Determination and evaluation of S/N curves for TiN and ZrN coated 316 L hip stems

Objective of this study is to perform fatigue testing of the total joint replacements made of 316L stainless steel to validate the safety of the component before clinical use. Thompson hip prosthesis was tested by using double cantilever beams bending machine designed and manufactured at Department of Metallurgical and Materials Science Engineering. The physiological environment, namely the body fluid, can be very corrosive for implant materials. In order to ensure the safety of a hip prosthesis against corrosion fatigue failure, fatigue tests must be performed in a corrosive medium with low frequency load application. Component fatigue tests were therefore performed in Ringer's solution (0.9% NaCl) at a frequency of 10 Hz in accordance with ISO 7206/4 standard. At this rate, a single hip stem fatigue test requires 11,5 days of continuous testing without any failure for a numbers of 10 cycles. Like mechanical testing, FEA has been applied to orthopaedic implants. 3-D model of prosthesis was constructed and loaded in a static manner by means of IDEAS to investigate stress distribution occurred the stem of hip prosthesis. As a result of static analyses of hip stem, stress concentration area corresponding to tensile stress presented on latero-anterior stem portion, was found to be located approximately 10 millimeters above the cement surface. It was determined that the maximum stress values computed under different loads were proportional to the applied loads.