加载速度对随机缺陷岩样破坏过程的影响

INFLUENCE OF LOADING VELOCITY ON FAILURE PROCESS OF ROCK SPECIMEN WITH INITIALLY RANDOM MATERIAL IMPERFECTIONS

在单轴平面应变压缩条件下,采用FLAC模拟加载速度对具有随机材料缺陷岩样破坏过程的影响。采用编写的FISH函数规定随机缺陷及统计发生破坏的单元数。密实岩石服从莫尔–库仑剪破坏与拉破坏复合的破坏准则,破坏之后呈现应变软化–理想塑性行为。缺陷破坏之后经历理想塑性行为。随着加载速度的提高,强度及其对应的应变提高,峰后应力–变形曲线变得平缓。在加载过程中,每10个时步内破坏单元数–轴向应变曲线中存在破坏单元数有显著增加的3个区段。随着加载速度的提高,该曲线的区段2及3变得开阔,区段2的峰值降低,区段3的峰值提高。在初始加载阶段和缺陷全部破坏之前,加载速度较高时的破坏单元总数–轴向应变曲线比较平缓,这是由于加载速度较高时试样内部的裂隙传播和应力转移不充分,当应变小于一定值时,在应变相同时,破坏单元数较少。破坏单元总数–应变曲线表明,随着加载速度的提高,试样最终遭受到更严重的破坏。

For heterogeneous rock specimen with smooth ends and initially random material imperfections in uniaxial plane strain compression,the effects of loading velocity on the failure process are modeled using FLAC.A few coded FISH functions are used to prescribe the random imperfections and to remember the number of failed elements.For intact rock exhibiting linear strain-softening behavior after the occurrence of failure and then ideal plastic behavior,the failure criterion is a composite Mohr-Coulomb criterion with tension cut-off.Imperfection undergoes ideal plastic behavior after the occurrence of failure.As loading velocity increases,the peak stress and corresponding axial strain increase;and the post-peak stress-axial strain curve becomes less steep.In the loading process,the number of failed elements per 10 time steps-axial strain curve possesses three stages with remarkable increase in the failed elements.At higher loading velocitiest,he second and third stages become widert;he peak of the second stage decreases,and the peak of the third stage increases.In the initially loading stage and before the failure of all imperfections,the number of failed elements-axial strain curve is less steep at higher loading velocities.Since the crack propagation and the stress transfer within the specimen are less sufficient at higher loading velocities,when axial strain is less than a certain value,the number of yielded elements can be lower at the same axial strain.It is found from the number of failed elements-axial strain curve that the specimen loaded at higher loading velocities is subjected to more severe failure in the final deformational stage.