Abstract
In 2012, a novel production line was developed to produce electric arc furnace steel sheet for automotive structure, as a national project in Japan. From the viewpoint of crashworthiness, the evaluation of joint strength under dynamic loading is essential. In this study, single-lap spot-welded joint specimens are prepared with the variation of welding current. The specimen sheet is 980-MPa grade electric arc furnace steel and 1.0 mm in thickness, which is supplied by Tokyo Steel Co., Ltd. Nugget diameter is recommended by a well-known empirical equation, , where is sheet thickness. The nugget diameter can be adjusted mainly by welding current. In order to find the optimum nugget diameter under dynamic tensile-shear, five values of welding current, 6.1, 6.4, 6.7, 7.0 and 7.3 kA are tried. The values are set for the recommended nugget diameter 5.00 mm, and ±5% and ±10% of the recommended diameter. Experimental results of quasi-static (loading velocity: 2.0 mm/min = 3.3×10-5 m/s) and dynamic (initial loading velocity: 7 m/s) tensile-shear tests shows that, despite of loading velocity and welding current (equivalent to nugget diameter), tensile-shear strengths are almost constant. Absorbed energies up to the strength give complicated tendencies. At the recommended welding current (equivalent to mm), the most stable strengths and energies are obtained.
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