Fractal Dimension: correlate performance to images

Fractal dimension (D or FD) is a measure of the complexity of self-similar data. One common method to quantify an image is to cover the picture with a grid of boxes, count the number of boxes in which the required feature appears, progressively increase the box size and count, then plot the detected feature measurement against box size. The slope of the line is D and the method works for images without self-similarity. The process is a feature of the NIH ImageJ freeware (other packages are available) image processing and analysis software. This technique reduces a processed image to a single real number, even where subjective assessment cannot perceive differences, which can then be used on one axis of a graph. The weave pattern of a woven reinforcement fabric, the permeability of reinforcement fabrics, the strength of fibre-reinforced composites, and reflections from a gel-coated surface have all been found to correlate to D. A rising issue is agglomeration of nanoparticles producing composites with reduced strength compared to uniformly distributed particles, which is normally discussed with qualitative judgement of microstructures, but the variation between images could easily be quantified by FD

In-Mould Gel-Coating for polymer composites

Surface coatings (gel-coats) are often used on commercial composite mouldings for cosmetic and/or durability reasons. They have traditionally been prepared in open moulds with styrene vapour allowed to escape to the workspace and environment. This paper considers the development of in-mould gel-coating processes. A Double Glass Plate Mould (DGPM) was used to prepare flat composite test panels. Laminates were manufactured by liquid composite moulding processes. Conventional hand painted gel-coat, innovative In-Mould Gel-Coating with a trilayer separator fabric (IMGC) or In-Mould Surfacing with a silicone shim (IMS) were studied. The surface quality of the final products was measured using a Wave-Scan device while the adhesion of the gel-coat was characterised by pull-off tests. The new processes offer reasonable properties in a cleaner, more controlled process

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

Voronoi cells, fractal dimensions and fibre composites.

The use of fibre-reinforced polymer matrix composite materials is growing at a faster rate than the gross domestic product (GDP) in many countries. An improved understanding of their processing and mechanical behaviour would extend the potential applications of these materials. For unidirectional composites, it is predicted that localized absence of fibres is related to longitudinal compression failure. The use of woven reinforcements permits more effective manufacture than for unidirectional fibres. It has been demonstrated experimentally that compression strengths of woven composites are reduced when fibres are clustered. Summerscales predicted that clustering of fibres would increase the permeability of the reinforcement and hence expedite the processing of these materials. Commercial fabrics are available which employ this concept using flow-enhancing bound tows. The net effect of clustering fibres is to enhance processability whilst reducing the mechanical properties. The effects reported above were qualitative correlations. To improve the design tools for reinforcement fabrics we have sought to quantify the changes in the micro/meso-structure of woven reinforcement fabrics. Gross differences in the appearance of laminate sections are apparent for different weave styles. The use of automated image analysis is essential for the quantification of subtle changes in fabric architecture. This paper considers Voronoi tessellation and fractal dimensions for the quantification of the microstructures of woven fibre-reinforced composites. It reviews our studies in the last decade of the process-property-structure relationships for commercial and experimental fabric reinforcements in an attempt to resolve the processing vs. properties dilemma. A new flow-enhancement concept has been developed which has a reduced impact on laminate mechanical properties

A review of bast fibres and their composites Part 4 ~ organisms and enzyme processes

There is an urgent need to halt the degradation of the ecosystems on Earth. For the acquisition, modification and disposal of natural fibres and their composites, the use of organisms and the associated enzymes offers a promising route to sustainable composites. This would potentially reduce the required energy and use milder reaction conditions. This paper reviews the use of organisms and enzymes for (a) extraction of fibres from plant material (retting), (b) surface modification of fibres, and (c) end-of-life treatments, in the context of bast fibres and their composites. The use of enzyme processes at large scale is limited by the extended treatment times, costs of the enzymes and equipment, wastewater treatment and the current low level of adoption by industry

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