Abstract
This paper describes the finite strain measurements by image analysis based on the Natural Strain theory. Since the Natural Strain theory is the reasonable strain expression, which can remove the rigid body rotation accurately and can satisfy the addition law of strain, the feature of Natural Strain theory is used effectively into the image analysis in this study. In our previous researches, using cylindrical specimens made from tough pitch copper, the experiments for uniaxial tension, simple shear and combined load of them have been conducted. Then, the effectiveness of this method has ever been confirmed by comparing the strain measurement by image analysis suggested in this study with the conventional measurement based on the displacement meter. In the present study, the rubber shaft, which is hyper-elastic body, is selected as the subject of this research. Focusing on the torsional deformation for a rectangular cross section shaft, the shearing strain and the warping on the surface of test piece is investigated based on the image analysis suggested in this study. And distributions along the cross section, which are generated under large shear deformation, are revealed and they are compared with the results based on the conventional torsional theory of square cross section.
