Dynamic Strain Measurements Using Digital Image Correlation

Abstract

Many structures in North America are reaching the end of their design lives but some are still fit for purpose while others require repair or replacement. Currently, to assess these structures, subjective visual inspections are relied upon. An alternative technology that can be used is Digital Image Correlation (DIC). DIC is a technique that uses digital images of an object (e.g. a critical element of a structure) before and after load is applied to create a 2-D displacement field for the object. If this displacement field can be measured with a sufficiently high resolution, these displacements can also be used to determine a 2-D strain field. Recent progress in this area has led to the development of contactless strain sensors that are suitable for lab use under quasi-static conditions. The current research explores the possibility of using high speed cameras to measure displacements and strains under dynamic conditions. An initial calibration exercise was performed to determine the potential accuracy of the high speed camera system. Image texture and quality were found to be crucial as measurement errors increased with decreasing texture and image quality. An experiment was then conducted using an axially loaded plate specimen with different amounts of texture and using two different types of lenses. Texture and image quality had a significant impact on dynamic strain measurement accuracy, however, when these factors are optimized, near strain gage accuracy can be achieved.