Development and implementation of a low cost image correlation system to obtain full-field in-plane displacement and strain data

Abstract

When using multi-axial testing, obtaining in-plane strain and displacement data can be difficult and costly. Montana State University's In Plane Loader (IPL) can apply any number of loads in the X and Y axes and as rotation but can only provide the displacement data at the grips. This project uses a Canon consumer-model digital single lens reflex camera and a series of matlab codes to provide in-plane displacement and strain data at as many points on the surface of the loaded specimen as required using Digital Image Correlation. The system has been successfully used to measure surface and boundary displacements on composite and aluminum samples, as well as on glued aluminum joints. The software system has been shown to estimate strains with a strain error of less then 0.0002 m/m or ±0.5% placing it within ASTM-B2 classification. It also has been shown to measure displacements to within 0.02 pixels accuracy, which for tests on the IPL translates to 0.007mm. The hardware/software system has also been used with the IPL to estimate Young's modulus of aluminum with less then 5% error and yield strength with just over 10% error.