Spongy bone deformation mechanisms

Abstract

In the fields of safety, ballistic protections and other medical applications, the accurate material constitutive law of spongy bone is needed to carry out valid finite element analyses for injury prediction. The direct identification of bone mechanical behaviour law is not easy since it is a complex network of intersecting osseous spans (trabeculae), where the space in and around the trabeculae contains bone marrow and fluids. In order to identify the spongy bone's mechanical behaviour, we performed compression tests on cylindrical samples. Experimental results show important dispersions and an unexpected inverse strain rate dependency at low range of loading velocities. The origin of the dispersions can be attributed to the combination of the architecture effect and the mechanical properties variation of the constitutive material. In order to reduce these dispersion sources and to understand the inverse strain rate sensitivity, we used a controlled constitutive material to build new equivalent samples with the spongy bone's architecture. These equivalent samples were subjected to compression tests. Numerical simulations of compression tests on the same architecture have been carried out with FE models built from µCt data. The obtained results are compared in term of final sample shape and the evolution of the compression force. This strain rate dependency can not be explained only by architecture effect.