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Mechanical behaviour of ideal elastic-plastic particles subjected to different triaxial loading conditions
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.
2017 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 315, p. 347-355Article in journal (Refereed) Published
Abstract [en]

The contact force development for two types of polymeric elastoplastic particles subjected to different triaxial loading conditions was studied experimentally utilising a unique triaxial testing apparatus. In order to evaluate the experimental results, a finite element analysis was performed. The experimental findings highlighted the importance of contact dependence, which manifested itself in two principally different ways. Firstly, a reduced stiffness was observed when plastic deformation ceased to be fully contained, which, depending on the loading conditions, occurred at an engineering strain of about 5-10%. Secondly, a markedly increased stiffness was observed when particle confinement inhibited further plastic deformation, making elastic volume reduction the predominant deformation mode. The experimental results could be well reproduced by the numerical simulations, provided that isotropic hardening was included in the elastoplastic model. In an attempt to invariantly describe the data, a nominal contact pressure was determined as a function of the volumetric constraint of the particle. This resulted in an adequate collapse of results obtained for different loading conditions onto a single master curve at large volumetric constraint. In summary, this paper should be considered as a step along the pathway towards our long term goal of introducing novel and improved contact models.

Place, publisher, year, edition, pages
2017. Vol. 315, p. 347-355
Keywords [en]
Particle mechanics, Triaxial, Compression, Spatial confinement, Contact dependence
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:uu:diva-323755DOI: 10.1016/j.powtec.2017.04.005ISI: 000401593600041OAI: oai:DiVA.org:uu-323755DiVA, id: diva2:1108797
Funder
Swedish Research Council, 621-2011-4049Available from: 2017-06-13 Created: 2017-06-13 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
Keywords
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, JohanFrenning, Göran

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