| 1. |
- Larsson, Ragnar, 1960, et al.
(författare)
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A micromechanically based model for dynamic damage evolution in unidirectional composites
- 2022
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Ingår i: International Journal of Solids and Structures. - : Elsevier Ltd. - 0020-7683 .- 1879-2146. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses the micromechanically motivated, quasistatic to dynamic, failure response of fibre reinforced unidirectional composites at finite deformation. The model draws from computational homogenization, with a subscale represented by matrix and fibre constituents. Undamaged matrix response assumes isotropic viscoelasticity–viscoplasticity, whereas the fibre is transversely isotropic hyperelastic. Major novelties involve damage degradation of the matrix response, due to shear in compression based on a rate dependent damage evolution model, and the large deformation homogenization approach. The homogenized quasi-brittle damage induced failure is described by elastically stored isochoric energy and plastic work of the undamaged polymer, driving the evolution of damage. The developed model is implemented in ABAQUS/Explicit. Finite element validation is carried out for a set of off-axis experimental compression tests in the literature. Considering the unidirectional carbon–epoxy (IM7/8552) composite at different strain rates, it appears that the homogenized damage degraded response can represent the expected ductile failure of the composite at compressive loading with different off-axes. Favourable comparisons are made for the strain and fibre rotation distribution involving localized shear and fibre kinking. © 2021 The Authors
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| 2. |
- Larsson, Ragnar, 1960, et al.
(författare)
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A micromechanically based model for strain rate effects in unidirectional composites
- 2020
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Ingår i: Mechanics of materials. - : Elsevier B.V.. - 0167-6636 .- 1872-7743. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- This article addresses dynamic behaviour of fibre reinforced polymer composites in terms of a transversely isotropic viscoelastic-viscoplastic constitutive model established at the unidirectional ply level. The model captures the prelocalized response of the ply in terms of rate dependent elasticity and strength without damage. A major novelty is that the model draws from computational homogenization, with matrix and fibre materials as subscale constituents for a representative volume element of the ply. The micromechanics of the strain rate dependent polymer matrix is represented by an isotropic pressure sensitive viscoelastic-viscoplastic prototype model. For the fibre material, transverse elasticity is assumed. The constituents are homogenized via the fluctuating strain of the subscale, where a simple ansatz is applied to allow for constant stress in the plane transverse to the fibre orientation. Despite the relatively simple modelling assumptions for the constituents, the homogenized model compares favourably to experimental data for an epoxy/carbon fibre based composite, subjected to a variety of challenging uniaxial off-axis tests. The model response clearly reflects observed strain rate dependencies under both tensile and compressive loadings.
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| 3. |
- Singh, Vivekendra, 1987
(författare)
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3-D rate dependent micromechanical model for polymer composites
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibre reinforced polymeric composites are in high demand in automotive and aviation industries to improve fuel efficiency. However, the dynamic behaviour of composites is not very well understood. Furthermore, dynamic loading together with the anisotropic nature and complex nonlinear behaviour of polymer composites results in a complex failure behaviour. This behaviour is of significant importance to account for in automobile crash simulation and impact modeling of aircraft structures. In this thesis, a micromechanics based constitutive model is developed to predict the nonlinear behaviour and failure of unidirectional fibre reinforced polymer composites subjected to compressive dynamic loading. The carbon fibres are assumed to be hyperelastic transversely isotropic. For the matrix, a viscoelastic-viscoplastic constitutive model with hardening enhanced by continuum damage is advocated. A three parameter Maxwell model is used for the linear viscoelastic behaviour of the matrix. The nonlinear viscoplastic behaviour is introduced by coupling a Perzyna-type Bingham/Norton model with an intralaminar matrix continuum damage model. The pressure dependence of the onset of plastic yielding in matrix shear dominated response under compressive loading is also considered. The proposed model is formulated in a geometrically nonlinear description that separates the fibre and the matrix contributions. The model draws from computational homogenization of the unidirectional ply level response,with the matrix and the fibres as subscale constituents. A major feature is that the subscale constituents are coupled via isostrain and isostress assumptions parallel and transverse to the fibres, respectively. An improved isostress formulation is proposed to include in a better way longitudinal fibre shear response. The elastic response is improved by considering a non-uniform stress distribution in the matrix. For intralaminar damage growth, a continuum damage enhanced formulation of Lemaitre type is proposed. This model is combined with a surface based cohesive model that describes interlaminar delamination. Based on the model, the shear induced failure behaviour in compression of the composite material is characterized. Finite element simulations are conducted to validate observed rate dependent properties of off-axis loaded unidirectional composites and angle-ply laminates. The predictions of the finite element simulations are compared to published experimental results of different material systems under compression loading at different strain rates. The results obtained are in reasonable agreement with the experiments. Typical applications are carbon/epoxy composites, where unidirectional carbon fibres are embedded in a polymer matrix. In the future, the model is possible to extend to orthotropic plies and textile reinforced composites. The model is micromechanically motivated, hence it is also possible to extend for rate dependent fibres, e.g. glass fibres.
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| 4. |
- Singh, Vivekendra, et al.
(författare)
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A micromechanics based model for rate dependent compression loaded unidirectional composites
- 2023
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Ingår i: Composites Science And Technology. - : Elsevier Ltd. - 0266-3538 .- 1879-1050. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- Strain-rate effects in a unidirectional non-crimp fabric carbon/epoxy composite are addressed. To allow for kink-band formation including strain-rate effects and damage in such composites, the paper advances a recent model focused on compression loading at small off-axis angles. The model is based on computational homogenization with a subscale represented by matrix and fibre constituents at finite deformation. The fibre constituent is assumed to be elastic transversely isotropic and the matrix is viscoelastic–viscoplastic with damage degradation. Novel model improvements of special importance to small off-axis loading relate to the isostress formulation of the homogenized response in transverse shear. In this context, an enhanced homogenized elastic response is proposed based on Halpin–Tsai corrections to account for the nonuniform stress distribution on the microscale. The model captures the strongly rate sensitive kink-band formation due to localized matrix shearing and fibre rotation, confirming the experimentally observed increase in compressive strength for high strain rates. © 2022 The Author(s)
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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Singh, Vivekendra, 1987
(författare)
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Strain rate dependent material model for polymer composites
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We propose a micromechanical model that is able to predict the nonlinear behaviour and failure of unidirectional fibre reinforced polymer composites subjected to dynamic loading conditions. This novel material model is heterogeneous on the micro level and homogeneous on the ply level. The fibres are assumed to be hyperelastic transversely isotropic and the matrix obeys a hypoelastic viscoelastic/plastic constitutive model enhanced by a continuum damage model. To model the matrix, a Zener rheological model for the viscoelastic behaviour combined with a Bingham model for the viscoplastic behaviour is assumed. The proposed model is formulated in a framework that separates the fibre and the matrix contributions. Typical applications are unidirectional composites manufactured, for example, from unidirectional fibres embedded in a polymer matrix. Generally, the quasi-brittle compressive failure behaviour of composites happens during fairly large strains in the matrix. Therefore, a geometrically nonlinear description has been developed. Finally, using this model, we characterize the shear induced post-failure behaviour in compression of the composite material. Finite element simulations are conducted to predict the rate dependent properties of unidirectional polymer composites. The predictions of the finite element simulations are compared to published experimental results of an IM7/8552 material system under compression loading at different strain rates. The results are in a reasonably good agreement with the experiments.
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