DUCTILE CRACK-GROWTH IN PRECRACKED CVN SPECIMENS - NUMERICAL-STUDIES

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.