端面约束对岩样全部变形特征的影响

Numerical Simulation of Effects of End-restraint on Overall Deformational Characteristics

利用编制的计算平面应变压缩岩样轴向、侧向、体积应变及泊松比的FISH函数,采用FLAC模拟了端面约束对含缺陷岩样剪切带花样、全部变形特征及侧向位移分布的影响。在峰值强度之前及之后,岩石的本构模型分别取为线弹性及莫尔库仑剪破坏与拉破坏复合的应变软化模型。计算表明,端面约束对岩样的破坏模式及剪切带倾角没有明显的影响,以致于不影响应力-轴向应变曲线及应力-侧向应变曲线软化段的斜率。端面光滑时剪切带的扩展速度及泊松比高于端面粗糙时。端面光滑时的应力-轴向应变曲线、应力-侧向应变曲线、侧向应变-轴向应变曲线及体积应变-轴向应变曲线均在端面粗糙时下方。端面光滑时的岩样失稳破坏前兆比端面粗糙时更明显。无论端面粗糙与否,岩样侧面上各节点水平位移分布都是不均匀的。通常,端面光滑时的最大侧向位移高于端面粗糙时。当轴向应变较高时,端面光滑时的侧向位移分布与端面粗糙时类似(端面上的节点除外),这反映了类似的破坏模式。

FISH functions written were used to calculate the axial, lateral and volumetric strains as well as the Poisson＇ s ratio of a rock specimen with a material imperfection closer to the left-upper corner in plane strain compression. Using FLAC, the effects of end-restraint （or end-constraint） on shear band pattern, entire deformational characteristics and lateral displacement distribution were investigated. In elastic and strain-softening stages, the constitutive relations were linear; a composite Mohr-Coulomb criterion with tension cut-off was used. The failure mode of rock specimen and shear band inclination are not nearly affected by end-restrain so that the post-peak slopes of stress-axial strain curve and stress-lateral strain curve do not depend on the end-restraint. Shear band propagation is faster in the specimen with smooth ends than that in the specimen with rough ends. For smooth ends, higher Poisson＇ s ratio is found. The stress-axial strain curve, stress-lateral strain curve, lateral strain-axial strain curve and volumetric strain-axial strain curve of rock specimen with smooth ends are enveloped by those of rock specimen with rough ends. For smooth ends, the precursor to shear failure is more apparent. For different end-restraints, the lateral displacement distribution of rock specimen is non-uniform. Generally, the maximum lateral displacement of rock specimen with smooth ends is higher. The similar lateral displacement distribution is observed at higher axial strain except for the nodes near the two ends of the specimen, reflecting the similar failure mode of rock specimen with different end-restraints .