PSI - Issue 51

Liting Shi et al. / Procedia Structural Integrity 51 (2023) 102–108 L. Shi et al. / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 2. Macrostructures of resistance spot welds of (a) AA6022 to itself, (b) two-sheet AA6022-HSLA and (c) three-sheet AA6022-HSLA CR780T.

3.2 Tensile and fatigue properties Tensile peak loads for tensile shear specimens of dissimilar materials aluminum-steel RSWs are greater than that of aluminum to itself RSWs (Fig. 3), which usually increases with increasing weld nugget diameters. The tensile peak loads in the two-sheet aluminum-steel RSWs and three-sheet aluminum-steel-steel RSWs are similar in both tensile shear and coach peel specimens.

Fig. 3. Tensile peak load in AA6022-AA6022, AA6022-HSLA and AA6022-HSLA-CR780T.

Fatigue life of dissimilar materials of aluminum to steel RSWs are longer than that of aluminum to itself RSWs for tensile shear and coach peel specimens (Fig. 4). In tensile shear specimens, the fatigue life of two-sheet aluminum steel RSW and three-sheet aluminum-steel-steel is similar. In coach peel specimens, the difference of fatigue life between two-sheet and three-sheet RSWs depends on the load levels. Fatigue life of two-sheet RSW is longer than that of three-sheet RSWs at high load range (above 160 N), while fatigue life of two-sheet RSW is shorter than that of three-sheet RSWs for load range below 160 N. This may be attributed, in part, to the complex loading condition which leads to different fatigue life in crack initiation and propagation at high and low load levels. The fatigue fracture modes were observed to be interfacial fracture at the interface of aluminum and steel for the three-sheet stack-ups, and pull out fracture in aluminum alloy sheet for tensile shear and coach peel specimens.