| 1. |
- Byström, Johan, et al.
(författare)
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An evaluation of different models for prediction of elastic properties of woven composites
- 2000
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Ingår i: Composites Part B. - 1359-8368 .- 1879-1069. ; 31:1, s. 7-20
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Tidskriftsartikel (refereegranskat)abstract
- A critical analysis of two simple and convenient analytical models for calculation of elastic properties of woven fabric composites is performed. Predictions of these models are compared with results obtained using the method of reiterated homogenization and with experimental data for plain weave glass fiber and carbon fiber polyester composites. Three different scales are identified in the analysis. The first scale predictions, which are the tow properties (obtained by applying Hashin's concentric cylinder model, the Halpin-Tsai expressions or mathematical homogenization technique), are the most critical because they form the input information for woven composite modeling. It appears that the uncertainty in this information causes larger differences in predictions than the deviations between models of different degree of accuracy. This fact sets limits on the required accuracy of the models. Model comparisons reveal that the woven compoiste model based on isostrain assumption in the compoiste plane and isostress assumption for out-of-plane components is in very good agreement with both experimental data and the reiterated homogenization method, whereas the modified mosaic parallel model fails to describe composites with large interlaced regions.
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| 2. |
- Edgren, FRedrik, et al.
(författare)
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Formation of damage and its effects on non-crimp fabric reinforced composites loaded in tension
- 2004
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Ingår i: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 64:5, s. 675-692
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Tidskriftsartikel (refereegranskat)abstract
- Non-crimp fabric (NCF) composites, manufactured by resin infusion techniques are one of the most promising next generation composite materials. They offer large potential for application in primary structures as they give excellent performance at low production costs. However, before NCF composites will be efficiently used in design, detailed understanding of governing micro mechanisms must be accumulated and described by predictive models. In the present study, NCF cross-ply laminates have been tested in tension. Intralaminar cracks caused in the 90° fibre bundle layers and their effect on laminate mechanical properties have been monitored. Occurrence of 'novel' type of cracks propagating in the load direction (longitudinal cracks) is explained by a thorough FE analysis using an Representative Volume Element (RVE) approach, revealing stress concentrations caused by 0° fibre bundle waviness. Effects of damage on mechanical properties are modelled using modified micro mechanical models developed for analysis of conventional laminated composites. The analysis reveals mechanical degradation to be ruled by the crack opening displacement (COD). However, unlike traditional composites, transverse cracks do not generally extend through the entire thickness of the 90° layer, but are rather contained in single fibre bundles, limiting the COD. © 2003 Elsevier Ltd. All rights reserved.
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| 3. |
- Eitzenberger, Johannes, et al.
(författare)
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Debond crack growth in fatigue along fiber in UD composite with broken fibers
- 2008
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Ingår i: 13th European Conference on Composite Materials.
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Konferensbidrag (refereegranskat)abstract
- Assuming that Paris law is applicable for individual debond crack propagation along the fiber/matrix interface, the related strain energy release rate in a unidirectional composite is analysed using FEM and also using simple analytical considerations based on self-similar debond crack propagation. Model with axial symmetry consisting of three concentric cylinders is used: partially debonded broken fiber in the middle is surrounded by matrix cylinder which is embedded in a large block of effective composite with properties calculated using rule of mixtures and Halpin-Tsai expressions. It is shown for pure mechanical loading that the fiber elastic properties have a huge effect on the released energy, whereas fiber content in the composite in the considered realistic range has effect only for short debonds. The interaction between debonds approaching from both fiber fragment ends is investigated and related to material properties and geometrical parameters. It is shown that the self-similar debond propagation model gives slightly overestimated values of the strain energy release rate which may be related to interaction effects not included in the analytical model.
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| 4. |
- Farge, L., et al.
(författare)
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Optically measured full-field displacements on the edge of a cracked composite laminate
- 2008
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 39:8, s. 1245-1252
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Tidskriftsartikel (refereegranskat)abstract
- The main objectives of this study are to visualize the displacement field on the edge of a [0, 554, -554]s GF/EP laminate specimen with multiple transverse cracks and to analyze the crack opening displacement dependence on the applied mechanical load. The specimen full-field displacement measurement was carried out using ESPI (Electronic Speckle Pattern Interferometry) and phase-shifting. ESPI is an optical technique that provides the displacement for every point on a surface. The measurement resolution is roughly 20 nm. The displacement measurement is along the tensile axis and takes place on the specimen edge. Using the displacement map, it is possible to obtain the displacement profiles along the tensile-axis. The different profiles were drawn along the specimen edge at several distances from the mid-plane corresponding to the different plies. Studies of the displacement discontinuities make it possible to carry out a measurement of the crack opening displacements corresponding to the cracks in the measurement field. The experimental results are in a good agreement with idealized straight crack model in low stress region and much larger in the high stress region, which is attributed to development of local inter-ply delaminations.
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| 5. |
- Farge, L., et al.
(författare)
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Study of the displacement field on the edge of cracked laminated composites
- 2008
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Ingår i: 13th European Conference on Composite Materials.
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Konferensbidrag (refereegranskat)abstract
- Using Electronic Speckle Pattern Interferometry (ESPI), the full-field displacement measurement was obtained on the edge of a cracked laminate subjected to a tensile loading. The displacement jumps corresponding to cracks are clearly visible and can be used to determine the Crack Opening Displacement (COD) values along the cracks. The main objective of this study is to determine if the application of high load may have modified the existing cracks and consequently changed the COD dependence on the applied stress. The profile of the opening was also studied.
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| 6. |
- Giannadakis, Konstantinos, et al.
(författare)
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Effect of thermal aging and fatigue on failure resistance of aerospace composite materials
- 2009
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Ingår i: 5th International EEIGM/AMASE/FORGEMAT Conference on Advanced Materials Research. - Bristol : IOP Publishing Ltd.
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Konferensbidrag (refereegranskat)abstract
- Exposing a laminate structure to thermal cycles and to temperatures close to the curing temperature, followed by mechanical fatigue, cause interlaminar and intralaminar cracks leading to degradation of the mechanical properties. The effect of thermal and mechanical fatigue, as well as thermal aging, on carbon fiber composite laminate structures is under study in the present paper.
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| 7. |
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| 8. |
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| 9. |
- Graciani, Enrique, et al.
(författare)
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Numerical analysis of debond propagation in the single fibre fragmentation test
- 2009
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 69:15-16, s. 2514-2520
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Tidskriftsartikel (refereegranskat)abstract
- A numerical analysis, using the Boundary Element Method, of the stress state within the specimen in the Single Fibre Fragmentation Test is presented first. Thermal residual stresses and fibre-matrix interfacial friction along the debonding crack faces have been considered in the study. Special attention has been paid to the axial stresses along the fibre and the interfacial tractions and relative displacements in the neighbourhood closest to the debonding crack tips. In order to analyze the debond propagation, the associated Energy Release Rate has been evaluated from the near-tip elastic solution. Numerical results show that both the effects of thermal residual stresses and of fibre-matrix interfacial friction are opposed to the debond propagation. Additionally, the effect of the debond propagation on the load transfer through the interface has been studied, showing that fibre-matrix interfacial friction has a weak influence on the distance needed to re-establish the nominal axial load within the fragment.
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| 10. |
- Graciani, Enrique, et al.
(författare)
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Single fiber fragmentation test : a BEM analysis
- 2003
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Ingår i: A collection of technical papers. - Reston, Va : American Institute of Aeronautics and Astronautics, AIAA. - 1563476258 ; , s. 988-997
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Konferensbidrag (refereegranskat)abstract
- Numerical analysis was performed with the aid of the Boundary Element Method (BEM). Contact conditions were taken into account using a weak formulation of the equilibrium compatibility equations along the interface of the solids. Comparison of the different kinds of failure was made in terms of the energy release rate
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