Digital image correlation

About: Digital image correlation is a research topic. Over the lifetime, 7842 publications have been published within this topic receiving 132166 citations.

A review of micro-scale focused ion beam milling and digital image correlation analysis for residual stress evaluation and error estimation

Abstract: In the past decade several versions of micro-scale residual stress analysis techniques have been developed based on Focused Ion Beam (FIB) milling at sample surface followed by Digital Image Correlation (DIC) for the determination of the resulting strain relief. Reliable and precise estimation of the error bounds on these measures is critical in determining the usefulness and accuracy of residual stress evaluation. Here we present an overview of the steps necessary for effective outlier removal, error propagation and estimation in order to provide reliable confidence limits for the stress value obtained. Error propagation analysis begins with DIC marker tracking errors that depend on imaging contrast and magnification, and can be improved with sub-pixel tracking and marker shift averaging. We demonstrate how the outliers and poorly tracked markers ought to be removed from the data set using correlation coefficient thresholding and/or correlation peak confidence intervals. Markers showing large displacements relative to their neighbours can also be identified as aberrant, and removed. By performing careful error propagation throughout the analysis chain we quantify the displacement and strain fields, and qualify them with the associated confidence intervals. These values, in combination with the elastic modulus confidence limits, are then used to provide the final confidence intervals for the determined residual stress values. The generic nature of the methodology presented ensures its suitability for all residual stress analysis techniques based on FIB milling and image correlation analysis. An example of implementation is presented for the micro-scale ring-core FIB–DIC approach.

Effect of surface roughness on the shaft resistance of non-displacement piles embedded in sand

Abstract: This paper presents the results of axial load tests performed on instrumented model piles pre-installed in a large-scale, half-circular chamber with a viewing window in its flat-side wall. Uniform silica sand samples were prepared with different densities using dry pluviation. The effects of pile surface roughness and soil density on the response of the soil during loading of the model piles were studied by analysing sequences of digital images using the digital image correlation technique. Test results show that the extent of the zone next to the pile that is affected by loading of the pile increases as the pile surface roughness and soil density increase. The development of a shear band next to the pile shaft was also studied by carefully analysing images taken with a digital microscope during loading of the model piles. The average thickness of the shear band is in the 3·2D50–4·2D50 range for rough model piles, whereas no shear band was observed for smooth model piles. Understanding of shear band forma...

Basic principle of digital image correlation for in-plane displacement and strain measurement

Abstract: The basic principle and the algorithm of a digital image correlation method, and the procedure for obtaining displacements and strains are described. In order to describe the basic principle precisely, only in-plane displacement and strain measurement of a planar object are explained. Gray levels between integer pixels of a digital image after deformation are interpolated to obtain displacements with subpixel resolution. Displacements are then determined by solving nonlinear simultaneous equations taking the deformation of a subset into consideration. Strains are obtainable by differentiating the measured displacements. In addition to the basic principle of digital image correlation, the example of the measurement and its results are shown.

The Application of Digital Image Correlation for Measuring Residual Stress by Incremental Hole Drilling

Abstract: Themeasurementofresidualstressusingtheincrementalholedri llingiswellestablished,�butthe� mainlimitationswiththeconventionalstraingaugeapproacharet herequirementsforsurface� preparation,�theneedforaccuratealignmentanddrilling,�therest rictedrangeofholegeometries� commensuratewiththespecificgaugedesigns,�andthelimitedra ngeofstraindataaveragedover� thefootprintofthestraingaugegrid.� Recentattemptstoextend� themethodhaveseenthe� applicationoffullfieldopticaltechniquessuchaselectronicspecklepatterninterferometryand� holographicinterferometryformeasuringthestrainfieldsaround �thehole,�butthesemethodsare� sensitivetovibrationandthislimitstheirpracticalusetocontrolledlabor atoryenvironments.� � TherearesignificantpotentialbenefitsthereforeofusingamorerobusttechniquebasedonDigital� ImageCorrelation�(DIC),�andworkispresentedinthisstudyonthe� developmentofthemethodfor� measuringsurfacedisplacementsandstrainfieldsgenerateddur ingincrementalholedrilling.�Some� ofthepracticalissuesassociatedwiththetechniquedevelopm ent,�includingtheoptimizationof� appliedpatterns,�thedevelopmentoftheopticalsystemandi ntegrationwithcurrentholedrilling� equipmentarediscussed,�andalthoughmeasurementsareonlypresente dforasingleloadcase�%�the� equi%biaxialstressstateintroducedduringshotpeening�%�thenovelaspectofthisworkisthe� integrationofDICmeasurementswithincrementaldrillingandan� applicationoftheIntegral�