Instantaneous and time-dependent effect:
When a load is applied on a specimen constantly for a period of time, the specimen initially extends rapidly giving the instantaneous effect and then less rapidly which yields to time dependent effect. After removing the load from the specimen, the recovery of extension is rapid at fixed and the slowly may be with a small amount of residual extension known as ‘permanent set’.
The instantaneous extension is composed of two quantities of extension,
❶ The elastic extension which can be recovered and.
❷ The plastic or permanent extension which cannot be recovered.
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Polymeric fiber always shows viscous and elastic property (as like as silly putty toy properties)
Behavior characteristic of viscoelasticity:
There are four major types of behavior characteristic of viscoelasticity.
❶ Time dependence strain: Time dependency behavior is one of the main characteristics of any viscoelastic materials. Viscoelasticity consists of a combination of time independent elastic behavior and time dependent viscous behavior.
❷ Temperature depending strain: Temperature-elongation.When temperature greater than Tg, then the polymer can easily elongate.
❸ Stress relaxation: The stress relaxation response of a viscoelastic material. This means that the stress will be reduced or will relax under a constant deformation.
❹ Stress rate dependence strain/creep: The creep response of a viscoelastic material can be observed by applying a constant load to the material and measuring the deformation of the material over time.