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 me...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 ps, 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
Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress-strain relation of various engineering materials at high strain-rates. The accuracy of an SHPB test...Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress-strain relation of various engineering materials at high strain-rates. The accuracy of an SHPB test is based on the assumption of uniaxial and uniform stress distribution within the specimen, which, however, is not always satisfied in an actual SHPB test due to the existence of some unavoidable negative factors, e.g., interface friction constrains. Kinetic interface friction tests based on a simple device for engineering materials testing on SHPB tests are performed. A kinetic interface friction model is proposed and validated by implementing it into a numerical model. It shows that the proposed simple device is sufficient to obtain kinetic interface friction results for common SHPB tests. The kinetic friction model should be used instead of the frequently used constant friction model for more accurate numerical simulation of SHPB tests.展开更多
The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown t...The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown that at high strain rates beyond about 1 000 s^-1, uniform deformation within the metallic glass specimen could not be achieved and dispersion in the transmitted pulse can lead to discrepancies in measuring the dynamic failure strength of the present Zr-based bulk metallic glass. Based on these reasons, a copper insert was placed between the strike bar and the input bar to obtain reliable and consistent experimental data for testing of the Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass using the SHPB. Negative strain rate sensitivity was found in the present Zr-based bulk metallic glass.展开更多
Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more...Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more challenging than their static counterparts. Dynamic tests are usually conducted using the split Hopkinson bar or Kolsl^j bar systems, which include both split Hopkinson pressure bar （SHPB） and split Hopkinson tension bar （SHTB） systems. Significant progress has been made on the quantification of various rock dynamic properties, owing to the advances in the experimental techniques of SHPB system. This review aims to fully describe and critically assess the detailed procedures and principles of tech- niques for dynamic rock tests using split Hopkinson bars. The history and principles of SHPB are outlined, followed by the key loading techniques that are useful for dynamic rock tests with SHPB （i.e. pulse shaping, momentum-trap and multi-axial loading techniques）. Various measurement techniques for rock tests in SHPB （i.e. X-ray micro computed tomography （CT）, laser gap gauge （LGG）, digital image corre- lation （DIC）, Moir~ method, caustics method, photoelastic coating method, dynamic infrared thermog- raphy） are then discussed. As the main objective of the review, various dynamic measurement techniques for rocks using SHPB are described, including dynamic rock strength measurements （i.e. dynamic compression, tension, bending and shear tests）, dynamic fracture measurements （i.e. dynamic imitation and propagation fracture toughness, dynamic fracture energy and fracture velocity）, and dy- namic techniques for studying the influences of temperature and pore water.展开更多
Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external ...Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external radius （ρ） under different loading rates. The results show that the dynamic tensile strength of disc rock specimen is approximately five times its static tensile strength. The failure modes of ring specimens are related to the dimension of the internal hole and loading rate. Under static loading tests, when the ratio of internal radius to external radius of the rock ring is small enough （ρ〈0.3）, specimens mostly split along the diametral loading line. With the increase of the ratio, the secondary cracks are formed in the direction perpendicular to the loading line. Under dynamic loading tests, specimens usually break up into four pieces. When the ratio ρreaches 0.5, the secondary cracks are formed near the input bar. The tensile strength calculated by Hobbs’ formula is greater than the Brazilian splitting strength. The peak load and the radius ratio show a negative exponential relationship under static test. Using ring specimen to determine tensile strength of rock material is more like a test indicator rather than the material properties.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 ps, 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.
文摘Split Hopkinson pressure bar (SHPB) has become a frequently used technique to measure the uniaxial compressive stress-strain relation of various engineering materials at high strain-rates. The accuracy of an SHPB test is based on the assumption of uniaxial and uniform stress distribution within the specimen, which, however, is not always satisfied in an actual SHPB test due to the existence of some unavoidable negative factors, e.g., interface friction constrains. Kinetic interface friction tests based on a simple device for engineering materials testing on SHPB tests are performed. A kinetic interface friction model is proposed and validated by implementing it into a numerical model. It shows that the proposed simple device is sufficient to obtain kinetic interface friction results for common SHPB tests. The kinetic friction model should be used instead of the frequently used constant friction model for more accurate numerical simulation of SHPB tests.
基金Sponsored by the Ministerial Level Research Foundation (00J12 1 7 BQ0123)
文摘The split Hopkinson pressure bar （SHPB） was used to determine the dynamic compressive strength of the high-strength Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass at strain rate on the order of 102 s^-1. It is shown that at high strain rates beyond about 1 000 s^-1, uniform deformation within the metallic glass specimen could not be achieved and dispersion in the transmitted pulse can lead to discrepancies in measuring the dynamic failure strength of the present Zr-based bulk metallic glass. Based on these reasons, a copper insert was placed between the strike bar and the input bar to obtain reliable and consistent experimental data for testing of the Zr38Ti17Cu10.5Co12Be22.5 bulk metallic glass using the SHPB. Negative strain rate sensitivity was found in the present Zr-based bulk metallic glass.
文摘Dynamic properties of rocks are important in a variety of rock mechanics and rock engineering problems. Due to the transient nature of the loading, dynamic tests of rock materials are very different from and much more challenging than their static counterparts. Dynamic tests are usually conducted using the split Hopkinson bar or Kolsl^j bar systems, which include both split Hopkinson pressure bar （SHPB） and split Hopkinson tension bar （SHTB） systems. Significant progress has been made on the quantification of various rock dynamic properties, owing to the advances in the experimental techniques of SHPB system. This review aims to fully describe and critically assess the detailed procedures and principles of tech- niques for dynamic rock tests using split Hopkinson bars. The history and principles of SHPB are outlined, followed by the key loading techniques that are useful for dynamic rock tests with SHPB （i.e. pulse shaping, momentum-trap and multi-axial loading techniques）. Various measurement techniques for rock tests in SHPB （i.e. X-ray micro computed tomography （CT）, laser gap gauge （LGG）, digital image corre- lation （DIC）, Moir~ method, caustics method, photoelastic coating method, dynamic infrared thermog- raphy） are then discussed. As the main objective of the review, various dynamic measurement techniques for rocks using SHPB are described, including dynamic rock strength measurements （i.e. dynamic compression, tension, bending and shear tests）, dynamic fracture measurements （i.e. dynamic imitation and propagation fracture toughness, dynamic fracture energy and fracture velocity）, and dy- namic techniques for studying the influences of temperature and pore water.
基金Project(2015CB060200)supported by the National Basic Research Program of ChinaProject(51474250)supported by the National Natural Science Foundation of ChinaProject(2015JJ3166)supported by the Natural Science Foundation of Hunan Province,China
文摘Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external radius （ρ） under different loading rates. The results show that the dynamic tensile strength of disc rock specimen is approximately five times its static tensile strength. The failure modes of ring specimens are related to the dimension of the internal hole and loading rate. Under static loading tests, when the ratio of internal radius to external radius of the rock ring is small enough （ρ〈0.3）, specimens mostly split along the diametral loading line. With the increase of the ratio, the secondary cracks are formed in the direction perpendicular to the loading line. Under dynamic loading tests, specimens usually break up into four pieces. When the ratio ρreaches 0.5, the secondary cracks are formed near the input bar. The tensile strength calculated by Hobbs’ formula is greater than the Brazilian splitting strength. The peak load and the radius ratio show a negative exponential relationship under static test. Using ring specimen to determine tensile strength of rock material is more like a test indicator rather than the material properties.
