Experimental Testing of Micro-Particles Collision
We performed experiments on the collisions of micrometer scale (200–300 μm) stainless steel (316 and 440 C) particles and studied the interaction properties and the coefficient of restitution. We used a novel experimental apparatus to enable non-contact m
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Experimental Testing of Micro-Particles Collision Wei-Hsun Lin and Chiara Daraio
Abstract We performed experiments on the collisions of micrometer scale (200–300 mm) stainless steel (316 and 440 C) particles and studied the interaction properties and the coefficient of restitution. We used a novel experimental apparatus to enable non-contact measurements based on laser excitations/detection and high-speed photography. The colliding particles were aligned in v-shaped grooves on a silicon wafer, fabricated using anisotropic etching techniques. We used high-power lasers to excite one of the particles (striker), and to control the impact velocity with high repeatability. The motion of the striker particle was triggered by partial laser ablation of its surface. The displacements of the particles involved in the collision were recorded with a high-speed camera mounted on an optical microscope. The particle velocities were obtained from the recorded images using digital image correlation. We calibrated the setup by tracking the dynamic excitation of single particles, and tested collisions between two particles. This study introduces a new experimental approach to understand the fundamental dynamic response of micro-particle collisions, and to test the limits of validity of the Hertzian interaction law. Keywords Collisions • Micro spheres
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Introduction
In this paper, we investigate the dynamic contact mechanics between micro-particles of different materials. Nature presents a large number of micrometer-scale granular particles – such as in the foam of soils, dust, and sand. A full understanding of the collective behavior of these particles requires an understanding of the fundamental interactions between them. These interactions are not necessarily similar to particle interactions on the macroscale, which are dominated by elastic Hertzian contact interactions. At the microscale, other effects such as electrostatic, magnetic, and hydrodynamic forces may be of comparable strength to the elastic interactions. Knowledge of the interparticle interaction potentials at this small scale obtained by direct experimental investigations should benefit studies such as the flow of granular particles [1], packing of randomly jammed particles [2], non-equilibrium thermal processes in granular gasses [3], and the propagation of acoustic waves in granular media [4]. Although the collision of millimeter-scale spheres has being studied extensively [5, 6], it is difficult to apply existing techniques to the study of collision between micro-particles. As an example, Foerster et al. imaged the collisions between two spheres in free-fall [5]. Their imaging system resolved the trajectory throughout the collision process and the rotational motion generated by the tangent interaction force. However, for micro-scale objects, the diffraction of visible light demands the use of very accurate focusing, requiring short focal lenses. These lenses greatly reduce the depth of field to a submillimeter region, which is then too small to allow accurate
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