Questions from class - Lecture 10

Question 1

Which behaviour is described by the term “viscoelasticity”?

Answer 1

Wikipedia: Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain when stretched and quickly return to their original state once the stress is removed. Viscoelastic materials have elements of both of these properties and, as such, exhibit time-dependent strain. Whereas elasticity is usually the result of bond stretching along crystallographic planes in an ordered solid, viscosity is the result of the diffusion of atoms or molecules inside an amorphous material.

Question 2

Which moduli are used for the description of purely elastic / purely viscous materials?

Answer 2

For purely elastic materials the following modules are used to describe the mechanical properties:

i. Bulk module (measurement of the substance’s resistance to uniform compression)
ii. Shear module (G)
iii. Tensile module (is a measure of stiffness of an elastic material, stress-strain curve).

For purely viscous materials the different types of viscosity as well as the liquid shear flow is the properties used for description.

Question 3

Which measurement geometries are used in order to determine the mechanical properties experimentally?

Answer 3

i) Cone- and plate geometry: to measure the viscoelastic behaviour
ii) Maxwell model: serial combination of elastic spring and viscous dashpot
iii) Voigt-Kelvin model: parallel of elastic spring and viscous dashpot.

Question 4

Which three types of experiments are usually carried out to characterise polymer melts/networks?

Answer 4

Three types of fundamental experiments:

i) creep experiment
ii) stress relaxation
iii) dynamic-mechanical experiments