PSI - Issue 54

Zahra Silvayeh et al. / Procedia Structural Integrity 54 (2024) 431–436 Z. Silvayeh et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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Figure 2. Representative cross-sections of SPR joints produced with rivet-die offsets of 0.0 mm (top row), 0.5 mm (middle row) and 1.0 mm (bottom row), and with rivets of hardness classes H0 (left column), H2 (middle column) and H4 (right column).

Figure 3 (a) shows the typical failure mode of the samples under quasi-static shear-tensile loading. The rivet was rotated/pulled out from the lower sheet and the upper sheet fractured close to the head of the rivet. In each of the tests the SPR joint was the weakest part of the sample, but fracture of the aluminum alloy sheets away from the joint did not occur. This characteristic quasi-static fracture behavior was confirmed in previous studies on aluminum alloy sheets lap-joined using high-strength steel self-piercing rivets (Domitner et al. (2022b), Li (2017), Li et al. (2012)). As the pullout of the rivet from the lower sheet is the decisive failure mechanism, the pullout resistance significantly influences the course of the tensile force-displacement curves that were monitored during shear-tensile testing. Figure 3 (b) shows representative force-displacement curves of samples joined either without any offset ( e = 0), with positive offset ( e = + 1 mm), or with negative offset ( e = – 1 mm) of the die in tension direction. The influence of positive ( e +) and negative ( e – ) offsets on the joint formation is also schematically illustrated. The maximum force of the joints produced without offset was ≈ 6.5 kN at the displacement of ≈ 2.5 mm, and the maximum displacement was ≈ 6-7 mm. Joints produced with negative offset showed higher maximum force of ≈ 6.9-7.4 kN, but lower maximum displacement of ≈ 5 mm. In contrast, joints produced with positive offset showed lower maximum force of ≈ 6-6.5 kN at the displacement of ≈ 2 mm, but greater maximum displacement of ≈ 8-9 mm.

Figure 3. (a) Setup used for quasi-static shear-tensile testing of the SPR joints (the detail illustrates the typical failure mode). (b) Comparison of force-displacement curves monitored in shear-tensile testing of samples with positive and negative offsets.