Study Of Rock's Damage Deformation And Size Effect

Rock is heterogeneous material, which decided that rock's mechanic behavior is complicated and discrete. Study on material damage and rupture is attention-getting and difficult aspect in field of mechanics. Solid material's damage is regarded as accumulative process of damage and accumulative process of macroscopical flaw.Generally, engineering structure has to be deflated in proportion to actual size when scientists take structure test in laboratory. So testing data can't represent actual structure's mechanical behavior entirely because of effect of rock's size effect. It is important in practice and in theory to study relationship between rock's mechanical behavior and size effect in order to forecast rock engineering structure's mechanical behavior effectively.Uniaxial compression test, uniaxial incremental Circulating compression test and uniaxial equal Circulating compression test is applied into practice and relationship between rock's mechanical behavior and size effect in loading process is studied in the light of rock's heterogeneity, then the following conclusion come out.1) The premise is set up that rock's maximum strain (strain nearby destroyed strain), unloading modulus and damage threshold (D_U) is equal with the same size rock and loading condition. And damage threshold is defined which equal 1 minus residual strength divided by maximum strength. Then rock's plastic deformation damage model is set up and is approved.2) The behavior of uniaxial compression test, uniaxial incremental circulating compression test and uniaxial equal circulating compression test is studied. Acoustic-emission counts damage model and acoustic-emission counts damage is set up, then conclusion comes out that the two damage models are in accord with plastic deformation damage model.3) The process that tangent modulus and Poisson ratio vary with uniaxial press is analyzed. Plastic strain damage model is applied to analyze the developing process of rock's damage when uniaxial stress and uniaxial strain are changing. Then the conclusion that the result of plastic strain damage model accord with the testing result comes out.4) Analyzing the result of uniaxial incremental circulating compression test, the plastic-loop of the lateral strain is plumper than the plastic-loop of the axial strain. Plastic strain damage model can describe the result that rock's damage keep increasing when circulating compressed time increases at circulating compressed intervals.5) Uniaxial equal circulating compression test is completed. Then plastic strain damage model is applied to analyze the testing data and the result come out that rock's damage keep increasing when circulating compressed time increases, but the incremental quantity of rock's damage is less and less each time.6) Rock with the same diameter and different ratio of height to diameter is tested under uniaxial compression, uniaxial incremental circulating compression and uniaxial equal circulating compression and the test data is analyzed. Then the result comes out that rock' critical stress, critical strain and elastic modulus vary with ratio of height to diameter. Plastic strain damage model is applied to study rock's size effect and it is obtained that rock's damage vary with ratio of height to diameter.7) The data of uniaxial compression test, uniaxial incremental circulating compression test and uniaxial equal circulating compression test is analyzed, then rock's mechanical behavior is illustrated.