Abstract
This study is about the fatigue strength improvement of lap welding. Lap joint has been widely used to design of weld of GMAW process in the automobile industry. Generally, it is recommended to weld both fillet parts of lapped specimen in the design of weld, called “Double-fillet lap joint”. In the auto industries, however, the fact is that one fillet part of a lapped specimen could be welded due to assembly properties of automobile structure. There are many factors which are affected fatigue strength – base metal, welded joint, load condition, surface condition of weld, weld crack and so on. As mentioned above, when lap joint is only welded one fillet part, as the result of stress analysis of lapped specimen, it could be known that stress concentration greatly occurs at the region which meets between upper a specimen and lower a specimen. It is estimative that stress concentration could affect fatigue strength drop. In order not to occur stress concentration, optimum welding conditions which do not exist stress concentration were chosen by making the variation of the lap length of specimens. To compare fatigue strength of welding conditions depending on existence and nonexistence of stress concentration, fatigue tests were made experiment. Fatigue-limit evaluation was measured by using Infrared Thermography to compare results of fatigue tests. As the result of fatigue test, fatigue strength of welding conditions which do not exist stress concentration is superior than the other. Through the results obtained from experiments, when weld is designed, weld geometry which does not occur stress concentration is necessary to be designed.
Keywords: Welding, Lap Joint, Fatigue Limit Evaluation, Fatigue Life, Lock-in Infrared Thermography