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.