含预制单裂隙石膏裂纹孕育与能量演化的应变率效应研究

基于高速相机和MTS万能试验机对含预制裂纹石膏样品进行了单轴压缩应变率效应试验研究,在应变率10^-5/s^10^-3/s之间选取6种应变率进行单轴压缩试验,对应力应变曲线、裂纹扩展路径、起裂应力、起裂角、弹性模量、峰值强度等与裂纹扩展相关的信息进行了应变率效应分析,并基于岩石材料破坏能量演化原理对其进行解释。试验表明:应变率在10^-5/s^2×10^-4/s范围时,石膏样品应力应变曲线台阶式上升或回落,波动较多.翼型裂纹发展充分,起裂应力、弹性模量、峰值强度等相差不大,裂纹起裂角82°左右,验证了最小应变能密度因子理论;应变率在5×10^-4/s、10^-3/s时,石膏样品应力应变曲线峰前斜率较大,峰后跌落快,表现出岩石类材料典型的脆性特征,起裂应力、弹性模量、峰值强度等力学参数明显增大,起裂角为105°,此时应变能密度因子理论不再适用。

Strain rate effect on crack propagation and energy evolution of gypsum containing pre-existing single fracture

Based on the MTSC 45.105 universal testing machine, the quasi-static uniaxial compression strain rate effect experiment of prefabricated single crack gypsum specimen was carried out. According to the quasi-static strain rates within the range between 10-5~10-3/s, six strain rates were selected in experiment. At the same time, a high-speed camera was used to capture the crack initiation and propagation under different strain rates. The stress-strain curves and crack propagation under different strain rates were analyzed. The variation of some relevant mechanical parameters, including crack initiation stress, peak stress and elastic modulus under different strain rates, was summarized. The crack initiation angle was analyzed and compared with the theoretical calculation result. The strain rate effect on the energy evolution was carried out. Results show that when strain rate is less than or equal to 2×10^-4/s, the stress and strain curve fluctuates obviously, and presents stepwise rise or fall patterns. The crack is well developed. Those mechanical parameters such as cracking stress, peak stress and elastic modulus fluctuate slightly. The crack initiation angle is about 82°, which is close to 82.3° calculated by the theory of strain energy density factor. When the strain rate is more than 2×10^-4/s, stress-strain curve before its peak is smooth, but decreases rapidly after its peak, which shows a more pure brittle characteristic. Those mechanical parameters such as crack initiation stress, peak stress and elastic modulus obviously increase, compared with their counterparts obtained under the low strain rate. The crack initiation angle increases to 105°, which is larger than the theoretical calculation result. Strain rate effect of the energy evolution during crack initiation was analyzed. The airfoil crack initiation process was analyzed based on energy release and dissipation theory.