On the low-velocity impact properties of CFRP/HAFRP interlayer hybrid fibre composite laminates

Hybrid fibre-reinforced polymer composites have been increasingly utilised in key engineering fields, such as the manufacture of aerospace structures, due to their high specific strength, stiffness, and design flexibility. This paper attempts to investigate the low-velocity impact performance and residual strength after impact of hybrid composites consisting of carbon fibre-reinforced polymer (CFRP) and heterocyclic aramid fibre-reinforced polymer (HAFRP). Since carbon fibres are brittle and vulnerable to impact loading despite their ultra-high strength, the aim of this study was to enhance the impact resistance of CFRP by hybridising it with high-toughness heterocyclic aramid fibres. The influence of hybrid layup configuration on the performance of both low-velocity impact and compression after impact (CAI) was explored. Four types of specimens, including pure CFRP and hybrid CFRP/HAFRP laminates with different layups, were manufactured and tested. Drop-weight impact tests were conducted on the specimens under impact energies of 25 J, 30 J and 40 J to measure the impact response, such as force-displacement and energy absorption curves. The internal impact damage was then assessed by ultrasonic C-scan method. The compressive strengths of specimens were measured both before and after low-velocity impact. The results indicated that hybrid laminates had better impact resistance than pure CFRP specimens, and the reduction in the compressive strength after impact for pure CFRP specimens was 24 times that of hybrid specimens. Therefore, hybridisation of heterocyclic aramid fibre with carbon fibre in composite laminates can retain high strength of carbon fibre while benefiting from the excellent fracture toughness of heterocyclic aramid fibre.