SHEARING STRAIN OF SQUARE CROSS-SECTION SHAFT BY IMAGE ANALYSIS IN LARGE TORSION AFTER AXIAL LOAD

Abstract

This paper describes the characteristics of the distribution of shearing strain along the cross section when a large torsion after axial load is applied to a test specimen having a square cross section made of natural rubber. As for the measurement of finite strain under large deformation, a method based on image analysis, which can continuously measure a wide range from infinitesimal deformation to large deformation, is effective. Therefore, in the present study, a method by image analysis is adopted as measurement of shearing strain that occurs under large torsion. On taking image data, marking-off lines are preliminarily drawn on the surface by describing equally-spaced parallel lines vertically as well as horizontally, and images of horizontal elements along cross sections at upper position or center position of the test specimen are taken with high-resolution cameras with macro lens. The shearing strain distributions in the transverse section are measured by using the image analysis reflecting the Natural Strain theory. Then, these distributions are compared to the distribution based on the torsion theory of shaft having square cross-section, commonly known as the Saint Venant's torsion theory, and the distribution of modified theory that considers the elongation between gauge points. Moreover, the experimental results in this study are compared with the results of our previous study, which is obtained by applying only large torsion, and the effects of initial axial load on the shearing strain distribution are revealed.