Effects of porosity on ultrasonic attenuation coefficient, shear properties and failure mechanisms of CF/EP laminates

Abstract

Carbon fiber reinforced epoxy composite (CF/EP) laminates with porosity ranged from 0% to 2.5% were prepared under inadequate curing pressures, and then applied to ultrasonic, metallographic and mechanical testings. Porosity was evaluated using an ultrasonic attenuation model, which was established by taking consideration of surface losses, material attenuation coefficient and void attenuation coefficient. Shear properties were determined via short beam shear (SBS) method and porosity-related failure mechanisms were characterized using ultrasonic B-Scan and metallographic analysis. The results show that there is a third-order polynomial correlation between porosity level and ultrasonic attenuation coefficient. The shear strength approximately drops by 15%, 30%, 40% and 45% with porosity level up to 1.0%, 1.5%, 2.0% and 2.5% respectively. The detrimental effects of Porosity can be attributed to the reduced bonding area between plies or among fiber-resin area as well as the crack initiation and propagation.