An analytical model for the prediction of through-thickness stiffness in tension-loaded composite bolted joints

This paper presents the development of an analytical model for replicating the through-thickness stiffness of single-bolt, single-lap composite joints subjected to secondary bending. The model is an extension of a spring-based method, where bolts and laminates are represented by a series of springs and masses. The model accounts for extension of the bolt, the stiffness of the clamped region of the joint due to bolt torque, as well as the flexural stiffness and anticlastic curvature within the laminates. In order capture bolt extension and the stiffness of the clamped region, a closed form approach is used. An approximation approach is used to model flexural stiffness and anticlastic curvature within the laminates. The method is validated against detailed three-dimensional finite element models of bolted composite plates and good agreement was obtained. The method is subsequently employed to calibrate the through-thickness stiffness of single-bolt, single-lap joints in highly-efficient numerical models.