An aircraft that could take off, climb through the atmosphere into space at hypersonic speeds and survive a scorching descent to land at its destination like a conventional airplane might be seen as the ultimate test of structural materials. To power itself into orbit on its own store of fuels the craft would need a structure built of substances at once lightweight and very stiff and strong, able to cope with great aerodynamic stresses. Materials in some parts of the airframe would need to retain their strength at a temperature of more than 1,000 degrees Celsius; materials in the engines would have to remain strong at still higher temperatures. The class of materials from which most of its airframe and parts of its engine would be made are known as composites.
The need for lightweight, stiffness and strength combined has led many designers of military and commercial aircraft, sports equipment and cars to turn to composites for many components. Composites that meet the added requirement of resistance to high temperatures are found in rocket-motor components and missile nose cones. Wherever advancing technology has created a need for combinations of properties which no single material can provide, composites are becoming the material of choice. Most of us, in our daily lives, have used something made from, or incorporating, composites - skis, golf clubs, sail boards, court racquets, sailing dingeys and yachts, and yet few have a realistic picture of their capabilities and the opportunities they present for innovative design.
Engineering designers are frequently admonished for their lack of knowledge and interest in the full range of materials options available for engineering components. In the designers defence it can be said that they have learned to mistrust the often inflated claims of the material developers. Each year a new crop of wonder materials seems to emerge from the laboratory, but for these the challenges of manufacturing have yet to be addressed and will in fact prove to be a significant obstacle to widespread industrial adoption. The truth is that it can take many years of development and testing for a new material to reach the stage where it can be adopted by the engineering industries. Composite materials fall into this category. The problem that has dogged engineering composites since their earliest use is the difficulty in adopting automated manufacturing processes and the cost penalty that this imposes.
An equally difficult challenge is to educate designers into a new way of thinking: 'How best can we use the properties and processing opportunities offered by these materials in a complete new design?' Rather than: 'How can we adapt our existing design to make some limited use of the material's capabilities?'
Composites are now the natural material for military aircraft, racing yachts and racing cars to the point that there has to be a good reason to revert to traditional materials. In other industries composites are increasingly being seen to offer cost savings in addition to performance benefits, drawing more manufacturers to these materials.
At UL I work in the composites manufacturing research unit, where I manage a BRITE/EURAM EC project. We're designing manufacturing techniques for thermoplastic and thermoset composites. These are mainly glass and carbon fibre reinforced plastics and they are currently used in the structural components of military and commercial aircraft and also in high performance sports equipment such as Formula 1 racing cars and the composite structured Lotus Sports bicycle on which Chris Boardman won the gold medal at the Barcelona Olympics. Thermoplastics and thermosets are usually supplied in 'prepreg' form. This implies that the fibres have been impregnated with the appropriate polymer. In general the thickness of a prepreg ply is such that when eight plies are consolidated, a laminate of 1mm thick is produced. My work involves designing moulds for thermoplastic composites. When a thermoplastic fibre-reinforced laminate is formed in a mould at a temperature above the melting point, cooled and removed from the mould, it assumes a shape which can be significantly different from the shape of the mould. I predict the thermal distortions and use them in the design of moulds in which parts to close dimensional tolerances can be made.
In this project there are six partners, including European Aerospace companies like Dornier of Germany, Casa of Spain and a number of European Universities. There are meetings every six months where each of the partners discuss their progress and the difficulties encountered. The meetings are held in turn at each of the partner's work establishments, and this provides opportunities to see other activities that are carried out in the composite design area.
I studied mechanical engineering and the area I'm working in now, composite engineering, is a branch of this. If you have an interest in the practical and science subjects, maths, physics and chemistry etc.,you should consider mechanical or aeronautical engineering when filling out your CAO form.
Ms. Margaret Mulherne is Project Manager for Brite-Euram project "Diaphram Form of Thermoplastics Composites". She is pursuing a Doctorate in "Mould Design for Advanced Composites".
No comments:
Post a Comment