Digital Image Correlation

2-D Digital Image Correlation

AP/ES, Inc. has on-site a system for performing 2-D Digital Image Correlation - a measurement of full-field strains that is based on optically measured displacements of a speckle-painted pattern on a static or fatigue test coupon. The system consists of a high-speed CCD camera (manufactured by Point Grey) that is interfaced with a dedicated MS Windows PC. The PC has software (Correlated Solutions, Inc.) for rapid acquisition of the digital images from the camera, and software for performing the correlation that computes the full-field strains based on a reference, unstrained image. The primary advantage of measuring full-field strains is that one is not limited to measuring strains at predetermined discrete points and vectors, which is a limitation if one is using traditional strain gage technology.

AP/ES has used this Digital Image Correlation system for verifying the ASTM-E8 strains measured by an extensometer, measuring strains due to cold working of a fastener hole, and measuring strain relaxation over time and over cyclical stress histories in a variety of specimens.