Laminated and sandwich panels subject to blast pulse loading

A recently developed optimisation technique is employed for relaxing the interlaminar stress concentration of laminated and sandwich flat panels undergoing impulsive pressure loading. We determine the through-the-thickness distribution of the core properties of sandwich panels and the in-plane distribution of the stiffness properties of their face sheets, as well as that of the constituent layers of laminates maximizing the energy absorbed through wanted modes (e.g., membrane and bending contributions) and minimizing the energy absorbed through unwanted modes (e.g., interlaminar shears). As a structural model, we employ a refined zigzag model with a piecewise high-order variation of in-plane and transverse displacements that fulfils a priori the interfacial stress and displacement contact conditions. The zigzag model, a characteristic feature of the method, is incorporated through a strain energy updating into a conventional shear deformable plate element, for the sake of reducing the computational effort required for accurately computing the stresses. The dynamic equations are solved using the Newmark implicit time integration scheme; various pulse pressure time histories are employed. Simple, suboptimal distributions of reinforcement fibres and core density compatible with current manufacturing processes are considered in the numerical applications. It appears that these distributions can effectively reduce the critical interlaminar stress concentration under impulsive loadings, with beneficial effects on the strength at the onset of damage, and improve the dynamic response properties as well.