Determination of the yield strength of nuclear reactor pressure vessel steels by means of amplitude-dependent internal friction

Amplitude-dependent internal friction measurements allow the determination of a critical amplitude which corresponds to the onset of plastic behaviour and is related to the yield stress (YS) in torsion. The results compare well with the YS obtained from static tensile tests on three different pressure vessel steels and can be fitted with a two- or three-component model comprising long- and short-range dislocation-defect interactions and grain-boundary effects. The effect of thermal aging is to emphasize the presence of dragging contributions to the yield strength, while neutron-irradiation results in an athermal increase in the YS related to irradiation-induced clustering.