不同加载条件下岩石强度尺寸效应的数值模拟

Numerical simulation of strength size effect of rocks under different loadings

岩石材料由于非均质性,其强度值具有明显的尺寸效应。而作为一种试验指标,岩石的强度尺寸效应与加载条件有关,不同的加载条件下其尺寸效应既有相同的规律,也存在差异。本文用真实破裂过程分析系统RFPA,对压缩试验、拉伸试验及三点弯曲试验进行数值模拟,得到不同加载条件下岩石强度尺寸效应的数值结果。由此可知,岩石的峰值强度和残余强度均随着尺寸的增加而降低,可以用Weibull尺寸效应律进行拟合,拟合效果较好,但其破坏形态不会显著改变。不同加载条件下岩石材料强度尺寸效应的差异可以通过其破坏时的均质度来反映,不同的加载条件有着不同的均质度,为一个动态参数。其值越大,表示岩石破坏时越均匀,尺寸效应越不明显。基于此,三点弯曲试验强度尺寸效应最为明显,单轴拉压试验次之,有侧压的压缩试验最不明显。在目前对尺寸效应的理论研究仍不尽人意的情况下,数值模拟可视为一种研究岩石强度尺寸效应的有效途径。

The strength of rock materials shows an obvious size effect due to heterogeneity,while as a test index it is also related to loading conditions.This means that the strength may follow a similar strength size effect law that should,however,vary slightly with different loadings.In this work,three loadings of compression,tension and three-point bending were numerically simulated using a realistic failure progress analysis（RFPA） code and test data of rock specimens in various sizes,and the results of three loadings were analyzed for each specimen volume.It was found that both the peak strength and residual strength decrease with the size,while the failure mode in each loading case is nearly the same no matter how specimen sizes are.The strength-volume relationship fits well the Weibull strength size effect law.It was also found that the difference of strength size effect in different loading cases can be represented by a homogeneity factor of the material at the failure stage,a parameter that is not static but dynamically varies with loading conditions.If this factor is greater,the material is more homogenous and the strength size effect shows less obvious.Based on this factor,it is easily shown that the strength size effect is more significant in the three-point bending test,while less significant in the confining compression test.Thus,besides theoretical approach,numerical test provides a suitable and effective tool in the study of rock material size effect.