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 op en cell copper foams. Slender specimens were found to have a slightly smaller effective stiffness than thick ones. This behaviour is consist ent 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 di ameters for the polymethacrylimide, depending on the grade of foam, an d from 0.3 to 0.4 cells in the copper foam. Effects of Cosserat (micro polar) elasticity, which would give rise to an effective stiffening of slender specimens, were not observed.