Implementation of Microstructure-Based Deformation and Failure Model for Compressive Mechanical Response of Human Skull

Inclusion of the nonlinear response and fracture of the human skull bone in finite element (FE) simulations aimed at evaluating head injury due to externally applied loading will increase the biofidelity of these simulations and provide a means of identifying fracture-based injury. A challenge to accurately modeling the mechanical response of the human skull is the intricate arrangement of bone within the sandwich structure of the skull. Recently, a power-law relationship between the localized bone volume fraction (BVF) and modulus within the human skull was developed at CCDC ARL based on quasi-static compression experiments. Then, the ability of this power law to simulate the compression experiment of the skull bone coupon was evaluated. A simple FE mesh was constructed, based only on the outer geometry of the specimen such that elements represented both bone and pores. Rather than explicitly meshing the internal bone microstructure, a new method was used to calculate the BVF of the physical volume which each element represented so as to assign element-specific moduli calculated from the BVF-modulus power relationship. This method of implementing microstructure-based moduli was able to simulate the linear portion of the experimental response, matching the experimental modulus to within 5%. Here, the method is also extended by including element-specific failure. Compressive and tensile failure criteria were calculated with power relationships based on the BVF of the elements. Modeling element-specific failure enabled the simulation to match the nonlinearity of the experimental stress-strain curve, and provided a method of identifying areas of material failure, both compressive and tensile, within the mesh.