Creep Compliance (J)

Creep Compliance (J) is the shear strain divided by shear stress as a measure of instantaneous continuous flexural deformation of a material under static 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.