Minimum-mass optimisation for high-rate manufacture of damage tolerant and unbuckled composite components

A significant increase in the rate of composite manufacture is needed to meet demand for short-range commercial aircraft. The enabling automated manufacturing processes can, however, induce undesirable process features such as wrinkles. Additionally, the potential for Barely Visible Impact Damage has resulted in widespread use of overly-conservative strain allowables which has led to overweight aircraft structures. Two new constraints are presented which enable formability and damage tolerance to be incorporated into a two-stage minimum-mass optimisation framework for performance and manufacturability. An efficient, approximate method is presented for determining a conservative lower bound on the strain required to propagate a single, circular delamination, given a general through-thickness position and an upper bound on delamination size. A Compatibility Index is used to predict the propensity for wrinkles to occur during a forming manufacturing process. Optimised stacking sequences for two benchmark design problems; a flat plate and blade-stiffened panel, are obtained subject to minimum formability, damage tolerance and buckling constraints alongside common industry design rules. The damage tolerance and formability constraints are met for a diverse set of design requirements, without increasing mass or reducing buckling load, thereby demonstrating that components may be optimised for manufacture using high-rate processes without detriment to performance.