Finite element simulation of nanoindentation in lamellar bone composites

Bone is a biological composite material with complex hierarchical structures from nanoscale to macroscale level. A number of research work has been done in multiscale modelling of bone mechanical behavior in different scale levels such as fibril scale, lamellae scale, osteon scale etc.,. Nonetheless, the ultrastructural property-structure of bone is still under investigation. In this study, we conducted several nanoindentation tests to further connect the relation of mechanical properties and the structure. A new multiscale model of lamellae ultrastructure was proposed. In the model, a partitioned geometry based axisymmetric specimen outlining the mineralized collagen fibrils, intrafibrillar matrix and extrafibrillar matrix were defined. The damaged plastic model criterion was employed to define the properties of lamellae constituents in the simulation. Then, a rigid berkovich contact indenter was assembled to simulate the process of nanoindentation to extract modulus and hardness values. The simulation results were compared with experimental data for gaining more insight about mechanical bone response. As age progresses, the simulation results indicated that change in distribution of volume fraction within the intrafibrillar and extrafibrillar matrix has noticeable impact on the modulus and hardness. Through the parametric study, it was found that the extrafibrillar matrix mainly contributes to the modulus and load carrying capacity of lamellae and mineralized collagen fibrils has dominant contribution to the hardness of the lamellae.