Analysis of bolted-bonded composite lap joints

Bolted, bonded, and hybrid bolted/bonded joints are three-dimensional in nature. Although the finite element method (FEM) is capable of addressing such joint configurations, it requires considerable computer resources, especially in the presence of multiple bolts. The presence of unknown contact regions between the bolts and laminates and the small length scale of the adhesive thickness require a fine mesh to achieve a reliable prediction of the stress field. Therefore, the identification of the critical design parameters and optimization of the joint strength have become a computational challenge with the finite element method. The present study presents a semi-analytical solution method that permits the determination of point-wise variations of displacement and stress components in singlelap bolted/bonded joints of composite laminates under in-plane as well as lateral loading. The derivation of governing equations of equilibrium of the joint is based on the principle of virtual work, where the displacement fields in the laminates are represented by local and global functions that are not required to satisfy the kinematic boundary conditions directly. The representations of the laminate and bolt displacements are based on the Mindlin plate theory and three-dimensional Timoshenko beam theory, respectively. For the adhesive, the displacement field is expressed in terms of those of laminates by using the shear-lag model to approximate both shearing and peeling deformations; hence, no assumed displacements are necessary for the adhesive.