Normalizing impact energy by face sheet thickness for composite sandwich structure compression after impact testing

Abstract

The amount of impact energy used to damage a composite laminate face sheet of a sandwich structure is a critical parameter when assessing residual compression strength. The compression after impact strength of impacted laminates used as face sheets on honeycomb core sandwich structure is dependent upon how thick the face sheet laminate is and this has traditionally been accounted for by normalizing (dividing) the impact energy by the laminate’s thickness. However when comparing compression after impact strength values for a given lay-up sequence and fiber/resin system, dividing the impact energy by the specimen thickness has been noted by the author to give higher compression after impact strength values for thicker face sheet laminates. A study was thus undertaken to assess the comparability of compression after impact strength data of sandwich structure by normalizing the impact energy by the face sheet thickness raised to a power to account for the higher strength of thicker laminates. Two data sets generated in this study were analyzed by dividing the impact energy by the face sheet thickness to the 1.0, 1.5, 2.0 and 2.5 powers. Results show that raising the face sheet thickness to a power of approximately 2.5 and dividing the impact energy by this quantity yields more comparable compression after impact strength data for comparing 8- and 16-ply face sheet laminates. For comparison of 24-ply face sheet laminates to 8- or 16-ply face sheet laminates, a value closer to 2 was found to give more comparable compression after impact strength data.