Abstract
Fatigue crack growth experiments were conducted on a 50 mm thick compact fracture specimen of SA508-2 in a 288°C PWR water environment. A constant alternating stress intensity factor (∆K) technique was used to test ∆K values in the range 16 to 55 for R ratios from 0.23 to 0.72 at loading frequencies from 10 to 0.0017 Hz. By means of this constant ∆K technique, crack growth rates (over a considerable amount of crack extension) could be determined with a high degree of confidence.
In most experiments it was possible to obtain steady state crack growth rates. However, at low loading frequencies, significant transient behavior was occasionally observed whereby the crack growth rate decreased with time until a steady state was obtained. At low frequency, for all experiments, steady state crack growth rates were up to four times the rate at high frequency. Crack growth rates at high frequency were no more than twice the rates given by the ASME XI air line.
An intermediate R ratio at a low loading frequency caused the greatest acceleration in crack growth rate as compared to the rate at high frequency. Low and high R ratios at low loading frequencies were equivalent in only slightly accelerating crack growth rates above those rates observed at a high loading frequency.
