Experimental and numerical study of static and fatigue properties of titanium alloy welded joints

Titanium and its alloys have high specific strength, good mechanical properties at high temperature, high resistance to corrosion and to attack by most acid solutions. Such characteristics make this material attractive for numerous applications because of recent improvements in welding techniques that allow to realize high quality welded joints. For example, new utilizations of titanium alloys are currently being studied in naval industry, where resistance to corrosion is a basic requirement in the choice of materials. Although fatigue strength of titanium alloys is the basic information required for designing navy structures, no official standard similar to Eurocode exists. Furthermore, data available in literature are still insufficient for reliably designing structure under fatigue loads. This paper aims to study static and fatigue behavior of butt welded joints made of titanium grade 2 and grade 5, all realized by laser welding technique. Experimental results of fatigue tests are presented both in terms of nominal stress amplitude σa and local strain amplitude εa. A finite element model is set on the basis of experimental results in order to assess the stress/strain concentration at the weld seam. Experimental tests show that fatigue failures in the titanium grade 2 and grade 5 specimens occur inside the base materials, but not at the weld location. Good correlation between experimental and numerical results is observed.