Repair effectiveness studies on impact damaged sandwich composite constructions

Experimental studies were carried out using sandwich composite panel specimens, consisting of both polyurethane foam core (PUF) and aramid honeycomb core (Nomex) type constructions. These specimens were subjected to impact damage at energy levels ranging between 7.56 and 15.6J. A ply-drop-patching technique was employed to repair the impact damaged sandwich specimens. The undamaged (virgin), impact damaged, and repaired specimens were then subjected to flexural (four point bending) and edgewise compression tests and strength recoveries were measured to determine the efficacy of the repair technique employed. In flexure, strength recoveries of up to 97% in PUF core and 90% in honeycomb core sandwich specimens were realized after repair, whereas in compression, the corresponding values were up to 90% in PUF core and 88% in honeycomb core sandwich specimens. A repair effectiveness factor (R-ef) has been conceived and introduced to quantify the efficiency of the repair technique. Further, the repair quality was assessed using a simple NDT method prior to subjecting the sandwich specimens for destructive tests.