Modelling Skull Fracture Using the eXtended Finite Element Method

The thesis was submitted to University College Dublin in part fulfilment of the requirements for the degree of Master of Mechanical Engineering. Background: Skull fracture accounts for almost one-third of all head injuries that occur. In recent years, improvements in computer modelling techniques have allowed for a better and more illustrative approach to understanding the biomechanical response of an impact to the head. Several computer modelling techniques have previously been employed to simulate skull fracture using Abaqus Finite Element modelling software. This project investigated if the eXtended Finite Element Method (XFEM) can prove useful in modelling skull fracture.  Methods: The XFEM was used to simulate the initiation and propagation of cracks in cortical bone. Firstly, a model was created to simulate Single-Edge Notched Bending (SENB) test that had been carried out on human cortical bone samples. Simplified 3-D models were then created to investigate the effect of using modelling crack propagation in three dimensions, taking into account the anisotropic behaviour of cortical bone. Results: Both the 2-D and 3-D models simulated crack propagation in the cortical bone that was very comparable to experimental fracture. XFEM allows for a crack to propagate in the material without defining the location of the crack. The max. principle stress criteria with displacement- type failure proved most accurate in recreating SENB tests that were carried out experimentally as the displacement at failure was a known value. In 3-D, the max. nominal stress criteria can be used to include the anisotropic behaviour of cortical bone. The force required to cause fracture in 3-D was lower than the experimental result however, the model only considered the outer table of cortical bone. The model was also a simplified geometry and so this result was expected. Conclusion: The XFEM can be effectively used to model fracture in cortical bone. The numerical solution depends highly on the material properties of the model. A very clear visual representation of fracture can be provided and a clear insight into the skull fracture phenomenon can be obtained through XFEM.