Glossaire

Relaxation

When a constant StrainStrain describes a deformation of a material, which is loaded mechanically by an external force or stress. Rubber compounds show creep properties, if a static load is applied.strain is applied to a rubber compound, the force necessary to maintain that strain is not constant but decreases with time; this behavior is known as StressStress is defined as a level of force applied on a sample with a well-defined cross section. (Stress = force/area). Samples having a circular or rectangular cross section can be compressed or stretched. Elastic materials like rubber can be stretched up to 5 to 10 times their original length.stress relaxation. The process responsible for StressStress is defined as a level of force applied on a sample with a well-defined cross section. (Stress = force/area). Samples having a circular or rectangular cross section can be compressed or stretched. Elastic materials like rubber can be stretched up to 5 to 10 times their original length.stress relaxation can be physical or chemical, and under normal conditions, both will occur at the same time. 

How to Determine if a Physical or a Chemical Process is responsible for the Relaxation?

At normal or low temperatures and/or at short time applying stress, the stress relaxation is dominated by physical processes. At high temperatures and/or at long time applying stress, it is dominated by chemical processes. The figure below presents a curve, showing the stress applied and its relaxation over time.

The stress relaxation can be measured with the NETZSCH DMA EPLEXOR® and DMA 242 Artemis.