Improvement on Fatigue Strength of Fillet Welded Joints by Spray Coating

钢桥等钢结构通常有许多角焊缝，如十字形、T形和腹板节点。在这些接头的焊趾处，疲劳损伤通常已经发生并扩展。与其他类型的角焊接头相比，腹板节点的疲劳强度特别低，容易遭受疲劳损伤。作为避免疲劳损伤的有效措施之一，通过对焊趾进行一定的处理，可以降低应力集中，提高疲劳强度。目前常用的焊趾修整方法有打磨法、TIG法等。通过这些方法，焊趾处的曲率半径变大，形状变得光滑。此外，在现有焊趾的基础上增加焊缝以减少应力集中，这是因为这种处理使得焊趾的形状光滑，侧面角度较大。本研究旨在改善FAT…通过在现有的焊趾上喷涂一些金属材料来提高熔化强度。为了验证该方法提高疲劳强度的可能性和程度，对五种试件进行了疲劳试验和有限元分析。分别是焊态试件和锌、镍-铝、铜-铝、钛喷涂层试件。主要研究结果如下：(1)四种喷涂层试件的疲劳强度基本相同。这些强度也与焊态试件相似。(2)喷涂层没有提高疲劳强度的原因如下。喷涂件的杨氏模数极低，早期喷涂件出现疲劳裂纹，失去了喷涂件的应力传递功能。(3)为了保证喷涂件的效果，建议喷涂层的厚度和杨氏模数分别大于钢的3 mm和1/2。较少

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