Digital Image Correlation for Shape and Deformation Measurements

Abstract

The essential concepts underlying the use of two-dimensional (2-D) digital image correlation for deformation measurements and three-dimensional (3-D) digital image correlation for shape and deformation measurements on curved or planar specimens are presented. Two-dimensional digital image correlation measures full-field surface displacements with accuracy on the order of ±0.01 pixels on nominally planar specimens undergoing arbitrary in-plane rotations and/or deformations. Three-dimensional digi-tal image correlation measures the complete 3-D surface displacement field on curved or planar specimens, with accuracy on the order of ±0.01 pixels for the in-plane components and Z/50 000 in the out-of-plane component, where Z is the distance from the object to the camera, for typi-cal stereo-camera arrangements. Accurate surface strains can be extracted from the measured dis-placement data for specimens ranging in size from many meters to microns and under a wide range of mechanical loading and environmental con-ditions, using a wide range of imaging systems including optical, scanning electron microscopy, and atomic force microscopy. In Sect. 20.2, the essential concepts underlying both 2-D DIC and 3-D DIC are presented. Sec-tion 20.3 introduces the pinhole imaging model and calibration procedures. Sections 20.4 and 20.5 describe the image digitization and image recon-struction procedures, respectively, for accurate, subpixel displacement measurement. Section 20.6 presents the basics for subset-based, image pat-tern matching. Section 20.7 provides a range of methods for applying random texture to a surface. Sections 20.8 and 20.9 provide the basics for cal-ibration and deformation measurements in 2-D DIC and 3-D DIC applications, respectively. Sec-tion 20.10 presents an example using 2-D image correlation to extract the local stress–strain response in a heterogeneous weld zone. Sections 20.11 and 20.12 present applications using 3-D image correlation to quantify material response during quasistatic and dynamic tension–torsion loading, respectively, of an edge-cracked spec-imen. Section 20.13 presents closing remarks regarding the developments.