Question

Items are sometimes fastened to plastic parts by screw driven into smooth holes molded in the parts. Over time, however, the screws loosen. To what common laboratory test of viscoelasticity does this correspond? (Provide explanation)

Answer 1

Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain when stretched and quickly return to their original state once the stress is removed. Viscoelastic materials have elements of both of these properties and, as such, exhibit time-dependent strain. Whereas elasticity is usually the result of bond stretching along crystallographic planes in an ordered solid, viscosity is the result of the diffusion of atoms or molecules inside an amorphous material.

Stress relaxation is defined as a gradual decrease instress with time under a constant deformation or strain. This behavior of polymer is studied by applying a constant deformation to the specimen and measuring the stress required to maintain that strain as a function of time. This stress relaxation is measured from the lossening of plastic screws.