Papers by Author: L. Evans

Abstract: This study aims to characterize the structure and properties of crocodile bone to assess the potential for use in biomedical applications. Crocodile bone samples obtained from Thailand (Crocodylus siamensis) and Australia (Crocodylus porosus), being the tail and the tibia respectively, were treated to remove organic material and the inner spongy (trabecular) material. The dense cortical bone was used for comparative instrumental analyses. Specific comparisons were made against bovine cortical bone and pure synthetic hydroxyapatite. The material was then analyzed using simultaneous differential thermal analysis/thermogravimetric analysis (DTA/TGA), Fourier- Transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). Imaging of full bone samples was also conducted using an environmental scanning electron microscopy (ESEM). The SEM provided valuable information through the imaging of samples, showing a markedincrease in bone porosity for crocodile material when compared to bovine samples. The crystallinity and/or crystallite size of carbonated hydroxyapatite has been found to be lower than synthetic apatite, with the tibia being the least crystalline of the bone types studied. The crystallinity index (CI) is used as a measure of crystallite size and internal strain. The strain is affected by substitutions in the structure and these results provide a starting point for comparison of the resulting mechanical properties. There is a need for any biomaterial chosen for bone replacement to allow adequate osteointegration. Thus the study this far shows that crocodile bone is a very promising source of carbonated apatite for biomedical applications.

Abstract: The localization of deformation in recrystallizing materials is investigated via a series of two-dimensional grain-scale numerical simulations. These simulations couple a grain size and strain dependant viscous rheology with grain size reduction and grain growth processes. The simulations are able to predict the mechanical, microstructural and strain evolution of the polycrystals to high strain, and allow us to examine the nature of the time dependent feedback between mechanical and microstructural behavior. It was found that significant strain localization occurred only when the grain size dependence of the viscosity was non-linear, and was greatly enhanced by the activity of the grain size modifying processes. The intensity and location of the zone of strain localization varied spatially and temporally, with the result that the finite strain state showed a much broader, and hence less intense, zone of localized deformation than the instantaneous state.