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Sample records for 1molow cycle fatigue

  1. PROBABILISTIC METHODOLOGY OF LOW CYCLE FATIGUE ANALYSIS

    Jin Hui; Wang Jinnuo; Wang Libin

    2003-01-01

    The cyclic stress-strain responses (CSSR), Neuber's rule (NR) and cyclic strain-life relation (CSLR) are treated as probabilistic curves in local stress and strain method of low cycle fatigue analy sis. The randomness of loading and the theory of fatigue damage accumulation (TOFDA) are consid ered. The probabilistic analysis of local stress, local strain and fatigue life are constructed based on the first-order Taylor's series expansions. Through this method proposed fatigue reliability analysis can be accomplished.

  2. High-cycle fatigue / low-cycle fatigue interactions in Ti-6Al-4V

    Knipling, Keith Edward

    2002-01-01

    The largest single cause of failure in fan and compressor components in the cold frontal sections of commercial and military gas turbine engines has been attributed to high cycle fatigue (HCF). Additionally, both high-cycle fatigue (HCF) and low-cycle fatigue (LCF) loadings are widely recognized as unavoidable during operation of these components and because the classic Linear Damage Rule (LDR) neglects to account for the synergistic interaction between these damage contributors, dangerous o...

  3. Low cycle fatigue problem in RAPP fuel

    In a nuclear power plant, the fuel sheath is subjected to power cycling during start-up and shut-down, and also during normal operation. Power reactors operating in relatively small electrical grids, as for example RAPS-1 are prone to large number of such power cycles. RAPS fuel sheath being of the collapsible design is subjected to high initial plastic strains. These environmental conditions pose serious low cycle fatigue problem in RAPS fuel operations. The limitations on fuel life due to low cycle fatigue are described. The low cycle fatigue behaviour of zircaloy under normal and irradiation is discussed. UO2 expansion model used for calculating plastic strains is also described. (author)

  4. High cycle fatigue properties of inconel 690

    Inconel 690 is presently used as sleeve material and a replacement alloy in degraded steam generators, as well as the material for new steam generators. But Inconel 690 has low thermal conductivity which are 3-8% less than that of Inconel 600 at operating temperature. For the same power output, conduction area must be increased. As a result, more fluid induced vibration can cause a fatigue damage of Inconel 690. High cycle fatigue ruptures occurred in the U-bend regions of North Anna Unit 1 and Mihama Unit 2 steam generators. At this study, the effect of temperature on fatigue crack growth rate in Inconel 690 steam generator tube was investigated at various temperature in air environment. With increasing temperature, fatigue crack growth rate increased and grain size effect decreased. Chromium carbides which have large size and semi-continuous distribution in the grain boundaries decreased fatigue crack growth rate

  5. Modified low-cycle fatigue (LCF) test

    M. Maj; A. Klasik; K. Pietrzak; D. Rudnik

    2015-01-01

    The fatigue test results obtained by the common low-cycle fatigue test (LCF) and its modified MLCF counterpart were presented. A satisfactory agreement of results was achieved for the two selected materials. With the MLCF method it is possible to examine from ten to twenty parameters using one single sample only. These parameters characterise the tested material in terms of its mechanical properties under the conditions of mechanical loads. Simultaneously, the study shows the implementation o...

  6. Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel

    The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

  7. Combined Cycle Fatigue Investigation Based on Energy Principle

    Kalynenko Mykyta

    2016-01-01

    We present a modified energy-principle based model of fatigue damage accumulation in high temperature alloys usually used in gas turbine engine under combined high cycle fatigue and low cycle fatigue (LCF/HCF) loading conditions. Our model is based on the energy principle which includes a modified approximation formula that describes fatigue crack origin depending on the relative amplitude of stress intensity in the ranges of both high- and low-cycle fatigue under non-isothermal loading. Func...

  8. Low cycle fatigue on crack initiation life basis

    A review is given of the following subjects: A proposed formula, from which the strain cycling fatigue strength can be estimated, on the basis of crack initiation life, from static tensile strength and reduction in area. Relation between crack initiation life and failure life. Distribution of strain cycling fatigue life. Cyclic characteristics of notch root strain and the interrelation between fatigue life of a notched plate subjected to load cycling and fatigue life of an hour-glass shaped specimen subjected to strain cycling. Effect of angular distribution and misalignment in a butt-welded joint on load-controlled low cycle fatigue strength. Fatigue strength ratio of bending to axial strain cycling. Low cycle bending fatigue strength of the fillet welded joint. Fatigue strength of welded tubular conncetions in offshore structures. Creep-fatigue interaction problems for stainless steels. Material constants in the simplified elastic-plastic analysis in ASME Sec. III. (orig.) 891 RW/orig. 892 RKD

  9. Very high cycle fatigue of high performance steels

    Kazymyrovych, Vitaliy

    2008-01-01

    Many engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of ...

  10. High cycle fatigue characteristics of 2124-T851 aluminum alloy

    LI Xue; YIN Zhimin; NIE Bo; ZHONG Li; PAN Qinglin; JIANG Feng

    2007-01-01

    The fatigue crack growth rate, fracture toughness and fatigue S-N curve of 2124-T851 aluminum alloy at high cycle fatigue condition were measured and fatigue fracture process and fractography were studied using optical microscopy (OM), X-ray diffraction (XRD) technique, trans-mission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that at room tempera-ture and R = 0.1 conditions, the characteristics of fatigue fracture could be observed. Under those conditions, the fatigue strength and the fracture toughness of a 2124-T851 thick plate is 243 MPa and 29.64 MPa·m1/2,respectively.At high cycle fatigue condition, the higher the stress amplitude,the wider the space between fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area, and the greater the ratio between the intermittent fracture area and the whole fracture area.

  11. HIGH CYCLE FATIGUE PROPERTIES OF NICKEL-BASE ALLOY 718

    K.Kobayashi; K.Yamaguchi; M.Hayakawa; M.Kimura

    2004-01-01

    The fatigue properties of nickel-base Alloy 718 with fine- and grain-coarse grains were investigated. In the fine-grain alloy, the fatigue strength normalized by the tensile strengtn was 0.51 at 107 cycles. In contrast, the fatigue strength of the coarse-grain alloy was 0.32 at the same cycles, although the fatigue strengths in the range from 103to 105 cycles are the same for both alloys. The fracture appearances fatigued at around 106 cycles showed internal fractures originating from the flat facets of austenite grains for both alloys. The difference in fatigue strength at 107 cycles between the fine- and coarse-grain alloys could be explained in terms of the sizes of the facets from which the fractures originated.

  12. Low cycle thermal fatigue testing of beryllium

    A novel technique has been used to test the relative low cycle thermal fatigue resistance of different grades of US and Russian beryllium, which is proposed as plasma facing armor for fusion reactor first wall, limiter and divertor components. The 30 kW electron beam test system at Sandia National Laboratories was used to sweep the beam spot along one direction at 1 Hz. This produces a localized temperature ''spike'' of 750 C for each pass of the beam. Large thermal stresses in excess of the yield strength are generated, due to very high spot heat flux, 25 MWm-2. Cyclic plastic strains on the order of 0.6% produced visible cracking on the heated surface in less than 3000 cycles. An in-vacuo fiber optic borescope was used to visually inspect the beryllium surfaces for crack initiation. Grades of US beryllium tested included: S-65C, S-65H, S-200F, S200F-H, SR-200, I-400, extruded high purity, HIP'd spherical powder, porous beryllium (94 and 98% dense), Be/30%, BeO, Be/60% BeO, and TiBe12. Russian grades included: TPG-56, TShGT, DShG-200, and TSHG-56. Both thenumber of cycles tocrack initiation and the depth of crack propagation, were measured. The most fatigue resistant grades were S-65C, DShG-200, TShGT and TShG-56. Rolled sheet Be (SR-200) showed excellent crack propagation resistance in the plane of rolling, despite early formation of delamination cracks. Only one sample showed no evidence of surface melting, Extruded (T). Metallographic and chemical analyses are provided. Good agreement was found between the measured depth of cracks and a 2-D elastic-plastic finite element stress analysis. (orig.)

  13. High temperature low cycle biaxial fatigue of two steels

    Biaxial low cycle fatigue tests at various temperatures and strain rates were performed on 1% Cr-Mo-V steel and AISI 316 stainless steel under combined torsional and axial loads. A correlation for fatigue strength has been derived, and it is also shown that if the Gough ellipse quadrant criterion is rephrased in terms of strain amplitudes, it may be used as a safe design rule for ductile metals in both the low and high cycle fatigue regimes. (author)

  14. A Very High-Cycle Fatigue Test and Fatigue Properties of TC17 Titanium Alloy

    Jiao, Shengbo; Gao, Chao; Cheng, Li; Li, Xiaowei; Feng, Yu

    2016-03-01

    The present work studied the very high-cycle fatigue (VHCF) test and fatigue properties of TC17 titanium alloy. The specimens for bending vibration were designed using the finite element method and the VHCF tests were conducted by using the ultrasonic fatigue testing system. The results indicated that there is no the fatigue limit for TC17 titanium alloy, and the S-N curve shows a continuously descending trend. The fatigue crack initiates at the specimen surface within the range of VHCF and the VHCF lives follow the log-normal distribution more closely.

  15. Understandiong of low cycle fatigue behaviour of ODS steels

    Kuběna, Ivo; Kruml, Tomáš

    Berlín: DMV, 2013, s. 439-444. ISBN 978-3-9814516-2-7. [LCF7 - International Conference on Low Cycle Fatigue /7./. Aachen (DE), 09.09.2013-11.09.2013] R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA ČR(CZ) GP13-28685P Institutional support: RVO:68081723 Keywords : crack nucleation * fatigue life prediction * low cycle fatigue * ODS steels * surface relief evolution Subject RIV: JL - Materials Fatigue, Friction Mechanics

  16. Influence Of Surface Roughness On Ultra-High-Cycle Fatigue Of Aisi 4140 Steel.

    Daniel Januário Cordeiro Gomes.; Ernani Sales Palma

    2015-01-01

    Low and high-cycle fatigue life regimes are well studied and are relatively well understood. However, recent fatigue studies on steels have shown that fatigue failures can occur at low amplitudes even below the conventional fatigue limit in the ultra-high-cycle fatigue range (life higher than 107 cycles). Fatigue life in the regime of 106 to 108 cycles-to-failure in terms of the influence of manufacturing processes on fatigue strength is examined. Specifically, the influe...

  17. Microstructural study of multiaxial low cycle fatigue

    Masao Sakane

    2015-07-01

    Full Text Available This paper discusses the relationship between the stress response and the microstructure under tension-torsion multiaxial proportional and nonproportional loadings. Firstly, this paper discusses the material dependency of additional hardening of FCC materials in relation with the stacking fault energy of the materials. The FCC materials studied were Type 304 stainless steel, pure copper, pure nickel, pure aluminum and 6061 aluminum alloy. The material with lower stacking fault energy showed stronger additional hardening, which was discussed in relation with slip morphology and dislocation structures. This paper, next, discusses dislocation structures of Type 304 stainless steel under proportional and nonproportional loadings at high temperature. The relationship between the microstructure and the hardening behavior whether isotropic or anisotropic was discussed. The re-arrangeability of dislocation structure was discussed in loading mode change tests. Microstructures of the steel was discussed in more extensively programmed multiaxial low cycle fatigue tests at room temperature, where three microstructures, dislocation bundle, stacking fault and cells, which were discussed in relation with the stress response. Finally, temperature dependence of the microstructure was discussed under proportional and nonproportional loadings, by comparing the microstructures observed at room and high temperatures.

  18. Thermal-mechanical low-cycle fatigue under creep-fatigue interaction on type 304 stainless steel

    Thermal-mechanical low-cycle fatigue tests as well as isothermal low-cycle fatigue tests were carried out on Type 304 stainless steels in order to investigate the fatigue failure properties under creep-fatigue interactions from the viewpoint of correlations between the failure life, and mode. Also an attempt was made to apply the strain rate partitioning method to thermal fatigue life prediction. The results are presented and discussed. (author)

  19. Low cycle fatigue and creep fatigue behavior of alloy 617 at high temperature

    Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the very high temperature nuclear reactor (VHTR), expected to have an outlet temperature as high as 950 C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanisms and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle fatigue specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens and the addition of a hold time at peak tensile strain degraded the cycle life. This suggests that creep-fatigue interaction occurs and that the environment may be partially responsible for accelerating failure. (authors)

  20. Combined Cycle Fatigue Investigation Based on Energy Principle

    Kalynenko Mykyta

    2016-01-01

    Full Text Available We present a modified energy-principle based model of fatigue damage accumulation in high temperature alloys usually used in gas turbine engine under combined high cycle fatigue and low cycle fatigue (LCF/HCF loading conditions. Our model is based on the energy principle which includes a modified approximation formula that describes fatigue crack origin depending on the relative amplitude of stress intensity in the ranges of both high- and low-cycle fatigue under non-isothermal loading. Functional dependence that presents the influence of HCF mechanisms on a fatigue life of our structural material is gradual and it has not breaks of the curve that yields a possibility to rewrite the equation of the S-N curve with taking into account combined cycle fatigue loading. We used the same number of parameters as the initial model. Note, that new parameter interpretation gives clear physical picture. The proposed model is verified by comparing the computed results with the experimental data for one high temperature alloy GH4133.

  1. Low cycle fatigue behavior of thermo-mechanically treated rebar

    Highlights: • Strain and stress controlled low cycle fatigue behavior of TMT rebar. • Decrease in the cyclic yield stress is responsible for cyclic softening of TMT rebar. • Fatigue crack initiates form the transverse rib root and propagate along the same region. • Stress concentration and high stress triaxiality observed at the root of the transverse rib. - Abstract: The strain and stress controlled low cycle fatigue behavior of thermo-mechanically treated rebar are examined in this current work at room temperature. Severe cyclic softening is observed in all applied strain amplitudes during strain controlled low cycle fatigue. Cyclic softening deteriorates the seismic resistance property of the rebar. Decrease in the cyclic yield stress (linear portion of the hysteresis loop) is responsible for cyclic softening. Cyclic softening results progressive opening up the hysteresis loop during stress controlled low cycle fatigue. It is experimentally observed that irrespective of control mode (stress/strain) and loading conditions, fatigue crack initiates form the transverse rib root and propagate along the same region. Finite element simulation result reveal that stress concentration takes place at the root of the transverse rib and stress triaxiality become higher in the same region. Tensile strain accumulation at the transverse rib root is detected in simulation. Simulation result explains the experimental fact that fatigue crack initiate and propagate along the transverse rib root

  2. Influence Of Surface Roughness On Ultra-High-Cycle Fatigue Of Aisi 4140 Steel.

    Daniel Januário Cordeiro Gomes

    2015-04-01

    Full Text Available Low and high-cycle fatigue life regimes are well studied and are relatively well understood. However, recent fatigue studies on steels have shown that fatigue failures can occur at low amplitudes even below the conventional fatigue limit in the ultra-high-cycle fatigue range (life higher than 107 cycles. Fatigue life in the regime of 106 to 108 cycles-to-failure in terms of the influence of manufacturing processes on fatigue strength is examined. Specifically, the influence of surface roughness of turned surfaces of AISI 4140 steel specimens on fatigue strength in the giga cycle or ultra-high-cycle fatigue range is evaluated. The fatigue experiments were carried out at room temperature, with zero mean stress, on a rotating-bending fatigue testing machine of the constant bending moment type. The fatigue strength of the specimens were determined using the staircase (or up-and-down method.

  3. Low cycle fatigue behaviour of ODS steels for nuclear application

    Kuběna, Ivo; Kruml, Tomáš; Fournier, B.; Polák, Jaroslav

    2011-01-01

    Roč. 465, - (2011), s. 556-559. ISSN 1013-9826 R&D Projects: GA ČR GA106/09/1954; GA ČR GA101/09/0867 Institutional research plan: CEZ:AV0Z20410507 Keywords : Generation IV nuclear reactors * fusion energy * ODS steels * low cycle fatigue * cyclic softening Subject RIV: JL - Materials Fatigue, Friction Mechanics

  4. Competition between microstructure and defect in multiaxial high cycle fatigue

    F. Morel

    2015-07-01

    Full Text Available This study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion on

  5. Low-cycle fatigue of type 316 stainless steel

    Creep tests, temperature and pressure transient tests, and low-cycle temperature and/or pressure tests were conducted on irradiated and unirradiated type 316 stainless steel. The resulting failure data were combined by means of cumulative damage formulism and the Larson-Miller Parameter (LMP) to establish a unified failure criterion. The LMP constants that characterize the material failure were found to be a strong function of the irradiation environment. Little or no fatigue effects were noted, and the low-cycle fatigue failures could be predicted entirely from creep test results. (author)

  6. High-cycle Fatigue Fracture Behavior of Ultrahigh Strength Steels

    Weijun HUI; Yihong NIE; Han DONG; Yuqing WENG; Chunxu WANG

    2008-01-01

    The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy (FESEM). It was found that the size of inclusion has significant effect on the fatigue behavior.For AISI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curvedisplays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 μm. In the case of internal inclusion-induced fractures at cycles beyond about 1×106 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet (GBF) was observed in the vicinity around the inclusion. The GBF sizes increasewith increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×106. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study.

  7. The effect of low cycle fatigue cracks and loading history on high cycle fatigue threshold

    Moshier, Monty Allen

    High cycle fatigue (HCF) has been of great concern of late in light of the many HCF gas turbine engine failures experienced by the U.S. Air Force. Due to the high frequency, failures occur rapidly when components sustain damage from other sources. Low cycle fatigue (LCF) can initiate cracks that produce such damage. This study investigates the HCF threshold of Ti-6A1-4V when naturally initiated small surface cracks (2a = 25 mum--600 mum) are present. Small surface cracks are initiated in notched specimens using two different LCF loading histories at room temperature and 10 Hz. Direct current potential difference (DCPD) is used to detect crack initiation. Surface crack measurements are made using a scanning electron microscope prior to HCF testing. Heat tinting prior to HCF testing is used to mark the crack front to allow for post fracture crack measurements. HCF thresholds at R = 0.1 and R = 0.5 are determined for each specimen using step loading at room temperature and 600 Hz. Additionally, the HCF threshold is measured at R = 0.1 for specimens with small cracks that have been stress relief annealed to eliminate residual stresses and load history. Long crack thresholds are determined using a similar step loading procedure at R = 0.1 and R = 0.5 for specimens which have been precracked using a range of Kmax. Long crack threshold measurements are also determined for specimens which have been precracked using a range of Kmax, but stress relief annealed prior to testing. Comparisons show that HCF threshold measurements, when naturally initiated small cracks are present, are dependent on the load histories that are used to initiate the cracks. Further comparisons show that the measured small crack thresholds follow similar trends for load history effects which occur in the long crack threshold data. Additionally, it is found that thresholds can be measured free of load history effects by using a stress relief annealing process after the precracking and prior to the

  8. A criterion for high-cycle fatigue life and fatigue limit prediction in biaxial loading conditions

    Pejkowski, Łukasz; Skibicki, Dariusz

    2016-08-01

    This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The criterion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S-N curves: tension-compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promising. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the non-proportionality of loading.

  9. PO2 cycling reduces diaphragm fatigue by attenuating ROS formation.

    Li Zuo

    Full Text Available Prolonged muscle exposure to low PO2 conditions may cause oxidative stress resulting in severe muscular injuries. We hypothesize that PO2 cycling preconditioning, which involves brief cycles of diaphragmatic muscle exposure to a low oxygen level (40 Torr followed by a high oxygen level (550 Torr, can reduce intracellular reactive oxygen species (ROS as well as attenuate muscle fatigue in mouse diaphragm under low PO2. Accordingly, dihydrofluorescein (a fluorescent probe was used to monitor muscular ROS production in real time with confocal microscopy during a lower PO2 condition. In the control group with no PO2 cycling, intracellular ROS formation did not appear during the first 15 min of the low PO2 period. However, after 20 min of low PO2, ROS levels increased significantly by ∼30% compared to baseline, and this increase continued until the end of the 30 min low PO2 condition. Conversely, muscles treated with PO2 cycling showed a complete absence of enhanced fluorescence emission throughout the entire low PO2 period. Furthermore, PO2 cycling-treated diaphragm exhibited increased fatigue resistance during prolonged low PO2 period compared to control. Thus, our data suggest that PO2 cycling mitigates diaphragm fatigue during prolonged low PO2. Although the exact mechanism for this protection remains to be elucidated, it is likely that through limiting excessive ROS levels, PO2 cycling initiates ROS-related antioxidant defenses.

  10. The effect of shot peening on notched low cycle fatigue

    Highlights: → Shot peening improves notched component three point bend low cycle fatigue life. → Notch shape does not affect the efficacy of the peening process. → Strain hardening and residual stress effects need separate consideration. → Loading direction residual stresses do not relax under bend load. - Abstract: The improvement in low cycle fatigue life created by shot peening ferritic heat resistant steel was investigated in components of varying geometries based on those found in conventional power station steam turbine blades. It was found that the shape of the component did not affect the efficacy of the shot peening process, which was found to be beneficial even under the high stress amplitude three point bend loads applied. Furthermore, by varying the shot peening process parameters and considering fatigue life it has been shown that the three surface effects of shot peening; roughening, strain hardening and the generation of a compressive residual stress field must be included in remnant life models as physically separate entities. The compressive residual stress field during plane bending low cycle fatigue has been experimentally determined using X-ray diffraction at varying life fractions and found to be retained in a direction parallel to that of loading and to only relax to 80% of its original magnitude in a direction orthogonal to loading. This result, which contributes to the retention of fatigue life improvement in low cycle fatigue conditions, has been discussed in light of the specific stress distribution applied to the components. The ultimate aim of the research is to apply these results in a life assessment methodology which can be used to justify a reduction in the length of scheduled plant overhauls. This will result in significant cost savings for the generating utility.

  11. In pile AISI 316L. Low cycle fatigue. Final report

    In pile testing of the effect of neutron irradiation on the fatigue life of the reference material AISI 316L was performed in the framework of the European fusion technology program. The overall programme, carried out at SCK CEN (Mol,Belgium), exists of two instrumented rigs for low cycle fatigue testing, which were consecutively loaded in the BR-2 reactor during periods Jan (94) June (94) and Aug (94)-Dec(94). In each experiment, two identical samples were loaded by means of a pneumatically driven system. The samples were instrumented with thermocouples, strain gages, linear variable displacement transducers, and activation monitors. The experimental conditions are given. Type of fatigue test: load controlled, symmetric, uniaxial, triangular wave shape; stress range: about 580 MPa; sample shape: hourglass, diameter 3.2 mm, radius 12.5 mm; environment: NaK (peritectic); temperature: 250 C; maximum dpa value up to fracture: 1.7. Two of four samples were broken (one in each experiment) after having experienced 17 419 respectively 11 870 stress cycles. These new data points confirm earlier results from pile fatigue tests: irradiation causes no degradation of fatigue life of AISI 316L steel, at least for the parameters corresponding to these experiments

  12. Strain cycling fatigue resistance of stainless steels at elevated temperature

    Strain cycling fatigue tests of 304 and 316 stainless steel at elevated temperatures of 3500, 5500 and 6500 were made using solid cylinder specimens. The strain rate was changed in the range of 0.01 to 0.5%/sec. A comparative study with American results exhibited the shorter life of Japanese results, approx. 1/4 of fatigue life of the American result in maximum. The possible reason for the difference in life are discussed from the points of specimen shape, temperature distribution, material and others. (orig.) 891 RW/orig. 892 RK

  13. Virtual stress amplitude-based low cycle fatigue reliability analysis

    A method for virtual stress amplitude-based low cycle fatigue reliability analysis is developed. Different from existent methods, probability-based modified Ramberg-Osgood stress-strain relations (P-ε-σ curves) are newly introduced to take into account the scatter of stress-strain responses, where the metallurgical quality of material is not enough good i.e. weld metal to show a same stress-strain response for different specimens under same loading level. In addition, a virtual stress amplitude-based analysis is used to be in agreement with the existent codes for nuclear components. i.e. ASME section III. The analysis is performed by a principle of the stochastic analysis system in same safety level concurrently. Combined the probability-based modified Ramberg-Osgood stress-strain relations, the probability-based Langer S-N curves (P-S-N curves) and the Neuber's local stress-strain rule, the method can be applied to predict the fatigue life at specified reliability and loading history and to estimate the reliability at specified loading history and expectation fatigue life. Applicability of the method has been indicated by a test analysis of 1Cr18Ni9ti steel-weld metal, which was used for machining the pipes of some nuclear reactors, during low cycle fatigue

  14. High Cycle Fatigue (HCF) Science and Technology Program

    Bartsch, Thomas M.

    2002-05-01

    This fifth annual report of the National Turbine Engine High Cycle Fatigue (HCF) Program is a brief review of work completed, work in progress, and technical accomplishments. This program is a coordinated effort with participation by the Air Force, the Navy, and NASA. The technical efforts are organized under seven action teams Materials Damage Tolerance Research, Forced Response Prediction, Component Analysis, Instrumentation, Passive Damping Technology, Component Surface Treatments, and Engine Demonstration and two Programs Test and Evaluation, and Transitions (ENSIP).

  15. The effect of shot peening on notched low cycle fatigue

    Soady, K.A.; B.G. Mellor; Shackleton, J; Morris, A.(School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom); Reed, P.A.S.

    2011-01-01

    The improvement in low cycle fatigue life created by shot peening ferritic heat resistant steel was investigated in components of varying geometries based on those found in conventional power station steam turbine blades. It was found that the shape of the component did not affect the efficacy of the shot peening process, which was found to be beneficial even under the high stress amplitude three point bend loads applied. Furthermore, by varying the shot peening process parameters and conside...

  16. Low-cycle fatigue properties of high manganese content steel

    Fatigue tests in the low-cycle range had been performed to investigate the fatigue crack initiation characteristics under a completely reversed push-pull load. The material used in this test is high manganese content austenitic steel (HM steel) in comparison with a typical austenitic stainless steel SUS304. Then, it is confirmed that there are no differences in the fatigue crack initiation and the relatively small crack growth properties, and that the Manson-Coffin law can be applied to these two kinds of materials. In addition, the gradient in the relationship between the plastic strain and the number of cycles under the strain-controlled condition becomes larger for HM steel than that for SUS304. On the other hand, HM steel shows the same properties as SUS304 in the relation between the cumulative plastic strain and the number of cycles to failure not only under the strain-controlled condition but also under the stress-controlled condition. (author)

  17. Low cycle fatigue of PM/HIP astroloy

    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.

  18. INVESTIGATION OF THE LOW-CYCLE FATIGUE AND FATIGUE CRACK GROWTH BEHAVIORS OF P91 BASE METAL AND WELD JOINTS

    H.C. Yang; Y. Tu; M.M. Yu; J. Zhao

    2004-01-01

    Low cycle fatigue tests and crack growth propagations tests on P91 pipe base metal and its weld joints were conducted at three different temperatures: room temperature,550℃ and 575℃. The strain-life was analyzed, and the changes in fatigue life behavior and fatigue growth rates with increasing temperature were discussed. The different properties of the base metal and its weld joint have been analyzed.

  19. Low Cycle Fatigue Behavior and Life Prediction of a Cast Cobalt-Based Superalloy

    Yang, Ho-Young; Kim, Jae-Hoon; Yoo, Keun-Bong

    Co-base superalloys have been applied in the stationary components of gas turbine owing to their excellent high temperature properties. Low cycle fatigue data on ECY-768 reported in a companion paper were used to evaluate fatigue life prediction models. In this study, low cycle fatigue tests are performed as the variables of total strain range and temperatures. The relations between plastic and total strain energy densities and number of cycles to failure are examined in order to predict the low cycle fatigue life of Cobalt-based super alloy at different temperatures. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

  20. A Modified Fatigue Damage Model for High-Cycle Fatigue Life Prediction

    Meng Wang

    2016-01-01

    Full Text Available Based on the assumption of quasibrittle failure under high-cycle fatigue for the metal material, the damage constitutive equation and the modified damage evolution equation are obtained with continuum damage mechanics. Then, finite element method (FEM is used to describe the failure process of metal material. The increment of specimen’s life and damage state can be researched using damage mechanics-FEM. Finally, the lifetime of the specimen is got at the given stress level. The damage mechanics-FEM is inserted into ABAQUS with subroutine USDFLD and the Python language is used to simulate the fatigue process of titanium alloy specimens. The simulation results have a good agreement with the testing results under constant amplitude loading, which proves the accuracy of the method.

  1. Low-cycle fatigue of turbine rotor wheels

    By means of low cycle fatigue achieved by the application of cyclic speed tests on turbine rotor wheels and in comparison with test values and by evaluating the formation of rim cracks caused by temperature change stress, the dangers of cracks appearing during operation in integrally moulded small gas turbine rotor wheels are assessed with the aid of fracture mechanisms. It was determined in short cycle tests that the objects under test with a higher stress gradient (1.0 mm-1) exhibited a higher endurance strength (104 stress cycle) than objects tested under a lower stress gradient. The results of these tests were put to discussion. In spite of a large dispersion of the cracking resistance factor Ksub(c), an additional operational life of up to 1,000 h could be approximated. Following further operational experience, it was shown that this approximation could be increased up to 2,000 h. (orig.)

  2. Very high cycle fatigue of duplex stainless steels and stress intensity calculations

    Tofique, Muhammad Waqas

    2014-01-01

    Very high cycle fatigue (VHCF) is generally considered as the domain of fatigue lifetime beyond 10 million (107) load cycles. Few examples of structural components which are subjected to 107-109 load cycles during their service life are engine parts, turbine disks, railway axles and load-carrying parts of automobiles. Therefore, the safe and reliable operation of these components depends on the knowledge of their fatigue strength and the prevalent damage/failure mechanisms. Moreover, the fati...

  3. High cycle thermal fatigue crack initiation behavior of type 304 stainless steel in pure water

    In order to maintain the integrity of engineering plants, it is necessary to evaluate the thermal fatigue life of certain structures. While low cycle thermal fatigue behavior has been widely studied in the past, high cycle thermal fatigue behavior has not been studied due to some difficulties with experiment. In this paper, an apparatus for performing high cycle thermal fatigue tests in pure water is described. High and low temperature water is continuously supplied into each passage in an autoclave, so that the surface of a revolving cylindrical specimen in the autoclave suffers from revolution synchronized thermal fatigue. The beat transfer coefficients between the water and the metal surface were considerably high. These were 50,000--70,OOOW/m 2K for the thermal cycle frequency less than 5Hz and 70,000--120,000W/m2K for the thermal cycle frequency higher than 5Hz. A high stress amplitude can therefore be obtained at a high thermal cycle frequency by the high heat transfer coefficient. Thermal fatigue cracks were observed in specimens under the testing conditions of fictitious stress amplitudes over 290MPa in Type 304 stainless steel. The thermal fatigue limit is therefore considered to be around 290MPa. The number of cycles to crack initiation agreed with that for the mechanical fatigue when the fictitious stress amplitudes were identical. It is considered that the thermal fatigue crack initiation life can be predicted from the mechanical fatigue crack initiation life

  4. Creep fatigue behavior of heat resistant steels under service-type strain cycling at high temperature

    On three typical heat resistant steels the creep fatigue behaviour is investigated up to about 10000 h test duration using a service-type strain cycle. In a creep fatigue life analysis the cyclic deformation behaviour and the applicability of the generalized damage accumulation rule are investigated and possibilities of long-term creep fatigue prediction are studied. (orig.)

  5. Thermal Fatigue with Freeze-thaw Cycles of Polymer Modified Bitumen

    Bachir Glaoui

    2011-01-01

    Full Text Available This research contributes to characterize the EVA polymer modified bitumen, which was subjected to thermal fatigue. The aim of this work was to determine the rheological components and their evolutions under thermal fatigue with freezing - thawing cycles. To represent thermal fatigue phenomenon of polymer modified bitumen in laboratory, both freezer and controlled temperature room were used to produce the real cycles of freeze-thaw of winter season. The results suggest that thermal fatigue is more complicated on rheological behavior of polymer modified bitumen. It is shown that thermal fatigue influenced thermal cracking, fatigue cracking and permanent deformation resistance. It is concluded that thermal fatigue due to thermal cycling, is a big problem to accelerate the degradation of pavement.

  6. HIGH-TEMPERATURE LOW CYCLE FATIGUE BEHAVIOR OFNICKEL BASE SUPERALLOY GH536

    M. Zhao; L.Y. Xu; K.S. Zhang; B.Y. Yang

    2001-01-01

    Low cycle fatigue tests on nickel base superalloy GH536 were performed at 600. 700and 800°C. The strain-life and cyclic stress-strain relationship were given at various temperatures. The change in fatigue life behavior and fatigue parameters with temperature increasing was discussed. At low and intermediate total strain amplitudes,the fatigue life was found to decrease with increasing temperature.``

  7. Fatigue performance of laser additive manufactured Ti-6Al-4V in very high cycle fatigue (VHCF regime up to 109 cycles

    Eric eWycisk

    2015-12-01

    Full Text Available Additive manufacturing technologies are in the process of establishing themselves as an alternative production technology to conventional manufacturing such as casting or milling. Especially laser additive manufacturing (LAM enables the production of metallic parts with mechanical properties comparable to conventionally manufactured components. Due to the high geometrical freedom in LAM the technology enables the production of ultra-light weight designs and therefore gains increasing importance in aircraft and space industry. The high quality standards of these industries demand predictability of material properties for static and dynamic load cases. However, fatigue properties especially in the very high cycle fatigue regime until 109 cycles have not been sufficiently determined yet. Therefore this paper presents an analysis of fatigue properties of laser additive manufactured Ti-6Al-4V under cyclic tension-tension until 107 cycles and tension-compression load until 109 cycles.For the analysis of laser additive manufactured titanium alloy Ti-6Al-4V Woehler fatigue tests under tension-tension and tension-compression were carried out in the high cycle and very high cycle fatigue regime. Specimens in stress-relieved as well as hot-isostatic-pressed conditions were analyzed regarding crack initiation site, mean stress sensitivity and overall fatigue performance. The determined fatigue properties show values in the range of conventionally manufactured Ti-6Al-4V with particularly good performance for hot-isostatic-pressed additive-manufactured material. For all conditions the results show no conventional fatigue limit but a constant increase in fatigue life with decreasing loads. No effects of test frequency on life span could be determined. However, independently of testing principle, a shift of crack initiation from surface to internal initiation could be observed with increasing cycles to failure.

  8. Low cycle fatigue behavior of high strength gun steels

    Maoqiu Wang; Han Dong; Qi Wang; Changgang Fan

    2004-01-01

    The low cycle fatigue (LCF) behavior of two high strength steels, with nominal chemical compositions (mass fraction, %)of 0.40C-1.5Cr-3Ni-0.4Mo-0.2V (PCrNi3MoV) and 0.25C-3Cr-3Mo-0.8Ni-0.1Nb (25Cr3Mo3NiNb), was investigated by using the smooth bar specimens subjected to strained-controlled push-pull loading. It is found that both steels show cyclic softening, but 25Cr3Mo3NiNb steel has a lower tendency to cyclic softening. 25Cr3Mo3NiNb steel has higher fatigue ductility, and its transition fatigue life is almost three times that of PCrNi3MoV. 25Cr3Mo3NiNb steel also shows higher LCF life either at a given total strain amplitude above 0.5% or at any given plastic strain amplitude, despite its lower monotonic tensile strength than that of PCrNi3MoV.It also means that 25Cr3Mo3NiNb steel can endure higher total strain amplitude and plastic strain amplitude at a given number of reversals to failure within 104. 25Cr3Mo3NiNb steel is expected to be a good gun steel with high LCF properties because only several thousand firings are required for gun barrel in most cases.

  9. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, High-Cycle and Low-Cycle Mechanical Fatigue, Creep and Thermal Fatigue Effects

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    The development of methodology for a probabilistic material strength degradation is described. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing predictions of high-cycle mechanical fatigue and high temperature effects with experiments are presented. Results from this limited verification study strongly supported that material degradation can be represented by randomized multifactor interaction models.

  10. Macroscopic cumulative fatigue damage of material under nonsymmetrical cycle

    盖秉政

    2002-01-01

    Hashin's macroscopic theory of fatigue damage is further discussed and a new method has been proposed for prediction of cumulative fatigue damage of material and its lifetime under nonsymmetrical cyclic loading.

  11. Effects of recrystallization on the low cycle fatigue behavior of directionally solidified superalloy DZ40M

    ZHAO Yang; WANG Lei; LI Hongyun; YU Teng; LIU Yang

    2008-01-01

    The effects of recrystallization on low cycle fatigue behavior were investigated on directionally solidified Co-base superalloy DZAOM.Optical microscopy and SEM were used to examine the mierostructure and fracture surface of the specimens.The mechanical testing results demonstrated that the low cycle fatigue property of DZ40M significantly decreased with the partial reerystallization.Fatigue cracks initiate near the carbides and the grain boundaries with slip-bands.Both the fatigue crack initiation and propagation can be accelerated with the occurrences of recrystallized grain boundaries.

  12. Influence of neodymium on high cycle fatigue behavior of die cast AZ91D magnesium alloy

    杨友; 李雪松

    2010-01-01

    High cycle fatigue behavior of die cast AZ91D magnesium alloy with different Nd contents was investigated.Axial mechanical fatigue tests were conducted at the stress ratio R=0.1 and the fatigue strength was evaluated using up-to-down load method on specimens of AZ91D with different Nd contents.The results showed that the grain of AZ91D alloy was refined,the size and amount of β-Mg17Al12 phase decreased and distributed uniformly with increasing Nd content.At the number of cycles to failure,Nf=107,the fatigue...

  13. A methodology for on line fatigue life monitoring : rainflow cycle counting method

    Green's function technique is used in on line fatigue life monitoring to convert plant data to stress versus time data. This technique converts plant data most efficiently to stress versus time data. To compute the fatigue usage factor the actual number of cycles experienced by the component is to be found out from stress versus time data. Using material fatigue properties the fatigue usage factor is to be computed from the number of cycles. Generally the stress response is very irregular in nature. To convert an irregular stress history to stress frequency spectra rainflow cycle counting method is used. This method is proved to be superior to other counting methods and yields best fatigue estimates. A code has been developed which computes the number of cycles experienced by the component from stress time history using rainflow cycle counting method. This postprocessor also computes the accumulated fatigue usage factor from material fatigue properties. The present report describes the development of a code to compute fatigue usage factor using rainflow cycle counting technique and presents a real life case study. (author). 10 refs., 10 figs

  14. Creep fatigue interaction. Hold time effects on low cycle fatigue resistance of 316 L steel at 6000C

    This is a study of hold time effects on the low cycle fatigue properties of 316 L austenitic stainless steel at 6000C 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 fracture occurs by the initiation and the propagation of a transgranular 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. Several approaches are used for evaluating creep-fatigue interaction damage and estimating the fatigue life. Among those proposed approaches, the linear damage rule and the strain range partitioning method are discussed

  15. Low cycle fatigue: high cycle fatigue damage accumulation in a 304L austenitic stainless steel; Endommagement et cumul de dommage en fatigue dans le domaine de l'endurance limitee d'un acier inoxydable austenitique 304L

    Lehericy, Y

    2007-05-15

    The aim of this study was to evaluate the consequences of a Low Cycle Fatigue pre-damage on the subsequent fatigue limit of a 304L stainless steel. The effects of hardening and severe roughness (grinding) have also been investigated. In a first set of tests, the evolution of the surface damage induced by the different LCF pre-cycling was characterized. This has permitted to identify mechanisms and kinetics of damage in the plastic domain for different surface conditions. Then, pre-damaged samples were tested in the High Cycle Fatigue domain in order to establish the fatigue limits associated with each level of pre-damage. Results evidence that, in the case of polished samples, an important number of cycles is required to initiate surface cracks ant then to affect the fatigue limit of the material but, in the case of ground samples, a few number of cycles is sufficient to initiate cracks and to critically decrease the fatigue limit. The fatigue limit of pre-damaged samples can be estimated using the stress intensity factor threshold. Moreover, this detrimental effect of severe surface conditions is enhanced when fatigue tests are performed under a positive mean stress (author)

  16. New energy-based low cycle fatigue model for reactor steels

    Highlights: • A novel low cycle fatigue model based on stored energy is proposed using an additional parameter to describe the plastic energy balance. • Low cycle fatigue tests were performed to validate the model, and its accuracy was demonstrated. - Abstract: A new low cycle fatigue criterion is presented based on the stored energy, which accumulates in the material’s microstructure during fatigue loading. The new damage parameters are based on the assumption that only the stored part of the introduced energy causes the changes in the microstructure, while the other part does not contribute to the fatigue process. Moreover the dissipated part may depends on the fatigue conditions, especially on the strain rate, which could affect the lifetime prediction accuracy of the applied models. To demonstrate the prediction capability of the proposed model a comprehensive experimental work were conducted on two types of reactor pressure vessel structural material. Investigation on the fraction of plastic work dissipated to heat was carried out to provide information on thermo-mechanical behavior on the tested materials, which can be used as input parameters of the new model. Furthermore isothermal and thermo-mechanical low cycle fatigue tests were performed with in-service loading conditions. The result is higher prediction accuracy than by the classical strain amplitude and strain energy based approaches. The developed model may provide a useful analytical tool for the low cycle fatigue evaluation of reactor components

  17. A method for calculation of finite fatigue life under multiaxial loading in high-cycle domain

    M. Malnati

    2014-04-01

    Full Text Available A method for fatigue life assessment in high-cycle domain under multiaxial loading is presented in this paper. This approach allows fatigue assessment under any kind of load history, without limitations. The methodology lies on the construction - at a macroscopic level - of an “indicator” in the form of a set of cycles, representing plasticity that can arise at mesoscopic level throughout fatigue process. During the advancement of the loading history new cycles are created and a continuous evaluation of the damage is made.

  18. Fatigue

    ... to help you find out what's causing your fatigue and recommend ways to relieve it. Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include Taking certain medicines, such as antidepressants, ...

  19. High-cycle fatigue behavior of ultrafine-grained austenitic stainless and TWIP steels

    High-cycle fatigue behavior of ultrafine-grained (UFG) 17Cr-7Ni Type 301LN austenitic stainless and high-Mn Fe-22Mn-0.6C TWIP steels were investigated in a reversed plane bending fatigue and compared to the behavior of steels with conventional coarse grain (CG) size. Optical, scanning and transmission electron microscopy were used to examine fatigue damage mechanisms. Testing showed that the fatigue limits leading to fatigue life beyond 4 x 106 cycles were about 630 MPa for 301LN while being 560 MPa for TWIP steel, and being 0.59 and 0.5 of the tensile strength respectively. The CG counterparts were measured to have the fatigue limits of 350 and 400 MPa. The primary damage caused by fatigue took place by grain boundary cracking in UFG 301LN, while slip band cracking occurred in CG 301LN. However, in the case of TWIP steel, the fatigue damage mechanism is similar in spite of the grain size. In the course of cycling neither the formation of a martensite structure nor mechanical twinning occurs, but intense slip bands are created with extrusions and intrusions. Fatigue crack initiates preferentially on grain and twin boundaries, and especially in the intersection sites of slip bands and boundaries.

  20. Influences of overload on low cycle fatigue behaviors of elbow pipe with local wall thinning

    Low cycle fatigue tests were conducted using 100A elbow pipe specimens with or without local wall thinning. Local wall thinning was machined on the inside of the extrados of test elbows to simulate metal loss due to flow-accelerated corrosion or liquid droplet impingement erosion. Low cycle fatigue tests were carried out under displacement control with an inner pressure of 9 MPa. To simulate seismic events, low cycle fatigue tests were carried out on elbow pipe subjected to cyclic overloads. Regardless of local wall thinning, fatigue life of overload pipe was not so different from that of the non-overload pipe in appearance. Miner's rule can be applied to evaluate fatigue life of the elbow pipes with and without wall thinning, even if overload is applied. (author)

  1. Identification of low cycle fatigue parameters of high strength low-alloy (HSLA) steel at room temperature

    Bulatović, S.; Lj. Milović; A. Sedmak; Samardžić, I.

    2014-01-01

    Low cycle fatigue test was performed in ambient atmosphere at room temperature. Cycle loading of material, in case of High strength low-alloy steel, entails modifications of its properties and in this paper is therefore shown behavior of fatigue life using low cycle fatigue parameters. More precisely, crack initiation life of tested specimens was computed using theory of Coffin-Manson relation during the fatigue loading. The geometry of the stabilized hysteresis loop of welded joint HSLA stee...

  2. Observation of fatigue crack initiation and growth in stainless steel to quantify low-cycle fatigue damage for plant maintenance

    Quantifying the low-cycle fatigue damage accumulated in nuclear power plant components is one of the important issues for aged plants. In this study, detailed observations of crack initiation and growth were made using scanning electron microscopy in order to correlate the crack size and the magnitude of the fatigue damage. Type 316 stainless steel specimens were subjected to the strain-controlled axial fatigue test (strain range: 1.2%) in air at room temperature. The test was interrupted several times in order to observe the specimen surface. The spatial distribution of inhomogeneously accumulated damage by cyclic loading was identified by crystal orientation measurements using the electron backscatter diffraction technique. Cracks were initiated at grain boundaries and slip steps, where relatively large damage accumulated. The changes in the number of cracks and their length were quantified. The crack growth rates were well correlated with the strain intensity factor. The change in crack size during the fatigue test was predicted using the obtained growth rate and assumed initial crack size. The fatigue lives estimated by the crack growth prediction agreed well with those obtained experimentally. It was concluded that the fatigue damage could be estimated from the crack size measured in plant components. (author)

  3. Numerical Studies of Low Cycle Fatigue in Forward Extrusion Dies

    Pedersen, Thomas Ø

    2000-01-01

    Forward extrusion dies typically fail due to transverse fatigue cracks or wear. Fatigue cracks are initiated in regions where the material is subjected to repeated plastic deformations, e.g. the transition radius in a forward extrusion die, in the present work, a material model capable of...

  4. Low-Cycle Fatigue in Ni-Base Superalloy IN738LC at Elevated Temperature

    For many years, high-strength nickel-base superalloys have been used to manufacture turbine blades because of their excellent performance at high temperatures. The prediction of fatigue life of superalloys is important for improving the efficiency of the turbine blades. In this study, low cycle fatigue tests are performed for different values of total strain and temperature. The relations between strain energy density and number of cycles before failure occurs are examined in order to predict the low cycle fatigue life of IN738LC super alloy. The results of low cycle fatigue lives predicted by strain energy methods are found to coincide with experimental data and with the results obtained by the Coffin-Manson method

  5. Real-time monitoring of acoustic linear and nonlinear behavior of titanium alloys during low-cycle fatigue and high-cycle fatigue

    Frouin, Jerome; Sathish, Shamachary; Na, Jeong K.

    2000-05-01

    An in-situ technique to measure sound velocity, ultrasonic attenuation and acoustic nonlinear property has been developed for characterization and early detection of fatigue damage in aerospace materials. For this purpose we have developed a computer software and measurement technique including hardware for the automation of the measurement. New transducer holder and special grips are designed. The automation has allowed us to test the long-term stability of the electronics over a period of time and so proof of the linearity of the system. Real-time monitoring of the material nonlinearity has been performed on dog-bone specimens from zero fatigue all the way to the final fracture under low-cycle fatigue test condition (LCF) and high-cycle test condition (HCF). Real-time health monitoring of the material can greatly contribute to the understanding of material behavior under cyclic loading. Interpretation of the results show that correlation exist between the slope of the curve described by the material nonlinearity and the life of the component. This new methodology was developed with an objective to predict the initiation of fatigue microcracks, and to detect, in-situ fatigue crack initiation as well as to quantify early stages of fatigue damage.

  6. Low cycle fatigue behavior of pressure vessel steels in high temperature pressurized water

    Low cycle fatigue behavior of low alloy steels ASTM A508 Cl.3(JIS SFVQ1A) and ASTM A533B Cl.1(JIS SQV2A) for nuclear reactor pressure vessels was investigated in high temperature pressurized water simulating BWR coolant environments. Total strain range, strain rate and dissolved oxygen concentration were varied from 0.5 to 2.2 %, 0.1 to 0.001 %/s and 10 to 8 000 ppb, respectively. Fatigue tests in ambient air and 561 K air were also conducted for comparison. It was found that fatigue lives in high temperature water were shorter than those in ambient air. However, the reduction of fatigue life decreased with decreasing total strain range and rather longer fatigue lives than those in ambient air were observed at lower total strain range. A533B material showed the distinct strain rate dependence of fatigue life compared with A508 material, while they showed the similar dependence on dissolved oxygen concentration. It was found that fatigue cracks initiated at corrosion pits generated by dissolution of MnS inclusions and the low cycle fatigue behavior depended on sulfur content of the material. It can be concluded that the materials tested possess safety margins in reactor coolant environments by judging from the fact that all the present data fell on a region above the design fatigue curves in the ASME Code Sec. III. (author)

  7. Effects of high mean stress on the high-cycle fatigue behavior of PWA 1480

    PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the Space Shuttle Main Engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. This paper describes results obtained in an ongoing program to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material

  8. Integrating Water Flow, Locomotor Performance and Respiration of Chinese Sturgeon during Multiple Fatigue-Recovery Cycles

    Cai, Lu; Chen, Lei; Johnson, David; Gao, Yong; Mandal, Prashant; Fang, Min; Tu, Zhiying; Huang, Yingping

    2014-01-01

    The objective of this study is to provide information on metabolic changes occurring in Chinese sturgeon (an ecologically important endangered fish) subjected to repeated cycles of fatigue and recovery and the effect on swimming capability. Fatigue-recovery cycles likely occur when fish are moving through the fishways of large dams and the results of this investigation are important for fishway design and conservation of wild Chinese sturgeon populations. A series of four stepped velocity tes...

  9. Sensitivity Variation on Low Cycle Fatigue Cracks Using Level 4/Method B Penetrant

    FULWOOD,HARRY; MOORE,DAVID G.

    1999-09-02

    The Federal Aviation Administration's Airworthiness Assurance NDI Validation Center (AANC) is currently conducting experiments with Level 4, Method B penetrant on low cycle fatigue specimens. The main focus of these experiments is to document the affect on penetrant brightness readings by varying inspection parameters. This paper discusses the results of changing drying temperature, drying time, and dwell time of both penetrant and emulsifier on low cycle fatigue specimens.

  10. Compilation of low-cycle fatigue data of reactor structural materials

    This report summarizes the low-cycle fatigue data of reactor structural materials, which had been acquired by a series of contract researches between JAERI and Japan Welding Engineering Society (JWES) concerning the fatigue life evaluation of reactor structural components and the material aging from FY1979 to FY1990. These contract researches had been executed by subcommittees organized under cooperation with universities, neutral institutions and the industry. Subsequently, the fatigue data base 'FADAL' was developed by accumulating fatigue data acquired by the above contract researches as well as those obtained from literature survey under contract between JAERI and High Pressure Institute of Japan (HPI). Low-cycle fatigue data compiled in this report are tabulated and illustrated as εta-Nf diagram by retrieving the FADAL. (author)

  11. High cycle fatigue crack propagation resistance and fracture toughness in ship steels (Short Communication

    R.S. Tripathi

    2001-04-01

    Full Text Available In this paper, two grades of steel, viz., plain carbon steel and low alloy steel used in naval ships have been selected for studies on high cycle fatigue, crack propagation, stress intensity and crack opening displacement (COD. Specimen for high cycle fatigue was prepared as per IS: 1608. High cycle fatigue was carried out up to 50,000 cycles at 1000 kgfto 2000 kgfloads. Up to 2000 kgfloads, both the materials were observed within elastic zones. A number of paran1eters, including stress, strain and strain range, which indicate elastic behaviour of steels, have been considered. Low alloy steel specimen was prepared as per ASTM standard: E-399 and subjected to 5,00,000 cycles. Crack propagation, COD, stress intensity, load-cycle variations, load-COD relation, and other related paran1eters have been studied using a modem universal testing machine with state-of-the-art technology

  12. Strength calculation of NPP equipment and pipelines during operation. Low- and high-cycle corrosion fatigue

    This paper presents empirical equations and design curves for structural steels employed in nuclear power facilities with light water reactors. These equations allow to take into account the effects of cycle asymmetry, water coolant and ductility decrease during operation. The fatigue curves cover the low-cycle and high-cycle regions (up to 1012 cycles). The equations include the mechanical characteristics of steels under static tension. The coolant effect on steel fatigue is allowed for using a model developed at the Argonne National Laboratory

  13. IN-SITU HIGH TEMPERATURE LOW CYCLE FATIGUE STUDY

    Petrenec, M.; Polák, Jaroslav; Šamořil, T.; Dluhoš, J.; Obrtlík, Karel

    Ostrava : Tanger Ltd, 2014. ISBN 978-80-87294-52-9. [23. mezinárodní konference metalurgie a materiálů METAL 2014. Brno (CZ), 21.05.2014-23.05.2014] R&D Projects: GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : In-situ * SEM * high temperature * fatigue * superalloy Subject RIV: JL - Materials Fatigue, Friction Mechanics

  14. Low-Cycle Fatigue Life Prediction in GTD-111 Superalloy at Elevated Temperatures

    The Ni-base super-heat-resistant alloy, GTD-111, is employed in gas turbines because of its high temperature strength and oxidation resistance. It is important to predict the fatigue life of this superalloy in order to improve the efficiency of gas turbines. In this study, low-cycle fatigue tests are performed as variables of total strain range and temperature. The relationship between the strain energy density and number of cycles to failure is examined in order to predict the low-cycle fatigue life of the GTD-111 superalloy. The fatigue life predicted by using the strain-energy methods is found to coincide with that obtained from the experimental data and from the Coffin-Manson method

  15. Monitoring Low-Cycle Fatigue Material-Degradation by Ultrasonic Methods

    R. Himawan

    2010-08-01

    Full Text Available Any system consisting of structural material often undergoes fatigue, which is caused by dynamic load cycle. As a structural system, nuclear power plant is very likely to have low-cycle fatigue at many of its components. Taking into account the importance of monitoring low-cycle fatigue on structural components to prevent them from getting failure, the authors have conducted a work to monitor material degradation caused by low-cycle fatigue by using ultrasonic method. An alloy of Cu-40Zn was used as a test specimen. Ultrasonic water immersion procedure was employed in this ultrasonic test. The probe used is a focusing type and has frequency as high as 15 MHz. The specimen area tested is in the middle part divided into 14 points × 23 points. The results, which were frequency spectrums, were analyzed using two parameters: frequency spectrum peak intensity and attenuation function gradient. The analysis indicates that peak intensity increases at the beginning of load cycle and then decreases. Meanwhile, gradient of attenuation function is lower at the beginning of fatigue process, and then consistently gets higher. It concludes that low-fatigue material degradation can be monitored by using ultrasonic method.

  16. Theoretical study on low cycle fatigue strength of elbows with local wall thinning

    Low cycle fatigue tests and finite element analysis were conducted using 100A elbow specimens made of STPT 410 steel with local wall thinning in order to investigate the influences of local wall thinning on the low cycle fatigue behavior of elbows with internal pressure. Local wall thinning was machined on the inside of the elbow and was prepared at extrados, crown and intrados. The parameters of the wall thinning were same (eroded ratio=0.5, eroded angle=180 degrees and eroded length=100mm) in the all test cases. The elbow specimens were subjected to the prescribed cyclic in-plane bending displacement with constant internal pressure of 0 to 12 MPa. Also, low cycle fatigue tests using sound elbows were carried out for comparison. Low cycle fatigue life of wall thinned elbows was not so different regardless of location of wall thinning. Low cycle fatigue strength of the elbow specimens were beneath the best fit fatigue curve and its reason can be explained by combining the equivalent strain range and cumulated damage theory, considering reduction of ductility under multi-axial stress state. (author)

  17. Fatigue limit investigation of 6061-T6 aluminum alloy in giga-cycle regime

    In order to investigate the fatigue limit micro-mechanism of a precipitation-hardened Al–Mg–Si alloy (6061-T6), the alloy was subjected to very-high-cycle fatigue (VHCF) of over 109 cycles by an ultrasonic fatigue method. Two kinds of specimens, one with smooth surface and the other with a small artificial hole on the surface, were compared. The smooth specimens showed no distinct fatigue limit. Conversely, the holed specimens showed clear fatigue limit which had been generally deemed to be absent in non-ferrous alloys. In addition to the conventional fatigue crack growth (FCG) observation by replica technique, metallographically critical analyses by electron backscattered diffraction (EBSD) and cross-sectional focused ion beam (FIB) were conducted to reveal the micro-plasticity associated with FCG. It was found that the fatigue life of smooth specimens at low stress amplitude was controlled by an unstoppable FCG mechanism mediated by persistent slip bands (PSBs). On the other hand, the emergence of distinct fatigue limit in holed specimens was attributed to a non-propagating crack having mode I characteristics in essence. No coaxing effect was, however, confirmed for such non-propagating cracks. The above results, which were somewhat different from previous ones obtained by rotating bending under normal frequency, were discussed in terms of both metallurgical and mechanical points of view

  18. Low-cycle fatigue of Fe-20%Cr alloy processed by equal- channel angular pressing

    Kaneko, Yoshihisa; Tomita, Ryuji; Vinogradov, Alexei

    2014-08-01

    Low-cycle fatigue properties were investigated on Fe-20%Cr ferritic stainless steel processed by equal channel angular pressing (ECAP). The Fe-20%Cr alloy bullets were processed for one to four passes via Route-Bc. The ECAPed samples were cyclically deformed at the constant plastic strain amplitude ɛpl of 5x10-4 at room temperature in air. After the 1-pass ECAP, low-angle grain boundaries were dominantly formed. During the low-cycle fatigue test, the 1-pass sample revealed the rapid softening which continued until fatigue fracture. Fatigue life of the 1-pass sample was shorter than that of a coarse-grained sample. After the 4-pass ECAP, the average grain size reduced down to about 1.5 μm. At initial stage of the low-cycle fatigue tests, the stress amplitude increased with increasing ECAP passes. At the samples processed for more than 2 passes, the cyclic softening was relatively moderate. It was found that fatigue life of the ECAPed Fe-20%Cr alloy excepting the 1-pass sample was improved as compared to the coarse-grained sample, even under the strain controlled fatigue condition.

  19. High-temperature low cycle fatigue behavior of a gray cast iron

    The strain controlled low cycle fatigue properties of the studied gray cast iron for engine cylinder blocks were investigated. At the same total strain amplitude, the low cycle fatigue life of the studied material at 523 K was higher than that at 423 K. The fatigue behavior of the studied material was characterized as cyclic softening at any given total strain amplitude (0.12%–0.24%), which was attributed to fatigue crack initiation and propagation. Moreover, this material exhibited asymmetric hysteresis loops due to the presence of the graphite lamellas. Transmission electron microscopy analysis suggested that cyclic softening was also caused by the interactions of dislocations at 423 K, such as cell structure in ferrite, whereas cyclic softening was related to subgrain boundaries and dislocation climbing at 523 K. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain amplitudes. It showed that the higher the temperature, the rougher the crack face of the examined gray cast iron at the same total strain amplitude. Additionally, the microcracks were readily blunted during growth inside the pearlite matrix at 423 K, whereas the microcracks could easily pass through pearlite matrix along with deflection at 523 K. The results of fatigue experiments consistently showed that fatigue damage for the studied material at 423 K was lower than that at 523 K under any given total strain amplitude. - Highlights: • The low cycle fatigue behavior of the HT250 for engine cylinder blocks was investigated. • TEM investigations were conducted to explain the cyclic deformation response. • The low cycle fatigue cracks of HT250 GCI were studied by SEM. • The fatigue life of the examined material at 523 K is higher than that at 423 K

  20. A multi-scale approach for high cycle anisotropic fatigue resistance: Application to forged components

    Forged components exhibit good mechanical strength, particularly in terms of high cycle fatigue properties. This is due to the specific microstructure resulting from large plastic deformation as in a forging process. The goal of this study is to account for critical phenomena such as the anisotropy of the fatigue resistance in order to perform high cycle fatigue simulations on industrial forged components. Standard high cycle fatigue criteria usually give good results for isotropic behaviors but are not suitable for components with anisotropic features. The aim is to represent explicitly this anisotropy at a lower scale compared to the process scale and determined local coefficients needed to simulate a real case. We developed a multi-scale approach by considering the statistical morphology and mechanical characteristics of the microstructure to represent explicitly each element. From stochastic experimental data, realistic microstructures were reconstructed in order to perform high cycle fatigue simulations on it with different orientations. The meshing was improved by a local refinement of each interface and simulations were performed on each representative elementary volume. The local mechanical anisotropy is taken into account through the distribution of particles. Fatigue parameters identified at the microscale can then be used at the macroscale on the forged component. The linkage of these data and the process scale is the fiber vector and the deformation state, used to calculate global mechanical anisotropy. Numerical results reveal an expected behavior compared to experimental tendencies. We proved numerically the dependence of the anisotropy direction and the deformation state on the endurance limit evolution.

  1. A Real-Time Fatigue Monitoring and Analysis System for Lower Extremity Muscles with Cycling Movement

    Szi-Wen Chen

    2014-07-01

    Full Text Available A real-time muscle fatigue monitoring system was developed to quantitatively detect the muscle fatigue of subjects during cycling movement, where a fatigue progression measure (FPM was built-in. During the cycling movement, the electromyogram (EMG signals of the vastus lateralis and gastrocnemius muscles in one leg as well as cycling speed are synchronously measured in a real-time fashion. In addition, the heart rate (HR and the Borg rating of perceived exertion scale value are recorded per minute. Using the EMG signals, the electrical activity and median frequency (MF are calculated per cycle. Moreover, the updated FPM, based on the percentage of reduced MF counts during cycling movement, is calculated to measure the onset time and the progressive process of muscle fatigue. To demonstrate the performance of our system, five young healthy subjects were recruited. Each subject was asked to maintain a fixed speed of 60 RPM, as best he/she could, under a constant load during the pedaling. When the speed reached 20 RPM or the HR reached the maximal training HR, the experiment was then terminated immediately. The experimental results show that the proposed system may provide an on-line fatigue monitoring and analysis for the lower extremity muscles during cycling movement.

  2. Low cycle fatigue behavior of Sanicro25 steel at room and at elevated temperature

    Austenitic heat resistant Sanicro 25 steel developed for high temperature applications in power generation industry has been subjected to strain controlled low cycle fatigue tests at ambient and at elevated temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress–strain curves and fatigue life curves were evaluated at room temperature and at 700 °C. The internal dislocation structures of the material at room and at elevated temperature were studied using transmission electron microscopy. High resolution surface observations and FIB cuts revealed early damage at room temperature in the form of persistent slip bands and at elevated temperature as oxidized grain boundary cracks. Dislocation arrangement study and surface observations were used to identify the cyclic slip localization and to discuss the fatigue softening/hardening behavior and the temperature dependence of the fatigue life

  3. Low-cycle fatigue/high-cycle fatigue (LCF/HCF) interaction studies using a 10- to 40-kHz HCF loading device

    Matikas, Theodore E.

    1999-02-01

    To simulate the testing conditions experienced by aircraft engine turbine blades, a new experimental facility was developed capable of providing interactive low cycle fatigue (LCF)/high cycle fatigue (HCF) loading. The new facility is based on a HCF cell that can operate in the 10-40 kHz frequency range. This HCF testing cell can also be interfaced to a servo-hydraulic load frame, which provides a second fatigue cycle. Sample geometry is critical for the HCF cell to produce the desired applied load on the specimen. The objective of this research is to develop analytical modeling necessary for the design of test coupons to be used in the new HCF testing cell operating at ultrasonic frequencies, and also to demonstrate the capabilities of the new device by performing LCF/HCF interaction studies in Ti-6Al-4V. The results of these studies clearly showed the effect of the HCF component of the load in spite the fact that the HCF component was only 15-19 percent of the overall load. It was also found that the HCF component of the load was the major cause of observed damage with the LCF component having much less effect. Eliminating the HCF component completely resulted in increasing the fatigue life at least an order of magnitude.

  4. Influence of interstitial nitrogen on low cycle plastic fatigue behaviour of austenitic stainless steels

    Effect of interstitial nitrogen on austenitic steels tensile properties and low cycle fatigue is examined. Nitrogen content increases elasticity and strength by reducing ductility. Cyclic hardening shows a softening for low deformation and a hardening for high deformations. Stress evolution during cycling is discussed, especially in the accommodation phase. This phase comprises a initial hardening growing with nitrogen content up to 0.1% and a softening for higher contents. Life span in low cycle fatigue increases continuously with N content, for an imposed deformation over 1%. Analysis structure shows that nitrogen make dislocations flat, homogeneous and that arrangement in cells is delayed

  5. High cycle fatigue property of Ti-600 alloy at ambient temperature

    Research highlights: Ti-600, developed by Northwest Institute for Nonferrous Metal Research (NIN) in China, is a near alpha titanium alloy designed for components used in turbine engines up to 600 deg. C. Mechanical behavior of the alloy at ambient temperature and its service temperature has widely been studied, the fatigue property for the alloy has never been systematically discussed. Smooth axial fatigue tests were taken for solutioned plus aged alloy, and the fractographies were observed. In order to get the damage mechanism, OM and TEM microstructures were also investigated. - Abstract: Smooth axial fatigue tests were carried out at ambient temperature on one kind of near alpha titanium alloy named after Ti-600 at a frequency of 120-130 Hz and with two kinds of load ratios. The high cycle fatigue (HCF) strength for the solutioned and aged alloy is found to be 475 MPa fatigued with a load ratio R of 0.1, and which is 315 MPa with a load ratio R of -1. The observed high HCF strength for the samples fatigued with a load ratio R of 0.1 is attributed to its overlapping fine and thin plate like α + β phase microstructure. During the crack propagation region, at the same stress of 600 MPa, the sample with a fatigue life of 1.78 x 106 cycles has a better fatigue resistance than that of the sample with a fatigue life of 8.61 x 105 cycles, because of its smaller striation distance, its well-developed secondary cracks, more wider and coarsened α lathes precipitated at grain boundaries, and the heavily arranged interlacing transformed β microsructures. The average grain size of rare earth phases varies from several micrometers to 0.2 μm, no cracks corresponding to rare earth particles can be initiated.

  6. The path to crack initiation during low cycle thermal shock fatigue

    Low cycle thermal shock fatigue crack initiation, and the microstructural changes in materials during this process, have been studied for three types of steam pipeline steels. The roles of thermal strain ageing, subgrain formation, dislocation density, high temperature void formation and grain boundary segregations have been studied and the number of cycles needed for the formation of microcracks has been established. (author)

  7. Very high cycle fatigue behavior of SAE52100 bearing steel by ultrasonic nanocrystalline surface modification.

    Cho, In Shik; He, Yinsheng; Li, Kejian; Oh, Joo Yeon; Shin, Keesam; Lee, Chang Soon; Park, In Gyu

    2014-11-01

    In this paper, the SAE52100 bearing steel contained large quantities of cementite dispersed in ferrite matrix was subjected to the ultrasonic nanocrystalline surface modification (UNSM) treatment that aims for the extension of fatigue life. The microstructure and fatigue life of the untreated and treated specimens were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and a developed ultra-high cycle fatigue test (UFT). After UNSM treatment, the coarse ferrite grains (- 10 μm) were refined to nanosize (- 200 nm), therefore, nanostructured surface layers were fabricated. Meanwhile, in the deformed layer, the number density and area fraction of cementite were increased up to - 400% and - 550%, respectively, which increased with the decrease in depth from the topmost treated surface. The improvement of hardness (from 200 Hv to 280 Hv) and high cycles fatigue strength by - 10% were considered the contribution of the developed nanostructure in the UNSM treated specimen. PMID:25958512

  8. Application of a cycle jump technique for acceleration of fatigue crack growth simulation

    Moslemian, Ramin; Karlsson, A.M.; Berggreen, Christian

    2010-01-01

    A method for accelerated simulation of fatigue crack growth in a bimaterial interface is proposed. To simulate fatigue crack growth in a bimaterial interface a routine is developed in the commercial finite element code ANSYS and a method to accelerate the simulation is implemented. The proposed...... method is based on conducting finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional FE simulations. The inputs of the developed method are the crack growth rate vs. energy...... release rate diagrams for different mode-mixities. Once these diagrams for a specific interface are available, fatigue crack growth in any structure with the same interface can be simulated. Using the developed method, fatigue crack growth in the interface of a sandwich beam is simulated. Results of the...

  9. High temperature low-cycle fatigue strength of Hastelloy-XR

    This paper describes the low-cycle fatigue and creep-fatigue interaction properties of Hastelloy-XR in air and helium containing a small quantity of impurity gas. All tests at temperatures of 700, 800, 900 and 1000 deg. C are carried out at the strain rate of 0.1 and 0.01%/sec under the control of axial strain. Wave forms are triangular for continuous cycling tests and trapezoidal for tension hold time tests. The test results are compared with the fatigue property of Hastelloy-X which is the original alloy of Hastelloy-XR. The applicability of linear damage rule in ASME Code Case N-47 is discussed about creep-fatigue interaction property of Hastelloy-XR in High Temperature Gas-Cooled Reactor's temperature region. (author). 6 refs, 7 figs, 2 tabs

  10. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 108 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines

  11. High cycle fatigue of nickel-based superalloy MAR-M 247 at high temperatures

    Šmíd, Miroslav; Kunz, Ludvík; Hutař, Pavel; Hrbáček, K.

    Amsterdam : Elsevier, 2014 - (Gulagliano, M.; Vergani, L.), s. 329-332 ISSN 1877-7058. - (Procedia Engineering. 74). [ICMFM 2014 International Colloquium on Mechanical Fatigue of Metals /17./. Verbania (IT), 25.06.2014-27.06.2014] R&D Projects: GA MPO FR-TI4/030; GA MŠk(CZ) EE2.3.20.0214 Institutional support: RVO:68081723 Keywords : High cycle fatigue * Superalloy * MAR-M 247 * High temperature * Fracture surface * S-N curve Subject RIV: JL - Materials Fatigue, Friction Mechanics

  12. High-cycle fatigue characterization of titanium 5Al-2.5Sn alloy

    Mahfuz, H.; Xin, Yu T.; Jeelani, S.

    1993-01-01

    High-cycle fatigue behavior of titanium 5Al 2.5Sn alloy at room temperature has been studied. S-N curve characterization is performed at different stress ratios ranging from 0 to 0.9 on a subsized fatigue specimen. Both two-stress and three-stress level tests are conducted at different stress ratios to study the cumulative fatigue damage. Life prediction techniques of linear damage rule, double linear damage rule and damage curve approaches are applied, and results are compared with the experimental data. The agreement between prediction and experiment is found to be excellent.

  13. Evolution of steel grain structure under high-cycle fatigue tests at electrostimulating conditions

    The use of electric pulses for a fatigue life increase is studied on stainless steel 08Kh18N10T specimens. Fatigue tests at 105 cycles are shown to result in a decrease of a mean grain size and a relative content of high anisotropy grains in the steel. Electrostimulation leads to some increase of high anisotropy grain size and to a decrease of a mean size for grains of medium anisotropy and for isotropic ones. The results obtained show that on fatigue testing under conditions of electrostimulation the process of recrystallization proceeds and gives rise to changes in grain structure of the steel

  14. Tensile hold time effects on isothermal and thermal low-cycle fatigue of 304 stainless steel

    In high temperature low-cycle fatigue tests, it has often been noted that the fatigue life can be reduced, sometimes drastically, by imposing hold periods under tensile strain and that the effect increases with the length of the hold time. The generally accepted reason for this is that creep effects become more significant with time, and this has sometimes been substantiated by metallographic evidence of increasingly brittle intergranular fracture with increasing hold time or with decreasing cyclic frequency. This paper presents results of Isothermal and Thermal-Mechanical low-cyclic fatigue tests on 304 stainless steel with various tensile hold times. (author)

  15. Effect of microstructure on low cycle fatigue properties of ODS steels

    Kuběna, Ivo; Fournier, B.; Kruml, Tomáš

    2012-01-01

    Roč. 424, 1-3 (2012), s. 101-108. ISSN 0022-3115 R&D Projects: GA ČR GA106/09/1954; GA MŠk(CZ) ED1.1.00/02.0068 Institutional research plan: CEZ:AV0Z20410507 Keywords : ODS steels * low cycle fatigue * fusion energy Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.211, year: 2012

  16. Non-local high cycle fatigue criterion for metallic materials with corrosion defects

    May Mohamed El; Saintier Nicolas; Palin-Luc Thierry; Devos Olivier

    2014-01-01

    Designing structures against corrosion fatigue has become a key problem for many engineering structures evolving in complex environmental conditions of humidity (aeronautics, civil engineering …). In this study, we investigate the effect of corrosion defects on the high cycle fatigue (HCF) strength of a martensitic stainless steel with high specific mechanical strength, used in aeronautic applications. A volumetric approach based on Crossland equivalent stress is proposed. This can be applied...

  17. High Cycle Fatigue Damage Mechanisms of MAR-M 247 Superalloy at High Temperatures

    Šmíd, Miroslav; Horník, Vít; Hutař, Pavel; Hrbáček, K.; Kunz, Ludvík

    2016-01-01

    Roč. 69, č. 2 (2016), s. 393-397. ISSN 0972-2815 R&D Projects: GA TA ČR(CZ) TA04011525; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : High cycle fatigue * S-N curves * Fractography * High temperature * EBSD analysis Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.615, year: 2014

  18. High-cycle fatigue of Ni-base superalloy Inconel 713LC

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

    2010-01-01

    Roč. 32, č. 6 (2010), s. 908-913. ISSN 0142-1123 R&D Projects: GA MPO FT-TA4/023; GA MŠk MEB080812 Institutional research plan: CEZ:AV0Z20410507 Keywords : IN 713LC * High-cycle fatigue * Effect of mean stress * Fractography * Casting defetcts * Extreme value statistics Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.799, year: 2010

  19. Low-cycle fatigue behavior of HT-9 alloy in a flowing-lithium environment

    Low-cycle fatigue data have been obtained on normalized/tempered or lithium-preexposed HT-9 alloy at 755 K in flowing lithium of controlled purity. The results show that the fatigue life of this material decreases with an increase in nitrogen content in lithium. A reduction in strain rate also decreases the fatigue life in high-nitrogen lithium. However, in the range from approx. 4 x 10-4 to 4 x 10-2 s-1, the strain rate has no effect on fatigue life in lithium containing <200 wppM nitrogen. The fatigue life of the HT-9 alloy in low-nitrogen lithium is significantly greater than the fatigue life of Fe-9Cr-1Mo steel or Type 403 martensitic steel in air. Furthermore, a 4.0-Ms preexposure to low-nitrogen lithium has no influence on fatigue life. The reduction in fatigue life in high-nitrogen lithium is attributed to internal corrosive attack of the material. The specimens tested in high-nitrogen lithium show internal corrosion along grain and martensitic lathe boundaries and intergranular fracture. This behavior is not observed in specimens tested in low-nitrogen lithium. Results for a constant-load corrosion test in flowing lithium are also presented

  20. On low cycle fatigue in metal matrix composites

    Pedersen, Thomas Ø; Tvergaard, Viggo

    2000-01-01

    , in which continuum damage mechanics is incorporated to model fatigue damage evolution. This material model uses a superposition of kinematic and isotropic hardening, and is able to account for the Bauschinger effect as well as ratchetting, mean stress relaxation, and cyclic hardening or softening. The cell...

  1. Comparison of low-cycle fatigue data of 2 1/4 % CrMo steels

    Data files have been produced on international strain-controlled fatigue information available for 2 1/4 %CrMo steels. The available data have been considered generally in terms of total strain range vs. cycles to failure (Nsub(f)), tensile stress at Nsub(f)/2 vs. cycles to failure and time to failure vs. cycles to failure. Where possible the continuous cycling data been statistically analysed in terms of the elastic and plastic strain components and cycles to failure to yield best-fit equations over defined temperature (T) regime viz: T 0C, 4270C 0C and 5500C 0C. Increasing test temperatures result in a progressive decrease in continuous cycling fatigue endurance and sustainable stress range

  2. Thermally Induced Ultra High Cycle Fatigue of Copper Alloys of the High Gradient Accelerating Structures

    Heikkinen, Samuli; Wuensch, Walter

    2010-01-01

    In order to keep the overall length of the compact linear collider (CLIC), currently being studied at the European Organization for Nuclear Research (CERN), within reasonable limits, i.e. less than 50 km, an accelerating gradient above 100 MV/m is required. This imposes considerable demands on the materials of the accelerating structures. The internal surfaces of these core components of a linear accelerator are exposed to pulsed radio frequency (RF) currents resulting in cyclic thermal stresses expected to cause surface damage by fatigue. The designed lifetime of CLIC is 20 years, which results in a number of thermal stress cycles of the order of 2.33•1010. Since no fatigue data existed in the literature for CLIC parameter space, a set of three complementary experiments were initiated: ultra high cycle mechanical fatigue by ultrasound, low cycle fatigue by pulsed laser irradiation and low cycle thermal fatigue by high power microwaves, each test representing a subset of the original problem. High conductiv...

  3. Thermal-structural response and low-cycle fatigue damage of channel wall nozzle

    Cheng Cheng; Wang Yibai; Liu Yu; Liu Dawei; Lu Xingyu

    2013-01-01

    To investigate the thermo-mechanical response of channel wall nozzle under cyclic work-ing loads, the finite volume fluid-thermal coupling calculation method and the finite element thermal-structural coupling analysis technique are applied. In combination with the material low-cycle fatigue behavior, the modified continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles. Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a significant role in the thermal-structural response by altering the material properties;the thermal-mechanical loads interaction results in serious defor-mation mainly in the front region of slotted liner. In particular, the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib, where the fatigue failure takes place initially;with the increase in nozzle work cycles, the residual plastic strain accumulates linearly, and the strain amplitude and increment in each work cycle are separately equal, but the fatigue damage grows up nonlinearly. As a result, a simplified nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle. The predicted node life is obviously conservative to the Miner’s life. In addition, several workable methods have also been proposed to improve the channel wall nozzle durability.

  4. Simulation and analysis of data for enhancing low cycle fatigue test procedures

    The simulation and analysis of data for enhancing low cycle fatigue test procedures is discussed in this report. The analysed materials are an austenitic stainless piping steel and an austenitic weld material. This project continues the work performed in 2003 and 2004. The fatigue test data treatment application developed within the project in 2004 for the preparation of the fatigue data has been developed further. Also, more fatigue test data has been analysed with the application than in 2004. In addition to this numerical fatigue simulations were performed with FEM code ABAQUS. With the fatigue test data treatment application one can e.g. both calculate cyclically certain relevant characteristic values, e.g. elastic range, and form a set of certain cyclical parameter values needed as a part of ABAQUS analysis input files. The hardening properties of metals were modelled with both isotropic and kinematic hardening models. The further development of the application included trimming of the analysed data, and consequently trimming of resulting hardening parameters. The need for the trimming arose from the fact that the analysed fatigue test data presents some scatter caused by the limited accuracy of the test equipment and the sampling rate. The hardening parameters obtained from the application analysis results were used in the subsequent ABAQUS analyses, and then the fatigue test data were compared with the ABAQUS simulation results. After finding a procedure to trim result data to get smooth curves for cyclic hardening, hardening and softening could be reproduced in ABAQUS analysis with a reasonable accuracy. The modelling of the fatigue induced initiation and growth of cracks was not considered in this study. On the other hand, a considerable part of the fatigue life of nuclear power plant (NPP) piping components is spent in the phase preceding the initiation and growth of cracks. (au)

  5. Crack propagation under conditions of low cycle fatigue

    A literature review is given of convenient concepts describing the mechanical behaviour of a cracked body under cyclic loading. Only the range of high growth rates is considered. However, caused by large scale yielding in this range, the application of linear elastic fracture mechanics is no longer possible. Mechanical parameters which control fatigue crack growth are a modified stress intensity factor, the J-integral, the crack tip opening displacement and a suitable strain amplitude. (orig.) With 20 figs

  6. Low cycle fatigue life of two nickel-base casting alloys in a hydrogen environment

    Results of low cycle fatigue tests on alloy Mar-M-246 and Inconel 713 are presented. Based on the limited data, it was concluded that the Mar-M-246 material had a cyclic life in hydrogen that averaged three times higher than the alloy 713LC material for similar strain ranges. The hydrogen environment reduced life for both materials. The life reduction was more than an order of magnitude for the 713LC material. Porosity content of the cast specimens was as expected and was an important factor governing low cycle fatigue life

  7. High cycle fatigue of a CoCrNi--TaC aligned eutectic

    High cycle tension-tension fatigue tests at room temperature and at 10000C were conducted on a Co-10%Ni-10%Cr-14Ta-1%C directionally solidified eutectic. The room temperature S-N plot exhibited two distinct curves which converged at lower stress levels. The upper curve results when no cracking of the TaC reinforcing fibers occurs except at the crack tip. The lower curve is observed either when widespread fiber cracking occurs on the first cycle (the maximum stress being above that required to fracture fibers), or when fibers are precracked by overload followed by fatigue testing conducted below the minimum stress required to break fibers. The fatigue crack path of all room temperature specimens was macroscopically oriented at 900 to the tensile axis but microscopically consisted of Stage I (crystallographic) facets. Fibers intersecting the fracture surface showed classical cleavage characteristics indicating brittle fracture. At 10000C fatigue strengths were reduced by a factor of three and precracking of fibers led to a still lower fatigue resistance. The characteristics of fatigue crack initiation and propagation are discussed in relation to the characteristic deformation of these alloys at each temperature

  8. A structural strain method for low-cycle fatigue evaluation of welded components

    In this paper, a new structural strain method is presented to extend the early structural stress based master S–N curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic or elastic–plastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master S–N curve adopted ASME B and PV Code since 2007. With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber's rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master S–N curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hooke's law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through

  9. Crack path for run-out specimens in fatigue tests: is it belonging to high- or very-high-cycle fatigue regime?

    A. Shanyavskiy

    2015-01-01

    Fatigue tests run-out specimens up to 106 – 5x107 load cycles are used to determine the stress level named “fatigue limit”. Nevertheless, it is not clear what kind of fatigue cracking takes or will take place in these specimens. To discuss this problem, fatigue tests of titanium alloy VT3-1 specimens have been performed under tension with different values of R-ratio and under rotating-bending after various thermo-mechanical treatments (tempering, surface hardening and their combin...

  10. A Direct Method For Predicting The High-Cycle Fatigue Regime In SMAs: Application To Nitinol Stents

    Colombé Pierre

    2015-01-01

    Full Text Available In fatigue design of metals, it is common practice to distinguish between high-cycle fatigue (occurring after 10000–100000 cycles and low-cycle fatigue. For elastic-plastic materials, there is an established correlation between fatigue and energy dissipation. In particular, high-cycle fatigue occurs when the energy dissipation remains bounded in time. Although the physical mechanisms in SMAs differ from plasticity, the hysteresis observed in the stress-strain response shows that some energy dissipation occurs, and it can be reasonably assumed that situations where the energy dissipation remains bounded is the most favorable for fatigue design. We present a direct method for determining if the energy dissipation in a SMA structure is bounded or not. That method relies only on elastic calculations, thus bypassing incremental nonlinear analysis. Moreover, only a partial knowledge of the loading (namely the extreme values is needed. Some results related to Nitinol stents are presented.

  11. A simple approximative procedure for taking into account low cycle fatigue loads

    Larsen, G.; Thomsen, K.

    1996-09-01

    In this paper a simple approximative algorithm for taking into account low cycle fatigue loads is presented. Traditionally, the fatigue life consumption of a wind turbine is estimated by considering a number of (independent) load cases and performing a rainflow counting analysis on each of those. These results are then subsequently synthesized into a total load spectrum by performing a weighed sum of the number of individual load case ranges. The fatigue life consumption is thus obtained by applying the Palmgren-Miner rule on the total load spectrum. However, due to the assumption of isolated basic load cases, the above procedure fail to represent the low-frequency contributions related to the transition between those load cases. The procedure to be described in the following aims at taking the fatigue contribution, related to the transitions between the defined load cases, into account in an approximative manner. (au)

  12. High-cycle Fatigue Life Extension of Glass Fiber/Polymer Composites with Carbon Nanotubes

    Christopher S Grimmer; C K H Dharan

    2009-01-01

    The present work shows that the addition of small volume fractions of multi-walled carbon nanotubes (CNTs) to the matrix results in a significant increase in the high-cycle fatigue life. It is proposed that carbon nanotubes tend to inhibit the formation of large cracks by nucleating nano-scale damage zones. In addition, the contribution to energy absorption from the fracture of nanotubes bridging across nano-scale cracks and from nanotube pull-out from the matrix are mechanisms that can improve the fatigue life. An energy-based model was proposed to estimate the additional strain energy absorbed in fatigue. The distributed nanotubes in the matrix appear to both distribute damage as well as inhibit damage propagation resulting in an overall improvement in the fatigue strength of glass fiber composites.

  13. Identification of low cycle fatigue parameters of high strength low-alloy (HSLA steel at room temperature

    S. Bulatović

    2014-10-01

    Full Text Available Low cycle fatigue test was performed in ambient atmosphere at room temperature. Cycle loading of material, in case of High strength low-alloy steel, entails modifications of its properties and in this paper is therefore shown behavior of fatigue life using low cycle fatigue parameters. More precisely, crack initiation life of tested specimens was computed using theory of Coffin-Manson relation during the fatigue loading. The geometry of the stabilized hysteresis loop of welded joint HSLA steel, marked as Nionikral 70, is also analyzed. This stabilized hysteresis loop is very important for determination of materials properties.

  14. Ratcheting Assessment of GFRP Composites in Low-Cycle Fatigue Domain

    Ahmadzadeh, G. R.; Varvani-Farahani, A.

    2014-06-01

    The present study intends to examine ratcheting response of Glass Fiber Reinforced Polymer (GFRP) composites over fatigue cycles by means of parametric variables. Stages of ratcheting deformation were related to stress cycles, lifespan, mechanical properties and cyclic stress levels by means of linear and non-linear functions. The coefficients B and C in the proposed ratcheting formulation calibrated ratcheting equation by means of material properties over ratcheting stages. Coefficients A and C calibrated the stages I and II of ratcheting strain curve over stress cycles. The ratcheting curve over initial and final stages was affected as composite modulus of elasticity ( E c ) increased. An increase in E c -dependent coefficients A and B increased the magnitude of ratcheting strains over stress cycles. Ratcheting data for continuous and short fiber GFRP composites with various volume fractions were employed to evaluate the proposed ratcheting formulation. Interaction of ratcheting and fatigue phenomena was further assumed when the proposed parametric ratcheting equation was coupled with a fatigue damage model developed earlier by present authors. Overall damage is achieved from accumulation of ratcheting and fatigue over stress cycles.

  15. Structure and low-cycle fatigue of steel AISI 316 after ECAP

    M. Greger

    2008-05-01

    Full Text Available Purpose: Main aim of this paper is to describe the plastic deformation executed by ECAP on low cycle fatigueof steel AISI 316. Among others was attention fixed on mechanical properties after this treatment.Design/methodology/approach: Experiments were planned and realised at the temperature ranging fromroom temperature up to 280 °C. After application of deformation the structure was investigated in dependence onaccumulation of deformation and deformation temperature as well as abovementioned final properties.Findings: Accumulated real (logarithmic deformation varied from the value 2 to 8. Investigation of structure byelectron microscopy was made with use of microscope JEOL JEM 2100. Mechanical properties were investigatedby conventional tensile test and penetration test. Selected samples were subjected to low-cycle fatigue. Statisticevaluation of angular disorientation and of size of grains/sub-grains was also made with use of electron diffraction(EBSD in combination with scanning electron microscope FEG SEM Philips.Practical implications: The Technology ECAP was applied on austenitic steel AISI 316. It was verificationof ECAP application possibility on steel AISI 316 importantly for following applying on similar kinds of steel,because ECap technology influence on fatigue properties was confirmed.Originality/value: It can be predicted on the basis of obtained results that, contrary to low-cycle fatigue theultra-fine grained material will manifest at fatigue load in the mode of constant amplitude of stress higher fatiguecharacteristics, particularly fatigue limit.

  16. Development of the ultrasonic fatigue testing machine due to study on giga-cycle fatigue at elevated temperature. 2001 annual report. Document on collaborative study

    An ultrasonic fatigue testing machine was developed to obtain the giga-cycle fatigue life at elevated temperature for safety and reliability of structural components in the faster breeder reactor (FBR). This testing machine consists of an amplifier, booster, horn and the equipments such as a system controller and data acquisition. The test specimen is attached at the end of the horn. The electric power generated in the amplifier is transformed into the mechanical vibration in the converter and is magnified in the booster and horn. The vibration was enough to fatigue the specimen. Since the test frequency is set at a resonant frequency, the shape and dimensions of specimen were designed so as to vibrate itself resonantly. However, the maximum amplitudes of stress and strain in the specimen can be calculated easily by measuring the amplitude of displacement at the end of the specimen. The developed ultrasonic fatigue testing machine enables to carry out the fatigue tests at 20 kHz so that it can perform the giga-cycle fatigue test within a very short time as compared with the regular fatigue testing machines such as a hydraulic fatigue testing machine. By clarifying the material strength characteristics in giga-cycle region, the life evaluation, design and examination of components will be more suitable than ever. This study will contribute to improve the safety and reliability of components in FBR. In this technical report, the specification and characteristics of the testing machine were described along with the several experimental results. (author)

  17. Effect of the Machining Processes on Low Cycle Fatigue Behavior of a Powder Metallurgy Disk

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

    2010-01-01

    A study has been performed to investigate the effect of various machining processes on fatigue life of configured low cycle fatigue specimens machined out of a NASA developed LSHR P/M nickel based disk alloy. Two types of configured specimen geometries were employed in the study. To evaluate a broach machining processes a double notch geometry was used with both notches machined using broach tooling. EDM machined notched specimens of the same configuration were tested for comparison purposes. Honing finishing process was evaluated by using a center hole specimen geometry. Comparison testing was again done using EDM machined specimens of the same geometry. The effect of these machining processes on the resulting surface roughness, residual stress distribution and microstructural damage were characterized and used in attempt to explain the low cycle fatigue results.

  18. Low cycle fatigue behaviors of elbow pipe containing local wall thinning

    Low cycle fatigue tests were conducted using 100A elbow specimens of STPT410 with local wall thinning. Local wall thinning was machined on the inside of elbow specimens in order to simulate erosion/corrosion metal loss. The local wall thinning areas were located at three different areas, called extrados, crown and intrados. The elbow specimens were subjected to cyclic in-plane bending under displacement control without internal pressure. The effects of eroded conditions, such as eroded ratio, eroded angle and position, on the low cycle fatigue behavior and fatigue life were discussed. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which could accurately predict the location of crack initiation and the crack growth direction. In addition, the safety margin of the eroded elbows against seismic loading was evaluated by comparing the fictitious stress of elbows and the design code against seismic loadings. (author)

  19. Low cycle fatigue behaviors of elbow pipe with local wall thinning

    Low cycle fatigue tests were conducted using 100A elbow specimens made of STPT410 carbon steel with local wall thinning. Local wall thinning by erosion/corrosion was simulated by machined pipe wall thinning. The local wall thinning areas were located at three different areas, called extrados, crown and intrados. The elbow specimens were subjected to cyclic in-plane bending under displacement control without internal pressure. The effects of eroded conditions, such as eroded ratio, eroded angle and position, on the low cycle fatigue behavior and fatigue life were discussed by using experimental results and finite element analyses. Also the location of crack initiation and the crack growth direction could be predicted by three dimensional elastoplastic finite element analyses. In addition, the safety margin of eroded elbows against seismic loading was discussed by comparing the fictitious stress of elbows with the allowable stress limit demanded by the design code. (author)

  20. Use of strainrange partitioning to predict high temperature low-cycle fatigue life. [of metallic materials

    Hirschberg, M. H.; Halford, G. R.

    1976-01-01

    The fundamental concepts of the strainrange partitioning approach to high temperature, low low-cycle fatigue are reviewed. Procedures are presented by which the partitioned strainrange versus life relationships for any material can be generated. Laboratory tests are suggested for further verifying the ability of the method of strainrange partitioning to predict life.

  1. Very high cycle regime fatigue of thin walled tubes made from austenitic stainless steel

    Carstensen, J.V.; Mayer, H.; Brøndsted, P.

    2002-01-01

    Fatigue life data of cold worked tubes (diameter 4 mm, wall thicknesses 0.25 and 0.30 mm) of an austenitic stainless steel, AISI 904 L, were measured in the regime ranging from 2 × 105 to 1010 cycles to failure. The influence of the loading frequency was investigated as data were obtained in...

  2. Modification of creep and low cycle fatigue behaviour induced by welding

    A. Carofalo

    2014-10-01

    Full Text Available In this work, the mechanical properties of Waspaloy superalloy have been evaluated in case of welded repaired material and compared to base material. Test program considered flat specimens on base and TIG welded material subjected to static, low-cycle fatigue and creep test at different temperatures. Results of uniaxial tensile tests showed that the presence of welded material in the gage length specimen does not have a relevant influence on yield strength and UTS. However, elongation at failure of TIG material was reduced with respect to the base material. Moreover, low-cycle fatigue properties have been determined carrying out tests at different temperature (room temperature RT and 538°C in both base and TIG welded material. Welded material showed an increase of the data scatter and lower fatigue strength, which was anyway not excessive in comparison with base material. During test, all the hysteresis cycles were recorded in order to evaluate the trend of elastic modulus and hysteresis area against the number of cycles. A clear correlation between hysteresis and fatigue life was found. Finally, creep test carried out on a limited number of specimens allowed establishing some changes about the creep rate and time to failure of base and welded material. TIG welded specimen showed a lower time to reach a fixed strain or failure when a low stress level is applied. In all cases, creep behaviour of welded material is characterized by the absence of the tertiary creep.

  3. Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure

    Xue-xia Xu; Yang Yu; Wen-long Cui; Bing-zhe Bai; Jia-lin Gu

    2009-01-01

    The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite (CFB/M) complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a fre-quency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 107 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fa-tigue cycle exceeds 107 , and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of "soft structure". It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fa-tigue mechanism was discussed and it is suggested that specific CFB/M complex microstrueture of the studied steel contributes to itssuperior properties.

  4. Fatigue

    ... enough sleep, good nutrition, or a low-stress environment, it should be evaluated by your doctor. ... relax. Try yoga or meditation. Maintain a reasonable work and ... or depression, treating it often helps the fatigue. Be aware ...

  5. Fatigue

    ... chemotherapy and radiation Recovering from major surgery Anxiety, stress, or depression Staying up too late Drinking too much alcohol or too many caffeinated drinks Pregnancy One disorder that causes extreme fatigue is chronic ...

  6. Effects of sodium on the low-cycle fatigue behavior of austenitic stainless steel

    Low-cycle fatigue data have been obtained on annealed Type 316 stainless steel specimens during exposure to well-characterized sodium. Instrumented sodium loops, in which the oxygen, carbon, and hydrogen concentrations in sodium are controlled and measured, provide the desired test environment. Two closed-loop servohydraulic testing machines have been used for the low-cycle fatigue tests, which have been conducted with axial stroke-control loading at a strain rate of approximately 4 x 10-3 sec-1. The fatigue life of annealed Type 316 stainless steel tested in sodium is substantially greater than that tested in air. The fatigue life of sodium-exposed stainless steel (1512 hr at 6000C) that resulted in surface carburization of the material has also been investigated. The applied stress range for the sodium-exposed specimens decreased by 15-20 percent relative to the annealed specimens. For total strain ranges below approximately 1 percent, the fatigue life was enhanced by the 1500-hr sodium exposure

  7. Low cycle fatigue analysis of a last stage steam turbine blade

    Měšťánek P.

    2008-11-01

    Full Text Available The present paper deals with the low cycle fatigue analysis of the low pressure (LP steam turbine blade. The blade is cyclically loaded by the centrifugal force because of the repeated startups of the turbine. The goal of the research is to develop a technique to assess fatigue life of the blade and to determine the number of startups to the crack initiation. Two approaches were employed. First approach is based on the elastic finite element analysis. Fictive 'elastic' results are recalculated using Neuber's rule and the equivalent energy method. Triaxial state of stress is reduced using von Mises theory. Strain amplitude is calculated employing the cyclic deformation curve. Second approach is based on elastic-plastic FE analysis. Strain amplitude is determined directly from the FE analysis by reducing the triaxial state of strain. Fatigue life was assessed using uniaxial damage parameters. Both approaches are compared and their applicability is discussed. Factors that can influence the fatigue life are introduced. Experimental low cycle fatigue testing is shortly described.

  8. Isothermal Low Cycle Fatigue of Uncoated and Coated Nickel-Base Superalloys

    High strength nickel-base superalloys have been used in turbine blades for many years because of their superior performance at high temperatures. However, the superalloys have limited oxidation and corrosion resistance and to solve this problem, protective coatings are deposited on the surface of the superalloys. The positive effect of coatings is based on protecting the surface zone in contact with hot gas atmosphere with elements like aluminium, chromium, which form a thermodynamically stable oxide layer that acts as a diffusion barrier to slow down the reaction between the substrate material and the aggressive environment. There are also other degradation mechanisms that affect nickel-base superalloys such as aging of microstructure, fatigue and creep. Long-term aging in metallic coating results in the changes of mechanical properties due to the significant interdiffusion of the main alloying elements between substrate and coatings. However, application of the coatings has mechanical side effects, the significance of which is not yet fully investigated. This work covers a study on the fatigue behaviour of a polycrystalline, IN792. and two single crystal nickel-base superalloys, CMSX-4 and SCB, coated with three different coatings. an overlay coating AMDRY997, a platinum aluminide modified diffusion coating RT22 and an innovative coating with an interdiffusion harrier of NiW called IC1, under low cycle fatigue loading conditions. Both low cycle fatigue properties, cyclic strain and stress response and fracture behaviour of the uncoated, coated and long-term aged coated specimens are presented. The main conclusions are that at 500 deg C the presence of the coatings have, in most cases, reduced the fatigue lives of the nickel-base substrates while at 900 deg C the coatings do improve the fatigue lives of the superalloys except RT22 coated on some superalloys and under certain test conditions. The reduction of the fatigue life at 500 deg C can be related to early

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

    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.

  10. Low cycle thermomechanical fatigue of reactor steels: Microstructural and fractographic investigations

    Fekete, Balazs, E-mail: fekete.mm.bme@gmail.com [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary); Department of Applied Mechanics, Budapest University of Technology and Economics, Muegyetem 5, Budapest H-1111 (Hungary); Kasl, Josef; Jandova, Dagmar [Výzkumný a zkušební ústav Plzeň s.r.o., Tylova 1581/46, 316 00 Plzen (Czech Republic); Jóni, Bertalan [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary); Eötvös Loránd University, Egyetem tér 1-3, Budapest H-1053 (Hungary); Misják, Fanni [Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege M. 29-33, Budapest H-1121 (Hungary); Trampus, Peter [College of Dunaujvaros, Tancsics 1A, Dunaujvaros H-2400 (Hungary)

    2015-07-29

    The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of a VVER-440 reactor pressure vessel were investigated under fully reversed total strain controlled low cycle fatigue tests. The measurements were carried out in isothermal conditions at 260 °C and with thermal-mechanical conditions in the range 150–270 °C using a GLEEBLE-3800 servo-hydraulic thermal-mechanical simulator. The low cycle fatigue results were evaluated with the Coffin–Manson law, and the parameters of the Ramberg–Osgood stress–strain relation were investigated. Fracture mechanics behavior was observed using scanning electron microscopic analysis of the crack shapes and fracture surfaces. Crack propagation was assessed in relation to the actual crack size and the loading level. Interrupted fatigue tests were also carried out to investigate the kinetics of the fatigue evolution of the materials. Microstructural evaluation of the samples was performed using light, scanning and transmission electron microscopy as well as X-ray diffraction, and measurement of dislocations was completed using TEM and XRD. The course of dislocation density in relation to cumulative usage factor was similar for both steels. However, the nature and distribution of dislocations were different in the individual steels and this resulted in different mechanical behaviors. The nature of the fracture surfaces of both steels appeared similar despite differences in dislocation arrangement. The distances between striation lines initially increased with increasing crack length and then became saturated. The low cycle fatigue behavior investigated can provide a reference for the remaining life assessment and lifetime extension analysis of nuclear power plant components.

  11. Monitoring fatigue loads on wind turbines using cycle counting data acquisition systems

    Soeker, H.; Seifert, H. [Deutsches Windenergie-Institut (Germany); Fragoulis, A.; Vionis, P.; Foussekis, D. [Center for Renewable Energy Sources (Greece); Dahlberg, J.A.; Poppen, M. [The Aeronautical Research Institue of Sweden (Sweden)

    1996-09-01

    As in any industrial application, the duration of a wind turbine`s life is a key parameter for the evaluation of its economic potential. Assuming a service life of 20 years, components of the turbine have to withstand a number of load cycles of up to 10{sup 8}. Such numbers of load cycles impose high demands on the fatigue characteristics of both, the used materials and the design. Nevertheless, fatigue loading of wind turbine components still remains a parameter of high uncertainty in the design of wind turbines. The specific features of these fatigue loads can be expected to vary with the type of turbine and the site of operation. In order to ensure the reliability of the next generation of larger scale wind turbines improved load assumptions will be of vital importance. Within the scope of the presented research program DEWI, C.R.E.S. and FFA monitored fatigue loads of serial produced wind turbines by means of a monitoring method that uses on-line cycle counting techniques. The blade root bending moments of two pitch controlled, variable speed wind turbines operating in the Hamswehrum wind farm, and also that of a stall controlled, fixed speed wind turbine operating in CRES` complex terrain test site, were measured by DEWI and CRES. In parallel FFA used their database of time series measurements of blade root bending moments on a stall controlled, fixed speed turbine at Alsvik Windfarm in order to derive semi-empirical fatigue load data. The experience gained from application of the on-line measurement technique is discussed with respect to performance, data quality, reliability and cost effectiveness. Investigations on the effects of wind farm and complex terrain operation on the fatigue loads of wind turbine rotor blades are presented. (au)

  12. Low cycle thermomechanical fatigue of reactor steels: Microstructural and fractographic investigations

    The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of a VVER-440 reactor pressure vessel were investigated under fully reversed total strain controlled low cycle fatigue tests. The measurements were carried out in isothermal conditions at 260 °C and with thermal-mechanical conditions in the range 150–270 °C using a GLEEBLE-3800 servo-hydraulic thermal-mechanical simulator. The low cycle fatigue results were evaluated with the Coffin–Manson law, and the parameters of the Ramberg–Osgood stress–strain relation were investigated. Fracture mechanics behavior was observed using scanning electron microscopic analysis of the crack shapes and fracture surfaces. Crack propagation was assessed in relation to the actual crack size and the loading level. Interrupted fatigue tests were also carried out to investigate the kinetics of the fatigue evolution of the materials. Microstructural evaluation of the samples was performed using light, scanning and transmission electron microscopy as well as X-ray diffraction, and measurement of dislocations was completed using TEM and XRD. The course of dislocation density in relation to cumulative usage factor was similar for both steels. However, the nature and distribution of dislocations were different in the individual steels and this resulted in different mechanical behaviors. The nature of the fracture surfaces of both steels appeared similar despite differences in dislocation arrangement. The distances between striation lines initially increased with increasing crack length and then became saturated. The low cycle fatigue behavior investigated can provide a reference for the remaining life assessment and lifetime extension analysis of nuclear power plant components

  13. Dwell effect on low cycle fatigue behaviour of cast superalloy Inconel 792-5A at 800 °C

    Šmíd, Miroslav; Obrtlík, Karel; Polák, Jaroslav

    Berlín: DMV, 2013, s. 113-118. ISBN 978-3-9814516-2-7. [LCF7 - International Conference on Low Cycle Fatigue /7./. Aachen (DE), 09.09.2013-11.09.2013] R&D Projects: GA ČR(CZ) GAP204/11/1453; GA ČR(CZ) GAP107/11/2065; GA MPO FR-TI4/030 Institutional support: RVO:68081723 Keywords : nickel base superalloy * low cycle fatigue * dwell * high temperature fatigue * surface relief * dislocation structure Subject RIV: JL - Materials Fatigue, Friction Mechanics

  14. Model-experiment dialog in low cycle fatigue of stainless steels

    In this HDR report (accreditation to supervise research), the author first proposes a synthesis of her research activities in the study of the mechanical behaviour in low cycle fatigue (cyclic hardening, plasticity surfaces), of modelling of the fatigue mechanical behaviour (phenomenological modelling, modelling with scale change), of progressive deformation (experimental analysis, analysis and simulation of plasticity at the microstructure scale). The second part addresses other activities in the field of research (behaviour and damage characterization of an austenitic-ferritic stainless steel), publication and education supervising, teaching

  15. Coupling damage and reliability model of low-cycle fatigue and high energy impact based on the local stress–strain approach

    Chen Hongxia; Chen Yunxia; Yang Zhou

    2014-01-01

    Fatigue induced products generally bear fatigue loads accompanied by impact processes, which reduces their reliable life rapidly. This paper introduces a reliability assessment model based on a local stress–strain approach considering both low-cycle fatigue and high energy impact loads. Two coupling relationships between fatigue and impact are given with effects of an impact process on fatigue damage and effects of fatigue damage on impact performance. The analysis of the former modifies the ...

  16. Estimation of low cycle fatigue life of elbows considering bi-axial stress effect

    Elbow pipes are commonly used in the piping systems of power plants and chemical plants. The stress states at elbow part are complex and quite different from those of the straight pipes. It is well known that the fatigue lives of metals under simple push-pull conditions were successfully predicted by the Manson's universal slope method. However, it have been pointed out by the several researchers that the low cycle fatigue lives of elbows under combined cyclic bending and inner pressure could not be predicted by the Manson's universal slope method. However, the reasons for this are not made clear. In this work, the low cycle fatigue tests and the finite element analysis of elbows under cyclic bending and inner pressures were carried out. It was found that the bi-axial stress ratio, which is a ratio of hoop stress and axial stress, at elbows are quite high. Considering the bi-axial stress ratio, the revised Manson's universal slope method was proposed in this paper. It was shown that the low cycle fatigue lives of elbows under combined cyclic bending and inner pressure were predicted conservatively by the proposed method. (author)

  17. Analysis of methods for determining high cycle fatigue strength of a material with investigation of titanium-aluminum-vanadium gigacycle fatigue behavior

    Pollak, Randall D.

    Today, aerospace engineers still grapple with the qualitative and quantitative understanding of fatigue behavior in the design and testing of turbine-driven jet engines. The Department of Defense has taken a very active role in addressing this problem with the formation of the National High Cycle Fatigue Science & Technology Program in 1994. The primary goal of this program is to further the understanding of high cycle fatigue (HCF) behavior and develop methods in order to mitigate the negative impact of HCF on aerospace operations. This research supports this program by addressing the fatigue strength testing guidance currently provided by the DoD to engine manufacturers, with the primary goal to investigate current methods and recommend a test strategy to characterize the fatigue strength of a material at a specified number of cycles, such as the 109 design goal specified by MIL-HDBK-1783B, or range of cycles. The research utilized the benefits of numerical simulation to initially investigate the staircase method for use in fatigue strength testing. The staircase method is a commonly used fatigue strength test, but its ability to characterize fatigue strength variability is extremely suspect. A modified staircase approach was developed and shown to significantly reduce bias and scatter in estimates for fatigue strength variance. Experimental validation of this proposed test strategy was accomplished using a dual-phase Ti-6Al-4V alloy. The HCF behavior of a second material with a very different microstructure (beta annealed Ti-6Al-4V) was also investigated. The random fatigue limit (RFL) model, a recently developed analysis tool, was investigated to characterize stress-life behavior but found to have difficulty representing fatigue life curves with sharp transitions. Two alternative models (bilinear and hyperbolic) were developed based on maximum likelihood methods to better characterize the Ti-6Al-4V fatigue life behavior. These models provided a good fit to the

  18. Effects of Hydrogen Gas Environment on Fatigue Strength at 107 cycles in Plain Specimen of Type 316L Stainless Steel

    Kawamoto, Kyohei; Ochi, Kazuhiko; Oda, Yasuji; Noguchi, Hiroshi

    In order to clarify the hydrogen effect on the fatigue strength at 107 cycles in a plain specimen of type 316L austenitic stainless steel, rotating bending fatigue tests in laboratory air and plane bending fatigue tests in 1.0 MPa dry hydrogen gas and in air at 313 K were carried out. The main results obtained are as follows. The observed fatigue behavior showed that the fatigue strength at 107 cycles in both environments is determined by the non-propagation of a fatigue crack of the order of the grain size. Also, the strength at 107 cycles in hydrogen gas is slightly higher than that in air. In the region of high-cycle fatigue, the fatigue life in hydrogen gas is longer than that in air, which is mainly caused by the longer crack initiation life in hydrogen gas. The crack propagation life in hydrogen gas is shorter than that in air but has only a small ratio to the fatigue life in this region.

  19. Prediction of three-dimensional crack propagation paths taking high cycle fatigue into account

    Guido Dhondt

    2016-01-01

    Full Text Available Engine components are usually subject to complex loading patterns such as mixed-mode Low Cycle Fatigue Loading due to maneuvering. In practice, this LCF Loading has to be superimposed by High Cyclic Fatigue Loading caused by vibrations. The changes brought along by HCF are twofold: first, the vibrational cycles which are superposed on the LCF mission increase the maximum loading of the mission and may alter the principal stress planes. Secondly, the HCF cycles themselves have to be evaluated on their own, assuring that no crack propagation occurs. Indeed, the vibrational frequency is usually so high that propagation leads to immediate failure. In the present paper it is explained how these two effects can be taken care of in a standard LCF crack propagation procedure. The method is illustrated by applying the Finite Element based crack propagation software CRACKTRACER3D on an engine blade.

  20. Life estimation of low-cycle fatigue of pipe elbows. Proposed criteria of low-cycle fatigue life under the multi-axial stress field

    Pipe elbows were important parts frequently used in the pipelines of nuclear power, thermal power and chemical plants, and their integrity needed to be assured under seismic loads and thermal stresses considering local wall thinning or complex stress distribution due to special configuration different from straight pipe. This article investigated in details elastic-plastic stress-strain state of pipe elbow using finite element analysis and clarified there existed high bi-axial stress field at side inner surface of pipe elbow axial cracks initiated. Bi-axial stress factor was around 0.6 for sound elbow and up to 0.95 for local wall thinning at crown. Fracture strain of 1.15 was reduced to around 0.15 for bi-axial stress factor from 0.6 to 0.9. Normalized fatigue life for bi-axial stress field (0.6 - 0.8) was largely reduced to around 15, 19 and 10% of fatigue life of uni-axial state dependent on material strength level. Proposed revised universal slopes taking account of multi-axial stress factor could explain qualitatively effects of strain range, internal pressure and ratchet strain (pre-strain) on low-cycle fatigue life of pipe elbow. (T. Tanaka)

  1. Low cycle fatigue damage in nickel-base superalloy single crystals at elevated temperature

    Fleury, E. (Centre des Materiaux P.M. Fourt, Ecole des Mines, 91 Evry (France)); Remy, L. (Centre des Materiaux P.M. Fourt, Ecole des Mines, 91 Evry (France))

    1993-08-15

    Low cycle fatigue tests on AM1 nickel-base superalloy single crystals were conducted under axial strain control at 650, 950 and 1100 C. The behaviour of the 001 orientation was investigated at the three temperatures, that of the 111, 101 and 213 specimens was studied at the two lower temperatures. The orientation dependence of fatigue life-total strain range curves was mainly due to variations in Young's modulus with orientation. Most cracks grow in stage II mode whatever the temperature. Cracks nucleate at micropores and in the interior of specimens at low temperatures; surface cracks induced by oxidation are dominant at high temperatures and low strain ranges. Most of fatigue life is spent in microcrack growth. (orig.)

  2. Low-cycle fatigue properties of stainless steels and aluminum alloys at liquid helium temperature

    Axial-strain controlled fatigue tests of stainless steels (SUS 304 L, SUS 316 L and WM-X) and aluminum alloys (A 5083-O and A 5356) were conducted at 4 K with the strain rate of 0.4 %/s and the strain ratio of -1. The fatigue tests at 77 and 300 K were also conducted for comparison. The TIG weld metal of stainless steel (WM-X) showed cyclic strain-hardening at 4 and 77 K, and cyclic strain-softening at 300 K, although other materials showed cyclic strain-hardening at 4, 77 and 300 K. It seemed that the strain-induced martensitic transformation influenced the cyclic stress responce of stainless steel. In the fatigue life range of 1000 cycles or more, the fatigue resistance, that means the strain capability at given cycles of fatigue life, of SUS 304 L, SUS 316 L, WM-X and A 5083-O at 4 K were nearly equal to or a bit higher than that at 77 K. At 4 K, the fatigue resistance of SUS 316 L was higher than that of SUS 304 L, but lied in the middle of a scatter band by a factor of 2 among base metals of stainless steels in literatures. The fatigue resistance of A 5083-O was the lowest in a scatter band by a factor of 1.4 among base metals of aluminum alloys in literatures. At 4 K, the fatigue resistance of WM-X was almost equivalent to that of SUS 304 L and was lower than that of SUS 316 L by 20 %, being away below that of base metals of stainless steels at 300 K. However, the fatigue resistance of the MIG weld metal of aluminum alloy (A 5356) was lower than that of A 5083-O by 45 %, being closer to that of base metals of aluminum alloy at 300 K. One must be careful to use the weld metal A 5356 at 4 K. (author)

  3. Energy Approach-Based Simulation of Structural Materials High-Cycle Fatigue

    Balayev, A. F.; Korolev, A. V.; Kochetkov, A. V.; Sklyarova, A. I.; Zakharov, O. V.

    2016-02-01

    The paper describes the mechanism of micro-cracks development in solid structural materials based on the theory of brittle fracture. A probability function of material cracks energy distribution is obtained using a probabilistic approach. The paper states energy conditions for cracks growth at material high-cycle loading. A formula allowing to calculate the amount of energy absorbed during the cracks growth is given. The paper proposes a high- cycle fatigue evaluation criterion allowing to determine the maximum permissible number of solid body loading cycles, at which micro-cracks start growing rapidly up to destruction.

  4. Cycle-Dependent Matrix Remodeling Gene Expression Response in Fatigue-Loaded Rat Patellar Tendons

    Hui B. Sun; Andarawis-Puri, Nelly; Li, Yonghui; Fung, David T.; Jonathan Y. Lee; Wang, Vincent M.; Basta-Pljakic, Jelena; Leong, Daniel J.; Sereysky, Jedd B.; Ros, Stephen J.; Klug, Raymond A.; Braman, Jonathan; Schaffler, Mitch B.; Jepsen, Karl J.; Flatow, Evan L.

    2010-01-01

    Expression profiling of selected matrix remodeling genes was conducted to evaluate differences in molecular response to low-cycle (100) and high-cycle (7,200) sub-failure-fatigue loading of patellar tendons. Using our previously developed in vivo patellar tendon model, tendons were loaded for 100 or 7,200 cycles and expression of selected metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), and collagens were quantified by real-time RT-PCR at 1- and 7-day post-loading. ...

  5. Influence of subsolvus thermomechanical processing on the low-cycle fatigue properties of haynes 230 alloy

    Vecchio, Kenneth S.; Fitzpatrick, Michael D.; Klarstrom, Dwaine

    1995-03-01

    Strain-controlled low-cycle fatigue tests have been conducted in air at elevated temperature to determine the influence of subsolvus thermomechanical processing on the low-cycle fatigue (LCF) behavior of HAYNES 230 alloy. A series of tests at various strain ranges was conducted on material experimentally processed at 1121 °C, which is below the M23C6 carbide solvus temperature, and on material fully solution annealed at 1232 °C. A comparative strain-life analysis was performed on the LCF results, and the cyclic hardening/softening characteristics were examined. At 760 °C and 871 °C, the fatigue life of the experimental 230/1121 material was improved relative to the standard 230/1232 material up to a factor of 3. The fatigue life advantage of the experimental material was related primarily to a lower plastic (inelastic) strain amplitude response for a given imposed total strain range. It appears the increase in monotonic flow stress exhibited by the finer grain size experimental material has been translated into an increase in cyclic flow stress at the 760 °C and 871 °C test temperatures. Both materials exhibited entirely transgranular fatigue crack initiation and propagation modes at these temperatures. The LCF performance of the experimental material in tests performed at 982 °C was improved relative to the standard material up to a factor as high as 2. The life advantage of the 230/1121 material occurred despite having a larger plastic strain amplitude than the standard 230/1232 material for a given total strain range. Though not fully understood at present, it is suspected that this behavior is related to the deleterious influence of grain boundaries in the fatigue crack initiations of the standard processed material relative to the experimental material, and ultimately to differences in carbide morphology as a result of thermomechanical processing.

  6. Influence of niobium alloying on the low cycle fatigue of cast TiAl alloys at room and high temperatures

    Kruml, Tomáš; Petrenec, Martin; Obrtlík, Karel; Polák, Jaroslav; Buček, Petr

    2010-01-01

    Roč. 2, č. 1 (2010), s. 2297-2305. ISSN 1877-7058. [Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GA106/08/1631; GA ČR GA106/07/0762 Institutional research plan: CEZ:AV0Z20410507 Keywords : Low cycle fatigue * lamellar TiAl alloy * fracture surface Subject RIV: JL - Materials Fatigue, Friction Mechanics

  7. Crack propagation mechanism and life prediction for very-high-cycle fatigue of a structural steel in different environmental medias

    Guian Qian; Chengen Zhou; Youshi Hong

    2013-01-01

    The influence of environmental medias on crack propagation of a structural steel at high and very-high-cycle fatigue (VHCF) regimes is investigated based on the fatigue tests performed in air, water and 3.5% NaCl aqueous solution. Crack propagation mechanisms due to different crack driving forces are investigated in terms of fracture mechanics. A model is proposed to study the relationship between fatigue life, applied stress and material property in different environmental medias, which refl...

  8. Electrostimulation of defect structure and phase composition of 18Cr-10Ni steel under low cycle fatigue tests

    The change of structure and phase composition of austenitic steel Kh18N10T subjected to low cyclic fatigue test under electric current impulses action are studied. It is shown that the electrostimulation slows down a dislocation substructure evolution. The result is a sharp decreasing a density of sites of microcrack formation, significant plastification of steel under fatigue loading and shift of fatigue curve to a large number of loading cycles

  9. The structure of austenitic steel AISI 316 after ECAP and low-cycle fatigue

    L. Kander

    2008-06-01

    Full Text Available Purpose: The article presents results of investigation of structure and properties of austenitic steel grade AISI 316 after application of Equal Channel Angular Pressing (ECAP at the temperature of approx. 290ºC.Design/methodology/approach: The ECAP method led to significant improvement of strength of investigated material. Experiments were planned and realised at the temperature ranging from room temperature up to above mentioned temperature.Findings: It was established with use of the EBSD technique that after 8 passes through the ECAP die the sub-grains with an angle of disorientation smaller than 10º formed less than 20% of resulting structure. Average size of austenitic grains with high angle boundary after 8 passes was approx. 0.32 µm. It was proven that the ECAP method enables obtaining of ultra fine-grained austenitic structure formed by recrystallised grains with very low density of dislocations.Practical implications: The Technology ECAP was applied on austenitic steel AISI 316. It was verification of ECAP application possibility on steel AISI 316 importantly for following applying on similar kinds of steel, because ECAP technology influence on fatigue properties was confirmed.Originality/value: It can be predicted on the basis of obtained results that, contrary to low-cycle fatigue the ultra-fine grained material will manifest at fatigue load in the mode of constant amplitude of stress higher fatigue characteristics, particularly fatigue limit.

  10. Low cycle fatigue failure propensity of WWER fuel rod under load following operation

    The evaluation of published results on fatigue properties of Zr-alloys leads to a Coffin-Manson relation, which is considered to describe the tolerable plastic strain range within the limit of low cycle fatigue of ZrNb-1 cladding with an accuracy corresponding to a factor of less than 2. WWER fuel rods were analysed by means of the one-dimensional, integral fuel rod performance modelling code STOFFEL-1. Stresses and strains of the cladding were calculated in dependence on a number of power ramps and power cycles with periods of one week and one day, respectively, and for various linear heat generation rates. The calculated permanent tangential strains at the inner surface of the cladding are assumed to represent the plastic strain range independently of their origin. This plastic strain range is used to estimate the number of cycles to failure according to the deduced Coffin-Manson relation. It follows that the contribution of pure low cycle fatigue under load following operation to the damage of fuel rod cladding is not critical. (author)

  11. Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480

    Majumdar, S.; Antolovich, S. D.; Milligan, W. W.

    1985-01-01

    PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

  12. Fatigue crack initiation and propagation in stainless steels subjected to thermal cycling conditions

    The thermal fatigue crack initiation and propagation promoted by thermal quenches of AISI 316 and 304 stainless steels have been studied to correlate with their known behaviour in isothermal strain cycling fatigue at elevated temperatures. Axially unconstrained specimens of rectangular section were held at bulk temperatures of 250-5000C and symmetrically water-quenched on the narrow faces to give equivalent surface strain ranges from 2.8 x 10-3 to 5.4 x 10-3. Crack initiation in smooth samples showed an apparent threshold at a surface strain range of 2.8 x 10-3 equivalent to a thermal amplitude of 1500C, no cracking being produced in 500000 cycles. The crack growth in prenotched samples was evaluated by direct observation and by subsequent fractography and showed two modes of growth. The crack growth was strain-controlled during the early stages of propagation where the crack tip was within the surface zone under conditions of fully plastic cyclic yield. At greater depths the propagation rates in the remaining elastically cycled material were found to correlate with calculated stress intensity values. In the chosen symmetrically quenched axially unconstrained configuration the crack growth rates decreased towards the centre of the specimen, indicating a crack arrest condition as expected from analysis. The results indicated a good correlation with the fracture behaviour observed from isothermal strain cycling fatigue behaviour in an air environment. (author)

  13. The Rehbinder effect in iron during giga-cycle fatigue loading

    Bannikov, M. V., E-mail: mbannikov@icmm.ru; Naimark, O. B. [Institute of Continuous Media Mechanics UrB RAS, Perm, 614013 (Russian Federation)

    2015-10-27

    The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.

  14. Integrating water flow, locomotor performance and respiration of Chinese sturgeon during multiple fatigue-recovery cycles.

    Lu Cai

    Full Text Available The objective of this study is to provide information on metabolic changes occurring in Chinese sturgeon (an ecologically important endangered fish subjected to repeated cycles of fatigue and recovery and the effect on swimming capability. Fatigue-recovery cycles likely occur when fish are moving through the fishways of large dams and the results of this investigation are important for fishway design and conservation of wild Chinese sturgeon populations. A series of four stepped velocity tests were carried out successively in a Steffensen-type swimming respirometer and the effects of repeated fatigue-recovery on swimming capability and metabolism were measured. Significant results include: (1 critical swimming speed decreased from 4.34 bl/s to 2.98 bl/s; (2 active oxygen consumption (i.e. the difference between total oxygen consumption and routine oxygen consumption decreased from 1175 mgO2/kg to 341 mgO2/kg and was the primary reason for the decrease in Ucrit; (3 excess post-exercise oxygen consumption decreased from 36 mgO2/kg to 22 mgO2/kg; (4 with repeated step tests, white muscle (anaerobic metabolism began contributing to propulsion at lower swimming speeds. Therefore, Chinese sturgeon conserve energy by swimming efficiently and have high fatigue recovery capability. These results contribute to our understanding of the physiology of the Chinese sturgeon and support the conservation efforts of wild populations of this important species.

  15. Crack mode and life of Ti-6Al-4V under multiaxial low cycle fatigue

    Takamoto Itoh

    2015-10-01

    Full Text Available This paper studies multiaxial low cycle fatigue crack mode and failure life of Ti-6Al-4V. Stress controlled fatigue tests were carried out using a hollow cylinder specimen under multiaxial loadings of λ=0, 0.4, 0.5 and 1 of which stress ratio R=0 at room temperature. λ is a principal stress ratio and is defined as λ=II/I, where I and II are principal stresses of which absolute values take the largest and middle ones, respectively. Here, the test at λ=0 is a uniaxial loading test and that at λ=1 an equi-biaxial loading test. A testing machine employed is a newly developed multiaxial fatigue testing machine which can apply push-pull and reversed torsion loadings with inner pressure onto the hollow cylinder specimen. Based on the obtained results, this study discusses evaluation of the biaxial low cycle fatigue life and crack mode. Failure life is reduced with increasing λ induced by cyclic ratcheting. The crack mode is affected by the surface condition of cut-machining and the failure life depends on the crack mode in the multiaxial loading largely.

  16. Surface-finish effects on the high-cycle fatigue of Alloy 718

    Alloy 718 us a precipitation-hardening nickel-base superalloy that is being specified for various components for liquid-meal fast breeder reactors (LMFBRs). This alloy maintains high strength at elevated temperatures making it a desirable structural material. But the property that justifies most LMFBR applications is the alloy's resistance to thermal striping damage due to its high fatigue endurance strength. Thermal striping is a high-cycle fatigue phenomenon caused by thermal stresses from the fluctuating mixing action of sodium streams of differing temperatures impinging on the metal surfaces. Most of the design data is generated from laboratory fatigue specimens with carefully controlled surface finishes prepared with a low-stress grind and buffed to a surface finish 8--12 in. Since Alloy 718 has been shown to be quite notch sensitive under cyclic loading, the detrimental effect on the high-cycle fatigue properties caused by shop surface finishes of actual components has been questioned. This report examines some of the surface finishes that could be produced in a commercial shop on an actual component

  17. The Rehbinder effect in iron during giga-cycle fatigue loading

    Bannikov, M. V.; Naimark, O. B.

    2015-10-01

    The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant.

  18. The Rehbinder effect in iron during giga-cycle fatigue loading

    The influence of the adsorptive strength reduction effect (the Rehbinder effect) on the fatigue life of pure iron under the giga-cycle loading regime was investigated. Specimens were loaded by an ultrasonic testing machine with a frequency of 20 kHz in air and in contact with eutectic alloy of gallium with tin and indium. A significant (by several orders of magnitude) worsening of the life-time of iron in contact with a molten metal as compared with tests in air was established. The liquid metal penetrates into the material to a depth of 200 μm to the center of a fatigue crack. The mechanism of the fatigue crack initiation in the giga-cycle regime of loading in contact with a surfactant is differing: the crack is formed on the surface of the specimen rather than within it as is the case for air. Based on the electron and optical microscopy data for the fracture surface, it can be concluded that exactly the change in the crack initiation mechanism reduces the fatigue life of iron in contact with a liquid metal because the initiated crack propagates regardless of the surfactant

  19. Fatigue

    ... organs. Your body also changes the way it processes foods and nutrients. All of these changes are stressful for your body and may lead to fatigue. Physical and psychological changes during pregnancy can also cause mental and emotional stress. This stress can add to your feelings ...

  20. Experimental study on properties of high cycle thermal fatigue. Outline and test plan of high cycle fatigue test equipment on sodium

    At a nuclear power plant, where fluids of high and low temperature flow into each other, it is necessary to prevent structural failure damage caused by high cycle thermal fatigue (thermal striping phenomenon). High cycle fatigue test equipment on thermal can be develop by modifying the thermal transient test facility for structure (TTS) in order to clarify the effect of temperature fluctuation induced by the thermal striping phenomenon on crack initiation and their propagation behavior. The test equipment has the following characteristic. (1) Fluid is controlled by a circulation pump, and by continuously changing the flow quantity ratio of high and low temperature Sodium, sinusoidal temperature fluctuations at various period of the test samples can be taken. (2) Mixing is done by the jet flow mix, thus it can generate axisymmetric temperature fluctuations by accelerating the mixing process of high and low temperature Sodium. (3) It can also control the temperature fluctuation, in which short and long term changes are superimposed. (4) Because the test sample cylinder is hollow, analysis of thermal stress and data from crack initiation to crack propagation can easily be obtained. Sinusoidal temperature fluctuations, random temperature fluctuations, and strength testing of the weld zone by test samples made of stainless steel are planned in the next stage. (author)

  1. Low cycle fatigue of mechanically heterogeneous welded joints

    A consideration is given to welded joints made of two dissimilar materials, namely, a material M of lesser strength and a material T of higher strength. It is shown that in near the contact mild - hard material zones under elastic - plastic deformation of the material M a triaxial stress state is realized as the strains are distributed irregularly. An increase in the rigidity of stress state results in a decrease of plasticity and durability of M material. Mild interlayers have a stronger effect on the strength of welded joint, especially, when low cycle loading. In mechanically nonuniform welded joints with V- and X- shaped welds in the most loaded zones the intensity of strains increases with a decrease of relative thickness of a root of penetration α0 for a mild weld, and with an increase of 2α angle for a hard material. Then, it is not recommended to take α048 grad

  2. Thermal High- and Low-Cycle Fatigue Behavior of Thick Thermal Barrier Coating Systems

    Miller, Robert A.

    1998-01-01

    Ceramic thermal barrier coatings have received increasing attention for advanced gas turbine and diesel engine applications because of their ability to provide thermal insulation to engine components. However, the durability of these coatings under the severe thermal cycling conditions encountered in a diesel engine (ref. 1) still remains a major issue. In this research at the NASA Lewis Research Center, a high-power laser was used to investigate the thermal fatigue behavior of a yttria-stabilized zirconia coating system under simulated diesel engine conditions. The mechanisms of fatigue crack initiation and propagation, and of coating failure under complex thermal low-cycle fatigue (LCF, representing stop/start cycles) and thermal high-cycle fatigue (HCF, representing operation at 1300 rpm) are described. Continuous wave and pulse laser modes were used to simulate pure LCF and combined LCF/HCF, respectively (ref. 2). The LCF mechanism was found to be closely related to the coating sintering and creep at high temperatures. These creep strains in the ceramic coating led to a tensile stress state during cooling, thus providing the major driving force for crack growth under LCF conditions. The combined LCF/HCF tests induced more severe coating surface cracking, microspallation, and accelerated crack growth than did the pure LCF test. HCF thermal loads also facilitated lateral crack branching and ceramic/bond coat interface delaminations. HCF is associated with the cyclic stresses originating from the high-frequency temperature fluctuation at the ceramic coating surface. The HCF thermal loads act on the crack by a wedging mechanism (ref. 1), resulting in continuous crack growth at temperature. The HCF stress intensity factor amplitude increases with the interaction depth and temperature swing, and decreases with the crack depth. HCF damage also increases with the thermal expansion coefficient and the Young's modulus of the ceramic coating (refs. 1 and 3).

  3. Generalization of low-cycle fatigue characteristics of R2MA rotor steel

    Generalized data are presented on low-cycle fatigue of the R2MA steel used for production of rotors of high-power steam turbines. A statistical method has been used due to a wide natural spread in the strength and deformation properties of steels under investigations in order to obtain the generalized deformation characteristics. A zeneral-purpose curve of cyclic deformation for the R2MA steel is given

  4. Experimental investigation of high cycle thermal fatigue in a T-junction piping system

    Selvam, P. Karthick; Kulenovic, Rudi; Laurien, Eckart [Stuttgart Univ. (Germany). Inst. of Nuclear Technology and Energy Systems (IKE)

    2015-10-15

    High cycle thermal fatigue damage of structure in the vicinity of T-junction piping systems in nuclear power plants is of importance. Mixing of coolant streams at significant temperature differences causes thermal fluctuations near piping wall leading to gradual thermal degradation. Flow mixing in a T-junction is performed. The determined factors result in bending stresses being imposed on the piping system ('Banana effect').

  5. Modification of creep and low cycle fatigue behaviour induced by welding

    A. Carofalo; V. Dattoma; R. Nobile; F.W. Panella; G. Alfeo; A. Scialpi; G.P. Zanon

    2014-01-01

    In this work, the mechanical properties of Waspaloy superalloy have been evaluated in case of welded repaired material and compared to base material. Test program considered flat specimens on base and TIG welded material subjected to static, low-cycle fatigue and creep test at different temperatures. Results of uniaxial tensile tests showed that the presence of welded material in the gage length specimen does not have a relevant influence on yield strength and UTS. However, elonga...

  6. Low-cycle-fatigue behavior of copper materials and their use in synchrotron beamline components

    The third generation synchrotron facilities such as the 7-GeV Advanced Photon Source Project (APS) generate x-ray beams with very high heat loads and heat flux levels. The front-end and beamline components are required to sustain total heat loads of 5 to 15 kW and heat flux levels exceeding 400 W/mm2. Grazing geometry and enhanced heat transfer techniques are used in the design of such components to reduce heat flux levels below the 30 W/mm2 level, which is sustainable by the special copper materials routinely used in the component design. Although the resulting maximum surface temperatures can be sustained, the structural stresses and the fatigue issues remain viable concerns for the copper, particularly under brazing or bonding of the parts. Brazing and bonding are almost always utilized in the design of the components, and the drastically lowered yield stress of the annealed copper subjected to bonding temperatures above 400 degree C is a real concern. Such materials with reduced post-bonding stress levels easily reach yield point under thermal stresses during ordinary use on the beamline. The resulting plastic deformation in each load cycle may cause low-cycle-fatigue problems. The two common copper materials are OFHC and Glidcop. This paper critically reviews the available literature for low-cycle-fatigue properties, of OFHC at the elevated temperatures typically found in synchrotron operations

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

    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)

  8. Experimental study on properties of high cycle thermal fatigue. 3. Results of sinusoidal temperature fluctuation test at 20 second cycle

    In a nuclear power plant, it is necessary to be attentive to fatigue fracture of the structural material caused by cyclic thermal stress due to the mixing of temperature different fluids. The purpose of this study is to obtain data to demonstrate high cycle thermal fatigue evaluation methods by applying the effects of the frequency of temperature fluctuation. A sinusoidal temperature fluctuation test of with a 20 second period was conducted using high cycle fatigue test equipment (SPECTRA). A SUS304 steel pipe was used as the test sample, at an average sodium temperature of 425 deg C, fluctuation amplitude of 200 deg C and a sodium flow rate of 300 l/min in the test pipe. The results obtained are as follows: (1) Valid strength data to verify evaluation methods could be obtained by applying a 20 second cycle temperature fluctuation to the test sample with SPECTRA. A Crack penetrated at about 157,150 cycles. (2) Numerous cracks in an axial direction were observed on the inner surface of the test sample in the upper flow area. An air fatigue test demonstrated the difference in the strength of the test sample between axial direction and circumferential direction, revealing that cracks were distributed in an axial direction since anisotropic influences easily appear on the high cycle side. (3) An approximated curve obtained by the common relation of crack and axial direction distance indicates that the boundary of a crack would be located about 430 mm downstream from the tapered end of the test sample with the upper flow. (4) Crack occurring on the inner surface progressed to a depth of 1 to 2 mm in the crystal grain, then progressed along the crystal grain boundary. Striations were formed on areas of the fracture surface in the grain, but were not found on the fracture surface of the grain boundary. Sinusoidal temperature fluctuation tests at the periods of 2, 5, 10, and 40 seconds are planned to confirm the influence of fluctuation frequency responsiveness on

  9. Diametral low-cycle fatigue testing. A comparison of first experimental results from diametral low-cycle fatigue tests with results from axial tests

    The first experimental results of diametral low-cycle fatigue tests on DIN 1.4948 (similar to AISI type 304) at 823 K are reported. The cyclic hardening behaviour of diametral tests and axial tests only differs for the first (ten) cycles. Due to progressive strain hardening this difference reduces at increasing number of cycles. The cyclic stresses of diametral and axial tests are equal after cyclic hardening to values of about twice the 0.2 yield stress or higher. At low strain ranges (Δepsilonsub(t) < 1.0%) the number of cycles to failure (Nsub(f)) of diametral tests on hour-glass specimens do not differ from those of axial tests on the uniform gauge length type (GRIM) specimen. At high strain ranges (Δepsilonsub(t) < 1.0%) Nsub(f)-values of diametral tests are higher. This is attributed to the hour-glass shape of the specimen which allows high compressive stresses without buckling. (Auth.)

  10. Resistance to fatigue and prediction of lifetime of wire tendons cast into concrete up to 10^8 cycles

    Heinrich, Jens; Heeke, Guido; Maurer, Reinhard; Müller, Christine H.

    2016-01-01

    Usually for verification of compliance, the fatigue resistance of prestressing steel is determined from tests of naked specimens at 2 million cycles. However, for design the fatigue resistance of tendons cast into concrete, is substantially lower. To verify the resistance of existing older prestressed concrete bridges and for the design of new bridges, S-N curves of prestressing steel in curved steel ducts embedded into concrete are needed. In bridges, the load cycles due to heavy...

  11. Leg joint power output during progressive resistance FES-LCE cycling in SCI subjects: developing an index of fatigue

    Faghri Pouran D; Haapala Stephenie A; Adams Douglas J

    2008-01-01

    Abstract Background The purpose of this study was to investigate the biomechanics of the hip, knee and ankle during a progressive resistance cycling protocol in an effort to detect and measure the presence of muscle fatigue. It was hypothesized that knee power output can be used as an indicator of fatigue in order to assess the cycling performance of SCI subjects. Methods Six spinal cord injured subjects (2 incomplete, 4 complete) between the ages of twenty and fifty years old and possessing ...

  12. The role of the microstructure and defects on crack initiation in 316L stainless steel under multiaxial high cycle fatigue

    GUERCHAIS, Raphaël; Morel, Franck; Saintier, Nicolas

    2014-01-01

    The aim of this study is to analyse the influence of both the microstructure and defects on the high cycle fatigue behaviour of the 316L austenitic stainless steel, using finite element simulations of polycrystalline aggregates. High cycle fatigue tests have been conducted on this steel under uniaxial (push-pull) and multiaxial (combined in-phase tension and torsion) loading conditions, with both smooth specimens and specimens containing artificial semi-spherical surface defects. 2D numerical...

  13. High cycle fatigue of a die cast AZ91E-T4 magnesium alloy

    This study reveals the micro-mechanisms of fatigue crack nucleation and growth in a commercial high-pressure die cast automotive AZ91E-T4 Mg component. Mechanical fatigue tests were conducted under R=-1 conditions on specimens machined at different locations in the casting at total strain amplitudes ranging from 0.02% to 0.5%. Fracture surfaces of specimens that failed in the high cycle fatigue regime with lives spanning two orders of magnitude were examined using a scanning electron microscope. The difference in lives for the Mg specimens was primarily attributed to a drastic difference in nucleation site sizes, which ranged from several hundred μm's to several mm's. A secondary effect may include the influence of average secondary dendrite arm spacing and average grain size. At low crack tip driving forces (Kmaxmax>3.5 MPa √ m fractured particles and boundary decohesion created weak paths for fatigue crack propagation, and consequently the cracks followed the interdendritic regions, leaving serrated markings as the crack progressed through this heterogeneous region. The ramifications of the results on future modeling efforts are discussed in detail

  14. Low cycle fatigue of steels for nuclear pressure vessels in hot water (ASTM-508 Cl 3)

    Low cycle fatigue analysis is a very important problem in structural mechanics, especially for nuclear pressure vessels. The design procedure is based on the knowledge of the experimental results on test specimen. The design curves are based on tests in air at room temperature. But the fatigue behavior may be affected by hot water environment when light water reactors are concerned. A general program on low cycle fatigue in hot water is in progress at Saclay in order to assess the conservatism of design fatigue curves. In order to keep control of water chemistry, the test rig is connected with the Primeau loop and therefore a constant flow of water is get through the specimens. Tested samples are small strips of rectangular cross section (2x10x61 mm). They are loaded in circular bending with controlled deflection. Practically they are placed between four supports, two moving and two fixed. The water temperature is kept near 2650C while the oxygen and hydrogen contents and the pH are monitored. A frequency as low as 0.1 cpm has been choosed in order to take into account time effects. Calibration tests in air at room temperature are also made with the same type of device. The steel is the french steel for light water reactor vessels, its specification is roughly according with the specification ASTM 508 (Cl 3), but with special requirements. For these tests results, the best fit curve can be written: epsilon a=5.6Nsup(-0.30) with epsilon a=strain amplitude, N=number of cycles at failure. There is no noticeable difference between hot water test results and air-room temperature results

  15. A Comparative Evaluation of the Effect of Low Cycle Fatigue and Creep-Fatigue Interaction on Surface Morphology and Tensile Properties of 316L(N) Stainless Steel

    Mariappan, K.; Shankar, Vani; Sandhya, R.; Bhaduri, A. K.; Laha, Kinkar

    2016-04-01

    In the present work, the deformation and damage evolution in 316L(N) stainless steel during low cycle fatigue (LCF) and creep-fatigue interaction (CFI) loadings have been compared by evaluating the residual tensile properties. Towards this, LCF and CFI experiments were carried out at constant strain amplitude of ±0.6 pct, strain rate of 3 × 10-3 s-1 and temperature of 873 K (600 °C). During CFI tests, 30 minutes hold period was introduced at peak tensile strain. Experiments were interrupted up to various levels of fatigue life viz. 5, 10, 30, 50, and 60 pct of the total fatigue life ( N f) under both LCF and CFI conditions. The specimens subjected to interrupted fatigue loadings were subsequently monotonically strained at the same strain rate and temperature up to fracture. Optical and scanning electron microscopy and profilometry were conducted on the untested and tested samples to elucidate the damage evolution during the fatigue cycling under both LCF and CFI conditions. The yield strength (YS) increased sharply with the progress of fatigue damage and attained saturation within 10 pct of N f under LCF condition. On the contrary, under CFI loading condition, the YS continuously increased up to 50 pct of N f, with a sharp increase of YS up to 5 pct of N f followed by a more gradual increase up to 50 pct of N f. The difference in the evolution of remnant tensile properties was correlated with the synergistic effects of the underlying deformation and damage processes such as cyclic hardening/softening, oxidation, and creep. The evolution of tensile properties with prior fatigue damage has been correlated with the change in surface roughness and other surface features estimated by surface replica technique and fractography.

  16. Impact of choice of stabilized hysteresis loop on the end result of investigation of high-strength low-alloy (HSLA steel on low cycle fatigue

    S. Bulatović

    2014-10-01

    Full Text Available High strength low-alloy steel under low cycle fatigue at a certain level of strain controlled achieve stabilized condition. During the fatigue loading stabilized hysteresis loop is determined, which typical cycle of stabilization is calculated as half number of cycles to failure. Stabilized hysteresis loop is a representative of all hysteresis and it’s used to determine all of the parameters for the assessment of low cycle fatigue. This paper shows comparison of complete strain-life curves of low cycle fatigue for two chosen stabilized hysteresis loop cycles of base metal HSLA steel marked as Nionikral 70.

  17. Dwell Notch Low Cycle Fatigue Behavior of a Powder Metallurgy Nickel Disk Alloy

    Telesman, J.; Gabb, T. P.; Yamada, Y.; Ghosn, L. J.; Jayaraman, N.

    2012-01-01

    A study was conducted to determine the processes which govern dwell notch low cycle fatigue (NLCF) behavior of a powder metallurgy (P/M) ME3 disk superalloy. The emphasis was placed on the environmentally driven mechanisms which may embrittle the highly stressed notch surface regions and reduce NLCF life. In conjunction with the environmentally driven notch surface degradation processes, the visco-plastic driven mechanisms which can significantly change the notch root stresses were also considered. Dwell notch low cycle fatigue testing was performed in air and vacuum on a ME3 P/M disk alloy specimens heat treated using either a fast or a slow cooling rate from the solutioning treatment. It was shown that dwells at the minimum stress typically produced a greater life debit than the dwells applied at the maximum stress, especially for the slow cooled heat treatment. Two different environmentally driven failure mechanisms were identified as the root cause of early crack initiation in the min dwell tests. Both of these failure mechanisms produced mostly a transgranular crack initiation failure mode and yet still resulted in low NLCF fatigue lives. The lack of stress relaxation during the min dwell tests produced higher notch root stresses which caused early crack initiation and premature failure when combined with the environmentally driven surface degradation mechanisms. The importance of environmental degradation mechanisms was further highlighted by vacuum dwell NLCF tests which resulted in considerably longer NLCF lives, especially for the min dwell tests.

  18. Effect of rare earth elements on high cycle fatigue behavior of AZ91 alloy

    Mokhtarishirazabad, M., E-mail: mehdi-mokhtari@hotmail.com [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Boutorabi, S.M.A. [School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Azadi, M.; Nikravan, M. [Irankhodro Powertrain Company (IPCO), Tehran (Iran, Islamic Republic of)

    2013-12-10

    This article investigates effects of adding rare earth elements (RE) into a magnesium–aluminum–zinc alloy (the AZ91 alloy) on its high cycle fatigue (HCF) behavior. For this purpose, AZ91 and AZ91+1% RE (AZE911) alloys were gravity casted in a metallic die. RE elements were added to the AZ91 alloy in the form of mischmetals. Microscopic evaluations with the scanning electron microscopy (SEM) and mechanical tests include tensile, hardness and HCF behaviors, were performed on prepared samples. Rotary bending fatigue tests were carried out at a stress ratio (R) of −1 and a frequency of 125 Hz, at the room temperature, in the air. The microscopic investigation demonstrates that the addition of 1% RE elements leads to the formation of Al{sub 11}RE{sub 3} intermetallic particles which is associated to the reduction of β-(Mg{sub 17}Al{sub 12}) phases. Results of mechanical experiments suggest a negligible effect of adding 1% RE elements on mechanical properties of the AZ91 alloy. Curves of stress-life (S–N) shows an increase in the fatigue strength at 10{sup 5} cycles, from 100±10 MPa to 135±10 MPa, when RE elements were added to the AZ91 alloy.

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

    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.)

  20. Impact of choice of stabilized hysteresis loop on the end result of investigation of high-strength low-alloy (HSLA) steel on low cycle fatigue

    Bulatović, S.; Burzić, Z.; Aleksić, V.; A. Sedmak; Lj. Milović

    2014-01-01

    High strength low-alloy steel under low cycle fatigue at a certain level of strain controlled achieve stabilized condition. During the fatigue loading stabilized hysteresis loop is determined, which typical cycle of stabilization is calculated as half number of cycles to failure. Stabilized hysteresis loop is a representative of all hysteresis and it’s used to determine all of the parameters for the assessment of low cycle fatigue. This paper shows comparison of complete strain-life curves of...

  1. Effects of environment and hold times on high temperature low cycle fatigue behaviour of 316L stainless steel

    Previous investigations of high temperature low cycle fatigue (LCF) of austenitic stainless steels have shown that a decrease in the number of cycles to fracture (Nsub(f)) is produced by an increase in test temperature, and that the incorporation of a tensile hold time (tsub(h)) into a continuous elevated temperature fatigue cycle may substantially reduce Nsub(f). In this study some critical experiments including a comparison of fatigue lives determined in air and in vacuum were conducted in order to answer this question. Moreover, since it is generally recognized that creep damage occurring when hold times are introduced into continuous fatigue may be coincident with a transition to intergranular failure, intergranular damage was measured using quantitative metallography. This part of the investigation is an attempt to use microstructural assessment of damage as a basis for modelling LCF behaviour by its incorporation into a predictive life assessment procedure in a manner already suggested for pure creep. (author)

  2. Microstructure and Low-Cycle Fatigue of a Friction-Stir-Welded 6061 Aluminum Alloy

    Feng, A. H.; Chen, D. L.; Ma, Z. Y.

    2010-10-01

    Strain-controlled low-cycle fatigue (LCF) tests and microstructural evaluation were performed on a friction-stir-welded 6061Al-T651 alloy with varying welding parameters. Friction stir welding (FSW) resulted in fine recrystallized grains with uniformly distributed dispersoids and dissolution of primary strengthening precipitates β″ in the nugget zone (NZ). Two low-hardness zones (LHZs) appeared in the heat-affected zone (HAZ) adjacent to the border between the thermomechanically-affected zone (TMAZ) and HAZ, with the width decreasing with increasing welding speed. No obvious effect of the rotational rate on the LHZs was observed. Cyclic hardening of the friction-stir-welded joints was appreciably stronger than that of base metal (BM), and it also exhibited a two-stage character where cyclic hardening of the friction-stir-welded 6061Al-T651 alloy at higher strain amplitudes was initially stronger followed by an almost linear increase of cyclic stress amplitudes on the semilog scale. Fatigue life, cyclic yield strength, cyclic strain hardening exponent, and cyclic strength coefficient all increased with increasing welding speed, but were nearly independent of the rotational rate. Most friction-stir-welded joints failed along the LHZs and exhibited a shear fracture mode. Fatigue crack initiation was observed to occur from the specimen surface, and crack propagation was mainly characterized by the characteristic fatigue striations. Some distinctive tiremark patterns arising from the interaction between the hard dispersoids/inclusions and the relatively soft matrix in the LHZ under cyclic loading were observed to be present in-between the fatigue striations.

  3. Effect of microstructure on non-linear behavior of ultrasound during low cycle fatigue of pearlitic steels

    Research highlights: → Development of online NLU parameter determination system with proper calibration. → Correlation of microstructural changes with the variation of NLU parameter during low cycle fatigue in 0.3 wt.% carbon steel. → NLU parameter follows fatigue hardening and softening trends during low cycle fatigue in test material. → Before failure, fracture of cementite plates due to compressive stress causes a sharp increase in NLU parameter that could be the alarm for failure of components. Hence this technique may prevent catastrophic failure of components. - Abstract: Influence of microstructural changes on the second harmonics of sinusoidal ultrasonic wave during low cycle fatigue (LCF) deformation in pearlitic steel was studied. Fatigue tests were interrupted and at every interruption, non-linear ultrasonic (NLU) parameter (β) was determined. Microstructures of cyclically deformed specimens at various cycles were examined by transmission electron microscopy (TEM). The variation of β with fatigue cycles was correlated with the microstructural changes and the results were explained through the variation in dislocation morphology and carbon content of the steel.

  4. Formation of stress/strain cycles for analytical assessment of fatigue crack initiation and growth

    This paper discusses standard techniques for setting up cycles of stresses, strains and stress intensity factors (SIF) for use in analysing the fatigue characteristics of crack-free components or the fatigue crack growth if crack-like flaws are present. A number of improved techniques are proposed. An enhanced procedure for analytical description of true metal stress-strain curves, covering plastic effects, is presented. This procedure involves standard physical and mechanical properties of the metal in question, such as ultimate stress, yield stress and elasticity modulus. It is emphasized that the currently practiced rain-flow method of design cycle formation, which is effective for an actual (truly known) cyclic loading history, is not suitable for a projected (anticipated) history, as it leaves out of account possible variations in the sequence of operating conditions. Improved techniques for establishing design stress/strain and SIF cycles are described, which make allowance for the most unfavourable sequence of events in the projected loading history. The paper points to a basic difference in the methods of design cycle formation, employed in assessment of the current condition of a component (with the actual history accounted for) and in estimation of the residual lifetime or life extension (for a projected history). (authors)

  5. Low-cycle fatigue behavior of a high manganese austenitic twin-induced plasticity steel

    The monotonic tensile properties and deformation mechanisms of Fe–Mn–C twinning-induced plasticity (TWIP) steels have been extensively studied; however, the low-cycle fatigue (LCF) properties of this series of advanced steels have not been well understood. The present paper addresses the cyclic deformation behavior and the deformed microstructure of an as-annealed TWIP steel. Fully reversed push–pull LCF tests were performed at room temperature under total strain amplitude control with a strain rate of 0.006 s−1 and strain amplitudes ranging from 0.002 to 0.01. The results show initial rapid cyclic hardening within the initial 10% of the fatigue life at all strain amplitudes, and demonstrate an obviously enhanced cyclic yield strength. Different types of cyclic stress responses were revealed, which are featured by initial cyclic hardening followed by cyclic saturation, or followed by cyclic softening and saturation, or followed by cyclic softening without saturation till the final fracture, depending on the strain amplitude applied. The microstructure prior to and after fatiguing were examined by means of optical and transmission electron microscopy. The typical optical microstructure of fatigued samples is characterized by increases in slip band density with increasing strain amplitude or number of cycles at a given strain amplitude applied. The substructures of the deformed samples are featured by the formation of stacking faults and vein/labyrinth dislocation structures, while fine twins and cell or wall dislocation structures, besides those generated at lower strain amplitudes, are formed at high strain amplitudes

  6. Low-cycle fatigue of austenitic welds. Analyses of collected data

    The austenitic stainless steels are used for the main vessel and other main components of LMFBRs. Various grades were specified in the past: 316 stainless steel for plants in the UK, 304 stainless steel for SNR 300, 316L steel modified for Superphenix. The weld metals used in relation to these parent materials were: (i) several grades of Mo containing weld metals as 17Cr8Ni2Mo (UK), 19Cr12Ni2Mo (France) and 16Cr8Ni2Mo (France and USA). (ii) CrNi weld metals (USA on 308 and Germany on 18Cr11Ni). In a preliminary part of this work, low-cycle fatigue (LCF) data were collected for a number of austenitic weld metals, over range of temperature (20 to 625 deg C), orientation and composition. The second part of this programme involves statistical analyses of the database, to determine the influence of a range of factors on fatigue life and on cyclic behaviour. Both fatigue stress strain and fatigue life results of welds have been compared to weld metal and base metal data. In each particular situation (strain, stress control cycle, stress, strain range, weld thickness) apparent discrepancies have been discussed. Mean curves have been established. Statistical analyses of available data on weld metals, with and without molybdenum addition, used respectively for welding of 316L (N) and 304 stainless steels, have been performed using three types of equations: Basquin-Manson-Coffin, Langer and multiple regression. The analysis of particular tests and comparison of the various mean curves have provided information about: comparison of regression analysis, orientation effects, temperature effect, composition effect, comparison with parent material, cyclic stress-strain behaviour. (author). 3 refs., 41 figs., 18 tabs

  7. Prediction of residual life of low-cycle fatigue in austenitic stainless steel based on indentation test

    In this study, a method to predict residual life of low-cycle fatigue in austenitic stainless steel (SUS316NG) was proposed based on indentation test. Low-cycle fatigue tests for SUS316NG were first conducted based on uniaxial tensile-compressive loading under the control of true strain range. Applied strain ranges were varied from about 3 to 12%. Their hysteresis loops of stress and strain were monitored during the fatigue tests. Plastic deformation range in hysteresis loop at each cycle could be roughly expressed by bi-linear hardening rule, whose plastic properties involve yield stress and work-hardening coefficient. The cyclic plastic properties were found to be dependent on the number of cycles and applied strain range, due to work-hardening. We experimentally investigated the empirical relationship between the plastic properties and number of cycles for each applied strain range. It is found that the relationship quantitatively predicts the applied strain range and number of cycles, when the plastic properties, or yield stress and work-hardening coefficient were known. Indentation tests were applied to the samples subjected to low cycle fatigue test, in order to quantitatively determine the plastic properties. The estimated properties were assigned to the proposed relationship, yielding the applied strain range and the cycle numbers. The proposed method was applied to the several stainless steel samples subjected to low cycle fatigue tests, suggesting that their residual lives could be reasonably predicted. Our method is thus useful for predicting the residual life of low-cycle fatigue in austenitic stainless steel. (author)

  8. Effect of severe shot peening on ultra-high-cycle fatigue of a low-alloy steel

    Highlights: • Severe shot peening was applied to obtain a nanostructured surface of 50Crmo4 steel. • An nanocrystalline structured is generated by severe shot peening. • Ultra-high-cycle fatigue test results show the remarkable effect of severe shot peening. • The results were discussed in the light the surface modifications induced by SSP. - Abstract: It is well known that shot peening is able to increase the fatigue strength and endurance of metal parts, especially with a steep stress gradient due to a notch. This positive effect is mainly put into relation with the ability of this treatment to induce a compressive residual stress state in the surface layer of material and to cause surface work hardening. Recently the application of severe shot peening (shot peening performed with severe treatment parameters) showed the ability to obtain more a remarkable improvement of the high cycle fatigue strength of steels. In this paper severe shot peening is applied to the steel 50CrMo4 and its effect in the ultra-high cycle fatigue regime is investigated. Roughness, microhardness, X-ray diffraction residual stress analysis and crystallite size measurement as well as scanning electron microscopy (SEM) observations were used for characterizing the severely deformed layer. Tension–compression high frequency fatigue tests were carried out to evaluate the effect of the applied treatment on fatigue life in the ultra-high cycle region. Fracture surface analysis by using SEM was performed with aim to investigate the mechanism of fatigue crack initiation and propagation. Results show an unexpected significant fatigue strength increase in the ultra-high cycle region after SSP surface treatment and are discussed in the light of the residual stress profile and crystallite size

  9. Coupling damage and reliability model of low-cycle fatigue and high energy impact based on the local stress–strain approach

    Chen Hongxia

    2014-08-01

    Full Text Available Fatigue induced products generally bear fatigue loads accompanied by impact processes, which reduces their reliable life rapidly. This paper introduces a reliability assessment model based on a local stress–strain approach considering both low-cycle fatigue and high energy impact loads. Two coupling relationships between fatigue and impact are given with effects of an impact process on fatigue damage and effects of fatigue damage on impact performance. The analysis of the former modifies the fatigue parameters and the Manson–Coffin equation for fatigue life based on material theories. On the other hand, the latter proposes the coupling variables and the difference of fracture toughness caused by accumulative fatigue damage. To form an overall reliability model including both fatigue failure and impact failure, a competing risk model is developed. A case study of an actuator cylinder is given to validate this method.

  10. Coupling damage and reliability model of low-cycle fatigue and high energy impact based on the local stress-strain approach

    Chen Hongxia; Chen Yunxia; Yang Zhou

    2014-01-01

    Fatigue induced products generally bear fatigue loads accompanied by impact processes, which reduces their reliable life rapidly. This paper introduces a reliability assessment model based on a local stress-strain approach considering both low-cycle fatigue and high energy impact loads. Two coupling relationships between fatigue and impact are given with effects of an impact process on fatigue damage and effects of fatigue damage on impact performance. The analysis of the former modifies the fatigue parameters and the Manson-Coffin equation for fatigue life based on material theories. On the other hand, the latter proposes the coupling variables and the difference of fracture toughness caused by accumulative fatigue damage. To form an overall reliability model including both fatigue failure and impact failure, a competing risk model is developed. A case study of an actuator cylinder is given to validate this method.

  11. The role of high cycle fatigue (HCF) onset in Francis runner reliability

    High Cycle Fatigue (HCF) plays an important role in Francis runner reliability. This paper presents a model in which reliability is defined as the probability of not exceeding a threshold above which HCF contributes to crack propagation. In the context of combined Low Cycle Fatigue (LCF) and HCF loading, the Kitagawa diagram is used as the limit state threshold for reliability. The reliability problem is solved using First-Order Reliability Methods (FORM). A study case is proposed using in situ measured strains and operational data. All the parameters of the reliability problem are based either on observed data or on typical design specifications. From the results obtained, we observed that the uncertainty around the defect size and the HCF stress range play an important role in reliability. At the same time, we observed that expected values for the LCF stress range and the number of LCF cycles have a significant influence on life assessment, but the uncertainty around these values could be neglected in the reliability assessment.

  12. Low cycle fatigue behavior of ITER-like divertor target under DEMO-relevant operation conditions

    Highlights: • LCF behavior of the cooling tube and the interlayer of an ITER-like divertor target is studied. • For the cooling tube, LCF failure will not be an issue under an HHF load of up to 18 MW/m2. • Plastic strain in the interlayer is concentrated at the free surface edge of the bond interface. • The predicted LCF lifetime of the interlayer may not meet the design requirement. - Abstract: In this work the low cycle fatigue (LCF) behavior of the copper alloy cooling tube and the copper interlayer of an ITER-like divertor target is reported for nine different combinations of loading and cooling conditions relevant to DEMO divertor operation. The LCF lifetime is presented as a function of loading and cooling conditions considered here by means of cyclic plasticity simulation and using LCF data of materials relevant for ITER. The numerical predictions indicate, that fatigue failure will not be an issue for the copper alloy tube under a high heat flux (HHF) load of up to 18 MW/m2 as long as it preserves its initial strength. In contrast, the copper interlayer exhibits significant plastic dissipation at the free surface edge of the bond interface adjacent to the cooling tube, where the LCF lifetime is predicted to be below 3000 load cycles for HHF loads higher than 15 MW/m2. Most of the bulk region of the copper interlayer away from the free surface edge does not experience severe plastic fatigue and hence does not pose any critical concern as the LCF lifetime is predicted to be at least 7000 load cycles. LCF lifetime decreases as HHF load is increased or coolant temperature is decreased

  13. Seismic risk evaluation of steel structures based on low-cycle fatigue

    A methodology to incorporate low-cycle fatigue as part of the ductility requirement in seismic risk assessment of steel structures is presented. As expected, the correction factor γ for the conventional ductility (i.e., ratio of maximum deformation to yield deformation) is proportional to strong motion duration and structural system characteristics (i.e., the expected number and distribution parameters of plastic excursions). For the example presented in this paper, γ was calculated to be between 1,35 to 2.6 for a strong motion duration of 7.5 seconds to 20 seconds. (orig./HP)

  14. RELIABILITY ANALYSIS FOR AN AERO ENGINE TURBINE DISK UNDER LOW CYCLE FATIGUE CONDITION

    C.L. Liu; Z.Z. Lü; Y.L. Xu

    2004-01-01

    Reliability analysis methods based on the linear damage accumulation law (LDAL) and load-life interference model are studied in this paper. According to the equal probability rule, the equivalent loads are derived, and the reliability analysis method based on load-life interference model and recurrence formula is constructed. In conjunction with finite element analysis (FEA) program, the reliability of an aero engine turbine disk under low cycle fatigue (LCF) condition has been analyzed. The results show the turbine disk is safety and the above reliability analysis methods are feasible.

  15. Low-cycle fatigue of welded joints of alloy AMg5

    The authors study the low-cycle fatigue of welded joints of aluminum alloy AMg5 in order to determine the cyclic strength coefficient of welded seams. Tests were carried out on cylindrical specimens of the parent metal, welded specimens, and models of welded vessels. The average values of mechanical properties of the specimens and the parent metal are shown. It is shown that when designing welded vessels of aluminum alloy AMg5, the permissible amplitudes of conventional compressive stresses are recommended to be determined as the lower of the two values calculated using the equations presented

  16. Simulation of Delamination Under High Cycle Fatigue in Composite Materials Using Cohesive Models

    Camanho, Pedro P.; Turon, Albert; Costa, Josep; Davila, Carlos G.

    2006-01-01

    A new thermodynamically consistent damage model is proposed for the simulation of high-cycle fatigue crack growth. The basis for the formulation is an interfacial degradation law that links Fracture Mechanics and Damage Mechanics to relate the evolution of the damage variable, d, with the crack growth rate da/dN. The damage state is a function of the loading conditions (R and (Delta)G) as well as the experimentally-determined crack growth rates for the material. The formulation ensures that the experimental results can be reproduced by the analysis without the need of additional adjustment parameters.

  17. Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics

    Girard, Olivier; Racinais, Sébastien

    2014-01-01

    Purpose This study investigated the isolated and combined effects of heat [temperate (22 °C/30 % rH) vs. hot (35 °C/40 % rH)] and hypoxia [sea level (FiO2 0.21) vs. moderate altitude (FiO2 0.15)] on exercise capacity and neuromuscular fatigue characteristics. Methods Eleven physically active subjects cycled to exhaustion at constant workload (66 % of the power output associated with their maximal oxygen uptake in temperate conditions) in four different environmental conditions [temperate/sea ...

  18. Low cycle fatigue improvement of powder metallurgy titanium alloy through thermomechanical treatment

    LIU Bin; LIU Yong; HE Xiao-yu; TANG Hui-ping; CHEN Li-fang

    2008-01-01

    A low-cost β type Ti-1.5Fe-6.8Mo-4.8Al-1.2Nd (mass fraction, %)(T12LCC) alloy was produced by blended elemental powder metallurgy(P/M) method and subsequent thermomechanical treatment. Low cycle fatigue(LCF) behavior of P/M T12LCC alloy before and after thermomechanical treatment was studied. The results show that the LCF resistance of P/M titanium alloy is significantly enhanced through the thermomechanical treatment. The mechanisms for the improvement of LCF behavior are attributed to the elimination of residual pores, the microstructure refining and homogenization.

  19. The hold-time effects on the low cycle fatigue behaviors of 316 SS in PWR primary environment

    The effects of the environments on fatigue life of the structural materials used in nuclear power plants (NPPs) were known to be significant according to the extensive test results. Accordingly, the fatigue analysis procedures and the design fatigue curves were proposed in the ASME Code. However, the implication that the existing ASME design fatigue curves did not sufficiently reflect the effect of the operation conditions of nuclear power plants emerged as an issue to be resolved. One of possible reasons to explain the discrepancy is that the laboratory test conditions do not represent the actual plant transients. Therefore, it is necessary to clarify the effects of light water environments on fatigue life while considering more plant-relevant transient conditions such as hold-time. For this reason, this study will focus on the fatigue life of type 316 stainless steel (SS) in the pressurized water reactor (PWR) environments while incorporating the hold-time during the low cycle fatigue (LCF) test in simulated PWR environments. The objective of this study is to characterize the effects of hold-time on the fatigue life of austenitic stainless steels in PWR environments in comparison with the existing fixed strain rate results. Low cycle fatigue life tests were conducted for the type 316 SS in 310 .deg. C air and simulated PWR environments. To simulate the heat-up and cool-down transient, sub-peak strain holding during the down-hill of strain amplitude was chosen. Currently, LCF tests with 60 seconds holding are in progress. The 0.4, 0.04%/s strain rate condition test results are presented in this study, which shows somewhat longer fatigue life

  20. The Effect of Boron on the Low Cycle Fatigue Behavior of Disk Alloy KM4

    Gabb, Timothy; Gayda, John; Sweeney, Joseph

    2000-01-01

    The durability of powder metallurgy nickel base superalloys employed as compressor and turbine disks is often limited by low cycle fatigue (LCF) crack initiation and crack growth from highly stressed surface locations (corners, holes, etc.). Crack growth induced by dwells at high stresses during aerospace engine operation can be particularly severe. Supersolvus solution heat treatments can be used to produce coarse grain sizes approaching ASTM 6 for improved resistance to dwell fatigue crack growth. However, the coarse grain sizes reduce yield strength, which can lower LCF initiation life. These high temperature heat treatments also can encourage pores to form. In the advanced General Electric disk superalloy KM4, such pores can initiate fatigue cracks that limit LCF initiation life. Hot isostatic pressing (HIP) during the supersolvus solution heat treatment has been shown to improve LCF initiation life in KM4, as the HIP pressure minimizes formation of the pores. Reduction of boron levels in KM4 has also been shown to increase LCF initiation life after a conventional supersolvus heat treatment, again possibly due to effects on the formation tendencies of these pores. However, the effects of reduced boron levels on microstructure, pore characteristics, and LCF failure modes in KM4 still need to be fully quantified. The objective of this study was to determine the effect of boron level on the microstructure, porosity, LCF behavior, and failure modes of supersolvus heat treated KM4.

  1. Thermal cycling fatigue behavior of hardfacing heat-resistant stainless steel for continuous caster rolls

    The variation of tensile properties and hardness as a function of tempering temperature and time has been investigated using a hardfacing 12%Cr stainless steel. The mechanical properties of the hardfacing 12%Cr stainless steel could be generalized by the Larson-Miller parameter, which concurrently considers the effects of tempering temperature and time. Thermal cycling fatigue behavior of a hardfacing 12%Cr stainless steel has been investigated using a special thermal fatigue testing apparatus. The resistance of thermal fatigue was deteriorated mainly by the low ductility and true fracture strength of material. The temperature distribution in the specimen was calculated using finite element program and compared to experimental results. The strain and stress distributions were evaluated taking into account the temperature distribution and the temperature dependence of the material properties. The results showed that maximum values of strain and stress were produced within the induction-heating region. The strain amplitude obtained in this study was much smaller than that of fully constrained case, which corresponds to thermal expansion due to temperature difference. This result arises from the reduction of the temperature gradient due to thermal conduction to the neighboring region. The magnitude of strain raised with the increase in the temperature gradient, which is due to the rapid cooling and heating rates in the induction-heating region

  2. Influence of microstructure of different stainless steels on their low cycle fatigue damage mechanisms

    The present study is focused on understanding low cycle fatigue damage mechanisms in three different kind of stainless steels. In all structures, crack propagation is conditioned by microstructural barriers. In single phase austenitic alloys, short cracks initiation and growth are crystallographic. Cracks are arrested by grain and twin boundaries both at surface and in the bulk. Grain size refinement improve the fatigue life at applied Δεp. The second barrier in the bulk is shown to be very efficient because of the important number of misoriented grains. In the metastable austenitic alloy, the martensitic transformation induced by cyclic straining leads to significant modifications of damage mechanisms. The fatigue behaviour has been investigated between -50 deg. C and 120 deg. C. The γ→α' transformation takes place at the surface, in the bulk (except at 120 deg. C) and locally at the crack tip. At all temperatures, the amount of martensite formed and the fatigue life increase as the grain size decreases, even if at the same Δεp, the maximal stresses are considerably higher than in a stable γ. Short cracks growth takes place in transformed regions, γ→α' transformation being assisted by strain concentrations at the crack tip. This mechanism consumes a part of plastic deformation, which would have been available for crack propagation. Such a dynamic barrier can decrease crack propagation rate. The austenite grain size is shown to have a decisive influence both on the amount of martensite formed and on the fatigue resistance through the effect of γ grain boundaries as indirect barriers to the crack propagation. The fatigue life of the 475 deg. C aged α/γ alloy decreases sharply at high applied Δεp compared to the solution annealed one. This behaviour is explained by the modification of short cracks nucleation sites. Indeed, cleavage occurs in the hard and brittle α phase, even if plastic deformation is concentrated in γ phase. Then, easy growth

  3. A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys

    Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

    2011-06-01

    Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

  4. Crack propagation mechanism and life prediction for very-high-cycle fatigue of a structural steel in different environmental medias

    Guian Qian

    2013-07-01

    Full Text Available The influence of environmental medias on crack propagation of a structural steel at high and very-high-cycle fatigue (VHCF regimes is investigated based on the fatigue tests performed in air, water and 3.5% NaCl aqueous solution. Crack propagation mechanisms due to different crack driving forces are investigated in terms of fracture mechanics. A model is proposed to study the relationship between fatigue life, applied stress and material property in different environmental medias, which reflects the variation of fatigue life with the applied stress, grain size, inclusion size and material yield stress in high cycle and VHCF regimes. The model prediction is in good agreement with experimental observations.

  5. Microstructure Variation and Hardness Diminution During Low Cycle Fatigue of 55NiCrMoV7 Steel

    2007-01-01

    The influence of temperature and hardness level on the cyclic behavior of 55NiCrMoV7 steel, and the microstructure variation and hardness diminution during low cycle fatigue behavior were investigated. By means of SEM and XRD, the modality of carbides and the full-width half-maximum (FWHM) of martensite (211) [M(211)] of Xray diffraction spectrum in fatigue specimen were studied. The results showed that the cyclic stress response behavior generally showed an initial exponential softening for the first few cycles, followed by a gradual softening without cyclic softening saturation. The fatigue behavior of the steel is closely related to the hardness level. The hardnessdiminution and the variation of half-width M(211) are remarkably influenced by the interaction between the cyclic plastic deformation and the thermal loading when the fatigue temperature exceeds the tempering temperature of the steel.

  6. High Cycle Fatigue Properties of Die-Cast Magnesium Alloy AZ91D with Addition of Different Concentrations of Cerium

    2006-01-01

    The effect of addition of different concentrations of Ce on high-cycle fatigue behavior of die-cast magnesium al-loy AZ91D was investigated. Mechanical fatigue tests were conducted at the stress ratio of R = 0.1, and fatigue strength was evaluated using up-and-down loading method. The results show that the grain size of AZ91D alloy is remarkably refined, and the amount of porosity decreases and evenly distributes with the addition of Ce. The fatigue strength of AZ91D alloy at room temperature increases from 96.7 up to 116.3 MPa (1% Ce) and 105.5 MPa (2% Ce), respectively, at the number of cycles to failure, Nf = 1 × 107. The fatigue crack of AZ91D alloy initiates at porosities and inclusions, and propagates along grain boundaries. The fatigue striations on fractured surface appear with Ce addition. The fatigue fracture surface of test specimens shows mixed-fracture characteristics of quasi-cleavage and dimple.

  7. Can the Lamberts and Lambert Submaximal Cycle Test Indicate Fatigue and Recovery in Trained Cyclists?

    Hammes, Daniel; Skorski, Sabrina; Schwindling, Sascha; Ferrauti, Alexander; Pfeiffer, Mark; Kellmann, Michael; Meyer, Tim

    2016-04-01

    The Lamberts and Lambert Submaximal Cycle Test (LSCT) is a novel test designed to monitor performance and fatigue/recovery in cyclists. Studies have shown the ability to predict performance; however, there is a lack of studies concerning monitoring of fatigue/recovery. In this study, 23 trained male cyclists (age 29 ± 8 y, VO2max 59.4 ± 7.4 mL · min-1 · kg-1) completed a training camp. The LSCT was conducted on days 1, 8, and 11. After day 1, an intensive 6-day training period was performed. Between days 8 and 11, a recovery period was realized. The LSCT consists of 3 stages with fixed heart rates of 6 min at 60% and 80% and 3 min at 90% of maximum heart rate. During the stages, power output and rating of perceived exertion (RPE) were determined. Heart-rate recovery was measured after stage 3. Power output almost certainly (standardized mean difference: 1.0) and RPE very likely (1.7) increased from day 1 to day 8 at stage 2. Power output likely (0.4) and RPE almost certainly (2.6) increased at stage 3. From day 8 to day 11, power output possibly (-0.4) and RPE likely (-1.5) decreased at stage 2 and possibly (-0.1) and almost certainly (-1.9) at stage 3. Heart-rate recovery was likely (0.7) accelerated from day 1 to day 8. Changes from day 8 to day 11 were unclear (-0.1). The LSCT can be used for monitoring fatigue and recovery, since parameters were responsive to a fatiguing training and a following recovery period. However, consideration of multiple LSCT variables is required to interpret the results correctly. PMID:26263163

  8. Influence of mechanical surface treatments on the high cycle fatigue performance of TIMETAL 54M

    Research highlights: → Effect of mean stress and environmental sensitivities on high cycle fatigue (HCF) performance in TIMETAL 54M compared to Ti-6Al-4V. → TIMETAL 54M shows normal mean stress sensitivity but Ti-6Al-4V shows anomalous mean stress. → Both alloys are sensitive to air environment. → HCF performance of TIMETAL 54 M was enhanced after shot peening and ball-burnishing but deteriorated in Ti-6Al-4V. - Abstract: TIMETAL 54M (in the following Ti-54M) is a newly developed (α + β) titanium alloy with nominal composition Ti-5Al-4V-0.6Mo-0.4Fe. The alloy can provide a cost benefit over Ti-6Al-4V due to improved machinability and formability. These attractive properties might be a driving force for replacing Ti-6Al-4V in many aircraft as well as biomedical applications. Since HCF performance is one of the most important requirements for these applications, it is essential to improve this property by microstructural optimization and by mechanical surface treatments such as shot peening or ball burnishing. The latter improvement is mainly the result of induced near-surface severe plastic deformation which results in work-hardening and the generation of compressive residual stresses that retard fatigue crack propagation. The main aim of the present study was to investigate the potential fatigue life improvements in Ti-54M due to shot peening and ball-burnishing. The process-induced residual stresses and stress-depth profiles were determined by energy-dispersive X-ray diffraction (ED) of synchrotron radiation with the beam energy of 10-80 keV. Results on Ti-54M and Ti-6Al-4V will be compared and correlated with the mean stress and environmental sensitivities of the fatigue strengths in the microstructures.

  9. Performance of a martensitic steel with 12 wt % Cr under low-cycle fatigue at elevated temperature

    Monotonic tensile strength and low-cycle fatigue tests between 350 and 600 deg C were performed on a martensitic stainless steel with 12% Cr improved with additions of Mo and V. The behaviour of this material essentially exhibits a cyclic softening phenomenon, both for the comparison of the monotonic hardening and cyclic curves and the change in the stress amplitude during the fatigue tests. The breaking facies have been the subject of macroscopic observations and by scanning microscopy. The study of the fatigue strength shows, for the deformation rate used, the dominating influence of the two parameters: plastic deformation amplitude and test temperature

  10. Influence of HVOF sprayed WC/Co coatings on the high-cycle fatigue strength of mild steel

    HVOF thermally sprayed WC/Co coatings are applied onto components which are exposed to wear caused by abrasion, erosion, fretting and sliding. Beside wear attacks and static stresses in lots of cases alternating mechanical stresses caused by dynamic loads occur additionally. Therefore, the fatigue resistance of WC/Co 88/12 and WC/Co 83/17 coated specimens was investigated by high-cycle fatigue tests (HCF). The results of the fatigue tests were documented in statistically ascertained Woehler-diagrams (S-N-curves). Furthermore, the mechanisms of failure are discussed

  11. Low Cycle Fatigue and Analysis of the Cyclic Stress-strain Response in Superalloy Inconel 738LC

    Tobiáš, Jiří; Chlupová, Alice; Petrenec, Martin; Polák, Jaroslav

    Praha: Institute of Theoretical and Applied Mechanics AS CR, v.v.i, 2012 - (Náprstek, J.; Fischer, C.), s. 1407-1411 ISBN 978-80-86246-40-6. [Engineering Mechanics 2012 /18./. Svratka (CZ), 14.05.2012-17.05.2012] R&D Projects: GA ČR(CZ) GAP204/11/1453 Institutional support: RVO:68081723 Keywords : low cycle fatigue * Inconel 738LC * hardening/softening curves * cyclic stress-strain curve * fatigue life curve Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.engmech.cz/2012/proceedings/

  12. LOW CYCLE FATIGUE BEHAVIOUR OF NICKEL BASE SUPERALLOYS IN713 LC AND MAR-M-247 HIP AT ELEVATED TEMPERATURE

    Šulák, Ivo; Obrtlík, Karel

    Lausanne: Federation of european materials societies, 2014 - (Hofmann, M.) [Junior Euromat 2014. 21.07.2014-25.07.2014, Lausanne] R&D Projects: GA MŠk(CZ) EE2.3.20.0214 Institutional support: RVO:68081723 Keywords : IN713LC LG * MAR-M247 * High Temperature * Low Cycle Fatigue Subject RIV: JL - Materials Fatigue, Friction Mechanics http://www.dgm.de/tagungen/?tgnr=1511& cat =prg&edate=25.07.2014&lg=en&op=us

  13. EFFECT OF HIP ON LOW CYCLE FATIGUE OF MAR-M247 AT 900°C

    Šulák, Ivo; Obrtlík, Karel; Škorík, Viktor; Hrbáček, K.

    Ostrava : Tanger Ltd, 2014. ISBN 978-80-87294-52-9. [METAL 2014. International Conference on Metallurgy and Materials /22./. Brno (CZ), 21.05.2014-23.05.2014] R&D Projects: GA MŠk(CZ) EE2.3.30.0063 Institutional support: RVO:68081723 Keywords : MAR-M-247 * High temperature * Low cycle fatigue Subject RIV: JL - Materials Fatigue, Friction Mechanics

  14. A discrete damage zone model for mixed-mode delamination of composites under high-cycle fatigue

    Jimenez, Stephen

    2014-01-01

    A discrete damage zone model (DDZM) is developed within the finite element framework to simulate mode-mix ratio- and temperature-dependent delamination in laminated composite materials undergoing high cycle fatigue loading. In the DDZM, discrete spring elements are placed at the finite element nodes along the laminate interface. Static and fatigue damage laws are used to define the behavior of the spring elements and model irreversible damage growth. The static damage model parameters are obt...

  15. Advanced Experimental and Analytical Investigations on Combined Cycle Fatigue (CCF) of Conventional Cast and Single-crystal Gas Turbine Blades

    Weser, S.; Gampe, U.; Raddatz, M.; Parchem, R.; Lukáš, Petr

    Volume 6. Vancouver: ASME, 2011, s. 19-28. ISBN 978-0-7918-5466-2. [ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition (GT2011). Vancouver (CA), 06.06.2011-10.06.2011] Institutional research plan: CEZ:AV0Z20410507 Keywords : superalloys * Inconel 713 * combined cycle fatigue * Ti6242 * CMSX-4 Subject RIV: JL - Materials Fatigue, Friction Mechanics http://dx.doi.org/10.1115/GT2011-45171

  16. Effects of processing and thermal ageing on the low cycle fatigue and creep-fatigue interaction behaviour of 9Cr-1Mo ferritic steel

    9Cr-1Mo ferritic steel is at present under consideration for thick-section tube plates and tubing for steam generators in liquid metal cooled fast breeder reactor. The low cycle fatigue (LCF) behaviour of 300mm thick section forged 9Cr-1Mo steel was studied under total axial strain control in simulated post-weld heat treatment (SPWHT) and isothermally aged (5000h at 793K) conditions at 793K. A symmetrical triangular wave form and a strain rate of 1 x 103s-1 were employed for all the LCF tests performed over strain amplitudes in the range of ±0.25% to ±1.0%. In both the material conditions cyclic softening was seen at all strain amplitudes. Prior ageing improved the fatigue resistance of simulated post weld heat treat (SPWHT). The fatigue life of forged thick section 9Cr-1Mo steel was lower than that of thin section rolled bar material. LCF life of SPWHT material could be predicted successfully using Tomkins crack growth model. A tentative fatigue design curve for 793K has been proposed based on the information generated in the laboratory using the philosophy outlined in the code case N-47. Creep-fatigue interaction tests, conducted by introducing one minute hold periods at maximum strain amplitude (±0.50%) in tension only, compression only and combined tension and compression, showed little effect on the fatigue life. Attempts at fitting the hold time data to the linear interaction damage model yielded a value of unity for the summation of creep and fatigue damages. (author). 26 refs., 14 figs., 2 tabs

  17. Effect of specimen geometry on low-cycle fatigue property of Inconel 617 at HTGR temperatures

    In order to select a suitable specimen geometry for the evaluation of environment effect on fatigue property at HTGR temperatures, comparison was made between low-cycle fatigue strengths obtained for two types of specimens, solid cylindrical and hourglass specimens. A set of low-cycle fatigue tests were carried out on Ni-base wrought alloy Inconel 617 at 800 deg C and 1000 deg C in air and helium 4-nine purity. Strain was measured by two types of extensometers; (1) Hourglass specimen with a diametral extensometer, (2) Solid cylindrical specimen with a diametral extensometer, and (3) Solid cylindrical specimen with an axial extensometer. In all cases, the axial strain was controlled. The life of the hourglass specimens was consistently longer than that of the solid cylindrical specimens in both environments. The life of test type (2) was nearly equal to that of type (1) in air, but in helium the life of type (2) was between those (1) and (3). The effects of segregation and grain size on the specimen geometry were discussed. In the cases of the specimens machined at right angle to the segregation layer and those with fine grains, the difference of the lives obtained for two types of specimens increased. Furthermore, the difference of crack initiation behaviors in air and helium was discussed. The internal oxidation layer and the decarburized zone were observed near the specimen surface in helium, and more surface cracks occured in helium than in air. These may be related to the larger difference in lives of two types of specimens in helium, compared to in air. (author)

  18. Evaluation of design values for strain limitation on the basis of cycling fatigue data

    The aim of the investigations was to describe the alternate deformation behaviour in the area of low fatigue cycle failure for large plastic strain amplitudes. The results of the tests should represent an expansion (TRD 301) or verification (KTA 3201.2) of the relevant control curves in the area < 100 LW. By means of strain-controlled alternating tensile-compressive tests, steels important for the manufacture of pipelines in nuclear technology were examined at room temperature and at 350deg C, according to the design temperature. The effect of speed of strain on the number of load cycles to the start of cracks was examined for the material 15 NiCuMoNb 5 (St 1.6368, WB 36). (orig./DG)

  19. On the reversibility of dislocation slip during small scale low cycle fatigue

    The evolution of low cycle fatigue damage in copper is studied by in situ micro Laue diffraction. Free standing single crystalline micro-cantilevers with a cross-section of 10 × 10 μm2 were loaded in displacement controlled mode with a surface strain amplitude up to 5%. The point to point misorientation and the diffraction peak width as a measure of geometrically necessary dislocation density was analyzed locally during deformation and globally after 0, 1/4, 1/2, 3/4, 1 and multiples up to a maximum of 22 full cycles. Two different behaviors were observed (i) samples geometrically suppressing cross-slip show a steady state deformation pattern with dislocations in a pile-up. (ii) The sample with cross-slip does not reach a steady state with dislocations accumulating at the neutral plane

  20. High Cycle Fatigue Crack Initiation Study of Case Blade Alloy Rene 125

    Kantzos, P.; Gayda, J.; Miner, R. V.; Telesman, J.; Dickerson, P.

    2000-01-01

    This study was conducted in order to investigate and document the high cycle fatigue crack initiation characteristics of blade alloy Rene 125 as cast by three commercially available processes. This alloy is typically used in turbine blade applications. It is currently being considered as a candidate alloy for high T3 compressor airfoil applications. This effort is part of NASA's Advanced Subsonic Technology (AST) program which aims to develop improved capabilities for the next generation subsonic gas turbine engine for commercial carriers. Wrought alloys, which are customarily used for airfoils in the compressor, cannot meet the property goals at the higher compressor exit temperatures that would be required for advanced ultra-high bypass engines. As a result cast alloys are currently being considered for such applications. Traditional blade materials such as Rene 125 have the high temperature capabilities required for such applications. However, the implementation of cast alloys in compressor airfoil applications where airfoils are typically much thinner does raise some issues of concern such as thin wall castability, casting cleaningness, and susceptibility to high-cycle fatigue (HCF) loading.

  1. Low cycle fatigue behavior of a quenched and tempered niobium bearing HSLA steel

    Kwun, S.I. (Korea Univ., Seoul); Fournelle, R.A.

    1980-08-01

    The low cycle fatigue behavior of a quenched and tempered niobium (columbium) bearing high strength low alloy steel heat treated to give tempered martensitic microstructures presumably with and without fine niobium carbides was studied by transmission electron microscopy, stress relaxation, X-ray diffraction line broadening and strain-controlled fatigue testing. The steel without the niobium carbides cyclically softened rapidly at all strain amplitudes studied. This softening was attributed to the rearrangement of the dislocation substructure into a cell structure and to the accompanying decrease in internal stress. The steel presumably containing the fine niobium carbides cyclically softened to a lesser extent. This correlated with the observation that dislocations in this steel did not rearrange themselves into a cell structure and, hence, there was less change in the internal stress during cycling. The steel without the niobium carbides exhibited somewhat better strain-life behavior at large strain amplitudes. This was attributed to the cell structure being able to accomodate a greater amount of plastic strain in that steel.

  2. Comparison of low-cycle fatigue data of 2 1/4%CrMo steels

    Data files have been produced on international strain-controlled fatigue information available for 2 1/4%CrMo steels; data assessment from these files is treated in three categories viz: annealed and isothermally annealed 2 1/4%Cr1%Mo steel; normalised and tempered and quenched and tempered 2 1/4%Cr1%Mo steel; and 2 1/4%CrMo variants. The available data have been considered generally in terms of total strain range vs. cycles to failure (Nsub(f)), tensile stress at Nsub(f)/2 vs. cycles to failure and time to failure vs. cycles to failure. Where possible the continuous cycling data have been statistically analysed in terms of the elastic and plastic strain components and cycles to failure to yield best-fit equations over defined temperature (T) regimes viz: T <= 427 deg. C, 427 deg. C < T <= 550 deg. C. and 550 deg. C < T <= 600 deg. C. The behaviour of the steels within the various classifications is discussed. (author)

  3. Effects of δ-ferrite and welding structure on high-cycle fatigue properties of austenitic stainless steels weld metals

    We studied the effects of δ-ferrite and welding structure on high-cycle fatigue properties for austenitic stainless steel weld metals at cryogenic temperatures. SUS304L and SUS316L weld metals contained 0% δ-ferrite (0% material) and 10% δ-ferrite (10% material) were prepared. High-cycle fatigue tests were carried out at 293, 77 and 4 K. The S-N curves of those weld metals shifted towards higher stress levels, i.e., the longer life side, with decreasing test temperature. The ratios of 106-cycles fatigue strength (FS) to tensile strength (TS) of 0% material decreased from 0.8 to 0.45 and those of 10% material decreased between 0.35 to 0.65 with decreasing test temperature. Fatigue crack initiation sites of SUS304L 10% material were almost at blowholes, and those of SUS316L 10% material were at weld pass interface boundaries. On the other hand, those of 0% materials were considered to be due to the interface of the solidification structure. Although δ-ferrite reduces toughness at cryogenic temperatures in austenitic stainless steel weld metals, the effects of δ-ferrite on high-cycle fatigue properties are not significant

  4. Low cycle fatigue and strengthening mechanism of cold extruded large diameter internal thread of Q460 steel

    Miao, Hong; Mei, Qing; Yuan, Jingyun; Zheng, Zaixiang; Jin, Yifu; Zuo, Dunwen

    2016-05-01

    large diameter internal thread of high-strength steel(LDITHSS) manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion process is an effective means to realize higher accuracy and longer life. The low-cycle fatigue properties of LDITHSS are obtained by experiments, and the initiation and propagation of fatigue cracks are observed by scanning electron microscope(SEM). Based on the mechanical properties, surface microstructure and residual stress, the strengthening mechanism of cold extruded large diameter internal thread(LDIT) is discussed. The results show that new grains or sub-grains can be formed on the surface of LDIT due to grain segmentation and grain refinement during cold extrusion. The fibrous structures appear as elongated and streamlined along the normal direction of the tooth surface which leads to residual compressive stress on the extruded surface. The maximum tension stress of LDIT after cold extrusion is found to be 192.55 kN. Under low stress cycling, the yield stress on thread increases, the propagation rate of crack reduces, the fatigue life is thus improved significantly with decreasing surface grain diameter and the average fatigue life increases to 45.539×103 cycle when the maximum applied load decreases to 120 kN. The low cycle fatigue and strengthening mechanism of cold extruded LDIT revealed by this research has significant importance to promote application of internal thread by cold extrusion processing.

  5. Laser High-Cycle Thermal Fatigue of Pulse Detonation Engine Combustor Materials Tested

    Zhu, Dong-Ming; Fox, Dennis S.; Miller, Robert A.

    2001-01-01

    Pulse detonation engines (PDE's) have received increasing attention for future aerospace propulsion applications. Because the PDE is designed for a high-frequency, intermittent detonation combustion process, extremely high gas temperatures and pressures can be realized under the nearly constant-volume combustion environment. The PDE's can potentially achieve higher thermodynamic cycle efficiency and thrust density in comparison to traditional constant-pressure combustion gas turbine engines (ref. 1). However, the development of these engines requires robust design of the engine components that must endure harsh detonation environments. In particular, the detonation combustor chamber, which is designed to sustain and confine the detonation combustion process, will experience high pressure and temperature pulses with very short durations (refs. 2 and 3). Therefore, it is of great importance to evaluate PDE combustor materials and components under simulated engine temperatures and stress conditions in the laboratory. In this study, a high-cycle thermal fatigue test rig was established at the NASA Glenn Research Center using a 1.5-kW CO2 laser. The high-power laser, operating in the pulsed mode, can be controlled at various pulse energy levels and waveform distributions. The enhanced laser pulses can be used to mimic the time-dependent temperature and pressure waves encountered in a pulsed detonation engine. Under the enhanced laser pulse condition, a maximum 7.5-kW peak power with a duration of approximately 0.1 to 0.2 msec (a spike) can be achieved, followed by a plateau region that has about one-fifth of the maximum power level with several milliseconds duration. The laser thermal fatigue rig has also been developed to adopt flat and rotating tubular specimen configurations for the simulated engine tests. More sophisticated laser optic systems can be used to simulate the spatial distributions of the temperature and shock waves in the engine. Pulse laser high-cycle

  6. Low-cycle fatigue of P91 and P92 steels used in the power engineering industry

    M. Cieśla; G. Junak

    2011-01-01

    Purpose: The aim of the study was to determine the life characteristics of low-cycle P91 and P92 steels used in the power unit components that work under the highest effort. The life of the steels was determined for constant ranges of total strain from the range of ∆εt= 0.6-1.2% and with the application of gradual loading two-stage.Design/methodology/approach: Low-cycle fatigue tests of the material in its initial state were performed at room temperature. The fatigue tests were conducted on a...

  7. Simulation of the high cycle fatigue life reduction due to internal hydrogen embrittlement using a commercial Finite Element program

    Riccius, Jörg; BRUCHHAUSEN MATTHIAS; Fischer, Burkhard

    2013-01-01

    The effect of internal hydrogen on the high cycle fatigue (HCF) life duration of Inconel X-750® in the hydrogen concentration range between 5 and 39 wppm at ambient temperature was investigated using an ultrasonic HCF test bench. For an alternating stress equal to 0.6 times the yield stress of the hydrogen-free material, a drop of two orders of magnitude in the high-cycle fatigue durability of the material has been measured over the investigated hydrogen concentration range. New tools have be...

  8. Leg joint power output during progressive resistance FES-LCE cycling in SCI subjects: developing an index of fatigue

    Faghri Pouran D

    2008-04-01

    Full Text Available Abstract Background The purpose of this study was to investigate the biomechanics of the hip, knee and ankle during a progressive resistance cycling protocol in an effort to detect and measure the presence of muscle fatigue. It was hypothesized that knee power output can be used as an indicator of fatigue in order to assess the cycling performance of SCI subjects. Methods Six spinal cord injured subjects (2 incomplete, 4 complete between the ages of twenty and fifty years old and possessing either a complete or incomplete spinal cord injury at or below the fourth cervical vertebra participated in this study. Kinematic data and pedal forces were recorded during cycling at increasing levels of resistance. Ankle, knee and hip power outputs and resultant pedal force were calculated. Ergometer cadence and muscle stimulation intensity were also recorded. Results The main findings of this study were: (a ankle and knee power outputs decreased, whereas hip power output increased with increasing resistance, (b cadence, stimulation intensity and resultant pedal force in that combined order were significant predictors of knee power output and (c knowing the value of these combined predictors at 10 rpm, an index of fatigue can be developed, quantitatively expressing the power capacity of the knee joint with respect to a baseline power level defined as fatigue. Conclusion An index of fatigue was successfully developed, proportionalizing knee power capacity during cycling to a predetermined value of fatigue. The fatigue index value at 0/8th kp, measured 90 seconds into active, unassisted pedaling was 1.6. This indicates initial power capacity at the knee to be 1.6 times greater than fatigue. The fatigue index decreased to 1.1 at 2/8th kp, representing approximately a 30% decrease in the knee's power capacity within a 4 minute timespan. These findings suggest that the present cycling protocol is not sufficient for a rider to gain the benefits of FES and thus

  9. Influence of precipitates on low-cycle fatigue and crack growth behavior in an ultrafine-grained aluminum alloy

    The strain-controlled fatigue and near-threshold fatigue crack growth behavior of an ultrafine-grained (UFG), age-hardening aluminum alloy after severe plastic deformation by equal-channel angular pressing (ECAP) are discussed. The main question addressed is how different precipitate morphologies affect low-cycle fatigue (LCF) and fatigue crack growth. An AlMg0.5Si0.4 alloy is subjected to two and eight passes of ECAP to obtain different degrees of grain refinement and fragmentation of the initially semi-coherent precipitates. Furthermore, a thermally recovered condition with newly formed, small coherent precipitates, which is obtained by aging after two ECAP passes, is considered. Strain-controlled fatigue tests and ΔK-controlled crack growth measurements are conducted and microstructural evolution during cycling and fracture surfaces are carefully analyzed using scanning and transmission electron microscopy. Most importantly, the results of this study show that newly formed, coherent precipitates in the thermally recovered condition directly contribute to a more planar slip behavior, to slip localization and to early failure during LCF loading. It is clearly demonstrated that precipitate morphology also affects fatigue crack propagation, and that this is closely related to slip reversibility, even in the UFG regime

  10. Effects of laser peening treatment on high cycle fatigue and crack propagation behaviors in austenitic stainless steel

    Laser peening without protective coating (LPwC) treatment is one of surface enhancement techniques using an impact wave of high pressure plasma induced by laser pulse irradiation. High compressive residual stress was induced by the LPwC treatment on the surface of low-carbon type austenitic stainless steel SUS316L. The affected depth reached about 1mm from the surface. High cycle fatigue tests with four-points rotating bending loading were carried out to confirm the effects of the LPwC treatment on fatigue strength and surface fatigue crack propagation behaviors. The fatigue strength was remarkably improved by the LPwC treatment over the whole regime of fatigue life up to 108 cycles. Specimens with a pre-crack from a small artificial hole due to fatigue loading were used for the quantitative study on the effect of the LPwC treatment. The fracture mechanics investigation on the pre-cracked specimens showed that the LPwC treatment restrained the further propagation of the pre-crack if the stress intensity factor range ΔK on the crack tip was less than 7.6 MPa√m. Surface cracks preferentially propagated into the depth direction as predicted through ΔK analysis on the crack by taking account of the compressive residual stresses due to the LPwC treatment. (author)

  11. Low cycle thermal fatigue testing of beryllium grades for ITER plasma facing components

    A novel technique has been used to test the relative low cycle thermal fatigue resistance of different grades of US and Russian beryllium, which is proposed as plasma facing armor for fusion reactor first wall, limiter, and divertor components. The 30 kW electron beam test system at Sandia National Laboratories was used to sweep the beam spot along one direction at 1 Hz. This produces a localized temperature ''spike'' of 750 degree C for each pass of the beam. Large thermal stresses in excess of the yield strength are generated due to very high spot heat flux, 250 MW/m2. Cyclic plastic strains on the order of 0.6% produced visible cracking on the heated surface in less than 3000 cycles. An in-vacuo fiber optic borescope was used to visually inspect the beryllium surfaces for crack initiation. Grades of US beryllium tested included: S-65C, S- 65H, S-200F, S-200F-H, SR-200, I-400, extruded high purity, HIP'd spherical powder, porous beryllium (94% and 98% dense), Be/30% BeO, Be/60% BeO, and TiBe12. Russian grades included: TGP-56, TShGT, DShG-200, and TShG-56. Both the number of cycles to crack initiation, and the depth of crack propagation, were measured. The most fatigue resistant grades were S-65C, DShG-200, TShGT, and TShG-56. Rolled sheet Be (SR-200) showed excellent crack propagation resistance in the plane of rolling, despite early formation of delamination cracks. Only one sample showed no evidence of surface melting, Extruded (T). Metallographic and chemical analyses are provided. Good agreement was found between the measured depth of cracks and a 2-D elastic-plastic finite element stress analysis

  12. Low cycle thermal fatigue testing of beryllium grades for ITER plasma facing components

    Watson, R.D.; Youchison, D.L. [Sandia National Labs., Livermore, CA (United States); Dombrowski, D.E. [Brush Wellman, Inc., Cleveland, OH (United States); Guiniatouline, R.N. [Efremov Institute, (Russia); Kupriynov, I.B. [Russian Institute of Inorganic Materials (Russia)

    1996-02-01

    A novel technique has been used to test the relative low cycle thermal fatigue resistance of different grades of US and Russian beryllium, which is proposed as plasma facing armor for fusion reactor first wall, limiter, and divertor components. The 30 kW electron beam test system at Sandia National Laboratories was used to sweep the beam spot along one direction at 1 Hz. This produces a localized temperature ``spike`` of 750{degree}C for each pass of the beam. Large thermal stresses in excess of the yield strength are generated due to very high spot heat flux, 250 MW/m{sup 2}. Cyclic plastic strains on the order of 0.6% produced visible cracking on the heated surface in less than 3000 cycles. An in-vacuo fiber optic borescope was used to visually inspect the beryllium surfaces for crack initiation. Grades of US beryllium tested included: S-65C, S- 65H, S-200F, S-200F-H, SR-200, I-400, extruded high purity, HIP`d spherical powder, porous beryllium (94% and 98% dense), Be/30% BeO, Be/60% BeO, and TiBe{sub 12}. Russian grades included: TGP-56, TShGT, DShG-200, and TShG-56. Both the number of cycles to crack initiation, and the depth of crack propagation, were measured. The most fatigue resistant grades were S-65C, DShG-200, TShGT, and TShG-56. Rolled sheet Be (SR-200) showed excellent crack propagation resistance in the plane of rolling, despite early formation of delamination cracks. Only one sample showed no evidence of surface melting, Extruded (T). Metallographic and chemical analyses are provided. Good agreement was found between the measured depth of cracks and a 2-D elastic-plastic finite element stress analysis.

  13. Hold-time effects on the low cycle fatigue of Ti-24Al-11Nb at 650 C

    The influence of hold time on fatigue of Ti-24Al-11Nb is studied at 650 C. At 0.167 Hz, the alloy exhibits cyclic hardening. A 100 s hold at peak tensile or compressive strain at ± 0.6% strain has no observable effect on cycles to failure. For hold times at ± 0.5% strain, however, the fatigue lives are nearly halved and specimens show extensive secondary cracking, similar to that observed in creep tests. At ± 0.6% strain, a transition from stress-assisted environmental degradation to fatigue characterized by PSB formation and cracking is observed when compression hold times are introduced. An energy based criterion appears to predict reasonably well the fatigue life

  14. Effects of Hot Rolling on Low-Cycle Fatigue Properties of Zn-22 wt.% Al Alloy at Room Temperature

    Dong, X. H.; Cao, Q. D.; Ma, S. J.; Han, S. H.; Tang, W.; Zhang, X. P.

    2016-06-01

    The effects of the reduction ratio (RR) on the low-cycle fatigue (LCF) properties of the Zn-22 wt.% Al (Zn-22Al) alloy were investigated. Various grain sizes from 0.68 to 1.13 μm were obtained by controlled RRs. Tensile and LCF tests were carried out at room temperature. Superplasticity and cyclic softening were observed. Strength and ductility of the rolled Zn-22Al alloy increased with the RR, owing to the decrease in its grain size. The RR did not affect the cyclic softening behavior of the alloy. The fatigue life of the alloy decreased with increasing strain amplitude, while the fatigue life first decreased and then increased with increasing RR. The longest fatigue life was observed for the alloy rolled at a RR of 60%. A bilinear Coffin-Manson relationship was observed to hold true for this alloy.

  15. Experimental study on elevated temperature low cycle fatigue of P92 steel

    A supercritical water cooled reactor (SCWR) is being considered as a candidate reactor of the Generation IV nuclear reactors due to its high thermal efficiency and simple system composition. A critical question to attain is to choose proper materials for the core components, especially for the fuel cladding. The mechanic properties, corrosion and stress corrosion cracking susceptibilities, radiation resistances, etc., of these materials at high temperature are extremely important for the safety of nuclear power plant. The paper presents the low cycle fatigue behaviors of P92, a kind of F/M type candidate materials for the SCWR. The experiments were carried out at 600 degree C and 650 degree C with total strain controlled. The strain range is from ±0.2%-±0.6%, respectively. The results show that P92 steel is cyclic strain softening at both temperatures, but stable cyclic phenomena were not observed. The decline ratio of macro-crack appearance with the strain range increasing is milder at 650 degree C than that at 600 degree C, and the cycles to failure are remarkably higher at 650 degree C than those at 600 degree C under the same total strain ranges. The relationship of cycle stable stress vs. strain range and number of cycles to failure vs. total strain range were obtained. (authors)

  16. Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine

    Shanyavskiy, A. A.

    2014-01-01

    In-service Very-High-Cycle-Fatigue (VHCF) regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17 and superalloy GS6K, respectively, was considered. Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades. Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface. This material behavior reflected lifetime limit that was reached by the criterion VHCF. In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet. This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology. In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream. Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations. Recommendations to continue aircrafts airworthiness were made for in-service blades.

  17. Challenges in high temperature low cycle fatigue testing of metallic materials

    The evaluation of the high strain Low Cycle Fatigue properties of structural materials is an involved and complicated procedure requiring skill and diligence from the experimentalist. This presentation describes the various testing methods to evaluate the LCF properties of structural materials, the complexities involved and some solutions to exacting requirements, not covered by the testing procedure standards. The basic components of servo-hydraulic fatigue testing machines is described, as are the calibration and maintenance procedures. Results of LCF tests conducted at the authors' laboratory on AISI 316L(N) stainless steel and Mod.9Cr-1Mo ferritic steel are described. The complications in total strain controlled testing of weld joints is brought out and soft zone development in Mod. 9Cr-1Mo ferritic steel is described. The special requirements for testing in environmental chambers is a challenging task. In-house chambers, designed to carry out testing in dynamic sodium environment is highlighted. These chambers have provision to accommodate extensometers for strain measurements, and also house all the safety instrumentation needed to carry out to mechanical testing in dynamic sodium environment. The variation of LCF results as a function of specimen geometry is examined. The various failure criteria adopted by laboratories in different countries are also touched upon. (author)

  18. Very high cycle fatigue strength and crack growth of thin steel sheets

    Mohand Ouarabi

    2016-03-01

    Full Text Available For basic observations or for industrial applications it is of interest to use flat specimens at very high frequency in the gigacycle regime. In this work, thin flat sheet, with 1.2 mm thickness of a complex phase ferrite-martensitic steels were considered for carrying out fatigue tests at high frequency (20 kHz up to the gigacycle regime (>109 cycles. The crack initiation tests were carried out with water cooling, while the crack growth test were carried out in laboratory air at room temperature. All the tests were carried out under loading ratio R=-1. To do that, special designs of specimens were made and computed using FEM for defining the stress amplitude for endurance tests. Special attachments for specimens to the ultrasonic system’s horn were enhanced. A particular FEM computing of the stress intensity range on crack growth specimens was carried out for determining the specimen dimensions and an equation that defines the stress intensity range as a function of the harmonic displacement amplitude, dynamic Young’s modulus, material density and crack length. Detailed procedures and fatigue results are presented in this paper.

  19. Problems of the high-cycle fatigue of the materials intended for the parts of modern gas-turbine engines and power plants

    Petukhov, A. N.

    2010-10-01

    The problems related to the determination of the life of the structural materials applied for important parts in gas-turbine engines and power plants from the results of high-cycle fatigue tests are discussed. Methods for increasing the reliability of the high-cycle fatigue characteristics and the factors affecting the operational reliability are considered.

  20. Effects of sodium on the low-cycle fatigue behaviour of 2.25Cr-1Mo steel in flowing sodium at high temperatures

    This paper describes the results of investigations of the low-cycle fatigue test, which were conducted to determine the effects of sodium on the low-cycle fatigue property of normalized and tempered 2 1/4 Cr-1Mo steel in flowing sodium at high temperatures. (author)

  1. High-Cycle Fatigue Resistance of Si-Mo Ductile Cast Iron as Affected by Temperature and Strain Rate

    Matteis, Paolo; Scavino, Giorgio; Castello, Alessandro; Firrao, Donato

    2015-09-01

    Silicon-molybdenum ductile cast irons are used to fabricate exhaust manifolds of internal combustion engines of large series cars, where the maximum pointwise temperature at full engine load may be higher than 973 K (700 °C). In this application, high-temperature oxidation and thermo-mechanical fatigue (the latter being caused by the engine start and stop and by the variation of its power output) have been the subject of several studies and are well known, whereas little attention has been devoted to the high-cycle fatigue, arising from the engine vibration. Therefore, the mechanical behavior of Si-Mo cast iron is studied here by means of stress-life fatigue tests up to 10 million cycles, at temperatures gradually increasing up to 973 K (700 °C). The mechanical characterization is completed by tensile and compressive tests and ensuing fractographic examinations; the mechanical test results are correlated with the cast iron microstructure and heat treatment.

  2. Comparison of the low cycle fatigue behaviour of F82H mod. and Eurofer 97 in water coolant

    A comparative study has been done about the susceptibility to environmentally induced damage of the reduced activation martensitic steels F82H mod and Eurofer 97. Both alloys were found to suffer premature fracture compared to air behaviour, during conventional fully reversed load controlled low cycle fatigue tests, run in high temperature aqueous environment with the alkaline chemistry specified for the lithium lead blanket water coolant. The different steel low cycle fatigue responses in water, especially, the scatter of fatigue lives and fracture modes observed from plate-to-plate and from specimen-to-specimen in F82H and Eurofer, respectively, appeared to coincide with the presence of different inclusion types, size and density. Based on electrochemical and fractographic indexes, the results were discussed with the support of the hydrogen decohesion model, in terms of mutually competitive trap effects on hydrogen diffusion and partitioning among the susceptible cracking sites

  3. Evaluation of the available data on the effect of the environment on the low cycle fatigue properties in light water reactor environments

    The existing design procedures for light water reactors doe not define the effect of the coolant environment on the fatigue properties of the materials. Although Section III of the ASME Boiler and pressure Vessel Code states that the tests on which the design fatigue curves are based did not include tests in the presence of corrosive environments which might accelerate fatigue failure, no guidance is given as to when environments may be corrosive. It is sometimes assumed the light water reactor (LWR) coolant environments are not corrosive. There are results from a number of research programs reported in the literature in which low cycle fatigue experiments have been conducted in simulated LWR environments and substantial effects observed. In this paper, the available low cycle fatigue data from the literature will be compared with the ASME fatigue data and design curve. In addition, the significant variables which appear to affect the fatigue properties of the material will be discussed

  4. Effect of the structure on the low-cycle fatigue behaviour of alloy 800

    Alloy 800 (grade I) is used for making the steam generators of liquid metal fast breeder reactors. At working temperature (5250C) alloy 800 is strengthned by γ' (Ni3(Ti,Al)) precipitation which occurs during thermal aging. The mechanical properties of this alloy depend on the parameters which define the γ' precipitation and obviously on the structural characteristics due to the thermomechanical treatments which govern the manufacture of the product. For one cast of alloy 800 this work aims to analyse the influence, on low cycle fatigue behaviour at 5500C, of structural and microstructural variations originating either in different elaboration procedures or in γ' precipitation obtained by a thermal aging of 3000h at 5500C with or without a preceeding cold working of 10%

  5. Corrosion and low-cycle fatigue properties of AISI 316L in flowing Pb-17Li

    Corrosion and low-cycle fatigue (LCF) tests were performed on AISI 316L steel specimens in a flowing lithium lead environment. The LCF and corrosion tests were conducted simultaneously in the ''LIFUS 2'' forced convection loop, at a temperature of 723 K and a flow velocity of approximately 0.01 m/s. The LCF tests, which had a strain amplitude ranging from 0.008 to 0.016, were compared with reference tests performed in an inert argon atmosphere. The results show that liquid Pb-17Li has no detrimental effect on the LCF behaviour of 316L at the test temperature of 723 K. The corrosion tests extended from 650 to 1600 h with intermediate steps. Metallographic and SEM-EDAX analyses indicated the presence of an irregular porous ferritic layer. The results are discussed in terms of ferrite growth rate and the effect of corrosion phenomena on LCF behaviour. ((orig.))

  6. Effect of adjusting pulse durations of functional electrical stimulation cycling on energy expenditure and fatigue after spinal cord injury

    Ashraf S. Gorgey, MPT, PhD, FACSM

    2015-02-01

    Full Text Available The purpose of the current study was to determine the effects of three different pulse durations (200, 350, and 500 microseconds [P200, P350, and P500, respectively] on oxygen uptake, cycling performance, and energy expenditure (EE percentage of fatigue of the knee extensor muscle group immediately and 48 to 72 h after cycling in persons with spinal cord injury (SCI. A convenience sample of 10 individuals with motor complete SCI participated in a repeated-measures design using a functional electrical stimulation (FES cycle ergometer over a 3 wk period. There was no difference among the three FES protocols on relative oxygen uptake or cycling EE. Delta EE between exercise and rest was 42% greater in both P500 and P350 than in P200 (p = 0.07, whereas recovery oxygen uptake was 23% greater in P350 than in P200 (p = 0.03. There was no difference in the outcomes of the three pulse durations on muscle fatigue. Knee extensor torque significantly decreased immediately after (p < 0.001 and 48 to 72 h after (p < 0.001 FES leg cycling. Lengthening pulse duration did not affect submaximal or relative oxygen uptake or EE, total EE, and time to fatigue. Greater recovery oxygen updake and delta EE were noted in P350 and P500 compared with P200. An acute bout of FES leg cycling resulted in torque reduction that did not fully recover 48 to 72 h after cycling.

  7. Biaxial high cycle fatigue: experimental investigation and two-scale damage model

    This research thesis first describes the multi-axial fatigue phenomenon in the cases of mechanical and complex loadings, discusses multi-axial fatigue criteria, and presents the approach of fatigue by incremental damage mechanics. Then, it reports an experimental investigation of fatigue crack initiation under biaxial polycyclic fatigue in 304L austenitic stainless steel and in titanium alloy. The author presents a probabilistic two-scale damage model, and then reports the assessment of multi-axial fatigue life by means of this model

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

    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.

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

    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

  10. Neuromuscular function and fatigue resistance of the plantar flexors following short-term cycling endurance training

    Martin eBehrens

    2015-05-01

    Full Text Available Previously published studies on the effect of short-term endurance training on the neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after eight weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0-100, 100-200 ms and isometric maximum voluntary contraction of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave, peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that the endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue

  11. Low cycle fatigue of GX12CrMoVNbN9-1 cast steel at elevated temperature

    S. Mroziński

    2011-11-01

    Full Text Available Purpose: The purpose of the paper is to characterize the low cycle fatigue of high - chromium martensitic GX12CrMoVNbN9-1 cast steel from the perspective of the strain and energy criterion.Design/methodology/approach: The tests of fatigue strength within the scope of small amount of cycles to failure at room temperature and elevated temperature (400, 550 and 600°C were carried out on GX12CrMoVNbN9-1 cast steel. The fatigue tests were run for five assumed levels of controlled amplitude of total strain εac (0.25; 0.30; 0.35; 0.50 and 0.60%. The loading applied in the experiment oscillated sinusoidally with the stress ratio R = -1 and frequency f = 0.2 Hz. The fatigue tests were performed by means of Instron 8501 hydropulser. Tests pieces for the fatigue tests were round and threaded.Findings: The examined cast steel during low cycle fatigue is subject to intense weakening. The period of stabilization was not revealed during the cyclic loading of the cast steel, neither at room temperature, nor elevated one. Moreover, it has been proved that the extent of changes in the cyclic properties is influenced by the level of strain and temperature.Practical implications: Obtained results of the tests are indispensable for the formulation of necessary characteristics of high-temperature creep resisting steels and cast steels.Originality/value: The paper presents the fatigue characteristics of GX12CrMoVNbN9-1 cast steel within the scope of small amount of cycles to failure. The fatigue characteristics of the examined cast steel was developed for both: room temperature and elevated temperature - 400, 550 and 600°C. Fatigue life of the investigated cast steel was described using the equations of Ramberg-Osgood and Manson-Coffin-Basquin, and presented from the perspective of the energy criterion.

  12. Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components

    Ko, William L.

    1989-01-01

    The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation. This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.

  13. LOW CYCLE FATIGUE OF COMPOSITE MATERIALS IN ARMY STRUCTURAL APPLICATIONS: A REVIEW OF LITERATURE AND RECOMMENDATIONS FOR RESEARCH

    Low cycle fatigue (LCF) of laminate composite structures used in Army applications is assessed to identify the key physical phenomena occurring during LCF processes and to determine their main characteristics. Special attention is given to the LCF conditions inherent in Army stru...

  14. Study on low cycle fatigue behaviors of Type 316 stainless steel in 310 .deg. C water environment

    The low cycle fatigue tests of type 316 stainless steel in 310 .deg. C low oxygen water were conducted to investigate the fatigue behaviors of the stainless steel. They depend on the environmental and loading conditions. The test strain rates and amplitudes were 0.4, 0.04, 0.008 %./s, and 1, 0.8, 0.6, 0.4 % respectively. The environmental condition was a temperature of 310 .deg. C, pressure of 15 MPa, conductivity of less than 0.1 μS/cm, dissolved oxygen level of< 1 ppb, pH level of 6.4. At cyclic stress response, the type 316 stainless steel showed primary hardening at all strain amplitude and rate conditions. The secondary hardening were only appeared at low strain amplitude. By the hysteresis loop analysis, the primary hardening was known to be happened by dynamic strain aging. Negative strain rate sensitivity was also appeared in cyclic stress response and caused by the increase of dislocation density and the changes of dislocation structure. Well developed striations were shown on the fatigue surface. Initial shape of the fatigue crack showed the film rupture slip dissolution symptoms, while the hydrogen induced cracking phenomena were observed at the later position of the fatigue surface. ε-N curve were well fitted with reference data from other laboratories. The data showed shorter fatigue lives in 310 .deg. C water environment than those of room temperature air condition

  15. Effect of strain rate on high-temperature low-cycle fatigue behavior of hastelloy X and hastelloy XR

    A series of strain controlled low-cycle fatigue tests at 900 deg C in the simulated HTGR helium environment were conducted on Hastelloy X and its modified version, Hastelloy XR, and the effect of strain rate on high-temperature low-cycle fatigue behavior was investigated. The results of this study provide the following conclusions; (1) Decreasing the strain rate led to notable reductions in the fatigue life. (2) Trends of strain softening and cyclic softening were observed at lower strain rates of 1 x 10-4 s-1 and 2 x 10-5 s-1. (3) Both fracture modes of the transgranular and the intergranular were recognized on the fracture surfaces, with the former mode being predominant at a comparatively high strain rate of 1 x 10-3 s-1. The intergranular fracture mode, however, became predominant at lower strain rates, 1 x 10-4 s-1 and 2 x 10-5 s-1. (4) The cumulative damage rule predicted an excessively coservative value for creep damage. (5) The data obtained lay on the straight line plots when the frequency modified fatigue life method was applied. No significant difference in fatigue behavior was resolved between Hastelloy X and Hastelloy XR under the test conditions employed. (author)

  16. Low cycle fatigue with hold times of cast superalloy Inconel 792-5A at 800 °C

    Šmíd, Miroslav; Obrtlík, Karel; Petrenec, Martin; Polák, Jaroslav

    Žilina: Žilinská univerzita, 2012, s. 65-68. ISBN 978-80-554-0477-6. [International of PhD. students´ seminar SEMDOK 2012 /17./. Terchová (SK), 25.01.2012-27.01.2012] R&D Projects: GA ČR(CZ) GAP204/11/1453; GA ČR(CZ) GAP107/11/2065 Keywords : low cycle fatigue * superalloy * hold time * high temperatures * surface relief Subject RIV: JL - Materials Fatigue, Friction Mechanics

  17. The examinations of fatigue durability in the range of low cycle number of 13HMF steel used for energy pipes

    The paper deals with the fatigue tests in the range of low number of cycles, for the materials used in energy pipelines. The tests are performed both for the initial and after the long-term operating period. The paper presents the evaluation of fatigue durability of 13HMF steel at room temperature and 550oC on the basis of the performed metallurgical studies 'the degree of depletion' of the material after operating period has been determined according to the adapted quality for criteria for structure class evaluation. (author)

  18. Low-cycle fatigue behaviour and microstructure of copper and alpha-brass under biaxial load paths

    Henkel, S; Fischer, J; Biermann, H [TU Bergakademie Freiberg, Institute for Materials Engineering, Gustav-Zeuner-Strasse 5, D-09599 Freiberg (Germany); Balogh, L; Ungar, T, E-mail: henkel@ww.tu-freiberg.d [Eoetvoes University, Department of General Physics, PO Box 32, 1518 Budapest (Hungary)

    2010-07-01

    The low-cycle fatigue behaviour of copper and a-brass CuZn30 was investigated in uniaxial and biaxial tests. Planar biaxial fatigue tests were carried out using cruciform samples with proportional stain paths with and without phase shift between the two axes. Microcharacterisation was performed by electron microscopy as well as by high-resolution X-ray line profile analysis. The biaxial cyclic stress-strain curves show good agreement with the uniaxial ones using the von Mises equivalent strain hypothesis. The dislocation densities and microhardness values of the biaxial case, however, show significantly lower values compared to the uniaxial case at equivalent von Mises stresses.

  19. An approach for low cycle fatigue life prediction of various metallic materials subjected to non-proportional multiaxial loading

    The safety and durability of structures is an important issue because the sudden failure of complex system such as nuclear power plants, automobiles, aircraft and pressure vessels may cause many injuries, much financial loss and even environmental damage. Since many of these systems are subjected to repeated multiaxial loading, evaluation of low-cycle fatigue (LCF) becomes one of the major considerations in the design structures. An approach for estimating the multiaxial low cycle fatigue life under non-proportional loading using the non-proportional parameter by Itoh, Sakane, Ohnami and Socie has been developed. The non-proportional parameter includes the maximum principal strain range, non-proportional factor (it's a function of only strain path) and has a material constant which is defined as the sensitivity of the material to the non-proportional loading. The paper proposes the different versions of the non-proportional parameter and reports an investigation on the applicability of these versions to LCF life prediction. The proposed parameter, which includes Pisarenko-Lebedev's equivalent strain (or equivalent strain of Coulomb-More type), has shown a very good correlation of multiaxial low-cycle fatigue lives for various non-proportional loading paths with different material fatigue data. (authors)

  20. Some considerations on low-cycle fatigue properties of anisotropic rolled steel plates

    In order to have fundamental understanding of the low-cycle fatigue properties of an anisotropic rolled steel plate, uniaxial and biaxial low-cycle fatique tests have been carried out. The material used was a thick rolled carbon steel plate with a pearlite-ferrite laminated microstructure and an array of deformed inclusions. The uniaxial fatique tests were carried out using an anticlastic beending of a rhombic plate specimen. All the specimens were cut out in the thickness plane of the rolled steel plate, in which the static mechanical properties, especially fracture ductility, showed most significant anisotropy. Micro- and macroscopic observations of the fatique process were performed in each fatique test. Depending on the loading orientation angle of the specimen, all the specimens showed anisotropy in fatique lives and fatique processes. Anisotropy in fatique strength under uniaxial loading was found to be predictable by using the Manson-Coffin relation, when the anisotropy in fracture ductility is taken into account. On the contrary, anisotropy in the biaxial fatique strength indicated slightly anormalous and could not be estimated by a simple extension of the results of the uniaxial fatique tests. (orig./RW) 891 RW/orig.- 892 RKD

  1. Thermal fatigue cycling of Be/Cu joining mock-ups

    To evaluate beryllium-to-copper joining techniques for potential use by US manufacturers in making first wall components for International Thermonuclear Experimental Reactor (ITER), we tested two mock-ups with S65C beryllium (Be) tiles Hot Isostatic Pressing (HIP) bonded to CuCrZr heat sinks. Under the aegis of the US ITER Project Office, Sandia prepared the mock-ups working with industrial vendors and performed high heat flux testing at Sandia's Plasma Material Test Facility (PMTF) to ascertain the robustness of the Be/Cu joints to 1000 thermal fatigue cycles at a heat flux level of 1.5 MW/m2. Thermal stress analysis provided insight into choosing the heat flux and flow conditions required for accelerated fatigue testing at 1000 cycles and 1.5 MW/m2 that is comparable to the 12,000 cycles and 0.875 MW/m2 required for the ITER First Wall Qualification Mock-ups. Each mock-up had three Be tiles, 35.5 mm square and 10 mm thick, bonded to a CuCrZr heat sink 134.5 mm x 36 mm x 25 mm with a single bored 12.7 mm (dia.) cooling channel. The bonding techniques included various interlayer metallizations and HIPping at 100 MPa pressure and temperature of 580 or 560 deg. C for 2 h. Each tile had a thermocouple (TC) in the center 1 mm below the Be/Cu interface. The test arrangement allowed for both mock-ups to be tested at the same time with alternate heating and cooling cycles of equal duration of 30 s. A total power of 12.7 kW was absorbed by the heated area of 4000 mm2 during the on-cycle. The mock-up was cooled by water at 2.3 m/s (0.27 kg/s), 1 MPa and 20 deg. C inlet temperature. These operating conditions did not permit the mock-ups to cool down to their initial temperature state during the off-cycle. Both mock-ups survived 1000 cycles with no significant changes. The temperature of the top surface on each reached 254 deg. C; while the center TCs reached 136 and 139 deg. C, respectively. Despite localized changes observed in the surface emissivity, the corrected

  2. Fatigue behaviors of Z2CND18.12N stainless steel under thermal-mechanical cycling

    Liubing WANG; Dunji YU; Fei XUE; Weiwei YU; Jian CHEN; Xu CHEN

    2011-01-01

    Tests under mechanical strain control were performed to investigate the TMF behavior of Z2CND18.12N within the temperature range between 150-550 ℃. Differentstrain amplitudes and phase-angles were applied. Total strain controlled low cycle fatigue test was also performed at the peak temperature of TMF cycling. The results show that the cyclic stress response of the material displayed an initial hardening regime followed by a saturation period and then cyclic softening till failure. The TMF cycling leads to the development of significant amounts of mean stress. Some life prediction models were employed to predict the TMF life of Z2CND18.12N, and the results indicate that the energy-based models provide good prediction on the thermal-mechanical fatigue behaviors of this material. An optical microscopic observation shows that the surface crack initiations and crack propagations are typicallytransgranular mode.

  3. Influence of temperature, environment, and thermal aging on the continuous cycle fatigue behavior of Hastelloy X and Inconel 617

    Results are presented for strain-controlled fatigue and tensile tests for two nickel-base, solution-hardened reference structural alloys for use in several High-Temperature Gas-Cooled Reactor (HTGR) concepts. These alloys, Hastelloy X and Inconel 617, were tested from room temperature to 8710C in air and impure helium. Materials were tested in both the solution-annealed and the preaged conditios, in which aging consisted of isothermal exposure at one of several temperatures for periods of up to 20,000 h. Comparisons are given between the strain-controlled fatigue lives of these and several other commonly used alloys, all tested at 5380C. An analysis is also presented of the continuous cycle fatigue data obtained from room temperature to 4270C for Hastelloy G, Hastelloy X, Hastelloy C-276, and Hastelloy C-4, an effort undertaken in support of ASME code development

  4. The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)

    Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.

    2000-01-01

    The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.

  5. Effect of δ-ferrite on the low cycle fatigue behavior of 12CrMoV steel

    The 12CrMoV steel subjected to high temperature will inevitably contain some δ-ferrite. The presence of δ-ferrite in this steel has been known to lead to discontinuites in the mechanical properties because of compositional differences and lack of cohesin between δ-ferrite and tempered martensite matrix. The strain controlled fatigue test was carried out to investigate the effect of δ-ferrite on the low cycle fatigue behavior of the 12CrMoV steel at room temperature. Two different microstructures, tempered martensite with and without δ-ferrite, were developed by heat treatment schedules. The tensile properties for the two different specimen conditions were very similar. The cyclic behavior was characterized by softening and the plastic strain range vs. the number of reversals plots obeyed the Manson-Coffin relationship. The fatigue crack propagation mode was a transgranular. However, the specimen with δ-ferrite had a longer fatigue life than that without δ-ferrite. Introduction of δ-ferrite resulted in the increase of cyclic strain hardening exponent and the more plastic work required to failure. The δ-ferrite had influence on the crack path as a soft obstacle, which resulted that the crack passed around δ-ferrite. An excess energy was required to propagate the crack and led locally to a decrease in crack growth rate. Therefore, the presence of δ-ferrite in tempered martensite increased the resistance to crack propagation and resulted in the increase in fatigue life

  6. Strain-Controlled Low-Cycle Fatigue Behavior of Friction Stir-Welded AZ31 Magnesium Alloy

    Yang, J.; Ni, D. R.; Wang, D.; Xiao, B. L.; Ma, Z. Y.

    2014-04-01

    Strain-controlled low-cycle fatigue (LCF) behavior of friction stir-welded (FSW) AZ31 joints, produced at rotation rates of 800 and 3500 rpm, was studied. The joints exhibited symmetric hysteresis loops, whereas asymmetric loops were observed for the parent material (PM). The fatigue resistance of the FSW joints was slightly improved as the rotation rate increased, and both the FSW joints possessed a fatigue life similar to that of the PM at the low strain amplitude of 0.1 pct. The obtained fatigue data for the PM and FSW joints can be well described using the Coffin-Manson and Basquin's relationships. For the FSW joints, during LCF deformation, the twinning originated from the nugget zone (NZ)/thermomechanically affected zone (TMAZ) boundary and then propagated to the NZ interior. This was attributed to different textures in these regions: the center of the NZ exhibited a hard orientation, whereas a soft orientation was observed in the region around the NZ/TMAZ boundary. The fatigue cracks initiated at the bottom of the joints and propagated along the NZ/TMAZ boundary or the NZ adjacent to the NZ/TMAZ boundary.

  7. Deformation-induced dissolution and growth of precipitates in an Al–Mg–Er alloy during high-cycle fatigue

    The dissolution and growth of Al3(Er, Zr) precipitates during tensile fatigue experiments were investigated by quasi-in situ and post-mortem scanning transmission electron microscopy with Z contrast imaging and X-ray energy dispersive spectroscopy. Al3(Er, Zr) particles were observed with both non-core–shell and core–shell structures, which were formed during multiple-stage precipitations, in an Al–Mg–Er alloy. After fatigue deformations, the average size of the non-core–shell structured precipitates increased significantly. By tracing the same precipitate particles before and after a high-cycle fatigue test, quasi-in situ electron microscopy revealed that the increase of average particle size is associated with the substantial dissolution of small non-core–shell structured Al3(Er, Zr) particles, whose diameters are generally less than 15 nm, and a consequent growth of larger non-core–shell Al3(Er, Zr) precipitates. On the contrary, the core–shell structured Al3(Er, Zr) precipitates remain stable during high-cycle fatigue tests. Possible mechanisms for the dissolution and growth of non-core–shell structured Al3(Er, Zr) precipitates are discussed in terms of particle size, interfacial energy and lattice mismatch, in comparison to the stable core–shell structured precipitates

  8. Effect of tensile dwell on low cycle fatigue of cast superalloy Inconel 792-5A at 800°C

    Šmíd, Miroslav; Obrtlík, Karel; Petrenec, Martin; Polák, Jaroslav

    488-489, - (2012) s. 735-738. ISSN 1013-9826 R&D Projects: GA ČR(CZ) GAP107/11/2065; GA ČR(CZ) GAP204/11/1453 Institutional research plan: CEZ:AV0Z20410507 Keywords : nickle base superalloy * elevated temperatures * low cycle fatigue * dwells Subject RIV: JL - Materials Fatigue, Friction Mechanics

  9. The effect of cycle waveshape on the low cycle fatigue behaviour of 20%Cr-25%Ni-Nb stainless steel at 650 deg C

    Low cycle fatigue tests at 650 deg C on 20% Cr-25% Ni-Nb stainless steel have been carried out under conditions of equal tension/compression ramp rates (10-3 s-1) and slow tension-fast compression ramp rates (10-6 s-1/10-3 s-1). It was found that the latter cycle significantly reduced endurance. Detailed metallography revealed that life reduction is due to the accumulation of creep damage during the slow tensile ramp. It is proposed that at high strain ranges, failure is creep dominated and this changes to a creep-fatigue interaction failure mechanism at low strain ranges. Predictive models have been developed based on cavity growth mechanisms and ductility exhaustion. Both techniques provide an accurate life prediction and only limited data are required to use them. (author)

  10. Predicting Blood Lactate Concentration and Oxygen Uptake from sEMG Data during Fatiguing Cycling Exercise

    Petras Ražanskas

    2015-08-01

    Full Text Available This article presents a study of the relationship between electromyographic (EMG signals from vastus lateralis, rectus femoris, biceps femoris and semitendinosus muscles, collected during fatiguing cycling exercises, and other physiological measurements, such as blood lactate concentration and oxygen consumption. In contrast to the usual practice of picking one particular characteristic of the signal, e.g., the median or mean frequency, multiple variables were used to obtain a thorough characterization of EMG signals in the spectral domain. Based on these variables, linear and non-linear (random forest models were built to predict blood lactate concentration and oxygen consumption. The results showed that mean and median frequencies are sub-optimal choices for predicting these physiological quantities in dynamic exercises, as they did not exhibit significant changes over the course of our protocol and only weakly correlated with blood lactate concentration or oxygen uptake. Instead, the root mean square of the original signal and backward difference, as well as parameters describing the tails of the EMG power distribution were the most important variables for these models. Coefficients of determination ranging from R2 = 0:77 to R2 = 0:98 (for blood lactate and from R2 = 0:81 to R2 = 0:97 (for oxygen uptake were obtained when using random forest regressors.

  11. The J-2X Fuel Turbopump - Turbine Nozzle Low Cycle Fatigue Acceptance Rationale

    Hawkins, Lakiesha V.; Duke, Gregory C.; Newman, Wesley R.; Reynolds, David C.

    2011-01-01

    The J-2X Fuel Turbopump (FTP) turbine, which drives the pump that feeds hydrogen to the J-2X engine for main combustion, is based on the J-2S design developed in the early 1970 s. Updated materials and manufacturing processes have been incorporated to meet current requirements. This paper addresses an analytical concern that the J-2X Fuel Turbine Nozzle Low Cycle Fatigue (LCF) analysis did not meet safety factor requirements per program structural assessment criteria. High strains in the nozzle airfoil during engine transients were predicted to be caused by thermally induced stresses between the vane hub, vane shroud, and airfoil. The heritage J-2 nozzle was of a similar design and experienced cracks in the same area where analysis predicted cracks in the J-2X design. Redesign options that did not significantly impact the overall turbine configuration were unsuccessful. An approach using component tests and displacement controlled fracture mechanics analysis to evaluate LCF crack initiation and growth rate was developed. The results of this testing and analysis were used to define the level of inspection on development engine test units. The programmatic impact of developing crack initiation/growth rate/arrest data was significant for the J-2X program. Final Design Certification Review acceptance logic will ultimately be developed utilizing this test and analytical data.

  12. Accelerated multiscale space-time finite element simulation and application to high cycle fatigue life prediction

    Zhang, Rui; Wen, Lihua; Naboulsi, Sam; Eason, Thomas; Vasudevan, Vijay K.; Qian, Dong

    2016-08-01

    A multiscale space-time finite element method based on time-discontinuous Galerkin and enrichment approach is presented in this work with a focus on improving the computational efficiencies for high cycle fatigue simulations. While the robustness of the TDG-based space-time method has been extensively demonstrated, a critical barrier for the extensive application is the large computational cost due to the additional temporal dimension and enrichment that are introduced. The present implementation focuses on two aspects: firstly, a preconditioned iterative solver is developed along with techniques for optimizing the matrix storage and operations. Secondly, parallel algorithms based on multi-core graphics processing unit are established to accelerate the progressive damage model implementation. It is shown that the computing time and memory from the accelerated space-time implementation scale with the number of degree of freedom N through ˜ O(N^{1.6}) and ˜ O(N), respectively. Finally, we demonstrate the accelerated space-time FEM simulation through benchmark problems.

  13. TEMPERATURE EFFECT ON LOW-CYCLE FATIGUE BEHAVIOR OF NICKEL-BASED SINGLE CRYSTALLINE SUPERALLOY

    Xianfeng Ma; Huiji Shi; Jialin Gu; Zhaoxi Wang; Harald Harders; Thomas Malow

    2008-01-01

    The low-cycle fatigue (LCF) behavior of a nickel-based single crystal superalloy with [001] orientation was studied at an intermediate temperature of To℃ and a higher temper ature of To + 250℃ under a constant low strain rate of 10-3 s-1 in ambient atmosphere.The superalloy exhibited cyclic tension-compression asymmetry which is dependent on the temper ature and applied strain amplitude.Analysis on the fracture surfaces showed that the surface and subsurface casting mieropores were the major crack initiation sites.Interior Ta-rich carbides were frequently observed in all specimens.Two distinct types of fracture were suggested by frac togaphy.One type was characterized by Mode-Ⅰ cracking with a microscopically rough surface at To + 250℃.Whereas the other type at lower temperature To℃ favored either one or several of the octahedral {111} planes,in contrast to the normal Mode-Ⅰ growth mode typically observed at low loading frequencies (several Hz).The failure mechanisms for two cracking modes are shearing of γ' precipitates together with the matrix at To℃ and cracking confined in the matrix and the γ/γ'interface at To + 250℃.

  14. Low cycle fatigue behavior of a ferritic reactor pressure vessel steel

    The cyclic stress–strain response and the low cycle fatigue (LCF) behavior of 20MnMoNi55 pressure vessel steel were studied. Tensile strength and LCF properties were examined at room temperature (RT) using specimens cut from rolling direction of a rolled block. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The cyclic strain–stress relationships and the strain–life relationships were obtained through the test results, and related LCF parameters of the steel were calculated. The studied steel exhibits cyclic softening behavior. Furthermore, analysis of stabilized hysteresis loops showed that the steel exhibits non-Masing behavior. Complementary scanning electron microscopy examinations were also carried out on fracture surfaces to reveal dominant damage mechanisms during crack initiation, propagation and fracture. Multiple crack initiation sites were observed on the fracture surface. The investigated LCF behavior can provide reference for pressure vessel life assessment and fracture mechanisms analysis

  15. Low cycle fatigue behavior of a ferritic reactor pressure vessel steel

    Sarkar, Apu, E-mail: asarkar@barc.gov.in; Kumawat, Bhupendra K.; Chakravartty, J.K.

    2015-07-15

    The cyclic stress–strain response and the low cycle fatigue (LCF) behavior of 20MnMoNi55 pressure vessel steel were studied. Tensile strength and LCF properties were examined at room temperature (RT) using specimens cut from rolling direction of a rolled block. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The cyclic strain–stress relationships and the strain–life relationships were obtained through the test results, and related LCF parameters of the steel were calculated. The studied steel exhibits cyclic softening behavior. Furthermore, analysis of stabilized hysteresis loops showed that the steel exhibits non-Masing behavior. Complementary scanning electron microscopy examinations were also carried out on fracture surfaces to reveal dominant damage mechanisms during crack initiation, propagation and fracture. Multiple crack initiation sites were observed on the fracture surface. The investigated LCF behavior can provide reference for pressure vessel life assessment and fracture mechanisms analysis.

  16. Low cycle fatigue behavior of an [alpha] + [beta] titanium alloy: Ti6246

    Beranger, A.S. (Dept. de Genie Mecanique, Univ. de Technologie de Compiegne, Centre de Recherche de Royallieu, 60 Compiegne (France)); Feaugas, X. (Dept. de Genie Mecanique, Univ. de Technologie de Compiegne, Centre de Recherche de Royallieu, 60 Compiegne (France)); Clavel, M. (Dept. de Genie Mecanique, Univ. de Technologie de Compiegne, Centre de Recherche de Royallieu, 60 Compiegne (France))

    1993-11-30

    The present study focused on the cyclic behavior of an [alpha] + [beta] titanium alloy, Ti6246. Low cycle fatigue tests were carried out between 20 C and 500 C under plastic strain control. The experimental results show that the 6246 alloy exhibits cyclic softening irrespective of the imposed temperature or strain. Nevertheless, careful analysis of the stress-strain hysteresis loops revealed that the physical origins and the underlying physical mechanisms of the softening are strongly temperature dependent. At room temperature, the softening appears to proceed from a decrease in the kinematic component of stress; it is governed by the gradual homogenization of the initially heterogeneous distribution of dislocations (localized slip bands) in the [alpha] phase in relation to the long-range internal stress field. In contrast, at high temperatures, the second phase shearing process due to the homogeneously distributed dislocations, and the occurrence of cross-slip, lower the isotropic contribution and lead to the observed cyclic softening. The mechanical results and the microstructural observations are therefore fairly consistent with one another. (orig.)

  17. Effect of thermo-mechanical loading histories on fatigue crack growth behavior and the threshold in SUS 316 and SCM 440 steels. For prevention of high cycle thermal fatigue failures

    High cycle thermal fatigue failure of pipes induced by fluid temperature change is one of the interdisciplinary issues to be concerned for long term structural reliability of high temperature components in energy systems. In order to explore advanced life assessment methods to prevent the failure, fatigue crack propagation tests were carried out in a low alloy steel and an austenitic stainless steel under typical thermal and thermo-mechanical histories. Special attention was paid to both the effect of thermo-mechanical loading history on the fatigue crack threshold, as well as to the applicability of continuum fracture mechanics treatment to small or short cracks. It was shown experimentally that the crack-based remaining fatigue life evaluation provided more reasonable assessment than the traditional method based on the semi-empirical law in terms of 'usage factor' for high cycle thermal fatigue failure that is employed in JSME Standard, S017. The crack propagation analysis based on continuum fracture mechanics was almost successfully applied to the small fatigue cracks of which size was comparable to a few times of material grain size. It was also shown the thermo-mechanical histories introduced unique effects to the prior fatigue crack wake, resulting in occasional change in the fatigue crack threshold. (author)

  18. Grain boundary precipitation treatment for improving high temperature low cycle fatigue strength of SSS113M for VHTR

    Grain boundary precipitation treatment was studied for the purpose of improving high temperature low cycle fatigue strength of a Ni-23% Cr-18% W alloy. SSS113M which had been developed as an intermediate heat exchanger material of VHTR and recognized as the best alloy in the national research project concerning nuclear steelmaking in Japan. Conventional single solid solution treatment of 13000C x 1h W.Q. does not cause any massive grain boundary precipitation in SSS113M, but additional heat treatment of 12500C x 1h W.Q. causes discontinuous grain boundary precipitation of α.W phase. This grain boundary precipitation treatment results in two- to fivefold increase of low cycle fatigue strength at 8000C as well as slightly higher creep and stress rupture strength at 10000C

  19. Ultrasonic evaluation of the effects of compressive residual stresses on aircraft engine turbine blades subjected to high cycle fatigue

    Bray, Don E.; Suh, Ui; Hough, C. L. ``Mickey''

    2002-05-01

    Experiments conducted on titanium (Ti-64) turbine blades with the LCR ultrasonic wave at 20 MHz showed significant differences in untreated blades and blades treated to increase the subsurface compressive residual stress. Group 1 showed significant differences in the treated and untreated areas, the top and bottom of the blades, high cycle fatigue and cracked and uncracked conditions. Group 2 blades showed significant difference between untreated and treated travel-times at probes located at the blade leading edge.

  20. Ultrasonic evaluation of the effects of compressive residual stresses on aircraft engine turbine blades subjected to high cycle fatigue

    Experiments conducted on titanium (Ti-64) turbine blades with the LCR ultrasonic wave at 20 MHz showed significant differences in untreated blades and blades treated to increase the subsurface compressive residual stress. Group 1 showed significant differences in the treated and untreated areas, the top and bottom of the blades, high cycle fatigue and cracked and uncracked conditions. Group 2 blades showed significant difference between untreated and treated travel-times at probes located at the blade leading edge

  1. Electrostimulated increase of steel 08Kh18N10T plasticity under conditions of low cycle fatigue

    The evolution of structure in steel 08Kh18N10T is studied in the course of low cycle fatigue tests and electrostimulation at the stages preceding microcrack formation. Electrostimulation is revealed to have no effect on grain size but results in a decrease of slip line and twin densities. It is assumed that application of electric current pulses promotes the relaxation of elastic stress fields and decelerates structural evolution

  2. Low cycle fatigue behaviour of neutron irradiated copper alloys at 250 and 350 deg. C

    Singh, B.N.; Stubbins, J.F.; Toft, P.

    2000-01-01

    speciments were fatigue tested in vacuum at the irradiation temperatures of 250 and 350 deg. C in a strain controlled mode with a loading frequency of 0.5Hz.Post-fatigue microstructures were examined using transmission electron microscopy and the fracture surfaces were investigated using scanning electron...

  3. Low cycle fatigue behavior of Sanicro25 steel at room and at elevated temperature

    Polák, Jaroslav; Petráš, Roman; Heczko, Milan; Kuběna, Ivo; Kruml, Tomáš; Chai, G.

    2014-01-01

    Roč. 615, OKT (2014), s. 175-182. ISSN 0921-5093 R&D Projects: GA ČR(CZ) GA13-23652S Institutional support: RVO:68081723 Keywords : Sanicro 25 steel * Cyclic plasticity * Dislocation structure * Fatigue life * Effect of temperature Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.567, year: 2014

  4. Investigation and modeling of low cycle fatigue behaviors of two Ni-based superalloys under dwell conditions

    The ability to predict fatigue behaviors of turbine-disk-materials under operating conditions is an important aspect of designing a safe turbine engine. Studies of two Ni-based superalloys, powder metallurgy (PM) FGH95 and Cast GH4169, have been undertaken to investigate their low cycle fatigue (LCF) behaviors with different dwell conditions reflecting the fatigue-creep interaction at high temperature of 650 deg. C. Based on the deformation behaviors obtained by the tests, the effects of dwell on mean stress and shape of hysteretic loop at half life have been analyzed and considered to be introduced in developing a new fatigue model. For the purpose, two groups of parameters are defined in order to introduce the effects of mean stress and shape of hysteretic loop, especially due to their changes caused by dwell. Finally, an energy-based fatigue model is given with modifying of the original energy-type damage parameter. As a comparison, four typical models of LCF are used to model the experimental results, which are the Strain Range Partitioning method (SRP), the Frequency Separation method (FS), the Damage Rate method (DR) and the Ostergren method. The experimental data of LCF of cast and wrought (CW) Rene95, and PM Rene95 from open resources are also used to verify abilities of the newly-developed model. The results show that the model can describe fatigue behaviors well, and the scatter bands are within ±2, even considering the dwell effects. The accuracy and adaptability of predicting LCF life of the model are better than those of the four existing models.

  5. Investigation and modeling of low cycle fatigue behaviors of two Ni-based superalloys under dwell conditions

    Wei Dasheng [School of Jet Propulsion, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China); Yang Xiaoguang [School of Jet Propulsion, Beijing University of Aeronautics and Astronautics, Beijing 100083 (China)], E-mail: yxg@buaa.edu.cn

    2009-09-15

    The ability to predict fatigue behaviors of turbine-disk-materials under operating conditions is an important aspect of designing a safe turbine engine. Studies of two Ni-based superalloys, powder metallurgy (PM) FGH95 and Cast GH4169, have been undertaken to investigate their low cycle fatigue (LCF) behaviors with different dwell conditions reflecting the fatigue-creep interaction at high temperature of 650 deg. C. Based on the deformation behaviors obtained by the tests, the effects of dwell on mean stress and shape of hysteretic loop at half life have been analyzed and considered to be introduced in developing a new fatigue model. For the purpose, two groups of parameters are defined in order to introduce the effects of mean stress and shape of hysteretic loop, especially due to their changes caused by dwell. Finally, an energy-based fatigue model is given with modifying of the original energy-type damage parameter. As a comparison, four typical models of LCF are used to model the experimental results, which are the Strain Range Partitioning method (SRP), the Frequency Separation method (FS), the Damage Rate method (DR) and the Ostergren method. The experimental data of LCF of cast and wrought (CW) Rene95, and PM Rene95 from open resources are also used to verify abilities of the newly-developed model. The results show that the model can describe fatigue behaviors well, and the scatter bands are within {+-}2, even considering the dwell effects. The accuracy and adaptability of predicting LCF life of the model are better than those of the four existing models.

  6. Effect of vanadium on the high-cycle fatigue fracture properties of medium-carbon microalloyed steel for fracture splitting connecting rod

    Highlights: • Effect of V up to 0.45% on fatigue property of medium carbon MA steel was studied. • Fatigue strength and fatigue strength ratio increase with increasing V content. • Excellent fatigue properties can be obtained when V is higher than ∼0.28%. • Strengthening ferrite is the key to improve fatigue property of MA steel. • The fatigue crack growth behavior is similar for the MA steel with exponent m ≈ 3.5. - Abstract: The present investigation effort was made to study the effect of V up to 0.45% on the high-cycle fatigue properties of medium-carbon microalloyed (MA) steel 37MnSiVS, for the development of new crackable MA forging steel with excellent fatigue properties. The results show that the amount of V(C,N) precipitates increases with increasing V content and most of the precipitates are less than 5 nm. Owing to the significant precipitation strengthening effect of these nanosized particles, the hardness increase of ferrite with increasing V content is higher than that of pearlite and accordingly a decrease of pearlite/ferrite hardness ratio. Therefore, both fatigue strength and fatigue strength ratio increase with increasing V content and excellent fatigue properties could be obtained when V content is higher than about 0.28%. The fatigue crack growth (FCG) behavior is similar for all the three 37MnSiVS samples with an exponent m ≈ 3.5. It is concluded that V can improve the fatigue properties of ferrite–pearlite steel mainly through precipitation strengthening and therefore it is anticipated that MA steel’s fatigue property could be further improved as well as more fine V(C,N) particles be obtained

  7. Influence of surface finish on the high cycle fatigue behavior of a 304L austenitic stainless steel

    This work has dealt with the influence of surface finish on the high cycle fatigue behavior of a 304L. The role played by roughness, surface hardening and residual stresses has been particularly described. First part of this study has consisted of the production of several surface finishes. These latter were obtained by turning, grinding, mechanical polishing and sandblasting. The obtained surfaces were then characterised in terms of roughness, hardening, microstructure and residual stresses. Fatigue tests were finally conducted under various stress ratios or mean stresses at two temperatures (25 C and 300 C). Results clearly evidenced an effect of the surface integrity on the fatigue resistance of the 304L. This influence is nevertheless more pronounced at ambient temperature and for a positive mean stress. For all explored testing conditions, the lowest endurance limit was obtained for ground specimens whereas polished samples exhibited the best fatigue strength. Results also cleared out a detrimental influence of a positive mean stress in the case of specimens having surface defaults of a great acuity. The study of the relative effect of each of the surface parameter, under a positive stress ratio and at the ambient temperature, showed that roughness profile and surface hardening are the two more influential factors. The role of the residual stresses remains negligible due to their rapid relaxation during the application of the first cycles of fatigue. The estimation of the initiation and propagation periods showed that mechanisms differed as a function of the applied stress ratio. Crack propagation is governed by the parameter DK at a positive stress ratio and by Dep/2 in the case of tension-compression tests. (author)

  8. Results of 300 low cycle fatigue tests at 723 K and 823 K on irradiated and unirradiated stainless steel DIN 1.4948 plate and welded joints

    Low cycle fatigue specimens of stainless steel DIN 1.4948 (similar to AISI type 304) have been irradiated at 723 K and 823 K up to fluence levels of 1x1023n.m-2 and 5x1024n.m-2 (E > 0.1 MeV). Post irradiation low-cycle fatigue tests were performed in air at irradiation temperature on specimens made from plate metal and welded joints. (Auth.)

  9. Damage estimates for European and U.S.sites using the U.S. high-cycle fatigue data base

    Sutherland, H.J. [Wind Energy Technology, Sandia National Lab., Albuquerque, NM (United States)

    1996-09-01

    This paper uses two high-cycle fatigue data bases, one for typical U.S. blade materials and one for European materials, to analyze the service lifetime of a wind turbine blade subjected to the WISPER load spectrum for northern European sites and the WISPER protocol load spectrum for U.S. wind farm sites. The U.S. data base contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a U.S. wind farm site, i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a U.S. wind farm site. Further, the analysis demonstrate that the European and the U.S. fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the U.S. data base predicting significantly shorter service lifetimes than the European data base. (au) 14 refs.

  10. A Cycling Movement Based System for Real-Time Muscle Fatigue and Cardiac Stress Monitoring and Analysis.

    Szi-Wen Chen

    Full Text Available In this study, we defined a new parameter, referred to as the cardiac stress index (CSI, using a nonlinear detrended fluctuation analysis (DFA of heart rate (HR. Our study aimed to incorporate the CSI into a cycling based fatigue monitoring system developed in our previous work so the muscle fatigue and cardiac stress can be both continuously and quantitatively assessed for subjects undergoing the cycling exercise. By collecting electrocardiogram (ECG signals, the DFA scaling exponent α was evaluated on the RR time series extracted from a windowed ECG segment. We then obtained the running estimate of α by shifting a one-minute window by a step of 20 seconds so the CSI, defined as the percentage of all the less-than-one α values, can be synchronously updated every 20 seconds. Since the rating of perceived exertion (RPE scale is considered as a convenient index which is commonly used to monitor subjective perceived exercise intensity, we then related the Borg RPE scale value to the CSI in order to investigate and quantitatively characterize the relationship between exercise-induced fatigue and cardiac stress. Twenty-two young healthy participants were recruited in our study. Each participant was asked to maintain a fixed pedaling speed at a constant load during the cycling exercise. Experimental results showed that a decrease in DFA scaling exponent α or an increase in CSI was observed during the exercise. In addition, the Borg RPE scale and CSI were positively correlated, suggesting that the factors due to cardiac stress might also contribute to fatigue state during physical exercise. Since the CSI can effectively quantify the cardiac stress status during physical exercise, our system may be used in sports medicine, or used by cardiologists who carried out stress tests for monitoring heart condition in patients with heart diseases.

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

    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)

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

    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. 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

  13. Strain Ratio Effects on Low-Cycle Fatigue Behavior of Gravity Cast Al-Si-Cu Alloys

    Fan, K. L.; Liu, X. S.; He, G. Q.; Cheng, H.; Lv, S. Q.

    2015-10-01

    The strain-controlled low-cycle fatigue properties of gravity cast Al-Si-Cu alloys for engine cylinder heads were investigated. At strain ratios of R ɛ = -2, 0, and 0.1, the cyclic stress amplitude progressively increased from initiation to the 450th cycle, and then proceeded into a steady stage until failure. At a strain ratio of R ɛ = -∞, the material exhibited a continuous cyclic hardening. The hysteresis loops in this alloy for the 2nd and half-life cycle were tension/compression asymmetry, which also corresponded well to the evolution of peak/valley stress. Transmission electron microscopy analysis suggested that cyclic hardening was caused by the dislocations multiplication/tangles at strain ratios of R ɛ = -∞ and 0. Besides, the presence of dislocation cross slip contributed to cyclic stabilization observed at later stage of deformation at a strain ratio of R ɛ = 0. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain ratios. It showed that the fatigue cracks initiated basically at the internal defects in the samples. Meanwhile, at strain ratios of R = -∞ and 0, the fracture surface was rough with a large number of small unequiaxed dimples and some tear ridges. Moreover, the localized pores offered a preferential crack path in the samples, where they were surrounded by silicon particles. At a strain ratio of R ɛ = -∞, the fatigue cracks preferentially initiated at pores rather than α-Fe phases. At a strain ratio of R ɛ = 0, where fatigue crack initiation was observed at the interface between plate-like branch of α-Fe phase and aluminum matrix.

  14. Avoiding thermal striping damage: Experimentally-based design procedures for high-cycle thermal fatigue

    In the coolant circuits of a liquid metal cooled reactor (LMR), where there is turbulent mixing of coolant streams at different temperatures, there are temperature fluctuations in the fluid. If an item of the reactor structure is immersed in this fluid it will, because of the good heat transfer from the flowing liquid metal, experience surface temperature fluctuations which will induce dynamic surface strains. It is necessary to design the reactor so that these temperature fluctuations do not, over the life of the plant, cause damage. The purpose of this paper is to describe design procedures to prevent damage of this type. Two such procedures are given, one to prevent the initiation of defects in a nominally defect-free structure or to allow initiation only at the end of the component life, and the other to prevent significant growth of undetectable pre-existing defects of the order of 0.2 to 0.4 mm in depth. Experimental validation of these procedures is described, and the way they can be applied in practice is indicated. To set the scene the paper starts with a brief summary of cases in which damage of this type, or the need to avoid such damage, have had important effects on reactor operation. Structural damage caused by high-cycle thermal fatigue has had a significant adverse influence on the operation of LMRs on several occasions. It is necessary to eliminate the risk of such damage at the design stage. In the absence of detailed knowledge of the temperature history to which it will be subject, an LMR structure can be designed so that, if it is initially free of defects more than 0.1 mm deep, no such defects will be initiated by high-cycle fatigue. This can be done by ensuring that the maximum source temperature difference in the liquid metal is less than a limiting value, which depends on temperature. The limit is very low, however, and likely to be restrictive. This method, by virtue of its safety margin, takes into account pre-existing surface crack

  15. High Temperature Low Cycle Fatigue Characteristics of Grit Blasted Polycrystalline Ni-base Superalloy

    Šulák, Ivo; Obrtlík, Karel; Čelko, L.

    Zurich: Trans Tech Publications, 2016 - (Bajić, D.; Tonković, Z.; Aliabadi, F.), s. 73-76. (Key Engineering Materials. 665). ISBN 978-3-03835-541-0. ISSN 1013-9826. [FDM 2015 - International Conference on Fracture and Damage Mechanics /14./. Budva (ME), 21.09.2015-23.09.2015] R&D Projects: GA ČR(CZ) GA15-20991S; GA TA ČR(CZ) TA04011525 Institutional support: RVO:68081723 Keywords : Grit Blasting * Fatigue life * Cyclic stress-strain response * High temperature fatigue * IN 713LC Subject RIV: JL - Materials Fatigue, Friction Mechanics

  16. Effect of deterioration on high temperature low cycle fatigue properties of low alloy steels

    Low cycle fatigue (LCF) tests were carried out at 839 K on Cr-Mo→V forgings and castings taken from various power plant components after long-term service. Δepsilonsub(e)-Nsub(c) and Δepsilonsub(p)-Nsub(c) properties of the used and artificially deteriorated materials were compared with the virgin material. The effect of deterioration on mechanical properties and its correlation with LCF properties were examined. The results obtained are summarized as follows. (1) Cr-Mo→V forging and casting became soft and/or brittle through long-term heat. Material deterioration (softening and embrittlement) changed LCF properties of these steels as follows. i) Δepsilonsub(e)-Nsub(c) relationship shifted downward by softening. ii) Δepsilonsub(p)-Nsub(c) relationship shifted downward when embrittlement became dominant. (2) Vickers hardness had good correlation with Δepsilonsub(e)-Nsub(c) coefficient C1, as long as hardness took the value from 200 to 260, while Δepsilonsub(e)-Nsub(c) expenent α1, Δepsilonsub(p)-Nsub(c) coefficient C2 and exponent α2 were insensitive to the change of hardness. (3) True fracture strain had no clear correlation with C1, α1, C2 and α2. (4) FATT (50 % fracture appearence transition temperature) had good correlation with C2 of casting. Embrittled casting had relatively high FATT and low C2. De-embrittled casting decreased FATT remarkably and increased C2 to some extent. By fractographic observation the former showed intergranular cracking, and the latter showed ductile striation pattern. The values of α2, C1 and α1 were insensitive to the change of FATT. As the effect of deterioration on LCF properties is complicated, further investigation is necessary. (author)

  17. Limitations of Spectral Electromyogramic Analysis to Determine the Onset of Neuromuscular Fatigue Threshold during Incremental Ergometer Cycling

    Latasa, Iban; Cordova, Alfredo; Malanda, Armando; Navallas, Javier; Lavilla-Oiz, Ana; Rodriguez-Falces, Javier

    2016-01-01

    Recently, a new method has been proposed to detect the onset of neuromuscular fatigue during an incremental cycling test by assessing the changes in spectral electromyographic (sEMG) frequencies within individual exercise periods of the test. The method consists on determining the highest power output that can be sustained without a significant decrease in spectral frequencies. This study evaluated the validity of the new approach by assessing the changes in spectral indicators both throughout the whole test and within individual exercise periods of the test. Fourteen cyclists performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. The mean and median frequencies (Fmean and Fmedian, respectively) of the sEMG power spectrum were calculated. The main findings were: (1) Examination of spectral indicators within individual exercise periods of the test showed that neither Fmean nor Fmedian decreased significantly during the last (most fatiguing) exercise periods. (2) Examination of the whole incremental test showed that the behaviour of Fmean and Fmedian with increasing power output was highly inconsistent and varied greatly among subjects. (3) Over the whole incremental test, half of the participants exhibited a positive relation between spectral indicators and workload, whereas the other half demonstrated the opposite behavior. Collectively, these findings indicate that spectral sEMG indexes do not provide a reliable measure of the fatigue state of the muscle during an incremental cycling test. Moreover, it is concluded that it is not possible to determine the onset of neuromuscular fatigue during an incremental cycling test by examining spectral indicators within individual exercise periods of the test. Key points The behaviour of spectral EMG indicators during the incremental test exhibited a high heterogeneity among individuals, with approximately half of the participants showing a positive

  18. Development of extensometer system for measuring displacement of gauge length of low cycle fatigue specimen in high temperature and high pressure water

    Low cycle fatigue experiment in high temperature and high pressure water have been conducted to evaluate environmental fatigue characteristics of nuclear materials which are used in the primary water. The experimental methods of evaluating low cycle fatigue properties are to control by either load or displacement. The study is about the development of extensometer system for measuring displacement in gauge length of low cycle fatigue specimen in autoclave which simulated high temperature and high pressure water. The developed extensometer system showed precise change of displacement data by controlling actuator in room temperature as well as high temperature and high pressure water. This device can be applied to various material testings in high temperature and high pressure environments and is expected to greatly contribute on acquiring more detailed test data.

  19. High cycle fatigue behavior of a nanostructured composite produced via extrusion of amorphous Al89Gd7Ni3Fe1 alloy powders

    A nanostructured composite Al89Gd7Ni3Fe1 alloy was created by extruding atomized amorphous Al89Gd7Ni3Fe1 powders at different extrusion ratios (ER = 5:1, 10:1, 20:1). The microstructures and mechanical properties produced were examined with special attention given to the high cycle fatigue properties. High cycle fatigue tests were conducted at room temperature under three-point bending at a stress ratio R = 0.1. Increasing the extrusion ratio (ER) improved the hardness, bend strength, and fatigue behavior, with alloys extruded at higher ER exhibiting bend strengths exceeding 1000 MPa and high cycle fatigue behavior well in excess of conventional aluminum alloys. The results obtained are compared to conventional aluminum alloys and particulate reinforced composites.

  20. The evaluation of low-cycle fatigue durability of the pipeline material working at high temperature in original state and after exploitation

    The paper deals with the fatigue tests in range of low cycle fatigue for the materials used in energetic pipelines. The tests are performed both for the initial state and after long term operating period. The paper presents the evaluation of fatigue durability of 13HMF steel at room temperature and 550oC. On the basis of performed metallurgical studies of material waste after operating period according to the adapted quality criteria has been described. Low-cycle fatigue tests of the material showed the increase of durability after operating period and simultaneously decrease of saturation stress σan. Decrease of saturation stress σan for the assumed ranges Δεc of the material after its operating period related to saturation stress at the initial state manifests its decreasing of low-cycle loading transmission capacity. (author)

  1. Strain-controlled low cycle fatigue properties of a rare-earth containing ZEK100 magnesium alloy

    Highlights: • Low (0.2 wt.%) Nd-containing ZEK100 alloy exhibits a relatively weak basal texture. • Cyclic stabilization sustains at lower strain amplitudes. • Longer fatigue life is obtained for this alloy than for rare earth-free Mg alloys. • Asymmetry and skewness of hysteresis loops are quantified through three parameters. • Pseudo-elastic behavior still remains in the Mg alloy despite rare earth additions. - Abstract: Low rare-earth (RE) containing magnesium alloys are being considered for the lightweight automotive applications to reduce fuel consumption and emissions. Design of magnesium components requires strain-controlled low-cycle fatigue (LCF) behavior. This study was aimed to evaluate the cyclic deformation characteristics and LCF life of a low (0.2 wt.%) Nd-containing ZEK100-O alloy. The alloy contained equiaxed grains along with some Mg12Nd particles, and exhibited a relatively weaker basal texture. While slight cyclic softening occurred at high strain amplitudes, cyclic stabilization remained at lower strain amplitudes. Fatigue life of ZEK100 alloy was longer than that of the extruded RE-free AZ31 and AM30 alloys, due to a fairly good combination of strength with ductility. The asymmetry and skewness of hysteresis loops, which were characterized by eccentricity, angle deviation, and relative slope change, respectively, were effectively improved relative to the extruded RE-free alloys, arising from less extensive twinning caused by texture weakening and grain refinement. While the pseudo-elastic behavior tended to decrease with RE addition, it largely remained. An additional term was thus introduced to calculate the total strain range, i.e., Δεt=Δεe+Δεp+Δεan, where the total anelastic strain range (Δεan) consisted of both tensile and compressive components. Fatigue crack initiated from the near-surface imperfections, and crack propagation was characterized by fatigue striation-like features

  2. Effect of high temperature water chemistry on the low cycle fatigue behaviour of F82H mod. steel

    Load controlled low cycle fatigue tests have been performed on F82H mod. martensitic steel in a number of high temperature aqueous environments with the objective to gain further insight about the relative effects of important parameters such as water conductivity, pH and oxidizing character, on the environmentally assisted cracking behaviour of such alloy, and to implement the data-base needed at a proper definition of a viable water coolant quality for DEMO. F82H fatigue lives were the longest in low conductivity, oxygen-free water with or without hydrogen, but decreased as either water conductivity, pH or oxidizing character increased. The predominant fracture modes identified by scanning electron microscopy were used to propose with the support of the electrochemical data, possible environment-related cracking mechanisms. (author)

  3. The study on the factors affecting the high temperature continuous low-cycle fatigue life of the welded 316LN stainless steel by GTAW

    The influence of weld defect on the continuous low cycle fatigue property for type 316LN stainless steel base metal and weldment was investigated with a strain rate of 4x10-3/sec in air atmosphere. Low cycle fatigue test were conducted at temperature of 823K and 873K. Total strain amplitude was controlled to be 0.4-0.6%. The 308L stainless steel was used as the welding rod. The welding was done by the GTAW process with the welding direction perpendicular to the rolling direction of the base metal. The microstructures of the base metal and weldment are γ phase γ/δ duplex-ferrite, respectively. The fatigue lives of the base metal had twice higher than those of weldment having no visible defect. From the tensile result, the uniform elongation of the base metal had twice higher than that of the weldment. For the base metal and HAZ, the fatigue lives at the same condition were reliable. But some results of the fatigue lives in the weldment had the lowest fatigue life at the same condition. From the observation of the fracture surface after fatigue tests, there were porosities and welding defects. For weldments having the many porosities and welding defects, the fatigue lives decreased 50% and 60-70%, respectively. From the observation of the microstructure near the internal crack, the internal weld defects was existed at the interface among the dendrites grown along the different direction

  4. Experimental investigation on both low cycle fatigue and fracture behavior of DZ125 base metal and the brazed joint at elevated temperature

    Highlights: → Mechanical properties of DZ125 base metal and brazed joint were investigated at 850 deg. C. → The brazed joint has the obvious softening phenomenon at stress range above 640 MPa. → The brazed joint shows lower fatigue life compared with the base metal. → All the brazed joints are fractured in the brazing seam. → The differences of fracture phenomena between two types of specimens were observed. - Abstract: Due to the different low cycle fatigue (LCF) properties and fatigue fracture behavior between DZ125 base metal and the brazed joint, the LCF tests are carried out systematically using tension cycling under stress amplitude control conditions (stress ratio R = 0) at elevated temperature in laboratory air. The present paper sets out to investigate the cyclic deformation response of DZ125 base metal and the brazed joint in two aspects, i.e. fatigue life and fatigue fracture behavior, with the comparative method. Furthermore, the comparative method on the typical fatigue fracture surface features (including fatigue source zone, crack propagation zone and fatigue fracture zone) of DZ125 base metal and the brazed joint cycled to failure is conducted in detail. Based on both the macro mechanical behavior and macro and micro fracture observations, experimental results show that: (1) for the brazed joint, the softening is not obvious at lower stress ranges. But from 640 to 720 MPa, it is very significant; (2) under the same test condition, the brazed joint shows lower fatigue life compared with DZ125 base metal and all brazed joints are fractured in the brazing seam observed by the Scanning Electron Microscope (SEM); and (3) there are many distinctive differences of the fracture phenomena between DZ125 base metal and the brazed joint as follows: (1) the crack initiation mode; (2) the crack propagation behavior; and (3) the morphology of dimple pattern at the fatigue fracture zone.

  5. Evaluation of the Effect of Surface Finish on High-Cycle Fatigue of SLM-IN718

    Lambert, D. M.

    2016-01-01

    The surface finish of parts produced by additive manufacturing processes is much rougher than the surface finish generated by machining processes, and a rougher surface can reduce the fatigue strength of a part. This paper discusses an effort to quantify that reduction of strength in high-cycle fatigue for selective laser melt (SLM) coupons. A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the SLM process. This factor is the percentage reduction from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition at the same fatigue life. Specimens were provided by a number of vendors, free to use their "best practice"; only one heat treat condition was considered; and several test temperatures were characterized, including room temperature, 800F, 1000F, and 1200F. The 1000F data had a large variance, and was omitted from consideration in this document. A first method used linear approximations extracted from the graphs, and only where data was available for both. A recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness no more than 4 micro-inches/inch) was established at approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce a similar life in the as-built surface condition. In this first evaluation, the knockdown factor did not appear to be a function of temperature. A second approach, the "KP method", incorporated the surface finish measure into a new parameter termed the pseudo-stress intensity factor, Kp, which was formulated to be similar to the fracture mechanics stress intensity factor. Using Kp, the variance seemed to be reduced across all sources, and knockdown factors were estimated using Kp over the range where data occurred. A

  6. The low cycle fatigue behavior of a plasma-sprayed coating material

    Gayda, J.; Gabb, T. P.; Miner, R. V., Jr.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  7. Low cycle fatigue behaviour of a plasma-sprayed coating material

    Gayda, J.; Gabb, T. P.; Miner, R. V.

    1986-01-01

    Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

  8. Study on high cycle thermal fatigue in mixing tee. Evaluation of transfer characteristics of temperature fluctuation from fluid to structure

    Thermal striping is observed at a point where hot and cold fluids are mixing. Evaluation of high cycle thermal fatigue on structural components is a significant issue for the reactor safety design. Japan Atomic Energy Agency (JAEA) has conducted experimental and numerical investigations to establish a quantitative evaluation method of high cycle thermal fatigue in a sodium-cooled fast reactor, based on the nature of the phenomena. A water experiment WATLON (as Water Experiment of Fluid Mixing in T-pipe with Long Cycle Fluctuation) has been conducted to clarify the thermal striping phenomena in a mixing tee area. In this study, water experiments WATLON were carried out to clarify the unsteady behavior of heat transfer under wall jet condition. In experiments, heat transfer coefficients between fluid and wall in the mixing region were obtained from temperature measurements using thermocouples (movable tree type in fluid and embedded type in wall). To clarify the relation between the local velocity and the wall temperature, those were measured simultaneously by the Particle Image Velocimetry (PIV) and the thermocouple measurement, respectively. Sampling time of the velocity by the PIV and the temperature by the thermocouple were synchronized in the measurement. The experimental results showed that the heat transfer coefficient was 2∼6 time larger than the reference value predicted by the Dittus-Boelter correlation in straight pipes and was increased as the local velocity near the wall. A CD-ROM is attached as an appendix. (J.P.N.)

  9. A Simulation Method for High-Cycle Fatigue-Driven Delamination using a Cohesive Zone Model

    Bak, Brian Lau Verndal; Turon, A.; Lindgaard, Esben;

    2015-01-01

    function of the energy release rate for the crack growth rate during cyclic loading. The J-integral has been applied to determine the energy release rate. Unlike other cohesive fatigue methods, the proposed method depends only on quasi-static properties and Paris' law parameters without relying on......A novel computational method for simulating fatigue-driven mixed-mode delamination cracks in laminated structures under cyclic loading is presented. The proposed fatigue method is based on linking a cohesive zone model for quasi-static crack growth and a Paris' law-like model described as a...... parameter fitting of any kind. The method has been implemented as a zero-thickness eight-node interface element for Abaqus and as a spring element for a simple finite element model in MATLAB. The method has been validated in simulations of mode I, mode II, and mixed-mode crack loading for both self...

  10. Comparison of Post Weld Treatment of High Strength Steel Welded Joints in Medium Cycle Fatigue

    Pedersen, Mikkel Melters; Mouritsen, Ole Ø.; Hansen, Michael Rygaard;

    2010-01-01

    This paper presents a comparison of three post-weld treatments for fatigue life improvement of welded joints. The objective is to determine the most suitable post-weld treatment for implementation in mass production of certain crane components manufactured from very high-strength steel. The...... the stress range can exceed the yield-strength of ordinary structural steel, especially when considering positive stress ratios (R > 0). Fatigue experiments and qualitative evaluation of the different post-weld treatments leads to the selection of TIG dressing. The process of implementing TIG dressing...... in mass production and some inherent initial problems are discussed. The treatment of a few critical welds leads to a significant increase in fatigue performance of the entire structure and the possibility for better utilization of very high-strength steel....

  11. High cycle thermal fatigue: benchmark at a Te junction piping system of the nuclear power plant Phenix

    This paper presents the studies of the benchmark concerning a high cycle thermal fatigue problem. This benchmark is based on an industrial case, a Te junction piping system of the french FBR Phenix. The main objectives were the comparison of the different methods used by the participants and the analysis of the damage evaluation methods capacity compared to the observed phenomena. This study took place in an international framework with the United Kingdom, Italy, Japan, Korea, Russia, India and France. (A.L.B.)

  12. Identification and analysis of slip systems activated during low-cycle fatigue in a duplex stainless steel

    El Bartali, A.; Aubin, V.; Sabatier, L. [Laboratoire de Mecanique de Lille, LML, UMR CNRS 8107, Ecole Centrale de Lille, BP 48, 59651 Villeneuve d' Ascq Cedex (France); Villechaise, P. [Laboratoire de Mecanique et de Physique des Materiaux, LMPM, UMR CNRS 6617, Ecole Nationale Superieure de Mecanique et Aerotechnique, Teleport 2, 1 Avenue C. Ader, BP 40109, 86961 Futuroscope, Chasseneuil Cedex (France); Degallaix-Moreuil, S. [Laboratoire de Mecanique de Lille, LML, UMR CNRS 8107, Ecole Centrale de Lille, BP 48, 59651 Villeneuve d' Ascq Cedex (France)], E-mail: suzanne.degallaix@ec-lille.fr

    2008-12-15

    This paper focuses on the identification of activated slip systems in low-cycle fatigue ({delta}{epsilon}{sub t}/2 = 5 x 10{sup -3}) in a duplex stainless steel. From electron backscattered diffraction measurements and scanning electron microscopy observations, the slip systems and their associated Schmid factor are analyzed in both constitutive phases. In austenitic grains, one or two slip systems are activated with Schmid factors greater than 0.25. While in the ferritic grains, several slip systems are activated, with a variety of Schmid factors.

  13. Identification and analysis of slip systems activated during low-cycle fatigue in a duplex stainless steel

    This paper focuses on the identification of activated slip systems in low-cycle fatigue (Δεt/2 = 5 x 10-3) in a duplex stainless steel. From electron backscattered diffraction measurements and scanning electron microscopy observations, the slip systems and their associated Schmid factor are analyzed in both constitutive phases. In austenitic grains, one or two slip systems are activated with Schmid factors greater than 0.25. While in the ferritic grains, several slip systems are activated, with a variety of Schmid factors

  14. Effectiveness of the modified fatigue criteria for biaxial loading of notched specimen in high-cycle region

    Major, Štěpán; Hubálovský, Š.; Kocour, Vladimír; Valach, Jaroslav

    Vol. 732. Zürich: Trans Tech Publications, 2015 - (Polach, P.), s. 63-70 ISBN 978-3-03835-413-0. ISSN 1660-9336. [EAN 2014. Conference on experimental stress analysis. /52./. Mariánské Lázně (CZ), 02.06.2014-05.06.2014] Institutional support: RVO:68378297 Keywords : notched specimen * multiaxial criteria * biaxial loading * fatigue life * bending-torsion loading * high-cycle loading Subject RIV: JM - Building Engineering http://www.scientific.net/AMM.732.63

  15. Fatigue failure kinetics and structural changes in lead-free interconnects due to mechanical and thermal cycling

    Fiedler, Brent Alan

    Environmental and human health concerns drove European parliament to mandate the Reduction of Hazardous Substances (RoHS) for electronics. This was enacted in July 2006 and has practically eliminated lead in solder interconnects. There is concern in the electronics packaging community because modern lead-free solder is rich in tin. Presently, near-eutectic tin-silver-copper solders are favored by industry. These solders are stiffer than the lead-tin near-eutectic alloys, have a higher melting temperature, fewer slip systems, and form intermetallic compounds (IMC) with Cu, Ni and Ag, each of which tend to have a negative effect on lifetime. In order to design more reliable interconnects, the experimental observation of cracking mechanisms is necessary for the correct application of existing theories. The goal of this research is to observe the failure modes resulting from mode II strain and to determine the damage mechanisms which describe fatigue failures in 95.5 Sn- 4.0 Ag - 0.5 Cu wt% (SAC405) lead-free solder interconnects. In this work the initiation sites and crack paths were characterized for SAC405 ball-grid array (BGA) interconnects with electroless-nickel immersion-gold (ENIG) pad-finish. The interconnects were arranged in a perimeter array and tested in fully assembled packages. Evaluation methods included monotonic and displacement controlled mechanical shear fatigue tests, and temperature cycling. The specimens were characterized using metallogaphy, including optical and electron microscopy as well as energy dispersive spectroscopy (EDS) and precise real-time electrical resistance structural health monitoring (SHM). In mechanical shear fatigue tests, strain was applied by the substrates, simulating dissimilar coefficients of thermal expansion (CTE) between the board and chip-carrier. This type of strain caused cracks to initiate in the soft Sn-rich solder and grow near the interface between the solder and intermetallic compounds (IMC). The growth near

  16. Degradation of TBC Coating during Low-Cycle Fatigue Tests at High Temperature

    Hutařová, S.; Obrtlík, Karel; Juliš, M.; Čelko, L.; Hrčková, M.; Podrábský, T.

    Zurich : Trans Tech Publications, 2014 - (Šandera, P.), s. 461-464 ISBN 978-3-03785-934-6. ISSN 1013-9826. - (Key Engineering Materials. 592-593). [MSMF 7 - International Conference on Materials Structure & Micromechanics of Fracture /7./. Brno (CZ), 01.07.2013-03.07.2013] R&D Projects: GA ČR(CZ) GAP107/11/2065; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : High temperature fatigue * YSZ * CoNiCrAlY * Inconel 713LC Subject RIV: JL - Materials Fatigue, Friction Mechanics

  17. Low-cycle fatigue of polycrystalline α-iron modified by mutually immiscible silver-ion implantation

    Cyclic deformations of annealed pure polycrystalline α-iron with and without further mutually immiscible silver-ion implantation (90 keV, 6 x 1016 ions cm-2) were studied in a plastic strain-controlled tension-compression fatigue test (triangular loading waveform, frequency 0.02-0.3 Hz, and plastic strain range 3 x 10-3 - 1.2 x 10-2). The obtained plastic strain-life (Δεp-Nf) curves showed that the iron specimens could survive for a greater number of cycles before failure when implanted. Comparison of the cyclic stress-strain curves suggested that the implanted specimens had maintained a relatively more stable microstructural change than those unimplanted ones which had undergone a violent cyclic hardening during cyclic deformation. This is proposed to be a strong indication that the fatigue ductility has been improved and the cross slip of screw dislocations, which leads to the evolution of the persistent slip bands for fatigue damage, was hindered to some extent after ion implantation. (author)

  18. 核电汽轮机转子在低周疲劳与高周疲劳交互作用下裂纹扩展寿命的研究%Study on Crack Propagation Life under Low Cycle Fatigue and High Cycle Fatigue of Nuclear Steam Turbine Rotors

    史进渊

    2015-01-01

    提出核电汽轮机转子在低周疲劳与高周疲劳交互作用下裂纹扩展寿命的计算与评定方法.介绍核电汽轮机转子的低周疲劳与高周疲劳的应力幅与应力范围、低周疲劳裂纹扩展寿命与高周疲劳扩展寿命的计算方法.给出了核电汽轮机转子在低周疲劳与高周疲劳交互作用下裂纹扩展日历寿命的计算与评定方法,以及1 000 MW级核电汽轮机焊接低压转子疲劳裂纹扩展日历寿命的计算与改进的应用实例.结果表明,高周疲劳对汽轮机转子疲劳裂纹扩展日历寿命有比较大的影响,新研制核电汽轮机的转子结构设计和在役核电汽轮机的转子安全性评定,需要评估转子在低周疲劳与高周疲劳交互作用下裂纹扩展寿命.%The calculation and assessment methods for the crack propagation life under low cycle fatigue and high cycle fatigue of nuclear steam turbine rotors is presented. The low high fatigue cycle stress amplitude and stress range as well as the crack propagation life calculation methods for low cycle fatigue and high cycle fatigue of nuclear steam turbine rotors are introduced. The calculation and assessment methods for the crack propagation calendar life under low cycle fatigue and high cycle fatigue of nuclear steam turbine rotors are given together with an application example for calculation and improvement of the fatigue crack propagation calendar life of a low pressure welded rotor for 1 000 MW nuclear steam turbines. The example results indicate that effect of the high cycle fatigue on the fatigue crack propagation calendar life of nuclear steam turbine rotors is bigger, it is necessary that assessment for the crack propagation life under low cycle fatigue and high cycle fatigue of rotors in the rotor structure design of new development for nuclear steam turbine and the rotor safety assessment for operation steam turbine for nuclear power plants.

  19. Influence of Al-Cr diffusion coating on low cycle fatigue behavior of cast nickel-base superalloy at 800 °C

    Obrtlík, Karel; Pospíšilová, S.; Juliš, M.; Podrábský, T.; Kruml, Tomáš

    Kazan : Kazan Scientific Centre of the RAS, 2012 - (Klingbeil, D.; Vormwald, M.; Eulitz, G.), Paper No. 330 ISBN 978-5-905576-18-8. [19th European Conference on Fracture:Fracture Mechanics for Durability, Reliability and Safety . Kazan (RU), 26.08.2012-31.08.2012] R&D Projects: GA ČR(CZ) GAP107/11/2065 Institutional support: RVO:68081723 Keywords : Inconel 713LC * diffusion coating * Low cycle fatigue Subject RIV: JL - Materials Fatigue, Friction Mechanics

  20. Bond and low cycle fatigue behavior of thermoset composite reinforcing for the concrete industry

    Barnes, B.

    1990-09-21

    This thesis encompasses two separate research projects. The first project, described in Chapter 2 was a project investigating the fatigue behavior of thermoset Fiber Composite (FC) sandwich wall ties. The second research project detailed in this thesis was a project studying the bond and tensile properties of FC rod and FC fibers.

  1. Evaluation of the Effect of Surface Finish on High-Cycle Fatigue for SLM-IN718

    Lambert, Dennis M.

    2016-01-01

    A high-cycle fatigue (HCF) knockdown factor was estimated for Inconel 718, manufactured with the selective laser melt (SLM) process. This factor is the reduction at a common fatigue life from the maximum stress in fatigue for low-stress ground (LSG) specimens to the maximum stress of those left with the original surface condition. Various vendors provided specimens. To reduce the number of degrees-of-freedom, only one heat treat condition was evaluated. Testing temperatures included room temperature, 800F, 1000F, and 1200F. The two surface conditions were compared at constant lives, where data was available. The recommended knockdown factor of the as-built surface condition (average roughness of approximately 245 micro-inches/inch) versus low-stress ground condition (roughness <= 4 micro-inches/inch) is approximately 1/3 or 33%. This is to say that for the as-built surface condition, a maximum stress of 2/3 of the stress for LSG can be expected to produce the same life in the as built surface condition. As an alternative method, the surface finish was incorporated into a new parameter with the maximum stress. The new parameter was formulated to be similar to the fracture mechanics stress intensity factor, and it was named the pseudo stress intensity factor, Kp. Using Kp, the variance seemed acceptable across all sources, and the knockdown factor was estimated over the range of data identified by Kp where data occurred. A plot of the results suggests that the knockdown factor is a function of temperature, and that for low lives the knockdown is greater than the knockdown observed above about one million cycles, where it stabilizes. One data point at room temperature was clearly different, and the sparsity of data in the higher life region reduces the value of these results. The method does appear to provide useful results, and further characterization of the method is suggested.

  2. Biaxial low-cycle fatigue failure of 316 stainless steel at elevated temperatures

    High-strain, biaxial fatigue tests between the limiting conditions of uniaxial push-pull and fully reversed pure torsional loading were repeated on two batches of AISI 316 stainless steel, one tested at 4000C, the other at 5500C. An equivalent plastic shear strain range was shown to be superior to the octahedral equivalent strain for correlating biaxial fatigue endurance data. The stable cyclic stress-strain behaviour for any biaxial state is best represented in terms of the maximum shear stress and shear strain. At 5500C dynamic strain aging has a significant effect on both plastic flow and endurance for certain strain rates. Both Stage I and Stage II cracks were identified in the biaxial tests. (author)

  3. Long-term behaviour of binary Ti–49.7Ni (at.%) SMA actuators—the fatigue lives and evolution of strains on thermal cycling

    Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti–49.7Ni-based actuators: the effect of the temperature interval used in thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. The fatigue lives of tested specimens and the evolution of transformation and plastic strains on thermal cycling were recorded. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. One of the major conclusions of the study is that the temperature interval used for thermal cycling has a major effect on fatigue endurance: decreasing the temperature interval used for thermal cycling increased the fatigue life markedly. When the transformation is complete, a 20 °C increase of the final temperature reduced the fatigue lives at the most by half for the studied Ti–49.7Ni wires. With partial transformations the effect is more distinct: even the 5 °C increase in the final temperature reduced the fatigue life by half. The stress level and heat-treatment state used had a marked effect on the actuator properties of the wires, but the effects on fatigue endurance were minor. The fatigue test results reveal that designing and controlling long-term behaviour of binary Ti–49.7Ni actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. Even 5 min longer heat-treatment time could generate, at the most, double plastic strain values and 30% lower stabilized transformation strain values. The amount of plastic strain can be stated as one of

  4. High Cycle Fatigue of Al and Cu Thin Films by a Novel High-Throughput Method

    Burger, Sofie

    2013-01-01

    In the last two decades, the reliability of small electronic devices used in automotive or consumer electronics gained researchers attention. Thus, there is the need to understand the fatigue properties and damage mechanisms of thin films. In this thesis a novel high-throughput testing method for thin films on Si substrate is presented. The specialty of this method is to test one sample at different strain amplitudes at the same time and measure an entire lifetime curve with only one experiment.

  5. Assessment of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720

    Gabb, Tomothy P.; Bonacuse, Peter J.; Ghosn, Louis J.; Sweeney, Joseph W.; Chatterjee, Amit; Green, Kenneth A.

    2000-01-01

    The fatigue lives of modem powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538 C (1000 F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions. Significant variations in life were observed as functions of the disk processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio R(sub epsilon) = epsilon(sub min)/epsilon(sub max) of 0 were different from those in tests at a strain ratio of -1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.

  6. Design and realization of a multisamples rotating high cycle fatigue machine

    Massimo Martorelli; Domenico Gentile

    2012-01-01

    In this work the design and the technical characteristic of a Moore rotating bending machine are presented. The machine has been realized at the University of Cassino in order to run tests on multiple specimens at different temperature. The user can choose independently the load and the temperature for each specimen. The machine has been designed to produce in short time a several numbers of data of materials fatigue strength at low costs. The machine is in assembling step at the Laboratory o...

  7. Dynamic speckle interferometry of high-cycle material fatigue: Theory and some experiments

    Vladimirov, A. P.

    2016-06-01

    The objective of this paper was theoretical analysis of speckle dynamics in the image plane of a thin transparent object. It was suggested that speckle dynamics develops in simultaneous periodic motion of the sample, micro- and macro-variations of its refraction index and its translational motion. The results of the theory were contrasted with the data obtained in the fatigue tests with transparent object.

  8. Influence of microstructure on high-cycle fatigue of Ti-6Al-4V: Bimodal vs. lamellar structures

    Nalla, R. K.; Ritchie, R. O.; Boyce, B. L.; Campbell, J. P.; Peters, J. O.

    2002-03-01

    The high-cycle fatigue (HCF) of titanium alloy turbine engine components remains a principal cause of failures in military aircraft engines. A recent initiative sponsored by the United States Air Force has focused on the major drivers for such failures in Ti-6Al-4V, a commonly used turbine blade alloy, specifically for fan and compressor blades. However, as most of this research has been directed toward a single processing/heat-treated condition, the bimodal (solution-treated and overaged (STOA)) microstructure, there have been few studies to examine the role of microstructure. Accordingly, the present work examines how the overall resistance to high-cycle fatigue in Ti-6Al-4V compares between the bimodal microstructure and a coarser lamellar ( β-annealed) microstructure. Several aspects of the HCF problem are examined. These include the question of fatigue thresholds for through-thickness large and short cracks; microstructurally small, semi-elliptical surface cracks; and cracks subjected to pure tensile (mode I) and mixed-mode (mode I+II) loading over a range of load ratios (ratio of minimum to maximum load) from 0.1 to 0.98, together with the role of prior damage due to sub-ballistic impacts (foreign-object damage (FOD)). Although differences are not large, it appears that the coarse lamellar microstructure has improved smooth-bar stress-life (S-N) properties in the HCF regime and superior resistance to fatigue-crack propagation (in pure mode I loading) in the presence of cracks that are large compared to the scale of the microstructure; however, this increased resistance to crack growth compared to the bimodal structure is eliminated at extremely high load ratios. Similarly, under mixed-mode loading, the lamellar microstructure is generally superior. In contrast, in the presence of microstructurally small cracks, there is little difference in the HCF properties of the two microstructures. Similarly, resistance to HCF failure following FOD is comparable in the

  9. Fatigue Damage in Wood

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben; Damkilde, Lars

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Fatigue failure is found to depend both on the total time under load and on the number of cycles.Recent accelerated fatigue research on wood is reviewed, and a discrepancy between...... 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation between stiffness reduction...

  10. A study on the continuous low cycle fatigue properties of 1%Cr-Mo-V steel and 12%Cr-Mo-V steel used in turbine rotors

    Continuous low cycle fatigue properties of 1%Cr-Mo-V steel and 12%Cr-Mo-V steel used in turbine rotors were investigated at 298, 773 and 873K in air atmosphere. The microstructure of 1%Cr-Mo-V steel and 12%Cr-Mo-V steel consisted of tempered upper bainite and tempered martensite, respectively. The experimental results show that the effect of the directionality of rotor on the fatigue life was rarely observed. The fatigue life of 1%Cr-Mo-V steel is significantly reduced at high temperature with decreasing plastic strain range, and the reason is considered to be the earlier crack initiation by oxidation damage. However, the effect of temperature on the fatigue life 12%Cr-Mo-V steel is known to be not existing throughout all the plastic strain range. This is suggested to be concerned with the increasing plastic ductility in tensile test with increasing test temperatures. (Author)

  11. The influence of temperature on low cycle fatigue behavior of prior cold worked 316L stainless steel (II) : life prediction and failure mechanism

    Tensile and low cycle fatigue tests on prior cold worked 316L stainless steel were carried out at various temperatures from room temperature to 650 deg. C. Fatigue resistance was decreased with increasing temperature and decreasing strain rate. Cyclic plastic deformation, creep, oxidation and interactions with each other are thought to be responsible for the reduction in fatigue resistance. Currently favored life prediction models were examined and it was found that it is important to select a proper life prediction parameter since stress-strain relation strongly depends on temperature. A phenomenological life prediction model was proposed to account for the influence of temperature on fatigue life and assessed by comparing with experimental result. LCF failure mechanism was investigated by observing fracture surfaces of LCF failed specimens with SEM

  12. Effect of Al-Si Pack Cementation Diffusion Coating on High-Temperature Low-Cycle Fatigue Behavior of Inconel 713LC

    Mansuri, Mohammadreza; Hadavi, Seyed Mohammad Mehdi; Zare, Esmail

    2016-01-01

    In this research, an Al-Si protective coating was applied on the surface of an IN713LC specimen using pack cementation method. Surface-treated and untreated specimens were exposed to low-cycle fatigue by tension-tension loading under total strain control at 1173 K (900 °C) in air. Based on the obtained results, the hardening/softening, cyclic stress-strain, and fatigue life curves were plotted and analyzed. The results showed that both the single-stage and two-stage coatings improved the fatigue life of the substrate. However, owing to more silicon content of single-stage coating compared to that of two-stage coating, the effect of single-stage coating was superior. The stress response of the treated material was lower compared with the untreated one. Observations of the specimen section and fracture surface examinations were used to analyze fatigue behavior of both coated and uncoated materials.

  13. Effect of strain rate on the high-temperature low-cycle fatigue properties of a NIMONIC PE-16 superalloy

    NIMONIC PE-16, chosen for the present investigation, is a nickel-iron-base superalloy that has wide application at high temperatures as a material for aircraft ducting systems; gas turbine flame tubes; missile hot components; superheater tubes; and wrapper tubes, clad tubes, and tie rods in nuclear reactors. Strain-rate effects on the low-cycle fatigue (LCF) behavior of a NIMONIC PE-16 superalloy have been evaluated in the temperature range of 523 to 923 K. Total-strain-controlled fatigue tests were performed at a strain amplitude of ±0.6 pct on samples possessing two different prior microstructures: microstructure A, in the solution-annealed condition; and microstructure B, in a double-aged condition with γ' of 18-nm diameter and M23C6 carbides. The cyclic stress response behavior of the alloy was found to depend on the prior microstructure, testing temperature, and strain rate. A softening regime was found to be associated with shearing of ordered γ' that were either formed during testing or present in the prior microstructure. Various manifestations of dynamic strain aging (DSA) included negative strain rate-stress response, serrations on the stress-strain hysteresis loops, and increased work-hardening rate. The calculated activation energy matched well with that for self-diffusion of Al and Ti in the matrix. Fatigue life increased with an increase in strain rate from 3 x 10-5 to 3 x 10-3s-1, but decreased with further increases in strain rate

  14. Application of the Seebeck effect for the monitoring of neutron embrittlement and low-cycle fatigue in nuclear reactor technology

    The monitoring of neutron embrittlement and low-cycle fatigue in nuclear reactor steel is an important topic in lifetime extension of nuclear power plants. We therefore investigated the application of the Seebeck effect for determining material degradation of common reactor pressure vessel (RPV) steel. The Seebeck coefficients (SC) of several irradiated Charpy specimens made from Japanese JRQ-steel were measured. The specimens suffered a fluence from 0 up to 4.5 E19 neutrons per cm2 with energies higher than 1 MeV. The measured changes of the SC within this range were about 500 nV, increasing continuously in the range under investigation. Some indications of saturation appeared at fluencies larger than 4.5 E19 neutrons per cm2. We obtained a linear dependency between the SC and the temperature shift . T41 of the Charpy energy vs. temperature curve which is widely used to characterize material embrittlement. Similar measurements were performed on specimens made from the austenitic stainless steel X6CrNiTi18-10 (according to DIN 1.4541) that were fatigued by applying a cyclic strain amplitude of 0.28%. Further investigations were made to quantify the size of the gauge volume in which the thermoelectric power is generated. It appeared that the information gathered from a Thermo Electric Power (TEP) measurement is very local. To overcome this problem we propose a novel TEP-method using a Thermoelectric Scanning Microscope (TSM). We finally conclude that the change of the SC has a potential for monitoring of material degradation due to neutron irradiation and thermal fatigue, but it has to be taken into account that several influencing parameters could contribute to the TEP in either an additional or extinguishing manner. A disadvantage of the method is the requirement of a clean surface without any oxide layer. This disadvantage can partially be avoided by using the proposed new TSM. (author)

  15. Investigation of thermal fatigue in fiber composite materials. [(thermal cycling tests)

    Fahmy, A. A.; Cunningham, T. G.

    1976-01-01

    Graphite-epoxy laminates were thermally cycled to determine the effects of thermal cycles on tensile properties and thermal expansion coefficients of the laminates. Three 12-ply laminate configurations were subjected to up to 5,000 thermal cycles. The cumulative effect of the thermal cycles was determined by destructive inspection (electron micrographs and tensile tests) of samples after progressively larger numbers of cycles. After thermal cycling, the materials' tensile strengths, moduli, and thermal expansion coefficients were significantly lower than for the materials as fabricated. Most of the degradation of properties occurred after only a few cycles. The property degradation was attributed primarily to the progressive development of matrix cracks whose locations depended upon the layup orientation of the laminate.

  16. The effects of dissolved hydrogen contents on the low cycle fatigue behaviors of a 316LN stainless steel in simulated PWR conditions

    The effects of dissolved hydrogen on the low cycle fatigue behaviors of a 316LN stainless steel in pressurized water reactor environments were investigated. Round bar-type specimens were tested at 310°C in a deoxygenated water, and simulated pressurized water reactor water chemistry with normal and high dissolved hydrogen contents. The test results showed that the fatigue life of 316LN stainless steel was slightly improved with increasing DH level, showing larger increase at large strain amplitude. However, the fatigue surface and crack morphology showed no significant differences due to different hydrogen contents. To understand the role of dissolved hydrogen during low cycle fatigue tests, hydrogen contents of tested bulk specimen and near the crack tip was measured, but the results showed no significant differences. It is thought that bulk dissolved hydrogen level have little effect on hydrogen absorption into stainless steel due to barrier role of oxide film. To clearly understand the effect of dissolved hydrogen on low cycle fatigue behaviors of structural materials in nuclear power plant, additional analysis about oxide film and hydrogen distribution near main crack tip should be performed. (author)

  17. The effects of texture and extension twinning on the low-cycle fatigue behavior of a rolled magnesium alloy, AZ31B

    Research highlights: → Due to in-plane texture symmetry, in-plane loadings show similar LCF resistances. → The through-thickness loading has a worse LCF resistance than in-plane loadings. → The resistance difference is attributed to different twinning-detwinning sequences. → The different activation sequences lead to inverted hysteresis loop shapes. - Abstract: The effect of texture on the low-cycle fatigue behavior of a rolled magnesium alloy, AZ31B, was studied at room temperature. It is shown that the Coffin-Manson and Basquin relationships can be used to describe the fatigue resistance of the alloy. The alloy loaded along the rolling direction exhibits only slightly better low-cycle fatigue resistance than that loaded along the transverse direction, due to the in-plane texture symmetry. The in-plane cases exhibit better fatigue behavior than the through-thickness loading. Neutron diffraction and synchrotron diffraction were employed to assist in making mechanistic understandings for the findings. The fundamental difference in the low-cycle fatigue behaviors between the in-plane and through-thickness loadings is attributed to the different activation sequences of twinning and detwinning mechanisms involved and, particularly, the greater requirement for c-axis compression of the grains during the through-thickness tests. The different activation sequences are essentially determined by the initial crystallographic texture, such that the inverted hysteresis-loop shapes are observed.

  18. A study on fatigue crack growth in the high cycle domain assuming sinusoidal thermal loading

    Radu, V., E-mail: vasile.radu@nuclear.r [Institute for Nuclear Research, 1st Campului Street, 115400 Mioveni, Arges POB 78, Pitesti (Romania); Paffumi, E. [European Commission, Joint Research Centre, Institute for Energy, Petten (Netherlands); Taylor, N. [European Commission, Joint Research Centre, Institute for Energy, Ispra (Italy); Nilsson, K.-F. [European Commission, Joint Research Centre, Institute for Energy, Petten (Netherlands)

    2009-12-15

    The assessment of fatigue crack growth due to turbulent mixing of hot and cold coolants presents significant challenges, in particular to determine the thermal loading spectrum and the associated crack growth. The sinusoidal method is a simplified approach for addressing this problem, in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface. The loading frequency is taken as that which gives the shortest crack initiation and growth life. Such estimates are intended to be conservative but not un-realistic. Several practical issues which arise with this approach have been studied using newly-developed analytical solutions for the temperature and stress fields in hollow cylinders, in particular the assumptions made concerning the crack orientation, dimensions and aspect ratio. The application of the proposed method is illustrated for the pipe geometry and loadings conditions reported for the Civaux 1 case where through wall thermal fatigue cracks developed in a short time, but the problem is relevant also for fast reactor components.

  19. In-service inspection of fatigue cracks in a 1/5th scale PWR vessel with pressure cycles

    The Joint Research Center (JRC) at ISPRA has undertaken for several years a study on the propagation of fatigue cracks in PWR vessels. The goal is to establish a relation between the size and the location of the defects and the residual life of the structure. In order to verify the validity of theoretical models developed, a mock-up at a 1/5th scale of a PWR vessel was built. It was submitted to a pressurization cycle representative of the operating conditions in a PWR. Therefore, it was necessary to have non-destructive methods which allow stable and reliable tracks over a long period of time. This paper reviews results obtained by CEA during 5 successive in-service inspections over a 4 year period

  20. Effect of secondary flow generated in 90-degree bend upon high-cycle thermal fatigue in a mixing tee

    In nuclear power plants, there are many T-junctions at which different temperature fluids are mixed. When the fluids with different temperature are mixed, temperature fluctuation in fluids reachs wall and high-cycle heat fatigue occurs. Depending on amplitude and frequency of temperature fluctuation, it could lead to pipe rupture accident at worst. In addition, in case of the T-junction with 90-degree bend at upstream, there is higher risk for pipe rupture accident due to secondary flow which arises in the 90-degree bend. In this study, the effects of temperature fluctuation above the T-junction in case of different distance of 90-degree bend outlet to the T-junction are investigated. (author)

  1. In service inspection of fatigue cracks in a 1/R th scale PWR vessel with pressure cycles

    THE JOINT RESEARCH CENTER (JRC) at ISPRA has undertaken for several years a study on the propagation of fatigue cracks in PWR vessels. The goal is to establish a relation between the size and the location of the defects on the one hand, and the residual life of the structure on the other hand/1/. In order to verify the validity of theoretical models which were developed, a mock-up at a 1/5th scale of a PWR vessel was built. It was submitted to pressurization cycles representative of the operating conditions in a PWR. Therefore, it was necessary to have Non-Destructive methods which allows a stable and reliable track on a long period of time. This paper makes a review of results obtained by CEA during 5 successive In-Service Inspections on a 4 years period

  2. Effects of geometry and materials on low cycle fatigue life of turbine blades in LOX/hydrogen rocket engines

    Ryan, R. M.; Gross, L. A.

    1986-01-01

    This paper presents the results of an advanced turbine blade test program aimed at improving turbine blade low cycle fatigue (LCF) life. A total of 21 blades were tested in a blade thermal tester. The blades were made of MAR-M-246(Hf)DS and PWA-1480SC in six different geometries. The test results show that the PWA-1480SC material improved life by a factor of 1.7 to 3.0 over the current MAR-M-246(Hf)DS. The geometry changes yielded life improvements as high as 20 times the baseline blade made of PWA-1480SC and 34 times the baseline MAR-M-246DS blade.

  3. Influence of nitrogen alloying and of previous aging on the low-cycle fatigue crack initiation and propagation at room temperature in austenitic stainless steels type 316L

    The crack growth rates during room temperature low-cycle fatigue of two austenitic stainless steels are evaluated through striation space measurements on the fracture surfaces of axisymmetric smooth specimens. The effect of nitrogen interstitials and of previous aging on the initiation and crack propagation phase durations is discussed

  4. Development of India-specific RAFM steel through optimization of tungsten and tantalum contents for better combination of impact, tensile, low cycle fatigue and creep properties

    Effects of tungsten and tantalum contents on impact, tensile, low cycle fatigue and creep properties of Reduced Activation Ferritic–Martensitic (RAFM) steel were studied to develop India-specific RAFM steel. Four heats of the steel have been melted with tungsten and tantalum contents in the ranges 1–2 wt.% and 0.06–0.14 wt.% respectively. Increase in tungsten content increased the ductile-to-brittle transition temperature (DBTT), low cycle fatigue and creep strength of the steel, whereas the tensile strength was not changed significantly. Increase in tantalum content increased the DBTT and low cycle fatigue strength of the steel whereas the tensile and creep strength decreased. Detailed TEM investigations revealed enhanced microstructural stability of the steel against creep exposure on tungsten addition. The RAFM steel having 1.4 wt.% tungsten with 0.06 wt.% tantalum was found to possess optimum combination of impact, tensile, low cycle fatigue and creep properties and is considered for Indian-specific RAFM steel

  5. High-Temperature, Low-Cycle Fatigue of Copper-Base Alloys for Rocket Nozzles. Part 1: Data Summary for Materials Tested in Prior Programs

    Conway, J. B.; Stentz, R. H.; Berling, J. T.

    1975-01-01

    A more detailed analysis of the results obtained in 188 previously reported low-cycle fatigue tests of various candidate materials for regeneratively-cooled, reusable rocket nozzle liners was reported. Plots of load range versus cycles were reported for each test along with a stress-strain hysteresis loop near half-life. In addition, a summary table was provided to compare N5 (cycles to a five percent load range drop) and Nf (cycles to complete specimen separation) values for each test.

  6. Statistical investigation of the crack initiation lives of piping structural welded joint in low cycle fatigue test of 240 degree C

    A statistical investigation into the fitting of four possible fatigue assumed distributions (three parameter Weibull, two parameter Weibull, lognormal and extreme maximum value distributions) for the crack initiation lives of piping structural welded joint in low cycle fatigue test of 240 degree C is performed by linear regression and least squares methods. The results reveal that the three parameters Weibull distribution may give misleading results in fatigue reliability analysis because the shape parameter is often less than 1. This means that the failure rate decreases with fatigue cycling which is contrary to the general understanding of the behaviour of welded joint. Reliability analyses may also affected by the slightly nonconservative evaluations in tail regions of this distribution. The other three distributions are slightly poor in the total fit effects, but they can be safety assumed in reliability analyses due to the non-conservative evaluations in tail regions mostly and the consistency with the fatigue physics of the structural behaviour of welded joint in the range of engineering practice. In addition, the extreme maximum value distribution is in good consists with the general physical understanding of the structural behaviour of welded joint

  7. Fatigue Damage in Wood

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben;

    1996-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Fatigue failure is found to depend both on the total time under load and on the number of cycles.Recent accelerated fatigue research on wood is reviewed, and a discrepancy between...... failure explanation under fatigue and static load conditions is observed. In the present study small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four frequencies ranging from 0.01 Hz to...... 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation between stiffness reduction...

  8. Arm-cycling sprints induce neuromuscular fatigue of the elbow flexors and alter corticospinal excitability of the biceps brachii.

    Pearcey, Gregory E P; Bradbury-Squires, David J; Monks, Michael; Philpott, Devin; Power, Kevin E; Button, Duane C

    2016-02-01

    We examined the effects of arm-cycling sprints on maximal voluntary elbow flexion and corticospinal excitability of the biceps brachii. Recreationally trained athletes performed ten 10-s arm-cycling sprints interspersed with 150 s of rest in 2 separate experiments. In experiment A (n = 12), maximal voluntary contraction (MVC) force of the elbow flexors was measured at pre-sprint 1, post-sprint 5, and post-sprint 10. Participants received electrical motor point stimulation during and following the elbow flexor MVCs to estimate voluntary activation (VA). In experiment B (n = 7 participants from experiment A), supraspinal and spinal excitability of the biceps brachii were measured via transcranial magnetic and transmastoid electrical stimulation that produced motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs), respectively, during a 5% isometric MVC at pre-sprint 1, post-sprint 1, post-sprint 5, and post-sprint 10. In experiment A, mean power output, MVC force, potentiated twitch force, and VA decreased 13.1% (p increased 40.1% (p = 0.038) from post-sprint 5 to post-sprint 10 and (ii) CMEPs increased 28.5% (p = 0.045) from post-sprint 1 to post-sprint 10. Overall, arm-cycling sprints caused neuromuscular fatigue of the elbow flexors, which corresponded with decreased supraspinal and increased spinal excitability of the biceps brachii. The different post-sprint effects on supraspinal and spinal excitability may illustrate an inhibitory effect on supraspinal drive that reduces motor output and, therefore, decreases arm-cycling sprint performance. PMID:26799694

  9. Experimental study of cyclic creep and high-cycle fatigue of welded joints of St3 steel by the DIC technique

    In the paper the mechanisms of plastic deformation and fracture of welded joints of steel St3 were investigated at high-cycle fatigue and cyclic creep by the digital image correlation (DIC) technique. The evolution of strain rate is studied for the following regions: base metal, HAZ, and fusion zone. This strain rate evolution can be considered as a mechanical response of material. Three stages of deformation evolution are shown: deformation hardening (I), fatigue crack initiation (II), and the last stage is related to main crack (III). Two criteria are offered to evaluate the current mechanical state of welded joints

  10. Impact of hydrogen on the high cycle fatigue behaviour of Inconel 718 in asymmetric push-pull mode at room temperature

    Bruchhausen, Matthias; Fischer, Burkhard; Ruiz, A.; Gonzalez Sanchez, Sergio; Hähner, Peter; Soller, Sebastian

    2014-01-01

    The influence of hydrogen on the high cycle fatigue (HCF) behaviour of Inconel 718 has been studied at room temperature in asymmetric push–pull mode using an ultrasonic HCF test rig. Fatigue tests have been carried out in gaseous hydrogen (GH2) and in Ar at a pressure of 30 MPa. Oscillating stresses with amplitudes (σa) up to 450 MPa and mean stresses (σm) up to 600 MPa have been applied. For a given σa and σm, the lifetime in Ar is generally longer than in GH2, which is explained by a hydrog...

  11. Effect of thermal barrier coating on low cycle fatigue behavior of cast Inconel 713LC at 900 °C

    Obrtlík, Karel; Hutařová, S.; Čelko, L.; Juliš, M.; Podrábský, T.; Šulák, Ivo

    Zurich : Trans Tech Publications, 2014 - (Clark, G.; Wang, C.), s. 848-853 ISBN 978-3-03835-008-8. ISSN 1022-6680. - (Advanced Materials Research. 891-892). [Fatigue 2014 - International Fatigue Congress /11./. Melbourne (AU), 02.03.2014-07.03.2014] R&D Projects: GA ČR(CZ) GAP107/11/2065; GA MPO FR-TI4/030 Institutional support: RVO:68081723 Keywords : High temperature fatigue * TBC * Inconel 713LC * Fatigue life Subject RIV: JL - Materials Fatigue, Friction Mechanics

  12. A comparison of the effects of fatigue on subjective and objective assessment of situation awareness in cycling.

    Knez, Wade L; Ham, Daniel J

    2006-01-01

    Maximal effort on a 30 km Time Trial (TT30) was examined to assess whether it would elicit changes in objective and subjective tests of the participants' perception of the environment and their ability to anticipate future occurrences (situation awareness; SA) and to determine the effect of post-exercise recovery on SA. Nine experienced (5.22 ± 2.77 years) road cyclists had their objective and subjective levels of SA assessed prior to and at the completion of two TT30. The participants' results were compared to measurements of maximal oxygen uptake (VO2max), peak power output (PPO), age and years of competitive cycle racing experience. Fatigue resulting from maximal effort on a TT30 produced significant changes in both the objective and subjective test of SA. Effect sizes of 0.93 and 0.99 indicated that the first and second TT30 were likely or almost certain to have a beneficial effect on the objective assessment of SA. However, the effect sizes of 0.97 and 0.95 relating to the subjective assessment of cognitive performance on the first and second TT30 showed that it was very likely the participants' had an increased difficulty in maintaining SA. A recovery period of up to three minutes post TT30 had no effect on SA. Changes in SA had no relationship with measurements of VO2max, peak power output (PPO), age and years of competitive cycle racing experience. The findings suggest that within a laboratory environment, participants consistently underestimate their ability to make accurate assessments of their cycling environment compared to objective measures of their SA. Key PointsExhaustive exercise from a TT30 produces significant changes in both subjective and objective SA.This study indicates that fatigued participants underestimate their ability to maintain SA.A time period of three minutes is not enough to observe a recovery effect on subjective or objective SA.Both the objective and subjective tests proved to be reliable assessments of SA. PMID:24198685

  13. Deformation twinning and twinning-related fracture in nickel-base single-crystal superalloys during thermomechanical fatigue cycling

    Thermomechanical fatigue (TMF) tests in four 〈0 0 1〉-oriented nickel-base single-crystal superalloys were studied with the aid of microstructural investigation. Three experimental observation methods – optical microscopy, scanning electron microscope and transmission electron microscopy – were combined to obtain new insights into the microstructural and fractographic characteristics after TMF cycling with and without a compressive hold time. After the TMF cycling, the fracture surface shows different fractographic characteristics due to the introduction of the hold time. Fundamental differences in the crack propagation mechanisms have also been discovered under the influence of the compressive hold time. Without a compressive hold time, the crack propagates inwards perpendicular to the axial stress with the aid of oxidation. During the propagation, the crack reaches the twinning plate and propagates rapidly along it with the aid of the stress field at the crack tip. There appear to be obvious steps at this propagation stage. With a compressive hold time, the crack could only propagate in approximately one twinning plate. It appears in only one crystallographic fracture plane. Due to a few deformation twins being formed in this section, the crack propagation path may change to run along other twinning plates

  14. Simulation of irreversible damage accumulation in the very high cycle fatigue (VHCF) regime using the boundary element method

    Hilgendorff, P.-M., E-mail: philipp.hilgendorff@uni-siegen.de [Institut für Mechanik und Regelungstechnik—Mechatronik, Universität Siegen, Siegen 57068 (Germany); Grigorescu, A. [Institut für Werkstofftechnik, Universität Siegen, Siegen 57068 (Germany); Zimmermann, M. [Institut für Werkstoffwissenschaft, Technische Universität Dresden, 01062 Dresden (Germany); Fritzen, C.-P. [Institut für Mechanik und Regelungstechnik—Mechatronik, Universität Siegen, Siegen 57068 (Germany); Christ, H.-J. [Institut für Werkstofftechnik, Universität Siegen, Siegen 57068 (Germany)

    2013-07-15

    Many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, the period of fatigue crack initiation and thus the localization of plastic deformation play an important role. Metastable austenitic stainless steel (AISI304) that is investigated in this study shows localization of plastic deformation in bands of intense slip. In order to provide a physically-based understanding of the relevant damage mechanisms under VHCF condition, simulation of irreversible damage accumulation in slip bands is performed. For this purpose, a microstructural simulation model is proposed which accounts for the damage mechanisms in slip bands documented by experimental results. The model describes the damage accumulation through formation of slip bands, sliding and multiplication of dislocations and the amount of irreversibility of such mechanisms in case of VHCF relevant loading conditions. The implementation of the simulation model into a numerical method allows the investigation of the damage accumulation in a real microstructure simulated on the basis of metallographic analysis. The numerical method used in this study is the two-dimensional (2-D) boundary element method which is based on two integral equations: the displacement and the stress boundary integral equation. Fundamental solutions within these integral equations represent anisotropic elastic behavior. By using this method, a 2-D microstructure can be reproduced that considers orientations as well as individual anisotropic elastic properties in each grain. Contours of shear stresses along most critical slip systems are compared with images of slip band formation at the surface of fatigued specimens provided by scanning electron microscopy (SEM). Results show that simulation of slip bands is in good agreement with experimental observations and that plastic deformation in slip bands has a high impact on shear stresses at grain boundaries acting as possible

  15. Simulation of irreversible damage accumulation in the very high cycle fatigue (VHCF) regime using the boundary element method

    Many components have to withstand a very high number of loading cycles due to high frequency or long product life. In this regime, the period of fatigue crack initiation and thus the localization of plastic deformation play an important role. Metastable austenitic stainless steel (AISI304) that is investigated in this study shows localization of plastic deformation in bands of intense slip. In order to provide a physically-based understanding of the relevant damage mechanisms under VHCF condition, simulation of irreversible damage accumulation in slip bands is performed. For this purpose, a microstructural simulation model is proposed which accounts for the damage mechanisms in slip bands documented by experimental results. The model describes the damage accumulation through formation of slip bands, sliding and multiplication of dislocations and the amount of irreversibility of such mechanisms in case of VHCF relevant loading conditions. The implementation of the simulation model into a numerical method allows the investigation of the damage accumulation in a real microstructure simulated on the basis of metallographic analysis. The numerical method used in this study is the two-dimensional (2-D) boundary element method which is based on two integral equations: the displacement and the stress boundary integral equation. Fundamental solutions within these integral equations represent anisotropic elastic behavior. By using this method, a 2-D microstructure can be reproduced that considers orientations as well as individual anisotropic elastic properties in each grain. Contours of shear stresses along most critical slip systems are compared with images of slip band formation at the surface of fatigued specimens provided by scanning electron microscopy (SEM). Results show that simulation of slip bands is in good agreement with experimental observations and that plastic deformation in slip bands has a high impact on shear stresses at grain boundaries acting as possible

  16. Non local approach in crystalline plasticity: study of mechanical behaviour of AISI 316LN stainless steel during low cycle fatigue

    If fatigue crack initiation is currently quite well understood for pure single crystals, its comprehension and prediction in cases of polycrystal alloys such as AISI 316LN stainless steel remain complicated. Experimentally our study focuses on the characterisation of the mechanical behaviour and on the study at different scales of the phenomenon leading to low cycle fatigue crack initiation in 316LN stainless steel. For straining amplitudes of?e/2 = 0,3 and 0,5%, the cyclic softening observed during testing has been related to the organisation of dislocations in band structures. These bands, formed due to the activation of slip systems having the greatest Schmid's factor, carry the most part of the deformation. Their emergence at free surfaces leads to the formation of intrusions and extrusions which help cracks initiate and spread. Numerically we worked on the mesoscopic scale, proposing a new model of crystalline plasticity. This model integrates geometrically necessary dislocations (GND) directly computed from the lattice curvature. Implemented in the finite element code AbaqusTM and Cast3mTM, it is based on single crystal finite deformations laws proposed by Peirce et al. (1983) and Teodosiu et al. (1993). Extended for polycrystals by Hoc (2001) and Erieau (2003), it has been improved by the introduction of GND (Acharya and Bassani, 2000). The simulations performed on different types of aggregates (2D/3D) have shown that taking GND into account enables:- the prediction of the grain size effect on a macroscopic and on a local scale,- a finer computation of local stress field.The influence of the elasticity and interaction matrices on the values and the evolution of the isotropic and kinematic mean stresses has been shown. The importance of boundary conditions on computed mechanical fields could also be pointed out. (author)

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

    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.

  18. The Effect of a Non-Gaussian Random Loading on High-Cycle Fatigue of a Thermally Post-Buckled Structure

    Rizzi, Stephen A.; Behnke, marlana N.; Przekop, Adam

    2010-01-01

    High-cycle fatigue of an elastic-plastic beam structure under the combined action of thermal and high-intensity non-Gaussian acoustic loadings is considered. Such loadings can be highly damaging when snap-through motion occurs between thermally post-buckled equilibria. The simulated non-Gaussian loadings investigated have a range of skewness and kurtosis typical of turbulent boundary layer pressure fluctuations in the vicinity of forward facing steps. Further, the duration and steadiness of high excursion peaks is comparable to that found in such turbulent boundary layer data. Response and fatigue life estimates are found to be insensitive to the loading distribution, with the minor exception of cases involving plastic deformation. In contrast, the fatigue life estimate was found to be highly affected by a different type of non-Gaussian loading having bursts of high excursion peaks.

  19. A COMPARISON OF THE EFFECTS OF FATIGUE ON SUBJECTIVE AND OBJECTIVE ASSESSMENT OF SITUATION AWARENESS IN CYCLING

    Wade L. Knez

    2006-03-01

    Full Text Available Maximal effort on a 30 km Time Trial (TT30 was examined to assess whether it would elicit changes in objective and subjective tests of the participants' perception of the environment and their ability to anticipate future occurrences (situation awareness; SA and to determine the effect of post-exercise recovery on SA. Nine experienced (5.22 ± 2.77 years road cyclists had their objective and subjective levels of SA assessed prior to and at the completion of two TT30. The participants' results were compared to measurements of maximal oxygen uptake (VO2max, peak power output (PPO, age and years of competitive cycle racing experience. Fatigue resulting from maximal effort on a TT30 produced significant changes in both the objective and subjective test of SA. Effect sizes of 0.93 and 0.99 indicated that the first and second TT30 were likely or almost certain to have a beneficial effect on the objective assessment of SA. However, the effect sizes of 0.97 and 0.95 relating to the subjective assessment of cognitive performance on the first and second TT30 showed that it was very likely the participants' had an increased difficulty in maintaining SA. A recovery period of up to three minutes post TT30 had no effect on SA. Changes in SA had no relationship with measurements of VO2max, peak power output (PPO, age and years of competitive cycle racing experience. The findings suggest that within a laboratory environment, participants consistently underestimate their ability to make accurate assessments of their cycling environment compared to objective measures of their SA

  20. Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

    Forman, Royce G.; Zanganehgheshlaghi, Mohannad

    2014-01-01

    The research results described in this paper presents a new understanding of the behavior of fatigue crack growth in the threshold region. It is believed by some crack growth experts that the ASTM load shedding test method does not produce true or valid threshold properties. The concern involves the observed fanning of threshold region da/dN data plots for some materials in which the low R-ratio data fans out or away from the high R-ratio data. This data fanning or elevation of threshold values is obviously caused by an increase in crack closure in the low R-ratio tested specimens. This increase in crack closure is assumed by some investigators to be caused by a plastic wake on the crack surfaces that was created during the load shedding test phase. This study shows that the increase in crack closure is the result of an extensive occurrence of crack bifurcation behavior in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the particular fanning behavior in aluminum alloys is a function of intrinsic dislocation property of the materials and that the fanned data represents valid material properties. However, for corrosion sensitive steel alloys used in this study the fanning was caused by a build-up of iron oxide at the crack tip from fretting corrosion.

  1. Power Cycling Test Circuit for Thermal Fatigue Resistance Analysis of Solder Joints in IGBT

    Dupont, Laurent; Lefebvre, Stéphane; Khatir, Zoubir; FAUGIERE, Jean Claude

    2003-01-01

    The paper will give a detailed presentation of an active power cycling test bench in high temperature conditions developed to ageing the solder between the Direct Copper Bonding (DCB) and the base of IGBT devices. The average junction temperature measurement protocol, the temperature regulation of the base plate, the acquisition of all the electrical signals, and the performance of the test circuit will be presented and discussed. Moreover, a thermal modelling presentation has been used to de...

  2. A study on the role of grain boundary engineering in promoting high-cycle fatigue resistance and improving reliability in nickel base superalloys for propulsion systems

    Gao, Yong

    High-cycle fatigue, involving the premature initiation and/or rapid propagation of small cracks to failure due to high-frequency (vibratory) loading, remains the principal cause of failures in military gas-turbine propulsion systems. The objective of this study is to examine whether the resistance to high-cycle fatigue failures can be enhanced by grain-boundary engineering, i.e., through the modification of the spatial distribution and topology of the grain boundaries in the microstructure. While grain boundary engineering has been used to obtain significant improvements in intergranular corrosion and cracking, creep and cavitation behavior, toughness and plasticity, cold-work embrittlement, and weldability, only very limited, but positive, results exist for fatigue. Accordingly, using a commercial polycrystalline nickel base gamma/gamma' superalloy, ME3, as a typical engine disk material, sequential thermomechanical processing, involving alternate cycles of strain and annealing, is used to (i) modify the proportion of special grain boundaries, and (ii) interrupt the connectivity of the random boundaries in the grain boundary network. The processed microstructures are then subjected to fracture-mechanics based high cycle fatigue testing to evaluate how the crack initiation and small- and large-crack growth properties are affected and to examine how the altered grain boundary population and connectivity can influence growth rates and overall lifetimes. The effect of such grain-boundary engineering on the fatigue-crack-propagation behavior of large (˜8 to 20 mm), through-thickness cracks at 25, 700, and 800°C was examined. Although there was little influence of an increased special boundary fraction at ambient temperatures, the resistance to near-threshold crack growth was definitively improved at elevated temperatures, with fatigue threshold-stress intensities some 10 to 20% higher than at 25°C, concomitant with a lower proportion (˜20%) of intergranular

  3. Long-term low-cycle corrosion fatigue of steel 08Kh18N10T and its welded joints in water of high parameters

    Steel 08Kh18N10T (similar to steel 321SS) and the weld metal of full-scale pipe of the WWER-440 main circulation pipeline were tested for fatigue in air environment (300 degC) and in deoxygenated water (9 MPa, 300 degC). Cantilevered specimens were loaded in a displacements-controlled symmetrical triangular cycle. The strain rate during tests in water was 1.1x10-3 to 6.7x10-2 % s-1. Given equal strain amplitudes, the number of cycles to failure in water, as compared with air testing, is reduced by a factor of 8-13 at the most with strain rate decrease. The results of testing steels 18-8 in PWR water show fair agreement with fatigue curves according to the equation based on the ANL model. This paper presents equations for calculating curves in case of loading in water and air, as well as design fatigue curves for austenitic stainless steels 18-8 under the given conditions. Fatigue crack growth was studied as found in the base metal and the weld in air, with the asymmetry coefficient R = 0.1 and 300 degC. The results were compared with the design curves for conditions of air and PWR water environment as well as with the design curve in air, calculated by the ASME Code. (author)

  4. Crack Growth Behavior in the Threshold Region for High Cycle Fatigue Loading

    Forman, R. G.; Zanganeh, M.

    2014-01-01

    This paper describes the results of a research program conducted to improve the understanding of fatigue crack growth rate behavior in the threshold growth rate region and to answer a question on the validity of threshold region test data. The validity question relates to the view held by some experimentalists that using the ASTM load shedding test method does not produce valid threshold test results and material properties. The question involves the fanning behavior observed in threshold region of da/dN plots for some materials in which the low R-ratio data fans out from the high R-ratio data. This fanning behavior or elevation of threshold values in the low R-ratio tests is generally assumed to be caused by an increase in crack closure in the low R-ratio tests. Also, the increase in crack closure is assumed by some experimentalists to result from using the ASTM load shedding test procedure. The belief is that this procedure induces load history effects which cause remote closure from plasticity and/or roughness changes in the surface morphology. However, experimental studies performed by the authors have shown that the increase in crack closure is a result of extensive crack tip bifurcations that can occur in some materials, particularly in aluminum alloys, when the crack tip cyclic yield zone size becomes less than the grain size of the alloy. This behavior is related to the high stacking fault energy (SFE) property of aluminum alloys which results in easier slip characteristics. Therefore, the fanning behavior which occurs in aluminum alloys is a function of intrinsic dislocation property of the alloy, and therefore, the fanned data does represent the true threshold properties of the material. However, for the corrosion sensitive steel alloys tested in laboratory air, the occurrence of fanning results from fretting corrosion at the crack tips, and these results should not be considered to be representative of valid threshold properties because the fanning is

  5. Structure-phase states evolution in Al-Si alloy under electron-beam treatment and high-cycle fatigue

    Konovalov, Sergey, E-mail: konovserg@gmail.com; Alsaraeva, Krestina, E-mail: gromov@physics.sibsiu.ru; Gromov, Victor, E-mail: gromov@physics.sibsiu.ru; Semina, Olga, E-mail: gromov@physics.sibsiu.ru [Siberian State Industrial University, Novokuznetsk, 654007 (Russian Federation); Ivanov, Yurii, E-mail: yufi55@mail.ru [Institute of High-Current Electronics SB RAS, Tomsk, 634055 (Russian Federation)

    2015-10-27

    By methods of scanning and transmission electron diffraction microscopy the analysis of structure-phase states and defect substructure of silumin subjected to high-intensity electron beam irradiation in various regimes and subsequent fatigue loading up to failure was carried out. It is revealed that the sources of fatigue microcracks are silicon plates of micron and submicron size are not soluble in electron beam processing. The possible reasons of the silumin fatigue life increase under electron-beam treatment are discussed.

  6. Order effect of strain applications in low-cycle cumulative fatigue at high temperatures

    Recent test results on cumulative damage with two strain levels on a stainless steel (AISI 304) at room temperature, 537 and 6500C show that the sum of cycle-ratios can be significantly smaller than unity for decreasing levels; the opposite has been noted for increasing levels. As a consequence, the use of the linear damage rule (Miner's law) for life predictions is not conservative in many cases. Since the double linear damage rule (DLDR), originally developed by Manson et al. for room temperature applications, takes the order effect of cyclic loading into consideration, an extension of this rule for high temperature cases may be a potentially useful tool. The present paper is concerned with such an extension. For cumulative damage tests with several levels, according to the DLDR, the summation is applied separately for crack initiation and crack propagation stages, and failure is then assumed to occur when the sum is equal to unity for both stages. Application of the DLDR consists in determining the crack propagation stage Nsub(p) associated with a particular number of cycles at failure N, i.e. Nsub(p)=PNsup(a) where exponent a and coefficient P had been assumed to be equal to 0.6 and 14 respectively for several materials at room temperature. When the DLDR is applied (with a=0.6 and P=14) to predict the remaining life at the second strain level (for two-level cumulative damage) for 304 stainless steel at room temperature 5370C and 6500C, the results show that the damage due to the first strain level is over-emphasized for decreasing levels when the damaging cycle-ratio is small. For increasing levels, the damage is underestimated and in some testing conditions this damage is simply ignored

  7. Daily Social Enjoyment Interrupts the Cycle of Same-day and Next-day Fatigue in Women with Fibromyalgia

    Yeung, Ellen W.; Davis, Mary C.; Aiken, Leona S.; Tennen, Howard A.

    2014-01-01

    Background Fatigue is a debilitating symptom of fibromyalgia (FM) that has limited treatment options. Some evidence, however, has linked positive social engagement with reduced within-day fatigue. Purpose This study elaborated longitudinal within-day and across-day relations between FM fatigue and social enjoyment. Methods 176 women with FM completed 21-day automated diaries assessing morning and end-of-day fatigue, and both afternoon social enjoyment and stress within two social domains: non-spousal and spousal. Results In the non-spousal domain, analysis supported a mediational path from lower morning fatigue to higher afternoon social enjoyment, which predicted lower end-of-day fatigue, and subsequently, lower next-morning fatigue. Enjoyment exerted a greater impact on within-day fatigue than did stress. Patterns in the spousal domain were similar, but the mediated path was nonsignificant. Conclusions Positive social engagement offers relief from FM fatigue that carries over across days and may provide an additional target to enhance the effectiveness of current interventions. PMID:25380634

  8. Low cycle fatigue tests of surface modified T91 steel in 10-6 wt% oxygen containing Pb45Bi55 at 550 deg. C

    Low cycle fatigue tests in air and LBE containing 10-6 wt% dissolved oxygen were conducted with T91 steel at 550 deg. C. T91 was employed in two modifications, one in the as-received state, and the other after alloying FeCrAlY into the surface by pulsed electron beam treatment (GESA process). Tests were carried out with symmetrical cycling (R = -1) with a frequency of 0.5 Hz and a total elongation Δεt/2 between 0.3% and 2%. No influence from LBE on fatigue could be detected. Results in air and LBE showed similar behaviour. Additionally, no difference was observed between surface treated and none treated T91 specimens

  9. Compressive Fatigue in Wood

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben; Damkilde, Lars

    1999-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four...... frequencies ranging from 0.01 Hz to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation is...

  10. Effects of warm laser peening at elevated temperature on the low-cycle fatigue behavior of Ti6Al4V alloy

    Zhou, J.Z.; Meng, X.K., E-mail: mengdetiankong10@126.com; Huang, S.; Sheng, J.; Lu, J.Z.; Yang, Z.R.; Su, C.

    2015-09-03

    This study focused on the effects of warm laser peening (WLP) on the fatigue behavior of Ti6Al4V titanium alloy during low-cycle fatigue (LCF) tests. The Ti6Al4V specimens were treated by laser peening at room temperature (RT-LP) and WLP at elevated temperatures from 100 °C to 400 °C. The residual stress relaxation (RSR) tests and LCF tests were conducted subsequently. In addition, the microstructure analysis of fracture surfaces was performed using scanning electron microscope (SEM). Finally, the fracture mechanism of the untreated, RT-LPed and 300 °C-WLPed samples during LCF was revealed. It is found that although the compressive residual stress (CRS) induced by WLP decreases at elevated temperatures, the depth and stability of CRS increase with the increasing treatment temperature, which help to retard the early fatigue crack initiation. Moreover, for the 300 °C-WLPed specimens, the growth rate of effective cracks is decreased and the lengths of crack growth paths are increased by the induced high angle boundaries (HABs) and nano-precipitates. Therefore, specimens treated by WLP at 300 °C are found to have a significantly extended fatigue life when subjected to low-cycle loads. This extended fatigue life is attributed to the great depth and stability of introduced CRS, as well as the enhanced fracture toughness. It can be concluded that 300 °C is the optimal temperature for WLP of Ti6Al4V titanium alloy from the perspective of LCF improvement.

  11. Effects of warm laser peening at elevated temperature on the low-cycle fatigue behavior of Ti6Al4V alloy

    This study focused on the effects of warm laser peening (WLP) on the fatigue behavior of Ti6Al4V titanium alloy during low-cycle fatigue (LCF) tests. The Ti6Al4V specimens were treated by laser peening at room temperature (RT-LP) and WLP at elevated temperatures from 100 °C to 400 °C. The residual stress relaxation (RSR) tests and LCF tests were conducted subsequently. In addition, the microstructure analysis of fracture surfaces was performed using scanning electron microscope (SEM). Finally, the fracture mechanism of the untreated, RT-LPed and 300 °C-WLPed samples during LCF was revealed. It is found that although the compressive residual stress (CRS) induced by WLP decreases at elevated temperatures, the depth and stability of CRS increase with the increasing treatment temperature, which help to retard the early fatigue crack initiation. Moreover, for the 300 °C-WLPed specimens, the growth rate of effective cracks is decreased and the lengths of crack growth paths are increased by the induced high angle boundaries (HABs) and nano-precipitates. Therefore, specimens treated by WLP at 300 °C are found to have a significantly extended fatigue life when subjected to low-cycle loads. This extended fatigue life is attributed to the great depth and stability of introduced CRS, as well as the enhanced fracture toughness. It can be concluded that 300 °C is the optimal temperature for WLP of Ti6Al4V titanium alloy from the perspective of LCF improvement

  12. Fatigue Strength of Weathering Steel

    Kunz, Ludvík; Lukáš, Petr; Klusák, Jan

    2012-01-01

    Fatigue behaviour of Atmofix 52 steel (comparable to COR-TENâ steel) exposed to atmospheric corrosion for 20 years was investigated. S-N curves for load symmetrical cycling and cycling with stress ratio R = 0 were determined on specimens detracted from a failed transmission tower. The data were compared with those on material without a rust layer. The fracture surfaces and, in particular, the sites of fatigue crack initiation were analyzed. Substantial decrease of fatigue life and fatigue lim...

  13. Effect of dynamic strain aging on the low cycle fatigue in SA508 C1.3 reactor pressure vessel steel

    The effect of dynamic strain aging on cyclic stress response and fatigue life of ASME SA508 Cl.3 forging steel for nuclear reactor pressure vessels was studied at temperatures ranging from room temperature to 500 .deg. C. Total strain ranges and strain rates were varied from 0.7 to 2.0% and from 1x10-2 to 4x10-4s-1, respectively. Test environments were the atmospheres of air and argon. Except for the temperature region of dynamic strain aging, 300 .deg. C, the initial cyclic hardening was immediately followed by cyclic softening at all strain rates in air atmosphere. The cyclic softening continued over 95% of the fatigue life. On the other hand, at the dynamic strain aging temperature, the operating temperature of nuclear pressure vessel, the variation of cyclic stress amplitude showed the primary and secondary hardening dependent on the strain rate and the total strain range. Dynamic strain aging was manifested as secondary hardening and a negative strain rate sensitivity by the maximum stress amplitude and micro-Vickers hardness. During the low cycle fatigue test at the dynamic strain aging regime in inert atmosphere, the variation of cyclic stress amplitude was nearly the same in air except for the occurrence of secondary hardening at the faster strain rate and the higher maximum strength. The earlier appearance of dynamic strain aging in inert atmosphere than in air may be caused by the reduced oxidation effect. Therefore, dynamic strain aging may be suppressed at the initial stage of deformation in air atmosphere. Dynamic strain aging in the oxidizing atmosphere enhanced the number of crack initiation sites by partitioning the local deformation but retarded the crack propagation rate by crack branching and by the suppressed plastic zone size. As the strain rate increased, the fatigue resistance increased at all temperatures. And the effect of dynamic strain aging on fatigue life in a smooth specimen was larger than oxidation effect, while the hardening by

  14. Effects of foreign object damage from small hard particles on the high-cycle fatigue life of titanium-(6)aluminum-(4)vanadium

    Hamrick, Joseph L., II

    Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: (1) impact with 2 mm. and 5 mm diameter glass spheres at 305 m/s, (2) impact with 2 mm and 4 mm diameter steel spheres at 305 m/s, (3) quasi-static displacement controlled indentation using steel chisels with 1 mm, 2 nun and 5 mm diameter tips and (4) shearing notches with a 2 mm. diameter chisel point under a quasi-static loading condition. Finite element analysis was used to study the relationship between the stress state created by the plastic damage and the fatigue strength. A new method of quantifying the amount of plastic damage from multiple methods was developed. The fatigue strength required for crack initiation at 10E7 cycles was found to be a function of the total depth from the edge of the undeformed specimen up to the end of the plastically deformed zone. For damage depths less than 1750 mum, the reduction in fatigue strength is proportional to the depth of total damage. For depths > 1750 mum, there appears to be a threshold value of fatigue strength.

  15. Tensile and low cycle fatigue properties of EUROFER97-steel after 16.3 dpa neutron irradiation at 523, 623 and 723 K

    Neutron-irradiated specimens of the reduced-activation tempered martensitic steel EUROFER97 were tested by tensile and low cycle conditions to detect the impact of irradiation on strength and lifetime. The irradiation temperature ranged from 523 to 723 K with an accumulated dose of up to 16.3 dpa. Tensile tests revealed a significant irradiation-induced hardening below 673 K with a peak of ∼430 MPa at 573 K but none was seen at 723 K, as expected. Despite the significant irradiation-induced reduction of uniform elongation, the total elongation is only reduced by about 50% below 673 K. Post-irradiation strain-controlled fatigue tests have been carried out at Tirrad = Ttest = 523, 623 and 723 K. Pronounced cyclic softening was observed in all specimens. At 623 and 723 K, neutron irradiation had no effect on fatigue life within the data scatter. A significant lifetime increase has been observed at Tirrad = Ttest = 523 K that advances with decreasing stress amplitude Δε (1% → 0.5%) up to a factor of ten. Scanning electron microscopy (SEM) analysis revealed ductile fracture and fatigue striations on the fracture surfaces. After push–pull fatigue testing, transmission electron microscopy (TEM) investigations showed the typical sub-cell formation, even at Tirrad = Ttest = 523 K

  16. Development of India-specific RAFM steel through optimization of tungsten and tantalum contents for better combination of impact, tensile, low cycle fatigue and creep properties

    Laha, K.; Saroja, S.; Moitra, A.; Sandhya, R.; Mathew, M. D.; Jayakumar, T.; Rajendra Kumar, E.

    2013-08-01

    Effects of tungsten and tantalum contents on impact, tensile, low cycle fatigue and creep properties of Reduced Activation Ferritic-Martensitic (RAFM) steel were studied to develop India-specific RAFM steel. Four heats of the steel have been melted with tungsten and tantalum contents in the ranges 1-2 wt.% and 0.06-0.14 wt.% respectively. Increase in tungsten content increased the ductile-to-brittle transition temperature (DBTT), low cycle fatigue and creep strength of the steel, whereas the tensile strength was not changed significantly. Increase in tantalum content increased the DBTT and low cycle fatigue strength of the steel whereas the tensile and creep strength decreased. Detailed TEM investigations revealed enhanced microstructural stability of the steel against creep exposure on tungsten addition. The RAFM steel having 1.4 wt.% tungsten with 0.06 wt.% tantalum was found to possess optimum combination of impact, tensile, low cycle fatigue and creep properties and is considered for Indian-specific RAFM steel. Low temperature impact energy of the RAFM steel is quite sensitive to the contents of tungsten and tantalum. The DBTT increased with both the tungsten and tantalum contents. Tungsten and tantalum contents in the investigated ranges had no appreciable effect on the tensile properties of the RAFM steel. Low cycle fatigue life of the RAFM steel increased with the increase in tungsten and tantalum contents. The softening rate with cyclic exposure was lowest for tungsten content of 1.4 wt.%, further increase in tungsten led to an increase in softening rate. Creep deformation and rupture strength of the RAFM steel were found to be quite sensitive to the tungsten and tantalum contents. Creep strength of the steel increased with increase in tungsten content and decreased with increase in tantalum content. Based on the study, the chemical composition of India-specific RAFM steel has been established as 9Cr-1.4W-0.06Ta-V, having optimum combination of strength and

  17. Effect of strain-induced martensitic transformation on high cycle fatigue behavior in cyclically-prestrained type 304

    The effects of the cyclic prestrain on the fatigue behavior in type 304 austenitic stainless steel were investigated. Rotating bending fatigue tests have been performed in laboratory air using the specimens subjected to ±5% cyclic prestrain at room temperature (R.T.) and -5°C. Martensitic phase volume fraction of the prestrained specimen at -5°C was 48% and larger than 3.8% at R.T. The prestrained specimens exhibited higher fatigue strengths than the as-received ones, and larger volume fraction of martensitic phase resulted in the higher fatigue limit. EBSD analysis revealed that the martensitic phases were more uniformly distributed in the austenitic matrix in the cyclically-prestrained specimens than in the monotonically-prestrained ones. Fatigue crack initiation from inclusion was observed only in the cyclically-prestrained specimens at -5°C. High volume fraction and uniform distribution of martensitic phase induced the transition of crack initiation mechanism and led to the higher fatigue limit. In type 304 stainless steel with high volume fraction of strain-induced martensitic phase, the prediction of fatigue limit based on Vickers hardness could give unconservative results. (author)

  18. Investigation into the low cycle fatigue of Type 321 stainless steel studs subjected to large strain controlled bending in the creep range

    Type 321 stainless steel studs are employed to provide a four stud fixing arrangement for an insulation coverplate on the pressure vessel wall of a gas cooled nuclear reactor. The coverplate expands under a temperature of 6500C and deflects the hot end of the studs into a yield condition. As the coverplate is thermally cycled, the studs are subjected to high strain low cycle fatigue in the creep range with dwell periods at either end of the strain cycle. Details of a theoretical and experimental investigation of the stud behavior under these conditions are given. The evolution of a satisfactory design from this study is described. A theoretical limit analysis of the stud load-deflection characteristic, based on plastic hinge considerations is presented. This analysis gave a good correlation with experimental results for both strain controlled bending and creep relaxation and provided an understanding of the fatigue mechanism. The experimental results were dominated by the interaction of creep and fatigue which produced two different, but interacting zones of failure. This is discussed in detail and experimental results presented of the tests which were carried out for different dwell times, strain ranges, material ductility, and designs of the critical stud to coverplate fixing geometry. The results reported relate to a stress situation well beyond that covered by present design codes. The difficulties in establishing reliable fatigue data in the presence of major variables, notably dwell time, in the creep range are clearly demonstrated. This study shows how a suitable design solution can be achieved under such circumstances when analytical and experimental work are directed towards a basic understanding of the mechanisms involved

  19. An investigation into the low cycle fatigue of type 321 stainless steel studs subjected to large strain controlled bending in the creep range

    Type 321 stainless steel studs are employed to provide a four stud fixing arrangement for an insulation coverplate on the pressure vessel wall of a gas cooled nuclear reactor. The coverplate expands under a temperature of 6500C and deflects the hot end of the studs into a yield condition. As the coverplate is thermally cycled, the studs are subjected to high strain low cycle fatigue in the creep range with dwell periods at either end of the strain cycle. This paper presents details of a theoretical and experimental investigation of the stud behaviour under these conditions. The evolution of a satisfactory design from this study is described. A theoretical limit analysis of the stud load-deflection characteristic, based on plastic hinge considerations is presented. This analysis gave a good correlation with experimental results for both strain controlled bending and creep relaxation and provided an understanding of the fatigue mechanism. The experimental results were dominated by the interaction of creep and fatigue which produced two different, but interacting zones of failure. This is discussed in detail and experimental results presented of the tests which were carried out for different dwell times, strain ranges, material ductility and designs of the critical stud to coverplate fixing geometry. The results reported relate to a stress situation well beyond that covered by present design codes. The difficulties in establishing reliable fatigue data in the presence of major variables, notably dwell time, in the creep range are clearly demonstrated. This study shows how a suitable design solution can be achieved under such circumstances when analytical and experimental work are directed towards a basic understanding of the mechanisms involved. (author)

  20. Effect of fatigue on the intra-cycle acceleration in front crawl swimming: A time-frequency analysis

    Tella, V.; Toca-Herrera, J. L.; Gallach, J. E.; J Benavent; Gonzalez, L.M.; Arellano, R.

    2008-01-01

    The present study analyzes the changes in acceleration produced by swimmers before and after fatiguing effort. The subjects (n=15) performed a 25-meter crawl series at maximum speed without fatigue, and a second series with fatigue. The data were registered with a synchronized system that consisted in a position transducer (1 kHz) and a video photogrametry (50Hz). The acceleration (ms-2) was obtained by the derivative analysis of the variation of the position with time. The amplitude in the t...

  1. A comparative study on low cycle fatigue behaviour of nano and micro Al2O3 reinforced AA2014 particulate hybrid composites

    Senthilkumar, R.; Arunkumar, N.; Manzoor Hussian, M.

    Aluminium based metal matrix composites have drawn more attraction due to their improved properties in structural applications for the past two decades. The fatigue behaviour of composite materials needs to be studied for their structural applications. In this work, powder metallurgy based aluminium (AA2014) alloy reinforced with micro and nano-sized alumina particles were fabricated and consolidated with the hot extrusion process. The evaluation of mechanical properties in the extruded composite was carried out. This composite was subjected to low cycle fatigue test with a constant strain rate. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images were used to evaluate the fatigue behaviour of aluminium-nano composite samples. Enhanced mechanical properties were exhibited by the nano alumina reinforced aluminium composites, when compared to the micron sized alumina reinforced composites. The failure cycle is observed to be higher for the nano alumina reinforced composites when compared with micron sized alumina composites due to a lower order of induced plastic strain.

  2. Study of mechanical features for low cycle fatigue samples of metastable austenitic steel AISI 321 by neutron stress analysis under applied load

    The elastoplastic properties of the austenitic matrix and martensitic volume areas induced during cyclic tensile-compressive loading of low carbon metastable austenitic stainless steel were studied in an in situ neutron diffraction stress rig experiment on the ENGIN instrument at the ISIS pulsed neutron facility. Samples prepared from the steel AISI 321 annealed at 1050 deg C and quenched in water were subjected to low-cycle fatigue under total-strain control with an amplitude of 1 % at a frequency of 0.5 Hz. Subsequent applied stress-elastic strain responses of the austenitic and martensitic phases were obtained by Rietveld and Le Bail refinements of the neutron diffraction spectra, and were used to determine the elastic constants of the phases as a function of fatigue level. The results of modified refinements accounting for the elastic anisotropy in polycrystalline materials under load are also presented. The residual strains in the austenitic matrix were determined as a function of fatigue cycling, using a noncycled sample as a reference sample. The residual macrostresses and the deviatoric components of the phase residual microstresses were determined assuming that the elastic properties of both phases are similar

  3. Microstructure characteristics and temperature-dependent high cycle fatigue behavior of advanced 9% Cr/CrMoV dissimilarly welded joint

    Advanced 9% Cr and CrMoV steels chosen as candidate materials are first welded by narrow-gap submerged arc welding (NG-SAW) to fabricate the heavy section rotor. The present work focuses on studying the high-cycle fatigue (HCF) behavior of advanced 9% Cr/CrMoV dissimilarly welded joint at different temperatures. Conditional fatigue strength of this dissimilarly welded joint was obtained by HCF tests at room temperature (RT), 400 °C and 470 °C. It was observed that the failure occurred at the side of CrMoV base metal (BM), weld metal (WM) and heat affected zone (HAZ) of CrMoV side over 5×107 cycles for the specimens tested at RT, 400 °C and 470 °C. The detailed microstructures of BMs, WMs and HAZs as well as fracture appearance were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Precipitation and aggregation of carbides along the grain boundaries were clearly detected with the increase of temperature, which brought a negative effect on the fatigue properties. It is interesting to note that the inclusion size leading to crack initiation became smaller for the HCF test at higher temperature. Therefore, reduction in the inclusion size in a welded joint helps to improve the HCF performance at high temperature

  4. The significance of ultrafine film-like retained austenite in governing very high cycle fatigue behavior in an ultrahigh-strength MN–SI–Cr–C steel

    Zhao, P., E-mail: zhaoping12@mails.tsinghua.edu.cn [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Zhang, B.; Cheng, C. [Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Misra, R.D K., E-mail: dmisra2@utep.edu [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical and Materials Engineering, University of Texas at El Paso, 500 W. University Avenue, El Paso, TX 79968-0520 (United States); Gao, G., E-mail: gaogh@bjtu.edu.cn [Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China); Bai, B.; Weng, Y. [Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Materials Science and Engineering Research Center, Beijing Jiaotong University, Beijing 100044 (China)

    2015-10-01

    We elucidate here the very high cycle fatigue (VHCF) behavior of an ultrahigh-strength medium carbon Mn–Si–Cr–C steel processed using the approach of bainite-based quenching and partitioning (BQ&P). The microstructure of BQ&P process comprised of bainite, carbon-depleted martensite, retained austenite (RA) and small amount of martensite/austenite island (M/A). The tensile strength (R{sub m}) and fatigue limit strength after 10{sup 9} cycles (σ{sub w9}) and in the non-failed condition were 1688 MPa and 875 MPa, respectively such that σ{sub w9}/R{sub m} exceeded conventional steels and was 0.52. Two types of failure modes were observed depending on the surface and microstructure, notably surface-induced failure and non-inclusion-induced failure, where the non-inclusion-induced failure was influenced by the microstructure. Inclusion-induced failure was absent. The study underscores that film-like retained austenite was the underlying reason for superior fatigue properties, hitherto not previously obtained.

  5. Study of Mechanical Features for Low Cycle Fatigue Samples of Metastable Austenitic Steel AISI 321 by Neutron Stress Analysis under Applied Load

    Taran, Yu V; Eifler, D; Nebel, Th; Schreiber, J

    2002-01-01

    The elastoplastic properties of the austenitic matrix and martensitic volume areas induced during cyclic tensile-compressive loading of low carbon metastable austenitic stainless steel were studied in an in situ neutron diffraction stress rig experiment on the ENGIN instrument at the ISIS pulsed neutron facility. Samples prepared from the steel AISI 321 annealed at 1050 ^{\\circ}C and quenched in water were subjected to low-cycle fatigue under total-strain control with an amplitude of 1 % at a frequency of 0.5 Hz. Subsequent applied stress?elastic strain responses of the austenitic and martensitic phases were obtained by Rietveld and Le Bail refinements of the neutron diffraction spectra, and were used to determine the elastic constants of the phases as a function of fatigue level. The results of modified refinements accounting for the elastic anisotropy in polycrystalline materials under load are also presented. The residual strains in the austenitic matrix were determined as a function of fatigue cycling, us...

  6. A study at understanding the mechanisms governing the high cycle fatigue and final fracture behavior of the titanium alloy: Ti-4Al-2.5V

    In this research paper, the cyclic stress amplitude-controlled high cycle fatigue properties and fracture behavior of a titanium alloy are presented and discussed. The material chosen for this study is a Ti-Al-V-Fe-O2 alloy that is marketed under the trade name ATI 425TM. This alloy was initially developed and put forth for use as a ballistic material but through the last few years it gained in stature for use in other areas due to a healthy combination of physical and mechanical properties. Test specimens were prepared, in conformance with the ASTM E-8 standard, from the as-received sheet stock, which was cold rolled and mill annealed, with the rolling direction both parallel (longitudinal) and perpendicular (transverse) to the length of the sheet. The test specimens were cyclically deformed at three different load ratios (R = 0.1, R = 0.3 and R = 0.033) and the cycles-to-failure (Nf) was recorded. The fatigue fracture surfaces were examined in a scanning electron microscope to examine the macroscopic fracture mode, the intrinsic features on the fatigue fracture surface and the role of magnitude of applied stress-microstructural feature interactions in governing failure.

  7. Investigation of in-plane biaxial low cycle fatigued austenitic stainless steel AISI 321. I. Mechanical testing on the planar biaxial load machine

    During fatigue loading of structural materials such as stainless steel, changes in the microstructure which affect the mechanical and physical properties occur. Experimental simulation of the loading conditions that induce the changes can be performed by mechanical loading, usually in the form of uniaxial tension-compression cycling. However, real machines and structures are subjected to more complex multiaxial stresses. Fatigue and fracture under multiaxial stresses are one of the most important current topics aimed at ensuring improved reliability of industrial components. The first step towards better understanding of this problem is to subject the materials to biaxial loading. The material examined was low austenitic stainless steel AISI 321 H. A set of the four samples of cruciform geometry was subjected to the biaxial tension-compression fatigue cycling with the frequency of 0.5 Hz at the applied load of 10-17 kN. The samples are intended for the neutron diffraction measurements of the residual stresses and the mechanical characterizations on a dedicated stress-diffractometer

  8. A comparative study on low cycle fatigue behaviour of nano and micro Al2O3 reinforced AA2014 particulate hybrid composites

    R. Senthilkumar

    2015-01-01

    Full Text Available Aluminium based metal matrix composites have drawn more attraction due to their improved properties in structural applications for the past two decades. The fatigue behaviour of composite materials needs to be studied for their structural applications. In this work, powder metallurgy based aluminium (AA2014 alloy reinforced with micro and nano-sized alumina particles were fabricated and consolidated with the hot extrusion process. The evaluation of mechanical properties in the extruded composite was carried out. This composite was subjected to low cycle fatigue test with a constant strain rate. Scanning Electron Microscope (SEM and Transmission Electron Microscope (TEM images were used to evaluate the fatigue behaviour of aluminium-nano composite samples. Enhanced mechanical properties were exhibited by the nano alumina reinforced aluminium composites, when compared to the micron sized alumina reinforced composites. The failure cycle is observed to be higher for the nano alumina reinforced composites when compared with micron sized alumina composites due to a lower order of induced plastic strain.

  9. The significance of ultrafine film-like retained austenite in governing very high cycle fatigue behavior in an ultrahigh-strength MN–SI–Cr–C steel

    We elucidate here the very high cycle fatigue (VHCF) behavior of an ultrahigh-strength medium carbon Mn–Si–Cr–C steel processed using the approach of bainite-based quenching and partitioning (BQ&P). The microstructure of BQ&P process comprised of bainite, carbon-depleted martensite, retained austenite (RA) and small amount of martensite/austenite island (M/A). The tensile strength (Rm) and fatigue limit strength after 109 cycles (σw9) and in the non-failed condition were 1688 MPa and 875 MPa, respectively such that σw9/Rm exceeded conventional steels and was 0.52. Two types of failure modes were observed depending on the surface and microstructure, notably surface-induced failure and non-inclusion-induced failure, where the non-inclusion-induced failure was influenced by the microstructure. Inclusion-induced failure was absent. The study underscores that film-like retained austenite was the underlying reason for superior fatigue properties, hitherto not previously obtained

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

    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

  11. Dwell effects on low cycle fatigue behaviour of diffusion coated nickel base superalloy IN 713LC at temperature of 800° C

    Šulák, Ivo; Obrtlík, Karel; Hutařová, S.; Juliš, M.; Podrábský, T.; Čelko, L.

    Karlsruhe: Karlsruhe Institute of Technology, 2015 - (Eifler, D.; Heilmaier, M.; Kraft, O.; Löhe, D.). s. 382-382 [ICM12 - International Conference on the Mechanical Behavior of Materials /12./. 10.05.2015-14.05.2015, Karlsruhe] R&D Projects: GA MŠk(CZ) EE2.3.20.0214; GA ČR(CZ) GA15-20991S; GA TA ČR(CZ) TA04011525 Institutional support: RVO:68081723 Keywords : High temperature * Low cycle fatigue * Dwell time * Diffusion coatings * Inconel 713LC Subject RIV: JL - Materials Fatigue, Friction Mechanics http://icm12.com/wp-content/uploads/2015/05/Book_of_Abstracts_ICM12.pdf

  12. Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-08-01

    Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

  13. Effect of aging and cold working on the high-temperature low-cycle fatigue behavior of alloy 800H: Part II continuous cyclic loading

    The individual and combined effects of cold working (5 and 10 pct) and aging (4000 and 8000 h in the temperature range 538 to 7600C) on the high-temperature low-cycle fatigue behavior of alloy 800H have been investigated. The specimens were tested at the aging temperatures. Both the saturation stress range and the fatigue life were found to be history dependent. A history-independent hardening mechanism, dynamic strain aging, was found to operate over the temperature range approx. 450 to 6500C and to be maximized at approx. 5500C. It is speculated that carbon is responsible for this dynamic strain aging. Finally, at temperatures above 5380C the Coffin-Manson plots indicate the possible existence of a history-independent softening mechanism

  14. Movement-Related Cortical Potential Amplitude Reduction after Cycling Exercise Relates to the Extent of Neuromuscular Fatigue.

    Spring, Jérôme Nicolas; Place, Nicolas; Borrani, Fabio; Kayser, Bengt; Barral, Jérôme

    2016-01-01

    Exercise-induced fatigue affects the motor control and the ability to generate a given force or power. Surface electroencephalography allows researchers to investigate movement-related cortical potentials (MRCP), which reflect preparatory brain activity 1.5 s before movement onset. Although the MRCP amplitude appears to increase after repetitive single-joint contractions, the effects of large-muscle group dynamic exercise on such pre-motor potential remain to be described. Sixteen volunteers exercised 30 min at 60% of the maximal aerobic power on a cycle ergometer, followed by a 10-km all-out time trial. Before and after each of these tasks, knee extensor neuromuscular function was investigated using maximal voluntary contractions (MVC) combined with electrical stimulations of the femoral nerve. MRCP was recorded during 60 knee extensions after each neuromuscular sequence. The exercise resulted in a significant decrease in the knee extensor MVC force after the 30-min exercise (-10 ± 8%) and the time trial (-21 ± 9%). The voluntary activation level (VAL; -6 ± 8 and -12 ± 10%), peak twitch (Pt; -21 ± 16 and -32 ± 17%), and paired stimuli (P100 Hz; -7 ± 11 and -12 ± 13%) were also significantly reduced after the 30-min exercise and the time trial. The first exercise was followed by a decrease in the MRCP, mainly above the mean activity measured at electrodes FC1-FC2, whereas the reduction observed after the time trial was related to the FC1-FC2 and C2 electrodes. After both exercises, the reduction in the late MRCP component above FC1-FC2 was significantly correlated with the reduction in P100 Hz (r = 0.61), and the reduction in the same component above C2 was significantly correlated with the reduction in VAL (r = 0.64). In conclusion, large-muscle group exercise induced a reduction in pre-motor potential, which was related to muscle alterations and resulted in the inability to produce a maximal voluntary contraction. PMID:27313522

  15. AREVA fatigue concept

    Modern state-of-the-art fatigue monitoring approaches gain in importance as part of the ageing management of nuclear power plant components. Consequently, lots of operators have to deal with demanding security requirements to ensure the safe operation of power plants. AREVA disposes of a long tradition in the development of fatigue and structural health monitoring solutions. Nuclear power plant applications require the qualified assessment of measured thermo-mechanical loads. The core challenge is the identification and qualified processing of realistic load-time histories. The related methodological requirements will be explained in detail within this contribution. In terms of the nuclear industry, the ageing management of power plant components is nowadays a main issue for all actors: states, regulatory agencies, operators, designers or suppliants. As regards fatigue assessment of nuclear components stringent safety standards imply the consideration of new parameters in the framework of the fatigue analysis process: new design fatigue curves, consideration of environmental fatigue (EAF) parameters and stratification effects. In this general context AREVA developed the integral approach AREVA Fatigue Concept (AFC) with new tools and methods in order to live up to operators’ expectations: Simplified Fatigue Estimation (SFE), Fast Fatigue Evaluation (FFE) and Detailed Fatigue Check (DFC). Based on real measured thermal loads (FAMOSi Local Measurements) and superposed mechanical loads the Fast Fatigue Evaluation (FFE) process allows a highly automated and reliable data processing to evaluate cumulative usage factors of mechanical components. Calculation and management of results are performed within the software frontend FAMOSi, thus impact of operating cycles on components in terms of stress and fatigue usage can be taken into account in order to plan optimized decisions relating to the plant operation or maintenance activities. The paper mainly describes the

  16. Low cycle fatigue life of two nickel-base casting alloys in a hydrogen environment. [for high-pressure oxidizer turbopump turbine nozzles

    Cooper, R. A.

    1976-01-01

    Samples of two nickel-base casting alloys, Mar-M-246 (a Martin Company alloy) and 713LC (a low-carbon modification of the alloy 713C developed by International Nickel Company) were tested as candidate materials for the high-pressure fuel and high-pressure oxidizer turbopump turbine nozzles. The samples were subjected to tensile tests and to low cycle fatigue tests in high-pressure hydrogen to study the influence of the hydrogen environment. The Mar-M-246 material was found to have a three times higher cyclic life in hydrogen than the 713LC alloy, and was selected as the nozzle material.

  17. Low cycle fatigue behaviour of Ti–6Al–5Zr–0.5Mo–0.25Si alloy at room temperature

    Anil Kumar Nag; K V U Praveen; Vakil Singh

    2006-06-01

    Low cycle fatigue (LCF) behaviour of the near titanium alloy, Ti–6Al–5Zr–0.5Mo–0.25Si (LT26A), was investigated in the ( + ) as well as treated conditions at room temperature. LCF tests were carried out under total strain controlled mode in the range of t/2: from ± 0.60% to ± 1.40%. The alloy shows cyclic softening in both the conditions. Also it exhibits dual slope Coffin–Manson (C–M) relationship in both the treated conditions.

  18. On the relation of microstructure and low-cycle fatigue properties of 301LN austenitic stainless steel after reversion annealing

    Chlupová, Alice; Man, Jiří; Polák, Jaroslav; Karjalalinen, L.P.

    Brno: Ústav fyziky materiálů AV ČR, v. v. i., 2015 - (Dlouhý, A.; Kunz, L.). s. 50-50 ISBN 978-80-87434-07-9. [ICSMA-17 International Conference on the Strength of Materials /17./. 09.08.2015-14.08.2015, Brno] R&D Projects: GA ČR GA13-32665S Institutional support: RVO:68081723 Keywords : fatigue * austenitic stainless steel * ultrafinegrained material Subject RIV: JL - Materials Fatigue, Friction Mechanics

  19. Effect of grit blasting surface treatment on high temperature low cycle fatigue life of Inconel 713LC

    Šulák, Ivo; Obrtlík, Karel; Čelko, L.; Gejdoš, P.

    Brno: Brno University of Technology, 2015 - (Dlouhý, I.; Jan, V.; Maca, K.; Válka, L.), s. 139-144 ISBN 978-80-214-5146-9. [Multi Scale Design of Advanced Materials. Velké Bílovice (CZ), 28.05.2015-29.05.2015] R&D Projects: GA MŠk(CZ) EE2.3.20.0214; GA ČR(CZ) GA15-20991S Institutional support: RVO:68081723 Keywords : Grit blasting * Surface relief * Surface microhardnes * High temperature fatigue life * Inocel 713LC Subject RIV: JL - Materials Fatigue, Friction Mechanics

  20. Effect of inclusion size on the high cycle fatigue strength and failure mode of a high V alloyed powder metallurgy tool steel

    Yao, Jun; Qu, Xuan-hui; He, Xin-bo; Zhang, Lin

    2012-07-01

    The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30 μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa·m1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.

  1. Micro-crack growth behavior and life in high temperature low cycle fatigue of blade root and disc joint for turbines

    Low cycle fatigue tests were carried out at a temperature of 600 deg. C using a component specimen of 12%-Cr steel, which simulates a blade root and disc joint for turbines. The growth behavior of micro-cracks in the joint region of the specimens was investigated to clarify the damage mechanism of blade-root joints used in high temperature environments and to improve life assessment methods using finite element analysis. Micro-crack growth behavior similar to that in smooth bar specimens was observed in the specimens tested under conditions of relatively high total strain. Micro-cracks initiation was observed at the notch region of the specimens at an early stage. The crack growth rate increased with surface crack length. The fatigue life of the component specimens under this condition was similar to that of smooth bar specimens. Meanwhile, the component specimens tested under conditions of relatively low total strain showed a different growth behavior. No cracks were observed at the notch region and some micro-cracks were initiated at the edge of the contact region of the specimens in the early stages. Almost no increase in the crack growth rate was observed. Life of the component specimens under this condition was shorter than that of the smooth bar specimens. This might be attributed to fretting fatigue at the contact edge and to mean stresses.

  2. Compressive Fatigue in Wood

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben;

    1999-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four...... frequencies ranging from 0.01 Hz to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation is...... observed between stiffness reduction and accumulated creep. A failure model based on the total work during the fatigue life is rejected, and a modified work model based on elastic, viscous and non-recovered viscoelastic work is experimentally supported, and an explanation at a microstructural level is...

  3. Deformation behaviour and fracture of Ni-base single crystals at simultaneous action of high-cycle fatigue and creep

    Kunz, Ludvík; Lukáš, Petr

    2007-01-01

    Roč. 14, č. 2 (2007), s. 15-20. ISSN 1335-0803 R&D Projects: GA ČR GA106/05/2112 Institutional research plan: CEZ:AV0Z20410507 Keywords : CMSX-4 * CM186LC * Fatigue life * Constant lifetime diagram Subject RIV: JG - Metallurgy

  4. Effect of fatigue on the intra-cycle acceleration in front crawl swimming: a time-frequency analysis.

    Tella, V; Toca-Herrera, J L; Gallach, J E; Benavent, J; González, L M; Arellano, R

    2008-01-01

    The present study analyzes the changes in acceleration produced by swimmers before and after fatiguing effort. The subjects (n = 15) performed a 25-m crawl series at maximum speed without fatigue, and a second series with fatigue. The data were registered with a synchronized system that consisted of a position transducer (1 kHz) and a video photogrametry (50 Hz). The acceleration (ms(-2)) was obtained by the derivative analysis of the variation of the position with time. The amplitude in the time domain was calculated with the root mean square (RMS); while the peak power (PP), the peak power frequency (PPF) and the spectrum area (SA) were calculated in the frequency domain with Fourier analysis. On the one hand, the results of the temporal domain show that the RMS change percentage between series was 67.5% (p < 0.001). On the other hand, PP, PPF, and SA show significant changes (p < 0.001). PP and SA were reduced by 63.1% and 59.5%, respectively. Our results show that the acceleration analysis of the swimmer with Fourier analysis permits a more precise understanding of which propulsive forces contribute to the swimmer performance before and after fatigue appears. PMID:17714719

  5. Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. II - Low cycle fatigue behavior

    Gabb, T. P.; Gayda, J.; Miner, R. V.

    1986-01-01

    The low cycle fatigue (LCF) properties of a single-crystal nickel-base superalloy Rene N4, have been examined at 760 and 980 C in air. Specimens having crystallographic orientations near the 001, 011, -111, 023, -236, and -145 lines were tested in fully reversed, total-strain-controlled LCF tests at a frequency of 0.1 Hz. At 760 C, this alloy exhibited orientation dependent tension-compression anisotropies of yielding which continued to failure. Also at 760 C, orientations exhibiting predominately single slip exhibited serrated yielding for many cycles. At 980 C, orientation dependencies of yielding behavior were smaller. In spite of the tension-compression anisotropies, cyclic stress range-strain range behavior was not strongly orientation dependent for either test temperature. Fatigue life on a total strain range basis was highly orientation dependent at 760 and 980 C and was related chiefly to elastic modulus, low modulus orientations having longer lives. Stage I crack growth on 111 planes was dominant at 760 C, while Stage II crack growth occurred at 980 C. Crack initiation generally occurred at near-surface micropores, but occasionally at oxidation spikes in the 980 C tests.

  6. Aspectos relacionados à fadiga durante o ciclismo: uma abordagem biomecânica Aspects related with fatigue during cycling: a biomechanical approach

    Fernando Diefenthaeler

    2008-10-01

    Full Text Available A fadiga muscular pode ser definida como a incapacidade funcional na manutenção de um nível esperado de força. As competições de ciclismo, especialmente provas de estrada, apresentam como característica longa duração e altas intensidades. Tais características resultam na instauração do processo de fadiga, que pode estar associado a mecanismos e fatores metabólicos que afetam os músculos (fadiga periférica e o sistema nervoso central (fadiga central. O objetivo deste trabalho é fazer uma revisão sobre aspectos relacionados com as mudanças na técnica de pedalada e na atividade elétrica dos músculos envolvidos nesse movimento durante o processo de fadiga. Alguns desses aspectos têm sido reportados na literatura e podem ter repercussão na (1 magnitude, direção e sentido de aplicação das forças no pedal; no (2 padrão de ativação muscular; na (3 geração de força e, conseqüentemente, no (4 desempenho do ciclista. No entanto, poucos estudos associam a fadiga muscular ao comportamento das forças aplicadas no pedal e ao padrão da ativação muscular. Os resultados dos estudos revisados demonstram a incapacidade dos ciclistas em manter a força desejada, perda da técnica de pedalada e mudança nos padrões de ativação elétrica sob condições de fadiga.Muscular fatigue can be defined as functional inability to maintain a desired force output. During cycling competition, especially road races, cyclists are required to exercise for extended duration at high intensities. These features often result in fatigue, which can be associated with metabolic mechanisms and factors affecting both muscles (peripheral fatigue and the central nervous system (central fatigue. The aim of this study is to review aspects related to alterations in the pedaling technique and electrical activation of the muscles during a fatiguing exercise bout. Some of these alterations have been reported in the literature and can reflect on the (1

  7. Experimental study on creep-fatigue loading history effect

    In order to extend the applicability of a creep-fatigue life prediction method based on the overstress to a loading history effect, a series of creep-fatigue tests has been conducted with 316FR stainless steel at 923K in a high vacuum environment. The creep-fatigue test program includes changes of strain wave form: changed from creep-fatigue type to fatigue type and that from fatigue type to creep-fatigue type. Additional tests have been conducted to simulate an effect of a safe shutdown earthquake (SSE) on a creep-fatigue. A fatigue type strain cycling with a large strain range from 50 to 120 cycles is introduced into the creep-fatigue cycling. It was experimentally investigated how the fatigue loading with a larger strain range affects the total creep-fatigue life. In these tests the conventional linear cumulative damage rule is used in evaluating the creep-fatigue life under the complex loading history

  8. Simulation Methods for High-Cycle Fatigue-Driven Delamination using Cohesive Zone Models - Fundamental Behavior and Benchmark Studies

    Bak, Brian Lau Verndal; Lindgaard, Esben; Turon, A.;

    2015-01-01

    A novel computational method for simulating fatigue-driven delamination cracks in composite laminated structures under cyclic loading based on a cohesive zone model [2] and new benchmark studies with four other comparable methods [3-6] are presented. The benchmark studies describe and compare the...... traction-separation response in the cohesive zone and the transition phase from quasistatic to fatigue loading for each method. Furthermore, the accuracy of the predicted crack growth rate is studied and compared for each method. It is shown that the method described in [2] is significantly more accurate...... than the other methods [3-6]. Finally, studies are presented of the dependency and sensitivity to the change in different quasi-static material parameters and model specific fitting parameters. It is shown that all the methods except [2] rely on different parameters which are not possible to determine...

  9. Effect of Forging Parameters on Low Cycle Fatigue Behaviour of Al/Basalt Short Fiber Metal Matrix Composites

    Karthigeyan, R.; Ranganath, G.

    2013-01-01

    This paper deals with metal matrix composites (MMCs) of Al 7075 alloy containing different weight percentage (2.5, 5, 7.5, and 10) basalt short fiber reinforcement and unreinforced matrix alloy. The samples were produced by the permanent stir casting technique. The casting ingots were cut into blanks to be forged in single stage and double stage, using MN press and graphite-based lubricant. The microstructures and fatigue properties of the matrix alloy and MMC samples were investigated in the...

  10. Fatigue Crack Growth in Complex Residual Stress Fields Due to Surface Treatment and Foreign Object Damage under Simulated Flight Cycles

    Zabeen, S.

    2011-01-01

    Foreign object damage (FOD) refers to the damage that generally takes place in aero engine fans and compressor blades, due to the ingestion of hard particles/debris during aeroplane take-off, taxiing, or landing. Such damage can reduce the fatigue life expectancy of the turbine engine components by 50%. Residual stresses and small microcracks induced by the high speed FOD impacts are two root causes that result in premature failure of these components. One way to mitigate the FOD related f...

  11. Effect of forging parameters on low cycle fatigue behaviour of Al/basalt short fiber metal matrix composites.

    Karthigeyan, R; Ranganath, G

    2013-01-01

    This paper deals with metal matrix composites (MMCs) of Al 7075 alloy containing different weight percentage (2.5, 5, 7.5, and 10) basalt short fiber reinforcement and unreinforced matrix alloy. The samples were produced by the permanent stir casting technique. The casting ingots were cut into blanks to be forged in single stage and double stage, using MN press and graphite-based lubricant. The microstructures and fatigue properties of the matrix alloy and MMC samples were investigated in the as cast state and in the single and double stage forging operations. The microstructure results showed that the forged sample had a uniform distribution of the basalt short fiber throughout the specimens. Evaluation of the fatigue properties showed that the forged samples had higher values than those of the as cast counterparts. After forging, the enhancement of the fatigue strength of the matrix alloy was so significant and high in the case of 2.5 and 5.0 wt. percentage basalt short fiber reinforced MMC, and there was no enhancement in 7.5 and 10 weight percentages short fiber reinforced MMCs. The fracture damage was mainly due to decohesion at the matrix-fiber interface. PMID:24298207

  12. Effect of fatigue on the intra-cycle acceleration in front crawl swimming: A time-frequency analysis

    Tella, V; Gallach, J E; Benavent, J; Gonzalez, L M; Arellano, R

    2008-01-01

    The present study analyzes the changes in acceleration produced by swimmers before and after fatiguing effort. The subjects (n=15) performed a 25-meter crawl series at maximum speed without fatigue, and a second series with fatigue. The data were registered with a synchronized system that consisted in a position transducer (1 kHz) and a video photogrametry (50Hz). The acceleration (ms-2) was obtained by the derivative analysis of the variation of the position with time. The amplitude in the time domain was calculated with the root mean square (RMS); while the peak power (PP), the peak power frequency (PPF) and the spectrum area (SA) was calculated in the frequency domain with Fourier analysis. On one hand, the results of the temporal domain show that the RMS change percentage between series was 67.5% (p<0.001). On the other hand, PP, PPF, and SA show significant changes (p<0.001). PP and SA were reduced by 63.1% and 59.5%, respectively. Our results show that the acceleration analysis of the swimmer with...

  13. Effect of Forging Parameters on Low Cycle Fatigue Behaviour of Al/Basalt Short Fiber Metal Matrix Composites

    R. Karthigeyan

    2013-01-01

    Full Text Available This paper deals with metal matrix composites (MMCs of Al 7075 alloy containing different weight percentage (2.5, 5, 7.5, and 10 basalt short fiber reinforcement and unreinforced matrix alloy. The samples were produced by the permanent stir casting technique. The casting ingots were cut into blanks to be forged in single stage and double stage, using MN press and graphite-based lubricant. The microstructures and fatigue properties of the matrix alloy and MMC samples were investigated in the as cast state and in the single and double stage forging operations. The microstructure results showed that the forged sample had a uniform distribution of the basalt short fiber throughout the specimens. Evaluation of the fatigue properties showed that the forged samples had higher values than those of the as cast counterparts. After forging, the enhancement of the fatigue strength of the matrix alloy was so significant and high in the case of 2.5 and 5.0 wt. percentage basalt short fiber reinforced MMC, and there was no enhancement in 7.5 and 10 weight percentages short fiber reinforced MMCs. The fracture damage was mainly due to decohesion at the matrix-fiber interface.

  14. Fatigue Strength of Weathering Steel

    Ludvík KUNZ

    2012-03-01

    Full Text Available Fatigue behaviour of Atmofix 52 steel (comparable to COR-TENâ steel exposed to atmospheric corrosion for 20 years was investigated. S-N curves for load symmetrical cycling and cycling with stress ratio R = 0 were determined on specimens detracted from a failed transmission tower. The data were compared with those on material without a rust layer. The fracture surfaces and, in particular, the sites of fatigue crack initiation were analyzed. Substantial decrease of fatigue life and fatigue limit due to corrosion exposition was found. Based on observation of surface layer with corrosion products and on fractographic analysis of failed specimens conclusions on fatigue damage mechanism were drawn. No grain boundary corrosion, which can be responsible for fatigue crack initiation, was observed. Initiation of fatigue cracks was related to surface roughness and took place exclusively on corrosion dimples.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1335

  15. Modifications on A-F hardening rule to assess ratcheting response of materials and its interaction with fatigue damage under uniaxial stress cycles

    Ahmadzadehrishehri, Gholamreza

    stress levels. The constructed calibration curves were employed to determine strain rate coefficients required to assess ratcheting response of materials under uniaxial loading conditions at various cyclic stress levels. The predicted ratcheting strain values based on the modified hardening rule were found in good agreements with the experimentally obtained ratcheting data over stages I and II under uniaxial loading conditions. The capability of the modified hardening rule to assess ratcheting deformation of materials under multi-step uniaxial loading spectra was also assessed. Subsequent load steps were considerably affected by previous load steps in multi-step loading conditions. Ratcheting strains for low-high stress steps were successfully predicted by the modified hardening rule. High-low loading sequences however resulted in an overestimated reversed ratcheting strain in the later load steps. The modified hardening rule proposed in this thesis was then employed to predict the ratcheting strain and its concurrent interaction with fatigue damage over stress cycles in steel alloys. The interaction of ratcheting and fatigue damage was defined based on mechanistic parameters involving the effects of mean stress, stress amplitude, and cyclic softening/hardening response of materials. The extent of ratcheting effect on the overall damage of steel samples was defined by means of the product of the average ratcheting strain rate over the stress cycles and the applied maximum cyclic stress, while fatigue damage was analysed based on earlier developed energy-based models of Xia-Ellyin and Smith-Watson-Topper. Overall damage induced by both ratcheting and fatigue was calibrated through a weighting factor at various ratios of mean stress/cyclic amplitude stress (sigmam/sigmaa). The estimated lives based on the proposed algorithm at different mean stresses and stress amplitudes showed good agreements as compared with experiments.

  16. Study on the Ultra High Cycle Bending Vibration Fatigue Test of Titanium Alloys%钛合金超高周弯曲振动疲劳性能试验

    申景生; 李全通; 吴晓峰; 高潮; 刘青川

    2011-01-01

    Based on the three-point bending method, an ultra high cycle bending vibration fatigue system is developed and the design method of fatigue test specimens is introduced too. The S - N curve of titanium alloy TC17 is determined by the ultra high cycle dissymmetrical bending fatigue system (20 kHz). The result shows that when stress ratio(R) is -1, the S - N curve of titanium alloy TC17 is a continuously declining curve, The specimens continue to fail over 107 stress cycles. In 107 weeks time, the samples don' t happen the fatigue damage, so it does not exist in the traditional sense fatigue limit.%在三点弯曲超高周疲劳试验的基础上,开发了悬臂梁式弯曲振动超高周疲劳试验系统,并介绍了疲劳试验试片的设计方法.利用超高周弯曲疲劳试验系统(20 kHz)测定了钛合金TC17的S-N曲线,结果表明,当应力比R=-1时TC17钛合金的S-N曲线是一条连续下降型曲线,在107周次以后,试样仍未发生疲劳破坏,不存在传统意义上的疲劳极限.

  17. Fatigue and thermal fatigue of Pb-Sn solder joints

    This paper presents a fundamental investigation of the fatigue and thermal fatigue characteristics, with an emphasis on the microstructural development during fatigue, of Sn-Pb solder joints. Fatigue tests were performed in simple shear on both 60Sn-40Pb and 5Sn-95Pb solder joints. Isothermal fatigue tests show increasing fatigue life of 60Sn-40Pb solder joints with decreasing strain and temperature. In contrast, such behavior was not observed in the isothermal fatigue of 5Sn-95Pb solder joints. Thermal fatigue results on 60Sn-40Pb solder cycled between -550C and 1250C show that a coarsened region develops in the center of the joint. Both Pb-rich and Sn-rich phases coarsen, and cracks form within these coarsened regions. The failure mode 60Sn-40Pb solder joints in thermal and isothermal fatigue is similar: cracks form intergranularly through the Sn-rich phase or along Sn/Pb interphase boundaries. Extensive cracking is found throughout the 5Sn-95Pb joint for both thermal and isothermal fatigue. In thermal fatigue the 5Sn-95Pb solder joints failed after fewer cycles than 60Sn-40Pb

  18. High-cycle fatigue of nickel-base superalloy Rene 104 (ME3): Interaction of microstructurally small cracks with grain boundaries of known character

    High-cycle fatigue (HCF), involving the premature initiation and/or rapid propagation of small cracks to failure due to high-frequency cyclic loading, has been identified as one of the leading causes of turbine engine failures in aircraft. In this work, we consider the feasibility of using grain-boundary engineering to improve the HCF properties of a polycrystalline nickel-base superalloy, Rene 104 (also known as ME3), through systematic modification of the grain-boundary distribution. In particular, we investigate the growth of microstructurally small fatigue cracks at ambient temperature in microstructures with varying proportions of 'special' vs. 'random' boundaries, as defined by coincident-site lattice theory. Specifically, we examine the interaction of propagating small (∼10-900 μm) surface cracks with grain boundaries of known character, with respect both to any deflection in crack trajectory that occurs at or near the boundary, and more importantly to any local changes in crack-growth rates. In addition, finite-element calculations are performed to evaluate the effective driving force and plastic-zone profile for such small-crack propagation, incorporating information from both the local microstructure (from electron backscattering diffraction scans) and the surface crack-path profile

  19. Low-cycle fatigue behavior and deformation substructure of Ti-2Al-2.5Zr alloy at 298 and 673 K

    Low-cycle fatigue (LCF) behavior of Ti-2Al-2.5Zr was investigated at 298 and 673 K. Cyclic stress response curves showed that initial cyclic hardening was followed by cyclic softening at 298 and 673 K, while secondary cyclic hardening appeared when testing temperature increased to 673 K. Ti-2Al-2.5Zr displayed higher LCF lives at 673 K than those at 298 K. Microstructural characterization with transmission electron microscopy (TEM) revealed that {101-bar 0} prismatic slip was primary plastic deformation mode in Ti-2Al-2.5Zr fatigued at 298 K. {12-bar 11} pyramidal slip could be activated at high cyclic strain amplitude. Whereas, multiple slips were simultaneously operated on {101-bar 0} prismatic and {12-bar 11} pyramidal planes in the range of tested cyclic strain amplitudes at 673 K. Plastic deformation mode changed from planar slip to wavy slip as testing temperature increased from 298 to 673 K. The improvement of LCF life of Ti-2Al-2.5Zr could be attributed to the increase of plastic deformation homogeneity due to activating multiple slips at 673 K.

  20. Fatigue crack initiation life prediction of railroad

    Study of multiaxial high-cycle fatigue initiation life prediction for railroad is done in this paper. Using ANSYS 11.0 software three dimensional elasto-plastic finite element model of rail/wheel contact is constructed and fine mesh technique in contact region is used to achieve both computational efficiency and accuracy. Stress analysis is performed and fatigue damage in railroad is evaluated numerically using multiaxial fatigue crack initiation model. Using the stress history during one loading cycle and fatigue damage model, the effects of vertical loading, material hardness material fatigue properties and wheel/rail contact situation on fatigue crack initiation life are investigated.

  1. 涡轮叶片复合疲劳特性曲线及其规律的试验%Experimental study on fatigue curve law of turbine blade under combined high and low cycle loading

    闫晓军; 孙瑞杰; 邓瑛; 刘芝娜; 聂景旭

    2011-01-01

    为了解高周振动载荷对于涡轮叶片高温疲劳性能的影响,对某型涡轮叶片进行高低周复合疲劳试验.试验结果表明,在低周载荷基础上叠加高频振动载荷,显著缩短了叶片的疲劳寿命;复合疲劳的分散性很大,且不存在疲劳极限,当叶片高周循环次数超过10^7时,继续试验叶片仍会发生断裂;在双对数坐标下,叶片的振动应力与其高周循环寿命成线性关系,即复合疲劳特性曲线(应力-寿命曲线、概率应力-寿命曲线)服从双对数线性规律,进一步研究发现该规律对于高温合金材料的复合疲劳特性曲线具有普遍性.%The effect of the high cycle vibration load on the high-temperature fatigue properties of the turbine blade were addressed. Combined high and low cycle fatigue tests were carried out on several blade specimens. The results show that the superposition of high-frequency vibration on low-cycle load can significantly reduce the fatigue life of the blade. It is noteworthy that combined high and low cycle fatigue has two features: great dispersion and no fatigue limit. The former is exhibited by much broader life range than the low cycle fatigue (LCF) test, and the latter indicated by fracture of the blades over 107 high cycles (which is considered as the life limit of the metal materials for the invariable-amplitude fatigue). In addition, the fatigue data suggest a double logarithmic linear relationship between vibration stress level and the combined fatigue life. Further research has found that the law for superalloys operates universally .

  2. 加载速率对汽轮机转子钢低周疲劳损伤的影响%Effect of Loading Rate on Low-cycle Fatigue Damage of Turbine Rotor Steel

    何建军; 陈荐; 孙清民; 邱玮; 周鹏展

    2011-01-01

    加载速率反映了汽轮机转子启停及运行时温度变化速度与负荷变化速率.对火电厂汽轮机转子30Cr1Mo1V钢在538℃温度下的低周疲劳损伤进行试验研究,研究加载速率对实际低周疲劳损伤和预测低周疲劳损伤的影响.结果表明:在相同的寿命分数下,加载应变速率越大,低周疲劳损伤越小;在同一加载速率下,总应变幅越大对应的低周疲劳损伤也越大;在同等应变幅条件下,转子钢高温低周疲劳预测损伤比实际损伤大,加载速率较低时,转子钢高温低周疲劳预测损伤比较大;加载速率对材料损伤有显著影响的取值范围为0.1%·s-1≤ε≤0.2%·s-1.%Loading rate is associated with high thermo-mechanical loads change rate of the turbine rotors during start-up and shut-down procedures. Low-cycle fatigue damage of power plant turbine rotor 30CrlMolV steel was studied at 538 ℃, and the effect on the actual low-cycle fatigue damage and the predicted low-cycle fatigue damage of the loading rate were also studied. The results show that higher strain loading rate leads to the smaller low-cycle fatigue damage in the same cycle life fraction. The greater total strain amplitude brings the greater low-cycle fatigue damage in the same loading rate. While in the same strain amplitude condition,the predicted low-cycle fatigue damage of the rotor steel is larger than the actual one, the low-cycle fatigue predicted damage is greater in the lower loading rate test process. The loading rate range which has significant effect to the material damage is 0.1%·s-1 ≤ ε≤ 0.2%·s-1.

  3. Leakage from CVCS pipe of regenerative heat exchanger induced by high-cycle thermal fatigue at Tsuruga Nuclear Power Station Unit 2

    On July 12, 1999 while Tsuruga-2, PWR 4-loop plant, was operating at full power (1,160 MWe), unidentified leakage inside the primary containment vessel was detected. As the leakage was identified, the plant promptly started to proceed to cold shutdown. Visual inspection after an isolation of the CVCS (Chemical and Volume Control System) revealed that the leakage was from a connecting pipe between the middle and lower stages in the CVCS regenerative heat exchanger. The CVCS regenerative heat exchanger has three shells, i.e. the upper shell, the middle shell and the lower shell. Each heat exchanger shell has an inner cylinder containing a heat exchanger tube bundle. Reactor coolant is cooled inside the inner cylinder, however, the temperature of the coolant which flows outside the inner cylinder keeps high. These two coolant flows are mixed around the outlet of the inner cylinder. Thermal hydraulic mock-up tests simulating internal flows in the heat exchanger were conducted along with thermal and structural analyses to investigate a high-cycle thermal fatigue mechanism. As a result of the investigation, the cause of the leakage from the connecting pipe was considered to be as follows; (1) Flow out of the lower temperature bypass flow region occurred repeatedly at the lower part of the shell which yielded a cyclic deformation of the shell due to thermal expansion and shrinkage. (2) This cyclic deformation caused a cyclic change of the gap between the inner cylinder support ring and shell, and consequently the cyclic change of the flow pattern at the region where the bypass flow and main flow mixed. (3) Superposition of lower frequent temperature change due to the change of flow pattern and higher frequent temperature fluctuation due the mixture of the bypass flow and main flow caused high-cycle thermal fatigue cracking. (author)

  4. Changes in urinary amino acids excretion in relationship with muscle activity markers over a professional cycling stage race: in search of fatigue markers.

    Corsetti, Roberto; Barassi, Alessandra; Perego, Silvia; Sansoni, Veronica; Rossi, Alessandra; Damele, Clara Anna Linda; Melzi D'Eril, Gianlodovico; Banfi, Giuseppe; Lombardi, Giovanni

    2016-01-01

    The aim of this study was to identify the relationship between metabolic effort, muscular damage/activity indices, and urinary amino acids profile over the course of a strenuous prolonged endurance activity, as a cycling stage race is, in order to identify possible fatigue markers. Nine professional cyclists belonging to a single team, competing in the Giro d'Italia cycling stage race, were anthropometrically characterized and sampled for blood and urine the day before the race started, and on days 12 and 23 of the race. Diet was kept the same over the race, and power output and energy expenditure were recorded. Sera were assayed for muscle markers (lactate dehydrogenase, aspartate aminotransferase, and creatine kinase activities, and blood urea nitrogen), and creatinine, all corrected for plasma volume changes. Urines were profiled for amino acid concentrations, normalized on creatinine excretion. Renal function, in terms of glomerular filtration rate, was monitored by MDRD equation corrected on body surface area. Creatine kinase activity and blood urea were increased during the race as did serum creatinine while kidney function remained stable. Among the amino acids, taurine, glycine, cysteine, leucine, carnosine, 1-methyl histidine, and 3-methyl histidine showed a net decreased, while homocysteine was increased. Taurine and the dipeptide carnosine (β-alanyl-L-histidine) were significantly correlated with the muscle activity markers and the indices of effort. In conclusion, the metabolic profile is modified strikingly due to the effort. Urinary taurine and carnosine seem useful tools to evaluate the muscle damage and possibly the fatigue status on a long-term basis. PMID:26306846

  5. A three dimensional discrete dislocation dynamics modelling of the early cycles of fatigue in an austenitic stainless steel 316L: dislocation microstructure and damage analysis

    A numerical code modelling the collective behaviour of dislocations at a mesoscopic scale (Discrete Dislocation Dynamics code) is used to analyse the cyclic plasticity that occurs in surface grains of an AISI 316L stainless steel, in order to understand the plastic mechanism involved in crack initiation in fatigue. Firstly, the analyses of both the formation and the evolution of the dislocation microstructures show the crucial role of cross-slip played in the strain localization in the form of slip bands. As the cycling proceeds, the slip bands exhibit well-organized dislocation arrangements that substitute to dislocation tangles, involving specific interaction mechanisms between primary and deviate systems. Secondly, both the surface displacements generated by plastic slip and the distortion energy induced by the dislocation microstructure have been analysed. We find that an irreversible surface relief in the form of extrusion/intrusion can be induced by cyclic slip of dislocations. The number of cycles for the crack initiation follows a Manson-Coffin type law. The analyses of the concentration of the distortion energy and its repartition in the slip bands show that beneficial energetic zones may be present at the very beginning of the cycling, and that mode-II crack propagation in the surface grains results from a succession of micro-crack initiations along primary slip plane, which is facilitated by various effects (stress concentration due to surface relief, environment effects...). Finally, a dislocation-based model for cyclic plasticity is proposed from Discrete Dislocation Dynamics results. (author)

  6. Fatigue approach for addressing environmental effects in fatigue usage calculation

    Laboratory tests consider simple trapezoidal, triangle, and sinusoidal signals. However, actual plant components are characterized by complex loading patterns and periods of holds. Fatigue tests in water environment show, that the damage from a realistic strain variation or the presence of hold-times within cyclic loading results in an environmental reduction factor (Fen) only half that of a simple waveform. This study proposes a new fatigue approach for addressing environmental effects in fatigue usage calculation for class 1 boiler and pressure vessel reactor components. The currently accepted method of fatigue assessment has been used as a base model and all cycles, which have been comparable with realistic fatigue tests, have been excluded from the code-based fatigue calculation and evaluated directly with the test data. The results presented show that the engineering approach can successfully be integrated in the code-based fatigue assessment. The cumulative usage factor can be reduced considerably.

  7. Role of butter layer in low-cycle fatigue behavior of modified 9Cr and CrMoV dissimilar rotor welded joint

    Highlights: • Modified 9Cr–CrMoV dissimilar turbine rotor was successfully welded by NG-SAW. • LCF properties of both welded joints were approximate at smaller strain amplitude. • Tempered martensite with amounts of carbides in HAZ contributed to weakest zones. • Matched BL determined LCF properties of whole joint for dissimilar welded rotor. - Abstract: The present work aims at studying the role of butter layer (BL) in low-cycle fatigue (LCF) behavior of modified 9Cr steel and CrMoV steel dissimilar welded joint. The significant difference of the chemical composition of base metals (BMs) makes it a challenge to achieve sound welded joint. Therefore, buttering was considered to obtain a transition layer between the dissimilar steels. The LCF tests of two kinds of specimens without and with butter layer were performed applying strain-controlled cyclic load with different axial strain amplitudes. The test results indicated that the number of cycles at higher strain amplitudes of welded joint without butter layer was greatly higher than that of the joint with butter layer, while the fatigue lifetime to crack initiation (2Nf) became closer to each other at low and middle strain amplitudes. The failure was in the tempered heat affected zone (HAZ) at the CrMoV side for specimens without BL, while the fracture occurred at the tempered HAZ in the BL for specimens with BL. The microstructure details of BM, BL, HAZ and weld metals (WMs) were revealed by optical microscopy (OM). It was found that the tempered martensite was major microstructure for welded joint and much more carbides were observed in tempered HAZ than other parts due to the repeated tempering. Microhardness test indicated a softest zone existing tempered HAZ of BL and also there was a softer zone in tempered HAZ at the CrMoV side due to repeated tempering during welding and post weld heat treatment (PWHT). And scanning electron microscopy (SEM) was applied to observe the fractography. It was

  8. Temperature dependence of liquid metal embrittlement susceptibility of a modified 9Cr-1Mo steel under low cycle fatigue in lead-bismuth eutectic at 160-450 °C

    Gong, Xing; Marmy, Pierre; Qin, Ling; Verlinden, Bert; Wevers, Martine; Seefeldt, Marc

    2016-01-01

    Low cycle fatigue properties of a 9Cr-1Mo ferritic-martensitic steel (T91) have been tested in a low oxygen concentration (LOC) lead-bismuth eutectic (LBE) environment and in vacuum at 160-450 °C. The results show a clear fatigue endurance "trough" in LOC LBE, while no such a strong temperature dependence of the fatigue endurance is observed when the steel is tested in vacuum. The fractographic observations by means of scanning electron microscopy (SEM) show that ductile microdimples are prevalent on the fracture surfaces of the specimens tested in vacuum, whereas the fracture surfaces produced in LOC LBE at all the temperatures are characterized by quasi-cleavage. Interestingly, using electron backscatter diffraction (EBSD), martensitic laths close to the fatigue crack walls or to the fracture surfaces of the specimens tested in vacuum are found to have transformed into very fine equiaxed subgrains. Nevertheless, such microstructural modifications do not happen to the specimens tested in LOC LBE at 160-450 °C. These interesting microstructural distinctions indicate that liquid metal embrittlement (LME) is able to occur throughout the fatigue crack propagation phase in the full range of the temperatures investigated, i.e. LME is not very sensitive to temperature during the fatigue crack propagation.

  9. Numerical implementation of a multiaxial cyclic plasticity model for the Local Strain Method in low cycle fatigue

    C. Madrigal

    2014-10-01

    Full Text Available Very often computations on structural elements or machine components subjected to variable loading require using an advanced finite element model. This paper reports the numerical implementation of a model for multiaxial cyclic elasticplastic behaviour developed to extend the tools of the local deformation method under fatigue to multiaxial conditions. A basic computer code for axialtorsional loads was developed with the commercial software Matlab and a more sophisticated code based on the finite element model for general multiaxial loads was developed as a UMAT subroutine in Abaqus. Stress integration was introduced in the two usual forms: implicitly and explicitly. A comparison of the results obtained with the implicit and explicit formulations revealed that, under certain loading conditions, the outcome of the process depends on the particular integration scheme used.

  10. Probabilistic Fatigue Damage Program (FATIG)

    Michalopoulos, Constantine

    2012-01-01

    FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

  11. Fatigue properties of weathering steel

    Zavadilová, Petra

    2012-01-01

    This work deals with the influence of atmospheric corrosion on high-cycle fatigue properties of a weathering steel ATMOFIX B. New experimental data on fatigue strength of a steel exposed for 20 years to an atmospheric corrosion were compared to those characterizing the base material. Reduction of the fatigue lifetime of the exposed material compared with the base material was predicted on the basic of fractographic examination of fracture surfaces and the influence of surface notches on fatig...

  12. Effect of liquid metal embrittlement on low cycle fatigue properties and fatigue crack propagation behavior of a modified 9Cr–1Mo ferritic–martensitic steel in an oxygen-controlled lead–bismuth eutectic environment at 350 °C

    Gong, Xing, E-mail: gongxingzfl@hotmail.com [SCK-CEN (Belgian Nuclear Research Centre), Boeretang 200, B-2400 Mol (Belgium); KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Marmy, Pierre, E-mail: pierre.marmy@sckcen.be [SCK-CEN (Belgian Nuclear Research Centre), Boeretang 200, B-2400 Mol (Belgium); Qin, Ling, E-mail: Ling.Qin@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Verlinden, Bert, E-mail: Bert.Verlinden@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Wevers, Martine, E-mail: Martine.Wevers@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium); Seefeldt, Marc, E-mail: Marc.Seefeldt@mtm.kuleuven.be [KU Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, Box 2450, B-3001 Heverlee (Belgium)

    2014-11-17

    The low cycle fatigue properties of a modified 9Cr–1Mo ferritic–martensitic steel (T91) have been tested in stagnant liquid lead–bismuth eutectic (LBE) with oxygen concentrations ranging from 1.16×10{sup −6} to 6.0×10{sup −10} wt% at 350 °C. The effect of liquid metal embrittlement (LME) on fatigue endurance, fatigue crack propagation modes and secondary cracking has been studied. The results showed that the fatigue lives of T91 steel in a low oxygen concentration LBE were drastically reduced compared to those in vacuum due to the presence of LME. The microstructural observations on the fatigue crack propagation modes revealed that fatigue cracks in LBE mainly propagate across prior-austenite grain boundaries and then cut through martensitic lath boundaries, simultaneously leaving a few plastic flow traces and characteristic brittle features. Intergranular and interlath cracking occurred occasionally and their occurrence depended on the orientation of the boundaries relative to the stress axis. The complexity of the LME-induced fracture features can be attributed to a mixture of the multiple failure modes. No obvious plastic shear strain localization was present around the crack tips when LME occurred. However, using a high resolution electron backscatter diffraction (EBSD) technique, highly localized plastic shear strain was observed in the vicinity of the crack tips in vacuum, manifested by the presence of very fine subgrains along the crack walls. A qualitative mechanism was proposed to account for the LME phenomenon in the T91/LBE system. In addition, the secondary cracking at fatigue striations was different in the presence of LBE compared to vacuum. This phenomenon was elucidated by taking into account the influence of the LME on the fatigue crack propagation rate.

  13. Effect of liquid metal embrittlement on low cycle fatigue properties and fatigue crack propagation behavior of a modified 9Cr–1Mo ferritic–martensitic steel in an oxygen-controlled lead–bismuth eutectic environment at 350 °C

    The low cycle fatigue properties of a modified 9Cr–1Mo ferritic–martensitic steel (T91) have been tested in stagnant liquid lead–bismuth eutectic (LBE) with oxygen concentrations ranging from 1.16×10−6 to 6.0×10−10 wt% at 350 °C. The effect of liquid metal embrittlement (LME) on fatigue endurance, fatigue crack propagation modes and secondary cracking has been studied. The results showed that the fatigue lives of T91 steel in a low oxygen concentration LBE were drastically reduced compared to those in vacuum due to the presence of LME. The microstructural observations on the fatigue crack propagation modes revealed that fatigue cracks in LBE mainly propagate across prior-austenite grain boundaries and then cut through martensitic lath boundaries, simultaneously leaving a few plastic flow traces and characteristic brittle features. Intergranular and interlath cracking occurred occasionally and their occurrence depended on the orientation of the boundaries relative to the stress axis. The complexity of the LME-induced fracture features can be attributed to a mixture of the multiple failure modes. No obvious plastic shear strain localization was present around the crack tips when LME occurred. However, using a high resolution electron backscatter diffraction (EBSD) technique, highly localized plastic shear strain was observed in the vicinity of the crack tips in vacuum, manifested by the presence of very fine subgrains along the crack walls. A qualitative mechanism was proposed to account for the LME phenomenon in the T91/LBE system. In addition, the secondary cracking at fatigue striations was different in the presence of LBE compared to vacuum. This phenomenon was elucidated by taking into account the influence of the LME on the fatigue crack propagation rate

  14. On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550?C

    Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

    2013-01-01

    The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed...

  15. Investigation of ultra-high cycle fatigue behavior of TC17 alloy at a frequency of 20kHz%20kHz下TC17钛合金超高周疲劳性能研究

    高潮; 程礼; 彭桦; 申景生; 邱辰霖; 刘延杰

    2012-01-01

    The bending fatigue system was developed using the piezoelectric ultrasonic fatigue testing technology and experimental investigation of the ultra-high cycles fatigue life for TC17 alloy subjected to bending fatigue deformation has been conducted.The experimental resultes show that the specimens were tested to failure in the range of 107-109 cycles and the fatigue limit decreases with the increasing number of cycles between 107 and 109 for R=-1.0 and there was no obvious fatigue limit.The S-N curve for TC17 is a continuous decline curve between 107 and 109 cycles.The fractographic study showes that fatigue failures are mostly initiated at the surface of the test specimens.When there are subsurface inclusions,fatigue cracks initiated from subsurface inclusions,and the composition of inclusions is mainly oxides of aluminums.%应用基于压电超声疲劳试验技术开发的20kHz弯曲疲劳试验系统,完成了室温下TC17合金超高周疲劳试验.结果表明:在疲劳循环大于107周次时,试样仍会发生疲劳断裂,疲劳强度随循环次数的增加而下降,并不存在明显的疲劳极限.TC17合金的应力-寿命(S-N)曲线在107~109周次的范围内为连续下降型.光学显微镜发现,TC17合金的疲劳破坏主要起源于试样表面.当存在夹杂物时,疲劳裂纹从距离表面很近的夹杂物处萌生,能谱分析表明夹杂物的成分主要是铝的氧化物.

  16. Influence of prior thermal ageing on creep and low cycle fatigue behaviour of forged thick section 9Cr-1Mo ferritic steel at 793 K

    Detailed investigations have been carried out to understand the influence of prior thermal ageing on creep and low cycle fatigue (LCF) behaviour of thick section 9Cr-1Mo ferritic steel forging. Creep tests were conducted in quenched and tempered (Q+T), simulated post weld heat treatment (SPWHT) and thermally aged (TA) conditions at 793 K. Total-axial-strain controlled continuous cycling LCF tests have been performed on SPWHT and TA specimens at 793 K. No significant variation in creep rupture properties was observed in the three material conditions investigated. The failure mode remained transgranular ductile characterized by void coalescence under all test conditions. LCF resistance of thermally aged material was found to be higher compared to SPWHT material. Both SPWHT and TA materials exhibited progressive cyclic softening and similar cyclic stress-strain behaviour obeying power-law relationship. The crack initiation and propagation modes remained transgranular in both material conditions. However, thermally aged material exhibited extensive particle decohesion and higher secondary cracking. The improved LCF resistance of thermally aged material has been ascribed mainly to the reduction in stress intensity at the tip of propagating main crack caused by enhanced particle decohesion and secondary cracks. (author). 37 refs., 13 figs., 1 tab

  17. The effects of environment on the mechanisms of damage and fracture in high temperature low-cycle fatigue of MAR-M200 + Hf superalloy

    The research dealt with the failure of MAR-M200 + Hf unidirectionally solidified nickel-base alloy at 975 degrees C under low-cycle fatigue loading. The cyclic load was constant and comprised creep tension and plastic compression. The crack initiation and propagation under the influence of different gas environments was studied by SEM, X-ray diffraction and Auger electron spectroscopy. The gaseous environments were components observed in actual service conditions of the turbine blades within the jet engine namely, O2, N2, CO2 and SO2. It was found that at the propagating crack tip under Ar + 20% O2, pure nitrogen and pure CO2 environments, internal chemical interaction (as a means of stress relaxation) controls the kinetics by coarsening of γ' precipitates, formation of uniphase layer and formation of external chemical compound phases (oxide, nitride, etc) by bulk diffusion. Under a mixture of gases (N2, CO2, O2, Ar) due to gas species depletion at the crack tip (stagnation) it was hypothesised that there is a synergistic progressive influence whereby the more active species initially takes part and when consumed, the rest most reactive gas controls the environment reaction. The addition of 20% O2 to the passive atmospheres (Ar, N2, CO2) prolongs the L.C.F. life (cycles to failure). Under atmospheres containing SO2 an accelerated failure was observed due to the existence of hot corrosion processes. 6 refs., 5 figs

  18. Fatigue evaluation algorithms: Review

    Passipoularidis, V.A.; Broendsted, P.

    2009-11-15

    A progressive damage fatigue simulator for variable amplitude loads named FADAS is discussed in this work. FADAS (Fatigue Damage Simulator) performs ply by ply stress analysis using classical lamination theory and implements adequate stiffness discount tactics based on the failure criterion of Puck, to model the degradation caused by failure events in ply level. Residual strength is incorporated as fatigue damage accumulation metric. Once the typical fatigue and static properties of the constitutive ply are determined,the performance of an arbitrary lay-up under uniaxial and/or multiaxial load time series can be simulated. The predictions are validated against fatigue life data both from repeated block tests at a single stress ratio as well as against spectral fatigue using the WISPER, WISPERX and NEW WISPER load sequences on a Glass/Epoxy multidirectional laminate typical of a wind turbine rotor blade construction. Two versions of the algorithm, the one using single-step and the other using incremental application of each load cycle (in case of ply failure) are implemented and compared. Simulation results confirm the ability of the algorithm to take into account load sequence effects. In general, FADAS performs well in predicting life under both spectral and block loading fatigue. (author)

  19. Application of cyclic J-integral to low cycle fatigue crack growth of Japanese carbon steel pipe

    Miura, N.; Fujioka, T.; Kashima, K. [and others

    1997-04-01

    Piping for LWR power plants is required to satisfy the LBB concept for postulated (not actual) defects. With this in mind, research has so far been conducted on the fatigue crack growth under cyclic loading, and on the ductile crack growth under excessive loading. It is important, however, for the evaluation of the piping structural integrity under seismic loading condition, to understand the fracture behavior under dynamic and cyclic loading conditions, that accompanies large-scale yielding. CRIEPI together with Hitachi have started a collaborative research program on dynamic and/or cyclic fracture of Japanese carbon steel (STS410) pipes in 1991. Fundamental tensile property tests were conducted to examine the effect of strain rate on tensile properties. Cracked pipe fracture tests under some loading conditions were also performed to investigate the effect of dynamic and/or cyclic loading on fracture behavior. Based on the analytical considerations for the above tests, the method to evaluate the failure life for a cracked pipe under cyclic loading was developed and verified. Cyclic J-integral was introduced to predict cyclic crack growth up to failure. This report presents the results of tensile property tests, cracked pipe fracture tests, and failure life analysis. The proposed method was applied to the cracked pipe fracture tests. The effect of dynamic and/or cyclic loading on pipe fracture was also investigated.

  20. Effect of shot peening treatment in the behavior of residual stress in duplex stainless steel during medium cycle fatigue; Efeito do tratamento de shot peening no comportamento das tensoes residuais em aco inoxidavel duplex durante fadiga de medio ciclo

    Pedrosa, Peter D.S.; Rebello, Joao Marcos A. [Coordenacao dos Programas de Pos-Graduacao de Engenharia (PEMM/COPPE/UFRJ), Rio de Janeiro, RJ (Brazil). Programa de Engenharia Metalurgica e de Materiais; Fonseca, Maria P. Cindra, E-mail: mcindra@vm.uff.b [Universidade Federal Fluminense (PGMEC/UFF), Niteroi, RJ (Brazil). Escola de Engenharia. Programa de Pos-Graduacao em Engenharia Mecanica

    2010-07-01

    The lifetime of duplex stainless steel parts experiencing cyclic fatigue is directly influenced by the residual stresses present in the ferrite and austenite phases. The motivation for this work was to analyze the behaviour of the residual stresses fields introduced by shot peening treatment in both phases, in the sample surface as in the subsurface layers, in low fatigue cycles, using the X-rays diffraction technique. The results shows that the compressive residual stresses introduced by the shot peening treatment in both phases improved fatigue life of the material. However, the cyclical loads produce partial or total relief in these residual stresses fields. It was verified that the shot peening process induced the formation of microcracks only in the ferrite phase. The largest variations in the total compressive residual stresses fields also occurred in this phase. The samples surfaces were analyzed by scanning electron microscopy. (author)

  1. Caffeine Alters Blood Potassium and Catecholamine Concentrations but not the Perception of Pain and Fatigue with a 1 km Cycling Sprint

    Dean M. Cordingley

    2016-07-01

    Full Text Available Background: Caffeine has been used by some athletes to improve short-term high-intensity exercise performance; however, the literature is equivocal. Objectives: The objective of this study was to investigate the effects of caffeine on plasma potassium and catecholamine concentrations, pain and fatigue perception, to determine whether potassium ion handling and altered perception related to the central nervous system are associated with enhanced performance during a 1 km cycling time trial.  Methods: Thirteen well trained men with a mean age of 27 ± 6 yrs (body mass: 76.4 ± 6.4 kg, height: 180 ± 7 cm, and max: 57.5 ± 4.6 ml·kg-1·min-1 were recruited.  Participants were randomized to a caffeine (5 mg·kg-1 or a placebo condition using a double blind, cross over design.  Results: Caffeine had no significant effects on the 1 km time-trial performance indicators of time (82.1 ± 2.4 vs. 81.9 ± 3.9s, peak (633.0 ± 83.6 vs. 638.7 ± 110.1 watts or average power (466.0 ± 37.3 vs. 467.5 ± 59.9 watts; caffeine and placebo conditions respectively.  In addition, caffeine had no significant effect on oxygen consumption ( (4.11 ± 0.24 vs 4.06 ± 0.29 L,the perception of pain (5.6 ± 2.4 vs. 5.5 ± 2.6 or fatigue (7.1 ± 1.8 vs.7.1 ± 1.8: caffeine and placebo conditions respectively.  There was a significantly greater increase in post-exercise blood lactate (p<0.05 and catecholamines (p<0.05 as well as a lower pre-exercise blood potassium concentration (p<0.05 in the caffeine condition. Conclusions: The results suggest that caffeine can enhance certain metabolic parameters, but these changes were unable to augment short-distance (1km, high-intensity cycling performance.Keywords: ergogenic, anaerobic exercise, performance, oxygen consumption

  2. Influence of foreign object damage on the high cycle fatigue tolerance of gas turbine aerofoils under complex loading

    Hall, R.; Byrne, Jim; Zhao, T.; Tong, Jie

    2008-01-01

    Vibratory loading at high frequencies can lead to catastrophic failure in rotating engine components because of the very high number of HCF cycles which can be encountered in very short times, therefore it is imperative to remain below the stress conditions corresponding to the onset of crack growth due to HCF. The HCF threshold and crack growth onset conditions from simulated FOD, representative of service induced damage, as compared with sharp precracks, will be determined for a titanium al...

  3. Polarization fatigue of organic ferroelectric capacitors

    Dong Zhao; Ilias Katsouras; Mengyuan Li; Kamal Asadi; Junto Tsurumi; Gunnar Glasser; Jun Takeya; Blom, Paul W. M.; de Leeuw, Dago M.

    2014-01-01

    The polarization of the ferroelectric polymer P(VDF-TrFE) decreases upon prolonged cycling. Understanding of this fatigue behavior is of great technological importance for the implementation of P(VDF-TrFE) in random-access memories. However, the origin of fatigue is still ambiguous. Here we investigate fatigue in thin-film capacitors by systematically varying the frequency and amplitude of the driving waveform. We show that the fatigue is due to delamination of the top electrode. The origin i...

  4. Fatigue Strain and Damage Analysis of Concrete in Reinforced Concrete Beams under Constant Amplitude Fatigue Loading

    Fangping Liu

    2016-01-01

    Full Text Available Concrete fatigue strain evolution plays a very important role in the evaluation of the material properties of concrete. To study fatigue strain and fatigue damage of concrete in reinforced concrete beams under constant amplitude bending fatigue loading, constant amplitude bending fatigue experiments with reinforced concrete beams with rectangular sections were first carried out in the laboratory. Then, by analyzing the shortcomings and limitations of existing fatigue strain evolution equations, the level-S nonlinear evolution model of fatigue strain was constructed, and the physical meaning of the parameters was discussed. Finally, the evolution of fatigue strain and fatigue damage of concrete in the compression zone of the experimental beam was analyzed based on the level-S nonlinear evolution model. The results show that, initially, fatigue strain grows rapidly. In the middle stages, fatigue strain is nearly a linear change. Because the experimental data for the third stage are relatively scarce, the evolution of the strain therefore degenerated into two phases. The model has strong adaptability and high accuracy and can reflect the evolution of fatigue strain. The fatigue damage evolution expression based on fatigue strain shows that fatigue strain and fatigue damage have similar variations, and, with the same load cycles, the greater the load level, the larger the damage, in line with the general rules of damage.

  5. Fatigue and corrosion fatigue of beryllium-copper spring materials

    Fine gage, 0.006-in. d(0.15-mm) thick, beryllium-copper (Be-Cu) spring materials with tensile strength in the range of 70 to 145 ksi were subjected to cyclic loading in air and salt water environments. Plain and notched (center hole) hour glass specimens were subjected to sinusoidal loading with R = (minimum/maximum) stress = 0.1 at cyclic frequencies of 50 Hz in air and 1 Hz in salt water. Fatigue life was typically from 104 to 106 cycles with crack initiation as the dominant fatigue process. The excellence fatigue performance of Be-Cu alloys in salt water is well-known, however, current findings demonstrate 10 to 37% reduction in fatigue strength of unnotched specimens in this environment for a life of 3 x 105 cycles. This strength degradation is attributed to the use of a lower cyclic frequency for present than for previous tests, i.e., 1 versus about 20 Hz. There was no effect of salt water on crack initiation in notched specimens. The ratios of the fatigue strengths, namely (cold-rolled/annealed) and (aged/annealed), for plain and notched specimens tested in air, decreased from 2 to about 1.4 as fatigue life increased from 104 to 106 cycles. This effect is attributed to cyclic hardening of the annealed material. The fatigue stress concentration factor, Kf = (plain/notched) fatigue strength, increased by about 30% as fatigue cycles increased from 104 to 106. The ranking of Kf values of the various material conditions from highest to lowest was: cold-rolled, aged, and annealed

  6. Low cycle fatigue behaviour of neutron irradiated copper alloys at 250 and 350 deg. C. (ITER R and D Task no. T213)[International Thermonuclear Experimental Reactor

    Singh, B.N.; Stubbins, J.F. [Illinois Univ., Dept. of Nuclear Engineering, Illinois (United States); Toft, P

    2000-03-15

    The fatigue behaviour of a dispersion strengthened and a precipitation hardened copper alloys was investigated with and without irradiation exposure. Fatigue specimens of these alloys were irradiated with fission neutrons in the DR-3 reactor at Risoe with a flux of {approx}2.5 x 10{sup 17} n/m{sup 2}s (E> 1 MeV) to influence levels of 1.0 - 1.5 x 10{sup 24} n/m{sup 2} (E> 1 MeV) at 250 and 350 deg. C. These irradiations were carried out in temperature controlled rigs where the irradiation temperature was monitored and controlled continuously throughout the whole irradiation experiment. Both unirradiated and irradiated specimens were fatigue tested in vacuum at the irradiation temperatures of 250 and 350 deg. C in a strain controlled mode with a loading frequency of 0.5Hz. Post-fatigue microstructures were examined using transmission electron microscopy and the fracture surfaces were investigated using scanning electron microscope. The present investigations demonstrated that the fatigue life decreases with increasing temperature and that the exposure to neutron irradiation causes further degradation in fatigue life at both temperatures. These results are discussed in terms of the observed post-fatigue microstructures and the fracture surface morphology. Finally, the main conclusions and their implications are summarised. (au)

  7. Low cycle fatigue behaviour of neutron irradiated copper alloys at 250 and 350 deg. C. (ITER R and D Task no. T213)

    The fatigue behaviour of a dispersion strengthened and a precipitation hardened copper alloys was investigated with and without irradiation exposure. Fatigue specimens of these alloys were irradiated with fission neutrons in the DR-3 reactor at Risoe with a flux of ∼2.5 x 1017 n/m2s (E> 1 MeV) to influence levels of 1.0 - 1.5 x 1024 n/m2 (E> 1 MeV) at 250 and 350 deg. C. These irradiations were carried out in temperature controlled rigs where the irradiation temperature was monitored and controlled continuously throughout the whole irradiation experiment. Both unirradiated and irradiated specimens were fatigue tested in vacuum at the irradiation temperatures of 250 and 350 deg. C in a strain controlled mode with a loading frequency of 0.5Hz. Post-fatigue microstructures were examined using transmission electron microscopy and the fracture surfaces were investigated using scanning electron microscope. The present investigations demonstrated that the fatigue life decreases with increasing temperature and that the exposure to neutron irradiation causes further degradation in fatigue life at both temperatures. These results are discussed in terms of the observed post-fatigue microstructures and the fracture surface morphology. Finally, the main conclusions and their implications are summarised. (au)

  8. Thermal fatigue of beryllium

    Deksnis, E.; Ciric, D.; Falter, H. [JET Joint undertaking, Abingdon (United Kingdom)] [and others

    1995-09-01

    Thermal fatigue life of S65c beryllium castellated to a geometry 6 x 6 x (8-10)mm deep has been tested for steady heat fluxes of 3 MW/m{sup 2} to 5 MW/m{sup 2} and under pulsed heat fluxes (10-20 MW/m{sup 2}) for which the time averaged heat flux is 5 MW/m{sup 2}. These tests were carried out in the JET neutral beam test facility A test sequence with peak surface temperatures {le} 600{degrees}C produced no visible fatigue cracks. In the second series of tests, with T{sub max} {le} 750{degrees}C evidence for fatigue appeared after a minimum of 1350 stress cycles. These fatigue data are discussed in view of the observed lack of thermal fatigue in JET plasma operations with beryllium PFC. JET experience with S65b and S65c is reviewed; recent operations with {Phi} = 25 MW/m{sup 2} and sustained melting/resolidification are also presented. The need for a failure criterion for finite element analyses of Be PFC lifetimes is discussed.

  9. Determination of the fatigue life of the AD33-V composite under conditions of low-cycle loading in pure bending

    Utkin, V.S.; Salibekov, S.E.; Chubarov, V.M.

    1986-06-01

    Specimens of AD33-V, an aluminum/boron composite, were tested in cyclic bending to determine the dependence of accumulated damage and fatigue life on the stress amplitude under conditions of pure bending. It is shown that the fatigue life of the composite is proportional to its ultimate strength. Conditional endurance limits are determined as a function of the permissible amount of accumulated damage.

  10. 海洋隔水管对接环焊缝接头高周疲劳性能研究%Research on High Cycle Fatigue Property for Butt Circumferential Weld of Marine Riser

    余钊辉; 党恩; 朱安达; 杨龙; 张建勋

    2013-01-01

    The four-point bend fatigue test method was used to measure the high cycle fatigue property of marine riser X80/X80J butt circumferential weld. The influence on crack initiation location of stress concentration,microstructure and hardness was analyzed comprehensively. The results showed that the fatigue crack of welded joint with weld reinforcement initiates from toes, and then extends to the heat affected zone from the weld reinforcement,while the crack initiates from weld and propagates along the weld without reinforcement. The stress concentration caused by the weld reinforcement is the main factor to reduce the welded joint fatigue performance. The fatigue limit of welded joint is 216 MPa for with reinforcement and 400 MPa for without the weld reinforcement.%采用四点弯曲疲劳试验法,测试了海洋隔水管道X80/X80J对接环焊缝高周疲劳性能。综合分析了应力集中、显微组织和硬度对裂纹萌生位置的影响。结果表明,有余高焊接接头疲劳裂纹在焊趾处萌生并向热影响区扩展,去除余高的焊接接头疲劳裂纹从焊缝处萌生并沿焊缝扩展;焊缝余高引起的应力集中是降低焊接接头疲劳性能的主要因素,有余高焊接接头的疲劳极限为216 MPa,去除余高的焊接接头疲劳极限为400 MPa。

  11. Fatigue processes in thermoplastic fibres; Les mecanismes de fatigue dans les fibres thermoplastiques

    Herrera Ramirez, J.M.

    2004-09-15

    The present study examines and compares the behaviour of the two types of PA66 fibres and two types of PET fibres under fatigue loading up to failure, and the correlation between the fibres (nano)structures and their structural heterogeneities, with fatigue lifetimes. Several techniques have been used to analyze the materials, such as scanning electron microscopy (SEM), microanalysis (EDS), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and micro-Raman spectroscopy. A meticulous analysis by scanning electron microscopy of the fracture morphology of fibres broken in tension and in fatigue, as well as a study of the fatigue life, were undertaken. The fatigue process occurs when the cyclic load amplitude is sufficiently large, however a condition for fatigue failure is that the minimum load each cycle must be lower than a threshold stress level. Failure under fatigue conditions leads to distinctive fracture morphologies which are very different from those seen after tensile or creep failure and this allows easy identification of the fatigue process. The fibres have been analyzed in the as received state and after fatigue failure in order to observe the microstructural changes resulting from the fatigue loading. The results will be compared with those obtained for fibres loaded under conditions where the fatigue process was hindered. The role of the microstructure of the fibres in determining fatigue will be discussed in this work and the possibility of improving their resistance to fatigue or eliminating the fatigue process will be discussed. (author)

  12. Multiscale Fatigue Life Prediction for Composite Panels

    Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.

    2012-01-01

    Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.

  13. The effect of seismic loading on the fatigue strength of welded joints

    Earthquakes sometimes damage steel structures. Structures which are not seriously damaged are still used after earthquakes but their fatigue strength may have been reduced by the large cyclic loadings imposed by the earthquakes. In order to clarify the effect of seismic loading on the fatigue strength of welded joints, high cycle fatigue and variable amplitude fatigue tests after a number of large initial strain cycles were performed. The large strain cycles formed a short crack at the toe of the weld in a low cycle fatigue that triggered a high cycle fatigue strength reduction. The high cycle fatigue limit of welded joints after initial strain cycles is governed by the threshold stress intensity factor of the short crack. The formation of short cracks also enhanced the damage accumulation for subsequent variable amplitude loading. It is important to keep all of the stress variations after earthquake below the fatigue limit of the cracked welded joints to avoid fatigue damage accumulation after an earthquake

  14. The effect of seismic loading on the fatigue strength of welded joints

    Kondo, Y. [Department of Intelligent Machinery and Systems, Kyushu University, Fukuoka 819-0395 (Japan)], E-mail: ykondo@mech.kyushu-u.ac.jp; Okuya, K. [Department of Residential and Architectural System Engineering, Kyushu Polytechnic College, Fukuoka 802-0985 (Japan)

    2007-11-15

    Earthquakes sometimes damage steel structures. Structures which are not seriously damaged are still used after earthquakes but their fatigue strength may have been reduced by the large cyclic loadings imposed by the earthquakes. In order to clarify the effect of seismic loading on the fatigue strength of welded joints, high cycle fatigue and variable amplitude fatigue tests after a number of large initial strain cycles were performed. The large strain cycles formed a short crack at the toe of the weld in a low cycle fatigue that triggered a high cycle fatigue strength reduction. The high cycle fatigue limit of welded joints after initial strain cycles is governed by the threshold stress intensity factor of the short crack. The formation of short cracks also enhanced the damage accumulation for subsequent variable amplitude loading. It is important to keep all of the stress variations after earthquake below the fatigue limit of the cracked welded joints to avoid fatigue damage accumulation after an earthquake.

  15. Chronic Fatigue Syndrome

    Chronic fatigue syndrome (CFS) is a disorder that causes extreme fatigue. This fatigue is not the kind of tired feeling that ... activities. The main symptom of CFS is severe fatigue that lasts for 6 months or more. You ...

  16. Improved Generalized Strain Energy Damage Function Method for High Temperature Low Cycle Fatigue-creep%高温低周疲劳-蠕变的改进型广义应变能损伤函数方法

    朱顺鹏; 黄洪钟; 何俐萍; 侯敏杰; 周乐旺

    2011-01-01

    通过对广义应变能损伤函数(GSEDF)法进行分析,用非弹性应变能表征低周疲劳(LCF)损伤,提出了一种高温低周疲劳-蠕变(LCF-C)寿命预测的改进型GSEDF模型,修正了GSEDF法中的能量参数,使其与工程实际更吻合.所提出的模型具有模型参数少、适用性广和试验数据利用率高等优点,且能综合反映加载方式、保载时间和平均应力的影响.最后,应用该模型对文献试验数据和轮盘用GH4133高温合金在不同温度和应变比(应力比)下的疲劳-蠕变寿命进行了预测,预测结果与实测结果吻合较好,精度明显优于GSEDF模型、SWT模型、应变能频率修正法和塑性应变能密度法.%The generalized strain energy damage function (GSEDF) model for low cycle fatigue-creep (LCF-C) is investigated, and by using the inelastic strain energy as an LCF damage parameter, an improved GSEDF model is proposed for high temperature low cycle fatigue-creep life prediction of high temperature components, which modifies the energy parameter in GSEDF model and is more consistent with the actual engineering than the GSEDF model. The proposed model has the advantage of less parameters in the expression of this model, wide application and higher utilization efficiency of experimental data. Furthermore, this model not only considers the mechanism of loading waveform and hold time, but also the mean stress effects on LCF life. The predicted fatigue lives based on the proposed model are found in good agreement with reported experimental results of aircraft turbine disk alloys GH4133 at different temperatures and strain (stress) ratios. Compared with the GSEDF model, the SWT model, the plastic strain energy density method and the strain energy frequency modified approach, the proposed model is widely applicable and more precise in predicting the life of low cycle fatigue-creep interaction.

  17. Thermal fatigue of pipes induced by fluid temperature change. Effect of multiaxial pre-loading on fatigue strength

    This study investigates an effect of pre-inelastic multiaxial loading on failure lives in a followed high cycle fatigue test for SUS316 steel. In the multiaxial low cycle fatigue test for the pre-loading, two types of strain paths were employed which are a push-pull straining and a circle straining. The circle straining is the non-proportional loading in which axial strain ε and shear strain γ has 90 degree phase difference. Using the specimen fatigued in the pre-loading test, high cycle fatigue test was conducted by a rotating bending fatigue testing machine. Based on the obtained results, property of fatigue life in high cycle fatigue which received pre-loading under non-proportional loading is discussed. (author)

  18. Investigation of High Cycle Fatigue Life of MW Grade Wind Turbine Ductile Iron Hub%兆瓦级风电轮毂球铁高周疲劳寿命研究

    刘佳; 曲迎东; 李荣德; 马广辉; 白彦华; 姜珂; 邱克强; 尤俊华; 王瑞春

    2012-01-01

    为了获得MW级风机轮毂QT350-22LT的高周疲劳寿命.通过拉-拉高周疲劳试验获得其疲劳极限,并通过数值模拟的方法确定QT350-22LT是否能够作为轮毂材料.疲劳试验在PW3-10程序控制高频万能疲劳试验机进行,采用实际生产的附铸试块进行拉-拉高周疲劳试验.试验结果表明:获得的兆瓦级风电轮毂QT350-22LT的疲劳极限值为250MPa,根据数据绘制的S-N曲线的拐点在290MPa;疲劳源的位置不同,所产生的瞬断区断口形貌也有所差别.对轮毂本身所能承受的最大应力进行有限元分析,得到最大应力为156MPa.应力集中部位的值没有超过材料的疲劳极限,这证明球铁QT350-22LT能够满足风机轮毂设计的应力要求.%The main purpose of this paper is to obtain high cycle fatigue life of MW grade the wheel hub (QT350-22 LT). Through the pull-pull high cycle fatigue tests, the fatigue limit is determined. The numerical simulation method was used to determine whether QT3 50-22 LT is able to be the hub material or not. The fatigue test equipment and materials are PW3-10 program control high frequency universal fatigue test machine and the practical production casting blocks, respectively. The results show that fatigue limit of the MW grade wind turbine hub QT350-22 LT is 250 MPa and inflection point of S-N curve draw according to data is 290 MPa; the morphologies of the transient breaking fracture are different due to the different crack sources. The maximum tensile stress of the hub is 156 MPa, which is obtained by the finite element analysis. The value of tensile stress concentration position is no more than the fatigue limit of the material, which proves that the ductile iron hub (QT350-22 LT) can satisfy the design requirement of stress.

  19. Microstructure degradation in high temperature fatigue of TiAl

    Kruml, Tomáš; Obrtlík, Karel

    2014-01-01

    Roč. 65, AUG (2014), s. 28-32. ISSN 0142-1123 R&D Projects: GA ČR(CZ) GAP107/11/0704 Institutional support: RVO:68081723 Keywords : Low cycle fatigue * lamellar TiAl alloy * high temperature fatigue * dislocations Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.275, year: 2014

  20. Use of Strain-life Models with Wavelet Bump Extraction (WBE) fro Prediction Fatigue Damage

    Yates, John R.; Choi Jae-Chil; Shahrum Abdullah; Joseph A. Giacomin

    2008-01-01

    This paper presents the use of strain-life fatigue damage models to observe the cycle sequence effects in the wavelet-based fatigue data editing algorithm. This algorithm is called Wavelet Bump Extraction (WBE), which was developed to produce a shortened signal by extracting fatigue damaging events from the original signal with the retention of the original cycle sequences. Current industrial practice uses the Plamgren-Miner linear damage rule to predict the fatigue life or fatigue damage und...

  1. Fatigue behaviour and energy dissipation of a nodular cast iron in ultrasonic fatigue loading

    H.Q. Xue

    2006-08-01

    Full Text Available Purpose: In the current research, fatigue tests of cast iron (GS51 have been conducted using the ultrasonicfatigue system and monitored by an advanced infrared imaging system in real time. Fatigue damage processeshas been observed and analyzed. Furthermore, heat condition effect has been to analyze.Design/methodology/approach: Fatigue behaviour in the very high cycle regime of 1010 cycles wereinvestigated with a cast iron (GS51 under ultrasonic fatigue test system in ambient air at room temperaturewith a stress ratio R=-1. The influence of frequency was examined by comparing similar data generated onconventional servo hydraulic test systems. An infrared camera was also used to record specimen temperaturesat various load levels caused by internal damping due to cycling at a very high frequency.Findings: The S-N curves obtained show that fatigue failure occurred beyond 109 cycles, fatigue limit does notexist for the cast iron and there is no evidence of frequency effect on the test results. A detailed study on fatiguespecimens subjected to ultrasonic frequency shows that the temperature evolution of the cast iron specimen isvery evident, the temperature increased just at the beginning of the test, the temperature increased depending onthe maximum stress amplitude.Research limitations/implications: Ultrasonic fatigue test methodology had been applied extensively inexploring fatigue lives at very high cycle regime. However, it is a predominant problem that the thermal energydissipation results in increasing of temperature of specimen at very high frequency fatigue experiment. In orderto investigate the heat dissipation of ultrasonic fatigue specimen and understand the influence of temperatureevolution on the fatigue properties, it is necessary to obtain the temperature response of vibratory specimen.Originality/value: Early stage of damage of the cast iron which lead to crack initiation and micro crack growthare characterized by local microstructure

  2. Research on Low Cycle Fatigue Reliability-based Robust Design Optimization of Turbine Blade%涡轮叶片低周疲劳可靠性稳健设计优化研究

    彭茂林; 杨自春; 曹跃云; 初珠立

    2013-01-01

    To solve the problem of low cycle fatigue reliability-based robust design optimization of turbine blade, a series of fatigue tests of the blade material under high temperature were completed. According to the tests data, the randomized approach of deterministic equation was introduced to obtain the probabilistic strain-life curves of the blade material. The Bezier curve was employed to establish the blade model line and the parameter models of the turbine blade and flow field. After, the thermal-aero-structure coupling finite element method was used to obtain the aerodynamic efficiency, stress and strain distribution of the blade. Then, the fatigue reliability-based robust design optimization model was established and the response surface method was used to simulate the output performance functions and the limit state functions of the blade. Finally, the design optimization result was calculated with the sequential quadratic programming method by taking the fatigue reliability as the basic constrain condition. The results prove that: the low cycle fatigue reliability and robustness of the blade are improved remarkably after design optimization; the model and the methods are correct and can be served as references for the low cycle fatigue reliability-based robust design optimization of turbine blade and other complex structures.%针对涡轮叶片低周疲劳可靠性稳健设计优化问题,对叶片材料进行了高温疲劳试验,采用定量方程随机化方法处理试验数据,获得叶片材料的概率-应变-寿命曲线.采用贝塞尔曲线描述叶片型线方程,建立了涡轮叶片结构及流场的参数化模型,采用热-流-固耦合有限元法对涡轮流场和叶片进行了数值分析,得到叶片动能效率和应力应变分布特性.建立了叶片疲劳可靠性稳健设计优化模型,并采用响应面法获得叶片结构性能函数和极限状态函数,将叶片低周疲劳可靠性作为基本约束条件,采用序列二次规

  3. High-temperature fatigue life prediction of turbopump turbine

    In general, many components are able to be operated under severe thermal conditions. The turbopump turbine is operated under these environments like high temperature and high centrifugal force due to high rotating velocity during operating time. Because these conditions may often cause low-cycle fatigue problem, strain life method is applied to predict low-cycle fatigue life of turbopump turbine. In this paper, strain life method is used to analyze low-cycle fatigue. First of all, to obtain strain history, thermal stress analysis is practised by ABAQUS/CAE. Considering elasticity and plasticity strain's effect, Coffin-Manson' equation is used. S.W.T's method is used to consider the mean stress effect. Low-cycle fatigue analysis is done for turbopump turbine which may have FCL(Fracture Critical Location). MSC.Fatigue is used to analyze low-cycle fatigue life of turbopump turbine.

  4. Seafarer fatigue

    Jepsen, Jørgen Riis; Zhao, Zhiwei; van Leeuwen, Wessel M. A.

    2015-01-01

    Background: The consequences of fatigue for the health and safety of seafarers has caused concern in the industry and among academics, and indicates the importance of further research into risk factors and preventive interventions at sea. This review gives an overview of the key issues relating to...

  5. Random accumulated damage evaluation under multiaxial fatigue loading conditions

    V. Anes

    2015-07-01

    Full Text Available Multiaxial fatigue is a very important physical phenomenon to take into account in several mechanical components; its study is of utmost importance to avoid unexpected failure of equipment, vehicles or structures. Among several fatigue characterization tools, a correct definition of a damage parameter and a load cycle counting method under multiaxial loading conditions show to be crucial to estimate multiaxial fatigue life. In this paper, the SSF equivalent stress and the virtual cycle counting method are presented and discussed, regarding their physical foundations and their capability to characterize multiaxial fatigue damage under complex loading blocks. Moreover, it is presented their applicability to evaluate random fatigue damage.

  6. ISOTHERMAL AND THERMOMECHANICAL FATIGUE OF A NICKEL-BASE SUPERALLOY

    Carlos Carvalho Engler-Pinto Júnior; Dirceu Spinelli

    2014-01-01

    Thermal gradients arising during transient regimes of start-up and shutdown operations produce a complex thermal and mechanical fatigue loading which limits the life of turbine blades and other engine components operating at high temperatures. More accurate and reliable assessment under non-isothermal fatigue becomes therefore mandatory. This paper investigates the nickel base superalloy CM 247LC-DS under isothermal low cycle fatigue (LCF) and thermomechanical fatigue (TMF). Test ...

  7. Interconnect fatigue design for terrestrial photovoltaic modules

    Mon, G. R.; Moore, D. M.; Ross, R. G., Jr.

    1982-03-01

    The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable (1) the prediction of cumulative interconnect failures during the design life of an array field, and (2) the unambiguous--ie., quantitative--interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field.

  8. Fatigue of High Purity Copper Wire

    Tanabe, N.; Kurosaka, A.; Suzuki, K.; Kohno, O.

    1995-01-01

    The fatigue properties of 7N, OFC and Tough-Pitch copper wires were evaluated by a rotational bending method. 7N copper wires, having RRR300K/4.2K of 7600, were produced by electro-refining, vacuum melting, zonerefining followed by suitable drawing processes, using 4N class commercial OFC plates as the starting material. The fatigue failure cycles of 7N copper increased with an increased pause period imposed during the fatigue test after 5x106 cycles. Remarkable recrystallizations initiated f...

  9. An overview of fatigue

    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)

  10. Breast Cancer and Fatigue

    Bardwell, Wayne A; Ancoli-Israel, Sonia

    2008-01-01

    Fatigue is a common and disabling symptom in breast cancer patients and survivors. A rather nebulous concept, fatigue overlaps with sleepiness and depressed mood. In this chapter, we cover methods for assessing fatigue; describe the occurrence of fatigue before, during and after initial treatment; present possible underlying mechanisms of fatigue; and, enumerate approaches to its treatment.

  11. Effect of sleep quality on day cycle fatigue in ward nurses%病房护士的睡眠质量对日周性作业疲劳的影响

    杨颖; 赵锐祎; 兰美娟; 阮春燕

    2008-01-01

    Objective To explore the effect of sleep quality on day cycle work fatigue inward nurses. Methods Through a cluster sampling of three hospitals, 479 clinical frontline nurses (Those in pregnancy or in sick leave were excluded) were investigated in Hangzhou, Zhejiang, China. Pittsburgh Sleep Quality Index (PSQI) was used to evaluate sleep quality; Self-reported work-related fatigue symptom scale was used to evaluate day cycle fatigue status; The common information was also collected. Results The sleep quality of ward nurses was generally poor, with total PSQI score of 7.31±3.45. 41.75% of ward nurses (200 nurses) had total PSQI score over 7. The total PSQI score showed a negative linear correlation with educational background (r=-0.11, P=0.01). The educational background also represented a negative correlation with sleep quality, sleep latency and sleep duration; There were no correlation between sleep and marriage, length of service, professional title and duty. Work-related fatigue was closely correlated with sleep quality: (1) Total PSQI score showed a positive correlation with four daytime points fatigue in the next day (r=0.42,r=0.34,r=0.25,r=0.33,P<0.01). (2) Total PSQI score was also related to five fatigue factors in four daytime points. (3) There was significant correlation between seven factors of sleep and fatigue levels of four time points. (4) Multiple regression analysis showed that sleep quality, day function; sleep disturbance and drug use played important roles in work fatigue. (5)There was no correlation between sleep quality and delayed off-work (r=0.06, P=0.17). Conclusion Managers should think highly of sleep quality of ward nurses, acknowledge its degree of work fatigue and apply evidence based methods to arrange work responsibility and follow sheet, then rationalize human resources management, emphasize sleep hygiene education, improve sleep quality and reduce work fatigue.%目的 探讨病房护士的睡眠质量对日周

  12. Experimental Study on High-Cycle Fatigue Property of Elastic Support with Multiple Squirrel-Cages%串联式鼠笼弹性支承高周疲劳性能试验

    粟勇; 杨正兵; 李光辉; 王继成

    2014-01-01

    To evaluate the high cycle fatigue performance of elastic support, a set of test specimen and ex-periment method have been designed based on the structure of elastic support system with multiple squirrel cages on an aero-engine. The testing results show that simulated rotor can better simulate the true stress with elastic support. The load adjustment and control during the test are more direct and convenient which provide support for fatigue life design of elastic support.%为评估弹性支承高周疲劳性能,根据某航空发动机串联式鼠笼弹性支承系统结构,设计了一套弹性支座疲劳试验件和试验参数测试方法,对弹性支座的高周疲劳性能进行试验研究。经试验验证,所设计的试验方案可以更好地模拟发动机工作状态下弹性支座的受力状态,试验过程中的载荷调节和控制更直接、便捷,为发动机弹性支承的疲劳寿命设计提供了方法支持。

  13. LIFE PREDICTION APPROACH FOR RANDOM MULTIAXIAL FATIGUE

    Wang Lei; Wang Dejun

    2005-01-01

    According to the concept of critical plane, a life prediction approach for random multiaxial fatigue is presented. First, the critical plane under the multiaxial random loading is determined based on the concept of the weight-averaged maximum shear strain direction. Then the shear and normal strain histories on the determined critical plane are calculated and taken as the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, a multiaxial fatigue life prediction model including the parameters resulted from multiaxial cycle counting is presented and applied to calculating the fatigue damage generated from each cycle. Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue prediction life is given. The experiments under multiaxial loading blocks are used for the verification of the proposed method. The prediction has a good correction with the experimental results.

  14. Brain Tumors and Fatigue

    ... for e-updates Please leave this field empty Fatigue SHARE Home > Treatment and Care > Side Effects and ... One of the most common side effects is fatigue. Fatigue may accompany surgery, radiation, chemotherapy or biologic ...

  15. Fatigue and Multiple Sclerosis

    Fatigue - National Multiple Sclerosis Society Skip to navigation Skip to content Menu Navigation National Multiple Sclerosis Society ... Twitter Email Home Symptoms & Diagnosis MS Symptoms Fatigue Fatigue Share Smaller Text Larger Text Print In this ...

  16. 基于有限差分法的汽轮机转子低周疲劳计算%Calculation for low cycle fatigue of steam turbine rotor based on finite difference method

    贺斌; 杨继明; 何健; 沈立业

    2012-01-01

    根据火电机组运行的实际数据,介绍了有限差分法计算汽轮机转子低周疲劳损耗的原理.结合模拟机组冷态启动和停机过程,采用该方法计算了转子上两个特征点的温度变化曲线和应力变化曲线,再根据Miner线性累积法则得到了转子的低周疲劳寿命损耗.通过计算发现,该方法具有计算精度高、计算速度快和实时性强等优点,能够很好地满足工程实际问题的需要.%Based on real operation data of the thermal power units,the principle that calculation for low cycle fatigue of steam turbine rotor based on finite difference method is introduced.Combination of the analog unit cold start and shutdown process,calculation for the temperature curve and the stress curve of the two feature points on the rotor with this method,and according to Miner's rule has been got the result of low cycle fatigue of steam turbine rotor.The method has high accuracy,the process of calculation is short,and it has a good real-time by calculation.So it can meet the needs of practical engineering problems well.

  17. Method and data analysis example of fatigue tests

    In the design and operation of a nuclear fusion reactor, it is important to accurately assess the fatigue life. Fatigue life is evaluated by preparing a database on the relationship between the added stress / strain amplitude and the number of cycles to failure based on the fatigue tests on standard specimens, and by comparing this relationship with the generated stress / strain of the actual constructions. This paper mainly chooses low-cycle fatigue as an object, and explains standard test methods, fatigue limit, life prediction formula and the like. Using reduced-activation ferrite steel F82H as a material, strain controlled low-cycle fatigue test was performed under room temperature atmosphere. From these results, the relationship between strain and the number of cycles to failure was analyzed. It was found that the relationship is asymptotic to the formula of Coffin-Manson Law under high-strain (low-cycle condition), and asymptotic to the formula of Basquin Law under low-strain (high-cycle condition). For F82H to be used for the blanket of a nuclear fusion prototype reactor, the arrangement of fatigue life data up to about 700°C and the establishment of optimal fatigue design curves are urgent tasks. As for fusion reactor structural materials, the evaluation of neutron irradiation effect on fatigue damage behavior and life is indispensable. For this purpose, it is necessary to establish standardized testing techniques when applied to small specimens. (A.O.)

  18. MANAGING FATIGUE IN SPORTS

    2006-01-01

    @@ Fatigue is a multifactorial process. Depletion of energy sources, including adenosine triphosphate (ATP), phosphocreatine (PCr), plus carbohydrates (CHO) like muscle glycogen and blood glucose can contribute to fatigue.

  19. Reserch on low cycle fatigue behavior of powder metallurgy superalloy FGH96%镍基粉末高温合金FGH96应变疲劳行为

    周磊; 王泓; 张国栋; 苏彬

    2009-01-01

    Low cycle fatigue (LCF) properties of Powder Metallurgy (PM) superalloy FGH96 at 750℃ were studied in this paper. After testing and analyzing the data, parameters of median and probability were given. Then the data is processed by Man-son-Coffin method and Zheng Xiulin (s method. The results show that FGH96 superalloy exhibits cyclic stress response of cyclic softing at 750℃, and of initial softing followed by hardening at △ε=0. 6%. Low cycle fatigue life prediction shows that the of Zheng method has a better life prediction capability in approving the existence of the endurance fatigue limit in theory than those of Manson-Coffiin's. Conclusions can be applied analytically in estimating the life of superalloy FGH96 and providing the basis of the aircraft engine's powder turbine disk design selection and mechanical properties under high temperature.%对镍基粉末高温合金FGH96在750℃、应变比R=0.05下的应变疲劳循环应力响应曲线、循环应力-应变曲线和应变-寿命曲线进行分析,通过非线性回归拟合,得到基于Manson-Goffin公式及郑公式两种处理模型的应变一寿命曲线及相关参数.结果表明,FGH96合金在实验加载条件下,出现了循环软化一稳定一再软化断裂的应力响应特性,并随着加载应变幅的提高而愈加明显.与Manson-Coffin公式相比,郑公式在宏观预测应变疲劳寿命,尤其是确定材料疲劳极限问题上取得很好的预测效果.

  20. Fatigue Properties of Cast Magnesium Wheels

    Li, Zhenming; Luo, Alan A.; Wang, Qigui; Peng, Liming; Zhang, Peng

    2016-05-01

    This paper investigates the fatigue properties and deformation behavior of a newly developed Mg-2.96Nd-0.21Zn-0.39Zr magnesium alloy wheel in both as-cast and T6 conditions. Compared with the as-cast alloy, the T6-treated alloy shows a significant increase in fatigue strength and cyclic stress amplitude. This is believed to be attributed to the change of defect type from porosity to oxides and the increased matrix strength in the T6 (peak-aged) condition. For the as-cast alloy wheel, fatigue failure mainly originated from the cast defects including porosity, oxide film, and inclusion at or near the sample surface. In the T6-treated alloy, however, oxides and inclusions or slip bands initiate the fatigue cracks. Solution treatment appears to reduce or eliminate the shrinkage porosity because of grain growth and dissolution of as-cast eutectic phases in the grain boundaries. The cyclic stress amplitude of the as-cast alloy increases with increasing the number of cycles, while the T6-treated alloy shows cyclic softening after the stress reaches a maximum value. The Coffin-Manson law and Basquin equation can be used to evaluate the life of low cycle fatigue. The developed long crack model and multi-scale fatigue (MSF) models can be used to predict high-cycle fatigue life of the Mg-2.96Nd-0.21Zn-0.39Zr alloys with or without casting defects.

  1. A three dimensional discrete dislocation dynamics modelling of the early cycles of fatigue in an austenitic stainless steel 316L: dislocation microstructure and damage analysis; Modelisation physique des stades precurseurs de l'endommagement en fatigue dans l'acier inoxydable austenitique 316L

    Depres, Ch

    2005-07-01

    A numerical code modelling the collective behaviour of dislocations at a mesoscopic scale (Discrete Dislocation Dynamics code) is used to analyse the cyclic plasticity that occurs in surface grains of an AISI 316L stainless steel, in order to understand the plastic mechanism involved in crack initiation in fatigue. Firstly, the analyses of both the formation and the evolution of the dislocation microstructures show the crucial role of cross-slip played in the strain localization in the form of slip bands. As the cycling proceeds, the slip bands exhibit well-organized dislocation arrangements that substitute to dislocation tangles, involving specific interaction mechanisms between primary and deviate systems. Secondly, both the surface displacements generated by plastic slip and the distortion energy induced by the dislocation microstructure have been analysed. We find that an irreversible surface relief in the form of extrusion/intrusion can be induced by cyclic slip of dislocations. The number of cycles for the crack initiation follows a Manson-Coffin type law. The analyses of the concentration of the distortion energy and its repartition in the slip bands show that beneficial energetic zones may be present at the very beginning of the cycling, and that mode-II crack propagation in the surface grains results from a succession of micro-crack initiations along primary slip plane, which is facilitated by various effects (stress concentration due to surface relief, environment effects...). Finally, a dislocation-based model for cyclic plasticity is proposed from Discrete Dislocation Dynamics results. (author)

  2. Corrosion fatigue of high strength fastener materials in seawater

    Tipton, D. G.

    1983-01-01

    Environmental effects which significantly reduce the fatigue life of metals are discussed. Corrosion fatigue is a major concern in the engineering application of high strength fasteners in marine environments. The corrosion fatigue failure of an AISI 41L4O high strength steel blade to hub attachment bolt at the MOD-OA 200 kW wind turbine generator was investigated. The reduction of fatigue strength of AISI 41L4O in marine environments and to obtain similar corrosion fatigue data for candidate replacement materials was studied. The AISI 4140, PH 13-8Mo stainless steel, alloy 718 and alloy MP-35N were tested in axial fatigue at a frequency of 20 Hz in dry air and natural seawater. The fatigue data are fitted by regression equations to allow determination of fatigue strength for a given number of cycles to failure.

  3. A preliminary bending fatigue spectrum for steel monostrand cables

    Winkler, Jan; Fischer, Gregor; Georgakis, Christos T.; Kotas, Agnieszka

    2011-01-01

    This paper presents the results of the experimental study on the bending fatigue resistance of high-strength steel monostrand cables. From the conducted fatigue tests in the high-stress, low-cycle region, a preliminary bending fatigue spectrum is derived for the estimation of monostrand cable...... service life expectancy. The presented preliminary bending fatigue spectrum of high-strength monostrands is currently unavailable in the published literature. The presented results provide relevant information on the bending mechanism and fatigue characteristics of monostrand steel cables in tension and...

  4. Influence of laser treatment on the fatigue of notched bar

    ZhangHui; LingWeiye; JiangShouwei

    2003-01-01

    Fatigue cutting is a new approach for separating material. Man-made fatigue can be realized by applying a rotating bending load to a notched bar. To better utilize the new method, laser treatment is adopted in this study. After laser radiation at the notch root, the fatigue cycle of the bar drops dramatically. Based on the experimental result, we draw the conclusion that the fatigue of the bar is influenced by the shape of the hardened area. A hardened area that has a small axial dimension and a relatively large radial dimension facilitates the fatigue. The desirable hardened area can be obtained by controlling the laser treatment parameters.

  5. Fatigue in tension perpendicular to the grain

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben;

    1999-01-01

    Traditinally fatigue resistance is quantified as number of cycles to failure at a given stress level. A previous study by the authors showed that fatigue in compression parallel to the grain is governed partly by duration of load and partly by an effect of loading, i.e. a combination of a creep...... mechanism and a mechanism connected to damage introduce in the loading sequences. The purpose of the present study is to disentangle the effect of duration of load from the effect of load oscillation in fatigue in tension perpendicular to the grain. Fatigue experiments are made on small specimens and on...... made on dowel type connections that have tension perpendicular to the grain as limiting strength parameter. Is is concluded that no significant influence of duration of load is observed when the fatigue resistance of small specimens at 0.01 Hz and 0.1 Hz are compared. A weak but inconclusive time...

  6. Fatigue In Tension Perpendicular to the Grain

    Clorius, Christian Odin; Pedersen, Martin Uhre; Hoffmeyer, Preben;

    2004-01-01

    Traditionally fatigue resistance is quantified as number of cycles to failure at a given stress level. A previous study by the authors showed that fatigue in compression parallel to the grain is governed partly by duration of load and partly by an effect of loading, i.e. a combination of a creep...... mechanism and a mechanism connected to damage introduced in the loading sequences. The purpose of the present study is to disentangle the effect of duration of load from the effect of load oscillation in fatigue in tension perpendicular to the grain. Fatigue experiments are made on small specimens and on...... made on dowel type connections that have tension perpendicular to the grain as limiting strength parameter. It is concluded that no significant influence of duration of load is observed w hen the fatigue resistance of small specimens at 0.01 Hz and 0.1 Hz are compared. A weak but inconclusive time...

  7. High speed rails. Fatigue behaviour

    In recent years, passenger train speed and freight train load have increased to enhance efficiency of rail road transportation. These trends have increased the severity of rail service conditions, calling for rails with greater wear resistance, strength and fatigue behaviour. In the United Stated and Europe, track site weld rails are made entirely by aluminothermic process. This work describes the results of experimental study conducted on bending fatigue strength of plain rails and aluminothermic welded rails with preheating procedures (oxipropane and air-induced propane) approved by railways authorities. Compliance with the required fatigue strength shall be ascertained by 4 point pulsating bending test in accordance with European standards by aluminothermic welding in rails. The locati method, based in the empirical Miner's law about the cumulative damage on a fatigue tested material, allows, once known the Wohler curve of the welding process in use to settle the fatigue tensile limit at 50% with only one test. The values obtained at 2.10''6 cycles for plain rails (Sf=353 MPa), oxipropane preheated aluminothermic weld rails (Sf=225 MPa), and propane-air induced aluminothermic weld rails (Sf=210 MPa) are very similar to those resulting from test method stated in the European Standard. From our point of view and due to its ease, speediness and savings, this is the most suitable test to check the quality and compare the aluminothermic processes in use. (Author) 15 refs

  8. Keep fatigue usage low for LTO. Benefits of load monitoring and related fatigue evaluations for long term operation

    Design fatigue calculations normally cover a service life of 40 years. Based on design transients with a specified number of cycles the evaluations have to prove that the fatigue usage after 40 years will stay below 1. In 40+ years of operation real loads can differ much from design loads so that premature ageing can occur. For long term operation, monitoring of real loads and detailed fatigue analysis for selected locations can be used to optimize operational modes in order to reduce the loads causing fatigue. As a result fatigue usage can be kept below 1 even for 60+ years. (author)

  9. [Fatigue in neuromuscular disease

    Engelen, B.G.M. van; Kalkman, J.S.; Schillings, M.L.; Werf, S.P. van der; Bleijenberg, G.; Zwarts, M.J.

    2004-01-01

    Chronic fatigue is a symptom of diseases such as cancer, multiple sclerosis, Parkinson's and cerebrovascular disease. Fatigue can also be present in people with no demonstrable somatic disease. If certain criteria are met, chronic-fatigue syndrome may be diagnosed in these cases. Fatigue is a multi-

  10. AI-Si-Cu-Mg(-Er)铸造铝合金的低周疲劳行为%Low-Cycle Fatigue Behavior of Cast AI-Si-Cu-Mg(-Er) Aluminum Alloy

    车欣; 徐志军; 陈立佳; 徐海健; 李锋

    2011-01-01

    对金属型铸造Al-Si-Cu-Mg和Al-Si-Cu-Mg-Er铝合金进行了疲劳试验,并研究了其室温下的低周疲劳行为.试验结果表明:金属型铸造Al-Si-Cu-Mg和Al-Si-Cu-Mg-Er铝合金表现为循环应变硬化和循环稳定,主要取决于外加总应变的高低;稀土元素Er的加入可提高金属型铸造Al-Si-Cu-Mg合金的循环变形抗力和疲劳寿命;金属型铸造Al-Si-Cu-Mg合金的塑性应变、弹性应变与断裂时的载荷反向次数之间呈直线关系,Al-Si-Cu-Mg-Er合金的弹性应变与疲劳断裂时的载荷反向次数之间也呈直线关系,但其塑性应变与疲劳断裂时的载荷反向次数之间则呈双线性关系.%Through the strain-controlled fatigue experiments, the low-cycle fatigue behavior of permanent-mold cast Al-Si-Cu-Mg and Al-Si-Cu-Mg-Er alloys at room temperature was investigated.The experimental results show that the Al-Si-Cu-Mg and Al-Si-Cu-Mg-Er alloys exhibit the cyclic strain hardening and cyclic stability, mainly depending on the imposed total strain amplitude. For the permanent-mold cast Al-Si-Cu-Mg alloy, the addition of Er can effectively enhance both cyclic deformation resistance and fatigue life of the alloys. A single-slope linear relation between plastic strain amplitude, elastic strain amplitude and reversals to failure is observed for permanent-mold cast Al-Si-Cu-Mg alloy. However, a two-slope linear relation between plastic strain amplitude and reversals to failure is noted for the Al-Si-Cu-Mg-Er alloy, although the corresponding relation between elastic strain amplitude and reversals to failure is linear.

  11. High-temperature fatigue in metals

    Halford, G. R.

    1982-01-01

    The presentation focuses primarily on the progress we at NASA Lewis Research Center have made. The understanding of the phenomenological processes of high temperature fatigue of metals for the purpose of calculating lives of turbine engine hot section components is discussed. Improved understanding resulted in the development of accurate and physically correct life prediction methods such as Strain-Range Partitioning for calculating creep fatigue interactions and the Double Linear Damage Rule for predicting potentially severe interactions between high and low cycle fatigue. Examples of other life prediction methods are also discussed.

  12. Predicting Fatigue Lives Under Complex Loading Conditions

    Mcgaw, Michael A.; Nelson, R. S.; Janitor, L. A.

    1995-01-01

    Cyclic Damage Accumulation (CDA) computer program performs high-temperature, low-cycle-fatigue life prediction for materials analysis. Designed to account for effects on creep-fatigue life of complex loadings involving such factors as thermomechanical fatigue, hold periods, wave-shapes, mean stresses, multiaxiality, cumulative damage, coatings, and environmental attack. Several features practical for application to actual component analysis using modern finite-element or boundary-element methods. Although developed for use in predicting crack-initiation lifetimes of gas-turbine-engine materials, also applied to other materials as well. Written in FORTRAN 77.

  13. Effect Of Solidification Speed On Fatigue Properties

    Mccay, M. H.; Schmidt, D. D.; Hamilton, W. D.; Alter, W. S.; Parr, R. A.

    1989-01-01

    Fast solidification increases fatigue life, but failure distribution becomes less predictable. Report describes effects of rate of solidification on nickel-based super-alloy MAR-M246(Hf) used in turbine blades. Based on experiments in which specimens directionally solidified at 5 cm/h and 30 cm/h, then tested for high cycle fatigue. Specimens also inspected by energy-dispersive x-ray (EDX) analysis and optical and electron microscopy.

  14. Material fatigue in high pressure piping

    Brunne, W.C. [Pro Novum, Research and Technological Services, Ltd, Katowice, (Poland)

    1998-12-31

    The present paper describes a type of damage to four-way cross pieces on live steam and reheated steam pipelines. The results of metallographic examination and strength tests are presented. The occurring mechanisms of material degradation, i.e. low-cycle fatigue and hydrogen corrosion are discussed. The both mechanisms result in the corrosion fatigue of the material causing the failure of cross pieces. A new design of cross piece was proposed. (orig.) 5 refs.

  15. Standard guide for fretting fatigue testing

    American Society for Testing and Materials. Philadelphia

    2010-01-01

    1.1 This guide defines terminology and covers general requirements for conducting fretting fatigue tests and reporting the results. It describes the general types of fretting fatigue tests and provides some suggestions on developing and conducting fretting fatigue test programs. 1.2 Fretting fatigue tests are designed to determine the effects of mechanical and environmental parameters on the fretting fatigue behavior of metallic materials. This guide is not intended to establish preference of one apparatus or specimen design over others, but will establish guidelines for adherence in the design, calibration, and use of fretting fatigue apparatus and recommend the means to collect, record, and reporting of the data. 1.3 The number of cycles to form a fretting fatigue crack is dependent on both the material of the fatigue specimen and fretting pad, the geometry of contact between the two, and the method by which the loading and displacement are imposed. Similar to wear behavior of materials, it is important t...

  16. Corrosion fatigue behavior and life prediction method under changing temperature condition

    Axially strain controlled low cycle fatigue tests of a carbon steel in oxygenated high temperature water were carried out under changing temperature conditions. Two patterns of triangular wave were selected for temperature cycling. One was in-phase pattern synchronizing with strain cycling and the other was an out-of-phase pattern in which temperature was changed in anti-phase to the strain cycling. The fatigue life under changing temperature condition was in the range of the fatigue life under various constant temperature within the range of the changing temperature. The fatigue life of in-phase pattern was equivalent to that of out-of-phase pattern. The corrosion fatigue life prediction method was proposed for changing temperature condition, and was based on the assumption that the fatigue damage increased in linear proportion to increment of strain during cycling. The fatigue life predicted by this method was in good agreement with the test results

  17. Cyclic deformation behavior of a nickel-base superalloy under fatigue loading

    Highlights: • The fatigue property of the alloy was analyzed. • The prediction of fatigue life was proposed. • The effects of strain amplitudes on cycle deformation behavior were analyzed. • The low cycle fatigue mechanism was discussed. • The nature of cycle deformation behaviors during fatigue process was discussed. - Abstract: Total strain-controlled low cycle fatigue (LCF) tests of a nickel-base superalloy were performed at 650 °C. Combined with fatigue test data, cyclic deformation behaviors of the alloy were analyzed. Fatigue cycle life decreases significantly with the increasing total strain amplitude. The cyclic hardening and cyclic softening phenomena occur during the LCF process, which are associated with the total strain amplitude. Fracture morphologies and dislocation characteristics were observed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The combined effects of brittle fracture and ductile fracture are the main LCF fracture mechanism of the alloy

  18. Simplified elastoplastic fatigue analysis

    Oligocyclic fatigue behaviour is a function of the local strain range. The design codes ASME section III, RCC-M, Code Case N47, RCC-MR, and the Guide issued by PNC propose simplified methods to evaluate the local strain range. After having briefly described these simplified methods, we tested them by comparing the results of experimental strains with those predicted by these rules. The experiments conducted for this study involved perforated plates under tensile stress, notched or reinforced beams under four-point bending stress, grooved specimens under tensile-compressive stress, and embedded grooved beams under bending stress. They display a relative conservatism depending on each case. The evaluation of the strains of rather inaccurate and sometimes lacks conservatism. So far, the proposal is to use the finite element codes with a simple model. The isotropic model with the cyclic consolidation curve offers a good representation of the real equivalent strain. There is obviously no question of representing the cycles and the entire loading history, but merely of calculating the maximum variation in elastoplastic equivalent deformations with a constant-rate loading. The results presented testify to the good prediction of the strains with this model. The maximum equivalent strain will be employed to evaluate fatigue damage

  19. Adaptations to isolated shoulder fatigue during simulated repetitive work. Part I: Fatigue.

    Tse, Calvin T F; McDonald, Alison C; Keir, Peter J

    2016-08-01

    Upper extremity muscle fatigue is challenging to identify during industrial tasks and places changing demands on the shoulder complex that are not fully understood. The purpose of this investigation was to examine adaptation strategies in response to isolated anterior deltoid muscle fatigue while performing simulated repetitive work. Participants completed two blocks of simulated repetitive work separated by an anterior deltoid fatigue protocol; the first block had 20 work cycles and the post-fatigue block had 60 cycles. Each work cycle was 60s in duration and included 4 tasks: handle pull, cap rotation, drill press and handle push. Surface EMG of 14 muscles and upper body kinematics were recorded. Immediately following fatigue, glenohumeral flexion strength was reduced, rating of perceived exertion scores increased and signs of muscle fatigue (increased EMG amplitude, decreased EMG frequency) were present in anterior and posterior deltoids, latissimus dorsi and serratus anterior. Along with other kinematic and muscle activity changes, scapular reorientation occurred in all of the simulated tasks and generally served to increase the width of the subacromial space. These findings suggest that immediately following fatigue people adapt by repositioning joints to maintain task performance and may also prioritize maintaining subacromial space width. PMID:26208429

  20. Design of Accelerated Fatigue Tests for Flame Free Refrigeration Fittings

    Wilson, Michael; Bowers, Chad D.

    2014-01-01

    Refrigerant leakage from failed braze joints is a multi-billion dollar problem for the global HVAC&R industry. Leaks are typically caused due to mechanical fatigue from extreme pressure cycling, temperature cycling including exposure to freeze/thaw cycles, or vibrational wear induced from rotating electrical machinery. Three tests to accelerate mechanical fatigue were devised to simulate real world extreme conditions to determine possible failure modes of refrigerant components. The first tes...