Experimental and analytical strength analysis of double-lap joints for marine applications

Weight-critical marine structures, such as high-speed craft, are often made of high-strength aluminium, and the usual joining method is welding. To improve the performance of high-speed craft there is a tendency to seeking lighter weight materials, especially in parts of the structure where weight-saving is particularly beneficial, such as in the superstructure. Light-weight materials can be fibre-reinforced composites. When joining structures made of composites to components of aluminium or steel, welding is no longer an option. On the other hand, adhesive bonding becomes an attractive joining method. Thus, there is a need to investigate the strength of bonded steel-composite joints.In the present paper, the stress distribution and strength of bonded double-lap steel-composite joints are investigated through theoretical analysis and experimental testing. The strength of a set of joints, with a variety of overlap lengths and two different bonding techniques and environmental conditions, has been measured experimentally. Furthermore, a new elastic–plastic stress analysis, accounting for adhesive shear deformations as well as axial and shear deformations in the adherends, has been derived.Predictions using the new theory derived herein as well as linear models are compared with the reported results. It is clearly demonstrated that linear theories are completely inappropriate for modelling such joints when loaded to failure. On the other hand, the strength predictions obtained by the new nonlinear theory agree well with the experimental results.