Improved three-dimensional image correlation for surface displacement measurement

A PC-based, 3-D surface profile and displacement measurement system capable of micron-level accuracy using moderately priced off-the-shelf equipment has been developed. For use in field applications, a simplified calibration process using precision grids and camera translations is developed. An improved image correlation process is developed which corrects for perspective distortions due to viewpoint differences between the two cameras. The accuracy of the system was assessed experimentally and results expressed using several different error measures, including a new error measure proposed by the authors. The accuracy for both the profile and displacement measurement systems was established through a series of profile and translation tests. The baseline tests confirmed that the measurement system is capable of highly accurate full-field measurements. The system was also used successfully to measure both the bending of a clamped circular plate under pressure loading and the local buckling which occurs during tension loading of a cracked plate. (C) 1996 Society of Photo-Optical Instrumentation Engineers.