A computational insight on damage-based constitutive modelling in femur mechanics

The present paper addresses femur failure mechanics, by numerically investigating the influence of brittle/ quasi-brittle bone constitutive description when combined with several failure criteria and different descriptions of bone ultimate parameters. Starting from computed tomography images of an experimentally-tested cadaveric femur, the bone geometry has been reconstructed through a semi-automatic segmentation procedure, and patient-specific material properties have been derived. Loading-induced loss of structural integrity has been simulated through a progressive thermodynamically-based damage model, by introducing different strain and stress-based damage evolution laws. An in-house displacement-driven incremental approach has been implemented in a finite element framework to mimic the in-vitro experimental procedure. An energy-based regularization technique allowed to obtain results which are mesh independent and therefore physically meaningful. Depending on the adopted modelling strategy, significant differences in terms of yield and failure load, as well as in fracture patterns, have been numerically experienced. Comparisons between the proposed numerical results and the available experimental outcomes have been carried out. For the femur model herein analysed, an elastic quasi-brittle bone description combined with strain-based failure criteria seems to be more effective in predicting the mechanical behaviour up to the fracture. Presented mesh-independent results therefore contribute to justify the need of damage-based approaches for predicting in an effective way failure mechanisms of femurs.