Although the viscoelastic response of a polymer can be very complex (time-dependent stress cycling for instance), two special loading scenarios are fairly simple to describe mathematically.
refers to scenarios for which the stress applied to a polymer must decay over time in order to maintain a constant strain. Otherwise, over time, the polymer chains will slip and slide past one another in response to a constant applied load and the strain will increase (in magnitude).
refers to scenarios for which a polymer will permanently flow over time in response a constant applied stress.

Viscoelastic stress relaxation

Viscoelastic creep

Explanation:

Viscoelastic stress refers to the reduction of tensile stress with the relaxation time that occurs when the body is kept at a certain length under tensile stress. The purpose of this study was to demonstrate viscoelastic stress relaxation Therefore, when the viscous tension stress occurs, the pressure decreases due to the steady-state stress of the phases.When under constant pressure, the viscoelastic material experiences a time-dependent increase in pressure. This phenomenon is called viscoelastic creep. Therefore the phase constant pressure decreases when there is relaxation in the viscoelastic stress