Issue 29

L. Zhao et alii, Frattura ed Integrità Strutturale, 29 (2014) 410-418; DOI: 10.3221/IGF-ESIS.29.36 417 steel and stainless steel have significantly lower SCC susceptibilities and growth rates, the crack growth law was only applied to the partial model including Alloy182 buttering and Alloy182 weld. 0 30 60 90 120 150 180 10 -9 10 -8 10 -7 10 -6 a=5mm a=7.5mm a=10mm Crack angle,  ( o ) EAC crack growth rate, d d /d t (mm/s) Figure 12 : Crack growth rate of Alloy 182 in the DMW joint. The shallow surface crack growth rate at both ends is much lower than that at the middle. However, the deep surface crack growth rate is relatively uniform and its increment slows down with the increasing crack depth. The gradients of plastic strain and plastic strain rates decrease as the crack advances. Due to the constraint of strong material, CGR of the deep surface crack locates in Alloy 182 buttering decreases sharply, and the crack growing in Alloy 182 buttering is inhibited. However, the partial crack locates in Alloy 182 weld comes to stable growth. The crack will no longer be ideal semi-elliptic with the continuous crack growing. The crack shape will change considerably. The welding residual stress referred here is a result of higher hoop stress in the DMW joint SCC susceptible region, and dropping off in the safe-end and nozzle regions. Finally, the crack shape development results in crack growth outside of the DMW region. C ONCLUSIONS onsidering the interactive effect of operating loads and welding residual stress, the stress-strain field ahead of inner surface axial crack fronts of a RPV outlet nozzle DMW joint is simulated by using EPFEM. The crack driving force, such as opening stress, plastic strain, plastic strain rate and J -integral are analyzed. Focusing on RS and crack depth, the SCC growth rate of a DMW joint was quantitatively predicted. Main conclusions can be summarized as follows: (1) Crack local stress-strain field, J -integral and crack growth rate of DMW joints are dominated by residual stress, not welded mechanical heterogeneity. The hoop stress and hoop strain varying through-thickness of the welded area is quite different with or without residual stress. The distributions of hoop stress and hoop strain are consistent with residual stress. (2) The strain rate ahead of deeper crack front decreases due to the constraint of high hardness material, whereas, J - integral increases in the interfacial region of Alloy 182 buttering and Alloy 182 weld. Path dependence of J -integral exists because of welded mechanical heterogeneity. Therefore, plastic strain rate should be a more reliable fracture parameter to evaluate the SCC behavior of DMW joint than J -integral. (3) The shallow surface crack growth rate at both ends is much lower than that at the middle. However, the deep surface crack growth rate is relatively uniform. Due to the constraint of strong material, located in Alloy 182 buttering, the crack growing is inhibited. The crack locates in Alloy 182 weld grows steady and the crack shape will change considerably. (4) Based on the film slip/dissolution oxidation model and EPFEM, a valid approach is provided to quantitatively estimate SCC growth rate of DMW joints in PWR environment. C