On the optimization of single lap metal/plastics adhesive joints

Adhesive joints offer an interesting solution to the problem of connecting a plastic composite plate to a metallic frame. This is, for example, the case of the doors for the baggage compartment of the buses, where the external sheet can be made by composite plastic, while the frame must be metallic in order to include the hinges and the handle. The design of this type of adhesive lap joint offers interesting possibilities for optimisation and several authors have already proposed the use of adhesive spews (i.e. shoulders of adhesive connecting the unloaded ends of the adherends) and, eventually, of chamfers at the ends of the adherends to reduce stress concentrations. Considering an hybrid joint between steel and FRP, this paper analyses in detail the effect of such solutions on the stress field, in order to identify the optimal condition and to assess design rules. It has been found that spew angles of about 45 degrees are sufficient to obtain a considerable reduction of the stress peaks.