspects of fatigue in welded elements. Crack growth results justified the use of a linear elastic expression for the stress intensity factor and provided an evaluation of a growth law which includes the threshold stress intensity factor. Needle peening fillet welded joints did not change the small proportion of crack initiation life to total fatigue life observed for untreated (not improved) welded joints. However, the measurement system demonstrated that needle peening retarded crack growth rates up to 1 mm depth below the weld toe

Surface profile evolution and fatigue crack initiation in Sanicro 25 steel at room temperature

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Petráš, Roman; Chai, G.; Škorík, Viktor

2016-01-01

Roč. 658, MAR (2016), s. 221-228 ISSN 0921-5093 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA MŠk(CZ) EE2.3.30.0063; GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : Sanicro 25 steel * Fatigue crack initiation * Persistent slip markings * Extrusions * Intrusions Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 3.094, year: 2016

Refined Analysis of Fatigue Crack Initiation Life of Beam-to-Column Welded Connections of Steel Frame under Strong Earthquake

Directory of Open Access Journals (Sweden)

Weilian Qu

2017-01-01

Full Text Available This paper presents a refined analysis for evaluating low-cycle fatigue crack initiation life of welded beam-to-column connections of steel frame structures under strong earthquake excitation. To consider different length scales between typical beam and column components as well as a few crucial beam-to-column welded connections, a multiscale finite element (FE model having three different length scales is formulated. The model can accurately analyze the inelastic seismic response of a steel frame and then obtain in detail elastoplastic stress and strain field near the welded zone of the connections. It is found that the welded zone is subjected to multiaxial nonproportional loading during strong ground motion and the elastoplastic stress-strain field of the welded zone is three-dimensional. Then, using the correlation of the Fatemi-Socie (FS parameter versus fatigue life obtained by the experimental crack initiation fatigue data of the structural steel weldment subjected to multiaxial loading, the refined evaluation approach of fatigue crack initiation life is developed based on the equivalent plastic strain at fatigue critical position of beam end seams of crucial welded connections when the steel frame is subjected to the strong earthquake excitation.

Creep fatigue design of FBR components

International Nuclear Information System (INIS)

Bhoje, S.B.; Chellapandi, P.

1997-01-01

This paper deals with the characteristic features of Fast Breeder Reactor (FBR) with reference to creep fatigue, current creep fatigue design approach in compliance with RCCMR (1987) design code, material data, effects of weldments and neutron irradiation, material constitutive models employed, structural analysis and further R and D required for achieving maturity in creep fatigue design of FBR components. For the analysis reported in this paper, material constitutive models developed based on ORNIb (Oak Ridge National Laboratory) and Chaboche viscoplastic theories are employed to demonstrate the potential of FBR components for higher plant temperatures and/or longer life. The results are presented for the studies carried out towards life prediction of Prototype Fast Breeder Reactor (PFBR) components. (author). 24 refs, 8 figs, 5 tabs

Life assessment of Mod.9Cr-1Mo steel. Quantitative evaluation of microstructural damage in creep interrupted specimens and in creep-fatigue specimens

International Nuclear Information System (INIS)

Maruyama, Kouichi; Kato, Syoichi; Nagae, Yuji

1999-02-01

Boiler and steam turbine components in power generating plants are used under creep and creep-fatigue conditions. It is important to measure both creep and creep-fatigue damage of the components in order to assess the residual life of the components. Modified 9Cr-1Mo steel, a candidate material for steam generator in FBR, has a tempered martensitic lath structure. It was proposed in the second report that lath width in the lath structure is closely related to creep strain, and using this relation one can assess residual creep life of a structural component made of the steel. The objectives of this study are to investigate the change of the lath structure during creep.fatigue deformation, and to estimate creep strain by measuring area of cell composing the lath structure. The area of cell can be a better measure of creep deformation than the lath width. The lath structure is covered during creep-fatigue deformation. The lath structure becomes equiaxed cell structure under creep-fatigue more quickly compared with the lath structure recovered during creep. The lath structure recovered under creep-fatigue has a stationary value of the lath width determined by maximum stress at Nf/2. (Nf: number of cycles) If the recovery process of the lath structure can be investigated under creep-fatigue, the lath width can be a measure of the life assessment under creep-fatigue. Area of cell composing the lath structure increases with creep deformation and reaches a stationary value S s determined by creep stress. The rate of increase in the area is faster at a higher stress and temperature. A normalized change in the area of cell, ΔS/ΔS s , was introduced as a measure of the recovery process of martensitic lath structure. ΔS is the change in area of cell from the initial value S 0 , ΔS s is the difference between S s and S 0 . ΔS/ΔS s is uniquely related to creep strain independent of creep conditions. However, the scatter of data in ΔS/ΔS s -strain relation is wider than

Creep fracture mechanics analysis for through-wall cracked pipes under widespread creep condition

International Nuclear Information System (INIS)

Huh, Nam Su; Kim, Yun Jae; Kim, Young Jin

2003-01-01

This paper compares engineering estimation schemes of C * and creep COD for circumferential and axial through-wall cracked pipes at elevated temperatures with detailed 3-D elastic-creep finite element results. Engineering estimation schemes included the GE/EPRI method, the reference stress method where reference stress is defined based on the plastic limit load and the enhanced reference stress method where the reference stress is defined based on the optimized reference load. Systematic investigations are made not only on the effect of creep-deformation behaviour on C * and creep COD, but also on effects of the crack location, the pipe geometry, the crack length and the loading mode. Comparison of the FE results with engineering estimations provides that for idealized power law creep, estimated C * and COD rate results from the GE/EPRI method agree best with FE results. For general creep-deformation laws where either primary or tertiary creep is important and thus the GE/EPRI method is hard to apply, on the other hand, the enhanced reference stress method provides more accurate and robust estimations for C * and COD rate than the reference stress method

In situ fatigue-crack-propagation experiment

International Nuclear Information System (INIS)

Ermi, A.M.; Chin, B.A.

1981-01-01

An in-reactor fatigue experiment was conducted in the Oak Ridge Research Reactor to determine the effects of dynamic irradiation on fatigue crack propagation. Eight 20% cold-worked 316 stainless steel specimens were precracked to various initial crack lengths, linked together to form a chain, and inserted into a specially designed in-reactor fatigue machine. Test conditions included a maximum temperature of 460 0 C, an environment of sodium, a frequency of 1 cycle/min, and a stress ratio of 0.10. Results indicated that (1) no effects of dynamic irradiation were observed for a fluence of 1.5 x 10 21 n/cm 2 (E > 0.1 MeV); and (2) crack growth rates in elevated temperature sodium were a factor of 3 to 4 lower than in room temperature air

A fracture- mechanics calculation of crack growth rate for a gas turbine blade

International Nuclear Information System (INIS)

Mirzaei, M.; Karimi, R.

2002-01-01

The existence of thermo-mechanical stresses, due to the frequent start-ups and shutdowns of gas turbines. Combined with high working temperatures may cause creep and fatigue failure of the blades. This paper describes a fracture-mechanics life assessment of a gas turbine blade. Initially, the distributions of thermal and mechanical stresses were obtained by using the finite element method. Accordingly; the crack modeling was performed in a high stress region at the suction side surface of the blade. Several crack growth increments were observed and the related crack tip parameters were calculated. Finally; the creep-fatigue crack growth in each cycle was calculated and the total number of start-stop cycles was determined

Interaction fatigue-creep-environment in an austenitic stainless steel Z2 CND 17-13 (Type 316 L) at 600 and 650 deg C. Microstructural evolution and damage

International Nuclear Information System (INIS)

Rezgui, B.

1982-12-01

The resistance of steel to continuous fatigue is directly related to its behaviour towards the surroundings (oxidation). This interaction considerably lowers resistance to crack initiation but has no effect on propagation, and rupture is transgranular. Conversely the influence of the environment is negligible under fatigue conditions with a hold time and rupture becomes intergranular whatever the surroudings. Cavities are created inside the material during the hold time and their interaction with each other and with cracks from the surface are the factors responsible for the degradation of fatigue properties. Transgranular rupture initiated in slip bands, which characterises damage by pure fatigue, is gradually replaced by intergranular rupture under fatigue with hold time. Meanwhile a new deformation mode appears: intergranular slip. The longer the hold time the stronger its effect, a tendency offset at high temperature. Hold time, temperature and deformation promote dynamic structural aging and restoration in the material. Since the mechanisms and kinetics of creep fatigue damage are different according to the deformation level and the hold time duration it would not be safe to extrapolate the results [fr

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.)

EPRI research program NDE techniques for crack initiation of steam turbine rotor

International Nuclear Information System (INIS)

Goto, T.; Kimura, J.; Kawamoto, K.; Kadoya, Y.; Viswanathan, R.

1990-01-01

EPRI RP 2481-8 aims at the development of nondestructive methods for the life assessment of steam turbine rotor for its crack initiation caused by creep and/or fatigue. As a part of the research project, the demonstration of the state of the art NDE techniques was conducted during June to August of 1988 at EPRI NDE Center, Charlotte, N.C. by Mitsubishi Heavy Industries, Ltd. using four rotors retired after long term service (16-22x10 4 hr). This paper introduces the results of the demonstration

Effects of Specimen Diameters on the Distribution of Corrosion Fatigue Cracks

OpenAIRE

石原, 外美; 塩澤, 和章; 宮尾, 嘉寿

1988-01-01

The distribution of corrosion fatigue cracks observed on the un-notched round specimen surface differs with specimen diameter, especially in the low stress amplitude region. At a constant fatigue life ratio, many long cracks are initiated on the larger specimen, 12 mm (diameter), in comparison with the smaller specimen, 6 mm (diameter). On the other hand, in the high stress amplitude region of corrosion fatigue and fatigue in laboratory air, the distribution of cracks during the fatigue proce...

Creep crack growth in a reactor pressure vessel steel at 360 deg C

Energy Technology Data Exchange (ETDEWEB)

Wu, Rui; Seitisleam, F; Sandstroem, R [Swedish Institute for Metals Research, Stockholm (Sweden)

1999-12-31

Plain creep (PC) and creep crack growth (CCG) tests at 360 deg C and post metallography were carried out on a low alloy reactor pressure vessel steel (ASTM A508 class 2) with different microstructures. Lives for the CCG tests were shorter than those for the PC tests and this is more pronounced for simulated heat affected zone microstructure than for the parent metal at longer lives. For the CCG tests, after initiation, the cracks grew constantly and intergranularly before they accelerated to approach rupture. The creep crack growth rate is well described by C*. The relations between reference stress, failure time and steady crack growth rate are presented for the CCG tests. It is demonstrated that the failure stress due to CCG is considerably lower than the yield stress at 360 deg C. Consequently, the CCG will control the static strength of a reactor vessel. (orig.) 17 refs.

Creep crack growth in a reactor pressure vessel steel at 360 deg C

Energy Technology Data Exchange (ETDEWEB)

Rui Wu; Seitisleam, F.; Sandstroem, R. [Swedish Institute for Metals Research, Stockholm (Sweden)

1998-12-31

Plain creep (PC) and creep crack growth (CCG) tests at 360 deg C and post metallography were carried out on a low alloy reactor pressure vessel steel (ASTM A508 class 2) with different microstructures. Lives for the CCG tests were shorter than those for the PC tests and this is more pronounced for simulated heat affected zone microstructure than for the parent metal at longer lives. For the CCG tests, after initiation, the cracks grew constantly and intergranularly before they accelerated to approach rupture. The creep crack growth rate is well described by C*. The relations between reference stress, failure time and steady crack growth rate are presented for the CCG tests. It is demonstrated that the failure stress due to CCG is considerably lower than the yield stress at 360 deg C. Consequently, the CCG will control the static strength of a reactor vessel. (orig.) 17 refs.

Tensile Creep and Fatigue of Sylramic-iBN Melt-Infiltrated SiC Matrix Composites: Retained Properties, Damage Development, and Failure Mechanisms

Science.gov (United States)

Morscher, Greg; Gowayed, yasser; Miller, Robert; Ojard, Greg; Ahmad, Jalees; Santhosh, Unni; John, Reji

2008-01-01

An understanding of the elevated temperature tensile creep, fatigue, rupture, and retained properties of ceramic matrix composites (CMC) envisioned for use in gas turbine engine applications are essential for component design and life-prediction. In order to quantify the effect of stress, time, temperature, and oxidation for a state-of-the-art composite system, a wide variety of tensile creep, dwell fatigue, and cyclic fatigue experiments were performed in air at 1204 C for the SiC/SiC CMC system consisting of Sylramic-iBN SiC fibers, BN fiber interphase coating, and slurry-cast melt-infiltrated (MI) SiC-based matrix. Tests were either taken to failure or interrupted. Interrupted tests were then mechanically tested at room temperature to determine the residual properties. The retained properties of most of the composites subjected to tensile creep or fatigue were usually within 20% of the as-produced strength and 10% of the as-produced elastic modulus. It was observed that during creep, residual stresses in the composite are altered to some extent which results in an increased compressive stress in the matrix upon cooling and a subsequent increased stress required to form matrix cracks. Microscopy of polished sections and the fracture surfaces of specimens which failed during stressed-oxidation or after the room-temperature retained property test was performed on some of the specimens in order to quantify the nature and extent of damage accumulation that occurred during the test. It was discovered that the distribution of stress-dependent matrix cracking at 1204 C was similar to the as-produced composites at room temperature; however, matrix crack growth occurred over time and typically did not appear to propagate through thickness except at final failure crack. Failure of the composites was due to either oxidation-induced unbridged crack growth, which dominated the higher stress regime (> 179 MPa) or controlled by degradation of the fibers, probably caused by

Oxide-assisted crack growth in hold-time low-cycle-fatigue of single-crystal superalloys

Directory of Open Access Journals (Sweden)

Suzuki Akane

2014-01-01

Full Text Available Compressive hold-time low-cycle fatigue is one of the important damage modes in Ni-based superalloy hot-gas path components. In strain controlled LCF, the compressive hold typically degrades fatigue life significantly due to creep relaxation and the resultant generation of tensile stress upon returning to zero strain. Crack initiation typically occurs on the surface, and therefore, the cracks are covered with layers of oxides. Recent finite element modeling based on experimental observations has indicated that the in-plane compressive stress in the alumina layer formed on the surface of the bond coat assists rumpling and, eventually, leads to initiation of cracks. The stress in the oxide layer continues to assist crack extension by pushing the alumina layer along the crack front during the compressive hold. In-situ measurements of the growth strains of alumina were performed using high energy synchrotron X-rays at Argonne National Lab. Specimens of single-crystal superalloys with and without aluminide coatings were statically pre-oxidized to form a layer of alumina at 1093 and 982 ∘C. For the in-situ synchrotron measurements, the specimens were heated up to the pre-oxidation temperatures with a heater. The alumina layers on both bare and coated specimens show compressive in-plane strains at both temperatures. The oxide strains on the superalloys showed dependency on temperature; on the other hand, the oxide strains in the aluminide coatings were insensitive to temperature. The magnitude of the compressive strains was larger on the superalloys than the ones on the aluminide coatings.

Influence of intermetallic particles on short fatigue crack initiation in AA2050-T8 and AA7050-T7451

Directory of Open Access Journals (Sweden)

Nizery Erembert

2014-06-01

Full Text Available Fatigue crack initiation at particles is studied in hot rolled 2050-T8 and 7050-T7451 material, using 1 to 4 mm cross section specimens. Both size and aspect ratio of particles are observed to affect their probability of being damaged. In 2050-T8 material, the probability that a matrix crack initiate at a cracked particle increases with its size, and no effect of aspect ratio is observed. In 2050-T8 specimens, matrix cracks initiate at both precracked (Al, Cu, Fe, Mn particles and particles cracked during cycling. Initiation in 7050-T74 specimens occur on Mg2Si particles which may be cracked or debonded, and Al7Cu2Fe particles that are cracked during cyclic loading.

The thermal fatigue behaviour of creep-resistant Ni-Cr cast steel

Directory of Open Access Journals (Sweden)

B. Piekarski

2007-12-01

Full Text Available The study gives a summary of the results of industrial and laboratory investigations regarding an assessment of the thermal fatigue behaviour of creep-resistant austenitic cast steel. The first part of the study was devoted to the problem of textural stresses forming in castings during service, indicating them as a cause of crack formation and propagation. Stresses are forming in carbides and in matrix surrounding these carbides due to considerable differences in the values of the coefficients of thermal expansion of these phases. The second part of the study shows the results of investigations carried out to assess the effect of carbon, chromium and nickel on crack resistance of austenitic cast steel. As a criterion of assessment the amount and propagation rate of cracks forming in the specimens as a result of rapid heating followed by cooling in running water was adopted. Tests were carried out on specimens made from 11 alloys. The chemical composition of these alloys was comprised in a range of the following values: (wt-%: 18-40 %Ni, 17-30 %Cr, 1.2-1.6%Si and 0.05-0.6 %C. The specimens were subjected to 75 cycles of heating to a temperature of 900oC followed by cooling in running water. After every 15 cycles the number of the cracks was counted and their length was measured. The results of the measurements were mathematically processed. It has been proved that the main factor responsible for an increase in the number of cracks is carbon content in the alloy. In general assessment of the results of investigations, the predominant role of carbon and of chromium in the next place in shaping the crack behaviour of creep-resistant austenitic cast steel should be stressed. Attention was also drawn to the effect of high-temperature corrosion as a factor definitely deteriorating the cast steel resistance to thermal fatigue.

Effect of sodium environment on the creep-rupture and low-cycle fatigue behavior of austenitic stainless steels

International Nuclear Information System (INIS)

Natesan, K.; Chopra, D.K.; Zeman, G.J.; Smith, D.L.; Kassner, T.F.

1977-01-01

Austenitic stainless steels used for in-core structural components, piping, valves, and the intermediate heat exchanger in Liquid-Metal Fast-Breeder Reactors (LMFBRs) are subjected to sodium at elevated temperatures and to complex stress conditions. As a result, the materials can undergo compositional and microstructural changes as well as mechanical deformation by creep and cyclic fatigue processes. In the present paper, information is presented on the creep-rupture and low-cycle fatigue behavior of Types 304 and 316 stainless steel in the solution-annealed condition and after long-term exposure to flowing sodium. The nonmetallic impurity-element concentrations in the sodium were controlled at levels similar to those in EBR-II primary sodium. Strain-time relationships developed from the experimental creep data were used to generate isochronous stress-creep strain curves as functions of sodium-exposure time and temperature. The low-cycle fatigue data were used to obtain relationships between plastic strain range and cycles-to-failure based on the Coffin-Manson formalism and a damage-rate approach developed at ANL. An analysis of the cyclic stress-strain behavior of the materials showed that the strain-hardening rates for the sodium-exposed steels were larger than those for the annealed material. However, the sodium-exposed specimens showed significant softening, as evidenced by the lower stress at half the fatigue life. Microstructural information obtained from the different specimens suggests that crack initiation is more difficult in the long-term sodium-exposed specimens when compared with the solution-annealed material. Based on the expected carbon concentrations in LMFBR primary system sodium, moderate carburization of the austenitic stainless steels will not degrade the mechanical properties to a significant extent, and therefore, will not limit the performance of out-of-core components. (author)

Strain localization and fatigue crack initiation in ultrafine-grained copper in high- and giga-cycle region

Czech Academy of Sciences Publication Activity Database

Kunz, Ludvík; Lukáš, Petr; Navrátilová, L.

2014-01-01

Roč. 58, JAN (2014), s. 202-208 ISSN 0142-1123 R&D Projects: GA ČR GAP108/10/2001; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : Fatigue crack initiation * Strain localization * Stability of ultrafine-grained structure * UFG Cu Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.275, year: 2014

Fatigue crack growth in EUROFER 97 at different temperatures. Final report, tasks: TW1-TTMS-002, D22 and TW2-TTMS-002a, D22

International Nuclear Information System (INIS)

Aktaa, J.; Lerch, M.

2005-05-01

For the assessment of cracks in First Wall structures built from EUROFER 97 of future fusion reactors the fatigue crack behaviour in EUROFER 97 was investigated at room temperature (RT), 300, 500 and 550 C. For this purpose fatigue crack growth tests were performed using CT specimens with two R-ratios, R=0.1 and R=0.5, respectively. Hence, fatigue crack threshold, fatigue crack growth behaviour in the near-threshold range and their dependences on temperature and R-ratio were determined and described using an analytical formula. The fatigue crack threshold showed a monotonic dependence on temperature which is for insignificantly small. The fatigue crack growth behaviour exhibited for a nonmonotonic dependence on temperature which is explained by the decrease of yield stress and the increase of creep damage when increasing the temperature [de

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.

Accelerated Near-Threshold Fatigue Crack Growth Behavior of an Aluminum Powder Metallurgy Alloy

Science.gov (United States)

Piascik, Robert S.; Newman, John A.

2002-01-01

Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low DK, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = Kmin/Kmax). The near threshold accelerated FCG rates are exacerbated by increased levels of Kmax (Kmax less than 0.4 KIC). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and Kmax influenced accelerated crack growth is time and temperature dependent.

Crack initiation through vibration fatigue of small-diameter pipes

International Nuclear Information System (INIS)

Comby, R.; Thebault, Y.; Papaconstantinou, T.

2002-01-01

Socket welds are used extensively for small bore piping connections in nuclear power plant systems. Numerous fatigue-related failures occurred in the past ten years mainly on safeguard systems and continue to occur frequently, showing that corrective actions did not take into account all aspects of the problem. Destructive examination of cracked small bore piping connections allowed a better understanding of failure mechanisms and a prediction of crack initiation site depending on nozzle fittings such as run pipe and small bore pipe thickness. A three-dimensional finite element model confirmed the conclusions of the lab examinations. For thick run pipes, it was shown that the failure tend to initiate predominantly at the socket weld toe or at the root, depending on the respective thickness of coupling and small bore pipe. Some additional studies, based on RSE-M code, are in progress in order to determine the maximum stresses location. Lessons learned through these investigations led to optimise the in-service inspection scope and to define solutions to be carried out to prevent failure of ''susceptible'' small bore pipe connections. Since July 2000, a large program is in progress to select all ''susceptible'' small bore pipes in safety-related systems and to apply corrective measures such as piping modifications or system operational modifications. (authors)

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

International Nuclear Information System (INIS)

Schwalbe, K.H.

2002-01-01

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

Creep-fatigue rules in the RCC-MR code

International Nuclear Information System (INIS)

Drubay, B.

1988-01-01

In 1978, CEA, Electricite de France (EDF) and NOVATOME decided to draw up a complete set of design and construction rules for LMFBR components. This RCC-MR code issued in June 1985 and completed in November 1987 was chosen as a sound basis for the next European Fast Reactor (EFR). The purpose of this paper is to describe the present RCC-MR creep-fatigue design rules to be applied with elastic analysis including the modifications adopted in the first addenda. This method is based on a separate evaluation of a fatigue usage fraction V and creep rupture usage fraction W with the common linear summation rule. The fatigue usage fraction is obtained from continuous fatigue curves (without hold times) and from total strain ranges (elastic + plastic + creep). The creep rupture usage fraction W is obtained from stress to rupture curves and a stress σk evaluating the stress generated during the cycle. (author)

A study on metallic creep-fatigue interaction at elevated temperatures

International Nuclear Information System (INIS)

Ohnami, Masateru; Sakane, Masao

1978-01-01

In order to investigate the difference between the hold-time effect in push-pull low-cycle fatigue and that in torsional one, both types of strain controlled fatigue tests of SUS 316 stainless steel were performed at 600 0 C with or without hold-time. Significant difference between the push-pull and torsional fatigue test data on the basis of equivalent total strain range of Mises' type was not observed in terms of number of cycles to failure, number of cycles to crack initiation and crack propagation rate. More precisely speaking, however, the push-pull test had a larger hold-time effect on the failure life and on the crack behaviors than the torsional test in lower strain range. That is, slower crack propagation rate was observed in the push-pull test without hold-time than in torsional one, but crack propagation was observed in the push-pull test with hold-time. This crack behavior was discussed from the influence of stress triaxiality near the crack tip on the crack propagation rate and also from the effect of hydrostatic stress. (author)

Fatigue crack initiation in nickel-based superalloys studied by microstructure-based FE modeling and scanning electron microscopy

Directory of Open Access Journals (Sweden)

Fried M.

2014-01-01

Full Text Available In this work stage I crack initiation in polycrystalline nickel-based superalloys is investigated by analyzing anisotropic mechanical properties, local stress concentrations and plastic deformation on the microstructural length scale. The grain structure in the gauge section of fatigue specimens was characterized by EBSD. Based on the measured data, a microstructure-based FE model could be established to simulate the strain and stress distribution in the specimens during the first loading cycle of a fatigue test. The results were in fairly good agreement with experimentally measured local strains. Furthermore, the onset of plastic deformation was predicted by identifying shear stress maxima in the microstructure, presumably leading to activation of slip systems. Measurement of plastic deformation and observation of slip traces in the respective regions of the microstructure confirmed the predicted slip activity. The close relation between micro-plasticity, formation of slip traces and stage I crack initiation was demonstrated by SEM surface analyses of fatigued specimens and an in-situ fatigue test in a large chamber SEM.

Nondestructive evaluation of creep-fatigue damage: an interim report

International Nuclear Information System (INIS)

Nickell, R.E.

1977-02-01

In view of the uncertainties involved in designing against creep-fatigue failure and the consequences of such failures in Class 1 nuclear components that operate at elevated temperature, the possibility of intermittent or even continuous non-destructive examination of these components has been considered. In this interim report some preliminary results on magnetic force and ultrasonic evaluation of creep-fatigue damage in an LMFBR steam generator material are presented. These results indicate that the non-destructive evaluation of pure creep damage will be extremely difficult. A set of biaxial creep-fatigue tests that are designed to discriminate between various failure theories is also described

Description of the initiation and progress of cracks for hot cracks in temperature resistant 1% CrMoV castings under creep or fatigue stress

International Nuclear Information System (INIS)

Bareiss, J.; Maile, K.; Berger, C.; Mayer, K.H.; Weiss, M.

1994-01-01

The results available so far have shown that under vibration stress at room temperature and at 530 C, the simplified equations of fracture mechanics are sufficient (in spite of the complicated fault geometries), in order to conservatively describe the behaviour of fault positions (open or partly-healed hot cracks) with regard to their crack initiation behaviour if combined with the findings US test technique. Here the sample castings which in the initial state showed fault indications of US type EET near the surface, tend to earlier initiation of a crack compared to lower fault positions of the samples. Internal fault positions (partially healed hot cracks) often only showed local cracks (trans-crystalline deformation cracks) within the fault area with an order of magnitude of about 10-50 μm, in spite of exceeding the threshold value Δ Ko. The comparison of the crack propagation behaviour of the sample castings, determined via the potential sensor method on medium lengths of fault with the results of crack growth of fracture mechanics samples in the da/dN- Δ K diagram showed for the evaluated sample castings with a relatively great initial depth or length of fault that the upper scatter band limit of the Paris Law determined for the material can be used to estimate the fault position behaviour. (orig./RHM) [de

Creep-fatigue life prediction method using Diercks equation for Cr-Mo steel

International Nuclear Information System (INIS)

Sonoya, Keiji; Nonaka, Isamu; Kitagawa, Masaki

1990-01-01

For dealing with the situation that creep-fatigue life properties of materials do not exist, a development of the simple method to predict creep-fatigue life properties is necessary. A method to predict the creep-fatigue life properties of Cr-Mo steels is proposed on the basis of D. Diercks equation which correlates the creep-fatigue lifes of SUS 304 steels under various temperatures, strain ranges, strain rates and hold times. The accuracy of the proposed method was compared with that of the existing methods. The following results were obtained. (1) Fatigue strength and creep rupture strength of Cr-Mo steel are different from those of SUS 304 steel. Therefore in order to apply Diercks equation to creep-fatigue prediction for Cr-Mo steel, the difference of fatigue strength was found to be corrected by fatigue life ratio of both steels and the difference of creep rupture strength was found to be corrected by the equivalent temperature corresponding to equal strength of both steels. (2) Creep-fatigue life can be predicted by the modified Diercks equation within a factor of 2 which is nearly as precise as the accuracy of strain range partitioning method. Required test and analysis procedure of this method are not so complicated as strain range partitioning method. (author)

Modelling probabilistic fatigue crack propagation rates for a mild structural steel

OpenAIRE

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

2014-01-01

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

Elastic creep-fatigue evaluation for ASME code

International Nuclear Information System (INIS)

Severud, L.K.; Winkel, B.V.

1987-01-01

Experience with applying the ASME Code Case N-47 rules for evaluation of creep-fatigue with elastic analysis results has been problematic. The new elastic evaluation methods are intended to bound the stress level and strain range values needed for use in employing the code inelastic analysis creep-fatigue damage counting procedures. To account for elastic followup effects, ad hoc rules for stress classification, shakedown, and ratcheting are employed. Because elastic followup, inelastic strain concentration, and stress-time effects are accounted for, the design fatigue curves in Case N-47 for inelastic analysis are used instead of the more conservative elastic analysis curves. Creep damage assessments are made using an envelope stress-time history that treats multiple load events and repeated cycles during elevated temperature service life. (orig./GL)

Creep-Fatigue Relationsihps in Electroactive Polymer Systems and Predicted Effects in an Actuator Design

Science.gov (United States)

Vinogradov, Aleksandra M.; Ihlefeld, Curtis M.; Henslee, Issac

2009-01-01

The paper concerns the time-dependent behavior of electroactive polymers (EAP) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride (PVDF) is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of electroactive polymers is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under oyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the NASA Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.

ESTIMATION MODEL OF RESIDUAL LIFE-TIME OF LOCOMOTIVE FRAME BOGIE WITH ALLOWANCE FOR CREEP

Directory of Open Access Journals (Sweden)

V. R. Skalskyi

2014-12-01

Full Text Available Purpose. The problem of determining the residual life of frame bogie elements of locomotives is a great importance for predicting their work safely and avoidance potential failures on the track. This especially concern cases when such elements have creep-fatigue cracks which grow under action of cyclic loading with excerpts T1 in the cycle and reach their critical size. Here the question of the propagation of such defects (cracks arises, their kinetics and about the period of subcritical cracks growth. The aim is to develop a calculation model for determination the period of subcritical creep-fatigue cracks growth in the bogies frames of electric locomotive. The model takes into account the basic parameters of load, geometry of the construction element and cracks. Methodology. The calculation model for determination the period of subcritical creep-fatigue cracks growth in structural elements of frame under conditions of variable load time has been formulated. It is based on the first law of thermodynamics concerning to mechanics of solids slow fracture at low temperature creep and variable loadings. It is assumed that the period of unsteady creep dominates here (the first section of the creep curve. Low-temperature creep is creep of materials at temperatures T0 < 0,5Tmp, where Tmp − the melting point of the material. Findings. The analytical formula for the determination of the stress intensity factor of truck bolster with technological hole has been obtained. It is shown that by experimentally established constants of the material using the proposed analytical relations can easily determine residual resource of the bogie frame elements. Originality. The new mathematical model for describing the kinetics of creep-fatigue cracks growth in the frames bogies of electric locomotive under variable in time loadings with various time excerpts and on this base the period determination of subcritical crack growth has been proposed. Practical value

Modelling probabilistic fatigue crack propagation rates for a mild structural steel

Directory of Open Access Journals (Sweden)

J.A.F.O. Correia

2015-01-01

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

Fatigue and creep-fatigue in sodium of 316 L stainless-steel

International Nuclear Information System (INIS)

Ardellier, A.

1981-03-01

The present paper describes test-facility developed to perform low-cycle fatigue and creep-fatigue interaction in sodium on stainless steel - 316 L . Fatigue life in sodium and in air are compared. A beneficial effect in sodium is noted

OBSERVATION OF FATIGUE CRACK PATHS IN NODULAR CAST IRON AND ADI MICROSTRUCTURES

Directory of Open Access Journals (Sweden)

Lukáš Bubenko

2009-07-01

Full Text Available When speaking about quality of construction materials, fatigue crack propagation resistance is one of the most important considered properties. That is essentially influenced by character of matrix. Here presented contribution deals with the fatigue crack propagation mode through the matrix of as-cast nodular cast iron (NCI and austempered ductile iron (ADI, whereas influence of microstructure has been considered and discussed. Experimental materials used in presented contribution were pearlitc-ferritic NCI and heat treated ADI 800. Pearlitic-ferritic NCI was used as the base for ADI production. Experiments were performed on mini round compact tension (RCT specimens using an Amsler vibrophore. Fatigue crack paths in both materials were investigated and compared. Light microscopy was used to analyze the microstructure, crack initiation and propagation within broken specimens. In both tested materials fatigue cracks always initiated at graphite-matrix interface, while graphite nodules remained generally unbroken, eventually only surface of nodules was damaged. Though, comparing two materials with different microstructures, the diversity of fatigue crack propagation modes at high deltaK and low deltaK was observed.

Small fatigue cracks; Proceedings of the Second International Conference/Workshop, Santa Barbara, CA, Jan. 5-10, 1986

Energy Technology Data Exchange (ETDEWEB)

Ritchie, R.O.; Lankford, J.

1986-01-01

Topics discussed in this volume include crack initiation and stage I growth, microstructure effects, crack closure, environment effects, the role of notches, analytical modeling, fracture mechanics characterization, experimental techniques, and engineering applications. Papers are presented on fatigue crack initiation along slip bands, the effect of microplastic surface deformation on the growth of small cracks, short fatigue crack behavior in relation to three-dimensional aspects and the crack closure effect, the influence of crack depth on crack electrochemistry and fatigue crack growth, and nondamaging notches in fatigue. Consideration is also given to models of small fatigue cracks, short crack theory, assessment of the growth of small flaws from residual strength data, the relevance of short crack behavior to the integrity of major rotating aero engine components, and the relevance of short fatigue crack growth data to the durability and damage tolerance analyses of aircraft.

Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions

Science.gov (United States)

Fujiyama, Kazunari; Kimachi, Hirohisa; Tsuboi, Toshiki; Hagiwara, Hiroyuki; Ogino, Shotaro; Mizutani, Yoshiki

EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values KAMave and GOSave were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As KAM values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters MεKAMnet and MεδKAMave were introduced as the sum of product of the noise subtracted KAMnet and the absolute change from initial value δKAMave with dislocation movement distance divided by pixel size. MεδKAMave parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

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

International Nuclear Information System (INIS)

Portch, D.J.

1979-09-01

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

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

3-D analysis of fatigue crack behaviour in a shot peened steam turbine blade material

Energy Technology Data Exchange (ETDEWEB)

He, B.Y., E-mail: Binyan.he@soton.ac.uk [Engineering Materials, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Katsamenis, O.L. [muVIS X-ray Imaging Centre, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Mellor, B.G.; Reed, P.A.S. [Engineering Materials, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2015-08-26

Serial mechanical sectioning and high resolution X-ray tomography have been used to study the three-dimensional morphology of small fatigue cracks growing in a 12 Cr tempered martensitic steam turbine blade material. A range of surface conditions has been studied, namely polished and shot peened (with varying levels of intensity). In the polished (unpeened) condition, inclusions (alumina and manganese sulphide) played an important role in initiating and controlling early fatigue crack behaviour. When fatigue cracks initiated from an alumina stringer, the crack morphology was normally dominated by single stringers, which were always in the centre of the fatigue crack, indicating its primary role in initiation. Manganese sulphide inclusion groups however seemed to dominate and affect the crack path along both the surface and depth crack growth directions. The more intensely shot peened condition did not however evidence inclusion or stringer affected fatigue crack initiation or growth behaviour; sub-surface crack coalescence being clearly observed by both serial sectioning and computed tomography (CT) imaging techniques at a depth of about 150–180 μm. These sub-surface crack coalescences can be linked to both the extent of the compressive residual stress as well as the depth of the plastic deformation arising from the intense shot peening process. Shot peening appears to provide a different defect population that initiates fatigue cracks and competes with the underlying metallurgical defect populations. The most beneficial shot peening process would in this case appear to “deactivate” the original metallurgical defect population and substitute a known defect distribution from the shot peening process from which fatigue cracks grow rather slowly in the strain hardened surface layer which also contains compressive residual stresses. A benefit to fatigue life in bending, even under Low Cycle Fatigue (LCF) conditions, has been observed in these tests if a

Influences of cyclic deformation on creep property and creep-fatigue life prediction considering them

International Nuclear Information System (INIS)

Takahashi, Yukio

2009-01-01

Evaluation of creep-fatigue is essential in design and life management of high-temperature components in power generation plants. Cyclic deformation may alter creep property of the materials and its consideration may improve predictability of creep-fatigue failure life. To understand them, creep tests were conducted for the materials subjected to cyclic loading and their creep rupture and deformation behaviors were compared with those of as-received materials. Both 316FR and modified 9Cr-1Mo steel were tested. (1) Creep rupture time and elongation generally tend to decrease with cyclic loading in both materials, and especially elongation of 316FR drastically decreases by being cyclically deformed. (2) Amount of primary creep deformation decreases by cyclic loading and the ways to improve its predictability were developed. (3) Use of creep rupture ductility after cyclic deformation, instead of that of as-received material, brought about clear improvement of life prediction in a modified ductility exhaustion approach. (author)

Evaluation of creep-fatigue life prediction methods for low-carbon/nitrogen-added SUS316

International Nuclear Information System (INIS)

Takahashi, Yukio

1998-01-01

Low-carbon/medium nitrogen 316 stainless steel called 316FR is a principal candidate for the high-temperature structural materials of a demonstration fast reactor plant. Because creep-fatigue damage is a dominant failure mechanism of the high-temperature materials subjected to thermal cycles, it is important to establish a reliable creep-fatigue life prediction method for this steel. Long-term creep tests and strain-controlled creep-fatigue tests have been conducted at various conditions for two different heats of the steel. In the constant load creep tests, both materials showed similar creep rupture strength but different ductility. The material with lower ductility exhibited shorter life under creep-fatigue loading conditions and correlation of creep-fatigue life with rupture ductility, rather than rupture strength, was made clear. Two kinds of creep-fatigue life prediction methods, i.e. time fraction rule and ductility exhaustion method were applied to predict the creep-fatigue life. Accurate description of stress relaxation behavior was achieved by an addition of 'viscous' strain to conventional creep strain and only the latter of which was assumed to contribute to creep damage in the application of ductility exhaustion method. The current version of the ductility exhaustion method was found to have very good accuracy in creep-fatigue life prediction, while the time fraction rule overpredicted creep-fatigue life as large as a factor of 30. To make a reliable estimation of the creep damage in actual components, use of ductility exhaustion method is strongly recommended. (author)

Evaluation of Creep-Fatigue Damage in 304 Stainless Steel using Ultrasonic Non-Destructive Test

Energy Technology Data Exchange (ETDEWEB)

Lee, Sung Sik [Safetech Co. Ltd., Kimhae (Korea, Republic of); Oh, Yong Jun [Hanbat National Univ., Daejon (Korea, Republic of); Nam, Soo Woo [KISTI ReSEAT Program, Seoul (Korea, Republic of)

2011-12-15

It is well known that grain boundary cavitation is the main failure mechanism in austenitic stainless steel under tensile hold creep-fatigue interaction conditions. The cavities are nucleated at the grain boundary during cyclic loading and grow to become grain boundary cracks. The attenuation of ultrasound depends on scattering and absorption in polycrystalline materials. Scattering occurs when a propagation wave encounters microstructural discontinuities, such as internal voids or cavities. Since the density of the creepfatigue cavities increases with the fatigue cycles, the attenuation of ultrasound will also be increased with the fatigue cycles and this attenuation can be detected nondestructively. In this study, it is found that individual grain boundary cavities are formed and grow up to about 100 cycles and then, these cavities coalesce to become cracks. The measured ultrasonic attenuation increased with the cycles up to cycle 100, where it reached a maximum value and then decreased with further cycles. These experimental measurements strongly indicate that the open pores of cavities contribute to the attenuation of ultrasonic waves. However, when the cavities develop, at the grain boundary cracks whose crack surfaces are in contact with each other, there is no longer any open space and the ultrasonic wave may propagate across the cracks. Therefore, the attenuation of ultrasonic waves will be decreased. This phenomenon of maximum attenuation is very important to judge the stage of grain boundary crack development, which is the indication of the dangerous stage of the structures.

Influence of the crystalline orientations on microcrack initiation in low-cycle fatigue

Energy Technology Data Exchange (ETDEWEB)

Mu, P. [Univ Lille Nord de France, F-59000 Lille (France); ECLille, LML, F-59650 Villeneuve d’Ascq (France); CNRS, UMR 8107, UMR 8579 (France); Aubin, V., E-mail: veronique.aubin@ecp.fr [ECP, MSSMat, F-92295 Châtenay-Malabry (France); CNRS, UMR 8107, UMR 8579 (France); Alvarez-Armas, I.; Armas, A. [IFIR, CONICET, Universidad Nacional de Rosario (Argentina)

2013-06-20

Present study aims at analyzing the crack initiation in an austenitic stainless steel in low-cycle fatigue. A fatigue test was carried out using a polished specimen. The surface of the specimen was observed in situ during the fatigue test, in order to establish the time of slip activity or crack initiation. After a number of cycles sufficient to initiate small cracks, the test was stopped and the surface observed by scanning electron microscopy. The electron backscattered diffraction technique (EBSD) was used to identify the orientations of surface grains in the central zone of the fatigue specimen. Crack-initiation sites and slip systems associated to the initiated microcracks were identified. The criterion of the maximum Schmid factor explains two-thirds of the cracks initiated in slip systems; however if the favorably oriented slip band with respect to this criterion makes an angle of around 45° to the loading direction, a crack may initiate in another slip system.

Study on creep-fatigue life of irradiated austenitic stainless steel

International Nuclear Information System (INIS)

Ioka, Ikuo; Miwa, Yukio; Tsuji, Hirokazu; Yonekawa, Minoru; Takada, Fumiki; Hoshiya, Taiji

2001-01-01

The low cycle creep-fatigue test with tensile strain hold of the austenitic stainless steel irradiated to 2 dpa was carried out at 823K in vacuum. The applicability of creep-fatigue life prediction methods to the irradiated specimen was examined. The fatigue life on the irradiated specimen without tensile strain hold time was reduced by a factor of 2-5 in comparison with the unirradiated specimen. The decline in fatigue life of the irradiated specimen with tensile strain hold was almost equal to that of the unirradiated specimen. The creep damage of both unirradiated and irradiated specimens was underestimated by the time fraction rule or the ductility exhaustion rule. The creep damage calculated by the time fraction rule or the ductility exhaustion rule increased by the irradiation. The predictions derived from the linear damage rule are unsafe as compared with the experimental fatigue lives. (author)

Novel experiments to characterise creep-fatigue degradation in VHTR alloys

International Nuclear Information System (INIS)

Simpson, J.A.; Wright, J.K.; Wright, R.N.

2015-01-01

It is well known in energy systems that the creep lifetime of high temperature alloys is significantly degraded when a cyclic load is superimposed on components operating in the creep regime. A test method has been developed in an attempt to characterise creep-fatigue behaviour of alloys at high temperature. The test imposes a hold time during the tensile phase of a fully reversed strain-controlled low cycle fatigue test. Stress relaxation occurs during the strain-controlled hold period. This type of fatigue stress relaxation test tends to emphasise the fatigue portion of the total damage and does not necessarily represent the behaviour of a component in-service well. Several different approaches to laboratory testing of creep-fatigue at 950 deg. C have been investigated for Alloy 617, the primary candidate for application in VHTR heat exchangers. The potential for mode switching in a cyclic test from strain control to load control, to allow specimen extension by creep, has been investigated to further emphasise the creep damage. In addition, tests with a lower strain rate during loading have been conducted to examine the influence of creep damage occurring during loading. Very short constant strain hold time tests have also been conducted to examine the influence of the rapid stress relaxation that occurs at the beginning of strain holds. (authors)

Biaxial fatigue crack propagation behavior of perfluorosulfonic-acid membranes

Science.gov (United States)

Lin, Qiang; Shi, Shouwen; Wang, Lei; Chen, Xu; Chen, Gang

2018-04-01

Perfluorosulfonic-acid membranes have long been used as the typical electrolyte for polymer-electrolyte fuel cells, which not only transport proton and water but also serve as barriers to prevent reactants mixing. However, too often the structural integrity of perfluorosulfonic-acid membranes is impaired by membrane thinning or cracks/pinholes formation induced by mechanical and chemical degradations. Despite the increasing number of studies that report crack formation, such as crack size and shape, the underlying mechanism and driving forces have not been well explored. In this paper, the fatigue crack propagation behaviors of Nafion membranes subjected to biaxial loading conditions have been investigated. In particular, the fatigue crack growth rates of flat cracks in responses to different loading conditions are compared, and the impact of transverse stress on fatigue crack growth rate is clarified. In addition, the crack paths for slant cracks under both uniaxial and biaxial loading conditions are discussed, which are similar in geometry to those found after accelerated stress testing of fuel cells. The directions of initial crack propagation are calculated theoretically and compared with experimental observations, which are in good agreement. The findings reported here lays the foundation for understanding of mechanical failure of membranes.

Influence of Prior Fatigue Cycling on Creep Behavior of Reduced Activation Ferritic-Martensitic Steel

Science.gov (United States)

Sarkar, Aritra; Vijayanand, V. D.; Parameswaran, P.; Shankar, Vani; Sandhya, R.; Laha, K.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

2014-06-01

Creep tests were carried out at 823 K (550 °C) and 210 MPa on Reduced Activation Ferritic-Martensitic (RAFM) steel which was subjected to different extents of prior fatigue exposure at 823 K at a strain amplitude of ±0.6 pct to assess the effect of prior fatigue exposure on creep behavior. Extensive cyclic softening that characterized the fatigue damage was found to be immensely deleterious for creep strength of the tempered martensitic steel. Creep rupture life was reduced to 60 pct of that of the virgin steel when the steel was exposed to as low as 1 pct of fatigue life. However, creep life saturated after fatigue exposure of 40 pct. Increase in minimum creep rate and decrease in creep rupture ductility with a saturating trend were observed with prior fatigue exposures. To substantiate these findings, detailed transmission electron microscopy studies were carried out on the steel. With fatigue exposures, extensive recovery of martensitic-lath structure was distinctly observed which supported the cyclic softening behavior that was introduced due to prior fatigue. Consequently, prior fatigue exposures were considered responsible for decrease in creep ductility and associated reduction in the creep rupture strength.

Influence of Initial Inclined Surface Crack on Estimated Residual Fatigue Lifetime of Railway Axle

Czech Academy of Sciences Publication Activity Database

Náhlík, Luboš; Pokorný, Pavel; Ševčík, Martin; Hutař, Pavel

2016-01-01

Roč. 7, č. 4 (2016), č. článku 1640007. ISSN 1756-9737. [FDM 2016 - International Conference on Fracture and Damage Mechanics /15./. Alicante, 14.09.2016-16.09.2016] R&D Projects: GA MŠk LM2015069; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : inclined crack * railway axle * residual fatigue lifetime * fatigue crack propagation Subject RIV: JL - Materials Fatigue, Friction Mechanics

Study on creep-fatigue life improvement and life evaluation of 316FR stainless steels

International Nuclear Information System (INIS)

Kobayashi, Kazuo; Yamaguchi, Koji; Yamazaki, Masayoshi; Hongo, Hiromichi; Nakazawa, Takanori; Date, Shingo; Tendo, Masayuki

2000-01-01

Creep rupture and creep-fatigue interaction tests were conducted at 550deg C for modified 316FR austenitic stainless steels in order to improve the creep-fatigue lives. Reducing the carbon contents from 0.01% to 0.002 or 0.003% and finning the grain size were effective for increasing the creep-fatigue lives and the creep rupture ductilities. From these results, an estimation method of the creep-fatigue lives by using the creep rupture ductilities in the modified 316FR steels was proposed. (author)

Crack growth in an austenitic stainless steel at high temperature

International Nuclear Information System (INIS)

Polvora, J.P.

1998-01-01

This study deals with crack propagation at 650 deg C on an austenitic stainless steel referenced by Z2 CND 17-12 (316L(NN)). It is based on an experimental work concerning two different cracked specimens: CT specimens tested at 650 deg C in fatigue, creep and creep-fatigue with load controlled conditions (27 tests), tube specimens containing an internal circumferential crack tested in four points bending with displacement controlled conditions (10 tests). Using the fracture mechanics tools (K, J and C* parameters), the purpose here is to construct a methodology of calculation in order to predict the evolution of a crack with time for each loading condition using a fracture mechanics global approach. For both specimen types, crack growth is monitored by using a specific potential drop technique. In continuous fatigue, a material Paris law at 650 deg C is used to correlate crack growth rate with the stress intensity factor range corrected with a factor U(R) in order to take into account the effects of crack closure and loading ratio R. In pure creep on CT specimens, crack growth rate is correlated to the evolution of the C* parameter (evaluated experimentally) which can be estimated numerically with FEM calculations and analytically by using a simplified method based on a reference stress approach. A modeling of creep fatigue growth rate is obtained from a simple summation of the fatigue contribution and the creep contribution to the total crack growth. Good results are obtained when C* parameter is evaluated from the simplified expression C* s . Concerning the tube specimens tested in 4 point bending conditions, a simulation based on the actual A 16 French guide procedure proposed at CEA. (authors)

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

International Nuclear Information System (INIS)

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

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

Effect of Notches on Creep-Fatigue Behavior of a P/M Nickel-Based Superalloy

Science.gov (United States)

Telesman, Jack; Gabb, Timothy P.; Ghosn, Louis J.; Gayda, John, Jr.

2015-01-01

A study was performed to determine and model the effect of high temperature dwells on notched low cycle fatigue (NLCF) and notch stress rupture behavior of a fine grain LSHR powder metallurgy (PM) nickel-based superalloy. It was shown that a 90 second dwell applied at the minimum stress (min dwell) was considerably more detrimental to the NLCF lives than similar dwell applied at the maximum stress (max dwell). The short min dwell NLCF lives were shown to be caused by growth of small oxide blisters which caused preferential cracking when coupled with high concentrated notch root stresses. The cyclic max dwell notch tests failed mostly by a creep accumulation, not by fatigue, with the crack origin shifting internally to a substantial distance away from the notch root. The classical von Mises plastic flow model was unable to match the experimental results while the hydrostatic stress profile generated using the Drucker-Prager plasticity flow model was consistent with the experimental findings. The max dwell NLCF and notch stress rupture tests exhibited substantial creep notch strengthening. The triaxial Bridgman effective stress parameter was able to account for the notch strengthening by collapsing the notched and uniform gage geometry test data into a singular grouping.

A method of creep damage summation based on accumulated strain for the assessment of creep-fatigue endurance

International Nuclear Information System (INIS)

Hales, R.

1983-01-01

A method of combining long term creep data with relatively short term mechanical behaviour to provide an estimate of creep-fatigue endurance is presented. It is proposed that the creep-fatigue effect in high temperature cyclic deformation is governed by a difference in strain rate around the cycle and the associated variation in ductility with strain rate. (author)

Fatigue crack growth studies on a tee junction using ultrasonic non-destructive methods

International Nuclear Information System (INIS)

Subramanian, C.V.; Thavasimuthu, M.; Ramesh, A.S.; Jayakumar, T.; Kalyanasundaram, P.; Baldev Raj

1996-01-01

Fatigue cracks need to be detected and sized to maintain structural integrity. The significance of cracks detected in service must also be assessed. This paper describes the on-line ultrasonic testing carried out on a Tee joint subjected to fatigue loading. The initiation and growth of the cracks were monitored for every 5,000 cycles up to 40,000 cycles. The study demonstrated the use of ultrasonic testing for fatigue crack growth detection and sizing. (author)

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

High temperature initiation and propagation of cracks in 12%Cr-steel turbine disks

Directory of Open Access Journals (Sweden)

S. Foletti

2013-10-01

Full Text Available This work aims to study the crack propagation in 12%Cr steel for turbine disks. Creep Crack Growth (CCG tests on CT specimens have been performed to define the proper fracture mechanics which describes the initiation of the crack propagation and the crack growth behaviour for the material at high temperature. Results have been used to study the occurrence of crack initiation on a turbine disk at the extreme working temperature and stress level experienced during service, and validate the use of C* integral in correlating creep growth rate on the disk component, in case C* is numerically calculated through FEM analysis or calculated by the use of reference stress concept.

A study on the evolution of crack networks under thermal fatigue loading

International Nuclear Information System (INIS)

Kamaya, Masayuki; Taheri, Said

2008-01-01

The crack network is a typical cracking morphology caused by thermal fatigue loading. It was pointed out that the crack network appeared under relatively small temperature fluctuations and did not grow deeply. In this study, the mechanism of evolution of crack network and its influence on crack growth was examined by numerical calculation. First, the stress field near two interacting cracks was investigated. It was shown that there are stress-concentration and stress-shielding zones around interacting cracks, and that cracks can form a network under the bi-axial stress condition. Secondly, a Monte Carlo simulation was developed in order to simulate the initiation and growth of cracks under thermal fatigue loading and the evolution of the crack network. The local stress field formed by pre-existing cracks was evaluated by the body force method and its role in the initiation and growth of cracks was considered. The simulation could simulate the evolution of the crack network and change in number of cracks observed in the experiments. It was revealed that reduction in the stress intensity factor due to stress feature in the depth direction under high cycle thermal fatigue loading plays an important role in the evolution of the crack network and that mechanical interaction between cracks in the network affects initiation rather than growth of cracks. The crack network appears only when the crack growth in the depth direction is interrupted. It was concluded that the emergence of the crack network is preferable for the structural integrity of cracked components

Report on FY15 Alloy 617 SMT Creep-Fatigue Test Results

Energy Technology Data Exchange (ETDEWEB)

Wang, Yanli [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Jetter, Robert I. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Baird, Seth T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pu, Chao [Univ. of Tennessee, Knoxville, TN (United States); Sham, Sam [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2015-06-22

viability of the Alloy 617 Code Case, the use of the current elastic analysis based rules in Subsection NH for the evaluation of strain limits (a precursor for the creep-fatigue rules) and the creep-fatigue rules themselves have been deemed inappropriate for Alloy 617 at temperatures above 650C (Corum and Brass, 1991). The rationale for this exclusion is that at higher temperatures it is not feasible to decouple plasticity and creep, which is the basis for the current simplified rules. This temperature, 650C, is well below the temperature range of interest for this material for the High Temperature Gas Cooled Reactor (HTGR) as well as the VHTR. The only current alternative is, thus, a full inelastic analysis which requires sophisticated material models which have not yet been formulated and verified. To address the prohibition on the use of current methods at very high temperatures, proposed Code rules have been developed which are based on the use of elastic-perfectly plastic (E-PP) analysis methods and which are expected to be applicable to very high temperatures. To provide data to implement the proposed rules and to verify their application, a series of tests have been initiated. One test concept, the Simplified Model Test (SMT), takes into account the stress and strain redistribution in real structures by including representative follow-up characteristics in the test specimen. The correlation parameter between test and design is the elastically calculated strain, and the dependent test variable is the observed cycles to failure. Although the initial priority for the SMT approach is to generate data to support validation of the E-PP Code Case for evaluation of creep-fatigue damage, the broader goal of the SMT approach is to develop a methodology for evaluation of creep fatigue damage which is simpler to implement than the current complex rules and applicable to the full temperature range from ambient conditions to the very high temperature creep regime of 900-950C. Also

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.

Fractal and probability analysis of creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses

Energy Technology Data Exchange (ETDEWEB)

Xu, Mengjia; Xu, Jijin, E-mail: xujijin_1979@sjtu.edu.cn; Lu, Hao; Chen, Jieshi; Chen, Junmei; Wei, Xiao

2015-12-30

Graphical abstract: - Highlights: • Statistical and fractal analysis is applied to study the creep fracture surface. • The tensile residual stresses promote the initiation of creep crack. • The fractal dimension of a mixed mode fracture surface shows a wavy variation. • The fractal dimension increases with increasing intergranular fracture percentage. • Height coordinates of intergranular fracture surface fit Gaussian distribution. - Abstract: In order to clarify creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses, creep crack tests were carried out on the tension creep specimens, in which the residual stresses were generated by local remelting and cooling. Residual stresses in the specimens were measured using Synchrotron X-ray diffraction techniques. The fracture surface of the creep specimen was analyzed using statistical methods and fractal analysis. The relation between fractal dimension of the fracture surface and fracture mode of the creep specimen was discussed. Due to different fracture mechanisms, the probability density functions of the height coordinates vary with the intergranular crack percentage. Good fitting was found between Gaussian distribution and the probability function of height coordinates of the high percentage intergranular crack surface.

Fractal and probability analysis of creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses

International Nuclear Information System (INIS)

Xu, Mengjia; Xu, Jijin; Lu, Hao; Chen, Jieshi; Chen, Junmei; Wei, Xiao

2015-01-01

Graphical abstract: - Highlights: • Statistical and fractal analysis is applied to study the creep fracture surface. • The tensile residual stresses promote the initiation of creep crack. • The fractal dimension of a mixed mode fracture surface shows a wavy variation. • The fractal dimension increases with increasing intergranular fracture percentage. • Height coordinates of intergranular fracture surface fit Gaussian distribution. - Abstract: In order to clarify creep crack growth behavior in 2.25Cr–1.6W steel incorporating residual stresses, creep crack tests were carried out on the tension creep specimens, in which the residual stresses were generated by local remelting and cooling. Residual stresses in the specimens were measured using Synchrotron X-ray diffraction techniques. The fracture surface of the creep specimen was analyzed using statistical methods and fractal analysis. The relation between fractal dimension of the fracture surface and fracture mode of the creep specimen was discussed. Due to different fracture mechanisms, the probability density functions of the height coordinates vary with the intergranular crack percentage. Good fitting was found between Gaussian distribution and the probability function of height coordinates of the high percentage intergranular crack surface.

Microstructural effects on the creep and crack propagation behaviors of γ-Ti aluminide alloy

International Nuclear Information System (INIS)

Lupinc, V.; Onofrio, G.; Nazmy, M.; Staubli, M.

1999-01-01

Gamma titanium aluminides class of materials possess several unique physical and mechanical properties. These characteristics can be attractive for specific industrial applications. By applying different heat treatment schedules one can change the microstructural features of this class of materials. In the present investigation, two heat treatment schedules were used to produce two different microstructures, duplex (D) and nearly lamellar (NL) in the cast and HIP'ed Ti-47Al-2W-0.5Si alloy. The tensile strength and creep behavior, in the 700--850 C temperature range, of this alloy have been determined and correlated to the corresponding microstructures. In addition, the fatigue crack propagation behavior in this alloy has been studied at different temperatures. The results on the creep behavior showed that the alloy with nearly lamellar microstructure has a strongly improved creep strength as compared with that of the duplex microstructure

The prediction of creep damage in Type 347 weld metal: part II creep fatigue tests

International Nuclear Information System (INIS)

Spindler, M.W.

2005-01-01

Calculations of creep damage under conditions of strain control are often carried out using either a time fraction approach or a ductility exhaustion approach. In part I of this paper the rupture strength and creep ductility data for a Type 347 weld metal were fitted to provide the material properties that are used to calculate creep damage. Part II of this paper examines whether the time fraction approach or the ductility exhaustion approach gives the better predictions of creep damage in creep-fatigue tests on the same Type 347 weld metal. In addition, a new creep damage model, which was developed by removing some of the simplifying assumptions that are made in the ductility exhaustion approach, was used. This new creep damage model is a function of the strain rate, stress and temperature and was derived from creep and constant strain rate test data using a reverse modelling technique (see part I of this paper). It is shown that the new creep damage model gives better predictions of creep damage in the creep-fatigue tests than the time fraction and the ductility exhaustion approaches

Damage assessment of low-cycle fatigue by crack growth prediction. Development of growth prediction model and its application

International Nuclear Information System (INIS)

Kamaya, Masayuki; Kawakubo, Masahiro

2012-01-01

In this study, the fatigue damage was assumed to be equivalent to the crack initiation and its growth, and fatigue life was assessed by predicting the crack growth. First, a low-cycle fatigue test was conducted in air at room temperature under constant cyclic strain range of 1.2%. The crack initiation and change in crack size during the test were examined by replica investigation. It was found that a crack of 41.2 μm length was initiated almost at the beginning of the test. The identified crack growth rate was shown to correlate well with the strain intensity factor, whose physical meaning was discussed in this study. The fatigue life prediction model (equation) under constant strain range was derived by integrating the crack growth equation defined using the strain intensity factor, and the predicted fatigue lives were almost identical to those obtained by low-cycle fatigue tests. The change in crack depth predicted by the equation also agreed well with the experimental results. Based on the crack growth prediction model, it was shown that the crack size would be less than 0.1 mm even when the estimated fatigue damage exceeded the critical value of the design fatigue curve, in which a twenty-fold safety margin was used for the assessment. It was revealed that the effect of component size and surface roughness, which have been investigated empirically by fatigue tests, could be reasonably explained by considering the crack initiation and growth. Furthermore, the environmental effect on the fatigue life was shown to be brought about by the acceleration of crack growth. (author)

Evaluation of Fatigue Crack Initiation for Volumetric Flaw in Pressure Tube

International Nuclear Information System (INIS)

Choi, Sung Nam; Yoo, Hyun Joo

2005-01-01

CAN/CSA.N285.4-94 requires the periodic inservice inspection and surveillance of pressure tubes in operating CANDU nuclear power reactors. If the inspection results reveal a flaw exceeding the acceptance criteria of the Code, the flaw must be evaluated to determine if the pressure is acceptable for continued service. Currently, the flaw evaluation methodology and acceptance criteria specified in CSA-N285.05-2005, 'Technical requirements for in-service evaluation of zirconium alloy pressure tubes in CANDU reactors'. The Code is applicable to zirconium alloy pressure tubes. The evaluation methodology for a crack-like flaw is similar to that of ASME B and PV Sec. XI, 'Inservice Inspection of Nuclear Power Plant Components'. However, the evaluation methodology for a blunt volumetric flaw is described in CSA-N285.05-2005 code. The object of this paper is to address the fatigue crack initiation evaluation for the blunt volumetric flaw as it applies to the pressure tube at Wolsong NPP

Structural integrity and fatigue crack propagation life assessment of welded and weld-repaired structures

Science.gov (United States)

Alam, Mohammad Shah

2005-11-01

Structural integrity is the science and technology of the margin between safety and disaster. Proper evaluation of the structural integrity and fatigue life of any structure (aircraft, ship, railways, bridges, gas and oil transmission pipelines, etc.) is important to ensure the public safety, environmental protection, and economical consideration. Catastrophic failure of any structure can be avoided if structural integrity is assessed and necessary precaution is taken appropriately. Structural integrity includes tasks in many areas, such as structural analysis, failure analysis, nondestructive testing, corrosion, fatigue and creep analysis, metallurgy and materials, fracture mechanics, fatigue life assessment, welding metallurgy, development of repairing technologies, structural monitoring and instrumentation etc. In this research fatigue life assessment of welded and weld-repaired joints is studied both in numerically and experimentally. A new approach for the simulation of fatigue crack growth in two elastic materials has been developed and specifically, the concept has been applied to butt-welded joint in a straight plate and in tubular joints. In the proposed method, the formation of new surface is represented by an interface element based on the interface potential energy. This method overcomes the limitation of crack growth at an artificial rate of one element length per cycle. In this method the crack propagates only when the applied load reaches the critical bonding strength. The predicted results compares well with experimental results. The Gas Metal Arc welding processes has been simulated to predict post-weld distortion, residual stresses and development of restraining forces in a butt-welded joint. The effect of welding defects and bi-axial interaction of a circular porosity and a solidification crack on fatigue crack propagation life of butt-welded joints has also been investigated. After a weld has been repaired, the specimen was tested in a universal

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

International Nuclear Information System (INIS)

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

1989-01-01

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

Fatigue crack layer propagation in silicon-iron

Science.gov (United States)

Birol, Y.; Welsch, G.; Chudnovsky, A.

1986-01-01

Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

Analysis of Fatigue Crack Growth in Ship Structural Details

Directory of Open Access Journals (Sweden)

Leheta Heba W.

2016-04-01

Full Text Available Fatigue failure avoidance is a goal that can be achieved only if the fatigue design is an integral part of the original design program. The purpose of fatigue design is to ensure that the structure has adequate fatigue life. Calculated fatigue life can form the basis for meaningful and efficient inspection programs during fabrication and throughout the life of the ship. The main objective of this paper is to develop an add-on program for the analysis of fatigue crack growth in ship structural details. The developed program will be an add-on script in a pre-existing package. A crack propagation in a tanker side connection is analyzed by using the developed program based on linear elastic fracture mechanics (LEFM and finite element method (FEM. The basic idea of the developed application is that a finite element model of this side connection will be first analyzed by using ABAQUS and from the results of this analysis the location of the highest stresses will be revealed. At this location, an initial crack will be introduced to the finite element model and from the results of the new crack model the direction of the crack propagation and the values of the stress intensity factors, will be known. By using the calculated direction of propagation a new segment will be added to the crack and then the model is analyzed again. The last step will be repeated until the calculated stress intensity factors reach the critical value.

Crack initiation and propagation in welded joints of turbine and boiler steels during low cycle fatigue

International Nuclear Information System (INIS)

Lindblom, J.; Sandstroem, R.; Linde, L.; Henderson, P.

1990-01-01

Low cycle fatigue (LCF) tests have been performed at 300 and 565 degrees C on welded joints and on microstructures to be found in or near welded joints in a low alloy ferritic steel 0.5 Cr, 0.5 Mo, 0.25 V. The difference in lifetimes between the 300 degrees C and 565 degrees C tests was small comparing the same microstructures and strain ranges, although the stress amplitude was greater at 300 degrees C. Under constant stress conditions the fatigue life depended on the fatigue life of the parent metal but under constant strain conditions the lifetime was governed by that of the bainitic structures. Strain controlled LCF tests have been performed at 750 degrees C on welded joints in the austenitic steel AISI 316 and on different parent and weld metals used in these joints. In continuously cycled samples all cracks were transgranular and initiated at the surface; hold-time samples displayed internally initiated intergranular cracking in the weld metal. Under constant strain conditions the 316 parent and weld metals exhibited similar lifetimes. When considering a constant stress situation the strength of the microsturctures decreased in the following order: Sanicro weld metal, cold deformed parent metal, undeformed parent metal and weld metal (K.A.E.)

Quantitative Acoustic Emission Fatigue Crack Characterization in Structural Steel and Weld

Directory of Open Access Journals (Sweden)

Adutwum Marfo

2013-01-01

Full Text Available The fatigue crack growth characteristics of structural steel and weld connections are analyzed using quantitative acoustic emission (AE technique. This was experimentally investigated by three-point bending testing of specimens under low cycle constant amplitude loading using the wavelet packet analysis. The crack growth sequence, that is, initiation, crack propagation, and fracture, is extracted from their corresponding frequency feature bands, respectively. The results obtained proved to be superior to qualitative AE analysis and the traditional linear elastic fracture mechanics for fatigue crack characterization in structural steel and welds.

Creep and Creep Crack Growth Behaviors for SMAW Weldments of Gr. 91 Steel

International Nuclear Information System (INIS)

Kim, Woo Gon; Yin, Song Nan; Park, Ji Yeon; Hong, Sung Deok; Kim, Yong Wan; Park, Jae Young

2010-01-01

High Cr ferritic resistance steels with tempered martensite microstructures posses enhanced creep strength at the elevated temperatures. Those steels as represented by a modified 9Cr-1Mo steel (ASME Grade 91, hereafter Gr.91) are regarded as main structural materials of sodium-cooled fast reactors (SFR) and reactor pressure vessel materials of very high temperature reactors (VHTR). The SFR and VHTR systems are designed during long-term duration reaching 60 years at elevated temperatures and often subjected to non-uniform stress and temperature distribution during service. These conditions may generate localized creep damage and propagate the cracks and ultimately may cause a fracture. A significant portion of its life is spent in crack propagation. Therefore, a creep crack growth rate (CCGR) due to creep damage should be assessed for both the base metal (BM) and welded metal (WM). Enough CCGR data for them should be provided for assessing their structural integrities. However, their CCGR data for the Gr. 91 steels is still insufficient. In this study, the CCGR for the BM and the WM of the Gr. 91 steel was comparatively investigated. A series of the CCG tests were conducted under different applied loads for the BM and the WM at 600 .deg. C. The CCGR was characterized in terms of the C parameter, and their CCG behavior were compared, respectively

Fatigue-creep life prediction for a notched specimen of 2[1]/[4]Cr-1Mo steel at 600 C

International Nuclear Information System (INIS)

Inoue, Tatsuo; Sakane, Masao; Fukuda, Yoshio; Igari, Toshihide; Miyahara, Mitsuo; Okazaki, Masakazu

1994-01-01

This paper presents the life prediction of 2[1]/[4]Cr-1Mo notched specimens subjected to fast-fast, slow-slow and hold-time loadings at 600 C. The crack initiation lives of notched specimens were estimated based on the local stress-strain calculated by inelastic finite element analyses. For the life prediction, combinations of seven different constitutive models and five fatigue-creep damage laws were used. The applicability of the constitutive model and damage law is discussed. The constitutive models predict similar stress-strain relations at the notch root, leading to similar predicted lives. The damage model, however, has a much larger influence on the life prediction. ((orig.))

Creep-fatigue-environment interaction of 9Cr-1Mo-V-Nb steel

International Nuclear Information System (INIS)

Shibata, Hiroyuki; Ishikawa, Akiyoshi; Asada, Yasuhide

1996-01-01

An extension of the creep-fatigue damage model has been conducted in the present study. The original damage model has been developed to the predict the creep-fatigue life of 9Cr-1Mo-V-Nb steel (Modified 9Cr-1Mo steel) in a very high vacuum environment. The present study is to extend an applicability of the model to the creep-fatigue damage accumulation in the air environment. (orig.)

Elastic creep-fatigue evaluation for ASME [American Society of Mechanical Engineers] code

International Nuclear Information System (INIS)

Severud, L.K.; Winkel, B.V.

1987-02-01

Reassessment of past ASME N-47 creep-fatigue rules have been under way by committee members. The new proposed elastic creep-fatigue methods are easier to apply than those previously in the code case. They also provide a wider range of practical application while still providing conservative assessments. It is expected that new N-47 code rules for elastic creep-fatigue evaluation will be adopted in the near future

Subsurface crack initiation and propagation mechanisms in gigacycle fatigue

International Nuclear Information System (INIS)

Huang Zhiyong; Wagner, Daniele; Bathias, Claude; Paris, Paul C.

2010-01-01

In the very high cycle regime (N f > 10 7 cycles) cracks can nucleate on inclusions, 'supergrains' and pores, which leads to fish-eye propagation around the defect. The initiation from an inclusion or other defect is almost equal to the total crack growth lifetime, perhaps much more than 99% of this lifetime in many cases. Integration of the Paris law allows one to predict the number of cycles to crack initiation. A cyclic plastic zone around the crack exists, and recording the surface temperature of the sample during the test may allow one to follow crack propagation and determine the number of cycles to crack initiation. A thermo-mechanical model has been developed. In this study several fish-eyes from various materials have been observed by scanning electron microscopy, and the fractographic results analyzed as they related to the mechanical and thermo-mechanical models.

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)

Short fatigue cracks nucleation and growth in lean duplex stainless steel LDX 2101

Energy Technology Data Exchange (ETDEWEB)

Strubbia, R., E-mail: strubbia@ifir-conicet.gov.ar [Instituto de Física Rosario – CONICET, Universidad Nacional de Rosario (Argentina); Hereñú, S.; Alvarez-Armas, I. [Instituto de Física Rosario – CONICET, Universidad Nacional de Rosario (Argentina); Krupp, U. [Faculty of Engineering and Computer Science, University of Applied Sciences Osnabrück (Germany)

2014-10-06

This work is focused on the fatigue damage of lean duplex stainless steels (LDSSs) LDX 2101. Special interest is placed on analyzing short fatigue crack behavior. In this sense, short crack initiation and growth during low cycle fatigue (LCF) and short crack nucleation during high cycle fatigue (HCF) of this LDSS have been studied. The active slip systems and their associated Schmid factors (SF) are determined using electron backscattered diffraction (EBSD). Additionally, the dislocation structure developed during cycling is observed by transmission electron microscopy (TEM). Regardless of the fatigue regime, LCF and HCF, short cracks nucleate along intrusion/extrusions in ferritic grains. Moreover, during the LCF phase boundaries decelerate short crack propagation. These results are rationalized by the hardness of the constitutive phases and the dependence of screw dislocation mobility in the ferrite phase on strain rate and stress amplitude.

An evaluation on fatigue crack growth in a fine-grained isotropic graphite

International Nuclear Information System (INIS)

Wang Hongtao; Sun Libin; Li Chenfeng; Shi Li; Wang Haitao

2012-01-01

Highlights: ► The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. ► The curves of the fatigue crack growth rate versus the SIF range show three stages. ► The fatigue microcrack propagation is very sensitive to graphite's microstructures. ► Graphite's microstructures have no significant impact on fatigue macrocrack growth. ► The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45°, showing the main cause of the fatigue fracture is the shear stress. There are also a large amount of secondary cracks inside unit cells and on cell walls

Muscle Activity Adaptations to Spinal Tissue Creep in the Presence of Muscle Fatigue

Science.gov (United States)

Nougarou, François

2016-01-01

Aim The aim of this study was to identify adaptations in muscle activity distribution to spinal tissue creep in presence of muscle fatigue. Methods Twenty-three healthy participants performed a fatigue task before and after 30 minutes of passive spinal tissue deformation in flexion. Right and left erector spinae activity was recorded using large-arrays surface electromyography (EMG). To characterize muscle activity distribution, dispersion was used. During the fatigue task, EMG amplitude root mean square (RMS), median frequency and dispersion in x- and y-axis were compared before and after spinal creep. Results Important fatigue-related changes in EMG median frequency were observed during muscle fatigue. Median frequency values showed a significant main creep effect, with lower median frequency values on the left side under the creep condition (p≤0.0001). A significant main creep effect on RMS values was also observed as RMS values were higher after creep deformation on the right side (p = 0.014); a similar tendency, although not significant, was observed on the left side (p = 0.06). A significant creep effects for x-axis dispersion values was observed, with higher dispersion values following the deformation protocol on the left side (p≤0.001). Regarding y-axis dispersion values, a significant creep x fatigue interaction effect was observed on the left side (p = 0.016); a similar tendency, although not significant, was observed on the right side (p = 0.08). Conclusion Combined muscle fatigue and creep deformation of spinal tissues led to changes in muscle activity amplitude, frequency domain and distribution. PMID:26866911

Fatigue and creep-fatigue strength of 304 steel under biaxial strain conditions

International Nuclear Information System (INIS)

Asayama, Tai; Aoto, Kazumi; Wada, Yusaku

1990-01-01

A series of fatigue and creep-fatigue tests were conducted with 304 stainless steel at 550degC under a variety of biaxial strain conditions. Fatigue life under nonproportional loading conditions showed a significant life reduction compared with that of proportional loading, and this life reduction was reasonably estimated by taking into account the strain paths along which the strain history is imposed. Furthermore, a marked life reduction was shown to occur under nonproportional loading by imposing a strain hold period at a peak tensile strain. This life reduction was evaluated by the linear damage rule. It was shown to be possible to estimate the fatigue damage and the creep damage under nonproportional loading by a linear damage rule by estimating a stress relaxation behavior by Mises-type equivalent stress or Huddleston-type equivalent stress. (author)

Shear-mode Crack Initiation Behavior in the Martensitic and Bainitic Microstructures

Directory of Open Access Journals (Sweden)

Wada Kentaro

2018-01-01

Full Text Available Fully reversed torsional fatigue tests were conducted to elucidate the behaviour of shear-mode crack initiation and propagation in one martensitic and two bainitic steels. The relationship between the crack initiation site and microstructure was investigated by means of an electron backscatter diffraction (EBSD technique. From the S-N diagram, two notable results were obtained: (i the shear-mode crack was initiated on the prior austenitic grain boundary in martensitic steel, while in bainitic steels, the crack was initiated along the {110} plane; one of the slip planes of bcc metals, and (ii the torsional fatigue limit of lower bainitic steel with finer grains was 60 MPa higher than that of upper bainitic steel with coarser grains even though the hardnesses were nearly equivalent. The mechanism determining the torsional fatigue strength in these steels is discussed from the viewpoint of microstructure morphology.

New specimen design for studying the growth of small fatigue cracks with surface acoustic waves

Science.gov (United States)

London, Blair

1985-08-01

The study of small surface fatigue cracks in AISI 4140 quenched and tempered steel by a nondestructive surface acoustic wave technique is summarized. A novel cantilevered bending, plate-type fatigue specimen is described that is compatible with the acoustic method. Small cracks are initiated from a 25-μm deep surface pit produced by an electrospark machine. The importance of studying these cracks which closely approximate naturally occurring fatigue cracks is briefly discussed.

Fatigue crack behaviour in mine excavator

Energy Technology Data Exchange (ETDEWEB)

Yin, Y.; Grondin, G.Y.; Elwi, A.E. [Alberta Univ., Edmonton, AB (Canada). Dept. of Civil and Environmental Engineering

2006-05-15

Fatigue cracking in excavation equipment represents a significant operating cost for oil sands operators. It is caused by high impact loads, the high frequency of load cycles, and large component sizes found in oil sands processing facilities. Monitoring and repair strategies for fatigue cracks are typically based on vendor specifications and the experience of maintenance personnel. This paper provided details of an optimized crack management program applied to a BE 395B shovel boom. The proposed crack management tool uses a chart to predict the remaining life of a corner crack in the shovel boom. Predictions are based on limited field measurements of operating loads as well as on data obtained from fatigue testing of boom material, and a finite element analysis of the shovel boom. Field and laboratory data are used along with fracture mechanics and finite element modelling to predict crack life. It was concluded that the tool will allow inspectors and planners to schedule repairs based on safe service life. The tool is applicable for any components subjected to fatigue loading. 3 refs., 21 tabs., 64 figs.

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)

Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

Energy Technology Data Exchange (ETDEWEB)

Carroll, L. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Carroll, M. [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2015-05-01

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatigue for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.

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.

The effect of creep-fatigue damage relationships upon HTGR heat exchanger design

International Nuclear Information System (INIS)

Kozina, M.M.; King, J.H.; Basol, M.

1984-01-01

Materials for heat exchangers in the high temperature gas-cooled reactor (HTGR) are subjected to cyclic loading, extending the necessity to design against fatigue failure into the temperature region where creep processes become significant. Therefore, the fatigue life must be considered in terms of creep-fatigue interaction. In addition, since HTGR heat exchangers are subjected to holds at constant strain levels or constant stress levels in high-temperature environments, the cyclic life is substantially reduced. Of major concern in the design and analysis of HTGR heat exchangers is the accounting for the interaction of creep and fatigue. The accounting is done in conformance to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Code Case N-47, which allows the use of the linear damage criterion for interaction of creep and fatigue. This method separates the damage incurred in the material into two parts: one due to fatigue and one due to creep. The summation of the creep-fatigue damage must be less than 1.0. Recent material test data have indicated that the assumption of creep and fatigue damage equals unity at failure may not always be valid for materials like Alloy 800H, which is used in the higher temperature sections of HTGR steam generators. Therefore, a more conservative creep-fatigue damage relationship was postulated for Alloy 800H. This more conservative bilinear damage relationship consists of a design locus drawn from D F =1.0, D C =0 to D F =0.1, D C =0.1 to D F =0, D C =1.0. D F is the fatigue damage and D C is the creep damage. A more conservative damage relationship for 2-1/4 Cr-1 Mo material consisted of including factors that degrade the fatigue curves. These revised relationships were used in a structural evaluation of the HTGR steam cycle/cogeneration (SC/C) steam generator design. The HTGR-SC/C steam generator, a once-through type, is comprised of an economizer-evaporator-superheater (ESS) helical bundle of 2-1/4 Cr-1

Developing works to detect fatigue cracks (small sodium leak detector and acoustic emission

International Nuclear Information System (INIS)

Kikuchi, M.; Sakakibara, Y.; Nagata, T.

1980-01-01

Continuous monitoring of fatigue cracks was performed (using both sodium leak detector and AE measuring system) through the creep-fatigue test of 304 stainless steel long elbow as part of the test series to establish the structural reliability of the Prototype FBR primary heat transport piping system. The sodium leak detector was a system composed mainly of SID (Sodium Ionization Detector) and DPD (Deferential Pressure Detector), that was developed by HITACHI Ltd. under a contract with PNC. The AE system was Synthetic AE Measuring and Analyzing system that was developed at FBR Safety Section to measure and analyze AE at various piping component tests. The test was continued until a sodium leakage was detected by the contact-type sodium leak detector attached to the test assembly, after about 4 weeks operation under cyclic loading at 600 deg. C. The following conclusions were obtained: (1) The sodium leak detector, both SID and DPD, indicated sodium leakage clearly, some hours before the contact-type detector did, even under an environment of air that contains ordinary humidity (Leaked sodium was estimated to be less than 15 grams after completion of the test); (2) The AE method indicated location and seriousness of the fatigue cracks, apparently before the crack penetration occurred. (author)

IFMIF - Design Study for in Situ Creep Fatigue Tests

International Nuclear Information System (INIS)

Gordeev, S.; Heinzel, V.; Simakov, St.; Stratmanns, E.; Vladimirov, P.; Moeslang, A.

2006-01-01

While the high flux volume (20-50 dpa/fpy) of the International Fusion Materials Irradiation Facility (IFMIF) is dedicated to the irradiation of ∼ 1100 qualified specimens that will be post irradiation examined after disassembling in dedicated Hot Cells, various in situ experiments are foreseen in the medium flux volume (1-20 dpa/fpy). Of specific importance for structural lifetime assessments of fusion power reactors are instrumented in situ creep-fatigue experiments, as they can simulate realistically a superposition of thermal fatigue or creep fatigue and irradiation with fusion relevant neutrons. Based on former experience with in situ fatigue tests under high energy light ion irradiation, a design study has been performed to evaluate the feasibility of in situ creep fatigue tests in the IFMIF medium flux position. The vertically arranged test module for such experiments consists basically of a frame similar to a universal testing machine, but equipped with three pulling rods, driven by independent step motors, instrumentation systems and specimen cooling systems. Therefore, three creep fatigue specimens may be tested at one time in this apparatus. Each specimen is a hollow tube with coolant flow in the specimen interior to maintain individual specimen temperatures. The recently established IFMIF global 3D geometry model was used together the latest McDeLicious code for the neutral and charged particle transport calculations. These comprehensive neutronics calculations have been performed with a fine special resolution of 0.25 cm 3 , showing among others that the specimens will be irradiated with a homogeneous damage rate of up to 13(∼ 9%) dpa/fpy and a fusion relevant damage to helium ratio of 10-12 appm He/dpa. In addition, damage and gas production rates as well as the heat deposition in structural parts of the test module have been calculated. Despite of the vertical gradients in the nuclear heating, CFD code calculations with STAR-CD revealed very

Creep-fatigue life assessment of cruciform weldments using the linear matching method

International Nuclear Information System (INIS)

Gorash, Yevgen; Chen, Haofeng

2013-01-01

This paper presents a creep-fatigue life assessment of a cruciform weldment made of the steel AISI type 316N(L) and subjected to reversed bending and cyclic dwells at 550 °C using the Linear Matching Method (LMM) and considering different weld zones. The design limits are estimated by the shakedown analysis using the LMM and elastic-perfectly-plastic material model. The creep-fatigue analysis is implemented using the following material models: 1) Ramberg–Osgood model for plastic strains under saturated cyclic conditions; 2) power-law model in “time hardening” form for creep strains during primary creep stage. The number of cycles to failure N ⋆ under creep-fatigue interaction is defined by: a) relation for cycles to fatigue failure N ∗ dependent on numerical total strain range Δε tot for the fatigue damage ω f ; b) long-term strength relation for the time to creep rupture t ∗ dependent on numerical average stress σ ¯ during dwell Δt for the creep damage ω cr ; c) non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N ⋆ for different Δt and Δε tot shows good quantitative agreement with experiments. A parametric study of different dwell times Δt is used to formulate the functions for N ⋆ and residual life L ⋆ dependent on Δt and normalised bending moment M -tilde , and the corresponding contour plot intended for design applications is created. -- Highlights: ► Ramberg–Osgood model is used for plastic strains under saturated cyclic conditions. ► Power-law model in time-hardening form is used for creep strains during dwells. ► Life assessment procedure is based on time fraction rule to evaluate creep damage. ► Function for cycles to failure is dependent on dwell period and normalised moment. ► Function for FSRF dependent on dwell period takes into account the effect of creep

A phenomenological approach for the analysis of combined fatigue and creep

International Nuclear Information System (INIS)

Bui-Quoc, T.; Biron, A.

1982-01-01

An approach is proposed for the life prediction, under cumulative damage conditions, for fatigue and for creep. An interaction effect is introduced to account for a modification in the material behavior due to previous loading. A predictive technique is then developed which is applied to several materials for fatigue and which could potentially be used for creep. With due consideration to the similarity of the formulation for both phenomena, the analysis for the combination of fatigue and creep is then carried out through a straightforward sequential use of the two damage functions. Several patterns are studied without and with an interaction effect. (orig.)

Crack propagation behaviour in stainless steel AISI 316L at elevated temperatures under static and cyclic loading

International Nuclear Information System (INIS)

Lange, H.

1991-01-01

Experimental investigations of crack growth under creep and creep-fatigue conditions are presented. The experiments were performed with the austenitic steel AISI 316L, that will be used in fast breeder reactors. A comparison of crack propagation behaviour at temperatures of T = 550deg C and T = 700deg C in common through-thickness cracked specimens and in plates containing surface cracks is carried out by application of several fracture mechanics parameters. The quantitative description of crack initiation times and crack velocities is persued particularly. The propagation rate of one-dimensional cracks under cyclic loading conditions at T = 550deg C is also treated with fracture mechanical methods. The influence of the hold periods on crack speed is discussed. (orig.) [de

Electrochemical investigation of crack initiation during corrosion fatigue of stainless steels in the passive state. Elektrochemische Untersuchung der Rissbildung bei Schwingungsrisskorrosion im stabil-passiven Werkstoffzustand

Energy Technology Data Exchange (ETDEWEB)

Spaehn, R. (Technische Hochschule Darmstadt (Germany, F.R.))

1991-03-01

The corrosion fatigue behaviour of three stainless steels - ferritic (12% Cr), austenitic (type 316 Ti) and austenitic-ferritic (type 31803; Duplex stainless steel) - was studied under rotating bending moments in aqueous sulphuric acid of 30deg C. An instrumental set-up for recording the transient currents of specimens during potentiostatically controlled corrosion fatigue is described. Based on this transient current signal technique, three stages on the corrosion fatigue process can be discerned. In the incubation period, small stochastic current transients are caused by the response of the passive layer to alternating stresses and environmental conditions. The appearance of sinusoidal current signals indicates crack initiation whereas the phase angle between a fixed marker - i.e. a light barrier signal -, and the anodic amplitude represents the site of initiating cracks. Finally, the crack growth period is characterized by an increasing cell current and steadily growing sinusoidal current signals caused by the interplay of microplastic and repassivation processes at the crack tip. (orig.).

Crack growth prediction for low-cycle fatigue regime

International Nuclear Information System (INIS)

Kamaya, Masayuki

2017-01-01

The objective of this study is to show a crack growth prediction procedure for the low-cycle fatigue regime. First, fatigue crack growth tests using Type 316 stainless steel specimens at room temperature were reviewed. It was seen that the crack growth rates correlated well with the equivalent stress intensify factor, which was derived using strain range instead of stress range. Furthermore, the effective equivalent stress intensify factor derived using the effective strain range exhibited excellent correlation with the crack growth rates obtained under various specimen geometries and loading conditions including high and low-cycle regimens. The obtained crack growth rates were also compared with the growth rate prescribed in the fitness-for-service code of the Japan Society of Mechanical Engineers (JSME). The test results agreed with the growth rate of JSME code. Finally, the procedure for predicting the low-cycle fatigue crack growth was shown. Although the JSME code is aimed at predicting fatigue crack growth for the so-called small scale yielding condition (high-cycle fatigue regime), the material constants determined for the high-cycle fatigue regime can be used even for the low-cycle fatigue regime. (author)

An evaluation on fatigue crack growth in a fine-grained isotropic graphite

Energy Technology Data Exchange (ETDEWEB)

Wang Hongtao; Sun Libin [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Li Chenfeng [College of Engineering, Swansea University, Singleton Park, Swansea SA2 8PP (United Kingdom); Shi Li [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Wang Haitao, E-mail: wanght@tsinghua.edu.cn [Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China)

2012-09-15

Highlights: Black-Right-Pointing-Pointer The propagation of micro- and macro-fatigue cracks in IG-11 graphite was studied. Black-Right-Pointing-Pointer The curves of the fatigue crack growth rate versus the SIF range show three stages. Black-Right-Pointing-Pointer The fatigue microcrack propagation is very sensitive to graphite's microstructures. Black-Right-Pointing-Pointer Graphite's microstructures have no significant impact on fatigue macrocrack growth. Black-Right-Pointing-Pointer The fatigue fracture surface indicates the fracture mechanism of the IG-11 graphite. - Abstract: The aim of this paper is to investigate the mechanism of fatigue crack propagation in IG-11 graphite, and determine the crack growth rate in relation to the stress level. Experimental studies were performed at both micro and macro scales. For fatigue microcrack propagation, single-edge-notch specimens were chosen for testing and the fatigue crack growth was measured in situ with a scanning electron microscope. For fatigue macrocrack propagation, CT specimens were used and the fatigue crack growth was measured with a high-accuracy optic microscope. Combining the two groups of experimental results, the following conclusions are derived: (1) The heterogeneous microstructures of the graphite material have significant impact on the fatigue microcrack growth, while their influence on fatigue macrocrack growth is very limited. (2) The relationship between the fatigue crack growth rate and the crack-tip stress intensity factor range can be expressed in the form of Paris formulae, which contains three stages: an initial rising part with a small slope, an abrupt rise with a very large acceleration, and a short final part with a small slope. (3) The fatigue fracture surface of the graphite material contains considerable sliding of leaf-shape graphite flakes combined with small cotton-shape plastic deformations. These sliding traces are approximately aligned at 45 Degree-Sign , showing the

Fatigue strength depending on position of cracks for weldments

International Nuclear Information System (INIS)

Lee, Hae Woo; Park, Won Jo

2006-01-01

This is a study of fatigue strength of weld deposits with transverse cracks in plate up to 50 mm thick. It is concerned with the fatigue properties of welds already with transverse cracks. A previous study of transverse crack occurrence, location and microstructure in accordance with welding conditions was published in the Welding Journal (Lee et al., 1998). A fatigue crack develops as a result of stress concentration and extends with each load cycle until fatigue occurs, or until the cyclic loads are transferred to redundant members. The fatigue performance of a member is more dependent on the localized state of stress than the static strength of the base metal or the weld metal. Fatigue specimens were machined to have transverse cracks located on the surface and inside the specimen. Evaluation of fatigue strength depending on location of transverse cracks was then performed. When transverse cracks were propagated in a quarter-or half-circle shape, the specimen broke at low cycle in the presence of a surface crack. However, when the crack was inside the specimen, it propagated in a circular or elliptical shape and the specimen showed high fatigue strength, enough to reach the fatigue limit within tolerance of design stresses

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

Low-cycle fatigue-cracking mechanisms in fcc crystalline materials

Science.gov (United States)

Zhang, P.; Qu, S.; Duan, Q. Q.; Wu, S. D.; Li, S. X.; Wang, Z. G.; Zhang, Z. F.

2011-01-01

The low-cycle fatigue (LCF) cracking behavior in various face-centered-cubic (fcc) crystalline materials, including Cu single crystals, bicrystals and polycrystals, Cu-Al and Cu-Zn alloys, ultrafine-grained (UFG) Al-Cu and Cu-Zn alloys, was systematically investigated and reviewed. In Cu single crystals, fatigue cracking always nucleates along slip bands and deformation bands. The large-angle grain boundary (GB) becomes the preferential site in bicrystals and polycrystals. In addition, fatigue cracking can also nucleate along slip bands and twin boundaries (TBs) in polycrystalline materials. However, shear bands and coarse deformation bands are observed to the preferential sites for fatigue cracking in UFG materials with a large number of GBs. Based on numerous observations on fatigue-cracking behavior, the fatigue-cracking mechanisms along slip bands, GBs, TBs, shear bands and deformation bands were systematically compared and classified into two types, i.e. shear crack and impingement crack. Finally, these fatigue-cracking behaviors are discussed in depth for a better understanding of their physical nature and the transition from intergranular to transgranular cracking in various fcc crystalline materials. These comprehensive results for fatigue damage mechanisms should significantly aid in obtaining the optimum design to further strengthen and toughen metallic materials in practice.

Fatigue crack growth in an aluminum alloy-fractographic study

Science.gov (United States)

Salam, I.; Muhammad, W.; Ejaz, N.

2016-08-01

A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

Stage I surface crack formation in thermal fatigue: A predictive multi-scale approach

International Nuclear Information System (INIS)

Osterstock, S.; Robertson, C.; Sauzay, M.; Aubin, V.; Degallaix, S.

2010-01-01

A multi-scale numerical model is developed, predicting the formation of stage I cracks, in thermal fatigue loading conditions. The proposed approach comprises 2 distinct calculation steps. Firstly, the number of cycles to micro-crack initiation is determined, in individual grains. The adopted initiation model depends on local stress-strain conditions, relative to sub-grain plasticity, grain orientation and grain deformation incompatibilities. Secondly, 2-4 grains long surface cracks (stage I) is predicted, by accounting for micro-crack coalescence, in 3 dimensions. The method described in this paper is applied to a 500 grains aggregate, loaded in representative thermal fatigue conditions. Preliminary results provide quantitative insight regarding position, density, spacing and orientations of stage I surface cracks and subsequent formation of crack networks. The proposed method is fully deterministic, provided all grain crystallographic orientations and micro-crack linking thresholds are specified. (authors)

Prediction of inelastic behavior and creep-fatigue life of perforated plates

International Nuclear Information System (INIS)

Igari, Toshihide; Yamauchi, Masafumi; Nomura, Shinichi.

1992-01-01

Prediction methods of macroscopic and local stress-strain behaviors of perforated plates in plastic and creep regime are proposed in this paper, and are applied to the creep-fatigue life prediction of perforated plates. Both equivalent-solid-plate properties corresponding to the macroscopic behavior and the stress-strain concentration around a hole were obtained by assuming the analogy between plasticity and creep and also by extending the authors' proposal in creep condition. The perforated plates which were made of Hastelloy XR were subjected to the strain-controlled cyclic test at 950degC in air in order to experimentally obtain the macroscopic behavior such as the cyclic stress-strain curve and creep-fatigue life around a hole. The results obtained are summarized as follows. (1) The macroscopic behavior of perforated plates including cyclic stress-strain behavior and relaxation is predictable by using the proposed method in this paper. (2) The creep-fatigue life around a hole can be predicted by using the proposed method for stress-strain concentration around a hole. (author)

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

Fatigue life assessment based on crack growth behavior in reduced activation ferritic/martensitic steel

International Nuclear Information System (INIS)

Nogami, Shuhei; Sato, Yuki; Hasegawa, Akira

2010-01-01

Crack growth behavior under low cycle fatigue in reduced activation ferritic/martensitic steel, F82H IEA-heat (Fe-8Cr-2W-0.2V-0.02Ta), was investigated to improve the fatigue life assessment method of fusion reactor structural material. Low cycle fatigue test was carried out at room temperature in air at a total strain range of 0.4-1.5% using an hourglass-type miniature fatigue specimen. The relationship between the surface crack length and life fraction was described using one equation independent of the total strain range. Therefore, the fatigue life and residual life could be estimated using the surface crack length. Moreover, the microcrack initiation life could be estimated using the total strain range if there was a one-to-one correspondence between the total strain range and number of cycles to failure. The crack growth rate could be estimated using the total strain range and surface crack length by introducing the concept of the normalized crack growth rate. (author)

Experimental and modeling results of creep fatigue life of Inconel 617 and Haynes 230 at 850 C

International Nuclear Information System (INIS)

Chen, Xiang; Sokolov, Mikhail A.; Sham, Sam; Erdman, Donald L. III; Busby, Jeremy T.; Mo, Kun; Stubbins, James

2013-01-01

Creep fatigue testing of Ni-based superalloy Inconel 617 and Haynes 230 were conducted in the air at 850 C. Tests were performed with fully reversed axial strain control at a total strain range of 0.5%, 1.0% or 1.5% and hold time at maximum tensile strain for 3, 10 or 30 min. In addition, two creep fatigue life prediction methods, i.e. linear damage summation and frequency-modified tensile hysteresis energy modeling, were evaluated and compared with experimental results. Under all creep fatigue tests, Haynes 230 performed better than Inconel 617. Compared to the low cycle fatigue life, the cycles to failure for both materials decreased under creep fatigue test conditions. Longer hold time at maximum tensile strain would cause a further reduction in both material creep fatigue life. The linear damage summation could predict the creep fatigue life of Inconel 617 for limited test conditions, but considerably underestimated the creep fatigue life of Haynes 230. In contrast, frequency-modified tensile hysteresis energy modeling showed promising creep fatigue life prediction results for both materials.

An Abnormal Increase of Fatigue Life with Dwell Time during Creep-Fatigue Deformation for Directionally Solidified Ni-Based Superalloy DZ445

Science.gov (United States)

Ding, Biao; Ren, Weili; Deng, Kang; Li, Haitao; Liang, Yongchun

2018-03-01

The paper investigated the creep-fatigue behavior for directionally solidified nickel-based superalloy DZ445 at 900 °C. It is found that the fatigue life shows an abnormal increase when the dwell time exceeds a critical value during creep-fatigue deformation. The area of hysteresis loop and fractograph explain the phenomenon quite well. The shortest life corresponds to the maximal area of hysteresis loop, i. e. the maximum energy to be consumed during the creep-fatigue cycle. The fractographic observation of failed samples further supports the abnormal behavior of fatigue life.

Finite Element Creep-Fatigue Analysis of a Welded Furnace Roll for Identifying Failure Root Cause

Science.gov (United States)

Yang, Y. P.; Mohr, W. C.

2015-11-01

Creep-fatigue induced failures are often observed in engineering components operating under high temperature and cyclic loading. Understanding the creep-fatigue damage process and identifying failure root cause are very important for preventing such failures and improving the lifetime of engineering components. Finite element analyses including a heat transfer analysis and a creep-fatigue analysis were conducted to model the cyclic thermal and mechanical process of a furnace roll in a continuous hot-dip coating line. Typically, the roll has a short life, modeling heat convection from hot air inside the furnace. The creep-fatigue analysis was performed by inputting the predicted temperature history and applying mechanical loads. The analysis results showed that the failure was resulted from a creep-fatigue mechanism rather than a creep mechanism. The difference of material properties between the filler metal and the base metal is the root cause for the roll failure, which induces higher creep strain and stress in the interface between the weld and the HAZ.

A survey of the French creep-fatigue design rules for LMFBR

International Nuclear Information System (INIS)

Tribout, J.; Cordier, G.; Moulin, D.

1987-01-01

The paper provides a survey of the creep-fatigue design rules for the LMFBR in France. These rules are the ones currently implemented in French component manufacturing. The background of each item is discussed and the trends for improvements currently investigated are described. The creep-fatigue rules apply to elastic analysis only. (orig.)

Study of creep crack growth behavior of 316LN welds

International Nuclear Information System (INIS)

Venugopal, S.; Kumar, Yatindra; Sasikala, G.

2016-01-01

Creep crack growth (CCG) behavior plays an important role in the assessment of structural integrity of components operating at elevated temperature under load/stress condition. Integrity of the welded components is decided primarily by that of the weld. Creep crack growth behavior of 316LN welds prepared using consumables developed indigenously for welding the 316L(N) SS components for the Prototype Fast Breeder Reactor has been studied. The composition of the consumable is tailored to ensure about 5 FN (ferrite number) of δ ferrite in the weld deposit. Constant load CCG tests were carried out as per ASTM E1457 at different applied loads at temperatures in the range 823-923 K on CT specimens fabricated from 'V-type' weld joints with notch in the weld centre. The creep crack growth rate (α) is commonly correlated to a time dependent fracture mechanics parameter known as C*. The α3-C* correlations (α=D(C*) φ ) were established in the temperature range 823-923 K. The crack growth rates at different temperature have been compared with that given in RCC-MR. Extensive microstructural and fractographic studies using optical and scanning electron microscopy were carried out on the CCG tested specimens to understand the effect of transformation of delta ferrite on the creep damage and fracture mechanisms associated with CCG in the weld metal at different test conditions. (author)

Deformation mechanisms in cyclic creep and fatigue

International Nuclear Information System (INIS)

Laird, C.

1979-01-01

Service conditions in which static and cyclic loading occur in conjunction are numerous. It is argued that an understanding of cyclic creep and cyclic deformation are necessary both for design and for understanding creep-fatigue fracture. Accordingly a brief, and selective, review of cyclic creep and cyclic deformation at both low and high strain amplitudes is provided. Cyclic loading in conjunction with static loading can lead to creep retardation if cyclic hardening occurs, or creep acceleration if softening occurs. Low strain amplitude cyclic deformation is understood in terms of dislocation loop patch and persistent slip band behavior, high strain deformation in terms of dislocation cell-shuttling models. While interesting advances in these fields have been made in the last few years, the deformation mechanisms are generally poorly understood

Thermal fatigue of a 304L austenitic stainless steel: simulation of the initiation and of the propagation of the short cracks in isothermal and aniso-thermal fatigue

International Nuclear Information System (INIS)

Haddar, N.

2003-04-01

The elbow pipes of thermal plants cooling systems are submitted to thermal variations of short range and of variable frequency. These variations bound to temperature changes of the fluids present a risk of cracks and leakages. In order to solve this problem, EDF has started the 'CRECO RNE 808' plan: 'thermal fatigue of 304L austenitic stainless steels' to study experimentally on a volume part, the initiation and the beginning of the propagation of cracks in thermal fatigue on austenitic stainless steels. The aim of this study is more particularly to compare the behaviour and the damage of the material in mechanic-thermal fatigue (cycling in temperature and cycling in deformation) and in isothermal fatigue (the utmost conditions have been determined by EDF for the metal: Tmax = 165 degrees C and Tmin = 90 degrees C; the frequency of the thermal variations can reach a Hertz). A lot of experimental results are given. A model of lifetime is introduced and validated. (O.M.)

Comparison of various 9-12%Cr steels under fatigue and creep-fatigue loadings at high temperature

International Nuclear Information System (INIS)

Fournier, B.; Dalle, F.; Sauzay, M.; Longour, J.; Salvi, M.; Caes, C.; Tournie, I.; Giroux, P.F.; Kim, S.H.

2011-01-01

The present article compares the cyclic behaviour of various 9-12%Cr steels, both commercial grades and optimized materials (in terms of creep strength). These materials were subjected to high temperature fatigue and creep-fatigue loadings. TEM examinations of the microstructure after cyclic loadings were also carried out. It appears that all the tempered ferritic-martensitic steels suffer from a cyclic softening effect linked to the coarsening of the sub-grains and laths and to the decrease of the dislocation density. These changes of the microstructure lead to a drastic loss in creep strength for all the materials under study. However, due to a better precipitation state, several materials optimized for their creep strength still present a good creep resistance after cyclic softening. These results are discussed and compared to the literature in terms of the physical mechanisms responsible for cyclic and creep deformation at the microstructural scale. (authors)

Effect of variable load on crack initiation microalloyed steel S 690-QL

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M. Burzić

2015-01-01

Full Text Available The accumulation of damage in the form of initiation and growth of micro-cracks is the first stage of destruction that ends when the merger microcracks form macro cracks. Cracks formed in the cycle number N =104 - 105 are the result of low cycle fatigue. From the need to evaluate low cycle fatigue life was carried out to investigate the low cycle fatigue microalloyed high-strength steel S690QL in the heat-treated.

Fatigue behaviour and crack growth of ferritic steel under environmental conditions

International Nuclear Information System (INIS)

Herter, K.H.; Schuler, X.; Weissenberg, T.

2012-01-01

The assessment of fatigue and cyclic crack growth behaviour of safety relevant components is of importance for the ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as a limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way. Fatigue tests were performed in the low cycle fatigue (LCF) und high cycle fatigue (HCF) regime with low alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in air and high temperature (HT) boiling water reactor environment to extend the state of knowledge of environmentally assisted fatigue (EAF) as it can occur in boiling water reactor (BWR) plants. Using the reactor pressure vessel (RPV) steel 22NiMoCr3-7 experimental data were developed to verify the influence of BWR coolant environment (high purity water as well as sulphate containing water with 90 ppb SO 4 at a test temperature of 240 C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor F en accounting for the environment. The experimental results are compared with international available mean data curves, the new design curves and on the basis of the environmental factor F en . Furthermore the behaviour of steel 22NiMoCr3-7 in oxygenated high temperature water under transient loading conditions was investigated with respect to crack initiation and cyclic crack growth. In this process the stress state of the specimen and the chemical composition of the high

Fatigue crack closure in submicron-thick freestanding copper films

International Nuclear Information System (INIS)

Kondo, Toshiyuki; Ishii, Takaki; Hirakata, Hiroyuki; Minoshima, Kohji

2015-01-01

The fatigue crack closure in approximately 500-nm-thick freestanding copper films were investigated by in situ field emission scanning electron microscope (FESEM) observations of the fatigue crack opening/closing behavior at three stress ratios of R=0.1, 0.5, and 0.8 in the low–K max (maximum stress intensity factor) region of K max <4.5 MPam 1/2 . The direct observation of fatigue cracks clarified that crack closure occurred at R=0.1 and 0.5, while the fatigue crack was always open at R=0.8. Changes in the gage distance across the fatigue crack during a fatigue cycle were measured from the FESEM images, and the crack opening stress intensity factor K op was evaluated on the basis of the stress intensity factor K vs. the gage distance relationship. The effective stress intensity factor range ΔK eff =K max −K op was then evaluated. The R-dependence of the da/dN vs. ΔK eff relationship was smaller than that of the da/dN vs. ΔK relationship. This suggests that ΔK eff is a dominating parameter rather than ΔK in the fatigue crack propagation in the films. This paper is the first report on the presence of the fatigue crack closure in submicron-thick freestanding metallic films

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

Fatigue crack initiation at complex flaws in hydrided Zr-2.5%Nb samples from CANDU pressure tubes

International Nuclear Information System (INIS)

Stoica, L.; Radu, V.

2016-01-01

The paper addresses the phenomena which occur at locations where the oxide layer of the inner surface of CANDU tube pressure is damaged by the contact with the fuel element or due to the action of hard particles at the interface between the tube pressure and bearing pad of fuel element. In such situations generate defects, which most often are defects known as ''bearing pad fretting flaws'' or ''debris fretting flaws''. In this paper the experiments are completed in a series of previous works on the mechanical fatigue phenomenon on samples prepared from the pressure tube Zr-2.5% Nb alloy. The phenomenon of variable mechanical stress (or fatigue) may lead to initiation of cracks at the tip of volumetric flaws, according to the accumulation of hydrides, which then fractures and can propagate through the tube wall pressure due to the mechanism of type DHC (Delayed Hydride Cracking). (authors)

A life evaluation under creep-fatigue-environment interaction of Ni-base wrought alloys

International Nuclear Information System (INIS)

Hattori, Hiroshi; Kitagawa, Masaki; Ohtomo, Akira; Itoh, Mitsuyoshi

1986-01-01

In order to determine a failure criteria under cyclic loading and affective environment for HTGR systems, a series of strain controlled low-cycle fatigue tests were carried out at HTGR maximum gas temperatures in air, in vacuum and in HTGR helium environments on two nickel-base wrought alloys, namely Inconel 617 and Hastelloy XR. This paper first describes the creep-fatigue-environment properties of these alloys followed by a proposal of an evaluation method of creep-fatigue-environment interaction based on the experimental data to define the more reasonable design criteria, which is a modification of the linear damage summation rule. Second, the creep-fatigue properties of Hastelloy XR at 900 deg C and the result evaluated by this proposed method are shown. This criterion is successfully applied to the life prediction at 900 deg C. In addition, the creep-fatigue properties of Hastelloy XR-II are discussed. (author)

Creep fatigue damage under multiaxial conditions

International Nuclear Information System (INIS)

Lobitz, D.W.; Nickell, R.E.

1977-01-01

When structural components are subjected to severe cyclic loading conditions with intermittent periods of sustained loading at elevated temperature, the designer must guard against a failure mode caused by the interaction of time-dependent and time-independent deformation. This phenomena is referred to as creep-fatigue interaction. The most elementary form of interaction theory (called linear damage summation) is now embodied in the ASME Boiler and Pressure Vessel Code. In recent years, a competitor for the linear damage summation theory has emerged, called strainrange partitioning. This procedure is based upon the visualization of the cyclic strain in a uniaxial creep-fatigue test as a hysteresis loop, with the inelastic strains in the loop counter-balanced in one of two ways. The two theories are compared and contrasted in terms of ease of use, possible inconsistencies, and component life prediction. Future work to further test the damage theories is recommended

Comparison of Crack Growth Test Results at Elevated Temperature and Design Code Material Properties for Grade 91 Steel

Energy Technology Data Exchange (ETDEWEB)

Lee, Hyeong-Yeon; Kim, Woo-Gon; Kim, Nak-Hyun [Korea Atomic Energy Reserach Institute, Daejeon (Korea, Republic of)

2015-01-15

The material properties of crack growth models at an elevated temperature were derived from the results of numerous crack growth tests for Mod.9Cr-1Mo (ASME Grade 91) steel specimens under fatigue loading and creep loading at an elevated temperature. These crack growth models were needed for defect assessment under creep-fatigue loading. The mathematical crack growth rate models for fatigue crack growth (FCG) and creep crack growth (CCG) were determined based on the test results, and the models were compared with those of the French design code RCCMRx to investigate the conservatism of the code. The French design code RCC-MRx provides an FCG model and a CCG model for Grade 91 steel in Section III Tome 6. It was shown that the FCG model of RCC-MRx is conservative, while the CCG model is non-conservative compared with the present test data. Thus, it was shown that further validation of the property was required. Mechanical strength tests and creep tests were also conducted, and the test results were compared with those of RCC-MRx.

Fatigue and creep-fatigue in sodium of 316 1 stainless steel

International Nuclear Information System (INIS)

Ardellier, A.

1982-01-01

Equipment and results obtained on type 316 L stainless stee1 at 450 0 C and 600 0 C with low-cycle fatique and creep fatigue tests are described. Comparison with runs in air on type 316 L stainless steel shows a better low-cycle fatigue behavior in a sodium environment. This beneficial effect can be attributed to the low oxygen content which limits the surface oxidazation

Influence of Pitting Corrosion on Fatigue and Corrosion Fatigue of Ship and Offshore Structures, Part II: Load - Pit - Crack Interaction

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