Decoupling shear and compression properties in composite polymer foams by introducing anisotropy at macro level

Abstract

Anisotropy in foams generally originates from cell elongation in a certain direction. In this study, a composite concept is utilized to create anisotropy in foams at macro level. For this, layered composite foam is proposed by combining discrete layers of expanded polystyrene foam foam with different densities. The layers are positioned in parallel with the prime loading direction. The compression and biaxial combined shear-compression behavior of the composite foams are studied and compared with single-layer expanded polystyrene foam of equivalent density. The biaxial shear-compression test results demonstrate that the composite concept enables to decouple shear and compression properties of foam for a given overall density. In compression loading, the composite foam behavior is similar to that of single-layer foam of similar density, while in biaxial loading, the composite foam shows lower shear resistance than single-layer foam. Moreover, in biaxial loading, parameters such as the number of layers and the density difference between the high- and low-density layers affect the extent of decrease in shear resistance, while the compression stress component depends solely on the overall density of the composite foam. One of the potential applications of this behavior could be in protective helmets for mitigation of the head rotational acceleration.