Analysis of jamming networks in sheared suspensions

Abstract

The results from the development of a novel technique for detecting and monitoring load bearing, percolating networks in a dense suspension (concentrated suspension) sheared in a narrow gap are presented. The technique employs an electrical method which allows for much higher sampling rates than with traditional mechanical measurements and can therefore reveal the occurrence of shorter lived phenomena. The suspensions under investigation were solder pastes (used in electronics manufacturing) since they inherently lend themselves to this technique. Solder pastes consist of spherical metal alloy particles suspended in an insulating non-Newtonian fluid (flux). Particles are polydisperse and commonly have diameters in the range of 10–75μm. Volume fraction of solid is typically 45%–50%. The particles have a native insulating oxide layer that is removed by the mechanical action of neighboring particles, allowing conduction across the particle interfaces. The manner and rate at which conduction occurs therefore provides information on the magnitude of the contact forces between the particles. Transient conduction spikes measured as current passes through the particles detect the occurrence, magnitude, and duration (lifetime) of load bearing percolating networks.