Thesis

A computational and experimental investigation into the micropolar elastic behaviour of cortical bone

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13705
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Abstract
  • Cortical bone is a natural composite, heterogeneous material with a complex hierarchical microstructure. The description of this microstructure in terms of the mechanical properties of cortical bone may be important in the understanding of periprosthetic stress concentrations. Micropolar elasticity is a higher order continuum theory which may more effectively describe the influence of the microstructure in cortical bone on its mechanical behaviour. Micropolar elasticity predicts a size effect in three-point bending, which has been investigated computationally and experimentally on bovine mid-diaphyseal cortical bone. Computational models of an idealised heterogeneous material, with vascular canal-like structures running along the length of the beam, demonstrated a size effect in the longitudinal and transverse directions which was dependent on the surface condition of the beam. Idealised models with smooth surface layers increased in stiffness as specimens decreased in size, whilst idealised model beams intersected by the internal microstructure demonstrated an equally strong, yet opposite, effect. These FE size effects were further corroborated by analytical studies which demonstrated similar size effects. Experimental three-point bending studies of bovine cortical bone specimens orientated both longitudinally and transversely were consistent with the equivalent numerical models where the internal microstructure intersected the surface. These results suggest the micropolar characteristic length in bending is of the order of the size of the Haversian canal system in secondary osteons and the vascular channels in plexiform cortical bone. The ramifications of this are that the microstructure of cortical bone is of fundamental importance in understanding size effects and stress concentrations in the material. This finding is important in understanding and developing the design and longevity of prosthetic devices and in being able to improve the interaction between an implant and the surrounding cortical bone.
Resource Type
DOI
Date Created
  • 2013
Former identifier
  • 1031363

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