Effect Of Notch Geometry Constraint On Creep Damage And Fracture Behavior In Alloy Steel And Welded Joint

In this paper,the finite element method based on the stress-regime dependent creep model and creep ductility was used to investigate the effects of notch geometry constraint on creep damage and fracture behavior in Cr-Mo-V steel and P92 welded joint.The mechanism of the notch geometry constraint effects were analyzed by the distribution of stress/strain near the notch.The main work and conclusions obtained are as followings:(1)The effects of notch radius on creep crack initiation,fracture life and creep crack growth in C(T)specimens have been investigated.The results show that with decreasing notch radius,the stress triaxiality near notch tip increases,the creep crack initiation time and creep fracture time decrease and the creep crack tends to initiate from the notch root.The notch radius has no effect on the creep crack growth rate in C(T)specimens,thus,the C(T)specimens with radius larger than that in the ASTM E1457 can be used to measure creep crack growth rate.The creep crack initiation time and fracture life in C(T)specimens for low creep ductility materials are not sensitive to the notch radius of specimens.(2)The effect of notch dimensions on the creep crack initiation and fracture life of V-type notched bar specimens has been investigated.The results show that with the increase of notch radius,notch depth and notch angle,the time of creep crack initiation and creep fracture life increase.(3)The effects and mechanism of creep ductility and notch constraint on creep damage and fracture in U-type notched bar specimens have been investigated.The results show that,for creep ductility materials,the U-type notch exhibits notch strengthening effect at a wide range of stress levels.With increasing notch constraint,the rupture life of notched bar specimens increases due to the decrease of equivalent stress.For creep brittle materials,the notch strengthening or weakening behavior is related to stress levels.With increasing notch constraint,the rupture life of bar specimens decreases.(4)The effects of notch geometry constraint and material constraint on the creep damage and fracture behavior in P92 welded joint have been investigated.The results show that fracture positions change with the stress levels due to the material constraint.For the bar specimens with different notch positions,the geometry constraint induced by notch increases the creep fracture life of specimens,the notch exhibits strengthening effect.The interaction between geometry constraint and material constraint under different stress levels influences creep damage distribution,creep crack initiation position and creep fracture life.(5)In creep life designs and assessments of high-temperature components containing notches,the material creep ductility,notch constraint,stress levels and material constraint need to be fully considered.