Background: Electrorheological fluids, when subjected to an external electric field, show
radical and reversible changes in their physical properties: Rheological, thermal, electrical - as a result
of the structuring of the dispersed phase particles. This article presents the results of experimental
studies of the viscoelastic properties of high-concentrated electrorheological fluids with complex dispersed
phase in a pre-yield area under shear stresses below the yield stress in different deformation
modes. The components of the dispersed phase were bentonite clay and chromium phosphate or
aerosil and chromium phosphate.
Objective: The objective of this work is to determine dependencies of the viscoelastic parameters of
high-concentrated electrorheological fluids with complex dispersed phase on electric field strength
and on dispersed phase composition in different regimes of mechanical tests, to establish general
regularities of electrorheological fluids deformation in non-stationary conditions.
Methods: The investigation of the rheological properties in a pre-yield area under shear stresses below
the yield stress were carried out in the following shear regimes: the forced tangential sinusoidal
oscillations with constant frequency, linear increase of shear stress, linear increase of normal stress
(compression mode), creep mode at constant shear stress and its cessation.
Results: It was found that the sample with dispersed phase based on bentonite clay and chromium
phosphate shows the biggest increase in the values of the components of the complex shear modulus
among the studied compositions. The most robust static structure is observed in the sample containing
aerosil and chromium phosphate. Preliminary holding in electric field (5 min) leads to hardening of
the structure: in creep mode and under linear increase of shear stress the deformation decreases by 2-3
times. In the compression mode fluids exhibit linear elasticity for high field strengths in the investigated
range of normal strains. At lower field strengths there is weakening of the structure and nonlinear
deformation development with shear strain increasing.
Conclusion: Variation of the regimes of mechanical tests and of electric field strength in combination
with purposefully changed composition of electrorheological fluids makes it possible to vary their
mechanical behavior. This allows one to create purposefully materials that have such characteristics
as rigid, elastic, viscous, plastic properties and their combinations. The experimental dependences obtained
in the work allowed the offering of a generalized non-stationary rheological model of elastoviscoplastic
behavior of electrorheological fluids.