Digital Image Correlation for Shape and Deformation Measurements

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 digital 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/50000 in the out-of-plane component, where Z is the distance from the object to the camera, for typical stereo-camera arrangements. Accurate surface strains can be extracted from the measured displacement data for specimens ranging in size from many meters to microns and under a wide range of mechanical loading and environmental conditions, 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. Section 20.3 introduces the pinhole imaging model imaging model and calibration procedures. Sections 20.4 and 20.5 describe the image digitization image digitization and image reconstruction procedures, respectively, for accurate, subpixel subpixel displacement measurement. Section 20.6 presents the basics for subset-based, image pattern matching pattern 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 calibration and deformation measurements in 2-D DIC and 3-D DIC applications, respectively. Section 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 tension–torsion loading, respectively, of an edge-cracked specimen. Section 20.13 presents closing remarks regarding the developments.