Effect of thermal aging on the low cycle fatigue behavior of Z3CN20.09M cast duplex stainless steel

Energy Technology Data Exchange (ETDEWEB)

Chen, Weifeng [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xue, Fei [Suzhou Nuclear Power Research Institute, Suzhou 215004 (China); Tian, Yang [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Yu, Dunji, E-mail: djyu@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Yu, Weiwei [Suzhou Nuclear Power Research Institute, Suzhou 215004 (China); Chen, Xu [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

2015-10-14

Nuclear grade Z3CN20.09M cast duplex stainless steel exhibits enhanced cyclic stress response and prolonged low cycle fatigue life at room temperature after thermal aging at 400 °C for up to 6000 h. The threshold strain amplitude for the onset of secondary hardening is shifted to a lower value after thermal aging. Microstructural observations reveal that fatigue cracks tend to initiate from phase boundaries in virgin specimens, but to initiate in the ferrite phase in aged ones. Denser fatigue striations are found on the fracture surface of fatigued specimen subjected to longer thermal aging duration. These observations are explained in the context of thermal aging induced embrittlement of the ferrite phase and deformation induced martensitic phase transformation in the austenite phase.

Electrochemical behaviour of a stainless steel coating after thermal fatigue and thermal shocks

International Nuclear Information System (INIS)

Boudebane, A.; Darsouni, A.; Chadli, H.; Boudebane, S.

2012-01-01

This work aims to study of the influence of thermal fatigue and thermal shock on the corrosion behaviour of coated steel AISI 304L. The coating was welded by TIG welding on specimens in ferritic-pearlitic steel grade AISI 4140. The study concerns three different states of deposit: sensitized, sensitized and strain hardened in surface and no sensitized. We realized electrochemical corrosion in an aqueous solution of NaCl 34 g/l. The corrosion of the specimens were evaluated by comparing the potentiodynamic curves for different states of the coating. Firstly, electrochemical characterization of deposits has shown a localized intergranular corrosion. Furthermore, the increase in the number of cycles of thermal fatigue accelerates the dissolution of deposit. Thermal shocks tend to improve resistance to corrosion. Against, the mechanical treatment of surfaces by burnishing decreases the dissolution rate of deposit cycles in thermal fatigue. (authors)

Imposed Thermal Fatigue and Post-Thermal-Cycle Wear Resistance of Biomimetic Gray Cast Iron by Laser Treatment

Science.gov (United States)

Sui, Qi; Zhou, Hong; Zhang, Deping; Chen, Zhikai; Zhang, Peng

2017-08-01

The present study aims to create coupling biomimetic units on gray cast iron substrate by laser surface treatment (LST). LSTs for single-step (LST1) and two-step (LST2) processes, were carried out on gray cast iron in different media (air and water). Their effects on microstructure, thermal fatigue, and post-thermal-cycle wear (PTW) resistance on the specimens were studied. The tests were carried out to examine the influence of crack-resistance behavior as well as the biomimetic surface on its post-thermal-cycle wear behavior and different units, with different laser treatments for comparison. Results showed that LST2 enhanced the PTW behaviors of gray cast iron, which then led to an increase in its crack resistance. Among the treated cast irons, the one treated by LST2 in air showed the lowest residual stress, due to the positive effect of the lower steepness of the thermal gradient. Moreover, the same specimen showed the best PTW performance, due to its superior crack resistance and higher hardness as a result of it.

Some aspects of thermal fatigue in stainless steel

International Nuclear Information System (INIS)

Iorio, A.F.; Crespi, J.C.

1987-01-01

This paper is concerned with the analysis of failures in a moderator circuit branch piping of the ATUCHA-I pressurized heavy water reactor (PHWR), made of austenitic steel to DIN 1.4550 specification (similar to AISI 347). These failures are considered to result from a thermal fatigue processes induced by fluctuations in a zone where stratified temperature layers occurred -the fluctuations being associated with variations in the heavy water flow. The first section evaluates the possibility of cracking due to thermal fatigue phenomena and concludes that under service conditions a crack may be initiated and growth through 7 mm of the wall thickness of the pipe. Laboratory thermal fatigue tests that simulated the thermomechanical conditions for such a component, showed that the number of cycles required to initiate a thermal fatigue crack in a notched modified standard fatigue specimen was about 10 3 . This value may be used to give a conservative prediction of the number of thermal cycles for crack initiation in actual station piping, including those who suffered a cold plug condition which is produced in some emergency shut-down and valve testing situations. It was also demonstrated that beyond a crack depth of 7 mm stress corrosion cracking has the main process in further crack propagation. The relevance of this prediction has been confirmed by microfractographic observations, since the brittle nature of the fracture surfaces under service conditions appears very different from the transgranular ductile striations found in both thermal and mechanical fatigue test specimens as a result of environmental effects. (Author)

Thermal fatigue strength estimation of 2.25Cr-1Mo steel under creep-fatigue interaction

International Nuclear Information System (INIS)

Kuwahara, Kazuo; Nitta, Akihito; Kitamura, Takayuki

1980-01-01

A 2-1/4Cr-1Mo steel is one of principal materials for high temperature equipments in nuclear and thermal power plants. The authors experimentally analyzed the high temperature fatigue strength and creep strength of a 2-1/4 Cr-1Mo steel main steam pipe which had been used in a thermal plant for operation up to 130,000 hours, and pointed out that the strain-range vs. life curves crossed each other due to the difference of temperature-strain phase in thermal fatigue. This suggests that it is difficult to estimate thermal fatigue life of steel materials having been subjected to different temperature-strain phase on the basis of isothermal low-cycle fatigue life at the upper limit temperature of thermal fatigue, and that it is urgently required to establish an appropriate method of evaluating thermal fatigue life. The authors attempted to prove that the strain range partitioning method used for the evaluation of thermal fatigue life in SUS 304 steels is applicable to this 2-1/4Cr-1Mo steel. Consequently, it was found that the thermal fatigue life could be estimated within a factor of 2.5 by the application of this method. (author)

Thermal-Acoustic Fatigue of a Multilayer Thermal Protection System in Combined Extreme Environments

Directory of Open Access Journals (Sweden)

Liu Liu

2014-06-01

Full Text Available In order to ensure integrity of thermal protection system (TPS structure for hypersonic vehicles exposed to severe operating environments, a study is undertaken to investigate the response and thermal-acoustic fatigue damage of a representative multilayer TPS structure under combined thermal and acoustic loads. An unsteady-state flight of a hypersonic vehicle is composed of a series of steady-state snapshots, and for each snapshot an acoustic load is imposed to a static steady-state TPS structure. A multistep thermal-acoustic fatigue damage intensity analysis procedure is given and consists of a heat transfer analysis, a nonlinear thermoelastic analysis, and a random response analysis under a combined loading environment and the fatigue damage intensity has been evaluated with two fatigue analysis techniques. The effects of thermally induced deterministic stress and nondeterministic dynamic stress due to the acoustic loading have been considered in the damage intensity estimation with a maximum stress fatigue model. The results show that the given thermal-acoustic fatigue intensity estimation procedure is a viable approach for life prediction of TPS structures under a typical mission cycle with combined loadings characterized by largely different time-scales. A discussion of the effects of the thermal load, the acoustic load, and fatigue analysis methodology on the fatigue damage intensity has been provided.

Thermal Fatigue Behavior of Air-Plasma Sprayed Thermal Barrier Coating with Bond Coat Species in Cyclic Thermal Exposure

Directory of Open Access Journals (Sweden)

Ungyu Paik

2013-08-01

Full Text Available The effects of the bond coat species on the delamination or fracture behavior in thermal barrier coatings (TBCs was investigated using the yclic thermal fatigue and thermal-shock tests. The interface microstructures of each TBC showed a good condition without cracking or delamination after flame thermal fatigue (FTF for 1429 cycles. The TBC with the bond coat prepared by the air-plasma spray (APS method showed a good condition at the interface between the top and bond coats after cyclic furnace thermal fatigue (CFTF for 1429 cycles, whereas the TBCs with the bond coats prepared by the high-velocity oxygen fuel (HVOF and low-pressure plasma spray (LPPS methods showed a partial cracking (and/or delamination and a delamination after 780 cycles, respectively. The TBCs with the bond coats prepared by the APS, HVOF and LPPS methods were fully delaminated (>50% after 159, 36, and 46 cycles, respectively, during the thermal-shock tests. The TGO thickness in the TBCs was strongly dependent on the both exposure time and temperature difference tested. The hardness values were found to be increased only after the CFTF, and the TBC with the bond coat prepared by the APS showed the highest adhesive strength before and after the FTF.

Detection of thermal fatigue in composites by second harmonic Lamb waves

International Nuclear Information System (INIS)

Li, Weibin; Cho, Younho; Achenbach, Jan D

2012-01-01

Composite materials which are widely used in the aerospace industry, are usually subjected to frequent variation of temperature. Thermal cyclic loading may induce material degradation. Considering the long-term service of aircraft composites and the importance of safety in the aircraft industry, even a little damage that may be accumulative via thermal fatigue is often of great concern. Therefore, there is a demand to develop non-destructive approaches to evaluate thermal fatigue damage in an early stage. Due to the sensitivity of acoustic nonlinearity to micro-damage, the nonlinear ultrasonic technique has been explored as a promising tool for early detection of micro-damage. This paper investigates an experimental scheme for characterizing thermal fatigue damage in composite laminates using second harmonic Lamb waves. The present results show a monotonic increase of acoustic nonlinearity with respect to thermal fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and thermal fatigue cycles in carbon/epoxy laminates verifies that nonlinear Lamb waves can be used to assess thermal fatigue damage rendering improved sensitivity over conventional linear feature based non-destructive evaluation techniques. Velocity and attenuation based ultrasonic studies are carried out for comparison with the nonlinear ultrasonic approach and it is found that nonlinear acoustic parameters are more promising indicators of thermal fatigue damage than linear ones. (paper)

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

International Nuclear Information System (INIS)

Haddar, N.

2003-04-01

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

Fatigue behaviour of the austenitic steel 1.4550 under mechanical and thermal cyclic loading

Energy Technology Data Exchange (ETDEWEB)

Siegele, D.; Fingerhuth, J.; Varfolomeev, I.; Moroz, S. [Fraunhofer Institute for Mechanics of Materials (IWM), Freiburg (Germany)

2014-07-01

Fatigue behaviour of the austenitic steel 1.4550 (X6CrNiNb18-10) under low-cycle fatigue and high-cycle thermal fatigue was investigated with in two research projects supported by the Federal Ministry of Economic Affairs and Energy and the Ministry of Education and Research. The objectives of the projects were the gain of deep understanding of the damage mechanisms under mechanical and thermal cyclic loading and the development of material models and simulation procedures for an improved lifetime assessment. In comparison to the advanced mechanism based material models engineering computational procedures were proven with respect to their applicability and conservatisms. For thermal cyclic loading, test equipment and technique were developed which allow for cyclic thermal loading with temperature ranges between 1 00 C and 300 C and frequencies between 0.1 and 1 Hz. As a result, tests with a temperature range of 150 C and lower showed no crack formation up to 300,000 cycles. For temperature ranges of 200 C and higher multiple crack patterns were observed with the deepest crack of about 1.3 mm after 1,000,000 cycles, whereas the difference in crack depth between 300,000 and 1,000,000 cycles was negligibly small. To model the fatigue lifetime, the D{sub TMF} damage parameter was applied to the low-cycle fatigue and the thermal, high frequent fatigue tests. For thermal fatigue, the analyses predicted in agreement with the tests crack initiation followed by crack propagation, subsequent retardation and arrest. This behaviour can be explained qualitatively and quantitatively using the methods of linear-elastic fracture mechanics, whereas the consideration of the interaction of multiple cracks is essential to describe the experimentally observed crack retardation. The results for thermal fatigue are in the scatterband of the mechanical p and thermo-mechanical fatigue results and the cycles to failure are 10 times higher than those estimated according to the KTA fatigue

Fatigue analysis through automated cycle counting using ThermAND

International Nuclear Information System (INIS)

Burton, G.R.; Ding, Y.; Scovil, A.; Yetisir, M.

2008-01-01

The potential for fatigue damage due to thermal transients is one of the degradation mechanisms that needs to be managed for plant components. The original design of CANDU stations accounts for projected fatigue usage for specific components over a specified design lifetime. Fatigue design calculations were based on estimates of the number and severity of expected transients for 30 years operation at 80% power. Many CANDU plants are now approaching the end of their design lives and are being considered for extended operation. Industry practice is to have a comprehensive fatigue management program in place for extended operation beyond the original design life. A CANDU-specific framework for fatigue management has recently been developed to identify the options for implementation, and the critical components and locations requiring long-term fatigue monitoring. An essential element of fatigue monitoring is to identify, count and monitor the number of plant transients to ensure that the number assumed in the original design is not exceeded. The number and severity of actual CANDU station thermal transients at key locations in critical systems have been assessed using ThermAND, AECL's health monitor for systems and components, based on archived station operational data. The automated cycle counting has demonstrated that actual transients are generally less numerous than the quantity assumed in the design basis, and are almost always significantly less severe. This paper will discuss the methodology to adapt ThermAND for automated cycle counting of specific system transients, illustrate and test this capability for cycle-based fatigue monitoring using CANDU station data, report the results, and provide data for stress-based fatigue calculations. (author)

Formation of thermal fatigue cracks in periodic rapid quenching of metal

Energy Technology Data Exchange (ETDEWEB)

Ots, A [Tallinn Technical University, Thermal Engineering Department, Tallinn (Estonia)

1999-12-31

Water lancing is an effective technique for cleaning boiler heating surfaces from ash deposits by burning low-grade fuels with complicated composition of mineral matter. In water cleaning cycles of boiler`s heat transfer surfaces due to rapid quenching destruction of corrosion protective oxide film and formation of thermal fatigue cracks on the outer surface of the tube`s metal occur. The criterion of the thermal fatigue cracks` formation and their growth intensity depend on the character of temperature field in the tube`s metal outer layer. The solution of non-stationary heat conductivity equation for metal rapid quenching conditions is given. The convective heat transfer coefficients from hot metal surface to water jet were established experimentally. Thermal fatigue crack growth intensity was investigated in real boilers` heat transfer surfaces` tubes as well as in laboratory conditions. The formula for predicting thermal fatigue cracks` depth depending on the number of cleaning cycles. (orig.) 5 refs.

Formation of thermal fatigue cracks in periodic rapid quenching of metal

Energy Technology Data Exchange (ETDEWEB)

Ots, A. [Tallinn Technical University, Thermal Engineering Department, Tallinn (Estonia)

1998-12-31

Water lancing is an effective technique for cleaning boiler heating surfaces from ash deposits by burning low-grade fuels with complicated composition of mineral matter. In water cleaning cycles of boiler`s heat transfer surfaces due to rapid quenching destruction of corrosion protective oxide film and formation of thermal fatigue cracks on the outer surface of the tube`s metal occur. The criterion of the thermal fatigue cracks` formation and their growth intensity depend on the character of temperature field in the tube`s metal outer layer. The solution of non-stationary heat conductivity equation for metal rapid quenching conditions is given. The convective heat transfer coefficients from hot metal surface to water jet were established experimentally. Thermal fatigue crack growth intensity was investigated in real boilers` heat transfer surfaces` tubes as well as in laboratory conditions. The formula for predicting thermal fatigue cracks` depth depending on the number of cleaning cycles. (orig.) 5 refs.

Hydro-Thermal Fatigue Resistance Measurements on Polymer Interfaces

Science.gov (United States)

Gurumurthy, Charan K.; Kramer, Edward J.; Hui, Chung-Yuen

1998-03-01

We have developed a new technique based on a fiber optic displacement sensor for rapid determination of hydro-thermal fatigue crack growth rate per cycle (da/dN) of an epoxy/polyimide interface used in flip chip attach microelectronic assembly. The sample is prepared as a trilayered cantilever beam by capillary flow of the epoxy underfill over a polyimide coated metallic beam. During hydro-thermal cycling the crack growth along the interface (from the free end) changes the displacement of this end of the beam and we measure the free end displacement at the lowest temperature in each hydro-thermal cycle. The change in beam displacement is then converted into crack growth rate (da/dN). da/dN depends on the maximum change in the strain energy release rate of the crack and the phase angle in each cycle. The relation between da/dN and maximum strain energy release rate characterizes the fatigue crack growth resistance of the interface. We have developed and used a simple model anhydride cured and a commercially available PMDA/ODA passivation for this study.

Study of the quantitative assessment method for high-cycle thermal fatigue of a T-pipe under turbulent fluid mixing based on the coupled CFD-FEM method and the rainflow counting method

Energy Technology Data Exchange (ETDEWEB)

Zhang, Y.; Lu, T., E-mail: likesurge@sina.com

2016-12-01

Highlights: • Two characteristic parameters of the temperature fluctuations are used for qualitative analysis. • A quantitative assessment method for high-cycle thermal fatigue of a T-pipe is proposed. • The time-dependent curves for the temperature and thermal stress are not always “in-phase”. • Large magnitude of thermal stresses may not mean large number of fatigue cycles. • The normalized fatigue damage rate and normalized RMS temperature are positively related. - Abstract: With the development of nuclear power and nuclear power safety, high-cycle thermal fatigue of the pipe structures induced by the flow and heat transfer of the fluid in pipes have aroused more and more attentions. Turbulent mixing of hot and cold flows in a T-pipe is a well-recognized source of thermal fatigue in piping system, and thermal fatigue is a significant long-term degradation mechanism. It is not an easy work to evaluate thermal fatigue of a T-pipe under turbulent flow mixing because of the thermal loads acting at fluid–structure interface of the pipe are so complex and changeful. In this paper, a one-way Computational Fluid Dynamics-Finite Element Method (CFD-FEM method) coupling based on the ANSYS Workbench 15.0 software has been developed to calculate transient thermal stresses with the temperature fields of turbulent flow mixing, and thermal fatigue assessment has been carried out with this obtained fluctuating thermal stresses by programming in the software platform of Matlab based on the rainflow counting method. In the thermal analysis, the normalized mean temperatures and the normalized root mean square (RMS) temperatures are obtained and compared with the experiment of the test case from the Vattenfall benchmark facility to verify the accuracy of the CFD calculation and to determine the position which thermal fatigue is most likely to occur in the T-junction. Besides, more insights have been obtained in the coupled CFD-FEM analysis and the thermal fatigue

Establishment of a JSME code for the evaluation of high-cycle thermal fatigue in mixing tees

International Nuclear Information System (INIS)

Moriya, Shoichi; Fukuda, Toshihiko; Matsunaga, Tomoya; Hirayama, Hiroshi; Shiina, Kouji; Tanimoto, Koichi

2004-01-01

This paper describes a JSME code for high-cycle thermal fatigue evaluation by thermal striping in mixing tees with hot and cold water flows. The evaluation of thermal striping in a mixing tee has four steps to screen design parameters one-by-one according to the severity of the thermal load assessed from design conditions using several evaluation charts. In order to make these charts, visualization tests with acrylic pipes and temperature measurement tests with metal pipes were conducted. The influence of the configurations of mixing tees, flow velocity ratio, pipe diameter ratio and so on was examined from the results of the experiments. This paper makes a short mention of the process of providing these charts. (author)

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

International Nuclear Information System (INIS)

Watson, R.D.; Youchison, D.L.; Dombrowski, D.E.; Guiniatouline, R.N.; Kupriynov, I.B.

1996-01-01

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 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 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

Comparison of evaluation results of piping thermal fatigue evaluation method based on equivalent stress amplitude

International Nuclear Information System (INIS)

Suzuki, Takafumi; Kasahara, Naoto

2012-01-01

In recent years, reports have increased about failure cases caused by high cycle thermal fatigue both at light water reactors and fast breeder reactors. One of the reasons of the cases is a turbulent mixing at a Tee-junction, where hot and cold temperature fluids are mixed, in a coolant system. In order to prevent thermal fatigue failures at Tee-junctions. The Japan Society of Mechanical Engineers published the guideline which is an evaluation method of high cycle thermal fatigue damage at nuclear pipes. In order to justify safety margin and make the procedure of the guideline concise, this paper proposes a new evaluation method of thermal fatigue damage with use of the 'equivalent stress amplitude.' Because this new method makes procedure of evaluation clear and concise, it will contribute to improving the guideline for thermal fatigue evaluation. (author)

On the estimation of durability during thermal fatigue tests

International Nuclear Information System (INIS)

Vashunin, A.I.; Kotov, P.I.

1981-01-01

It is shown that during thermal fatigue tests under conditions of varying loading rigidity the value of stored one-sided deformation in a fracture zone tends to the limit value of material ductility. Holding at Tsub(max) is semicycle of compression increases irreversible deformation on value of Atausub(confer)sup(a), which does not depend on loading rigidity. It is established that the Use of curves of thermal fatigue as basic ones for determination of resistance of non-isothermal low-cycle fatigue is possible only at values of stored quasistatical damage, constituting less than 5% from available ductility [ru

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

International Nuclear Information System (INIS)

Korth, G.E.

1981-06-01

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

Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue for the austentic stainless steels, and application of multiaxial fatigue criteria

Energy Technology Data Exchange (ETDEWEB)

Fissolo, Antoine; Gourdin, Cedric [DM2S/SEMT/LISN, Gif sur Yvette (France); Vincent, Ludovic [DMN/SRMA/LCD, Gif sur Yvette (France)

2009-07-01

For nuclear reactor components, uniaxial isothermal fatigue curves are used to estimate the crack initiation under thermal fatigue. However, such approach would be not sufficient in some cases where cracking was observed. To investigate differences between uniaxial and thermal fatigue damage, tests have been carried out at CEA using the thermal fatigue devices SPLASH and FAT3D: a bi-dimensional (2-D) loading status is obtained in SPLASH, whereas a tri-dimensional (3-D) loading status is obtained in FAT3D. All the analysed tests clearly show that crack initiation in thermal fatigue is faster than in uniaxial isothermal fatigue conditions: for identical levels of strain, the number of cycles required to achieve crack initiation is significantly lower. The enhanced damaging effect probably results from a pure mechanical origin: a nearly perfect biaxial state corresponds to an increased hydrostatic stress. Consequently, multiaxial fatigue criteria must be applied. The Zamrik's strain criterion and the energy criterion proposed by Ecole Polytechnique provide the best estimations. In that framework, the proposed new method coupling both RCC-MR strain estimations and Zamrik's criterion appears to be more promising for the designer. (orig.)

Thermal fatigue appears to be more damaging than uniaxial isothermal fatigue for the austentic stainless steels, and application of multiaxial fatigue criteria

International Nuclear Information System (INIS)

Fissolo, Antoine; Gourdin, Cedric; Vincent, Ludovic

2009-01-01

For nuclear reactor components, uniaxial isothermal fatigue curves are used to estimate the crack initiation under thermal fatigue. However, such approach would be not sufficient in some cases where cracking was observed. To investigate differences between uniaxial and thermal fatigue damage, tests have been carried out at CEA using the thermal fatigue devices SPLASH and FAT3D: a bi-dimensional (2-D) loading status is obtained in SPLASH, whereas a tri-dimensional (3-D) loading status is obtained in FAT3D. All the analysed tests clearly show that crack initiation in thermal fatigue is faster than in uniaxial isothermal fatigue conditions: for identical levels of strain, the number of cycles required to achieve crack initiation is significantly lower. The enhanced damaging effect probably results from a pure mechanical origin: a nearly perfect biaxial state corresponds to an increased hydrostatic stress. Consequently, multiaxial fatigue criteria must be applied. The Zamrik's strain criterion and the energy criterion proposed by Ecole Polytechnique provide the best estimations. In that framework, the proposed new method coupling both RCC-MR strain estimations and Zamrik's criterion appears to be more promising for the designer. (orig.)

Fatigue crack growth behavior under cyclic thermal transient stress

International Nuclear Information System (INIS)

Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.

1986-01-01

Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)

Fatigue crack growth behavior under cyclic transient thermal stress

International Nuclear Information System (INIS)

Ueda, Masahiro; Kano, Takashi; Yoshitoshi, Atsushi.

1987-01-01

Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplified methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results. (author)

Assessment of thermal fatigue crack propagation in safety injection PWR lines

International Nuclear Information System (INIS)

Simos, N.; Reich, M.; Costantino, C.J.; Hartzman, M.

1990-01-01

Cyclic thermal stratification resulting in alternating thermal stresses in pipe cross sections has been identified as the primary cause of high cycle thermal fatigue failure. A number of piping lines in operating plants around the world, susceptible to thermal stratification, have experienced circumferential cracking as a result of high levels of alternating bending stresses. This paper addresses the mechanisms of crack initiation and crack growth and provides estimates of fatigue cycles to failure for a typical safety injection line with such cyclic load history. Utilizing a 3-D finite element analysis, the temperature profile and the corresponding thermal stress field of a complete thermal cycle in a safety injection line consisting of a horizontal pipe section and an elbow, is obtained. Since the observed cracking occurred in the region of the elbow-to-horizontal pipe weld, the analysis performed assessed (1) the impact of the level of local geometric discontinuities on the initiation of an inside surface flaw is greatest and (2) the number of thermal cycles required to drive a small surface crack through the pipe wall. 12 refs., 14 figs., 2 tabs

Thermal fatigue. Fluid-structure interaction at thermal mixing events

International Nuclear Information System (INIS)

Schuler, X.; Herter, K.H.; Moogk, S.; Laurien, E.; Kloeren, D.; Kulenovic, R.; Kuschewski, M.

2012-01-01

In the framework of the network research project ''Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue'' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behaviour under transient thermal-mechanical stress conditions (high cycle fatigue - HCF) are carried out. The project's background and its network of scientific working groups with their individual working tasks are briefly introduced. The main focus is especially on the joint research tasks within the sub-projects of MPA and IKE which are dealing with thermal mixing of flows in a T-junction configuration and the fluidstructure- interactions (FSI). Therefore, experiments were performed with the newly established FSI test facility at MPA which enables single-phase flow experiments of water in typical power plant piping diameters (DN40 and DN80) at high pressure (maximum 75 bar) and temperatures (maximum 280 C). The experimental results serve as validation data base for numerical modelling of thermal flow mixing by means of thermo-fluid dynamics simulations applying CFD techniques and carried out by IKE as well as for modelling of thermal and mechanical loads of the piping structure by structural mechanics simulations with FEM methods which are executed by MPA. The FSI test facility will be described inclusively the applied measurement techniques, e. g. in particular the novel near-wall LED-induced Fluorescence method for non-intrusive flow temperature measurements. First experimental data and numerical results from CFD and FEM simulations of the thermal mixing of flows in the T-junction are presented.

Hydrogen enhanced thermal fatigue of y-titanium aluminide

NARCIS (Netherlands)

Dunfee, William; Gao, Ming; Wei, Robert P.; Wei, W.

1995-01-01

A study of hydrogen enhanced thermal fatigue cracking was carried out for a gamma-based Ti-48Al-2Cr alloy by cycling between room temperature and 750 or 900 °C. The results showed that hydrogen can severely attack the gamma alloy, with resulting lifetimes as low as three cycles, while no failures

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

International Nuclear Information System (INIS)

Lehericy, Y.

2007-05-01

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)

High cycle fatigue properties of inconel 690

International Nuclear Information System (INIS)

Lee, Young Ho; Lee, Byong Whi; Kim, In Sup; Park, Chi Yong

1997-01-01

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

Thermal fatigue of a 304L austenitic stainless steel: simulation of the initiation and of the propagation of the short cracks in isothermal and aniso-thermal fatigue; Fatigue thermique d'un acier inoxydable austenitique 304L: simulation de l'amorcage et de la croissance des fissures courtes en fatigue isotherme et anisotherme

Energy Technology Data Exchange (ETDEWEB)

Haddar, N

2003-04-01

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

Influence of different temperatures on the thermal fatigue behavior and thermal stability of hot-work tool steel processed by a biomimetic couple laser technique

Science.gov (United States)

Meng, Chao; Zhou, Hong; Zhou, Ying; Gao, Ming; Tong, Xin; Cong, Dalong; Wang, Chuanwei; Chang, Fang; Ren, Luquan

2014-04-01

Three kinds of biomimetic non-smooth shapes (spot-shape, striation-shape and reticulation-shape) were fabricated on the surface of H13 hot-work tool steel by laser. We investigated the thermal fatigue behavior of biomimetic non-smooth samples with three kinds of shapes at different thermal cycle temperature. Moreover, the evolution of microstructure, as well as the variations of hardness of laser affected area and matrix were studied and compared. The results showed that biomimetic non-smooth samples had better thermal fatigue behavior compared to the untreated samples at different thermal cycle temperatures. For a given maximal temperature, the biomimetic non-smooth sample with reticulation-shape had the optimum thermal fatigue behavior, than with striation-shape which was better than that with the spot-shape. The microstructure observations indicated that at different thermal cycle temperatures the coarsening degrees of microstructures of laser affected area were different and the microstructures of laser affected area were still finer than that of the untreated samples. Although the resistance to thermal cycling softening of laser affected area was lower than that of the untreated sample, laser affected area had higher microhardness than the untreated sample at different thermal cycle temperature.

Thermal fatigue. Fluid-structure interaction at thermal mixing events

Energy Technology Data Exchange (ETDEWEB)

Schuler, X.; Herter, K.H.; Moogk, S. [Stuttgart Univ. (Germany). MPA; Laurien, E.; Kloeren, D.; Kulenovic, R.; Kuschewski, M. [Stuttgart Univ. (Germany). Inst. of Nuclear Technology and Energy Systems

2012-07-01

In the framework of the network research project ''Thermal Fatigue - Basics of the system-, outflow- and material-characteristics of piping under thermal fatigue'' funded by the German Federal Ministry of Education and Research (BMBF) fundamental numerical and experimental investigations on the material behaviour under transient thermal-mechanical stress conditions (high cycle fatigue - HCF) are carried out. The project's background and its network of scientific working groups with their individual working tasks are briefly introduced. The main focus is especially on the joint research tasks within the sub-projects of MPA and IKE which are dealing with thermal mixing of flows in a T-junction configuration and the fluidstructure- interactions (FSI). Therefore, experiments were performed with the newly established FSI test facility at MPA which enables single-phase flow experiments of water in typical power plant piping diameters (DN40 and DN80) at high pressure (maximum 75 bar) and temperatures (maximum 280 C). The experimental results serve as validation data base for numerical modelling of thermal flow mixing by means of thermo-fluid dynamics simulations applying CFD techniques and carried out by IKE as well as for modelling of thermal and mechanical loads of the piping structure by structural mechanics simulations with FEM methods which are executed by MPA. The FSI test facility will be described inclusively the applied measurement techniques, e. g. in particular the novel near-wall LED-induced Fluorescence method for non-intrusive flow temperature measurements. First experimental data and numerical results from CFD and FEM simulations of the thermal mixing of flows in the T-junction are presented.

CFD-FEM coupling for accurate prediction of thermal fatigue

International Nuclear Information System (INIS)

Hannink, M.H.C.; Kuczaj, A.K.; Blom, F.J.; Church, J.M.; Komen, E.M.J.

2009-01-01

Thermal fatigue is a safety related issue in primary pipework systems of nuclear power plants. Life extension of current reactors and the design of a next generation of new reactors lead to growing importance of research in this direction. The thermal fatigue degradation mechanism is induced by temperature fluctuations in a fluid, which arise from mixing of hot and cold flows. Accompanied physical phenomena include thermal stratification, thermal striping, and turbulence [1]. Current plant instrumentation systems allow monitoring of possible causes as stratification and temperature gradients at fatigue susceptible locations [1]. However, high-cycle temperature fluctuations associated with turbulent mixing cannot be adequately detected by common thermocouple instrumentations. For a proper evaluation of thermal fatigue, therefore, numerical simulations are necessary that couple instantaneous fluid and solid interactions. In this work, a strategy for the numerical prediction of thermal fatigue is presented. The approach couples Computational Fluid Dynamics (CFD) and the Finite Element Method (FEM). For the development of the computational approach, a classical test case for the investigation of thermal fatigue problems is studied, i.e. mixing in a T-junction. Due to turbulent mixing of hot and cold fluids in two perpendicularly connected pipes, temperature fluctuations arise in the mixing zone downstream in the flow. Subsequently, these temperature fluctuations are also induced in the pipes. The stresses that arise due to the fluctuations may eventually lead to thermal fatigue. In the first step of the applied procedure, the temperature fluctuations in both fluid and structure are calculated using the CFD method. Subsequently, the temperature fluctuations in the structure are imposed as thermal loads in a FEM model of the pipes. A mechanical analysis is then performed to determine the thermal stresses, which are used to predict the fatigue lifetime of the structure

Two scale damage model and related numerical issues for thermo-mechanical high cycle fatigue

International Nuclear Information System (INIS)

Desmorat, R.; Kane, A.; Seyedi, M.; Sermage, J.P.

2007-01-01

On the idea that fatigue damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), a three-dimensional two scale damage model has been proposed for High Cycle Fatigue applications. It is extended here to aniso-thermal cases and then to thermo-mechanical fatigue. The modeling consists in the micro-mechanics analysis of a weak micro-inclusion subjected to plasticity and damage embedded in an elastic meso-element (the RVE of continuum mechanics). The consideration of plasticity coupled with damage equations at micro-scale, altogether with Eshelby-Kroner localization law, allows to compute the value of microscopic damage up to failure for any kind of loading, 1D or 3D, cyclic or random, isothermal or aniso-thermal, mechanical, thermal or thermo-mechanical. A robust numerical scheme is proposed in order to make the computations fast. A post-processor for damage and fatigue (DAMAGE-2005) has been developed. It applies to complex thermo-mechanical loadings. Examples of the representation by the two scale damage model of physical phenomena related to High Cycle Fatigue are given such as the mean stress effect, the non-linear accumulation of damage. Examples of thermal and thermo-mechanical fatigue as well as complex applications on real size testing structure subjected to thermo-mechanical fatigue are detailed. (authors)

Fatigue cycles evaluation of 500 MWe PHWR coolant channel sealdisc

International Nuclear Information System (INIS)

Chawla, D.S.; Vaze, K.K.; Kushwaha, H.S.; Gupta, K.S.; Bhambra, H.S.

1998-07-01

At each end of coolant channel there is one sealing plug assembly. The sealdisc is a part of sealing plug assembly. The sealdisc is used to avoid leakage of heavy water. The importance of sealdisc can be understood by the fact that there are 784 sealdiscs in one 500 MWe PHWR unit. During the life time of reactor the sealdisc will be subjected to cyclic loads due to reactor startup, shutdown, power setback and also due to refuelling operations. Excessive reversal of stresses may lead to fatigue failure. The sealdisc failure may cause loss of coolant accidents. Since sealdisc is safety class 1 component, it has to be qualified according to ASME Section III Division 1 NB. For cyclic loads, the fatigue analysis is essential to assess the allowable number of cycles and also to check the total usage factor due to different cyclic loads. To evaluate the allowable fatigue cycles, the analysis is carried out using finite element method. The present report deals with the fatigue cycles evaluation of 500 MWe PHWR sealdisc. The finite element model having eight noded axisymmetric elements is used for the analysis. The various loads considered in the analysis are mechanical loads arising due to refuelling operations and number of temperature-pressure transients. During refuelling, the sealdisc is removed and reinstalled back by use of fuelling machine ram which applies load at centre as well as at rocker point of sealdisc. The stress analysis is carried out for each stage of loading during refuelling and fatigue cycles are evaluated. For temperature transient, decoupled thermal analysis is carried out. At various instants of time, the stresses are computed using temperatures calculated in thermal analysis. The pressure variation is also considered along with temperature variation. The fatigue cycles are evaluated for each transient using maximum alternating stress intensities. The usage factors are calculated for various temperature/pressure transients and refuelling loads

Thermal fatigue testing of a diffusion-bonded beryllium divertor mock-up under ITER relevant conditions

International Nuclear Information System (INIS)

Youchison, D.L.; Guiniiatouline, R.; Watson, R.D.

1994-01-01

Thermal response and thermal fatigue tests of four 5 mm thick beryllium tiles on a Russian divertor mock-up were completed on the Electron Beam Test System at Sandia National Laboratories. The beryllium tiles were diffusion bonded onto an OFHC copper saddleblock and a DSCu (MAGT) tube containing a porous coating. Thermal response tests were performed on the tiles to an absorbed heat flux of 5 MW/m 2 and surface temperatures near 300 degrees C using 1.4 MPa water at 5.0 m/s flow velocity and an inlet temperature of 8-15 degrees C. One tile was exposed to incrementally increasing heat fluxes up to 9.5 MW/m 2 and surface temperatures up to 690 degrees C before debonding at 10 MW/m 2 . A third tile debonded after 9200 thermal fatigue cycles at 5 MW/m 2 , while another debonded after 6800 cycles. In all cases, fatigue failure occurred in the intermetallic layers between the beryllium and copper. No fatigue cracking of the bulk beryllium was observed. During thermal cycling, a gradual loss of porous coating produced increasing sample temperatures. These experiments indicate that diffusion-bonded beryllium tiles can survive several thousand thermal cycles under ITER relevant conditions without failure. However, the reliability of the diffusion bonded Joint remains a serious issue

Basic thermal-mechanical properties and thermal shock, fatigue resistance of swaged + rolled potassium doped tungsten

Science.gov (United States)

Zhang, Xiaoxin; Yan, Qingzhi; Lang, Shaoting; Xia, Min; Ge, Changchun

2014-09-01

The potassium doped tungsten (W-K) grade was achieved via swaging + rolling process. The swaged + rolled W-K alloy exhibited acceptable thermal conductivity of 159.1 W/m K and ductile-to-brittle transition temperature of about 873 K while inferior mechanical properties attributed to the coarse pores and small deformation degree. Then the thermal shock, fatigue resistance of the W-K grade were characterized by an electron beam facility. Thermal shock tests were conducted at absorbed power densities varied from 0.22 to 1.1 GW/m2 in a step of 0.22 GW/m2. The cracking threshold was in the range of 0.44-0.66 GW/m2. Furthermore, recrystallization occurred in the subsurface of the specimens tested at 0.66-1.1 GW/m2 basing on the analysis of microhardness and microstructure. Thermal fatigue tests were performed at 0.44 GW/m2 up to 1000 cycles and no cracks emerged throughout the tests. Moreover, recrystallization occurred after 1000 cycles.

Influence of grain orientation on evolution of surface features in fatigued polycrystalline copper: A comparison of thermal and uniaxial mechanical fatigue results

International Nuclear Information System (INIS)

Aicheler, Markus

2010-01-01

Surface state plays a major role in the crack nucleation process of pure metals in the High-Cycle-Fatigue (HCF) as well as in the Ultra-High-Cycle-Fatigue (UHCF) regime. Therefore, in studies dealing with HCF or UHCF, special attention is paid to the evolution of surface degradation during fatigue life. The accelerating structures of the future Compact Linear Collider (CLIC) under study at CERN will be submitted to a high number of thermal-mechanical fatigue cycles, arising from Radio Frequency (RF) induced eddy currents, causing local superficial cyclic heating. The number of cycles during the foreseen lifetime of CLIC reaches 2x10 11 . Fatigue may limit the lifetime of CLIC structures. In order to assess the effects of superficial fatigue, specific tests are defined and performed on polycrystalline Oxygen Free Electronic (OFE) grade Copper, a candidate material for the structures. Surface degradation depends on the orientation of near-surface grains. Copper samples thermally fatigued in two different fatigue experiments, pulsed laser and pulsed RF-heating, underwent postmortem Electron Backscattered Diffraction measurements. Samples fatigued by pulsed laser show the same trend in the orientation-fatigue damage behavior as samples fatigued by pulsed RF-heating. It is clearly observed that surface grains, oriented [1 1 1] with respect to the surface, show significantly more damage than surface grains oriented [1 0 0]. Results arising from a third fatigue experiment, the ultrasound (US) swinger, are compared to the results of the mentioned experiments. The US swinger is an uniaxial mechanical fatigue test enabling to apply within several days a total number of cycles representative of the life of the CLIC structures, thanks to a high repetition rate of 24 kHz. For comparison, laser fatigue experiments have much lower repetition rates. The dependence of surface degradation on grain orientation of samples tested by the US swinger was monitored during the fatigue life

Very high cycle fatigue testing of concrete using ultrasonic cycling

Energy Technology Data Exchange (ETDEWEB)

Karr, Ulrike; Schuller, Reinhard; Fitzka, Michael; Mayer, Herwig [Univ. of Natural Resources and Life Sciences, Vienna (Austria). Inst. of Physics and Materials Science; Denk, Andreas; Strauss, Alfred [Univ. of Natural Resources and Life Sciences, Vienna (Austria)

2017-06-01

The ultrasonic fatigue testing method has been further developed to perform cyclic compression tests with concrete. Cylindrical specimens vibrate in resonance at a frequency of approximately 20 kHz with superimposed compressive static loads. The high testing frequency allows time-saving investigations in the very high cycle fatigue regime. Fatigue tests were carried out on ''Concrete 1'' (compressive strength f{sub c} = 80 MPa) and ''Concrete 2'' (f{sub c} = 107 MPa) under purely compressive loading conditions. Experiments at maximum compressive stresses of 0.44 f{sub c} (Concrete 1) and 0.38 f{sub c} (Concrete 2) delivered specimen failures above 109 cycles, indicating that no fatigue limit exists for concrete below one billion load cycles. Resonance frequency, power required to resonate the specimen and second order harmonics of the vibration are used to monitor fatigue damage in situ. Specimens were scanned by X-ray computed tomography prior to and after testing. Fatigue cracks were produced by ultrasonic cycling in the very high cycle fatigue regime at interfaces of grains as well as in cement. The possibilities as well as limitations of ultrasonic fatigue testing of concrete are discussed.

Basic thermal–mechanical properties and thermal shock, fatigue resistance of swaged + rolled potassium doped tungsten

Energy Technology Data Exchange (ETDEWEB)

Zhang, Xiaoxin; Yan, Qingzhi, E-mail: qzyan@ustb.edu.cn; Lang, Shaoting; Xia, Min; Ge, Changchun

2014-09-15

Highlights: • The potassium doped tungsten grade was achieved via swaging + rolling process. • The cracking threshold of the W–K alloy was in the range of 0.44–0.66 GW/m{sup 2}. • Recrystallization occurred at 0.66–1.1 GW/m{sup 2} during the thermal shock tests. • No cracks emerged during the thermal fatigue tests (0.44 GW/m{sup 2}, 1000 cycles). • Recrystallization occurred after 1000 cycles during the thermal fatigue tests. - Abstract: The potassium doped tungsten (W–K) grade was achieved via swaging + rolling process. The swaged + rolled W–K alloy exhibited acceptable thermal conductivity of 159.1 W/m K and ductile-to-brittle transition temperature of about 873 K while inferior mechanical properties attributed to the coarse pores and small deformation degree. Then the thermal shock, fatigue resistance of the W–K grade were characterized by an electron beam facility. Thermal shock tests were conducted at absorbed power densities varied from 0.22 to 1.1 GW/m{sup 2} in a step of 0.22 GW/m{sup 2}. The cracking threshold was in the range of 0.44–0.66 GW/m{sup 2}. Furthermore, recrystallization occurred in the subsurface of the specimens tested at 0.66–1.1 GW/m{sup 2} basing on the analysis of microhardness and microstructure. Thermal fatigue tests were performed at 0.44 GW/m{sup 2} up to 1000 cycles and no cracks emerged throughout the tests. Moreover, recrystallization occurred after 1000 cycles.

Probabilistic multi-scale models and measurements of self-heating under multiaxial high cycle fatigue

International Nuclear Information System (INIS)

Poncelet, M.; Hild, F.; Doudard, C.; Calloch, S.; Weber, B.

2010-01-01

Different approaches have been proposed to link high cycle fatigue properties to thermal measurements under cyclic loadings, usually referred to as 'self-heating tests'. This paper focuses on two models whose parameters are tuned by resorting to self-heating tests and then used to predict high cycle fatigue properties. The first model is based upon a yield surface approach to account for stress multi-axiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of micro-plasticity at the scale of slip-planes. Both model identifications are cost effective, relying mainly on quickly obtained temperature data in self-heating tests. They both describe the influence of the stress heterogeneity, the volume effect and the hydrostatic stress on fatigue limits. The thermal effects and mean fatigue limit predictions are in good agreement with experimental results for in and out-of phase tension-torsion loadings. In the case of fatigue under non-proportional loading paths, the mean fatigue limit prediction error of the critical shear stress approach is three times less than with the yield surface approach. (authors)

Probabilistic multi-scale models and measurements of self-heating under multiaxial high cycle fatigue

Energy Technology Data Exchange (ETDEWEB)

Poncelet, M.; Hild, F. [Univ Paris 11, PRES, Univ Paris 06, LMT Cachan, ENS Cachan, CNRS, F-94235 Cachan (France); Doudard, C.; Calloch, S. [Univ Brest, ENIB, ENSIETA, LBMS EA 4325, F-29806 Brest, (France); Weber, B. [ArcelorMittal Maizieres Res Voie Romaine, F-57283 Maizieres Les Metz (France)

2010-07-01

Different approaches have been proposed to link high cycle fatigue properties to thermal measurements under cyclic loadings, usually referred to as 'self-heating tests'. This paper focuses on two models whose parameters are tuned by resorting to self-heating tests and then used to predict high cycle fatigue properties. The first model is based upon a yield surface approach to account for stress multi-axiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of micro-plasticity at the scale of slip-planes. Both model identifications are cost effective, relying mainly on quickly obtained temperature data in self-heating tests. They both describe the influence of the stress heterogeneity, the volume effect and the hydrostatic stress on fatigue limits. The thermal effects and mean fatigue limit predictions are in good agreement with experimental results for in and out-of phase tension-torsion loadings. In the case of fatigue under non-proportional loading paths, the mean fatigue limit prediction error of the critical shear stress approach is three times less than with the yield surface approach. (authors)

Fatigue diminishes motoneuronal excitability during cycling exercise.

Science.gov (United States)

Weavil, Joshua C; Sidhu, Simranjit K; Mangum, Tyler S; Richardson, Russell S; Amann, Markus

2016-10-01

Exercise-induced fatigue influences the excitability of the motor pathway during single-joint isometric contractions. This study sought to investigate the influence of fatigue on corticospinal excitability during cycling exercise. Eight men performed fatiguing constant-load (80% W peak ; 241 ± 13 W) cycling to exhaustion during which the percent increase in quadriceps electromyography (ΔEMG; vastus lateralis and rectus femoris) was quantified. During a separate trial, subjects performed two brief (∼45 s) nonfatiguing cycling bouts (244 ± 15 and 331 ± 23W) individually chosen to match the ΔEMG across bouts to that observed during fatiguing cycling. Corticospinal excitability during exercise was quantified by transcranial magnetic, electric transmastoid, and femoral nerve stimulation to elicit motor-evoked potentials (MEP), cervicomedullary evoked potentials (CMEP), and M waves in the quadriceps. Peripheral and central fatigue were expressed as pre- to postexercise reductions in quadriceps twitch force (ΔQ tw ) and voluntary quadriceps activation (ΔVA). Whereas nonfatiguing cycling caused no measureable fatigue, fatiguing cycling resulted in significant peripheral (ΔQ tw : 42 ± 6%) and central (ΔVA: 4 ± 1%) fatigue. During nonfatiguing cycling, the area of MEPs and CMEPs, normalized to M waves, similarly increased in the quadriceps (∼40%; P fatiguing cycling. As a consequence, the ratio of MEP to CMEP was unchanged during both trials (P > 0.5). Therefore, although increases in muscle activation promote corticospinal excitability via motoneuronal facilitation during nonfatiguing cycling, this effect is abolished during fatigue. We conclude that the unaltered excitability of the corticospinal pathway from start of intense cycling exercise to exhaustion is, in part, determined by inhibitory influences on spinal motoneurons obscuring the facilitating effects of muscle activation.

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

Energy Technology Data Exchange (ETDEWEB)

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.

Evolution of thermal fatigue management of piping in US LWRs

International Nuclear Information System (INIS)

McDewitt, M.; Wolfe, K.; McGill, R.

2015-01-01

Fatigue usage caused by cyclic changes of thermally stratified reactor coolant in Light Water Reactor (LWR) pressure boundary piping was not an original consideration in US Nuclear Power Plant (NPP) designs. During the mid 1980's, several events involving cracking and leakage due to thermal cycling occurred in reactor coolant system branch piping at both US and International NPPs. In 1988, the US Nuclear Regulatory Commission (US NRC) issued Bulletin 88-08 to alert LWR licensees of the potential for piping failures due to stratified thermal cycling. In response to these events, the US nuclear industry developed initiatives to identify susceptible components and established measures to monitor and prevent future failures. These initiatives have been effective in preventing leakage events, but have also identified fewer defects than expected based on screening model predictions. Improved analytical techniques are being investigated to maintain program effectiveness while minimizing unnecessary non-destructive examinations. This paper discusses the evolution of the US thermal fatigue initiatives, and analytical concepts being evaluated to improve program efficiency. (authors)

Fatigue life prediction of Ni-base thermal solar receiver tubes

Energy Technology Data Exchange (ETDEWEB)

Hartrott, Philipp von; Schlesinger, Michael [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany); Uhlig, Ralf; Jedamski, Jens [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany)

2010-07-01

Solar receivers for tower type Solar Thermal Power Plants are subjected to complex thermo-mechanical loads including fast and severe thermo-mechanical cycles. The material temperatures can reach more than 800 C and fall to room temperature very quickly. In order to predict the fatigue life of a receiver design, receiver tubes made of Alloy 625 with a wall thickness of 0.5 mm were tested in isothermal and thermo-cyclic experiments. The number of cycles to failure was in the range of 100 to 100,000. A thermo-mechanical fatigue life prediction model was set up. The model is based on the cyclic deformation of the material and the damage caused by the growth of fatigue micro cracks. The model reasonably predicts the experimental results. (orig.)

Study on Tensile Fatigue Behavior of Thermal Butt Fusion in Safety Class III High-Density Polyethylene Buried Piping in Nuclear Power Plants

Energy Technology Data Exchange (ETDEWEB)

Kim, Jong Sung; Lee, Young Ju [Sunchon National University, Suncheon (Korea, Republic of); Oh, Young Jin [KEPCO E and C, Yongin (Korea, Republic of)

2015-01-15

High-density polyethylene (HDPE) piping, which has recently been applied to safety class III piping in nuclear power plants, can be butt-joined through the thermal fusion process, which heats two fused surfaces and then subject to axial pressure. The thermal fusion process generates bead shapes on the butt fusion. The stress concentrations caused by the bead shapes may reduce the fatigue lifetime. Thus, investigating the effect of the thermal butt fusion beads on fatigue behavior is necessary. This study examined the fatigue behavior of thermal butt fusion via a tensile fatigue test under stress-controlled conditions using finite element elastic stress analysis. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low-cycle fatigue region while having a negligible effect in the medium- and high-cycle fatigue regions.

Study on Tensile Fatigue Behavior of Thermal Butt Fusion in Safety Class III High-Density Polyethylene Buried Piping in Nuclear Power Plants

International Nuclear Information System (INIS)

Kim, Jong Sung; Lee, Young Ju; Oh, Young Jin

2015-01-01

High-density polyethylene (HDPE) piping, which has recently been applied to safety class III piping in nuclear power plants, can be butt-joined through the thermal fusion process, which heats two fused surfaces and then subject to axial pressure. The thermal fusion process generates bead shapes on the butt fusion. The stress concentrations caused by the bead shapes may reduce the fatigue lifetime. Thus, investigating the effect of the thermal butt fusion beads on fatigue behavior is necessary. This study examined the fatigue behavior of thermal butt fusion via a tensile fatigue test under stress-controlled conditions using finite element elastic stress analysis. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low-cycle fatigue region while having a negligible effect in the medium- and high-cycle fatigue regions

Microstructure analysis and damage patterns of thermally cycled Ti–49.7Ni (at.%) wires

International Nuclear Information System (INIS)

Karhu, Marjaana; Lindroos, Tomi

2012-01-01

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 on 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. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. This paper concentrates on the systematic fractographic analysis of the fatigue fractured Ti–49.7Ni wires. The aim was to discover the relationships between the macro-scale behaviour and the microstructural changes of the material. During thermal cycling the surfaces of the Ti–49.7Ni wires were examined with an optical microscope. Clear connections between the detected surface defects and fracture nucleation sites were not established. Multiple cracks were initiated and grew during thermal cycling. SEM examinations showed that the fracture surfaces can be divided into different and separate zones: a smooth surface region with radial marks indicating the fatigue crack propagation area, a rougher ductile fracture surface region area and the roughest surface region on the interface of these two surfaces. It was detected that the size of the crack propagation area is related to the fatigue lives of the thermally cycled wires. Surface cracking and subsequent crack growth proved to be responsible for the accumulation of fatigue damage in the studied wires. It was detected from the fracture surface cross-sections that cracks were not initiated at the oxide layer. The major factor for nucleating the surface cracking and then shortening the

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

International Nuclear Information System (INIS)

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

1985-03-01

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. 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

Study on cylindrical specimen subjected to oligocyclic thermal fatigue

International Nuclear Information System (INIS)

Cesari, F.; Battistella, P.; Quaranta, S.; Arduino, M.

1993-01-01

During the last years the development in the analysis of the thermal fatigue phenomenon was remarkable in particularly in industry. This improvement was more and more evident on the specific power of the engines, involving a general rise in the working temperature and in the stress level of oligocyclic thermal fatigue due to the start /stop of the engine. As far as this is concerned, the theoretical capabilities of the LIN (Nuclear Engineering Laboratory of Montecuccolino) has been requested in the frame of a collaboration with the IVECO Spa of Turin in view of verifying experimental data. The investigation of the thermal fatigue consequences has been undertaken by analyzing a cylindrical sample; its material was similar to that of the engine's head. Its was axially clamped in the two extremes and subjected to repeated thermal cycles. Beginning from the first experimental results supplied by IVECO, a theoretical - numerical campaign has been started in order to attempt a correct interpretation of the experimental behavior. The computer codes adopted in this study are mainly two typical FE programs (CASTEM and ANSYS) which have been carried out in parallel. First, both the physical and mechanical experimental conditions have been accurately reproduced in the model prepared for structural analysis. Second, several runs of calculations ware worked out to obtain a stress-strain description during some load - unload cycles. The material law is obviously non-linear because the strong variations in the temperature distributions cause high stress levels well above the yielding point

Study on cylindrical specimen subjected to oligocyclic thermal fatigue

Energy Technology Data Exchange (ETDEWEB)

Cesari, F; Battistella, P [Nuclear Engineering Laboratory ' Montecuccolino' , University of Bologna (Italy); Quaranta, S; Arduino, M [IVECO Engineering, Torino (Italy)

1993-07-01

During the last years the development in the analysis of the thermal fatigue phenomenon was remarkable in particularly in industry. This improvement was more and more evident on the specific power of the engines, involving a general rise in the working temperature and in the stress level of oligocyclic thermal fatigue due to the start /stop of the engine. As far as this is concerned, the theoretical capabilities of the LIN (Nuclear Engineering Laboratory of Montecuccolino) has been requested in the frame of a collaboration with the IVECO Spa of Turin in view of verifying experimental data. The investigation of the thermal fatigue consequences has been undertaken by analyzing a cylindrical sample; its material was similar to that of the engine's head. Its was axially clamped in the two extremes and subjected to repeated thermal cycles. Beginning from the first experimental results supplied by IVECO, a theoretical - numerical campaign has been started in order to attempt a correct interpretation of the experimental behavior. The computer codes adopted in this study are mainly two typical FE programs (CASTEM and ANSYS) which have been carried out in parallel. First, both the physical and mechanical experimental conditions have been accurately reproduced in the model prepared for structural analysis. Second, several runs of calculations ware worked out to obtain a stress-strain description during some load - unload cycles. The material law is obviously non-linear because the strong variations in the temperature distributions cause high stress levels well above the yielding point.

Evaluation of fatigue damage induced by thermal striping in a T junction using the three dimensional coupling method and frequency response method

Energy Technology Data Exchange (ETDEWEB)

Kim, Sun Hye; Choi, Jae boong; Kim, Moon Ki [Sungkyunkwan Univ., Seoul (Korea, Republic of); Huh, Nam Su [Seoul Nat' l Univ., Seoul (Korea, Republic of); Lee, Jin Ho [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

2012-10-15

Thermal fatigue cracking induced by thermal stratification, cycling and striping have been observed in several PWR plants. Especially, thermal striping, the highly fluctuating thermal layer, became one of the significant problems, since it can cause un predicted high cycle thermal fatigue (HCTF) at piping systems. This problem are usually found in T junctions of energy cooling systems, where cold and hot flows with high level of turbulence mix together. Thermal striping can cause the networks of fatigue crack at the vicinity of weld parts and these cracks can propagate to significant depth in a relatively short time. Therefore, thermal striping and fatigue crack initiations should be predicted in advance to prevent the severe failure of piping systems. The final goal of this research is to develop a rational thermal and mechanical model considering thermohydraulic characteristics of thermal striping and an evaluation procedure to predict the initiation of thermal fatigue crack. As a first step, we evaluated the fatigue damage in a T junction using two widely used methods. Then, we analyzed the results of each method and conducted comparisons and verifications.

Thermal Acoustic Fatigue Apparatus

Data.gov (United States)

Federal Laboratory Consortium — The Thermal Acoustic Fatigue Apparatus (TAFA) is a progressive wave tube test facility that is used to test structures for dynamic response and sonic fatigue due to...

Study of regularities in propagation of thermal fatigue cracks

International Nuclear Information System (INIS)

Tachkova, N.G.; Sobolev, N.D.; Egorov, V.I.; Rostovtsev, Yu.V.; Ivanov, Yu.S.; Sirotin, V.L.

1978-01-01

Regularities in the propagation of thermal fatigue cracks in the Cr-Ni steels of the austenite class depending upon deformation conditions in the crack zone, have been considered. Thin-walled tube samples of the Kh16N40, Kh18N20 and Kh16N15 steels have been tested in the 10O reversible 400 deg C and 100 reversible 500 deg C regimes. The samples have possessed a slot-shaped stress concentrator. Stress intensity pseudocoefficient has been calculated for the correlation of experimental data. The formula for determining crack propagation rate has been obtained. The experiments permit to conclude that propagation rate of thermal fatigue cracks in the above steels depends upon the scope of plastic deformation during a cycle and stress intensity pseudocoefficient, and is determined by plastic deformation resistance during thermal cyclic loading

Assessment of Pressure Fluctuation Effect for Thermal Fatigue in a T-junction Using Thermo-Hydro Analysis

Energy Technology Data Exchange (ETDEWEB)

Pyo, Jaebum; Kim, Jungwoo; Huh, Namsu [Seoul National Univ. of Science and Technology, Seoul (Korea, Republic of); Kim, Sunhye [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

2013-10-15

As a result, when evaluating thermal fatigue for the mixing tee, temperature fluctuation is dominant for this phenomenon, it can be reasonably assumed that the pressure is constant on the pipe inner wall. Recently, thermal fatigue due to mixing of the fluids having different temperatures has been considered as an important issue on the fatigue evaluation of nuclear piping. Mainly, this phenomenon occurs in a T-junction operating with the fluids consisted of different temperatures. Because of the turbulent mixing of hot and cold water, the temperature on the inner wall of the pipe fluctuates rapidly, causing the variation of thermal stresses in the pipe and resulting in high cycle thermal fatigue. In practice, cracking by high cycle thermal fatigue is reported at a T-junction in the residual heat removal system at Civaux unit 1 in France. However, because of irregular flow inside the pipe, the pressure also fluctuates rapidly as well as temperature in the inner wall of the pipe. Therefore, in this paper, three-dimensional thermo-hydro analysis was performed for the mixing tee of the shutdown cooling system of the pressurized water reactor plant, examining the pressure variation at the pipe inner wall. Based on the analysis result, this study aims at assessing the pressure fluctuation effect on the thermal fatigue. In this paper, it is verified that there is pressure fluctuation as well as temperature on the inner wall of mixing tee operating with the fluids having different temperatures. However, since the amplitude of pressure is relatively smaller than design pressure of the shutdown cooling system, the effect wouldn't be important for the thermal fatigue.

Characterization of the temperature evolution during high-cycle fatigue of the ULTIMET superalloy: Experiment and theoretical modeling

Science.gov (United States)

Jiang, L.; Wang, H.; Liaw, P. K.; Brooks, C. R.; Klarstrom, D. L.

2001-09-01

High-speed, high-resolution infrared thermography, as a noncontact, full-field, and nondestructive technique, was used to study the temperature variations of a cobalt-based ULTIMET alloy subjected to high-cycle fatigue. During each fatigue cycle, the temperature oscillations, which were due to the thermal-elastic-plastic effects, were observed and related to stress-strain analyses. A constitutive model was developed for predicting the thermal and mechanical responses of the ULTIMET alloy subjected to cyclic deformation. The model was constructed in light of internal-state variables, which were developed to characterize the inelastic strain of the material during cyclic loading. The predicted stress-strain and temperature responses were found to be in good agreement with the experimental results. In addition, the change of temperature during fatigue was employed to reveal the accumulation of fatigue damage, and the measured temperature was utilized as an index for fatigue-life prediction.

High cycle thermal fatigue: benchmark at a Te junction piping system of the nuclear power plant Phenix; Fatigue a grand nombre de cycles: benchmark d'un te de tuyauterie de la centrale Phenix

Energy Technology Data Exchange (ETDEWEB)

Gelineau, O.; Simoneau, J.P. [NOVATOME, a Div. of Framatome, 69 - Lyon (France); Roubin, P. [CEA Cadarache, DER, 13 - Saint-Paul-lez-Durance (France)

2001-07-01

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.)

Damage evaluation under thermal fatigue of a vertical target full scale component for the ITER divertor

International Nuclear Information System (INIS)

Missirlian, M.; Escourbiac, F.; Merola, M.; Durocher, A.; Bobin-Vastra, I.; Schedler, B.

2007-01-01

An extensive development programme has been carried out in the EU on high heat flux components within the ITER project. In this framework, a Full Scale Vertical Target (VTFS) prototype was manufactured with all the main features of the corresponding ITER divertor design. The fatigue cycling campaign on CFC and W armoured regions, proved the capability of such a component to meet the ITER requirements in terms of heat flux performances for the vertical target. This paper discusses thermographic examination and thermal fatigue testing results obtained on this component. The study includes thermal analysis, with a tentative proposal to evaluate with finite element approach the location/size of defects and the possible propagation during fatigue cycling

Thermal fatigue behavior of a SUS304 pipe under longitudinal cyclic movement of axial temperature distribution

International Nuclear Information System (INIS)

Yamauchi, Masafumi; Ohtani, Tomomi; Takahashi, Yukio

1996-01-01

In a structural thermal fatigue test which imposed an oscillating axial temperature distribution on a SUS 304 pipe specimens, different crack initiation lives were observed between the inner and the outer surfaces, although the values of the von-Mises equivalent strain range calculated by FEM inelastic analysis were almost the same for both surfaces. The outer surface condition was an in-phase thermal cycle and an almost uniaxial cyclic stress (low hydrostatic stress). The inner surface condition was an out-of-phase thermal cycle and an almost equibiaxial cyclic stress (high hydrostatic stress). A uniaxial thermal fatigue test was performed under the simulated conditions of the outer and inner surfaces of the pipe specimen. The in-phase uniaxial thermal fatigue test result was in good agreement with the test result of the pipe specimen for the outer surface. The out-of-phase uniaxial thermal fatigue test which simulated the inner surface condition, showed a longer life than the in-phase uniaxial test, and thus contradicted the result of the structural model test. However, the structural model test life for the inner surface agreed well with the uniaxial experimental measurement when the strain range of the inner surface was corrected by a triaxiality factor

In-Pile thermal fatigue of First Wall mock-ups under ITER relevant conditions

International Nuclear Information System (INIS)

Blom, F.; Schmalz, F.; Kamer, S.; Ketema, D.J.

2006-01-01

The objective of this study is to perform in-pile thermal fatigue testing of three actively cooled First Wall (FW) mock-ups to check the effect of neutron irradiation on the Be/CuCrZr joints under representative FW operation conditions. Three FW mock-ups with Beryllium armor tiles will be neutron irradiated at 1 dpa (in Be) with parallel thermal fatigue testing for 30,000 cycles. The temperatures, stress distributions and stress amplitudes at the Be/CuCrZr interface of the mock-ups will be as close as possible to the values calculated for ITER FW panels. For this objective the PWM mocks-up subjected to thermal fatigue will be integrated with high density (W) plates on the Be-side to provide heat flux by nuclear heating. The assembly will be placed in the pool-side facility of the HFR and thermal cycling is then arranged by mechanical movement towards and from the core box. As the thermal design of the irradiation rig is very critical a pilot-irradiation will be performed to cross check the models used in the thermal design of the rig. The project is currently in the design phase of both the pilot and actual irradiation rig. The irradiation of the actual rig is planned to start at mid 2007 and last for two years. (author)

Crack growth prediction for low-cycle fatigue regime

International Nuclear Information System (INIS)

Kamaya, Masayuki

2017-01-01

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

Thermal fatigue behavior of valves

International Nuclear Information System (INIS)

Moinereau, D.; Scliffet, L.; Capion, J.C.; Genette, P.

1991-01-01

This paper reports that valves of pressurized water reactors are exposed to thermal shocks during transient operations. The numerous thermal shock tests performed on valves on the EDF test facilities have shown the sensibility of fillets and geometrical discontinuities to thermal fatigue: cracks can appear in those areas and grow through the valve body. Valves systems designated as level 1 must be designed to withstand fatigue up to the second isolation valve: the relevant rule is specified in the paragraph B 3500 of the French RCCM code. It is a simplified method which doesn't require finite element calculations. Many valve systems have been designed according to this rule and have been operated without accident. However, in one case, important cracks were found in the fillet of a check-valve after numerous thermal shocks. Calculation of the valve's behavior according to the RCCM code to estimate the fatigue damage resulting from thermal shocks led to a low damage factor, which doesn't agree with the experimental results. This was confirmed by new testings and showed the inadequacy of B 3500 rule for thermal transients. On this base a new rule is proposed to estimate fatigue damage resulting from thermal shocks. An experimental program has been realized to validate this rule. Axisymetrical analytical mock-ups with different geometries and one check-valve in austenitic stainless steel 316 L have been submitted to hot thermal shocks of 210 degrees C magnitude

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

International Nuclear Information System (INIS)

Ando, Kotoji; Takahashi, Koji; Matsuo, Kazuya; Urabe, Yoshio

2013-01-01

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)

Influence of Thermal Aging on Tensile and Low Cycle Fatigue Behavior of Type 316LN Austenitic Stainless Steel Weld Joint

Science.gov (United States)

Suresh Kumar, T.; Nagesha, A.; Ganesh Kumar, J.; Parameswaran, P.; Sandhya, R.

2018-05-01

Influence of short-term thermal aging on the low-cycle fatigue (LCF) behavior of 316LN austenitic stainless steel weld joint with 0.07 wt pct N has been investigated. Prior thermal exposure was found to improve the fatigue life compared with the as-welded condition. Besides, the treatment also imparted a softening effect on the weld metal, leading to an increase in the ductility of the weld joint which had a bearing on the cyclic stress response. The degree of cyclic hardening was seen to increase after aging. Automated ball-indentation (ABI) technique was employed toward understanding the mechanical properties of individual zones across the weld joint. It was observed that the base metal takes most of the applied cyclic strain during LCF deformation in the as-welded condition. In the aged condition, however, the weld also participates in the cyclic deformation. The beneficial effect of thermal aging on cyclic life is attributed to a reduction in the severity of the metallurgical notch leading to a restoration of ductility of the weld region. The transformation of δ-ferrite to σ-phase during the aging treatment was found to influence the location of crack initiation. Fatigue cracks were found to initiate in the base metal region of the joint in most of the testing conditions. However, embrittlement in the weld metal caused a shift in the point of crack initiation with increasing strain amplitude under LCF.

Thermal fatigue life evaluation of SnAgCu solder joints in a multi-chip power module

Science.gov (United States)

Barbagallo, C.; Malgioglio, G. L.; Petrone, G.; Cammarata, G.

2017-05-01

For power devices, the reliability of thermal fatigue induced by thermal cycling has been prioritized as an important concern. The main target of this work is to apply a numerical procedure to assess the fatigue life for lead-free solder joints, that represent, in general, the weakest part of the electronic modules. Starting from a real multi-chip power module, FE-based models were built-up by considering different conditions in model implementation in order to simulate, from one hand, the worst working condition for the module and, from another one, the module standing into a climatic test room performing thermal cycles. Simulations were carried-out both in steady and transient conditions in order to estimate the module thermal maps, the stress-strain distributions, the effective plastic strain distributions and finally to assess the number of cycles to failure of the constitutive solder layers.

Thermal fatigue life evaluation of SnAgCu solder joints in a multi-chip power module

International Nuclear Information System (INIS)

Barbagallo, C; Petrone, G; Cammarata, G; Malgioglio, G L

2017-01-01

For power devices, the reliability of thermal fatigue induced by thermal cycling has been prioritized as an important concern. The main target of this work is to apply a numerical procedure to assess the fatigue life for lead-free solder joints, that represent, in general, the weakest part of the electronic modules. Starting from a real multi-chip power module, FE-based models were built-up by considering different conditions in model implementation in order to simulate, from one hand, the worst working condition for the module and, from another one, the module standing into a climatic test room performing thermal cycles. Simulations were carried-out both in steady and transient conditions in order to estimate the module thermal maps, the stress-strain distributions, the effective plastic strain distributions and finally to assess the number of cycles to failure of the constitutive solder layers. (paper)

The origins of Asteroidal rock disaggregation: Interplay of thermal fatigue and microstructure

Science.gov (United States)

Hazeli, Kavan; El Mir, Charles; Papanikolaou, Stefanos; Delbo, Marco; Ramesh, K. T.

2018-04-01

The distributions of size and chemical composition in regolith on airless bodies provide clues to the evolution of the solar system. Recently, the regolith on asteroid (25143) Itokawa, visited by the JAXA Hayabusa spacecraft, was observed to contain millimeter to centimeter sized particles. Itokawa boulders commonly display well-rounded profiles and surface textures that appear inconsistent with mechanical fragmentation during meteorite impact; the rounded profiles have been hypothesized to arise from rolling and movement on the surface as a consequence of seismic shaking. This investigation provides a possible explanation of these observations by exploring the primary crack propagation mechanism during thermal fatigue of a chondrite. Herein, we present the evolution of the full-field strains on the surface as a function of temperature and microstructure, and examine the crack growth during thermal cycling. Our experimental results demonstrate that thermal-fatigue-driven fracture occurs under these conditions. The results suggest that the primary fatigue crack path preferentially follows the interfaces between monominerals, leaving the minerals themselves intact after fragmentation. These observations are explained through a microstructure-based finite element model that is quantitatively compared with our experimental results. These results on the interactions of thermal fatigue cracking with the microstructure may ultimately allow us to distinguish between thermally induced fragments and impact products.

Thermal fatigue evaluation of piping system Tee-connections

International Nuclear Information System (INIS)

Metzner, K.J.; Braillard, O.; Faidy, C.; Marcelles, I.; Solin, J.; Stumpfrock, L.

2004-01-01

Thermal fatigue is one significant long-term degradation mechanism nuclear power plants (NPP), in particular, as operating plants become older and life time extension activities have been initiated. In general, the common thermal fatigue issues are understood and controlled by plant instrumentation systems. However, incidents in some plants indicate that certain piping system Tees are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentation. The THERFAT project has been initiated to advance the accuracy and reliability of thermal fatigue load determination in engineering tools and research oriented approaches to outline a science based practical methodology for managing thermal fatigue risks in Tee-connections susceptible to high cyclic thermal fatigue. (orig.)

Effects of carbon content on high-temperature mechanical and thermal fatigue properties of high-boron austenitic steels

Directory of Open Access Journals (Sweden)

Xiang Chen

2016-01-01

Full Text Available High-temperature mechanical properties of high-boron austenitic steels (HBASs were studied at 850 °C using a dynamic thermal-mechanical simulation testing machine. In addition, the thermal fatigue properties of the alloys were investigated using the self-restraint Uddeholm thermal fatigue test, during which the alloy specimens were cycled between room temperature and 800°C. Stereomicroscopy and scanning electron microscopy were used to study the surface cracks and cross-sectional microstructure of the alloy specimens after the thermal fatigue tests. The effects of carbon content on the mechanical properties at room temperature and high-temperature as well as thermal fatigue properties of the HBASs were also studied. The experimental results show that increasing carbon content induces changes in the microstructure and mechanical properties of the HBASs. The boride phase within the HBAS matrix exhibits a round and smooth morphology, and they are distributed in a discrete manner. The hardness of the alloys increases from 239 (0.19wt.% C to 302 (0.29wt.% C and 312 HV (0.37wt.% C; the tensile yield strength at 850 °C increases from 165.1 to 190.3 and 197.1 MPa; and the compressive yield strength increases from 166.1 to 167.9 and 184.4 MPa. The results of the thermal fatigue tests (performed for 300 cycles from room temperature to 800 °C indicate that the degree of thermal fatigue of the HBAS with 0.29wt.% C (rating of 2–3 is superior to those of the alloys with 0.19wt.% (rating of 4–5 and 0.37wt.% (rating of 3–4 carbon. The main cause of this difference is the ready precipitation of M23(C,B6-type borocarbides in the alloys with high carbon content during thermal fatigue testing. The precipitation and aggregation of borocarbide particles at the grain boundaries result in the deterioration of the thermal fatigue properties of the alloys.

Estimates of thermal fatigue due to beam interruptions for an ALMR-type ATW

International Nuclear Information System (INIS)

Dunn, F. E.; Wade, D. C.

1999-01-01

Thermal fatigue due to beam interruptions has been investigated in a sodium cooled ATW using the Advanced Liquid Metal mod B design as a basis for the subcritical source driven reactor. A k eff of 0.975 was used for the reactor. Temperature response in the primary coolant system was calculated, using the SASSYS- 1 code, for a drop in beam current from full power to zero in 1 microsecond.. Temperature differences were used to calculate thermal stresses. Fatigue curves from the American Society of Mechanical Engineers Boiler and Pressure Vessel Code were used to determine the number of cycles various components should be designed for, based on these thermal stresses

Effect of high pressure hydrogen on low-cycle fatigue

International Nuclear Information System (INIS)

Rie, K.T.; Kohler, W.

1979-01-01

It has been shown that the fatigue life can be influenced in low-cycle range by high pressure hydrogen while the effect of high pressure hydrogen on high-cycle fatigue will not be as significant. The paper reports the details and the results of the investigations of the effect of high pressure hydrogen on the low-cycle endurance of commercially pure titanium. The results of this study indicate that: 1. The degradation of the fatigue life in low-cycle region for commercially pure titanium under high pressure hydrogen can be described by Nsub(cr)sup(α x Δepsilon)sub(pl)sup(=c) 2. The fatigue life decreases with decreasing strain rate. 3. The fatigue life decreases with increasing hydrogen pressure. It was found that the semilogarithmic plot of the fatigue life versus the hydrogen pressure gives a linear relationship. The Sievert's law does not hold in low-cycle fatigue region. 4. HAC in titanium in low-cycle fatigue region is the result of the disolution of hydrogen at the crack tip and of the strain-induced hybride formation. (orig.) 891 RW/orig. 892 RKD [de

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

International Nuclear Information System (INIS)

Cabet, Celine; Carroll, Laura; Wright, Richard

2013-01-01

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)

Effects of irradiation on low cycle fatigue properties for reduced activation ferritic/martensitic steel

International Nuclear Information System (INIS)

Kim, S.W.; Tanigawa, H.; Hirose, T.; Kohyama, A.

2007-01-01

Full text of publication follows: In materials life decision for a commercial blanket, thermal fatigue property of materials is a particularly important. The loading of structural materials in fusion reactor is, besides the plasma surface interactions, a combined effect of high heat fluxes and neutron irradiation. Depending on the pulse lengths, the operating conditions, and the thermal conductivity, these oscillating temperature gradients will cause elastic and elastic-plastic cyclic deformation giving rise to (creep-) fatigue in structural first wall and blanket components. Especially, investigation of the fatigue property in Reduced Activation Ferritic/Martensitic (RAF/M) steel and establishment of the evaluation technology are demanded in particular immediately for design/manufacturing of ITER-TBM. And also, fatigue testing after irradiation will be carried out in hot cells with remote control system. Considering limited ability of specimen manipulation in the cells, the specimen and the test method need to be simple for operation. The existing data bases of RAF/M steel provide baseline data set including post-irradiation fatigue data. However, to perform the accurate fatigue lifetime assessment for ITER-TBM and beyond utilizing the existing data base, the mechanical understanding of fatigue fracture is mandatory. It has been previously reported by co-authors that dislocation cell structure was developed on low cycle fatigued RAF/M steel, and led the fatigue crack to develop along prior austenitic grain boundary. In this work, the effects of nuclear irradiation on low cycle fatigue properties for RAF/M steels and its fracture mechanisms were examined based on the flow stress analysis and detailed microstructure analysis. Fracture surfaces and crack initiation site were investigated by scanning electron microscope (SEM). Transmission electron microscopy (TEM) was also applied to clarify the microstructural features of fatigue behavior. It is also important to

Effects of irradiation on low cycle fatigue properties for reduced activation ferritic/martensitic steel

Energy Technology Data Exchange (ETDEWEB)

Kim, S.W. [Kyoto Univ., Graduate School of Energy Science (Japan); Tanigawa, H. [Japan Atomic Energy Agency, Tokai-mura, Naga-gun, Ibaraki-ken (Japan); Hirose, T. [Blanket Engineering Group, Japan Atomic Energy Agency, Naka, Ibaraki (Japan); Kohyama, A. [Kyoto Univ., lnstitute of Advanced Energy (Japan)

2007-07-01

Full text of publication follows: In materials life decision for a commercial blanket, thermal fatigue property of materials is a particularly important. The loading of structural materials in fusion reactor is, besides the plasma surface interactions, a combined effect of high heat fluxes and neutron irradiation. Depending on the pulse lengths, the operating conditions, and the thermal conductivity, these oscillating temperature gradients will cause elastic and elastic-plastic cyclic deformation giving rise to (creep-) fatigue in structural first wall and blanket components. Especially, investigation of the fatigue property in Reduced Activation Ferritic/Martensitic (RAF/M) steel and establishment of the evaluation technology are demanded in particular immediately for design/manufacturing of ITER-TBM. And also, fatigue testing after irradiation will be carried out in hot cells with remote control system. Considering limited ability of specimen manipulation in the cells, the specimen and the test method need to be simple for operation. The existing data bases of RAF/M steel provide baseline data set including post-irradiation fatigue data. However, to perform the accurate fatigue lifetime assessment for ITER-TBM and beyond utilizing the existing data base, the mechanical understanding of fatigue fracture is mandatory. It has been previously reported by co-authors that dislocation cell structure was developed on low cycle fatigued RAF/M steel, and led the fatigue crack to develop along prior austenitic grain boundary. In this work, the effects of nuclear irradiation on low cycle fatigue properties for RAF/M steels and its fracture mechanisms were examined based on the flow stress analysis and detailed microstructure analysis. Fracture surfaces and crack initiation site were investigated by scanning electron microscope (SEM). Transmission electron microscopy (TEM) was also applied to clarify the microstructural features of fatigue behavior. It is also important to

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

Science.gov (United States)

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.

Numerical analysis and nuclear standard code application to thermal fatigue

International Nuclear Information System (INIS)

Merola, M.

1992-01-01

The present work describes the Joint Research Centre Ispra contribution to the IAEA benchmark exercise 'Lifetime Behaviour of the First Wall of Fusion Machines'. The results of the numerical analysis of the reference thermal fatigue experiment are presented. Then a discussion on the numerical analysis of thermal stress is tackled, pointing out its particular aspects in view of their influence on the stress field evaluation. As far as the design-allowable number of cycles are concerned the American nuclear code ASME and the French code RCC-MR are applied and the reasons for the different results obtained are investigated. As regards a realistic fatigue lifetime evaluation, the main problems to be solved are brought out. This work, is intended as a preliminary basis for a discussion focusing on the main characteristics of the thermal fatigue problem from both a numerical and a lifetime assessment point of view. In fact the present margin of discretion left to the analyst may cause undue discrepancies in the results obtained. A sensitivity analysis of the main parameters involved is desirable and more precise design procedures should be stated

Thermal stress analysis and thermo-mechanical fatigue for gas turbine blade

International Nuclear Information System (INIS)

Hyun, J. S.; Kim, B. S.; Kang, M. S.; Ha, J. S.; Lee, Y. S.

2002-01-01

The numerical analysis for gas turbine blades were carried out under several conditions by compounding temperature field, velocity field, thermal conduction of blade, and cooling heat transfer. The three types of 1,100 deg. C class 1st-stage gas turbine blades were analyzed. The analysis results are applied to the study on evaluating the remaining life for thermo-mechanical fatigue life. The thermo-mechanical fatigue experiments under out-of-phase and in-phase have been performed. The physical-based life prediction models which considered the contribution of different damage mechanisms have been applied. These models were applied to the temperature and strain rate dependences of isothermal cycling fatigue lives, and the strain-temperature history effect on the thermo-mechanical fatigue lives

Proceedings of the specialists meeting on experience with thermal fatigue in LWR piping caused by mixing and stratification

International Nuclear Information System (INIS)

1998-01-01

This specialists meeting on experience with thermal fatigue in LWR piping caused by mixing and stratification, was held in June 1998 in Paris. It included five sessions. Session 1: operating experience (7 papers): Historical perspective; EDF experience with local thermohydraulic phenomena in PWRs: impacts and strategies; Thermal fatigue in safety injection lines of French PWRs: technical problems, regulatory requirements, concerns about other areas; US NRC Regulatory perspective on unanticipated thermal fatigue in LWR piping; Failure to the Residual Heat Removal system suction line pipe in Genkai unit 1 caused by thermal stratification cycling; Emergency Core Cooling System pipe crack incident at Tihange unit 1; Two leakages induced by thermal stratification at the Loviisa power plant). Session 2: thermal hydraulic phenomena (5 papers): Thermal stratification in small pipes with respect to fatigue effects and so called 'Banana effect'; Thermal stratification in the surge line of the Korean next generation reactor; Thermal stratification in horizontal pipes investigated in UPTF-TRAM and HDR facilities; Research on thermal stratification in un-isolable piping of reactor pressure boundary; Thermal mixing phenomena in piping systems: 3D numerical simulation and design considerations. Session 3: response of material and structure (5 papers): Fatigue induced by thermal stratification, Results of tests and calculations of the COUFAST model; Laboratory simulation of thermal fatigue cracking as a basis for verifying life models; Thermo-mechanical analysis methods for the conception and the follow up of components submitted to thermal stratification transients; Piping analysis methods of a PWR surge line for stratified flow; The thermal stratification effect on surge lines, The VVER estimation. Session 4: monitoring aspects (4 papers): Determination of the thermal loadings affecting the auxiliary lines of the reactor coolant system in French PWR plants; Expected and

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-10-01

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

Thermal fatigue loading for a type 304-L stainless steel used for pressure water reactor: investigations on the effect of a nearly perfect biaxial loading, and on the cumulative fatigue life

International Nuclear Information System (INIS)

Fissolo, A.; Gourdin, C.; Bouin, P.; Perez, G.

2010-01-01

Fatigue-life curves are used in order to estimate crack-initiation, and also to prevent water leakage on Pressure Water Reactor pipes. Such curves are built exclusively from push-pull tests performed under constant and uniaxial strain or stress-amplitude. However, thermal fatigue corresponds to a nearly perfect biaxial stress state and severe loading fluctuations are observed in operating conditions. In this frame, these two aspects have been successively investigated in this paper: In order to investigate on potential difference between thermal fatigue and mechanical fatigue, tests have been carried out at CEA using thermal fatigue devices. They show that for an identical level of strain-amplitude, the number of cycles required to achieve crack-initiation is significantly lower under thermal fatigue. This enhanced damage results probably from a perfect biaxial state under thermal fatigue. In this frame, application of the multiaxial Zamrik's criterion seems to be very promising. In order to investigate on cumulative damage effect in fatigue, multi-level strain controlled fatigue tests have been performed. Experimental results show that linear Miner's rule is not verified. A loading sequence effect is clearly evidenced. The double linear damage rule ('DLDR') improves significantly predictions of fatigue-life. (authors)

Thermal fatigue behaviour for a 316 L type steel

Science.gov (United States)

Fissolo, A.; Marini, B.; Nais, G.; Wident, P.

1996-10-01

This paper deals with initiation and growth of cracks produced by thermal fatigue loadings on 316 L steel, which is a reference material for the first wall of the next fusion reactor ITER. Two types of facilities have been built. As for true components, thermal cycles have been repeatedly applied on the surface of the specimen. The first is mainly concerned with initiation, which is detected with a light microscope. The second allows one to determine the propagation of a single crack. Crack initiation is analyzed using the French RCC-MR code procedure, and the strain-controlled isothermal fatigue curves. To predict crack growth, a model previously proposed by Haigh and Skelton is applied. This is based on determination of effective stress intensity factors, which takes into account both plastic strain and crack closure phenomena. It is shown that estimations obtained with such methodologies are in good agreement with experimental data.

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

International Nuclear Information System (INIS)

Betts, C.; Judd, A.M.; Lewis, M.W.J.

1994-01-01

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

Thermal fatigue cracking of austenitic stainless steels

International Nuclear Information System (INIS)

Fissolo, A.

2001-01-01

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

Thermal cycling fatigue of organic thermal interface materials using a thermal-displacement measurement technique

Science.gov (United States)

Steill, Jason Scott

The long term reliability of polymer-based thermal interface materials (TIM) is essential for modern electronic packages which require robust thermal management. The challenge for today's materials scientists and engineers is to maximize the heat flow from integrated circuits through a TIM and out the heat sink. Thermal cycling of the electronic package and non-uniformity in the heat flux with respect to the plan area can lead to void formation and delamination which re-introduces inefficient heat transfer. Measurement and understanding at the nano-scale is essential for TIM development. Finding and documenting the evolution of the defects is dependent upon a full understanding of the thermal probes response to changing environmental conditions and the effects of probe usage. The response of the thermal-displacement measurement technique was dominated by changes to the environment. Accurate measurement of the thermal performance was hindered by the inability to create a model system and control the operating conditions. This research highlights the need for continued study into the probe's thermal and mechanical response using tightly controlled test conditions.

Specific features of high-cycle and ultra-high-cycle fatigue

Czech Academy of Sciences Publication Activity Database

Lukáš, Petr; Kunz, Ludvík

2002-01-01

Roč. 25, - (2002), s. 747-753 ISSN 8756-758X R&D Projects: GA AV ČR KSK1010104; GA AV ČR IAA2041002 Institutional research plan: CEZ:AV0Z2041904 Keywords : ultra high cycle fatigue * fatigue mechanisms * cyclic plastic deformation Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.701, year: 2002

Thermal-mechanical fatigue of high temperature structural materials

Science.gov (United States)

Renauld, Mark Leo

Experimental and analytical methods were developed to address the effect of thermal-mechanical strain cycling on high temperature structural materials under uniaxial and biaxial stress states. Two materials were used in the investigation, a nickel-base superalloy of low ductility, IN-738LC and a high ductility material, 316 stainless steel. A uniaxial life prediction model for the IN-738LC material was based on tensile hysteresis energy measured in stabilized, mid-life hysteresis loops. Hold-time effects and temperature cycling were incorporated in the hysteresis energy approach. Crack growth analysis was also included in the model to predict the number of TMF cycles to initiate and grow a fatigue crack through the coating. The nickel-base superalloy, IN-738LC, was primarily tested in out-of-phase (OP) TMF with a temperature range from 482-871sp°C (900-1600sp°F) under continuous and compressive hold-time cycling. IN-738LC fatigue specimens were coated either with an aluminide, NiCoCrAlHfSi overlay or CoNiCrAlY overlay coating on the outer surface of the specimen. Metallurgical failure analysis via optical and scanning electron microscopy, was used to characterize failure behavior of both substrate and coating materials. Type 316 SS was subjected to continuous biaxial strain cycling with an in-phase (IP) TMF loading and a temperature range from 399-621sp°C (750-1150sp°F). As a result, a biaxial TMF life prediction model was proposed on the basis of an extended isothermal fatigue model. The model incorporates a frequency effect and phase factors to assess the different damage mechanisms observed during TMF loading. The model was also applied to biaxial TMF data generated on uncoated IN-738LC.

Method for identification of fluid mixing zones subject to thermal fatigue damage

International Nuclear Information System (INIS)

Vole, O.; Beaud, F.

2009-01-01

High cycle thermal fatigue due to the mixing of hot and cold fluids may initiate cracking in pipes of safety related circuits. A method has been developed to identify such fluid mixing zones subjected to potential thermal fatigue damage. This method is based on a loading model and a mechanical model that depend on the main characteristics of the mixing zone and on the material properties. It is supported by a large experimental program. This method has been applied to all the mixing zones of safety related circuits of the EDF pressurised water reactors, allowing to identify sensitive zones and to apply an appropriate inspection program that ensures the control of the risk due to this damage mechanism. (authors)

Effect of thermal fatigue on the structure and properties of Ni3Al-based alloy single crystals

Science.gov (United States)

Povarova, K. B.; Drozdov, A. A.; Bazyleva, O. A.; Bulakhtina, M. A.; Alad'ev, N. A.; Antonova, A. V.; Arginbaeva, E. G.; Morozov, A. E.

2014-05-01

The effect of thermal fatigue during tests of and single crystals according to the schedules 100 ai 850°C, 100 ai 1050°C, 100 ai 1100°C at a peak-to-peak stress Δσtc = 700-1000 MPa (sum of the maximum tensile and compressive stresses in a thermal cycle) on the structure, the fracture, and the fatigue life of an Ni3Al-based VKNA-1V alloy is studied. It is found that, at 103 thermal cycles, the single crystals have the maximum thermal fatigue resistance at the maximum cycle temperature of 850 and 1050°C, and the properties of the and samples are almost the same at the maximum thermal cycle temperature of 1100°C. After thermal cycling at the maximum temperature of 850°C, the γ layers in the two-phase γ' + γ region in dendrites remain a single-phase structure, as in the as-cast material, and the layer thickness is 100-150 nm. When the maximum thermal cycle temperature increases to 1050 or 1100°C, the discontinuous γ-phase layers in the γ'(Ni3Al) matrix change their morphology and become shorter and wider (their thickness is 300-700 nm). The nickel-based supersaturated solid solution in these layers decomposes with the formation of secondary γ'(Ni3Al)-phase (γ'sec) precipitates in the form of cuboids 50 and 100 nm in size at the maximum cycle temperature of 1050 and 1100°C, respectively. The alternating stresses that appear during thermal cycling cause plastic deformation. As in nickel superalloys, this deformation at the first stage proceeds via the slip of screw dislocations along octahedral {111} planes. Networks of 60° dislocation segments form at γ'/γ interfaces in this case. Fracture begins at the lines of intersection of the slip planes of the {111} octahedron with the sample surface. During fractional, a crack passes from one octahedral plane to another and forms terraces and steps (crystallographic fracture); as a result, the fracture surface bends and becomes curved. In all cases, the fracture surfaces have a mixed brittle-ductile character

Development of thermal fatigue evaluation methods of piping systems

International Nuclear Information System (INIS)

Kasahara, Naoto; Itoh, Takamoto; Okazaki, Masakazu; Okuda, Yukihiko; Kamaya, Masayuki; Nakamura, Akira; Nakamura, Hitoshi; Machida, Hideo; Matsumoto, Masaaki

2013-01-01

Nuclear piping has various kinds of thermal fatigue failure modes. Main causes of thermal loads are structural responses to fluid temperature changes during plant operation. These phenomena have complex mechanisms and so many patterns, that their problems still occur even though well-known issues. To prevent thermal fatigue due to above thermal loads, the JSME guideline is adopted. Both thermal load and fatigue failure mechanism have been investigated and summarized into the knowledgebase. Based on above knowledge, improved methods for the JSME guideline and Numerical simulation methods for thermal fatigue evaluation were studied. Furthermore, probabilistic failure analysis approach with main influence parameters were investigated to be applied for the plant system safety. (author)

Thermal fatigue behaviour for a 316 L type steel

International Nuclear Information System (INIS)

Fissolo, A.; Marini, B.; Nais, G.; Wident, P.

1996-01-01

This paper deals with initiation and growth of cracks produced by thermal fatigue loadings on 316 L steel, which is a reference material for the first wall of the next fusion reactor ITER. Two types of facilities have been built. As for true components, thermal cycles have been repeatedly applied on the surface of the specimen. The first is mainly concerned with initiation, which is detected with a light microscope. The second allows one to determine the propagation of a single crack. Crack initiation is analyzed using the French RCC-MR code procedure, and the strain-controlled isothermal fatigue curves. To predict crack growth, a model previously proposed by Haigh and Skelton is applied. This is based on determination of effective stress intensity factors, which takes into account both plastic strain and crack closure phenomena. It is shown that estimations obtained with such methodologies are in good agreement with experimental data. (orig.)

Analysis of thermal fatigue events in light water reactors

Energy Technology Data Exchange (ETDEWEB)

Okuda, Yasunori [Institute of Nuclear Safety System Inc., Seika, Kyoto (Japan)

2000-09-01

Thermal fatigue events, which may cause shutdown of nuclear power stations by wall-through-crack of pipes of RCRB (Reactor Coolant Pressure Boundary), are reported by licensees in foreign countries as well as in Japan. In this paper, thermal fatigue events reported in anomalies reports of light water reactors inside and outside of Japan are investigated. As a result, it is clarified that the thermal fatigue events can be classified in seven patterns by their characteristics, and the trend of the occurrence of the events in PWRs (Pressurized Water Reactors) has stronger co-relation to operation hours than that in BWRs (Boiling Water Reactors). Also, it is concluded that precise identification of locations where thermal fatigue occurs and its monitoring are important to prevent the thermal fatigue events by aging or miss modification. (author)

Thermal fatigue evaluation of partially cooled pipes

International Nuclear Information System (INIS)

Kawasaki, N.; Kasahara, N.; Takasho, H.

2004-01-01

Concerning thermal striping phenomenon with a cold/hot spot, effect of the thermal spot on fatigue strength was investigated. The thermal spot causes membrane stress and enhances bending stress in the structure. Increased stress shortens the fatigue life and accelerates the crack propagation rate. The mechanism to increase stress was found to be the structural constraint of thermal strain by the thermal spot. To consider this mechanism, constraint efficiency factors were introduced to the thermal stress evaluation method based on frequency transfer functions developed by authors. Proposed method with these factors was validated through comparisons with cyclic FEA considering thermal spots. (orig.)

Monitoring Low-Cycle Fatigue Material-Degradation by Ultrasonic Methods

Directory of Open Access Journals (Sweden)

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.

Effect of tungsten and tantalum on the low cycle fatigue behavior of reduced activation ferritic/martensitic steels

Energy Technology Data Exchange (ETDEWEB)

Shankar, Vani, E-mail: vani@igcar.gov.in [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603102 (India); Mariappan, K.; Nagesha, A.; Prasad Reddy, G.V.; Sandhya, R.; Mathew, M.D.; Jayakumar, T. [Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam-603102 (India)

2012-05-15

Highlights: Black-Right-Pointing-Pointer Effect of tungsten and tantalum on low cycle fatigue behavior of RAFM steels. Black-Right-Pointing-Pointer Both alloying elements W and Ta improved fatigue life. Black-Right-Pointing-Pointer Increase in Ta content improved fatigue life more than W. Black-Right-Pointing-Pointer Optimization of W content at 1.4 wt.%. Black-Right-Pointing-Pointer Softening behavior closely related to W and Ta content. - Abstract: Reduced activation ferritic/martensitic (RAFM) steels are candidate materials for the test blanket modules of International Thermonuclear Experimental Reactor (ITER). Several degradation mechanisms such as thermal fatigue, low cycle fatigue, creep fatigue interaction, creep, irradiation hardening, swelling and phase instability associated irradiation embrittlement must be understood in order to estimate the component lifetime and issues concerning the structural integrity of components. The current work focuses on the effect of tungsten and tantalum on the low cycle fatigue (LCF) behavior of RAFM steels. Both alloying elements tungsten and tantalum improved the fatigue life. Influence of Ta on increasing fatigue life was an order of magnitude higher than the influence of W on improving the fatigue life. Based on the present study, the W content was optimized at 1.4 wt.%. Softening behavior of RAFM steels showed a strong dependence on W and Ta content in RAFM steels.

Fatigue Life Analysis and Prediction of 316L Stainless Steel Under Low Cycle Fatigue Loading

Energy Technology Data Exchange (ETDEWEB)

Oh, Hyeong; Myung, NohJun; Choi, Nak-Sam [Hanyang Univ., Seoul (Korea, Republic of)

2016-12-15

In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.

Low cycle fatigue behavior of titanium carbide coated molybdenum

International Nuclear Information System (INIS)

Nishi, Hiroshi; Oku, Tatsuo; Kodaira, Tsuneo; Kikuyama, Toshihiko

1985-09-01

Sintered molybdenum coated by TiC is used for the first wall such as a troidal fixed limiter and a magnetic limiter plate in JT-60, that is being operated at JAERI presently. This report describes the low cycle fatigue behavior of sintered molybdenum and the influence of TiC coating on fatigue strength. The low cycle fatigue test was conducted at room temperature and 500 0 C. The test results was also analyzed by fractographic observation, metallography and element analysis using EPMA. The low cycle fatigue strength of the molybdenum coated by TiC at 500 0 C is decreased compared with the one at room temperature. (author)

Multiaxial low cycle fatigue life under non-proportional loading

International Nuclear Information System (INIS)

Itoh, Takamoto; Sakane, Masao; Ohsuga, Kazuki

2013-01-01

A simple and clear method of evaluating stress and strain ranges under non-proportional multiaxial loading where principal directions of stress and strain are changed during a cycle is needed for assessing multiaxial fatigue. This paper proposes a simple method of determining the principal stress and strain ranges and the severity of non-proportional loading with defining the rotation angles of the maximum principal stress and strain in a three dimensional stress and strain space. This study also discusses properties of multiaxial low cycle fatigue lives for various materials fatigued under non-proportional loadings and shows an applicability of a parameter proposed by author for multiaxial low cycle fatigue life evaluation

Materials performance in prototype Thermal Cycling Absorption Process (TCAP) columns

International Nuclear Information System (INIS)

Clark, E.A.

1992-01-01

Two prototype Thermal Cycling Absorption Process (TCAP) columns have been metallurgically examined after retirement, to determine the causes of failure and to evaluate the performance of the column container materials in this application. Leaking of the fluid heating and cooling subsystems caused retirement of both TCAP columns, not leaking of the main hydrogen-containing column. The aluminum block design TCAP column (AHL block TCAP) used in the Advanced Hydride Laboratory, Building 773-A, failed in one nitrogen inlet tube that was crimped during fabrication, which lead to fatigue crack growth in the tube and subsequent leaking of nitrogen from this tube. The Third Generation stainless steel design TCAP column (Third generation TCAP), operated in 773-A room C-061, failed in a braze joint between the freon heating and cooling tubes (made of copper) and the main stainless steel column. In both cases, stresses from thermal cycling and local constraint likely caused the nucleation and growth of fatigue cracks. No materials compatibility problems between palladium coated kieselguhr (the material contained in the TCAP column) and either aluminum or stainless steel column materials were observed. The aluminum-stainless steel transition junction appeared to be unaffected by service in the AHL block TCAP. Also, no evidence of cracking was observed in the AHL block TCAP in a location expected to experience the highest thermal shock fatigue in this design. It is important to limit thermal stresses caused by constraint in hydride systems designed to work by temperature variation, such as hydride storage beds and TCAP columns

Fracture resistance of Zr–Nb alloys under low-cycle fatigue tests

Energy Technology Data Exchange (ETDEWEB)

Nikulin, S.A.; Rozhnov, A.B. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Gusev, A.Yu. [A.A. Bochvar All-Russia Research Institute of Inorganic Materials (VNIINM), Rogova St. 5a, 123060 Moscow (Russian Federation); Nechaykina, T.A. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Rogachev, S.O., E-mail: csaap@mail.ru [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation); Zadorozhnyy, M.Yu. [The National University of Science and Technology ‘‘MISIS’’, Leninsky pr. 4, 119049 Moscow (Russian Federation)

2014-03-15

Highlights: •Low-cycle fatigue tests of Zr–Nb alloys using DMA have been carried out. •The characteristics of low-cycle fatigue of the Zr–Nb alloy at 25/350 °C were determined. •Increasing test temperature up to 350 °C leads to a decrease of fatigue life. •The test temperature doesn’t have an effect on the character of fatigue curves. -- Abstract: Comparative low-cycle fatigue tests of small-scale specimens cut from the cladding tubes of E110, E125, E110opt zirconium alloys at temperatures of 25 and 350 °C using a dynamic mechanical analyzer have been carried out. It is shown that the limited cycles fatigue stress for all alloys is 50% less at temperature of 350 °C comparing to 25 °C. Besides it has been revealed that the limited cycles fatigue stress increases with increasing the strength of zirconium alloy.

Failure Mechanisms of SAC/Fe-Ni Solder Joints During Thermal Cycling

Science.gov (United States)

Gao, Li-Yin; Liu, Zhi-Quan; Li, Cai-Fu

2017-08-01

Thermal cycling tests have been conducted on Sn-Ag-Cu/Fe- xNi ( x = 73 wt.% or 45 wt.%) and Sn-Ag-Cu/Cu solder joints according to the Joint Electron Device Engineering Council industrial standard to study their interfacial reliability under thermal stress. The interfacial intermetallic compounds formed for solder joints on Cu, Fe-73Ni, and Fe-45Ni were 4.5 μm, 1.7 μm, and 1.4 μm thick, respectively, after 3000 cycles, demonstrating excellent diffusion barrier effect of Fe-Ni under bump metallization (UBM). Also, two deformation modes, viz. solder extrusion and fatigue crack formation, were observed by scanning electron microscopy and three-dimensional x-ray microscopy. Solder extrusion dominated for solder joints on Cu, while fatigue cracks dominated for solder joints on Fe-45Ni and both modes were detected for those on Fe-73Ni. Solder joints on Fe-Ni presented inferior reliability during thermal cycling compared with those on Cu, with characteristic lifetime of 3441 h, 3190 h, and 1247 h for Cu, Fe-73Ni, and Fe-45Ni UBM, respectively. This degradation of the interfacial reliability for solder joints on Fe-Ni is attributed to the mismatch in coefficient of thermal expansion (CTE) at interconnection level. The CTE mismatch at microstructure level was also analyzed by electron backscatter diffraction for clearer identification of recrystallization-related deformation mechanisms.

Design, simulation and fabrication of a flexible bond pad with a hollow annular protuberance to improve the thermal fatigue lifetime for through-silicon vias

International Nuclear Information System (INIS)

Wang, Guilian; Ding, Guifu; Luo, Jiangbo; Niu, Di; Zhao, Junhong; Zhao, Xiaolin; Wang, Yan; Liu, Rui

2014-01-01

This paper presents a flexible bond pad (FBP) with a hollow annular protuberance to improve the thermal fatigue lifetime for its application to through-silicon vias (TSVs). The hollow annular protuberance structure across the interface between the filled copper in TSV and silicon substrate not only isolates the FBP from stress/strain concentration regions (the corners of the TSV) but also disperses TSV-induced deformation. The plastic strain distributions of the FBP and conventional plate-type bond pad (CPBP) were simulated by finite element method (FEM) under the temperature cycles. Based on the simulation results, the thermal fatigue lifetimes of the CPBP and the FBP with different TSV diameters were predicted by the Coffin–Manson equation. The results indicate that thermal fatigue lifetimes of the FBP are significantly greater than those of the CPBP and their fatigue lifetimes both decrease with the increase of TSV diameter. To examine the reliability of the predicted results, the CPBP and the FBP with TSV diameter of 100 µm were fabricated by MEMS technology and temperature cycling tests (TCTs) were performed to obtain their thermal fatigue lifetimes. The test results are in good agreement with the numerical simulation results, and it shows that the proposed FBP can effectively improve the thermal fatigue lifetime for TSVs. (paper)

Thermal fatigue tests with actively cooled divertor mock-ups for ITER

International Nuclear Information System (INIS)

Roedig, M.; Duwe, R.; Linke, J.; Schuster, A.; Wiechers, B.; Ibbott, C.; Jacobson, D.; Le Marois, G.; Lind, A.; Lorenzetto, P.; Vieider, G.; Peacock, A.; Ploechl, L.; Severi, Y.; Visca, E.

1998-01-01

Mock-ups for high heat flux components with beryllium and CFC armour materials have been tested by means of the electron beam facility JUDITH. The experiments concerned screening tests to evaluate heat removal efficiency and thermal fatigue tests. CFC monoblocks attached to DS-Cu (Glidcop Al25) and CuCrZr tubes by active metal casting and Ti brazing showed the best thermal fatigue behaviour. They survived more than 1000 cycles at heat loads up to 25 MW m -2 without any indication of failure. Operational limits are given only by the surface temperature on the CFC tiles. Most of the beryllium mock-ups were of the flat tile type. Joining techniques were brazing, hot isostatic pressing (HIP) and diffusion bonding. HIPed and diffusion bonded Be/Cu modules have not yet reached the standards for application in high heat flux components. The limit of this production method is reached for heat loads of approximately 5 MW m -2 . Brazing with and without silver seems to be a more robust solution. A flat tile mock-up with CuMnSnCe braze was loaded at 5.4 MW m -2 for 1000 cycles without damage The first test with a beryllium monoblock joined to a CuCrZr tube by means of Incusil brazing shows promising results; it survived 1000 cycles at 4.5 MW m -2 without failure. (orig.)

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

Directory of Open Access Journals (Sweden)

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.

Thermal fatigue of austenitic stainless steel: influence of surface conditions through a multi-scale approach

International Nuclear Information System (INIS)

Le-Pecheur, Anne

2008-01-01

Some cases of cracking of 304L austenitic stainless steel components due to thermal fatigue were encountered in particular on the Residual Heat Removal Circuits (RHR) of the Pressurized Water Reactor (PWR). EDF has initiated a R and D program to understand assess the risks of damage on nuclear plant mixing zones. The INTHERPOL test developed at EDF is designed in order to perform pure thermal fatigue test on tubular specimen under mono-frequency thermal load. These tests are carried out under various loadings, surface finish qualities and welding in order to give an account of these parameters on crack initiation. The main topic of this study is the research of a fatigue criterion using a micro:macro modelling approach. The first part of work deals with material characterization (stainless steel 304L) emphasising the specificities of the surface roughness link with a strong hardening gradient. The first results of the characterization on the surface show a strong work-hardening gradient on a 250 microns layer. This gradient does not evolved after thermal cycling. Micro hardness measurements and TEM observations were intensively used to characterize this gradient. The second part is the macroscopic modelling of INTHERPOL tests in order to determine the components of the stress and strain tensors due to thermal cycling. The third part of work is thus to evaluate the effect of surface roughness and hardening gradient using a calculation on a finer scale. This simulation is based on the variation of dislocation density. A goal for the future is the determination of the fatigue criterion mainly based on polycrystalline modelling. Stocked energy or critical plane being available that allows making a sound choice for the criteria. (author)

Thermal fatigue behavior of C/C composites modified by SiC-MoSi2-CrSi2 coating

International Nuclear Information System (INIS)

Chu Yanhui; Fu Qiangang; Li Hejun; Li Kezhi

2011-01-01

Highlights: → The low-density C/C composites were modified by SiC-MoSi 2 -CrSi 2 multiphase coating by pack cementation. → The thermal fatigue behavior of the modified C/C composites was studied after undergoing thermal cycling for 20 times under the different environments. → The decrease of the flexural strength of the modified C/C composites during thermal cycle in air was primarily attributed to the partial oxidation of the modified C/C samples. - Abstract: Carbon/carbon (C/C) composites were modified by SiC-MoSi 2 -CrSi 2 multiphase coating by pack cementation, and their thermal fatigue behavior under thermal cycling in Ar and air environments was investigated. The modified C/C composites were characterized by scanning electron microscopy and X-ray diffraction. Results of tests show that, after 20-time thermal cycles between 1773 K and room temperature in Ar environment, the flexural strength of modified C/C samples decreased lightly and the percentage of remaining strength was 94.92%. While, after thermal cycling between 1773 K and room temperature in air for 20 times, the weight loss of modified C/C samples was 5.1%, and the flexural strength of the modified C/C samples reduced obviously and the percentage of remaining strength was only 75.22%. The fracture mode of modified C/C samples changed from a brittle behavior to a pseudo-plastic one as the service environment transformed from Ar to air. The decrease of the flexural strength during thermal cycle in air was primarily attributed to the partial oxidation of modified C/C samples.

Evolution of surface topography in dependence on the grain orientation during surface thermal fatigue of polycrystalline copper

CERN Document Server

Aicheler, M; Taborelli, M; Calatroni, S; Neupert, H; Wuensch, W; Sgobba, S

2011-01-01

Surface degradation due to cyclic thermal loading plays a major role in the Accelerating Structures (AS) of the future Compact Linear Collider (CLIC) In this article results on surface degradation of thermally cycled polycrystalline copper as a function of the orientation of surface grains are presented Samples with different grain sizes were subjected to thermal fatigue using two different methods and were then characterized using roughness measurements and Orientation Imaging Scanning-Electron-Microscopy (OIM-SEM) Samples fatigued by a pulsed laser show the same trend in the orientation-fatigue damage accumulation as the sample fatigued by pulsed Radio-Frequency-heating (RF) it is clearly shown that 11 1 1] surface grains develop significantly more damage than the surface grains oriented in {[}100] and three reasons for this behaviour are pointed out Based on observations performed near grain boundaries their role in the crack initiation process is discussed The results are in good agreement with previous f...

Aspects of fatigue life in thermal barrier coatings

Energy Technology Data Exchange (ETDEWEB)

Brodin, H.

2001-08-01

Thermal barrier coatings (TBC) are applied on hot components in airborne and land based gas turbines when higher turbine inlet temperature, meaning better thermal efficiency, is desired. The TBC is mainly applied to protect underlying material from high temperatures, but also serves as a protection from the aggressive corrosive environment. Plasma sprayed coatings are often duplex TBC's with an outer ceramic top coat (TC) made from partially stabilised zirconia - ZrO{sub 2} + 6-8% Y{sub 2}O{sub 3}. Below the top coat there is a metallic bond coat (BC). The BC is normally a MCrAlX coating (M=Ni, Co, Fe... and X=Y, Hf, Si ... ). In gas turbine components exposed to elevated temperatures nickel-based superalloys are commonly adopted as load carrying components. In the investigations performed here a commercial wrought Ni-base alloy Haynes 230 has been used as substrate for the TBC. As BC a NiCoCrAlY serves as a reference material and in all cases 7% Yttria PS zirconia has been used. Phase development and failure mechanisms in APS TBC during service-like conditions, have been evaluated in the present study. This is done by combinations of thermal cycling and low cycle fatigue tests. The aim is to achieve better knowledge regarding how, when and why thermal barrier coatings fail. As a final outcome of the project a model capable of predicting fatigue life of a given component will help engineers and designers of land based gas turbines for power generation to better optimise TBC's. In the investigations it is seen that TBC life is strongly influenced by oxidation of the BC and interdiffusion between BC and the substrate. The bond coat is known to oxidise with time at high temperature. The initial oxide found during testing is alumina. With increased time at high temperature Al is depleted from the bond coat due to inter-diffusion and oxidation. Oxides others than alumina start to form when the Al content is reduced below a critical limit. It is here believed

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

International Nuclear Information System (INIS)

Mukhopadhyay, N.K.; Dutta, B.K.; Kushwaha, H.S.

1992-01-01

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

Thermal fatigue cracking of austenitic stainless steels; Fissuration en fatigue thermique des aciers inoxydables austenitiques

Energy Technology Data Exchange (ETDEWEB)

Fissolo, A

2001-07-01

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

Robust design and thermal fatigue life prediction of anisotropic conductive film flip chip package

International Nuclear Information System (INIS)

Nam, Hyun Wook

2004-01-01

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF(Anisotropic Conductive Film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue life of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear bi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design Of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2 nd DOE was conducted to obtain RSM equation for the choose 3 design parameter. The coefficient of determination (R 2 ) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for Feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430μm, and 78μm, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter

Examination of high heat flux components for the ITER divertor after thermal fatigue testing

International Nuclear Information System (INIS)

Missirlian, M.; Escourbiac, F.; Schmidt, A.; Riccardi, B.; Bobin-Vastra, I.

2011-01-01

An extensive development programme has been carried out in the EU on high heat flux components within the ITER project. In this framework, a full-scale vertical target (VTFS) prototype was manufactured with all the main features of the corresponding ITER divertor design. The fatigue cycling campaign on CFC and W armoured regions, proved the capability of such a component to meet the ITER requirements in terms of heat flux performances for the vertical target. This paper discusses metallographic observations performed on both CFC and W part after this intensive thermal fatigue testing campaign for a better understanding of thermally induced mechanical stress within the component, especially close to the armour-heat sink interface.

Examination of high heat flux components for the ITER divertor after thermal fatigue testing

Energy Technology Data Exchange (ETDEWEB)

Missirlian, M., E-mail: marc.missirlian@cea.fr [CEA, IRFM, F-13108 Saint Paul lez Durance (France); Escourbiac, F., E-mail: frederic.escourbiac@cea.fr [CEA, IRFM, F-13108 Saint Paul lez Durance (France); Schmidt, A., E-mail: a.schmidt@fz-juelich.de [Forschungszentrum Juelich, IFE-2 (Germany); Riccardi, B., E-mail: Bruno.Riccardi@f4e.europa.eu [Fusion For Energy, E-08019 Barcelona (Spain); Bobin-Vastra, I., E-mail: isabelle.bobinvastra@areva.com [AREVA-NP, 71200 Le Creusot (France)

2011-10-01

An extensive development programme has been carried out in the EU on high heat flux components within the ITER project. In this framework, a full-scale vertical target (VTFS) prototype was manufactured with all the main features of the corresponding ITER divertor design. The fatigue cycling campaign on CFC and W armoured regions, proved the capability of such a component to meet the ITER requirements in terms of heat flux performances for the vertical target. This paper discusses metallographic observations performed on both CFC and W part after this intensive thermal fatigue testing campaign for a better understanding of thermally induced mechanical stress within the component, especially close to the armour-heat sink interface.

Low cycle fatigue behaviour of zirconium alloys at 3000C

International Nuclear Information System (INIS)

Hosbons, R.R.

1975-01-01

The low cycle fatigue lives of two zirconium alloys, zirconium--2.5 wt percent niobium and zirconium--1.1 wt percent chromium--0.1 wt percent iron, have been determined at 300 0 C. Both annealed material and cold-worked and stress-relieved material have similar fatigue lives to annealed Zircaloy-2 but β-quenched zirconium--niobium and zirconium--chromium--iron have lower fatigue lives than annealed Zircaloy-2. An atmosphere containing a concentration of iodine lower than that required for stress corrosion cracking still significantly lowers the fatigue life. A mathematical relationship between fatigue life and short-term tensile properties was used to estimate the fatigue life of zirconium alloy fuel sheaths and it was estimated that for a strain cycle of 0.1 percent a cyclic frequency exceeding 0.116 Hz (10,000 cycles/ day) would be required to cause fatigue failure of the sheath before its design life is realized

Low cycle fatigue behaviour of zirconium alloys at 3000C

International Nuclear Information System (INIS)

Hosbons, R.R.

1975-01-01

The low cycle fatigue lives of two zirconium alloys, zirconium-2.5 wt% niobium and zirconium-1.1 wt% chronium-0.1 wt% iron, have been determined at 300 0 C. Both annealed material and cold-worked and stress-relieved material have similar fatigue lives to annealed Zircaloy-2 but β-quenched zirconium-niobium and zirconium-chromium-iron have lower fatigue lives than annealed Zircaloy-2. An atmosphere containing a concentration of iodine lower than that required for stress corrosion cracking still significantly lowers the fatigue life. A mathematical relationship between fatigue life and short-term tensile properties was used to estimate the fatigue life of zirconium alloy fuel sheaths and it was estimated that for a strain cycle of 0.1 per cent a cyclic frequency exceeding 0.116 Hz (10 000 cycles/day) would be required to cause fatigue failure of the sheath before its design life is realized. (author)

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

Energy Technology Data Exchange (ETDEWEB)

Taheri, Said, E-mail: Said.taheri@edf.fr [EDF-LAB, IMSIA, 7 Boulevard Gaspard Monge, 91120 Palaiseau Cedex (France); Julan, Emricka [EDF-LAB, AMA, 7 Boulevard Gaspard Monge, 91120 Palaiseau Cedex (France); Tran, Xuan-Van [EDF Energy R& D UK Centre/School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester M13 9PL (United Kingdom); Robert, Nicolas [EDF-DPN, UNIE, Strategic Center, Saint Denis (France)

2017-01-15

Highlights: • For crack growth analysis, weld residual stress field must be considered through its SIF in presence of a crack. • Presence of cracks of same depth proves their arrest, where equal depth is because mean stress acts only on crack opening. • Not considering amplitudes under a fatigue crack growth threshold (FCGT) does not compensate the lack of FGCT in Paris law. • Propagation rates are close for axisymmetric and circumferential semi-elliptical cracks. - Abstract: High cycle thermal crazing has been observed in some residual heat removal (RHR) systems made of 304 stainless steel in PWR nuclear plants. This paper deals with two types of analyses including logical argumentation and simulation. Crack arrest in networks is demonstrated due to the presence of two cracks of the same depth in the network. This identical depth may be proved assuming that mean stress acts only on crack opening and that cracks are fully open during the load cycle before arrest. Weld residual stresses (WRS) are obtained by an axisymmetric simulation of welding on a tube with a chamfer. Axisymmetric and 3D parametric studies of crack growth on: representative sequences for variable amplitude thermal loading, fatigue crack growth threshold (FCGT), permanent mean stress, cyclic counting methods and WRS, are performed with Code-Aster software using XFEM methodology. The following results are obtained on crack depth versus time: the effect of WRS on crack growth cannot be determined by the initial WRS field in absence of crack, but by the associated stress intensity factor. Moreover the relation between crack arrest depth and WRS is analyzed. In the absence of FCGT Paris’s law may give a significant over-estimation of crack depth even if amplitudes of loading smaller than FCGT have not been considered. Appropriate depth versus time may be obtained using different values of FCGT, but axisymmetric simulations do not really show a possibility of arrest for shallow cracks in

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

International Nuclear Information System (INIS)

Taheri, Said; Julan, Emricka; Tran, Xuan-Van; Robert, Nicolas

2017-01-01

Highlights: • For crack growth analysis, weld residual stress field must be considered through its SIF in presence of a crack. • Presence of cracks of same depth proves their arrest, where equal depth is because mean stress acts only on crack opening. • Not considering amplitudes under a fatigue crack growth threshold (FCGT) does not compensate the lack of FGCT in Paris law. • Propagation rates are close for axisymmetric and circumferential semi-elliptical cracks. - Abstract: High cycle thermal crazing has been observed in some residual heat removal (RHR) systems made of 304 stainless steel in PWR nuclear plants. This paper deals with two types of analyses including logical argumentation and simulation. Crack arrest in networks is demonstrated due to the presence of two cracks of the same depth in the network. This identical depth may be proved assuming that mean stress acts only on crack opening and that cracks are fully open during the load cycle before arrest. Weld residual stresses (WRS) are obtained by an axisymmetric simulation of welding on a tube with a chamfer. Axisymmetric and 3D parametric studies of crack growth on: representative sequences for variable amplitude thermal loading, fatigue crack growth threshold (FCGT), permanent mean stress, cyclic counting methods and WRS, are performed with Code-Aster software using XFEM methodology. The following results are obtained on crack depth versus time: the effect of WRS on crack growth cannot be determined by the initial WRS field in absence of crack, but by the associated stress intensity factor. Moreover the relation between crack arrest depth and WRS is analyzed. In the absence of FCGT Paris’s law may give a significant over-estimation of crack depth even if amplitudes of loading smaller than FCGT have not been considered. Appropriate depth versus time may be obtained using different values of FCGT, but axisymmetric simulations do not really show a possibility of arrest for shallow cracks in

Research and development studies for predicting the thermal fatigue

International Nuclear Information System (INIS)

Moulin, D.; Garnier, J.; Fissolo, A.; Lejeail, Y.; Stephan, J.M.; Moinereau, D.; Masson, J.

2001-01-01

This paper presents some studies in development or realized in the EDF and CEA laboratories, concerning the thermal fatigue damage in nuclear reactor components. The first part presents the basic principles and the methods of lifetime prediction. The second part gives some examples on sodium loop, water loop, welded junctions resistance to thermal fatigue and tests on fatigue specimen. (A.L.B.)

Thermal cycling in LWR components in OECD-NEA member countries - CSNI integrity and ageing working group

International Nuclear Information System (INIS)

Faidy, Claude; Chapuliot, Stephane; Mathet, Eric

2005-01-01

Thermal cycling is a widespread and recurring problem in nuclear power plants worldwide. Several incidents with leakage of primary water inside the containment challenged the integrity of NPPs although no release outside of containment occurred. Thermal cycling was not taken into account at the design stage. Regulatory bodies, utilities and researchers have to address it for their operating plants. It is a complex phenomenon that involves and links thermal hydraulic, fracture mechanic, materials and plant operation. Thermal cycling is connected either to operating transients (low cycle fatigue) or to complex phenomenon like stratification, vortex and mixing (low and high cycle fatigue). The former is covered by existing rules and codes. The latter is partially addressed by national rules and constitutes the subject of this report. In 2002, the Committee on the Safety of Nuclear Installations (CSNI) requested the working group on the integrity of reactor components and structures (IAGE WG) to prepare a program of work on thermal cycling to provide information to NEA member countries on operational experience, regulatory policies, countermeasures in place, current status of research and development, and to identify areas where research is needed both at national and international levels. The working group proposed a 3 fold program that covered: - Review of operating experience, regulatory framework, countermeasures and current research; - Benchmark to assess calculation capabilities in NEA member countries for crack initiation and propagation under a cyclic thermal loading, and ultimately to develop screening criteria to identify susceptible components; results of the benchmark were published in 2005; - Organisation of an international conference in cooperation with the EPRI and the USNRC on fatigue of reactor components. This conference reviews progress in the areas and provides a forum for discussion and exchange of information between high level experts. The

The Effects of Hot Bending on the Low Cycle Fatigue Behaviors of 347 SS in PWR Primary Environment

Energy Technology Data Exchange (ETDEWEB)

Kim, Ho-Sub; Hong, Jong-Dae; Lee, Junho; Jang, Changheui [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

2014-10-15

Fatigue damage could be significant for some locations, especially the welds and bends where stress concentration is typically high. As a possible solution, a large radius hot-bending method has been suggested to eliminate some weld joints and all tight bends. However, for the hot-bending process which involves a high temperature thermal cycle, there is a concern about changes in mechanical properties including low cycle fatigue behaviors. In APR1400, Type 347 SS have been used as surge line pipes. Therefore, to verify the applicability of hot-bending on 347 SS surge line pipes, an environmental fatigue test program was initiated. In this paper, the preliminary results of the on-going test program are introduced. Also, the low cycle fatigue behaviors of 347 SS are compared with those of other grade of stainless steels. The effects of hot bending on the low cycle fatigue behavior of 347 SS were quantitatively evaluated. The fatigue life was compared with the estimated values per NUREG 6909 rev. 1. There are no distinct differences between NUREG 6909 and LCF tests. According to fractography and cross section analysis in progress, basically, the reduction of LCF life of 347 SS in PWR water was caused by operation of HIC mechanism. The cyclic stress responses shows that there is no secondary hardening in 330 .deg.C air and PWR water.

Thermal cycling reliability of Cu/SnAg double-bump flip chip assemblies for 100 μm pitch applications

Science.gov (United States)

Son, Ho-Young; Kim, Ilho; Lee, Soon-Bok; Jung, Gi-Jo; Park, Byung-Jin; Paik, Kyung-Wook

2009-01-01

A thick Cu column based double-bump flip chip structure is one of the promising alternatives for fine pitch flip chip applications. In this study, the thermal cycling (T/C) reliability of Cu/SnAg double-bump flip chip assemblies was investigated, and the failure mechanism was analyzed through the correlation of T/C test and the finite element analysis (FEA) results. After 1000 thermal cycles, T/C failures occurred at some Cu/SnAg bumps located at the edge and corner of chips. Scanning acoustic microscope analysis and scanning electron microscope observations indicated that the failure site was the Cu column/Si chip interface. It was identified by a FEA where the maximum stress concentration was located during T/C. During T/C, the Al pad between the Si chip and a Cu column bump was displaced due to thermomechanical stress. Based on the low cycle fatigue model, the accumulation of equivalent plastic strain resulted in thermal fatigue deformation of the Cu column bumps and ultimately reduced the thermal cycling lifetime. The maximum equivalent plastic strains of some bumps at the chip edge increased with an increased number of thermal cycles. However, equivalent plastic strains of the inner bumps did not increase regardless of the number of thermal cycles. In addition, the z-directional normal plastic strain ɛ22 was determined to be compressive and was a dominant component causing the plastic deformation of Cu/SnAg double bumps. As the number of thermal cycles increased, normal plastic strains in the perpendicular direction to the Si chip and shear strains were accumulated on the Cu column bumps at the chip edge at low temperature region. Thus it was found that the Al pad at the Si chip/Cu column interface underwent thermal fatigue deformation by compressive normal strain and the contact loss by displacement failure of the Al pad, the main T/C failure mode of the Cu/SnAg flip chip assembly, then occurred at the Si chip/Cu column interface shear strain deformation

Thermal Fatigue Evaluation of Pb-Free Solder Joints: Results, Lessons Learned, and Future Trends

Science.gov (United States)

Coyle, Richard J.; Sweatman, Keith; Arfaei, Babak

2015-09-01

Thermal fatigue is a major source of failure of solder joints in surface mount electronic components and it is critically important in high reliability applications such as telecommunication, military, and aeronautics. The electronic packaging industry has seen an increase in the number of Pb-free solder alloy choices beyond the common near-eutectic Sn-Ag-Cu alloys first established as replacements for eutectic SnPb. This paper discusses the results from Pb-free solder joint reliability programs sponsored by two industry consortia. The characteristic life in accelerated thermal cycling is reported for 12 different Pb-free solder alloys and a SnPb control in 9 different accelerated thermal cycling test profiles in terms of the effects of component type, accelerated thermal cycling profile and dwell time. Microstructural analysis on assembled and failed samples was performed to investigate the effect of initial microstructure and its evolution during accelerated thermal cycling test. A significant finding from the study is that the beneficial effect of Ag on accelerated thermal cycling reliability (measured by characteristic lifetime) diminishes as the severity of the accelerated thermal cycling, defined by greater ΔT, higher peak temperature, and longer dwell time increases. The results also indicate that all the Pb-free solders are more reliable in accelerated thermal cycling than the SnPb alloy they have replaced. Suggestions are made for future work, particularly with respect to the continued evolution of alloy development for emerging application requirements and the value of using advanced analytical methods to provide a better understanding of the effect of microstructure and its evolution on accelerated thermal cycling performance.

Finite Element Modeling of Material Fatigue and Cracking Problems for Steam Power System HP Devices Exposed to Thermal Shocks

Directory of Open Access Journals (Sweden)

Pawlicki Jakub

2016-09-01

Full Text Available The paper presents a detailed analysis of the material damaging process due to low-cycle fatigue and subsequent crack growth under thermal shocks and high pressure. Finite Element Method (FEM model of a high pressure (HP by-pass valve body and a steam turbine rotor shaft (used in a coal power plant is presented. The main damaging factor in both cases is fatigue due to cycles of rapid temperature changes. The crack initiation, occurring at a relatively low number of load cycles, depends on alternating or alternating-incremental changes in plastic strains. The crack propagation is determined by the classic fracture mechanics, based on finite element models and the most dangerous case of brittle fracture. This example shows the adaptation of the structure to work in the ultimate conditions of high pressure, thermal shocks and cracking.

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

International Nuclear Information System (INIS)

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

2010-01-01

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

Using lamb waves tomonitor moisture absorption thermally fatigues composite laminates

Energy Technology Data Exchange (ETDEWEB)

Lee, Jae Sun; Cho, Youn Ho [School of Mechanical Engineering, Pusan National University, Busan (Korea, Republic of)

2016-06-15

Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.

Predominantly elastic crack growth under combined creep-fatigue cycling

International Nuclear Information System (INIS)

Lloyd, G.J.

1979-01-01

A rationalization of the various observed effects of combined creep-fatigue cycling upon predominantly elastic fatigue-crack propagation in austenitic steel is presented. Existing and new evidence is used to show two main groups of behaviour: (i) material and cycling conditions which lead to modest increases (6-8 times) in the rate of crack growth are associated with relaxation-induced changes in the material deformation characteristics, and (ii) material and cycling conditions severe enough to generate internal fracture damage lead to significant (up to a factor of 30) increases in crack growth rate when compared with fast-cycling crack propagation rates at the same temperature. A working hypothesis is presented to show that the boundary between the two groups occurs when the scale of the nucleated creep damage is of the same magnitude as the crack tip opening displacement. This leads to the possibility of unstable crack advance. Creep crack growth rates are shown to provide an upper bound to creep-fatigue crack growth rates when crack advance is unstable. If the deformation properties only are affected by the creep-fatigue cycling then creep crack growth rates provide a lower bound. The role of intergranular oxygen corrosion in very low frequency crack growth tests is also briefly discussed. (author)

Fatigue life estimation on coke drum due to cycle optimization

Science.gov (United States)

Siahaan, Andrey Stephan; Ambarita, Himsar; Kawai, Hideki; Daimaruya, Masashi

2018-04-01

In the last decade, due to the increasing demand of petroleum product, the necessity for converting the heavy oil are increasing. Thus, demand for installing coke drum in whole world will be increase. The coke drum undergoes the cyclic high temperature and suddenly cooling but in fact is not designed to withstand that kind of cycle, thus the operational life of coke drum is much shorter in comparison to other equipment in oil refinery. Various factors determine in order to improve reliability and minimize the down time, and it is found that the cycle optimization due to cycle, temperature, and pressure have an important role. From this research it is found that the fatigue life of the short cycle is decrease by a half compare to the normal cycle. It also found that in the preheating stage, the stress peak is far exceed the yield strength of coke drum material and fall into plastic deformation. This is happened because of the temperature leap in the preheating stage that cause thermal shock in the upper part of the skirt of the coke drum.

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

Energy Technology Data Exchange (ETDEWEB)

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)

Microstructure evolution during high cycle fatigue in Mg–6Zn–1Mn alloy

Energy Technology Data Exchange (ETDEWEB)

Yu, Daliang [College of Materials Science and Engineering, Chongqing University, Chongqing 400045 (China); National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Zhang, Dingfei, E-mail: zhangdingfei@cqu.edu.cn [College of Materials Science and Engineering, Chongqing University, Chongqing 400045 (China); National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Luo, Yuanxin [College of Mechanical Engineering, Chongqing University, Chongqing 400030 (China); Sun, Jing; Xu, Junyao [College of Materials Science and Engineering, Chongqing University, Chongqing 400045 (China); National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Pan, Fusheng [National Engineering Research Center for Magnesium Alloys, Chongqing University, Chongqing 400044 (China); Chongqing Academy of Science and Technology, Chongqing 401123 (China)

2016-03-21

Microstructure evolution during high cycle fatigue in extruded Mg–6Zn–1Mn alloy was investigated by servo-hydraulic fatigue testing machine with pull–push sinusoidal loading. The results show that in high stress cycles (cyclic stress≥129 MPa) high cycle fatigue tests promote deformation; however, in low stress cycles (cyclic stress≤125 MPa) high cycle fatigue tests make a contribution to room temperature recrystallization in Mg–6Zn–1Mn alloy. The grain refinement increased with increasing cycles. Electron Back-Scattered Diffraction (EBSD) analyses showed that dynamic recrystallization (DRX) has occurred in post-fatigued alloys, accompanied by the presence of a high number density of low-angle grain boundaries (LAGBs). LAGBs generated in the vicinity of initiation grain boundaries and subdivided coarse grains. In the specimens that subjected to higher cycles, the fraction of LAGBs decreased and high-angle grain boundaries (HAGBs) gradually increased. With the cyclic number increasing the texture intensity was significantly weakened. The DRX in post-fatigued specimens was related to Continuous DRX (CDRX) mechanism.

Development of thermal fatigue evaluation methods of piping systems

International Nuclear Information System (INIS)

Kasahara, Naoto; Itoh, Takamoto; Okazaki, Masakazu; Okuda, Yukihiko; Kamaya, Masayuki; Nakamura, Akira; Nakamura, Hitoshi; Machida, Hideo; Matsumoto, Masaaki

2014-01-01

Nuclear piping has various kinds of thermal fatigue failure modes. Main causes of thermal loads are structural responses to fluid temperature changes during plant operation. These phenomena have complex mechanisms and many patterns, so that their problems still occur in spite of well-known issues. The guideline of the JSME (Japan Society of Mechanical Engineering) for estimation of thermal fatigue failures in piping system is employed as Japanese regulation. To improve this guideline, generation mechanisms of thermal load and fatigue failure have been investigated and summarized into the knowledgebase. And numerical simulation methods to replace experimental based methods were studied. Furthermore, probabilistic failure analysis approach with main influence parameters was investigated to be applied for the plant system safety. Thus, based on the knowledge, estimation methods revised from the JSME guideline were proposed. (author)

Low cycle fatigue of irradiated LMFBR materials

International Nuclear Information System (INIS)

Blackburn, L.D.

1976-01-01

A review of low cycle fatigue data on irradiated LMFBR materials was conducted and extensive graphical representations of available data are presented. Representative postirradiation tensile properties of annealed 304 and 316 SS are selected and employed in several predictive methods to estimate irradiated material fatigue curves. Experimental fatigue data confirm the use of predictive methods for establishing conservative design curves over the range of service conditions relevant to such CRBRP components as core former, fixed radial shielding, core barrel, lower inlet module and upper internals structures. New experimental data on fatigue curves and creep-fatigue interaction in irradiated 20 percent cold worked (CW) 316 SS and Alloy 718 would support the design of removable radial shielding and upper internals in CRBRP. New experimental information on notched fatigue behavior and cyclic stress-strain curves of all these materials in the irradiated condition could provide significant design data

Orientation dependence of the thermal fatigue of nickel alloy single crystals

Energy Technology Data Exchange (ETDEWEB)

Dul' nev, R A; Svetlov, I L; Bychkov, N G; Rybina, T V; Sukhanov, N N

1988-11-01

The orientation dependence of the thermal stability and the thermal fatigue fracture characteristics of single crystals of MAR-M200 nickel alloy are investigated experimentally using X-ray diffraction analysis and optical and scanning electron microscopy. It is found that specimens with the 111-line orientation have the highest thermal stability and fatigue strength. Under similar test conditions, the thermal fatigue life of single crystals is shown to be a factor of 1.5-2 higher than that of the directionally solidified and equiaxed alloys. 6 references.

Lifetime prediction of structures submitted to thermal fatigue loadings

International Nuclear Information System (INIS)

Amiable, S.

2006-01-01

The aim of this work is to predict the lifetime of structures submitted to thermal fatigue loadings. This work lies within the studies undertaken by the CEA on the thermal fatigue problems from the french reactor of Civaux. In particular we study the SPLASH test: a specimen is heated continuously and cyclically cooled down by a water spray. This loading generates important temperature gradients in space and time and leads to the initiation and the propagation of a crack network. We propose a new thermo-mechanical model to simulate the SPLASH experiment and we propose a new fatigue criterion to predict the lifetime of the SPLASH specimen. We propose and compare several numerical models with various complexity to estimate the mechanical response of the SPLASH specimen. The practical implications of this work are the reevaluation of the hypothesis used in the French code RCC, which are used to simulate thermal shock and to interpret the results in terms of fatigue. This work leads to new perspectives on the mechanical interpretation of the fatigue criterion. (author)

A model for high-cycle fatigue crack propagation

Energy Technology Data Exchange (ETDEWEB)

Balbi, Marcela Angela [Rosario National Univ. (Argentina); National Council of Scientific Research and Technology (CONICET) (Argentina)

2017-02-01

This paper deals with the prediction of high-cycle fatigue behavior for four different materials (7075-T6 alloy, Ti-6Al-4 V alloy, JIS S10C steel and 0.4 wt.-% C steel) using Chapetti's approach to estimate the fatigue crack propagation curve. In the first part of the paper, a single integral equation for studying the entire propagation process is determined using the recent results of Santus and Taylor, which consider a double regime of propagation (short and long cracks) characterized by the model of El Haddad. The second part of the paper includes a comparison of the crack propagation behavior model proposed by Navarro and de los Rios with the one mentioned in the first half of this work. The results allow us to conclude that the approach presented in this paper is a good and valid estimation of high-cycle fatigue crack propagation using a single equation to describe the entire fatigue crack regime.

Thermal stress analysis for fatigue damage evaluation at a mixing tee

International Nuclear Information System (INIS)

Kamaya, Masayuki; Nakamura, Akira

2011-01-01

Highlights: → Thermal stress and fatigue damage have been analyzed for a mixing tee. → Fatigue damage was accumulated near boundaries of the cold spot. → It was found that fatigue damage was brought about by fluctuation of cold spot. → Simple one-dimensional analysis could derive stress for fatigue evaluation. - Abstract: Fatigue cracks have been found at mixing tees where fluids of different temperature flow in. In this study, the thermal stress at a mixing tee was calculated by the finite element method using temperature transients obtained by a fluid dynamics simulation. The simulation target was an experiment for a mixing tee, in which cold water flowed into the main pipe from a branch pipe. The cold water flowed along the main pipe wall and caused a cold spot, at which the membrane stress was relatively large. Based on the evaluated thermal stress, the magnitude of the fatigue damage was assessed according to the linear damage accumulation rule and the rain-flow procedure. Precise distributions of the thermal stress and fatigue damage could be identified. Relatively large axial stress occurred downstream from the branch pipe due to the cold spot. The variation ranges of thermal stress and fatigue damage became large near the position 20 o from the symmetry line in the circumferential direction. The position of the cold spot changed slowly in the circumferential direction, and this was the main cause of the fatigue damage. The fatigue damage was investigated for various differences in the temperature between the main and branch pipes. Since the magnitude of accumulated damage increased abruptly when the temperature difference exceeded the value corresponding to the fatigue limit, it was suggested that the stress amplitude should be suppressed less than the fatigue limit. In the thermal stress analysis for fatigue damage assessment, it was found that the detailed three-dimensional structural analysis was not required. Namely, for the current case, a one

Experimental study on high cycle thermal fatigue in T-junction. Effect of local flow velocity on transfer of temperature fluctuation from fluid to structure

International Nuclear Information System (INIS)

Kimura, Nobuyuki; Ono, Ayako; Miyakoshi, Hiroyuki; Kamide, Hideki

2009-01-01

A quantitative evaluation on high cycle thermal fatigue due to temperature fluctuation in fluid is of importance for structural integrity in the reactor. It is necessary for the quantitative evaluation to investigate occurrence and propagation processes of temperature fluctuation, e.g., decay of fluctuation intensity near structures and transfer of temperature fluctuation from fluid to structures. The JSME published a guideline for evaluation of high-cycle thermal fatigue of a pipe as the JSME guideline in 2003. This JSME standard covers T-pipe junction used in LWRs operated in Japan. In the guideline, the effective heat transfer coefficients were obtained from temperature fluctuations in fluid and structure in experiments. In the previous studies, the effective heat transfer coefficients were 2 - 10 times larger than the heat transfer coefficients under steady state conditions in a straight tube. In this study, a water experiment of T-junction was performed to evaluate the transfer characteristics of temperature fluctuation from fluid to structure. In the experiment, temperatures in fluid and structure were measured simultaneously at 20 positions to obtain spatial distributions of the effective heat transfer coefficient. In addition, temperatures in structure and local velocities in fluid were measured simultaneously to evaluate the correlation between the temperature and velocity under the non-stationary fields. The large heat transfer coefficients were registered at the region where the local velocity was high. Furthermore it was found that the heat transfer coefficients were correlated with the time-averaged turbulent heat flux near the pipe wall. (author)

Thermal fatigue behavior of US and Russian grades of beryllium

International Nuclear Information System (INIS)

Watson, R.D.; Youchison, D.L.; Dombrowski, D.E.; Guiniatouline, R.N.; Kupriynov, I.B.

1996-01-01

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 degrees C for each pass of the beam. Large thermal stress in excess of the yield strength are generated due to very high spot heat flux, 250 MW/m 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-300F-H, Sr-200, I-400, extruded high purity. HIP'd sperical powder, porous beryllium (94% and 98% dense), Be/30% BeO, Be/60% BeO, and TiBe 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

Low cycle fatigue of the European type 316L reference steel for the NET first wall and blanket

International Nuclear Information System (INIS)

Schaaf, B. van der; Hoepen, J. van.

1992-12-01

This report gives a comprehensive overview of the experiments performed on Type 316L steel at the Netherlands Energy Research Foundation in Petten. It is observed that the effects of neutron irradiation, resulting in 3-4 dpa and 30-40 appm helium are limited. The strain rate dependence of low cycle fatigue endurance is not negligible for material in the three conditions considered: irradiated, as-received and thermal control condition. All fatigue cracks propagated in a ductile manner in the parameter range were investigated. Both fatigue strain rate effects and crack initiation effects should be taken into account for the NET/ITER design. (author). 24 refs., 18 figs., 13 tabs

Identification of low cycle fatigue parameters

Directory of Open Access Journals (Sweden)

Balda M.

2009-12-01

Full Text Available The article describes a new approach to the processing of experimental data coming from low-cycle fatigue (LCF tests. The data may be either tables from the standard tests, or a time series of loading processes and corresponding numbers of cycles to damage. A new method and a program for the evaluation of material parameters governing the material behavior under a low cycle loading have been developed. They exploit a minimization procedure for an appropriate criterion function based on differences of measured and evaluated damages.

Thermal-mechanical and isothermal fatigue of IN 792 CC

International Nuclear Information System (INIS)

Beck, T.; Pitz, G.; Lang, K.-H.; Loehe, D.

1997-01-01

The cyclic deformation and lifetime behaviour of the cast Ni-base superalloy IN 792 CC was investigated both under thermal-mechanical fatigue (TMF) and isothermal fatigue (IF) conditions. During TMF the phase relations between temperature and mechanical strain were in-phase and out-of-phase, respectively. For both phase relations a similar cyclic deformation behaviour is observed. In all cases out-of-phase TMF causes tensile mean stresses, whereas in-phase TMF leads to compressive mean stresses. At T max below 800 C out-of-phase cycling results in smaller lifetimes than in-phase loading. In spite of the rather high compressive mean stresses developing at T max above 800 C, at these temperatures in-phase loading causes shorter lifetimes than out-of-phase TMF. This effect is due to the different damage mechanisms caused by in-phase and out-of-phase loadings: at higher T max considerable intergranular damage caused by in-phase loading reduces the lifetime below the respective values measured during out-of-phase TMF, after which no intergranular damage could be detected. A comparison of the TMF data with the cyclic deformation and lifetime behaviour under IF conditions shows that the material's reactions under TMF cannot be assessed satisfactorily by the results obtained from isothermal fatigue tests. (orig.)

Study of Thermal Fatigue Resistance of a Composite Coating Made by a Vacuum Fusion Sintering Method

Institute of Scientific and Technical Information of China (English)

无

2003-01-01

Thermal fatigue behavior of a Ni-base alloy chromium carbide composite coating made by a vacuum fusion sintering method are discussed. Results show that thermal fatigue behavior is associated with cyclic upper temperature and coating thickness. As the thickness of the coating decreases, the thermal fatigue resistance increases. The thermal fatigue resistance cuts down with the thermal cyclic upper temperature rising. The crack growth rate decreases with the increase in cyclic number until crack arrests. Thermal fatigue failure was not found along the interface of the coating/matrix. The tract of thermal fatigue crack cracks along the interfaces of phases.

Application of a unified fatigue modelling to some thermomechanical fatigue problems

International Nuclear Information System (INIS)

Dang, K. van; Maitournam, H.; Moumni, Z.

2005-01-01

Fatigue under thermomechanical loadings is an important topic for nuclear industries. For instance, thermal fatigue cracking is observed in the mixing zones of the nuclear reactor. Classical computations using existing methods based on strain amplitude or fracture mechanics are not sufficiently predictive. In this paper an alternative approach is proposed based on a multiscale modelling thanks to shakedown hypothesis. Examples of predictive results are presented. Finally an application to the RHR problem is discussed. Main ideas of the fatigue modelling: Following an idea of Professor D. Drucker who wrote in 1963 'when applied to the microstructure there is a hope that the concept of endurance limit and shakedown are related, and that fatigue failure can be related to energy dissipated in idealized material when shakedown does not occur.' we have developed a theory of fatigue based on this concept which is different from classical fatigue approaches. Many predictive applications have been already done particularly for the automotive industry. Fatigue resistance of structures undergoing thermomechanical loadings in the high cycle regime as well as in the low cycle regime are calculated using this modelling. However, this fatigue theory is until now rarely used in nuclear engineering. After recalling the main points of the theory, we shall present some relevant applications which were done in different industrial sectors. We shall apply this modelling to the prediction of thermal cracking observed in the mixing zones of RHR. (authors)

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

Energy Technology Data Exchange (ETDEWEB)

Fan, K.L., E-mail: 12klfan@tongji.edu.cn; He, G.Q.; She, M.; Liu, X.S.; Lu, Q.; Yang, Y.; Tian, D.D.; Shen, Y.

2014-12-15

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.

Isothermal and thermal-mechanical fatigue of VVER-440 reactor pressure vessel steels

Science.gov (United States)

Fekete, Balazs; Trampus, Peter

2015-09-01

The fatigue life of the structural materials 15Ch2MFA (CrMoV-alloyed ferritic steel) and 08Ch18N10T (CrNi-alloyed austenitic steel) of VVER-440 reactor pressure vessel under completely reserved total strain controlled low cycle fatigue tests were investigated. An advanced test facility was developed for GLEEBLE-3800 physical simulator which was able to perform thermomechanical fatigue experiments under in-service conditions of VVER nuclear reactors. The low cycle fatigue results were evaluated with the plastic strain based Coffin-Manson law, and plastic strain energy based model as well. It was shown that both methods are able to predict the fatigue life of reactor pressure vessel steels accurately. Interrupted fatigue tests were also carried out to investigate the kinetic of the fatigue evolution of the materials. On these samples microstructural evaluation by TEM was performed. The investigated low cycle fatigue behavior can provide reference for remaining life assessment and lifetime extension analysis.

Fatigue during maximal sprint cycling: unique role of cumulative contraction cycles.

Science.gov (United States)

Tomas, Aleksandar; Ross, Emma Z; Martin, James C

2010-07-01

Maximal cycling power has been reported to decrease more rapidly when performed with increased pedaling rates. Increasing pedaling rate imposes two constraints on the neuromuscular system: 1) decreased time for muscle excitation and relaxation and 2) increased muscle shortening velocity. Using two crank lengths allows the effects of time and shortening velocity to be evaluated separately. We conducted this investigation to determine whether the time available for excitation and relaxation or the muscle shortening velocity was mainly responsible for the increased rate of fatigue previously observed with increased pedaling rates and to evaluate the influence of other possible fatiguing constraints. Seven trained cyclists performed 30-s maximal isokinetic cycling trials using two crank lengths: 120 and 220 mm. Pedaling rate was optimized for maximum power for each crank length: 135 rpm for the 120-mm cranks (1.7 m x s(-1) pedal speed) and 109 rpm for the 220-mm cranks (2.5 m x s(-1) pedal speed). Power was recorded with an SRM power meter. Crank length did not affect peak power: 999 +/- 276 W for the 120-mm crank versus 1001 +/- 289 W for the 220-mm crank. Fatigue index was greater (58.6% +/- 3.7% vs 52.4% +/- 4.8%, P < 0.01), and total work was less (20.0 +/- 1.8 vs 21.4 +/- 2.0 kJ, P < 0.01) with the higher pedaling rate-shorter crank condition. Regression analyses indicated that the power for the two conditions was most highly related to cumulative work (r2 = 0.94) and to cumulative cycles (r2 = 0.99). These results support previous findings and confirm that pedaling rate, rather than pedal speed, was the main factor influencing fatigue. Our novel result was that power decreased by a similar increment with each crank revolution for the two conditions, indicating that each maximal muscular contraction induced a similar amount of fatigue.

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

Energy Technology Data Exchange (ETDEWEB)

Hamada, A.S. [Materials Engineering Laboratory (4KOMT), Box 4200, University of Oulu, 90014 Oulu (Finland); Metallurgical and Materials Engineering Department, Faculty of Petroleum and Mining Engineering, Suez Canal University, Box 43721, Suez (Egypt); Karjalainen, L.P., E-mail: pentti.karjalainen@oulu.fi [Materials Engineering Laboratory (4KOMT), Box 4200, University of Oulu, 90014 Oulu (Finland)

2010-08-20

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 10{sup 6} 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.

The High Performance Shape Memory Effect (HP-SME in Ni Rich NiTi Wires: In Situ X-Ray Diffraction on Thermal Cycling

Directory of Open Access Journals (Sweden)

Coduri Mauro

2015-01-01

Full Text Available A novel approach for using Shape Memory Alloys (SMA was recently proposed and named highperformance shape memory effect (HP-SME. The HP-SME exploits the thermal cycling of stress-induced martensite for producing extremely high mechanical work with a very stable functional fatigue behaviour in Ni rich NiTi alloy. The latter was found to differ significantly from the functional fatigue behaviour observed for conventional SMA. This study was undertaken in order to elucidate the microstructural modifications at the basis of this particular feature. To this purpose, the functional fatigue was coupled to in situ Synchrotron Radiation X-Ray Diffraction, by recording patterns on wires thermally cycled by Joule effect under a constant applied stress (800 MPa. The accurate analysis the line profile XRD data suggests the accumulation of defects upon functional cycling, while the fibre texture was not observed to change. The functional fatigue exhibits a very similar behaviour as the line broadening of XRD peaks, thus suggesting the accumulation of dislocations as the origin of the mechanism of the permanent deformation.

Environmental Assisted Fatigue Evaluation of Direct Vessel Injection Piping Considering Thermal Stratification

International Nuclear Information System (INIS)

Kim, Taesoon; Lee, Dohwan

2016-01-01

As the environmentally assisted fatigue (EAF) due to the primary water conditions is to be a critical issue, the fatigue evaluation for the components and pipes exposed to light water reactor coolant conditions has become increasingly important. Therefore, many studies to evaluate the fatigue life of the components and pipes in LWR coolant environments on fatigue life of materials have been conducted. Among many components and pipes of nuclear power plants, the direct vessel injection piping is known to one of the most vulnerable pipe systems because of thermal stratification occurred in that systems. Thermal stratification occurs because the density of water changes significantly with temperature. In this study, fatigue analysis for DVI piping using finite element analysis has been conducted and those results showed that the results met design conditions related with the environmental fatigue evaluation of safety class 1 pipes in nuclear power plants. Structural and fatigue integrity for the DVI piping system that thermal stratification occurred during the plant operation has conducted. First of all, thermal distribution of the piping system is calculated by computational fluid dynamic analysis to analyze the structural integrity of that piping system. And the fatigue life evaluation considering environmental effects was carried out. Our results showed that the DVI piping system had enough structural integrity and fatigue life during the design lifetime of 60 years

Thermo-mechanical Fatigue Failure of Thermal Barrier Coated Superalloy Specimen

Science.gov (United States)

Subramanian, Rajivgandhi; Mori, Yuzuru; Yamagishi, Satoshi; Okazaki, Masakazu

2015-09-01

Failure behavior of thermal barrier coated (TBC) Ni-based superalloy specimens were studied from the aspect of the effect of bond coat material behavior on low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) at various temperatures and under various loading conditions. Initially, monotonic tensile tests were carried out on a MCrAlY alloy bond coat material in the temperature range of 298 K to 1273 K (25 °C to 1000 °C). Special attention was paid to understand the ductile to brittle transition temperature (DBTT). Next, LCF and TMF tests were carried out on the thermal barrier coated Ni-based alloy IN738 specimen. After these tests, the specimens were sectioned to understand their failure mechanisms on the basis of DBTT of the bond coat material. Experimental results demonstrated that the LCF and TMF lives of the TBC specimen were closely related to the DBTT of the bond coat material, and also the TMF lives were different from those of LCF tests. It has also been observed that the crack density in the bond coat in the TBC specimen was significantly dependent on the test conditions. More importantly, not only the number of cracks but also the crack penetration probability into substrate were shown to be sensitive to the DBTT.

Thermal fatigue equipment to test joints of materials for high heat flux components

International Nuclear Information System (INIS)

Visca, E.; Libera, S.; Orsini, A.; Riccardi, B.; Sacchetti, M.

2000-01-01

The activity, carried out in the framework of an ITER divertor task, was aimed at defining a suitable method in order to qualify junctions between armour materials and heat sink of plasma-facing components (PFCs) mock-ups. An equipment able to perform thermal fatigue testing by electrical heating and active water-cooling was constructed and a standard for the sample was defined. In this equipment, during operation cycles, two samples are heated by thermal contact up to a relevant temperature value (350 deg. C) and then the water flow is switched on, thus producing fast cooling with time constants and gradients close to the real operating conditions. The equipment works with a test cycle of about 60 s and is suitable for continuous operation. A complete test consists of about 10000 cycles. After the assembling, the equipment and the control software were optimized to obtain a good reliability. Preliminary tests on mock-ups with flat CFC tiles joined to copper heat sink were performed. Finite-elements calculations were carried out in order to estimate the value of the thermal stresses arising close to the joint under the transient conditions that are characteristic of this equipment

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

International Nuclear Information System (INIS)

Kamaya, Masayuki; Taheri, Said

2008-01-01

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

Areva fatigue concept. Fast fatigue evaluation, a new method for fatigue analysis

International Nuclear Information System (INIS)

Heinz, Benedikt; Bergholz, Steffen; Rudolph, Juergen

2011-01-01

Within the discussions on the long term operation (LTO) of nuclear power plants the ageing management is on the focus of that analysis. The knowledge of the operational thermal cyclic load data on components of the power plants and their evaluation in the fatigue analysis is a central concern. The changes in fatigue requirements (e.g. the consideration of environmentally assisted fatigue - EAF) recently discussed and LTO efforts are a strong motivation for the identification of margins in the existing fatigue analysis approaches. These margins should be considered within new approaches in order to obtain realistic (or more accurate) analysis results. Of course, these new analysis approaches have to be manageable and efficient. The Areva Fatigue Concept (AFC) offers the comprehensive conceptual basis for the consideration of fatigue on different levels and depths. The combination of data logging and automated fatigue evaluation are important modules of the AFC. Besides the established simplified stress based fatigue estimation Areva develops a further automated fatigue analysis method called Fast Fatigue Evaluation (FFE). This method comprises highly automated stress analyses at the fatigue relevant locations of the component. Hence, a component specific course of stress as a function of time is determined based on FAMOS or similar temperature measurement systems. The subsequent application of the rain flow cycle counting algorithm allows for the determination of the usage factor following the rules of the design code requirements. The new FFE approach constitutes a cycle counting method based on the real stresses in the component, and determined as result a rule-conformity cumulative usage factor. (orig.)

Low-cycle fatigue behaviors of pre-hardening Hadfield steel

Energy Technology Data Exchange (ETDEWEB)

Chen, Chen [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, Bo [College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China); Wang, Fei [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, Fucheng, E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004 (China)

2017-05-17

Low-cycle fatigue behaviors of the pre-hardening (PH) and the water-quenching (WQ) Hadfield steel were studied using optical microscopy, transmission electron microscopy, and electron backscatter diffraction technique. The effect of the PH treatment on low-cycle fatigue behavior of the Hadfield steel was analyzed through comparing the cyclic hardening/softening behaviors and the changing regulations of stress amplitude, internal stress, and effective stress at different total strain amplitudes. Results showed obvious differences in fatigue behaviors between the PH (with a cold rolling deformation degree of 40%) and the WQ Hadfield steels. Transient hardening followed by cyclic stability behavior occurred in the PH Hadfield steel under cyclic loading, whereas cyclic softening behavior was barely observed. The fatigue life of the PH Hadfield steel was higher than that of the WQ Hadfield steel at relatively low strain amplitudes, while a contrary result was obtained at relatively high strain amplitudes. At low strain amplitudes, the deformation twins induced in the PH Hadfield steel could enhance the multiplication and slip process of dislocations, which actually improved the deformation uniformity. The long-range motion of dislocations was intensified at high strain amplitudes. However, the dislocation motion was also blocked by twin boundaries. As a result, the interactions between dislocations and deformation twins enhanced, finally causing severe dislocation accumulation. These two effects of deformation twins on dislocation motion eventually resulted in different low-cycle fatigue behaviors of the PH Hadfield steel.

High cycle fatigue test and regression methods of S-N curve

International Nuclear Information System (INIS)

Kim, D. W.; Park, J. Y.; Kim, W. G.; Yoon, J. H.

2011-11-01

The fatigue design curve in the ASME Boiler and Pressure Vessel Code Section III are based on the assumption that fatigue life is infinite after 106 cycles. This is because standard fatigue testing equipment prior to the past decades was limited in speed to less than 200 cycles per second. Traditional servo-hydraulic machines work at frequency of 50 Hz. Servo-hydraulic machines working at 1000 Hz have been developed after 1997. This machines allow high frequency and displacement of up to ±0.1 mm and dynamic load of ±20 kN are guaranteed. The frequency of resonant fatigue test machine is 50-250 Hz. Various forced vibration-based system works at 500 Hz or 1.8 kHz. Rotating bending machines allow testing frequency at 0.1-200 Hz. The main advantage of ultrasonic fatigue testing at 20 kHz is performing Although S-N curve is determined by experiment, the fatigue strength corresponding to a given fatigue life should be determined by statistical method considering the scatter of fatigue properties. In this report, the statistical methods for evaluation of fatigue test data is investigated

Numerical modeling of thermal fatigue cracks from the viewpoint of eddy current testing

International Nuclear Information System (INIS)

Yusa, Noritaka; Hashizume, Hidetoshi; Virkkunen, Iikka; Kemppainen, Mika

2012-01-01

This study discusses a suitable numerical modeling of a thermal fatigue crack from the viewpoint of eddy current testing. Five artificial thermal fatigue cracks, introduced into type 304L austenitic stainless steel plates with a thickness of 25 mm, are prepared; and eddy current inspections are carried out to gather signals using an absolute type pancake probe and a differential type plus point probe. Finite element simulations are then carried out to evaluate a proper numerical model of the thermal fatigue cracks. In the finite element simulations, the thermal fatigue cracks are modeled as a semi-elliptic planar region on the basis of the results of the destructive tests. The width and internal conductivity are evaluated by the simulations. The results of the simulations reveal that the thermal fatigue cracks are regarded as almost nonconductive when the internal conductivity is assumed to be uniform inside. (author)

Analysis result for OECD benchmark on thermal fatigue problem

International Nuclear Information System (INIS)

Kamaya, Masayuki; Nakamura, Akira; Fujii, Yuzou

2005-01-01

The main objective of this analysis is to understand the crack growth behavior under three-dimensional (3D) thermal fatigue by conducting 3D crack initiation and propagation analyses. The possibility of crack propagation through the wall thickness of pipe, and the accuracy of the prediction of crack initiation and propagation are of major interest. In this report, in order to estimate the heat transfer coefficients and evaluate the thermal stress, conventional finite element analysis (FEA) is conducted. Then, the crack driving force is evaluated by using the finite element alternating method (FEAM), which can derive the stress intensity factor (SIF) under 3D mechanical loading based on finite element analysis without generating the mesh for a cracked body. Through these two realistic 3D numerical analyses, it has been tried to predict the crack initiation and propagation behavior. The thermal fatigue crack initiation and propagation behavior were numerically analyzed. The conventional FEA was conducted in order to estimate the heat transfer coefficient and evaluate the thermal stress. Then, the FEAM was conducted to evaluate the SIFs of surface single cracks and interacting multiple cracks, and crack growth was evaluated. The results are summarized as follows: 1. The heat transfer coefficients were estimated as H air = 40 W/m 2 K and H water = 5000 W/m 2 K. This allows simulation of the change in temperature with time at the crack initiation points obtained by the experiment. 2. The maximum stress occurred along the line of symmetry and the maximum Mises equivalent stress was 572 MPa. 3. By taking the effect of mean stress into account according to the modified Goodman diagram, the equivalent stress range and the number of cycles to crack initiation were estimated as 1093 MPa and 3.8x10 4 , respectively, although the tensile strength was assumed to be 600 MPa. 4. It was shown from the evaluated SIFs that longitudinal cracks can penetrate the wall of the pipe

Low-cycle fatigue of dissimilar friction stir welded aluminum alloys

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, R.I. [The University of Alabama, Department of Mechanical Engineering, Tuscaloosa, AL 35487 (United States); Jordon, J.B., E-mail: bjordon@eng.ua.edu [The University of Alabama, Department of Mechanical Engineering, Tuscaloosa, AL 35487 (United States); Allison, P.G. [The University of Alabama, Department of Mechanical Engineering, Tuscaloosa, AL 35487 (United States); Rushing, T.; Garcia, L. [Engineering Research and Development Center, Army Corps of Engineers, Vicksburg, MS 39180 (United States)

2016-01-27

In this work, experiments were conducted to quantify structure-property relations of low-cycle fatigue behavior of dissimilar friction stir welding (FSW) of AA6061-to-AA7050 high strength aluminum alloys. In addition, a microstructure-sensitive fatigue model is employed to further elucidate cause-effect relationships. Experimental strain-controlled fatigue testing revealed an increase in the cyclic strain hardening and the number-of cycles to failure as the tool rotational speed was increased. At higher applied strain amplitudes (>0.3%), the corresponding stress amplitude increased and the plastic strain amplitude decreased, as the number of cycles increased. However, at 0.2% strain amplitude, the plastic strain decreased until it was almost negligible. Inspection of the hysteresis loops demonstrated that at low strain amplitudes, there was an initial stage of strain hardening that increased until it reached a maximum strain hardening level, afterwards a nearly perfect elastic behavior was observed. Under fully-reversed fatigue loading, all samples failed at the region between the heat-affected and thermomechanically-affected zones. Inspection of the fractured surfaces under scanning electron microscopy revealed that the cracks initiated at either the crown or the root surface of the weld, and from secondary intermetallic particles located near the free surface of the weld. Lastly, a microstructure-sensitive multistage fatigue model was employed to correlate the fatigue life of the dissimilar FSW of AA6061-to-AA7050 considering microstructural features such as grain size, intermetallic particles and mechanical properties.

Influences of Processing and Fatigue Cycling on Residual Stresses in a NiCrY-Coated Powder Metallurgy Disk Superalloy

Science.gov (United States)

Gabb, T. P.; Rogers, R. B.; Nesbitt, J. A.; Miller, R. A.; Puleo, B. J.; Johnson, D.; Telesman, J.; Draper, S. L.; Locci, I. E.

2017-11-01

Oxidation and corrosion can attack superalloy disk surfaces exposed to increasing operating temperatures in some turbine engine environments. Any potential protective coatings must also be resistant to harmful fatigue cracking during service. The objective of this study was to investigate how residual stresses evolve in one such coating. Fatigue specimens of a powder metallurgy-processed disk superalloy were coated with a NiCrY coating, shot peened, and then subjected to fatigue in air at room and high temperatures. The effects of this processing and fatigue cycling on axial residual stresses and other aspects of the coating were assessed. While shot peening did induce beneficial compressive residual stresses in the coating and substrate, these stresses relaxed in the coating with subsequent heating. Several cast alloys having compositions near the coating were subjected to thermal expansion and tensile stress relaxation tests to help explain this response of residual stresses in the coating. For the coated fatigue specimens, this response contributed to earlier cracking of the coating than for the uncoated surface during long intervals of cycling at 760 °C. Yet, substantial compressive residual stresses still remained in the substrate adjacent to the coating, which were sufficient to suppress fatigue cracking there. The coating continued to protect the substrate from hot corrosion pitting, even after fatigue cracks initiated in the coating.

Effect of alumina-silica-zirconia eutectic ceramic thermal barrier coating on the low cycle fatigue behaviour of cast polycrystalline nickel-based superalloy at 900 °C

Czech Academy of Sciences Publication Activity Database

Obrtlík, Karel; Čelko, L.; Chráska, Tomáš; Šulák, Ivo; Gejdoš, P.

2017-01-01

Roč. 318, MAY (2017), s. 374-381 ISSN 0257-8972. [RIPT - International Meeting on Thermal Spraying /7./. Limoges, 09.12.2015-12.12.2015] R&D Projects: GA ČR(CZ) GA15-20991S Institutional support: RVO:68081723 ; RVO:61389021 Keywords : Thermal barrier coating * Nickel-based superalloy * Plasma spraying * High temperature fatigue * Fatigue life * Cyclic stress-strain curve Subject RIV: JL - Materials Fatigue, Friction Mechanics; JL - Materials Fatigue, Friction Mechanics (UFP-V) OBOR OECD: Audio engineering, reliability analysis; Audio engineering, reliability analysis (UFM-A); Audio engineering, reliability analysis (UFP-V) Impact factor: 2.589, year: 2016

Development of a Very High Cycle Fatigue (VHCF multiaxial testing device

Directory of Open Access Journals (Sweden)

M. Vieira

2016-07-01

Full Text Available The very high cycle region of the S-N fatigue curve has been the subject of intensive research on the last years, with special focus on axial, bending, torsional and fretting fatigue tests. Very high cycle fatigue can be achieved using ultrasonic exciters which allow for frequency testing of up to 30 kHz. Still, the multiaxial fatigue analysis is not yet developed for this type of fatigue analyses, mainly due to conceptual limitations of these testing devices. In this paper, a device designed to produce biaxial fatigue testing using a single piezoelectric axial exciter is presented, as well as the preliminary testing of this device. The device is comprised of a horn and a specimen, which are both attached to the piezoelectric exciter. The steps taken towards the final geometry of the device are presented. Preliminary experimental testing of the developed device is made using thermographic imaging, strain measurements and vibration speeds and indicates good behaviour of the tested specimen.

Effects of HTGR helium on the high cycle fatigue of structural materials

International Nuclear Information System (INIS)

Soo, P.; Sabatini, R.L.; Gerlach, L.

1982-01-01

High cycle fatigue tests have been conducted on Incoloy 800H and Hastelloy X in air and in HTGR helium environments containing low and high levels of moisture. For the helium environments, a higher mositure level usually gives a lower fatigue strength. For air, however, the strength is usually much lower than those for helium. For long test times at higher test temperatures, the fatigue strengths for Incoloy 800H often show a large decrease, and the fatigue limits are much lower than those anticipated from low cycle tests. Optical and scanning electron microscope observations were made to correlate fatigue life with surface and bulk microstructural changes in the material during test. Oxide scale cracking and spallation, surface recrystallization and intergranular attack appear to contribute to losses in fatigue strength

Thermographic Inspection of Fatigue Crack by Using Contact Thermal Resistance

Energy Technology Data Exchange (ETDEWEB)

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

2013-04-15

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

Thermographic Inspection of Fatigue Crack by Using Contact Thermal Resistance

International Nuclear Information System (INIS)

Yang, Seung Yong; Kim, No Hyu

2013-01-01

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

Reinforcement architectures and thermal fatigue in diamond particle-reinforced aluminum

Energy Technology Data Exchange (ETDEWEB)

Schoebel, M., E-mail: michaels@mail.tuwien.ac.at [Institute of Materials Science and Technology, Vienna University of Technology, Karlsplatz 13, A-1040 Vienna (Austria); Degischer, H.P. [Institute of Materials Science and Technology, Vienna University of Technology, Karlsplatz 13, A-1040 Vienna (Austria); Vaucher, S. [Advanced Materials Processing, EMPA - Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkstrasse 39, CH-3602 Thun (Switzerland); Hofmann, M. [Forschungsneutronenquelle Heinz Maier-Leibnitz, Lichtenbergstrasse 1, D-85747 Garching (Germany); Cloetens, P. [European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, F-38043 Grenoble (France)

2010-11-15

Aluminum reinforced by 60 vol.% diamond particles has been investigated as a potential heat sink material for high power electronics. Diamond (CD) is used as reinforcement contributing its high thermal conductivity (TC {approx} 1000 W mK{sup -1}) and low coefficient thermal expansion (CTE {approx} 1 ppm K{sup -1}). An Al matrix enables shaping and joining of the composite components. Interface bonding is improved by limited carbide formation induced by heat treatment and even more by SiC coating of diamond particles. An AlSi7 matrix forms an interpenetrating composite three-dimensional (3D) network of diamond particles linked by Si bridges percolated by a ductile {alpha}-Al matrix. Internal stresses are generated during temperature changes due to the CTE mismatch of the constituents. The stress evolution was determined in situ by neutron diffraction during thermal cycling between room temperature and 350 deg. C (soldering temperature). Tensile stresses build up in the Al/CD composites: during cooling <100 MPa in a pure Al matrix, but around 200 MPa in the Al in an AlSi7 matrix. Compressive stresses build up in Al during heating of the composite. The stress evolution causes changes in the void volume fraction and interface debonding by visco-plastic deformation of the Al matrix. Thermal fatigue damage has been revealed by high resolution synchrotron tomography. An interconnected diamond-Si 3D network formed with an AlSi7 matrix promises higher stability with respect to cycling temperature exposure.

The effect of shot peening on notched low cycle fatigue

International Nuclear Information System (INIS)

Soady, K.A.; Mellor, B.G.; Shackleton, J.; Morris, A.; Reed, P.A.S.

2011-01-01

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.

Multiaxial Cycle Deformation and Low-Cycle Fatigue Behavior of Mild Carbon Steel and Related Welded-Metal Specimen

Directory of Open Access Journals (Sweden)

Weilian Qu

2017-01-01

Full Text Available The low-cycle fatigue experiments of mild carbon Q235B steel and its related welded-metal specimens are performed under uniaxial, in-phase, and 90° out-of-phase loading conditions. Significant additional cyclic hardening for 90° out-of-phase loading conditions is observed for both base metal and its related weldment. Besides, welding process produces extra additional hardening under the same loading conditions compared with the base metal. Multiaxial low-cycle fatigue strength under 90° out-of-phase loading conditions is significantly reduced for both base-metal and welded-metal specimens. The weldment has lower fatigue life than the base metal under the given loading conditions, and the fatigue life reduction of weldment increases with the increasing strain amplitude. The KBM, FS, and MKBM critical plane parameters are evaluated for the fatigue data obtained. The FS and MKBM parameters are found to show better correlation with fatigue lives for both base-metal and welded-metal specimens.

Large eddy simulation of a T-Junction with upstream elbow: The role of Dean vortices in thermal fatigue

International Nuclear Information System (INIS)

Tunstall, R.; Laurence, D.; Prosser, R.; Skillen, A.

2016-01-01

Highlights: • A T-Junction with an upstream bend is studied using wall-resolved LES and POD. • The bend generates Dean vortices which remain prominent downstream of the junction. • Dean vortex swirl-switching results in an unsteady secondary flow about the pipe axis. • This provides a further mechanism for near-wall temperature fluctuations. • Upstream bends can have a crucial role in T-Junction thermal fatigue problems. - Abstract: Turbulent mixing of fluids in a T-Junction can generate oscillating thermal stresses in pipe walls, which may lead to high cycle thermal fatigue. This thermal stripping problem is an important safety issue in nuclear plant thermal-hydraulic systems, since it can lead to unexpected failure of the pipe material. Here, we carry out a large eddy simulation (LES) of a T-Junction with an upstream bend and use proper orthogonal decomposition (POD) to identify the dominant structures in the flow. The bend generates an unsteady secondary flow about the pipe axis, known as Dean vortex swirl-switching. This provides an additional mechanism for low-frequency near-wall temperature fluctuations downstream of the T-Junction, over those that would be produced by mixing in the same T-Junction with straight inlets. The paper highlights the important role of neighbouring pipe bends in T-Junction thermal fatigue problems and the need to include them when using CFD as a predictive tool.

Numerical methods for the prediction of thermal fatigue due to turbulent mixing

International Nuclear Information System (INIS)

Hannink, M.H.C.; Blom, F.J.

2011-01-01

Research highlights: → Thermal fatigue due to turbulent mixing is caused by moving temperature spots on the pipe wall. → Passing temperature spots cause temperature fluctuations of sinusoidal nature. → Input parameters for a sinusoidal model can be obtained by linking it with a coupled CFD-FEM model. → Overconservatism of the sinusoidal method can be reduced, having more knowledge on thermal loads. - Abstract: Turbulent mixing of hot and cold flows is one of the possible causes of thermal fatigue in piping systems. Especially in primary pipework of nuclear power plants this is an important, safety related issue. Since the frequencies of the involved temperature fluctuations are generally too high to be detected well by common plant instrumentation, accurate numerical simulations are indispensable for a proper fatigue assessment. In this paper, a link is made between two such numerical methods: a coupled CFD-FEM model and a sinusoidal model. By linking these methods, more insight is obtained in the physical phenomenon causing thermal fatigue due to turbulent mixing. Furthermore, useful knowledge is acquired on the determination of thermal loading parameters, essential for reducing overconservatism, as currently present in simplified fatigue assessment methods.

Low Cycle Fatigue of Steel in Strain Controled Cyclic Bending

Directory of Open Access Journals (Sweden)

Kulesa Anna

2016-03-01

Full Text Available The paper presents a comparison of the fatigue life curves based on test of 15Mo3 steel under cyclic, pendulum bending and tension-compression. These studies were analyzed in terms of a large and small number of cycles where strain amplitude is dependent on the fatigue life. It has been shown that commonly used Manson-Coffin-Basquin model cannot be used for tests under cyclic bending due to the impossibility of separating elastic and plastic strains. For this purpose, some well-known models of Langer and Kandil and one new model of authors, where strain amplitude is dependent on the number of cycles, were proposed. Comparing the results of bending with tension-compression it was shown that for smaller strain amplitudes the fatigue life for both test methods were similar, for higher strain amplitudes fatigue life for bending tests was greater than for tension-compression.

Stochastic modeling of thermal fatigue crack growth

CERN Document Server

Radu, Vasile

2015-01-01

The book describes a systematic stochastic modeling approach for assessing thermal-fatigue crack-growth in mixing tees, based on the power spectral density of temperature fluctuation at the inner pipe surface. It shows the development of a frequency-temperature response function in the framework of single-input, single-output (SISO) methodology from random noise/signal theory under sinusoidal input. The frequency response of stress intensity factor (SIF) is obtained by a polynomial fitting procedure of thermal stress profiles at various instants of time. The method, which takes into account the variability of material properties, and has been implemented in a real-world application, estimates the probabilities of failure by considering a limit state function and Monte Carlo analysis, which are based on the proposed stochastic model. Written in a comprehensive and accessible style, this book presents a new and effective method for assessing thermal fatigue crack, and it is intended as a concise and practice-or...

The low cycle fatigue factor in the construction of sodium-cooled fast reactors

International Nuclear Information System (INIS)

Petrequin, Pierre; Mottot, Michel; Valibus, Louis; Grattier, Georges

1976-01-01

The working conditions of fast neutron reactors are such that it is essential to know the resistance of the component steels to low cycle fatigue. The behavior of Z2CND17-13 type austenitic stainless steels and of welds was studied in three laboratories. The steels offer an excellent resistance to low cycle fatigue, in keeping with their good ductility and very strong aptitude for cyclic strain hardening. Increasing the testing temperature from 20 to 600 deg C reduces the resistance to some extent (about an order of magnitude on the number of cycles to failure). Steels possessing improved mechanical properties without loss of ductility show greater fatigue resistance. Welds characterized by an austenitic ferritic structure and a slightly cold-hardened state are less ductile than laminated steels. Their resistance to low cycle fatigue is lower at strong deformations. At high temperature (600 deg C) a reduced test frequency or a pause at each cycle leads to a considerable drop in the number of cycles to failure and the appearance of intergranular cracking [fr

Thermal-structural Analysis and Fatigue Life Evaluation of a Parallel Slide Gate Valve in Accordance with ASME B and PVC

Energy Technology Data Exchange (ETDEWEB)

Kim, Tae Ho; Han, Jeong Sam [Andong Nat’l Univ., Andong (Korea, Republic of); Jae Seung Choi [Key Valve Technologies Ltd., Siheung (Korea, Republic of)

2017-02-15

A parallel slide gate valve (PSGV) is located between the heat recovery steam generator (HRSG) and the steam turbine in a combined cycle power plant (CCPP). It is used to control the flow of steam and runs with repetitive operations such as startups, load changes, and shutdowns during its operation period. Therefore, it is necessary to evaluate the fatigue damage and the structural integrity under a large compressive thermal stress due to the temperature difference through the valve wall thickness during the startup operations. In this paper, the thermal-structural analysis and the fatigue life evaluation of a 16-inch PSGV, which is installed on the HP steam line, is performed according to the fatigue life assessment method described in the ASME B and PVC VIII-2; the method uses the equivalent stress from the elastic stress analysis.

Research and development studies for predicting the thermal fatigue; Etudes de R and D pour la prediction de la fatigue thermique

Energy Technology Data Exchange (ETDEWEB)

Moulin, D.; Garnier, J.; Fissolo, A.; Lejeail, Y. [CEA, 75 - Paris (France); Stephan, J.M.; Moinereau, D.; Masson, J. [Electricite de France, Les Renardieres, 77 - Moret sur Loing (France). Direction des Etudes et Recherches

2001-07-01

This paper presents some studies in development or realized in the EDF and CEA laboratories, concerning the thermal fatigue damage in nuclear reactor components. The first part presents the basic principles and the methods of lifetime prediction. The second part gives some examples on sodium loop, water loop, welded junctions resistance to thermal fatigue and tests on fatigue specimen. (A.L.B.)

A low cycle fatigue model for low carbon manganese steel including the effect of dynamic strain aging

Energy Technology Data Exchange (ETDEWEB)

Huang, Zhi Yong, E-mail: huangzy@scu.edu.cn [Sichuan University, School of Aeronautics and Astronautics, No.29 Jiuyanqiao Wangjiang Road, Chengdu 610064 (China); Wagner, Danièle [Université Paris Ouest Nanterre La Défense (France); Wang, Qing Yuan; Khan, Muhammad Kashif [Sichuan University, School of Aeronautics and Astronautics, No.29 Jiuyanqiao Wangjiang Road, Chengdu 610064 (China); Chaboche, Jean–Louis [ONERA, DMSM, 29 avenue de la Division Lecerc, F-92320, Chatillon (France)

2016-01-27

Carbon–manganese steel A48 (French standards) is used in steam generator pipes of the nuclear power plant where it is subjected to the cyclic thermal load. The Dynamic Strain Aging (DSA) influences the mechanical behavior of the steel in low cycle fatigue (LCF) at favorable temperature and strain rate. The peak stress of A48 steel experiences hardening–softening–hardening (HSH) evolution at 200 °C and 0.4% s{sup −1} strain rate in fatigue loading. In this study, isotropic and kinematic hardening rules with DSA effect have been modified. The HSH evolution of cyclic stress associated with cumulative plastic deformation has also been estimated.

PO2 cycling reduces diaphragm fatigue by attenuating ROS formation.

Science.gov (United States)

Zuo, Li; Diaz, Philip T; Chien, Michael T; Roberts, William J; Kishek, Juliana; Best, Thomas M; Wagner, Peter D

2014-01-01

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.

PO2 cycling reduces diaphragm fatigue by attenuating ROS formation.

Directory of Open Access Journals (Sweden)

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.

Effect of cyclic plastic pre-strain on low cycle fatigue life

International Nuclear Information System (INIS)

Kanno, Satoshi; Nakane, Motoki; Yorikawa, Morio; Takagi, Yoshio

2010-01-01

In order to evaluate structural integrity of nuclear components subjected large seismic load which produce locally plastic strain, low cycle fatigue life was examined using cyclic plastic pre-strained materials of austenitic steel (SUS316, SUS316L, SUS304TP: JIS (Japanese Industrial Standards)) and ferritic steel (SFVQ1A, STS480, STPT410, SFVC2B, SS400: JIS). It was not found that cyclic plastic pre-strain up to range of 16%, 2.5 times affected on low cycle fatigue life. The validity of existing procedure of fatigue life estimation based on usage factor was confirmed when large seismic load brought nuclear materials cyclic plastic strain. (author)

Thermal stratification and fatigue stress analysis for pressurizer surge line

International Nuclear Information System (INIS)

Yu Xiaofei; Zhang Yixiong

2011-01-01

Thermal stratification of pressurizer surge line induced by the inside fluid results in the global bending moments, local thermal stresses, unexpected displacements and support loadings of the pipe system. In order to avoid a costly three-dimensional computation, a combined 1D/2D technique has been developed and implemented to analyze the thermal stratification and fatigue stress of pressurize surge line of QINSHAN Phase II Extension Nuclear Power Project in this paper, using the computer codes SYSTUS and ROCOCO. According to the mechanical analysis results of stratification, the maximum stress and cumulative usage factor are obtained. The results indicate that the stress and fatigue intensity considering thermal stratification satisfies RCC-M criterion. (authors)

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

International Nuclear Information System (INIS)

Dong, P.; Pei, X.; Xing, S.; Kim, M.H.

2014-01-01

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

Development of a high cycle vibration fatigue diagnostic system with non-contact vibration sensing

International Nuclear Information System (INIS)

Yoshitsugu, Nekomoto; Satoshi, Kiriyama; Moritatsu, Nishimura; Kenji, Matsumoto; Eiji, O'shima

2001-01-01

Nuclear power plants have a large number of pipes. Of these small-diameter pipe branches in particular are often damaged due to high-cycle fatigue. In order to ensure the reliability of a plant it is important to detect the fatigues in pipe branches at an early stage and to develop the technology to predict and diagnose the advancement of fatigue. Further, in order to carry out the diagnosis of the piping system effectively during operation, non-contact evaluation is useful. Hence, we have developed a 'high-cycle fatigue diagnostic system with non-contact vibration sensing', where the vibration of the pipe branch is measured using a non-contact sensor. Since the contents of the developed sensor technology has already been reported, this paper mainly describes the newly developed high-cycle fatigue diagnostic system. (authors)

Study of the damage processes induced by thermal fatigue in stainless steels F17TNb and R20-12 for automobile application; Etude de l'endommagement en fatigue thermique des aciers inoxydables F17TNb et R20-12 pour application automobile

Energy Technology Data Exchange (ETDEWEB)

Bucher, L.

2004-12-15

Thermal cycling is the main cause of fatigue failure in automobile exhaust manifolds for which the use of stainless steel now rivals that of cast iron which has been traditionally used. An original fatigue test has been developed by Ugine and ALZ, a stainless steel producer, so as to be able to compare different grades of stainless steel alloys. This test is representative of the thermal conditions encountered in the critical zones of exhaust manifolds. However, it has revealed significant differences in damage processes in the ferritic and austenitic grades tested. The subject of this thesis is the damage processes induced by thermal fatigue in stainless steels used for automotive exhaust manifolds. Two stainless steels were studied: a ferritic grade, F17TNb (17%Cr and stabilized with Ti and Nb), and an austenitic grade, R20-12, containing 20% Cr and 12% Ni. The first objective was to understand the different damage processes induced by thermal fatigue in the ferritic and austenitic grades. The second was to develop a numerical design tool of the thermally tested structures. (author)

Cyclic fatigue of near-isotopic graphite: influence of stress cycle and neutron irradiation

International Nuclear Information System (INIS)

Price, R.J.

1977-11-01

Near-isotropic graphites H-451 and PGX were tested in uniaxial cyclic fatigue, and fatigue life (S-N) curves were generated to a maximum of 10 5 cycles. The stress ratio, R (minimum stress during a cycle divided by maximum stress) ranged from -1 to +0.5. With R = - 1, the homologous stress limits (maximum applied fatigue stress divided by the tensile strength) for 50% specimen survival to 10 5 cycles averaged 0.63 in the axial direction and 0.74 in the radial direction. Corresponding homologous stress limits for 99% specimen survival (99/95 tolerance limits) were 0.48 and 0.53. Higher R-values resulted in longer fatigue lives and increased stress limits. H-451 graphite specimens irradiated with fast neutrons at 1173 to 1263 0 K at fluences of up to 10 26 n/m 2 (equivalent fission fluence) showed fatigue stress limits of about twice the unirradiated levels when the unirradiated tensile strength was used as the basis for normalization

Low cycle fatigue of PM/HIP astroloy

Energy Technology Data Exchange (ETDEWEB)

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

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

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

International Nuclear Information System (INIS)

Robert, G.; Mathiot, A.; Regnard, C.; Dessus, J.; Claret, J.

1982-04-01

Alloy 800 (grade I) is used for making the steam generators of liquid metal fast breeder reactors. At working temperature (525 0 C) alloy 800 is strengthned by γ' (Ni 3 (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 550 0 C, of structural and microstructural variations originating either in different elaboration procedures or in γ' precipitation obtained by a thermal aging of 3000h at 550 0 C with or without a preceeding cold working of 10% [fr

Effect of grain size on high temperature low-cycle fatigue properties of inconel 617

International Nuclear Information System (INIS)

Hattori, Hiroshi; Kitagawa, Masaki; Ohtomo, Akira

1982-01-01

The effect of grain size on the high temperature low-cycle fatigue behavior and other material strength properties of Inconel 617 was studied at 1 273 K in air. The strain controlled low-cycle fatigue tests were conducted with a symmetrical (FF type) and an asymmetrical (SF type) strain wave forms. The latter wave form was used for the evaluation of creep-fatigue interaction. The main results obtained in this study are as follows: 1) The tensile strength slightly increased with the increase of the grain diameter. On the other hand, the tensile ductility remarkabley decreased with the increase of the grain diameter. 2) The creep rupture life remarkabley increased with the increase of the grain diameter, especially at the lower stress levels. The effect of grain size on creep ductility has not detailed. 3) The low-cycle fatigue life remarkably decreased with the increase of the grain diameter, especially at the lower strain ranges. 4) The creep-fatigue life was less sensitive to the grain diameter than the fatigue life, because the grain size effects on creep and on fatigue were contrary. It is seemed that the creep-fatigue life is determined by the proportion of the creep and fatigue contribution. 5) The fatigue and creep-fatigue test results have good relations with the tensile and creep ductilities at the test temperature. (author)

A model for life predictions of nickel-base superalloys in high-temperature low cycle fatigue

Science.gov (United States)

Romanoski, Glenn R.; Pelloux, Regis M.; Antolovich, Stephen D.

1988-01-01

Extensive characterization of low-cycle fatigue damage mechanisms was performed on polycrystalline Rene 80 and IN100 tested in the temperature range from 871 to 1000 C. Low-cycle fatigue life was found to be dominated by propagation of microcracks to a critical size governed by the maximum tensile stress. A model was developed which incorporates a threshold stress for crack extension, a stress-based crack growth expression, and a failure criterion. The mathematical equivalence between this mechanistically based model and the strain-life low-cycle fatigue law was demonstrated using cyclic stress-strain relationships. The model was shown to correlate the high-temperature low-cycle fatigue data of the different nickel-base superalloys considered in this study.

Mesoscopic scale thermal fatigue damage

International Nuclear Information System (INIS)

Robertson, C.; Fissolo, A.; Fivel, M.

2001-01-01

In an attempt to better understand damage accumulation mechanisms in thermal fatigue, dislocation substructures forming in 316L steel during one specific test were examined and simulated. Hence, thin foils taken out of massive, tested specimens were first observed in transmission electron microscopy (TEM). These observations help in determining one initial dislocation configuration to be implemented in a 3-D model combining 3D discrete dislocation dynamics simulation (DDD) and finite element method computations (FEM). It was found that the simulated mechanical behaviour of the DDD microstructure is compatible with FEM and experimental data. The numerically generated dislocation microstructure is similar to ladder-like dislocation arrangements as found in many fatigued f.c.c. materials. Distinct mechanical behaviour for the two active slip systems was shown and deformation mechanisms were proposed. (authors)

Mesoscopic scale thermal fatigue damage

Energy Technology Data Exchange (ETDEWEB)

Robertson, C.; Fissolo, A. [CEA Saclay, Dept. des Materiaux pour le Nucleaire, DMN, 91 - Gif sur Yvette (France); Fivel, M. [Centre National de la Recherche Scientifique, CNRS-GPM2, 38 - Saint Martin d' Heres (France)

2001-07-01

In an attempt to better understand damage accumulation mechanisms in thermal fatigue, dislocation substructures forming in 316L steel during one specific test were examined and simulated. Hence, thin foils taken out of massive, tested specimens were first observed in transmission electron microscopy (TEM). These observations help in determining one initial dislocation configuration to be implemented in a 3-D model combining 3D discrete dislocation dynamics simulation (DDD) and finite element method computations (FEM). It was found that the simulated mechanical behaviour of the DDD microstructure is compatible with FEM and experimental data. The numerically generated dislocation microstructure is similar to ladder-like dislocation arrangements as found in many fatigued f.c.c. materials. Distinct mechanical behaviour for the two active slip systems was shown and deformation mechanisms were proposed. (authors)

THERMAL FATIGUE OF INCONEL ALLOY DA718

Science.gov (United States)

2016-10-27

this material meets the required improvement and offers a low cost alternative to powder metallurgy Rene’95. However, its thermal fatigue resistance...chromel-alumel thermocouple, spot- welded to the mid-length of the specimen. The thermal strain, induced by the expansion and contraction of the...12 FOR OFFICIAL USE ONLY 13. J. F. Radavich, “The Physical Metallurgy of Cast and Wrought Alloy 718,” in Superalloy 718 – Metallurgy and

Results from low cycle fatigue testing of 316L plate and weld material

International Nuclear Information System (INIS)

Kaellstroem, R.; Josefsson, B.; Haag, Y.

1993-01-01

Specimens for low cycle fatigue testing from the second heat of the CEC reference 316L plate and from Tungsten Inert Gas (TIG) weld material have been neutron irradiated near room temperature to a displacement dose of approximately 0.3 dpa. The low cycle fatigue testing of both irradiated and unirradiated specimens was performed at 75, 250 and 450 degrees C, and with strain ranges of 0.75, 1.0 and 1.5%. There is no clear effect of the irradiation on low cycle fatigue properties. For the weld material the endurance is shorter than for plate, and the dependences on temperature and strain range are not clear

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

Directory of Open Access Journals (Sweden)

B. Piekarski

2007-12-01

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

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

Directory of Open Access Journals (Sweden)

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.

Low cycle fatigue analysis of a last stage steam turbine blade

Directory of Open Access Journals (Sweden)

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.

Thermal cycling tests of actively cooled beryllium copper joints

Energy Technology Data Exchange (ETDEWEB)

Roedig, M.; Duwe, R.; Linke, J.; Schuster, A.; Wiechers, B. [Forschungszentrum Juelich GmbH (Germany)

1998-01-01

Screening tests (steady state heating) and thermal fatigue tests with several kinds of beryllium-copper joints have been performed in an electron beam facility. Joining techniques under investigation were brazing with silver containing and silver-free braze materials, hot isostatic pressing (HIP) and diffusion bonding (hot pressing). Best thermal fatigue performance was found for the brazed samples. (author)

ISOTHERMAL AND THERMOMECHANICAL FATIGUE OF A NICKEL-BASE SUPERALLOY

Directory of Open Access Journals (Sweden)

Carlos Carvalho Engler-Pinto Júnior

2014-06-01

Full Text Available 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 temperatures range from 600°C to 1,000°C. The behavior of the alloy is strongly affected by the temperature variation, especially in the 800°C-1,000°C range. The Ramberg-Osgood equation fits very well the observed isothermal behavior for the whole temperature range. The simplified non-isothermal stress-strain model based on linear plasticity proposed to represent the thermo-mechanical fatigue behavior was able to reproduce the observed behavior for both in-phase and out-of-phase TMF cycling.

Study of system safety evaluation on LTO of national project. Thermal fatigue evaluation of piping systems

International Nuclear Information System (INIS)

Kasahara, Naoto; Itoh, Takamoto; Okazaki, Masakazu; Okuda, Yukihiko; Kamaya, Masayuki; Nakamura, Akira; Nakamura, Hitoshi; Machida, Hideo

2012-01-01

Nuclear piping has various kinds of thermal fatigue failure modes. Main causes of thermal loads are structural responses to fluid temperature changes during plant operation. These phenomena have complex mechanisms and so many patterns, that their problems still occur even though well-known issues. To prevent thermal fatigue due to above thermal loads, the JSME guideline is adopted. Both thermal load and fatigue failure mechanism have been investigated and summarized into the knowledgebase. Numerical simulation methods for thermal fatigue evaluation were studied to replace structural tests. Theses knowledge was utilized to validate and justify the JSME guideline. Furthermore, new studies have been launched to apply above knowledge to enhance plant system safety. (author)

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

International Nuclear Information System (INIS)

Van Nieuwenhove, R.; Moons, F.

1994-12-01

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

Analysis of fatigue crack initiation in cycled austempered ductile cast irons

Czech Academy of Sciences Publication Activity Database

Petrenec, Martin; Beran, Přemysl; Dluhoš, J.; Zouhar, Michal; Ševčík, Martin

2010-01-01

Roč. 2, č. 1 (2010), s. 2337-2346 E-ISSN 1877-7058. [ Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GAP108/10/2371; GA ČR GD106/09/H035 Institutional research plan: CEZ:AV0Z20410507; CEZ:AV0Z10480505 Keywords : Low cycle fatigue * ADI * Finite element modelling * Neutron diffraction Subject RIV: JL - Materials Fatigue , Friction Mechanics

High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

Science.gov (United States)

Zhao, Jing; Ji, Honghong

2017-01-01

The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite. PMID:29286325

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

International Nuclear Information System (INIS)

Strizak, J.P.; Brinkman, C.R.; Booker, M.K.; Rittenhouse, P.L.

1982-04-01

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 871 0 C 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 538 0 C. An analysis is also presented of the continuous cycle fatigue data obtained from room temperature to 427 0 C for Hastelloy G, Hastelloy X, Hastelloy C-276, and Hastelloy C-4, an effort undertaken in support of ASME code development

Improvement in thermal fatigue resistance of cast iron piston; Chutetsu piston no tainetsu hiro sekkei

Energy Technology Data Exchange (ETDEWEB)

Amano, K; Uosaki, Y; Takeshige, N [Mazda Motor Corp., Hiroshima (Japan)

1997-10-01

Cast iron piston is superior in reduction of diesel engine emission to aluminum piston because of its characteristic of heat insulation. In order to study thermal fatigue characteristics of cast iron, thermal fatigue tests were carried out on two kinds of ferrite ductile cast iron. Differences between cast iron piston and aluminum piston in thermal fatigue resistance have been investigated by using FEM analysis. 5 refs., 14 figs., 1 tab.

Effects of environment on the low-cycle fatigue behavior of Type 304 stainless steel

International Nuclear Information System (INIS)

Maiya, P.S.; Burke, W.F.

1979-12-01

The low-cycle fatigue behavior of Type 304 stainless steel has been investigated at 593 0 C in a dynamic vacuum of better than 1.3 x 10 -6 Pa (10 -8 torr). The results concerning the effects of strain range, strain rate and tensile hold time on fatigue life are presented and compared with results of similar tests performed in air and sodium environments. Under continuous symmetrical cycling, fatigue life is significantly longer in vacuum than in air; in the low strain range regime, the effect of sodium on fatigue life appears to be similar to that of vacuum. Strain rate (or frequency) strongly influences fatigue life in both air and vacuum. In compressive hold-time tests, the effect of environment on life is similar to that in a continuous-cycling test. However, tensile hold times are nearly as damaging in vacuum as in air. Thus, at least for austenitic stainless steels, the influence of the environment of fatigue life appears to depend on the loading waveshape

Crack propagation under thermal cycling loading inducing a thermal gradient in the specimen thickness

International Nuclear Information System (INIS)

Le, H.N.

2009-05-01

This study aims to figure out the crack growth phenomenon by thermal fatigue induced by thermal gradient through thickness of specimen. Firstly, an experimental facility has been developed: a rectangular parallelepiped specimen is subjected to thermal cycling between 350 C and 100 C; the specimen is freed to expand and contract. Two semi-circular notches (0,1 mm depth and 4 mm length) have been machined on the surface of the specimen. A series of interrupted tests has been carried out to characterize and quantify the crack growth in depth and surface of the pre-existing crack. Next, a three-dimensional crack growth simulation has been implemented in ABAQUS. Automation using Python was used to simulate the propagation of a crack under thermal cycling, with re-meshing at crack front after each calculation step. No assumption has been taken on the crack front during the crack propagation. A comparison with test results showed very good agreement on the evolution of crack front shape and on the kinetics of propagation on the edge and the heart of pre-existing crack. An analytical approach was also developed based on the calculation of stress intensity factors (SIC). A two-dimensional approach was first introduced enabling us to better understand the influence of various thermal and geometric parameters. Finally, a three dimensional approach, with an elliptical assumption crack shape during the propagation, leading to a prediction of crack growth on the surface and in depth which is very similar to that obtained numerically, but with computational time much lower. (author)

Low-cycle fatigue-cracking mechanisms in fcc crystalline materials

Science.gov (United States)

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

2011-01-01

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

Effect of electrical pulse treatment on the thermal fatigue resistance of bionic compacted graphite cast iron processed in water

International Nuclear Information System (INIS)

Liu, Yan; Zhou, Hong; Su, Hang; Yang, Chunyan; Cheng, Jingyan; Zhang, Peng; Ren, Luquan

2012-01-01

Highlights: ► Electrical pulse treatment can reduce cracks on bionic units before thermal fatigue tests. ► Electrical pulse treatment can reduce crack sources during thermal fatigue tests. ► Thermal fatigue resistance of bionic units processed in water is enhanced. ► Thermal fatigue resistance of bionic CGI processed in water is improved. -- Abstract: In order to further enhance the thermal fatigue resistance of bionic compacted graphite cast iron (CGI) which is processed by laser in water, the electrical pulse treatment is applied to improve the thermal fatigue resistance of bionic units. The results show that the electrical pulse treatment causes the supersaturated carbon atoms located in the lattice of austenite to react with the iron atoms to form the Fe 3 C. The microstructures of the bionic units processed in water are refined by the electrical pulse treatment. The cracks on the bionic units are reduced by the electrical pulse treatment before the thermal fatigue tests; and during the tests, the thermal fatigue resistance of bionic units is therefore enhanced by reducing the crack sources. By this way, the thermal fatigue resistance of bionic CGI processed in water is improved.

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

International Nuclear Information System (INIS)

Sato, Kyohei; Ogino, Kanako; Takahashi, Koji; Ando, Kotoji; Urabe, Yoshio

2011-01-01

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)

Damage and failure modeling of lotus-type porous material subjected to low-cycle fatigue

Directory of Open Access Journals (Sweden)

J. Kramberger

2016-01-01

Full Text Available The investigation of low-cycle fatigue behaviour of lotus-type porous material is presented in this paper. Porous materials exhibit some unique features which are useful for a number of various applications. This paper evaluates a numerical approach for determining of damage initiation and evolution of lotus-type porous material with computational simulations, where the considered computational models have different pore topology patterns. The low-cycle fatigue analysis was performed by using a damage evolution law. The damage state was calculated and updated based on the inelastic hysteresis energy for stabilized cycle. Degradation of the elastic stifness was modeled using scalar damage variable. In order to examine crack propagation path finite elements with severe damage were deleted and removed from the mesh during simulation. The direct cyclic analysis capability in Abaqus/Standard was used for low-cycle fatigue analysis to obtain the stabilized response of a model subjected to the periodic loading. The computational results show a qualitative understanding of pores topology influence on low-cycle fatigue under transversal loading conditions in relation to pore orientation.

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

International Nuclear Information System (INIS)

Yonezu, Akio; Touda, Yuya; Kim, HakGui; Yoneda, Keishi; Sakihara, Masayuki; Minoshima; Kohji

2011-01-01

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)

Modification of creep and low cycle fatigue behaviour induced by welding

Directory of Open Access Journals (Sweden)

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.

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

Directory of Open Access Journals (Sweden)

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.

The numerical high cycle fatigue damage model of fillet weld joint under weld-induced residual stresses

Science.gov (United States)

Nguyen Van Do, Vuong

2018-04-01

In this study, a development of nonlinear continuum damage mechanics (CDM) model for multiaxial high cycle fatigue is proposed in which the cyclic plasticity constitutive model has been incorporated in the finite element (FE) framework. T-joint FE simulation of fillet welding is implemented to characterize sequentially coupled three-dimensional (3-D) of thermo-mechanical FE formulation and simulate the welding residual stresses. The high cycle fatigue damage model is then taken account into the fillet weld joints under the various cyclic fatigue load types to calculate the fatigue life considering the residual stresses. The fatigue crack initiation and the propagation in the present model estimated for the total fatigue is compared with the experimental results. The FE results illustrated that the proposed high cycle fatigue damage model in this study could become a powerful tool to effectively predict the fatigue life of the welds. Parametric studies in this work are also demonstrated that the welding residual stresses cannot be ignored in the computation of the fatigue life of welded structures.

High-Cycle, Push–Pull Fatigue Fracture Behavior of High-C, Si–Al-Rich Nanostructured Bainite Steel

Directory of Open Access Journals (Sweden)

Jing Zhao

2017-12-01

Full Text Available The high-cycle, push–pull fatigue fracture behavior of high-C, Si–Al-rich nanostructured bainitic steel was studied through the measurement of fatigue limits, a morphology examination and phase composition analysis of the fatigue fracture surface, as well as fractography of the fatigue crack propagation. The results demonstrated that the push–pull fatigue limits at 107 cycles were estimated as 710–889 MPa, for the samples isothermally transformed at the temperature range of 220–260 °C through data extrapolation, measured under the maximum cycle number of 105. Both the interior inclusion and the sample surface constituted the fatigue crack origins. During the fatigue crack propagation, a high amount of secondary cracks were formed in almost parallel arrangements. The apparent plastic deformation occurred in the fracture surface layer, which induced approximately all retained austenite to transform into martensite.

Lifetime prediction of structures submitted to thermal fatigue loadings; Prediction de duree de vie de structures sous chargement de fatigue thermique

Energy Technology Data Exchange (ETDEWEB)

Amiable, S

2006-01-15

The aim of this work is to predict the lifetime of structures submitted to thermal fatigue loadings. This work lies within the studies undertaken by the CEA on the thermal fatigue problems from the french reactor of Civaux. In particular we study the SPLASH test: a specimen is heated continuously and cyclically cooled down by a water spray. This loading generates important temperature gradients in space and time and leads to the initiation and the propagation of a crack network. We propose a new thermo-mechanical model to simulate the SPLASH experiment and we propose a new fatigue criterion to predict the lifetime of the SPLASH specimen. We propose and compare several numerical models with various complexity to estimate the mechanical response of the SPLASH specimen. The practical implications of this work are the reevaluation of the hypothesis used in the French code RCC, which are used to simulate thermal shock and to interpret the results in terms of fatigue. This work leads to new perspectives on the mechanical interpretation of the fatigue criterion. (author)

Calculation of Local Stress and Fatigue Resistance due to Thermal Stratification on Pressurized Surge Line Pipe

Science.gov (United States)

Bandriyana, B.; Utaja

2010-06-01

Thermal stratification introduces thermal shock effect which results in local stress and fatique problems that must be considered in the design of nuclear power plant components. Local stress and fatique calculation were performed on the Pressurize Surge Line piping system of the Pressurize Water Reactor of the Nuclear Power Plant. Analysis was done on the operating temperature between 177 to 343° C and the operating pressure of 16 MPa (160 Bar). The stagnant and transient condition with two kinds of stratification model has been evaluated by the two dimensional finite elements method using the ANSYS program. Evaluation of fatigue resistance is developed based on the maximum local stress using the ASME standard Code formula. Maximum stress of 427 MPa occurred at the upper side of the top half of hot fluid pipe stratification model in the transient case condition. The evaluation of the fatigue resistance is performed on 500 operating cycles in the life time of 40 years and giving the usage value of 0,64 which met to the design requirement for class 1 of nuclear component. The out surge transient were the most significant case in the localized effects due to thermal stratification.

Low Cycle Fatigue Behavior of Alloy617 Weldment at 850°C

Energy Technology Data Exchange (ETDEWEB)

Hwang, Jeong Jun; Kim, Seon Jin [Pukyong Nat’l Univ., Busan (Korea, Republic of); Kim, Woo Gon; Kim, Eung-Seon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2017-03-15

Alloy 617 is one of the primary candidate materials to be used in a very high temperature reactor (VHTR) system as an intermediate heat exchanger (IHX). To investigate the low cycle fatigue behavior of Alloy 617 weldments at a high temperature of 850℃, fully reversed strain-controlled fatigue tests were conducted with the total strain values ranging from 0.6~1.5%. The weldment specimens were machined using the weld pads fabricated with a single V-grove configuration by gas tungsten arc welding (GTAW) process. The fatigue life is reduced as the total strain range increases. For all testing conditions, the cyclic stress response behavior of the Alloy 617 weldments exhibited the initial cyclic strain hardening phenomenon during the initial small number of cycles. Furthermore, the overall fatigue cracking and the propagation or cracks showed a transgranular failure mode.

Effects of striated laser tracks on thermal fatigue resistance of cast iron samples with biomimetic non-smooth surface

International Nuclear Information System (INIS)

Tong, Xin; Zhou, Hong; Liu, Min; Dai, Ming-jiang

2011-01-01

In order to enhance the thermal fatigue resistance of cast iron materials, the samples with biomimetic non-smooth surface were processed by Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser. With self-controlled thermal fatigue test method, the thermal fatigue resistance of smooth and non-smooth samples was investigated. The effects of striated laser tracks on thermal fatigue resistance were also studied. The results indicated that biomimetic non-smooth surface was benefit for improving thermal fatigue resistance of cast iron sample. The striated non-smooth units formed by laser tracks which were vertical with thermal cracks had the best propagation resistance. The mechanisms behind these influences were discussed, and some schematic drawings were introduced to describe them.

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

Directory of Open Access Journals (Sweden)

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.

Fatigue behaviour and failure analysis of IN 713LC in high-cycle fatigue region

Czech Academy of Sciences Publication Activity Database

Mintách, R.; Kunz, Ludvík; Bokůvka, O.

2009-01-01

Roč. 16, 3a (2009), s. 37-40 ISSN 1335-0803 R&D Projects: GA MPO FT-TA4/023 Institutional research plan: CEZ:AV0Z20410507 Keywords : Ni base superalloy * casting defect * high-cycle fatigue Subject RIV: JG - Metallurgy

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

Czech Academy of Sciences Publication Activity Database

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

Effect of additional holes on transient thermal fatigue life of gas turbine casing

Directory of Open Access Journals (Sweden)

H. Bazvandi

2017-10-01

Full Text Available Gas turbines casings are susceptible to cracking at the edge of eccentric pin hole, which is the most likely position for crack initiation and propagation. This paper describes the improvement of transient thermal fatigue crack propagation life of gas turbines casings through the application of additional holes. The crack position and direction was determined using non-destructive tests. A series of finite element patterns were developed and tested in ASTM-A395 elastic perfectly-plastic ductile cast iron. The effect of arrangement of additional holes on transient thermal fatigue behavior of gas turbines casings containing hole edge cracks was investigated. ABAQUS finite element package and Zencrack fracture mechanics code were used for modeling. The effect of the reduction of transient thermal stress distribution around the eccentric pin hole on the transient thermal fatigue crack propagation life of the gas turbines casings was discussed. The result shows that transient thermal fatigue crack propagation life could be extended by applying additional holes of larger diameter and decreased by increasing the vertical distance, angle, and distance between the eccentric pin hole and the additional holes. The results from the numerical predictions were compared with experimental data.

Fatigue of Austempered Ductile Iron with Two Strength Grades in Very High Cycle Regime

Science.gov (United States)

Zhang, Jiwang; Li, Wei; Song, Qingpeng; Zhang, Ning; Lu, Liantao

2016-03-01

In this study, Austempered ductile irons (ADIs) with two different strength grades were produced and the fatigue properties were measured at 109 cycles. The results show that the S-N curves give a typical step-wise shape and there is no fatigue limit in the very high cycle fatigue regime. The two grades ADI have the similar fracture behaviors and fatigue failure can initiate from defects at specimen surface and subsurface zone. On the fracture surfaces of some specimens, the `granular-bright-facet' area with rich carbon distribution is observed in the vicinity of the defect. The microstructure affects the crack behaviors at the early propagation stage. The ADI with upper and lower bainite shows higher fatigue strength compared with the ADI with coarse upper bainite.

Thermal fatigue and creep evaluation for the bed in tritium SDS

Energy Technology Data Exchange (ETDEWEB)

Choi, Woo-seok, E-mail: wschoi@kaeri.re.kr [Korea Atomic Energy Research Institute, Yuseong, Daejeon (Korea, Republic of); Park, Chang-gyu [Korea Atomic Energy Research Institute, Yuseong, Daejeon (Korea, Republic of); Ju, Yong-sun [KOASIS, Yuseong, Daejeon (Korea, Republic of); Kang, Hyun-goo; Jang, Min-ho; Yun, Sei-hun [National Fusion Research Institute, Yuseong, Daejeon (Korea, Republic of)

2016-11-01

Highlights: • To evaluate the integrity of the ITER tritium SDS bed, three kinds of assessments were conducted. • The structural analysis showed that the stress induced from the thermal load and the internal pressure is within the design stress intensity. • The combined fatigue and creep assessment was also performed according to the procedure of ASME code Subsection NH. • A new operation procedure to obtain more integrity margin was recommended. • The other operation procedure could be considered which makes the rapid operation possible giving up the marginal integrity. - Abstract: The primary vessel of ITER tritium SDS bed is made of stainless steel. It is heated beyond 500 °C to desorb tritium. During this process the primary vessel is subject to thermal stress. And it is also subject to thermal fatigue by the iterative process of absorption and desorption. In addition, its operation temperature range is in the thermal creep temperature region. Therefore, the tritium SDS bed should have sufficient design stress intensity under the high temperature operating conditions. It should also be free of damage due to fatigue during the design life. Thermal analysis and structural analysis was performed using a finite element method to calculate the temperature and the stress distribution of the ITER tritium SDS bed due to the internal pressure and thermal loads. The thermal fatigue and creep effects were also evaluated since the tritium SDS bed was heated to hot temperature region where creep occurs. Based on the distribution of the primary stress and secondary stress results, two evaluation cross-sections were selected. The evaluation showed that the calculated value on the cross-sections satisfied all of the limits of the design code requirements.

Low cycle corrosion fatigue properties of F316Ti in simulated LWR primary environment

International Nuclear Information System (INIS)

Xu Xuelian; Ding Yaping; Katada, Y.; Sato, S.

1998-11-01

Environment effect on fatigue performance of materials used for Pressurized boundary, including fatigue life and crack growth rate, are of importance to nuclear safety. To predict the fatigue life of nuclear materials and to improve the design of nuclear materials, it is necessary to investigated the material fatigue performances in corrosive environment and to get the fatigue data under its environment to be used in. Low cycle corrosion fatigue (CF) performance investigation of domestic F316Ti in simulated BWR and PWR primary environment was carried out. The result shows that the high temperature water environment is one of the most important factors on CF properties. For the same material, the low cycle fatigue life in high temperature air is longer than that in simulated BWR and PWR primary environments. In high temperature water, domestic F316Ti has almost the same low cycle corrosion fatigue performance as F316 (made in Japan). All of the fatigue data are scattered within ASME best-fit curve and ASME design fatigue curve. In high strain range, there is no significant difference of the CF performance for F316Ti in both of BWR and PWR primary environments. With the decrease of strain amplitude, the difference appears gradually. The data is located at the short life side of the fatigue data in simulated BWR primary environment. Titanium is distributed uniformly in F316Ti manufactured in Fushun Steel Factory. Ni, Cr, Mo in this material are located at the high side of the alloy chemical composition range. So, F316Ti has a better CF property in high temperature water

High-cycle fatigue properties of small-bore socket-welded pipe joint

International Nuclear Information System (INIS)

Maekawa, Akira; Noda, Michiyasu; Suzuki, Michiaki

2009-01-01

Piping and equipment in nuclear power plants are structures including many welded joints. Reliability of welded joints is one of high-priority issues to improve the safety of nuclear power plants. However, occurrence of fatigue failures in small-bore socket-welded pipe joints by high-cycle vibrations is still reported. In this study, fatigue experiments on a socket-welded joint of austenitic stainless steel pipe was conducted under excitation conditions similar to those in actual plants to investigate vibration characteristics and fatigue strength. It was found that the natural frequency of pipe with socket-welded joint gradually decreased as fatigue damage developed, according to the Miner rule for fatigue life evaluation. The results indicate that the fatigue life of the welded pipe joint could be estimated by monitoring the decreasing ratio of the natural frequency of the pipe. The evaluation of decreasing ratio of the natural frequency in addition to fatigue damage evaluation by the Miner rule could enhance the accuracy of fatigue life evaluation. (author)

Low cycle fatigue behavior of die cast Mg-Al-Mn-Ce magnesium alloy

Directory of Open Access Journals (Sweden)

Wu Wei

2013-11-01

Full Text Available Fatigue failure is a main failure mode for magnesium and other alloys. It is beneficial for fatigue design and fatigue life improvement to investigate the low cycle fatigue behavior of magnesium alloys. In order to investigate the low cycle fatigue behavior of die cast Mg-Al-Mn-Ce magnesium alloy, the strain controlled fatigue experiments were performed at room temperature and fatigue fracture surfaces of specimens were observed with scanning election microscopy for the alloys under die-cast and aged states. Cyclic stress response curves, strain amplitude versus reversals to failure curve, total strain amplitude versus fatigue life curves and cyclic stress-strain curves of Mg-Al-Mn-Ce alloys were analyzed. The results show that the Mg-Al-Mn-Ce alloys under die-cast (F and aged (T5 states exhibit cyclic strain hardening under the applied total strain amplitudes, and aging treatment could greatly increase the cyclic stress amplitudes of die cast Mg-Al-Mn-Ce alloys. The relationships between the plastic strain amplitude, the elastic strain amplitude and reversals to failure of Mg-Al-Mn-Ce magnesium alloy under different treatment states could be described by Coffin-Manson and Basquin equations, respectively. Observations on the fatigue fracture surface of specimens reveal that the fatigue cracks initiate on the surface of specimens and propagate transgranularly.

Low Cycle Fatigue Behaviour of DP Steels: Micromechanical Modelling vs. Validation

Directory of Open Access Journals (Sweden)

Ghazal Moeini

2017-07-01

Full Text Available This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue tests were performed. In the numerical part, the representative volume element (RVE was employed to study the effect of the DP steel microstructure of the low cycle fatigue behavior of DP steel. A dislocation-density based model was utilised to identify the tensile behavior of ferrite and martensite. Then, by establishing a correlation between the monotonic and cyclic behavior of ferrite and martensite phases, the cyclic deformation properties of single phases were estimated. Accordingly, Chaboche kinematic hardening parameters were identified from the predicted cyclic curve of individual phases in DP steel. Finally, the predicted hysteresis loop from low cycle fatigue modelling was in very good agreement with the experimental one. The stabilised hysteresis loop of DP steel can be successfully predicted using the developed approach.

Development of a high cycle vibration fatigue diagnostic system with non-contact vibration sensing

International Nuclear Information System (INIS)

Nekomoto, Yoshitsugu; Tanaka, Masanori; Nishimura, Moritatsu; Matsumoto, Kenji; O'shima, Eiji

2004-01-01

Nuclear power plants have a large number of pipes. These small-diameter pipe branches in particles are often damaged due to high-cycle fatigue. In order to ensure the reliability of a plant it is important to detect fatigue damages in pipe branches at an early stage and to develop the technology to predict and diagnose the advancement of fatigue. Further, in order to carry out the diagnosis of the piping system effectively during operation, non-contact evaluation is useful. Hence, we have developed a ''high-cycle fatigue diagnostic system with non-contact vibration sensing'', which measures the vibration of the pipe branch using a non-contact sensor. (author)

A Combined High and Low Cycle Fatigue Model for Life Prediction of Turbine Blades

Directory of Open Access Journals (Sweden)

Shun-Peng Zhu

2017-06-01

Full Text Available Combined high and low cycle fatigue (CCF generally induces the failure of aircraft gas turbine attachments. Based on the aero-engine load spectrum, accurate assessment of fatigue damage due to the interaction of high cycle fatigue (HCF resulting from high frequency vibrations and low cycle fatigue (LCF from ground-air-ground engine cycles is of critical importance for ensuring structural integrity of engine components, like turbine blades. In this paper, the influence of combined damage accumulation on the expected CCF life are investigated for turbine blades. The CCF behavior of a turbine blade is usually studied by testing with four load-controlled parameters, including high cycle stress amplitude and frequency, and low cycle stress amplitude and frequency. According to this, a new damage accumulation model is proposed based on Miner’s rule to consider the coupled damage due to HCF-LCF interaction by introducing the four load parameters. Five experimental datasets of turbine blade alloys and turbine blades were introduced for model validation and comparison between the proposed Miner, Manson-Halford, and Trufyakov-Kovalchuk models. Results show that the proposed model provides more accurate predictions than others with lower mean and standard deviation values of model prediction errors.

Lifetime evaluation for thermal fatigue: application at the first wall of a tokamak fusion reactor

International Nuclear Information System (INIS)

Merola, M.; Biggio, M.

1989-01-01

Thermal fatigue seems to be the most lifetime limiting phenomenon for the first wall of the next generation Tokamak fusion reactors. This work deals with the problem of the thermal fatigue in relation to the lifetime prediction of the fusion reactor first wall. The aim is to compare different lifetime methodologies among them and with experimental results. To fulfil this purpose, it has been necessary to develop a new numerical methodology, called reduced-3D, especially suitable for thermal fatigue problems

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

International Nuclear Information System (INIS)

Sanderson, S.J.; Petrequin, P.; Nieuwland, H.C.D.; Breuer, H.J.

1983-01-01

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 0 C, 427 0 C 0 C and 550 0 C 0 C. Increasing test temperatures result in a progressive decrease in continuous cycling fatigue endurance and sustainable stress range

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

Science.gov (United States)

Bast, Callie Corinne Scheidt

1994-01-01

This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. 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 four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, creep, and thermal fatigue was performed. 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 a combination of mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

Low-cycle compression fatigue of reinforced concrete structures

NARCIS (Netherlands)

Stroeven, P.

2010-01-01

Paper reports on experiments performed in the low-cycle compression fatigue domain, considering two relatively high upper load levels and several lower ones. Two frequency levels were emphasized, i.e. 17.5 Hz and 0.175 Hz. An overview is given of characteristics of mechanical behaviour and of the

Instantaneous quantification of skeletal muscle activation, power production, and fatigue during cycle ergometry.

Science.gov (United States)

Coelho, A C; Cannon, D T; Cao, R; Porszasz, J; Casaburi, R; Knorst, M M; Rossiter, H B

2015-03-01

A rapid switch from hyperbolic to isokinetic cycling allows the velocity-specific decline in maximal power to be measured, i.e., fatigue. We reasoned that, should the baseline relationship between isokinetic power (Piso) and electromyography (EMG) be reproducible, then contributions to fatigue may be isolated from 1) the decline in muscle activation (muscle activation fatigue); and 2) the decline in Piso at a given activation (muscle fatigue). We hypothesized that the EMG-Piso relationship is linear, velocity dependent, and reliable for instantaneous fatigue assessment at intolerance during and following whole body exercise. Healthy participants (n = 13) completed short (5 s) variable-effort isokinetic bouts at 50, 70, and 100 rpm to characterize baseline EMG-Piso. Repeated ramp incremental exercise tests were terminated with maximal isokinetic cycling (5 s) at 70 rpm. Individual baseline EMG-Piso relationships were linear (r(2) = 0.95 ± 0.04) and velocity dependent (analysis of covariance). Piso at intolerance (two legs, 335 ± 88 W) was ∼45% less than baseline [630 ± 156 W, confidence interval of the difference (CIDifference) 211, 380 W, P fatigue and muscle fatigue (one leg) were 97 ± 55 and 60 ± 50 W, respectively. Mean bias ± limits of agreement for reproducibility were as follows: baseline Piso 1 ± 30 W; Piso at 0-min recovery 3 ± 35 W; and EMG at Piso 3 ± 14%. EMG power is linear, velocity dependent, and reproducible. Deviation from this relationship at the limit of tolerance can quantify the "activation" and "muscle" related components of fatigue during cycling. Copyright © 2015 the American Physiological Society.

In situ observation of high temperature tensile deformation and low cycle fatigue response in a nickel-base superalloy

Energy Technology Data Exchange (ETDEWEB)

Lu, Xudong, E-mail: lxdong0700@hotmail.com; Du, Jinhui; Deng, Qun

2013-12-20

High temperature tension and low cycle fatigue experiments of IN718 alloy have been performed in the electro-hydraulic servo system with scanning electron microscope at 455 °C. Fatigue crack initiation and propagation process are investigated in situ. Results show that the carbide and twin grain are the crack source of the low cycle fatigue of IN718 alloy, and the low cycle fatigue life of the alloy increases with the decrease in grain size.

Effect of microstructure on low cycle fatigue properties of ODS steels

Energy Technology Data Exchange (ETDEWEB)

Kubena, Ivo, E-mail: kubena@ipm.cz [IPM, Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, Brno (Czech Republic); Fournier, Benjamin [CEA/DEN/DANS/DMN/SRMA, Bat. 453, 91191 Gif-sur-Yvette Cedex (France); Kruml, Tomas [CEITEC IPM, Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, Brno (Czech Republic)

2012-05-15

Highlights: Black-Right-Pointing-Pointer Three various ODS steels are studied and compared. Black-Right-Pointing-Pointer Low cycle fatigue data at RT, 650 Degree-Sign C and 750 Degree-Sign C are given. Black-Right-Pointing-Pointer Microstructural characterization. Black-Right-Pointing-Pointer Detailed discussion of strengthening mechanisms. - Abstract: Low cycle fatigue properties at room temperature, 650 Degree-Sign C and 750 Degree-Sign C of three high chromium steels (9%Cr ferritic-martensitic and two 14%Cr ferritic steels) strengthened by oxide dispersion were studied and compared. Cyclic softening/hardening curves, cyclic deformation curves, S-N curves and Coffin-Manson curves are presented together with microstructural observations. Differences in cyclic response, stress level and fatigue life are attributed to differences in the matrix microstructure. The oxide particles stabilize the cyclic response, even if cyclic softening is detected for some experimental conditions. The strength of these steels is discussed in terms of strengthening mechanisms such as grain size effect, particle-dislocations interaction and dislocation density. Comparing three different ODS steels offers an opportunity to tests the contribution of individual mechanisms to the cyclic strength. The reduction of fatigue life in one of the ferritic steels is explained by the presence of large grains, facilitating the fatigue crack nucleation and the early growth.

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

Energy Technology Data Exchange (ETDEWEB)

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.

Low cycle fatigue properties of CLAM steel at 823 K

Energy Technology Data Exchange (ETDEWEB)

Hu, Xue [Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049 (China); Huang, Lixin [Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Yan, Wei; Wang, Wei [Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Sha, Wei [School of Planning, Architecture and Civil Engineering, Queen' s University Belfast, Belfast BT9 5AG (United Kingdom); Shan, Yiyin, E-mail: yyshan@imr.ac.cn [Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Yang, Ke, E-mail: kyang@imr.ac.cn [Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)

2014-09-08

China Low Activation Martensitic (CLAM) steel is considered to be the main candidate material for the first wall components of future fusion reactors in China. In this paper, the low cycle fatigue (LCF) behavior of CLAM steel is studied under fully reversed tension–compression loading at 823 K in air. Total strain amplitude was controlled from 0.14% to 1.8% with a constant strain rate of 2.4×10{sup −3} s{sup −1}. The corresponding plastic strain amplitude ranged from 0.023% to 1.613%. The CLAM steel displayed continuous softening to failure at 823 K. The relationship between strain, stress and fatigue life was obtained using the parameters obtained from fatigue tests. The LCF properties of CLAM steel at 823 K followed Coffin–Manson relationship. Furthermore, irregular serration was observed on the stress–strain hysteresis loops of CLAM steel tested with the total strain amplitude of 0.45–1.8%, which was attributed to the dynamic strain aging (DSA) effect. During continuous cyclic deformation, the microstructure and precipitate distribution of CLAM steel changed gradually. Many tempered martensitic laths were decomposed into subgrains, and the size and number of M{sub 23}C{sub 6} carbide and MX carbonitride precipitates decreased with the increase of total strain amplitude. The response cyclic stress promoted the recovery of martensitic lath, while the thermal activation mainly played an important role on the growth of precipitates in CLAM steel at 823 K. In order to have a better understanding of high-temperature LCF behavior, the potential mechanisms controlling stress–strain response, DSA phenomenon and microstructure changes have also been evaluated.

Investigation of thermal fatigue of chromium-molybdenum steels, used for calcining and agglomeration constructions

International Nuclear Information System (INIS)

Sinyavskij, D.P.; Gorkalo, A.P.

1979-01-01

The technique for investigating thermal fatigue of materials is described. The data on sample stress deformed state and current temperature values are taken from the local volume of the material studied. Results of investigating thermal fatigue of the 15KhMl and 20KhMl steels are presented

Current state of low-cycle fatigue research based on multiaxial stress intensity and its challenges. Part 1. Focusing on low-cycle fatigue strength evaluation method of elbow piping subjected to in-plane cyclic bending displacement load

International Nuclear Information System (INIS)

Urabe, Yoshio

2017-01-01

The R and D of fatigue strength at multiaxial stress intensity is recognized to become extremely important in the future in terms of the elaboration of low-cycle fatigue evaluation of various structures including piping systems and reflection on those standards. This paper focuses on the evaluation method developed by the author, namely cumulative damage rule in consideration of multiaxial stress intensity, and explains the concept and the results of verification and evaluation. It also discusses the engineering problems of the current low cycle fatigue assessment technology that were clarified in the process of developing low-cycle fatigue assessment method based on multiaxial stress intensity. The conservative lifespan and somewhat more conservative actual lifetime of elbow piping can be estimated by the conventional 'revised universal slope method' and 'advanced revised universal slope method.' However, these are empirical rules, and the theoretical basis is not clear. From 'cumulative damage rule in consideration of multiaxial stress intensity,' the author calculated furthermore 'low cycle fatigue evaluation formula based on cumulative damage rule in consideration of multi-axial stress intensity,' and examined it. As a result, an evaluation formula that can reasonably assume the equivalent thermoplastic strain range could be obtained at half of the repeat count as targeted. Furthermore, at the stage where future high precision FEM analysis can be used, direct low-cycle fatigue life curve can be established. (A.O.)

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

Energy Technology Data Exchange (ETDEWEB)

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

2013-06-20

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

Behaviour of Ti-doped CFCs under thermal fatigue tests

Energy Technology Data Exchange (ETDEWEB)

Centeno, A. [Instituto Nacional del Carbon (CSIC), Apdo. 73, 33080 Oviedo (Spain); Pintsuk, G.; Linke, J. [Forschungszentrum Juelich GmbH, EURATOM Association, 52425 Juelich (Germany); Gualco, C. [Ansaldo Energia, I-16152 Genoa (Italy); Blanco, C., E-mail: clara@incar.csic.es [Instituto Nacional del Carbon (CSIC), Apdo. 73, 33080 Oviedo (Spain); Santamaria, R.; Granda, M.; Menendez, R. [Instituto Nacional del Carbon (CSIC), Apdo. 73, 33080 Oviedo (Spain)

2011-01-15

In spite of the remarkable progress in the design of in-vessel components for the divertor of the first International Thermonuclear Experimental Reactor (ITER), a great effort is still put into the development of manufacturing technologies for carbon armour with improved properties. Newly developed 3D titanium-doped carbon fibre reinforced composites and their corresponding undoped counterparts were brazed to a CuCrZr heat sink to produce actively cooled flat tile mock-ups. By exposing the mock-ups to thermal fatigue tests in an electron beam test facility, the material behaviour and the brazing between the individual constituents in the mock-up was qualified. The mock-ups with titanium-doped CFCs exhibited a significantly improved thermal fatigue resistance compared with those undoped materials. The comparison of these mock-ups with those produced using pristine NB31, one of the reference materials as plasma facing material for ITER, showed almost identical results, indicating the high potential of Ti-doped CFCs due to their improved thermal shock resistance.

Thermomechanical fatigue of Sn-37 wt.% Pb model solder joints

International Nuclear Information System (INIS)

Liu, X.W.; Plumbridge, W.J.

2003-01-01

The fatigue of Sn-37 wt.% Pb model solder joints has been investigated under thermomechanical and thermal cycling. Based upon an analysis of displacements during thermomechancial cycling, a model solder joint has been designed to simulate actual joints in electronic packages. The strain-stress relationship, characterised by hysteresis loops, was determined during cycling from 30 to 125 deg. C, and the stress-range monitored throughout. The number of cycles to failure, as defined by the fall in stress range, was correlated to strain range and strain energy. The strain hardening exponent, k, varied with the definition of failure and, when a stress-range drop of 50% was used, it was 0.46. Cracks were produced during pure thermal cycling without external strains applied. These arose due to the local strains caused by thermal expansion mismatches between the solder and Cu 6 Sn 5 intermetallic layer, between the phases of solder, and due to the anisotropy of the materials. The fatigue life under thermomechanical cycling was significantly inferior to that obtained in isothermal mechanical cycling. A factor contributing to this inferiority is the internal damage produced during temperature cycling

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

International Nuclear Information System (INIS)

Wang, Hong; Lee, Sung-Min; Wang, James L.; Lin, Hua-Tay

2014-01-01

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 10 8 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

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

Science.gov (United States)

Wang, Hong; Lee, Sung-Min; Wang, James L.; Lin, Hua-Tay

2014-12-01

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.

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

Energy Technology Data Exchange (ETDEWEB)

Wang, Hong, E-mail: wangh@ornl.gov; Lee, Sung-Min; Wang, James L. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Lin, Hua-Tay [School of Mechanical and Electronic Engineering, Guangdong University of Technology, Guangzhou, 510006 (China)

2014-12-21

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 10{sup 8} 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.

Effect of microstructure on low cycle fatigue properties of ODS steels

Czech Academy of Sciences Publication Activity Database

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

Interconnect fatigue design for terrestrial photovoltaic modules

Science.gov (United States)

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.

Acoustic events during fatigue test of structural steels

Energy Technology Data Exchange (ETDEWEB)

Por, Gabor; Fekete, Balazs; Csicso, Gabor; Trampus, Peter [College of Dunaujvaros (Hungary)

2014-11-01

Acoustic emission sensors were applied recording noises during low cycle fatigue tests in steel materials. The test specimens were machined from the base metal (15H2MFA) and the anticorrosive cladding metal (08H18N10T) of the VVER-440/V-213 (Russian designed PWR) reactor pressure vessel. During the first period, the measurements were carried out with isothermal condition at 260 C on GLEEBLE 3800 servo-hydraulic thermal-mechanical simulator. The tests were run under uniaxial tension-compression loading with total strain control. The programmed waveform was triangular for all the fatigue tests with the frequency of 0.08 Hz. The cyclic loading was started from the compressed side. It was observed that besides rare acoustic emission events regular 10 msec Acoustic Barkhausen Noise (ABN) burst were recorded due to 50Hz AC current drive for heating and maintaining the constant temperature. The amplitude of MABN was higher under pressure than during relaxing and drawing-out by a factor of 2-5. We have carried out also thermo-mechanical fatigue experiment with the same strain-controlled mechanical cycle and simultaneous thermal cycle between 150 C and 270 C. The total number of cycles was terminated, when the force level necessary for the original elongation had been reduced to 75% of its original value. Visual examination showed always some at least surface cracks after stopping the fatigue test. ABN events registered during the beginning cycle exhibited different spectra from the middle and especially from the last cycles before the end of the test, where also double ABN bursts could be recorded. At the end of the test explicit AE events could be found by a new technique. The most interesting result is the possibility to use ABN for testing reactor materials, which could have practical application for fatigue testing.

Submerged Arc Stainless Steel Strip Cladding—Effect of Post-Weld Heat Treatment on Thermal Fatigue Resistance

Science.gov (United States)

Kuo, I. C.; Chou, C. P.; Tseng, C. F.; Lee, I. K.

2009-03-01

Two types of martensitic stainless steel strips, PFB-132 and PFB-131S, were deposited on SS41 carbon steel substrate by a three-pass submerged arc cladding process. The effects of post-weld heat treatment (PWHT) on thermal fatigue resistance and hardness were evaluated by thermal fatigue and hardness testing, respectively. The weld metal microstructure was investigated by utilizing optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). Results showed that, by increasing the PWHT temperature, hardness decreased but there was a simultaneous improvement in weldment thermal fatigue resistance. During tempering, carbide, such as (Fe, Cr)23C6, precipitated in the weld metals and molybdenum appeared to promote (Fe, Cr, Mo)23C6 formation. The precipitates of (Fe, Cr, Mo)23C6 revealed a face-centered cubic (FCC) structure with fine grains distributed in the microstructure, thereby effectively increasing thermal fatigue resistance. However, by adding nickel, the AC1 temperature decreased, causing a negative effect on thermal fatigue resistance.

Fatigue Life Assessment of Selected Engineering Materials Based on Modified Low-Cycle Fatigue Test

Directory of Open Access Journals (Sweden)

Maj M.

2013-03-01

Full Text Available In this study, the mechanical tests were carried out on ductile iron of EN-GJS-600-3 grade and on grey cast iron of EN-GJL-250 grade. The fatigue life was evaluated in a modified low-cycle fatigue test (MLCF, which enables the determination of parameters resulting from the Manson-Coffin-Morrow relationship. The qualitative and quantitative metallographic studies conducted by light microscopy on selected samples of ductile iron with spheroidal graphite and grey cast iron with lamellar graphite (showing only small variations in mechanical properties, confirmed also small variations in the geometrical parameters of graphite related with its content and morphological features.

Fatigue Life Assessment of Selected Engineering Materials Based on Modified Low-Cycle Fatigue Test

Directory of Open Access Journals (Sweden)

M. Maj

2013-01-01

Full Text Available In this study, the mechanical tests were carried out on ductile iron of EN-GJS-600-3 grade and on grey cast iron of EN-GJL-250 grade.The fatigue life was evaluated in a modified low-cycle fatigue test (MLCF, which enables the determination of parameters resulting fromthe Manson-Coffin-Morrow relationship.The qualitative and quantitative metallographic studies conducted by light microscopy on selected samples of ductile iron with spheroidalgraphite and grey cast iron with lamellar graphite (showing only small variations in mechanical properties, confirmed also smallvariations in the geometrical parameters of graphite related with its content and morphological features.

System-Level Heat Transfer Analysis, Thermal- Mechanical Cyclic Stress Analysis, and Environmental Fatigue Modeling of a Two-Loop Pressurized Water Reactor. A Preliminary Study

Energy Technology Data Exchange (ETDEWEB)

Mohanty, Subhasish [Argonne National Lab. (ANL), Argonne, IL (United States); Soppet, William [Argonne National Lab. (ANL), Argonne, IL (United States); Majumdar, Saurin [Argonne National Lab. (ANL), Argonne, IL (United States); Natesan, Ken [Argonne National Lab. (ANL), Argonne, IL (United States)

2015-01-03

This report provides an update on an assessment of environmentally assisted fatigue for light water reactor components under extended service conditions. This report is a deliverable in April 2015 under the work package for environmentally assisted fatigue under DOE's Light Water Reactor Sustainability program. In this report, updates are discussed related to a system level preliminary finite element model of a two-loop pressurized water reactor (PWR). Based on this model, system-level heat transfer analysis and subsequent thermal-mechanical stress analysis were performed for typical design-basis thermal-mechanical fatigue cycles. The in-air fatigue lives of components, such as the hot and cold legs, were estimated on the basis of stress analysis results, ASME in-air fatigue life estimation criteria, and fatigue design curves. Furthermore, environmental correction factors and associated PWR environment fatigue lives for the hot and cold legs were estimated by using estimated stress and strain histories and the approach described in NUREG-6909. The discussed models and results are very preliminary. Further advancement of the discussed model is required for more accurate life prediction of reactor components. This report only presents the work related to finite element modelling activities. However, in between multiple tensile and fatigue tests were conducted. The related experimental results will be presented in the year-end report.

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

International Nuclear Information System (INIS)

Milesi, M.; Chastel, Y.; Hachem, E.; Bernacki, M.; Loge, R.E.; Bouchard, P.O.

2010-01-01

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.

The effects of state anxiety and thermal comfort on sleep quality and eye fatigue in shift work nurses.

Science.gov (United States)

Dehghan, Habibollah; Azmoon, Hiva; Souri, Shiva; Akbari, Jafar

2014-01-01

Psychological problems as state anxiety (SA) in the work environment has negative effect on the employees life especially shift work nurses, i.e. negative effect on mental and physical health (sleep quality, eye fatigue and comfort thermal). The purpose of this study was determination of effects of state anxiety and thermal comfort on sleep quality and eye fatigue in shift work nurses. This cross-sectional research conducted on 82 shift-work personnel of 18 nursing workstations of Isfahan hospitals in 2012. To measure the SA, sleep quality, visual fatigue and thermal comfort, Spielberger state-trait anxiety inventory, Pittsburg sleep quality index, eye fatigue questionnaire and thermal comfort questionnaire were used respectively. The data were analyzed with descriptive statistics, student test and correlation analysis. Correlation between SA and sleep quality was -0.664(P thermal comfort was -0.276(P = 0.016) and between SA and eye fatigue was 0.57 (P thermal conditions and reduce state anxiety level can be reduce eye fatigue and increase the sleep quality in shift work nurses.

Low cycle fatigue testing in flowing sodium at elevated temperatures

International Nuclear Information System (INIS)

Flagella, P.N.; Kahrs, J.R.

1976-01-01

The paper describes equipment developed to obtain low cycle strain-controlled fatigue data in flowing sodium at elevated temperatures. Operation and interaction of the major components of the system are discussed, including the calibration technique using remote strain measurement and control. Confirmation of in-air results using the special technique is demonstrated, with data presented for Type 316 stainless steel tested in high purity flowing sodium at 593 0 C. The fatigue life of the material in sodium is essentially the same as that obtained in air for delta epsilon/sub t/= 1 percent. On the other hand, sodium pre-exposure at 650 0 C for 5000 hours increased the fatigue life in-sodium by a factor of two, and sodium pre-exposure at 718 0 C for 5000 hours increased the fatigue life in-sodium by a factor of three

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

International Nuclear Information System (INIS)

Filatov, V.M.; Evropin, S.V.

2004-01-01

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 10 12 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

Fatigue and failure responses of lead zirconate titanate multilayer actuator under unipolar high-field electric cycling

Science.gov (United States)

Zeng, Fan Wen; Wang, Hong; Lin, Hua-Tay

2013-07-01

Lead zirconate titanate (PZT) multilayer actuators with an interdigital electrode design were studied under high electric fields (3 and 6 kV/mm) in a unipolar cycling mode. A 100 Hz sine wave was used in cycling. Five specimens tested under 6 kV/mm failed from 3.8 × 105 to 7 × 105 cycles, whereas three other specimens tested under 3 kV/mm were found to be still functional after 108 cycles. Variations in piezoelectric and dielectric responses of the tested specimens were observed during the fatigue test, depending on the measuring and cycling conditions. Selected fatigued and damaged actuators were characterized using an impedance analyzer or small signal measurement. Furthermore, involved fatigue and failure mechanisms were investigated using scanning acoustic microscope and scanning electron microscope. The extensive cracks and porous regions were revealed across the PZT layers on the cross sections of a failed actuator. The results from this study have demonstrated that the high-field cycling can accelerate the fatigue of PZT stacks as long as the partial discharge is controlled. The small signal measurement can also be integrated into the large signal measurement to characterize the fatigue response of PZT stacks in a more comprehensive basis. The former can further serve as an experimental method to test and monitor the behavior of PZT stacks.

Surface phenomena associated with thermal cycling of copper and their impact on the service life of particle accelerator structures

CERN Document Server

Aicheler, Markus; Theisen, Werner; Sgobba, Stefano

2010-01-01

The performance of accelerating structures (AS) in the Compact LInear Collider (CLIC) is sensitive to a variety of parameters, including the surface quality of key elements of the AS. Processes which affect the surface quality are therefore of particular concern. The present work addresses surface modifications associated with thermal cycling during operation. This type of operating condition represents a specific type of fatigue loading. Four fatigue test procedures were used in the present study in order to investigate the fatigue behaviour of oxygen{free{electronic (OFE) copper, the candidate material of the CLIC-AS: conventional fatigue (CVF), ultrasonic swinger (USS), laser fatigue (LAF) and radio{frequency fatigue (RFF). During operation of the accelerator the material of the AS will be subjected to cyclic temperature changes of approx. Delta T = 56 K, from about 40° C to about 100° C. These temperature changes will result in cyclic biaxial strains in the surface of the order of epsilon(biax) = 9.2 x ...

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

Energy Technology Data Exchange (ETDEWEB)

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)

Raman spectral markers of collagen denaturation and hydration in human cortical bone tissue are affected by radiation sterilization and high cycle fatigue damage.

Science.gov (United States)

Flanagan, Christopher D; Unal, Mustafa; Akkus, Ozan; Rimnac, Clare M

2017-11-01

Thermal denaturation and monotonic mechanical damage alter the organic and water-related compartments of cortical bone. These changes can be detected using Raman spectroscopy. However, less is known regarding Raman sensitivity to detect the effects of cyclic fatigue damage and allograft sterilization doses of gamma radiation. To determine if Raman spectroscopic biomarkers of collagen denaturation and hydration are sensitive to the effects of (a) high cycle fatigue damage and (b) 25kGy irradiation. Unirradiated and gamma-radiation sterilized human cortical bone specimens previously tested in vitro under high-cycle (> 100,000 cycles) fatigue conditions at 15MPa, 25MPa, 35MPa, 45MPa, and 55MPa cyclic stress levels were studied. Cortical bone Raman spectral profiles from wavenumber ranges of 800-1750cm -1 and 2700-3800cm -1 were obtained and compared from: a) non-fatigue vs fatigue fracture sites and b) radiated vs. unirradiated states. Raman biomarker ratios 1670/1640 and 3220/2949, which reflect collagen denaturation and organic matrix (mainly collagen)-bound water, respectively, were assessed. One- and two-way ANOVA analyses were utilized to identify differences between groups along with interaction effects between cyclic fatigue and radiation-induced damage. Cyclic fatigue damage resulted in increases in collagen denaturation (1670/1640: 1.517 ± 0.043 vs 1.579 ± 0.021, p Raman spectroscopy can detect the effects of cyclic fatigue damage and 25kGy irradiation via increases in organic matrix (mainly collagen)-bound water. A Raman measure of collagen denaturation was sensitive to cyclic fatigue damage but not 25kGy irradiation. Collagen denaturation was correlated with organic matrix-bound water, suggesting that denaturation of collagen to gelatinous form may expose more binding sites to water by unwinding the triple alpha chains. This research may eventually be useful to help identify allograft quality and more appropriately match donors to recipients. Copyright �

A New Multiaxial High-Cycle Fatigue Criterion Based on the Critical Plane for Ductile and Brittle Materials

Science.gov (United States)

Wang, Cong; Shang, De-Guang; Wang, Xiao-Wei

2015-02-01

An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.

Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances

Directory of Open Access Journals (Sweden)

Eriksson Robert

2018-01-01

Full Text Available Gas turbine disks contain many notch-like features acting as stress raisers. The fatigue life based on the notch root stress may be overly conservative as the steep stress gradient in front of the notch may give rise to so-called notch support. In the current work, the theory of critical distances was applied to the prediction of the total fatigue life of low cycle fatigued, notched specimens made from alloy 718. The fatigue tests were performed at 450 °C and 550 °C. It was found that, for lives shorter than 5000–10000 cycles, the notched specimens had longer lives than would have been expected based on the notch root strain. For lives longer than 5000–10000 cycles, there were no notch support. The life prediction for notched specimens could be significantly improved by basing the prediction on the strain chosen some distance from the notch (the critical distance. An expression for calculating the critical distance based on the notch root strain was suggested.

Thermal fatigue crack growth in mixing tees nuclear piping - An analytical approach

International Nuclear Information System (INIS)

Radu, V.

2009-01-01

The assessment of fatigue crack growth due to cyclic thermal loads arising from turbulent mixing presents significant challenges, principally due to the difficulty of establishing the actual loading spectrum. So-called sinusoidal methods represent a simplified approach in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface. The need for multiple calculations in this process has lead to the development of analytical solutions for thermal stresses in a pipe subject to sinusoidal thermal loading, described in previous work performed at JRC IE Petten, The Netherlands, during the author's stage as seconded national expert. Based on these stress distributions solutions, the paper presents a methodology for assessment of thermal fatigue crack growth life in mixing tees nuclear piping. (author)

Model-experiment dialog in low cycle fatigue of stainless steels

International Nuclear Information System (INIS)

Aubin, Veronique

2008-01-01

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

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

International Nuclear Information System (INIS)

Hattori, Shuji; Itoh, Takamoto

2002-03-01

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)

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

Directory of Open Access Journals (Sweden)

Chao He

2017-01-01

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

Development of a Fatigue Model for Low Alloy Steels Using a Cycle-Dependent Cohesive Zone Law

Directory of Open Access Journals (Sweden)

Kyungmok Kim

2014-03-01

Full Text Available A fatigue model for SAE 4130 steels is developed using a cycle-dependent cohesive zone law. Reduction of fracture energy and degradation of stiffness are considered to describe failure resistance after certain number of cycles. The reduction rate of fracture energy is determined with experimental stress (S- number of cycles to failure (N scatter found in the literature. Three-dimensional finite element models containing a cohesive zone are generated with commercial software (ABAQUS. Calculated fatigue lives at different stress ratios are in good agreement with experimental ones. In addition, fatigue behavior of hardened SAE 4130 steels is predicted with that of normalized material.

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

Science.gov (United States)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

2016-03-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

Energy based study of quasi-static delamination as a low cycle fatigue process

NARCIS (Netherlands)

Amaral, L.; Yao, L.; Alderliesten, R.C.; Benedictus, R.

2015-01-01

This work proposes to treat quasi-static mode I delamination growth of CFRP as a low-cycle fatigue process. To this end, mode I quasi-static and fatigue delamination tests were performed. An average physical Strain Energy Release Rate (SERR), derived from an energy balance, is used to characterize

Effect of biomimetic non-smooth unit morphology on thermal fatigue behavior of H13 hot-work tool steel

Science.gov (United States)

Meng, Chao; Zhou, Hong; Cong, Dalong; Wang, Chuanwei; Zhang, Peng; Zhang, Zhihui; Ren, Luquan

2012-06-01

The thermal fatigue behavior of hot-work tool steel processed by a biomimetic coupled laser remelting process gets a remarkable improvement compared to untreated sample. The 'dowel pin effect', the 'dam effect' and the 'fence effect' of non-smooth units are the main reason of the conspicuous improvement of the thermal fatigue behavior. In order to get a further enhancement of the 'dowel pin effect', the 'dam effect' and the 'fence effect', this study investigated the effect of different unit morphologies (including 'prolate', 'U' and 'V' morphology) and the same unit morphology in different sizes on the thermal fatigue behavior of H13 hot-work tool steel. The results showed that the 'U' morphology unit had the optimum thermal fatigue behavior, then the 'V' morphology which was better than the 'prolate' morphology unit; when the unit morphology was identical, the thermal fatigue behavior of the sample with large unit sizes was better than that of the small sizes.

Thermal cycling in multifilamentary superconducting composites

International Nuclear Information System (INIS)

Aragao, E.E.A. de.

1984-01-01

NbTi-Cu multifilamentary superconducting composites were embedded, polished, characterized by microscopic techniques, and analyzed in a qualitative and semiquantitative way by energy dispersion technique. The superconductors were submitted to thermal cycling between the ambient temperature and the boiling point of helium (4.2K), for different number of cycles. The aims were to study the correlation between the possible microstructural damages due to thermal stresses arising in the composite during cycling and the variation of properties of the material with the number of cycles as well as to verify the validity of an elastic model for thermal stresses for low temperature cycles. (author)

Simple Theory of Thermal Fatigue Caused by RF Pulse Heating

CERN Document Server

Kuzikov, S

2004-01-01

The projects of electron-positron linear colliders imply that accelerating structures and other RF components will undergo action of extremely high RF fields. Except for breakdown threat there is an effect of the damage due to multi-pulse mechanical stress caused by Ohmic heating of the skin layer. A new theory of the thermal fatigue is considered. The theory is based on consideration of the quasi-elastic interaction between neighbor grains of metal due to the expansion of the thermal skin-layer. The developed theory predicts a total number of the RF pulses needed for surface degradation in dependence on temperature rise, pulse duration, and average temperature. The unknown coefficients in the final formula were found, using experimental data obtained at 11.4 GHz for the copper. In order to study the thermal fatigue at higher frequencies and to compare experimental and theoretical results, the experimental investigation of degradation of the copper cavity exposed to 30 GHz radiation is carried out now, basing...

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

International Nuclear Information System (INIS)

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

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

Low cycle fatigue of alloy 718 in cryogenic environment

International Nuclear Information System (INIS)

Vergara Aimone, J.

1989-01-01

A specially processed Ni-Fe base superalloy 718 has been selected as a structural material for a critical component in ALCATOR C-MOD, the new fusion experimental facility at the Massachusetts Institute of Technology. Draw bars made out of this material will be subjected to large alternating loads while operating at 77 0 K. Monotonic and cyclic mechanical properties were determined in order to evaluate the reactor's maintenance schedule with special emphasis in developing a Low Cycle Fatigue database for this special alloy. Improved monotonic properties over conventionally heat treated alloy 718 were observed. Partial hardening was observed at 77 0 K at 1% of the fatigue life, while softening was observed at room temperature, both relative to their respective monotonic stress strain curves. The fatigue curves were corrected for non-zero mean stress allowing satisfactory safety margin for the expected alternating stress. (author)

The reliability and validity of fatigue measures during short-duration maximal-intensity intermittent cycling.

Science.gov (United States)

Glaister, Mark; Stone, Michael H; Stewart, Andrew M; Hughes, Michael; Moir, Gavin L

2004-08-01

The purpose of the present study was to assess the reliability and validity of fatigue measures, as derived from 4 separate formulae, during tests of repeat sprint ability. On separate days over a 3-week period, 2 groups of 7 recreationally active men completed 6 trials of 1 of 2 maximal (20 x 5 seconds) intermittent cycling tests with contrasting recovery periods (10 or 30 seconds). All trials were conducted on a friction-braked cycle ergometer, and fatigue scores were derived from measures of mean power output for each sprint. Apart from formula 1, which calculated fatigue from the percentage difference in mean power output between the first and last sprint, all remaining formulae produced fatigue scores that showed a reasonably good level of test-retest reliability in both intermittent test protocols (intraclass correlation range: 0.78-0.86; 95% likely range of true values: 0.54-0.97). Although between-protocol differences in the magnitude of the fatigue scores suggested good construct validity, within-protocol differences highlighted limitations with each formula. Overall, the results support the use of the percentage decrement score as the most valid and reliable measure of fatigue during brief maximal intermittent work.

Low cycle fatigue numerical estimation of a high pressure turbine disc for the AL-31F jet engine

Directory of Open Access Journals (Sweden)

Spodniak Miroslav

2017-01-01

Full Text Available This article deals with the description of an approximate numerical estimation approach of a low cycle fatigue of a high pressure turbine disc for the AL-31F turbofan jet engine. The numerical estimation is based on the finite element method carried out in the SolidWorks software. The low cycle fatigue assessment of a high pressure turbine disc was carried out on the basis of dimensional, shape and material disc characteristics, which are available for the particular high pressure engine turbine. The method described here enables relatively fast setting of economically feasible low cycle fatigue of the assessed high pressure turbine disc using a commercially available software. The numerical estimation of accuracy of a low cycle fatigue depends on the accuracy of required input data for the particular investigated object.

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

Science.gov (United States)

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.

A review of typical thermal fatigue failure models for solder joints of electronic components

Science.gov (United States)

Li, Xiaoyan; Sun, Ruifeng; Wang, Yongdong

2017-09-01

For electronic components, cyclic plastic strain makes it easier to accumulate fatigue damage than elastic strain. When the solder joints undertake thermal expansion or cold contraction, different thermal strain of the electronic component and its corresponding substrate is caused by the different coefficient of thermal expansion of the electronic component and its corresponding substrate, leading to the phenomenon of stress concentration. So repeatedly, cracks began to sprout and gradually extend [1]. In this paper, the typical thermal fatigue failure models of solder joints of electronic components are classified and the methods of obtaining the parameters in the model are summarized based on domestic and foreign literature research.

Identification of error sources in fatigue analyses for thermal loadings

International Nuclear Information System (INIS)

Binder, Franz; Gantz, Dieter

2006-09-01

To identify thermal loadings (thermal shocks and thermal stratification), in German NPPs, special fatigue monitoring systems have been installed. The detailed temperature measurement uses sheathed thermocouples, which are located on the external component surface. Tightening straps are used for the widespread method of locking the thermocouples into position. The calculation of material fatigue for a loading sequence has to be carried out based on the measured temperature profile of the outer component surface. Should the analysis comply with the ASME III code, Section NB, alternatively the Articles NB-3200 or NB-3600 can be applied. In fatigue analyses based on the outer-surface temperature, the thermal situation at the inner-surface has to be determined (inverse temperature-field calculation). This leading analysis step is not regulated in the ASME III code. Using general purpose finite element programs, this problem cannot be explicitly solved, because it requires knowledge of the thermal situation at all boundaries (temperature or heat transfer). In the frequently practiced method in a finite element calculation, the inner surface temperature profile is varied until a satisfactory compliance of the calculated outer surface temperature with the measured profile is obtained. Since the input parameters are derived from a variable field, the variation process is large-scale and non-explicit (another input-configuration may cause a similar outer surface temperature). Furthermore, the remaining deviation cannot be quantified regarding the resulting error in the calculated material fatigue. Five typical thermocouple installation methods existing in German LWRs were compared and evaluated regarding the quality of outer surface temperature acquisition. With the evaluation of the experimental data, the essential finding is that for the test transients the maximum of the true outer surface temperature change rate is registered incorrectly with all thermocouple

Thermal stress relaxation in magnesium composites during thermal cycling

Energy Technology Data Exchange (ETDEWEB)

Trojanova, Z.; Lukac, P. (Karlova Univ., Prague (Czech Republic)); Kiehn, J.; Kainer, K.U.; Mordike, B.L. (Technische Univ. Clausthal, Clausthal-Zellerfeld (Germany))

1998-01-01

It has been shown that the internal friction of Mg - Saffil metal matrix composites can be influenced by thermal stresses, if MMCc are submitted to thermal cycling between room temperature and an upper temperature of cycling. These stresses can be accommodated by generation and motion of dislocations giving the formation of the microplastic zones. The thermal stress relaxation depends on the upper temperature of cycling, the volume fraction of reinforcement and the matrix composition and can result in plastic deformation and strain hardening of the matrix without applied stress. The internal friction measurements can be used for non destructive investigation of processes which influence the mechanical properties. (orig.)

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

International Nuclear Information System (INIS)

Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Zhang, Weihong; Van Herpen, Alain

2016-01-01

This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well. (paper)

Interaction of high cycle fatigue and creep in 9%Cr-1%Mo steel at elevated temperature

International Nuclear Information System (INIS)

Vasina, R.; Lukas, P.; Kunz, L.; Sklenicka, V.

1995-01-01

High-cycle-fatigue/creep experiments were performed on a 9%Cr-1%Mo tempered martensite ferritic steel at 873 K in air. The stress ratio R = σ min /σ max ranged from -1 (''pure'' fatigue) to 1 (''pure'' creep). The maximum stress σ max was kept constant at 240 MPa.The lifetime depends on the stress ratio R in a non-monotonic way. In the stress ratio interval 0.6 mean of the stress cycle. In the stress ratio interval -1 a . The fatigue/creep interaction occurs in between these intervals. The fatigue/creep loading induces transformation of the tempered martensite ferritic structure into an equiaxed subgrain structure. The resulting subgrain size depends strongly on the stress ratio. (author)

Influence of martensitic transformation on the low-cycle fatigue behaviour of 316LN stainless steel at 77 K

International Nuclear Information System (INIS)

Botshekan, M.; Degallaix, S.; Desplanques, Y.

1997-01-01

Tensile and low-cycle fatigue tests were performed on a 316LN austenitic stainless steel at 300 and 77 K. The tensile and low-cycle fatigue properties were obtained and analysed in terms of influence of temperature on the plastic deformation process, and particularly on the strain-induced martensite formation. The martensite content was measured by a magnetic-at-saturation method. No martensite was detected at 300 K. On the contrary, strain-induced martensite transformation is responsible for the higher tensile elongation at 77 K and for the secondary hardening observed on softening-hardening curves in low-cycle fatigue at 77 K. The induced martensite content in tensile tests is a function of the strain according to Angel's model, and in low-cycle fatigue it is a function of the strain level and of the accumulated plastic strain. (orig.)

A new lease of life for turbine rotors subject to low-cycle fatigue at elevated temperature

International Nuclear Information System (INIS)

Coulon, P.A.; Knosp, B.; Saisse, H.

1989-01-01

The purpose of the study was to determine the depth of the zone damaged during fatigue crack initiation at the notch root in a Cr Mo V ferritic steel used for the manufacture of steam turbine rotors. Low cycle fatigue tests were conducted at 500 and 550 0 C (932 0 F and 1022 0 F) and the Manson - Coffin curves have been plotted. The results showed firstly that for Na * = 10,000 cycles (Number of cycles for crack initiation Na = 12,500 cycles) the damaged zone in the test-pieces the authors used corresponded to h ≅0.4 mm, and secondly that this zone had the same order of magnitude as the cyclic plastic zone determined according to the mechanical properties of the material studied. Conclusion is clear: if the turbine rotors are remachined over a depth h greater than ≅0.4 mm, their initial low cycle fatigue properties are considered as largely restored

Implementation of creep-fatigue model into finite-element code to assess cooled turbine blade.

CSIR Research Space (South Africa)

Dedekind, MO

1994-01-01

Full Text Available Turbine blades which are designed with airfoil cooling are subject to thermo-mechanical fatigue as well as creep damage. These problems arise due to thermal cycling and high operating temperatures in service. An implementation of fatigue and creep...

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

Directory of Open Access Journals (Sweden)

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

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

Science.gov (United States)

Haapala, Stephenie A; Faghri, Pouran D; Adams, Douglas J

2008-04-26

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. 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. 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. 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 raises speculation as to whether or not progressive resistance

A study on variations of the low cycle fatigue life of a high pressure turbine nozzle caused by inlet temperature profiles and installation conditions

Energy Technology Data Exchange (ETDEWEB)

Huh, Jae Sung; Kang, Young Seok; Rhee, Dong Ho [Aero-propulsion Research Office, Korea Aerospace Research Institute, Daejeon (Korea, Republic of); Seo, Do Young [School of Mechanical and Aerospace Engineering, Pusan National University, Busan (Korea, Republic of)

2015-11-15

High pressure components of a gas turbine engine must operate for a long life under severe conditions in order to maximize the performance and minimize the maintenance cost. Enhanced cooling design, thermal barrier coating techniques, and nickel-base superalloys have been applied for overcoming them and furthermore, material modeling, finite element analysis, statistical techniques, and etc. in design stage have been utilized widely. This article aims to evaluate the effects on the low cycle fatigue life of the high pressure turbine nozzle caused by different turbine inlet temperature profiles and installation conditions and to investigate the most favorable operating condition to the turbine nozzle. To achieve it, the structural analysis, which utilized the results of conjugate heat transfer analysis as loading boundary conditions, was performed and its results were the input for the assessment of low cycle fatigue life at several critical zones.

A Study on Variations of the Low Cycle Fatigue Life of a High Pressure Turbine Nozzle Caused by Inlet Temperature Profiles and Installation Conditions

Energy Technology Data Exchange (ETDEWEB)

Hur, Jae Sung; Kang, Young Seok; Rhee, Dong Ho [Korea Aerospace Research Institute, Daejeon (Korea, Republic of); Seo, Do Young [Pusan National Univ., Busan (Korea, Republic of)

2015-11-15

High pressure components of a gas turbine engine must operate for a long life under severe conditions in order to maximize the performance and minimize the maintenance cost. Enhanced cooling design, thermal barrier coating techniques, and nickel-base superalloys have been applied for overcoming them and furthermore, material modeling, finite element analysis, statistical techniques, and etc. in design stage have been utilized widely. This article aims to evaluate the effects on the low cycle fatigue life of the high pressure turbine nozzle caused by different turbine inlet temperature profiles and installation conditions and to investigate the most favorable operating condition to the turbine nozzle. To achieve it, the structural analysis, which utilized the results of conjugate heat transfer analysis as loading boundary conditions, was performed and its results were the input for the assessment of low cycle fatigue life at several critical zones.

Prediction of thermal fatigue life of ceramics

International Nuclear Information System (INIS)

Kamiya, N.; Kamigaito, O.

1979-01-01

On the assumption that the thermal fatigue life of ceramics is determined mainly by the duration over which a crack reaches a small critical length, a prediction of the life was made by application of fracture mechanics to ceramics based on subcritical crack growth. Approximated formulae were derived. Experimental examination showed that the formulae proved to be valid for glass, sintered mullite under moderate shock severity, and zirconia. Data given by other authors also prove their validity. The deviation of the life from the formulae for sintered mullite under a thermal shock of extremely low severty, suggests that a certain mechanism, for example strengthening, is needed to understand the life of the sintered mullite. (author)

A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

Science.gov (United States)

Sun, Chengqi; Liu, Xiaolong; Hong, Youshi

2015-06-01

In this paper, ultrasonic (20 kHz) fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue (VHCF) regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area (FGA) centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.

PO2 Cycling Reduces Diaphragm Fatigue by Attenuating ROS Formation

OpenAIRE

Zuo, Li; Diaz, Philip T.; Chien, Michael T.; Roberts, William J.; Kishek, Juliana; Best, Thomas M.; Wagner, Peter D.

2014-01-01

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 monito...

Low and high cycle fatigue behaviour of steel-X6CRNI1811 (Type 304 SS) in air and flowing sodium

International Nuclear Information System (INIS)

Huthmann, H.; Jenner, G.

Strain controlled LCF-tests were performed on X6CrNi1811 steel (Type 304 SS) in air and flowing sodium in a non-isothermal sodium loop. The results measured at 550 deg. C in an upstream position of the sodium loop show an increase in fatigue life in the strain range from about 1.5% to 0.4% for the base material in the as-received condition while the welded joints remain unaffected by the environment. The LCF-behaviour of base material specimens tested at 500 deg. C in a downstream position after a prior pre-exposure to sodium (4058 h, 500 deg. C) is also improved in comparison to parallel specimens tested in air with comparable thermal aging. Load controlled HCF-tests performed on X6CrNi1811 steel at 550 deg. C show a significant increase in fatigue life in the low cycle region (Nsub(f) 6 cycles) and a higher endurance limit for the base material in sodium but no influence of the environment is indicated for the welded joints. (author)

Fatigue Crack Growth in Bodies with Thermally Sprayed Coating

Czech Academy of Sciences Publication Activity Database

Kovářík, O.; Haušild, P.; Medřický, Jan; Tomek, L.; Siegl, J.; Mušálek, Radek; Curry, N.; Björklund, S.

2016-01-01

Roč. 25, 1-2 (2016), s. 311-320 ISSN 1059-9630. [ITSC 2015: International Thermal Spray Conference and Exposition. Long Beach, California, 11.05.2015-14.05.2015] R&D Projects: GA ČR GB14-36566G Institutional support: RVO:61389021 Keywords : Thermal barrier coating * fatigue * crack growth * digital image correlation * digital image correlation Subject RIV: JK - Corrosion ; Surface Treatment of Materials Impact factor: 1.488, year: 2016 http://link.springer.com/article/10.1007%2Fs11666-015-0329-9

Lamb Wave Assessment of Fatigue and Thermal Damage in Composites

Science.gov (United States)

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.

2004-01-01

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper describes two studies which monitor fatigue damage and two studies which monitor thermal damage in composites using Lamb waves. In the fatigue studies, the Lamb wave velocity is compared to modulus measurements obtained using strain gage measurements in the first experiment and the velocity is monitored along with the crack density in the second. In the thermal damage studies, one examines samples which were exposed to varying temperatures for a three minute duration and the second includes rapid thermal damage in composites by intense laser beams. In all studies, the Lamb wave velocity is demonstrated to be an excellent method to monitor damage in composites.

Effect of autoclave sterilization on the cyclic fatigue resistance of thermally treated Nickel-Titanium instruments.

Science.gov (United States)

Zhao, D; Shen, Y; Peng, B; Haapasalo, M

2016-10-01

To compare the cyclic fatigue resistance of HyFlex CM, Twisted Files (TF), K3XF, Race, and K3, and evaluate the effect of autoclave sterilization on the cyclic fatigue resistance of these instruments both before and after the files were cycled. Five types of NiTi instruments with similar size 30, .06 taper were selected: HyFlex CM, TF, K3XF, Race and K3. Files were tested in a simulated canal with a curvature of 60° and a radius of 3 mm. The number of cycles to failure of each instrument was determined to evaluate cyclic fatigue resistance. Each type of instruments was randomly divided into four experimental groups: group 1 (n = 20), unsterilized instruments; group 2 (n = 20), pre-sterilized instruments subjected to 10 cycles of autoclave sterilization; group 3 (n = 20), instruments tested were sterilized at 25%, 50% and 75% of the mean cycles to failure as determined in group 1, and then cycled to failure; group 4 (n = 20), instruments cycled in the same manner as group 3 but without sterilization. The fracture surfaces of instruments were examined by scanning electron microscopy (SEM). HyFlex CM, TF and K3XF had significantly higher cyclic fatigue resistance than Race and K3 in the unsterilized group 1 (P Autoclave sterilization significantly increased the MCF of HyFlex CM and K3XF (P Autoclaving extended the cyclic fatigue life of HyFlex CM and K3XF. © 2015 International Endodontic Journal. Published by John Wiley & Sons Ltd.

Thermomechanical fatigue of shape memory alloys

International Nuclear Information System (INIS)

Lagoudas, D C; Kumar, P K; Miller, D A; Rong, L

2009-01-01

As shape memory alloys (SMAs) gain popularity as high energy density actuators, one characteristic that becomes particularly important is the thermomechanical transformation fatigue life, in addition to maximum transformation strain and stability of actuation cycles. In this paper, a novel test frame design and testing protocol are discussed, for investigating the thermally activated transformation fatigue characteristics of SMAs under various applied loads for both complete and partial phase transformation. A Ni 50 Ti 40 Cu 10 (at.%) SMA was chosen for this investigation and the effects of various heat treatments on the transformation temperatures and the transformation fatigue lives of actuators were studied. For selected heat treatments, the evolution of recoverable and irrecoverable strains up to failure under different applied stress levels was studied in detail. The influence of complete and partial transformation on the fatigue life is also presented. The irrecoverable strain accumulation as a function of the number of cycles to failure for different stress levels is presented by a relationship similar to the Manson–Coffin law for both partial and complete transformations

Low cycle fatigue of Alloy 690 and welds in a simulated PWR primary water environment

Energy Technology Data Exchange (ETDEWEB)

Hong, Jongdae; Cho, Pyungyeon; Jang, Changheui [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Cho, Pyungyeon [Khalifa Univ., Abu Dhabi (United Arab Emirates); Kim, Tae Soon; Lee, Yong Sung [Korea Hydro and Nuclear Power Co., Daejeon (Korea, Republic of)

2013-05-15

In this study, environmental fatigue tests for these materials were performed and the new prediction model of fatigue life of Alloy 690 and weld in primary water condition was proposed. To evaluate the fatigue life of Alloy 690 and 52M in a PWR environment, low cycle fatigue tests were performed and revised fatigue life prediction models and environmental factor were proposed. With the revised Fen model for Alloy 690 and 52M, the reliability of the fatigue life prediction has been improved. The reduction of low cycle fatigue life of metallic materials in the primary coolant water environments has been the subject of debate between the utility and regulator since 1980s. It became the significant licensing problem since the issue of RG-1.207 by U. S. NRC. The statistical model for the environmental factor, Fen, specified in RG-1.207 was based on the extensive test results accumulated by the ANL and Japanese national program. Of the materials, the limited fatigue life data of Ni-Cr-Fe alloys were used to develop the Fen for the alloys. Furthermore, test data for Alloy 690 and its weld are limited. Considering that Alloy 690 will be extensively used in the new nuclear power plants, additional effort to validate or improve current Fen model is required.

Low cycle fatigue strength of some austenitic stainless steels at room temperature and elevated temperatures

International Nuclear Information System (INIS)

Type 304, 316, and 316L stainless steels were tested from room temperature to 650 0 C using two kinds of bending test specimens. Particularly, Type 304 was tested at several cyclic rates and 550 0 and 650 0 C, and the effect of cyclic rate on its fatigue strength was investigated. Test results are summarized as follows: (1) The bending fatigue strength at room temperature test shows good agreement with the axial fatigue one, (2) Manson--Coffin's fatigue equation can be applied to the results, (3) the ratio of crack initiation to failure life becomes larger at higher stress level, and (4) the relation between crack propagation life and total strain range or elastic strain range are linear in log-log scale. This relation also agrees with the equations which were derived from some crack propagation laws. It was also observed at the elevated temperature test: (1) The reduction of fatigue strength is not noticeable below 500 0 C, but it is noted at higher temperature. (2) The cycle rate does not affect on fatigue strength in faster cyclic rate than 20 cpm and below 100,000 cycles life range. (3) Type 316 stainless steel shows better fatigue property than type 304 and 316L stainless steels. 30 figures

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

Czech Academy of Sciences Publication Activity Database

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: 0.533, year: 2016

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

International Nuclear Information System (INIS)

Cooper, R.A.

1976-01-01

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

Fatigue behaviour of coke drum materials under thermal-mechanical cyclic loading

Directory of Open Access Journals (Sweden)

Jie Chen

2014-01-01

Full Text Available Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.

High-temperature low-cycle fatigue behaviour of HIP treated and untreated superalloy MAR-M247

Czech Academy of Sciences Publication Activity Database

Šulák, Ivo; Obrtlík, Karel; Čelko, L.

2016-01-01

Roč. 54, č. 6 (2016), s. 471-481 ISSN 0023-432X R&D Projects: GA TA ČR(CZ) TA04011525; GA ČR(CZ) GA15-20991S Institutional support: RVO:68081723 Keywords : hot isostatic pressing * high-temperature low cycle fatigue * fatigue life curves * Ni-based superalloy * dislocation structures * planar bands Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 0.366, year: 2016

Comparison of low cycle fatigue of ductile cast irons with different matrix alloyed with nickel

Czech Academy of Sciences Publication Activity Database

Petrenec, Martin; Tesařová, H.; Beran, Přemysl; Šmíd, Miroslav; Roupcová, Pavla

2010-01-01

Roč. 2, č. 1 (2010), s. 2307-2316 E-ISSN 1877-7058. [ Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GAP108/10/2371 Institutional research plan: CEZ:AV0Z20410507; CEZ:AV0Z10480505 Keywords : Low cycle fatigue * ferritic ductile cast iron * ADI * nickel alloying * neutron diffraction Subject RIV: JL - Materials Fatigue , Friction Mechanics

Low cycle fatigue properties of CLAM steel at 450 °C and 550 °C

Energy Technology Data Exchange (ETDEWEB)

Zhao, Yanyun; Zhai, Xiangwei; Liu, Shaojun, E-mail: shaojun.liu@fds.org.cn

2016-11-15

Highlights: • Low cycle fatigue properties of CLAM steel were investigated at 450 °C and 550 °C. • CLAM steel showed the continuous softening up to fail failure under cyclic loading. The degree of softening increased with increasing temperature. • Dislocation density decrease and subgrain coarsening during the test process were the possible reasons for the cyclic softening of the CLAM steel. - Abstract: The low cycle fatigue behavior of China Low Activation Martensitic (CLAM) steel has been studied using a constant strain rate of 8 × 10{sup −3}/s with the strain amplitudes ranging from 0.3% to 0.8% at 450 °C and 550 °C. Cyclic stress response showed a gradual softening until complete failure. The fatigue life decreased with increasing test temperature, and the effect of temperature on fatigue life was more pronounced at lower strain amplitudes. The cyclic deformation behavior at different temperatures has been analyzed according to the hysteresis loop, and the mechanism of cyclic softening was interpreted in view of the changes taking place in dislocation density and lath structures. Evaluation of low cycle fatigue properties of CLAM steel at 450 °C and 550 °C can help in design of the Chinese Test Blanket Module (TBM) for the International Thermonuclear Experimental Reactor (ITER) and a future fusion power plant.

Competition between microstructure and defect in multiaxial high cycle fatigue

Directory of Open Access Journals (Sweden)

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

Low-cycle fatigue of welded joints: coupled initiation propagation model

International Nuclear Information System (INIS)

Madi, Yazid; Recho, Naman; Matheron, Philippe

2004-01-01

This paper deals with the low-cycle fatigue (LC) design of welded structures, the aim being the critical analysis of the rule used in the RCC-MR [Design and construction rules for mechanical components of FBR nuclear islands, AFCEN, 1993], for the design and construction of fast breeder reactors. The study takes into account the evolution of the material behavior laws and damage accumulation during the fatigue loading. The adopted model consists of analyzing separately the behavior and the damage evolutions. It allows us to determine the damage ratio corresponding to initiation and propagation of a significant crack in order to determine the life duration. This model suggests the existence of a threshold level of loading, above which micro-cracks initiate. The initiation fatigue life can then be neglected below the threshold level. This work shows also that the RCC-MR rules are valid below this threshold load level

Low cycle fatigue and creep-fatigue interaction behavior of nickel-base superalloy GH4169 at elevated temperature of 650 °C

Energy Technology Data Exchange (ETDEWEB)

Chen, G., E-mail: agang@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Y. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xu, D.K. [Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Lin, Y.C. [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

2016-02-08

Total strain-controlled low cycle fatigue (LCF) tests of a nickel based superalloy were performed at 650 °C. Various hold times were introduced at the peak tensile strain to investigate the high-temperature creep-fatigue interaction (CFI) effects under the same temperature. A substantial decrease in fatigue life occurred as the total strain amplitude increased. Moreover, tensile strain holding further reduced fatigue life. The saturation phenomenon of holding effect was found when the holding period reached 120 s. Cyclic softening occurred during the LCF and CFI process and it was related to the total strain amplitude and the holding period. The relationship between life-time and total strain amplitude was obtained by combining Basquin equation and Coffin-Manson equation. The surface and fracture section of the fatigued specimens were observed via scanning electronic microscope (SEM) to determine the failure mechanism.

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

International Nuclear Information System (INIS)

Gagnon, M; Tahan, S A; Bocher, P; Thibault, D

2012-01-01

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.

Study on high-cycle fatigue behavior of candidate Fe-Cr-Ni alloys for SCWR

International Nuclear Information System (INIS)

Zhao Yuxiang; Liu Guiliang; Tang Rui; Xiong Ru; Qiao Yingjie

2014-01-01

In the design for supercritical water reactor (SCWR), the operating temperature, pressure, burn up and irradiation damage are very high, so it seems vital to make correct choice of structural materials in core and obtain their key application behavior which would beneficial the research and development of SCWR. In this paper, the high cycle fatigue (HCF) tests of commerce austenite alloys including 6XN and 825 were conducted under bending and rotating loads at room temperature (RT) as well as at 550 ℃ in air. The experimental data were analyzed and the S-N curves were processed, the fracture morphology was also observed by SEM. The results indicate that the fatigue limited stresses at RT for the 2 Fe-Cr-Ni alloy were in such order of 825 < 6XN, which consistent with the order of their tensile strength. Elevated temperature would accelerate the oxidation of the specimen and therefore the fatigue life would decrease, among them 6XN was more sensitive to high temperature with the larger decreasing tendency which make the fatigue limited stress of the two alloys more closer at 550 ℃. While 825 is more sensitive to the stress cycles. All the two alloys have good resistance to high cycle fatigue when comparing their experimental data with the calculated value from the empirical formula. The fracture morphology presents areas of crack initiation, crack growth and fracture, the fracture area has much dimples. This work can be applied to the conceptional design for SCWR. (authors)

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

International Nuclear Information System (INIS)

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

2010-01-01

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

Development of a procedure for estimating the high cycle fatigue strength of some high temperature structural alloys

International Nuclear Information System (INIS)

Soo, P.; Chow, J.G.Y.

1979-01-01

The generation of strain controlled fatigue data, for the standard strain rate of 4 x 10 -3 sec -1 , presents a problem when the cycles to failure exceed 10 5 because of the prohibitively long test times involved. In an attempt to circumvent this difficulty an evaluation has been made of a test procedure involving a fast cycling rate (40 Hz) and load controlled conditions. The validity of this procedure for extending current fatigue curves from 10 5 to 10 8 cycles and beyond, hinges upon the selection of an appropriate effective strain value, since the strain usually changes rapidly during the early stage of fatigue. Results from annealed 2 1/4 Cr-1 Mo, type 304 stainless steel, Incoloy 800H and Hastelloy X, tested over a wide range of temperatures, show that the strain measured N/sub f/2 is a reasonable estimate since it gives an excellent correlation between the strain and load controlled tests in the 10 5 cycle range where the data overlap. It seems clear that the differences in cycling rate and early stress-strain history for the two tests do not significantly affect the correlation. It may, therefore, be concluded that such load control test procedures may be used as a valid fast way for extending currently available fatigue curves from 10 5 to 10 8 cycles, and beyond

High-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures

OpenAIRE

Wan, Aoshuang; Xiong, Junjiang; Lyu, Zhiyang; Li, Kuang; Du, Yisen; Chen, Kejiao; Man, Ziyu

2016-01-01

A modified model is developed to characterize and evaluate high-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures by considering the stress ratio effect. The model is informed by the relationship surface between maximum nominal stress, stress ratio and fatigue life. New formulae are derived to deal with the test data for estimating the parameters of the proposed model. Fatigue tests are performed on Co-based superalloy 9CrCo subjected to constant amplitude loading a...

Very high cycle fatigue crack initiation in electroplated Ni films under extreme stress gradients

International Nuclear Information System (INIS)

Baumert, E.K.; Pierron, O.N.

2012-01-01

A characterization technique based on kilohertz micro-resonators is presented to investigate the very high cycle fatigue behavior of 20 μm thick electroplated Ni films with a columnar microstructure (grain diameter less than 2 μm). The films exhibit superior fatigue resistance due to the extreme stress gradients at the surface. The effects of stress amplitude and environment on the formation of fatigue extrusions and micro-cracks are discussed based on scanning electron microscopy and the tracking of the specimens’ resonant frequency.

Influence of the number of cycles on shear fatigue strength of resin composite bonded to enamel and dentin using dental adhesives in self-etching mode.

Science.gov (United States)

Tsujimoto, Akimasa; Barkmeier, Wayne W; Erickson, Robert L; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi

2018-01-30

The influence of the number of cycles on shear fatigue strength to enamel and dentin using dental adhesives in self-etch mode was investigated. A two-step self-etch adhesive and two universal adhesives were used to bond to enamel and dentin in self-etch mode. Initial shear bond strength and shear fatigue strength to enamel and dentin using the adhesive in self-etch mode were determined. Fatigue testing was used with 20 Hz frequency and cycling periods of 50,000, 100,000 and 1,000,000 cycles, or until failure occurred. For each of the cycling periods, there was no significant difference in shear fatigue strength across the cycling periods for the individual adhesives. Differences in shear fatigue strength were found between the adhesives within the cycling periods. Regardless of the adhesive used in self-etch mode for bonding to enamel or dentin, shear fatigue strength was not influenced by the number of cycles used for shear fatigue strength testing.

High temperature low cycle fatigue behavior of Ni-base superalloy M963

International Nuclear Information System (INIS)

He, L.Z.; Zheng, Q.; Sun, X.F.; Guan, H.R.; Hu, Z.Q.; Tieu, A.K.; Lu, C.; Zhu, H.T.

2005-01-01

The cyclic stress-strain response and the low cycle fatigue life behavior of solution treated Ni-base superalloy M963 were studied. Fully reversed strain-controlled tests were performed at temperature range from 700 to 950 deg. C in air at a constant total strain rate. The dislocation characteristics and failed surface observation were evaluated through scanning electron microscopy and transmission electron microscopy, respectively. The alloy exhibited the cyclic hardening, softening, or stable cyclic stress response, which was dependent on the temperature and total strain range. The fracture surface observation revealed that fatigue crack initiation was transgranular and closely related to the total strain range; however, fatigue crack propagation exhibited a strong dependence on testing temperature. The dramatic reduction in fatigue life and intergranular cracking observed at 900 and 950 deg. C were attributed to oxidation

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

Directory of Open Access Journals (Sweden)

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.

High cycle fatigue of austenitic stainless steels under random loading

International Nuclear Information System (INIS)

Gauthier, J.P.; Petrequin, P.

1987-08-01

To investigate reactor components, load control random fatigue tests were performed at 300 0 C and 550 0 C, on specimens from austenitic stainless steels plates in the transverse orientation. Random solicitations are produced on closed loop servo-hydraulic machines by a mini computer which generates random load sequence by the use of reduced Markovian matrix. The method has the advantage of taking into account the mean load for each cycle. The solicitations generated are those of a stationary gaussian process. Fatigue tests have been mainly performed in the endurance region of fatigue curve, with scattering determination using stair case method. Experimental results have been analysed aiming at determining design curves for components calculations, depending on irregularity factor and temperature. Analysis in term of mean square root fatigue limit calculation, shows that random loading gives more damage than constant amplitude loading. Damage calculations following Miner rule have been made using the probability density function for the case where the irregularity factor is nearest to 100 %. The Miner rule is too conservative for our results. A method using design curves including random loading effects with irregularity factor as an indexing parameter is proposed

Thermomechanical fields measurement for fatigue investigation under cyclic thermal shocks

International Nuclear Information System (INIS)

Charbal, Ali

2017-01-01

Thermal fatigue occurs in nuclear power plant pipes. The temperature variations are due to the turbulent mixing of fluids that have different temperatures. Many experimental setups have been designed but the measured temperatures have only been punctual and out of the zone of interest (e.g., via thermocouples). The equivalent strain variation in the crack initiation region is calculated with numerical thermomechanical simulations. In many cases, the comparisons between numerical and experimental results have shown that the crack initiation predictions in thermal fatigue are non-conservative. a new testing setup is proposed where thermal shocks are applied with a pulsed laser beam while the thermal and kinematic fields on the specimen surface are measured with infrared (IR) and visible cameras, respectively. Experimental testings are performed and different measurement techniques for temperature and kinematic fields are used. IR camera and pyrometers allow to measure the temperature variations in the zone impacted by the laser beam. To estimate the absolute temperature, the surface emissivities at the respective wavelengths are determined by different methods. The absolute temperature field is then used to apply the actual thermal loading in a decoupled FE model after an identification process of the parameters of the laser beam. Once the thermal loading is generated based upon the experimental data, the stress and strain fields can be computed in the region of interest with an elastoplastic law.The experimental strain variations calculated from the DIC measurements are compared with the predictions obtained with the FE simulation. (author) [fr

Ratcheting and low cycle fatigue behavior of SA333 steel and their life prediction

International Nuclear Information System (INIS)

Paul, Surajit Kumar; Sivaprasad, S.; Dhar, S.; Tarafder, S.

2010-01-01

Ratcheting and low cycle fatigue (LCF) experiments have been conducted at 25 o C temperature in laboratory environment under different loading conditions. SA333 steel exhibits cyclic hardening throughout its life during LCF. It is found that ratcheting strain increases with both increasing mean stress and stress amplitude. It has also been noticed that plastic strain amplitude and plastic strain energy decrease with increase in mean stress at constant stress amplitude. Ratcheting and LCF life in the range of 10 2 -10 5 cycles have been predicted with the help of a mean stress-based fatigue lifing equation.

Effects of pulse current stimulation on the thermal fatigue crack propagation behavior of CHWD steel

International Nuclear Information System (INIS)

Lin, H.Q.; Zhao, Y.G.; Gao, Z.M.; Han, L.G.

2008-01-01

The fatigue crack propagating behaviors of cast hot working die (CHWD) steel untreated and treated by an electric current in the intermediate stage of thermal fatigue were investigated in the present study. The circle/elliptical heating affected zone (HAZ) was formed ahead of the notch tip on the fatigued specimens after pulse electric current stimulation. Both SEM observation and X-ray diffraction analysis revealed that pulse electric current stimulation refined grains/subgrains in the HAZs. With the prolonging of discharging duration, the grains/subgrains decreased in size and the dislocation density and microhardness increased gradually. The grain refinement and dislocation density increase played an important role in the material strengthening, which inevitably enhanced the propagation resistance and delayed the propagation of thermal fatigue cracks. Therefore, the pulse electric current stimulation was an effective method to improve the service lifetime of die material

Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part 2; Effect of Thermal Cycling

Science.gov (United States)

Raj, S. V.; Noebe, R. D.

2013-01-01

This paper is the first report on the effect prior low temperature creep on the thermal cycling behavior of NiTi. The isothermal low temperature creep behavior of near-stoichiometric NiTi between 300 and 473 K was discussed in Part I. The effect of temperature cycling on its creep behavior is reported in the present paper (Part II). Temperature cycling tests were conducted between either 300 or 373 K and 473 K under a constant applied stress of either 250 or 350 MPa with hold times lasting at each temperature varying between 300 and 700 h. Each specimen was pre-crept either at 300 or at 473 K for several months under an identical applied stress as that used in the subsequent thermal cycling tests. Irrespective of the initial pre-crept microstructures, the specimens exhibited a considerable increase in strain with each thermal cycle so that the total strain continued to build-up to 15 to 20 percent after only 5 cycles. Creep strains were immeasurably small during the hold periods. It is demonstrated that the strains in the austenite and martensite are linearly correlated. Interestingly, the differential irrecoverable strain, in the material measured in either phase decreases with increasing number of cycles, similar to the well-known Manson-Coffin relation in low cycle fatigue. Both phases are shown to undergo strain hardening due to the development of residual stresses. Plots of true creep rate against absolute temperature showed distinct peaks and valleys during the cool-down and heat-up portions of the thermal cycles, respectively. Transformation temperatures determined from the creep data revealed that the austenitic start and finish temperatures were more sensitive to the pre-crept martensitic phase than to the pre-crept austenitic phase. The results are discussed in terms of a phenomenological model, where it is suggested that thermal cycling between the austenitic and martensitic phase temperatures or vice versa results in the deformation of the austenite and

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

Energy Technology Data Exchange (ETDEWEB)

Straub, Thomas

2016-07-01

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

A Predictive Framework for Thermomechanical Fatigue Life of High Silicon Molybdenum Ductile Cast Iron Based on Considerations of Strain Energy Dissipation

Science.gov (United States)

Avery, Katherine R.

Isothermal low cycle fatigue (LCF) and anisothermal thermomechanical fatigue (TMF) tests were conducted on a high silicon molybdenum (HiSiMo) cast iron for temperatures up to 1073K. LCF and out-of-phase (OP) TMF lives were significantly reduced when the temperature was near 673K due to an embrittlement phenomenon which decreases the ductility of HiSiMo at this temperature. In this case, intergranular fracture was predominant, and magnesium was observed at the fracture surface. When the thermal cycle did not include 673K, the failure mode was predominantly transgranular, and magnesium was not present on the fracture surface. The in-phase (IP) TMF lives were unaffected when the thermal cycle included 673K, and the predominant failure mode was found to be transgranular fracture, regardless of the temperature. No magnesium was present on the IP TMF fracture surfaces. Thus, the embrittlement phenomenon was found to contribute to fatigue damage only when the temperature was near 673K and a tensile stress was present. To account for the temperature- and stress-dependence of the embrittlement phenomenon on the TMF life of HiSiMo cast iron, an original model based on the cyclic inelastic energy dissipation is proposed which accounts for temperature-dependent differences in the rate of fatigue damage accumulation in tension and compression. The proposed model has few empirical parameters. Despite the simplicity of the model, the predicted fatigue life shows good agreement with more than 130 uniaxial low cycle and thermomechanical fatigue tests, cyclic creep tests, and tests conducted at slow strain rates and with hold times. The proposed model was implemented in a multiaxial formulation and applied to the fatigue life prediction of an exhaust manifold subjected to severe thermal cycles. The simulation results show good agreement with the failure locations and number of cycles to failure observed in a component-level experiment.

Low cycle fatigue studies on a type 304 stainless steel

International Nuclear Information System (INIS)

Bhanu Sankara Rao, K.; Valsan, M.; Sandhya, R.; Ray, S.K.; Rodriguez, P.

The effects of temperature and strain rate on the low cycle fatigue behaviour were investigated for an AISI 304 stainless steel under total axial strain control mode at 823 and 923 K. The fatigue life was strongly dependent on cyclic deformation rate for this material at these temperatures, decreasing markedly with decreasing strain rate. The cyclic stress-strain response recorded in the form of hysterisis loops exhibited serrations at low strain rates at 823 and 923 K. Cyclic stress-strain response at 823 K has shown an increase in saturation stress and decrease in plastic strain range whereas there is an increase in plastic strain range without marked variation in saturation stress level at 923 K with decreasing strain rate. It has been observed that there are three simultaneous effects namely environment, creep and cyclic strain ageing which contribute to the observed degradation in fatigue life at low strain rates. At 823 K, where the creep damage as well as environmental damage is relatively small, the fatigue life is considered mainly to be affected by dynamic strain ageing effect which depends on strain rate. At 923 K, on the other hand, the strain rate dependence of fatigue life is considered to be determined by the combination of creep and environmental effects. Deformation and fracture studies have also confirmed that the wedge type crack propagation is accelerated by oxidation effect. (author)

The thermal fatigue resistance of vermicular cast iron coupling with H13 steel units by cast-in process

International Nuclear Information System (INIS)

Wang, Chengtao; Zhou, Hong; Lin, Peng Yu; Sun, Na; Guo, Qingchun; Zhang, Peng; Yu, Jiaxiang; Liu, Yan; Wang, Mingxing; Ren, Luquan

2010-01-01

This paper focuses on improving the thermal fatigue resistance on the surface of vermicular cast iron coupling with inserted H13 steel blocks that had different cross sections, by cast-in processing. The microstructure of bionic units was examined by scanning electron microscope. Micro-hardness and thermal fatigue resistance of bionic samples with varied cross sections and spacings were investigated, respectively. Results show that a marked metallurgical bonding zone was produced at interface between the inserted H13 steel block and the parent material - a unique feature of the bionic structure in the vermicular cast iron samples. The micro-hardness of the bionic samples has been significantly improved. Thermal resistance of the samples with the circular cross section was the highest and the bionics sample with spacing of 2 mm spacing had a much longer thermal fatigue life, thus resulting in the improvement for the thermal fatigue life of the bionic samples, due to the efficient preclusion for the generation and propagation of crack at the interface of H13 block and the matrix.

Frequency interpretation of hold-time experiments on high temperature low-cycle fatigue of steels for LMFBR

International Nuclear Information System (INIS)

Udoguchi, T.; Asada, Y.; Ichino, I.

1975-01-01

The effect of frequency or hold-time on the low-cycle fatigue strength of AISI 316 stainless steel and SCM 3 Cr--Mo steel for fuel cladding, piping, and other structural members of LMFBR is investigated under high temperature conditions. Push-pull fatigue tests are conducted in air under conditions of fully reversed axial strain-control with a tensile strain hold-time ranging fromm 0 to 120 min for AISI 316, and with a tensile and an equal compressive strain hold-time ranging from 0 to 995 s for SCM 3. In these tests, a decrease of fatigue life is observed as the hold-time is increased. An empirical formula is presented which can predict well the effect of hold-time on high temperature low-cycle fatigue life in terms of frequency. The formula is a little different from those in the literature

Life Prediction of Low Cycle Fatigue for Ni-base Superalloy GTD111 DS at Elevated Temperature

Energy Technology Data Exchange (ETDEWEB)

Kim, Jin Yeol; Yoon, Dong Hyun; Kim, Jae Hoon [Chungnam Nat’l Univ., Daejeon (Korea, Republic of); Bae, Si Yeon; Chang, Sung Yong; Chang, Sung Ho [KEPCO Research Institute, Daejeon (Korea, Republic of)

2017-08-15

GTD111 DS of nickel base superalloy has been used for gas turbine blades. In this study, low cycle fatigue test was conducted on the GTD111 DS alloy by setting conditions similar to the real operating environment. The low cycle fatigue tests were conducted at room temperature, 760 °C, 870 °C, and various strain amplitudes. Test results showed that fatigue life decreased with increasing total strain amplitude. Cyclic hardening response was observed at room temperature and 760 °C; however, tests conducted at 870 °C showed cyclic softening response. Stress relaxation was observed at 870 °C because creep effects occurred from holding time. A relationship between fatigue life and total strain range was obtained from the Coffin-Manson method. The fratography using a SEM was carried out at the crack initiation and propagation regions.

Application of a Cycle Jump Technique for Acceleration of Fatigue Crack Growth Simulation

DEFF Research Database (Denmark)

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

2010-01-01

A method for accelerated simulation of fatigue crack growth in a bimaterial interface is proposed. To simulate fatigue crack growth in a bimaterial interface a routine is developed in the commercial finite element code ANSYS and a method to accelerate the simulation is implemented. The proposed m...... of the simulation show that with fair accuracy, using the cycle jump method, more than 70% reduction in computation time can be achieved....

Low cycle fatigue behavior in a medium-carbon carbide-free bainitic steel

Energy Technology Data Exchange (ETDEWEB)

Kang, J. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Zhang, F.C., E-mail: zfc@ysu.edu.cn [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Long, X.Y. [State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004 (China); Lv, B. [College of Environmental and Chemical Engineering, Yanshan University, Qinhuangdao 066004 (China)

2016-06-01

In the paper, different morphologies of bainite were obtained through isothermal quenching at 320 °C and 395 °C in a medium-carbon carbide-free bainitic steel. The cyclic deformation mechanism was explored by using low cycle fatigue testing. The volume fraction of retained austenite was measured by X-ray diffraction and the space partitioning of the solute atoms was constructed by three-dimensional atom probe. Results showed that the fatigue life at 320 °C was always higher than that at 395 °C under low and high total strain amplitude. The cyclic softening at the early fatigue stage increased the plastic strain of the sample which was responsible for the reduction of the fatigue life at 395 °C. Strain-induced retained austenite to martensite contributed to initial cyclic hardening, but almost having no effect on the subsequent cyclic stable/softening behaviors. The finer bainitic ferrite sheaves obtained at 320 °C changed the small fatigue crack propagation direction and delayed the crack propagation rate, which was beneficial for the fatigue properties. In addition, the substitutional atoms did not redistribute between the retained austenite and bainitic ferrite before and after cyclic deformation.

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

Energy Technology Data Exchange (ETDEWEB)

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)

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

Directory of Open Access Journals (Sweden)

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.

Thermal fatigue in mixing tees: A step by step simplified procedure

International Nuclear Information System (INIS)

Faidy, Claude

2003-01-01

Following the CIVAUX 1 incident of a leak on RHR system, EDF has developed a step by step procedure to screen and analyse similar locations: mixing tees with long duration at high ΔT between the 2 fluids. The paper present the procedure, the background of the methodology and few R and D work that support this procedure. The procedure is based on: screening criteria on maximum DT and minimum duration. screening criteria without any duration consideration, only DT and material. a simplified and conservative estimation of a usage factor. a detailed analysis of usage factor and crack growth rate, based on specific data collection of operating transients. Around that procedure EDF launched an R and D program on fatigue curves and fatigue reduction factors for high cycle fatigue. The procedure is compared with field experience and recent R and D fatigue tests. (author)

Study on high-cycle fatigue behavior of candidate stainless steels for SCWR

International Nuclear Information System (INIS)

Xiong Ru; Zhao Yuxiang; Zhang Qiang; Wang Hao; Tang Rui; Qiao Yingjie

2013-01-01

The fatigue experiments of commerce stainless steels including 347, 316Ti and 310 were conducted under bending and rotating loadings. The environments were at room temperature (RT) as well as at 550℃ in air. The fracture morphology was observed by SEM, and the S-N curves were processed according to the experimental data. The results indicate the fatigue limited stresses for the 3 stainless steels were in the order of 347 < 316Ti < 310, which consistent with the order of their tensile strength. Elevated temperature would accelerate the oxidation and therefore the fatigue life would decrease, among them 347 was more sensitive to temperature with the maximum decreasing tendency. All the 3 stainless steels have good resistance to high cycle fatigue when comparing their experimental data with the calculated value from the empirical formula. The fracture morphology presents areas of crack initiation, crack growth and fracture, the width of fatigue ripples is about 1 μm, the fracture area has much dimples, and 347 presents much cavities of different sizes in dimples. (authors)

Stochastic modelling of thermal fatigue crack growth for applying in the structural reliability of nuclear piping

International Nuclear Information System (INIS)

Radu, V.

2016-01-01

The problem of thermal fatigue in mixing areas arises in nuclear piping where a turbulent mixing or vortices produce rapid fluid temperature fluctuations with random frequencies. The assessment of fatigue crack growth due to cyclic thermal loads arising from turbulent mixing presents significant challenges, principally due to the difficulty of establishing the actual loading spectrum. To apply the Stochastic approach of thermal fatigue, a frequency temperature response function is proposed. For the elastic thermal stresses distribution solutions, the magnitude of the frequency response function is first derived and checked against the prediction by FEA. The connection between SIF.s power spectral density (PSD) and temperature.s PSD is assured with SIF frequency response function modulus. The frequency of the peaks of each magnitude for KI is supposed to be a stationary narrow-band Gaussian process. The probabilities of failure are estimated by means of the Monte Carlo methods considering a limit state function. (authors)

Cycle counting procedure for fatigue failure preditions for complicated multi-axial stress histories

International Nuclear Information System (INIS)

Jones, D.P.; Friedrich, C.M.; Hoppe, R.G.

1977-12-01

A procedure has been developed to determine the cumulative fatigue damage in structures experiencing complicated multi-axial stress histories. The procedure is a generalization of the rainflow method developed by Matsuishi and Endo for one-dimensional situations. It provides a consistent treatment of three-dimensional stress states that is especially suited to computer programming applications for the post-processing of finite element stress data. The procedure includes a unique method to account for the rotation of principal stresses with time during the stress history and for the cumulative fatigue damage resulting from partial stress reversals within a stress cycle. The general procedure and necessary equations for programming are presented. Comparisons are made with life predictions using Section III of the ASME Boiler and Pressure Vessel Code for two hypothetical multi-axial stress histories for which the principal stresses are rotating with time. These comparisons show that the cycle counting method provides a consistent unambiguous interpretation of the fatigue design procedure in the ASME Code for these cases. Finally, the fatigue life of a perforated plate, as analyzed by finite elements, is computed for the combination of several hypothetical stress histories. This example demonstrates the utility of the proposed method when used in conjunction with finite element programs

Effect of cyclic pre-strain on low cycle fatigue life at middle high temperature

International Nuclear Information System (INIS)

Nakane, Motoki; Kanno, Satoshi; Takagi, Yoshio

2011-01-01

This study examined the effect of cyclic plastic pre-strain on low cycle fatigue life at middle high temperature to evaluate the structural integrity of the nuclear components introduced plastic strain to the local portion by the large seismic load. The materials selected in this study were austenitic steel (SUS316NG) and ferritic steel (SFVQ1A, STS410: JIS (Japanese Industrial Standards). The low cycle fatigue tests at RT and middle high temperature (300 degrees C) were carried out using cyclic plastic pre-strained materials. The results obtained here show that the damage by the cyclic plastic pre-strain, which is equivalent to usage factor UF=0.2, does not affect the fatigue lives of the materials. In addition, it is confirmed that the estimation based on the usage factor UF can also be useful for the life prediction at 300 degrees C as well as RT. (author)

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

Science.gov (United States)

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.

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

International Nuclear Information System (INIS)

Chopra, O.K.; Smith, D.L.

1983-06-01

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

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

International Nuclear Information System (INIS)

Bate, S.K.

1997-01-01

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