A purely elastic material differs widely in its deformational characteristics from a purely viscous material. The stress in a purely elastic material is a function of the instantaneous magnitude of deformation only, whereas the stress is a function of the instantaneous rate of deformation only, in a purely viscous material. Many substances, including dispersions and composites, exhibit viscoelastic behavior. They flow under the influence of applied stresses, unlike purely elastic materials, which exhibit a constant strain and no flow. Both steady and unsteady shear measurements are carried out to evaluate viscoelasticity of materials. In steady shearing motion, elasticity causes normal stress effects. Among the various techniques available to study the linear viscoelastic behavior of materials, oscillatory testing at small strain amplitudes is very popular. In the oscillatory shear experiment, the material is subjected to a sinusoidal shearing strain, which may be represented by either a sine or a cosine function.