PSI - Issue 57

Kalle Lipiäinen et al. / Procedia Structural Integrity 57 (2024) 785–792 Lipiäinen et al. / Structural Integrity Procedia 00 (2019) 000 – 000

791

7

a = 0.06 mm

a = 0.018 mm

a = 0.05 mm

a = 0.1 mm

3000

3000

3000

3000

4R ref stress

4R ref stress

4R ref stress

4R ref stress

Unnotched 50 μ m Shear cut hole 50 μm W-EDM hole 50 μ m Unnotched TCD Shear cut TCD

Unnotched 50 μ m Shear cut hole 50 μm W-EDM 50 μ m Unnotched - Plain TCD Shear cut - Plain TCD

Unnotched 50 μ m Shear cut hole 50 μm W-EDM 50 μ m Unnotched - Plain TCD Shear cut - Plain TCD

Unnotched 50 μ m Shear cut hole 50 μm W-EDM 50 μ m Unnotched - Plain TCD Shear cut - Plain TCD

300

300

300

300

10000

100000 1000000

10000

100000 1000000

10000

100000 1000000

10000

100000 1000000

Fatigue life [cycles]

Fatigue life [cycles]

Fatigue life [cycles]

Fatigue life [cycles]

Geometric SCFs highlighted and quality neglected

Local quality highlighted and SCF neglected

Quality and and geometric SCFs balanced

Increases

Influence of 4R mean stress correction

Decreases

Evaluation not working properly with VA loads and quality parameter removed from analysis

Result of combined effect in fatigue strength assessment

Scatter and uncertainties increased and conservative results on unnotched details

Fig. 8. 4R reference stresses with from 0.065 mm to 0.1 mm stress averaging distances and influence of stress averaging distance on fatigue strength assessment.

6. Conclusions and discussion The studied HR 800 MPa automotive steels show high fatigue performance after shear cutting, which is important in automotive applications due to high productivity demands in large production series. Fatigue performance assessment based on local properties with TCD-based 4R method was found beneficial. Residual stresses induced from shear cutting were utilized in analysis resulting reasonable local mean stress correction with external loading. Variable amplitude (VA) loading of these 800 MPa automotive steels will be evaluated in future studies as it is natural extension to quality based 4R method fatigue strength assessment. Similar fatigue test data including equivalent crack sizes from (Lipiäinen, Ahola, & Björk, 2022; Lipiäinen, Ahola, Kaijalainen, et al., 2022) and supplemented with 800 MPa automotive steels VA-data should be re-analysed. Re-analysis could be used to verify the method with larger dataset including different geometries, material strength, residual stresses and equivalent crack sizes. Acknowledgements The authors wish to thank Business Finland for funding via FOSSA project and SSAB Europe for providing materials for experimental testing. References Ahola, A., Skriko, T., & Björk, T. (2020). Fatigue strength assessment of ultra-high-strength steel fillet weld joints using 4R method. Journal of Constructional Steel Research , 167 . https://doi.org/10.1016/j.jcsr.2019.105861 Björk, T., Ahola, A., Skriko, T., & Lipiäinen, K. (2023). On the backward design — an advanced concept for the design of welded structures for demanding applications. Welding in the World . https://doi.org/10.1007/s40194-023 01483-w ISO 6892-1:2019 Metallic materials — Tensile testing — Part 1: Method of test at room temperature. (2019). ISO 16630:2017 Metallic materials — Sheet and strip — Hole expanding test . (2017). Kaijalainen, A., Kesti, V., Vierelä, R., Ylitolva, M., Porter, D., & Kömi, J. (2017). The effect of microstructure on the sheared edge quality and hole expansion ratio of hot-rolled 700 MPa steel. Journal of Physics: Conference Series , 896 (1). https://doi.org/10.1088/1742-6596/896/1/012103