In this research project, ER Fluid consisting of 2.5 μm glass particles and nano-sized PZT particles were used. A new ER property enhancement method called "Creep-Recovery cycles" has been introduced. By applying constant shear stress to the ER Fluid, followed by a recovery process, shear modulus and yield stress is greatly enhanced. This phenomenon can be explained by the removal of defects and re-formation of chains under constant shear stress. The re-formed chains will then combined to form stronger columns during the recovery process....[ Read more ]

In this research project, ER Fluid consisting of 2.5 μm glass particles and nano-sized PZT particles were used. A new ER property enhancement method called "Creep-Recovery cycles" has been introduced. By applying constant shear stress to the ER Fluid, followed by a recovery process, shear modulus and yield stress is greatly enhanced. This phenomenon can be explained by the removal of defects and re-formation of chains under constant shear stress. The re-formed chains will then combined to form stronger columns during the recovery process.

The enhancement effect depends on 1) time duration of constant shear stress; 2) magnitude of constant shear stress; 3) number of Creep-Recovery cycles used. The time duration of constant shear stress should be suitably chosen so that it can provide sufficient time for the chains to re-form, but not too long to avoid any destruction to the ER structure. The magnitude of constant shear stress increases with the enhancement effect until a critical value, beyond which the ER Fluid will flow and no enhancement effect will be observed. The enhancement effect also increases with the number of Creep-Recovery cycles used. However, after a large number of Creep-Recovery cycles, the ER Fluid will reach a stable state where no further enhancement effect will be observed.

Since purely elastic deformation is desirable for the shear modulus measurement, shear modulus can be measured after having the Creep-Recovery cycles because only elastic deformation exists. However, the number of Creep-Recovery cycles must be large enough so that the ER Fluid has reached a maximum enhanced state at which no further enhancement can be observed.