Experimental Study of Size Effects and Surface Damage in Closed-Cell Polymethacrylimide and Open-Cell Copper Foams

This article describes experimental investigations of size effects in torsion and bending of lathe cut closed-cell polymethacrylimide and open cell copper foams. Slender specimens were found to have a slightly smaller effective stiffness than thick ones. This behaviour is consistent with a model of surface damage to the outermost cells of the foam. The surface damage layer was inferred to be from 0.13 to 0.37 cell diameters for the polymethacrylimide, depending on the grade of foam, and from 0.3 to 0.4 cells in the copper foam. Effects of Cosserat (micropolar) elasticity, which would give rise to an effective stiffening of slender specimens, were not observed.