Rolling, sliding and torsion of micron-sized silica particles: experimental, numerical and theoretical analysis

Abstract

The contact mechanics of individual, very small particles with other particles and walls is studied using a nanoindenter setup that allows normal and lateral displacement control and measurement of the respective forces. The sliding, rolling and torsional forces and torques are tested with borosilicate microspheres, featuring radii of about 10 µm. The contacts are with flat silicon substrates of different roughness for pure sliding and rolling and with silicon based, ion-beam crafted rail systems for combined rolling and torsion. The experimental results are discussed and compared to various analytical predictions and contact models, allowing for two concurrent interpretations of the effects of surface roughness, plasticity and adhesion. This enables us to determine both rolling and torsion friction coefficients together with their associated length scales. Interestingly, even though normal contacts behave elastically (Hertzian), all other modes of motion display effects due to surface roughness and consequent plastic deformation. The influence of adhesion is interpreted in the framework of different models and is very different for different degrees of freedom, being largest for rolling.

Compaction of granular material inside confined geometries

“…These values have previously been calibrated to mimic 20 micron silica beads [16]. Here we neglect the role of adhesion between particles, which will become increasingly important as the physical size of the particles reduces.…”

Probabilistic calibration of discrete element simulations using the sequential quasi-Monte Carlo filter

“…Experimental studies were also conducted to improve the theories based on measured micromechanical [13,37] and microstructural behaviors [19,36] of grains and granular assemblies. Nevertheless, calibrating contact laws using microscopic measurements to reproduce the micromechanics at contacts does not necessarily recover the mechanical behavior at the macro-scale.…”

Particles, contacts, bulk-behavior

“…The papers in this thematic issue on particles, contacts and bulk behaviour are sorted according to the theme from particles (simple, spherical [1,2] to complex, non-spherical [3,4]), via their contacts (from simple, linear to non-linear, frictional, elasto-plastic, cohesive [2]) towards rapid impact [5,6], and the bulk behaviour [7][8][9][10]. For particles and their contacts, the state-of-the-art in constitutive modelling of elastic, elastic-adhesion, elastic-dissipative, plastic-adhesion and plastic-dissipative contact deformation response of a single particle is discussed in most papers in this special issue [1][2][3][4][5][6][7][8][9][10]; furthermore, on all levels from particles, their contacts and on the macroscopic bulk-flow level, models are shown but also experimentally validated.…”

“…For particles and their contacts, the state-of-the-art in constitutive modelling of elastic, elastic-adhesion, elastic-dissipative, plastic-adhesion and plastic-dissipative contact deformation response of a single particle is discussed in most papers in this special issue [1][2][3][4][5][6][7][8][9][10]; furthermore, on all levels from particles, their contacts and on the macroscopic bulk-flow level, models are shown but also experimentally validated.…”

“…The consequences of elastic-dissipative, elastic-plastic, frictional unloading and reloading paths of normal and tangential forces, rolling and torsional moments are discussed, and novel test techniques on single particle contact level are shown [1,3,6,7,9].…”