Constitutive modeling of cortical bone considering anisotropic inelasticity and damage evolution

Researchers have conducted finite element (FE) analyses with human models to predict injuries due to traffic accidents or falling. In most of their analyses, cortical bone was simply modeled as a general isotropic elastoplastic material. In this study, a constitutive model of cortical bone considering anisotropic inelasticity and damage evolution was developed to predict injuries more accurately. The new model can satisfactorily represent mechanical properties of cortical bone including anisotropy of elastic modulus and yield stress with strain-rate dependency, and asymmetric stress–strain curves in tension and compression. Simultaneously the included damage-evolution equation enables to predict failure stress and strain with rate dependency in bone fracture simulations. The proposed model was verified using experimental data obtained from the literature. We applied the proposed model to a simple cylindrical FE model of the human femur, and performed simulations under loading conditions such as tension, compression, and torsion. The results showed some tendency of characteristic fracture patterns such as transverse fracture in tensile loading, oblique fracture in compression, and spiral fracture in torsion. The proposed constitutive model would have the potential for better injury prediction in the future.