Papers by Author: Richard Curtis

Abstract: This work investigates the sensitivity of a superplastic material’s tensile test to the major geometrical parameters of the selected test specimen. This required generating a large number of specimens by systematically varying the gauge length, gauge width, grip length and width of a standard geometry. The specimens were prepared from a moderately superplastic AZ31B-H24 magnesium alloy sheet and were then stretched at a selected rate and temperature. Deformation in each specimen was tracked via an electrochemically-etched fine grid which was particularly used to quantify the amount of material flow from the grip into the gauge region. The consequences of the latter on the accuracy of measured stresses and strains were correlated back to the corresponding geometrical parameters. Ultimately, the results were utilized to set the guidelines for selecting the optimum parameters in a “proper” specimen, for testing the unique class of superplastic materials.

Abstract: Steinemann, 1998 [1] reported an observation made several decades earlier in 1951, by Leventhal [2] in which ‘bone reaction was studied by the insertion of up to 80 titanium screws into the femora of rats. At the end of sixteen weeks the screws were so tight that in one specimen the femur was fractured when an attempt was made to remove the screw’. Consequently, the main reasons given for the suitability of titanium for surgical implantation are its strength, its failure to cause tissue reaction, and the fact that bone becomes attached to titanium. Now, we call this attachment osseointegration which is considered to be the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant. However, osseointegration is not considered to be a chemical bond between titanium and bone. Implant materials that actually bond to bone are considered to be bioactive. Materials for clinical use can be classified into three categories: resorbable, bioactive and nearly inert materials. A bioactive material is defined as a material that elicits a specific biological response at the interface of the material, which results in the formation of a bond between the tissue and that material. Whereas specific bioceramics are considered to be bioactive, titanium alloys are not normally considered to be so. However, recent surface modification of titanium alloys provide evidence that titanium alloys can become bioactive after treatment with NaOH and the ensuing development of a titanate gel on the metal surface.