IMPACT AND POSTIMPACT BEHAVIOR OF FOAM CORE SANDWICH STRUCTURES

Low velocity, instrumented impact tests were carried out on sandwich p anels made of glass fiber reinforced plastic facings and polyvinylchlo ride foam core. Three different core densities and three core thicknes ses were examined. A damage parameter D was defined to account for the fiber damage size as evaluated through visual inspection. The experim ental results demonstrate that D depends only on impact energy, wherea s it is substantially independent of core density and thickness. An ex planation for this behavior is formulated on the basis of recorded imp act history. The results of tensile tests, performed to assess the res idual strength after impact of the facing material, were analyzed usin g a previous model, modified according to the findings of an experimen tal work carried out by Cantwell and Morton. A correlation is found be tween the strength loss determined by impact damage and artificially i mplanted circular holes. Accordingly, a procedure is presented to allo w for an accurate prediction of residual strength after impact as a fu nction of kinetic energy. Finally, it is shown that residual strength can be reasonably predicted on the basis of damage parameter D, althou gh in some cases this can result in a non-conservative estimate of the composite load-carrying capability.