Volume 8, Issue 10 (November 2011)
Evaluation of the Testing and Analysis Methods in ASTM E2760-10 Creep-Fatigue Crack Growth Testing Standard for a Range of Steels
The development of the ASTM E2760-10, “Creep/Fatigue Crack Growth Testing” standard has initiated a phase of testing, analysis, and round robin initiatives associated with high temperature cyclic loading crack growth tests. Creep and fatigue are two complex independent mechanisms which may assist each other to drive the crack. A simplification of the macro creep/fatigue crack growth response of structures is therefore required. Using a linear cumulative damage method, as proposed in ASTM E2760, and other codes of practice, data for a range of steels are analysed. Limited crack growth data, using test methods similar to ASTM E2760, from previous collaborative projects for a range of steels are presented and analysed to identify the difficulties in the process. Creep-fatigue crack growth tests at frequencies ranging from 10 to 0.001 Hz are examined to consider the testing methodologies and in order to assess the effect of data scatter, dwell times, and the interaction region between creep crack growth (CCG) and fatigue crack growth mechanisms. Given the limited data available and the level of scatter, it can still be shown that the linear cumulative summation of static and high frequency data may be sufficient to predict creep/fatigue interaction both in terms of C* and ΔK, and the level of creep ductility will dictate appropriateness of the correlating parameter employed. Finally, in order to show that the level of data scatter can be dealt with in a predictive manner, the crack initiation and growth rates are also analysed using the NSW CCG model.