Creep

Question 1

What is creep

Answer 1

The tendency for a solid to undergo slow deformation

Question 2

At calculate the minimum temperature for creep to start occurring in a material, homogeneous temperature

Answer 2

when the ratio is around 0.4 or higher

= T / Tmp
T = temperature of environment
Tmp = melting point

Question 3

Which properties of a polymer change at its glass transition temperature

Answer 3

all it’s properties, strength and stiffness

Question 4

What are creep design considerations

Answer 4

Creep strain:
(the gradual deformation over time)
- size of piece
- blades, high temp environments, etc
Stress relaxation:
(decrease in stress over time while maintaining a constant strain, due to atomic movements)
- bolts, washers, seals, polymers, etc
Stress rupture:
- failure of a material
- bottles, pipes, pressure vessels, etc

Question 5

How do you reduce creep in a metal

Answer 5

Limit difffusion
- increase grain size
- choose material with a low homogeneous temperature
Limit dislocations
- introduce precipitates
- use ordered structure

Question 6

How do you reduce creep in a polymer

Answer 6

• choose material with a high glass transition temperature (Tg)
• introduce cross links, connecting chains together (+Tg)
• add branch’s to restrict rotation (+Tg)

Question 7

what is the tangent modulus a measure of

Answer 7

describes the modulus at a single point (gradient of tangent)

Question 8

what is the secant modulus a measure of

Answer 8

describes average modulus up to the point (gradient from point to origin)

Question 9

what is the secant modulus a measure of

Answer 9

is a measure of the modulus when the material is under bending

Question 10

under high stress and temperatures what is likely to happen

Answer 10

• dislocation climb