加载速度对岩样全部变形特征的影响

Effect of loading rate on entire deformational characteristics of rock specimen

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模拟了加载速度对剪切带图案及岩样全部变形特征的影响。在峰前及峰后,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。加载速度较低及适中时,岩样发生单剪切破坏,剪切带倾角及宽度不受加载速度影响,应力-轴向应变曲线及应力与侧向应变曲线软化段的斜率不依赖于加载速度;高加载速度使岩样发生X型剪切破坏,两种曲线软化段较平缓;在相同的轴向应变时,高加载速度使剪切带长度降低。随着加载速度的增加,岩样失稳破坏的前兆越来越明显,当加载速度较高时,前兆反而不明显,这是由于应力存在较大的波动,导致不正确地估计了应力峰值所对应的轴向应变。在应变软化阶段,高加载速度使侧向应变与轴向应变曲线、泊松比与轴向应变曲线及体积应变与轴向应变曲线变平缓,也使体积应变与轴向应变曲线的峰值及对应的轴向应变增加。

FISH functions written are used to calculate axial, lateral and volumetric strains as well as Poisson＇s ratio of rock specimen in plane strain compression. Influence of loading rate on shear band （SB） pattern and entire deformational characteristics is investigated numerically using FLAC. In elastic and strain-softening stages, the constitutive relations are linear. A composite Mohr-Coulomb criterion with tension cut-off is used. For lower and moderate loading rates, a SB whose inclination angle and thickness are not influenced by loading rate bisects the specimen, so that the post-peak slopes of stress-axial strain curve and stress-lateral strain curve are not related to loading rate. Higher loading rate leads to the conjugate SBs, resulting in less steep post-peak stress-axial strain curve and stress-lateral strain curve. At the same axial strain, higher loading rate leads to shorter SB.With an increase of loading rate, the precursor to failure is more apparent unless the loading rate is very high. At higher loading rate, the great fluctuation in stress exists so that the axial strain corresponding to the peak stress is estimated inappropriately. In strain-softening stage, higher loading rate results in ductile lateral strain-axial strain curve, Poisson＇s ratio-axial strain curve and volumetric strain-axial strain curve as well as higher peak of volumetric strain and the COlTesponding axial strain.