A new tailoring optimization approach for improving structural response and energy absorption capability of laminated and sandwich composites

In this paper a technique for tuning the energy absorption properties of laminated and sandwich composites through a new tailoring concept is presented. The purpose is to minimize the energy absorbed through unwanted modes (ones involving interlaminar strengths) and maximize that absorbed through desired modes (ones involving membrane strengths) by finding a suited in-plane variable distribution of stiffness properties. Herein mode is intended as a strain energy contribution, such as bending energy, in-plane and out-of-plane shear energy, etc., and no vibration mode. This distribution is obtained making extremal certain strain energy contributions of interest (for example, membrane, bending, in-plane, and out-of-plane shear energies) under in-plane variation of the plate stiffness properties. The effect of this technique is to act as an energy absorption tuning, since it minimizes or maximizes the amount of energy absorbed by specific modes. Although the present technique could be applied to laminates or to the face sheets of sandwich composites, in this paper a preliminary application is presented to single plies with variable stiffness coefficients over their plane. Once incorporated into a laminate or a sandwich composite, these layers are shown to have beneficial effects on the strength at the onset of delamination in sample cases where laminated and sandwich composites are subjected to low velocity, low energy impacts.