13th International Conference on Fracture June 16–21, 2013, Beijing, China coalesce. Void coalescence results in significant inhomogeneity of voids distribution over a material. Voids distribution inhomogeneity is described by the following formula [21] w w inh 2 w w inh w w inh w max w S (S ) ~ for S (S ) ~ α exp S (S ) ~ 1 for S ~ S . (21) where is maximal local swelling (in volume of grain); max wS wS ~ is average swelling of specimen; α is material constant. In a region with swelling about , fracture occurs at stress < σY and disk-shaped microcrack initiates with size equal to grain size. Fracture stress is calculated by the collapse criterion (See (Eq. 6). This microcrack begins to grow due to ductile fracture of moving “process zone” without increasing stresses. It is possible as the fracture strain of material with vacancy voids is very small and level of local stress and strain in very small “process zone’ is sufficiently high. max wS collaps Nσ collaps Nσ Figure 5 shows the calculation of ultimate strength of material as a function of radiation swelling. Figure 5. Calculation of ultimate strength of material as a function of swelling wS ~ (a-b-c-d line): m ul σ – ultimate strength of material without swelling; collaps Nσ – stress corresponds to fracture of grain with swelling (disk-shaped crack nucletion); max wS RCM min σ - minimal stress for running collapse mechanism; Σ m ul 1 A σ – ultimate strength decrease due to net-section decrease. 6. Conclusions (1) The model of ductile fracture was developed, which makes it possible to describe the influence of stress state triaxiality, neutron irradiation and radiation swelling on the critical parameters controlling fracture: fracture strain εf and the critical value of J-integral Jc. (2) Predictions were made on the influence of a neutron dose on εf and fracture toughness Jc. It was shown that as stress state triaxiality increases the irradiation influence on εf increases. The calculation results of Jc showed that this parameter for D ≥6 dpa decreases by ~6 times. 0 200 400 600 800 1000 0 1 20 30 0 Sw, % МПа a b c d RCM min σ 1 A σ m ul σ, MPa collaps Nσ wS ~ , % -9-
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