Based on conventional triaxial cyclic loading–unloading compression tests, the axial and lateral elastic–plastic strains of sandstone under confining pressures of 5, 10, 20 and 30 MPa were analyzed. The results showed that the lateral stress–strain plastic hysteresis loop is more obvious than the axial direction under cyclic loading. The axial and lateral elastic strains of the specimens are nonlinearly related to the axial deviatoric stress, and the axial and lateral plastic strains of the specimens show obvious non-linear plastic hardening characteristics. The Duncan–Chang model is used to analyze the elastic stress–strain characteristics of sandstone during loading. Without considering the initial stage of fracture compaction, the tangent elastic modulus of the sandstone specimens decreases continuously with the increase of the axial elastic strain and the Poisson’s ratio increases continuously with the increase of lateral elastic strain under the same confining pressure. Based on the plastic strain characteristics of sandstone specimens, the corresponding plastic flow equation is established, which can preferably describe the axial and lateral strain characteristics of the specimen. The plastic flow rate of the specimens increases nonlinearly with the increase of the axial deviatoric stress, which approaches the ideal plastic flow state near the peak strength.

中文翻译：

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三轴循环荷载作用下砂岩峰前变形及能量耗散特性分析

基于常规的三轴循环加载-卸载压缩试验，分析了在5、10、20和30 MPa的承压下砂岩的轴向和横向弹性塑性应变。结果表明，在循环载荷下，侧向应力应变塑性滞后回线比轴向方向更明显。试样的轴向和横向弹性应变与轴向偏应力非线性相关，并且试样的轴向和横向塑性应变表现出明显的非线性塑性硬化特性。Duncan-Chang模型用于分析加载过程中砂岩的弹性应力-应变特性。不考虑压实初期，在相同围压下，砂岩试样的切线弹性模量随着轴向弹性应变的增加而连续减小，泊松比随横向弹性应变的增加而连续增加。根据砂岩试件的塑性应变特性，建立了相应的塑性流动方程，该方程可以较好地描述试件的轴向和横向应变特性。试样的塑性流动速率随着轴向偏应力的增加而非线性增加，接近峰值强度时接近理想的塑性流动状态。建立相应的塑性流动方程，该方程可优选描述样品的轴向和横向应变特性。试样的塑性流动速率随着轴向偏应力的增加而非线性增加，接近峰值强度时接近理想的塑性流动状态。建立相应的塑性流动方程，该方程可优选描述样品的轴向和横向应变特性。试样的塑性流动速率随着轴向偏应力的增加而非线性增加，接近峰值强度时接近理想的塑性流动状态。