Harmonic analysis in rheological property measurement

Sudden change in the linear stress-strain relationship has long been known to produce interesting discontinuities in the flow properties of polymer melts, concentrated particle suspensions, and gels as the shear rate amplitude is increased. The non-linear effect produces stress harmonics, which contain information about the material properties that is otherwise difficult to obtain. This note describes a generalized procedure for extracting yield stress material functions from the discrete Fourier transform of the stress signal.