Volume 24, Issue 5

It is well known that the shear and shear rate are not uniform in the azimuthal flow within the gap between parallel concentric disks - perhaps the most versatile among the geometries used in rheometry. This flow inhomogeneity represents a disadvantage, because the data analysis becomes intricate. Typically the stress is calculated at the rim with the assumption that it varies linearly with the radial coordinate, and then a correction is applied. This correction may be very large, depending on the nature of the sample, type of test, and range of parameters. While for steady-state shear flow different methods for correcting the stress are available, for transient flows they are rather scarce and in some cases unavailable. In this work we analyze in detail the stress correction for the main rheometric experiments, and discuss when it is needed. To this end, we performed different tests with a commercial hair gel and a polyacrylamide solution. For oscillatory flows, a simple equation to correct the stress amplitude is obtained in terms of the amplitudes of the torque and shear rate.

This historical study deepens the rheologist’s understanding of the motto of The Society of Rheology, of its history, and of its many typographies. The motto “παντα ῥει̃” is not verbatim something written or said by the ancient Greek Ionian philosopher Heraclitus, ca. 540- 480 BCE. Rather it is first encountered much later, in the writings of the Roman Simplicius ca. 490- 560CE. Thus, although it is uniformly agreed by Greek scholars that it correctly and concisely distills Heraclitian philosophy, that of constant change, and although this is appropriately used as the motto of The Society of Rheology, there is little point in trying to rewrite it into another form (for example to capitalize it) in an effort to be more faithful to an ancient prototype. Rather, we suggest simply reinstating the two missing diacritical marks, and thus, to express it as “πάντα ῥει̃“ which is the form in which the motto was introduced in 1929. This is also consistent with current typography of ancient Greek writings, in use since the ninth century CE, following the byzantine scholars. We provide Table 1 to facilitate accurate typesetting of the motto.

Large amplitude oscillatory shear (LAOS) rheology is often performed in order to complement steady simple shear (SSS) rheology, i.e., probe rheological properties of materials that cannot be not observed with SSS alone. However, it is difficult to measure the SSS rheology of some problematic materials due to fracture and ejection, and LAOS may alleviate these issues, at least partially. Therefore, it is of interest to obtain SSS rheology information from LAOS measurements. We show that a constitutive modeling approach may be used to unify the analysis of LAOS data obtained from different viscometric geometries and modes of control and that the LAOS data may be used to predict SSS profiles. A model elastoviscoplastic material, a Carbopol solution, was used to validate the approach experimentally. LAOS rheometry of problematic biomass slurries was also performed, and the SSS profiles for the slurries were predicted with more confidence than could be obtained from SSS measurements directly.

The aim of this study is to propose a theoretical frame that is able to lead someone to an appropriate way of modeling cementbased material extrusion. It clearly appears that different extrusion scenarios may occur. Cement-based materials are viscoplastic materials that may undergo drainage during an extrusion process carried out at low velocity. Four material behaviors can be encountered: perfect plastic, viscoplastic, frictional plastic (with evolving properties) and frictional viscoplastic (that has never been reported in the literature as drainage occurs when ram velocity is low and thus when viscous effects can be neglected). In this work, criteria are proposed to choose the more relevant way to model extrusion. Then, models are proposed for the possible extrusion scenarios.

In this work, the viscosity of soybean oil subjected to thermal degradation has been determined and related to the chemical composition of the oil. In particular, it is found a linear relationship between the viscosity value and the triglycerides content during the degradation process (an increase of the former is associated to a decrease of the latter). Thus, it is shown that viscosity provides us a reliable way of measuring oil degradation and, insofar as proportional to flow time, it allows for the design of simple devices to control the oil quality. Besides, the study of the viscosity behavior along with the changes in composition during the cooking time, i.e. the period of time that the oil is being heated, give us valuable information about the type of chemical reactions occurring within the oil.