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An apparatus for confined triaxial testing of single particles
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
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2015 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 270, p. 121-127Article in journal (Refereed) Published
Abstract [en]

A novel triaxial apparatus employing overlapping rigid boundaries has been designed and constructed for experimental measurement of contact forces under confined compression of single granules in the mm-scale. The performance of the apparatus was evaluated by performing uniaxial and triaxial compression experiments on ideal elastic-plastic materials. Compression curves were compared with the fully plastic Abbott-Firestone contact model and with results from FEM simulations. The increase in contact force associated with confined conditions was observed in the compression curves from triaxial compression experiments, as supported by predictions from simulations using single particle contact models. Hence, a new method for the assessment of mechanical behaviour of single particles under confined compression can be considered as established.

Place, publisher, year, edition, pages
2015. Vol. 270, p. 121-127
Keyword [en]
Compression, Triaxial, Single particles, Confined conditions, Apparatus design, Contact mechanics
National Category
Pharmaceutical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-239203DOI: 10.1016/j.powtec.2014.10.016ISI: 000347579300014OAI: oai:DiVA.org:uu-239203DiVA, id: diva2:773633
Funder
Swedish Research Council, 621-2011-4049
Available from: 2014-12-19 Created: 2014-12-19 Last updated: 2018-04-12Bibliographically approved
In thesis
1. Confined Compression of Single Particles: Development of a Novel Triaxial Testing Instrument and Particle-Scale Modelling
Open this publication in new window or tab >>Confined Compression of Single Particles: Development of a Novel Triaxial Testing Instrument and Particle-Scale Modelling
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When predicting the performance of a powder compaction process, assessing the behaviour of the particles comprising the powder bed is of central relevance. Currently, however, no experimental methods are available for mimicking the multiaxial loading conditions imposed on the individual particles in a powder bed during compaction, and such analyses are therefore usually performed in silico. Thus, the purpose of this thesis is to introduce a novel experimental method that enables experimental evaluation of confined triaxial loading conditions on individual particles in the mm-scale.

The work underlying the thesis consists of three major parts. Firstly, the triaxial instrument was designed and developed, after which its performance was evaluated using nominally ideal elastic-plastic spheres as model materials. These initial experiments showed that the instrument was able to successfully impose confined triaxial conditions on the particles, something that was verified by finite element method (FEM) simulations.

Secondly, the triaxial instrument was used to investigate differences in deformation characteristics under uniaxial and triaxial loading conditions for four different microcrystalline cellulose (MCC)-based granules. It was shown that fragmentation, associated with unconfined uniaxial compression, was impeded under confined triaxial conditions, despite the emergence of cracks. In addition, it was observed that the primary crack always occurs in a plane parallel to the most deformed direction, and that the location of the largest pore has a pronounced influence on the path of the crack.

Thirdly, the influence of different triaxial loading ratios were evaluated on polymer spheres, after which a unified description of contact pressure development was devised. Data from these experiments were then successfully used to calibrate a contact model for simulating bulk powder compression with the discrete element method (DEM).

All in all, a novel experimental method has been established, which has proven useful as an alternative and complement to numerical studies when studying single particle deformation under confined triaxial conditions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 58
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 255
Keyword
Powder compaction, Compression, Single particle, Particle mechanics, Powder mechanics, Confined conditions, Triaxial, Apparatus design, Modelling
National Category
Pharmaceutical Sciences
Research subject
Pharmaceutics
Identifiers
urn:nbn:se:uu:diva-348091 (URN)978-91-513-0329-1 (ISBN)
Public defence
2018-06-05, B21, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2018-05-09 Created: 2018-04-12 Last updated: 2018-05-09

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Jonsson, HenrikGråsjö, JohanNordström, JosefinaJohansson, NiklasFrenning, Göran
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