Improvement on Fatigue Strength of Fillet Welded Joints by Spray Coating

钢结构如钢桥等通常有许多角焊缝，如十字形、t形和蹼形接缝。在这些接头的焊接脚趾处，疲劳损伤经常发生并扩展。一般来说，与其他类型的角焊接头相比，腹板扣板焊接接头的疲劳强度特别低，容易产生疲劳损伤。通过对焊接趾进行处理，降低应力集中，提高疲劳强度，是避免焊接趾疲劳损伤的有效对策之一。焊接脚趾采用研磨、TIG等加工方式。通过这些方法，焊缝脚趾处的曲率半径变大，形状变得光滑。此外，有时利用在现有焊趾上附加焊缝来降低应力集中，因为这种处理使焊接的焊趾形状光滑，侧面角大。本研究的目的是通过在现有的焊趾上喷涂一些金属材料来提高焊趾的强度。为了验证该方法提高疲劳强度的可能性和程度，对5种类型的试件进行了疲劳试验和有限元分析。它们是焊接和Zn， Ni-Al, Cu-Al， Ti喷涂试样。这些检查的主要结果如下。(1) 4种喷涂试样的疲劳强度基本相同。这些强度也与焊接试样相似。(2)喷涂不能提高疲劳强度的原因考虑如下：喷涂件的杨氏模量极低，喷涂件在早期就产生疲劳裂纹，失去了喷涂件的应力传递功能。(3)为保证喷涂效果，建议喷涂涂层的厚度和杨氏模量分别大于钢的3mm和一半。少

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 … More 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