Evaluation of Small Fatigue Crack Growth Rates in HIP FGH96 Superalloy Under Microstructural Influences

The effects of different evaluation methods and microstructural characteristics on the surface small fatigue crack growth rate of HIP FGH96 superalloy were quantitatively investigated using SEM in situ and other testing technologies. The results indicate that the effect of projected length a(1) and physical length a(2) on the small fatigue crack growth rate can be ignored, even if there are some deflection angles in small crack growth path. However, clear distinctions emerge when evaluating the small fatigue crack growth rate near the crack growth threshold under mixed-mode (Mode I/II) conditions, where the influence is quantitatively assessed using the maximum tangential stress criterion. Furthermore, differences between various evaluation methods of small fatigue crack growth rates and several important damage tolerance design parameters, such as Delta K-th, a(eq), or sigma(w), were quantitatively predicted based on Weibull distribution analysis.