| 1. |
- Stigh, Ulf, 1956-
(författare)
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Applications of equilibrium of configurational forces for the measurement of cohesive laws
- 2016
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Ingår i: Proceedings ECCM17. - : European Conference on Composite Materials, ECCM. - 9783000533877 - 3000533877
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Konferensbidrag (refereegranskat)abstract
- A methodology to develop experimental methods to measure cohesive laws is introduced. This methodology is based on the property of all configurational forces equilibrium acting on a specimen to be in equilibrium. Two applications are given. The first shows a method to measure the cohesive law for shear representing the mechanical behaviour of an adhesive layer. The second application is a method to measure the cohesive law for the formation of a kink-band in a unidirectional composite. It is concluded that the methodology is critically dependent on the ability to associate a pseudopotential to the inelastic properties of the deforming material where the fracture process takes place. The importance to clearly identify the material that is modelled with the cohesive zone is also stressed.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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| 11. |
- 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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| 12. |
- Loukil, Mohamed, et al.
(författare)
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Characterization of damaged composite laminates using Electronic Speckle Pattern Interferometry (ESPI)
- 2016
-
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
- The degradation of the elastic properties of composite laminates with intralaminar cracks is caused by reduced stress in the damaged layer which is mainly due to two parameters: the crack opening displacement (COD) and the crack sliding displacement (CSD). In this paper these parameters are measured experimentally providing laminate stiffness reduction models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edges of a [0/ +704/ -704]s glass fiber/epoxy laminate specimens with multiple intralaminar cracks is studied and the COD and CSD dependence on the applied mechanical load is measured. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry). By studying the displacement discontinuities, the crack face displacements were measured. A comparison between the COD and the CSD (for the same crack) is performed
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| 13. |
- Molker, Henrik, 1979, et al.
(författare)
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Identifying failure initiation in automotive structures made of NCF reinforced composites for hot spot analysis
- 2016
-
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, intrabundle failure initiation in NCF reinforced composite materials is predicted based on a finite element model built with shell elements. The full 3D stress state is estimated based on the shell results and used in a state of the art 3D failure criterion. The procedure considers predictions of the transverse shear and normal stresses from stress equilibrium. By using this approach on shell elements, more efficient modelling strategies suited to identify hot spots in larger structures can be pursued.
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| 14. |
- Olsson, Robin, et al.
(författare)
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Testing and modelling of tension after impact of a thin ply textile composite
- 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
- This paper presents an experimental and numerical study of impact response, damage and tension after impact of thin ply HTS45/RTM6 carbon/epoxy laminates, manufactured via resin transfer moulding. A plain weave from carbon fibre spread-tow bands was used in a quasi-isotropic layup. Finite element simulations were performed using layered shell elements accounting for in-plane damage mechanics, with cohesive surfaces between a few layers of shell elements to account for delamination. The damage was found to include a combination of fibre damage and delaminations, in contrast to a previous study on similar cross-ply laminates, where fibre damage dominated. The rate of decrease in tensile strength after impact was similar to prepreg laminates with conventional ply thickness, but the impacted strength was slightly higher due to a higher undamaged strength for thin ply laminates.
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| 15. |
- Remmers, Joris, et al.
(författare)
-
Strategies for modelling delamination growth using isogeometric continuum shell elements
- 2016
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Ingår i: Proceedings of ECCM17 - 17th European Conference on Composite Materials. - 9783000533877 ; , s. Code 126913-
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Konferensbidrag (refereegranskat)abstract
- The computational efficiency of CAE models and methods for analysing failure progression in compositesis important to enable their use in full scale models. In particular, efficient approximation andsolution methods for delamination modelling is crucial to meet today’s requirements on virtual developmentlead times. For that purpose, several papers have been published that present alternative methodsfor modelling concepts which support laminate failure analyses requiring only one shell element throughthe thickness and where arbitrary delamination propagation is accounted for only in areas where it isneeded. The proposed new concepts however need to be further developed before they can bereadily applied to solve engineering problems. As for the alternative concept based on an isogeometricapproach by Hosseini et al., there is a need to handle successive introduction of new discontinuitiesby means of knot-insertion in an automated fashion. To this end, better predictions of the throughthe-thickness distribution of out-of-plane stresses are needed. In this paper we focus on the furtherdevelopment of the isogeometric continuum shell element to allow for an automated insertion of discontinuities.
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| 16. |
- Saseendran, Sibin, 1989-, et al.
(författare)
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Viscoelastic behavior of LY5052 epoxy resin in rubbery state during curing
- 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
- The aim of the presented work is to investigate the relationship between the rubbery modulus and the degree of cure for partially to fully cured LY5052 epoxy resin. In particular, this work experimentally tests an existing model defined in shear modulus by redefining into the elastic tensile modulus. Experiments were performed in a Dynamic Mechanical and Thermal Analysis (DMTA) machine in the frequency domain. After the model is tested, super-master curves generated using time-temperature-cure superposition are normalized using the model so that the rubbery modulus made independent on the state of cure, which further simplifies the super-master curves. This results in a unique master curve that describes the viscoelastic behavior of the LY5052 epoxy resin for the given conditions. This consequently could help formulate simplified models to predict viscoelastic behaviour and also develop better experimental methodologies to characterize them.
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| 17. |
- Sethi, Jatin, 1986-, et al.
(författare)
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Semi-interpenetrating network derived from polylactic acid/polyurethane blend and reinforced with celulose nanocrystals
- 2016
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Ingår i: ECCM 2016. - : European Conference on Composite Materials. - 9783000533877 ; , s. 539-546
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Konferensbidrag (refereegranskat)abstract
- The current work aims to prepare and characterize bionanocomposites based on cellulose nanocrystals and semi interpenetrating networks prepared from PLA and PU. Nanocrystals were dispersed in PU phase with an innovative, novel method called as co-solvent assisted surfactant-less method. The characterization of the materials was done by tensile testing, differential scanning calorimetry and thermogravimetric analysis. The results were progressive and supported the premise that SIPNs are a viable option to prepare mechanically enhanced hybrid matrix that can impart improved mechanical properties to nanocomposites. Additionally, the dispersion method produced excellent dispersion of nanocrystals in the polyol phase, which was successfully transferred to the nanocomposite
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| 18. |
- Tsampas, Spyros, et al.
(författare)
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The effect of high temperature on the mechanical performance of novel high Tg polyimide-based carbon fibre-reinforced laminates
- 2016
-
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 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).
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| 19. |
- Varna, Janis, et al.
(författare)
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Stiffness prediction of damaged laminates based on the concept of laminate effective stiffness
- 2016
-
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
- The concept of the effective stiffness of a unidirectional layer with intralaminar cracks is revisited performing 3-D FEM parametric analysis of symmetric and balanced laminates with damaged 90-layer. The effective stiffness of the damaged layer is obtained from the difference between damaged and undamaged laminate stiffness. The effective longitudinal modulus and Poisson's ratio of the layer are equal to their initial values. A very simple expression for the effective transverse modulus change with normalized crack density has sufficient accuracy and generality to be used in laminate theory to predict macroscopic elastic property change with crack density in laminates with very different lay-ups and made of different UD composites.
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| 20. |
- Wilhelmsson, Dennis, 1980, et al.
(författare)
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Effect of specimen width on strength in off-axis compression tests
- 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
- Compression tests have been performed according to ASTM D6641 to check whether 12 mm is a sufficient width for off-axis tests of a unidirectional Non Crimp Fabric (NCF) reinforced carbon-fibre composite. Various off-axis angles are tested in a larger context and it is important to establish a representative material volume. The test matrix consists of two different widths for two off-axis cases, 15° and 20° with a total sample size of 24. A two-sample T-test is performed for each off-axis angle to check if there is a statistically significant difference of the compressive strength between specimens with different widths. The null hypothesis, that there is no difference between the mean values is tested with a double-tailed test on a 5 % significance level. Neither of the cases may be rejected, i.e. there is no statistically significant difference on the 5 % level. The 15° off-axis case returns a p-value of 7.4 % and the 20° off-axis case gives a p-value of 21.3 %. It can be concluded that the effect is small and not statistically significant. It means that remaining off-axis testing in the larger context can proceed with the nominal width of 12 mm.
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| 21. |
- Xu, Johanna, et al.
(författare)
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Multifunctional composites : Modeling intercalation induced stresses in constituents of micro-battery
- 2016
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Ingår i: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM.
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Konferensbidrag (refereegranskat)abstract
- A structural battery that simultaneously carries mechanical loads while storing electrical energy offers the potential of significantly reduced total vehicle weight owing to the multifunctionality. Carbon fiber is employed as negative electrode of the battery and also as a composite reinforcement material. It is coated with a solid polymer electrolyte working as an ion conductor and separator whilst transferring mechanical loads. The coated fiber is surrounded by a conductive positive electrode material. This paper demonstrates a methodology for addressing mechanical stresses arising in a conceptualized micro battery cell during electrochemical cycling, caused by time dependent gradients in lithium ion concentration distribution in the carbon fiber.
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