Rheology is the science for flow and deformation of matters. Although rheology is closely related to tribology as seen in the Stribeck diagram, it must be separately considered. For instance, rheology has been developed for linear viscoelasticity owing to the linear response theory, whereas the material response discussed in tribology is in general under highly non-equilibrium. Besides, even under fast and large deformations, rheological measurements are usually performed under laminar flows and non-slip boundary conditions, which are far from the tribological conditions.
Paints are manufactured by dispersing raw materials. Paint films are formed via coating, drying, and curing process. In other words, the functions of paints express after a lot of processes. To control the processes mentioned above especially coating process, altering the rheological properties of paints is effective. In this session, we introduce the application of rheology through some examples in practice. First, we explain why rheology is useful for controlling each process. Then, we introduce the relation between each process and the shear rate in steady flow, which is usually measured in order to control the processes. Finally, we explain the development of spatter-less paint for roller-coating based on rheological analysis, which is a good example of industrial application of rheology.
This paper first outlines the rheological model used for flow analysis of fresh concrete that has not yet hardened. Next, the classification of the flow analysis method for fresh concrete is shown, and examples of analysis by the MPS method, which the authors have been working on in recent years, is described. Finally, I would like to describe the expectations and prospects for the rheology of fresh concrete.
“Rheology”is very useful in the development of cosmetics. Rheological measurement is effective in obtaining quantitative and reproducible results, although the sensory evaluation is the mainstream method for evaluating the usability of cosmetics. The feeling of the cream correlates with its viscosity at a shear rate of 103 s−1, which can be measured with a commercial rheometer. To obtain a better correspondence, it was found to be effective to measure the viscosity in the high shear rate range (104-105 s−1) by narrowing the gap between samples. The viscosity of α-gel, a base material for cosmetics, showed a two-step change with aging, and the frequency sweep indicated the existence of two relaxation mechanisms. It was suggested that these changes corresponded to the multi-lamellar vesicle and the lamellar structure, which undergo the phase transition with aging. We performed to visualize the change in internal structure under shear flow by Rheo-SALS measurement. In some samples, the internal structure was elongated (oriented) in the flow direction with applied shearing, suggesting that it may be necessary to consider the structural recovery and stability. Rheo-optic measurements such as Rheo-SALS can be used to evaluate the formation of millimeter-sized structures based on the molecular orientation induced by shear flow, and thus can be expected to be used for the above-mentioned studies in the future.
Food rheology is the study of deformation and flow of food materials and processed foods under well-defined conditions, it has been shown to be closely correlated with food texture. There are many areas where rheological data are required by the food industry including plant design, process control, quality control, evaluation of sensory attributes, assessment of food structure and conformation of constituents. Food texture encompasses chemical, physical, physiological, and psychological characteristics perceived by the senses. Hydrogels are water insoluble, cross-linked, three-dimensional networks of polymer chains, containing water in the voids between polymer chains. Cross-linking facilitates insolubility in water and provides required mechanical strength and physical properties. The ability of a hydrogel to hold a significant amount of water infers that the polymer chains must have at least moderate hydrophilic character. This article summarizes the type and microstructure of hydrogel, palatability of foods, perceptual process of food texture, objective evaluation methods of food texture, and the relation between microstructure and food texture of hydrogel foods.
Vascular endothelial cells are constantly exposed to mechanical stimuli, including fluid shear stress, caused by blood flow. It has been widely known that fluid shear stress can modulate cell alignment, proliferation, differentiation, migration, and cytokine secretion. These morphological and functional responses of cells to the stimuli play important roles not only in the maintenance of physiological functions of the blood vessel but also in the development and progression of diseases. This review summarizes cellular responses induced by fluid shear stress on vascular endothelial cells, which have been extensively investigated in vitro over the last three decades. In addition, the possible mechanisms by which endothelial cells sense shear stress are also introduced briefly.
Oil film and cavitation are formed around the EHL contact area in machinery that utilize rolling contact mechanism. The shape of these regions has a great influence on the supply of lubricating oil to the EHL contact area. However, many researchers only treated the oil films under low load or low peripheral velocity conditions. Therefore, in our previous study, we visualized the oil film and the cavitation under the high load and the high peripheral velocity conditions. As a result, it was confirmed that cavitation decreased in high peripheral velocity and the atmosphere was sucked in from the rear part of the oil film. Moreover, it was concluded that these phenomena occur caused by the pressure difference of oil film around the EHL contact area. Therefore, in this study, the pressure distributions in the oil film were estimated utilizing the PIV analysis results and the Navier-Stokes equation. As a result, it was found that the change of pressure around the cavitation with respect to the peripheral velocity was related to the change in the cavitation length. Moreover, it was also found that the pressure on both sides of the rear region in the oil film was the lowest.
Rolling element bearings are required to rotate with as little energy as possible. For grease lubricated rolling element bearings, the behavior of grease inside the bearings is a factor in the friction torque. In order to reduce bearings friction torque, it is important to control the grease behavior. However, it is difficult to predict or observe the grease behavior inside the bearing, and its behavior is not well understood due to complex mechanical properties. In this study, authors have developed a visualization method of the grease behavior inside bearings. This visualization uses colorant added grease which changes color as the grease passes through narrow clearances in micro meters inside the bearings. This paper reports the visually obtained grease behavior inside a deep groove ball bearing 6204 under different rotational speeds. When the friction torque of the bearing is high, it is presumed that grease is passing through the clearance between the cage and the ball or the vicinity of EHL contact area.
We characterized the adsorption and desorption behavior of a sulfur-type extreme-pressure (EP) agent in a mixture of dodecane and methyl oleate (MO) as a model polar oil. The solid material used in this study was iron oxide or steel. The quartz crystal microbalance with dissipation monitoring technique revealed that the residual mass of the EP agent, measured after rinsing the adsorption film by dodecane or the mixture of dodecane and MO, was smaller in the mixed oil than in dodecane. This indicates the lesser adsorption ability of the EP agent in the mixed oil, resulting from the facts that (i) the solubility of the EP agent in the mixed oil is larger than that in dodecane, and (ii) the competitive adsorption between the EP agent and MO occurs on the iron oxide surface. We also analyzed the surface composition of the steel substrate, followed by thermal treatment of the adsorption film. The addition of MO required higher temperatures to yield a reaction film of the EP agent. Although the residual mass of the EP agent in the mixed oil was smaller than that in dodecane, no significant difference in a lubrication ability was observed between the two reaction films.