Bone and Bone Surrogate Fragmentation Under Dynamic Compression

Abstract

The rate-dependent compressive response and resulting fragmentation characteristics of dry ox cortical bone and cyanoacrylate-based cortical bone surrogate material was investigated in two material orientations. Tests were conducted under quasi-static (10 -3 s -1 ) and dynamic (10 3 s -1 ) loading in the longitudinal and transverse direction with respect to the osteon and die-press orientation. The fragments resulting from dynamic loading were analyzed by fitting 2D ellipses of representative distributions using post-mortem optical microscopy, and are related to existing flaws in the microstructure and the energetics of dynamic fracture evolution. The compressive strength of the bone surrogate increases 20-27 % (±7 %) from quasi-static to dynamic when loaded in either the longitudinal or transverse orientation, while the compressive strength of the ox bone increased 43-66 % (±9 %). Resulting bone fragments had a mean size of 266 ± 28 lm for longitudinal and 410 ± 19 lm for transverse loading, while the bone surrogate produced larger fragments with mean sizes of 431 ± 14 lm for longitudinal and 694 ± 25 lm for transverse. Fragment size distributions exhibit a power-law dependence on length, as the onset of fracture asymptotes to a range of length scales where the fragmentation is self-similar and fractal. Pre-and postmortem scanning electron microscopy reveals that the bone surrogate has pre-existing flaws of pores and microcracks in a nominally homogeneous microstructure which resulted in a larger characteristic fragmentation length, whereas the ox bone has an inherently anisotropic composition that resulted in fragments linked to microstructural features of the internal canal system.

Celebrating 75 Years of the Society for Experimental Mechanics and the Study of Dynamic Behavior of Materials

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