VISCOELASTIC PLASTIC MODEL AND EXPERIMENTAL VALIDATION FOR A GRANULAR ENERGETIC MATERIAL

A numerical viscoelastic plastic constitutive model is proposed to simulate the non-linear behavior of a granular energetic material under quasi-static conditions. This model is restricted to an isotropic framework. It includes a damage evolution and two separate uncoupled failure criteria. The yield criterion is parabolic and based on the two first stress invariants in order to take into account the pressure. The plastic flow rule is non-associated and is introduced through a compaction/dilatancy parameter. The viscoelastic part is described by a generalized Maxwell model. The model is calibrated using an extended experimental database that includes a dynamic mechanical analysis test, cyclic compression, and tensile tests with relaxation and recovery stages. Some compressive tests include a confinement pressure. The parallel structure of the model allows for separate identification of the elastoplastic and viscoelastic parts. The model constitutive equations and its implementation in a commercial finite-element code are presented. The model validation is based on a three-point bending test and a Brazilian test. The simulations show good correlation with the uniaxial experimental results. Some discrepancies are observed between the experimental and simulated results for the Brazilian test, which are related to a biaxial load case. This highlights the induced damage anisotropy observed from cyclic tests, which is not taken into account in our model.