The effect of pre-strain and strain-path changes on ductile fracture: experiment and computational modeling

Based on experiments and computational modeling, this study examines the fa ilure behavior of structural steel, HY-100, which has been pre-strained at a high stress triaxiality and subsequently failed at a lower stress triaxia lity. Both tensile tests of circumferentially notched specimens and the ass ociated fractography show that even a small pre-strain at high stress triax iality promotes an extension of the low ductility, 'void-sheet' mode of fai lure to lower stress triaxialities. Thus, there is a decrease in the failur e strain compared to that if the material is deformed only at the lower str ess triaxiality. These results imply that the pre-strain damage nucleates e longated voids whose growth is critical to the development of void-sheet fa ilure. Micro-mechanical modeling using finite element analysis confirms tha t localization of plastic flow should occur between elongated 'hole shaped voids', despite their rather small initial cross-section size (2.5 mu m) an d comparatively large spacing (70 mu m). Furthermore, employing a local fai lure criterion, the computational analysis predicts failure strains which a re in good agreement with those observed after the pre-strain and strain-pa th change. (C) 2000 Elsevier Science S.A. All rights reserved.