| 1. |
- Bru, Thomas, 1990, et al.
(författare)
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Biaxial transverse compression testing for a fibre reinforced polymer material
- 2020
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Ingår i: ECCM 2018 - 18th European Conference on Composite Materials.
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Konferensbidrag (refereegranskat)abstract
- Unidirectional laminates have been tested under uniaxial transverse compression and under biaxial transverse compression. Failure occurred by shear in an inclined failure plane parallel to the fibres. The transverse shear response of the material on the failure plane was evaluated from the tests. In the biaxial tests, the failure load was considerably higher than in the uniaxial tests. For a given transverse shear strain the transverse shear stress was also higher in the case of biaxial compression. It is also shown that using waisted specimens instead of prismatic specimens does not seem to bring noticeable benefits for through-thickness uniaxial compression tests. The experimental results presented here are important input to the development and the validation of damage models of fibre reinforced polymer materials accounting for the matrix nonlinear response in shear and compression.
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| 2. |
- Bru, Thomas, et al.
(författare)
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Use of the Iosipescu test for the identification of shear damage evolution laws of an orthotropic composite
- 2017
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Ingår i: Composite structures. - : Elsevier BV. - 0263-8223 .- 1879-1085. ; 174, s. 319-328
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Tidskriftsartikel (refereegranskat)abstract
- The experimental evaluation of the shear response of fibre-reinforced plies is a requirement for accurate material models predicting progressive damage. In the first part of the paper, the quality of the Iosipescu shear test is investigated with full-field strain measurements and finite element analyses. In the second part, the in-plane and through-thickness shear response of an orthotropic carbon/epoxy uni-weave non-crimp fabric composite are compared, and the stress–strain curves used as input for two continuum damage mechanics models. Both models were able to predict accurately the nonlinear shear behaviour of the material. The model parameters and the damage evolution laws could easily be extracted from cyclic Iosipescu tests.
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| 3. |
- Bru, Thomas, et al.
(författare)
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Validation of a novel model for the compressive response of FRP:experiments with different fibre orientations
- 2017
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Konferensbidrag (refereegranskat)abstract
- Crush tests have been performed on flat unidirectional non-crimp fabric (NCF) coupons with differentfibre orientations as part of the validation of a ply-based damage model for crash. The fibre off-axisangle with respect to the crushing direction ranged from 0º to 90°. The results of the tests indicate thatthe crush stress remains unchanged for off-axis angles between 0° and 15°. The failure mode in thesespecimens was out-of-plane kinking. For 20° and 25° off-axis angles the crush stress dropped 20% andevidence of out-of-plane kinking were harder to find. For 45° off-axis angle a network of matrixcracks develops in the specimen and for 90° off-axis angle a brittle shear failure is observed. It issuggested that the out-of-plane kinking is promoted because of the natural waviness of NCF materialsand that the high in-plane shear stress generated from 20-25° off-axis loading results in a transitionfrom out-of-plane kinking to in-plane kinking. These hypotheses need, however, to be verified by anextended failure analysis of the crush specimens.
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| 4. |
- Bru, Thomas, 1990, et al.
(författare)
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Validation of a novel model for the compressive response of FRP: experiments with different fibre orientations
- 2017
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Ingår i: ICCM International Conferences on Composite Materials. ; 2017
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Konferensbidrag (refereegranskat)abstract
- Crush tests have been performed on flat unidirectional non-crimp fabric (NCF) coupons with different fibre orientations as part of the validation of a ply-based damage model for crash. The fibre off-axis angle with respect to the crushing direction ranged from 0º to 90°. The results of the tests indicate that the crush stress remains unchanged for off-axis angles between 0° and 15°. The failure mode in these specimens was out-of-plane kinking. For 20° and 25° off-axis angles the crush stress dropped 20% and evidence of out-of-plane kinking were harder to find. For 45° off-axis angle a network of matrix cracks develops in the specimen and for 90° off-axis angle a brittle shear failure is observed. It is suggested that the out-of-plane kinking is promoted because of the natural waviness of NCF materials and that the high in-plane shear stress generated from 20-25° off-axis loading results in a transition from out-of-plane kinking to in-plane kinking. These hypotheses need, however, to be verified by an extended failure analysis of the crush specimens.
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| 5. |
- Costa, Sergio, 1987, et al.
(författare)
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Validation of a novel model for the compressive response of FRP: Numerical simulation
- 2017
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Ingår i: ICCM International Conferences on Composite Materials. ; 2017-August
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Konferensbidrag (refereegranskat)abstract
- A progressive damage model for matrix compression is complemented with matrix tension in a physically based manner. The interaction of damage mechanisms undergoes a preliminary validation using single elements. The crushing response is validated with two different flat specimens with the fibres oriented transversely and at 45 degrees to the load. The model combines friction with damage to model the shear response accurately, which is necessary for reliable crush simulations. The behaviour in tension is history dependent, i.e. the model accounts for the stiffness reduction and strength to carry load in tension when previously damaged occurs in compression. The validation is performed against different tests showing the reliability of the model for different fibre orientation, specimen geometry and multiaxial loading scenarios. The crush response is well captured as well as the geometry and location of the different damage mechanisms.
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| 6. |
- Marklund, Erik, et al.
(författare)
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Modelling of textile composites with variable stiffness
- 2015
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Ingår i: ICCM International Conferences on Composite Materials. - : International Committee on Composite Materials.
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Konferensbidrag (refereegranskat)abstract
- Functional composite materials allowing stiffness reduction upon external stimulation are being developed within the European projects ENLIGHT and SafeEV. The aim is to develop material concepts to reduce the severity of injuries involving vulnerable road users. The current work addresses the development of textile composite material models aimed to be employed in a car front structure during static loading to low velocity impact situations. The modelled material is a non-crimp fabric reinforced thermoplastic (LPET) composite, in which the stiffness reduction relies on resistive heating of the carbon reinforcement upon application of electric current through the fibres. The stiffness reduction is achieved by a phase transformation of the thermoplastic matrix material. In this paper it is shown how a micro- and mesomodelling methodology in concert with only a few simple DMTA measurements can be utilized to model the macroscopic stiffness response of an impacted beam at various temperatures and loading rates. The material models used for simulation of the material show a good correlation with the experimental data despite the exclusion of a damage model and failing to account for the temperature variation within the specimens used in the experimental testing. The peak loads are well predicted.
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| 7. |
- Vyas, Gaurav, et al.
(författare)
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Toward lightweight smart automotive hood structures for head impact mitigation : Integration of active stiffness control composites
- 2019
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Ingår i: Journal of Intelligent Materials Systems and Structures. - : SAGE Publications Ltd. - 1045-389X .- 1530-8138. ; 31:1, s. 71-83
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Tidskriftsartikel (refereegranskat)abstract
- Recently, novel material concepts for high-performance carbon fiber–reinforced composites with active stiffness control were presented in the literature. Although this new class of intelligent, smart, and responsive materials has wide application potential, actual design concepts using active stiffness control are still rare. The integration of smart materials into conventional products often requires radically new design concepts. This communication presents an innovative automotive hood design concept, which integrates active stiffness control composites in order to achieve improved design performance trade-offs in terms of structural weight reduction and vulnerable road user safety. The integration of active stiffness control composites in the hood structure aims to enable active stiffness reduction of the hood or bonnet structure in order to reduce head impact injuries in case of a collision, while satisfying the structural stiffness requirements and lightweight objectives under normal operating conditions. The design concept is investigated using simulation-based evaluation of static, dynamic, and lightweight design criteria. The results are promising, and the presented concept design is a step toward the realization of lightweight smart hood structures for head impact mitigation. Several design features could also be of interest for the integration of active stiffness control composites, in other applications. © The Author(s) 2019.
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| 8. |
- Wysocki, Maciej, et al.
(författare)
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Constitutive models for transversely isotropic fibreprefrom in composite manufacturing
- 2016
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Ingår i: 13th International Conference on Flow Processes in Composite Materials (FPCM 13).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present contribution is an attempt to model a prepreg that is assumed to have approximatelystraight and parallel fibers which in an unloaded state has a transversely isotropicsymmetry about the fiber axis n. It is further assumed that the prepreg behaves elastic undera purely volumetric deformation, as well as under axial stretching in the fiber direction.A two-scale flow highly coupled to the fiber bed deformation is also being modelled usingporomechanics. The framework comprises a nonlinear compressible fiber network saturatedwith incompressible fluid phase.
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