Experimental Study of the Rheological and Thermomechanical Properties of Greases

Greases are structured multicomponent systems whose performance depends on the composition of the base oil, the type and concentration of the thickener, the presence of functional additives, temperature, and the deformation regime. Standard reference characteristics of greases do not allow a full assessment of their actual mechanical state. This is due to the fact that viscosity, dynamic moduli, and shear resistance change non-linearly. Materials of the same class with minor compositional differences may exhibit different reactions to external influences. This makes it important to compare the performance of materials under identical deformation conditions. An experimental study of four greases was performed in this work: CIATIM-221, CIATIM-221F, TOMFLON SK 170FH, and TOMFLON SBS 240FM. Tests were conducted on a Discovery HR2 rotational viscometer with a thermal measurement system in a temperature range from −40 to +80 °C and dynamic deformation frequencies from 0.01 to 100 Hz. The study included two types of experiments: (i) temperature sweeps at a fixed deformation amplitude; (ii) frequency sweeps at a constant temperature. It was established that for all materials across the entire studied temperature range, the storage modulus exceeds the loss modulus . This corresponds to indicating a predominantly elastic or gel-like structural state at small oscillating deformations. Upon cooling, a pronounced non-linear increase in viscosity and shear stresses is observed, most pronounced at sub-zero temperatures. The frequency dependence of the shear stress is satisfactorily described by the Ostwald–de Waele power law. The exponent remains less than one, which corresponds to a pseudoplastic behavior and a decrease in effective viscosity with increasing shear rate. Comparative analysis of the materials shows that the greatest differentiation of properties manifests at sub-zero temperatures.