PSI - Issue 23

Sergiy Kotrechko et al. / Procedia Structural Integrity 23 (2019) 413–418 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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According to the obtained results, taking into account the crucial role of threshold stress th  is especially important for correct description of the scatter limits for fracture toughness IC K in transition region, as well as of its temperature dependence for small values of the fracture probability (5%), i.e. for description of the lower envelope of IC K . As generally known, this is of paramount importance in predicting the integrity of the critical structural elements (reactor pressure vessels, gas pipelines etc.) Conclusions : 1. The relatively high density of the crack nuclei formed in iron and structural steels enables determining the value of the threshold cleavage stress from the results of testing tensile specimens with a circumferential notch of a special geometry. 2. Ignoring the threshold stress value gives rise to an overestimation of the shape parameter magnitude by 1.5 times for cast steel and 2 times for RPV steel. 3. In the Local Approach, accounting for the magnitude of threshold stress is especially important for correctly predicting the temperature dependence of the fracture toughness C K I for low probabilities of fracture (  P =5% or less). This is of considerable practical importance for predicting the integrity of critical structural elements. Acknowledgements This work was supported by the National Academy of Sciences of Ukraine (grants’ number # 0116U003048) and Bilateral Czech-Ukrainian project. Bordet S.R., Karstensen A.D., Knowles D.M., Wiesner C.S., 2005. A new statistical local criterion for cleavage fracture in steel. Part I: Model presentation. Engineering Fracture Mechanics72, 435-452. Kotrechko S., Strnadel B., Dlouhy I., 2005. Fracture toughness prediction of cast Mn steel applying Local Approach. Theoretical and Applied Fracture Mechanics 12, 25. Kotrechko S., Meshkov Yu., 2001. Physical fundamentals of a local approach to analysis of brittle fracture of metals and alloys.Materials Science37, 4, 583-597. Kotrechko S., 2013 The key problems of local approach to cleavage fracture Journal of Theoretical and Applied Mechanics 51, 75-89, Warsaw. Kotrechko S., Gryshchenko V.,Kozak V., Dlouhy I., 2017. Methods of threshold stress determination for a Local Approach to cleavage fracture Solid State Phenomena258,281-285. Gao X., Ruggieri C. and Dodds R.H., 1998.Calibration of Weibull stress parameters using fracture toughness data.International Journal of Fracture 92, 175-200. Gao X. and Dodds R.H., 2000.Constraint effects on the ductile-to-brittle transition temperature of ferritic steels: a Weibull stress modelInternational Journal of Fracture 102, 43 – 69. Pineau A.,2006. Development of the local approach to fracture over the past 25 years: Theory and applications. International Journal of Fracture 138, 139 – 166. Ruggieri C., 2001. Influence of threshold parameters on cleavage fracture predictions using the Weibull stress model. International Journal of Fracture 110, 281-304. References