Impact damage resistance and tolerance of high-performance polymeric composites subjected to environmental aging

This study investigates the impact damage resistance and tolerance of two high-performance polymeric composite systems after exposure to environmental aging. The material systems under study were IM8/954-2, a thermoplastic-toughened cyanate ester thermoset resin reinforced with graphite fibers and IM8/ITX, a semicrystalline thermoplastic resin reinforced with graphite fibers. [0] 8s unidirectional composites and [+45 −45] 2s cross-ply composites were tested in the experimental program. Specimens were aged at 150 °C in two different environments (ambient atmospheric air and inert nitrogen gas) for periods of up to 18 months prior to testing. Impact tests were conducted at impact velocities (V i) of 6.3, 10.1, 14.6, 19.8 and 254 m s −1 by using a gas-gun. The damage area was evaluated by C-scan and X-radiography techniques and resistance to damage evaluated by the threshold velocity, V c and damage area growth rate, C. In both the unidirectional and cross-ply composites, damage increased progressively with aging time. Aging environment also had a significant effect on damage resistance, as shown by the fact that specimens aged in nitrogen for 18 months had equivalent damage to those aged in air for only 2 months. Tension-after impact (TAI) strength tests were also conducted on the cross-ply composites. Strength values fell by as much as 70–75% of original tensile strength in both material systems and were dependent on variables such as aging time, aging environment and impact velocity.