Fatigue Properties and Life Assessment of Titanium Alloy Weldments

Titanium alloys have a good combination of high specific strength, corrosion resistance and high temperature properties. They have been widely used in the military, aerospace, vehicles, off-shore equipment, sports equipment and biomedical implants. In engineering applications, titanium alloys often need to be welded, and fatigue is the most important failure mode of welded structures. Because the material microstructures, geometry and flaws near the welds are not easy to be controlled, the traditional fatigue analysis method must be modified. To offer engineering applications, a number of associations developed fatigue design codes for welded structures according to the regression of fatigue failure data. However, unlike steel weldments and aluminum alloy weldments, the fatigue data of titanium welded structures are still quite limited, and only one fatigue design code (AWS D1.9/D1.9M) of welded titanium was developed.This is a two-year project. The material is Ti-6Al-4V titanium alloy. Welding methods including electron beam welding and vacuum brazing will be used since they can produce high-quality weldments. The fatigue properties of Ti-6Al-4V alloy and its weldments under constant and variable amplitude loadings will be obtained, respectively. In the first year, methods for the fatigue evaluation of base metal and weldments are assessed from the view points of original designed structures. We will examine the suitability of related design code, and establish the best fatigue life analysis method for the titanium structures under variable amplitude cyclic loading. In the second year, we will investigate methods for the residual life estimation of cracked Ti-6Al-4V alloy and its weldments. Fatigue design of these two perspectives can complement each other and construct a complete fatigue design system.