Enhanced dielectric standoff and mechanical failure in field-structured composites

We report dielectric breakdown experiments on electric-field-structured com posites of high-dielectric-constant BaTiO3 particles in an epoxy resin. The se experiments show a significant increase in the dielectric standoff stren gth perpendicular to the field structuring direction, relative to control s amples consisting of randomly dispersed particles. To understand the relati on of this observation to microstructure, we apply a simple resistor-short breakdown model to three-dimensional composite structures generated from a dynamical simulation. In this breakdown model the composite material is ass umed to conduct primarily through particle contacts, so the simulated struc tures are mapped onto a resistor network where the center of mass of each p article is a node that is connected to neighboring nodes by resistors of fi xed resistance that irreversibly short to perfect conductors when the curre nt reaches a threshold value. This model gives relative breakdown voltages that are in good agreement with experimental results. Finally, we consider a primitive model of the mechanical strength of a field-structured composit e material, which is a current-driven, conductor-insulator fuse model. This model leads to a macroscopic fusing behavior and can be related to mechani cal failure of the composite. [S0163-1829(99)14433-3].