Stress-drop effect on brittleness evaluation of rock materials

Abstract

Uniaxial or triaxial compression test of cylindrical rock specimens using rock mechanics testing machine is a basic experimental method to study the strength and deformation characteristics of rock and the development process of rock fracture. Extensive literature review has been conducted on this issue; meanwhile, experimental and numerical studies have been conducted on the stress-drop effect on the brittleness of rock materials. A plastic flow factor of λ is proposed to describe the stress-drop effect. Evaluation methods of the factor λ corresponding to the four yield criteria of rock mass are proposed. Those four yield criteria are Tresca criterion, von-Mises criterion, Mohr-Coulomb criterion and Drucker-Prager criterion. For simplicity purposes, an engineering approximation approach has been proposed to evaluate the stress-drop with a non-zero strain increment. Numerical simulation results validated the effectiveness of the plastic flow factors λ as well as the engineering approximation approach. Based on the results in this study, finite element code can be programmed for brittle materials with stress-drop, which has the potential to be readily incorporated in finite element codes.

摘要

利用岩石力学试验机对圆柱岩石试样进行单轴和三轴压缩试验, 是研究岩石强度和岩石裂隙发 展过程的基本试验方法。针对岩石材料应力降效应的问题, 首先进行了广泛的文献调研; 然后, 分别 利用室内试验和数值模拟的方法, 研究了应力陡降效应对岩石类材料脆性特征的影响。为了描述应力 降效应, 本文提出了塑性流变因λ, 且基于Tresca 准则、Von-Mises 准则、Mohr-Coulomb 准则和Drucker-Prager 准则等四类岩体屈服准则, 对塑性流变因子λ 进行了评价。此外, 为了简便, 在非零应变增量 下, 提出利用工程近似方法研究应力降。研究结果表明: 数值模拟和工程近似方法均验证了塑性流变 因子的有效性; 脆性材料的应力降, 可以通过有限元代码编码实现, 且该代码可以与原有限元代码简 单有效融合。