The brittleness index of rocks is able to provide crucial guidance to the operation of the drilling and hydraulic fracturing. The definition and evaluation method of the rock brittleness has not yet been unified and standardized due to their diversity. We therefore develop an evaluation method of the rock brittleness based on statistical damage relation. A set of uniaxial compression tests on different rock samples are conducted, and corresponding experimental data is collected and analyzed. Then we establish piecewise damage constitutive models based on different combinations of statistical distribution functions, including power function distribution, Weibull distribution, lognormal distribution and logistic distribution. A new evaluation method of rock brittleness based on energy method and the piecewise statistical damage constitutive model is proposed, and the evaluation results show that the increase of damage variable of peak strain will undermine rock brittleness, and the mineral composition contents have influence on the brittleness of rocks. Comparison work between this proposed method and previous brittleness criteria shows that the brittleness index $B_{43}$ exhibits enhanced stability and consistency in rock brittleness. This study presents a novel method to studying rock brittleness, enhancing current evaluation methods and deepening our understanding of the rock index. Regarding practical application, some field operations involved with the process of drilling or fracturing lead the continuous damage evolution of rocks under loading conditions. The brittleness index from the proposed evaluation method is comparatively reliable and practical for on-site drilling and fracturing.

岩石的脆性指标能够为钻井和水力压裂作业提供重要指导。由于岩石脆性的定义和评价方法多种多样，目前尚未统一和规范。因此，我们开发了一种基于统计损伤关系的岩石脆性评价方法。对不同岩石样品进行了一组单轴压缩试验，并收集和分析了相应的实验数据。然后，我们建立了基于统计分布函数的不同组合的分段损伤本构模型，包括幂函数分布、威布尔分布、对数正态分布和逻辑分布。提出了一种基于能量法和分段统计损伤本构模型的岩石脆性评价新方法，评价结果表明峰值应变损伤变量的增大会破坏岩石脆性，矿物成分含量对脆性有影响的岩石。该方法与以前的脆性标准之间的比较工作表明，脆性指数${乙}_{43}$表现出增强的岩石脆性稳定性和一致性。这项研究提出了一种研究岩石脆性的新方法，增强了现有的评估方法并加深了我们对岩石指数的理解。在实际应用中，一些涉及钻井或压裂过程的现场作业导致岩石在加载条件下不断损伤演化。该评价方法得出的脆性指标对于现场钻井压裂来说比较可靠、实用。