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Publications (10 of 24) Show all publications
Al-Ramahi, N., Joffe, R. & Varna, J. (2019). Numerical stress analysis in adhesive joints under thermo-mechanical load using model with special boundary conditions. In: IOP Conference Series: Materials Science and Engineering, Volume 518, Mechanical and Materials Engineering: Materials Science and Engineering. Paper presented at 2nd International Conference on Sustainable Engineering Techniques, ICSET 2019, 6 March 2019 through 7 March 2019. Institute of Physics Publishing (3)
Open this publication in new window or tab >>Numerical stress analysis in adhesive joints under thermo-mechanical load using model with special boundary conditions
2019 (English)In: IOP Conference Series: Materials Science and Engineering, Volume 518, Mechanical and Materials Engineering: Materials Science and Engineering, Institute of Physics Publishing , 2019, no 3Conference paper, Published paper (Refereed)
Abstract [en]

A numerical study of the adhesivejoint made of similar and dissimilar adherends subjected to thermo-mechanical loading is presented. A comprehensive numerical model was used for this purpose with the novel displacement coupling conditions which are able to correctly represent monoclinic materials (off-axis layers of composite laminates). The geometrical nonlinearity as well as nonlinear material model are also taken into account. Three different types of single-lap and double-lap adhesive joints are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). This paper focuses on the parameters which have the majoreffect on the peel and shear stress distribution within adhesive layer at the overlap ends. The comparison of behaviour of single-and double-lap joints in relation to these parameters is made. The master curves for maximum stress (peel and shear) at the ends of the overlap with respect to the bending stiffness and axial modulus of the adherends are constructed by analysing stress distributions in the middle of the adhesive.The main conclusions of this paper are: the maximum peel stress value for SLJ is reduced with increase of the adherend bending stiffness and for DLJ,similar behaviour was observed at the end next to the inner plate corner, while, at the end next to the outer plate corner peel stress is reduced with increase of adherend axial modulus.

Place, publisher, year, edition, pages
Institute of Physics Publishing, 2019
Keywords
Adhesive joints, Laminated composites, Shear stress, Stiffness, Stress analysis, Stress concentration, Sustainable development, Dissimilar adherends, Geometrical non-linearity, Monoclinic materials, Nonlinear material models, Numerical stress analysis, Quasiisotropic laminates, Thermo mechanical loads, Thermo-mechanical loading, Adhesives
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-39383 (URN)10.1088/1757-899X/518/3/032061 (DOI)2-s2.0-85067803354 (Scopus ID)
Conference
2nd International Conference on Sustainable Engineering Techniques, ICSET 2019, 6 March 2019 through 7 March 2019
Note

Funding text 1: The research leading to these results was financially supported by Middle Technical University (Baghdad, Iraq), by Polymeric Composite Materials group at Luleå University of Technology (Luleå, Sweden) and by the strategic innovation programme LIGHTer provided by Vinnova (Sweden).

Available from: 2019-07-08 Created: 2019-07-08 Last updated: 2020-01-28Bibliographically approved
Gong, G., Nyström, B., Sandlund, E., Eklund, D., Noel, 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.

Keywords
Carbon nanotube, Electrophoretic deposition, Multi-scale carbon reinforcement, Multifunctional composites
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-36931 (URN)10.3390/fib6040071 (DOI)2-s2.0-85058692640 (Scopus ID)
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2020-01-28Bibliographically approved
Al-Ramahi, N. J., Joffe, R. & Varna, J. (2018). FEM analysis of stresses in adhesive single-lap joints with non-linear materials under thermo-mechanical loading. In: ECCM 2018 - 18th European Conference on Composite Materials: . Paper presented at 18th European Conference on Composite Materials, ECCM 2018, 24 June 2018 through 28 June 2018. Applied Mechanics Laboratory
Open this publication in new window or tab >>FEM analysis of stresses in adhesive single-lap joints with non-linear materials under thermo-mechanical loading
2018 (English)In: ECCM 2018 - 18th European Conference on Composite Materials, Applied Mechanics Laboratory , 2018Conference paper, Published paper (Refereed)
Abstract [en]

This study presents comprehensive numerical stress analysis in the adhesive layer of a single-lap joint subjected to various loading scenarios (mechanical and thermal loading). For this purpose numerical model (finite element method) with novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates) has been developed. This model includes nonlinear material model and geometrical nonlinearity is also accounted for. The effect of thermal residual stresses (in adhesive) is analysed for various methods of manufacturing of single lap joint. The sequences of application of thermal and mechanical loads for the analysis of the thermal residual stresses in joints are proposed. It is shown that the most common approach used in many studies of linear superposition of thermal and mechanical stresses works well only for linear materials and produces wrong results if material is non-linear. The present study demonstrates suitable method to apply combined thermal and mechanical loads to get accurate stress distributions. Based on the analysis of these stress distributions the conclusions concerning the effect of the thermal residual stresses on peel and shear stress concentrations are made. The comparison between effect of thermal stresses in case of the one-step and two-step joint manufacturing techniques is made

Place, publisher, year, edition, pages
Applied Mechanics Laboratory, 2018
Keywords
Adhesive joining, Numerical stress analysis, Residual thermal stresses, Single-lap joint, Thermo-mechanical load
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-43462 (URN)2-s2.0-85067807576 (Scopus ID)9781510896932 (ISBN)
Conference
18th European Conference on Composite Materials, ECCM 2018, 24 June 2018 through 28 June 2018
Note

Funding text 1: The work was financially supported by Middle Technical University (Iraq), by Goup of Polymeric Composite Materials at LTU (Sweden) and by Vinnova funded LIGHTer programme (Sweden).

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-01-31Bibliographically approved
Al-Ramahi, N., Joffe, R. & Varna, J. (2018). Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials. International Journal of Adhesion and Adhesives, 87, 191-204
Open this publication in new window or tab >>Investigation of end and edge effects on results of numerical simulation of single lap adhesive joint with non-linear materials
2018 (English)In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 87, p. 191-204Article in journal (Refereed) Published
Abstract [en]

This paper presents systematic numerical study of stresses in the adhesive of a single-lap joint with the objective to improve understanding of the main material and geometrical parameters determining performance of adhesive joints. For this purpose a 3D model as well as 2D model, optimized with respect to the computational efficiency by use of novel displacement coupling conditions able to correctly represent monoclinic materials (off-axis layers of composite laminates), are employed. The model accounts for non-linearity of materials (adherend and adhesive) as well as geometrical non-linearity. The parameters of geometry of the joint are normalized with respect to the dimensions of adhesive (e.g. thickness) thus making analysis of results more general and applicable to wide range of different joints. Optimal geometry of the single-lap joint allowing to separate edge effect from end effects is selected based on results of the parametric analysis by using peel and shear stress distributions in the adhesive layer as a criterion. Three different types of single lap joint with similar and dissimilar (hybrid) materials are considered in this study: a) metal-metal; b) composite-composite; c) composite-metal. In case of composite laminates, four lay-ups are evaluated: uni-directional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/-45]S and [90/45/0/-45]S). The influence of the abovementioned parameters on peel and shear stress distributions in the adhesive layer is examined carefully and mechanical parameters governing the stress concentrations in the joint have been identified, this dependence can be described by simple but accurate fitting function. The effect of the used material model (linear vs non-linear) on results is also demonstrated.

Keywords
Composites (B), Finite element method, Hybrid joints (D), Single-lap adhesive joint, Stress analysis (C), Stress distribution (D), Adhesive joints, Computational efficiency, Geometry, Hybrid materials, Laminated composites, Metal analysis, Shear flow, Shear stress, Stress analysis, Stress concentration, Geometrical non-linearity, Hybrid joints, Mechanical parameters, Monoclinic materials, Nonlinear materials, Parametric -analysis, Quasiisotropic laminates, SINGLE-LAP ADHESIVE JOINTS, Adhesives
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-35991 (URN)10.1016/j.ijadhadh.2018.10.007 (DOI)2-s2.0-85055248042 (Scopus ID)
Note

 Funding details: Luleå Tekniska Universitet, LTU; Funding details: LighterLife; Funding text 1: The research leading to these results was financially supported by Middle Technical University (Baghdad, Iraq), by Polymeric Composite Materials group at Luleå University of Technology (Luleå, Sweden) and by the strategic innovation programme LIGHTer provided by Vinnova (Sweden).

Available from: 2018-11-08 Created: 2018-11-08 Last updated: 2020-01-28Bibliographically 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) In press
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.

Keywords
Wood fiber composites, PLA, Tencel fibers, dynamic sheet former, stiffness, strength
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-33933 (URN)10.1080/17480272.2018.1482368 (DOI)2-s2.0-85048019947 (Scopus ID)
Available from: 2018-06-12 Created: 2018-06-12 Last updated: 2020-01-28Bibliographically approved
Gong, G., Nyström, B., Sandlund, E., Eklund, D., Noel, M., Westerlund, R., . . . Pupurs, A. (2018). SCALING-UP PRODUCTION OF CNT-COATEDFIBRE REINFORCEMENT USING CONTINUOUS EPDFOR HIGH-PERFORMANCE ANDMULTIFUNCTIONAL COMPOSITES. In: : . Paper presented at 14th International Conference on Flow Processingin Composite Materials.
Open this publication in new window or tab >>SCALING-UP PRODUCTION OF CNT-COATEDFIBRE REINFORCEMENT USING CONTINUOUS EPDFOR HIGH-PERFORMANCE ANDMULTIFUNCTIONAL COMPOSITES
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2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Itis important within the composite community to improve out-of-plane performance ofcomposites dominated by polymer matrix and properties of matrix-rich regions formed in the gapsbetween the interlaced fibre bundles. These properties are difficult to modify with traditional fibrereinforcement. Various nanoscale materials have been explored for such purpose, among which carbonnanotube (CNT) has been suggested as an ideal candidate because of its outstanding mechanical,electrical and thermal properties (1). Electrophoretic deposition (EPD) is considered as a cost-effectivemethod to deposit CNTs onto substrates with mild working conditions, requiring relatively simpleequipment and being amenable to scaling up (2,3). Due to the shortcoming of existing laboratory setupwhich corresponds to a non-continuous process, EPD has not been used at even a pilot plant scale fornano-coated fibre reinforcement. The current work presents the development of a prototype andmethod for continuous EPD process. Geometric defect of fibre reinforcement introduced during thedeposition, which can shadow the reinforcing effect of CNT deposit, was discovered. Enhancement ofcomposite properties by the CNT deposit was hence shown.

Keywords
Continuous electrophoretic deposition; carbon nanotube; multifunctional fibre
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34847 (URN)
Conference
14th International Conference on Flow Processingin Composite Materials
Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2020-01-28Bibliographically approved
Andersons, J., Modniks, J., Joffe, R., Madsen, B. & Nättinen, K. (2016). Apparent interfacial shear strength of short-flax-fiber/starch acetate composites. International Journal of Adhesion and Adhesives, 64, 78-85
Open this publication in new window or tab >>Apparent interfacial shear strength of short-flax-fiber/starch acetate composites
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2016 (English)In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 64, p. 78-85Article in journal (Refereed) Published
Abstract [en]

The paper deals with an indirect industry-friendly method for identification of the interfacial shear strength (IFSS) in a fully bio-based composite. The IFSS of flax fiber/starch acetate is evaluated by a modified Bowyer and Bader method based on an analysis of the stress-strain curve of a short-fiber-reinforced composite in tension. A shear lag model is developed for the tensile stress-strain response of short-fiber-reinforced composites allowing for an elastic-perfectly plastic stress transfer. Composites with different fiber volume fractions and a variable content of plasticizer have been analyzed. The apparent IFSS of flax/starch acetate is within the range of 5.5-20.5 MPa, depending on composition of the material. The IFSS is found to be greater for composites with a higher fiber loading and to decrease with increasing content of plasticizer. The IFSS is equal or greater than the yield strength of the neat polymer, suggesting good adhesion, as expected for the chemically compatible constituents.

Place, publisher, year, edition, pages
Elsevier Ltd, 2016
Keywords
Flax fiber, Green composite, Interfacial shear strength, Thermoplastic starch, Fiber reinforced plastics, Flax, Linen, Plasticizers, Reinforced plastics, Reinforcement, Sheet molding compounds, Stress-strain curves, Yarn, Apparent interfacial shear strength, Elastic perfectly plastic, Fiber volume fractions, Green composites, Short-fiber-reinforced composites, Fibers
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-41058 (URN)10.1016/j.ijadhadh.2015.10.007 (DOI)2-s2.0-84945578051 (Scopus ID)
Available from: 2019-12-10 Created: 2019-12-10 Last updated: 2020-01-28Bibliographically approved
Tsampas, S., Fernberg, P. & Joffe, R. (2016). The effect of high temperature on the mechanical performance of novel high Tg polyimide-based carbon fibre-reinforced laminates. In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials: . Paper presented at 17th European Conference on Composite Materials, ECCM 2016, 26 June 2016 through 30 June 2016. European Conference on Composite Materials, ECCM
Open this publication in new window or tab >>The effect of high temperature on the mechanical performance of novel high Tg polyimide-based carbon fibre-reinforced laminates
2016 (English)In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2016Conference paper, Published paper (Refereed)
Abstract [en]

In this study, the outcomes from the mechanical testing of the carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R at ambient and elevated temperatures are presented. These results are compared to assess the effect of mechanical loading at 320°C on the performance of the system in tension, compression and Short-Beam Shear. The experimental campaign indicated that the mechanical loading at 320°C had a trivial effect on the tensile properties (fibre-dominated) whilst a more pronounced effect was noted on the compression and Short-Beam Shear (matrix and fibre/matrix interface-dominated properties).

Place, publisher, year, edition, pages
European Conference on Composite Materials, ECCM, 2016
Keywords
Carbon fibres, Failure, High temperature, Mechanical behaviour, Polyimide, Carbon fibers, Composite materials, Computer system recovery, Fibers, Mechanical testing, Polyimides, Reinforcement, Elevated temperature, Experimental campaign, Fibre reinforced, Fibre/matrix interfaces, Mechanical loading, Mechanical performance, Shear flow
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-42153 (URN)2-s2.0-85018580460 (Scopus ID)9783000533877 (ISBN)
Conference
17th European Conference on Composite Materials, ECCM 2016, 26 June 2016 through 30 June 2016
Available from: 2020-01-09 Created: 2020-01-09 Last updated: 2020-01-28Bibliographically approved
Pupure, L., Varna, J. & Joffe, R. (2015). Applications and limitations of non-linear viscoelastic model for simulation of behaviour of polymer composites. In: ICCM International Conferences on Composite Materials: . Paper presented at 20th International Conference on Composite Materials, ICCM 2015, 19 July 2015 through 24 July 2015. International Committee on Composite Materials
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)In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2015Conference paper, Published paper (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. 

Place, publisher, year, edition, pages
International Committee on Composite Materials, 2015
Keywords
Material model, Non-linearity, Viscoelasticity, Viscoplasticity
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-42217 (URN)2-s2.0-85053117892 (Scopus ID)
Conference
20th International Conference on Composite Materials, ICCM 2015, 19 July 2015 through 24 July 2015
Note

Funding text 1: Part of this study was financially supported by EXCEL project, “Increased competitiveness and visibility of Composite Centre Sweden through excellence in bio-nano multi-scale composites and high-temperature composites” funded by local government Norrbotten, SWEDEN. Swerea SICOMP is acknowledged for supplying of materials and help with manufacturing.

Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2020-01-28Bibliographically approved
Miettinen, A., Joffe, R., Pupure, L. & Madsen, B. (2015). Identification of true microstructure of composites based on various flax fibre assemblies by means of three-dimensional tomography. In: ICCM International Conferences on Composite Materials: . Paper presented at 20th International Conference on Composite Materials, ICCM 2015, 19 July 2015 through 24 July 2015. International Committee on Composite Materials
Open this publication in new window or tab >>Identification of true microstructure of composites based on various flax fibre assemblies by means of three-dimensional tomography
2015 (English)In: ICCM International Conferences on Composite Materials, International Committee on Composite Materials , 2015Conference paper, Published paper (Refereed)
Abstract [en]

Lately it has been demonstrated that natural fibres may be an environmentally superior alternative for, e.g., glass fibres. In order to estimate properties of composite materials made of natural fibres, models designed for synthetic fibres are often used. The models usually do not account for irregularities in the material, e.g., suboptimal fibre orientation due to the twisting angle of fibres in yarns. Use of models without taking those features into account might lead to unreliable results. Methods to quantify the microstructural properties of natural fibre composites with X-ray microtomography and three-dimensional image analysis are demonstrated in this work. The methods are applied to flax fibre composites made from three different kinds of pre-forms. Microstructural parameters estimated with the methods are used in micromechanical models for the stiffness of the composite. Comparison between rule-of-mixtures and classical laminate theory is made, highlighting the requirement for accurate parameter estimation and use of a model that accounts for significant structural features of the material. 

Place, publisher, year, edition, pages
International Committee on Composite Materials, 2015
Keywords
Flax, Microstructure, Natural fibres, Tomography
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-42229 (URN)2-s2.0-85053131982 (Scopus ID)
Conference
20th International Conference on Composite Materials, ICCM 2015, 19 July 2015 through 24 July 2015
Available from: 2019-12-17 Created: 2019-12-17 Last updated: 2020-01-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5210-4341

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