花岗岩单轴压缩侧向变形及脆性破坏机制实验研究

Experimental Study of Granite Brittle Fracture Mechanism in Lateral Deformation Due to Uniaxial Compression

为研究花岗岩侧向变形及脆性破坏机制,对花岗岩试件进行单轴压缩实验。利用动态应变采集系统、数字散斑相关方法(DSCM)和显微观测手段,记录并分析花岗岩试件在单轴压缩过程中的宏观侧向应变、局部侧向应变以及破裂面形貌,并与水泥砂浆试件的破坏过程对比,讨论了花岗岩脆性破坏机制。实验与分析结果表明:(1)花岗岩试件在加载初期发生侧向收缩变形,产生并发展于压密阶段,消失于线弹性阶段初期,这主要由于试件内部裂纹闭合造成的;此后,宏观侧向应变持续增长,当侧向应变与轴向应变之比接近0.5时试件破坏;(2)在峰值载荷前很长一段时间内,局部侧向应变在一定范围内波动,临近试件破坏时局部侧向应变最大值和最小值均出现较大幅度的波动,二者差值迅速增大,试件不均匀程度增大,最终导致试件破坏;(3)在峰值载荷前有无塑性屈服阶段是峰值载荷后脆性破坏程度的重要影响因素,而宏观裂纹的贯通程度是峰值载荷后应力降大小的决定因素。

In order to study granite brittle fracture mechanism and lateral deformation, uniaxial compression experiment of granite specimens was conducted. Macroscopic lateral strain, local lateral strain and fracture section mophology of granite specimens during uniaxial compression process were record and analyzed by using dynamic strain acquisition system, digital speckle correlation method （DSCM） and microscopic observation method. Granite brittle failure mechanism was discussed by comparing with the failure procedure of cement mortar samples. Experimental results show that （1） granite specimens present lateral shrink deformation at the preliminary stage of loading, which occurs and develops in consolidation process and vanishes at the initial linear elastic stage. The lateral shrink deformation was mainly caused by the closUre of specimen＇ s internal cracks. After that, the macroscopic lateral strain sustains growth, and specimen＇s failure occurs when the ratio of lateral strain and axial strain is close to 0.5; （2） during a long period of time before peak load, local lateral strain fluctuates within a certain range~ when approaching specimen＇s failure, both the maximum value and the minimum value of local lateral strain present large fluctuation and their difference increases rapidly~ specimen＇s uneven level increases, resulting in its destruction; （3） with or without plastic yield stage before peak load is the important factor influencing on the brittle failure degree, while the level of macroscopic crack transfixion is the determining factor influencing on stress drop value after peak load.