Specimen size and loading rate effects on cleavage fracture of ferriti
c steels tested in the ductile-to-brittle transition region remain key
issues for the application of pre-cracked Charpy specimens. This inve
stigation employs 3-D, nonlinear finite element analyses to assess cra
ck-front stress triaxiality in quasi-static and impact-loaded pre-crac
ked CVN specimens, with and without side grooves. Crack-front conditio
ns are characterized in terms of the Weibull stress which reflects the
statistical effects on cleavage fracture. These 3-D computations indi
cate that a less strict size/deformation limit, relative to the limits
indicated by previous plane-strain analyses, is needed to maintain sm
all-scale yielding conditions at fracture under quasi-static and impac
t loading conditions. For impact toughness values which violate these
size/deformation limits, a toughness scaling methodology is described
to remove the effects of constraint loss. The new scaling model also e
nables prediction of the distribution of quasi-static fracture toughne
ss values from a measured distribution of impact toughness values (and
vice versa). This procedure is applied to experimental data obtained
from a Cr-Ni-Mo-V pressure vessel steel and accurately predicts quasi-
static fracture toughness values in IT-SE(B) specimens from impact-loa
ded, pre-cracked CVN specimens. These 3-D analyses also yield eta-tota
l values for use in impact testing to infer thickness average and mid-
thickness J-values from measured work quantities. (C) 1997 Elsevier Sc
ience Ltd.