Void nucleation by inclusion cracking
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5/5/04
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Void Nucleation by Inclusion Cracking M.N. SHABROV, E. SYLVEN, S. KIM, D.H. SHERMAN, L. CHUZHOY, C.L. BRIANT, and A. NEEDLEMAN Void nucleation is studied both experimentally and computationally with the aim of identifying a macroscopic criterion for nucleation by particle cracking. Three types of circumferentially notched cylindrical specimens made of a low-alloy steel were used, in order to vary the stress triaxiality in the notch region. The tensile tests were interrupted at various loads below the fracture load. The specimens were sectioned parallel to the loading axis, and the locations of cracked and uncracked titanium-nitride inclusions were identified. No evidence was found of void nucleation by inclusion debonding. Finite-element calculations were carried out for each specimen geometry using conventional isotropic-hardening plasticity theory. The ability of various potential void-nucleation criteria to predict the onset of void nucleation by inclusion cracking is explored.
I.
INTRODUCTION
ROOM-TEMPERATURE ductile fracture in structural metals is a problem of technological importance and scientific interest that has received extensive attention from a variety of perspectives. The voids generally nucleate by decohesion or fracture of second-phase particles and grow by plastic deformation of the surrounding matrix. Void coalescence occurs either by necking down of the matrix material between adjacent voids or by localized shearing between wellseparated voids. The role played by void nucleation, growth, and coalescence was identified by Tipper,[1] and, subsequently, the phenomenology of this process was documented by Puttick,[2] Rogers,[3] Beachem,[4] and Gurland and Plateau.[5] Mechanics modeling of the ductile-fracture process originated with the pioneering work of McClintock[6] and Rice and Tracey.[7] Reviews of various aspects of the ductile-fracture literature with extensive references can be found in the articles by Goods and Brown,[8] Garrison and Moody,[9] Tvergaard[10] and in a series of reviews articles in a volume honoring F.A. McClintock.[11–14] Although much progress has been made, development of quantitative descriptions of ductile fracture continues to be an active area of research; recent studies and further references to the recent literature can be found in References 15 through 19. Of particular focus here is ductile failure in steels, which has been a research topic of great interest for many years; refer, for example, to References 20, 21, and 24 through 26, in addition to references in the reviews already cited. Although the main body of this work is aimed at providing a description of microvoid growth and coalescence (e.g., References 1 through 3, 5, and 27 through 31), the process of void nucleation also received attention in, for example, M.N. SHABROV, Graduate Student, and C.L. BRIANT and A. NEEDLEMAN, Professors of Engineering, are with the Division of Engineering, Brown University, Providence, RI 02912. S. KIM, formerly Post Doctoral Researcher, Division
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