Elastocon Relaxation

Stress Relaxation and Creep Systems


Stress relaxation tests on rubber materials have become highly popular for determining the properties of rubber. From the beginning stress relaxation tests were predominantly used in scientific projects at universities, but a growing use in industrial applications has been shown in recent years, mainly due to the introduction of stress relaxation tests in different product standards, such as sealing rings for pipes and in specifications in the automotive industry.



Aeration and Liquid Exchange Test

When testing stress relaxation in fuels and oils the liquid
may be ageing faster than the rubber, so the liquid has to
be replaced at intervals.
The testing is traditionally done in a closed container
without oxygen present and this does not correlate with
the actual situation in a fuel tank or a motor.
To make it possible to perform more realistic ageing
tests we have developed a system where we replace the
liquid by pumping and we add air and have an agitation
of the liquid to get the air and newly inserted liquid
evenly distributed. The rate of liquid exchange and air
can be programmed.

Additional Benefit

Stress relaxation is a reduction in the counterforce for maintaining the applied strain, the force is not constant but decreases with time when the material ages. This is expressed as a percentage of the initial force.
The process that is mainly responsible for stress relaxation may be chemical or physical in nature, and under normal conditions both types of process will occur simultaneously.
However at low or normal temperatures, and/or over a short time, stress relaxation is dominated by physical processes whilest over long time periods or high temperatures chemical processes are dominant.

Cell Ovens For Stress Relaxation

Elastocon offers cell ovens designated for stress relaxation
tests. This means that the inner height of the cells are
adapted to fit our relaxation rigs so that they will achieve
as good thermal contact as possible with the bottom of
the cell.
The ovens have an integrated draught hood that eliminates
the changes in the force during the test, due to temperature
changes in the environment around the top part of the rigs.