Anisotropic Compressive Behavior of Rigid PVC and PES Foams at Elevated Strain Rates Up to 200 s-1

In this study, closed cell polyvinyl chloride (PVC) foam with five different densities ranging from 45 to 200 kg/m3, and polyethersulfone (PES) foam with three different densities ranging from 50 to 130 kg/m3, were subjected to compressive loading under quasi static and elevated strain rates for mechanical material assessment. Three orthogonal loading directions, (i.e., parallel and perpendicular to foam rise directions) were considered to investigate structural anisotropy. The elevated strain rate tests were performed using a customized drop tower device at three different strain rates of 50, 100, and 200 s-1. Engineering stress/strain behavior, energy dissipation, and maximum stress capacity were obtained for each density and compared against each other. Experimental results indicated that elastic modulus, compressive strength, plateau stress, and energy absorbing capacity of both PVC and PES foams were highly dependent on foam density. Except for the PVC foam with the lowest density of 45 kg/m3, strain rate effects were clearly observed through increased compressive strength and plateau stress when loading in the foam rise direction for both PVC and PES foams. The strain rate effect was more evident at higher densities. When loading perpendicular to the foam rise direction, no significant strain rate effect was observed for PVC foam. However, a slight strain rate effect was observed for PES foam at the highest density of 130 kg/m3 in one of the perpendicular to foam rise directions. Scanning electron microscopy (SEM) analysis showed that the cell wall thickness of both PVC and PES foams continuously increased with the increase of foam density. However, cell sizes were not simply dependent on foam density. For both quasi static and elevated strain rate tests, plastic hinges were the primary deformation mechanism for both PVC and PES foam cells.