PSI - Issue 34

Benjamin Möller et al. / Procedia Structural Integrity 34 (2021) 160–165 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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since some lower stress values (for peel T-joints) are found in the range 4·10 5 < N < 2·10 6 , showing non-conservative results towards FAT 160. Due to higher notch stresses for lap joints with fillet welds compared to the joint types with I-shape welds, the scatter of an overall notch stress S-N curve increases to T  = 1 : 2.03.

Fig. 3. Notch stress assessment based on von Mises stresses at the fatigue relevant weld toe radii.

4. Fatigue assessment of a battery carrier by structural stresses For the fatigue assessment under industrial preconditions, a simplified assessment approach towards the notch stress approach is required, since the size of the model increases significantly compared to component level, e.g. full car body simulation in the automotive industry. Therefore, for the fatigue assessment of a battery carrier consisting of laser beam welds between AM structural connection nodes and extruded aluminum sections (Figure 4(a)), a structural stress approach has been chosen. From three investigated battery carriers, seven failure areas are found: four times AM node failures and three times seam weld failures , as it can be seen from seam weld ‘N1’ of node 8 in Figure 4(b). To connect both welding partners, hexahedral elements are set in between, which are connected to the surfaces of the structures by rigid body elements. The hexahedral elements reveal a stress distribution along the modeled seam weld, as maximum principal stresses for the simplified variant in Figure 4(c) show. The maximum stress value at the node of the hexahedral element is used for the assessment. Together with evaluated structural stresses from analogous load simulations of the corresponding seam weld specimens with I-shape, estimated fatigue lives result. For the exam ple of seam weld ‘N1’ of node 8 from battery carrier ‘BT1h’, a calculated fatigue life of N = 37,067 ( P S = 50 %) results, whereas the experimental fatigue life for a failure criterion ‘crack initiation’ based on laser displacement measurement data is approx. 10,000 cycles.

Fig. 4. Fatigue failure of a) the battery carrier ‘BT1h’ tested at F a = 2000 kN showing b) a crack starting from seam weld ‘N1’ at the AM structural node no. 8 and c) the numerical simulation result of the corresponding laser beam weld (I-shape).