ABBREVIATION
ASTM American Society for Testing and Materials
ASME American Society of Mechanical Engineers
C(T) Compact Tension
FE Finite Element
RR Riedel and Rice
Sp. Specimen
1. INTRODUCTION
In assessing structural integrity of high-temperature power-plant components, it is essential to understand crack initiation and growth behaviour under creep and creep-fatigue loadings. High-temperature crack initiation and growth behaviours of a Grade 91 steel under constant load have been investigated by many researchers [1-10]. It is known that the creep crack initiation time and growth rate can be correlated with the time-dependent fracture mechanicsC* -integral [11-18]. Under creep-fatigue cyclic loading condition, the interaction of creep and fatigue is involved in the crack initiation and growth. Creep-fatigue crack growth tests have been extensively performed [3, 19-29], but most of the tests were conducted under tension-tension creep-fatigue loading condition [3, 21-27, 29]. On the other hand, creep-fatigue crack growth tests under tension-compression creep-fatigue loading are limited [19-20, 28].
The previous study [28] showed that the crack growth rate under tension-tension creep fatigue loading was generally well correlated by the C* parameter, but that under tension-compression creep-fatigue loading was overestimated by the conventional approach using the C*parameter. To fully understand the singularity of the crack growth behavior under tension-compression creep-fatigue loading, the effect of creep-fatigue loading condition on crack tip deformation, stress and strain fields should be studied, but previous studies [30-39] were only for pure fatigue loading condition, not for creep-fatigue loading condition.
In this study, creep-fatigue crack growth tests of Grade 91 steel at 600oC using the compact tension specimens under various load ratios and hold times [28] are simulated by using finite element debond analysis to investigate the effect of creep-fatigue loading condition on crack tip deformation and stress fields at crack initiation and growth. Section 2 presents the creep-fatigue creep growth test data used in this study. Section 3 describes the FE analysis. The effect of creep-fatigue loading condition on crack tip deformation and stress fields at crack initiation and growth is presented in Section 4. Section 5 concludes the presented work.