Lecture based on Materials
(Book: The science of strong materials, Penguin Publishers.) The aeronautical journal (Library can order for you), one article written in 1996, by Peal, I.J.Mocolm. Ceramic Science, pg 123-131. (Relevant to exam)
There are two key reasons for using thermoplastic composites: * save time & handling costs in production
* eliminate labour-intensive riveting & bonding
* can produce large profile sections that are some 20 % lighter than metal & alloys. * materials are exceptionally stiff and can tolerate vibrations
A380 (largest passenger plane) - 25 % of the structure & components are composites. And in the next generation of aircraft, the content of composites will double. A350 is expected to take off for the first time in 2011 with over 50 % of its total weight made up of fibre-reinforced composite materials. The Dreamliner, Boeing 787 – 50% of the components are produced from composite materials. Airbus itself manufacture ribs, stiffeners and other elements from the PPS composites. The individual components are welded together to form a strong, inseparable unit. This process eliminates the need for costly drilling & riveting operations & achieves higher strength and safety – reducing weight & saves time and money. Components made from PPS composites remain hard, impact-resistant, stiff & stable, even when exposed to high temperatures. PPS is also resistant to aviation fuel, engine and hydraulic oils, solvents and antifreezes. A very precise welding method in which the components are only welded at the points where it is necessary, meeting very high safety standards.
One of the most important part is the wing, they have to be RIGID to help lift. If they are not rigid they will bend increasingly across the wing. The aeroplane moving forward causes the air to move over & under the wing, giving a lift, the lift is greatest at the tips of the wings. As aircraft starts to move, the wing bends upwards and one of the most important aspects of wing materials is that it should resist the bending. (Resistance to bending) Youngs Modulus E (measured in Giga Nutons per square meter)
Any material used to build a wing should have the highest E value. The highest value known is 400 (diamond) but we cannot use this as its too expensive and not realistic. However a few years ago the Russians perfected a method of making diamond at a low temperature of 600-800 degrees centigrade (usually you need 3000 degrees & massive pressure). So perhaps in the future we may get a diamond coating as it may become cheap in the future as it will make it safe and stable. Recently the Americans have done this on several wings so it is possible.
Are very poor, have average E value of 40 so not very good. You need strength, Tensile (pulling/tearing strength).
There are 3 common ways of defining strength:
Tensile (pulling/tearing strength)
Sheer (pulling one way & pushing the other way)
Compressive (squeezing a material till it breaks).
Compressive strength value is higher than sheering & tensile. Tensile strength should be as high as possible as its carrying the load (250 tonnes). Also wings need a high Fatigue Resistance, and nowhere on the wing do we allow more than 20 mega nutons per sq meter. Until recently wings were made from metals but the regular movement of the wing metals causes the material to lose fatigue strength. So we need to ask how long it takes before it loses the strength? Usually this is very short time in metals. We didn’t know that until after the 1970’s after air accidents were examined. The job of an aeroplane is to carry as much as possible for as long as it can. The lighter the aircraft, the less mass we need to make it to have the high strengths, the lighter the better – Low Density. So the key properties of materials we need to focus on are Young’s Modulus, Tensile Strength, Fatigue Resistance and Low...
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