Damage accumulation and failure of HY-100 steel
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THE tensile fracture of structural alloys usually proceeds by a damage-accumulation process involving void nucleation, void growth, and void coalescence. For many structural alloys such as high-strength steels, voids frequently initiate at comparatively small strains, in which case material failure is controlled primarily by void growth and void coalescence. Based on the combined void growth and coalescence criteria, several mechanics-based relationships have been developed to predict ductile fracture at low temperatures (for example, References 1 through 8). In these analyses, void growth is usually based on the Rice and Tracey relationship developed for the growth behavior of an isolated void,[9] and it is often introduced as a void-volume-fraction parameter that accounts for the effects of damage in a dilatational constitutive model; refer to Gurson[10] and others.[11,12] Void coalescence and the onset of material failure has been addressed on the basis of several criteria. Commonly used coalescence criteria include a critical void growth rate or a critical void volume fraction,[13,14,15] a “critical void fraction” that relates to the onset of deformation localization between voids and a loss of material stress-carrying capacity,[1,16] a geometric void size/spacing ratio,[17] and the plastic-load limit of the intervoid matrix.[6,18,19] For materials in which the void nucleation strain is small, the fracture strain may then be predicted as a function of stress state by employing the appropriate void-growth and coalescence relationships. Such analyses understandably depend, in a sensitive manner, on the void volume fraction and its dependence on the strain and stress state. While numerous computational and theoretical analyses have been performed to predict microvoid ductile fracture, V. JABLOKOV, formerly Graduate Research Assistant, Department of Materials Science and Engineering, Penn State University, is Engineer, Siemens Westinghouse Power Corp., Orlando, FL 32817. D.M. GOTO, formerly Graduate Research Assistant, Department of Materials Science and Engineering, Penn State University, is Engineer, Lawrence Livermore National Laboratory, Livermore, CA 94551. D.A. KOSS, Professor, is with the Department of Materials Science and Engineering, Penn State University, University Park, PA 16802. Manuscript submitted April 19, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
few experimental studies detail the evolution of damage during the fracture process, and most of these are limited to uniaxial tension. Based primarily on the uniaxial behavior of spheroidized plain-carbon steels, several early studies established that the volume fraction of voids (including both void-growth and void-nucleation contributions) increased with strain in a manner that accelerated near the fracture strain.[20–24] There are also related studies of cavity growth and damage evolution based on powder-processed compacts with varying densities; most of these studies were also limited to uniaxial deformation.[25,26,27] Despite the st
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