Technical note: correcting for shear strain in an oscillatory squeeze flow rheometer

Currently, rheologists working in the field of oscillatory squeeze flow use extensional strain to characterize the deformations. Due to the shear-dominated flow observed in low Trouton ratio fluids undergoing squeeze flow, it is proposed that an alternate geometry-dependent definition for shear strain in squeeze flow be used instead. Through the use of finite element modelling, it has been shown that this geometry-dependent strain definition allows for better comparison of measurements between both squeeze flow rheometers of different geometric configurations and rotational rheometers. This idea was then explored through laboratory experiments, further supporting this hypothesis. While this definition of strain will only hold true within the bounds of a material’s linear viscoelastic regime, it will help to determine where this boundary is, and thus allow for more accurate material characterization. This type of relationship will become increasingly important with the growing use of squeeze flow rheometers for large-amplitude oscillatory squeezing trials.