A numerical investigation of mid-femoral injury tolerance in axial compression and bending loading

Abstract

Bone fractures occur frequently at mid-shaft femoral site of the front seat vehicle occupants during frontal and offset automotive crashes. A numerical investigation of femoral shaft tolerance under axial and bending loading corresponding to traffic accidents is presented in the current study. A subject specific finite element (FE) model of a femur is developed and the parameters of two material models of cortical bone (isotropic elastic–plastic and elastic transversally isotropic) are identified based on three-point bending test data using optimisation techniques. A Monte Carlo analysis is performed on a surface approximation of the optimised models over a domain of +/− 20% of the optimised parameter values and showed that the elastic moduli of femur are the most influential parameters on the bone stiffness curve prior to bone fracture. The mid-shaft femoral tolerance curves demonstrate sensitivity with respect to the impact direction of transversal load due to the initial curvature of the femur, but insignificant dependence on the material model, or the failure criteria used for femoral cortical bone. The results highlight the predominant role of bending in a combined axial-bending loading of the femur, which may be used in redefining the current injury criteria of femur used in anthropometric test devices.

Keywords:

• femur
• finite element
• optimisation
• Monte Carlo method
• impact biomechanics

Acknowledgements

The author thanks Dr. James Funk, Dr. Jason Kerrigan and Dr. Jeff Crandall for their support given to this work.