PSI - Issue 42

Rafael Magalhães de Melo Freire et al. / Procedia Structural Integrity 42 (2022) 672–679 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

679

8

A simple evaluation method for the increased risk of brittle fracture due to repeated pre-straining was formulated. In order to add pre-strain patterns to the FEM analysis, a local approach model was defined, which enables pre-strained materials to be evaluated in a unified manner. The pre-strain pattern was added by using the newly defined Weibull stress as the limiting condition for the occurrence of brittle fracture. Based on the knowledge obtained in this study, the general form of the simplified evaluation equation was determined, the constant coefficients were fitted to fit the experimental data and the additional pre-strain from the simulations, and the simplified evaluation equation was successfully formulated. 4. Conclusion • The calculation of the Weibull stresses using Beremin ’s and Bordet’s models showed more scattered results in comparison to the new approach. Those models do not consider the effect of the Bauschinger effect and aspects of the dislocation movements, while the new equation of Weibull stress takes into account the back stress rate in order to portray a higher probability of microcrack initiation due to the dislocation annihilation and pile-up on the other side when the load is reversed. Therefore, this new approach provides more accurate results, considering the difference between material’s behavior that had the last pre-strain cycle done by tensile load or compression. • A simplified evaluation equation was proposed, taking into account that fracture toughness will reduce until a certain value as the plastic deformation increases. • In order to obtain the effect on the material damage degree and the critical CTOD due to pre-strain, specific terms were added to the critical CTOD equation considering the difference in the movement of the dislocations and the Bauschinger effect. Constants were calibrated and the results of the predicted MOTE of critical CTOD from the new equation of fracture toughness were satisfactory. Kosuge H., Kawabata T., Okita T., Murayama H., Takagi S., 2020. Establishment of damage estimation rules for brittle fracture after cyclic plastic prestrain in steel. Materials and Design, 185, 5, 108222 Miki C., Sasaki E., Kyuba H., Takenoi I., 2000. Deterioration of Fracture Toughness of Steel by Effect of Tensile and Compressive Prestrain. Journal of JSCE, 640, 165-175 Coffin L. F., 1954. A study of the effect of cyclic thermal stresses on a ductile metal. Transactions of the American Society of Mechanical Engineers, 76, 931-950 Manson S. A., 1965. A complex subject-Some simple approximations. Experimental Mechanics, 5, 193-226. Miner M. A., 1945. Cumulative Damage in Fatigue. Journal of Applied Mechanics-Transactions of the American Society of Mechanical Engineers, 12, 159-164 Ozawa, T., Kawabata, T., and Yoshiki, M., 1945. Proposal of NewMOTEMethods for Brittle Fracture Toughness Determination. ISIJ International 62.6 (2022): 1301-1311. Dassault Systemes®, 2018. Abaqus v.6.18. Tateishi K., Hanji T., Minami K., 2004. Prediction model for extremely low cycle fatigue life under variable strain amplitude. Journal of Japan Society of Civil Engineers Civil Engineers, 773, 149-158 Beremin F. M., 1983. A local criterion for cleavage fracture of a nuclear pressure vessel steel. Metallurgical Transactions A, 14, 2277-2287. Bordet S. R., 2005. A new statistical local criterion for cleavage fracture in steel: Part I: model presentation. Engineering Fracture Mechanics, 72, 3, 435-452 Bordet S. R., 2005. A new statistical local criterion for cleavage fracture in steel: Part II: application to an offshore structural steel. Engineering Fracture Mechanics, 72, 3, 453-474 Ashby M. F., 1970. The deformation of plastically non-homogeneous materials, Philosophical Magazine, 21, 399-424. Freire, R. M. D. M., Aihara, S., Shinohara, A. H., Yoshizu, S., Mesquita, P. B., 2021. Estimation of the Fracture Probability Parameters for Specimens Made by JIS SM490A Steel. Materials Research, 24. Ruggieri, C., Minami, F., Toyoda, M., Hagiwara, Y., Inoue, T., 1992. Local approach to notch depth dependence of CTOD results. Journal of the Society of Naval Architects of Japan, (171), 493-499. Chaboche, J. L., 1989. Constitutive equations for cyclic plasticity and cyclic viscoplasticity, International Journal of Plasticity, 5, 247-302. Lemaitre, J., Chaboche, J. L., 1994. Mechanics of Solid Materials, Published by Cambridge University, 584. References