Glossary

Creep Compliance (J) 

Creep Compliance (J) is the shear 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 divided by shear 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 as a measure of instantaneous continuous flexural deformation of a material under static 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 loading over time, reported in Pa-1:
J(t)=γ(t)∕σ

It is mathematically the inverse of a material´s complex shear modulus, and can be considered a normalized strain (displacement) based on the applied stress.

In a creep test, a sample is subjected to a shear stress set by the user ‘instantaneously‘ and the resulting deformation is monitored as a function of time. After a set time period, the load is removed and the deformation is again determined. The figure below shows the three typical reaction courses.

Since the actual change in deformation depends on the load applied, it is normally referred to as compliance rather than deformation. Compliance is simply defined as the ratio of deformation to applied stress and is marked with the letter J (J 0 = deformation/load). Due to this, creep curves can even then be compared if they were not measured under the same shear stress applied.