YOUR AIMS
On completion of this lesson you should be able to:
- understand the difference between composite materials and other materials
- classify given examples of composite material according to matrix type, dispersed phase type and the geometry of the dispersion
- appreciate that composite materials possess properties that neither component, acting alone, possesses
- understand that the properties of fibre composites may be highly anisotropic (exhibit different values in different directions)
- distinguish between the mechanisms of reinforcement prevalent in large particle and small particle composites
- appreciate the reasons for the potential high strength and stiffness of materials in fibrous form
- understand the role of the matrix in determining composite behaviour
- apply the 'rule of mixtures'.
1. How might a 0°/90°/0° crossply laminate be described if the reference direction was changed? Give two examples, carefully illustrating the reference direction chosen.
(Hint: Choose two new reference directions mutually perpendicular to the original reference direction.)
2. How does the strengthening and stiffening mechanism (i.e. reinforcement mechanism) differ between large particle and small particle composites?
3. Mention is made in the text of carbon fibre/carbon matrix composites and silicon carbide fibre/silicon carbide matrix composites. How might it be possible to gain improved performance by 'reinforcing' a matrix with a fibre of the same material?
4. What is the surface area per gram of material (m2 g-1) for carbon black particles of 20 nm diameter?
(The density of carbon black is 2.2 × 103 kg m-3. Assume smooth spheres.)
5. Explain how the strength of a given material may be affected by its morphology.
6. Why is it that all graphite fibres are carbon fibres, but not all carbon fibres are graphite fibres?
7. It is commonly observed that short glass fibres are stronger than long glass fibres. Why might this be?
8. Discuss the function of the matrix in the context of a discontinuous glass fibre/nylon composite.