Topology optimization of adhesively bonded double lap joints

Current studies show great, but unutilized potential for mechanical optimization of adhesively bonded joints. There are different approaches, e. g. mixed adhesive joints; tapered adherends or joints with spew fillets, all of which try to redistribute the stress peaks, occurring at the ends of adhesive layer overlap, in favor to the load capacity. However, these investigations fail to take a general approach to find optimal geometric solutions to the problem of joining two materials by means of adhesive bonding. Instead the geometry is changed by predefined parameters such as tapering angles, spew fillet radii or the number of adhesives in mixed adhesive joints. To allow a non-parametric optimization, this paper proposes and investigates an extended bi-directional evolutionary structural optimization methodology based on a failure criterion to account for othotropic materials, which are often used in the context of bonding. The optimized joint geometry, generated by the proposed algorithm, resulted in a fairly constant distribution of elemental failure probability compared to the non-optimized state, thus eliminating underutilized spots of material and increasing the efficiency of the connection. Furthermore the influence of different parameters such as the overlap-length to adherend thickness ratio; the stiffness between adherend and adhesive as well as the adherend degree of orthotropy were investigated for optimal joint geometry.