| Budget Amount *help |
¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2001: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2000: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
The steel structures such as steel bridges and others usually have many fillet welds such as cruciform, T-shaped and web-gusset joints. At the weld toes of these joints, fatigue damages have usually occurred and propagated. In general the web-gusset welded joints have especially low fatigue strength and apt to suffer fatigue damages compared with other types of fillet welded joints. As one of effective countermeasures to avoid the fatigue damages, it is considered to reduce the stress concentration and increase the fatigue strength by giving some treatments to the welded toes. It is popular to finish the welded toes with grinding, TIG and others. By using these methods, the radius of curvature at the weld toe becomes large and their shape become smooth. In addition, additional weld to the existing weld toe is sometimes utilized to reduce the stress concentration because this treatment makes the welded toe's shape smooth and the flank angle large.
This study aims at an improvement of fat
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igue strength by applying spray coating of some metallic materials to the existing weld toe. In order to examine the possibility and degree of improving fatigue strength by this method, the fatigue tests and the finite element analyses were carried out on five types of specimens. They are as welded and Zn, Ni-Al, Cu-Al, Ti spray-coated specimens. The main findings of these examinations are as follows.
(1) The fatigue strength of four types of spray-coated specimens was almost the same as each other. These strength was also similar to that of the as-welded specimen.
(2) The reason why the fatigue strength was not improved by the spray coating is considered as follows. The Young's modulus of the spray-coated parts was extremely low and the fatigue crack occurred from the spray-coated parts at early stage, and the stress transmitting function of the spray-coated parts was lost.
(3) In order to make sure of the effect of the spray coating, it is recommended that the thickness and Young's modulus of the spray coating is larger than 3mm and a half of the steel, respectively. Less
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