Endre søk
Begrens søket
1 - 10 of 10
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Larberg, Ylva
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Deformability of unidirectional prepreg materials2009Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

     To reduce cost of structural composites the development of more efficient manufacturing methods is of great interest. Sheet forming of thermoset prepreg, also known as hot drape forming, has been a promising manufacturing method for decades. An automatic tape layer (ATL) can be used to perform the lay-up in an efficient way. The flatly stacked unidirectional prepreg forms a sheet to be formed over a given mould. Knowledge about the materials forming behaviour is important to reach the required shape without flaws, such as wrinkles.

    An experimental approach is developed to investigate the intra- (within the layer) and interply deformation. The intraply deformation properties are registered by the use of a bias-extension test and a digital image correlation (DIC) equipment. To measure the interlaminar (between the layers) friction in the prepreg/prepreg interface a specialized rig is designed and built.

    The two tested materials are Cycom® HTA/977-2 from Cytec and HexPly® T700/M21 from Hexel, which are examples of the second and third generation of carbon fibre/epoxy prepreg. Where M21 includes craze stoppers in form of thermoplastic particles, the 977-2 has the same function but in melted stage. These particles seem to influence both the intraply deformation modes and increase the level of friction between layers.

    The results from the bias-extension test was compared with the theory of pin-jointed net (PJN) and it was found that M21 behaves accordingly. The measured rotation for 977-2 is less than the theoretical, this due to slippage. The rate of deformation seems to have an influence not only on the load level, but also in the mode of deformation. Both for the interlaminar and intraply deformation the resistance to motion were much larger for M21 than 977-2.

  • 2.
    Larberg, Ylva
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Forming of stacked unidirectional prepreg materials2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    To reduce cost of structural composites, the development of more efficient manufacturing methods is of great interest. An automatic tape layer (ATL) can be used to perform the layup in an efficient way for flat sheets and the second step is by pressure forming the prepreg stack onto a given mould. Sheet forming of thermoset prepreg, also known as hot drape forming, is a promising manufacturing method when combined with automatically stacked laminates. To reach the desired shape, without flaws such as wrinkles and severe fibre angle deviation, knowledge about the forming behaviour of stacked material is important. A simulation of the forming can add to the understanding of mechanisms causing defects and also how to avoid them.

    A continuum mechanical finite element approach is used to model the forming of stacked unidirectional prepreg. This with the aim of finding mechanisms causing defects, such as out-of-plane wrinkling and in-plane waviness. Data from experimental characterisation of the materials are required for the constitutive material models. An experimental approach is used to investigate the intraply (within the layer) and interply (between the layers) deformation. The intraply deformation behaviour is investigated by a bias extension test, where resistance to deform and fibre rotation are registered. The interlaminar friction characteristics in the prepreg/prepreg interface are retrieved from tests performed with a specially designed rig. Measurements on the bending stiffness of the prepreg, both transverse to and in the fibre direction, are used in the out-of-plane model.

    Different aerospace-grade thermoset prepreg materials are tested and major differences in behaviour are found. Since epoxy is brittle, the resin is toughened by thermoplastics, for some materials in liquid phase and for others by solid particles. These particles seem to influence both the intraply deformation modes and increase the level of friction between layers.

    The experimental data from shear, friction and bending tests are used to calibrate the chosen material models. In-plane forming simulations confirm the affect stacking sequence have on the forming behaviour. Full-scale forming simulations on a joggles beam are performed with one of the tested material systems. Two different stacking sequences, with the same amount of fibre in the main directions, are analysed and compared. Both numerical and experimental forming shows that the coupling between layers, due to the interply friction, will affect the forming behaviour and in some cases create wrinkles. Wrinkles can develop both in the plane and out-of-plane, where only the in-plane waviness is present in the performed forming simulations.

  • 3.
    Larberg, Ylva R.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    In-plane properties of cross-plied unidirectional prepreg2007Inngår i: 16th International Conference on Composite Materials, ICCM-16, 2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sheet forming of thermoset composites is a promising method to achieve reduction in manufacturing time and therefore cost. The behaviour of weaves has been thoroughly investigated and the PJN assumption is widely used. Cross-plied UD prepreg may initially show similar behaviour to weaves; however, the complete deformation is more complex, including slippage. Thus, the forming of cross-plies can offer a possibility of increased drapability compared to woven fabrics, but imposes difficulties in predicting forming limits and final fibre angles. The work presented herein aims to characterise the in-plane properties of cross-plied UD prepreg with the bias extension test method. Understanding the deformation modes and its limits could reduce the number of iterations from idea to component in production. The forming of a preplied stack depends on many parameters. The study shows that a higher crosshead rate consequently results in a higher load response. In addition, the type of deformation mode changes due to both speed and temperature.

  • 4.
    Larberg, Ylva
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    In-plane deformation of multi-layered unidirectional thermoset prepreg - Modelling and experimental verification2014Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 56, s. 203-212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sheet forming of unidirectional prepregs is gaining increased interest as a cost efficient alternative manufacturing method. Its potential lies within the use of automatically and efficiently stacked flat prepregs, which in a second step can be formed. A successful forming requires understanding of the properties of the uncured material. Here, the in-plane deformation behaviour of two different unidirectional thermoset prepregs is investigated. Experimental measurements are performed, showing the importance of stacking sequence and its effect on the forming behaviour of stacked prepreg. Finite element models are developed, using material models calibrated from bias extension tests and interlaminar friction tests. The method developed can be used to predict the reaction force and fibre reorientation during in-plane forming of thermoset prepreg, for one of the considered material systems. Further, it enables prediction of the effect of stacking sequence, which is promising for future full-scale forming simulations.

  • 5.
    Larberg, Ylva
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    On the interply friction of different generations of carbon/epoxy prepreg systems2011Inngår i: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, nr 9, s. 1067-1074Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using pre-stacked material that is formed as a first step in the manufacturing process offers reduced process cycle time for production of complex structural components. The forming is achieved by forcing layers to deform by e.g. intraply deformation and interply slippage, where the latter is the scope of this study. The prepreg-prepreg friction is experimentally determined for four unidirectional carbon/epoxy prepreg systems. The materials differ considering volume fraction of fibres, fibre stiffness and phase of thermoplastic toughener (solved or particles). The study shows large individual differences between the tested materials, where the material systems with particle tougheners seem to obey a boundary lubrication friction, while the other materials show hydrodynamically dominated friction. A large difference between the high and low friction materials, almost a factor of 10, correlates to trends seen in the herein performed surface roughness measurements. Vacuum as well as autoclave consolidated materials are tested.

  • 6.
    Larberg, Ylva
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    On the interply friction of different generations of unidirectional prepreg materials2008Inngår i: Proceedings of 13th European Conference on Composite Materials (ECCM 13), 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    With the aim of reducing cost of prepreg composite components, manufacturing methods are developed and refined. An automatic tape laying machine can shorten the process cycle by stacking prepreg flat and thereafter allow for forming into desired shapes. Forming of stacked prepreg requires knowledge about the uncured properties of prepreg, such as viscosity of the matrix, intra- and interply deformation properties. This study focuses on the interply friction, i.e. the friction at the prepreg-prepreg interface, and how this affects the forming. The conclusions presented here show that the difference between prepreg material systems is significant. Further, it is concluded that the prepreg-prepreg friction is governed by a combination of Coulomb and hydrodynamic friction, where different mechanical phenomena dominate depending on the test conditions.

  • 7.
    Larberg, Ylva
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Norrby, Monica
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    On the in-plane deformability of cross-plied unidirectional prepreg2011Inngår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 46, nr 8, s. 929-939Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The work presented herein aims to characterise the in-plane properties of cross-plied unidirectional prepreg using the bias extension method. The study is focusing on carbon fibre/epoxy material systems and testing is performed at elevated temperatures to enhance formability. Using digital image correlation (DIC), the specimen deformation and fibre rotation is captured during tests. The study shows that the cross-plied unidirectional material deforms at different characteristic length scales as deformation continues: first seemingly continuous and later in form of bands. Further, the different type of prepreg materials investigated behaves differently; for one type the pin-jointed net theory fit well, enabling simple estimation of resulting fibre angle, while for another not. Different loading speed, temperatures and layup methods are investigated in order to pin-point its influence on the deformability.

  • 8.
    Larberg, Ylva
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Åkermo, Malin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Sjölander, Jens
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hallander, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Forming simulation of multi-layered unidirectional thermoset prepregsArtikkel i tidsskrift (Annet vitenskapelig)
  • 9.
    Åkermo, Malin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Larberg, Ylva
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hallander, Per
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Forming of advanced components out of pre-stacked crossplied UD prepreg2011Inngår i: 18th International Conference on Composite Materials, ICCM-18, 2011Konferansepaper (Fagfellevurdert)
  • 10.
    Åkermo, Malin
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Larberg, Ylva
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Sjölander, Jens
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hallnader, Per
    Saab.
    Influence of interply friction on the forming of stacked prepreg2013Inngår i: Proceedings of 19th International Conference on Composite Materials (ICCM19), Curran Associates, Inc., 2013, s. 919-928Konferansepaper (Fagfellevurdert)
1 - 10 of 10
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf