Oscillatory Extension

Viscoelastic materials exhibit viscous response in slow deformations and elastic response in fast deformations. Small amplitude oscillatory deformations may be used to measure the change from viscous to elastic response. The material between the sample plates in the VADER 1000 is subjected to a small amplitude oscillatory deformation of frequency ω around a mean separation.

The results for the force on the plates are reported in terms of the storage modulus G' and loss modulus G'' as shown in Figure X. It is seen that G''>G' for small frequency implying that the material response to such frequencies is primarily viscous. Conversely for large frequency G' > G'', which implies an elastic material response. The frequency at which G' = G'' is denoted the cross-over frequency. The inverse of this frequency may be taken as a time constant for the viscoelastic material.