An Approach to Analyse Errors Introduced in the Random Grid Strain Measurement Method

摘要

The present work refers to the errors imposed by the recently introduced random-grid mesh-free full field strain measurement method. Excluding systematic errors of the digital camera, the method itself is not an error-free procedure. A possible cause of errors could be the misplacement of the spot-centre (centroid) with regard of the spot boundaries. Another cause of errors is the limited order of approximation in the field function. A third one, emerges from the so-called 'sub-pixel effect'. This kind of error is difficult to trace, so direct comparison between the results of the method and exact solutions is required. In the present work, proper analytical or numerical derivations of those errors are presented and reasonable upper limits are estimated. Finally, numerical and experimental examples are presented to demonstrate the accuracy of the method.