Macromechanical behavior of oxide nanopowders during compaction processes

TL;DR

This study uses granular dynamics simulations to analyze the macromechanical behavior of oxide nanopowders during various compaction processes, revealing their stress responses, dilatancy effects, and loading surface characteristics.

Contribution

It introduces a detailed simulation approach for nanopowder compaction, including bond formation and destruction, and characterizes their stress-strain behavior and loading surfaces.

Findings

Loading surfaces are elliptical and shifted towards compression.

Positive dilatancy observed during shear deformation.

Deformation vectors are nonorthogonal to loading surfaces.

Abstract

Two granular systems (I and II) corresponding oxide nanopowders having different agglomeration tendency are simulated by the granular dynamics method. The particle size is 10 nanometer. The interaction of particles involves the elastic forces of repulsion, the tangential forces of "friction", the dispersion forces of attraction, and in the case of II system the opportunity of creation/destruction of hard bonds of chemical nature. The processes of the uniaxial compaction, the biaxial (radial) one, the isotropic one, the compaction combined with shear deformation as well as the simple shear deformation are studied. The effect of the positive dilatancy is found out in the processes of shear deformation. The loading surfaces of nanopowders are constructed in the space of stress tensor invariants, i.e., the hydrostatic pressure and the deviator intensity. It is revealed that the form of the loading surfaces is similar to an ellipse, which is shifted along the hydrostatic axis to compressive pressures. The associated flow rule is analyzed. The nonorthogonality of the deformation vectors to the loading surface is established in the both systems modeled.