Fatigue Strength of CP Grade 2 Titanium Fillet Welded Joint for Ship Structure

摘要

Titanium is suitable for the material of ship hull structures because of high specific strength responding to high-speed demanding and high corrosion resistance in marine environment. In Japan, CP titanium plates have been already used for the structural members of fishing boats. However, there is no application of the structural members of merchant or government ships where the authorized standard is strict, because there is no suitable rule or recommendation for welded built-up titanium plate structures. Additionally, there is little research concerned with the fatigue strength of titanium fillet welded joints that are indispensable to ship structure. In this study, for promoting the development of titanium ships, the fatigue tests of butt-welded joints, transverse fillet welded joints and longitudinal fillet welded joints were carried out. As a result of that, the effectiveness of the fatigue strength of steel was investigated for designing on the safety judgment of titanium-welded joints. The relations between equivalent stress and number of cycle to failure are obtained by adapting the modified MIL-HDBK-5 method to the test results where fatigue crack initiates in weld toe section. These relations are also useful for the safety evaluation of the test specimens where crack initiates in base metal section.