Implementation of strength-based failure criteria in the lamination parameter design space

Lamination parameters have proven to be exceedingly useful for the efficient design optimization of composite structures due to their continuous nature and flexibility in the final choice of stacking sequence with a reduced number of design variables. So far, failure criteria could only be incorporated into the lamination parameter design space for a predefined combination of fiber 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 fiber 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 optimization process. The derived strength envelope is then used to compare strength- and stiffness-based designs. The results clearly indicate that the degree of correlation between stiffness- and strength-driven designs depends on the properties of the material under consideration.