Cortical bone fracture analysis using XFEM

What is it about?

We aim to achieve an accurate simulation of human cortical bone fracture using the extended finite element method within a commercial finite element software ABAQUS. A two-dimensional unit cell model of cortical bone is built based on a microscopy image of the mid-diaphysis of tibia of a 70-year-old human male donor. Each phase of this model, an interstitial bone, a cement line, and an osteon, are considered linear elastic and isotropic with material properties obtained by nanoindentation, taken from literature. The effect of using fracture analysis methods (cohesive segment approach versus linear elastic fracture mechanics approach), finite element type, and boundary conditions (traction, displacement, and mixed) on cortical bone crack initiation and propagation are studied. In this study cohesive segment damage evolution for a traction separation law based on energy and displacement is used. In addition, effects of the increment size and mesh density on analysis results are investigated. We find that both cohesive segment and linear elastic fracture mechanics approaches within the extended finite element method can effectively simulate a cortical bone fracture. Mesh density and simulation increment size can influence analysis results when employing either approach and using finer mesh and/or smaller increment size does not always provide more accurate results. Both approaches provide close but not identical results, and crack propagation speed is found to be slower when using the cohesive segment approach. Also, using reduced integration elements along with the cohesive segment approach decreases crack propagation speed compared with using full integration elements.

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Why is it important?

Bone fracture is an outstanding clinical problem. Risk of bone fracture depends on various factors: age, genetics, diet, exercise, and state of health. Fracture toughness is the measure of material’s resistance to cracking. Understanding of bone’s resistance to fracture is important for the diagnosis of bone diseases and assessment of treatments.

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