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Publications (10 of 23) Show all publications
Olsson, E. & Jelagin, D. (2019). A contact model for the normal force between viscoelastic particles in discrete element simulations. Powder Technology, 342, 985-991
Open this publication in new window or tab >>A contact model for the normal force between viscoelastic particles in discrete element simulations
2019 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 342, p. 985-991Article in journal (Refereed) Published
Abstract [en]

DEM modeling of granular materials composed of viscoelastic particles can provide valuable insights into the mechanical behavior of a wide range of engineering materials. In this paper, a new model for calculating the normal contact force between visoelastic spheres is presented based on contact mechanics that takes the mechanical behavior of the DEM particles into account. The model relies on an application of the viscoelastic correspondence principle to elastic Hertz contact. A viscoelastic relaxation function for the contact is defined and a generalized Maxwell material is used for describing this function. An analytical expression for the increment in contact force given an increment in overlap is derived leading to a computationally efficient model. The proposed model provides the analytical small deformation solution upon loading but provides an approximate solution at unloading. Comparisons are made with FEM simulations of contact between spheres of different sizes of equal and dissimilar materials. An excellent agreement is found between the model and the FEM simulations for almost all cases except at cyclic loading where the characteristic times of the viscoelastic behavior and the loading are similar.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Discrete element method, Viscoelastic contact, Contact mechanics, Contact law, Finite elements
National Category
Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-241184 (URN)10.1016/j.powtec.2018.10.022 (DOI)000454375100097 ()2-s2.0-85056464283 (Scopus ID)
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-06-10Bibliographically approved
Olsson, E., Jelagin, D. & Forquin, P. A. (2019). Computational framework for analysis of contact-induced damage in brittle rocks. International Journal of Solids and Structures
Open this publication in new window or tab >>Computational framework for analysis of contact-induced damage in brittle rocks
2019 (English)In: International Journal of Solids and StructuresArticle in journal (Refereed) Published
Abstract [en]

This paper presents a numerical approach for predicting damage in rock materials caused by contact loading. The rock material is modelled using a constitutive description that combines pressure dependent plasticity, for capturing shear deformation under high confining pressure, with an anisotropic damage model for capturing mode I cracking in tension. Material parameters for the model are taken from a recently performed investigation on a granite material. The model has been used to simulate two types of contact loading experiments from the literature, cyclic loading and monotonic loading up to fracture. In order to achieve accurate predictions, the model has been extended to account for small loaded volumes which occur at contact loading. The results show that the main damage mechanism at cyclic loading is crack propagation due to Hertzian stresses whereas in the monotonic experiments sub-surface cracks could initiate. All features measured in the contact loading experiments are captured by the model and hence, the modelling framework is judged to be able to capture contact damage if real stone geometries are studied in FEM.

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Cracks, Cyclic loads, Finite element method, Granite, Indentation, Models, Accurate prediction, Anisotropic damage model, Computational framework, High confining pressure, Induced damage, Material parameter, Modelling framework, Numerical approaches, Loading
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-252118 (URN)10.1016/j.ijsolstr.2019.03.001 (DOI)000468711900003 ()
Note

QC 20190523

Available from: 2019-05-23 Created: 2019-05-23 Last updated: 2019-06-11Bibliographically approved
Olsson, E., Jelagin, D. & Partl, M. (2019). New discrete element framework for modelling asphalt compaction. International Journal on Road Materials and Pavement Design
Open this publication in new window or tab >>New discrete element framework for modelling asphalt compaction
2019 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402Article in journal (Refereed) Published
Abstract [en]

During asphalt mixture compaction, loads in the material are mainly transferred through contact between the stones and the interaction between the stones and the binder. The behaviour of such materials is suitable to model using the Discrete Element Method (DEM). In this study, a new DEM modelling approach has been developed for studying the asphalt compaction process, incorporating contact and damage laws based on granular mechanics. In the simulations, aggregate fracture is handled by a recently developed method of incorporating particle fracture in DEM, based on previously performed fracture experiments on granite specimens. The binder phase is modelled by adding a viscoelastic film around each DEM particle. This surface layer has a thickness that obtains the correct volume of the binder phase and has mechanical properties representative for the binder at different temperatures. The ability of the model to capture the influence of mixture parameters on the compactability and the eventual stone damage during compaction is examined for the cases of compaction flow test and gyratory compaction. Explicitly, the influence of different aggregate gradations, mixture temperatures and binder properties are studied. The results show that the proposed DEM approach is able to capture qualitatively and quantitatively responses in both cases and also provide predictions of aggregate damage. One large benefit with the developed modelling approach is that the influence of different asphalt mixture parameters could be studied without re-calibration of model parameters. Furthermore, based on comparative DEM simulations, it is shown that the proposed approach provides more realistic force distribution networks in the material.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2019
Keywords
asphalt compaction, discrete element method, modelling, aggregate damage
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-255412 (URN)10.1080/14680629.2019.1633750 (DOI)000473843200001 ()
Note

QC 20190814

Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
Staf, H., Olsson, E., Lindskog, P. & Larsson, P.-L. (2018). Determination of the Frictional Behavior at Compaction of Powder Materials Consisting of Spray-Dried Granules. Journal of materials engineering and performance (Print), 27(3), 1308-1317
Open this publication in new window or tab >>Determination of the Frictional Behavior at Compaction of Powder Materials Consisting of Spray-Dried Granules
2018 (English)In: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 27, no 3, p. 1308-1317Article in journal (Refereed) Published
Abstract [en]

The frictional behavior during powder compaction and ejection is studied using an instrumented die with eight radial sensors. The average friction over the total powder pillar is used to determine a local friction coefficient at each sensor. By comparing forces at compaction with forces at ejection, it can be shown that the Coulomb's friction coefficient can be described as a function of normal pressure. Also stick phenomena has been investigated in order to assess its influence on the determination of the local friction coefficient.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Coulomb friction, cutting inserts, die friction, FEM, finite element simulations, granular powder, powder compaction, reverse engineering, stick, wall friction, WC-Co powder
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-224684 (URN)10.1007/s11665-018-3205-1 (DOI)000426701000041 ()2-s2.0-85042867461 (Scopus ID)
Note

QC 20180326

Available from: 2018-03-26 Created: 2018-03-26 Last updated: 2018-03-26Bibliographically approved
Staf, H., Olsson, E., Lindskog, P. & Larsson, P.-L. (2017). On rate-dependence of hardmetal powder pressing of cutting inserts. Powder Metallurgy, 60(1), 7-14
Open this publication in new window or tab >>On rate-dependence of hardmetal powder pressing of cutting inserts
2017 (English)In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 60, no 1, p. 7-14Article in journal (Refereed) Published
Abstract [en]

The rate-dependence of hardmetal powder pressing in cutting insert production is investigated experimentally and numerically. In the latter case, the finite element method is relied upon using a continuum mechanics approach. In particular, possible rate-dependency due to creep deformation and rate-dependent friction is discussed with the experimental investigation focusing mainly on dimensional changes during sintering but also pressing forces. The results indicate that rate-dependent frictional effects are the dominating feature and accordingly, it can be argued that for the metal powders investigated here, creep deformations do not have to be accounted for in the constitutive description at the timescales relevant for powder pressing and when the shape after sintering is concerned. For the present powder, the apparent frictional effect decreases at higher pressing rates. Additional details of the friction behavior are studied comparing finite element simulations with experiments.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2017
Keywords
Rate-dependence, powder compaction, friction, creep, WC-Co powder, cutting inserts, material model, finite element simulations
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-205172 (URN)10.1080/00325899.2016.1260904 (DOI)000396619000003 ()2-s2.0-85007143910 (Scopus ID)
Note

QC 20170411

Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-06-29Bibliographically approved
Olsson, E. & Larsson, P.-L. (2016). A unified model for the contact behaviour between equal and dissimilar elastic-plastic spherical bodies. International Journal of Solids and Structures, 81, 23-32
Open this publication in new window or tab >>A unified model for the contact behaviour between equal and dissimilar elastic-plastic spherical bodies
2016 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 81, p. 23-32Article in journal (Refereed) Published
Abstract [en]

A unified method for calculating the contact force and the contact area between two dissimilar elastic-plastic spheres is presented with the aim of simulating granular materials using particle methods. Explicit equations are presented for the case when the plastic behaviour of the spheres is described with three material parameters. This makes the analysis applicable for a wide range of materials. The model is partly based on dimensionless quantities emerging from the Brinell hardness test. Large deformation of the contact is accounted for in the analysis, which allows for accurate contact relations up to indentation depths relevant for powder compaction. The presented model shows excellent agreement with finite element simulations of two spheres in contact and the results found in literature. An implementation of the contact model in Python is provided together with the online version of this paper.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Contact mechanics, Force-displacement relations, Elastic-plastic material, Large deformations, Discrete element method
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-183306 (URN)10.1016/j.ijsolstr.2015.10.004 (DOI)000370089200003 ()2-s2.0-84956688028 (Scopus ID)
Note

QC 20160309

Available from: 2016-03-09 Created: 2016-03-07 Last updated: 2017-11-30Bibliographically approved
Larsson, P. L. & Olsson, E. (2016). Elastic-plastic contact between hard metal particles. In: Key Engineering Materials: (pp. 86-99).
Open this publication in new window or tab >>Elastic-plastic contact between hard metal particles
2016 (English)In: Key Engineering Materials, 2016, p. 86-99Conference paper, Published paper (Refereed)
Abstract [en]

In the present study contact between elastic-plastic dissimilar spherical particles are investigated. The investigation is based on analytical and numerical methods and in the latter case in particular the finite element method. The results presented are pertinent to force-displacement relations at contact when elastic and plastic deformations are of equal magnitude. Especially, hard metal particles are considered with a typical application area being analysis of powder compaction.

Keywords
Contact mechanics, Elastic-plastic deformation, Force-displacement relations, Hard metals, Spherical particles
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-186764 (URN)10.4028/www.scientific.net/KEM.681.86 (DOI)2-s2.0-84959543060 (Scopus ID)
Note

QC 20160530

Available from: 2016-05-30 Created: 2016-05-13 Last updated: 2016-05-30Bibliographically approved
Olsson, E., Olander, A. & Öberg, M. (2016). Fatigue of gears in the finite life regime: Experiments and probabilistic modelling. Engineering Failure Analysis, 62, 286-286
Open this publication in new window or tab >>Fatigue of gears in the finite life regime: Experiments and probabilistic modelling
2016 (English)In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 62, p. 286-286Article in journal (Refereed) Published
Abstract [en]

Fatigue of case hardened gears is investigated experimentally and numerically with focus on the finite fatigue life regime. Pulsating tooth bending fatigue experiments are performed at different load levels on two types of gears of different sizes to determine load–fatigue life relations. The experiments are compared with a probabilistic model for the finite life regime based on weakest-link theory. The stress fields, needed in the evaluations, are obtained by finite element simulations taking residual stresses, both due to case hardening and plastic deformation, into account. The stress history at each element is summarized into two different effective fatigue stress measures; one based on the largest principal stress and the Findley multiaxial fatigue stress. The material parameter needed in the Findley stress is determined by a linear correlation of the parameter with the Vickers hardness of the material using multiaxial fatigue data found in the literature. Both equivalent stress measures show equal behaviour and the probabilistic model shows good agreement with the experimental data in the finite fatigue life regime.

Place, publisher, year, edition, pages
Elsevier, 2016
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-184165 (URN)10.1016/j.engfailanal.2016.01.012 (DOI)000372850500022 ()
Note

QC 20160419

Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2017-11-30Bibliographically approved
Larsson, P.-L. & Olsson, E. (2015). A numerical study of the mechanical behavior at contact between particles of dissimilar elastic-ideally plastic materials. Journal of Physics and Chemistry of Solids, 77, 92-100
Open this publication in new window or tab >>A numerical study of the mechanical behavior at contact between particles of dissimilar elastic-ideally plastic materials
2015 (English)In: Journal of Physics and Chemistry of Solids, ISSN 0022-3697, E-ISSN 1879-2553, Vol. 77, p. 92-100Article in journal (Refereed) Published
Abstract [en]

In the present study contact between elastic-ideally plastic dissimilar spheres are investigated in detail. The investigation is based on numerical methods and in particular the finite element method. The numerical results presented are discussed with respect to correlation of global contact properties as well as the behavior of local field variables such as contact pressure distribution and the evolution of the effective plastic strain. Large deformation effects are accounted for and discussed in detail. The constitutive behavior is described by classical Mises plasticity. It is shown that correlation of the dissimilar contact problem can be accurately achieved based on the Johnson contact parameter with the representative stress chosen as the yield stress of the softer material.

Keywords
Alloys, Metals, Mechanical properties
National Category
Physical Sciences Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-159349 (URN)10.1016/j.jpcs.2014.08.016 (DOI)000346952600012 ()2-s2.0-84908429060 (Scopus ID)
Note

QC 20150202

Available from: 2015-02-02 Created: 2015-01-29 Last updated: 2017-12-05Bibliographically approved
Larsson, P.-L. & Olsson, E. (2015). Contact between elastic-plastic hardmetal powder particles. In: Proceedings Euro PM 2015: International Power Metallurgy Congress and Exhibition. Paper presented at International Power Metallurgy Congress and Exhibition, Euro PM 2015, 4 October 2015 through 7 October 2015. European Powder Metallurgy Association
Open this publication in new window or tab >>Contact between elastic-plastic hardmetal powder particles
2015 (English)In: Proceedings Euro PM 2015: International Power Metallurgy Congress and Exhibition, European Powder Metallurgy Association , 2015Conference paper, Published paper (Refereed)
Abstract [en]

In the present study contacts between elastic-plastic dissimilar spherical particles are investigated. The investigation is based on analytical and numerical methods and in the latter case in particular the finite element method. The results presented are pertinent to force-displacement relations at contact when elastic and plastic deformations are of equal magnitude. Especially, hard metal particles are considered with a typical application area being analysis of powder compaction.

Place, publisher, year, edition, pages
European Powder Metallurgy Association, 2015
Keywords
Elastoplasticity, Metallurgy, Numerical methods, Particles (particulate matter), Powder metals, Analytical and numerical methods, Elastic and plastic deformation, Elastic-Plastic, Force-displacement relations, Hardmetal powder, Powder compactions, Spherical particle, Typical application, Finite element method
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-202897 (URN)2-s2.0-85002789319 (Scopus ID)9781899072477 (ISBN)
Conference
International Power Metallurgy Congress and Exhibition, Euro PM 2015, 4 October 2015 through 7 October 2015
Note

QC 20170309

Available from: 2017-03-09 Created: 2017-03-09 Last updated: 2017-03-09Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7674-8582

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