岩石单轴压缩应力–应变特征的率相关性及能量机制试验研究

 岩石渐进性破坏过程分为5个阶段：裂纹闭合阶段、弹性阶段、裂纹起裂和稳定扩展阶段、裂纹加速扩展阶段和峰后段。利用变频动态加载岩石力学试验系统，研究不同应变率加载条件下岩石破坏过程中的特征应力，即起裂应力、扩容应力以及峰值强度，结果显示，特征应力随应变率的变化情况基本满足以下规律：应变率 ＜5×10－4 s－1时，随着应变率的变化，特征应力基本不随应变率的增减发生变化，其率敏感性不明显； ＞5×10－4  s－1时，特征应力随着应变率的增长而增长，表现出较强的率敏感性。而3个量纲一的参数，即起裂应力和扩容应力与峰值强度的比值以及起裂应力与扩容应力的百分比分别为50%～60%，70%～80%和80%～90%，与应变率无明显相关性。基于能量守恒法则，对岩石破坏过程中的能量特征及能量机制进行分析，结果表明：岩石单位体积吸收的总应变能和弹性应变能均随应变率的增长而增长，损伤应变能则随着应变率的增长先增大后减小。吸收的总应变能和弹性应变能随应变率的变化规律与应力随应变率的变化规律一致，即 ＜5×10－4 s－1时，吸收应变能和弹性应变储能率敏感性不随应变率的变化发生变化，无明显率敏感性； ＞5×10－4 s－1时，吸收的应变能和弹性应变能则随应变率的增加而增加，具有较强的敏感性。应变率一定的情况下，岩石所吸收的应变能主要以弹性应变能的形式储存，损伤应变能基本保持不变，临近峰值点时岩石中损伤应变能才有所增加；一旦过了峰值点，岩石中储存的弹性能快速释放，体现在应变–应变能曲线上则为弹性应变能曲线的迅速下降和损伤应变能曲线的迅速上升。  

EXPERIMENTAL INVESTIGATIONS ON RATE-DEPENDENT STRESS-STRAIN CHARACTERISTICS AND ENERGY MECHANISM OF ROCK UNDER UNIAIXAL COMPRESSION

The progressive failure of rock can be divided into five stages,including crack closure stage,elastic stage,crack initiation and stable growth stage,and accelerated crack growth and post-peak stage.The characteristic stresses in the progressive failure process of rock under different strain rates were studied by using the dynamic mechanical system of rock with changing frequencies.The results show that:(1) When the strain rate ε&<5×10-4s-1,rock strength is slightly dependent on the strain rate;when ε&>5×10-4s-1,the rock strength is significantly dependent on strain rate.(2) The ratios of crack initial stress and dilatancy stress to the peak strength and the ratio of crack initial stress to dilatancy stress are 50%–60%,70%–80% and 80%–90%,respectively,showing no evident dependence of strain rate.Based on the energy conservation law,the energy characteristics and energy mechanism in the process of rock failure were analyzed.Some conclusions are dram as follows.(1) Both of the total absorbed strain energy and the elastic strain energy increase with the growth of strain rate;but the damage strain energy increases firstly and then decreases.(2) When ε&<5×10-4s-1,the absorbed energy and the elastic energy are slightly dependent on strain rate;when ε&>5×10-4 s-1,the absorbed energy and the elastic energy are significantly dependent on strain rate.(3) If the strain rate is fixed,the strain energy absorbed by rock is stored mainly in the form of elastic strain energy,but the damage strain energy remains nearly unchanged,which only increases near the peak strength.Once the peak strength is reached,the strain energy stored in the rock is quickly released.