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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The force-displacement curves of the SPR joints produced without any offset ( e = 0, brown curves) can be used as reference when analyzing the effect of the offset on the load-bearing capacity. If the die offset is positive ( e = + 1 mm, green curves), the maximum force for rotating/pulling out the rivet from the lower sheet decreases, since the pullout starts at the “short” side of the rivet shank. Nevertheless, the displacement required for the final pullout of the “ long ” side of the rivet shank increases. In contrast, if the die offset is negative ( e = – 1 mm, blue curves), the maximum force for rotating/pulling out the rivet from the lower sheet increases, since the pullout starts at the “ long ” side of the rivet shank. However, the displacement required for the final pullout of the “ short ” side of the rivet shank decreases. 4. Summary and conclusions The influence of irregular offsets (eccentric misalignments) between rivet and die on the quality/integrity and on the load-bearing capacity of self-piercing-riveted (SPR) lap joints was experimentally investigated. Commercial 1.5 mm-thick EN AW-6016-T4 aluminum alloy sheets were joined by high-strength steel (HSS) rivets of different hardness. Characteristic cross-section features of the joints were assessed and their quasi-static shear-tensile strength was tested. Based on the results the following conclusions can be drawn: (1) The rivet-die offset was identified to influence significantly the deformation of the rivet shank and thus to affect the cross-section symmetry of the joints, in particular, if soft rivets were used. With increasing rivet-die offset and with decreasing rivet hardness the asymmetry of the joints became more considerable. However, the asymmetry was not clearly indicated by the force-displacement curves monitored during the SPR process. (2) The shear-tensile strength indicated by the maximum tensile force was acceptable even for very asymmetric joints, because the horizontal undercut (the interlock) of the rivet in the lower sheet was still sufficient for the lap joint configuration investigated. Hence, the integrity and the load-bearing capacity of the joints were only little affected, although the offset caused asymmetric deformation of the rivet shank. (3) The results of this study are related to SPR joints featuring two ductile aluminum alloy sheets of identical thickness. However, attention must be paid when transferring the results to, e.g., joints of brittle dissimilar materials with different thicknesses. Whether irregular rivet-die offsets are actually critical with respect to the joint integrity and to the load-bearing capacity has to be assessed for any particular combination of sheets to be joined. Acknowledgement The authors would like to thank STANLEY ® Engineered Fastening, Tucker GmbH, for sponsoring the SPR system and the steel rivets as well as AMAG rolling GmbH for sponsoring the aluminum alloy sheets that were used for the riveting experiments. References Barnes, T.A., Pashby, I.R., 2000. Joining techniques for aluminium spaceframes used in automobiles Part I – solid and liquid phase welding. Journal of Materials Processing Technology 99, 62 – 71. Barnes, T.A., Pashby, I.R., 2000. Joining techniques for aluminium spaceframes used in automobiles Part II – adhesive bonding and mechanical fasteners. Journal of Materials Processing Technology 99, 72 – 79. Domitner, J., Silvayeh, Z., Shafiee Sabet, A., Öksüz, K.I., Pelcastre, L., Hardell, J., 2021. Characterization of wear and friction between tool steel and aluminum alloys in sheet forming at room temperature. Journal of Manufacturing Processes 64, 774 – 784. Domitner, J., Auer, P., Stippich, J., Silvayeh, Z., Jessernig, S., Peiser, L., Hönsch, F., Sommitsch, C., 2022a. Riv-bonding of aluminum alloys with high-strength steels against the favorable joining direction. Journal of Materials Engineering and Performance 31(9), 6970 – 6979. Domitner, J., Silvayeh, Z., Predan, J., Auer, P., Stippich, J., Sommitsch, C., Gubeljak, N., 2022b. Load-bearing capacities and fracture modes of self-piercing-riveted, adhesive-bonded and riv-bonded aluminum joints at quasi-static and cyclic loadings. Journal of Materials Engineering and Performance 32, 7622 – 7632. Domitner, J., Silvayeh, Z., Predan, J., Jerenec, F., Auer, P., Stippich, J., Ferlič, L., Štefane , P., Sommitsch, C., Gubeljak, N., 2022c. Influence of the sheet edge condition on the fracture behavior of riv-bonded aluminum-magnesium joints. Key Engineering Materials 926, 1541 – 1548. Domitner, J., Silvayeh, Z., Predan, J., Auer, P., Stippich, J., Enzinger, N., Gubeljak, N., 2023. Load-bearing capacity of hybrid riv-bonded aluminum-magnesium joints at quasi-static and cyclic loadings. Journal of Manufacturing Processes 87, 133 – 140.