Anisotropic coalescence criterion for nanoporous materials
Résumé
Ductile fracture through void growth and coalescence depends significantly on the plastic anisotropy of the material and on voidsize, as shown by experiments and-or numerical simulations through several studies. Macroscopic (homogenized) yield criterionaiming at modeling nanoporous materials have been proposed only for the growth regime, i.e. non-interacting voids. The aim ofthis study is thus to provide a yield criterion for nanoporous materials relevant for the coalescence regime, i.e. when plastic flowis localized between voids. Through homogenization and limit analysis, and accounting for interface stresses at the void-matrixinterface, analytical coalescence criterion is derived under the following conditions axisymmetric loading, orthotropic materialobeying Hill-s plasticity, cylindrical voids in cylindrical unit-cell. Incidentally, an orthotropic extension of the existing isotropicmodeling of interface stresses through limit analysis is described and used. The proposed coalescence criterion is then extended toaccount for combined tension and shear loading conditions. Numerical limit analysis have been performed under specific conditions- materials parameters to get exact results of coalescence stress, for spheroidal voids relevant for applications. A good agreementbetween the analytical coalescence criteria derived in this study and exact results is found, making them usable to predict the onsetof void coalescence in ductile fracture modeling of nanoporous materials.