Optimisation of damage tolerant structures using a 3D biological algorithm

Abstract The paper presents a methodology for shape optimisation of structures with fracture strength as the design objective. There have been limited applications of durability based optimisation to realistic structures. To overcome this, we present a 3D biological algorithm that uses fracture parameters as the design criteria. Damage tolerance optimisation is illustrated via the problem of optimal design of ‘a through-hole in a rectangular block under biaxial loading’. A wide range of 3D flaws were considered to investigate the effect of crack parameters on optimal shapes. It was found that the optimum hole shapes were approximately elliptical with the aspect ratios being dependent on crack sizes, structural geometry and boundary conditions. It has been shown that the fracture strength optimised shape can be quite different from the corresponding stress optimised solution. This emphasises the need to explicitly consider fracture strength as the design objective. In all cases, a significant reduction in the maximum stress intensity factor was achieved with the generation of a ‘near uniform’ fracture critical surface. The effect of crack aspect ratio on the optimal solutions was also investigated and it was found that the relative dominance of the stress intensity factors at the deepest and surface points of the cracks governs the optimal shapes. The design space near the ‘optimal’ region was found to be relatively flat. This is beneficial as a significant structural performance enhancement can be achieved without the precise identification of the local/global optimum solution.