Experimental Research of the Weakening of the Fuselage Skin by RFSSW Single Row Joints

The paper presents the results of experimental investigations, the aim of which was to determine the degree of weakening of skin sheet of the thin-walled structure through a single-row welded joints made by Refill Friction Stir Spot Welding (RFSSW) technology. At the beginning, a short metallographic analysis of the weld was carried out, defining the characteristic areas of the microstructure. Then, comparative tests were carried out on the thin-walled structure sample in the form of a single-row skin-stringer joint. The structures made with the discussed technology of welding were compared with the traditionally joined structure by riveting. It has been shown that in the case of the welded structure, the skin sheet is weakened by more than 6% to a lesser extent than in the case of riveted. However, it was shown that the cracking path in the tensiled welded sheet runs along an unpredictable path, deviating from the line marked by the welds’ row. While in the case of riveted joint the cracking propagation along the row of rivets was revealed. The analyzes of fracture surfaces for both cases using scanning electron microscopy were also undertaken, thus undertaking preliminary considerations on the mechanism of fracture.