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a b s t r a c tThe effect of out-of-plane motion (including out-of-plane translation and rotation) on two-dimensional (2D) and three-dimensional (3D) digital image correlation measurements is demonstrated using basic theoretical pinhole image equations and experimentally through synchronized, multi-system measurements. Full-field results obtained during rigid body, out-of-plane motion using a singlecamera vision system with (a-1) a standard f55mm Nikon lens and (a-2) a single Schneider-Kreuznach Xenoplan telecentric lens are compared with data obtained using a two-camera stereovision system with standard f55mm Nikon lenses.Results confirm that the theoretical equations are in excellent agreement with experimental measurements. Specifically, results show that (a) a single-camera, 2D imaging system is sensitive to out-of-plane motion, with in-plane strain errors (a-1) due to out-of-plane translation being proportional to DZ/Z, where Z is the distance from the object to the pin hole and DZ the out-of-plane translation displacement, and (a-2) due to out-of-plane rotation are shown to be a function of both rotation angle and the image distance Z; (b) the telecentric lens has an effective object distance, Z eff , that is 50 Â larger than the 55 mm standard lens, with a corresponding reduction in strain errors from 1250 ms/mm of outof-plane motion to 25 ms/mm; and (c) a stereovision system measures all components of displacement without introducing measurable, full-field, strain errors, even though an object may undergo appreciable out-of-plane translation and rotation.

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Optical methods that give displacement or strain fields are now widely used in experimental mechanics. Some of the methods can only measure in plane displacements/strains on planar specimens and some of them can give both in plane and out of plane displacement/ strain fields on any kind of specimen (planar or not). In the present paper, the stereovision technique that uses two cameras to measure 3 D displacement/strain fields on any 3 D object is presented. Additionally, a quite inclusive list of references on applications of stereovision (and 3 D DIC) to experimental mechanics is given at the end of the paper.

A novel approach for correcting both spatial and drift distortions that are present in scanning electron microscope (SEM) images is described. Spatial distortion removal is performed using a methodology that employs a series of in-plane rigid body motions and a generated warping function. Drift distortion removal is performed using multiple, time-spaced images to extract the time-varying relative displacement field throughout the experiment. Results from numerical simulations clearly demonstrate that the correction procedures successfully remove both spatial and drift distortions. Specifically, in the absence of intensity noise the distortion removal methods consistently give excellent results with errors on the order of ±0.01 pixels. Results from the rigid body motion and tensile loading experiments at 200× indicate that, after correction for distortions, (a) the displacements have nearly random variability with a standard deviation of 0.02 pixels; (b) the measured strain fields are unbiased and in excellent agreement with previous full-field experimental data obtained with optical illumination; (c) the strain field variability is on the order of 60 microstrain in all components with a spatial resolution on the order of 25 pixels. Taken together, the analytical, computational and experimental studies clearly show that the correction procedures successfully remove both spatial and drift distortions while retaining excellent spatial resolution, confirming that the SEM-based method can be used for both micromaterial and nanomaterial characterization in either the elastic or elastic-plastic deformation regimes.

To cite this version:D Garcia, Jean-José Orteu, Luc Penazzi. A combined temporal tracking and stereo-correlation technique for accurate measurement of 3D displacements: application to sheet metal forming. Journal of Materials Processing Technology, Elsevier, 2002Elsevier, , 125-126, pp.736-742. 10.1016 AbstractOptical methods that give displacement or strain fields are now emerging significantly in the mechanical sciences. Much work has been done on two dimensional (2D) displacement/strain measurement from a single camera but the proposed methods give only in plane strains. A binocular correlation based stereovision technique has been developed: (a) to measure the three dimensional (3D) shape of a static object or (b) to measure the strains of an object undergoing some 3D mechanical or thermal stress.In this paper, the application of the stereo correlation technique to measure accurately the 3D shape of a stamped sheet metal part or the surface strain field undergone by the part during the stamping process is presented.

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