Unstable neck formation in a ductile ring subjected to impulsive radial loading

Formation and growth of diffuse necks in thin metal rings undergoing high-r ate radial expansion under plane strain conditions is studied numerically. The material is described by an elastic-viscoplastic internal variable cons titutive relation, so that failure by nucleation and void-growth is taken i nto account. Adiabatic heating due to plastic dissipation is also incorpora ted. The influence of imperfections in the form of non-uniform wall thickne ss and of variations in constitutive parameters is studied. The computation s show that long wavelength thickness imperfections gradually increase in a mplitude after some initial inelastic deformation but do not result in high ly localized neck formation. Instead, a critical, nearly periodic mode with short wavelength appears at rather large overall strain levels, It is from this critical mode that complete ductile failure develops. (C) 2000 Elsevi er Science Ltd. All rights reserved.