Titanium is well recognized as a modern and high performance metal that is much stronger and lighter than the most widely used steels in the industry. There is a growing need to reduce the part weight, cost and lead time, while concurrently facilitating enhanced performance of structural parts made from titanium and titanium alloys. Structural components made from titanium have the advantage of high strength-to-weight ratio, and high stiffness-to-weight ratio. Owing to good resistance to corrosion and superior ballistic properties, titanium is used in several defense applications. This thesis presents a summary of the research conducted on welded built-up titanium beams so as to eventually facilitate the design, fabrication, and implementation of titanium in large structural members.
An alternative to machining a structural component from thick plates or billets is to fabricate beams using the built-up concept. Rolled plates and sheets of titanium alloys can be cut to size and welded together to fabricate a built-up structural component. The primary objective of this project is to investigate structural performance of built-up welded beams fabricated from commercially pure (Grade 2) titanium and a common alloy (Ti-6Al-4V) under both static and fatigue loading conditions. Six welded built-up titanium beams were fabricated and tested to experimentally and theoretically evaluate structural performance. Analysis and design approaches for static and fatigue performance of built-up beams were also studied and it is clearly demonstrated that it is feasible to fabricate large built-up titanium beams by welding parts together using GMAW-P welding process. The welds produced by this method were found to be sound and without any visible cracks. The study also revealed that there is no deleterious influence of welding on structural performance of the built-up welded beams of commercially pure titanium and Ti-6Al-4V titanium alloy.
With suitable modifications to the current AISC steel design specifications a preliminary design methodology was developed for the titanium beams. The failure loads, deflections and strains of welded built-up titanium beams are predictable to a reasonably good level of accuracy. The test beams also demonstrated significant reserve strength and ductility following yielding. The deflection curves and the load versus strain relationships obtained from the test results demonstrate a reasonably close match between the theoretical predictions and experimental test results up until the elastic limit of the material. The fatigue tests conducted for this research revealed that the welded built-up beams made from the commercially pure titanium have better life than those made from the Ti-6Al-4V. However additional work is required to develop further insight into the fatigue behavior of welded built-up titanium beams.
Finally the proposed welded built-up beam approach is anticipated to be a cost effective alternative to fabricating large structural elements and members by machining of the parts from thick plates or billets.