Non-Linear Oscillation Testing with a Separate Motor Transducer Rheometer

The non-linear stress response in an oscillation experiment on the SMT rheometer can be analyzed in two ways: 1. Fast sampling of stress as a function of time followed by discrete Fourier analysis or decomposition of the stress signal into an elastic and viscous component. 2. Direct correlation of the measured signals to determine the magnitude and phase of the fundamental and harmonics up to the 9th order. This method can be conveniently integrated into standard oscillation test modes providing the desired results G'. G' or magnitude ratio In(on)/I1(o)) and phase instantaneously. Nonlinear oscillation measurements on a 4 wt% Xanthan gum solution have been performed as a function of strain amplitude. Fourier coefficients of the stress signal are evaluated by direct correlation, discrete Fourier transformation and decomposition of the measured stress in a contribution in phase with the strain and one in phase with the strain rate.