This paper tries to conjugate an improvement of stiffness and delamination damage resistance. A number of published results allow us to guess the existence of fibre orientations that are a good compromise for an optimal absorption of the incoming energy and for maintaining of a high stiffness. Optimal absorption is herein intended as a way not involving weak properties, such as interlaminar strength. We seek for an optimal orientation of reinforcement fibres through definition of stationary conditions for bending and shear energy contributions under in-plane variation of plate stiffness coefficients. Our goal is to tune the energy absorption as desired. Two kinds of optimized layers are studied, that are compatible with current production technologies: type 1 reduces bending without substantially increasing the transverse shear stresses, type 2 reduces transverse shear stresses without substantially increasing deflections. Incorporation into the laminates of couples of these layers with opposite features and the same mean properties of those they substitute allows an energy transfer from an unwanted to a wanted mode, as shown by the numerical applications. In this way, the deflections and the stresses inducing delamination damage of laminates subjected to impact and blast pulse loads were reduced, while damping should not substantially change since the variation of the orientation of fibres lies in a range where mild variations of it are induced.
Parameter studies and evaluation principles of delamination damage in laminated composites
