I would like to know if there is a way to determine the creep rate of a
polymer under strain.
Is it something that can be calculated or is it something that needs to be
I am looking for very low level creep (um and sub-um).
Not being a materials specialist, any pointers would be helpfull.
There is no universal technique for measuring the rheological
characteristics of polymers, which is not surprising given the very
wide range of mechanical properties that you can get from polymers
(extremely soft to extremely strong).
Ferry's book has 3 chapters alone on measuring these types of
properties, and there are new techniques coming all the time.
Be careful to define your terms. To most people "creep" means
deformation that is not recoverable; ie. inelastic.
However many materials exhibit slow but fully elastic, recoverable
deformation often called "delayed elasticity".
I think that many people include "delayed elasticity" in their
definition of "creep" because in many practical cases the consequences
are the same. However that is not true in all cases.
For example, say you are marketing straight glass rods. If those rods
are stored by leaning them against a wall, they may appear to be
permanently deformed after some time has passed. If the deformation
was due to creep they are indeed permanently deformed. On the other
hand, if the deformation was due to delayed elasticlty the rods will
slowly straighten themselves out after the stress is removed.
Well Dave, you got me, I meant delayed elasticity.
When applying axial strain (less than 0.5%) on acrylate coated optical fiber
I want to know if it is possible the delayed elasticity dispplacement to the
Sorry for being vague.
Oops, bad phrase.
Is it possible to predict/calculate the delayed elasticity to the micron
Any pointers ?
Has this been done before for SMF-28?
I could not find any specific data, I assume most of it to be proprietary.
It should be easy to estimate by experiment.
Bend a coated fiber into a circle such that the maximum strain is 0.5%
(this is a circle with a diameter of about 100 fiber diameters.) This
is a lot of strain by the way.
Hold the fiber in the circular shape for some length of time then
If the fiber does not return to its perfectly straight original state
then the system is not perfectly elastic. You can monitor its return
to the original straight state to see how much of the deformation is
permanent and how much is due to delayed elastic effects.
This is done by measuring the radius of curvature of the fiber as a
function of time. strain ~ (fiber radius)/(Radius of curvature of the
Do the same experiment with an uncoated fiber to see if the fiber
itself shows any non-ideal behavior.
The difference in behavior is due to the coating.
Remember the fiber's modulus is much greater than that of the polymer
so a little residual curvature may imply a lot of polymer strain.
Optical fiber is after all a composite composed of some secret materials. I
guess there is no realy good way besides experimenting.
I have tried Corning, but so far service is better from this NG.
There is good information out there on how to conduct such an experiment and
I have access to a MTS so it is just a matter of fixturing and perhaps
procuring an extensiometer.