The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,a...The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,and high-cycle fatigue properties,were studied.The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material.The maximum surface residual compressive stress was−661 MPa,and the compressive-stress-affected depth was greater than 1000μm.The roughness and Vickers micro-hardness increased with the number of shocks,and the maximum hardness-affected depth was about 700μm after three LSP treatments.LSP enhanced the fraction of low-angle grain boundaries,changed the grain preferred orientations,and notably increased the pole density ofαphase on the near surface from 2.41 to 3.46.The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening,while the LSP had a limited effect on the tensile properties.The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20%compared with that of the untreated sample,which was caused by the suppression of the initiation and propagation of fatigue cracks.展开更多
The strength and fatigue fracture behavior of A1-Zn-Mg-Cu-Zr（-Sn） alloys were studied by performing tensile tests and fatigue crack propagation （FCP） tests. The microstructures of the experimental alloys were furt...The strength and fatigue fracture behavior of A1-Zn-Mg-Cu-Zr（-Sn） alloys were studied by performing tensile tests and fatigue crack propagation （FCP） tests. The microstructures of the experimental alloys were further analyzed using optical microscopy （OM）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）; phase analysis of these alloys was conducted with an X-ray diffraction （XRD）. The results show that when Sn is included, growth of the recrystallization grains in the solution-treated A1-Zn-Mg-Cu-Zr alloy is obstructed, the precipitation-free zone （PFZ） of the overaged A1-Zn-Mg-Cu-Zr-Sn alloy becomes narrow, and the grain boundary precipitates are smaller. Consequently, the FCP resistance is higher. In addition, the overaged Sn-containing alloy has considerably higher tensile strength than the alloy without Sn.展开更多
The fatigue properties of laser shock processing （LSP） on both side surfaces of fastener hole with diameter of 3 mm in the LY12CZ aluminum alloy specimens were investigated. The superficial residual stress was measu...The fatigue properties of laser shock processing （LSP） on both side surfaces of fastener hole with diameter of 3 mm in the LY12CZ aluminum alloy specimens were investigated. The superficial residual stress was measured by X-ray diffraction method. Fatigue experiments of specimens with and without LSP were performed, and the microstructural features of fracture of specimens were characterized by scanning electron microscopy （SEM）. The results indicate that the compressive residual stress can be induced into the surface of specimen, and the fatigue life of the specimen with LSP is 3.5 times as long as that of specimen without LSP. The location of fatigue crack initiation is transferred from the top surface to the sub-surface after LSP, and the fatigue striation spacing of the treated specimen during the expanding fatigue crack is narrower than that of the untreated specimen. Furthermore, the diameters of the dimples on the fatigue crack rupture zone of the specimen with LSP are relatively bigger, which is related to the serious plastic deformation in the material with LSP.展开更多
In order to more accurately predict the contact fatigue life of rolling bearing, a prediction method of fatigue life of rolling bearing is proposed based on elastohydrodynamic lubrication （EHL）, the 3-paameter Weibu...In order to more accurately predict the contact fatigue life of rolling bearing, a prediction method of fatigue life of rolling bearing is proposed based on elastohydrodynamic lubrication （EHL）, the 3-paameter Weibull distribution ad fatigue strength. First,the contact stress considering elliptical EHL is obtained by mapping film pressure onto the Hertz zone. Then,the basic strength model of rolling bearing based on the 3-parameter Weibull distribution is deduced by the series connection reliability theory. Considering the effect of the type of stress, variation of shape and fuctuation of load, the mathematical models of the 尸 -tS-TV curve of the minimum life and the characteristic life for rolling bearing are established, respectively, and thus the prediction model of fatigue life of rolling bearing based on the 3-paameter Weibull distribution and fatigue strength is further deduced. Finally, the contact fatigue life obtained by the proposed method ad the latest international standard （IS0281： 2007） about the fatigue life prediction of rolling bearing are compared with those obtained by the statistical method. Results show that the proposed prediction method is effective and its relative error is smaier than that of the latest international standard （IS0281： 2007） with reliability R 〉 0. 93.展开更多
Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon （C/C） using isothermal chemical vapor infiltration （CVI）. The bending fatigue behavior of the infiltrated C/C com...Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon （C/C） using isothermal chemical vapor infiltration （CVI）. The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.展开更多
The dynamic interaction between maglev vehicle and three-span continuous guideway is discussed. With the consideration of control system, the dynamic interaction model has been developed. Numerical simulation has been...The dynamic interaction between maglev vehicle and three-span continuous guideway is discussed. With the consideration of control system, the dynamic interaction model has been developed. Numerical simulation has been performed to study dynamic characteristics of the guideway. The results show that bending rigidity, vehicle speed, span ratio and primary frequency all have important influences on the dynamic characteristics of the guideway and there is no distinct trend towards resonance vibration when fl/（v/l） equals 1.0. The definite way is to control impact coefficient and acceleration of the guideway. The conclusions can serve the design of high-speed maglev three-span continuous guideway.展开更多
The influence of ageing time on microstructure and mechanical properties of low-cost beta （LCB） titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstruc...The influence of ageing time on microstructure and mechanical properties of low-cost beta （LCB） titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstructure and fatigue crack initiation and growth was also studied. Increasing ageing time tended to increase the volume fraction of the secondary α-precipitates, β-grain size and partial spheroidization of primary α-phase. The maximum tensile strength （1565 MPa） and fatigue limit （750 MPa） were obtained for the samples aged at 500 °C for 0.5 h, while the minimum ones of 1515 MPa and 625 MPa, respectively, were reported for the samples aged at 500 °C for 4 h. The samples aged at 500 °C for 4 h showed a transgranular fracture mode. However, the samples aged at 500 °C for 0.5 h revealed a mixture fracture mode of transgranular and intergranular. The formed cracks on the outer surface of the fatigue samples were found to propagate through the β-grains connecting the primary α-particles existing at the β-grain boundaries.展开更多
The Ti-35%Nb(mass fraction) foams were prepared by a powder metallurgy method,and the microstructure and the mechanical properties of the foams under monotonic and cyclic loading were investigated.The microstructure o...The Ti-35%Nb(mass fraction) foams were prepared by a powder metallurgy method,and the microstructure and the mechanical properties of the foams under monotonic and cyclic loading were investigated.The microstructure of the foams mainly consists of β phase,and the foams exhibit the homogenous pore distribution with the average pore size of 252 μm.The foams with 66% porosity show a typical stress-strain curve of the open-cell foams,and the plateau stress is about 56 MPa.The fatigue strength of the foam is 15.12 MPa at 107 cycles.The fractographic analysis of the foams reveals that the cracks nucleate within the struts and grow in a fatigue mechanism,resulting in the acceleration of the fatigue damage of the foams.展开更多
This paper reports investigation conducted to study the fatigue performance of steel fibre reinforced concrete (SFRC) containing fibres of mixed aspect ratio. An extensive experimental program was conducted in which 9...This paper reports investigation conducted to study the fatigue performance of steel fibre reinforced concrete (SFRC) containing fibres of mixed aspect ratio. An extensive experimental program was conducted in which 90 flexural fatigue tests were carried out at different stress levels on size 500 mm×100 mm×100 mm SFRC specimens respectively containing 1.0%, 1.5% and 2.0% volume fraction of fibres. About 36 static flexural tests were also conducted to determine the static flexural strength prior to fatigue testing. Each volume fraction of fibres incorporated corrugated mixed steel fibres of size 0.6 mm×2.0 mm×25 mm and 0.6 mm×2.0 mm×50 mm in ratio 50:50 by weight. The results are presented both as S-N relationships, with the maximum fatigue stress expressed as a percentage of the strength under static loading, and as relationships between actually applied fatigue stress and number of loading cycles to failure. Two-million-cycle fatigue strengths of SFRC containing different volume fractions of mixed fibres were obtained and compared with plain concrete.展开更多
基金the National Natural Science Foundation of China(No.52205240).
文摘The effects of laser shock peening(LSP)on the microstructural evolution and mechanical properties of the Ti6242 alloy,including the residual stress,surface roughness,Vickers microhardness,tensile mechanical response,and high-cycle fatigue properties,were studied.The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material.The maximum surface residual compressive stress was−661 MPa,and the compressive-stress-affected depth was greater than 1000μm.The roughness and Vickers micro-hardness increased with the number of shocks,and the maximum hardness-affected depth was about 700μm after three LSP treatments.LSP enhanced the fraction of low-angle grain boundaries,changed the grain preferred orientations,and notably increased the pole density ofαphase on the near surface from 2.41 to 3.46.The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening,while the LSP had a limited effect on the tensile properties.The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20%compared with that of the untreated sample,which was caused by the suppression of the initiation and propagation of fatigue cracks.
基金Project(2010CB731706) supported by the National Basic Research Program of China
文摘The strength and fatigue fracture behavior of A1-Zn-Mg-Cu-Zr（-Sn） alloys were studied by performing tensile tests and fatigue crack propagation （FCP） tests. The microstructures of the experimental alloys were further analyzed using optical microscopy （OM）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）; phase analysis of these alloys was conducted with an X-ray diffraction （XRD）. The results show that when Sn is included, growth of the recrystallization grains in the solution-treated A1-Zn-Mg-Cu-Zr alloy is obstructed, the precipitation-free zone （PFZ） of the overaged A1-Zn-Mg-Cu-Zr-Sn alloy becomes narrow, and the grain boundary precipitates are smaller. Consequently, the FCP resistance is higher. In addition, the overaged Sn-containing alloy has considerably higher tensile strength than the alloy without Sn.
基金Project (51175002) supported by the National Natural Science Foundation of ChinaProject (090414156) supported by the Natural Science Foundation of Anhui Province,China
文摘The fatigue properties of laser shock processing （LSP） on both side surfaces of fastener hole with diameter of 3 mm in the LY12CZ aluminum alloy specimens were investigated. The superficial residual stress was measured by X-ray diffraction method. Fatigue experiments of specimens with and without LSP were performed, and the microstructural features of fracture of specimens were characterized by scanning electron microscopy （SEM）. The results indicate that the compressive residual stress can be induced into the surface of specimen, and the fatigue life of the specimen with LSP is 3.5 times as long as that of specimen without LSP. The location of fatigue crack initiation is transferred from the top surface to the sub-surface after LSP, and the fatigue striation spacing of the treated specimen during the expanding fatigue crack is narrower than that of the untreated specimen. Furthermore, the diameters of the dimples on the fatigue crack rupture zone of the specimen with LSP are relatively bigger, which is related to the serious plastic deformation in the material with LSP.
基金The National Defense Advance Research Program(No.81302XXX)
文摘In order to more accurately predict the contact fatigue life of rolling bearing, a prediction method of fatigue life of rolling bearing is proposed based on elastohydrodynamic lubrication （EHL）, the 3-paameter Weibull distribution ad fatigue strength. First,the contact stress considering elliptical EHL is obtained by mapping film pressure onto the Hertz zone. Then,the basic strength model of rolling bearing based on the 3-parameter Weibull distribution is deduced by the series connection reliability theory. Considering the effect of the type of stress, variation of shape and fuctuation of load, the mathematical models of the 尸 -tS-TV curve of the minimum life and the characteristic life for rolling bearing are established, respectively, and thus the prediction model of fatigue life of rolling bearing based on the 3-paameter Weibull distribution and fatigue strength is further deduced. Finally, the contact fatigue life obtained by the proposed method ad the latest international standard （IS0281： 2007） about the fatigue life prediction of rolling bearing are compared with those obtained by the statistical method. Results show that the proposed prediction method is effective and its relative error is smaier than that of the latest international standard （IS0281： 2007） with reliability R 〉 0. 93.
基金Projects(50832004,51105132)supported by the National Natural Science Foundation of ChinaProject(B08040)supported by Program of Introducing Talents of Discipline to Universities,China
文摘Laminated carbon fiber clothes were infiltrated to prepare carbon fiber reinforced pyrolytic carbon （C/C） using isothermal chemical vapor infiltration （CVI）. The bending fatigue behavior of the infiltrated C/C composites was tested under two different stress levels. The residual strength and modulus of all fatigued samples were tested to investigate the effect of maximum stress level on fatigue behavior of C/C composites. The microstructure and damage mechanism were also investigated. The results showed that the residual strength and modulus of fatigued samples were improved. High stress level is more effective to increase the modulus. And for the increase of flexural strength, high stress level is more effective only in low cycles. The fatigue loading weakens the bonding between the matrix and fiber, and then affects the damage propagation pathway, and increases the energy consumption. So the properties of C/C composites are improved.
基金Project (No. 2005AA505440) supported by the Hi-Tech Researchand Development Program (863) of China
文摘The dynamic interaction between maglev vehicle and three-span continuous guideway is discussed. With the consideration of control system, the dynamic interaction model has been developed. Numerical simulation has been performed to study dynamic characteristics of the guideway. The results show that bending rigidity, vehicle speed, span ratio and primary frequency all have important influences on the dynamic characteristics of the guideway and there is no distinct trend towards resonance vibration when fl/（v/l） equals 1.0. The definite way is to control impact coefficient and acceleration of the guideway. The conclusions can serve the design of high-speed maglev three-span continuous guideway.
文摘The influence of ageing time on microstructure and mechanical properties of low-cost beta （LCB） titanium alloy with a chemical composition of Ti-6.6Mo-4.5Fe-1.5Al was investigated. The correlation between microstructure and fatigue crack initiation and growth was also studied. Increasing ageing time tended to increase the volume fraction of the secondary α-precipitates, β-grain size and partial spheroidization of primary α-phase. The maximum tensile strength （1565 MPa） and fatigue limit （750 MPa） were obtained for the samples aged at 500 °C for 0.5 h, while the minimum ones of 1515 MPa and 625 MPa, respectively, were reported for the samples aged at 500 °C for 4 h. The samples aged at 500 °C for 4 h showed a transgranular fracture mode. However, the samples aged at 500 °C for 0.5 h revealed a mixture fracture mode of transgranular and intergranular. The formed cracks on the outer surface of the fatigue samples were found to propagate through the β-grains connecting the primary α-particles existing at the β-grain boundaries.
基金Projects(09A089,08XZX07) supported by Scientific Research Fund of Hunan Provincial Education Department and Xiangtan University,China
文摘The Ti-35%Nb(mass fraction) foams were prepared by a powder metallurgy method,and the microstructure and the mechanical properties of the foams under monotonic and cyclic loading were investigated.The microstructure of the foams mainly consists of β phase,and the foams exhibit the homogenous pore distribution with the average pore size of 252 μm.The foams with 66% porosity show a typical stress-strain curve of the open-cell foams,and the plateau stress is about 56 MPa.The fatigue strength of the foam is 15.12 MPa at 107 cycles.The fractographic analysis of the foams reveals that the cracks nucleate within the struts and grow in a fatigue mechanism,resulting in the acceleration of the fatigue damage of the foams.
基金Project supported by the Indian Council for Cultural Relations,India
文摘This paper reports investigation conducted to study the fatigue performance of steel fibre reinforced concrete (SFRC) containing fibres of mixed aspect ratio. An extensive experimental program was conducted in which 90 flexural fatigue tests were carried out at different stress levels on size 500 mm×100 mm×100 mm SFRC specimens respectively containing 1.0%, 1.5% and 2.0% volume fraction of fibres. About 36 static flexural tests were also conducted to determine the static flexural strength prior to fatigue testing. Each volume fraction of fibres incorporated corrugated mixed steel fibres of size 0.6 mm×2.0 mm×25 mm and 0.6 mm×2.0 mm×50 mm in ratio 50:50 by weight. The results are presented both as S-N relationships, with the maximum fatigue stress expressed as a percentage of the strength under static loading, and as relationships between actually applied fatigue stress and number of loading cycles to failure. Two-million-cycle fatigue strengths of SFRC containing different volume fractions of mixed fibres were obtained and compared with plain concrete.
