| 1. |
- Neagu, R. C., et al.
(författare)
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Processing and mechanical properties of novel wood fibre composites foams
- 2009
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Ingår i: ICCM International Conferences on Composite Materials.
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Konferensbidrag (refereegranskat)abstract
- Wood fibre reinforced polylactic acid (PLA) composite foams have been successfully produced using supercritical carbon dioxide. A significant increase of specific properties, both stiffness and strength, was achieved by adding 5-10 wt% wood fibres. The experimental stiffness was comparable with a superposed micromechanical model for a three phase fibre reinforced foam. These first results on the integration of wood fibres into cellular PLA polymer are very encouraging.
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| 2. |
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| 3. |
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Mixed numerical-experimental methods in woodmicromechanics
- 2012
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Ingår i: COST Action FP 0802. - Edinburgh, Scotland : Proceedings of the Annual Workshop of COST Action FP0802: Micro-characterisation of wood materials and properties. ; , s. 86-87
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Proceedings (redaktörskap) (refereegranskat)
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| 4. |
- Afshar, R., et al.
(författare)
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A micro-CT investigation of densification in pressboard due to compression
- 2023
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Ingår i: Strain. - : John Wiley & Sons. - 0039-2103 .- 1475-1305. ; 59:4
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Tidskriftsartikel (refereegranskat)abstract
- As a non-destructive inspection method, micro-computed tomography has been employed for determining local properties of a cellulose-based product, specifically pressboard. Furthermore, by utilizing the determined properties in a detailed numerical model, by means of a finite element analysis, we demonstrate a continuum anisotropic viscoelastic-viscoplastic model. Through such a combination of non-invasive experiments with accurate computations in mechanics, we attain a better understanding of materials and its structural integrity at a pre-production stage increasing the success of the first prototype. In detail, this combination of micro-computed tomography and finite element analysis improves accuracy in predicting materials response by taking into account the local material variations. Specifically, we have performed indentation tests and scanned the internal structure of the specimen for analysing the densification patterns within the material. Subsequently, we have used a developed material model for predicting the response of material to indentation. We have computed the indentation test itself by simulating the mechanical response of high-density cellulose-based materials. In the end, we have observed that pressboard, having initially a heterogeneous density distribution through the thickness, shows a shift in the densification to the more porous part after indentation. The densification maps of the simulated results are presented by comparing with the experimental results. A reasonable agreement is observed between the experimental and the simulated densifications patterns, which suggests that the proposed methodology can be used to predict densification also for other fibre-based materials during manufacturing or in service loading.
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| 5. |
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| 6. |
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| 7. |
- Gamstedt, E.K., et al.
(författare)
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Fatigue damage mechanisms in unidirectional carbon-fibre-reinforced plastics
- 1999
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 34:11, s. 2535-2546
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue life behaviour and the underlying micromechanisms have been studied in two different Types of unidirectional carbon-fibre-reinforced plastics loaded in tension-tension along the fibre direction. The carbon fibres (AS4) were the same in the two composite systems. One thermoplastic matrix (polyetheretherketone, PEEK) and one thermosetting matrix (epoxy toughened with a thermoplastic additive) were used. The macroscopic fatigue behaviour was characterised by fatigue life diagrams. Surface replicas were taken intermittently during the course of the fatigue tests to monitor the active fatigue damage micromechanisms. The thermoset based composite showed a higher fatigue resistance with few microcracks initiated at distributed fibre breaks growing at a decelerating rate. The thermoplastic composite had a more pronounced fatigue degradation with a steeper fatigue life curve, which was caused by widespread propagating debonds and matrix cracks. The use of a tougher and more ductile matrix results in an inferior fatigue life performance, due to a more widely distributed accumulation of damage that propagates at a higher rate.
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| 8. |
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| 9. |
- Gamstedt, E.K., et al.
(författare)
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Micromechanisms in tension-compression fatigue of composite laminates containing transverse plies
- 1999
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 49:2, s. 167-178
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Tidskriftsartikel (refereegranskat)abstract
- For both monotonic and fatigue loading conditions, debonding is the subcritical micromechanism which leads to transverse cracking and ultimately influences final failure of the composite structure. Previous studies show that tension-compression fatigue is more detrimental than tension-tension fatigue to transverse and multidirectional laminates. By analysing the debonding mechanisms and modelling thereof, the macroscopic fatigue behaviour can be better understood. Also, the dominant crack-propagation mode can be identified which may be of use in selection of constituent material properties to optimise fatigue resistance. In this study, glass-fibre-reinforced vinyl-ester was used. The adverse effect of compressive load excursions was verified by counting the transverse cracks in cross-ply laminates. The mechanisms were studied in low-cycle fatigue of a specimen containing a single transverse fibre. Compressive load cycles led to significantly increased debond growth. In tension, contact zones developed at the crack tips for sufficiently large debonds. Because of the mismatch in elastic properties, an opening zone appeared at the tips of the interfacial crack when the same debond was subjected to a compressive load. Since debond propagation is more susceptible to mode I loading, the sensitivity to tension-compression fatigue is explained by the effective crack-tip opening in compressive loading for sufficiently large debond cracks. This has also been verified by finite-element analysis.
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| 10. |
- Gamstedt, E. Kristofer, et al.
(författare)
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Synthesis of unsaturated polyesters for improved interfacial strength in carbon fibre composites
- 2002
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Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 33:9, s. 1239-1252
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Tidskriftsartikel (refereegranskat)abstract
- Carbon fibres are gaining use as reinforcement in glass fibre/polyester composites for increased stiffness as a hybrid composite. The mechanics and chemistry of the carbon fibre-polyester interface should be addressed to achieve an improvement also in fatigue performance and off-axis strength. To make better use of the versatility of unsaturated polyesters in a carbon fibre composite, a set of unsaturated polyester resins have been synthesized with different ratios of maleic anhydride, o-phthalic anhydride and 1,2-propylene glycol as precursors. The effective interfacial strength was determined by micro-Raman spectroscopy of a single-fibre composite tested in tension. The interfacial shear strength with untreated carbon fibres increased with increasing degree of unsaturation of the polyester, which is controlled by the relative amount of maleic anhydride. This can be explained by a contribution of chemical bonding of the double bonds in the polymer to the functional groups of the carbon fibre surface.
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