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- 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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| 2. |
- 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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| 3. |
- 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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