Retardation is the delayed response to an applied
force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...
or stress and can be described as "delay of the elasticity".
Ideal elastic materials show an immediate
deformation after applying a jump-like
stress, and an immediate reformation after removing the stress afterwards in the jump-like form again. For
viscoelastic
In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linear ...
samples, this elastic behaviour occurs with a certain time delay.
The term "
relaxation time
In the physical sciences, relaxation usually means the return of a perturbed system into equilibrium.
Each relaxation process can be categorized by a relaxation time τ. The simplest theoretical description of relaxation as function of time ' ...
" has been described. It is used in combination with tests presetting the strain (
deformation) or
strain rate
In materials science, strain rate is the change in strain ( deformation) of a material with respect to time.
The strain rate at some point within the material measures the rate at which the distances of adjacent parcels of the material change ...
(
shear rate
In physics, shear rate is the rate at which a progressive shearing deformation is applied to some material.
Simple shear
The shear rate for a fluid flowing between two parallel plates, one moving at a constant speed and the other one stationary ...
), eg, when performing
relaxation tests.
On the other hand, the term "retardation time" is used for tests when presetting the stress, eg, when performing
creep tests.
See also
*
Creep-testing machine A creep-testing machine measures the alteration of a material after it has undergone stresses.
Engineers use Creep machines to determine the stability and behaviour of a material when put through ordinary stresses. They determine how much stra ...
References
Rheology
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