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Design for fracture control and the mechanical properties of the equine hoof wall

University of British Columbia

Morphological and mechanical studies were conducted on the equine hoof wall to help elucidate the relationship between form and function of this complex, hierarchically organized structure. Numerous levels of the morphological hierarchy were investigated to ascertain the functional significance (if any) of each level, and to determine if the presence of any levels reflect manufacturing limitations. Mechanical tests included tensile, fracture and dynamic tests; morphological studies utilized scanning electron, bright field, and polarized light (using both circularly and plane polarized light) microscopy. A universal stage was utilized to permit the accurate determination of fiber orientation in three dimensions. Mechanical tests indicate that the fracture toughness of hoof wall is independent of loading rate, and the wall is highly resistant to the propagation of cracks initiated in all directions tested here. Cracks initiated along potentially dangerous paths appear to be redirected by morphological crack diversion mechanisms formed by specific alignments of α-keratin intermediate filaments. Hoof wall structure at all levels may be explained in terms of fracture control, suggesting that the evolution of hoof wall design has been driven primarily by fracture issues. To avoid compromising the effective transfer of loads to the bony skeletal elements which may otherwise result from crack diversion mechanisms, the properties of α-keratin have been adjusted through the wall thickness. Although inner wall tubules appear to offer some degree of reinforcement, the similarities in mechanical properties of α-keratin from cells of tubules and intertubular material (which form the hoof wall) from the same area of the wall, suggest that these elements are not analogous to fibers and matrix (respectively) of typical composites, but are instead necessary for the proper alignment of intermediate filaments in the hoof wall. Empirical and derived data suggest that the production of hollow (rather than solid) structures is likely the reflection of a manufacturing limitation.

Thesis/Dissertation

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2009-06-03

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http://hdl.handle.net/2429/8680

Zoology

University of British Columbia

UBCV

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