Assessment of damage tolerance in composites

Abstract

Damage tolerance to processing and normal service damage has been assessed for carbon epoxy coupons and built-up panels in uniaxial loading. In coupons, the low velocity impact damage is more severe than damage in holes, delaminations or porosity and it causes compression strength loss from 58% at the barely visible threshold to 73% at the easily visible threshold. Damaged coupon fatigue ( R = 10 ) S-N curves are relatively flat with 67% strength loss at 10 6 cycles for impact damage. In built-up panels representing multispar (M-S) and multirib (M-R) wing designs, again impact damage is more severe than delaminations and the impacted M-R design is stronger than the impacted M-S design. Damage in two adjacent M-S midbays and at the edge of the M-R stringer flange are the critical locations for impact, but damage area strongly depends on the panel configuration. Impact damage grows under constant amplitude fatigue ( R = 10 ) with peak load at 65% of damaged static strength for both M-S and M-R designs. Built-up configuration of the panels provides a significant increase in impact damage tolerance over that of coupons.