Determination of Fatigue Life of Titanium Alloys Used As a Locking Screw in Medical Applications

Abstract

Titanium alloys are used in a wide range of applications including implant materials for the surgery and dental applications because of their
outstanding mechanical properties such as superior strength, high corrosion resistance, lower modulus of elasticity and excellent biocompatibility. Ti6Al4V ELI is a typical Ti alloy accepted as an alternative metallic material for failed bone fractures because of good machinability
and excellent mechanical properties, especially when direct contact with tissue or bone is required. During its service, most of the metallic
implants are subjected to cyclic loading inside the human body which leads to the possibility of fatigue fracture. An evaluation of the fracture
characteristics of fatigued implant materials can offer information about the fatigue life and the residual fracture resistance of these materials. In
this study; Ti6Al4V ELI Grade 23 material medical screw test samples were designed and tested in accordance with the ASTM Bending Fatigue
Test Procedure using 2,5 kN capacity test machine at room atmospheric conditions. Initial loading conditions determined based 75, 50, and 25
% of the bending strength found in accordance with the static 3P bending tests. The data generated from a series of tests were compiled and the
results presented as a Fatigue Strength-the Number of Cycles (S/N) diagrams. For validation of the experimental studies; fatigue behaviors of
screws were also analyzed with Ansys software using Finite Element Analysis (FEA) under dynamic loads.