18,217 research outputs found
Experimental study of the compaction dynamics for 2D anisotropic granular materials
We present an experimental study of the compaction dynamics for
two-dimensional anisotropic granular systems. Compaction dynamics is measured
at three different scales : (i) the macroscopic scale through the packing
fraction , (ii) the mesoscopic scale through both fractions of aligned
grains and ideally ordered grains , and (iii) the
microscopic scale through both rotational and translational grain mobilities
. The effect of the grain rotations on the compaction dynamics has
been measured. At the macroscopic scale, we have observed a discontinuity in
the late stages of the compaction curve. At the mesoscopic scale, we have
observed the formation and the growth of domains made of aligned grains. From a
microscopic point of view, measurements reveal that the beginning of the
compaction process is essentially related to translational motion of the
grains. The grains rotations drive mainly the process during the latest stages
of compaction.Comment: 8pages, 11 figure
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Direct Formation of Structural Components Using a Martian Soil Simulant.
Martian habitats are ideally constructed using only locally available soils; extant attempts to process structural materials on Mars, however, generally require additives or calcination. In this work we demonstrate that Martian soil simulant Mars-1a can be directly compressed at ambient into a strong solid without additives, highlighting a possible aspect of complete Martian in-situ resource utilization. Flexural strength of the compact is not only determined by the compaction pressure but also significantly influenced by the lateral boundary condition of processing loading. The compression loading can be applied either quasi-statically or through impact. Nanoparticulate iron oxide (npOx), commonly detected in Martian regolith, is identified as the bonding agent. Gas permeability of compacted samples was measured to be on the order of 10-16 m2, close to that of solid rocks. The compaction procedure is adaptive to additive manufacturing
Using small-angle X-ray scattering to investigate the compaction behaviour of a granulated clay
The compaction behaviour of a commercial granulated clay (magnesium aluminium smectite, gMgSm) was investigated using macroscopic pressure-density measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray microtomography (XμT) and small-angle X-ray scattering (SAXS). This material was studied as a potential compaction excipient for pharmaceutical tabletting, but also as a model system demonstrating the capabilities of SAXS for investigating compaction in other situations.
Bulk compaction measurements showed that the gMgSm was more difficult to compact than polymeric pharmaceutical excipients such as spheronised microcrystalline cellulose (sMCC), corresponding to harder granules. Moreover, in spite of using lubrication (magnesium stearate) on the tooling surfaces, rather high ejection forces were observed, which may cause problems during commercial tabletting, requiring further amelioration. Although the compacted gMgSm specimens were more porous, however, they still exhibited acceptable cohesive strengths, comparable to sMCC. Hence, there may be scope for using granular clay as one component of a tabletting formulation.
Following principles established in previous work, SAXS revealed information concerning the intragranular structure of the gMgSm and its response to compaction. The results showed that little compression of the intragranular morphology occurred below a relative density of 0 · 6, suggesting that granule rearrangements or fragmentation were the dominant mechanisms during this stage. By contrast, granule deformation became considerably more important at higher relative density, which also coincided with a significant increase in the cohesive strength of compacted specimens.
Spatially-resolved SAXS data was also used to investigate local variations in compaction behaviour within specimens of different shape. The results revealed the expected patterns of density variations within flat-faced cylindrical specimens. Significant variations in density, the magnitude of compressive strain and principal strain direction were also revealed in the vicinity of a debossed feature (a diametral notch) and within bi-convex specimens. The variations in compaction around the debossed notch, with a small region of high density below and low density along the flanks, appeared to be responsible for extensive cracking, which could also cause problems in commercial tabletting
Technologies for restricting mould growth on baled silage
End of project reportSilage is made on approximately 86% of Irish farms, and 85% of these make some baled silage. Baled silage is particularly important as the primary silage making, storage and feeding system on many beef and smaller sized farms, but is also employed as a secondary system (often associated with facilitating grazing management during mid-summer) on many dairy and larger sized farms (O’Kiely et al., 2002). Previous surveys on farms indicated that the extent of visible fungal growth on baled silage was sometimes quite large, and could be a cause for concern. Whereas some improvements could come from applying existing knowledge and technologies, the circumstances surrounding the making and storage of baled silage suggested that environmental conditions within the bale differed from those in conventional silos, and that further knowledge was required in order to arrive at a secure set of recommendations for baled silage systems. This report deals with the final in a series (O’Kiely et al., 1999; O’Kiely et al., 2002) of three consecutive research projects investigating numerous aspect of the science and technology of baled silage. The success of each depended on extensive, integrated collaboration between the Teagasc research centres at Grange and Oak Park, and with University College Dublin. As the series progressed the multidisciplinary team needed to underpin the programme expanded, and this greatly improved the amount and detail of the research undertaken. The major objective of the project recorded in this report was to develop technologies to improve the “hygienic value” of baled silage
Experimental investigation of the elastoplastic response of aluminum silicate spray dried powder during cold compaction
Mechanical experiments have been designed and performed to investigate the
elasto-plastic behaviour of green bodies formed from an aluminum silicate spray
dried powder used for tiles production. Experiments have been executed on
samples obtained from cold compaction into a cylindrical mould and include:
uniaxial strain, equi-biaxial flexure and high-pressure triaxial
compression/extension tests. Two types of powders have been used to realize the
green body samples, differing in the values of water content, which have been
taken equal to those usually employed in the industrial forming of traditional
ceramics. Yielding of the green body during compaction has been characterized
in terms of yield surface shape, failure envelope, and evolution of cohesion
and void ratio with the forming pressure, confirming the validity of previously
proposed constitutive models for dense materials obtained through cold
compaction of granulates.Comment: 17 pages; Journal of the European Ceramic Society, 201
Rammed Earth Construction: A Proposal for a Statistical Quality Control in the Execution Process
Unlike other common contemporary construction materials such as concrete, mortars,
or fired clay bricks, which are widely supported by international standards and regulations,
building with rammed earth is barely regulated. Furthermore, its quality control is usually problematic,
which regularly encourages the rejection of this technique. In the literature, many authors have
suggested ways to safely build a rammed earth wall, but only a few of them have delved into its
quality control before and during the construction process. This paper introduces a preliminary
methodology and establishes unified criteria, based in a statistical analysis, for both the production
and the quality control of this constructive technique in cases dealing with both samples and walls
Effects of grain shape on packing and dilatancy of sheared granular materials
Granular material exposed to shear shows a variety of unique phenomena:
Reynolds dilatancy, positional order and orientational order effects may
compete in the shear zone. We study granular packings consisting of macroscopic
prolate, oblate and spherical grains and compare their behaviour. X-ray
tomography is used to determine the particle positions and orientations in a
cylindrical split bottom shear cell. Packing densities and the arrangements of
individual particles in the shear zone are evaluated. For anisometric
particles, we observe the competition of two opposite effects. One the one
hand, the sheared granulate is dilated, but on the other hand the particles
reorient and align with respect to the streamlines. Even though aligned
cylinders in principle may achieve higher packing densities, this alignment
compensates for the effect of dilatancy only partially. The complex
rearrangements lead to a depression of the surface above the well oriented
region while neigbouring parts still show the effect of dilation in the form of
heaps. For grains with isotropic shapes, the surface remains rather flat.
Perfect monodisperse spheres crystallize in the shear zone, whereby positional
order partially overcompensates dilatancy effects. However, already slight
deviations from the ideal monodisperse sphere shape inhibit crystallization.Comment: 12 pages, 13 figures, accepted in Soft Matte
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