三轴循环荷载下砂岩损伤耗能比演化特征研究

为了研究循环载荷下岩石能量演化特征，引入耗能比?，开展砂岩不同围压下轴向循环加卸载试验，探究全应力-应变过程中?值演化特征，进而探讨岩石试样循环加卸载作用下损伤变形演化规律。试验结果表明：对应全应力-应变曲线的5个阶段，?值演化过程可划分为线性下降、稳定发展、缓慢增加、突然增加和平缓变化5个阶段，在?值整个演化过程呈现“勺”演化特征，该特征充分反映了试样变形演化过程中的能量转化关系及损伤演化程度；随着围压的增大，?值整体呈现减小趋势；同一应变水平下，不同围压下?值在线性下降阶段、稳定发展阶段差值逐渐减小，在缓慢增加阶段、突然增加阶段差值逐渐增大，在平缓变化阶段差值减小并趋于一个稳定值；分析循环加载下岩石材料参数演化特征，考虑围压作用及耗能比演化规律，建立岩石试样循环加卸载作用下的应力-应变演化理论公式，并进行了试验曲线拟合，验证了该理论公式的合理性。

Energy consumption ratio evolution law of sandstones under triaxial cyclic loading

By introducing the energy consumption ratio (?), the axial cyclic loading test was carried out to study the energy evolution of sandstones under different confining pressures. The evolution law of ? was analyzed during the full stress-strain process, and then the damage deformation was further explored under cyclic loading. The test results showed that five stages of ? were corresponding to the stages of full stress-strain curves, which were divided into linear decline, stable development, slow increase, sudden increase and gently change, presenting a spoon-shaped evolution feature. It fully reflected the relationship of energy transformation and degree of damage development during the deformation evolution of specimens. In general, the energy consumption ratio (?) reduced as the confining pressure increased. At the same strain level, with the increase of confining pressure, the difference of ? at the stages of linear decline and stable development decreased, then it increased gradually at the stages of slow increase and sudden increase, and finally it decreased to a stable value at the stage of gently change. The variation of material parameters was analyzed, and then a theoretical formula of stress-strain evolution under cyclic loading was deduced by considering the confining pressure and evolution law of ?. The formula was well fitted with test results, which verified its rationality.