Abstract
Mechanical properties and failure behaviors of friction stir spot welded (FSSW) joints of two dissimilar ferrous alloys, cold-rolled carbon steel (SPCC) and 409L stainless steel (SUS 409L), are investigated under opening-dominant combined loads. The texture of dissimilar FSSW joints depends on the upper sheet material. The failure contours for the FSSW joints under combined loads are constructed in terms of the axial load and shear load by modifying existing failure criteria for resistance spot welds. The shape of the failure contour also depends on the upper sheet material. The failure contours are nearly elliptic in shape when the upper sheet is SPCC and are relatively straight lines when the upper sheet is SUS 409L.
Highlights
Friction stir spot welding (FSSW) is a solid-state joining process that originated from friction stir welding (FSW), a technique patented in 1991 by TWI [1]
EBSD analysis shows that extremely fine homogeneous grains developed in the stir zone, while the texture of dissimilar FSSW joints depends on the upper sheet material
The failure contours for the FSSW joints under combined loads were constructed in terms of the axial load and shear load by modifying existing failure criteria for resistance spot welding (RSW)
Summary
Friction stir spot welding (FSSW) is a solid-state joining process that originated from friction stir welding (FSW), a technique patented in 1991 by TWI [1]. Lee et al [17] performed a failure test of RSW joints in U-shaped specimens under combined shear and tension loads and proposed an ultimate strength model to fit their experimental results. Lin et al [18, 19] analyzed the failure mechanism of spot welds in square-cup specimens made from mild steel and HSLA steel under combined loads. They proposed a quadratic-form engineering failure criterion in terms of the normalized axial and shear loads with consideration of the sheet thickness and the nugget radius under combined loads. The failure behavior of FSSW joints under combined or multiaxial loads has been rarely investigated until recently, even though the failure behavior of FSSW joints can differ from that of RSW joints [21] due to the different joining
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