| 1. |
- Aitomäki, Yvonne, et al.
(författare)
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Hydrogel state impregnation of cellulose fibre-phenol composites: Effects of fibre size distribution
- 2016
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Ingår i: ECCM 2016. - : European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- Whilst it has been well established that cellulose nanofibres (CNF) networks produce films that have high stiffness and strength, they are difficult to impregnate. Investigated in this study is whether by controlling the degree of nanofibrillation of cellulose, composites based on micro- and nano-size cellulose fibres can be made that are more easily manufactured and have better impregnation than solely cellulose nano-fibre based composites. To evaluate this, cellulose at different stages of ultrafine grinding, extracted at time intervals of 30, 60 and 290 mins, were used to make composites. To achieve good impregnation a novel strategy was used based on impregnation with phenol resin whilst the fibrillated cellulose is in a hydrogel state. The composites were subsequently dried and consolidated by hot press. The current results show that this method of impregnation is successful and the phenol matrix greatly improves the properties of the cellulose with a low degree of fibrillation. In general, as the degree of fibrillation and the proportion of nanofibres increases, the mechanical properties of the networks and their composites increase. The addition of the matrix appears to restrict the deformation of CNF network, increasing the modulus and yield strength but decreasing the ultimate strength. The method also appears to restrict the consolidation and voids remain in the composite, which reduces the modulus when compared to theoretical maximum values for this material. More work on the consolidation process is necessary to achieve the full potential of these composites.
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| 2. |
- Akbarpour, S., et al.
(författare)
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Metal reinforcement around fastener holes in composites
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- One way of improving the load capacity of bolted joints in composite components is to use metal inserts locally at the holes in order to reduce the bearing stress. In this paper an innovative local reinforcement concept is introduced where metal inserts are implemented in the form of stacked patches at the holes in order to improve the bearing strength of the composite. After doing some initial tests and a parameter study, some specimens with optimized stacked patch inserts were designed and tested. The specimens with optimized inserts show 50-60% improved bearing strength in pin-loaded tests which corresponds to a potential weight reduction of about 30%. These very promising results indicates that the efficiency of joints in composites can be improved significantly.
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| 3. |
- Björnsson, Andreas, 1981-, et al.
(författare)
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Robot-forming of prepreg stacks - Development of equipment and methods
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- Within the aerospace industry the manufacturing of composite components with complex shapes, such as spars, ribs and beams are often manufactured using manual layup and forming of prepreg material. Automated processes for prepreg layup and efficient forming techniques like vacuum forming are sometimes difficult to employ to these type of products due to technical limitations. This paper describes the development of tools and the forming sequence needed to automate sequential forming of a complex shape using an industrial robot. Plane prepreg stacks are formed to the final shape using a dual-arm industrial robot equipped with rolling tools. Tests show that the developed tools and the employed sequence can be used to form stacks to the desired shape with acceptable quality.
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| 4. |
- Costa, Sergio, 1987, et al.
(författare)
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Finite element implementation of a model for longitudinal compressive damage growth with friction
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- A model for the longitudinal response of laminated fibre-reinforced composites during compressive damage growth is implemented in a Finite Element (FE) package and validated for mesh objectivity. The current work details the FE implementation of the fibre kinking model and in particular challenges associated with mesh objectivity. The numerical way to solve the stress equilibrium and stress compatibility equations simultaneously in an FE framework is also presented. The results show that the current model can be used to predict the kinking response and thus account for the correct energy absorption.
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| 5. |
- Fernberg, Patrik
(författare)
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Fibre reinforced polyimide composites and structures manufactured with resin transfer moulding - Overview of procedures and properties
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- In this paper, the major outcomes from a recently completed research program with ambition to develop polyimide carbon fibre composites with temperature ability above 360°C are reported. Data from characterisation of the processing properties such as viscosity and cure behaviour are presented alongside with data on the mechanical properties at room temperature of quasi-isotropic composites based on the developed resin and 8-harness satin weave carbon fibre fabrics. The paper also contains a demonstration of the use the material system in a demonstrator component.
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| 6. |
- Främby, Johannes, 1983, et al.
(författare)
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Delamination initiation and propagation modelling with an enriched shell element formulation
- 2016
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Ingår i: ECCM17 - 17th European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- For achieving good predictability of the deformation of structural composite components in crash simulations, a proper modelling of the delamination process is crucial. However, due to industrial restrictions on the simulation time of crash simulations, detailed modelling of each ply by separate elements through the thickness is not feasible. A potential remedy is to adopt the concept of adaptive shell elements which can be enriched whenever delaminations need to be accounted for. Hence, a structural model of a thinwalled laminate can thereby initially be built up from a single layer of shell elements through the thickness. During loading, the model is then enriched locally in critical areas where delamination is predicted. In this con- tribution, we show the potential of such an approach, where delamination cracks are adaptively introduced in the analysis based on a stress criterion in terms of the transverse stresses. A specific challenge is that these stresses are predicted with low accuracy in the FE model, whereby a post-processing step is proposed where an improved prediction is reconstructed based on the momentum balance equations. We show the potential of the proposed methodologys ability to capture initiating and propagating delaminations, and can conclude that the proposed methodology appears to be suitable for the simulation of thin-walled structures undergoing substantial delaminations.
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| 7. |
- Grammatikos, Sotirios, 1985, et al.
(författare)
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Non-linear response of environmentally aged polymer composites: A physicochemical and mechanical study
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- In this paper, the anomalous behaviour of polymer composites subjected to hygrothermal aging is discussed in reference to the results of a characterization study on polyester matrix fibre reinforced polymer (FRP) composites. Hygrothermal aging, the combination of moisture and elevated temperatures, has been proven to affect the durability of FRPs. Significant structural degradation can be expected as a consequence of hygrothermal aging, however it has been shown that some material properties exhibit a strong non-linear and even beneficial behaviour as a consequence of hygrothermal exposure, indicating the presence of different competing mechanisms. To study these different mechanisms which control the structural performance of an exposed material, FRP samples were exposed to short-term hygrothermal aging for 112 days. Moisture absorption characteristics and mechanical performance were assessed at prescribed time frames throughout aging. With a view to examining any induced intrinsic and surface characteristics, Computed Tomography scan (CT-scan) and Scanning Electron Microscopy (SEM) were also employed. Lastly, impedance spectroscopy was used as an innovative tool to efficiently follow moisture absorption during aging.
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| 8. |
- Hajlane, Abdelghani, et al.
(författare)
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Environmentally friendlier method to deposit cellulose nanocrystals on regenerated cellulose filaments and effect of the treatment on mechanical properties of fibers
- 2016
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Ingår i: ECCM 2016. - : European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 9. |
- Joffe, Roberts, et al.
(författare)
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Effect of surface modification of regenerated cellulose fibers on moisture absorption and fiber/matrix adhesion
- 2016
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Ingår i: ECCM 2016. - : European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Larsson, Ragnar, 1960, et al.
(författare)
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Modelling of kink-band growth based on the geometrically non-linear theory
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - 9783000533877
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We propose a new and computationally ecient continuum damage based model, able to predict fibre /matrix shear failure under longitudinal compression for a UD ply. A structure tensor based continuum damage formulation is placed in context with the UD ply, where the elastic material response is governed by transverse isotropy. To represent the proper energy dissipation, an elastic damage model is formulated in the invariants of fibre/matrix shear and fibre compression, including failure initiation and progressive damage modeling. We are guided by the anisotropic elastic model to define four strain invariants, representing key features of the UD-ply microstructure. The damage model is applied to a Non-Crimp Fabric (NCF) composite and compared to a state of the art model based on kinking theory [6]. Instead of invoking the geometric instability into the material model, a key feature is to consider the geometrical fibre kinking instability on the macro-level based on a finite strain formulation
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