A review of bast fibres and their composites. Part 3: modelling

This paper extends an earlier two-part review of bast fibres and their composites. The paper presents recent statistical models which have been applied to natural fibre reinforcements for composite systems. Recent research suggests that the rules-of-mixture should be extended to include the effects of porosity, fibre diameter and yarn twist. A new fibre area correction factor is introduced to correct for the over-estimate of fibre cross-section which occurs when an apparent cross-sectional area is calculated from the "diameter" measured normal to the fibre axis.No Full Tex

Ranking of fibre-reinforced composite plate surface finish quality by wavelet texture analysis

In the automotive and other industries, the visual appearance of external surfaces is a key factor in perceived product quality. Traditionally, the quality of automotive surface finish has been judged by expert human auditors. A set of 17 fibre-reinforced composite plates was previously manufactured to have a range of surface finish quality, and these plates were previously ranked by three expert observers and also optically digitally imaged. Following validation of the previous rankings, we applied the wavelet texture analysis (WTA) technique to the digital photographs to derive an instrumental measure of surface finish quality based on the panel images. The rank correlation between the human expert surface finish quality ratings and those from the WTA image analysis process was found to be positive, large and statistically significant. This finding indicates that WTA could form the basis of an inexpensive practical instrumental method for the ranking of fibre-reinforced composite surface finish quality

Silane modification of the flax/epoxy system interface

Natural fibres (NF) are normally subjected to pre-treatment to ensure good fibre to matrix bonding and consequent mechanical properties and durability. To enhance the sustainability of NF composite systems, it would be sensible to minimise processes that incur environmental burdens. This research considers that addition of silane coupling agent to epoxy resin hardener may be an alternative to the direct chemical pre-treatment of NF before composites manufacture. The current study indicates that silane-in-hardener can eliminate the pre-treatment of fibres and generates composites with optimum mechanical properties

Overview of the BlockNormal Event Trigger Generator

In the search for unmodeled gravitational wave bursts, there are a variety of methods that have been proposed to generate candidate events from time series data. Block Normal is a method of identifying candidate events by searching for places in the data stream where the characteristic statistics of the data change. These change-points divide the data into blocks in which the characteristics of the block are stationary. Blocks in which these characteristics are inconsistent with the long term characteristic statistics are marked as Event-Triggers which can then be investigated by a more computationally demanding multi-detector analysis.Comment: GWDAW-8 proceedings, 6 pages, 2 figure

Fibre Area Correction Factors (FACF) for the extended rules-of-mixtures for natural fibre reinforced composites

Special issue of the journal devoted to the 4th International Conference on Natural Fibers (ICNF2019) ~ smart sustainable solutions, Fibrenamics, Porto ~ Portugal, 01-03 July 2019.The prediction of the properties of fibre-reinforced composite materials normally uses rules-of-mixture (RoM), but accuracy is constrained by the validity of data input to the model. A common error is the use of the fibre “apparent diameter” to determine the cross-sectional area of the polygonal fibre, and hence the fibre modulus and strength values are low. New equations are presented which can produce improved predictions of the in-plane moduli and strengths of natural fibre composites. Provisional data for the Fibre Area Correction Factors required by the new equations, based on recent publications in the scientific literature, are provided

Enhanced rules-of-mixture for natural fibre reinforced polymer matrix (NFRP) composites (comment on Lau et al in volume 136)

The use of rules-of-mixture to predict the elastic modulus and strength of natural fibre-reinforced composites is often compromised by the fibre properties used in the calculations being derived with an assumption of circular cross-section, when real fibres have polygonal cross-section. A fibre area correction factor (FACF) has been proposed to address this inaccuracy and has been demonstrated to improve the predictions

The mechanical properties of flax fibre reinforced poly(lactic acid) bio-composites to wet, freezing and humid environments

Publisher policy: author can archive post-print on institutional repository. Publisher copyright and source must be acknowledged. Publisher's version/PDF cannot be used. Must link to publisher version with DOI.Bio-composites are increasingly being perceived as a green alternative to synthetic composites in many applications. However, the overall long-term durability of bio-composites is a major concern, particularly their ability for sustained performance under harsh and changing environmental conditions. This paper reports a detailed study on the effect of environmental conditions on the performance of flax/poly(lactic acid) bio-composites. Neat poly(lactic acid) and biocomposite samples were exposed to environments similar to those found outdoors: wet, freezing and humid. Moisture absorption and physical changes of specimens were periodically examined. Flexural and tensile properties were evaluated periodically to determine the detrimental effect of each exposure condition on the mechanical performance of biocomposites. Direct contact with liquid water is the most deteriorating environment for bio-composites. A drying process can partially restore the mechanical performance of these materials. Bio-composites can survive reliably in warm humid environments and in those that could create freeze and thaw cycles for short-term outdoor applications. The mechanisms and reasons involved in the degradation of the properties of green composites are discussed

Design, manufacture, mechanical testing and numerical modelling of an asymmetric composite crossbow limb

This paper considers the design, manufacture, mechanical testing and numerical analysis of a crossbow beam (limb). The limb should be lightweight and permit a high deflection of the beam's tip in order to achieve a good ballistic performance. Consequently, fibre-reinforced polymer matrix composites are suitable candidate materials. However, carbon fibres were considered too brittle for this application. Aramid fibres combine low density and high stiffness but are weak in compression. E-glass fibres are relatively flexible but are of high density. The optimised design developed here uses aramid fibres on the tension face with E-glass fibres on the compression side. This component was manufactured using resin infusion, modelled using a commercial finite element code (Abaqus (R)) and the model was validated by mechanical testing. A good correlation was found between the experimentally measured deflections and the numerical results. (C) 2008 Elsevier Ltd. All rights reserved

Sustainable Manufacture of Natural Fibre Reinforced Epoxy Resin Composites with Coupling Agent in the Hardener

Lignocellulosic natural fibres are hydrophilic, while many matrix systems for composites are hydrophobic. The achievement of good mechanical properties for natural fibre-reinforced polymer (NFRP) matrix composites relies on good fibre-to-matrix bonding at the interface. The reinforcement is normally coated with an amphiphilic coupling agent to promote a strong interface. A novel alternative approach is to dissolve the coupling agent in the hardener for the resin before creating the stoichiometric mix with the base epoxy resin. During composite manufacture, the hydrophilic (polar) end of the coupling agent migrates to surfaces (internal interfaces) and bonds to the fibres. The hydrophobic (non-polar) end of the coupling agent remains embedded in the mixed resin. Mechanical testing of composite samples showed that silane added directly to the matrix produced a NFRP composite with enhanced longitudinal properties. As pre-process fibre coating is no longer required, there are economic (shorter process times), environmental (elimination of contaminated solvents) and social (reduced worker exposure to chemical vapours) benefits arising from the new technique