Minimum mass laminate design for uncertain in-plane loading

Balanced laminates, with zero in-plane to out-of-plane stiffness coupling are optimised over a range of tri-axial (Nx, Ny and Nxy) critical design loadings for minimum normalised elastic energy; equivalent to optimising for minimum mass in the absence of matrix failure. Laminates comprising standard angle plies (0, ±45 and 90) are designed for either a fixed design loading with a 10% minimum ply percentage rule (current practice) or directly for an uncertain design loading. Results show that the 10% rule performs well for the majority of design loadings. Nevertheless, for 8% of design loads considered, significantly lower mass (>10%) designs are achieved with standard angle plies when designing directly for uncertain loading. Expansion of the ply envelope to include designs with continuous angles (0° ≤ θ ≤ 180°) under an uncertain loading allows maximum mass savings up to 16% over current design practice. However, when designing directly for an uncertain loading, no significant mass reductions are achieved through the use of continuous angles.