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A Method for Evaluation of Tensile Properties of a Nugget Zone in a Spot-Welded Joint Considering the Strain Rate
|저자명||N. Park, M. Park, and H. Huh|
This paper deals with a method for evaluation of tensile properties of a nugget zone in a spot-welded joint at various strain rates using a micro material testing machine. In order to properly consider the load requirement, a driving and a load measuring part of a Static Micro Material Testing Machine (SMMTM) and a High-Speed Micro Material Testing Machine (HSMMTM) were replaced respectively. A jig and a gripping device are designed to meet the requirements of the specimen shape and strength. Two kinds of specimens for the tensile tests were obtained each from the center of the welded spot and 1 mm away from the centerline at the spot welded joint of the DP980 by wire Electric Discharged Machining (EDM). The thickness of the specimen was 0.3 mm and the gage length of the specimen was 1 mm. Digital Image Correlation method (DIC) was applied to measure the longitudinal strain. A method for speckle pattern generation was also improved for application of the DIC method to the micro-specimen. Quasi-static tests were performed with SMMTM at strain rates of 0.001 s−1 and 0.1 s−1 and dynamic tests were performed with HSMMTM at strain rates of 1 s−1, 10 s−1 and 100 s−1, respectively. A comparative evaluation was performed between the material properties of the base metal and the nugget region in spot welded joint, based on the obtained stress−strain curves.