Effect of loading variables on the fatigue crack growth rate in SA508 C1.3 pressure vessel steel

Abstract

The influence of loading variable (stress ratio and frequency) and temperature on fatigue crack growth rate in SA508 cl.3 reactor pressure vessel steel was investigated in air environment. Fatigue crack growth tests were performed on compact tension (CT) specimens made to thickness 12.7mm. Compact tension test specimens were tested using sinusoidal waveform and the crack length was monitored by compliance method. Tests were conducted at two load ratios 0.1 and 0.5, at frequencies 10 and 1 Hz, at room temperature and 288℃. To investigate further details of the temperature effect, tests were conducted at R=0.5, f=1Hz in a range of temperature from room temperature to 400℃. The effect of R-ratio on the growth rate at each testing frequency and temperature shows that a significant influence of R-ratio on the fatigue crack growth rate is observed at the high temperature. The results also showed that the fatigue crack growth rate a given stress intensity level did not show distinct difference at RT and 120℃. However, at above 120℃, the fatigue crack growth rate increased as test temperature increases. In addition, it was found that the influence of the frequency on fatigue crack growth rate increased at higher temperatures. It is suggested that the frequency and temperature influence may be associated with environmental effects due to oxidation at crack tip.