岩石紧凑拉伸断裂过程及其尺寸效应的三维数值模拟

Numerical study on three dimensional compact tension fracture of single notched rocks and associated scale effects by parallel computing

采用最近开发的三维岩石破裂过程分析软件RFPA3D模拟单边裂纹紧凑拉伸断裂过程。试验中五个不同尺寸的岩样具有相同的力学性质参数分布,模拟结果得到了裂纹扩展中的应力场、位移场和声发射的空间分布以及单边裂纹扩展贯通的过程。单边裂纹拉伸断裂的路径是一个复杂的空间三维曲面,三维裂纹比二维裂纹更为复杂。分析了岩石试样的峰值强度和试样尺寸之间的关系。随着岩样尺寸的增加,峰值强度逐渐减小,并且延性破坏特征更加明显,模拟结果满足岩石的尺寸效应规律。最后模拟了三组不同均匀性的试样拉伸破坏过程,结果表明细观上的非均匀性对岩石尺寸效应有很大影响,随着非均匀性的增加,岩石宏观强度随之提高,即使在均匀材料中一样存在尺寸效应。

A new numerical code RFPA was developed tO simulate rock failure process by taking the heterogeneities of mechanical properties into consideration. Parameters such as peak strength, elastic modulus and Poisson ratio are randomly distributed among all elements in the numerical model. A simple constitutive law was introduced into the model, and massive parallel computing method was applied to calculate the stress and displacement field. Five specimens with a single pre-existing crack were prepared to undertake direct tension test. The specimens with different scales have the same mechanical properties. The fracture process, including crack propagation and coalescence, was obtained as well as the complete stress-strain curves. Different from other numerical code, RFPA^3D can simulate the stress field and strain field during the whole loading process. The crack propagation along a three-dimensional curved path, much more complicated than two-dimensional cracks. The relation between peak strength and scale fits the rule of scale effects proposed by other investigators in experimental studies. Another three groups of specimens with different homogeneity and different sizes are undertaken uniaxial tensile tests. It concludes that the macro scale effects do not only result essentially from heterogeneities on mesoscopic scale. The RFPA^3D model is proved to be a useful and effective tool to analyze the failure process of brittle materials.