正交异性纯弯梁应力强度因子的研究

RESEARCHES ON STRESS-INTENSITY FACTORS OF ORTHOTROPlC PURE BENDING BEAM

本文运用复合材料断裂理论推导出带单边切口的纯弯梁不同纤维增强方向时v位移分量与K_Ⅰ、K_Ⅱ的关系式。用贴片云纹干涉法与有限元法确定纯弯梁裂纹尖端v位移,从而得出应力强度因子值。文中给出了复合材料纯弯梁不同裂纹长度,不同纤维增强方向时的云纹图,最后将测试结果与有限元计算值进行了误差对比。

Based on the theory of linear-elastic fracture mechanics, the crack tip stress field of orthotropic plate is still controlled by the stress-intensity factors, therefore to study the stress-intensity factors of orthotropic plate is an important problem in studying the fracture of composite materials. At present, not a few papers calculate the stress-intensity factors by finite element theory, but few by testing technique.With composite material fracture theory, the paper derives the relation formulas between the KI, KII and the v displacement with different fiber-reinforced directions. In this paper, the glass fiber-reinforced orthotropic plate is worked into the pure bending beam with a unilateral cut on it, which is tested by using the sticking film moire interferometry. Through testing, the full-field displacement of the moire pattern is given, the KI and KII values are further calculated from the displacement in the crack-tip. The patterns that the pure bending beam has different crack lengthes and is in different fiber-reinforced directions are given in this paper. Being exposed twice, the grating density of the moire pattern can reach 1260 line/mm. At the same time, the same specimen is calculated by using SAP-84 plate element program on microcomputer for inspecting the testing precision. At last, the test results are compared with the calculating ones in error.All of the testing and calculating results show: a. For isotropic materials, the formula of KI isb. For orthotropic materials, the stress-intensity factor varies with the fiber direction and/or the crack length, and the formula KI iswhere a is the crack length, w is the specimen's height, a is the flexibility matrix coefficient, a is the angle between the crack direction and the fiberreinforced direction.It can be seen from the moire pattern (a = 45°) that the moire pattern isn't symmetric when t e crack line isn't in the principal material direction, even if the structure and the force are symmetric. The displacement of crack tip is in mixed-mode, KI and KII exist simultaneously. From the moire pattern (a=45°), the orthotropic coupling effect is best explained.The test result shows that the sticking film moire interferometry can be not only used to test isotropic mitsrials but also orthotropic ones, therefore, this method can be spread to analyze the fracture of composite materials.