Damage results in a loss of material continuity, which distinguishes it from other types of material degradation. The loss of continuity can have an adverse effect on mechanical properties, and may be manifested in the form of cracks and/or voids. Bone tissue, as a composite material, contains voids and other non-homogeneities that are naturally occurring and distinct from damage. However, when subjected to mechanical loading, such as indentation, further damage accumulation may occur. Figure 1 shows a cross-section of a bovine cortical bone specimen after high-load conical indentation to a depth of 300 μm, resulting in a large permanently deformed region. Nanoindentation, using a Berkovich tip at 10 mN maximum load, was then performed at numerous locations within three defined damage “zones”. Zone 1 is adjacent to the bottom of the indent, defined at 25% of the maximum indent depth. Zones 2 and 3 extend further away, both scaled as a function of the indentation depth, d. Figure 2 shows the variation in Young’s modulus in the three damage zones, averaged over approximately 25 indents per zone. The data suggest that local changes in mechanical properties may occur as a result of compaction of voids or cracks. The purpose of this work, therefore, is to investigate the application of a plastic-damage model for simulation of bone nano- and micro-scale indentation behavior.

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