This study describes plane strain, finite element analyses to model du
ctile crack extension in pre-cracked Charpy specimens subjected to sta
tic and impact loading. The Gurson-Tvergaard (GT) dilatant plasticity
model for voided materials describes the degradation of material stres
s capacity. Fixed-size, computational cell elements defined over a thi
n layer along the crack plane provide an explicit length scale for the
continuum damage process. Outside of this layer, the material remains
undamaged by void growth, consistent with metallurgical observations.
The finite strain constitutive models include the effects of high str
ain rates on the material flow properties. Parametric studies focusing
on numerically generated R-curves quantify the relative influence of
impact velocity, material strain rate sensitivity, and properties of t
he computational cells (thickness and the initial cell porosity). In a
ll cases, impact loading elevates significantly the R-curve by increas
ing the amount of background plasticity. The strong effects of impact
loading on the driving force for cleavage fracture are illustrated thr
ough evolution of the Weibull stress. The analyses suggest a negligibl
e, additional effect of tearing on the Weibull stress under impact loa
ding. Validation of the computational cell approach to predict loading
rate effects on R-curves is accomplished by comparison to static and
impact experimental sets of R-curves for three different steels. (C) 1
998 Published by Elsevier Science S.A. All rights reserved.