Stress relaxation

This should not be confused with creep, which is a constant state of stress with an increasing amount of strain.

Since relaxation relieves the state of stress, e equipment reactions.

Thus, relaxation has the same effect as cold springing, except it occurs over a longer period of time.

The amount of relaxation which takes place is a function of time, temperature and stress level, thus the actual effect it has on the system is not precisely known, but can be bounded.

Because they are viscoelastic, polymers behave in a nonlinear, non-Hookean fashion.

Experimentally, stress relaxation is determined by step strain experiments, i.e. by applying a sudden one-time strain and measuring the build-up and subsequent relaxation of stress in the material (see figure), in either extensional or shear rheology.

One viscoelastic model, called the Maxwell model predicts behavior akin to a spring (elastic element) being in series with a dashpot (viscous element), while the Voigt model places these elements in parallel.

The extracellular matrix and most tissues are stress relaxing, and the kinetics of stress relaxation have been recognized as an important mechanical cue that affects the migration, proliferation, and differentiation of embedded cells.

is the maximum stress at the time the loading was removed (t*), and n is a material parameter.

Vegener et al. use a power series to describe stress relaxation in polyamides:[3]

To model stress relaxation in glass materials Dowvalter uses the following:[3]

The following non-material parameters all affect stress relaxation in polymers:[3]