Stress relaxation

If you stretch a component at an elevated temperature and then keep the stretch constant through the action of external forces ( compression is a negative stretch), you will notice a decrease ( relaxation ) in the amount of stress . Stress relaxation can be observed:

• under the influence of temperature in plastics and rubber
• under "normal temperature" for prestressed steel in prestressed concrete .

The cause of the stress relaxation is that, due to diffusion processes in the structure , part of the elastic strain changes over time into plastic strain ( creep deformation ). This relieves the tension until a new equilibrium position is reached between the molecules .

In the case of rubber under long-term stress , there is also a chemical rearrangement in addition to the physical : the sulfur networks are opened and re-form in "relaxed" positions. A measurement method for stress relaxation in rubber is described in ISO  3384.

a) Applied strain and b) evoked stress as a function of time in a viscoelastic material.

Stress relaxation can be explained using rheological models .

See also

• Mechanical spectroscopy
• Relaxation attempt
• Complex shear modulus