Implementation of Strength-Based Failure Criteria in the Lamination Parameter Design Space

Lamination parameters have proven to be exceedingly useful for ecient design optimisation of composite structures due to their continuous nature, and flexibility in final choice of stacking sequence with reduced number of design variables. So far, failure criteria could only be incorporated into the lamination parameter design space for a predefined combination of fibre angles. This drastically limits the design space available to the designer. This paper investigates incorporating the Tsai-Wu failure criterion into the lamination parameter design space in the most general setting. A conservative failure envelope is derived that guarantees a failure free region of the lamination parameter space regardless of the fibre orientations in the laminate stacking sequence. The proposed approach allows strength criteria to be included both as a constraint as well as an objective function during the optimisation process. The derived strength envelope is then used to compare strengthbased and stiness-based designs. It is shown that for several composite materials, the strength and stiness driven optima appear to coincide exceptionally well, especially for unbalanced designs. Thus confirming the intuitively accepted equivalence between strength and stiness driven optimisation.