This program examined the fatigue resistance of titanium alloy welded structures, particularly those with minor welding imperfections. Fatigue testing checked for differences based on heat treatment, bending versus tension, weld configuration, cut edge condition, and various welding-related imperfections. Titanium 6Al-4V and welds with as-welded cap and root profiles were used throughout the testing. Fatigue design recommendations were derived from a combination of the test results, results from the literature, and existing design recommendations for steel and aluminum alloys. These design recommendations change the slope of the design lines to 1/-3.5 to better fit fatigue crack growth rate and fatigue S/N test results.
Welded structural titanium can be used in a large variety of structures, having an advantage where both high strength and light weight are prized. Land-based military hardware has recently been a particular focus, since welded titanium can allow lighter, more easily transported structures. However, no current design standard is available that covers simple types of titanium welded joints like attachment welds or butt welds where the caps and roots are not removed by subsequent grinding. Part of the service life of transported structures involves cyclic loading. However, no existing design standard recommends fatigue design allowables for a range of welded joints. Also, the welding quality that is required to provide acceptable fatigue performance is currently estimated using workmanship standards. These standards cover such items as surface condition and internal porosity.
This program was designed to provide fatigue data and analysis as a basis for a design standard and for welding quality requirements that are appropriate to transportable military structures and could also be extended for more general use in titanium structure design. The program data has been used during the development of the AWS structural welding code titanium D1.9.
