Impact damage of partially foam-filled co-injected honeycomb core sandwich composites

The present study considers filling of honeycomb type cores with foam to produce sandwich constructions. The potential benefits of this approach are enhancement of damage resistance, and ability to process honeycomb type sandwich structures through cost-effective vacuum assisted resin transfer molding (VARTM). As weight penalty is incurred in complete filling of honeycomb cells with foam, an alternative approach to reduce weight is partial filling of the cells, without losing the advantage of VARTM processing of the core.. Two cores are considered, a polyurethane foam for full filling of honeycomb cells, and syntactic foam for partial filling, in conjunction with carbon-epoxy facesheets. Their impact response was investigated under low and high velocity impact (LVI and HVI respectively). For both cores, the foam filling was found to provide confinement to the cells. The resistance to penetration, energy absorbed and damage modes in LVI and HVI were a function of core stiffness, extent of filling and number of facesheet plies. The results illustrate that partial syntactic foam filled sandwich plate (with reduced weight penalty in comparison to full filling) can provide LVI response improvement in the order of 56% increase in peak load, and for HVI about 74% improvement in ballistic limit.