The brittleness of rocks plays an important role in the fracture network fracturing process of unconventional oil and gas reservoirs, the drilling efficiency of rock breaking and wall stability, and mining engineering. Rock brittleness has become one of the key parameters in the study of many rock mechanics and related engineering problems. However, there is still no widely accepted definition of brittleness. Although many criteria have been proposed to characterize rock brittleness, their applicability and reliability have yet to be verified. Therefore, brittleness evaluations require further study. In this paper, we divided the rocks under an external load into the unruptured area (body I system) and ruptured area (body II system). We considered that the body I system provided energy for the fracture of the II body. The brittleness of rock is understood as the ability of energy release when a post-peak fracture occurs in the II system. Therefore, the quasi-static energy-balanced equation of a double-body system was established and a new brittleness index was defined as the elastic energy release between an unsteady quasi-static state to the stable state of body II. The new index for brittleness evaluation proposed in this paper can not only quantify the brittleness of rock through the relation between the extremum of a softening modulus at the inflection point in the post-peak deformation curve of body II and the elastic modulus of body I but also ensure the position of the failure strain in the post-peak stage as well as reviewing the instant characteristics of the rock’s brittle crack. It is a new method to evaluate rock brittleness. Taking sandstone with different contents of brittle minerals as an example, the variation of the brittle index with the content of brittle minerals was studied.

中文翻译：

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单轴压缩下基于双体分析的岩石脆性评价标准

岩石的脆性在非常规油气藏的裂隙网络压裂过程，破岩的钻进效率和壁稳性以及采矿工程中起着重要的作用。岩石脆性已成为研究许多岩石力学和相关工程问题的关键参数之一。但是，仍然没有被广泛接受的脆性定义。尽管已经提出了许多表征岩石脆性的标准，但它们的适用性和可靠性尚未得到验证。因此，脆性评估需要进一步研究。在本文中，我们将外力作用下的岩石分为未破裂区域（I体系统）和破裂区域（II体系统）。我们认为I体系统为II体的破裂提供了能量。岩石的脆性被理解为II系统中发生峰后断裂时释放能量的能力。因此，建立了双体系统的准静态能量平衡方程，并定义了新的脆性指标，即非稳态准静态到本体II稳态之间的弹性能量释放。本文提出的新的脆性评估指标不仅可以通过II体峰后变形曲线拐点处的软化模量的极值与I体的弹性模量之间的关系来量化岩石的脆性，而且还可以确保峰值后阶段的破坏应变位置，以及查看岩石脆性裂纹的即时特征。它是评估岩石脆性的一种新方法。