stress measurement, photoelasticity, stress-optic coefficient, high-speed polarization camera, soft matter, Mechanical engineering and machinery, TJ1-1570, Engineering machinery, tools, and implements, TA213-215

Present study aims to develop a high-speed photoelasticity with a high-speed polarization camera for evaluating the stress loading on a pressure-sensitive gel by fingertip movements. Prior to this, normal stress loading and phase retardation field on the pressure-sensitive gel were measured with the calibration experiment system combining a stress loading device and the high-speed photoelasticity. The stress-optic coefficient indicating the performance of pressure-sensitive gels was calculated from the data. For the calculation of stress-optic coefficient, we performed the phase unwrapping process to remove the effect of phase wrapping on the visualization data of phase retardation field. It was experimentally confirmed that the trend in the stress-optic law was satisfied. In addition, the temporal evolution of shear stress loading by fingertip movement such as rubbing and tapping on the pressure-sensitive gel was also visualized by the high-speed photoelasticity. As a result, it was suggested that our method has a high degree of accuracy, enabling to measure slight time variation of shear stress at a level too small to be recognized by the subject performing the fingertip movements.