The fatigue life of numerous aerospace,locomotive,automotive and biomedical structures may go beyond 10~8 cycles.Determination of long life fatigue behavior becomes extremely important for better understanding and des...The fatigue life of numerous aerospace,locomotive,automotive and biomedical structures may go beyond 10~8 cycles.Determination of long life fatigue behavior becomes extremely important for better understanding and design of the components and structures.Initially,before the invention of ultrasonic fatigue testing,most of the engineering materials were supposed to exhibit fatigue life up to 10~7 cycles or less.This paper reviews current understanding of some fundamental aspects on the development of accelerated fatigue testing method and its application in ultra-high cycle fatigue,crack initiation and growth mechanisms of internal fracture,S-N diagram,fatigue limit and life prediction, etc.展开更多
The high-cycle fatigue performance of different microstructures of aluminide coating- superalloy system has been studied at 900℃.The single phase coating of coarse equiaxial grain NiAI(β)has unfavorable eJfect onJat...The high-cycle fatigue performance of different microstructures of aluminide coating- superalloy system has been studied at 900℃.The single phase coating of coarse equiaxial grain NiAI(β)has unfavorable eJfect onJatigue life of the coating-superalloy.The fatigue life may shorten if the coating of NiAl(β)was an enrichment of coarse refractory metal grains. While an improvement can be made by dispersing numerous secondary phase particles such as extreme.fine γ′,quasi-σ-phase and others.展开更多
High-cycle rotating bending fatigue behavior of SRR99 nickel-base single crystal alloy at 700 and 900℃ was investigated. The fatigue strengths for 107 cycles are 350 and 335MPa at 700 and 900℃, respectively. T...High-cycle rotating bending fatigue behavior of SRR99 nickel-base single crystal alloy at 700 and 900℃ was investigated. The fatigue strengths for 107 cycles are 350 and 335MPa at 700 and 900℃, respectively. The total fatigue life becomes shorter when the temperature increases regardless of the loading stress and frequency. With the number of cycles decreasing, the difference in fatigue strength at the two temperatures becomes smaller. Typical fatigue rupture process including crack initiation site, crack propagation region and final rupture region exhibits at 700℃. The fracture surface is basically characterized by cleavage rupture at 900℃.展开更多
The effect of minimum and the maximum stresses on the fatigue behaviour of a 30 mm thick plate of a 7B04-T7451(Al-Zn-Mg-Cu) subjected to a tensile pre-strain level of 2% was investigated,including the fatigue crack gr...The effect of minimum and the maximum stresses on the fatigue behaviour of a 30 mm thick plate of a 7B04-T7451(Al-Zn-Mg-Cu) subjected to a tensile pre-strain level of 2% was investigated,including the fatigue crack growth(FCG) rate,microstructure observation,fractographic examination and fatigue S-N curve,etc. The results show that the characteristics of fatigue facture can be observed obviously under high cycle fatigue condition,and the higher the stress amplitude,the wider the space between fatigue striations,the faster the rate of fatigue crack developing and going into the intermittent fracture and the greater the ratio of the intermittent fracture area to the whole fracture area.展开更多
Crack initiation is an essential stage of fatigue process due to its direct effect on fatigue failure.However,for titanium alloys in high-temperature high cycle fatigue(HCF),the crack initiation mechanisms remain uncl...Crack initiation is an essential stage of fatigue process due to its direct effect on fatigue failure.However,for titanium alloys in high-temperature high cycle fatigue(HCF),the crack initiation mechanisms remain unclear and the understanding for the defect sensitivity is also lacking.In this study,a series of fatigue tests and multi-scale microstructure characterizations were conducted to explore the high-temperature failure mechanism,and the coupled effect of temperature and defect on TC17 titanium alloy in HCF.It was found that an oxygen-rich layer(ORL)was produced at specimen surface at elevated temperatures,and brittle fracture of ORL at surface played a critical role for surface crack initiation in HCF.Besides,internal crack initiation with nanograins at high temperatures was a novel finding for the titanium alloy.Based on energy dispersive spectroscopy,electron backscatter diffraction and transmission electron microscope characterizations,the competition between surface and internal crack initiations at high temperatures was related to ORL at surface and dislocation resistance in inner microstructure.The fatigue strengths of smooth specimens decreased at elevated temperatures due to the lower dislocation resistance.While the fatigue strengths of the specimens with defect were not very sensitive to the temperatures.Finally,a fatigue strength model considering the coupled effect of temperature and defect was proposed for TC17titanium alloy.展开更多
Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700 ？ C, and in the frame of unified visoco-plastic cyclic constitutive mod...Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700 ？ C, and in the frame of unified visoco-plastic cyclic constitutive model and continuum damage mechanics theory, the damage-coupled multi-axial time-dependent constitutive model and fatigue failure model were proposed. In the model, the evolution equation of damage was introduced in and the time-dependent effects, e.g. holding time, loading rate, were taken into account. The model was applied to the simulation of whole-life cyclic deformation behaviors and prediction of LCF life for SS304 stainless steel in multiaxial time-dependent low cycle fatigue tests. It is shown that the simulated results agree well with experimental ones.展开更多
基金supported by the National Natural Science Foundation of China(10925211)the Program for Changjiang Scholars and Innovative Research Team (IRT1027)
文摘The fatigue life of numerous aerospace,locomotive,automotive and biomedical structures may go beyond 10~8 cycles.Determination of long life fatigue behavior becomes extremely important for better understanding and design of the components and structures.Initially,before the invention of ultrasonic fatigue testing,most of the engineering materials were supposed to exhibit fatigue life up to 10~7 cycles or less.This paper reviews current understanding of some fundamental aspects on the development of accelerated fatigue testing method and its application in ultra-high cycle fatigue,crack initiation and growth mechanisms of internal fracture,S-N diagram,fatigue limit and life prediction, etc.
文摘The high-cycle fatigue performance of different microstructures of aluminide coating- superalloy system has been studied at 900℃.The single phase coating of coarse equiaxial grain NiAI(β)has unfavorable eJfect onJatigue life of the coating-superalloy.The fatigue life may shorten if the coating of NiAl(β)was an enrichment of coarse refractory metal grains. While an improvement can be made by dispersing numerous secondary phase particles such as extreme.fine γ′,quasi-σ-phase and others.
文摘High-cycle rotating bending fatigue behavior of SRR99 nickel-base single crystal alloy at 700 and 900℃ was investigated. The fatigue strengths for 107 cycles are 350 and 335MPa at 700 and 900℃, respectively. The total fatigue life becomes shorter when the temperature increases regardless of the loading stress and frequency. With the number of cycles decreasing, the difference in fatigue strength at the two temperatures becomes smaller. Typical fatigue rupture process including crack initiation site, crack propagation region and final rupture region exhibits at 700℃. The fracture surface is basically characterized by cleavage rupture at 900℃.
基金Project (2005DFA50550) supported by the Key International Science and Technology Cooperation Project of China
文摘The effect of minimum and the maximum stresses on the fatigue behaviour of a 30 mm thick plate of a 7B04-T7451(Al-Zn-Mg-Cu) subjected to a tensile pre-strain level of 2% was investigated,including the fatigue crack growth(FCG) rate,microstructure observation,fractographic examination and fatigue S-N curve,etc. The results show that the characteristics of fatigue facture can be observed obviously under high cycle fatigue condition,and the higher the stress amplitude,the wider the space between fatigue striations,the faster the rate of fatigue crack developing and going into the intermittent fracture and the greater the ratio of the intermittent fracture area to the whole fracture area.
基金financially supported by the National Natural Science Foundation of China(No.91860112)the International Postdoctoral Exchange Fellowship Program(China)。
文摘Crack initiation is an essential stage of fatigue process due to its direct effect on fatigue failure.However,for titanium alloys in high-temperature high cycle fatigue(HCF),the crack initiation mechanisms remain unclear and the understanding for the defect sensitivity is also lacking.In this study,a series of fatigue tests and multi-scale microstructure characterizations were conducted to explore the high-temperature failure mechanism,and the coupled effect of temperature and defect on TC17 titanium alloy in HCF.It was found that an oxygen-rich layer(ORL)was produced at specimen surface at elevated temperatures,and brittle fracture of ORL at surface played a critical role for surface crack initiation in HCF.Besides,internal crack initiation with nanograins at high temperatures was a novel finding for the titanium alloy.Based on energy dispersive spectroscopy,electron backscatter diffraction and transmission electron microscope characterizations,the competition between surface and internal crack initiations at high temperatures was related to ORL at surface and dislocation resistance in inner microstructure.The fatigue strengths of smooth specimens decreased at elevated temperatures due to the lower dislocation resistance.While the fatigue strengths of the specimens with defect were not very sensitive to the temperatures.Finally,a fatigue strength model considering the coupled effect of temperature and defect was proposed for TC17titanium alloy.
基金supported by the Fundamental Research Funds for the Central Universities (No.SWJTU09ZT35)National Science Fund for Distinguished Young Scholars of China (No.11025210)
文摘Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700 ？ C, and in the frame of unified visoco-plastic cyclic constitutive model and continuum damage mechanics theory, the damage-coupled multi-axial time-dependent constitutive model and fatigue failure model were proposed. In the model, the evolution equation of damage was introduced in and the time-dependent effects, e.g. holding time, loading rate, were taken into account. The model was applied to the simulation of whole-life cyclic deformation behaviors and prediction of LCF life for SS304 stainless steel in multiaxial time-dependent low cycle fatigue tests. It is shown that the simulated results agree well with experimental ones.
