3D discrete modeling of plasma sprayed ceramics microstructure
LONGCHAMP V. 2, ANDRÉ D. 1, GIRARDOT J. 2, MALAISE F. 3, IORDANOFF I. 2
1 IRCER - Limoges university, Limoges, France; 2 Arts et Métiers Science et Technologie – I2M, Talence, France; 3 CEA CESTA, Le Barp, France
Ceramic coatings obtained by atmospheric plasma spraying have a particular microstructure composed of pores and cracks. This gives them very interesting properties to attenuate the mechanical waves generated during debris impacts or laser shock experiments at very high velocity. It is essential to understand the influence of the microstructure on the behavior of these materials in order to better exploit their capabilities. Due to the scale of observation and the rapidity of the phenomena to be studied, an experimental approach is not very suitable. On the contrary, thanks to the numerous advances in terms of computational means, and fine 3D characterization methods, the study of the behavior by microscopic numerical modeling is becoming an increasingly interesting approach. Nevertheless, the classical numerical methods based on the mechanics of continuous media reach their limit when it comes to represent heterogeneous media and discontinuous phenomena. Another numerical paradigm has emerged: the discrete element method or DEM. With this approach, a continuous medium can be represented by a set of discrete elements connected by links. In fact, this method is particularly well adapted to the representation of heterogeneous media and complex nonlinear phenomena such as cracking. This work focuses on the possibilities offered by the DEM to numerically reproduce a complex microstructure in order to predict its effect on the macro mechanical behavior of the material in compression. To do this, a modeling approach has been implemented. It is based on high precision 3D acquisitions obtained by FIB-SEM. The micro-defects are detected and analyzed by image processing before being integrated into a digital model of discrete elements. The originality of this work is based on the classification of porosities according to their size and shape in order to discretize them as well as possible, while preserving reasonable computation times. Thus, a particular attention is paid to the representation of cracks and their initial opening via the application of a specific treatment on the links connecting the discrete elements. 3D discrete numerical models thus obtained are subjected to various types of quasi-static or dynamic loading. These numerical simulations allow the link between the microstructure and the macroscopic response of plasma sprayed ceramics. A non-linear behavior under compression, in agreement with the literature, has been successfully reproduced thanks to the ability of the model to treat crack closure. The activation of a cracking criterion should also allow the study of the compaction mechanisms by multi-fracturing of the medium and the macroscopic failure in traction.