Stress And Strain And Things

Question 1

Poissons ratio

Answer 1

The ratio of compressive strain to tensile strain
- most metals have poissons ratio of around 0.3
- 0.5 signifies perfect conservation of volume (incompressible)

Question 2

Creep and relaxation

Answer 2

Creep: The tendency of a material to keep extending under constant load
Relaxation: The tendency of stresses to decrease under constant extension

Question 3

What is a viscoelastic material

Answer 3

A material that exhibits time-dependent material characteristics

Question 4

How does a dashpot work and how does it relate to viscoelasticity?

Answer 4

• piston with a hole in it eg a syringe
• rate of extension is proportional to applied load
• application of a constant force causes plunger to move at a constant rate
• demonstrates creep as it continues to displace under constant load
• demonstrates relaxation as load reduces to zero at fixed displacement

Question 5

Maxwell model of viscoelasticity

Answer 5

Maxwell
- dashpot and spring in series
- under application of a load, spring stretches instantly and dashpot moves with constant speed - linear rate of extension with time
- when load ceases the spring returns to original length and dashpot stops moving

Question 6

Voigt model of viscoelasticity

Answer 6

Voigt
- dashpot and spring in parallel
- under applied load spring wants to extend instantly but response is dampened by dashpot
- spring extends until until all load appears across the spring
- when load ceases the spring wants to instantly contract but response is dampened by dashpot
- steady transfer of dashpot to spring

Question 7

Kelvin model of viscoelasticity

Answer 7

Kelvin
- combination of Maxwell and Voigt
- model shows inadequacy of the simpler models in accounting for rate of dissipation of energy under cyclic loading