camera iphone 8 plus apk Evolution of particle breakage studied using x-ray tomography and the discrete element method

Zeynep Karatza (1,2,*), Edward Andò (2), Stefanos-Aldo Papanicolopulos (1), Gioacchino Viggiani (2), and Jin Y. Ooi (1),
(1) School of Engineering, The University of Edinburgh, Edinburgh EH9 3JL, U.K.
(2) Univ. Grenoble Alpes, CNRS, Grenoble INP*, 3SR, F-38000 Grenoble, France
(*) Institute of Engineering Univ. Grenoble Alpes

Particles exist in great abundance in nature, such as in sands and clays, and they also constitute 75% of the materials used in industry (e.g., mineral ores, medicine, paint, detergent powders). When a load is applied the response of a granular material at the bulk (macro) scale originates from the changes at the particle scale. If particle breakage occurs, the grading of the material and the shape and size of its particles will change and these induce changes in the contact network from where forces are transmitted. As a result, changes at the micro-scale can significantly affect the mechanical behaviour of a granular material and this explains why the mechanisms leading to particle breakage have been a common subject among several fields, including geomechanics. Here, oedometric compression tests are performed on zeolite granules specimens and x-ray computed micro-tomography (XCT) is employed, to acquire high resolution (pixel size = 0.01mm) 3D images of the specimens throughout the test. The images are processed, to describe breakage spatially and quantify it throughout the test and gain information about the mechanisms leading to particle breakage. In addition to the image processing, the discrete element method (DEM) is used to study the initiation and likelihood of particle breakage, by simulating the experimental test during the early stages of loading and using quantitative results from the images to inform and validate the DEM model. A discrete digital image correlation is used, in order to incrementally identify intact grains and simultaneously get results about the strain field within the specimen, as well as the kinematics of individual grains and fragments. In the initial stages of breakage, there is a clear boundary effect on the spatial distribution of breakage, as it is concentrated at the moving boundary (more than 90% of total breakage) and circumferentially (more than 70% of total breakage) close to the apparatus cell. Three main breakage patterns are observed and related to the coordination number; lower coordination numbers lead to intricate breakage patterns, whereas intact particles have consistently a higher number of contacts. The DEM model can reproduce the bulk response of the material until the point where substantial breakage governs the macroscopic response and it starts to soften. Additionally, the spatial distribution of the force network matches the localisation of breakage radially (which also explains the increase of the K0), but it does not seem to localise close to the loading platen. When particles start to break, in the DEM there is an increase to the friction ratio and significant amount of particles are experiencing slipping. Additionally, the amount of particles breaking (as measured from XCT) agrees with the number of particles experiencing the breakage force in DEM at the same loading increments. This analysis will enrich our understanding of the mechanisms and evolution of particle breakage, as from the XCT we can investigate contacts and breakage patterns and to complete this analysis we can get information from the DEM regarding the amount and distribution of contact forces.

camera iphone 8 plus apk Evolution of particle breakage studied using x-ray tomography and the discrete element method
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Science & Technology	Upload TimePublished on 19 Jun 2017

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