IMPACT AND POSTIMPACT BEHAVIOR OF FOAM CORE SANDWICH STRUCTURES

Low velocity, instrumented impact tests were carried out on sandwich panels made of glass fiber reinforced plastic facings and polyvinylchloride foam core. Three different core densities and three core thicknesses were examined. A damage parameter D was defined to account for the fiber damage size as evaluated through visual inspection. The experimental results demonstrate that D depends only on impact energy, whereas it is substantially independent of core density and thickness. An explanation for this behavior is formulated on the basis of recorded impact history. The results of tensile tests, performed to assess the residual strength after impact of the facing material, were analyzed using a previous model, modified according to the findings of an experimental work carried out by Cantwell and Morton. A correlation is found between the strength loss determined by impact damage and artificially implanted circular holes. Accordingly, a procedure is presented to allow for an accurate prediction of residual strength after impact as a function of kinetic energy. Finally, it is shown that residual strength can be reasonably predicted on the basis of damage parameter D, although in some cases this can result in a non-conservative estimate of the composite load-carrying capability.