基于SEVNDB试样岩石复合断裂韧度测试:数值分析与标定

提出了一种利用非对称三点弯曲加载下的单边垂直切槽深梁试件(SEVNDB)开展岩石Ⅰ-Ⅱ复合断裂韧度测试方法。通过有限元法对试件的无量纲应力强度因子进行了数值分析与标定,研究了无量纲应力强度因子YⅠ、YⅡ及无量纲T应力T*与裂纹长度a、支座间距S1、S2之间的关系,定量刻画了实现纯Ⅱ型加载对应的裂纹长度a、支座间距(S1和S2)数值。研究结果表明,该方法在不改变试样裂缝倾角的前提下,通过调整裂缝长度a和支座间距S1、S2,即可方便地实现从纯Ⅰ型到纯Ⅱ型任意复合度载荷作用下的岩石断裂韧度测试。

Mixed-mode Fracture Toughness Testing of Rocks Using SEVNDB Specimens: Numerical Analysis and Calibration

To improve the testing of rock mixed-mode fracture toughness,a new method which could test Ⅰ-Ⅱ mixed-mode fracture toughness of rocks,was proposed by using single edge vertical notched deep beam specimens(SEVNDB).And asymmetric three-point bend loading was employed in the method.The finite element method(FEM)was used to analyze and calibrate the mode Ⅰ and mode Ⅱ dimensionless stress intensity factors(i.e.YⅠ and YⅡ)and the dimensionless T-stress(i.e.T^*)of the specimen used in the new method.The effects of the crack length a and the bottom supports distance S1,S2 on the modeⅠ and mode Ⅱ dimensionless stress intensity factors(i.e.YⅠ and YⅡ)and the dimensionless T-stress(i.e.T^*)of crack tip was studied.In addition,the loading condition of crack length a and bottom support distance S1,S2 was found when the purelyⅡtype fracture was achieved.Numerical results demonstrated that the method based on SEVNDB specimen could indeed test the mixed-mode fracture toughness of rocks in a full range of mode mixities from pure mode Ⅰ to pure mode Ⅱ easily by different combinations of the crack length a and the bottom supports distance S1,S2.