Elucidating the mechanisms of damage in foam core sandwich composites under impact loading and low temperatures

Abstract

Recent interest in Arctic exploration has brought new challenges concerning the mechanical behavior of lightweight materials for offshore structures. Exposure to seawater and cold temperatures are known to degrade the mechanical properties of several materials, thus, compromising the safety of personnel and structures. This study aims to investigate the low-velocity impact behavior of woven carbon/vinyl ester sandwich composites with Polyvinyl chloride (PVC) foam core at low temperatures for marine applications. The tests were performed in a drop tower impact system with an in-built environmental chamber. Impact responses, such as the contact force, displacement and absorbed energy, at four impact energies of 7.5 J, 15 J, 30 J, and 60 J were determined at four in-situ temperatures of 25°C, 0°C, −25°C and −50°C. Results showed that temperature has a significant influence on the dynamic impact behavior of sandwich composites. The sandwich composites were rendered stiff and brittle as the temperature decreased, which has a detrimental effect on their residual strength and durability. At 7.5 J at all temperatures, the samples experienced matrix cracking, fiber fracture, and delamination at the top face sheet. The samples impacted at 15 J at all temperatures experienced fiber fracture, matrix cracking, and delamination at the top facesheet and localized core crushing/fracture. At 30 J for all the temperatures, the samples exhibited perforation of the top facesheet and penetration into the core. As the temperature decreased, the penetration of the striker into the core increased. At 60 J for all temperatures, the samples experienced perforation of the top facesheet and core, and the back facesheet exhibited varying extent of damage. At −25°C and −50°C, the sandwich composite samples were almost completely perforated. In general, low temperatures rendered the sandwich composites stiff and brittle, resulting in an increase in the degree of damage and more pronounced damage modes. At all impact energies, the sandwich composites were rendered stiff and brittle as the temperature decreased, which has a detrimental effect on their residual strength and durability.