不同温度-应力场下泥岩蠕变特性及本构模型

为探讨不同温度-应力场下泥岩的蠕变力学行为特征,对泥岩开展了常温(25 ℃)、60 ℃和120 ℃下的三轴分级加载蠕变试验,得到了各温度-应力场下对应的蠕变历时曲线和蠕变参数,给出了考虑温度和损伤效应的蠕变本构模型。研究结果表明:高温促进了泥岩内部分子运动,减弱了颗粒之间的相互胶结力,使其蠕变特征明显,而围压则能在一定程度上抑制泥岩内部损伤的发展;稳态蠕变速率随偏应力和温度的升高呈指数型函数增加,随围压升高则呈线性减小;各温度场下,泥岩的长期强度和长期抗剪强度特征参数随围压的升高呈良好的线性关系,相同围压下,温度越高,长期强度越小;在经典西原模型基础上,结合温度-应力场下泥岩的温度效应和损伤效应,建立了热-力耦合作用下的蠕变损伤本构模型,能很好地模拟各温度-应力场下泥岩的蠕变特征,拟合结果表明,弹性模量和黏性系数随温度的升高呈线性减小,而α则随温度的升高呈对数型函数增加。

Creep Behavior and Constitutive Model of Mudstone under Different Temperature and Stress Fields

To explore the creep mechanical behavior of mudstone under different temperature and stress fields, we carried out triaxial step-loading creep test on mudstone at room temperature (25 ℃), 60 ℃ and 120 ℃, and built a constitutive creep model in consideration of damage and temperature effect according to the obtained creep curves and creep parameters under different temperature and stress fields. Results show that high temperature promoted the internal molecular motion of mudstone, weakened the mutual cementitious force between particles, and made the creep characteristic more obvious; confining pressure inhibited the internal damage development of mudstone to some extent. Steady creep rate increased in an exponential function with the rising of deviatoric stress and temperature; but reduced linearly with the increase of confining pressure. Under each temperature field, the long-term strength and the long-term shear strength parameters of mudstone increased in a good linear relationship with the increase of confining pressure; under the same confining pressure, however, the long-term strength weakened with the rising of temperature. The constitutive creep model coupling heat-mechanical effect on the basis of classic Nishihara model could well simulate the creep behaviors of mudstone under temperature and stress fields. Fitting results suggest that the elastic modulus and viscosity of mudstone reduced linearly with the rising of temperature, while α increased with the rising of temperature.