基于岩石破坏全过程能量演化的脆性评价指数

 目前用于评价页岩可压性的脆性指数大都孤立地考虑峰值前后的力学特性，并不能反映岩石整个破坏过程的脆性特征。基于岩石的全应力–应变曲线，分析岩石材料由塑性变形转化为脆性断裂过程中各种应变能的演化规律，认为峰前耗散能和峰后断裂能水平是决定岩石是否发生脆性断裂的本质因素。结合这2种能量建立能反映岩石破坏前后力学特征的脆性评价指数，对不同岩石材料在不同围压下的脆性特征以及页岩脆性的各向异性进行评价。研究结果表明：建立的脆性评价指数能同时反映岩石脆性破坏的难易程度和脆性的强弱，可评价不同力学条件下的脆性变化特征。不同岩石材料峰前耗散能以及峰后断裂能随着围压增大而增大，脆性程度不断降低，但降低趋势有所不同，红砂岩和页岩分别在低围压时和高围压时出现了脆–塑性的转化，而花岗岩在围压不断增大的整个过程中都保持着较强的脆性。另外页岩脆性具有明显的各向异性，不同层理方向的页岩所表现出的脆性程度差异显著，随着层理倾角?的增大，页岩脆性表现出稳–减–增的变化趋势，? = 0°时页岩的脆性程度要强于? = 90°时，? = 60°时页岩脆性最弱且表现出很强的塑性特征。实验结果很好地验证了提出的脆性指数的可靠性，研究成果为岩石脆性的定量评价提供了一条新思路。

Brittleness evaluation index based on energy variation in the whole process of rock failure

The current indices used to evaluate the shale brittleness consider mostly the mechanical properties before or after the peak separately and cannot reflect the brittleness characteristics in the whole process of rock failure. In this paper，the variation of the various types of strain energy of rock materials in the process of plastic deformation to brittle fracturing was analysed based on the complete stress-strain curves. The levels of the pre-peak dissipation energy and the post-peak fracturing energy are the key factors to determine whether the brittle fracturing occurs. The brittleness estimation indices which represent comprehensively the mechanical properties of rock in pre-peak and post-peak periods were proposed by combining the pre-peak dissipation energy and the post-peak fracturing energy. The brittle characteristics of different rock materials under different confining pressures and the anisotropy of shale brittleness were evaluated with these brittleness indices. The results show that the proposed brittleness indices can simultaneously reflect the difficulty of brittle failure and the scale of brittleness and can evaluate the change of brittle characteristics under different mechanical conditions. The pre-peak dissipation energy and post-peak fracturing energy of different rock materials increase with the increase of the confining pressure. The brittleness decreases constantly with the increase of the confining pressure，but the decrease trends are different. The red sandstone and shale show the transformation of brittleness-plasticity at low and high confining pressures，while the granite has the strong brittleness in the whole process of the confining pressure increasing. The brittleness of shale is anisotropic. The brittleness of shale specimens with different inclination angles of bedding plane has significant difference. The shale brittleness shows a transition process of stable，increase to decrease as the inclination angle of bedding planes ? increases. When ? = 0°，the degree of brittleness of shale is stronger than that of ? = 90°. When ? = 60°，shale has the weakest brittleness and shows the plastic characteristic.