Fatigue Crack Growth and Life Assessment of Titanium Alloy Weldments

Titanium alloys have many excellent properties and have been widely used. Electron beam welding (EBW)and vacuum brazing (VB) are operated under vacuum environment and can produce high-quality components.Fatigue is the most important failure mode of welded structures in engineering applications. However, unlikesteel weldments and aluminum alloy weldments, the fatigue data of titanium welded structures are still limited.In the previous project (MOST 105-2221-E-008-046), we have dealt with the fatigue life prediction with stresslife(S-N) approach. We will further investigate the fatigue crack growth life prediction with fracture mechanicsapproach in this project. Fatigue design methods of these two projects can construct a complete fatigue designsystem.This is a two-year project. The first year, we will adopt Ti-6Al-4V EBW weldment as the specimen. Theobjectives are as follows. (1) To obtain the materials properties such as fatigue crack growth rate, crack closurestress and fracture toughness. (2) To understand the effects of stress ratio and overload ratio on the fatiguecrack growth rate. (3) To establish the optimum method for the residual life estimation of a cracked weldment.The second year, the specimen is a Ti-6Al-4V VB weldment and the investigated items are the same as thoseof the first year. The results of this project will have academic merit and raise the fatigue design level in themilitary, aerospace and vehicle industries.