This paper describes the effectiveness of image analysis based on the Natural Strain theory for measuring the finite strain. Since the additive law of strain on an identical line element can be satisfied and the rigid body rotation can clearly be removed from the shearing strain components, the Natural Strain theory is significantly effective for representing the stress-strain behavior under large elasto-plastic deformation. In this study, the strain measurements under large deformation are conducted by making use of such merits into the image analysis. In our previous studies, in order to verify the effectiveness of this method, the results of strain measurement by image analysis have been compared with the results of conventional strain measurement based on the displacement meter. Consequently, since the results of both measurements almost coincide, the validity of this image analysis has been confirmed. However, these experiments were limited to uniform deformation fields, although in the range of finite deformation. Hence, as for the local deformation, the detailed measurements have not been carried out yet in our previous study. So, in this paper, the local deformations generated under uniaxial tension and simple shear are investigated as the fundamental research. Especially, the progress of local deformations is revealed by comparing the measured values of upper and middle positions in the specimen.
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