Limit analysis and lower/upper bounds to the macroscopic criterion of Drucker-Prager materials with spheroidal voids

The paper is devoted to a numerical Limit Analysis of a hollow spheroidal model with a Drucker-Prager solid matrix, for several values of the corresponding friction angle phi. In the first part of this study, the static and the mixed kinematic 3D-codes recently evaluated in [1] are modified to use the geometry defined in [2] for spheroidal cavities in the context of a von Mises matrix. The results in terms of macroscopic criteria are satisfactory for low and medium values of phi, but not enough for phi = 30 in the highly compressive part of the criterion. To improve these results, an original mixed approach, dedicated to the axisymmetric case, was elaborated with a specific discontinuous quadratic velocity field associated with the triangular finite element. Despite the less good conditioning inherent to the axisymmetric modelization, the resulting conic programming problem appears quite efficient, allowing one take into account numerical discretization refinements unreachable with the corresponding 3D mixed code. After a first validation in the case of spherical cavities whose exact solution is known, the final results for spheroidal voids are given for three usual values of the friction angle and two values of the cavity aspect factor. (C) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.