A Numerical Study of the Influence of Void Growth on Ductile Fracture and Metal Extrusion

Abstract

176 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.Large deformation finite element analysis is used to study the near crack tip growth of long cylindrical holes aligned parallel to the plane of a mode I plane strain crack. The near crack tip stress and deformation fields are analyzed. The results show that the holes are pulled towards the crack tip and change their shape to approximately elliptical with the major axis radial to the crack. Several crack-hole coalescence criteria are discussed and estimates for the conditions for fracture initiation are given and compared with experimental results. The range of estimates now available from finite element calculations coincides quite well with the range of experimental data for materials containing inclusions which are only loosely bonded to the matrix.Using large deformation finite element analysis together with Gurson's constitutive model, we also study the behavior of microvoids nucleated at second phase particles during direct axisymmetric extrusion. Two different die-designs are analyzed. Comparison of the stress fields of the two die-designs provides a possible explanation of how central bursting initiates and why it appears after several steps of multi-step extrusions. The finite element results are in agreement with experimental observation and show that the finite element method can be successfully used to predict the formation of central bursts during extrusion.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD