Crack Growth Model to Evaluate the Fatigue Life of Ti-6Al-4V Medical-Grade Material

Prediction of life of a component made of a certain material would be beneficial to both the manufacturer and the user. Life prediction requires knowledge of material properties such as grain size and microstructure, as well as the stress levels induced by the maximum possible loads, particularly cyclic loads under in-vivo conditions. A mathematical model was developed to assess the lifetime of components made from Ti-6Al-4V; a medical-grade titanium alloy extensively used for implant manufacturing. Attention was given to crack initiation and growth in the microstructural short cracks and physically small cracks regions, where a significant portion of the fatigue life was accumulated. Rotary-bending experiments were conducted to assess the fatigue endurance limit of the material.  The surface crack was replicated at specific stages of the life to assess its propagation and thereby the crack propagation rate was calculated. The threshold values of crack length and stress intensity factor determined in this study are in good agreement with existing literature, thereby confirming the accuracy of the results. MATLAB and Microsoft Excel were used to develop mathematical models and thereby to assess the material constants. Predicted fatigue lives were validated with the experimental results, with accuracies ranging from 0.7% to 14.5%.