Prediction of creep crack initiation in Cr–Mo–V steel specimens with different geometries

Abstract

By using stress dependent creep ductility and strain rate model in a ductility exhaustion based damage model, the creep crack initiation (CCI) behaviour in Cr–Mo–V steel specimens with different geometries and dimensions (different constraints) over a wide range of C^* has been predicted by finite element simulations. The predicted creep crack initiation time agree well with the existing experimental data. In low and transition C^* regions, the constraint induced by specimen geometries and dimensions has obvious influence on CCI time. With increasing constraint level of specimens, the CCI time decreases due to the increase of stress triaxiality ahead of crack tip. Different CCI trends and constraint effects on CCI behaviour in a wide range of C^* result from the interaction of crack-tip stress state and stress dependent creep ductility of the steel. It is suggested that in CCI life assessments of high temperature components, the long-term CCI time data at low C^* region should be obtained and used, and the constraint effects need to be considered by using constraint dependent CCI data.

Keywords:

• Creep crack initiation
• constraint effects
• creep ductility
• specimen geometry
• Cr–Mo–V steel

Abbreviations:

• 2RN: two-region Norton
• 3-D: three-dimensional
• C3D8R: eight node brick elements
• CCI: creep crack initiation
• CCG: creep crack growth
• C(T): compact tension
• C(T)2: compact tension specimen with 2 mm thickness
• C(T)5: compact tension specimen with 5 mm thickness
• C(T)10: compact tension specimen with 10 mm thickness
• DEN(T): double-edge notched tension
• FE: finite element
• M(T): middle cracked tension
• M(T)2: middle-cracked tension specimen with 2 mm thickness
• SEN(T): single-edge notched tension
• SEN(T)2: single-edge notched tension specimen with 2 mm thickness
• SEN(T)5: single-edge notched tension specimen with 5 mm thickness