Structural efficiency via minimisation of elastic energy in damage tolerant laminates

Genetic Algorithm and exhaustive search techniques identify balanced symmetric stacking sequences that minimise elastic energy to produce optimal structural efficiency under combined loading. Constraints are added to account for use of standard ply angles, laminate design rules and damage tolerance. The damage tolerant strength constraint produces a bilevel optimization problem: surface plies are orientated to sufficiently minimise energy available for sublaminate buckling driven delamination propagation; core plies are orientated to maximise stiffness in response to a uniaxial load case. The proposed methodology demonstrates that current, standard ply angle, aerospace designs can be near optimal for undamaged strength. However, continuous angles and relaxation of design rules offer significant scope for improved damage tolerance.