Biosystems Engineering | 2019
Tensile strength of pressure-agglomerated potato starch determined via diametral compression test: Discrete element method simulations and experiments
Abstract
Starch is important excipient and binder in agglomerates, tablets, capsules, briquettes, and pellet formulations for food, pharmaceutical, biomass, coal/biomass fuel, and metallurgy applications. The aim of this study was to compare the results of determination of the tensile strength of cylindrical starch agglomerates via a diametral compression test using a macro-approach following Hertz s solution, with those obtained via the micro-approach using the discrete element method (DEM). Potato starch with moisture contents of 12% and 17% was compacted in a cylindrical die 10\xa0mm in diameter with a displacement velocity of 0.02\xa0mm\xa0s−1 and compressed to 38, 76, 115, and 153\xa0MPa. The tensile strength was measured in the diametral compression test with a deformation rate of 0.033\xa0mm\xa0s−1. EDEM software was used to perform numerical simulations. The components of the stress tensor in the agglomerate were determined in the representative volume element with the shape of a cuboid (0.25\xa0×\xa00.25\xa0×\xa01\xa0mm3). DEM simulations using the linear elastic–plastic model with linear adhesion exhibited good agreement with the experimental results. With the agglomerate deformation, the curvature of the compressive-force chains—in the shape of two arches combined with the tension-force chains—increased. At failure, the crack was initiated in the vicinity of the agglomerate centre and propagated towards the loading platens, damaging the connections between the compressive-force chains. Hertz s formula correctly described the tensile strength of the agglomerates for an adhesive stiffness-to-plastic stiffness ratio higher than 0.04.