Post-yield mechanical properties of bovine trabecular bone - Relationships with bone volume fraction and strain rate

Bone finite element models, which are increasingly used to assess fracture risk in patients with degenerative bone diseases, require extensive experimental data to adequately model the material properties being assigned. Previous studies have demonstrated that bone elastic mechanical properties are dependent on density as well as strain rate, however, the effect these same variables on the post-yield behaviour of trabecular bone has not been thoroughly studied. For this study, bovine femoral samples were tested at several strain rates using three different tests devices: a conventional constant strain rate apparatus for low strain rates, a Drop Weight Impact Test device for the intermediate regime and a Split Hopkinson Pressure Bar System with magnesium bar and a PVCA pulse shaper for high strain rates. Ultimate and plateau stress, as well as absorbed energy were recorded. The results of this experimentation show that post-yield mechanical properties of trabecular bone are strain rate and volume fraction dependant. Two constitutive material models describing the Ultimate strength, Plateau stress and absorbed energy are proposed based on published models valid for elastic properties of trabecular bone.