<P> The secondary bonds of a polymer constantly break and reform due to thermal motion . Application of a stress favors some conformations over others, so the molecules of the polymer will gradually "flow" into the favored conformations over time . Because thermal motion is one factor contributing to the deformation of polymers, viscoelastic properties change with increasing or decreasing temperature . In most cases, the creep modulus, defined as the ratio of applied stress to the time - dependent strain, decreases with increasing temperature . Generally speaking, an increase in temperature correlates to a logarithmic decrease in the time required to impart equal strain under a constant stress . In other words, it takes less work to stretch a viscoelastic material an equal distance at a higher temperature than it does at a lower temperature . </P> <P> Extreme cold temperatures can cause viscoelastic materials to change to the glass phase and become brittle . For example, exposure of pressure sensitive adhesives to extreme cold (dry ice, freeze spray, etc .) causes them to lose their tack, resulting in debonding . </P> <P> When subjected to a step constant stress, viscoelastic materials experience a time - dependent increase in strain . This phenomenon is known as viscoelastic creep . </P> <P> At a time t 0 (\ displaystyle t_ (0)), a viscoelastic material is loaded with a constant stress that is maintained for a sufficiently long time period . The material responds to the stress with a strain that increases until the material ultimately fails, if it is a viscoelastic liquid . If, on the other hand, it is a viscoelastic solid, it may or may not fail depending on the applied stress versus the material's ultimate resistance . When the stress is maintained for a shorter time period, the material undergoes an initial strain until a time t 1 (\ displaystyle t_ (1)), after which the strain immediately decreases (discontinuity) then gradually decreases at times t> t 1 (\ displaystyle t> t_ (1)) to a residual strain . </P>

During which type of stretching does viscoelastic creep occur