Low-energy impact effects on candidate automotive structural composites

The objective of the work described in this paper was to experimentally characterize the susceptibility of three candidate automotive structural composites to incidental, low-energy impact damage. The composites, each of which had the same urethane matrix, were produced by a rapid molding process suitable for high-volume automotive applications. The reinforcement for the first composite was a random chopped-glass fiber, while the remaining two were reinforced with stitch-bonded carbon-fiber mats, one in a crossply layup, and the other in a quasi-isotropic layup. A pendulum device, representative of events such as tool drops, and a gas-gun projectile, representative of events such as kickups of roadway debris, were used to impact plate specimens. Brick-drop tests were also performed to assess the applicability of the baseline pendulum and gas-gun data to other events. Following the impacts, the damage areas were measured and the plates were cut into either tensile, standard compressive, or compression-after-impact specimens for determining strength degradation. The glass-fiber composite was least susceptible to damage, followed by the crossply carbon-fiber laminate, which had the same thickness. The quasi-isotropic carbon-fiber composite, which was thinner than the other two, sustained the most damage. While compressive strength was significantly degraded by moderate damage in the random-glass-fiber composite, tensile strength was not. On the other hand, both tensile and compressive strengths were degraded in the crossply carbon-fiber laminate (only compressive strength loss was measured in the quasi-isotropic laminate). Compressive strength degradation for a given damage area was similar in the two carbon-fiber laminates. Both showed lesser degradation than did the glass-fiber composite. For the quasi-isotropic carbon-fiber laminate, it was shown that strength degradation produced by an open circular hole provides a reasonable lower bound to the degradation due to an impact damage area of the same size.