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Spatial DIC Errors due to Pattern-Induced Bias and Grey Level Discretization

  • S. S. FayadEmail author
  • D. T. Seidl
  • P. L. Reu
Research paper
  • 125 Downloads

Abstract

Digital image correlation (DIC) is an optical metrology method widely used in experimental mechanics for full-field shape, displacement and strain measurements. The required strain resolution for engineering applications of interest mandates DIC to have a high image displacement matching accuracy, on the order of 1/100th of a pixel, which necessitates an understanding of DIC errors. In this paper, we examine two spatial bias terms that have been almost completely overlooked. They cause a persistent offset in the matching of image intensities and thus corrupt DIC results. We name them pattern-induced bias (PIB), and intensity discretization bias (IDB). We show that the PIB error occurs in the presence of an undermatched shape function and is primarily dictated by the underlying intensity pattern for a fixed displacement field and DIC settings. The IDB error is due to the quantization of the gray level intensity values in the digital camera. In this paper we demonstrate these errors and quantify their magnitudes both experimentally and with synthetic images.

Keywords

Digital image correlation Pattern induced bias Intensity discretization bias Pattern induced errors Uncertainty quantification 

Notes

Acknowledgements

Thank you to Mr. Paul Farias for his assistance during the experimental work, Dr. Daniel Turner for his assistance during internal writing review, and Dr. Elizabeth Jones for advising and review in the writing process. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

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Copyright information

© Society for Experimental Mechanics 2019

Authors and Affiliations

  1. 1.Sandia National LaboratoriesAlbuquerqueMexico

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