Nils Audry1, Barthélémy Harthong1, Didier Imbault1.
1 Univ. Grenoble Alpes, CNRS, Grenoble INP, 3SR, F-38000 Grenoble, France
Purpose. The prediction of tensile strength properties of compacts remains an important industrial issue. In particular, one of the major problems of the powder compaction process is the failure of compacts. Such defects are related to the capacity of a powder to create adhesion at contacts between particles and thus are a consequence of phenomena occurring at the particle scale and below, down to the molecular scale.
Methods. A particle-scale, numerical method called the multi-particle finite-element method was used. Such a method allowed to explicitly model the microstructure of an idealized granular medium considered as an assembly of elastic-plastic spheres. The particles were meshed such that their deformations were fully taken into account, using a continuum-mechanics-based material model. The interactions between particles were managed using finite-element contact formulations [1].
Results. A multi-scale, cohesive contact model was adapted from the literature and implemented into the multi-particle finite-element method. The contact model was based on the Lennard-Jones potential, expressed as a stress [2], associated to the Pullen and Williamson roughness model [3]. This model was then used to predict the mesoscopic properties such as yield or failure surfaces for strongly deviatoric loadings as well as the cracking phenomena appearing for this type of loadings.
Conclusions. A particle-scale approach based on the surface energy was developed to predict the adhesion between powder particles and relate it to the macroscopic cohesion of powder compacts. Such a method intends to be a help toward the development of an efficient continuum model for the modelling of the powder compaction process.
References
[1] N. Abelmoula, B. Harthong, D. Imbault and P. Dorémus. A study on the uniqueness of the plastic flow direction for granular assemblies of ductile particles using discrete finite-element simulations. Journal of the Mechanics and Physics of Solids, Vol. 109:142–159, July 2017.
[2] N. Yu and A. A. Polycarpou. Adhesive contact based on the Lennard–Jones potential: a correction to the value of the equilibrium distance as used in the potential. Journal of Colloid and Interface Science, Vol. 278:428–435, June 2004.
[3] J. Pullen and J.B.P. Williamson. On the plastic contact of rough surfaces. Proceedings of the Royal Society of London, Vol. 327 :159–173, July 1970.