Multiscale electro-thermal modeling of the Branly effect in oxidized copper granular media

This study investigates the dielectric breakdown of copper granular media covered by a native semiconducting oxide layer (Cu 2 O) under DC stress. This insulator-to-conductor transition, known as the Branly effect, initiates powder consolidation in Spark Plasma Sintering (SPS) by disrupting native oxide diffusion barriers. The phenomenon is analyzed through a multiscale approach combining the Discrete Element Method (DEM), Finite Element Method (FEM), and analytical modeling. Locally, a 3D electro-thermal FEM model validates an analytical breakdown criterion based on thermal runaway. Macroscopically, unlike models focusing on post-breakdown metallic percolation, the 3D DEM framework integrates the oxide's thermal degradation to actively drive the transition. Results reveal a two-stage macroscopic breakdown: a "soft" regime of power-driven filamentation that stabilizes the electric field, followed by a "hard" regime where the metallic failure of a minute contact fraction (< 0.1%) establishes a percolating path. This numerical approach provides a deeper understanding of the breakdown mechanisms and the induced current percolation, offering physical insights to optimize the early activation and densification stages in SPS.