Effects of specimen load-bearing and free surface layers on the compressive mechanical properties of cellular materials

The influence of load-bearing surface layers on Young's modulus was determined for cancellous bone and polyurethane foam specimens of three different heights cut from each material: 16, 9, and 5 mm for bone specimens (cross-sectional area A = 81 mm 2) ranging in density from 0.04 to 0.32 g cm −3; 20, 10, and 5 mm for foam specimens ( A = 100 mm 2) ranging in density from 0.064 to 0.64 g cm −3. The compressive elastic modulus of the 5 mm bone specimens was significantly smaller (42%) than that of the 16 mm bone specimens. A similar change in elastic modulus was also observed for the foam specimens, but the height effect diminished in a relatively linear manner as the foam density increased. For a height change from 20 to 5 mm, the foam modulus difference ranged from a 41% decrease for the lowest density specimens (ϱ = 0.064 g cm −3) to an insignificant change (