Influence of liquid shim on the bearing strength of a composite bolted joint

Abstract: The objective of this thesis has been to investigate the effect a liquid shim has on the bearing strength of a composite bolted joint. The shim is necessary to close gaps that occur during the assembly of the joints, preventing the structural parts from being fastened correctly. The shim however increases the load eccentricity of the joint and will have a negative effect on the joint strength, but the significance of this weakening is not well understood.This thesis primarily focuses on a parametric finite element study on the effect the liquid shim has on the bearing of both a homogenised carbon fibre/epoxy model and a fully detailed laminate model based upon the same material. Parameters studied were the plate and shim thicknesses, lateral support, number of fasteners, bolt pre-tension and bolt diameter and the relative strength decreases were documented.A literature study was also conducted to consider previous results concering the strength change due to the inclusion of a shim. It was found that the results show a large spread dependent on material system, geometry and assumptions regarding numerical behaviour. The finite element simulation was compared with the results from these studies, showing fairly good agreement.The analysis conducted has shown that there is a major increase in stress and strain on the bearing surface because of the shim. Moreover, it is shown that this strength reduction is dependent on both model and parameters studied, which necessitates experimental testing in order to verify which is the more applicable for future methodology.