Résumé
The nuclear fuel is manufactured by means of the ceramisation process, which includes the grinding, pressing and sintering steps. All these steps are strongly dependent on the mechanical behaviour of agglomerate powders, the pressing process reflecting the quasi-static or pseudo dynamic mechanical loading and the organisation of the chain forces depends on the IntEr-Agglomerate Interactions (IEAI) between particles. The agglomerate strength depends on its elastic-plastic behaviour, which depends on its microstructure. The microstructure of the agglomerates is composed by unbreakable aggregates and the aggregates are compose by elementary particles. The brittlelity of the agglomerates base on the IntrA-Agglomerate Interactions (IAAI) and the cohesion force between each aggregates. The porosity network and the crack propagation modify the cohesion forces. This behaviour is different if you change the size, the shape and the composition of the aggregate inside the agglomerate. The quasi-static mechanical behavior of agglomerates has been studied to show these phenomena by means of in-situ micro-compression tests at the Fuel characterisation laboratory of CEA-Marcoule Atalante facility. These tests enable to extract the elasto-plastic parameters of agglomerates. To obtain clear insights on the physical origins of the deformation and failure of agglomerates, we use a Discrete Element method (DEM) to build numerical spherical agglomerates composed of aggregates with different shapes by means of radial compaction. We investigate the influence of aggregate shapes and friction coefficient between aggregates on the microstructure and properties of the agglomerates such as packing fraction, connectivity, and bulk elastic modulus. After adding an adhesion force law between aggregates, the agglomerates are allowed to relax and then subjected to diametral compression between two plates. We determine the fracture modes and breakage threshold as a function of cohesion parameters and aggregate shapes. The simulation parameters are partially adjusted to experimental measurements and the results are compared with micro-compression tests.