Validated Analysis Method for Bolted Composite Lap Joints

Abstract

This study presents a validated analysis method to determine the stress field and bolt load distribution in single- and double-lap joints. The joints are made of composite laminates and metals. The solution procedure accounts for the variation of stresses in the thickness direction by augmenting a two-dimensional analysis with a one-dimensional through-the- thickness analysis. The combined in-plane and through-the-thickness analysis produces the bolt/hole displacement in the thickness direction, as well as the stress state in each ply. The two-dimensional in-plane solution method based on the combined complex potential and variational formulation satisfies the equilibrium equations exactly, and satisfies the boundary conditions and constraints by minimizing the total potential. Under general loading conditions, this method is applied to various bolt configurations without requiring symmetry conditions while explicitly accounting for the contact phenomenon and the interaction among the bolts. It provides accurate contact stresses and contact regions, as well as the bolt load distribution, as part of the solution procedure. It is capable of accounting for finite laminate planform dimensions, laminate thickness and lay-up, interaction among bolts, bolt flexibility, bolt size, and bolt-hole clearance. The through-the-thickness analysis is based on the model of a beam on an elastic foundation. The bolt represented as a short beam rests on springs where the spring coefficients represent the resistance of the composite laminate to bolt deformation. Validation of the model is demonstrated by considering single- and double-lap joints of metal plates bolted to composite laminates.