Research On LTTE In Improving Fatigue Strengths Of Welded Joints And Distribution Of Residual Stresses

Welding is one most important connection method for iron and steel materials. Welded structures have made up to 45% of total production of steel in weight, especially in developed countries this proportion is up to 70%. However, the fracture accidents often occur. Many statistical data show that 90% of fracture accidents of the welded structures are caused by fatigue failure of welded joints. Fatigue cracks mainly initiate at the weld toe. The fatigue strengths of welded joints in welded structures are much lower than those of the base metal because there are stress concentrations and tensile residual stresses at weld toes.The use of low transformation temperature electrodes (LTTE) is new developed methods for improving the fatigue strengths of welded joints. The fatigue tests of LTTE dressing are carried out on both transverse and longitudinal fillet welded joints. The fatigue strengths of LTTE dressing are 154.7MPa and 173.9MPa respectively at cycles of 2×106 improved by 101.4% and 100.3% compared with TIG dressing. This shows that LTTE dressing in improving fatigue strength is useful or better than TIG dressing, meanwhile, LTTE dressing is easier than TIG dressing and can deal with different position of welded beams. Meanwhile, the International Institute of Welding (IIW) has made a systematically study on TIG dressing. The conclusion is TIG dressing is the most useful method in industry. For this, LTTE dressing technology has its value in dressing.ANSYS is one kind of large-scale finite element software. This article also carries on thermal and stress simulations on welded beams which are welded by ordinary electrodes and LTTE electrodes. Thus we can obtained that LTTE is more useful than ordinary electrodes in reducing stress concentrations.Above all, LTTE dressing technology is an economical and useful method in improving fatigue strengths. We can carry on its suitable promotion for consideration.