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Joffe, Roberts
Publications (10 of 186) Show all publications
Tsampas, S., Fernberg, P. & Joffe, R. (2018). Development of novel high Tg polyimide-based composites: Part II: Mechanical characterisation. Journal of composite materials, 52(2), 261-274
Open this publication in new window or tab >>Development of novel high Tg polyimide-based composites: Part II: Mechanical characterisation
2018 (English)In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 52, no 2, p. 261-274Article in journal (Refereed) Published
Abstract [en]

In this study, the mechanical performance assessment of a newly developed carbon fibre-reinforced polyimide composite system T650/NEXIMID® MHT-R is presented. This system was subjected to a series of mechanical tests at ambient and elevated temperature (320℃) to determine basic material properties. Moreover, an additional test was conducted, using a T650/NEXIMID® MHT-R laminate in which the fibre sizing was thermally removed prior to laminate manufacturing, to investigate the effect of fibre treatment on mechanical performance. The experimental results indicated that the T650/NEXIMID® MHT-R composites along with exceptionally high Tg (360–420℃) exhibited competitive mechanical properties to other commercially available polyimide and epoxy-based systems. At elevated temperature, the fibre-dominated properties were not affected whilst the properties defined by matrix and fibre/matrix interface were degraded by approximately 20–30%. Finally, the fibre sizing removal did not affect the tensile and compressive strength, however, the shear strength obtained from short-beam shear test was deteriorated by approximately 15%. to serve as baseline for further studies.

Place, publisher, year, edition, pages
Sage Publications, 2018
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-63439 (URN)10.1177/0021998317705706 (DOI)000419136300010 ()2-s2.0-85040032640 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-01-19 (andbra)

Available from: 2017-05-18 Created: 2017-05-18 Last updated: 2018-01-23Bibliographically 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)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: 2018-05-28Bibliographically approved
Suñer Moreno, S., Gowland, N., Craven, R., Emami, N., Joffe, R. & Tripper, J. (2018). Ultrahigh molecular weight polyethylene/graphene oxide nanocomposites: wear characterization and biological response to wear particles. Journal of Biomedical Materials Research. Part B - Applied biomaterials, 106(1), 183-190
Open this publication in new window or tab >>Ultrahigh molecular weight polyethylene/graphene oxide nanocomposites: wear characterization and biological response to wear particles
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2018 (English)In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 106, no 1, p. 183-190Article in journal (Refereed) Published
Abstract [en]

In the field of total joint replacements, polymer nanocomposites are being investigated as alternatives to ultrahigh molecular weight polyethylene (UHMWPE) for acetabular cup bearings. The objective of this study was to investigate the wear performance and biocompatibility of UHMWPE/graphene oxide (GO) nanocomposites. This study revealed that low concentrations of GO nanoparticles (0.5 wt %) do not significantly alter the wear performance of UHMWPE. In contrast, the addition of higher concentrations (2 wt %) led to a significant reduction in wear. In terms of biocompatibility, UHMWPE/GO wear particles did not show any adverse effects on L929 fibroblast and PBMNC viability at any of the concentrations tested over time. Moreover, the addition of GO to a UHMWPE matrix did not significantly affect the inflammatory response to wear particles. Further work is required to optimize the manufacturing processes to improve the mechanical properties of the nanocomposites and additional biocompatibility testing should be performed to understand the potential clinical application of these materials

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Composite Science and Engineering
Research subject
Machine Elements; Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-61091 (URN)10.1002/jbm.b.33821 (DOI)000417576500019 ()2-s2.0-85006833606 (Scopus ID)
Note

Validerad;2018;Nivå 2;2017-12-12 (svasva)

Available from: 2016-12-15 Created: 2016-12-15 Last updated: 2018-03-08Bibliographically approved
Hajlane, A., Kaddami, H. & Joffe, R. (2017). Chemical modification of regenerated cellulose fibres by cellulose nano-crystals: Towards hierarchical structure for structural composites reinforcement. Industrial crops and products (Print), 100, 41-50
Open this publication in new window or tab >>Chemical modification of regenerated cellulose fibres by cellulose nano-crystals: Towards hierarchical structure for structural composites reinforcement
2017 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 100, p. 41-50Article in journal (Refereed) Published
Abstract [en]

A simple and innovative new route, with less negative impact on the environment, for depositing and hope-grafting cellulose nano-crystals onto the surface of regenerated cellulose fibres (Cordenka 700 Super 3), using γ-methacryloxypropyltrimethoxysilane as coupling agent, is presented. Hierarchical cellulosic structure involving micro-scale fibres and nano-scale cellulose crystal network was created as verified by the scanning electron microscopy. The fibres were initially oxidised by optimized concentration of cerium ammonium nitrate to generate radicals on the cellulose backbone in order to polymerize the coupling agent at the surface. Infrared spectroscopy and scanning electron microscopy confirmed the chemical polymerisation of MPS onto regenerated cellulose fibres without enabling to show the chemical bonding between silane and nano-crystals. However, tensile test which was performed to study the impact of different treatments on mechanical properties of regenerated cellulose fibres, revealed that the modification by silane decreased the stiffness and strength of fibres (22% and 10% decrease, respectively) while the strain at failure was increased. These changes were attributed to the treatment conditions which may have induced the disorder and the misalignment of the structure of cellulose fibres (e.g. axial orientation of molecular chains and crystalline phase of the fibre has been reduced). This assumption is supported by the results from successive loading-unloading test of the fibre bundle. However, after depositing cellulose nano-crystals onto the fibre’s surface, the stiffness was recovered (20% increase in comparison to MPS treated fibres) while the strength and strain at failure remained at the same order of magnitude as for fibres treated only by the coupling agent.

National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-62097 (URN)10.1016/j.indcrop.2017.02.006 (DOI)000397687200005 ()2-s2.0-85012964625 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-02-21 (andbra)

Available from: 2017-02-21 Created: 2017-02-21 Last updated: 2018-05-22Bibliographically approved
Ansari, F., Granda, L. A., Joffe, R., Berglund, L. A. & Vilaseca, F. (2017). Experimental evaluation of anisotropy in injection molded polypropylene/wood fiber biocomposites. Composites. Part A, Applied science and manufacturing, 96, 147-154
Open this publication in new window or tab >>Experimental evaluation of anisotropy in injection molded polypropylene/wood fiber biocomposites
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2017 (English)In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 96, p. 147-154Article in journal (Refereed) Published
Abstract [en]

Although the anisotropy of wood fibers is reasonably well established, the anisotropy of injection molded wood fiber composites is not well understood. This work focuses on chemo-thermomechanical pulp (CTMP) reinforced polypropylene (PP) composites. A kinetic mixer (Gelimat) is used for compounding CTMP/PP composites, followed by injection molding. Effects from processing induced orientation on mechanical properties are investigated. For this purpose, a film gate mold was designed to inject composites in the shape of plates so that specimens in different directions to the flow could be evaluated in tensile tests. Observations from tensile tests were complemented by performing flexural tests (in different directions) on discs cut from the injected plates. SEM was used to qualitatively observe the fiber orientation in the composites. At high fiber content, both modulus and tensile strength could differ by as much as 40% along the flow and transverse to the flow. The fiber orientation was strongly increased at the highest fiber content, as concluded from theoretical analysis.

National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-61943 (URN)10.1016/j.compositesa.2017.02.003 (DOI)000399850600016 ()2-s2.0-85014372994 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-03-07 (rokbeg)

Available from: 2017-02-10 Created: 2017-02-10 Last updated: 2018-01-16Bibliographically approved
Andersons, J., Modniks, J., Joffe, R., Madsen, B. & Nättinen, K. (2016). Apparent interfacial shear strength of short-flax-fiber/starch acetate composites (ed.). Paper presented at . 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 elasticperfectly 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 to 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.

National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-7925 (URN)10.1016/j.ijadhadh.2015.10.007 (DOI)65b5ef31-685a-4dbf-a3fd-e28cfad4c0d0 (Local ID)65b5ef31-685a-4dbf-a3fd-e28cfad4c0d0 (Archive number)65b5ef31-685a-4dbf-a3fd-e28cfad4c0d0 (OAI)
Note
Validerad; 2016; Nivå 2; 20150326 (joffe)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-01-16Bibliographically approved
Joffe, R., Hajlane, A. & Kaddami, H. (2016). Effect of surface modification of regenerated cellulose fibers on moisture absorption and fiber/matrix adhesion (ed.). In: (Ed.), ECCM 2016: Proceeding of the 17th European Conference on Composite Materials. Paper presented at 17th European Conference on Composite Materials, Munich, Germany, 26-30th June 2016. European Conference on Composite Materials
Open this publication in new window or tab >>Effect of surface modification of regenerated cellulose fibers on moisture absorption and fiber/matrix adhesion
2016 (English)In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes the effect of surface modification of regenerated cellulose fibers by chemical treatment and deposition of cellulose nano-crystals onto fibers. The effect of this modification on themoisture absorption by fibers and interface properties with epoxy matrix has been studies. The preliminary results show positive trends in reducing moisture uptake by fibers and improving interfacial shear strength.The deposition of cellulose nano-crystals at different concentrations onto regenerated cellulose fibers creates a network covering surface of fibers and interconnecting them. This resulted in rather significant reduction of the moisture absorption compare to untreated fibers (8% vs 12% respectively)and improving interfacial shear strength of regenerated cellulose fiber/epoxy system. The increase of the interfacial shear strength measured from bundle pull-out test on fibers conditioned at 64% relative humidity has been observed. Thus, the hierarchical structure created by grafting nano-crystals onmicro-sized cellulose fibers resulted in improvement of fiber/matrix adhesion by reducing water absorption.

Place, publisher, year, edition, pages
European Conference on Composite Materials, 2016
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-27553 (URN)2-s2.0-85017668512 (Scopus ID)10cf963c-819c-4c9b-81b2-3b133fec2cb3 (Local ID)978-3-00-053387-7 (ISBN)10cf963c-819c-4c9b-81b2-3b133fec2cb3 (Archive number)10cf963c-819c-4c9b-81b2-3b133fec2cb3 (OAI)
Conference
17th European Conference on Composite Materials, Munich, Germany, 26-30th June 2016
Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-22Bibliographically approved
Hajlane, A., Kaddami, H. & Joffe, R. (2016). Environmentally friendlier method to deposit cellulose nanocrystals on regenerated cellulose filaments and effect of the treatment on mechanical properties of fibers (ed.). In: (Ed.), ECCM 2016: Proceeding of the 17th European Conference on Composite Materials. Paper presented at 17th European conference on composite materials, ECCM-17, Munich, Germany, 26-30 June 2016. European Conference on Composite Materials
Open this publication in new window or tab >>Environmentally friendlier method to deposit cellulose nanocrystals on regenerated cellulose filaments and effect of the treatment on mechanical properties of fibers
2016 (English)In: ECCM 2016: Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials , 2016Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents environmentally friendlier technique for deposition of cellulose nano-whiskers onto the surface of regenerated cellulose fibres using γ-methacryloxypropyltrimethoxysilane as coupling agent. The result of this treatment is hierarchical reinforcement consisting of micro-scale fibres and nano-scale cellulose crystal network. In order to evaluate influence of treatment on fibre performance, tensile tests of fibre bundles were carried out. The results show that there is significant impact on stiffness of fibres only by first modification by silane, whereas grafting of cellulose nanowhiskers onto the surface of the fibre allowed recovery of initial properties. It is assumed that thetreatment may have induced the misalignment of macromolecular chains and crystalline cellulose phase with respect to the fibre axis.

Place, publisher, year, edition, pages
European Conference on Composite Materials, 2016
National Category
Composite Science and Engineering
Research subject
Polymeric Composite Materials
Identifiers
urn:nbn:se:ltu:diva-30265 (URN)2-s2.0-85017721749 (Scopus ID)406ebcea-d3b8-43ce-9334-7941e11b5da4 (Local ID)978-3-00-053387-7 (ISBN)406ebcea-d3b8-43ce-9334-7941e11b5da4 (Archive number)406ebcea-d3b8-43ce-9334-7941e11b5da4 (OAI)
Conference
17th European conference on composite materials, ECCM-17, Munich, Germany, 26-30 June 2016
Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-05-22Bibliographically 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 ()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: 2018-05-28Bibliographically approved
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