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.

Mechanical Response of Fiber-Filled Automotive Body Panels Manufactured with the Ku-FizzTM Microcellular Injection Molding Process

“…The compact specimen exhibited a sharper drop in the post-peak regime, which indicates higher damage as higher energy is dissipated over a short global deformation (Figure 16a). Open curves without rebound can be seen for all tests, indicating the complete penetration and perforation of both types of samples [63,64].…”

“…Based on the force-displacement responses, the equivalent impac stiffness was 222 N/mm and 310 N/mm for foamed and compact parts, respectively. The compact specimen exhibited a sharper drop in the post-peak regime, which indicate higher damage as higher energy is dissipated over a short global deformation (Figure 16a) Open curves without rebound can be seen for all tests, indicating the complete penetration and perforation of both types of samples [63,64]. Average tanδ values of 0.0391 and 0.0394 were found for foamed and compact conditions, respectively, over the tested frequency range.…”

Crushable polymer foam behavior at cold temperatures

“…These results were later confirmed by Castellanos and Prabhakar. 5 While the aforementioned studies addressed foam-core sandwich panel behavior, there has been very little research concerning the low temperature behavior of Divinycell foams specifically. In some recent experiments, 6 we found that Divinycell H-foams undergo a ductile-to-brittle transition when temperatures are around À50°C.…”