含多部位损伤搭接结构应力强度因子三维有限元分析

应力强度因子(Stress intensity factor,SIF)分析是含多部位损伤(Multiple site damage,MSD)结构剩余强度和裂纹扩展寿命预测的基础和关键。考虑接触与摩擦,建立了含MSD搭接结构的三维有限元模型,研究了不同裂纹长度、铆钉类型以及损伤模式下裂纹尖端SIF分布情况和变化规律。结果表明,搭接件孔边裂纹Ⅰ型SIF起主导作用,Ⅱ型和Ⅲ型SIF可忽略不计。由于次弯曲、铆钉变形和板厚度等因素,SIF在外表面最小,接触面一侧较大,最大值多位于蒙皮内部。MSD会使裂纹间的干涉作用增强,SIF增大,且裂纹间距离越近干涉作用越强。裂纹长度相同时,埋头铆钉的孔边裂纹SIF积分均值大于平头铆钉,且接触面的SIF埋头铆钉大于平头铆钉,外表面则相反。

Three-Dimensional Finite Element Analysis of Stress Intensity Factors of Lap Joints with Multiple Site Damage

Stress intensity factor (SIF) is the foundation and key of predicting the residual strength and fatigue crack growth for structures with multiple site damage (MSD). Considering the contaction and friction, three-dimensional finite element models of lap joints with MSD are established. The distribution and variation of SIFs at each crack tip with different crack lengths, rivet types and damage modes are investigated. Results show that K_I is dominant, while K_II and K_III are negligible. Due to the secondary bending, rivet deformation and plate thickness, the SIF reaches minimum at outside surface, and the faying surface side is larger, while the maximum is located in the plate for almost all crack length. The SIFs values increase substantially due to the interaction of MSD cracks. The shorter the distance between cracks, the stronger the interaction. When the crack length is the same, the integral average value of SIFs along the crack front for the countersunk rivet is larger than that of the flat head rivet. The SIF value at the faying surface of countersunk rivet is larger than that of the flat head rivet, while the trend of SIF at the outside surface is opposite.