半圆弯拉下岩石内裂纹扩展规律数值模拟研究

岩石内部固有缺陷的存在和扩展是导致其断裂的重要因素,半圆弯拉试验是该领域的重要实验。为研究半圆弯拉下含三维内裂纹试件扩展路径及断裂特性,基于Franc3D有限元自适应网格划分技术开展含三维内裂纹SCB试样数值模拟,结果表明:(1)基于Franc3D软件的三维裂纹扩展与室内试验具有较好的一致性,该软件是三维裂纹数值模拟的重要工具。(2)通过M积分得到裂纹尖端应力强度因子,分析得出对称加载模型为K_Ⅰ与底部加载跨距呈正相关的Ⅰ型断裂模式;非对称加载模型中出现复合断裂模式,随着右侧加载跨距的增加,K_Ⅰ先降低再升高,K_Ⅱ及K_Ⅲ先变化至0,再逐渐升高。(3)基于最大拉应力准则得到裂纹扩展路径,对称加载模型在I型断裂模式下进行平面扩展后破坏,非对称加载模型出现复合断裂模式,伴随翼型起裂并扩展至破坏。(4)定量分析对称加载模型裂纹内部扩展规律得出,裂纹下端扩展速率最大,上端扩展速率最小。

Numerical simulation of internal crack propagation in rocks under semi-circle bending

In order to study the propagation path and fracturing characteristics of the rock specimen with 3-D internal cracks，the numerical simulation on the SCB specimens containing 3-D internal cracks is carried out based on the technique of finite element adaptive mesh generation of Franc3D. The result shows that ( 1) the result from the Franc3D-based numerical simulation on the 3- D crack propagation is better consistent with that from the indoor test，and then the software is an important tool for the numerical simulation of 3-D crack; ( 2) through M-integral，the stress intensity factor at crack tip is obtained，and then it is obtained from the relevant analysis that the symmetric loading model is the fracture-mode I that KⅠ is positively correlated with the bottom loaded span，while composite fracture modes occur in the asymmetric loading model. Along with the increase of the right-side loaded span，KⅠ is decreased at first and then increased and KⅡ ，KⅢ is changed to 0 and then gradually increased; ( 3) the crack propagation path is obtained in accordance with the maximum tensile stress criterion，from which the symmetric loading model is destructed after planar propagation under the fracturing mode I，while composite fracture modes occur in the asymmetric loading model，which are extended to destruction along with winged-cracking; ( 4) it is obtained from the relevant quantitative analysis of the internal propagation law of the symmetric loading model that the propagating rate at the lower end of crack is the largest，while the propagating rate at the upper end is the smallest.