碳纤维增强复合材料沉头螺栓搭接结构强度及渐进损伤分析

Analysis of structural strength and progressive damage of countersunk bolt lap joint with CFRP

碳纤维增强复合材料(CFRP)因其优异的力学性能在航空工业中得到了广泛的应用,评估复合材料沉头螺栓连接结构的极限承载和损伤扩展对航空器连接结构的经济性和安全性意义重大。本文首先创建复合材料沉头螺栓搭接三维模型,并采用虚拟热变形法施加螺栓预紧力,然后利用Fortran语言编写VUMAT用户自定义程序,将所选的刚度退化模式与3D Hashin失效准则嵌入渐进损伤模型中,建立有限元损伤预测模型,研究不同搭接端距对复合材料沉头螺栓连接结构失效的影响。研究结果表明:搭接端距主要影响连接结构的剪切强度,端距越小,其极限承载强度越小,当搭接端径比达到2.5时,极限承载强度随着端径比的增大变化较小;基体拉伸损伤首先出现在最底层的0°铺层,纤维压缩损伤首先出现在锪孔和直孔转折处,失效单元沿施载方向扩展至自由边界失效。

Carbon fiber reinforced polymer(CFRP)has been widely used in aviation industry due to its excellent mechanical properties.It is of great significance to evaluate the ultimate load and damage propagation of composite countersunk head bolt joints for the economy and safety of aircraft joints.In this paper,a three-dimensional model of composite countersunk head bolt lapping is established,and the pre-tightening force of the bolt is applied by virtual thermal deformation method,then the VUMAT user-defined program is written in FORTRAN language though finite element simulation.The selected stiffness degradation mode and 3 D Hashin failure criterion are embedded into the progressive damage model to establish the finite element damage prediction model,and study different lap end distance on the composite material single screw countersunk bolt connection structure failure.The results show that the lap end distance mainly affects the shear strength of the connection structure.The smaller the end distance is,the smaller the ultimate bearing strength is.When the short diameter ratio of the lap joint reaches 2.5,the ultimate bearing strength changes little with the increase of the end diameter ratio.The tensile damage of the matrix first appears in the 0°ply of the bottom layer,the fiber compression damage first appears in the turning point of the countersink and straight hole,and the failure element expands along the loading direction until the free boundary fails.