Viscoelasticity: Linear viscoelasticity and thermal effects

Question 1

How does the conservation of volume apply to deformation?

Answer 1

• any elongation in 1 direction must be counteracted by shrinking in the other directions

Question 2

How does deformation occur at the microscale?

Answer 2

Same as the macroscale - the polymer chain deform the same amount as the macro deformation

Question 3

Where does most of the energy from deformation go?

Answer 3

It is released as entropy (the enthalpy is very small since no chains are broken)

• entropy is based on the elongation of the chains

Question 4

What is the difference between true stress and engineering stress?

Answer 4

stress is calculated as the force applied divided by the cross-sectional area

True stress uses the area after the stretch has occurred
Engineering stress uses instantaneous area (doesn’t use the area after stress is applied)

Question 5

How does observed stress and applied strain interact based on the viscoelasticity of the material?

Answer 5

They are out of phase with a lag between the observed stress and applied strain of delta

– for liquids, delta is 90 degrees

Question 6

What does the out of phase stress give?

Answer 6

The viscous component (the energy lost to permanent deformation)

The total energy is the stored and loss energy which are found as complex number with angle delta

**these values can be mapped across the different transition regions

Question 7

What is the time-temperature superposition?

Answer 7

Instead of testing deformation over very long periods of time, can instead look at how it occurs at different temperatures that correspond to different time amounts