It has been shown that human compact bone has the ability to plastically (permanently) deform a significant amount when loaded, though the controlling microstrural defomation mechanisms have not be clearly established. The objective of this project is to investigate the relative contribution of microstructural deformation mechanisms to the macroscopic permanent deformation of compact human bone. This goal will be achieved by examining the hypothesis that the macroscopic permanent deformation of compact human bone subjected to static loads van be modelled as a function of test and material variables. For metals and ceramics, microstructural deformation mechanisms have been identified by modelling the effect of such variables on the macroscopic creep deformatin (the time- dependent change in strain caused by the application of a constant load). Because human compact bone has been shown to experience a classic creep response like that of metals and ceramics, the same approach will be applied. The effect of temperature, stress, specimen orientation and specimen size on the creep behavior of compact human bone will be determine. The results will be used to determine the activation energy values for microstructural deformation mechanisms. These values may be correlated to the energy requirements for processes such as collagen bond disruption or cement line fracture. In addition, specimen orientation and size with respect to the bone microstructure will be varied in a further effort to determine the contribution of microstructural deformation mechanisms to the macroscopic deformation response. It is believed that this approach will successfully lead to the development of a hypothesis that microstructural deformation mechanisms of human compact bone can be identified from the model of its macroscopic permanent deformation behavior.
