三维复合型疲劳裂纹扩展试验研究与数值分析

Experimental study and numerical analysis of three-dimensional mixed fatigue crack propagation

本文在MTS810试验机上进行了不同加载角度的有机玻璃三维Ⅰ-Ⅱ复合型疲劳裂纹扩展试验,通过显微镜记录试样的裂纹扩展过程,同时采用扩展有限元计算出有机玻璃三维Ⅰ-Ⅱ复合型裂纹尖端应力强度因子。结果表明,不同加载角度下的裂纹扩展方向基本与外载荷方向垂直,裂纹扩展路径近似为一条直线,且裂纹扩展角度值随加载角度的增大而增加,试验结果符合最大周向应力准则;在厚度方向上,Ⅰ型应力强度因子呈拱形分布,试样厚度中心Ⅰ型应力强度因子最大,由中心向两端逐渐降低,自由表面处最小,同时发现试验过程中裂纹也是从中心开始起裂,两者相符。Ⅱ型应力强度因子数值分布与Ⅰ型类似,趋近于自由表面时会发生微小突变,但其值总小于Ⅰ型应力强度因子,整个扩展过程中,Ⅰ型应力强度因子占主导。

Three-dimensional I-Ⅱ-type complex fatigue crack propagation tests of PMMA under different loading angles are conducted on the MTS810 test machine.Crack propagation process of sample is recorded by microscope.Using the extended finite element method,the stress intensity factor at the crack tips is obtained.The results show that under different loading angles,the crack propagation direction is perpendicular to the external load direction,and the initial extension path is approximately close to a straight line.The crack initiation angle increases with the increase of loading angle,consistent with the maximum circumferential tensile stress criterion.Along the thickness direction,I-type stress intensity factor is symmetrically distributed along the center line,and the largest stress intensity factor is located in the center of sample thickness,decreasing from center to both sides and reducing to the minimum value at free surface.It is found that the crack also starts from the center during the test.The numerical distribution ofⅡ-type stress intensity factor is similar to that of I-type,and tiny protrusions occur when approaching to the free surface,but the values ofⅡ-type stress intensity factor are always less than those of I-type stress intensity factor,and the I-type stress intensity factor is dominant during the entire process of extension.