Study On Tensile Properties And Damage Evolution Mechanism Of Coal Measures Sandstone Under High Strain Rate

The academic and experimental research of rock dynamic mechanics has aroused wide concern with the rapid development of geotechnical engineering and enormous rock dynamic problems.The rock is a typical anisotropic media,whose tensile property is far lower than compressive property.Tensile failure is the primary failure mode.Therefore,studying of the tensile properties and failure mechanism of rock under high strain rate is of great significance for dynamic theory research and its engineering application.This dissertation took the coal measures sandstone as the object of investigation.Using methods such as experimentation,theoretical analysis and advanced testing technology and equipment,and combining modern mechanics,it made systematic research on rock tensile properties and failure mechanism under high strain rate.So the study yielded the following innovations:(1)Based on SHTB system and private bonded technique for direct tensile test under high strain rate,the variation of rock's tensile properties and macroscopic failure characteristics along with strain rate was obtained.And the differentiation between uniaxial compression test and splitting tensile test was given a quantitative result.The results show that the tensile strength,dynamic elastic modulus and peak strain increase with increasing strain rate,and decrease with increasing in length-diameter ratio.The fracture feature was mainly tensile damage along the cross section of rock specimens.(2)Based on SHPB system for splitting tensile test under high strain rate,the variation of rock's tensile properties and macroscopic failure characteristics along with strain rate was obtained.The results show that the tensile strength increases with the increase of strain rate and length-diameter ratio.Compared with the results of direct tensile test under the same strain rate,it was more safety in splitting tensile test,and was less than 20%.(3)Based on the water-containing nature of coal measures sandstone,effects of moisture content on rock's tensile properties and failure rules were studied.So the uniaxial tension test,macroscopic failure and energy dissipation changing with strain rate were obtained,and the failure law was revealed.(4)Based on SEM system for fracture morphology,the microscopic features,damage fracture mode,crack nucleation and extended mechanism changing with strain rate were given,and the micro-failure law of coal measures sandstone under high strain rate was revealed effectively.(5)Based on the damage fracture theory of rocks,the damage evolution equation and damage constitutive model in direct tensile test under high strain rate were established,and the according parameter identification results basing on uniaxial tensile stress-strain curves were given.It showed a great confirmation between the established constitutive model and test results.The research results can provide important references for dynamic fracture analysis of coal measures rock structure and the design of engineering.