A true triaxial unloading damage intrinsic model for sandstone based on the double shear unified strength criterion
In order to improve the damage constitutive model and parameter determination method of sandstone under true triaxial loading and unloading conditions,based on the true triaxial fluid-solid coupling test system,the sandstone loading and unloading tests are carried out under different intermediate principal stresses and different maximum principal stress loading rates in true triaxial,to analyze the deformation characteristics of sandstone under different stress paths,the gradual damage characteristics of sandstone at different phases,and strength characteristics.Choosing the applicable strength criterion under the conditions of true triaxial loading and unloading,a damage constitutive model that can effectively describe the process of stress cracking of sandstone is established.The results show that the cracking stress,damage stress and peak strength of sandstone specimens increase with the increase of intermediate principal stress and loading rate.Under the two types of stress paths,the double-shear uniform strength criterion can accurately describe the strength characteristics of sandstone.By transforming the double-shear uniform strength criterion into a suitable yield function form and considering the damage evolution characteristics of the specimens in different principal stress directions,a true triaxial damage constitutive model was established to compare and analyze the effects of model parameters on the strain hardening characteristics.The model analysis results match with the actual test stress-strain curves in different principal stress directions,and the fitting results are more stable.The model can accurately reflect the influence of sandstone microelement strength by the stress state,and better reflect the force rupture process of sandstone in different principal stress directions,which can provide better theoretical guidance for the actual rock engineering practice.
rock mechanicsunloadingprogressive damagedouble shear unified strength criteriondamage principal structure model
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