Stress relief and stress relaxation are two entirely different concepts. Sometime they are confused with each other. In this article we will explain what each of these terms means.

What is Stress Relief?

Stress Relief is the heat treatment of a material to reduce residual stress. Stress relieving may be used with a variety of materials including plastics, steels and non-ferrous materials such as copper alloys and aluminum. 

In general, stress relieving involves heating components to a temperature where the yield strength is sufficiently low, and the residual stresses can redistribute and relieve themselves.

There are several types of stress relief processes such as vacuum stress relief, air stress relief and deep cryogenics.

What is Stress Relaxation?

Stress relaxation is a time-dependent decrease in stress under a constant strain [1]. The figure below shows a typical stress-time curve for a polymeric material.

Stress relaxation typically occurs in viscoelastic materials, especially polymeric materials.

Hopefully this article clears up any confusion related to these terms.

[1]  Thermoforming of Single and Multilayer Laminates, Syed Ali Ashter