较低和较高围压下煤岩三轴试验及其塑性特征新表述

Triaxial tests of coal under low and high confining pressures and its plastic characteristics description

对煤岩进行了较低和较高多个围压下的常规三轴加卸载试验研究,给出了系统的试验成果。试验表明,较低围压下,卸载路径和加载路径几乎完全重合,煤岩应力-应变特性呈现明显的线弹性特征,并表现出一定的脆性破坏特性;而较高围压下,应力-应变呈现明显的非线性特征,卸载路径不再原路返回,呈明显的塑性变形特征。为了定量刻画煤岩的塑性硬化特性,提出了根据硬化参量的几何意义计算其值的方法,并选择累积塑性应变作为塑性硬化参量,计算了27MPa围压下试验曲线的硬化参量,作为对比还计算了采用直接卸载法计算的该试验曲线的累积塑性应变值。结果发现,随着轴向变形逐渐增加,煤岩的塑性硬化逐渐增长,并且用该方法计算出的塑性硬化参量远大于用直接卸载法计算的结果。由于该方法完全符合路径积分的限制条件,因此,更加合理。

Loading and unloading triaxial tests for coal samples under various confining pressures are conducted. The tests show that when the confining pressure is relatively low, the loading and unloading loci are almost coincident. The coal samples show the characteristics of linear elasticity and brittle failure. While under the relatively higher confining pressures, the stress-strain curve is nonlinear, and the unloading path does not come back along the loading locus any more. Moreover, the residual deformation appears, this shows the plastic characteristics of the coal so as to describe the hardening plasticity quantitatively; a new computing method for the hardening parameter based on its geometric meaning is presented in principal strain space. The accumulated plastic strain is chosen and computed with the test data of 27 MPa confining pressure. This hardening parameter increases with the increase of axial strain, the hardening parameter value computed with this method is higher than that of another traditional method. But the method presented is more rational.