| 1. |
- Auenhammer, Robert, 1991, et al.
(författare)
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Fibre orientation distribution function mapping for short fibre polymer composite components from low resolution/large volume X-ray computed tomography
- 2024
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Ingår i: Composites Part B: Engineering. - 1359-8368. ; 275
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Tidskriftsartikel (refereegranskat)abstract
- Short glass fibre injection moulded composites, used in interior and exterior automotive parts, are exposed to complex stress states, for example during a crash. As the fibre scale dominates the composite’s material properties, numerical models need to account for the local fibre orientation. In recent years, mould flow simulation results have been exploited to predict the fibre orientations for finite element models, albeit with limited accuracy. Alternatively, X-ray computed tomography can be used to directly image and analyse fibre orientations. Traditionally, achieving the necessary resolution to image individual fibres restricts the imaging to small regions of the component. However, this study takes advantage of recent advancements in imaging and image analysis to overcome this limitation. As a result, it introduces, for the first time, a reliable, fast, and automated fibre orientation mapping for a full component based on image analysis at the individual fibre level; even for cases where the pixel size is significantly larger than the fibre diameter. By scanning at lower resolutions, a drastically larger volume of interest can be achieved. The resulting fibre orientation analysis and mapping algorithm, based on X-ray computed tomography, is well matched to the level of information required for automotive crash modelling with a standard element-size of a few millimetres. The entire process, encompassing image acquisition, image analysis and fibre orientation mapping, can be directly integrated into an industrial full component application in a matter of hours.
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| 2. |
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| 3. |
- Bru, Thomas, et al.
(författare)
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Development of a test method for evaluating the crushing behaviour of unidirectional laminates
- 2017
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Ingår i: Journal of composite materials. - : SAGE Publications Ltd. - 0021-9983 .- 1530-793X. ; 51:29, s. 4041-4051
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Tidskriftsartikel (refereegranskat)abstract
- More fundamental test methods are needed to assist the development of physically based and truly predictive simulation tools for composite materials under crash conditions. In this paper, a unidirectional flat specimen that can be used to validate the predicted behaviour from a simulation to the physical behaviour in the experiment is developed. A systematic experimental investigation is conducted to evaluate the influence of the trigger geometry on the crushing response by selecting two trigger types and different trigger angles. For longitudinal crushing, the traditional bevel trigger leads to out-of-plane failure by splaying with a limited amount of in-plane fracture, while the proposed trigger achieves a high amount of compressive fragmentation failure. For transverse crushing, the symmetry of the proposed new trigger improves the specimen stability during the crushing process. It is also observed that the weft threads of the unidirectional fabric reinforcement used for the tests have a strong influence on the longitudinal crushing response. The boundary conditions of the test and the information on the specimen failure gleaned from video recordings and microscopic inspections are discussed in order to facilitate a future correlation with modelling results.
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| 4. |
- Larsson, Ragnar, 1960, et al.
(författare)
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Compressive failure and kink-band formation modeling
- 2023
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 99
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Tidskriftsartikel (refereegranskat)abstract
- To increase the use of polymeric structural composites, a major issue is to properly account for intra-laminar failure mechanisms, such as fiber kinking induced under compression. We propose a new continuum damage model that can predict the fiber kinking response at the ply level. The model is based on a previous structure tensor-based model for the response of UD-plies. A novel feature is that the compressive UD-ply response at the macroscale includes the effect of the fiber misalignment shaped as a kink-band that is resolved at the sub-scale. Concepts of computational homogenization are used to include the fiber-shear of the kink-band at the sub-scale. The model calibration is adapted to account for either kink-band formation or shear-splitting depending on the off-axis loading. Finally, the model is validated at the laminate level against experimental data for OHC-tests available in the literature. A good agreement is found for predicted strength values and observed fracture patterns of the laminates. The size effect experienced when different hole sizes are tested is also addressed.
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| 5. |
- Larsson, Ragnar, 1960, et al.
(författare)
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Damage growth and strain localization in compressive loaded fiber reinforced composites
- 2018
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Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 127, s. 77-90
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Tidskriftsartikel (refereegranskat)abstract
- To increase the use of polymeric structural composites, a major issue is to properly account for intra-laminar failure mechanisms, such as fiber kinking which is typically induced in compression. We propose a new set of continuum damage models that are able to predict fiber kinking response under compression. A structure tensor based formulation is established at the unidirectional ply level, where the elastic material response is governed by transverse isotropy. To consider geometrical effects in conjunction with fiber kinking instability, a continuum damage formulation at finite strain is developed. The fracture area progression includes a convective and a local damage production involving a finite progression speed. In this framework, two damage evolution models are considered; one non–local model including the gradient damage effect and a local one, without the gradient enhancement. The models are implemented in a FE–code and validated for a compression loaded specimen. The models are computationally robust and can predict the localized nature of fiber kinking. A thorough sensitivity study is presented to show how the different formulations influence the predicted responses.
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| 6. |
- Molker, Henrik, 1979, et al.
(författare)
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Efficient screening of composite structures using the extended 2D FEM approach in Meta together with a state of the art failure initiation criterion
- 2019
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Ingår i: Proceeding of the 8 Before Reality Conference.
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Konferensbidrag (refereegranskat)abstract
- In order to assess complex composite structures, the full 3D stress tensor is needed to ensure that all possible failure modes can be captured. Conventional shell elements only give accurate results for the in-plane stress components, while the out-of-plane components are neglected. The implementation of the Extended 2D FEM approach [1] into Metapost [2] makes it possible to get the full 3D stress tensor from second order shell elements. With the full stress tensor, state of the art set of failure initiation criteria can be used to evaluate the component. Two different cases are used to show the applicability of the procedure. The first example is a simply supported plate from the literature [3] is in particular used to demonstrate the visualisation capabilities in Metapost. The second example is a set-up used to measure the out-of-plane strength of composite materials [4], it is here analysed using both the Extended 2D FEM approach and a state of the art set of failure initiation criteria, LaRC05 [5].
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| 7. |
- Molker, Henrik, 1979, et al.
(författare)
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Framework for durability analysis of composite structures in the automotive industry
- 2019
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Ingår i: ICCM International Conferences on Composite Materials. ; 2019, s. 1712-1723
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Konferensbidrag (refereegranskat)abstract
- High performance composite materials possess properties that make them great candidates for reducing the weight of cars. However, analysis of large structures or assemblies with complex geometries made from fibre reinforced composite materials is a difficult task. Modern state of the art set of failure initiation criteria are based on the full stress state while efficient standard shell models cannot provide this. This either requires high fidelity models or the risk that potentially critical failure modes may be neglected due to assumptions made in the numerical models. In this paper, a framework for computationally efficient durability analysis of composite structures in automotive industry is presented.
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| 8. |
- Molker, Henrik, 1979, et al.
(författare)
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Hot spot Analysis in complex composite material structures
- 2019
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Ingår i: Composite Structures. - : Elsevier BV. - 0263-8223. ; 207, s. 776-786
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, failure initiation in composite structures due to high out-of-plane load components is predicted. The predictions are based on finite element models built with shell elements, intended for global models. The full 3D stress state is estimated through stress recovery by the extended 2D FEM approach. Failure initiation is predicted with state of the art failure criteria for transversely isotropic composite materials. The approach is validated for a range of geometries with different modelling resolutions. Finally, the methodology is verified on a complex composite structure. With the proposed approach, using shell elements, efficient modelling strategies of large structures can be pursued using hot spot analyses to identify critical locations.
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| 9. |
- Molker, Henrik, 1979, et al.
(författare)
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Industrial framework for identification and verification of hot-spots in automotive composite structures
- 2019
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Ingår i: SAE International Journal of Materials and Manufacturing. - : SAE International. - 1946-3987 .- 1946-3979. ; 12:2, s. 17-120
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Tidskriftsartikel (refereegranskat)abstract
- In this article, a framework for efficient strength analysis of large and complex automotive composite structures is presented. This article focuses on processes and methods that are compliant with common practice in the automotive industry. The proposed framework uses efficient shell models for identification of hot spots, automated remodelling and analysis of found hot spots with high-fidelity models and finally an automated way of post-processing the detailed models. The process is developed to allow verification of a large number of load cases in large models and still consider all potential failure modes. The process is focused on laminated composite primary structures. This article highlights the challenges and tools for setting up this framework.
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| 10. |
- Molker, Henrik, 1979, et al.
(författare)
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Verification of hot-spot in complex composite structures using detailed FEA
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Motivation Current shell-element based design tools used in the automotive industry do not allow for failure prediction in complex composite structures. An automated method to identify and analyse structural hot-spots for all potential failure modes is therefore needed.
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