Analysis Of Stress And Strain At The Tip Of Stress Corrosion Cracking In Structural Materials Of Nuclear Power Plant

Austenitic stainless steel and nickel-based alloy have been widely used in structuralmaterials of nuclear power plant, due to their good corrosion resistance and mechanicalproperties. However, the stress corrosion cracking (SCC) in these materials in hightemperaturewaterenvironments ofnuclearpressurevesselsandpipingisa keyissueofsafetyandlife in nuclearpowerplant.Themicro-mechanicalstateattheSCCtipisoneofimportantfactors of affecting SCC growth rate. Using multi-scale method to analyze fracture processzone at the SCC tip has also become a popularapproach in the SCC researches. Based on thenumerical simulation method, combined macro with micro scale model, the stress and strainat the SCC tip in structural materials of nuclear power plant is analyzed in this dissertation.Main studyingcontentsandconclusionsareasfollows:(1)Based on the numerical simulation method, the global macro model of standardcompact tension specimen (CT specimen) and micro sub-model of fracture process zone areconstructed by finite element software ABAQUS. The research is focused on the stress andstrainattheSCCtip composedbyoxidefilmandbasemetal.(2)The SCC tip is analyzed under a constant stress intensity factor K. The effect of theyield stress ofbase metal material, the yield stress of oxide film material and the thickness ofoxide film on stress and strain at the SCC tip is discussed respectively. The results indicatethat the yield stress increasing of base metal material will induce the stress and straindecreasing in theoxidefilm zone,thestress increasingandstraindecreasingin the basemetalzone; the yield stress increasing of the oxide film material will induce the stress increasingand strain decreasing in oxide film zone, the stress and strain decreasing in the base metalzone; the thickness increasing ofthe oxide film will induce thestress and strain decreasinginbothoxidefilmandbasemetalzone. (3)The SCC tip is analyzed under different stress intensity factor K. The effects ofdifferent loading conditions on stress and strain at the SCC tip are discussed. The resultsindicate that theincreasingofKwillinduce thestress andstrainincreasing inbothoxidefilmand base metal zone. The increased extent of stresswill decrease, and the increased extent ofstrain will keepbasicallyconstantasKincrease.(4)The equivalent plastic strain rate at the SCC tip is analyzed. The results indicate thatthe closer of distance from the crack tip, the greater the strain rate; both the yield stressincreasing of the base metal and oxide film, and the K decreasing will also induce plasticstrainratedecreaseatthesamedistancefromthecracktip.The results and conclusions in this dissertationprovide a base for quantitative predictionof SCC growth rate in Austenitic stainless steel and nickel-based alloy in high temperatureenvironments ofthenuclearpowerplant.