Illustration of the WPS benefit through BATMAN test series: Tests on large specimens under WPS loading configurations

To study the effects of warm pre-stressing on the toughness of reactor pressure vessel steel, the “Commissariat à l’Energie Atomique”, in collaboration with “Electricité De France” and AREVA-NP, has made a study combining modeling and a series of experiments on large specimens submitted to a thermal shock or isothermal cooling. The tests were made on 18MND5 ferritic steel bars, containing a short or large fatigue pre-crack.The effect of “warm pre-stressing” was confirmed, in the two cases of a fast thermal shock creating a gradient across the thickness of the bar and for gradual uniform cooling. In both cases, no propagation was observed during the thermal transient. Fracture occurred under low temperature conditions, at the end of the test when the tensile load was increased. The failure loads then recorded were substantially higher than during pre-stressing.To illustrate the benefit of the WPS effect, numerical interpretations were performed using either global approach or local approach criteria. WPS effect and capability of models to predict it were then clearly shown.