J.L.A. Ferreira

Influence of Heat Treatment on Fatigue Resistance of Sintered Ti 35Nb 7Zr 5Ta β Alloy

Mean stress on fatigue strength of Ti-35Nb-7Zr-5Ta, used in the manufacture of orthopedic prosthesis, was evaluated. Samples of Ti-35Nb-7Zr-5Ta were pressureless sintered and tested using microhardness (Vickers) and four point bending fatigue apparatus. Characterization was carried out using optical microscopy, scanning electron microscopy, EDS analysis, oxygen analysis and density. The density analysis shows almost 98% of density and microscopy reveals some precipitates of α phase and presumably ω phase at the grain and grain boundaries. The bending fatigue resistance limit reached (Se (106) 88 MPa), due to, presumably, the influence of coarse α phase precipitates at grain boundaries as well as the high oxygen content in the material after sintering (0.96 %). In this study, Kwofie model best explains the influence of mean stress on fatigue strength of this alloy.

Fatigue Strength of Ti-35Nb-7Zr-5Ta

Mean stress on fatigue strength of Ti-35Nb-7Zr-5Ta, used in the manufacture of orthopedic prostheses, was evaluates. Samples of Ti-35Nb-7Zr-5Ta were pressureless, sintered and tested using microhardness (Vickers) and four point bending fatigue conditions. Characterization was carried out using optical microscopy, scanning electron microscopy, EDS analysis, oxygen analysis and density. The microstructural analysis shows low densification after sintering (almost 86% of theoretical) and some precipitates of α phase and presumably ω phase at the grain and grain boundaries. The bending fatigue resistance limit reached (Se (106) = 90 MPa), due to, presumably, the influence of the medium-high porosity, α phase precipitates at grain boundaries as well as the high oxygen content in the material after sintering (0.96 %). In this case, Kwofie model best explains the influence of mean stress on fatigue strength of this alloy.

A New Model to Determine the Dispersion of Fatigue Damage Evaluations

Reliable predictions of remaining lives of civil or mechanical structures subjected to fatigue damage are very difficult to be made. In general, fatigue damage is extremely sensitive to the random variations of material mechanical properties, environment and loading. These variations may induce large dispersions when the structural fatigue life has to be predicted. Wirsching (1970) mentions dispersions of the order of 30 to 70 % of the mean calculated life. The presented paper introduces a model to estimate the fatigue damage dispersion based on known statistical distributions of the fatigue parameters (material properties and loading). The model is developed by expanding into Taylor series the set of equations that describe fatigue damage for crack initiation.