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Failure Modes of Friction Stir Spot Welds in Lap-Shear Specimens of Dissimilar Advanced High Strength Steels under Quasi-Static and Cyclic Loading Conditions
- Seung-Hoon Hong - Univ. of Michigan-Ann Arbor ,
- Kulthida Sripichai - Univ. of Michigan-Ann Arbor ,
- Chia-Siung Yu - Univ. of Michigan-Ann Arbor ,
- Katherine Avery - Univ. of Michigan-Ann Arbor ,
- Jwo Pan - Univ. of Michigan-Ann Arbor ,
- Tsung-Yu Pan - Oak Ridge National Laboratory ,
- Michael Santella - Oak Ridge National Laboratory
ISSN: 1946-3979, e-ISSN: 1946-3987
Published April 16, 2012 by SAE International in United States
Citation: Hong, S., Sripichai, K., Yu, C., Avery, K. et al., "Failure Modes of Friction Stir Spot Welds in Lap-Shear Specimens of Dissimilar Advanced High Strength Steels under Quasi-Static and Cyclic Loading Conditions," SAE Int. J. Mater. Manf. 5(2):375-381, 2012, https://doi.org/10.4271/2012-01-0479.
Failure modes of friction stir spot welds in lap-shear specimens of dissimilar high strength dual phase steel (DP780GA) and hot stamped boron steel (HSBS) sheets are investigated under quasi-static and cyclic loading conditions based on experimental observations. Optical micrographs of dissimilar DP780GA/HSBS friction stir spot welds made by a concave tool before and after failure are examined. The micrographs indicate that the failure modes of the welds under quasi-static and cyclic loading conditions are quite similar. The micrographs show that the DP780GA/HSBS welds mainly fail from cracks growing through the upper DP780GA sheets where the concave tool was plunged into during the welding process. Based on the observed failure modes, a kinked fatigue crack growth model is adopted to estimate fatigue lives. The fatigue life estimations are reasonably in agreement with the experimental results under low-cycle loading conditions but lower than the experimental results under high-cycle loading conditions.