Characterization of damage mechanisms in cortical bone: Quantification of fracture resistance, critical strains, and crack tortuosity.

One step towards understanding bone fragility and degenerative diseases is to unravel the links between fracture resistance and the compositional and structural characteristics of cortical bone. In this study, we explore an optical method for automatic crack detection to generate full fracture resistance curves of cortical bone. We quantify fracture toughness, critical failure strains at the crack tip, and crack tortuosity in three directions and analyze how they relate to cortical bone microstructure. A three-point bending fracture test of single-edge notched beam specimens in three directions (cracks propagating transverse, radial and longitudinal to the microstructure) from bovine cortical bone was combined with 2D-digital image correlation. Crack growth was automatically monitored by analyzing discontinuities in the displacement field using phase congruency analysis. Fracture resistance was analyzed using J-R-curves and strains were quantified at the crack tip. Post-testing, a subset of specimens was scanned using micro-tomography to visualize cracks and to quantify their tortuosity. Both fracture toughness and crack tortuosity were significantly higher in the transverse direction compared to the other directions. Similar fracture toughness was found for radial and longitudinal directions, albeit 20% higher crack tortuosity in the radial specimens. This suggests that radial crack deflections are not as efficient toughening mechanisms. Strains at crack initiation were ∼0.4% for all tissue orientations, while at fully developed damage process zones failure strains were significantly higher in the transverse direction (∼1.5%). Altogether, we present unique quantitative data including different aspects of bone damage in three directions, illustrating the importance of cortical bone microstructure.

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Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.

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Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Anna Gustafsson reports financial support was provided by Swedish Research Council. Hanna Isaksson reports financial support was provided by Swedish Research Council. Anna Gustafsson reports financial support was provided by Royal Swedish Academy of Sciences. Anna Gustafsson reports financial support was provided by Crafoord Foundation. Anna Gustafsson reports financial support was provided by Foundation of Greta and Johan Kock. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.