RESIDUAL STRENGTH OF IMPACT DAMAGED COMPOSITE SANDWICH STRUCTURES

摘要

The compression strength of fiber placed quartz/epoxy honeycomb sandwich panels subjected to impact damage was determined as part of an ONR-sponsored program. A total of twenty-four specimens were tested including four undamaged control panels and twenty panels with varying levels of impact damage. Three impact energy levels were tested (8.1 N-m, 27 N-m, and 47 N-m) using two impactor sizes. Panel specimens were tested under edgewise compression in accordance with ASTM C-364. Experimental results show that impact energy level has a strong effect on both the compressive strength and failure mode. Specifically, the compressive strength decreases with an increase in impact energy level. Edgewise compressive failure of undamaged panels is by catastrophic fiber/matrix interfacial cracking of the face sheets combined with bending-induced fiber breaks. Low impact damage as characterized by visible matrix cracking results in an insignificant change in failure mode and load. An increase to 27 N-m of impact energy causes the failure to be progressive in nature and a 15% drop in the compressive strength. Even greater impact damage (47 N-m) leads to catastrophic skin/core interfacial failure due to initial impact damage of the skin/core interface and a 37% drop in the compressive strength.