Assessment of ageing effect on the mechanical and damping characteristics of thin quasi-isotropic hybrid carbon-Kevlar/epoxy intraply composites

Abstract

Hybrid polymer laminates employed in advanced engineering fields are susceptible to atmospheric conditions, such as moisture and temperature throughout their service life, which may impact their mechanical and damping properties. This research focuses on the influence of three distinct environmental situations: ambient ageing at 25°C, sub-zero ageing at −10°C, and environmental chamber humid ageing at 40°C with 60% RH (relative humidity) on the mechanical and damping characteristics of quasi-isotropic carbon-Kevlar fibre reinforced intraply hybrid composites. Compression molding process was incorporated for the fabrication of the laminates and specimens were aged until the moisture saturation point was reached. The mechanical and vibrational properties of post-aged specimens, including tensile, three-point flexure, short-beam shear strength (SBS), and hammer impact tests, were investigated and compared with pristine specimens. The results showed that the experimental degree of moisture absorption closely followed the Fick’s first law, with a greater moisture diffusion rate in the early phase of ageing and moisture saturation in the laminates were ranging from 1.162% to 4.167%. The study also unveiled that diffusion of moisture has a negative impact on the mechanical and vibrational behaviour of the composites. Mechanical strength deterioration was discovered to be highest in the ambient aged specimens followed by humid and sub-zero aged specimens. To evaluate the damage morphology, post-tensile test coupons were analysed by employing a Scanning Electron Microscope (SEM). The predominant failure mechanisms found in aged composites were fibre fractures, interfacial degradation due to matrix deterioration, matrix cracks, and delamination.