Impact Behavior of Carbon Fiber/Epoxy Composites and Fiber Metal Laminates with Open Holes

Abstract

This paper describes an experimental investigation performed to evaluate the low-velocity impact behavior of prepreg-based carbon fiber reinforced polymers (CFRPs) and fiber metal laminates (FMLs) with and without open holes subjected to different impact energies. The laminates were made of carbon fiber/epoxy prepregs and aluminum layers and manufactured by using autoclave. The impact responses of these laminates were experimentally obtained using a drop-weight tower at impact energies of 15, 20 and 30 J. After testing, the impact damage area of tested specimens was quantified from C-scan ultrasonic technique. In addition, an X-ray tomography analysis was performed to assess the through-thickness distribution of damage in FMLs with and without open holes. The results showed that the woven FMLs exhibit the highest impact peak force compared to that of CFRP plates due to the presence of aluminum layers, which induce a higher deformation capability to the laminates. The presence of open holes in laminates tends to augment their damage extension and decreases their impact peak force due to the local stress concentration effect. Nevertheless, it was observed by C-scan ultrasonic images that the aluminum layers reduce the extent of delamination of laminates during the impact event. Postimpact evaluation using X-ray computed tomography showed that impact causes a severe damage to the laminates around their impact point and confirmed that matrix cracking and delamination are the principal damage mechanisms induced on the through-thickness direction of the FML plates. In specific, the results confirm that the aluminum layers provide good impact properties and damage resistance when they are added to the CFRPs.