Influence of Loading Rate on the Deformation and Ductile Fracture of A533B Steel at 70C

Abstract

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.

Rate‐dependent Deformation and Fracture of Α‐titanium

“…For sustained load conditions in A533B steel Smith and Garwood [8] found that if yielding is contained ductile crack growth would diminish. However, the present results for @-titanium under sustained loading and in contained yielding, particularly for CT specimen L5, crack growth continues until eventual failure.…”

“…For the carbon-manganese steel it was shown there was a loading rate effect on the R-curve, but for the A533B steel there was no significant effect. Smith and Garwood [8] conducted further work on A533B steel and found that there were marginally different R-curves in terms of J and CTOD for different loading rates provided that the tests were conducted under clip gauge displacement rate control.…”

A new model for characterizing primary creep damage

“…Krempl and Kallianpur [35], Garwood [36], Ingham and Morland [37], among others (see [36]) have clearly demonstrated this phenomenon for a number of engineering materials. Little, Krempl and Shih [38] have also carried out finite element analyses examining the stress and strain states near a crack tip for the small scale yielding problem.…”

Time‐dependent fracture of type 316L(N) steel at ambient temperature

“…Under sustained loading, time‐dependent deformation and crack growth can occur in ductile ferritic and austenitic steels at temperatures well below the conventional creep range 1–7 . However, failure is generally found to occur only if the sustained loads are close to the monotonic collapse load 7 .…”

“…In bodies containing defects, the appropriate stress is the so‐called reference stress, a measure of the overall level of plasticity within the body, which controls the crack‐tip stress and strain fields within the J ‐estimation approach 9 underlying R6. Time‐dependent plasticity or ‘cold creep’ has been attributed to the sensitivity of the material's stress–strain curve to loading rate, 1,2 and R6 advises that sustained load effects need only be considered at susceptible temperatures, currently considered to be below 200 °C in austenitic steel. The effect of limited crack extension on the integrity of a structure needs to be carefully assessed within the susceptible range.…”