| 1. |
- Al-Ramahi, Nawres, 1980-, et al.
(author)
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Criteria for crack path deviation in adhesive layer of bi-material DCB specimen
- 2021
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 147
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Journal article (peer-reviewed)abstract
- An alternative to traditional fracture mechanics methodology to predict direction for crack propagation in the adhesive layer of bonded stiff materials is demonstrated. The approach is based on the analysis of the location of maximum of the hoop stress in relation to the existing crack tip. Such method is very convenient and fast as it does not require a lot of computational resources and is easy to implement compared to other known numerical methods dealing with similar problems (e.g. X-FEM). The method is validated by fracture mechanics approach using energy release rate to predict crack propagation direction. The verification is done by using bi-material DCB specimen with relatively thick adhesive layer as an example.After proving the applicability of the maximum hoop stress criterion the parametric study on factors affecting crack propagation in the adhesive layer is carried out. Such parameters as bending stiffness of beams, thickness of the adhesive layer, distance to the bond-line, length of the initial pre-crack are analyzed.
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| 2. |
- Arcieri, Nicolò, et al.
(author)
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Crack growth study of wood and transparent wood-polymer composite laminates by in-situ testing in weak TR-direction
- 2023
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 173
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Journal article (peer-reviewed)abstract
- TW transparent wood/polymer biocomposite laminates are of interest as multifunctional materials with good longitudinal modulus, tensile strength and optical transmittance. The effect of filling the pore space in wood with a polymer matrix on fracture toughness and crack growth is not well understood. Here, we carried out in-situ fracture tests on neat birch wood and laminates made of four layers of delignified birch veneers impregnated with poly(methyl methacrylate) (PMMA) and investigated crack growth in the tangential-radial (TR) fracture system. Fracture toughness KIc and JIc at crack initiation were estimated, including FEM analysis. SEM microscopy revealed that cracks primarily propagate along the ray cells, but cell wall peeling and separation between the PMMA and wood phases also take place. A combination of in-situ tests and strain field measured by digital image correlation (DIC) showed twice as long fracture process zone of TW laminates compared with neat birch.
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| 3. |
- Chinga-Carrasco, Gary, et al.
(author)
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Side streams from flooring laminate production – Characterisation and recycling in biocomposite formulations for injection moulding
- 2022
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 153
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Journal article (peer-reviewed)abstract
- Side streams were collected from three locations in a flooring factory and their suitability in biocomposite formulations was assessed. The side stream (S3) that contained mainly residues from high-density fibreboards (HDF) was selected for further material testing. The effect of different fractions of S3, thermomechanical pulp (TMP) fibres and polylactic acid (PLA) were assessed in terms of their mechanical, melt flow and thermal properties. A biocomposite made from PLA, 20 wt% TMP fibres and 10 wt% S3 revealed a significant increase in modulus (5800 MPa), compared to the neat PLA (3598 MPa), and a similar melt-flow index (MFI = 4.5). The tensile strength was however somewhat reduced from 66 to 58 MPa. Importantly, numerical modelling and simulations were applied to demonstrate that building a model chair out of biocomposite can potentially reduce the material volume by 12% while maintaining similar load bearing capacity, compared to neat PLA. © 2021 The Author(s)
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| 4. |
- Costa, Sergio, et al.
(author)
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A unified physically-based finite deformation model for damage growth in composites
- 2022
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 161
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Journal article (peer-reviewed)abstract
- Two 3D homogenized models for damage growth in a unidirectional (UD) composite ply are simplified and merged into a unified model. The fibre kinking behaviour is based on fibre kinking theory handled in a finite deformation framework. The nonlinear shear behaviour is pressure dependent and is modelled by combining damage and friction on the fracture plane. Fibre kinking growth and transverse behaviour are modelled with a single damage variable. This allows both modes to occur simultaneously and mutually influence each other in an efficient and physically-based way. For validation the model is tested against micro-mechanical Finite Element (FE) simulations under pure longitudinal compression and influenced by shear. The results show nearly perfect agreement for stiffness, strength and crushing stress. The model validation is performed against two different components under three-point bending and a quasi-static crash scenario. Both simulation show good correlation with experiments, validating thus the present unified model. © 2022 The Author(s)
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| 5. |
- Dutta, Abhik, et al.
(author)
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Interply friction between unidirectional carbon/epoxy prepreg plies : Influence of fibre orientation
- 2023
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 166, s. 107375-
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Journal article (peer-reviewed)abstract
- This work investigates the role of fibre orientation on interply friction. Interply friction tests were performed on a novel snap-cure unidirectional (UD) carbon/epoxy prepreg for five fibre orientations over a broad range of normal pressures and sliding speeds. The test method used closely mimicked the actual processing condition of the prepreg prior to forming including consolidation of the interface. The results show that fibre orientation of the prepreg has a large influence on interply friction. In fact, interply friction for various fibre orientation combinations varies substantially both in magnitude and behaviour of the curve. Further, the range of this variation is dependent on processing conditions such as consolidation, normal pressure and sliding speed. These findings make a strong case for including direction dependent friction models in forming simulations and presents opportunities to tailor the laminate stacking sequence for better forming outcomes.
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| 6. |
- Ehman, Nanci, et al.
(author)
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Chemical compatibility between poly(ethylene) and cellulose nanofibers from kraft pulps containing varying amounts of lignin : An aqueous acetylation strategy and its effect on biocomposite properties
- 2024
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 184
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Journal article (peer-reviewed)abstract
- Previous efforts to acetylate fibers and cellulose nanofibers (CNFs) are methodologically demanding and usually based on organic solvents catalyzed by acids. Hence, the purpose of this study was to introduce an improved method to acetylate unbleached (2 % and 5 % lignin) and bleached fibers (<1% lignin), and the corresponding CNFs, using a one-pot strategy in an aqueous alkaline medium. The lignin content in the pulp fibers (5 %) influenced the morphology of the corresponding fibrillated materials, i.e., increased secondary fines (92 %) and mean fibril area (36 %). Additionally, the pulps and CNFs (0 % and 5 % lignin content) were acetylated and compounded with high-density poly(ethylene) (HDPE). Acetylation improved the mechanical strength from 19 MPa (HDPE) to 30–40 MPa (when including acetylated fibers or CNFs). Finally, acetylation revealed a positive effect on melt-flow-index and elongation at break, and the water absorption of injection molded specimens was reduced to roughly 0.6 % after 10 days of testing.
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| 7. |
- Gebart, Rikard
(author)
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Thermal runaway criterion for thick polymer composites
- 2024
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 182
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Journal article (peer-reviewed)abstract
- An analytical solution has been developed for the curing of thick polymer composite laminates that shows how the temperature profile responds to arbitrary changes to the material properties and process parameters and that curing with slow reactions and a low exotherm temperature is impossible if the Damköhler number is above a well-defined limit. The thermal runaway criterion can be recast as a criterion for the maximum allowable thickness of the laminate. The thermal runaway criterion was found to agree well with some results for thick laminates from the literature, but the peak temperature in the laminate was underpredicted for stable conditions. The model has a constant that can be adjusted to improve the peak temperature prediction, but more validation data is needed before the model can be optimized to simultaneously predict the peak temperature and thermal runaway with high accuracy.
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| 8. |
- Grankäll, Tommy, 1977-, et al.
(author)
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Moisture In Composite Cure Tools
- 2022
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 158
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Journal article (peer-reviewed)abstract
- Composite cure tools are preferable to metal tools regarding in-plane thermal expansion, quicker part processing using the tool and potentially lower cost. However, durability is often questioned and moisture in the tool is often assumed to be a negative factor. In order to increase understanding of the durability of composite cure tools sorption and swelling, two high performance prepreg tooling materials using Benzoxazine and Bismaleimide resin reinforced with carbon fibre fabric were measured over a six-month period. An Epoxy-based prepreg was also studied. The experimentally acquired material characteristics were used in simulation of water content and swelling in a composite cure tool during use. It was concluded that gradient moisture content and swelling will always be present which presents a considerably different shape distortion compared to isotropic water content. The data presented may contribute to informed selection of composite cure tool material and facilitate optimisation of tool maintenance.
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| 9. |
- Huang, Tianxiao, et al.
(author)
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Effect of cellulose oxalate as cellulosic reinforcement in ternary composites of polypropylene/maleated polypropylene/cellulose
- 2020
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 134
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Journal article (peer-reviewed)abstract
- Micro-sized cellulosic materials are promising reinforcements for thermoplastic composites. In this study, a new type of microcellulose - cellulose oxalate (COX) was used as reinforcement for polypropylene-based composites and its reinforcing effect was evaluated. COX and microcrystalline cellulose (MCC), which was used for comparison, were subjected to ball milling process for different times to obtain milled cellulose powders. Ternary composites consisting of 60 wt% polypropylene (PP) as the matrix, 10 wt% maleic anhydride grafted polypropylene (MAPP) as the coupling agent and 30 wt% milled or non-milled cellulose powder as reinforcement were prepared by melt-extrusion and injection molding. Tensile test results showed that 1 h milled COX-containing composite exhibited the best tensile properties (e.g., tensile strength and Young's modulus are 16.1% and 106.0% respectively higher than those of neat PP) and MCC generally exhibited a poorer reinforcing effect than COX with same milling time.
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| 10. |
- Hörberg, Erik, 1977-, et al.
(author)
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Moisture effect on shape distortions of curved quasi-isotropic prepreg composite laminates
- 2021
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In: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 145
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Journal article (peer-reviewed)abstract
- The influence from moisture on shape distortion of curved thermoset composite laminates is investigated experimentally. The objects of study are L-shaped carbon/epoxy specimens with a quasi-isotropic layup and a thickness varying between 1 and 12 mm. The effect on the shape distortion is quantified by means of angle measurements vs. accelerated moisture uptake utilising a climate chamber at 90 ?C and 95% relative humidity. The results show a strong dependence from laminate moisture content ? the effect is in fact in the same order of magnitude as the spring-in from thermal and chemical shrinkage during curing. Moisture does thus not only affect the spring-in angle but also has to be taken into consideration, and be carefully controlled, when assessing shape distortions due to other parameters. Finally, a closed form expression based on the experimental results is presented, predicting how the bracket angle varies with the specimen thickness and moisture content.
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