The Effect of Load Ratio on the Fatigue Crack Growth Rate of Type 304 Stainless Steels in Air and High Temperature Deaerated Water at 482 °F

A test program has been completed that re-examined the effect of load ratio, R, on fatigue crack growth rates (FCGRs) of austenitic stainless steel in 482 °F air and deaerated water. Data for the test program were collected at R between 0.1 and 0.95 and ΔK values between 2.5 and 50 ksi√in to ensure an overlapping dataset in R and ∆K. In contrast to the single Paris slope relationship in the ASME code, results from air tests revealed a three-regime curve across many R: a high ΔK regime similar to ASME, an intermediate ΔK regime with a decreased power law exponent and a low ΔK region where FCGR exhibit a steep downturn. Water FCGRs showed two regimes—a single power law regime and a steep low ΔK regime. FCGR sensitivity to R was greatest in the low ΔK regime for both environments.