Bonded metallic inserts for bolted joints in composite laminates

The use of adhesively bonded metallic inserts as a technique to improve the behaviour of bolted joints in composite laminates is investigated. A stress-failure analysis based on a three-dimensional finite element model including bolt-insert contact analysis, damage prediction in the laminate and the elastoplastic behaviour of the adhesive is performed. The effects of the insert material and thickness on the performance of the joint are determined. It is concluded that the use of bonded metallic inserts redistributes the stresses acting on the laminate's hole, thus reducing the stress concentration factors. However, for the configuration investigated, failure in the adhesive is predicted before the full strength of the laminate is used, and this effect can justify the experimental results, showing a small, if any, strength improvement when inserts are used.