Sandstone Damage Evolution And Its Constitutive Model Under Cyclic Loading And Unloading

Rock damage is a process of the deteriorating of mechanical properties of rock, caused bythe emergence and development of internal microcracks of rock under the external loads. In thispaper, the sandstone’s cyclic loading and unloading experiments were firstly conducted, Base onthat, the adaptability of elastic modulus, dissipation energy and sound velocity damage variabledefinition method for the analysis of sandstone’s damage evolution, and the damage evolutioncharacteristics of sandstone are discussed with the three methods; Then the strengthcharacteristics of sandstone was discussed, and its damage constitutive relation was establishedwith dissipation energy method. The results are as follows:（1）As the increasing of loading stress，the elastic modulus value of sandstone firstlyincreased, and then became stable, finally its value decreased; Elastic modulus method isapplicable only at the initial stage and latter stage of sandstone’s cracking, and the damagethreshold value obtained was slightly large while the damage value was small.（2）In the loading process, elastic strain energy, dissipation energy and total strain energyincreased with the increasing of loading stress; At the compaction and elastic deformation stage,more energy was converted into elastic strain energy instead of dissipation energy, meanwhiledissipation energy possessed the most before and after the failure stage. So dissipation energymethod can be used for the representation of damage evolution characteristics of sandstone.（3）Sound velocity decreased with the increasing of loading stress, and the decreasing rategradually increased; Sound velocity method is suitable for the analysis of sandstone’s damagevalue，but it cann’t represent the completely damage stage of sandstone.（4）The sandstone’s damage evaluation curves obtained from the three damage variabledefinition methods were in a shape of “concave upward”；At the compaction and elasticdeformation stage, damage value was small, and it increased slightly; As is approaching to peakstress point the damage value increased rapidly, and its value reached0.45at the peak stress;After the entire failure of sandstone, damage value grew fast；The sandstone’s damage valueconcentrated mainly at peak stress point and at the failure stage.（5）Base on dissipation energy method, the quantitative relation of damage strength and damage value was established; then damage constitutive’s equation of sandstone under cyclicloading and unloading was derived. The theoretical results agreed well with the experimentalones, and the feasibility of parameter inversion method was verified and the damageconstitutive’s equation was proved to be rational.