应变速率和尺寸效应对岩石能量积聚与耗散影响的试验

Experimental on the effect of strain rate and size on the energy accumulation and dissipation of rock

岩石的变形破坏过程是能量积聚与耗散的过程,岩石变形破坏是能量驱动的结果。基于不同尺寸与应变速率下的岩石单轴压缩试验,计算了不同尺寸与应变速率下岩样吸收的总能量、弹性应变能及耗散能,研究了能量积聚与耗散的演化规律,分析了在岩样变形破坏不同阶段的能量分配规律,并从能量角度分析了岩样破裂失稳的原因。研究表明:在单轴压缩试验时,岩样变形各阶段的能量特征有所差异,岩样吸收的总能量U0与耗散能Ud曲线呈非线性增加趋势,弹性应变能Ue曲线呈先增加后减小的趋势。岩样的能量与其高径比呈负相关的关系,两者呈幂函数关系;而与应变速率呈正相关,两者呈对数关系。岩石高径比越小或应变速率越大,岩石强度越高,单位体积岩样所吸收的能量也越高,造成岩样的破碎程度越大。在压密与弹性阶段,基本上将吸收的能量全部转化为弹性应变能储存于岩样内,弹性应变能是能量分配的主体。在塑性阶段,虽然弹性应变能的数值增大,但其所占比率有所下降;而耗散能比率有所增加,耗散能逐渐成为能量分配的主体。在峰后破坏阶段,弹性应变能瞬间释放,岩样吸收的能量几乎全部转化为耗散能,被裂隙面滑移摩擦而耗散掉,在峰后破坏阶段耗散能是能量分配的主体。

Rock deformation and failure are the process of energy accumulation and dissipation that are resulted from energy.Based on the uniaxial compression experiment in the condition of different strain rates and rock sample sizes,the total absorption energy,elastic strain energy and dissipation energy were calculated.The evolution law of energy accumulation and dissipation was investigated.In addition,the energy distribution rule of the rock sample at different deformation and failure stages,and the reason of rock steady failure from the perspective of energy were analyzed. The study shows that the energy feature at each rock deformation stage has some differences in uniaxial compression test.The curves of total absorption energy U0 and the dissipation energy Udshow a trend of nonlinear increase,while the curve of elastic strain energy Ueshows a trend of initial increase and then decrease.There is a negative correlation rela-tionship between energy and the ratio of height to diameter,their relationship is power function.However,the relationship between rock energy and strain rate is a positive correlation relationship,and it shows a logarithmic relationship.The smaller the ratio of height to diameter,or the greater the strain rate,the higher the rock strength. If the absorbed energy in per unit volume of rock sample is high,it causes a greater degree of fragmentation.At the consolidation and elastic stages,the total absorbed energy is mainly translated into the elastic strain energy which is stored in the rock.Elastic strain energy is a main source of energy distribution.At the plastic stage,the elastic strain energy is large while its percentage declines.The percentage of dissipated energy increases and gradually becomes the main source of energy distribution.At the failure stage after peak strength,the elastic strain energy of rock sample releases instantly,almost all of the absorbed energy is converted to dissipation energy,which dissipates by fracture surface sliding friction.The dissipation energy is a main source of energy distribution at the failure stage.