| 1. |
- Frishfelds, Vilnis, et al.
(author)
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Automatic recognition and analysis of scanned non-crimp fabrics for calculation of their fluid flow permeability
- 2007
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In: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 26:3, s. 285-296
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Journal article (peer-reviewed)abstract
- Automatic recognition of scanned images of distorted bi-axial fiber bundle arrangements is considered in order to obtain the overall permeability of the formed fiber network. Scanned images are pre-processed with color normalization followed by usage of a threshold to find the pixels belonging to the bundles, the threads keeping the bundles together, and the distinct gaps formed between the bundles. Since the scanned images virtually have a perfect grayscale, the intensity can be treated as a corresponding signal of the image. Next the regular character of the fiber network is investigated using Fourier analysis on the fiber bundles as well as on the threads. The direction, position, and spatial separation of the fiber bundle and the threads are obtained in this way. In order to recognize the bottom fiber bundle layer a fine structure technique is used. Small clusters falsely identified as belonging to the bottom bundle layer are removed by application of a threshold to the perimeter of the cluster. The gaps in the top bundle layer are identified more clearly in this way. Next, a local Fourier analysis is applied to obtain the local distortion of the bundle and the thread structure yielding the characteristic distribution of the gaps between the bundles. Finally the distribution of the width of the threads is obtained by simply identifying the minimal distance between the sides of the threads.
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| 2. |
- Frishfelds, Vilnis, et al.
(author)
-
Lattice-gas analysis of fluid front in non-crimp fabrics
- 2008
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In: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19). - : University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science.
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Conference paper (peer-reviewed)abstract
- The fluid flow front during impregnation of non-crimp fabrics is considered. Irregularities in fiber bundle architecture lead to generation of bubbles at the fluid front. The velocity of this interface is highly influenced by capillary forces mainly caused by the small fibers inside the bundles. In order to derive the shapes of the fluid front, a lattice-gas model has been applied. First, the macroscopic properties of the solved gas in the fluid are discussed. Next, the bubble inclusions are analyzed as to fluid-liquid interface position and concentrations of minor component in each phase. Finally, the flow in the interior of the fiber bundles is scrutinized, where the viscous stresses are considered, as well.
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| 3. |
- Frishfelds, Vilnis, et al.
(author)
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Permeability of clustered fibre networks : modelling of unit cell
- 2003
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In: Mechanics of composite materials. - 0191-5665 .- 1573-8922. ; 39:3, s. 265-272
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Journal article (peer-reviewed)abstract
- The paper is focused on estimating the permeability of a clustered fiber network by variational methods. First, a laminar flow in ducts is considered by using polynomial trial functions. Then, a longitudinal flow through a square array is described by expanding the flow-rate field in trigonometric and Laurent series. Finally, a formal scheme for estimating the longitudinal permeability in a cluster with an irregular distribution of fibers is given. The irregular distribution is modeled by setting an individual effective radius for each fiber and then letting this fiber reach its minimum gravitational energy. The results obtained here form a basis for future predictions of the permeability of fibrous reinforcements.
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| 4. |
- Johansson, Simon, et al.
(author)
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Characteristics of flow and temperature distribution in a Ruthner process
- 2010
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In: Proceedings of Modeling for Material Processing, 6th International Scientific Colloquium. - : University of Latvia Press. ; , s. 317-322
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Conference paper (peer-reviewed)abstract
- This study is devoted to CFD modelling of the gas flow and particle dynamics inside the reactor of a furnace used for regeneration of hydrochloric acid from iron chloride - a rest product from the pickling process in the steel industry. The understanding of the dynamics inside the reactor has shown to be of great importance in order to optimize the process. So far the process has been a black box, where only the inflow conditions are known together with the quality of the final product. In this work the gas flow is resolved together with the thermal distribution and the particle trajectory for the injected acid molecules.
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| 5. |
- Lundström, Staffan, et al.
(author)
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A statistical approach to permeability of clustered fibre reinforcements
- 2004
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In: Journal of composite materials. - : SAGE Publications. - 0021-9983 .- 1530-793X. ; 38:13, s. 1137-1149
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Journal article (peer-reviewed)abstract
- The focus is set on mesoscale modelling of permeability of real fabrics used in composite manufacturing. Of particular interest is the effect of expected perturbations from perfect geometries, such as fibre bundle crimp, on the permeability. To start with, variational methods are used to calculate the perme-ability of individual gaps between fibre bundles. Based on this study a network of unit cells is formed enabling studies of two- and three-dimensional flow through the structure. From such an analysis the overall permeability of an arbitrary distribution of unit cell permeabilities can be calculated. Here random and controlled distributions are simulated. The former is an approximate representation of a continuous strand mat and the latter may describe Non-Crimp Fabrics. The result is that for random distributions, the permeability decreases with the maximum variation in unit cell while for a controlled permeability distribution the overall permeability can as well increase as decrease depending on the type of perturbation. In both cases the type of flow: one-, two- or three-dimensional strongly influence on the quantitative result. Hence, for the type of fabrics studied, it is necessary to model the full 3D-flow through to get a correct permeability value.
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| 6. |
- Lundström, Staffan, et al.
(author)
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Bubble formation and motion in non-crimp fabrics with perturbed bundle geometry
- 2010
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 41:1, s. 83-92
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Journal article (peer-reviewed)abstract
- The motion of the liquid front during impregnation of non-crimp fabrics has been considered by using Sethian's level set method. Particular attention is put on the creation of bubbles at the liquid front and a virtual 3D model mimicking biaxial fabrics has been built for this purpose. The saturated fluid flow is governed by the Navier-Stokes Equations and Darcy law, while capillary pressure has been accounted for at the liquid flow front and continuity maintained. The influence of perturbation in the bundle geometry has been investigated. Local correlations of the dimensions of neighbouring gaps formed between the bundles are of paramount importance. Focus is on inter-bundle bubbles. An existing model for bubble dynamics is used based on a probabilistic approach for bubbles moving, splitting, merging, and dissolving. The same approach was used for intra-bundle bubbles, the difference being that their motion appears to be much slower. The obtained void fractions of inter-bundle bubbles at different vacuum levels applied at the liquid flow front are compared to those from real mouldings with a high degree of conformity.
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| 7. |
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| 8. |
- Lundström, Staffan, et al.
(author)
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Wetting dynamics in multiscale porous media : porous pore-doublet model, experiment and theory
- 2008
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In: AIChE Journal. - : Wiley. - 0001-1541 .- 1547-5905. ; 54:2, s. 372-380
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Journal article (peer-reviewed)abstract
- Fiber reinforced composite materials often consist of fibers gathered in bundles. Thus, during manufacturing, a liquid resin impregnates a multiscale porous medium. For wetting systems the capillary pressure jump becomes much higher in the smaller pores, i.e., within the bundles, and in addition to any applied pressure gradient there will be a local driving pressure gradient between the small- and large-scale areas. Such gradients will influence mechanisms, such as void formation and particle filtration. Hence, it is of interest to clarify the mechanisms for the wetting in general and the influence from the detailed geometry of the fiber network in particular. In this article, a porous pore-doublet model is studied in order to determine if an overflow of liquid can explain a leading flow in the smaller capillaries, and at which conditions it takes place. Experiments, as well as theoretical calculations on this generic geometry show that the leading front can be in the smaller capillary, as well as in the larger one. The outcome is dependent on the actual permeability of the porous material being a parameter that determines to what extent the larger capillary feeds the smaller one.
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| 9. |
- Mannberg, Peter, et al.
(author)
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Moisture absorption and degradation of Glass fiber/Vinylester composites
- 2010
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In: Selected papers of the International Scientific Colloquium "Modelling for Material Processing". - Salaspils : University of Latvia Press. ; , s. 157-162
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Conference paper (peer-reviewed)abstract
- Vacuum Infusion is a closed mould manufacturing process that can replace open mould processes. To improve resin flow it is common to add flow enhancement layers to the reinforcement stack. This paper is aimed to analyze water uptake in these materials and its effect on mechanical performance. Ageing data for 3000 h in 90ºC water are presented for GF NCF/VE composite without flow layer and three composites with it. Tensile tests demonstrate degradation of mechanical properties and increasing viscoelastic and viscoplastic strains in wet composites.
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| 10. |
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