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Materials Lecture 9+1
Fichas del conjunto (18)
- 1What are the advantages of thermoplastics?No cross linking required
No additional heat is generated during manufacturing
We can heat and cool the sample far more rapidly than thermosets - 2Where is a composite most likely to fail?In the polymer matrix as the mechanical properties are significantly lower than the fibres.
Cracks grows in the polymer matrix in the inter laminar spacing - 3What is the most common failure method of composites?Delimitation cracking due to the inferior matrix properties where there is no fibre reinforcement.
- 4What can be a cause of delamination which is almost counter intuitive?Repairs, regular tool dropping or drilling can cause it and the delimitation is usually below surface and barely visible.
- 5How can the composites be treated in order to reduce cracking likelihood?Rubber toughening, yielding of rubber particles during crack propagation increases energy absorption during crack growth and can trap or reduce crack growth.
- 6How else may rubber particles help composites?Help to bridge gap between layers of fibres during crack propagation and can reduce rate of crack growth.
- 7How else can inter laminar composites be toughened?Insertion of level pins through thickness (highest toughness option)
Stitching - 8How can the few micron gap between carbon fibres be reinforced?Conventional carbon fibres too large, but carbon nanotubes can be used by growing them on the surface of the carbon fibres.
This improves inter laminar fracture toughness - 9Use of this technique?Piranha boat:
75% lighter and much stronger than conventional carbon fibres.
Improved fuel efficiency, reduced emissions, higher capacity for payload. - 10What would this technique look like under a microscope?
- 11How can cracks be 'self healed'?
- 12How often do commercial flights experience lightening strikes? How are they equipped for them~1000hrs flying time
Composites much lower electrical conductivity than aluminium but can undergo serious damage due to lightening. - 13How can the composites counteract these strikes?Copper aluminium mesh as outer layer of carbon fibre composite skin protecting it from these strikes much better
- 14What can poor fibre matrix interaction lead to?Failure at the interface
- 15How do you improve fibre matrix interfacial bonding?Carbon/glass fibres have low surface energy so it will not bond strongly to polymer resin like epoxy. Chemical modification necessary to achieve good bonding.
- 16What is this chemical modification?Amine group used to crosslink the carbon fibre and the epoxy matrix
- 17How else can the interface be improved?Treat the surface of the fibres
- 18How can they be treated?
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- Uni Materials Fichas sobre Materials Lecture 9+1, creado por Luke Hansford el 09/04/2016.
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- Luke Hansford
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