called as pacl 15 3 with five different electric field strengths when electric field is not applied the shear stress increases linearly with the shear rate increase however after electric field is applied the shear stress is jumped up to and then maintained at a certain value until the shear rate reaches a u201c critical shear rate u201d while the shear viscosity decreases with shear rate the decrease of shear viscosity is larger with electrical field increase that shows general shear thinning behavior because of the high volume fraction of nanocomposite particles in the er fluid non newtonian behavior with a slope less than 1 is observed even with no applied electric field furthermore a u201c critical shear rate u201d for pseudo newtonian behavior has been observed in the high shear rate region herein the term u201c critical shear rate u201d means a critical point in which a shear stress increases again after decrease or maintenance so that the fluid exhibits newtonian behavior 0030 fig5 a and 5b compare the shear stress and shear viscosity curves with three different er fluids among them the pacl 15 3 system shows the highest er property in the case of the fluid containing the particle pacl 30 it seems not to show er behavior it is assumed that the optimized condition exists near pacl 15 3 0031 fig6 shows the change of static yield stress u03c4 y with different electric fields e in a functional form of u03c4 y u221d e 1 86 this result differs from the theoretical prediction that u03c4 y is proportional to e 2 the difference would be due to.