Improvement on Fatigue Strength of Fillet Welded Joints by Spray Coating

在钢桥等钢结构中，角焊缝较多，如十字形、T形、腹板-节点板等。在这些接头的焊趾处，通常发生疲劳损伤并扩展。与其它类型的角焊节点相比，腹板-节点板焊接节点的疲劳强度普遍较低，且容易发生疲劳破坏。作为避免疲劳损伤的有效措施之一，对焊趾进行适当的处理，可以降低应力集中，提高疲劳强度。焊接焊趾一般采用打磨、TIG焊等方法。通过使用这些方法，焊趾处的曲率半径变大并且它们的形状变得平滑。此外，有时还采用在现有焊趾上附加焊缝的方法来减少应力集中，因为这种处理使焊趾形状光滑，侧面角大。 关于我们 通过在现有焊趾上喷涂一些金属材料来提高焊接强度。为了检验这种方法提高疲劳强度的可能性和程度，对五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)四种喷涂层试样的疲劳强度基本相同。这些强度也类似于焊接试样的强度。(2)疲劳强度没有通过喷涂得到改善的原因如下。喷涂件的杨氏模量极低，疲劳裂纹从喷涂件早期产生，喷涂件的应力传递功能丧失。(3)为保证喷涂效果，建议喷涂层厚度大于3 mm，杨氏模量大于钢的一半。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