Strain analysis in deformation experiments with pattern matching or a stereoscope

Abstract

The subject of this paper is the analysis of planar deformation in deformation experiments where the specimen can be observed throughout deformation, or at regular intervals. The critical step in the analysis of deformation is the determination of displacements of material points over a deformation increment. Pattern matching is a useful and accurate method to perform this task. This method is most suited for the measurement of strain over small deformation increments, where it can produce better results than strain measurements with strain markers or inscribed grids. It is well suited for geological deformation experiments with for instance sand or clay boxes or transparent deformation cells. The distribution of strain can be made visible with a stereoscope and two images of the deforming specimen taken at different stages of deformation. The differences in relative displacement of features on the images are translated by the brain to apparent elevation. The gradient of the slope depends on the magnitude of finite strain. A stereoscope is thus a cheap and simple tool to quickly and qualitatively assess strain distribution in a deforming specimen.