13th International Conference on Fracture June 16–21, 2013, Beijing, China This prediction is in complete agreement with the experimental data. (3) The model predicts a severe decrease of Jc with a growth of swelling in relation to Jc of a material irradiated under the condition when radiation swelling is absent. (4) It is shown that the root causes of ductile fracture of highly irradiated austenitic steels at low stresses (less than yield strength) and sharp reduction of ultimate strength are the following: - formation of inhomogeneous distribution of vacancy voids at some critical level of swelling (Sw)inh; - fracture in “process zone” which has nano sizes (80-400 nm) considerably less than grain size. (5) Initiation of fracture in a grain with high level of swelling and unstable microcrack propagation result in fracture of specimen at stress less than yield strength. Unstable microcrack propagation occurs due to local ductile fracture of moving “process zone” (this mechanism is named as “running collapse mechanism”). (6) The proposed model allows one to predict the swelling effect on sharp reduction of ultimate strength. References [1] A.L. Gurson, Continuum theory of ductile rupture by void nucleation and growth: Part 1-yeild criteria and flow rules for porous ductile media. J. Engng Mater Techn, 99 (1977) 2-13. [2] V. Tvergaard and A. Needleman, Analysis of the cupcone fracture in a round tensile bar. Acta Met, 32 (1984) 157-169. [3] B.Z. Margolin, G.P. Karzov, V.I. Kostylev, V.A. Shvetsova, Modelling for transcrystalline and intercrystalline fracture by void nucleation and growth. Fatigue Fract. Eng. Mater. Struct. 21 (1998) 123-137. [4] B.Z. Margolin, V.A. Shvetsova, A.G. Gulenko, V.I. Kostylev, Prometey local approach to brittle fracture: development and application. Eng. Fract. Mech. 75 (2008) 3483 – 3498. [5] B.Z. Margolin, V.A. Shvetsova, A.G. Gulenko, E.V. Nesterova, Brittle fracture local criterion and radiation embrittlement of reactor pressure vessel steels. Strength of Materials. 42 (2010) 506-527 [6] F.M. Beremin, Cavity formation from inclusions in ductile fracture of A508 Steel, Met. Trans. 12A (1981) 723-731. [7] E.A. Little, Fracture mechanics evaluation of neutron irradiated type 321 austenitic steel. J. of Nuc. mat. 139 (1986) 261-276. [8] Y. Huang, Accurate dilatation rates for spherical voids in triaxial stress fields. Transaction of the ASME, Ser. E, Journal of Applied Mechanics. 58 (1991) 1084-1086. [9] B.Z. Margolin, V.I. Kostylev, A.V. Il’in, A.I. Minkin, Simulation of JR-curves for reactor pressure vessels steels on the basis of a ductile fracture model. Int. J. Pres. Ves.& Piping. Vol. 78, Issue 10 (2001) 715-725. [10] C.C. Chu and A. Needleman. Void nucleation effects in biaxially stretched sheets. J Engng Mater, 102 (1980) 249-256 [11] A.A. Sorokin, B.Z. Margolin, I.P. Kursevich, A.I. Minkin, V.S. Neustroev, S.V. Belozerov, Effect of neutron irradiation on mechanical properties of the WWWER-type reactor internals. Voprosy Materialovedenia (Problems of Material Science). 66 (2011) 131-152 (in Russian). [12] Bridgman PW. Studies in large plastic flow and fracture. New York: McGraw-Hill, 1952. -10-
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