Split Hopkinson pressure bar(SHPB) apparatus, usually used for testing behavior of material in median and high strain-rate, is now widely used in the study of rock dynamic constitutive relation, damage evolvement mech...Split Hopkinson pressure bar(SHPB) apparatus, usually used for testing behavior of material in median and high strain-rate, is now widely used in the study of rock dynamic constitutive relation, damage evolvement mechanism and energy consumption. However, the possible reasons of sampling disturbance, machining error and so on often lead to the scattering of test results, and bring ultimate difficulty for forming general test conclusion. Based on the stochastic finite element method, the uncertain parameters of specimen density ρs, specimen radius Rs, specimen elastic modulus Es and specimen length Ls in the data processing of SHPB test were considered, and the correlation between the parameters and the test results was analyzed. The results show that the specimen radius Rs has direct correlation with the test result, improving the accuracy in preparing and measuring of specimen is an effective way to improve the accuracy of test and minish the scattering of results for SHPB test.展开更多
A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method...A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.展开更多
In high-speed machining,hardened steel materials are subjected to high temperatures and high strain rates.Under these conditions,the composition and microstructure of the material may change,and phenomena,such as ther...In high-speed machining,hardened steel materials are subjected to high temperatures and high strain rates.Under these conditions,the composition and microstructure of the material may change,and phenomena,such as thermal softening,emerge.These effects are difficult to detect by only observing the chip morphology.Here,using a microscopic detection method,the dynamic mechanical behavior and microstructure of SDK11 hardened steel(62HRC)is investigated at high temperature and high strain-rate,and the relationship between strain hardening,thermal softening,and strain-rate strengthening is determined.The metallographic phases of specimens treated using a split-Hopkinson pressure bar,and″chips″generated during high-speed machining at high temperature and high strain rate state are compared.The results indicate that the phase composition at low temperature and low strain rate differs from that at high temperature and high strain rate.It is further concluded that shear slip occurs at high temperature and high strain rate,and the shear behavior is more pronounced at higher strain rates.展开更多
基金Projects(50490274, 50534030) supported by the National Natural Science Foundation of ChinaProject supported by the Natural Science Foundatin of Hunan Province, China
文摘Split Hopkinson pressure bar(SHPB) apparatus, usually used for testing behavior of material in median and high strain-rate, is now widely used in the study of rock dynamic constitutive relation, damage evolvement mechanism and energy consumption. However, the possible reasons of sampling disturbance, machining error and so on often lead to the scattering of test results, and bring ultimate difficulty for forming general test conclusion. Based on the stochastic finite element method, the uncertain parameters of specimen density ρs, specimen radius Rs, specimen elastic modulus Es and specimen length Ls in the data processing of SHPB test were considered, and the correlation between the parameters and the test results was analyzed. The results show that the specimen radius Rs has direct correlation with the test result, improving the accuracy in preparing and measuring of specimen is an effective way to improve the accuracy of test and minish the scattering of results for SHPB test.
基金supported by the 111 Project (B07050)the National Natural Science Foundation of China (10932008)
文摘A novel approach is proposed in determining dy- namic fracture toughness （DFT） of high strength steel, using the split Hopkinson tension bar （SHTB） apparatus, com- bined with a hybrid experimental-numerical method. The center-cracked tension specimen is connected between the bars with a specially designed fixture device. The fracture initiation time is measured by the strain gage method, and dynamic stress intensity factors （DSIF） are obtained with the aid of 3D finite element analysis （FEA）. In this approach, the dimensions of the specimen are not restricted by the connec- tion strength or the stress-state equilibrium conditions, and hence plane strain state can be attained conveniently at the crack tip. Through comparison between the obtained results and those in open publication, it is concluded that the ex- perimental data are valid, and the method proposed here is reliable. The validity of the obtained DFT is checked with the ASTM criteria, and fracture surfaces are examined at the end of paper.
基金the Key Program of the NSFC-Guangdong Joint Fund,China(No.U1201245)
文摘In high-speed machining,hardened steel materials are subjected to high temperatures and high strain rates.Under these conditions,the composition and microstructure of the material may change,and phenomena,such as thermal softening,emerge.These effects are difficult to detect by only observing the chip morphology.Here,using a microscopic detection method,the dynamic mechanical behavior and microstructure of SDK11 hardened steel(62HRC)is investigated at high temperature and high strain-rate,and the relationship between strain hardening,thermal softening,and strain-rate strengthening is determined.The metallographic phases of specimens treated using a split-Hopkinson pressure bar,and″chips″generated during high-speed machining at high temperature and high strain rate state are compared.The results indicate that the phase composition at low temperature and low strain rate differs from that at high temperature and high strain rate.It is further concluded that shear slip occurs at high temperature and high strain rate,and the shear behavior is more pronounced at higher strain rates.
