Abstract
An experimental study was conducted to explore the normal force of lithium-based magnetorheological (MR) grease under quasi-static shear. Firstly, MR grease with various carbonyl iron (CI) particles content was prepared. Then the influence of magnetic field strength, CI particles content, shear rate and temperature on the normal force–strain curves for MR grease under a quasi-static monotonic shear condition were investigated. The results exhibit that the normal force of MR grease under quasi-static monotonic shear decreases first and then maintains constant along with the increase of shear strain, and the critical strain is affected by the magnetic field strength and CI particles content. Finally, the normal force versus shear strain curves under different magnetic fields and shear strains were obtained by using quasi-static cyclic shear. It was found that the normal force of MRG-70 under quasi-static monotonic shear exhibits peak phenomenon at the beginning of the unloading stage, and the peak value increases with the enlargement of shear strain. Furthermore, when the strain amplitude is higher than 40%, normal force exhibits an abrupt change during the transition from the loading stage to the unloading stage.
Highlights
MR grease is a member of the family of MR intelligent materials with tunable rheological properties under the in uence of an external magnetic eld
See et al conducted an experiment to study the normal force of MR uid under ow conditions, the results showed that the normal force of MR uid is correlated with the shear rate
MR grease used in this paper consist of carbonyl iron (CI) particles dispersed in a commercial lithium-based grease
Summary
MR grease is a member of the family of MR intelligent materials with tunable rheological properties under the in uence of an external magnetic eld. When an external magnetic eld is applied, the CI particles in MR grease can form a chain or cluster structure, causing a change in the yield stress of MR grease. In the eld of engineering application of MR devices, the external loading condition that applied to MR device are mainly classi ed into three types, i.e. static load, quasi-static load and dynamic load, which are o en differentiate by loading rate (shear rate). For real-life engineering applications of MR grease dampers to civil infrastructures, i.e., building and bridge, MR grease is o en subjected to the combination of large deformation and quasi-static shear loadings. The in uence of the shear rate and temperature on the magnetic-induced normal force of MR grease with different CI particles content under quasi-static monotonic shear were tested and analyzed. The shear strain dependence magnetic-induced normal force under quasi-static cyclic shear were investigated in detail
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