Effects Of Interaction Between Geometry And Material Constraint On Creep Crack Growth Behavior In P92 Welded Joints

In this paper, the finite element method (FEM) based on ductility exhaustion model was used to investigate P92 steel welded joints. The effects of geometry constraint (different specimen geometry and out-of-plane), material constraint (initial crack positions, creep strength, and creep ductility mismatch), load levels, and their interaction on creep crack incubation (CCI) time, creep crack growth (CCG) rate, CCG path, and rupture life of welded joints were studied systematically. The mechanism was analyzed by the distribution of stress triaxiality and Mises stress ahead of the crack tip. The main conclusions are as follows:(1) There exists interaction between geometry and material constraints in terms of their effects on CCG rate and CCI time of welded joints. With low geometry constraint, the effects of material constraint on CCG rate and CCI time is more obvious, and the low geometry constraint strengthens the material constraint. The effects is the opposite with high geometry constraint.(2) The CCI time and CCG rate are not sensitive the material constraint under high load level, and they are sensitive to material constraint under low constraint. The effects of material constraint on CCG rate and CCI time need to be considered in the creep life assessment and design for the welded joints for the actual components are served under low load level.(3) The HAZ/BM interface crack (heat affected Zone and base metal interface) was investigated. The effects of creep strength, creep ductility,and thire interaction from both sides of the interface crack on the distribution of stress triaxility and Mises stress ahead of the crack tip changes the CCG rate, CCG path, CCI time, and rupture. The creep ductility mismatch on the CCG path, CCG rate, CCI time and rupture life were investigated under different creep strength mismatch.(4) The effects of interaction between out-of-plane constraint and material constraint on the distribution of stress triaxility and Mises stress ahead of crack tip changes the CCG rate and path. Under low out-of-plane constraint, the CCG rate is lower and the material constraint has small effect on the CCG path. Under high out-of-plane constraint, the CCG rate is high and the material constraint has large effect on the CCG path.(5) The interaction between load level and creep ductility affects the CCG path. The CCG path is sensitive to the material constraint under the condition of low load level and high creep ductility. Otherwise, the CCG path is not sensitive to the material constraint under the condition of high load level and low creep ductility. The load level causes the changes of crack path due to the stress-regime dependent creep constitutive.(6) The effects of interaction between geometry constraint and material constraint, load level, and creep ductility mismatch, creep strength mismatch and their interaction between weldment constitutes on creep crack incubation (CCI) time, creep crack growth (CCG) rate, CCG path, and rupture life of welded joints should be fully considered in the creep life assessment and design for the welded joints at high temperature.