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

Journal Article · 06 November 2019 · Experimental Mechanics

DOI: https://doi.org/10.1007/s11340-019-00553-9 · OSTI ID:1574475

Fayad, S. S.  ^[1]; Seidl, D. T. ^[1]; Reu, P. L. ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

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.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; NA0003525
• OSTI ID: 1574475
• Report Number(s): SAND--2019-13784J; 681363
• Journal Information: Experimental Mechanics, Journal Name: Experimental Mechanics Vol. 60; ISSN 0014-4851
• Publisher: SpringerCopyright Statement
• Country of Publication: United States
• Language: English