Analysis Of Fracture Parameters On Stress Corrosion Cracking Of Structural Material In Nuclear Power Plants Under Micro-scale

Austenitic stainless steel and nickel-based alloy have been widely used in structuralmateirals of nuclear power plant, due to their good corrosion resistance and mechanicalproperties. However, the stress corrosion cracking (SCC) in these mateirals in hightemperature water environments of nuclear pressure vessels and piping is a key issue of safetyand life in nuclear power plant. Recently the stress corrosion crack tip mechanical state of themicro-region is considered as one of the three major factors affecting the crack growth rate,and study of SCC crack tip rfacture process zone environment, material and mechanicalatmosphere using multi-scale methods is one of the important tools to the furtherunderstanding of the mechanism and propagation rate of stress corrosion cracking. Based onthe numerical simulation method，combined macro with micro scale model, the stress andstrain at the SCC tip in structural materials of nuclear power plant was analyzed in thisdissertation.Main research work completed are as follows:(1)Basedon the numerical simulation method, the global macro model of standardcompact tension specimen and micro sub-model of fracture process zone were constructed byfinite element sotfware ABAQUS. The research focused on the stress and strain at the SCC tipcomposed by oxide film and base metal. Under the condition of constant k，the base metalmateiral and the oxide iflm material were respectively taken as the affecting factor，thevairation of fracture parameters at a crack tip region was analyzed; under the condition ofconstant k，oxide film thickness was taken as the affecting factor，the variation of rfactureparameters at a crack tip region was analyzed.(2)Onthe basis of oxide film model, combined with the theory of electrochemistry, theconcept of groove-shaped crack was proposed. In the macroscopic model analysis foundation, using finite element software ABAQUS sub-model technology, stress and strain field andstrain rate of SCC crack tip，which is composed by oxide iflm and base metal, were mainlystudied in groove-shaped crack model. As groove-shaped crack in the formation process is adynamic process，on the condition of constant load K，the effect of groove-shaped cracklength changing on the rfacture parameters in crack tip zone was analyzed. Due to nuclearmateiral prone to split under stress corrosion crack，on the condition of constant load K，theeffect of groove-shaped crack bifurcation on the rfacture parameters in crack tip zone wasanalyzed. On the basis of the metallographic analysis of stress corrosion cracking，nuclearmateiral is prone to propagate along crystal, and its direction will constantly change. On thecondition of constant K，the effect of crack propagation direction on rfacture parameters incrack tip zone was analyzed.(3)Actually，SCC crack propagation process is dynamic and very complex, which is thebase to establish a dynamic propagating model of SCC crack with oxide film. And on thisbasis, the fracture parameters in crack tip of this dynamic propagating process were speciallyanalyzed.(4)On the condition of constant and varying K, the crack tip plastic strain rate in thestationary crack tip zone was analyzed respectively. Similarly, the crack tip plastic strain ratein the dynamically propagating crack tip zone was analyzed.The results and conclusions in this dissertation provide a base for quantitative predictionof SCC growth rate in austenitic stainless steel and nickel-based alloy in high temperatureenvironments of the nuclear power plant.