Creep testing experimental techniques

There are several other comparable rheological experimental methods involving linear viscoelastic behavior. Among them are creep tests (constant stress), dynamic mechanical fatigue tests (forced periodic oscillation), and torsion pendulum tests (free oscillation). Viscoelastic data obtained from any of these techniques must be consistent data from the others. 

Creep or stress relaxation tests may be made at a series of different stresses or strains to create a family of curves. A relation where strain is a function of stress and time will exist between the curves, and this relationship can be represented as a surface in three dimensions. Computer techniques allow this surface function to be generated, including smoothing of the experimental data. 

To determine the movements of the whole chain and those of subchains, various techniques are accessible and available to the experimenter, including dielectric spectroscopy and mechanical spectrometry. Dielectric techniques are suitable for the study of polymers in a wide range of frequencies (between 10 Hz and 10 ° Hz), while the mechanical dynamic characterization of polymers provides access to long relaxation times (>10 s) through creep and stress relaxation tests. 

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