Evaluation Method of Shear Layer Generation at Yield Behavior of Softmaters

The yield behavior and the shear layer formation during the shear flow of gels were investigated using a twin-drive rheometer, which is equipped with two driving and measuring systems. The stress-ramp test was conducted and each stress acting on the upper and lower plates was separately evaluated and compared. As a result, it was found that the stress on the fixed side plate significantly shifts from the others when the yield behavior occurs. When the stress increase rate in the stress sweep test is sufficiently low, the stress difference is eliminated after the yield and the same stresses are obtained on both plates, however, when the stress increase rate is high, the stress difference continues to occur during the test. These results demonstrated the generation of a thin shear layer at and after the yield behavior and it exists until the end of the stress-ramp test because of its non-equilibrium stress condition.