Mechanics unit 5 - Fracture under stress deck 3

Question 1

What are polymers constructed from ?

Answer 1

Long chains of molecules which are formed by smaller molecules called monomers

Question 2

What are the advantages of polymers ?

Answer 2

1. Lightweight/ low density
2. Corrosion resistant
3. Electrical insulators
4. Easily manufactured

Question 3

what is the general behaviour of polymers on a stress-strain curve ?

Answer 3

The display non-linear and time dependent behaviour - usually both elastic and plastic behaviour

There strength is usually low in comparison to other materials

Question 4

Do SAQ 16

Question 5

What are the 2 main sub-types of polymers ?

Answer 5

Plastics and elastomers

Question 6

What 2 main categories can plastics be divided up into based upon their behaviour when heated

Answer 6

1. Thermoplastic
2. Thermoset

Question 7

What type of behaviour do thermoplastics display at high temps and comment on the stability of them at high temps?

Answer 7

Plastic behaviour

The are quite stable at high temps so they can be heated and remodelled without altering their behaviour

Question 8

Can thermoset plastics be reformed and what happens to them at high temps ?

Answer 8

• No they cannot
• They harden at high temps

Question 9

What is the characteristic feature of elastomers ?

Answer 9

They can deform by enormous amounts without permanently changing shape - high level of elasticity

Question 10

Do SAQ 17

Question 11

What are the general features of ceramics ?

Answer 11

• They are hard and brittle materials (they do not creep)
• Have high melting points
• Low electrical and thermal conductivity
• Good chemical and thermal stability
• High compressive strength

Question 12

Give an example of the use of ceramics ?

Answer 12

Heads of hip prostheses

Question 13

What are composites ?

Answer 13

They are what is formed when 2 or more materials are joined to give a combination of properties that could not be obtained from the original materials

Question 14

What are the 3 main types of composite materials and describe them ?

Answer 14

1. Particluate -reinforced: have particles of a hard brittle material dispersed within a softer more ductile material
2. Fibre- reinforced: have fibres of a strong, stiff brittle material within a softer more ductile
3. Laminar- reinforced: a thin coating may cover a material to improve corrosion resistance or thicker layers may be laminated together to improve strength

Question 15

Do SAQ 18

Question 16

Do SAQ 19