PSI - Issue 13

Reza H. Talemi et al. / Procedia Structural Integrity 13 (2018) 775–780 Author name / Structural Integrity Procedia 00 (2018) 000–000

780

6

Fig. 3. (a) comparison between force versus displacement curves obtained from the FE model and the experimental observations for both configurations tested at 25°C; (b) comparison between the absorbed energy for crack initiation between the numerical results and the experimental observations for both configurations at all tested temperatures; (c) normalized critical stress ( σ max ) by the yield stress ( σ y ) at different tested temperatures. For instance, for the tested AHSS steel slab in this study, the maximum thermal/mechanical stresses should not be more than ൎ 2.4 times of the yield stress of the slab material if the steel slab is being reheated from the room temperature (25°C). The suggested critical cleavage stress could be used as a design parameter in a thermal FE model, for predicting the steel slabs temperature evolution which could be mapped to the stress models as thermal load, during the stack cooling and the reheating process. 5. Conclusion During production process of AHSS some steel grades must be warm charged due to the risk of brittle crack formation caused by mechanical and thermal stresses induced by transportation and reheating, respectively. The current rules that define which grades are on the critical list were determined by chemistry and estimation of the thermal conductivity based on the chemistry and/or the ductility of the grade at low temperatures. The main objective of this study was to predict the brittle fracture of the steel slab materials by means of both experimental and numerical approaches. Therefore, the DWTT set-up was used to investigate the fracture response of steel slabs at different elevated temperatures i.e. 25°C to 500°C. The fracture surfaces of broken samples were analyzed using SEM to understand the ductile and brittle fracture appearances at elevated temperatures. In terms of numerical modelling, the XFEM-based cohesive segment technique was used to model the DWTT of steel slab at all tested temperatures. The obtained results from FE models were in good agreement with the observed experiments. Using the developed model, a set of critical cleavage stresses were defined for cold/hot charged steel slabs. References Hojjati-Talemi, R., Cooreman, S., Van Hoecke, D., 2016. Finite element simulation of dynamic brittle fracture in pipeline steel: A XFEM-based cohesive zone approach. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 1464420715627379. Nonn, A., Wessel, W., & Schmidt, T., 2013. Application of Finite Element Analyses for Assessment of Fracture Behavior of Modern High Toughness Seamless Pipeline Steels. In: Proceedings of the Twenty-third International Offshore and Polar Engineering Conference. Scheider, I., Nonn, A., Völling, A., Mondry, A., Kalwa, C., 2014. A Damage Mechanics based Evaluation of Dynamic Fracture Resistance in Gas Pipelines. Procedia Materials Science 3, 1956-1964. Talemi, R., 2016. Numerical simulation of dynamic brittle fracture of pipeline steel subjected to DWTT using XFEM-based cohesive segment technique. Frattura ed Integritá Strutturale 36, 151. Talemi, R. H., Brown, S., Martynov, S., Mahgerefteh, H., 2016. Hybrid fluid–structure interaction modelling of dynamic brittle fracture in steel pipelines transporting CO 2 streams. International Journal of Greenhouse Gas Control 54, 702-715. Wu, Y., YU, H., Lu, C., Tieu, A. K., Godbole, A., Michal, G. (2013). Transition of ductile and brittle fracture during DWTT by FEM. In: Proceedings of 13 th International Conference on Fracture.