Pressure distribution in an assembly of wooden cylinders with various aspect ratios under uniaxial confined compression

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.

Anisotropic particles strengthen granular pillars under compression

“…These aspects are commonly present in materials undergoing ductile failure [3], so our apparatus can serve as a model system for this type of material failure. An important distinction between this apparatus and other uniaxially driven granular systems [41,50] is that we do not restrict expansion of the system with any sort of hard boundary or soft membrane, nor is the compression direction along or against the direction of gravity. We performed 5 trials for each type of pillar composition, with the specifics of the microscopic initial structure varying from run to run, but initial dimensions remaining constant as described above.…”

Numerical analysis of compression mechanics of highly polydisperse granular mixtures with different PSD-s

“…Material properties include density, stiffness and surface roughness, while the geometric properties of particles include their size, size distribution and shape. Each of these parameters has been found to determine the structure and the mechanical response of granular materials to external shear and compressive loads [1][2][3][4][5][6][7][8][9][10].…”

On the challenges facing the handling of solid biomass feedstocks

“…Due to biomass elasticity, research into compacted storage beyond traditional stress analyses is required, with a focus on measurement of tensile force due to the bulk solids’ ‘springiness’. A number of authors have investigated different aspects associated with this behaviour, covering compression, elastic recovery (springback), stress strain behaviour and the density pressure relationship . Improved characterisation techniques are required to quantify unrestrained, unconsolidated dilation, beyond current compressibility assessment methods.…”

“…b). The relationship is similar to that observed during testing of wooden cylinders in a uniaxial apparatus . These results demonstrate that wattle has been granulated and in this way, closer to behaving like the coal and iron ore materials.…”

“…Typically, compressibility is assessed in a chamber of known volume with the application of an increasing external compressive load. For biomass feedstocks, it is dilation due to biomass tensile response, rather than compressive load, that is of great significance . Due to springiness/elasticity, biomass is much more difficult to consolidate to critical condition and fail.…”