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Polymer Composites
Suggested answers
Activity 1
Describe why it is important to protect the glass layers in aircraft windows from scratching.
Scratching will produce a stress raiser in the glass that has a potential to cause a crack and breakage. A breakage may cause the aircraft to depressurise thus placing the passengers in serious danger.
Activity 2
Why does a composite have more desirable properties than either of its two constituent materials on their own?
By combining two different materials, the overall properties are enhanced as both of each materials desirable properties are ulitised. Each material complements the other. For example, manufactured composites combine tensile strength with rigidity of shape and thus we have a useful structure for the wing of an aeroplane.
Activity 3
Try to think of six examples of composites and divide them into natural composites and synthetic composites for the table below. An example of a natural composite is timber which contain cellulose and lignin. One common synthetic composite is glass reinforced plastic (GRP).
| Natural composites | Synthetic composites |
|---|---|
| wood : cellulose and lignin | concrete and reinforced concrete |
| bone : collagen and lime | asphalt paving |
| human body | cements |
| sedimentary rocks, e.g. sandstone | laminates |
| leather | plywood |
| metamorphic rocks, e.g. marble | galvanised iron |
| horn | vitreous coatings |
Activity 4
- What areas of the aircraft are prone to airborne erosion?
All forward facing surfaces, e.g. fuel tanks.
- What two factors influence the rate of erosion?
Impact velocity of over 100 metres per second and the angle of impact.
- In the case of laminates, the interface of the layers
can be subject to shear stresses. What problem does erosion by rain cause here?
Delamination
|