PSI - Issue 59

V. Sidyachenko et al. / Procedia Structural Integrity 59 (2024) 265–270 V. Sidyachenko and V. Pokrovskii / Structural Integrity Procedia 00 (2019) 000 – 000

270

6

It is seen from Fig. 4 that the critical cleavage stress σ c at a distance r c from the crack tip after WPS is attained at K f = 22 МPа m 1/2 , which is twice smaller than K Ic = 40 МPа m 1/2 without WPS. Moreover, the maximum tensile stresses arise off the crack plane by approximately 72 0 , which corresponds to the experimentally found angle of deviation of the mode-I crack propagation after WPS under mode II. Moreover, it should be noted that despite of the fact that modeling of the WPS effect did not coincide with the experimentally determined value K f =10 МPа m 1/2 due to the simplified two-dimensional model and other man-made assumptions, a tendency towards decrease of the mode-I K f value after WPS under mode II is confirmed. 5. Conclusions The article presents the results of experimental investigations of the influence of WPS on fracture toughness of steels under mixed mode loading conditions. The results showed that the fracture toughness after WPS under mixed mode loading increases to a greater extent for brittle steels compared to ductile steels. It has been shown that the characteristics of Mode II crack resistance are lower than those of Mode I crack resistance at the temperature above the brittle – ductile transition temperature and vice versa. It has been found that the Mode I fracture toughness of embrittled reactor steels decreases after Mode II WPS, which is due to the asymmetric system of residual stresses in the vicinity of the crack tip. References Ayatollahi, M.R., Mostafavi, M., 2007. Finite element analysis of a center crack specimen warm pre-stressed under different modes of loading. Computational Material Science 38, 847 – 856. Chell, G.G., Haigh, J.R., Vitek, V., 1981. A theory of warm prestressing: experimental validation and the implications for elastic plastic failure criteria. International Journal Fracture 17, 61 – 81. Pokrovsky, V.V., Troshchenko, V.T., Kaplunenko, V.G., Podkol’zin , V.Y., Fiodorov, V.G., Dragunov, Y.G., 1994. A promising method for enhancing resistance of pressure vessels to brittle fracture. International Journal of Pressure Vessels and Piping 58, 9 – 24. Pokrovskii, V.V., Ezhov, V.N., Sidyachenko, V.G., 2017. Thermomechanical preloading-governed temperature dependency of crack resistance on mixed I+III modes. Strength of Materials 49, 788 – 795. Pokrovskii, V.V., Sidyachenko, V.G., 2013. Effect of mode I and II thermomechanical pre-loading on the fracture toughness of heat-resistant vessel steels. Strength of Materials 45(1), 56 – 63. Richard, H.A., Eberlein, A., Kullmer, G., 2017. Concepts and experimental results for stable and unstable crack growth under 3D-mixed-mode loadings. Engineering Fracture Mechanic 174, 10 – 20. Ritchie, R.O., Knott, J. F., Rice, J. R., 1973. On the relationship between critical tensile stress and fracture toughness in mild steel. Journal of the Mechanic and Physics of Solids 21, 395 – 410. Smith, D.J., Hadidimoud, S, Fowler, H., 2004. The effects of warm pre-stressing on cleavage fracture. Part 1: evaluation of experiments. Engineering Fracture Mechanic 71, 2015 – 2032. Swankie, T.D., Smith, D.J., 1998. Low temperature mixed mode fracture of a pressure vessel steel subject to prior loading. Engineering Fracture Mechanic 61, 387 – 405. Yasnii, P.V., Okipnyi, I.B., Pyndus, Yu.I., 2010. Assessment of brittle strength of nuclear reactor pressure vessel steel upon warm prestressing. Strength of Materials 42(1), 32 – 37.