All Composition

All Composition

Next Generation Fibre Reinforced Composites

Introduction

Composite fibre products are not new. The first composite material known was made in Egypt around 3,000 years ago when clay was reinforced with straw to build walls. With the advent of metals, the use of natural fibre for reinforcing declined. The rise of composite materials began during the 1960s when glass fibres in combination with tough rigid resins could be produced on a large scale. Fibre Composites consist of polymers (plastics) reinforced with carbon, glass and/or Aramid (Kevlar) fibres. These materials are up to 6 times stronger than steel and concrete at a fraction of the weight. They are also non-corroding, non-magnetic and can be designed to locate strength and stiffness where it is needed. The potential cost advantages are significant.

Composite materials (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure.

Why Use Composites?

To satisfy the increasing demand for housing and infrastructure, industry and government are constantly looking for building materials and structures that are strong, economical, and easy to assemble and durable. Fibre composites satisfy these requirements.

Specific advantages of fibre composites in structural engineering include:

More appropriate and economical structures:

Case histories demonstrate that in many applications (even with today's material costs and processing technologies) fibre composites are directly competitive in initial cost, substantially less expensive in terms of installed cost, and far less costly in maintenance.

More attractive structures:

Because of the high strength, low weight and excellent design flexibility, fibre composite structures are commonly smaller, easier to blend in with the environment and more pleasing to the eye.

More environmentally friendly structures:

The high corrosion resistance of fibre composites eliminates the need for chemical treatment (as required for most timbers), or protection by toxic paints (as with steel). Consequently there is less danger of leaching of dangerous chemicals into the environment.

Composite materials are also becoming more sustainable:

Significant effort is being made in the development of polymer resins made from plant oils. Soy based resins are already in use for non-structural components, and natural fibres such as flax are being used to create sustainable composites from renewable resources.

A Nickel-Carbon-Fibre Composite for Large Adaptive Mirrors

The next generation of ground-based optical telescopes is currently under development. These telescopes will have primary mirrors of 30-50m in diameter and are termed Extremely Large Telescopes (ELTs). Most design studies for ELTs have identified the need for an integrated large adaptive mirror ranging in size from 2-4 metres and either flat, convex or concave in profile. Currently there is a move towards large, ultra-thin glass mirrors, however these are fragile, costly to produce and unlikely to be made to the sizes required for ELTs, needing a less desirable segmented arrangement of smaller mirrors to obtain the required diameter.

An alternative solution could be to use carbon-fibre composite (CFC) substrates - these are very robust even at high length to thickness aspect ratios and are scalable to the maximum sizes proposed. Some of the benefits in using CFC material are its low density, high stiffness and good thermal stability - these properties and others can be optimized for the project in question by careful choice of the fibre/resin ply matrix and design of the laminate lay-up sequence.

Carbon Fibre Reinforced Composite Car

Carbon dioxide emissions and world hydrocarbon fuel reserves means that there is considerable interest in technologies that reduce fuel consumption for passenger cars. In the area of vehicle design, body weight is the most important target for improvement, as a reduction in the weight of a vehicles body means that a smaller engine, and a lighter drive train and assembly can be used. So that various studies have indicated a potential for savings of up to 65% by using carbon fibre composites instead of steel wherever possible.

The Aero-Stable Carbon Car (ASCC) programme has been investigating the limitations to maximizing fuel economy in a lightweight car manufactured using carbon fibre composites (CFC). Current lightweight composite vehicles, such as racing cars, use a monocoque stressed-skin design for both weight and manufacturing cost reasons.

The monocoque approach having been discarded, a more efficient design that does not need to transfer large loads through panel joints, is to use a very stiff framework of complex shaped beams and struts, covered by thin panels, bonded using low stiffness adhesives. This approach also offers benefits in vehicle assembly and fitting, since loading and attachment points can be provided on the framework and the panels can be attached near the end of the process to provide clear access through frame apertures.

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