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Micromechanical Investigation of the Fracture Behavior of Powder Materials
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).ORCID iD: 0000-0001-7674-8582
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).ORCID iD: 0000-0001-6232-8819
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. Vol. 286, 31 p.11185
Keyword [en]
Powder compaction, Fracture mechanisms, Contact mechanics, Experiments, Discrete element method, Green strength
National Category
Mechanical Engineering
URN: urn:nbn:se:kth:diva-159084DOI: 10.1016/j.powtec.2015.08.018ISI: 000364247200034ScopusID: 2-s2.0-84940023110OAI: diva2:782385

QC 20151130

Available from: 2015-01-21 Created: 2015-01-21 Last updated: 2016-01-22Bibliographically approved
In thesis
1. Micromechanics of Powder Compaction
Open this publication in new window or tab >>Micromechanics of Powder Compaction
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.
, TRITA-HLF, ISSN 1104-6813 ; 0565
National Category
Engineering and Technology
Research subject
Solid Mechanics
urn:nbn:se:kth:diva-159142 (URN)978-91-7595-430-1 (ISBN)
Public defence
2015-02-13, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20150122

Available from: 2015-01-22 Created: 2015-01-22 Last updated: 2015-01-22Bibliographically approved

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