Experimental determination of elastic properties of impact damage in carbon fibre/epoxy laminates

This paper describes an investigation of in-plane elastic properties of imp act damaged regions in composite laminates. Quasi-isotropic carbon fibre/ep oxy laminates were impacted and the impact damage examined by ultrasonic C- scanning, optical microscopy and thermal deplying. After impact damage obse rvations, specimens were cut from the laminates and tested in tension and c ompression. The elastic modulus of the impact damage was, in both tension a nd compression, mainly controlled by the amount of fibre breakage. Interest ingly, layers with broken fibres could sustain some load in compression, wh ich led to higher elastic modulus in compression than in tension. The effec t of delaminations on the elastic modulus was quite small in both tension a nd compression. The through-the-thickness variation of in-plane stiffness w as studied by successively removing plies. The variation in stiffness was n egligible, probably as a result of the very uniform distribution of delamin ations and fibre breakage through the thickness of the laminates. (C) 2001 Elsevier Science Ltd. All rights reserved.