| 1. |
- Tsampas, Spyros, et al.
(author)
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The effect of high temperature on the mechanical performance of novel high Tg polyimide-based carbon fibre-reinforced laminates
- 2016
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In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9783000533877
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Conference paper (peer-reviewed)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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| 2. |
- Aitomäki, Yvonne, et al.
(author)
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Novel reactive bicomponent fibres : Material in composite manufacturing
- 2012
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In: Journal of Nanostructured Polymers and Nanocomposites. - 1790-4439. ; 8:1, s. 5-11
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Journal article (peer-reviewed)abstract
- The hypotheses that reactive uncured, thermoset bicomponent fibres can be prepared and mixed with reinforcing fibres and ultimately used in preparation of a composite was tested and is described. It is thought that such fibres have the two potential advantages: (1) to enable manufacturing with particle doped resins e.g. nanocomposites which add functionality to composites and (2) increased efficiency of structural composite manufacturing by increasing the level of automation. The structure of the thermoset fibres comprises of a sheath of thermoplastic and a core of uncured thermoset resin. Once manufactured, the fibres were wound with a reinforced fibre onto a plate, consolidated and cured. The resulting composite was examined and compared to other composites made with the same manufacturing method from commercially available materials. The results show that a laminate can be produced using these reactive bicomponent fibres. The resin system successfully impregnates the reinforcing carbon fibres and that the thermoplastic separates from the epoxy resin system during consolidation. In comparison to reference material, the bicomponent laminate shows promising characteristics. However, the processes developed are currently on a lab-scale and considerable improvement of various bicomponent fibre properties, such as the strength, are required before the technology can be used on a larger scale.
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| 3. |
- Alnersson, Gustaf
(author)
-
Towards 3D modelling of Compression Moulding of SMC
- 2021
-
Licentiate thesis (other academic/artistic)abstract
- The automotive industry is facing ever increasing demands for reduced emissions, and lightweight solutions are thusly required. One field that has significant potential in this regard is composite materials, which can offer a good combination of weight reduction and mechanical properties. However, the rapid development cycles in the automotive industry mean that tools for numerical modeling are necessary, both regarding manufacturing processes and prediction of mechanical properties. The material that has been of interest for this work is Sheet Moulding Compound (SMC). SMC consists of sheets of resin and chopped fibres. When used for manufacturing the sheets are cut into appropriate size and shape. The cut sheets are then placed in a pre-heated mould. When this mould is closed, the sheets melt and the fibre-filled resin flows out and fills the mould cavity; the resin then cures and solidifies. A significant advantage of SMC compared to other composite solutions is that the process has comparatively short cycle times, which is a necessity for automotive applications. However, it is a rather complicated process to model numerically for a number of reasons, including the complex rheological properties of the charge, the often rather significant temperature gradients throughout the thickness, often complicated three-dimensional effects in the flow, and the chopped fibres present in the charge. These fibres will move and change orientation as the charge is pressed, which is a significant challenge to model properly.The first part of this work is a review and discussion of the difficulties described above, and some solutions that have been suggested. The second part concerns a suggestion for a three-dimensional flow model for the compression moulding process, which takes into account factors that have been suggested to influence the flow behavior, such as temperature distribution and shear strain rate. Some simulation results are presented along with comparison to previous experimental results, and similar flow patterns are observed serving as a qualitative validation. The third part concerns the expansion of this model to include the effects of the flow on the fibre orientation.
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| 4. |
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| 5. |
- Carlson, Tony
(author)
-
Multi-functional composite materials : CFRP thin film capacitors
- 2011
-
Licentiate thesis (other academic/artistic)abstract
- The use of lightweight materials in structural applications is ever increasing. Today, lightweight engineering materials are needed to realise greener, safer and more competitive products. A route to achieve this could be to combine more than one primary function in a material or component to create multi-functionality, thus reducing the number of components and ultimately the overall weight. This thesis presents an approach towards realising novel multi-functional polymer composites. A series of structural capacitor materials made from carbon fibre reinforced polymers have been developed, manufactured and tested. In papers I and II, capacitors have been manufactured using different papers and polymer films as dielectric separator employing carbon fibre/epoxy pre-pregs as structural electrodes. Plasma treatment was used as a route for improved epoxy/polymer film adhesion. The manufactured materials were evaluated for mechanical performance by ILSS and tearing tests and electrical performance by measuring capacitance and dielectric breakdown voltage. In paper III the concept was extended in a parametric study using the most promising approach with a polymer film as dielectric separator. Three thicknesses of PET (50, 75 and 125 µm) were used as dielectric separator with carbon fibre/epoxy pre-pregs as structural electrodes. PET was chosen due to availability in different thicknesses as well as the frequent use in ordinary capacitors making it a suitable candidate. As in paper I and II, plasma treatment was used to improve the PET/epoxy adhesion. The capacitor materials were evaluated for mechanical performance by tensile tests and ILSS and for electrical performance by measuring capacitance and dielectric breakdown voltage. The multifunctional materials shows good potential for replacing steel and other materials with lower specific mechanical properties but cannot match the high specific mechanical performance of mono-functional materials. Both mechanical and electrical performance could have large benefits from developing new separator materials adapted for use in multifunctional applications and could be an interesting field for extended research.
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| 6. |
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| 7. |
- Engström, Jonas, et al.
(author)
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Characterization of carbon nanotube doped carbon fiber prepreg laminate
- 2012
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In: Proceedings of the 15th European Conference on Composite Materials. - Venice : European Conference on Composite Materials, ECCM. - 9788888785332
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Conference paper (peer-reviewed)abstract
- The current paper reports results from a preliminary study on PREGCYL™ NC R2HM-01 which is a carbon nanotube doped prepreg produced by Nanocyl. The work consisted of sample manufacturing in autoclave, microcopy analysis with XHR-SEM and mechanical testing. The mechanical testing consisted of tensile tests of unidirectional (in longitudinal direction) and cross-ply laminates. Test of unidirectional laminates showed that stiffness of the PREGCYL material is slightly higher than that of MTM55 composites (111GPa vs 102GPa). The results from tests of cross-ply laminates indicated that damage (transverse cracks) initiation is delayed in PREGCYL composites compare to the MTM55 material. Damage accumulation also seems to be slower in nano-doped composites.
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| 8. |
- Fernberg, Patrik, et al.
(author)
-
Carbon nanotube treated carbon fibre preforms for improved properties of aeronautical grade composites
- 2012
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In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials. - Padova : European Conference on Composite Materials, ECCM. - 9788888785332
-
Conference paper (peer-reviewed)abstract
- The current paper reports work on development of enhanced carbon fibre composites manufactured by resin transfer moulding (RTM). In particular, the possibility to obtain a toughened composite through deposition of carbon nanotubes (CNT) on the fibres is investigated. The hypothesis is that deposition of CNT on the fibre surface has two major advantages: a) filtering problems during manufacturing are eliminated and b) CNT can contribute to a local toughening in the vicinity of fibres, where stress concentrations often are high. Unidirectional and multi-axial composites, with and without CNT-modification, were manufactured using conventional RTM-technique and HexFlow®RTM6 epoxy resin. The composites were characterized by means of mechanical testing (interlaminar shear strength, ILSS) and microscopy. Significant improvements by 13 to37 % in ILSS values were achieved with the addition of CNT. Stiffness degradation tests were also performed. The results from these tests were not completely conclusive. Some treatments promoted stiffness degradation whereas others had no apparent effect.
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| 9. |
- Fernberg, Patrik, et al.
(author)
-
Damage detection in carbon fibre cross-ply laminates by aid of carbon nanotube doped resin
- 2008
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In: 13th European Conference on Composite Materials.
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Conference paper (peer-reviewed)abstract
- The possibility to use resistance variations of carbon nanotube (CNT) doped carbon fibre reinforced plastics (CFRP) to characterise the level of microstructural damage in the form of transverse cracking is experimentally investigated in the current work. The resistance of CNT-doped and unmodified CFRP was measured after they had been subjected to stepwise increased tensile loading. Both increase and decrease resistance was observed which made it difficult to make any firm statement that the changes we observed were due to damage. The conductivity along carbon fibres is dominating electrical conductivity of the studied cross-ply laminate. Any disturbance of conductive CNT based nanocomposite matrix by transverse cracks in 90-layer therefore caused too small changes of resistance to be measured with current experimental setup.
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| 10. |
- Fernberg, Patrik, et al.
(author)
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"Detect" - a new defect detection method and its use on sheet moulding compound (SMC) substrates
- 2008
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In: Composites for sustainable progress. - Stockholm.
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Conference paper (peer-reviewed)abstract
- A novel optical method for detection of surface porosities on SMC substrates is presented. Detection is facilitated by observation of how a liquid film on the surface evaporates. The method utilizes the fact that complete evaporation takes longer time in the pores than elsewhere. The rate of change of a laser speckle pattern gives a measure of the changes at the surface and indicates where pores causes prolonged evaporation. A pilot measurement unit was built that shows that the principle ideas of the system work. Attempts were made to develop the pilot unit so that it could provide quantitative numbers of actual defects on an SMC substrate. The results are encouraging in the sense that the unit can automatically identify areas with higher number of defects.
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| 11. |
- Fernberg, Patrik, et al.
(author)
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Determination of bridging laws for SMC materials from DENT tests
- 2003
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In: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 63:15, s. 2143-2153
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Journal article (peer-reviewed)abstract
- A bridging law (or cohesive zone law) approach is employed to evaluate the fracture of double edge notched tensile (DENT) specimen from two SMC materials (Std-SMC and Flex-SMC) with considerable difference in fracture characteristics. Linear- and non-linear FEM was used to separate volumetric body contributions and true crack opening from measured displacements (measured with extensometer) over the cracked region. We found that extrinsic non-linear material response gave a significant contribution to measured displacements. The paper also considers the influence of specimen dimensions on the characteristics of fracture. This is of great importance since stable crack growth is required in order to allow a complete determination of the bridging law in a single experiment. By applying corrections for volumetric displacements in the data reduction scheme we were able to estimate the bridging laws of the two SMCs respectively. They were found to be of decreasing nature and two distinct regions were identified. For small δ, a steeply decreasing part where debonding and fiber fracture are major micro-scale failure mechanism, is identified. At larger δ, a transition to a less steep bridging law response is observed. Pullout friction governs the bridging law at that stage. © 2003 Elsevier Ltd. All rights reserved.
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| 12. |
- Fernberg, Patrik, et al.
(author)
-
Development of novel high Tg polyimide-based composites. Part I : RTM processing properties
- 2018
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In: Journal of composite materials. - : SAGE Publications. - 0021-9983 .- 1530-793X. ; 52:2, s. 253-260
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Journal article (peer-reviewed)abstract
- In this study, an assessment of the composite processing-related properties of a newly developed 6-FDA-based phenylethynyl-terminated polyimide (available under the tradename NEXIMID®MHT-R) is presented. Processing schemes, used for preparing high quality carbon fibre-reinforced composites by the use of conventional resin transfer moulding are developed and presented. The influences of manufacturing parameters on glass transition temperature of the composites are presented. The results confirm that composites with exceptionally high Tg, in the range between 350 and 460℃ can be achieved. A manufacturing scheme that yields in composites with Tg of 370℃ is presented and proposed as a good candidate to serve as baseline for further studies.
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| 13. |
- Fernberg, Patrik
(author)
-
Fiber bridging concepts applied to short fiber composites
- 2000
-
Licentiate thesis (other academic/artistic)abstract
- Polymer composite materials are in wide-spread use in the transportation industry. In aerospace industry the use these materials are established while in automotive industry the interest is increasing. The attention of automotive industry is to a great deal focused on various kinds of molded composites such as glass mat reinforced thermoplastics (GMT) and sheet molding compound (SMC). Their interest is to a large extent driven by the possibility to manufacture components of complex geometry in a cost- efficient process with these materials. An increasing number of car and truck manufacturers are using SMC for external panels such as trunk covers, hoods, roofs and spoilers. A property of obvious importance for an external car- or truck-panel is its capacity to withstand impact. In this context, improved understanding of crack growth and toughening mechanisms of the material is of great interest. A major part of the work presented in this thesis is driven by an interest to increase the understanding of how material composition and microstructure of short fiber composites influence their overall fracture behaviour. In materials such as metals and unreinforced polymers, linear elastic fracture mechanics (LEFM) is widely used, often with great success, both in design and in development of new materials. Unfortunately, problems arise when LEFM is applied to short fiber composites. This is due to the large process zone that develops ahead of a crack in these materials. The fundamental assumption of LEFM, that the damage zone at the tip of the crack is small compared to crack length, is often violated in experiments. The presented thesis considers a different approach, in which the damage ahead of a crack tip is described by a bridging-law. By considering the bridging-law as the major failure property of the material, a coupling between mechanisms acting on a microscale and the macroscopic failure behaviour can be established. No such information can be obtained using a LEFM approach where the material behaviour is described in terms of a single value, the fracture toughness. Bridging-laws for three different short fiber composites are experimentally determined and presented in the first paper of the thesis. A matter of key importance for future work in this field is that there are methods available for experimental verification of the suggested fiber bridging approach. Optical strain field measurement methods are therefore very useful. The thesis contains a pilot study to evaluate the use of two recently developed optical methods , Stereoscopic Digital Speckle Photography (Stereo-DSP) and combined DSP-DSPI (Digital Speckle Pattern Interferometry), for measurements of fracture behaviour of notched short fiber composites. We found Stereo-DSP to be a versatile technique that can be used when knowledge of overall displacement fields is required. The combined technique can with advantage be used when detailed information about large deformation at small areas is of interest, e.g. the complex fiber bridging interaction at the crack tip of a short fiber composite. The last paper in the thesis presents a study where the influence of fiber surface treatment on transverse cracking in cross-ply laminates was investigated. In the case of tubes and pressure vessels, the formation of transverse cracks ultimately leads to leakage since cracks connect and form a path through the wall. In the presented study, our ambition was to investigate the influence of film former polymer on transverse cracking properties of cross-ply laminates.Both onset of transverse cracking and tendency for multiple crack development were strongly affected by the different film formers. The strong film former effect was proposed to be due to a combination of improved interfacial adhesion and the plasticizing effect from the film former on the interphase region. The thesis is composed by the following papers: Patrik Fernberg, Lars Berglund, Bridging law and toughness characterisation of CSM and SMC composite, to be submitted. Angelica Andersson, Patrik Fernberg, Mikael Sjödahl, Optical methods to study fracture of notched glass mat composites. Proceedings of the International Conference on trends in Optical Nondestructive Testing, Lugano, Switzerland, May 3-6, 2000 (in press). Patrik Fernberg, Lars Berglund, Effects of glass fiber size composition (film former type) on transverse cracking in cross-ply laminates. Accepted for publication in Composites, Part A.
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| 14. |
- Fernberg, Patrik
(author)
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Fibre reinforced polyimide composites and structures manufactured with resin transfer moulding - Overview of procedures and properties
- 2016
-
In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9783000533877
-
Conference paper (peer-reviewed)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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| 15. |
- Fernberg, Patrik, et al.
(author)
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Mechanisms controlling particle distribution in infusion molded composites
- 2006
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In: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 25:1, s. 59-70
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Journal article (peer-reviewed)abstract
- This article presents results from an experimental investigation in which two grades of aluminatrihydroxide (ATH) particles are added to liquid resin and used in infusion molding experiments. Based on the results, potential key mechanisms controlling resin flow and hence also the final particle distribution are proposed. A pore doublet model is proposed to explain the seemingly random spatial distribution of particle-dense regions within the final material. These dense regions are found within flow channels, at locations where local shear strain rates are low. This suggests that they are formed as a consequence of a Bingham type of viscosity behavior observed for the suspension and/or due to filtering of particles during fiber bundle impregnation. © 2006 SAGE Publications.
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| 16. |
- Fernberg, Patrik, et al.
(author)
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Piezoresistive performance of long-fiber composites with carbon nanotube doped matrix
- 2009
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In: Journal of Intelligent Materials Systems and Structures. - 1045-389X .- 1530-8138. ; 20:9, s. 1017-1023
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Journal article (peer-reviewed)abstract
- The electrical and mechanical properties of carbon nanotube (CNT) doped epoxy resin and composites based on this matrix were studied. The investigation was carried out on neat nanocomposites and on structural composites i.e., when the nanocomposite is used as matrix in composite materials reinforced with long continuous fibers. Tensile tests showed that CNT doped epoxy exhibited clear piezoresistive behavior. It was, however, also shown that geometrical changes of the specimen also contribute significantly to resistance changes during tensile loading. Particular effort was made to establish the relations between transverse cracking in glass fiber cross-ply laminates with nanotube doped matrix and changes of electrical resistance. It was shown that changes of electrical resistance during tensile loading of composites containing CNT doped matrix gives highly relevant information about the damage state of the material. In an unloaded state the resistance change is proportional to the relative change of stiffness. This work demonstrates that there are three different mechanisms, which contribute to changes of electrical resistance of a composite specimen subjected to tensile strain. These three mechanisms are: (a) geometrical changes of the specimen (b) piezoresistive material response, and (c) accumulation of micro-damage.
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| 17. |
- Fernberg, Patrik, et al.
(author)
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Piezoresistive performance of long fibre composites with carbon nanotube doped matrix
- 2007
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In: Proceedings of COMP07.
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Conference paper (peer-reviewed)abstract
- The electrical and mechanical properties of carbon nanotube doped epoxy resin and composites based on this matrix were studied. The investigation was carried out on neat nanocomposites and on structural composites i.e. when the nanocomposite is used as matrix in composite materials reinforced with long continuous fibers. Tensile tests showed that carbon nanotube (CNT) doped epoxy exhibited a clear piezoresistive behavior. It was however also shown that geometrical changes of the specimen also contribute significantly to resistance changes during tensile loading. Particular effort was made to establish the relations between transverse cracking in glass fibre cross-ply laminates with nanotube doped matrix and resistance changes. It was shown that resistance changes during tensile loading of composites containing CNT doped matrix gives highly relevant information about the damage state of the material. In an unloaded state the resistance change is proportional to the relative change of stiffness. This work demonstrates that there are three different mechanisms which contribute to resistance changes of a composite specimen subjected to tensile strain. These three mechanisms are: a) geometrical changes of the specimen b) piezoresistive material response and c) accumulation of micro-damage
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| 18. |
- Fernberg, Patrik, et al.
(author)
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Processing and properties of new polyimide composites with high temperature ability
- 2014
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In: 16th European Conference on Composite Materials, ECCM 2014. - : European Conference on Composite Materials, ECCM. - 9780000000002
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Conference paper (peer-reviewed)abstract
- The communication present results from work on development and evaluation of new polymeric carbon fiber composites with extreme temperature performance: Tg up to 360°C is targeted. The anticipated use of such composites is found in aeroengine-applications. In the work we are exploring a new and tailored phenyl ethynyl terminated imide (PETI) formulation, specially developed for the program. The formulation utilizes crosslinkers of the Nexamide" type (from Nexam Chemical AB, Sweden). The resins are initially evaluated from a processing and property perspective. Both DSC-measurements and rheology characterization are utilized in the development. Suitable RTM-processing schemes are investigated from a viscosity point of view. The schemes are used in the composite sample manufacturing. Besides a processing perspective the study also present the first results on physical behavior of the polymers and their composites.
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| 19. |
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| 20. |
- Fernberg, Patrik, et al.
(author)
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Strain and damage sensing during loading of carbon nanotube doped composites
- 2009
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In: ICCM International Conferences on Composite Materials. - London : IOM Communications.
-
Conference paper (peer-reviewed)abstract
- This work explores the possibility to use resistance changes in a carbon nanotube (CNT) doped composites to monitor deformations and damage. Most other studies in the field are done on simplified uniaxial loading whereas current work also evaluates the possibilities to monitor strain in more complex loading case, such as bending.
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| 21. |
- Fernberg, Patrik
(author)
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Toughness of short fiber composites : an approach based on crack-bridging
- 2002
-
Doctoral thesis (other academic/artistic)abstract
- The presented work considers how to properly characterize fracture properties of short fiber composites (SFC). Associated with fracture of SFC is the creation of a comparably widespread fracture process zone. This zone develops since a number of inelastic failure mechanisms (e.g. debonding, microcracking, fiber failure and fiber pull-out) take place in the vicinity of an advancing crack. In the present approach, a bridging law (or cohesive zone law) approach is adopted in order to characterize the fracture toughness of the material. Conventional fracture toughness measures, such as KIC were in most cases found not to be applicable. This was because fundamental small-scale yielding geometry requirements could not be fulfilled in experiments. The bridging law approach captures previously mentioned mechanisms in terms of a closure stress (bridging stress). This stress acts between two fictitious crack planes. The relation between crack opening displacement and bridging stress is governed by the bridging law. Parts of the presented work consider determination of bridging laws from experiments (Paper I and Paper III). Different experimental configurations, double cantilever beam (DCB) specimens loaded with pure moments and double edge notched tension (DENT) specimens, were used in the two studies. A main conclusion from Paper I is that the large differences in fracture characteristics between two sheet molding compound (SMC) composites could be explained on the basis of bridging laws and their influence on fracture energy. Similar observations were made in Paper III. In Paper III, it also was evident that the intrinsic non-linearity of bulk SMC material has to be considered separately in the data reduction of experimental results, in order to capture the bridging law. Bilinear approximations of decreasing bridging laws were obtained as a result from the study. A closer investigation on the mechanical behavior of SMC with varied composition was performed in Paper II. Various mechanical tests, including tension, compression, in situ studies, DCB and stiffness degradation measurements through quasi-static cyclic loading-unloading experiments, were employed. The purpose was to characterize and understand observed differences between conventional and toughened SMC with low density additives. The applicability of the proposed bridging law approach is confirmed by the work presented in Paper IV and Paper V. In these papers, the previously measured (Paper I and Paper III) bridging relations are used as a constitutive property in predictions of structural behavior of specimens with varied geometry. Paper IV considers that bridging law parameters can be used to predict and explain the change in notch-sensitivity observed on SMC DENT-specimens with varied geometry. A comparably simple analytical route (neglecting non-linear bulk behavior and shape of bridging law) is employed with satisfactory results. In Paper V, the use of the finite element method (FEM) in conjunction with measured bilinear bridging laws, allows reconstruction of experimentally measured compact tension (CT) specimen load vs. displacement curves with good accuracy. Three different CT specimen geometries are considered. Modeling and experimental results from Paper V also shows that compression failure often is of equal importance as tensile, in real structures and loading conditions.
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| 22. |
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| 23. |
- Fernberg, S. Patrik, et al.
(author)
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Influence of post-cure on carbon fibre polyimide composites with glass transition temperatures above 400ºC
- 2015
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In: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials.
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Conference paper (peer-reviewed)abstract
- The current communication present results from work on polymeric composites with extreme temperature performance. We are studying carbon fibre composites based on a new phenyl ethynyl terminated polyimide formulation NEXIMID® MHT-R (Nexam Chemicals AB, Sweden) based on hexafluoroisopropylidene bisphthalic dianhydride (6-FDA), 4-(Phenylethynyl)Phthalic Anhydride (4-PEPA) and ethynyl bis-phthalic anhydride (EBPA). This study in particular investigates how post-cure conditions such as time, temperature and atmosphere influence Tg of the composites. In addition to this we also trace and analyse the consequences of post-cure on weight loss and occurrence of micro-cracks. We are considering three different post-curing temperatures: 400°C, 420°C and 440°C in the study. Two different atmospheres, air and inert by nitrogen, were also investigated. In summary the results reveal that remarkably high Tg, up to around 460°C, is achieved with only very limited weight loss. It was also observed that some, but limited amounts of, micro-cracks are developed within the laminates due to the inevitable high thermal stresses generated upon cooling from cure temperature.
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| 24. |
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| 25. |
- Gonçalves Nunes, Stephanie, et al.
(author)
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SHIFT FACTOR DEPENDENCE ON PHYSICAL AGING AND TEMPERATURE FOR VISCOELASTIC RESPONSE OF POLYMERS
- 2022
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In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials. - Lausanne : Composite Construction Laboratory (CCLab), Ecole Polytechnique Federale de Lausanne (EPFL). - 9782970161400 ; , s. 431-438
-
Conference paper (peer-reviewed)abstract
- As polymeric resins are used as matrix in reinforced composites, understanding of their viscoelastic-viscoplastic response is critical for long-term performance design. However, during service life, thermosets are not in a thermodynamic equilibrium state, resulting in physical aging, which affects failure and viscoelastic (VE) properties, becoming a concern for industries. In this paper, an alternative methodology for testing and parameter determination for aging polymer, at different temperatures (TA) and times (tA), is proposed. The experimental data analysis was performed using a Schapery's type thermo-aging-rheologically simple VE model with constant coefficients in Prony series and the effect of temperature and aging included by two shift factors (aT, aA). Results showed that the shift factor can be presented as the product of shifts aT and aA. Furthermore, for short tA the change rate of the aA with tA does not depend on TA, whereas for long tA at high TA the rate increases.
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