不同加载速率作用下含平行裂隙岩石的试验研究:能量耗散与损伤演化

Experimental study of rock with parallel cracks under different loading rates:energy dissipation and damage evolution

为了研究平行双裂隙岩石在动荷载作用下的能量耗散和损伤变化规律,利用改进的分离式霍普金森杆(SHPB)试验装置,对预制平行裂隙岩石进行动态冲击试验,探究裂隙角度和加载速率对岩石能耗规律和损伤变化的影响。试验结果表明:随着加载速率的增大,0°裂隙岩石的弹性应变能先下降后上升,45°和90°裂隙岩石表现出相反的规律。根据能量转换和分配原理,建立应变能密度变化函数模型,该模型能较好地反应峰值应力前岩石的能量耗散特性。弹性应变能与塑性应变能的比值可以用来表示岩石破坏前能量的变化指标,峰值应力前岩石能量吸收、储存和释放的过程中存在自我控制行为。不同加载速率作用下岩石的损伤变量分为稳定和加速发展两个阶段,加载速率效应影响损伤变量置信区间的变化趋势,损伤变量随着裂隙角度的增大先减小后增大。损伤变量分别和加载速率、单位体积吸收能具有良好的非线性拟合关系。基于数学推导法研究了裂隙角度和加载速率对岩石损伤曲线的影响,建立了损伤力学模型。损伤曲线的斜率先增大后减小,损伤因子m_(0)整体逐渐上升,F_(0)逐渐下降。其研究结果可以为深部裂隙岩石工程设计和岩石破碎效率优化等工程实践提供科学依据。

In order to study the effect of internal flaw on rock energy dissipation and damage change law under impact loading,intact granite specimens and specimens with different flaw inclination are tested by a modified split Hopkinson pressure bar(SHPB).The results of experiment and theoretical analysis show that the elastic strain energy of 0°flaw decreases first and then increases,while 45°and 90°flaws increases first and then decreases with increasing the loading rate.According to the principle of energy conversion and distribution,a function model is constructed considering the variation of strain energy density,which can well reflect the energy dissipation characteristics of rock before peak stress.In this study,the ratio of dissipated energy to elastic energy is used as the energy indicator of rock failure precursor.During the absorption,storage,and release of energy before the peak stress,there exists self-control of energy.The damage variable of rock under different loading rates is divided into two stages,damage stable development and damage acceleration.Besides,the damage variable shows obvious rate effect,which decreases first and then increases with the increase of crack angle,and it has a good nonlinear relationship with the loading rate and the energy dissipation density,respectively.Based on the mathematical derivation method,the damage evolution equation of the fractured rock under impact loading is constructed,the influence of different fracture angles and loading rates on rock damage curve are also studied.The slope of the damage curve first increases and then decreases,while the damage factor m_(0)increases and F_(0)gradually decreases.These conclusions should provide scientific basis for the practical projects of deep rock engineering design and improve the efficiency of rock excavation and rock breakage to some extend.