Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped metho...Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped method for estimating fatigue cycles to failure. Damage summation rule was applied to estimate the fatigue damage accumulated over a given period of engine operation. The concept of fatigue factor which indicates how well engine is operated was introduced to make engine life tracking feasible. The developed fatigue life tracking method was incorporated in PYTHIA, Cranfield University in-house software and applied to 8 months of engine operation. The results obtained are similar to those of real engine operation. At a set power level, fatigue life decreases with increase in ambient temperature with the magnitude of decrease greater at higher power levels. The fatigue life tracking methodology developed could serve as a useful tool to engine operators.展开更多
The influences of strain amplitude ranges and dwell time at peak strains on the low cycle fatigue (LCF) properties at 600℃ of a new near α high temperature titanium alloy containing rare earth Nd are investigated. ...The influences of strain amplitude ranges and dwell time at peak strains on the low cycle fatigue (LCF) properties at 600℃ of a new near α high temperature titanium alloy containing rare earth Nd are investigated. The creep fatigue interaction behavior is discussed in this paper in terms of a creep fatigue interaction cumulative law and fatigue crack propagation model. The results show that the creep fatigue interaction is largely dependent on the strain amplitude range, and the tensile dwell periods, as well as compressive dwell periods, have a great influence on the LCF life of this alloy.展开更多
The cyclic stress response and lowcycle fatigue life for wrought nickelbased superalloy GH4049 were investigated in the temperature range from 500 to 800 The relationship between the strain amplitude and the number o...The cyclic stress response and lowcycle fatigue life for wrought nickelbased superalloy GH4049 were investigated in the temperature range from 500 to 800 The relationship between the strain amplitude and the number of stress reversals was given. The behavior of cyclic hardening was observed for higher strain amplitudes at all testing temperatures and the lowcycle fatigue life generally decreased with increasing testing temperature for the same strain range. In addition, fracture surfaces of the fatigued samples were examined by using a scanning electron microscope.展开更多
Reliability analysis methods based on the linear damage accumulation law (LDAL) and load-life interference model are studied in this paper. According to the equal probability rule, the equivalent loads are derived, an...Reliability analysis methods based on the linear damage accumulation law (LDAL) and load-life interference model are studied in this paper. According to the equal probability rule, the equivalent loads are derived, and the reliability analysis method based on load-life interference model and recurrence formula is constructed. In conjunction with finite element analysis (FEA) program, the reliability of an aero engine turbine disk under low cycle fatigue (LCF) condition has been analyzed. The results show the turbine disk is safety and the above reliability analysis methods are feasible.展开更多
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 in...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.展开更多
Magnesium alloy Mg-3%Al-1%Zn (AZ31) billets prepared from equal channel angular pressing (ECAP) were utilized in low-cycle fatigue tests in order to investigate their fatigue life. Fully reversed strain-controlled...Magnesium alloy Mg-3%Al-1%Zn (AZ31) billets prepared from equal channel angular pressing (ECAP) were utilized in low-cycle fatigue tests in order to investigate their fatigue life. Fully reversed strain-controlled tension-compression fatigue tests were conducted at the frequency of 1 Hz in ambient air. The microstructures were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The hysteresis loops of the ECAP processed and conventionally extruded samples display obviously different shapes in the total strain amplitude range from 0.2% to 0.6%. Accordingly, the low cycle fatigue lives of ECAP processed samples are found to be longer than those of extruded samples, which can be attributed to the different in the hysteresis energy incorporating tensile strain energy.展开更多
Fatigue failure is one of the main failure forms of Al-Si-Cu-Mg aluminum alloys.To feature their mechanical aspect of fatigue behavior,the low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg all...Fatigue failure is one of the main failure forms of Al-Si-Cu-Mg aluminum alloys.To feature their mechanical aspect of fatigue behavior,the low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys at room temperature was investigated.The experimental results show that both permanent mold cast and die-cast Al-Si-Cu-Mg alloys mainly exhibit cyclic strain hardening.At the same total strain amplitude,the die-cast Al-Si-Cu-Mg alloy shows higher cyclic deformation resistance and longer fatigue life than does the permanent mold cast Al-Si-Cu-Mg alloy.The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior,and can be described by the Basquin and Coffin-Manson equations,respectively.展开更多
An investigation was conducted to examine the low cycle symmetric push-pull fatigue behaviour of the Cr-Mn-N dual-phase stainless steel.Two groups of specimens,A and B, were used,they were solution treated at 1050 and...An investigation was conducted to examine the low cycle symmetric push-pull fatigue behaviour of the Cr-Mn-N dual-phase stainless steel.Two groups of specimens,A and B, were used,they were solution treated at 1050 and 1250℃,respectively.The.fatigue life of group A is almost twice as long as that of group B under the same total strain amplitude.The energy loss during the fatigue tests and the mophology of the fracture surfaces have been stu- died and discussed.展开更多
The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room temperature.The fatigue life...The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room temperature.The fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were discussed.The results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium,and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress load.Therefore,the SWT mean stress correction model and three-parameter power curve model are proposed,and the test results are verified.The final research shows that the threeparameter power surface model has better representation.By studying the mean stress relaxation phenomenon under the condition of R≠-1,it is revealed that the stress ratio and the strain amplitude are the factors that significantly afiect the mean stress relaxation rate,and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain ratios.The fracture morphology of the samples was observed by SEM,and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage fracture.The toughness of the material increases with the increase of strain ratio at the same strain amplitude.展开更多
Three cumulative damage models are examined for the case of cyclic loading of AISI 6150 steel, S2 glass fibre/epoxy and E glass fibre/epoxy composites. The Palmgren-Miner, Broutman-Sahu and Hashin-Rotem models are com...Three cumulative damage models are examined for the case of cyclic loading of AISI 6150 steel, S2 glass fibre/epoxy and E glass fibre/epoxy composites. The Palmgren-Miner, Broutman-Sahu and Hashin-Rotem models are compared to determine which of the three gives the most accurate estimation of the fatigue life of the materials tested. In addition, comparison of the fatigue life of the materials shows the superiority of AISI 6150 steel and S2 glass fibre/epoxy at lower mean stresses, and that of steel to the composites at higher mean stresses.展开更多
Energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented. The models are based on energy dissipation during average of cycles, cycles to crack propagation and tota...Energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented. The models are based on energy dissipation during average of cycles, cycles to crack propagation and total cycles to failure. Plastic strain energy per cycle was determined and found as an important characteristic for initiation and propagation of fatigue cracks for high-strength structural steels. Fatigue strain-life curves were generated using plastic energy dissipation per cycle (loop area) and compared with the Coffin-Manson relation. Low cycle fatigue life was found similar from both methods. The material showed Masing-type behavior. The cyclic hysterisis energy per cycle was calculated from cyclic stress-strain parameters. The fracture surfaces of the fatigue samples were characterized by scanning electron microscope and the fracture mechanisms were discussed.展开更多
Laser shock peening (LSP) is a novel effective surface treatment method to improve the fatigue performance of turbine blades. To study the effect of LSP on combined low- and high-cycle fatigue (CCF) life of turbin...Laser shock peening (LSP) is a novel effective surface treatment method to improve the fatigue performance of turbine blades. To study the effect of LSP on combined low- and high-cycle fatigue (CCF) life of turbine blades, the CCF tests were conducted at elevated temperatures on two types of full-scale turbine blades, which were made of K403 by casting and GH4133B by forging. Probabilistic analysis was conducted to find out the effect of LSP on fatigue life of those two kinds of blades. The results indicated that LSP extended the CCF life of both casting blades and forging blades obviously, and the effect of LSP on casting blades was more evident; besides, a threshold vibration stress existed for both casting blades and forging blades, and the CCF life tended to be extended by LSP only when the vibration stress was below the threshold vibra- tion stress. Further study of fractography was also conducted, indicating that due to the presence of compressive residual stress and refined grains induced by LSP, the crack initiation sources in LSP blades were obviously less, and the life of LSP blades was also longer; since the compressive residual stress was released by plastic deformation, LSP had no effect or adverse effect on CCF life of blade when the vibration stress of blade was above the threshold vibration stress.展开更多
The low-cycle fatigue (LCF) behavior of directionally solidified nickel-based superalloy Ti-6A1-4V was studied under bare and electron beam welding condi- tions at room temperature. Results show that: (1) under t...The low-cycle fatigue (LCF) behavior of directionally solidified nickel-based superalloy Ti-6A1-4V was studied under bare and electron beam welding condi- tions at room temperature. Results show that: (1) under the same test conditions, all the joints exhibit lower LCF lifetime than Ti-6A1-4V; (2) the failure of welded structures is mainly ascribed to the welding defect. A novel lifetime prediction methodology based on continuum damage mechanics is proposed to predict the lifetime of Ti-6A1-4V and its welded joints.展开更多
Ti2AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties.The aim of this study was to evaluate monotonic and cycli...Ti2AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties.The aim of this study was to evaluate monotonic and cyclic deformation behavior of an as-cast Ti-22A1-20Nb-2V-1Mo-0.25Si(at.%)intermetallic compound in relation to its microstructure.The alloy containing an abundant fine lamellar O-Ti2AlNb phase exhibited a good combination of strength and plasticity,and superb fatigue resistance in comparison with other intermetallic compounds.Cyclic stabilization largely remained except slight cyclic hardening occurring at higher strain amplitudes.While fatigue life could be described using the common Coffin-Mason-Basquin equation,it could be better predicted via a weighted energy-based approach.Fatigue crack growth was characterized mainly by crystallographic cracking,along with fatigue striationlike features being unique to appear in the intermetallics.The results obtained in this study lay the foundation for the safe and durable applications of Ti2AlNb-based lightweight intermetallic compounds.展开更多
The low cycle fatigue (LCF) behavior of a high-strength structural steel was investigated in the strain rate range of 4×10^-6 -0.12 s^-1 (0. 001-3 Hz) under constant total strain (±1%) control. The cyc...The low cycle fatigue (LCF) behavior of a high-strength structural steel was investigated in the strain rate range of 4×10^-6 -0.12 s^-1 (0. 001-3 Hz) under constant total strain (±1%) control. The cyclic stress response at all strain rates exhibited behavior of rapid softening in the early stage of fatigue life and subsequent saturation up to failure. It was found that the stress amplitude, the plastic strain amplitude, the plastic strain energy density and the fatigue life depend mainly on the strain rate. The strain rate of 0. 012 s-1 was found as a transition point where the LCF of the steel showed different behavior from low strain rate to high strain rate. The relationship between the time to failure and strain rate was expressed well by a power law relation. The fracture surfaces of the fatigue sam-ples were characterized by using a scanning electron microscope (SEM) and the fracture mechanisms were discussed in terms of time-dependent deformation of the steel.展开更多
Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important co...Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important concern in these pressure vessels,which are subjected to alternative loads.Even though several codes and standards have guidelines on these pressure vessels,there are no relevant design methods on fatigue failure.To understand the fatigue properties of ASS 1.4301(equivalents include UNS S30400 and AISI 304) in solution-annealed(SA) and cold-stretched conditions(9% strain level) and the response of fatigue properties to cold stretching(CS),low-cycle fatigue(LCF) tests were performed at room temperature,with total strain amplitudes ranging from -.4% to -.8%.Martensite transformations were measured during the tests.Comparisons on cyclic stress response,cyclic stress-strain behavior,and fatigue life were carried out between SA and CS materials.Results show that CS reduces the initial hardening stage,but prolongs the softening period in the cyclic stress response.Martensite transformation helps form a stable regime and subsequent secondary hardening.The stresses of monotonic and cyclic stress-strain curves are improved by CS,which leads to a lower plastic strain and a much higher elastic strain.The fatigue resistance of the CS material is better than that of the SA material,which is approximately 1?03 to 2?04 cycles.The S-N curve of the ASME standard for ASS is compared with the fatigue data and is justified to be suitable for the fatigue design of cold-stretched pressure vessels.However,considering the CS material has a better fatigue resistance,the S-N curve will be more conservative.The present study would be helpful in making full use of the advantages of CS to develop a new S-N curve for fatigue design of cold-stretched pressure vessels.展开更多
A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element(RVE)of the nickel-based GH4169 superalloy.Considering the plastic deformation mechanism at the grain level an...A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element(RVE)of the nickel-based GH4169 superalloy.Considering the plastic deformation mechanism at the grain level and the Bauschinger effect,a crystal plasticity model reflecting the nonlinear kinematic hardening of crystal slipping system is applied.The microscopic inhomogeneous deformation during cyclic loading is calculated through numerical simulation of crystal plasticity.The deformation inhomogeneity on the free surface of the RVE under cyclic loading is described respectively by using the following parameters:standard deviation of the longitudinal strain in macro tensile direction,statistical average of first principal strains,and standard deviation of longitudinal displacement.The relationship between the fatigue cycle number and the evolution of inhomogeneous deformation of the material’s free surface is investigated.This research finds that:(1)The inhomogeneous deformation of the material free surface is significantly higher than that of the RVE inside;(2)the increases of the characterization parameters of inhomogeneous deformation on the free surface with cycles reflect the local maximum deformation of the RVE growing during cyclic loading;(3)these parameters can be used as criteria to assess and predict the low-cycle fatigue life rationally.展开更多
To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads,the fnite volume fluid-thermal coupling calculation method and the fnite element thermal-structural coupling analysis tec...To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads,the fnite volume fluid-thermal coupling calculation method and the fnite element thermal-structural coupling analysis technique are applied.In combination with the material lowcycle fatigue behavior,the modifed continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles.Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a signifcant role in the thermal-structural response by altering the material properties;the thermal-mechanical loads interaction results in serious deformation mainly in the front region of slotted liner.In particular,the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib,where the fatigue failure takes place initially;with the increase in nozzle work cycles,the residual plastic strain accumulates linearly,and the strain amplitude and increment in each work cycle are separately equal,but the fatigue damage grows up nonlinearly.As a result,a simplifed nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle.The predicted node life is obviously conservative to the Miner's life.In addition,several workable methods have also been proposed to improve the channel wall nozzle durability.展开更多
文摘Low cycle fatigue life consumption analysis was carried out in this work. Fatigue cycles accumulation method suitable even if engine is not often shut down was applied together with the modified universal sloped method for estimating fatigue cycles to failure. Damage summation rule was applied to estimate the fatigue damage accumulated over a given period of engine operation. The concept of fatigue factor which indicates how well engine is operated was introduced to make engine life tracking feasible. The developed fatigue life tracking method was incorporated in PYTHIA, Cranfield University in-house software and applied to 8 months of engine operation. The results obtained are similar to those of real engine operation. At a set power level, fatigue life decreases with increase in ambient temperature with the magnitude of decrease greater at higher power levels. The fatigue life tracking methodology developed could serve as a useful tool to engine operators.
文摘The influences of strain amplitude ranges and dwell time at peak strains on the low cycle fatigue (LCF) properties at 600℃ of a new near α high temperature titanium alloy containing rare earth Nd are investigated. The creep fatigue interaction behavior is discussed in this paper in terms of a creep fatigue interaction cumulative law and fatigue crack propagation model. The results show that the creep fatigue interaction is largely dependent on the strain amplitude range, and the tensile dwell periods, as well as compressive dwell periods, have a great influence on the LCF life of this alloy.
文摘The cyclic stress response and lowcycle fatigue life for wrought nickelbased superalloy GH4049 were investigated in the temperature range from 500 to 800 The relationship between the strain amplitude and the number of stress reversals was given. The behavior of cyclic hardening was observed for higher strain amplitudes at all testing temperatures and the lowcycle fatigue life generally decreased with increasing testing temperature for the same strain range. In addition, fracture surfaces of the fatigued samples were examined by using a scanning electron microscope.
基金Supports provided by Aviation Basic Science Foundation(00B53010)Aerospace Science Foundation(N3CH0502)Shaanxi Province Natural Science Foundation(N3CS0501)are gratefully appreciated.
文摘Reliability analysis methods based on the linear damage accumulation law (LDAL) and load-life interference model are studied in this paper. According to the equal probability rule, the equivalent loads are derived, and the reliability analysis method based on load-life interference model and recurrence formula is constructed. In conjunction with finite element analysis (FEA) program, the reliability of an aero engine turbine disk under low cycle fatigue (LCF) condition has been analyzed. The results show the turbine disk is safety and the above reliability analysis methods are feasible.
基金financially supported by the Science and Technology Research Project of Liaoning Province Education Department(L2012038)
文摘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.
基金Funded by the National Natural Science Foundation of China (No 50901042)the NUST Research Funding(No.2011YBXM156)
文摘Magnesium alloy Mg-3%Al-1%Zn (AZ31) billets prepared from equal channel angular pressing (ECAP) were utilized in low-cycle fatigue tests in order to investigate their fatigue life. Fully reversed strain-controlled tension-compression fatigue tests were conducted at the frequency of 1 Hz in ambient air. The microstructures were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The hysteresis loops of the ECAP processed and conventionally extruded samples display obviously different shapes in the total strain amplitude range from 0.2% to 0.6%. Accordingly, the low cycle fatigue lives of ECAP processed samples are found to be longer than those of extruded samples, which can be attributed to the different in the hysteresis energy incorporating tensile strain energy.
文摘Fatigue failure is one of the main failure forms of Al-Si-Cu-Mg aluminum alloys.To feature their mechanical aspect of fatigue behavior,the low-cycle fatigue behavior of permanent mold cast and die-cast Al-Si-Cu-Mg alloys at room temperature was investigated.The experimental results show that both permanent mold cast and die-cast Al-Si-Cu-Mg alloys mainly exhibit cyclic strain hardening.At the same total strain amplitude,the die-cast Al-Si-Cu-Mg alloy shows higher cyclic deformation resistance and longer fatigue life than does the permanent mold cast Al-Si-Cu-Mg alloy.The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior,and can be described by the Basquin and Coffin-Manson equations,respectively.
文摘An investigation was conducted to examine the low cycle symmetric push-pull fatigue behaviour of the Cr-Mn-N dual-phase stainless steel.Two groups of specimens,A and B, were used,they were solution treated at 1050 and 1250℃,respectively.The.fatigue life of group A is almost twice as long as that of group B under the same total strain amplitude.The energy loss during the fatigue tests and the mophology of the fracture surfaces have been stu- died and discussed.
基金Funded by National Natural Science Foundation of China(No.51474170)the Key Laboratory Project of Shaanxi Provincial Department of Education(No.20js075)。
文摘The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room temperature.The fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were discussed.The results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium,and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress load.Therefore,the SWT mean stress correction model and three-parameter power curve model are proposed,and the test results are verified.The final research shows that the threeparameter power surface model has better representation.By studying the mean stress relaxation phenomenon under the condition of R≠-1,it is revealed that the stress ratio and the strain amplitude are the factors that significantly afiect the mean stress relaxation rate,and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain ratios.The fracture morphology of the samples was observed by SEM,and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage fracture.The toughness of the material increases with the increase of strain ratio at the same strain amplitude.
文摘Three cumulative damage models are examined for the case of cyclic loading of AISI 6150 steel, S2 glass fibre/epoxy and E glass fibre/epoxy composites. The Palmgren-Miner, Broutman-Sahu and Hashin-Rotem models are compared to determine which of the three gives the most accurate estimation of the fatigue life of the materials tested. In addition, comparison of the fatigue life of the materials shows the superiority of AISI 6150 steel and S2 glass fibre/epoxy at lower mean stresses, and that of steel to the composites at higher mean stresses.
基金Item Sponsored by National Natural Science Foundation of China (50978174,10925211)
文摘Energy-based models for predicting the low-cycle fatigue life of high-strength structural steels are presented. The models are based on energy dissipation during average of cycles, cycles to crack propagation and total cycles to failure. Plastic strain energy per cycle was determined and found as an important characteristic for initiation and propagation of fatigue cracks for high-strength structural steels. Fatigue strain-life curves were generated using plastic energy dissipation per cycle (loop area) and compared with the Coffin-Manson relation. Low cycle fatigue life was found similar from both methods. The material showed Masing-type behavior. The cyclic hysterisis energy per cycle was calculated from cyclic stress-strain parameters. The fracture surfaces of the fatigue samples were characterized by scanning electron microscope and the fracture mechanisms were discussed.
基金This work was supported by National Natural Science Foundation of China (Grant Nos. 11602010 and 51505018).
文摘Laser shock peening (LSP) is a novel effective surface treatment method to improve the fatigue performance of turbine blades. To study the effect of LSP on combined low- and high-cycle fatigue (CCF) life of turbine blades, the CCF tests were conducted at elevated temperatures on two types of full-scale turbine blades, which were made of K403 by casting and GH4133B by forging. Probabilistic analysis was conducted to find out the effect of LSP on fatigue life of those two kinds of blades. The results indicated that LSP extended the CCF life of both casting blades and forging blades obviously, and the effect of LSP on casting blades was more evident; besides, a threshold vibration stress existed for both casting blades and forging blades, and the CCF life tended to be extended by LSP only when the vibration stress was below the threshold vibra- tion stress. Further study of fractography was also conducted, indicating that due to the presence of compressive residual stress and refined grains induced by LSP, the crack initiation sources in LSP blades were obviously less, and the life of LSP blades was also longer; since the compressive residual stress was released by plastic deformation, LSP had no effect or adverse effect on CCF life of blade when the vibration stress of blade was above the threshold vibration stress.
基金financially supported by the Hi-Tech Research and Development Program of China(No.2012AA052102)the Innovation Foundation for Ph.D.Graduates of Beihang University(No.YWF-14-YJSY-016)the Program of International Science and Technology Cooperation of China(No.2013DFA61590)
文摘The low-cycle fatigue (LCF) behavior of directionally solidified nickel-based superalloy Ti-6A1-4V was studied under bare and electron beam welding condi- tions at room temperature. Results show that: (1) under the same test conditions, all the joints exhibit lower LCF lifetime than Ti-6A1-4V; (2) the failure of welded structures is mainly ascribed to the welding defect. A novel lifetime prediction methodology based on continuum damage mechanics is proposed to predict the lifetime of Ti-6A1-4V and its welded joints.
基金supported by the National Natural Science Foundation of China (NSFC)(Grant No. 51871168)the Natural Sciences and Engineering Research Council of Canada (NSERC) in the form of international research collaboration+4 种基金China Scholarships Council (CSC) for providing a PhD student scholarshipthe financial support by the Premier’s Research Excellence Award (PREA)NSERC-Discovery Accelerator Supplement (DAS) AwardCanada Foundation for Innovation (CFI)Ryerson Research Chair (RRC) program
文摘Ti2AlNb-based intermetallic compounds are considered as a new category of promising lightweight aerospace materials due to their balanced mechanical properties.The aim of this study was to evaluate monotonic and cyclic deformation behavior of an as-cast Ti-22A1-20Nb-2V-1Mo-0.25Si(at.%)intermetallic compound in relation to its microstructure.The alloy containing an abundant fine lamellar O-Ti2AlNb phase exhibited a good combination of strength and plasticity,and superb fatigue resistance in comparison with other intermetallic compounds.Cyclic stabilization largely remained except slight cyclic hardening occurring at higher strain amplitudes.While fatigue life could be described using the common Coffin-Mason-Basquin equation,it could be better predicted via a weighted energy-based approach.Fatigue crack growth was characterized mainly by crystallographic cracking,along with fatigue striationlike features being unique to appear in the intermetallics.The results obtained in this study lay the foundation for the safe and durable applications of Ti2AlNb-based lightweight intermetallic compounds.
基金Item Sponsored by National Natural Science Foundation of China ( 50978174 , 10925211 )
文摘The low cycle fatigue (LCF) behavior of a high-strength structural steel was investigated in the strain rate range of 4×10^-6 -0.12 s^-1 (0. 001-3 Hz) under constant total strain (±1%) control. The cyclic stress response at all strain rates exhibited behavior of rapid softening in the early stage of fatigue life and subsequent saturation up to failure. It was found that the stress amplitude, the plastic strain amplitude, the plastic strain energy density and the fatigue life depend mainly on the strain rate. The strain rate of 0. 012 s-1 was found as a transition point where the LCF of the steel showed different behavior from low strain rate to high strain rate. The relationship between the time to failure and strain rate was expressed well by a power law relation. The fracture surfaces of the fatigue sam-ples were characterized by using a scanning electron microscope (SEM) and the fracture mechanisms were discussed in terms of time-dependent deformation of the steel.
基金Project supported by the National Key Technology R&D Program (No.2011BAK06B0205)the International Science and Technology Cooperation Project (No. 2010DFB42960)the Key Technology Innovation Team of Zhejiang Province (No. 2010R50001),China
文摘Cold-stretched pressure vessels from austenitic stainless steels(ASS) are widely used for storage and transportation of liquefied gases,and have such advantages as thin wall and light weight.Fatigue is an important concern in these pressure vessels,which are subjected to alternative loads.Even though several codes and standards have guidelines on these pressure vessels,there are no relevant design methods on fatigue failure.To understand the fatigue properties of ASS 1.4301(equivalents include UNS S30400 and AISI 304) in solution-annealed(SA) and cold-stretched conditions(9% strain level) and the response of fatigue properties to cold stretching(CS),low-cycle fatigue(LCF) tests were performed at room temperature,with total strain amplitudes ranging from -.4% to -.8%.Martensite transformations were measured during the tests.Comparisons on cyclic stress response,cyclic stress-strain behavior,and fatigue life were carried out between SA and CS materials.Results show that CS reduces the initial hardening stage,but prolongs the softening period in the cyclic stress response.Martensite transformation helps form a stable regime and subsequent secondary hardening.The stresses of monotonic and cyclic stress-strain curves are improved by CS,which leads to a lower plastic strain and a much higher elastic strain.The fatigue resistance of the CS material is better than that of the SA material,which is approximately 1?03 to 2?04 cycles.The S-N curve of the ASME standard for ASS is compared with the fatigue data and is justified to be suitable for the fatigue design of cold-stretched pressure vessels.However,considering the CS material has a better fatigue resistance,the S-N curve will be more conservative.The present study would be helpful in making full use of the advantages of CS to develop a new S-N curve for fatigue design of cold-stretched pressure vessels.
基金supported by the National Natural Scientific Foundation of China (Fund Nos. 11472085 and 11632007)the Guangxi Science Research and Technology Development Project (Fund No. GKH1599005-2-5)the Innovation Project of Guangxi Graduate Education (Fund no. YCBZ2015008)
文摘A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element(RVE)of the nickel-based GH4169 superalloy.Considering the plastic deformation mechanism at the grain level and the Bauschinger effect,a crystal plasticity model reflecting the nonlinear kinematic hardening of crystal slipping system is applied.The microscopic inhomogeneous deformation during cyclic loading is calculated through numerical simulation of crystal plasticity.The deformation inhomogeneity on the free surface of the RVE under cyclic loading is described respectively by using the following parameters:standard deviation of the longitudinal strain in macro tensile direction,statistical average of first principal strains,and standard deviation of longitudinal displacement.The relationship between the fatigue cycle number and the evolution of inhomogeneous deformation of the material’s free surface is investigated.This research finds that:(1)The inhomogeneous deformation of the material free surface is significantly higher than that of the RVE inside;(2)the increases of the characterization parameters of inhomogeneous deformation on the free surface with cycles reflect the local maximum deformation of the RVE growing during cyclic loading;(3)these parameters can be used as criteria to assess and predict the low-cycle fatigue life rationally.
文摘To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads,the fnite volume fluid-thermal coupling calculation method and the fnite element thermal-structural coupling analysis technique are applied.In combination with the material lowcycle fatigue behavior,the modifed continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles.Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a signifcant role in the thermal-structural response by altering the material properties;the thermal-mechanical loads interaction results in serious deformation mainly in the front region of slotted liner.In particular,the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib,where the fatigue failure takes place initially;with the increase in nozzle work cycles,the residual plastic strain accumulates linearly,and the strain amplitude and increment in each work cycle are separately equal,but the fatigue damage grows up nonlinearly.As a result,a simplifed nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle.The predicted node life is obviously conservative to the Miner's life.In addition,several workable methods have also been proposed to improve the channel wall nozzle durability.