Effect of notch angle on creep deformation and rupture behavior of 304HCu SS

Abstract

Multiaxial creep deformation behaviour of U-notched 304HCu austenitic stainless steel (304HCu SS) has been studied by altering the angle of the U-notch, by 300, 600, 900, and 1200, for a fixed root radius of 1.25 mm. The associated stress concentration factor for the U-notch geometry is about 1.8-1.86 with decrease in notch angle. Creep rupture lives of all notched specimens are above the un-notched specimen. However, decrease in rupture life and increase in creep rupture ductility has been observed with an increase in notch angle. At all notch angles, nearly intergranular creep cavitation failure with isolated cavities was observed at the notch center. In contrast, at the notch root, with decrease in notch angle the fracture mode changed from mixed mode to intergranular fracture. Finite element analysis (FEA) of stationary state of stress distribution indicated that von-Mises stress throughout the notch throat plane and maximum principal stress near the notch root region were found to increase with increase in notch angle. However, away from the notch root the maximum principal stress was found to decrease with increase in notch angle. Hydrostatic stress distribution remained same near the notch root at all the notch angles, but tends to increase towards the specimen center with decrease in notch angle. Similarly, at the notch throat plane, triaxiality factor (TF) was found to increase with decrease in notch angle. The creep damage evaluated through FEA coupled with continuum damage mechanics (CDM) proposed by Kachanov-Rabotov (K-R) model was found to increase with an increase in notch angle, resulting in decrease in creep rupture life. Creep damage evaluated as a function of notch depth, during initial creep exposure, revealed significant damage for 1.675 mm notch depth in comparison to 2 and 2.5 mm notch depths which resulted in lower rupture life for 1.675 mm notch depth.