An aging elasto-viscoplastic model for ceramics

• An ageing elasto-viscoplastic model for ceramics is proposed.
• This model is established mainly on experimental results on uranium dioxide.
• This model well reproduces some special aspects of ceramics mechanical behavior.
• The model is developed in a 1D framework and extended to a 3D model.
• Simulations of compressive tests of pellets show an asymmetric strain localization.

A model reproducing strain softening behavior in ceramic materials is proposed. This model is base on a critical treatment of previous mechanical experimental results, mainly on uranium dioxide. The main hypothesis is that the strain softening phenomenon is related to an aging process, where some point defects move towards the dislocations and modify their velocity. This is different from most of models used up to now, as they were based on the hypothesis that only the initial lack of dislocations was responsible of the strain softening behavior. A model is first developed in a simple 1D framework. Evolution of the mechanical behavior with strain rate and temperature is well reproduced by this model. Then, the 1D model is extended to a 3D mechanical model, and mechanical compressive tests on UO2UO2 pellets are simulated. The 3D model well reproduces the observed asymmetrical shape of the compressed pellet if one considers that the material is not initially perfectly homogeneous, which highlights the importance of accounting for spatial heterogeneity of materials in models.