TiO2 전기유변 유체의 수직 응력을 실험적으로 측정하고 전산모사도 수행하였다. 전기장 하에서 수직 응력은 입자

사이의 수직 방향의 정전기 인력에 의해 음수 값을 보였고, 수직 응력의 절대값은 전기장의 증가에 따라 급격하게 상

승하였다. 전단 응력에서처럼 수직 항복 응력도 E2에 비례하는 특성을 보여, 수직 응력을 전기유변 현상의 평가에 활

용할 수 있음을 나타냈다. 수직 응력의 거동을 이해하기 위해 수행한 전산모사는 수직 응력이 실험 결과와 정성적으로

잘 일치함을 보여 주었다. 또한 전기장 하에서는 전단 속도가 증가함에 따라 수직 응력의 절대값이 줄어드는 경향은

전단 속도에 따른 입자들의 구조 변화로 발생하는 것으로 나타났다.

The normal stress of TiO2 ER fluid under an electric field showed negative values due to the electrostatic

attraction force in the normal direction between particles and the absolute value increased dramatically with electric field

strengths. The normal yield stress exhibited E2 dependence similar to the dynamic yield stress, indicating that normal

stress can be utilized for evaluating the ER effect. Numerical simulation demonstrated good qualitative agreement with

the experimental data and suggested that the decrease in the absolute value of normal stress with increasing shear rates

was attributed to the rearrangement of particle configurations under shear.

Electrorheology, Normal stress, Electrorheological fluids, Polarization model, Dynamic simulation

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