| 1. |
- Arkitektur & teknik 2020/21, Årskurs 3, et al.
(författare)
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Resedagbok Schweiz augusti 2021
- 2021
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Arkitektur och tekniks årliga studieresa till Schweiz är på många sätt unik. Vi transporterar oss själva genom det vackra alplandskapet och besöker några av landets vackraste broar och byggnader. De vilda bergsmassiven och den förfinade byggnadskulturen väver sig in i varandra under hela vår magiska arkitektursafari. Resan i augusti 2021 blev nästan ett år försenad på grund av pandemin. I stället för en förberedelse av studierna i årskurs 3 blev det en festlig avslutning på kandidattiden på Chalmers. Vid sidan om våra gängse besöksmål, från Robert Maillarts och Jürg Conzetts konstruktioner till Le Corbusier och Peter Zumthors arkitektur, hade vi den här resan ett särskilt fokus på materialen lera, kalk, sten och cement, och på restaurering av broar och byggnader i dessa material.
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| 2. |
- 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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| 3. |
- Costa, Sergio, 1987, et al.
(författare)
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Improvement and validation of a physically based model for the shear and transverse crushing of orthotropic composites
- 2019
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Ingår i: Journal of Composite Materials. - : SAGE Publications. - 1530-793X .- 0021-9983. ; 53:12, s. 1681-1696
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Tidskriftsartikel (refereegranskat)abstract
- This paper details a complete crush model for composite materials with focus on shear dominated crushing under a three-dimensional stress state. The damage evolution laws and final failure strain conditions are based on data extracted from shear experiments. The main advantages of the current model include the following: no need to measure the fracture toughness in shear and transverse compression, mesh objectivity without the need for a regular mesh and finite element characteristic length, a pressure dependency of the nonlinear shear response, accounting for load reversal and some orthotropic effects (making the model suitable for noncrimp fabric composites). The model is validated against a range of relevant experiments, namely a through-the-thickness compression specimen and a flat crush coupon with the fibres oriented at 45° and 90° to the load. Damage growth mechanisms, orientation of the fracture plane, nonlinear evolution of Poisson's ratio and energy absorption are accurately predicted.
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| 4. |
- Fagerström, Martin, 1979, et al.
(författare)
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MODELLING AND TESTING THE CRASH BEHAVIOUR OF COMPOSITE VEHICLES COMPONENTS
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the current contribution we will present the latest developments in the project “Modelling crash behaviour in future lightweight composite vehicles – Step 2”, involving 11 Swedish partners. On the material modelling side, a fully three-dimensional model to describe fibre kinking has recently been developed. The model is physically based and considers the fibre rotation during kink-band formation under large deformations. The FE implementation of the model is straightforward which allows for easy implementation. The validation of the model for stiffness and strength shows good correlation with the experiments. The influence of initial misalignments on the stiffness is well captured, the strength defined at the onset of unstable fibre rotation, is well predicted, and, in addition, the crushing response shows very good agreement with experimental results in terms of morphology in the crushing zone, as well as in the load response. To allow for computational efficiency, we have also developed and implemented (as a user element in LS-DYNA) an adaptive modelling strategy which allows for laminates to be initially modelled with only one element over the thickness.The user element kinematics can be adaptively enriched by introducing new degrees of freedom during the simulation to allow for more accurate stress predictions in critical regions by introducing discrete material interfaces, and for the modelling of delamination crack growth by introducing discrete crack surfaces interconnected with a cohesive zone law. In this work, special care has been taken to develop a robust method for explicit crash analysis. In the element, we also able to consider the correct intralaminar fracture toughness regularisation for various spatial discretisations. To assess and validate the models developed in the project, we have also conducted a series of bending and crushing experiments on component level. Three-point bending tests (in total 45 beams) have been conducted for three different carbon-epoxy material systems (pre-preg and vacuum infused), two different span lengths and two different lay-ups at several impact speeds. Similarly, crushing tests have been conducted for the same material systems by crushing tubes (in total 35 tubes) at various angles, with two different lay-ups and at two different loading speeds (quasi-static and dynamic). We believe that these tests serve as a very strong basis for any crash model validation.
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| 5. |
- Olsson, Robin, 1958, et al.
(författare)
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Design, Manufacture, and Cryogenic Testing of a Linerless Composite Tank for Liquid Hydrogen
- 2024
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Ingår i: Applied Composite Materials. - 1573-4897 .- 0929-189X. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes design, manufacture, and testing of a linerless composite vessel for liquid hydrogen, having 0.3 m diameter and 0.9 m length. The vessel consists of a composite cylinder manufactured by wet filament winding of thin-ply composite bands, bonded to titanium end caps produced by additive manufacturing. The aim was to demonstrate the linerless design concept with a thin-ply composite for the cylinder. The investigation is limited to the internal pressure vessel, while real cryogenic tanks also involve an outer vessel containing vacuum for thermal insulation. Thermal stresses dominate during normal operation (4 bar) and the layup was selected for equal hoop strains in the composite cylinder and end caps during filling with liquid hydrogen. Two vessels were tested in 20 cycles, by filling and emptying with liquid nitrogen to 4 bar, without signs of damage or leakage. Subsequently, one vessel was tested until burst at almost 30 bar.
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| 6. |
- Singh, Vivekendra, 1987, et al.
(författare)
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Application of a Rate Dependent Model on a UD NCF Carbon/Epoxy Composite
- 2021
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Ingår i: PROCEEDINGS - 8th ECCOMAS THEMATIC CONFERENCE ON THE MECHANICAL RESPONSE OF COMPOSITES. - : CIMNE.
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Konferensbidrag (refereegranskat)abstract
- To support the modelling of composites under rapid transient loading, e.g. impact, crash, and vibrations, a computational multiscale constitutive model has been developed for the progressive failure of unidirectional carbon fibre composites. The model is computationally efficient and captures anticipated failure modes to an acceptable accuracy. Computational homogenization and micromechanics are utilized in the modelling at the ply scale. A major focus is to predict the strain rate dependent nonlinear constitutive behaviour of unidirectional composite plies. The fibres are assumed transversely isotropic, whereas the polymer is viscoelastic–viscoplastic, including a pressure-dependent strength. Degradation of the polymer matrix is described by a recently developed continuum damage mechanics approach. The model has been successfully implemented as a VUMAT subroutine in Abaqus/Explicit. Figure 1 shows FE simulation of strain localization as compared to experimental results of IM7/8552 in dynamic off-axis compression. Reasonable correlation was found between the measured and numerically predicted results. In the present paper the model is applied to simulate quasi-static and dynamic off-axis tension and compression experiments on composite coupons studied in two of our collaborative projects. The composite is a unidirectional (UD) carbon fibre non-crimp fabric (NCF) uniweave impregnated with LY556 epoxy, manufactured by Resin Transfer Moulding (RTM). The tests have been performed using a high-speed hydraulic test machine and a Split Hopkinson Bar (SHB) setup, involving strain rates of up to about 140 /s in tension and 1100 /s in compression.
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| 7. |
- Singh, Vivekendra, 1987, et al.
(författare)
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Effect of strain rate at compressive and tensile loading of unidirectional plies in structural composites
- 2019
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Ingår i: PROCEEDINGS - 7th ECCOMAS THEMATIC CONFERENCE ON THE MECHANICAL RESPONSE OF COMPOSITES. - : European Community on Computational Methods in Applied Science (ECCOMAS).
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Konferensbidrag (refereegranskat)abstract
- Fibre-reinforced polymer composites are widely used in structural applications due to their high specific stiffness and strength. In some applications the response of dynamically loaded composite components must be analysed. For example, in crash analyses of structural components, where very high loading rates occurs, the composite behaviour is not fully understood. For this, we present a novel transversely isotropic viscoelastic-viscoplastic constitutive model for a unidirectional carbon-epoxy composite. The model is micromechanically motivated so that the matrix and fibre materials of the composite are treated as micromechanical constituents at the ply scale. Based on the Hill-Mandel condition, the phases are homogenized via the macroscopic and fluctuating strain fields. To arrive at a simple but still representative model, a simplistic ansatz is applied to the structure of the fluctuating strains leading to a non-standard homogenized response of the composite. The model is applied to the non-linear rate dependent anisotropic ply behaviour under quasi-static and dynamic loading at different off-axis angles. For a simple viscoelastic-viscoplastic prototype for the rate dependent matrix response, there is a good correlation between measured and model response of the IM7-8552 material system in compression and tension.
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| 8. |
- Singh, Vivekendra, 1987, et al.
(författare)
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Rate dependent compressive failure and delamination growth in multidirectional composite laminates
- 2024
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Ingår i: Journal of Composite Materials. - : SAGE Publications Ltd. - 1530-793X .- 0021-9983. ; 58:3, s. 419-431
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Forskningsöversikt (refereegranskat)abstract
- A novel intralaminar model has, for the first time, been applied and validated for the rate-dependent failure of multidirectional carbon/epoxy laminates. Quasi-static compressive failure is evaluated by the growth of intralaminar ratedependent damage combined with the interaction of cohesive zones for interlaminar delamination. A special feature of the intralaminar model is the homogenised ply response, allowing simultaneous damage-degradation of the polymer matrix combined with the fibres. To model the observed quasi-brittle failure response of the plies under finite deformation, we have used a viscoelastic-viscoplastic matrix combined with damage and isotropic hardening behaviour. Elastic transverse isotropy is used to model the fibre reinforcement of the plies. Standard cohesive surfaces are used to model the initiation and propagation of delamination. Numerical simulations using ABAQUS/Explicit are performed to predict the growth and delamination of intralaminar damage under compression in different laminates with 56 plies of IM7/8552 carbon/epoxy. Predictions of stress versus strain and damage growth are shown to agree well with experimental results for a range of strain rates and stacking sequences.
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