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Publications (10 of 35) Show all publications
Varna, J. & Pupure, L. (2019). Characterization of viscoelasticity, viscoplasticity, and damage in composites (2ed.). In: Rui Miranda Guedes (Ed.), Creep and Fatigue in Polymer Matrix Composites: (pp. 497-530). Elsevier
Open this publication in new window or tab >>Characterization of viscoelasticity, viscoplasticity, and damage in composites
2019 (English)In: Creep and Fatigue in Polymer Matrix Composites / [ed] Rui Miranda Guedes, Elsevier, 2019, 2, p. 497-530Chapter in book (Refereed)
Abstract [en]

Empirical inelastic constitutive material models for composites and testing methodology for parameter determination in these models are analyzed. Short fiber as well as long unidirectional fiber reinforced composites are analyzed in situations when the main sources of inelastic behavior are a combination of (a) nonlinear viscoelasticity; (b) nonlinear viscoplasticity; and (c) microdamage-induced reduction of thermoelastic properties, all three evolving with time and stress. These phenomena are included in a common material model. The necessary tests for model identification are tensile quasistatic loading-unloading tests and creep tests at different stress levels with recorded strain recovery after load removal. The methodology is demonstrated presenting models for (a) shear in layers of [45/−45]s laminates; (b) response of short fiber composites (SMC with glass fiber bundles; composites with natural or man-made cellulosic fibers in bio-based resins).

Place, publisher, year, edition, pages
Elsevier, 2019 Edition: 2
Series
Woodhead Publishing Series in Composites Science and Engineering
Keywords
Fiber composites, Stiffness reduction, Viscoelasticity, Viscoplasticity, Creep
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-73438 (URN)10.1016/B978-0-08-102601-4.00016-3 (DOI)978-0-08-102601-4 (ISBN)
Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-04-05Bibliographically approved
Basso, M., Piselli, A., Simonato, M., Furlanetto, R., Pupure, L., Joffe, R. & De Nardo, L. (2019). Effect of food chemicals and temperature on mechanical reliability of bio-based glass fibers reinforced polyamide. Composites Part B: Engineering, 157, 140-149
Open this publication in new window or tab >>Effect of food chemicals and temperature on mechanical reliability of bio-based glass fibers reinforced polyamide
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2019 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 157, p. 140-149Article in journal (Refereed) Published
Abstract [en]

This paper presents an experimental study to assess the effects of food chemicals and temperature on the mechanical performance of glass fiber reinforced bio-based polyamide. The diffusion of food chemicals was mainly driven by thermal energy, following Arrhenius law in all tested environments. Degradation of mechanical properties and decrease in reliability were assessed, due to the plasticization of polymer matrix. Secondary but not negligible effect on flexural strength degradation is given by the different chemical interaction between polymeric chains and molecules of food chemicals. Colour change was measured and resulted to be positively correlated to diffusion.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-70638 (URN)10.1016/j.compositesb.2018.08.078 (DOI)000452939900014 ()2-s2.0-85052484539 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-31 (andbra)

Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2019-03-27Bibliographically approved
Basso, M., Pupure, L., Simonato, M., Furlanetto, R., De Nardo, L. & Joffe, R. (2019). Nonlinear creep behaviour of glass fiber reinforced polypropylene: Impact of aging on stiffness degradation. Composites Part B: Engineering, 163, 702-709
Open this publication in new window or tab >>Nonlinear creep behaviour of glass fiber reinforced polypropylene: Impact of aging on stiffness degradation
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2019 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 163, p. 702-709Article in journal (Refereed) Published
Abstract [en]

Nonlinear creep behavior of one commercial short glass fiber reinforced polypropylene was investigated using tensile creep tests and stiffness degradation measurements. The impact of thermal aging and following quenching was evaluated on the latter mechanical property. Experimental results were modeled applying nonlinear viscoelastic model used by Pupure et al. (2013) and developed by Lou and Schapery [1,2]. Results showed that this model can describe nonlinear behavior of short glass fiber reinforced polymer composites, where microdamage is given by debonding of fiber-matrix interfaces already at low strains, where cracks propagate and lead to tensile creep fracture.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Polymer-matrix composites (PMCs), Creep, Analytical modelling, Mechanical testing
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-72884 (URN)10.1016/j.compositesb.2019.01.052 (DOI)000461262500069 ()2-s2.0-85060028172 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-13 (johcin)

Available from: 2019-02-13 Created: 2019-02-13 Last updated: 2019-04-12Bibliographically approved
Gong, G., Nyström, B., Sandlund, E., Eklund, D., Noël, M., Westerlund, R., . . . Joffe, R. (2018). Development of Electrophoretic Deposition Prototype for Continuous Production of Carbon Nanotube-Modified Carbon Fiber Fabrics Used in High-Performance Multifunctional Composites. Fibers, 6(4), Article ID 71.
Open this publication in new window or tab >>Development of Electrophoretic Deposition Prototype for Continuous Production of Carbon Nanotube-Modified Carbon Fiber Fabrics Used in High-Performance Multifunctional Composites
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2018 (English)In: Fibers, ISSN 2079-6439, Vol. 6, no 4, article id 71Article in journal (Refereed) Published
Abstract [en]

An electrophoretic deposition (EPD) prototype was developed aiming at the continuous production of carbon nanotube (CNT) deposited carbon fiber fabric. Such multi-scale reinforcement was used to manufacture carbon fiber-reinforced polymer (CFRP) composites. The overall objective was to improve the mechanical performance and functionalities of CFRP composites. In the current study, the design concept and practical limit of the continuous EPD prototype, as well as the flexural strength and interlaminar shear strength, were the focus. Initial mechanical tests showed that the flexural stiffness and strength of composites with the developed reinforcement were significantly reduced with respect to the composites with pristine reinforcement. However, optical microscopy study revealed that geometrical imperfections, such as waviness and misalignment, had been introduced into the reinforcement fibers and/or bundles when being pulled through the EPD bath, collected on a roll, and dried. These defects are likely to partly or completely shadow any enhancement of the mechanical properties due to the CNT deposit. In order to eliminate the effect of the discovered defects, the pristine reinforcement was subjected to the same EPD treatment, but without the addition of CNT in the EPD bath. When compared with such water-treated reinforcement, the CNT-deposited reinforcement clearly showed a positive effect on the flexural properties and interlaminar shear strength of the composites. It was also discovered that CNTs agglomerate with time under the electric field due to the change of ionic density, which is possibly due to the electrolysis of water (for carboxylated CNT aqueous suspension without surfactant) or the deposition of ionic surfactant along with CNT deposition (for non-functionalized CNT aqueous suspension with surfactant). Currently, this sets time limits for the continuous deposition.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
electrophoretic deposition, carbon nanotube, multi-scale carbon reinforcement, multifunctional composites
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-72826 (URN)10.3390/fib6040071 (DOI)000455068600004 ()2-s2.0-85058692640 (Scopus ID)
Available from: 2019-02-08 Created: 2019-02-08 Last updated: 2019-08-19Bibliographically approved
Pupure, L., Varna, J., Joffe, R., Berthold, F. & Miettinen, A. (2018). Mechanical properties of natural fiber composites produced using dynamic sheet former. Wood Material Science & Engineering
Open this publication in new window or tab >>Mechanical properties of natural fiber composites produced using dynamic sheet former
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2018 (English)In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280Article in journal (Refereed) Epub ahead of print
Abstract [en]

Composites formed from wood fibers and man-made cellulosic fibers in PLA (polylactic acid) matrix, manufactured using sheet forming technique and hot pressing, are studied. The composites have very low density (due to high porosity) and rather good elastic modulus and tensile strength. As expected, these properties for the four types of wood fiber composites studied here improve with increasing weight fraction of fibers, even if porosity is also increasing. On the contrary, for man-made cellulosic fiber composites with circular fiber cross-section, the increasing fiber weight fraction (accompanied by increasing void content) has detrimental effect on stiffness and strength. The differences in behavior are discussed attributing them to fiber/ fiber interaction in wood fiber composites which does not happen in man-made fiber composites, and by rather weak fiber/matrix interface for man-made fibers leading to macro-crack formation in large porosity regions.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials; Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-69464 (URN)10.1080/17480272.2018.1482368 (DOI)
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-13
Pupure, L., Varna, J. & Joffe, R. (2018). Methodology for macro-modeling of bio-based composites with inelastic constituents. Composites Science And Technology, 163, 41-48
Open this publication in new window or tab >>Methodology for macro-modeling of bio-based composites with inelastic constituents
2018 (English)In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 163, p. 41-48Article in journal (Refereed) Published
Abstract [en]

Methodology for development of a macro-scale model (with strain as an input) for Regenerated Cellulose fiber (RCF) composites with highly non-linear (viscoelastic (VE) and viscoplastic (VP)) constituents is presented and demonstrated. The VE is described by Schapery's models and Zapas' model is used for VP. For a purely VE constituent the model can be identified from stress relaxation in constant strain tests. In the presence of VP the constant strain test does not render VE stress relaxation functions, because part of the applied strain is VP and the VE strain is changing. As an alternative creep and strain recovery tests are suggested to find the plasticity law and also the nonlinear creep compliances to identify the VE model where stress is an input. The incremental form of this model is then inverted and used to simulate the VE relaxation tests and the simulated relaxation functions are used to identify the VE model with VE strain as an input.

Models for constituents are used in micromechanics simulations of the composite behavior in arbitrary ramps including the composite VE relaxation test. Using the latter, a macro-model is developed and its validity and accuracy are demonstrated.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-68687 (URN)10.1016/j.compscitech.2018.05.015 (DOI)000438323000006 ()2-s2.0-85046756325 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-05-15 (rokbeg)

Available from: 2018-05-09 Created: 2018-05-09 Last updated: 2018-08-07Bibliographically approved
Varna, J., Pupure, L. & Joffe, R. (2016). Incremental forms of Schapery’s model: convergence and inversion to simulate strain controlled ramps (ed.). Mechanics of time-dependant materials, 20(4), 535-552
Open this publication in new window or tab >>Incremental forms of Schapery’s model: convergence and inversion to simulate strain controlled ramps
2016 (English)In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 20, no 4, p. 535-552Article in journal (Refereed) Published
Abstract [en]

Schapery’s nonlinear viscoelastic model is written in incremental form, and three different approximations of nonlinearity functions in the time increment are systematically analysed with respect to the convergence rate. It is shown that secant slope is the best approximation of the time shift factor, leading to significantly higher convergence rate. This incremental form of the viscoelastic model, Zapas’ model for viscoplasticity, supplemented with terms accounting for damage effect is used to predict inelastic behaviour of material in stress controlled tests. Then the incremental formulation is inverted to simulate stress development in ramps where strain is the input parameter. A comparison with tests shows good ability of the model in inverted form to predict stress–strain response as long as the applied strain is increasing. However, in strain controlled ramps with unloading, the inverted model shows unrealistic hysteresis loops. This is believed to be a proof of the theoretically known incompatibility of the stress and strain controlled formulations for nonlinear materials. It also shows limitations of material models identified in stress controlled tests for use in strain controlled tests.

National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-3085 (URN)10.1007/s11043-016-9311-2 (DOI)000388186900004 ()2-s2.0-84963641799 (Scopus ID)0db3b547-04c5-4062-98dc-939c3979e74b (Local ID)0db3b547-04c5-4062-98dc-939c3979e74b (Archive number)0db3b547-04c5-4062-98dc-939c3979e74b (OAI)
Note

Validerad; 2016; Nivå 2; 2016-11-22 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Pupure, L., Varna, J. & Joffe, R. (2016). Natural fiber composite: Challenges simulating inelastic response in strain-controlled tensile tests (ed.). Paper presented at . Journal of composite materials, 50(5), 575-587
Open this publication in new window or tab >>Natural fiber composite: Challenges simulating inelastic response in strain-controlled tensile tests
2016 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 50, no 5, p. 575-587Article in journal (Refereed) Published
Abstract [en]

Problems occurring, when nonlinear time-dependent material model with parameters identified in creep tests is applied to simulate high-strain response in strain-controlled tests, are described and analyzed. Reasons for discrepancies with experimental loading curves are revealed. Presented numerical/experimental examples deal with three bio-based composites showing highly nonlinear behavior due to damage, nonlinear viscoelasticity and viscoplasticity. Schapery's approach for viscoelasticity and Zapas' model for viscoplasticity are used. The model is generalized to include microdamage effect. It is shown that the main problem in simulations at high stresses is the reliability of data from creep test for model identification in this region because creep rupture limits the available data region and extrapolation to higher stresses is rather uncertain. Alternative solution is to employ relaxation tests at high strains to obtain the missing information. However, it would work only in absence of viscoplastic strains: viscoelastic relaxation functions cannot be determined by maintaining constant total strain if viscoplastic-strain is developing. Based on sensitivity analysis of composite response to variations of the elastic modulus, damage, viscoelastic and viscoplastic parameters, suggestions are made for improving (further “tuning”) the model in high stress region by using tensile stress–strain curves in quasi-static loading.

National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-9188 (URN)10.1177/0021998315579435 (DOI)000370416500001 ()2-s2.0-84958206258 (Scopus ID)7c048132-2bbc-44f6-b894-67b8bb8273b3 (Local ID)7c048132-2bbc-44f6-b894-67b8bb8273b3 (Archive number)7c048132-2bbc-44f6-b894-67b8bb8273b3 (OAI)
Note
Validerad; 2016; Nivå 2; 20150401 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Pupure, L., Varna, J. & Joffe, R. (2015). Applications and limitations of non-linear viscoelastic model for simulation of behaviour of polymer composites (ed.). Paper presented at International Conference on Composite Materials : 19/07/2015 - 24/07/2015. Paper presented at International Conference on Composite Materials : 19/07/2015 - 24/07/2015.
Open this publication in new window or tab >>Applications and limitations of non-linear viscoelastic model for simulation of behaviour of polymer composites
2015 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

There are two alternative formulation of non-linear viscoelastic model to describe strain and stress controlled tests. Both models for non-linear viscoelastic materials are not compatible, and cannot be directly inverted if so required in certain cases. In order to do it numerical procedures has to be employed. Methodology for simulating nonlinear stress-strain response in iso-strain situations of fiber composites based on properties on constituents is presented.

Keywords
viscoelastic, material model, simulation, Materials science - Construction materials, Teknisk materialvetenskap - Konstruktionsmaterial
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-35888 (URN)a9b98e3f-5bc8-4c09-a08d-78fd29118e9d (Local ID)a9b98e3f-5bc8-4c09-a08d-78fd29118e9d (Archive number)a9b98e3f-5bc8-4c09-a08d-78fd29118e9d (OAI)
Conference
International Conference on Composite Materials : 19/07/2015 - 24/07/2015
Note
Godkänd; 2015; 20150818 (joffe)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-28Bibliographically approved
Pupure, L., Joffe, R. & Varna, J. (2015). Identification Of Parameters For Direct And Inverted Model To Predict Performance Of Materials Exhibiting Non-Linear Viscoelastic Behavior (ed.). In: (Ed.), C. González; C. López; J. LLorca (Ed.), Proceedings of 7th International Conference on Composites Testing and Model Identification: . Paper presented at International Conference on Composites Testing and Model Identification : 08/04/2015 - 10/04/2015. Madrid, Spain: IMDEA, Madrid (SPAIN)
Open this publication in new window or tab >>Identification Of Parameters For Direct And Inverted Model To Predict Performance Of Materials Exhibiting Non-Linear Viscoelastic Behavior
2015 (English)In: Proceedings of 7th International Conference on Composites Testing and Model Identification / [ed] C. González; C. López; J. LLorca, Madrid, Spain: IMDEA, Madrid (SPAIN) , 2015Conference paper, Meeting abstract (Refereed)
Place, publisher, year, edition, pages
Madrid, Spain: IMDEA, Madrid (SPAIN), 2015
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-27319 (URN)0bba9437-4356-48e9-8886-c98f6463a5ac (Local ID)0bba9437-4356-48e9-8886-c98f6463a5ac (Archive number)0bba9437-4356-48e9-8886-c98f6463a5ac (OAI)
Conference
International Conference on Composites Testing and Model Identification : 08/04/2015 - 10/04/2015
Note
Godkänd; 2015; 20150410 (joffe)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-28Bibliographically approved
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