Rheological tests in
large-amplitude oscillatory shear flow (LAOS)

Paulo R. DE SOUZA MENDES

Professor, Rheology Group, Pontifícia Universidade Católica, Rio de Janeiro, BRAZIL

Le 27 mai 2025 à 13h30, To be communicated

Abstract: 

We present the quasi-linear LAOS (QL-LAOS) approach, which uses large amplitude oscillatory shear (LAOS) experiments to determine—simply, directly, and robustly—the mechanical behavior of various classes of materials that may exhibit solid-like, liquid-like, viscoelastic, viscoplastic, and/or thixotropic properties. By independently varying stress amplitude and frequency, two distinct classes of material response emerge: (i) Structure-changing motions, characterized by a non-sinusoidal response, occur when the stress amplitude is sufficient to induce microstructural changes and the frequency is comparable to the inverse of the microstructural relaxation time; and (ii) Constant-structure motions, characterized by a sinusoidal response, arise either when the stress amplitude is too low to cause microstructural changes or when it is high enough to induce such changes, but the frequency is much greater than the inverse of the structural relaxation time. These two motion classes were theoretically predicted by de Souza Mendes and Thompson (Rheol Acta 52(7), 2013, pp. 673–694) and have since been experimentally validated for viscoplastic materials, viscoelastic liquids, and more recently, shear-thickening fluids. Whereas conventional LAOS analyses focus primarily on structure-changing motions, the QL-LAOS methodology is based largely on constant-structure motions. This shift significantly simplifies both the experimental procedures and the analysis, yielding material functions with clear and intuitive physical interpretations.In this talk we present results for a hair gel (viscoplastic), a polyacrylamide solution (viscoelastic), and a concentrated suspension of fumed silica in polypropylene glycol (shear-thickening).