Automobile chassis components are parts that support the full load of the vehicle and are subject to repeated fatigue loads during vehicle operation. In addition, chassis components are mostly manufactured by arc welding with a lap fillet joint. Generally, welds are known to act as structural and metallurgical discontinuities that reduce the fatigue strength [3
]. Stress concentration is one of the representative factors of structural discontinuity. Metallurgical discontinuities include differences in properties between the base material, the welded part, and the heat-affected zone due to welding heat input. However, it has been reported that the effect of the weld bead on the metallurgical discontinuity is difficult to confirm because the stress concentration effect on the weld bead is dominant in the lap-fillet-joint-shaped arc weld [4
]. Therefore, a number of previous studies have been carried out to clarify the relationship between weld bead shape and fatigue strength in lap fillet joint arc welding. Ahiale et al. [5
] compared the fatigue strengths of the welds of gas metal arc welding (GMAW) and plasma arc welding (PAW) in lap fillet joints. It is reported that the shape of the PAW weld is wider and gentler than that of the GMAW weld, improving the fatigue characteristics. Kognti et al. [6
] presented different welds by varying the welding conditions at the lap fillet joint and compared the fatigue strength of the welds and it was confirmed that the fatigue strength was increased by increasing the weld toe angle. Chung et al. [7
] showed welds with different weld toe angles and fatigue strength according to the change of torch and push angle. It was also confirmed that the fatigue life was increased about two times as the toe angle increased by 30°. Feng et al. [8
] confirmed the fatigue strength of various combinations of advanced high strength steel (AHSS) in lap fillet joints, and as a result, it was confirmed that the fatigue strength increased with increasing weld toe angle and weld toe radius. In addition, the fatigue strength is predicted through the stress concentration factor Kt
of weld toe. Beretta et al. [9
] obtained the stress concentration factor of the weld toe and root by the finite element method (FEM) in the lap fillet joint of Al alloy and predicted the fatigue strength through the Kt.
Kim et al. [10
] developed a process to predict the fatigue life of automotive mufflers in lap fillet joints. In order to predict the fatigue life, the Kt
was obtained by FEM after modeling the shape of the welded part. Based on the Kt
, the fatigue life predicted by the change of weld toe angle and weld toe radius was estimated. As mentioned above, the previous studies on the arc weld and fatigue characteristics of lap fillet joints show that the improvement of weld toe angle increases the fatigue strength. However, none of the studies investigated the relationship between fatigue strength and other factors except weld toe angle. Kim et al. [11
] calculated the stress concentration factor (Kt
) by using the radius and the degree of the toe and the height of the welded part in the butt weld, calculated the fatigue notch coefficient (Kf
) for the fatigue life prediction and then predicted the fatigue life using the alternative method. The residual stress in welds also affects the fatigue strength of welded joint. Richter-Trummer et al. [12
] measured the residual stress distribution in a 6082-T6 Al alloy metal inert gas (MIG) butt welded thin plate using the contour method and compared the fatigue behavior of the plate with and without residual stress. Wang et al. [13
] investigated the residual stress and fatigue strength of hybrid laser-metal inert gas welded Al alloy compared with the MIG welded joint and it was confirmed that the fatigue strength was improved by the narrow weld and heat affected zone (HAZ), weak softening behavior, and low residual stress level.
In this study, the shape of weld beads affecting the fatigue strength in the arc welds of lap fillet joints was investigated. For this purpose, four types of welds with different shapes were fabricated. The stress-number of cycles to failure (S–N) curve was derived from the fatigue test to confirm the fatigue strength in order to determine the bead shape of the welded part affecting the fatigue strength, angle, length and area of the weld bead. The relationship between the fatigue strength and the bead shape factor of the weld is discussed.