材料缺陷对岩样变形局部化影响的数值模拟

在平面应变压缩条件下，采用拉格朗日元法研究了材料缺陷对岩样应变局部化及宏观力学行为的影响。在数值计算中，采用了莫尔-库仑与拉破坏复合的破坏准则，峰后岩石的本构关系为线性应变软化。对于理想岩样（不含任何缺陷），从剪切应变率的等值线图及变形网格图发现，变形场相对试样垂直对称轴对称。在试样的边界上设置材料缺陷后，变形场的对称性被打破。材料缺陷附近是局部化现象启动的主要位置。与不含材料缺陷试样相比，含缺陷试样的局部化提前启动。当缺陷位于试样左边界中部附近时，试样内部出现多条剪切带，发生韧性剪切破坏，峰后应力-轴向应变曲线和应力-侧向应变曲线均倾向于韧性，岩样的稳定性增强；当缺陷位于试样上、下端面附近时，仅出现一条贯穿试样左右边界的剪切带，发生脆性剪切破坏，峰后两种曲线倾向于脆性，易发生失稳破坏。从数值结果中还观测到了剪切带的跳跃或迁移现象及剪切带的相互竞争、此消彼涨的现象。当岩样中不包含任何缺陷时，试样应力-变形曲线的峰值强度最高。随着缺陷的上移，峰值强度下降，直到峰值强度基本保持不变。缺陷越接近于岩样的下端，对岩样应力-变形曲线的峰值强度的影响越小。

Numerical simulation of influence of material imperfection on strain localization

Strain localization and macroscopically mechanical behaviors of rock specimen with and without material imperfection in plane strain compression were modeled numerically by FLAC.The adopted failure criterion was a composite Mohr-Coulomb criterion with tension cut-off and the post-peak constitutive relation of rock was linear strain-softening.For ideal specimen without any material imperfection,the deformation of the specimen is symmetrical with respect to the vertical axis of the specimen.If an imperfection is introduced in the form of a null element at one lateral edge,then the deformation no longer remains symmetrical.Shear strain localization is mainly initiated in the vicinity of the imperfection.For imperfect specimen,the onset of strain localization is earlier than that of ideal specimen.When the imperfection approaches to the middle of left edge of the specimen,multiple shear bands are formed so that the relatively ductile shear failure modes are expected and the post-peak stress-axial deformation curve and stress-lateral strain curve of the specimen tend to be less brittle.If the imperfection is closer to the top and base of the specimen,only a shear band is formed,going through the two lateral edges of the specimen,and the macroscopically mechanical behaviors of the specimen tend to be more brittle at post-peak.Migration or jump of shear band and competition between the two shear bands are observed.For ideal specimen,the peak strength is higher than those of imperfect specimens.When the imperfection moves away from the fixed end(base of the specimen),the peak strength decreases and finally approaches to a constant.