PSI - Issue 82

Andreas Taucher et al. / Procedia Structural Integrity 82 (2026) 295–301 A. Taucher et al. / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction Components with complex geometries and high stiffness that are formed from sheet metals are widely used in the automotive industry for body-in-white (BiW) and chassis applications, since such components offer the possibility to decrease the vehicle weight (Rosenthal et al., 2020; Zheng et al., 2018). Using finite element (FE) simulation software tools can exploit the potential of sheet metal components by optimizing forming processes and component geometries. The prediction quality and accuracy of the simulations strongly depends on the quality of the data available for creating the simulation models, including geometry, tribology and material data (Bruschi et al., 2014; Hosford et al., 1999; Hou et al., 2023). Typical simulations of sheet metal forming processes require at least the elastic properties, the flow curve and the yield surface as input parameters to model the elastoplastic deformation of the sheets. The flow curve describes the increase of the flow stress with increasing plastic true strain of a work-hardening material. Flow curves are usually derived from results of material tests by using established mathematical extrapolation criteria (e.g., Hockett and Sherby, 1975; Hollomon, 1945; Ludwik, 1909; Swift, 1952; Voce 1948), as exemplarily shown in Figure 1a. The yield surface describes the transition from elastic to plastic deformation depending on the multiaxial stress state (Banabic, 2010). Most simulation software tools provide selected yield criteria (e.g., Barlat, 1989; Banabic-Balan-Comsa, 2005; Hill, 1948; Vegter, 2017) that define the yield surface in the biaxial stress state as usually considered in sheet metal forming. Figure 1b compares three commonly used yield criteria.

(a)

(b)

Fig. 1. Different criteria for (a) flow curves and (b) yield surfaces, adapted from Banabic (2010).

The forming limit curve (FLC) plotted in the so-called forming limit diagram (FLD) defines the limits of formability depending on the biaxial strain state. Figure 2 exemplarily shows the result of a deep-drawing simulation, which enables analyzing forming failures such as insufficient stretching, excessive thinning and cracking. The FLC can be determined using material tests (e.g., Nakajima, 1971; Marciniak, 1964) or empirical methods. As material tests are usually time-consuming, they consider only linear strain paths and the results may notably scatter, empirical methods for predicting the FLC have gained popularity (Abspoel et al., 2013). In order to identify common strategies and methodologies for acquiring material data that can be used for the FE simulation of sheet metal forming processes, this study comprises a series of semi-structured interviews with experts from the automotive industry. These interviews were conducted within the framework of a qualitative exploratory survey.

Fig. 2. Deep-drawn aluminum alloy component with areas of potential drawing failures (left) and corresponding forming limit diagram (right) calculated using the AutoForm FE software, adapted from Hodži ć et al. (2023a).