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Micromechanics of Powder Compaction
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).ORCID iD: 0000-0001-7674-8582
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Compaction of powders followed by sintering is a convenient manufacturing method for products of complex shape and components of materials that are difficult to produce using conventional metallurgy. During the compaction and the handling of the unsintered compact, defects can develop which could remain in the final sintered product. Modeling is an option to predict these issues and in this thesis micromechanical modeling of the compaction and the final components is discussed. Such models provide a more physical description than a macroscopic model, and specifically, the Discrete Element Method (DEM) is utilized.

An initial study of the efect of particle size distribution, performed with DEM, was presented in Paper A. The study showed that this effect is small and is thus neglected in the other DEM studies in this thesis. The study also showed that good agreement with experimental data can be obtained if friction effects is correctly accounted for.

The most critical issue for accurate results in the DEM simulations is the modeling of normal contact between the powder particles. A unified treatment of this problem for particles of a strain hardening elastic-plastic material is presented in Paper B. Results concerning both the elastic-plastic loading, elastic unloading as well as the adhesive bonding between the particles is included. All results are compared with finite element simulation with good agreement with the proposed model.

The modeling of industry relevant powders, namely spray dried granules is presented in Paper C. The mechanical behavior of the granules is determined using two types of micromechanical experiments, granule compression tests and nanoindentation testing. The determined material model is used in an FEM simulation of two granules in contact. The resulting force-displacement relationships are exported to a DEM analysis of the compaction of the granules which shows very good agreement with corresponding experimental data.

The modeling of the tangential forces between two contacting powder particles is studied in Paper D by an extensive parametric study using the finite element method. The outcome are correlated using normalized parameters and the resulting equations provide the tangential contact force as function of the tangential displacement for different materials and friction coefficients.

Finally, in Paper E, the unloading and fracture of powder compacts, made of the same granules as in Paper C, are studied both experimentally and numerically. A microscopy study showed that fracture of the powder granules might be of importance for the fracture and thus a granule fracture model is presented and implemented in the numerical model. The simulations show that incorporating the fracture of the granules is essential to obtain agreement with the experimental data.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , viii, 22 p.
Series
TRITA-HLF, ISSN 1104-6813 ; 0565
National Category
Engineering and Technology
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-159142ISBN: 978-91-7595-430-1 (print)OAI: oai:DiVA.org:kth-159142DiVA: diva2:782727
Public defence
2015-02-13, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150122

Available from: 2015-01-22 Created: 2015-01-22 Last updated: 2015-01-22Bibliographically approved
List of papers
1. On the effect of particle size distribution in cold powder compaction
Open this publication in new window or tab >>On the effect of particle size distribution in cold powder compaction
2012 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 79, no 5, 051017- p.Article in journal (Refereed) Published
Abstract [en]

The effect of particle size distribution in powder compaction has been studied using the discrete element method. Both isostatic compaction and closed die compaction are studied together during the entire loading process. Particle rotation and frictional effects are accounted for in the analysis. The particles are, constitutively described by rigid plasticity, assumed to be spherical with the size of the radii that follows a truncated normal distribution. The results show that size distribution effects are small on global compaction properties like compaction pressure if the size distribution is small. Furthermore, the size distribution had no influence at all on the macroscopic behavior at unloading. To verify the model, comparisons were made on two different sets of experiment found in the literature where the particles were of varying sizes. Good agreement was found both on fundamental properties like the average number of contacts per particle and on more important properties from a practical point of view, like the compaction pressure.

Keyword
Discrete element method, Particle size distribution, Powder compaction
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-83869 (URN)10.1115/1.4006382 (DOI)000308413800017 ()2-s2.0-84865126805 (Scopus ID)
Funder
Vinnova
Note

QC 20120913

Available from: 2012-02-13 Created: 2012-02-13 Last updated: 2017-12-07Bibliographically approved
2. On force-displacement relations at contact between elastic-plastic adhesive bodies
Open this publication in new window or tab >>On force-displacement relations at contact between elastic-plastic adhesive bodies
2013 (English)In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 61, no 5, 1185-1201 p.Article in journal (Refereed) Published
Abstract [en]

The loading-unloading of dissimilar adhesive elastic-plastic bodies is studied both analytically and numerically, including elastic-ideal plastic and deformation hardening behavior. The contacting bodies are assumed to be spherical in the region of contact and consequently the presented model is partly based on results pertinent to Brinell indentation. The problem of adhesive unloading is solved in two steps; first the unloading in the absence of adhesion is studied and then an adhesive pressure term is added. The analytical model is derived using fracture mechanics arguments and is based on one parameter, the fracture energy. The model is finally verified with finite element simulations by introducing a cohesive behavior between the modeled spheres. The analytical model shows very good agreement with the FE-simulations both during loading and unloading and also concerning the case of force and displacement at separation.

Keyword
Powder compaction, Contact mechanics, Elastic-plastic material, Finite elements, Cohesive surfaces
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-117602 (URN)10.1016/j.jmps.2013.01.004 (DOI)000317163300002 ()2-s2.0-84875220365 (Scopus ID)
Funder
Vinnova
Note

QC 20130520

Available from: 2013-01-31 Created: 2013-01-31 Last updated: 2017-12-06Bibliographically approved
3. A numerical analysis of cold powder compaction based on micromechanical experiments
Open this publication in new window or tab >>A numerical analysis of cold powder compaction based on micromechanical experiments
2013 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 243, 71-78 p.Article in journal (Refereed) Published
Abstract [en]

The discrete element method (DEM) is used for predicting the compaction behavior of two types of spray dried cemented carbide granules. The material model of the granules is determined by micromechanical experiments. First, compression tests are performed on single granules giving information of the deformation behavior at relatively small deformations. For larger deformations, nanoindentation tests are performed to give further information of the constitutive behavior indicating a strong hardening behavior at high strains. The material model is implemented in an FE model of two particles in contact and the relation between contact force and indentation depth is exported to a DEM program. The DEM program is used to simulate presently performed uniaxial die compaction experiments where the geometry of the die is taken into account. Excellent agreement is found between the experiments and the numerical predictions in the range where results from DEM simulations are valid.

Keyword
Cemented carbides, Contact mechanics, Discrete element method, Granule strength measurements, Nanoindentation, Powder compaction
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-134166 (URN)10.1016/j.powtec.2013.03.040 (DOI)000320143000009 ()2-s2.0-84876474506 (Scopus ID)
Funder
Vinnova
Note

QC 20131120

Available from: 2013-11-20 Created: 2013-11-18 Last updated: 2017-12-06Bibliographically approved
4. On the tangential contact behavior at elastic–plastic spherical contact problems
Open this publication in new window or tab >>On the tangential contact behavior at elastic–plastic spherical contact problems
2014 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 319, no 1/2, 110-117 p.Article in journal (Refereed) Published
Abstract [en]

The problem of tangential contact between an elastic-plastic sphere and a rigid plane is studied analytically and numerically with the specific aim to derive force-displacement relations to be used in numerical simulations of granular materials. The simulations are performed for both ideal-plastic and strain hardening materials with different yield stresses and including large deformation effects in order to draw general conclusions. The results are correlated using normalized quantities pertinent to the correlation of indentation testing experiments leading to a general description of the tangential contact problem. Explicit formulas for the normal and tangential forces are presented as a function of the tangential displacement using data that are easily available from axi-symmetric analyses of spherical contact. The proposed model shows very good agreement when compared with the FE-simulations.

Keyword
Spherical contact, Powder compaction, Shear stresses, Finite element simulations, Elastic-plastic materials, Mises plasticity
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-159081 (URN)10.1016/j.wear.2014.07.016 (DOI)000345061600012 ()2-s2.0-84907682156 (Scopus ID)
Funder
Vinnova
Note

QC 20150222

Available from: 2015-01-21 Created: 2015-01-21 Last updated: 2017-12-05Bibliographically approved
5. Micromechanical Investigation of the Fracture Behavior of Powder Materials
Open this publication in new window or tab >>Micromechanical Investigation of the Fracture Behavior of Powder Materials
2015 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 286, 31 p.11185Article in journal (Refereed) Published
Abstract [en]

Fracture of compacted powder has been studied experimentally and numerically using a micromechanicalapproach. In the experimental investigation, the compacts are crushed in two dierent directions to accountfor general stress states and a microscopy study shows that fracture of the powder granules plays asignicant role in the fracture process. The numerical analysis is based on the Discrete Element Method(DEM) and a novel approach is presented to account for the fracture of the particles in the numericalmodel. The force-displacement relations for two particles in contact, which are needed in DEM, are derivedusing micomechanical experiments together with nite element analyses of the contact problem. The contactmodel accounts for plastic compression, elastic unloading and adhesive bonding together with frictionand tangential bonding. The model shows a very good agreement with the experimental data both for theelastic behavior during unloading and, if failure of the particles is accounted for, the fracture of the compacts.

Place, publisher, year, edition, pages
Elsevier, 2015. 31 p.
Keyword
Powder compaction, Fracture mechanisms, Contact mechanics, Experiments, Discrete element method, Green strength
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-159084 (URN)10.1016/j.powtec.2015.08.018 (DOI)000364247200034 ()2-s2.0-84940023110 (Scopus ID)
Note

QC 20151130

Available from: 2015-01-21 Created: 2015-01-21 Last updated: 2017-12-05Bibliographically approved

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