The Effect of Intrafibrillar Post-Yield Behavior on Fracture of Mineralized Collagen Fibril Arrays

Abstract

Mineralized collagen fibrils (MCFs) are important building blocks of bone at the submicroscale, and the mechanical performance of MCF arrays has a great influence on fracture resistance of bone at large length scales. In this study, we carry out the analyses of fracture process in MCF arrays under tensile loading. The plastic deformation of extrafibrillar matrix (EFM), post-yield behavior of MCFs, MCF breakage and debonding of the MCF-EFM interface are accounted for in the calculations. It is found that the fracture mechanisms of MCF arrays depend on the post-yield characteristics of MCFs. Shear-band-induced cracking of MCFs is the dominant fracture mechanism in the case of strain softening of MCFs, while strain hardening of MCFs promotes the MCF-EFM interfacial debonding, which controls fracture of MCF arrays. In addition, we reveal that plastic energy dissipation of MCFs and EFM provides major contribution to toughness of MCF arrays. Compared with the case of strain softening of MCFs, the MCFs exhibiting post-yield strain hardening can give rise to larger plastic deformation zone in MCFs and activate higher levels of plastic strain of EFM, enhancing plastic energy dissipation and thereby amplifying toughness of MCF arrays. The findings of this study shed new light on the fracture mechanisms of bone associated with alterations in submicroscale structure and composition.