Flexural analysis of balsa core sandwich composite: failure mechanisms, core grain orientation and padding effect

A comprehensive investigation was undertaken to study failure mechanisms of sandwich composites and their influence on flexural behavior (load-displacement curve). Sandwich composite panels were cured from compression thermoforming of E-glass/epoxy skins and a low density balsa wood core. Balsa core grain orientation is found to have major effect on flexural response and failure modes. Flexural behavior, failure mode and its sequence varies with different core grain orientations. Indentation, skin failure, core shear failure were dominant failure modes observed for various cases. Skin-core interface adhesion was reasonably good, as delamination was not the first failure mode in sandwich beam with balsa core. Indentation of skin is a major concern under localized loading, as the skin failure is premature as compared to its normal compressive strength. Hence, the effect of padding on sandwich beam with soft core was also completed as part of this work. Finite element analysis for modeling this type of sandwich composite beam is conducted using LS-Dyna. Several material parameters required for finite element analysis were determined from extensive testing and data from literature. Composite failure model and wood material model available in LS-Dyna were applied for skin and core of sandwich beam. At the skin-core interface, nodes were merged as delamination was not a prominent failure mode. Flexural analysis response from FEA shows good correlation with experimental behavior