At low deformation G' and G'' are constant; the sample structure is undisturbed. This region is called linear-viscoelastic (LVE). As soon as the moduli start to decrease, the structure is disturbed, viz. the end of the LVE-region is reached: the plateau value of G' in the LVE-region describes the rigidity of the sample at rest; the plateau value G'' is a measure for the viscosity of the unsheared sample. The ratio of the two moduli gives information about the characteristic of the sample: If the storage modulus is larger than the loss modulus - like shown in figure 1- the sample behaves more like a viscoelastic solid. In the opposite case - G'' > G' in the LVE-region - the sample has the properties of a viscoelastic fluid.
As larger the difference between the moduli as more the samples show the properties of a pure fluid and solid, respectively.
With the amplitude sweep also the yield point can be determined. Therefore two special points can be used: the end of the LVE-region and the intersection of the curves for G' and G''. In most cases the intersection of G' and G'' is of more practical importance.