Characterization of nonlinear viscoelasticity of magnetorheological grease under large oscillatory shear by using Fourier transform-Chebyshev analysis

Abstract

Magnetorheological (MR) grease, which is a type of magneto-sensitive smart material, exhibits complex viscoelastic behavior under different magnetic fields. Storage and loss moduli from oscillatory test are commonly used to characterize such field-dependent viscoelastic behavior. However, they are not able to represent the higher harmonic nonlinearity appeared in oscillatory responses under large amplitude oscillatory (LAOS) shear. In this paper, an investigation is conducted on the characterization of the filed-dependent nonlinearity of MR grease under LAOS by utilizing of Fourier transform (FT)-Chebyshev analysis. To capture the higher harmonic nonlinearity for the modeling and analysis, a comprehensive test program has been conducted. Firstly, MR grease with 70% weight percentage of carbonyl iron particles (MRG-70) is prepared and the stress response of MRG-70 under the oscillatory shear from small to large strain amplitudes with different magnetic field are measured. Then the higher harmonics in stress response signal are used to detect the intercycle nonlinearity of MRG-70 and compare with the traditional analysis method of dynamic modulus. Further, the elastic and viscous measures from FT-Chebyshev analysis are obtained to capture the inter-/intracycle nonlinear behaviors, that is, strain stiffening/softening, shear thickening/thinning, of MRG-70 under LAOS. It is found that, in the presence of magnetic fields, the onset of the intercycle nonlinearities of MRG-70 is originated from shear thickening of MR grease. With the further increase of the shear strain, MRG-70 exhibits the nonlinearities with different combinations of strain stiffening/softening and shear thickening/thinning.

Rheological Performance of Magnetorheological Grease with Embedded Graphite Additives

“…This suggests that more energy dissipated through heat at high magnetic field strength, promoting more inter-particle interactions between CIPs [ 39 ]. However, the increasing loss modulus at a higher magnetic field might be due to the complicated structure attributed to the combination of the grease’s matrix fiber structure with an induced-magnetizable chain structure [ 40 ].…”

Field-Dependent Viscoelastic Properties of Graphite-based Magnetorheological Grease

“…In order to understand the viscoelastic behavior of MRG, rheological analysis under oscillatory mode with varied strain and frequency range need to be carried out. The viscoelasticity behavior of MRG basically was studied through storage (G') and loss (G'') modulus [22]. Storage modulus refers to the elastic behavior of the samples that depends on the formation of a chain-like structure and is related to energy storage [23].…”

Effect of magnetic field on the lubricating performance of nano magnetorheological grease at different temperatures

“…As a new type of smart material, magnetorheological grease, particularly its unique rheological properties, has received considerable attention from researchers. Wang et al (2021) prepared carbonyl iron powder magnetorheological grease. The stress response of the magnetorheological grease under oscillatory shear from small to large strain amplitude was observed under different magnetic fields.…”