PSI - Issue 37

Liting Shi et al. / Procedia Structural Integrity 37 (2022) 351–358 L Shi et al/ Structural Integrity Procedia 00 (2022) 000 – 000

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therefore interesting to understand how the notch root angle alters the maximum principal strain in the AA5754-HSLA RSWs. The finite element analysis results of AA5754-HSLA RSWs with different uniform notch root angles are shown in Fig. 5a. Fig. 5a demonstrates that the maximum principal strain is 42% to 50% greater in an AA5754-HSLA RSW with a notch root angle of 10  at a given load level than that with a notch root angle of 36  . In AA5754-HSLA RSWs with asymmetric notch root angles, the local stress in the leading edge is tensile while the local stress in the trailing edge is compressive indicating that only the leading edge should be discussed further as it is responsible for fatigue crack initiation and growth. As an example, the run-out point in tensile shear fatigue testing at a maximum fatigue load of 1988 N (where the red arrow pointed in Fig. 4a) is used to highlight the effect of asymmetric notch root angles on maximum principal strain. This specimen has a notch root angle of 32  in the leading edge and 16  in the trailing edge (refer to the metallographic image of the tested specimen inserted in Fig. 4a). FEA was performed on this specimen and the results are summarized in Fig. 6b. From Fig. 6b, it is shown that a 59% difference in maximum principal strain values could be realized between the two notch root angles (0.0122 for 32  vs. 0.00767 for 16  ). This suggests that the large scatter in fatigue life could be simply caused by which notch root angle was positioned at the leading edge for fatigue testing.

(b)

Fig. 6 Effect of notch root angle on maximum principal strain at the weld notch tip in AA5754 to HSLA RSWs with (a) uniform notch root angles; (b) asymmetric notch root angles of 16  degrees and 32  .

5. Conclusions 1.1 mm thick AA5754 sheet was resistance spot welded to 2.0 mm thick high-strength low-alloy (HSLA) steel sheet using multi-ring domed (MRD) electrodes and multiple solidification weld schedules to achieve acceptable static joint strength. Load-controlled fatigue test results show that the fatigue life is longer in the AA5754-HSLA steel spot welds than that of the 1.1 mm thick AA5754 sheet joined to itself. Using the structural stress range, all fatigue life data points from both the lap shear and coach peel configurations fall onto a single master curve indicating that the weld nugget diameter is the controlling parameter for fatigue life. Finite element simulation considering material inhomogeneity in the weld further confirms that a large notch root angle at the weld nugget is beneficial to yield longer fatigue life as less maximum principal strain occurs in the aluminum sheet in the AA5754-HSLA steel spot welds. Acknowledgements The authors are grateful for the financial support from Canadian Federal Government Energy Innovation Program, Office of Energy R&D – Mission and Innovation – Energy End User Program, Natural Resources Canada, GM Canada and CanmetMATERIALS. The authors also acknowledge the technical support from Jie Liang, Babak Shalchi Amirkhiz, Mark Gesing at CanmetMATERIALS. The authors are also thankful to Chad Clark (Fusion Welding Solutions) for his welding assistance.