Temperature- and Rate-Dependent Failure in Dynamically Loaded Viscoplastic Materials
This work aims at studying experimentally and reproducing numerically the failure mechanisms of a ship structure constitutive material when submitted to airblast loading. With this aim in view, a physically motivated approach has been developed and applie
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Temperature- and Rate-Dependent Failure in Dynamically Loaded Viscoplastic Materials Patrice Longe`re, Anne-Gae¨lle Geffroy, Bruno Leble´, and Andre´ Dragon
Abstract This work aims at studying experimentally and reproducing numerically the failure mechanisms of a ship structure constitutive material when submitted to airblast loading. With this aim in view, a physically motivated approach has been developed and applied in order to describe the transition of behaviour between dense metal plasticity and micro-porous metal plasticity in the context of dynamic plasticity and failure. The viscoplastic material is supposed to be initially exempt of micro-voids. Subjected to a monotonic loading involving a positive or null stress triaxiality, it behaves elastic-(visco) plastically. As soon as the conditions of plastic strain, plastic strain rate, temperature and stress triaxiality for the germination of a given volume fraction of voids are satisfied, the material behaviour becomes pressure dependent. Its damage-plastic yielding is consequently described using a micro-porous metal plasticity potential. The latter is proposed in the form of a modified version of the Gurson-Tvergaard-Needleman model allowing for describing cavity growth and further fracture under shear loading. The 3D constitutive equations are implemented as user material in the engineering finite element computation code Abaqus®. Numerical simulations are conducted and compared with experiments considering airblast loaded ship structures. The numerical results show clearly the influence of the hole nucleation criterion related constants and of the loading conditions (temperature, strain rate) on the damage and further fracture of the material. Keywords Dynamics • Air-blast • Viscoplasticity • Ductile fracture • Numerical simulation
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Introduction
Several authors have attempted to describe the consequences of ductile damage on the bulk material behaviour. These consequences are double: a progressive loss of the overall properties of the bulk material and the appearance, in addition to the isochoric plastic deformation due to dislocation glide in the matrix material, of an inelastic dilatancy due to void growth. Based on a micromechanical analysis, Gurson [1] developed a plastic potential for slightly porous and perfectly plastic metals accounting explicitly for the concentration of voids and hydrostatic stress. Tvergaard and Needleman [2] modified Gurson’s model in order to take notably into account isotropic strain hardening and strain rate effects, see also [3]. The socalled GTN (for Gurson-Tvergaard-Needleman) model is widely used by the community of researchers dealing with ductile damage. Using the rate type formulation coupled with physical concepts, Perzyna [4] developed an elliptic plastic potential taking into consideration cooperative effects of void growth, strain rate sensitivity and heating. Finally, relying on Rice and
P. Longe`re (*) Universite´ de Toulouse, Institut Supe´rieur de l’Ae´ronautique et de l’Espace – Institut Cle´ment Ade
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