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1.	Asp, Leif, et al. (författare) An experimental investigation of the influence of delamination growth on the residual strength of impacted laminates 2001 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 32:9, s. 1229-1235 Tidskriftsartikel (refereegranskat)abstract This study concerns an experimental investigation to establish data for validation of residual strength models for impacted composite panels. The work focuses on compression tests of panels with embedded artificial delaminations at various depths. Accompanying tests on undamaged and impact-damaged panels are reported and the relevance of the tests on artificially delaminated panels is assessed. In the experiments both the artificially delaminated and the impacted plates failed by delamination growth. Consequently, the same mechanism governed failure in the two cases. Hence, the artificially delaminated plate test is reliable for validation of methods developed for analysis of the residual strength of impact-damaged panels. However, for impacted plates, the load at global plate buckling was consistently 10% lower than that of the artificially delaminated plates and 20% lower than that of the undamaged plates. Hence, conservative prediction of the global buckling load of an impacted composite panel require s methods that consider influence of stiffness reduction of the damaged zone. © 2001 Elsevier Science Ltd. All rights reserved.
2.	Dweib, M.A., et al. (författare) Fibre structure and anisotropy of glass reinforced thermoplastics 2000 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier Science Ltd, Exeter, United Kingdom. - 1359-835X .- 1878-5840. ; 31:3, s. 235-244 Tidskriftsartikel (refereegranskat)abstract The fibre structure and orientation distribution of two commercially available glass mat thermoplastics reinforced by continuous glass fibre was studied to investigate the anisotropic behaviour under compression moulding and mechanical loading, and to investigate the influence of the fibre structure and orientation on the anisotropic behaviour. Circular samples were deformed into ellipses when moulded, due to the anisotropic fibre orientation. The fibre content and orientation were examined in different locations of the elliptically deformed specimens. X-ray pictures were taken of the material in order to develop images of the fibres, before and after compression moulding. In another procedure, the matrix was burned off and the fibre network structures were studied in each case. A CCD camera was used to scan the fibres as digital images to measure the orientation distribution functions of the fibres. The fibre orientation measuring process was facilitated by subroutines implemented in the source code of the public domain NIH-image analysis software using simulated Fraunhofer diffraction.
3.	Fernberg, S. P., et al. (författare) Effects of glass fiber size composition (film-former type) on transverse cracking in cross-ply laminates 2000 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 31:10, s. 1083-1090 Tidskriftsartikel (refereegranskat)abstract Transverse cracking is an important phenomenon in the context of fluid leakage in pipes and pressure vessels. Multiple transverse cracking in [0/90](S) glass-fiber-reinforced vinylester and epoxy laminates with six different fiber surface treatments (size) is examined. Film-former composition is the variable since this component can be easily changed also in commercial size formulations. The influence of the film-former polymer on transverse cracking is significant in epoxy laminates and very strong in vinylester laminates. Both onset of transverse cracking and slope of crack density vs, strain are influenced. Remarkably low crack densities were observed in some vinylester laminates. Micromechanisms of cracking are interpreted. Correlation is established between transverse cracking behavior and interfacial shear strength measured by single fragmentation tests. The strong film-former effect is proposed to be due to a combination of improved interfacial adhesion and the plasticizing effect from the film-former on the interphase region.
4.	Gamstedt, E. Kristofer, et al. (författare) Synthesis of unsaturated polyesters for improved interfacial strength in carbon fibre composites 2002 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 33:9, s. 1239-1252 Tidskriftsartikel (refereegranskat)abstract Carbon fibres are gaining use as reinforcement in glass fibre/polyester composites for increased stiffness as a hybrid composite. The mechanics and chemistry of the carbon fibre-polyester interface should be addressed to achieve an improvement also in fatigue performance and off-axis strength. To make better use of the versatility of unsaturated polyesters in a carbon fibre composite, a set of unsaturated polyester resins have been synthesized with different ratios of maleic anhydride, o-phthalic anhydride and 1,2-propylene glycol as precursors. The effective interfacial strength was determined by micro-Raman spectroscopy of a single-fibre composite tested in tension. The interfacial shear strength with untreated carbon fibres increased with increasing degree of unsaturation of the polyester, which is controlled by the relative amount of maleic anhydride. This can be explained by a contribution of chemical bonding of the double bonds in the polymer to the functional groups of the carbon fibre surface.
5.	Holmberg, J.A., et al. (författare) Manufacturing and performance of RTM U-beams 1997 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 28:6, s. 513-521 Tidskriftsartikel (refereegranskat)abstract Geometrical limitations and robustness of resin transfer moulding were investigated for single curved laminates. The design of experiments approach was used to determine how the out of plane tensile strength is affected by variations in performing method, radius, fibre content and vacuum assistance. U-beams with an inner radius of 0.8 mm were manufactured and demonstrated good mechanical performance. The strength of these beams was in fact less sensitive to defects than the strength of beams with a 5 mm radius. Different preforming methods can have a strong influence on beam strength due to effects on the void content in the finished laminates. The particular preforming problems encountered are described and possible solutions are suggested and tested. For example utilisation of vacuum assistance during mould filling reduces void content, which in turn tends to reduce the sensitivity of the beam strength to other defects such as wrinkling.
6.	Holmberg, J.A., et al. (författare) Micromechanisms of delamination failure in RTM U-beams 1997 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 28:8, s. 709-717 Tidskriftsartikel (refereegranskat)abstract In a previous study, resin transfer moulded U-beams were subjected to opening tensile loads applied to the flanges. The failure behaviour was sensitive to the void content of the material. In the present study, we use optical microscopy of polished edges to observe mechanisms of failure in-situ as delaminations develop in the beam radius. Descriptions of these failure mechanisms are presented. Voids were found to facilitate the growth phase of the delamination process in the beam radius. The mechanisms described will be used in a forthcoming stress analysis to explain the experimentally observed failure behaviour of beams with different radii and void contents.
7.	Joffe, Roberts, et al. (författare) Strength and adhesion characteristics of elementary flax fibres with different surface treatments 2003 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 34:7, s. 603-612 Tidskriftsartikel (refereegranskat)abstract It is known that the best flax fibres can compete in terms of mechanical properties with glass fibres. However, during the manufacturing process flax fibres are often damaged, and hence, the properties can be lowered. Furthermore, these properties change from batch to batch (depending on the time and place of harvest), which means that they are somewhat unpredictable. The most affected fibre property is strength, which can vary in very wide interval due to defects introduced by the manufacturing process. Therefore, there is a need for a simple but reliable testing procedure that allows the estimation of the strength of flax fibres, so called quality control. Regarding the final goal, that is the development of natural fibre composites, another crucial property is the fibre/matrix adhesion. The objective of this study is to investigate the possibility to use the single fibre fragmentation test to characterize strength distribution of flax fibres and to evaluate the adhesion. Untreated flax fibres and fibres coated by a special surface treatment are used. Fragmentation tests are performed on flax fibres embedded in thermoset, vinylester and polyester, resins. Results show that there is a definite improvement in interfacial strength when a fibre surface treatment is applied. Fibre strength distribution is obtained from SFFT and compared with limited results available from single flax fibre tests.
8.	Lundström, Staffan, et al. (författare) In-plane permeability measurements : a Nordic round-robin study 2000 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 31:1, s. 29-43 Tidskriftsartikel (refereegranskat)abstract Three methods to measure the in-plane permeability are compared. The methods are based on the wetting and saturated parallel flow techniques and the wetting radial flow technique. It is found that the stability of all three methods is very good. The best repeatability in the results is obtained with the wetting parallel flow technique. A main drawback of this method is, however, that the samples are not saturated hence, the saturated parallel flow method is suggested for continued evaluation. The standard deviation from repeatable measurements of this method is 14 and 20% for the two fabrics tested. By a round-robin comparison at three laboratories it is found that the reproducibility of the saturated parallel flow technique is in the same range as the repeatability of the method. Furthermore, it is shown that the liquid tested and the pressure applied have very small influence on the results. It is clear that most of the scatter is due to the sample preparation and variations in the material. Accordingly, a continued work should be concentrated on improvements of the sample preparation, and development of methods to reduce the influence, from small errors, in sample preparation on the results.
9.	Lundström, Staffan (författare) Measurement of void collapse during resin transfer moulding 1997 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 28:3, s. 201-214 Tidskriftsartikel (refereegranskat)abstract This paper considers the dissolution of cylindrical voids trapped between fibres during the resin transfer moulding process. To study the behaviour of the tiny voids, a system is used which consists of a transparent mould loaded with a glass fibre reinforcement. The mould is placed under a microscope and a small area of the preform is monitored during the injection of a vinylester resin. The length of the voids decreases at a relatively fast rate and they disappear in the order of minutes due to diffusion. The experimental results are rationalized through a theory showing how certain parameters influence the rate of dissolution. The investigation shows the significance of degassing the resin before injection. This is especially important when low pressures are utilized during injection.
10.	Lundström, Staffan (författare) Permeability of non-crimp stitched fabrics 2000 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 31:12, s. 1345-1353 Tidskriftsartikel (refereegranskat)abstract Non-crimp stitched fabrics are becoming increasingly popular as reinforcing materials in high-performance composites due to their high mechanical properties. Hence, it is of interest to investigate the processability of this type of fabrics. Focus is here set on the permeability of the fabrics. The methods of this investigation are: (i) a theoretical analysis; (ii) microscopic studies of the geometry of the fabrics and (iii) measurements of the permeability. From the experiments, it is found that only small variations of the geometry change the permeability up to three times. Furthermore, the simple model proposed works surprisingly well in certain cases, while in others it fails to predict the permeability. From the experimental results and a comparison between the model and the experiments, some guidelines are presented how to design a high-permeable fabric.
11.	Melin, L. Gunnar, et al. (författare) A study of the displacement field around embedded fibre optic sensors 1999 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 30:11, s. 1267-1275 Tidskriftsartikel (refereegranskat)abstract Deformation fields around optical fibres embedded in carbon fibre/epoxy composite specimens have been measured using moiré interferometry. The inclusion of the optical fibre resulted in large strain gradients. Calculated displacements from finite element analysis were compared to the experimental results. The numerical analysis showed that the displacement field on the specimen surface is smoothed out through the moiré grating thickness, an effect which is most pronounced at the material interfaces. With this influence taken into consideration a reasonable good quantitative agreement between the experiments and the finite element analysis was obtained. The finite element analysis also showed that the grating stiffness did not affect the measured displacements as long as the grating had a lower stiffness than the specimen
12.	Melin, L. Gunnar, et al. (författare) Effects of strain rate on transverse tension properties of a carbon/epoxy composite: studied by moiré photography 1999 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 30:3, s. 305-316 Tidskriftsartikel (refereegranskat)abstract The dependence on strain rate of the mechanical properties of a high performance carbon fibre/epoxy composite loaded in transverse tension has been investigated. Dog-bone shaped specimens have been tested in quasi-static and dynamic loading conditions. The dynamic tests were performed in a split Hopkinson bar at strain rates between 100 and 800 s-1. A moiré technique combined with high-speed photography, at framing rates of 0.25-1 MHz, was used for extraction of the local strain fields. The transverse mechanical properties were found to have weak or no dependence on strain rate. The average transverse modulus did not depend on strain rate, whereas the strain to and stress at failure were found to increase slightly with increased strain rate. For these dog-bone shaped specimens the strain evaluated by conventional Hopkinson bar technique was found to underestimate the true strain field measured by moiré technique. Finally, the moiré technique facilitated crack-propagation monitoring in real time. Crack speeds up to 2300 m s-1 were measured at transverse crack propagation.
13.	Nilsson, G., et al. (författare) Strain field inhomogeneities and stiffness changes in GMT containing voids 2002 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 33:1, s. 75-85 Tidskriftsartikel (refereegranskat)abstract During compression moulding of glass mat thermoplastics (GMT), voids may form. However, it is not clear whether voids are as critical to mechanical performance in GMT as in thermoset composites. The present investigation also considers the general problem of damage mechanisms in GMT. Conventional tensile tests, acoustic emission, a stiffness degradation test and a speckle technique for strain field measurements are used as well as optical microscopy of polished cross-sections. The void content (up to 5%) does not significantly influence the strength or stiffness degradation process. The reason is the large inhomogeneity of the strain fields in GMT. Failure occurs in locally soft regions and void effects are of secondary importance. Details of the failure process are discussed, emphasising the large local strains in matrix-rich regions.
14.	Oldenbo, M., et al. (författare) Mechanical behaviour of SMC composites with toughening and low density additives 2003 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 34:9, s. 875-885 Tidskriftsartikel (refereegranskat)abstract A new type of SMC material (Flex-SMC) developed for automotive exterior body panels has been investigated. Flex-SMC contains hollow glass micro-spheres and thermoplastic toughening additives. A conventional SMC (Std-SMC) was used as a reference material. Materials were tested in monotonic tension and compression. Stiffness degradation with strain as well as fracture toughness was determined. In situ SEM was used to study failure mechanisms. Flex-SMC has a density almost 20% lower than Std-SMC and has higher impact resistance. The damage threshold strain of the Flex-SMCs is higher than for Std-SMC. Flex-SMCs have more than twice the fracture toughness of Std-SMC. The major reason identified is that Flex-SMCs shows extensive fibre pullout.
15.	Oldenbo, M., et al. (författare) Mechanical behaviour of SMC composites with toughening and low density additives 2003 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 34:9, s. 875-885 Tidskriftsartikel (refereegranskat)abstract A new type of SMC material (Flex-SMC) developed for automotive exterior body panels has been investigated. Flex-SMC contains hollow glass micro-spheres and thermoplastic toughening additives. A conventional SMC (Std-SMC) was used as a reference material. Materials were tested in monotonic tension and compression. Stiffness degradation with strain as well as fracture toughness was determined. In situ SEM was used to study failure mechanisms. Flex-SMC has a density almost 20% lower than Std-SMC and has higher impact resistance. The damage threshold strain of the Flex-SMCs is higher than for Std-SMC. Flex-SMCs have more than twice the fracture toughness of Std-SMC. The major reason identified is that Flex-SMCs shows extensive fibre pullout. © 2003 Elsevier Ltd. All rights reserved.
16.	Sjögren, A., et al. (författare) Effects of fibre coating (size) on properties of glass fibre/vinyl ester composites 1999 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 30:8, s. 1009-1015 Tidskriftsartikel (refereegranskat)abstract Effects of fibre coating (size) on transverse cracking has been investigated. Two glass fibre/vinyl ester model composites were studied, denoted CA and NoCA and based on different size compositions. Various single fibre tests were not able to quantify the interfacial failure of CA as the interface never failed. The CA size consisted of a film former and a methacrylsilane-coupling agent whereas the NoCA size did not contain any coupling agent. The study reveals limitations with single fibre composite tests for fibre/matrix combinations with high interfacial toughness. Cross-ply laminates based on NoCA demonstrated significant inferior transverse cracking toughness as compared with CA laminates. Composites based on commercially sized glass fibre were also investigated and they performed almost as poorly as the NoCA material, demonstrating large potential for improvement in commercial composites. Results further indicate that the remarkable transverse cracking toughness of the CA material stems partly from strong fibre/matrix adhesion but also from high ductility of the matrix region close to the fibre surface.
17.	Sjögren, A., et al. (författare) Experimental determination of elastic properties of impact damage in carbon fibre/epoxy laminates 2001 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 32:9, s. 1237-1242 Tidskriftsartikel (refereegranskat)abstract This paper describes an investigation of in-plane elastic properties of impact damaged regions in composite laminates. Quasi-isotropic carbon fibre/epoxy laminates were impacted and the impact damage examined by ultrasonic C-scanning, optical microscopy and thermal deplying. After impact damage observations, specimens were cut from the laminates and tested in tension and compression. The elastic modulus of the impact damage was, in both tension and compression, mainly controlled by the amount of fibre breakage. Interestingly, layers with broken fibres could sustain some load in compression, which led to higher elastic modulus in compression than in tension. The effect of delaminations on the elastic modulus was quite small in both tension and compression. The through-the-thickness variation of in-plane stiffness was studied by successively removing plies. The variation in stiffness was negligible, probably as a result of the very uniform distribution of delaminations and fibre breakage through the thickness of the laminates.
18.	Svanberg, Magnus, et al. (författare) An experimental investigation on mechanisms for manufacturing induced shape distortions in homogeneous and balanced laminates 2001 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 32:6, s. 827-838 Tidskriftsartikel (refereegranskat)abstract Manufacturing induced shape distortions is a common problem for composite manufacturers. For single curved geometries the phenomenon is known as spring-in. Today a lot of effort is spent to develop modelling tools for prediction of spring-in and shape distortions in general. However, good experimental data is rare in the literature and there are no established constitutive models capable of account for the effect from different cure schedules. In this paper, experimental data for spring-in of glass-fibre epoxy composites are presented. The experiments were performed with angle brackets manufactured by RTM, in a steel mould with accurate temperature control. Different in-mould temperature have been used to point out and separate different mechanisms responsible for spring-in. © 2001 Elsevier Science Ltd.
19.	Varna, Janis, et al. (författare) Transverse single-fibre test for interfacial debonding in composites : 2. Modelling 1997 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 28:4, s. 317-326 Tidskriftsartikel (refereegranskat)abstract A method was developed for determination of interfacial toughness parameters from a new transverse single-fibre test. In previous work, experimental procedures were developed. Interfacial debond growth in the arc and fibre direction was measured for transparent matrix polymer composites. In the present study, an earlier stress analysis by Toya was modified and combined with a critical energy release rate criterion, taking mode mixity effects into account. The developed model was used to determine interfacial toughness parameters. The model was able to describe and explain the main experimental observations of the debonding process. Treatment of the contact problem present for large debond angles is of interest for future work
20.	Zhang, H., et al. (författare) Transverse single-fibre test for interfacial debonding in composites : 1. Experimental observations 1997 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 28:4, s. 309-315 Tidskriftsartikel (refereegranskat)abstract Micromechanical methods for studies of interfacial debonding in fibre composites provide the possibility of comparing different materials. Since most previous composite studies focus on shear loading of the fibre matrix interface, the debonding process in single-fibre glass fibre/epoxy composites was studied in situ by optical microscopy during transverse tensile loading. Specimens had cylindrical debond cracks of known dimensions created in fragmentation tests. Mechanisms for debond growth were described for two materials where the difference was in glass fibre surface treatment. As the debonds reached a critical size in the arc (circumferential) direction, unstable debond growth occurred in the fibre direction. The debond angle at instability was fairly similar for both materials, although the material based on glass fibre treated with a coupling agent reached twice as high stress before instability.
21.	Al-Ramahi, Nawres, 1980-, et al. (författare) Criteria for crack path deviation in adhesive layer of bi-material DCB specimen 2021 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 147 Tidskriftsartikel (refereegranskat)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.
22.	Andersons, J., et al. (författare) Estimation of the tensile strength of an oriented flax fiber-reinforced polymer composite 2011 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 42:9, s. 1229-1235 Tidskriftsartikel (refereegranskat)abstract Unidirectional orientation of natural fibers in a polymer composite ensures the highest efficiency of reinforcement. Flax fiber reinforcement is discontinuous due to limited fiber length and heterogeneous due to the presence of elementary fibers and their bundles. In order to assess the upper limit of tensile strength of such slightly misoriented, nominally UD natural fiber composite, a statistical strength model of continuous UD fiber reinforced composites is applied. It is found that the experimental strength of UD flax composites, produced from rovings or manually aligned fibers, approaches the theoretical limit only at relatively low fiber volume fraction ca. 0.2, being markedly below it at higher fiber content.
23.	Andrieux, Sebastien, et al. (författare) Monodisperse highly ordered chitosan/cellulose nanocomposite foams 2019 Ingår i: Composites. Part A, Applied science and manufacturing. - : ELSEVIER SCI LTD. - 1359-835X .- 1878-5840. ; 125 Tidskriftsartikel (refereegranskat)abstract In solid foams, most physical properties are determined by the pore size and shape distributions and the organisation of the pores. For this reason, it is important to control the structure of porous materials. We recently tackled this issue with the help of microfluidic-aided foam templating, which allowed us to generate mono-disperse and highly ordered chitosan foams. However, the properties of foams also depend on the properties of the pore wall constituents. In case of chitosan-based foams, the foams have poor absolute mechanical properties, simply due to the fact that the solubility of chitosan in water is very low, so that the relative density of the freeze-dried foams becomes very small. Drawing inspiration from the field of nanocomposites, we incorporated cellulose nanofibres into the foamed chitosan solutions, with a view to strengthening the pore walls in the foam and thus the mechanical properties of the final foam. We report here how the cellulose nanofibres affect the structure of both the liquid foam template and the solid foam. The resulting nanocomposite foams have improved mechanical properties, which, however, are not proportional to the amount of cellulose nanofibres in the composites. One reason for this observation is the disturbance of the porous structure of the solid foams by the cellulose nanofibres.
24.	Ansari, Farhan, et al. (författare) Cellulose nanofiber network for moisture stable, strong and ductile biocomposites and increased epoxy curing rate 2014 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 63, s. 35-44 Tidskriftsartikel (refereegranskat)abstract Nanocomposites with high volume fractions (15-50 vol%) of nanofibrillated cellulose (NFC) were prepared by impregnation of a wet porous NFC network with acetone/epoxy/amine solution. Infrared spectroscopy studies revealed a significant increase in curing rate of epoxy (EP) in the presence of NFC. The NFC provided extremely efficient reinforcement (at 15 vol%: 3-fold increase in stiffness and strength to 5.9 GPa and 109 MPa, respectively), and ductility was preserved. Besides, the glass transition temperature increased with increasing NFC content (from 68 degrees C in neat epoxy to 86 degrees C in 50 vol% composite). Most interestingly, the moisture sorption values were low and even comparable to neat epoxy for the 15 vol% NFC/EP. This material did not change mechanical properties at increased relative humidity (90% RH). Thus, NFC/EP provides a unique combination of high strength, modulus, ductility, and moisture stability for a cellulose-based biocomposite. Effects from nanostructural and interfacial tailoring are discussed.
25.	Ansari, Farhan, et al. (författare) Experimental evaluation of anisotropy in injection molded polypropylene/wood fiber biocomposites 2017 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 96, s. 147-154 Tidskriftsartikel (refereegranskat)abstract Although the anisotropy of wood fibers is reasonably well established, the anisotropy of injection molded wood fiber composites is not well understood. This work focuses on chemo-thermomechanical pulp (CTMP) reinforced polypropylene (PP) composites. A kinetic mixer (Gelimat) is used for compounding CTMP/PP composites, followed by injection molding. Effects from processing induced orientation on mechanical properties are investigated. For this purpose, a film gate mold was designed to inject composites in the shape of plates so that specimens in different directions to the flow could be evaluated. Observations from tensile tests were complemented by performing flexural tests (in different directions) on discs cut from the injected plates. SEM was used to qualitatively observe the fiber orientation in the composites. At high fiber content, both modulus and tensile strength could differ by as much as 40% along the flow and transverse to the flow. The fiber orientation was strongly increased at the highest fiber content, as concluded from theoretical analysis.
26.	Ansari, Farhan, et al. (författare) Hierarchical wood cellulose fiber/epoxy biocomposites : Materials design of fiber porosity and nanostructure 2015 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 74, s. 60-68 Tidskriftsartikel (refereegranskat)abstract Delignified chemical wood pulp fibers can be designed to have a controlled structure of cellulose fibril aggregates to serve as porous templates in biocomposites with unique properties. The potential of these fibers as reinforcement for an epoxy matrix (EP) was investigated in this work. Networks of porous wood fibers were impregnated with monomeric epoxy and cured. Microscopy images from ultramicrotomed cross sections and tensile fractured surfaces were used to study the distribution of matrix inside and around the fibers - at two different length scales. Mechanical characterization at different relative humidity showed much improved mechanical properties of biocomposites based on epoxy-impregnated fibers and they were rather insensitive to surrounding humidity. Furthermore, the mechanical properties of cellulose-fiber biocomposites were compared with those of cellulose-nanofibril (CNF) composites; strong similarities were found between the two materials. The reasons for this, some limitations and the role of specific surface area of the fiber are discussed.
27.	Arcieri, Nicolò, et al. (författare) Crack growth study of wood and transparent wood-polymer composite laminates by in-situ testing in weak TR-direction 2023 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 173 Tidskriftsartikel (refereegranskat)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.
28.	Baghaei, Behnaz, et al. (författare) Manufacture and characterisation of thermoplastic composites made from PLA/hemp co-wrapped hybrid yarn prepregs 2013 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 50, s. 93-101 Tidskriftsartikel (refereegranskat)abstract PLA/hemp co-wrapped hybrid yarns were produced by wrapping PLA filaments around a core composed of a 400 twists/m and 25 tex hemp yarn (Cannabis Sativa L) and 18 tex PLA filaments. The hemp content varied between 10 and 45 mass%, and the PLA wrapping density around the core was 150 and 250 turns/metre. Composites were fabricated by compression moulding of 0/90 bidirectional prepregs, and characterised regarding porosity, mechanical strength and thermal properties by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). Mechanical tests showed that the tensile and flexural strengths of the composites markedly increased with the fibre content, reaching 59.3 and 124.2 MPa when reinforced with 45 mass% fibre, which is approximately 2 and 3.3 times higher compared to neat PLA. Impact strength of the composites decreased initially up to 10 mass% fibre; while higher fibre loading (up to 45 mass%) caused an increase in impact strength up to 26.3 KJ/m2, an improvement of about 2 times higher compared to neat PLA. The composites made from the hybrid yarn with a wrapping density of 250 turns/metre showed improvements in mechanical properties, due to the lower porosity. The fractured surfaces were investigated by scanning electron microscopy to study the fibre/matrix interface.
29.	Baghaei, Behnaz, et al. (författare) Novel aligned hemp ﬁbre reinforcement for structural biocomposites : Porosity, water absorption, mechanical performances and viscoelastic behaviour 2014 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 61, s. 1-12 Tidskriftsartikel (refereegranskat)abstract This paper examines the thermal and mechanical behaviour as well as moisture absorption of aligned hemp composites using hemp/PLA wrap spun yarns. Uniaxial composites were fabricated with 30 mass% hemp using compression moulding. The properties of composites in terms of hemp fibre orientation (aligned and random), off-axis angle and alkali treatment were investigated. It was found that the testing direction influenced the mechanical properties of the composites. Compared with all the fabricated composites, the aligned alkali hemp/PLA yarn composite possessed the best mechanical properties, including tensile, flexural and impact strengths, lower porosity and water absorption. The water absorption for all composites was higher than for neat PLA, both at room temperature and 80 C. The PLA in its treated composites had higher crystallinity, which was attributed to effective heterogeneous nucleation induced by hemp. Based on SEM observation and theoretical analysis of DMTA data, there was a favourable interfacial adhesion in all composites.
30.	Bakare, Fatimat O., et al. (författare) Thermomechanical properties of bio-based composites made from a lactic acid thermoset resin and flax and flax/basalt fibre reinforcements 2016 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 83, s. 176-184 Tidskriftsartikel (refereegranskat)abstract Low viscosity thermoset bio-based resin was synthesised from lactic acid, allyl alcohol and pentaerythritol. The resin was impregnated into cellulosic fibre reinforcement from flax and basalt and then compression moulded at elevated temperature to produce thermoset composites. The mechanical properties of composites were characterised by flexural, tensile and Charpy impact testing whereas the thermal properties were analysed by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results showed a decrease in mechanical properties with increase in fibre load after 40 wt.% for the neat flax composite due to insufficient fibre wetting and an increase in mechanical properties with increase fibre load up to 60 wt.% for the flax/basalt composite. The results of the ageing test showed that the mechanical properties of the composites deteriorate with ageing; however, the flax/basalt composite had better mechanical properties after ageing than the flax composite before ageing.
31.	Bengtsson, Magnus, et al. (författare) Extrusion and mechanical properties of highly filled cellulose fibre-polypropylene composites 2007 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 38:8, s. 1922-1931 Tidskriftsartikel (refereegranskat)abstract This study focused on manufacturing of highly filled cellulose fibre-polypropylene composites and evaluation of the mechanical properties of the composites. Cellulose fibre reinforced polypropylene composites with up to 60 wt-% of fibres with and without coupling agent were manufactured by extrusion. In order to achieve consistent feeding of the fibres into the extruder a pelletization technique was used where the fibres were pressed into pellets. Two commercial grades of cellulose fibres were used in the study, bleached sulfite and bleached kraft fibres. Fibre dimension measurements showed that the pelletization process and extrusion at high fibre loading caused the most severe fibre breakage. Flexural testing showed that increased fibre loading made the composites stiffer but reduced the toughness. Addition of maleic anhydride grafted coupling agent increased the stiffness and strength of the composites significantly. In general, there was no significant difference in the mechanical properties between the composites with kraft and sulfite fibres. Scanning electron microscopy showed that addition of coupling agent improved the interfacial adhesion between the fibres and polypropylene matrix.
32.	Bengtsson, Magnus, et al. (författare) The use of silane technology in crosslinking polyethylene/wood flour composites 2006 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 37:5, s. 752-765 Tidskriftsartikel (refereegranskat)abstract In this study, the use of silane technology in crosslinking polyethylene-wood flour composites have been investigated. Composites were produced in a one-step process using a co-rotating twin-screw extruder. The composites were stored in a sauna and at room temperature to study the effect of humidity on the degree of crosslinking. Crosslinked composites showed improved toughness and creep properties compared to non-crosslinked composites. The flexural modulus, on the other hand, was lower in the crosslinked samples than in the non-crosslinked ones. FTIR was used to study the crosslinking reaction in the samples. X-ray mapping of the silicon signal was also performed to locate the silane in the composites. This study provides a basis for proposing, that part of the silane is grafted onto polyethylene and wood thereby creating a crosslinked network in the matrix with chemical bonds (covalent and hydrogen bonding) to wood. The other part of the silane remains un-reacted and blends into the system.
33.	Bondeson, Daniel, et al. (författare) Polylactic acid/cellulose whisker nanocomposites modified by polyvinyl alcohol 2007 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 38:12, s. 2486-2492 Tidskriftsartikel (refereegranskat)abstract The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.
34.	Butylina, Svetlana, et al. (författare) Accelerated weathering of wood-polypropylene composites containing minerals 2012 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 43:11, s. 2087-2094 Tidskriftsartikel (refereegranskat)abstract Accelerated weathering tests were carried out on wood-polypropylene composites containing minerals. Three different mineral fillers were studied: calcium carbonate, wollastonite and talc. Colour changes were evaluated after distinct periods; the total time of exposure of the composites to UV irradiation was 2000 h. The weathering resulted in significant colour fading of the composites. The composites containing mineral fillers had higher changes of colour (lightness) than the reference composite. Scanning electron microscopy analysis revealed deterioration of the polymer surface layer in all weathered composites. Exposure of the reference composite to UV irradiation resulted in the disappearance of the polypropylene surface layer and disclosure of wood fibres, which led to a higher drop in the lignin content of this composite compared to mineral-containing composites. A substitution of part of the wood with mineral fillers resulted in decreased water absorption and thickness swelling of mineral-containing composites, compared to the reference composite. Exposure to water immersion-freeze-thaw cyclic treatment and UV irradiation led to a decrease in the Charpy impact strength of the composites, except for the composite containing talc
35.	Chinga-Carrasco, Gary, et al. (författare) Side streams from flooring laminate production – Characterisation and recycling in biocomposite formulations for injection moulding 2022 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 153 Tidskriftsartikel (refereegranskat)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)
36.	Correa, E., et al. (författare) Effects of the presence of compression in transverse cyclic loading on fibre-matrix debonding in unidirectional composite plies 2007 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 38:11, s. 2260-2269 Tidskriftsartikel (refereegranskat)abstract Fatigue of composite materials is of great concern in load-carrying structures. The first type of damage to appear is generally transverse cracks in off-axis plies. These cracks form when fibre-matrix debonds coalesce. The underlying mechanism is hence fatigue growth of debonds at the fibre-matrix interfaces. In the present study, debond growth has been characterized under tensile and compressive cyclic loading of single glass fibres embedded in polymer matrix. The debond length was deter-mined by in situ microscopy with transmitted polarized light showing the more damaging effect of tension-compression cyclic loading than tension-tension cyclic loading. A boundary element model has been developed and interfacial fracture mechanics concepts applied over the numerical results aiming to give an explanation of this experimental fact. These results may be used to formulate a fatigue growth law at a local microscopic level, at a stage prior to the formation of any visible damage, i.e. transverse cracks. Ideas of how to develop this methodology further are also discussed.
37.	Costa, Sergio, et al. (författare) A unified physically-based finite deformation model for damage growth in composites 2022 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 161 Tidskriftsartikel (refereegranskat)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)
38.	Craven, R., et al. (författare) Delamination buckling: A finite element study with realistic delamination shapes, multiple delaminations and fibre fracture cracks 2010 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 41:5, s. 684-692 Tidskriftsartikel (refereegranskat)abstract This paper presents a finite element model of a carbon fibre composite laminate with multiple delaminations of realistic shape and including fibre fracture cracks loaded under compression. The modelling technique is initially applied on circular and elliptical delaminations of single ply sublaminates, which are compared with existing analytical solutions. The techniques are then applied to models with multiple delaminations of realistic shape and their behaviour in buckling and post-buckling is captured. An inverse method is used to determine the stiffness reduction caused by the damage, and shows significant stiffness reduction caused by peanut shaped delaminations. When fibre fracture cracks are added, their contribution to further stiffness reduction is minimal but they have some significant effects on the buckling shapes. © 2010 Elsevier Ltd. All rights reserved.
39.	Das, Oisik, et al. (författare) An all-gluten biocomposite : Comparisons with carbon black and pine char composites 2019 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 120, s. 42-48 Tidskriftsartikel (refereegranskat)abstract Three different charcoals (gluten char, pine bark char and carbon black) were used to rectify certain property disadvantages of wheat gluten plastic. Pyrolysis process of gluten was investigated by analysing the compounds released at different stages. Nanoindentation tests revealed that the gluten char had the highest hardness (ca. 0.5 GPa) and modulus (7.8 GPa) followed by pine bark char and carbon black. The addition of chars to gluten enhanced the indenter-modulus significantly. Among all the charcoals, gluten char was found to impart the best mechanical and water resistant properties. The addition of only 6 wt% gluten char to the protein caused a substantial reduction in water uptake (by 38%) and increase of indenter-modulus (by 1525%). It was shown that it is possible to obtain protein biocomposites where both the filler and the matrix are naturally sourced from the same material, in this case, yielding an all-gluten derived biocomposite.
40.	Das, Oisik, et al. (författare) Nanoindentation and flammability characterisation of five rice husk biomasses for biocomposites applications 2019 Ingår i: Composites. Part A, Applied science and manufacturing. - : ELSEVIER SCI LTD. - 1359-835X .- 1878-5840. ; 125 Tidskriftsartikel (refereegranskat)abstract Five different rice husks (RHs) having different geographical origins were characterised for their mechanical and fire reaction properties using nanoindentation and cone calorimetry, respectively. Analyses relating to ash and extractives contents, density and morphologies were also performed. The RHs had statistically similar extractives content, nanoindentation properties and peak heat release rates (PHRRs). The polypropylene-based composites made from these RHs also had insignificant differences in their tensile moduli, elongation and PHRR values. The RH inclusion conserved the tensile/flexural strengths while enhancing the moduli of the composites, as compared to the neat polypropylene. The material characteristics being ubiquitous amongst the different RH types enable the creation of biocomposites with foreseeable performance properties. Moreover, the individual nanoindentation and fire reaction properties of the RI-Is allowed the presaging of the bulk biocomposites' properties using theoretical models. Good agreements between predicted and experimental moduli/PHRRs were achieved using rule of mixtures and Halpi-Pegano models.
41.	Duanmu, Jie, et al. (författare) Studies on mechanical properties of wood fiber reinforced cross-linked starch composites made from enzymatically degraded allylglycidyl ether-modified starch 2010 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 41:10, s. 1409-1418 Tidskriftsartikel (refereegranskat)abstract In a previous work we introduced a new family of thermoset composites of softwood fiber and allylglycidyl ether modified potato starch (AGE-starch with a degree of substitution of 1.3 and 2.3) prepared by hot pressing. To improve the processability of AGE-starch with a DS = 1.3 (LDS-3) and to increase hygromechanical properties, the LDS-3 matrix has now been partially degraded by a-amylase at 45 degrees C (pH 6) for 0.5, 6 and 18 h. The study shows that already a 30 min enzymatic hydrolysis has a marked effect on the modified starch molecular weight and its thermal properties. The new composites with enzyme hydrolyzed AGE-starch, generically named D-LDS-3, showed good fiber dispersion and excellent interface between the fiber and matrix as studied by SEM. Premixes of D-LDS-3 matrix and fiber showed improved processability. The water vapor absorption was evaluated at 43.2% and 82.2% RH and the stiffness and strength properties were measured. The water uptake was shown to be reduced. The strength of neat matrix D-LDS-3-6 at ambient 68% RH reached 63 MPa and Young's modulus 3200 MPa and with 40 wt.% wood fiber reinforcement impressive 128 MPa and 4500 MPa, respectively.
42.	Duchemin, Benoit, et al. (författare) All-cellulose composites by partial dissolution in the ionic liquid 1-butyl-3-methylimidazolium chloride 2009 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 40:12, s. 2031-2037 Tidskriftsartikel (refereegranskat)abstract Fully bio-based and biodegradable all-cellulose composites were prepared in the form of films by partial dissolution of two cellulose sources: a commercially available microfibrillated cellulose (MFC) and filter paper (FP). The solvent selected for this work was the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl). Both cellulose sources were partially dissolved at 80 °C and consolidated by partial dissolution, resulting in excellent mechanical properties. X-ray diffraction and electron microscopy demonstrated that partial dissolution was a viable path to transform FP into a continuous paracrystalline matrix reinforced with cellulose I crystallites. In contrast, partially dissolved MFC was not as thoroughly dissolved and large amounts of undissolved material were still visible along the center line of the films after the longest dissolution times. Consequently, partially dissolved MFC retained its initially high crystallinity. The degree of polymerization of the materials after dissolution was significantly reduced.
43.	Dutta, Abhik, et al. (författare) Interply friction between unidirectional carbon/epoxy prepreg plies : Influence of fibre orientation 2023 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 166, s. 107375- Tidskriftsartikel (refereegranskat)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.
44.	Edgren, Fredrik, et al. (författare) Approximate Analytical Constitutive Model for Non-Crimp Fabric Composites 2005 Ingår i: Composites. Part A, Applied science and manufacturing. - 1359-835X .- 1878-5840. ; 36:2, s. 173-181 Tidskriftsartikel (refereegranskat)abstract In this paper, a study set on development and validation of constitutive models to account for out-of-plane fibre waviness in Non-crimp fabric (NCF) composites is presented. For this purpose, a mathematical model based on Timoshenko beam theory applied on curved beams, representing wavy tows in a NCF composite layer is employed. Stiffness knock-down factors operating at the ply level are established and introduced in laminate theory. The developed models are validated on laminates by comparison between predictions and experimental data as well as by comparison with numerical results for a cross-ply laminate. Application of the models on NCF composite laminates (cross-ply and quasi-isotropic) reveals that the models successfully predict laminate elastic properties.
45.	Ehman, Nanci, et al. (författare) 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 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier Ltd. - 1359-835X .- 1878-5840. ; 184 Tidskriftsartikel (refereegranskat)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.
46.	Espert, Ana, et al. (författare) Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties 2004 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 35:11, s. 1267-1276 Tidskriftsartikel (refereegranskat)abstract Environmentally beneficial composites can be made by replacing glass fibres with various types of cellulose fibres. Fibres from pine or eucalyptus wood and also one-year crops such as coir, sisal, etc. are all good candidates. The poor resistance towards water absorption is one of the drawbacks of natural fibres/polypropylene composites. New natural fibres/polypropylene composites were made and the water absorption in them was studied by immersion of the composites in water at three different temperatures, 23, 50 and 70 degreesC. The process of absorption of water was found to follow the kinetics and mechanisms described by Fick's theory. In addition, the diffusivity coefficient was dependent on the temperature as estimated by means of Arrhenius law. A decrease in tensile properties of the composites was demonstrated, showing a great loss in mechanical properties of the water-saturated samples compared to the dry samples. The morphology change was monitored by scanning electron microscopy studies of the samples before and after exposure to water and the devastating effect of water on the fibre structure was shown.
47.	Farge, L., et al. (författare) Optically measured full-field displacements on the edge of a cracked composite laminate 2008 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 39:8, s. 1245-1252 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.
48.	Frishfelds, Vilnis, et al. (författare) Bubble motion through non-crimp fabrics during composites manufacturing 2008 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 39:2, s. 243-251 Tidskriftsartikel (refereegranskat)abstract Bubbles motion through inter bundle channels in bi-axial non crimp fabrics is modelled. The scenario is that formed bubbles move with the resin through these channels and are trapped if the channels become too narrow. By usage of a permeability network model, existing criteria on bubble deformation and a variety of analytical and probabilistic methods it is found that the paths of the bubbles depend significantly on the position of the threads keeping the fabric together and the number of fibres crossing the interbundle channels. Another result is that the pressure difference over a trapped bubble increases with 50 % in a 3D geometry possible helping the bubble to escape. A third result is that, on average, the bubbles move biased to the direction of the tows. Finally it is found that the predicted void distribution of bubbles after a major part of bubbles have moved through the system are in qualitative agreement with experimental data.
49.	Gebart, Rikard (författare) Thermal runaway criterion for thick polymer composites 2024 Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier. - 1359-835X .- 1878-5840. ; 182 Tidskriftsartikel (refereegranskat)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.
50.	George, G., et al. (författare) Novel bio-commingled composites based on jute/polypylene yarns : Effect of chemical treatment on the mechanical properties 2012 Ingår i: Composites. Part A, Applied science and manufacturing. - : Pergamon. - 1359-835X .- 1878-5840. ; 43:1, s. 219-230 Tidskriftsartikel (refereegranskat)abstract This paper mainly investigates the fabrication process of jute yarn reinforced, bidirectional thermoplastic commingled composites (both untreated and treated). Commingling method was used to prepare the composites wherein the Polypropylene yarn (PP yarn) and jute yarn were wound together onto a metal plate in a particular configuration and then compression moulded. The mechanical properties of the composites prepared from chemically treated jute yarn were found to increase substantially compared to those of untreated ones. The surface morphologies of the fracture surfaces of the composites were recorded using scanning electron microscope (SEM). The SEM micrographs reveal that interfacial bonding between the treated jute yarn and the matrix has improved significantly by chemical treatments. The various chemical treatment mechanisms have been supported by FT-IR spectra. Theoretical modelling was used to predict the tensile properties and was found to be in accordance with the experimental results.

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