Filled Rubbers Missing High Harmonics in LAOS

In the present work, the rheological properties of a number of filled elastomers under large amplitude oscillatory shear conditions are investigated. In the nonlinear regime the stress outputs of filled rubbers are surprisingly sinusoidal and essentially absent of any high harmonics. Fourier transform analysis shows that the ratio of the third to the first harmonic responses (I₃/I₁) in the range when G’ loses 70% of its original value and G” passes through its maximum is typically less than 4%. As the strain amplitude increases the ratio I₃/I₁ also displays a maximum and can be linearly corrected with the damping factor tanδ. Such a relationship is independent of the filler content and may reveal some important fundamentals behind this phenomenon.