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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1. Introduction Aluminum-based lightweight design of car bodies improves the efficiency of fossil fuels and, thus, it significantly contributes to the global goal of reducing CO 2 emissions and air pollution (Hirsch (2014), Miller et al. (2000)). In this context, the industrial research has focused on forming – mainly on deep drawing – of 5xxx and 6xxx aluminum alloy sheets for automotive applications (e.g., Domitner et al. (2021), Hodžić et al. (2023a, 2023b), Shafiee Sabet et al. (2021)). However, not only reliable forming processes but also stable and cost-efficient joining processes are in dispensible for integrating aluminum alloy components into car bodies-in-white (Barnes and Pashby (2000a, 2000b), Gould (2012)). Because of technological challenges, the applicability of resistance spot welding (RSW), which has preferentially been used for joining steels in the automotive serial production, is quite limited for aluminum alloys (Manladan et al. (2017)). Innovative welding technologies have been developed for thermal joining of aluminum alloys with similar (Feng et al. (2009), Pickin and Young (2006)) and dissimilar (Gullino et al. (2019), Silvayeh et al. (2020)) materials in car body manufacturing. However, self-piercing riveting (SPR) has established as standard technology for mechanical joining of thin aluminum alloy sheets, as riveted joints have basically more favorable properties than welded joints (He et al. (2008), Li et al. (2017)). Moreover, SPR can be combined with adhesive bonding to obtain hybrid joints of superior load-bearing capacity under quasi-static and cyclic conditions (Domitner et al. (2022b), Moroni (2019)). This so-called “ riv-bonding ” technology is not only suitable for joining similar materials, e.g., aluminum-aluminum (Liu et al. (2021), Potgorschek (2020)), but also for joining dissimilar materials, e.g., aluminum-steel (Domitner et al. (2022a)) or aluminum-magnesium (Domitner et al. (2022c, 2023)). Controlling the quality of SPR joints is of utmost interest in the automotive serial production. Evaluating charac teristic features of joint cross-sections, including particularly the protrusion height of the rivet head, the horizontal undercut of the rivet and the minimum bottom thickness of the lower sheet, has become common practice for assessing the general joint quality/integrity (Haque (2018)). The characteristic features were identified to depend on the SPR process parameters and to correlate with the static shear-tensile strength of the lap joints (Li (2017), Li et al. (2012)). Besides assessing the characteristic features, the punch force-displacement curve is often monitored during the SPR process, which can be employed for the in-line process control as well as for the validation of finite element (FE) process simulations (Hönsch et al. (2020)). The influence of irregular SPR process conditions, such as variation of setting force and pre-clamping force, poor fit of the sheets, angular misalignment of the joint and edge offset distance on the cross-section features and on the shear-tensile strength of aluminum-steel lap joints was experimentally investigated (Jeong et al. (2020)). The setting force was identified as parameter that generally has the most significant influence, whereas the angular misalignment and the edge offset distance were found to influence particularly the shear-tensile strength. However, the influence of an irregular offset between rivet and die has not been studied, although this may also affect the interlock between the rivet and the components to be joined. Therefore, the present work focuses on the influence of the rivet-die offset (of eccentric misalignments of rivet and die) on the integrity and on the load-bearing capacity of SPR lap joints. 2. Materials and methods Coupons with dimensions of 100 mm × 90 mm were shear-cut from commercial 1.5 mm-thick EN AW-6016-T4 aluminum alloy sheets. For each of the samples two coupons were riveted together using two commercial semi tubular Tucker C5.3×5.0 (C-type rivet with diameter of 5.3 mm and height of 5.0 mm) high-strength manganese boron steel rivets of the three hardness classes H0 (soft), H2 (medium) and H4 (hard). Total length, total width and overlapping length of the samples were approx. 180 mm, 90 mm and 20 mm, respectively, and the distance between the rivet axes was 45 mm (Domitner et al. (2022b, 2022c, 2023)). The Tucker riveting system shown in Figure 1 (a) was used for preparing the joints, which consisted of a massive C-frame, an ERC control unit, an electrically driven ERT80 spindle and a T021 die. The punch velocity was 100 mm/s and the blankholder force was 8 kN. As shown in the detail, an adapter with an eccentric drill hole for inserting the die was used for achieving the offset between the blankholder axis that is in-line with the rivet axis and the die axis. Different offsets of 0.5 mm and 1.0 mm were achieved by using different adapters.