PSI - Issue 28

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B.W. Williams et al. / Procedia Structural Integrity 28 (2020) 1024–1038 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Figure 13: Brittle failure stress as a function of temperature

6. Conclusions A coupled ductile-brittle fracture model for TC128B steel was developed that is valid for temperatures between - 80 and 24 °C at quasi-static and dynamic strain-rates. To capture ductile fracture, the Modified-Mohr-Coulomb (MMC) damage mechanics model was used in which the failure strain is dependant on both stress triaxiality and Lode angle. As a starting point, a well calibrated damage model from literature for TC128 was used which was based on a single temperature (room temperature) and strain-rate (quasi-static). This model was calibrated and verified using several mechanical tests, finite element simulations and optimization methods. Geometries that were shown to be well described by the model included notched tension, shear, biaxial, and fracture geometries such as SEB and CT. In the present work, the damage model coefficients were adjusted to account for different temperatures and strain-rates by only calibrating based on the hardening response from tensile tests and the fracture response from Charpy tests. The trend of failure strain with stress triaxiality and Lode angle was maintained. The damage model accurately captured the load-displacement response for ductile fracture but could not capture the sudden load drop associated with cleavage fracture. To capture cleavage fracture when preceded by ductile fracture, a brittle failure stress criterion was used based on the maximum principle stress at the crack front. It was shown that the brittle failure stress was a function of temperature. Acknowledgements The authors would like to acknowledge many useful discussions with Dr. Hari Simha at the University of Guelph, Mark Gesing and Dr. Bill Tyson of CanmetMATERIALS, and Ian Whittal and Kiran Shoib of Transport Canada. Funding for this work was provided by the Transportation of Dangerous Goods Programs Scientific Research & Analysis branch at Transport Canada. References Bai, Y. and Wierzbicki, T., 2010. Application of extended Mohr-Coulomb criterion to ductile fracture. International Journal of Fracture 161, 1-20. Beremin, F.M., 1983. A local criterion for cleavage fracture of a nuclear pressure vessel steel. Metallurgical Transactions A 14A, 2277-2287. Carolan, M., Perlman, B., and Gonzàlez III, F., 2018. Validation of puncture simulations of railroad tank cars using full-scale impact test data. In: Proceedings of the ASME 2018 Verification and Validation Symposium, VVS2018-9322, May 16-18, Minneapolis, MN, USA.