Prediction of the surface finishing roughness effect on the fatigue resistance of Ti-6Al-4V ELI for implants applications

Based on the theors of elasticity for linear elastic materials and strain partitioning, a method was developed to predict fatigue lives of load bearing Ti-6Al-4V ELI implants with surfaces modified in the micrometer scale to promote bioactive materials and accelerate osseointegration. Notched fatigue specimens were characterized by confocal laser scanning microscopy (CLSM) and subjected to axial fatigue tests at a constant maximum stress to determine the Siebel and Stieler's C constant. The mean value obtained for C was employed to determine the fatigue resistance (Kf factor) allowing the life prediction of samples with different sized notches. The method was validated by performing fatigue tests with samples modified at two scales, 2 μm and 10 μm, typical values that can be produced in industrial conditions. It was confirmed that the prediction method was in agreement with the experimental results. In addition, the prediction method clarified the strong reduction in the fatigue resistance from 850 MPa to 594 MPa due to small differences in surface roughness, a result unexplained in the literature so far.