Softening of Cosserat sensitivity in a foam: warp effects

Abstract Buckling gives rise to softening of the structural stiffness of columns; buckling of ribs gives rise to softening of the incremental elastic modulus of foams. Softening of Cosserat characteristic lengths occurs in pre-compressed foam material as determined from warp of cross sections of a square bar in torsion. Warp in the foam is reduced considerably in comparison with the predictions of classical elasticity. Pre-compression increases the warp in comparison with the warp observed without pre-compression. The effect is attributed to release of energy stored via pre-compression.