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Plasticity and ductile fracture of IF steels: experiments and micromechanical modeling
Institution:1. Christian Doppler Laboratory for Micromechanics of Materials, Institute of Mechanics, Montanuniversität Leoben, Franz-Josef-Straße 18, A-8700 Leoben, Austria;2. Chair A for Mechanics, Technical University of Munich, Boltzmannstraße 15, D-85748 Garching, Germany;3. Institute of Mechanics, Christian Doppler Laboratory for Micromechanics of Materials, Montanuniversität Leoben, Austria;1. Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, 711103, India;2. Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, 247 667, India;3. National Institute of Foundry and Forge Technology, Hatia, Ranchi, 834 003, India;1. Seagate Technology, 1 Disc Drive, Springtown, Derry, BT48 0BF Northern Ireland, UK;2. IFW Dresden, Institute for Metallic Materials, Helmholtzstraße 20, 01069 Dresden, Germany;3. Center for Integrated Sensor Systems, Danube University Krems, Viktor Kaplan Str. 2E, 2700 Wiener Neustadt, Austria;1. Max-Planck-Institut für Eisenforschung GmbH, 40237, Düsseldorf, Germany;2. Department of Materials, Royal School of Mines, Imperial College, Prince Consort Road, London, SW7 2BP, UK
Abstract:If one aims at the simulation of plasticity and failure of multiphase materials, the choice of an appropriate material law is of major importance. Plasticity models for porous metals contain, in addition to the yield surface and the flow potential, also functions describing the void nucleation, dependent on some macroscopically observable quantities, and the growth of these voids. In this paper, a micromechanically based method to develop a void nucleation function for porous plasticity models is proposed which is valid for all possible microstructures as long as the amount of second phase particles is low (i.e. the particles do not interact with respect to the stress and strain fields), and as long as the particles are large enough (above 0.1 μm) justifying a continuum mechanical approach. The method described consists of two stages: In the first stage, the microstructure is investigated via a finite element model. The FE model implicitly contains the effects of the shape of the precipitates, of the material parameters of both the matrix and the precipitates, of the void nucleation hypothesis (by the assumption of “nucleation limits” for characteristic damage-related quantities), and of the applied stress state. In the second stage, during postprocessing, the volume fraction of precipitates as well as the influences of the particle orientation distribution, size distribution, and size dependence of the damage-related quantities are taken into account. The model is applied to the microstructure of IF (Interstitially Free) steel, a material with a ductile matrix and rigid second phase particles of cubical shape. This microstructure is particularly suited for investigating shape and size effects. The model shows that either the size effect or the shape effect dominate the void nucleation behavior: in the case of particles of roughly the same size, the size distribution will hardly alter the nucleation strain distribution obtained by taking into account only the shape and orientation effects. For particles of very different sizes, the size effect will completely override the rather “sharp” original distribution regarding particle shape and orientation.
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