Abstract
Understanding how forces propagate in granular assemblages is important for equipment design and process control in many technologies. Yet, it remains poorly understood. In this study, a cuboidal assembly comprising cylinders of various lengths (aspect ratios AR ranging from 0.9 to 3.6) were subjected to uniaxial confined compression tests. Samples were vertically compressed until the top platen exerted a pressure of 50 kPa on the uppermost particles. This maximum pressure corresponds to the hydrostatic pressure of an approximately 15 m high column of chopped wood that may be encountered in real storage structures. The nonlinear loading curves were obtained depended on the aspect ratios of the cylinders. The modulus of elasticity, calculated from the linear elastic part of the stress–strain curve, monotonically decreased from 10.2 to 8.6 MPa as the aspect ratio increased from 1.2 to 3.6. The elastic modulus and volume fraction exhibited similar trends as functions of the aspect ratio. The horizontal-to-vertical pressure ratio was calculated as the horizontal pressure exerted on the wider walls to the vertical pressure exerted on the top lid during loading–unloading cycles. For ARs up to 3.6, the pressure ratio was approximately 0.31; for the longest cylinders (AR = 3.6), it decreased to approximately 0.27, probably because the assumption of the representative chamber volume was invalidated at this AR.
Highlights
The geometrical features of granular assemblies, those of packed spherical particles, have been extensively studied over the last few decades [1,2,3]
The geometrical properties of assemblies of variously shaped particles are important in crystallography, geology, chemical
The present study focused on the mechanical behaviors of assembled wooden cylindrical particles under uniaxial confined compression
Summary
The geometrical features of granular assemblies, those of packed spherical particles, have been extensively studied over the last few decades [1,2,3]. Even granular packings of spherical particles can become inherently anisotropic under gravity and friction effects. Donev et al [4] observed a sharp increase in the density and number of contacts in randomly packed assemblies of ellipsoids as the length of the packed particles increased (equivalently, as the aspect ratio, defined as the length-to-diameter ratio, increased from 1.0 to 1.5). As the aspect ratio increased beyond 1.5, the relative density decreased probably because of strong exclusion-volume effects [4]. The volume fraction was 0.58 for the shortest particles with an aspect ratio of 6.8, and decreased with increasing particle elongation. Härtl and Ooi [7]
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