iDICs 2017 Abstract Submission

Evaluation of external errors relating to portable use of Digital Image Correlation Scott Matthews, University of Surrey/ Dstl, s.j.matthews@surrey.ac.uk, 07917653225

A strength of Digital Image Correlation (DIC) is the potential manoeuvrability of the system. It is noted, however, that by increasing the range of locations in which analysis is carried out, the number of uncontrollable variables grow. For example, when testing outside there may be changes to ambient lighting or there may be external vibrations occurring and these effects may alter measurement accuracy.

The overall objective of this research is to quantify errors associated with the use of DIC in different (non-ideal) locations and, associated with this, to find methods of limiting the effect of the potential error sources.

The reference test sample is a thin-walled shell into which defects can be introduced at specified locations, thus disturbing the local strain field.

A portable test rig, which makes use of an internal vacuum, to cause a pressure differential on the component, has been designed and deployed to explore the potential of using DIC as a method of non-destructive evaluation. Preliminary results have been conducted in a laboratory setting to ensure that the strain data correlate with finite element analysis. Following from initial experimentation, successive investigations into the effects of possible external error sources have been conducted. These include: ground vibrations, increased airflow and changes in ambient lighting. Each experiment is repeated five times to allow for random error of the testing process.

DIC has been shown to be a powerful tool in identifying the strain perturbation associated with the presence of defects. Initial results indicate that environment conditions have the potential to lead to perturb ation of results, but that these may be identified and minimised and/or corrected if care is taken.