基于内时理论的软岩流变本构模型

Endochronic rheological constitutive model of soft rock

从内时理论出发 ,通过在内蕴时间中引入牛顿时间 ,在Helmholtz自由能中引入损伤变量 ,对它们分别进行重新构造 ,利用连续介质不可逆热力学的基本原理推导了软岩的内时流变本构方程。然后 ,对该方程在单轴应力条件下进行了求解、分析与试验验证。结果表明 :该方程能有效地描述软岩蠕变过程中衰减蠕变、稳定蠕变和加速蠕变等三个阶段的力学特性 ;当损伤尚未发生或未明显出现时 ,该方程能用来描述软岩蠕变第一、二阶段的特性及松弛特性 ,当损伤开始发生或出现时 ,该方程描述的是蠕变第三阶段的特性 ;造成软岩蠕变加速阶段出现的原因是损伤起始于或明显显现于蠕变第二阶段之末。

Starting from the endochronic theory, the basic principle of the irreversible thermodynamics of continuum media was used to derive a new endochronic rheological constitutive equation of soft rock by introducing Newton time into intrinsic time and a damage variable into the Helmholtz free energy to rebuild them. The solution, analysis and experimental validation of the new equation under uniaxial stress were performed. The results show that, the new constitutive equation can effectively describe the mechanics characteristics of three creep stages of the decaying, stable and accelerating creep of soft creep; the damage variable performs an important effect in the new equation, which can describe the characteristics of the first and second creep stage and relaxation when damage dose not happen, and the characteristics of the third creep stage when damage appears. The new equation correctly reflects such a fact as that the creep damage starts or appears at the end of the second stage and results in the accelerating creep and failure.