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Cold compaction of composite powders
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Powder compaction is a production method commonly used in the manufacturing industry today. In order to minimize costly experiments and to optimize serial production of details several methods to analyze the powder compaction process are developed and used. One method is to use micromechanical analysis where the local description of contact between two individual particles is of great importance. In this dissertation a visco-plastic contact law has been used and further developed in order to understand the powder compaction process at packing, low relative density compaction up to high relative density compaction.

In order to relax some assumptions from previous theoretical studies simulation with the discrete element method (DEM) was performed. Up to 10.000 spherical particles were used in packing and early compaction simulation. It was found that rearrangement of particles is one of the major densification mechanisms in the early phases of compaction. At die compaction this effect of rearrangement was shown to be more pronounced than predicted from theoretical analyses. It was also found that the size ratio of particles is of importance when the number fraction of small particles in the compound is high.

The finite element method has been used for numerical analyses to investigate the local contact problem between two particles when self-similarity no longer prevail. Based on the numerical results a suggestion for an approximate compliance relation was made. With this approximate formula the local compliance behaviour between two dissimilar particles was analysed. These findings are directly applicable to simulations with the discrete element method. Finally, an investigation using the finite element method to evaluate the range of the accuracy for theoretical and approximate compliance formula has been done with compounds of different regular lattices. It was found that the range of accuracy is much dependent on the number of contacts within the lattices, specially new forming contacts during the compaction.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , vii, 15 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0389
Keyword [en]
micromechanical modelling, composite powders, descrete element method
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-417OAI: oai:DiVA.org:kth-417DiVA: diva2:11040
Public defence
2005-09-23, Sal B2, Brinellvägen 23, Stockholm, 10:00
Opponent
Supervisors
Note

QC 20101007

Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2013-01-14Bibliographically approved
List of papers
1. On discrete element modelling of compaction of powders with size ratio
Open this publication in new window or tab >>On discrete element modelling of compaction of powders with size ratio
2004 (English)In: Computational materials science, ISSN 0927-0256, Vol. 31, 131-146 p.Article in journal (Refereed) Published
Abstract [en]

A numerical procedure, based on a discrete element method (DEM), for analysing cold compaction of spherical powders, is presented. In the numerical model, packing followed by compaction of up to 10,000 powder particles is simulated. Perfectly plastic material behaviour is assumed for convenience, but not for necessity, and as a result, local contacts between frictionless particles are described by a linear force–displacement relation. The numerical model is described in detail and its applicability to compaction problems of different complexity is discussed. Explicit results are presented for the case of isostatic compaction of spherical powders with size ratio and include applied pressure as function of densification as well as the evolution of contacts for individual particles. The present results are compared in detail with corresponding results from previous theoretical, experimental and numerical studies and the validity of fundamental assumptions made in previous theoretical analyses are discussed.

Keyword
Powder, Isostatic compaction, Discrete element modelling
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6348 (URN)10.1016/j.commatsci.2004.02.005 (DOI)000223950500012 ()2-s2.0-4344581627 (Scopus ID)
Note
QC 20101007 Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2011-09-23Bibliographically approved
2. Cold compaction of composite powders with size ratio
Open this publication in new window or tab >>Cold compaction of composite powders with size ratio
2004 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 52, no 7, 1871-1884 p.Article in journal (Refereed) Published
Abstract [en]

Cold compaction of composite powders with size ratio has been analysed in this study using a discrete element method. Powder aggregates consisting of up to 10,000 particles and formed by two powder populations with known material strength and size ratios have been compacted both isostatically and uniaxially. The particles were assumed constitutively to be either perfectly plastic or rigid, and as a result. local contacts between the particles were described by a linear force-displacement relation. The results of this study include the presentation of relevant compaction quantities as a function of densification, and a detailed comparison with previous theoretical. numerical, and experimental studies. Particular emphasis has been placed on investigating the predictive capability of the fundamental assumptions frequently used in theoretical analyses of compaction problems.

Keyword
cold isostatic pressing, composite powder, micromechanical modelling
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6349 (URN)10.1016/j.actamat.2003.12.026 (DOI)000221001300011 ()2-s2.0-1842450400 (Scopus ID)
Note
QC 20101007Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2011-10-28Bibliographically approved
3. Local contact compliance relations at compaction of composite powders
Open this publication in new window or tab >>Local contact compliance relations at compaction of composite powders
2007 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 74, no 1, 164-168 p.Article in journal (Refereed) Published
Abstract [en]

Local contact behavior of composite powders has been investigated by using the finite element method. In previous analyses of such problems it has in general been assumed that one of the powder materials is rigid while the other deforms at loading as in such a case self-similarity prevails. This is a very good approximation for ceramic/metallic composites but may not be so when the composite consists of two materials of roughly equal hardness. An approximate compliance formula for describing this feature is proposed showing good agreement with corresponding finite element results for representative cases.

Keyword
discrete element method, power-law creep, cold compaction, particle deformation, inelastic contact, plasticity theory, size ratio, indentation, solids, brinell
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6350 (URN)10.1115/1.2165240 (DOI)000243485900019 ()2-s2.0-34248192774 (Scopus ID)
Note
Uppdaterad från submitted till published: 20101007. QC 20101007Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2010-10-07Bibliographically approved
4. On the local contact behaviour in regular lattices of composite powders
Open this publication in new window or tab >>On the local contact behaviour in regular lattices of composite powders
2007 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, Vol. 184, no 1-3, 312-318 p.Article in journal (Refereed) Published
Abstract [en]

The local contact behaviour of composite powders arranged in regular lattices has been investigated in this study with the finite element method. Numerical results related to isostatic and die compaction of unit cells of simple cubic and body-centered cubic lattices have been compared to previous analytical and numerical findings describing in particular local but also global contact at powder compaction. The finite element calculations are continued up to full density of solid material in the unit cells.

Keyword
composite powder compaction, unit cell calculation, micromechanical modelling, finite element simulation
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6351 (URN)10.1016/j.jmatprotec.2006.11.099 (DOI)000244811800043 ()2-s2.0-33846820049 (Scopus ID)
Note
Uppdaterad från submitted till published: 20101007. QC 20101007Available from: 2005-09-14 Created: 2005-09-14 Last updated: 2010-10-07Bibliographically approved

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