An Image-based Measurement Method for Plane Strain and Crack Observations

An Image-based Measurement Method for Plane Strain and Crack Observations

A simple image-based method for measuring plane strain fields on the surface of specimens in earthquake engineering experiments was developed. This method integrated camera calibration, stereo triangulation, image metric rectification and image template matching techniques to develop a method that was cost-effective, easy to apply and provided a satisfactory level of measurement accuracy. A zero-strain test conducted using this method showed that the measurement accuracy achieved was 0.04 pixels. That is, the relative displacement accuracy achieved was 0.005 mm and the strain accuracy was 0.001. This level of accuracy was achieved using eight-mega-pixel digital cameras to measure a 17cm-by-28cm measurement region. Cracks that were 0.012 mm wide were identified in the concrete by examining the displacement fields calculated through the application of this image-based method in an RC-wall experiment. Further descriptions of this method can be found in.