Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengthes were experimentally studied by rotating bending tests,to investigate the effects of the tensile strength obtained by different heat t...Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengthes were experimentally studied by rotating bending tests,to investigate the effects of the tensile strength obtained by different heat treatment processes on very high cycle fatigue failure mechanisms.The material with higher tensile strength of 1 710 MPa exhibited typical gigacycle fatigue failure characteristics,whereas one with lower tensile strength of 1 010 MPa showed only traditional fatigue limit during the tests and no gigacycle failure could be found even when the specimen ran up to more than 10 8 cycles.Metallographic and fractographic analysis were carried out by an optical microscope （OM） and scanning electron microscope （SEM）.It showed two different crack initiation mechanisms that for the specimen with lower tensile strength the crack prefers surface initiation and for that with higher strength the crack initiates from subsurface inclusions revealed by a fish-eye like microstructure.展开更多
The effects of pre-stress and bending angle on the flex fatigue lifetimes of para-aramids have been studied choosing the Twaron 2000 high performance filament as the studying subject by use of the self-developed flex ...The effects of pre-stress and bending angle on the flex fatigue lifetimes of para-aramids have been studied choosing the Twaron 2000 high performance filament as the studying subject by use of the self-developed flex fatigue apparatus. The fractography of the fatigue-breaking end of the single filaments has been obtained and the fatigue-breaking mechanisms have been analyzed using the LM and SEM. The differences of the fatigue properties and fractography of a variety of high performance fibers such as Kevlar 129, Kevlar 29 and UHMW PE have been discussed.展开更多
基金supported by funds of MHI Corporation,the National Natural Science Foundation of China (10872105)
文摘Gigacycle fatigue behaviors of two SNCM439 steels with different tensile strengthes were experimentally studied by rotating bending tests,to investigate the effects of the tensile strength obtained by different heat treatment processes on very high cycle fatigue failure mechanisms.The material with higher tensile strength of 1 710 MPa exhibited typical gigacycle fatigue failure characteristics,whereas one with lower tensile strength of 1 010 MPa showed only traditional fatigue limit during the tests and no gigacycle failure could be found even when the specimen ran up to more than 10 8 cycles.Metallographic and fractographic analysis were carried out by an optical microscope （OM） and scanning electron microscope （SEM）.It showed two different crack initiation mechanisms that for the specimen with lower tensile strength the crack prefers surface initiation and for that with higher strength the crack initiates from subsurface inclusions revealed by a fish-eye like microstructure.
文摘The effects of pre-stress and bending angle on the flex fatigue lifetimes of para-aramids have been studied choosing the Twaron 2000 high performance filament as the studying subject by use of the self-developed flex fatigue apparatus. The fractography of the fatigue-breaking end of the single filaments has been obtained and the fatigue-breaking mechanisms have been analyzed using the LM and SEM. The differences of the fatigue properties and fractography of a variety of high performance fibers such as Kevlar 129, Kevlar 29 and UHMW PE have been discussed.
