Composites part 1 - e Flashcards Preview

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Flashcards in Composites part 1 - e Deck (21)
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1
Q

How are polyester resins formed? How is it cross linked?

A

by a condensation reaction between glycol and an unsaturated dibasic acid. The unsaturated resin is dissolved in a monomer solvent, usually styrene, and cross linked by the addition of a catalyst and heat.

2
Q

How can the cross linking of polyester be speeded up?

A

An accelerator may be added to speed up the reaction

3
Q

What is the shrinkage of polyesters on curing typically?

A

Between 4 and 7% by volume

4
Q

How are vinyl-esters similar to polyesters?

A

In that they cure by radical initiated polymerization.

5
Q

How are vinylesters formed?

A

From the reaction of an epoxy resin with acrylic or methacrylic acid and properties can be varied using different epoxy resins.

6
Q

What are the advantages of vinyl-esters?

A

They are generally tougher, have improved chemical resistance and are capable of higher operating temps than polyesters. They fall between polyesters and epoxies in terms of performance and cost.

7
Q

How are epoxies formed?

A

By condensation of epichlorhydrin and polyhydroxy compounds.

8
Q

How are epoxies normally supplied?

A

As a single constituent, the resin, with a second constituent, the hardener or cross-linking agent, that has to be added.

9
Q

How are a range of properties possible with epoxies?

A

By combining different resins and hardeners

10
Q

What are the advantages of epoxies?

A
  • higher strength and adhesion to fibres than polyesters.
11
Q

What is the shrinkage of epoxies on curing?

A

between 0.25 and 2% by volume.

12
Q

How are phenolics formed?

A

By condensation of phenol and aldehyde. The condensation reaction is usually promoted by heat but can also be initiated using a strong acid catalyst.

13
Q

What are the advantages of phenolics?

A

Good fire resistance with low smoke and toxic fume emission characteristics

14
Q

What are the disadvantages of phenolics?

A

During cure they produce highly volatile contents, predominantly water and are unstable at room temperature. The pot life of the resin is therefore low and a high proportion of the mass of the hardened resin is made up of water. The resin cannot be pigmented, the color being unstable. The shrinkage upon curing is between 8 and 10%

15
Q

What is gel coat?

A

A dense, void-free layer of resin on the exterior of moulding to improve the surface finish.

16
Q

How is gel coating applied?

A

It is applied to the mould and then partly cured prior to applying the resin.

17
Q

What are the advantages of gel coat?

A

Tough, resilient films, most can be pigmented

18
Q

What is pre-preg?

A

A thin sheet of partially cured, or b-staged, resin containing reinforced fibers. The fibers can be woven or unidirectional. The pre-preg sheet usually comes with a plastic backing sheet or release film which is removed prior to laminating. Normally supplied as rolls.

19
Q

What are the parameters that can typically be specified for pre-pregs?

A
  • fiber type and grade
  • surface treated?
  • resin type
  • resin content
  • cured ply thickness
20
Q

What are the disadvantages of pre-pregs?

A
  • limited shelf life due to partially cured state

- has to be stored at low temps in a freezer

21
Q

How are pre-pregs processed?

A
  • hand lay-up, vacuum bad and autoclave moulding