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Kroon, Martin
Publications (10 of 81) Show all publications
Olsson, P. A. T., Hyldgaard, P., Schröder, E., Jutemar, E. P., Andreasson, E. & Kroon, M. (2018). Ab initio investigation of monoclinic phase stability and martensitic transformation in crystalline polyethylene. Physical Review Materials, 2(7), Article ID 075602.
Open this publication in new window or tab >>Ab initio investigation of monoclinic phase stability and martensitic transformation in crystalline polyethylene
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2018 (English)In: Physical Review Materials, E-ISSN 2475-9953, Vol. 2, no 7, article id 075602Article in journal (Refereed) Published
Abstract [en]

We study the phase stability and martensitic transformation of orthorhombic and monoclimic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft librational phonon modes, the monoclimic phase is predicted not to be stable at zero pressure and temperature, but becomes stable when subjected to compressive transverse deformations that pin the chains and prevent them from wiggling freely. This theoretical characterization, or prediction, is consistent with the fact that the monoclimic phase is only observed experimentally when the material is subjected to mechanical loading. Also, the estimated threshold energy for the combination of lattice deformation associated with the T1 and T2 transformation paths (between the orthorhombic and monoclimic phases) and chain shuffling is found to be sufficiently low for thermally activated back transformations to occur. Thus, our prediction is that the crystalline part can transform back from the monoclimc to the orthorhombic phase upon unloading and/or annealing, which is consistent with experimental observations. Finally, we observe how a combination of such phase transformations can lead to a fold-plane reorientation from {110} to {100} type in a single orthorhombic crystal.

Place, publisher, year, edition, pages
American Physical Society, 2018
National Category
Biomaterials Science
Research subject
Technology (byts ev till Engineering)
Identifiers
urn:nbn:se:lnu:diva-77005 (URN)10.1103/PhysRevMaterials.2.075602 (DOI)000438044900003 ()
Available from: 2018-07-27 Created: 2018-07-27 Last updated: 2018-08-28Bibliographically approved
Olsson, P. A. T., in't Veld, P. J., Andreasson, E., Bergvall, E., Jutemar, E. P., Petersson, V., . . . Kroon, M. (2018). All-atomic and coarse-grained molecular dynamics investigation of deformation in semi-crystalline lamellar polyethylene. Polymer, 153, 305-316
Open this publication in new window or tab >>All-atomic and coarse-grained molecular dynamics investigation of deformation in semi-crystalline lamellar polyethylene
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2018 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 153, p. 305-316Article in journal (Refereed) Published
Abstract [en]

In the present work we have performed classical molecular dynamics modelling to investigate the effects of different types of force-fields on the stress-strain and yielding behaviours in semi-crystalline lamellar stacked linear polyethylene. To this end, specifically the all-atomic optimized potential for liquid simulations (OPLS-AA) and the coarse-grained united-atom (UA) force-fields are used to simulate the yielding and tensile behaviour for the lamellar separation mode. Despite that the considered samples and their topologies are identical for both approaches, the results show that they predict widely different stress-strain and yielding behaviours. For all UA simulations we obtain oscillating stress-strain curves accompanied by repetitive chain transport to the amorphous region, along with substantial chain slip and crystal reorientation. For the OPLS-AA modelling primarily cavitation formation is observed, with small amounts of chain slip to reorient the crystal such that the chains align in the tensile direction. This force-field dependence is rooted in the lack of explicit H-H and C-H repulsion in the UA approach, which gives rise to underestimated ideal critical resolved shear stress. The computed critical resolved shear stress for the OPLS-AA approach is in good agreement with density functional theory calculations and the yielding mechanisms resemble those of the lamellar separation mode. The disparate energy and shear stress barriers for chain slip of the different models can be interpreted as differently predicted intrinsic activation rates for the mechanism, which ultimately are responsible for the observed diverse responses of the two modelling approaches.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Semi-crystalline polyethylene, Plasticity, Molecular dynamics
National Category
Polymer Chemistry
Research subject
Technology (byts ev till Engineering), Mechanical Engineering
Identifiers
urn:nbn:se:lnu:diva-78466 (URN)10.1016/j.polymer.2018.07.075 (DOI)000445783300034 ()
Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2018-10-24Bibliographically approved
Kroon, M., Andreasson, E., Persson Jutemar, E., Petersson, V., Persson, L., Dorn, M. & Olsson, P. (2018). Anisotropic elastic-viscoplastic properties of at finite strains of of injection-moulded low-density polyethylene. Experimental mechanics, 58(1), 75-86
Open this publication in new window or tab >>Anisotropic elastic-viscoplastic properties of at finite strains of of injection-moulded low-density polyethylene
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2018 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 58, no 1, p. 75-86Article in journal (Refereed) Published
Abstract [en]

Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters.

National Category
Textile, Rubber and Polymeric Materials
Research subject
Technology (byts ev till Engineering), Mechanical Engineering
Identifiers
urn:nbn:se:lnu:diva-68972 (URN)10.1007/s11340-017-0322-y (DOI)
Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2018-01-18Bibliographically approved
Kroon, M. (2018). Crack Growth in Low-density Polyethylene. In: Presented at EMMC16, European Mechanics of Materials Conference in Nantes, France, 26-28 March, 2018: . Paper presented at European Mechanics of Materials Conference in Nantes, France, 26-28 March, 2018.
Open this publication in new window or tab >>Crack Growth in Low-density Polyethylene
2018 (English)In: Presented at EMMC16, European Mechanics of Materials Conference in Nantes, France, 26-28 March, 2018, 2018Conference paper, Oral presentation with published abstract (Refereed)
National Category
Polymer Technologies
Research subject
Technology (byts ev till Engineering), Mechanical Engineering
Identifiers
urn:nbn:se:lnu:diva-72219 (URN)
Conference
European Mechanics of Materials Conference in Nantes, France, 26-28 March, 2018
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-05Bibliographically approved
Kroon, M., Andreasson, E., Petersson, V. & Olsson, P. (2018). Experimental and numerical assessment of the work of fracture in injection-moulded low-density polyethylene. Engineering Fracture Mechanics, 192, 1-11
Open this publication in new window or tab >>Experimental and numerical assessment of the work of fracture in injection-moulded low-density polyethylene
2018 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 192, p. 1-11Article in journal (Refereed) Published
Abstract [en]

The fracture mechanics properties of injection-moulded low-density polyethylene (LDPE) sheets were investigated both experimentally and numerically. The total work of fracture was determined experimentally, by means of fracture mechanics testing of sheets of injection-moulded LDPE with side cracks of different lengths. A multi-specimen method, proposed by Kim and Joe (1987), was employed. The total work of fracture was estimated to 13 kJ/m(2). The experiments were simulated numerically using the finite element method. Crack growth was enabled by inclusion of a cohesive zone, and the constitutive response of this zone was governed by a traction-separation law. The local (or essential) work of fracture was estimated through numerical analyses, where the initiation of crack growth was simulated and the outcome was compared to the experimental results. The local (i.e. essential) work of fracture was estimated to 1.7 kJ/m(2), which is consistent with previous experimental measurements for the material in question. The total work of fracture, retrieved from the present experiments, agreed well with the far field values of the J-integral in the numerical analyses.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Polymer Technologies
Research subject
Technology (byts ev till Engineering)
Identifiers
urn:nbn:se:lnu:diva-72216 (URN)10.1016/j.engfracmech.2018.02.004 (DOI)000427628100001 ()
Funder
Knowledge Foundation, 20150165
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-06Bibliographically approved
Kroon, M., Andreasson, E. & Olsson, P. (2018). Modelling of Damage and Crack Growth in Semi-crystalline Polymers. In: Presented at International Conference on Plasticity, Damage and Fracture 2018, Puerto Rico: . Paper presented at ICPDF, International Conference on Plasticity, Damage and Fracture 3-9 January, 2018, Puerto Rico. Neat press
Open this publication in new window or tab >>Modelling of Damage and Crack Growth in Semi-crystalline Polymers
2018 (English)In: Presented at International Conference on Plasticity, Damage and Fracture 2018, Puerto Rico, Neat press , 2018Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material direction were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. In parallel to the experimental testing, an anisotropic plasticity model for finite strains was developed, which accounts for orthotropic elasticity and orthotropic plastic yielding and hardening. That plasticity model was implemented as a user subrouting in Abaqus. The crack growth experiments were then simulated using Abaqus, using the implemented plasticity model in combination with a damage model. Different types of crack initiation and growth criteria were explored, and the force-displacement-crack length data from the experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

Place, publisher, year, edition, pages
Neat press, 2018
National Category
Polymer Technologies
Research subject
Technology (byts ev till Engineering), Mechanical Engineering
Identifiers
urn:nbn:se:lnu:diva-72218 (URN)978-0-9911654-5-2 (ISBN)
Conference
ICPDF, International Conference on Plasticity, Damage and Fracture 3-9 January, 2018, Puerto Rico
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-05Bibliographically approved
Olsson, P. A. T., Schroder, E., Hyldgaard, P., Kroon, M., Andreasson, E. & Bergvall, E. (2017). Ab initio and classical atomistic modelling of structure and defects in crystalline orthorhombic polyethylene: Twin boundaries, slip interfaces, and nature of barriers. Polymer, 121, 234-246
Open this publication in new window or tab >>Ab initio and classical atomistic modelling of structure and defects in crystalline orthorhombic polyethylene: Twin boundaries, slip interfaces, and nature of barriers
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2017 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 121, p. 234-246Article in journal (Refereed) Published
Abstract [en]

We study the stability of twin boundaries and slip in crystalline orthorhombic polyethylene by means of density functional theory (DFT), using a nonempirical, truly nonlocal density function, and by means of classical molecular dynamics (MD). The results show that, in accordance with experimental observations, there is a clear preference to chain slip over transverse slip for all considered slip planes. The activation energy for pure chain slip lies in the range 10-20 mJ/m(2) while that for transverse slip corresponds to 40-280 mJ/m(2). For the (110)-slip plane the energy landscape is non-convex with multiple potential energy minima, indicating the presence of stable stacking faults. This suggests that dissociation of perfect dislocations into partials may occur. For the two low-energy twin boundaries considered in this work, {110} and {310}, we find that the former is more stable than the latter, with ground state energies corresponding to 8.9 and 28 mJ/m2, respectively. We have also evaluated how well the empirical MD simulations with the all-atom optimized potential for liquid MD simulations (OPLS-AA) and the coarsegrained united atom (UA) potential concur with the DFT results. It is found that an all-atom potential is necessary to partially capture the gamma-surface energy landscapes obtained from the DFT calculations. The OPLS-AA predicts chain slip activation energies comparable with DFT data, while the transverse slip energy thresholds are low in comparison, which is attributed to weak close ranged monomer repulsion. Finally, we find that the H-H interaction dominates the slip activation. While not explicitly represented in the UA potential, its key role is revealed by correlating the DFT energy landscape with changes in the electron distributions and by MD simulations in which components of the OPLS-AA intermolecular potential are selectively silenced. (C) 2017 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Polyethylene, Atomistic modelling, Slip
National Category
Polymer Chemistry
Research subject
Technology (byts ev till Engineering)
Identifiers
urn:nbn:se:lnu:diva-67399 (URN)10.1016/j.polymer.2017.06.008 (DOI)000405747100026 ()
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2017-08-24Bibliographically approved
Kroon, M., Olsson, P. & Andreasson, E. (2017). An Anisotropic Lagrangian Plasticity Model for Semi-crystalline Polymers. In: International Conference on Plasticity, Damage, and Fracture, Puerto Vallarta, Mexico, Jan 3-9, 2017: . Paper presented at International Conference on Plasticity, Damage, and Fracture, Puerto Vallarta, Mexico, Jan 3-9, 2017.
Open this publication in new window or tab >>An Anisotropic Lagrangian Plasticity Model for Semi-crystalline Polymers
2017 (English)In: International Conference on Plasticity, Damage, and Fracture, Puerto Vallarta, Mexico, Jan 3-9, 2017, 2017Conference paper, Oral presentation with published abstract (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:lnu:diva-59977 (URN)
Conference
International Conference on Plasticity, Damage, and Fracture, Puerto Vallarta, Mexico, Jan 3-9, 2017
Available from: 2017-01-19 Created: 2017-01-19 Last updated: 2017-03-15Bibliographically approved
Kroon, M. (2017). An Anisotropic Lagrangian Plasticity Model for Semi-crystalline Polymers at Finite Strains. In: US National Congress on Computational Mechanics, Montreal, July 17-20, 2017: . Paper presented at US National Congress on Computational Mechanics, Montreal, July 17-20, 2017.
Open this publication in new window or tab >>An Anisotropic Lagrangian Plasticity Model for Semi-crystalline Polymers at Finite Strains
2017 (English)In: US National Congress on Computational Mechanics, Montreal, July 17-20, 2017, 2017Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The present work concerns modelling of semi-crystalline polymers, such as polyethylene. Semi-crystalline polymers constitute a material group with an increasing industrial importance. Constitutive response (stress-strain relation) as well as fracture properties are of great importance for this class of materials. We propose an anisotropic plasticity model for semi-crystalline polymers, formulated in the reference configuration (Lagrangian formulation). In addition to plasticity, the model accounts for effects of viscoelasticity. The model is evaluated using uniaxial tensile tests, where polyethylene sheets are tested. The model is able to predict the hardening and rate-dependency observed in the experiments very well. Numerical examples are also presented, where the model is applied to a few different geometries

National Category
Engineering and Technology
Identifiers
urn:nbn:se:lnu:diva-68975 (URN)
Conference
US National Congress on Computational Mechanics, Montreal, July 17-20, 2017
Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2018-01-18Bibliographically approved
Kroon, M., Andreasson, E. & Olsson, P. (2017). Assessment of fracture energy of polyethylene. In: Svenska mekanikdagar 2017 Uppsala 12-13 juni: . Paper presented at Svenska mekanikdagarna, 12-13 juni, 2017, Uppsala (pp. 49-49). Uppsala universitet
Open this publication in new window or tab >>Assessment of fracture energy of polyethylene
2017 (English)In: Svenska mekanikdagar 2017 Uppsala 12-13 juni, Uppsala universitet, 2017, p. 49-49Conference paper, Oral presentation with published abstract (Refereed)
Place, publisher, year, edition, pages
Uppsala universitet, 2017
National Category
Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:lnu:diva-68973 (URN)
Conference
Svenska mekanikdagarna, 12-13 juni, 2017, Uppsala
Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2018-01-18Bibliographically approved
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