 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
An
anelastic material is one that shows a temporal shift between an applied
stress and the resulting strain. If the applied stress is periodic as shown
in the diagram, this material behavior will result in a phase shift between
the stress and strain in the steady state. The stress strain curve will
have some included area, the value of which is the work done by the external
forces per unit volume of the material. The material response (phase
shift) will be frequency dependent, and the area of the cyclic stress-strain
curve will, therefore, depend on the frequency. |
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
From:
Courtney,
"Mechanical
Behavior of Materials,"
McGraw
Hill (1990) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
The
maximum area occurs when the driving frequency is the reciprocal of the
material relaxation time responsible for the phase shift. At this resonant
condition the work done on the material will be a maximum and a temperature
increase will occur unless heat is removed from the sample. In low melting
point materials, sample failure can occur due to this hysteretic heating.
Elastomers may also degrade due to the temperature increase. |
|
|