Viscoelastic Behavior of Plastics

The stress-strain behavior of most materials can be approximated quite accurately, over certain ranges of stress and strain, by a simple mathematical relation. This relation, known as Hooke\u27s law, states that the stress applied to a material is proportional to the resulting strain. This type of behavior is known as linear elastic behavior. Linear elastic behavior is independent of time, since stress depends only on the amount of strain or vice versa. In this respect viscoelastic behavior is quite unlike linear elastic behavior for viscoelastic behavior is a time dependent phenomenon. Specifically, viscoelastic behavior is dependent on the rate at which stress or strain is applied. In addition, viscoelastic behavior can also be distinguished from linear elastic behavior by the presence of creep, increasing deformation with time, when a constant load is maintained. Similarly, viscoelastic phenomenon whereby stress decreases with the passage of time when a constant strain is maintained