高应力强卸荷条件下大理岩损伤破裂的应变能转化过程机制研究

基于高应力条件下大理岩峰前卸围压试验和能量原理，研究岩样吸收应变能、塑性变形及裂纹扩展耗散应变能、环向变形消耗应变能和弹性应变能储存及释放的能量转化全过程特征，揭示其损伤破裂演化的应变能转化机制。峰前储存的弹性应变能较耗散应变能多，耗散应变能仅在临近峰值强度点附近才明显增加。峰后应力快速跌落伴随着弹性应变能的迅速释放和快速的塑性变形及裂隙扩展所耗散应变能。峰前、峰后应变能转化速率均随卸荷速率的增大而明显增大，特别是峰后转化速率增大得更为剧烈。而初始围压对应变能转化速率的影响与卸荷速率密切相关，快速卸荷时应变能转化速率随初始围压的升高而明显增大，而较慢速卸荷时随围压变化相对不明显，但初始围压增大明显加强峰前弹性应变能储存。峰后弹性应变能释放速率远大于环向变形消耗应变能速率，而吸收的应变能约与耗散应变能基本相等，故高应力强卸荷条件下硬性岩石常表现为近垂直于卸荷方向的张性破裂或劈裂特征，甚至出现岩爆现象。高应力强卸荷条件下大理岩具有峰前快速储存较多弹性应变能和相对较少的损伤耗能，而峰后弹性应变能快速大量释放和耗散，并伴有相对较快速地向卸荷方向的张裂变形消耗应变能的释放与耗散机制。

MECHANISM OF STRAIN ENERGY CONVERSION PROCESS FOR MARBLE DAMAGE AND FRACTURE UNDER HIGH STRESS AND RAPID UNLOADING

Based on energy theory and marble test of unloading confining pressure before peak strength under high stress，the whole process of strain energy conversion is researched，including absorbing strain energy for axial compression，dissipating strain energy for plastic deformation and cracks propagation，expending strain energy for circumferential deformation，storing and releasing elastic strain energy. The mechanism of strain energy conversion for marble specimens? damage evolution is revealed. The elastic strain energy stored is more than strain energy dissipated before the peak；and the quantity of strain energy dissipation can be significantly increased only near the peak. The stress quickly drops companying with elastic strain energy being rapidly released and strain energy fast dissipated for plastic deformation and fracture expansion after the peak. The rate of strain energy conversion obviously increases with the increasing unloading rate whenever before and after the peak，especially more intensely after the peak. The influence of initial confining pressure on the rate of strain energy conversion is closely related to unloading rate；and the rate of strain energy conversion clearly increases with the increasing initial confining pressure when the rate of unloading is faster；but the change is not obvious relatively when the rate of unloading is slower. The increasing initial confining pressure significantly enhances elastic strain energy storage before the peak. The rate of elastic strain energy release is far larger than that of strain energy expenditure for circumferential deformation；and the strain energy absorbed for axial compression is almost equal to that dissipated for plastic deformation and cracks propagation. So，the hard rock often presents the characteristics of tensional fracture or rip with the orient proximately perpendicular to unloading orientation，even rock burst appears. The mechanism of strain energy dissipation and release for marble damage and fracture under rapid unloading and high stress is that the elastic strain energy stored is more than the strain energy dissipated before the peak；and the elastic strain energy is quickly and largely released and dissipated after the peak；and companies with expending the strain energy for relatively fast confining tensile deformation towards unloading orientation.