Mechanical Behavior of Composite Sandwich Structures Subjected to Impact Damage

摘要

The compression strength of composite sandwich panels subjected to drop-weight impact damage was determined as part of an ONR-sponsored research program. A total of twenty-four specimens were tested including four control panels, which contained no impact damage. The remaining twenty specimens had varying levels of impact damage. Three impact energy levels were tested; 6 ft-lbs, 20 ft-lbs, and 35 ft-lbs, where 6 ft-lbs represents a low energy level and 20 and 35 ft-lbs both represent high energy levels in combination with two impactor sizes, 0.5 in and 1.0 in diameter. Each panel was manufactured using fiber placement technology and consisted AQII/977-3 Astroquartz/Epoxy upper and lower face sheets and HRP/F50-5.5 Flexcore core. Panel specimens were tested under edgewise compression in accordance with ASTM C-364 using a 50-kip SATEC universal testing machine. Results show that impact energy level has a strong effect on both the compressive strength and failure mode of the panel specimens while limited data for impactor size suggests that this factor is much less important. Specifically, the compressive strength decreases with an increase in impact energy level. Edgewise compressive failure of undamaged quartz/epoxy honeycomb sandwich 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 20 ft-lbs of impact energy causes the failure to be progressive in nature and a 15% drop in the compressive strength. Even greater impact damage (35 ft-lbs) leads to catastrophic skin/core interfacial failure due to initial impact damage of the skin/core interface (unseen by visual inspection). Failure by face sheet separation (35 ft-lbs) leads to a 37% drop in the compressive strength.