Authors: Niranjan Desai, Joel Poling, Gregor Fischer and Christos Georgakis
Structural health monitoring (SHM) assists engineers in maintaining structures, making them safer and more cost effective. Digital image correlation (DIC) techniques applied to SHM are non-contact, fast, and accurate techniques that are easy to apply. This investigation compared the accuracy of the smallest strain accurately measurable by the state-of-the-art DIC – based tools ARAMIS and iMETRUM, in a specimen moving out-of-plane. Initially undetected damage at low strains in connections of a realworld bridge motivated this investigation, whose detection would have restricted its spread, leading to lower repair costs. The study expands upon a preliminary study that determined the smallest strains measurable using the same DIC-based tools in a specimen that was not subjected to controlled out-of-plane movement. This initial study demonstrated that small out-of-plane specimen movements that inadvertently occurred even in controlled laboratory conditions led to noise in the DIC-based strain measurements. Hence, prior to implementing this technique in a real structure to detect small strains, it is desirable to determine the limits of out-of-plane specimen displacement within which it is practical to use this technique to measure strain. A cantilevered plate specimen was transversely loaded in the laboratory, and the longitudinal strain was measured at a selected location at different values of out-of-plane specimen displacement, using the DIC-based tools. The DIC strains were compared against those measured by traditional strain gauges. The smallest strains accurately measurable using both DIC-based tools, over a range of specimen out-of-plane displacement amplitudes, were determined.
Keywords: Structural Health Monitoring, Digital Image Correlation