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Porous coated Ti-6Al-4V has a bending fatigue strength that is approximately one-third that of the uncoated material. This reduction in strength is due primarily to stress concentrations caused by the interfacial geometry between the porous coating and the substrate. An unconventional interfacial geometry, the porous coated nodule, has been shown to reduce the stress concentration factor compared to conventional porous coatings in finite element modeling. We report here on bending fatigue testing to determine whether the fatigue strength of the new geometry is better than that of the conventional porous coating geometry. We also report on modeling of shear loading to determine whether the new geometry lowers stress concentrations under this mode of loading as well as under bending loading. The fatigue strength of the nodule geometry was found to be 305 (+/- 12) MPa, which is greater than the strength of conventional porous coated specimens. In addition, the porous coated nodule was seen to reconcile the differences in the results for modeling under shear and bending loads and can thus reduce stress concentrations under both modes of loading.
porous coated implants, stress concentrations, fatigue, Ti-6Al-4V, finite element analysis, shear loading
Research scientist, FDA, Rockville, MD
Professor, University of Pennsylvania, Philadelphia, PA