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.