Post-impact behaviour of aerospace composites for high-temperature applications: experiments and simulations

The post-impact performance of different carbon-fabric-reinforced composite materials were studied experimentally and analytically. Three types of thermosetting matrix were considered: conventional epoxy, high-temperature curing epoxy and epoxy-isocyanate. Experimental testing consisted of impacting rectangular specimens at different energy levels by using a spring-driven impact apparatus that was able to impart velocities of up to 5 m s⁻¹ to masses of 0.5, 1.0, 2.5 and 5.0 kg travelling horizontally. After impact, coupons were non-destructively inspected by means of opaque-enhanced dye-penetrant X-radiography and tested in static compression to correlate impact energy, damage extent and residual strength. Epoxy composites contain damage within a narrow region, while epoxy-isocyanate materials propagate the damage far away from impact point. Epoxy composites show an asymptotically decreasing failure strength with impact energy up to a lower threshold (0.3–0.4 times that of the undamaged material), while epoxy-isocyanate material shows a trend of ever decreasing residual strength. An analytical study was performed by means of the finite element code PAM-FISS, used to simulate the compression-after-impact (CAI) tests. Type, size and location of damage, as well as the mechanisms leading to final failure, were reproduced quite well by the finite element analysis (FEA), while some discrepancies between FEA and experimental CAI residual strength tests were found (7% for undamaged specimens and 10% for blister-delaminated specimens); higher errors were found in the case of completely delaminated specimens, mainly owing to the inability of the present software and hardware to conveniently model the complete state of damage.