Many engineering materials exhibit rate- or time-dependent inelastic deformation. This phenomenon is generally associated with the strain rate sensitivity of the flow stress. The main objective of the work described in this paper is to examine the influence of loading rate on the deformation and ductile fracture of a reactor pressure vessel steel, A533B Class 1, at 70C.
The reported experimental work is in three parts, examining the behavior of (1) uniaxial specimens, (2) small-scale notched bend specimens, and (3) large-scale notched plate specimens (wide plates). The tests on the notched bend and the plate specimens were part of an earlier test program conducted at The Welding Institute. To complement the previous experimental work, the rate dependence of plastic deformation was examined using uniaxial specimens. The observed rate dependence of the flow stress is shown to agree with collated data from the literature. The amount of creep deformation under sustained loading is shown to be large.
A detailed examination of earlier small-scale notched bend experiments shows that there is an influence of applied loading rate on the material's resistance to continuing ductile fracture in terms of J and crack-tip opening displacement. However, the data obtained are of a limited nature. A distinction is drawn between locally controlled displacement rates and globally controlled loading conditions. For the latter case, the resistance curve obtained is considered to be a locus through a series of resistance curves obtained from locally controlled bend tests.
The wide-plate tests have also been examined in detail. The plate deformations during sustained loading are shown to be extensive. Furthermore, clear evidence of crack growth during the load hold periods has been found. The resistance curves for the large-scale specimens are shown to be significantly influenced by the creep deformation.
The effect of loading rate on the resistance curves for A533B steel at 70C is shown to be marginal and in agreement with the weak strain-rate sensitivity of the flow stress. However, the wide-plate specimens, which exhibit less constraint than bend specimens, are more likely to creep under uncontained yielding conditions than to exhibit continuing ductile crack growth.