Dorian Garcia

Metrology in a scanning electron microscope: theoretical developments and experimental validation

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 x 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.

A combined temporal tracking and stereo-correlation technique for accurate measurement of 3D displacements: application to sheet metal forming

Optical 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.

A speckle texture image generator

We propose a framework for obtaining synthetic speckle-pattern images based on successive transformations of Perlins coherent noise function. In addition we show how a given displacement function can be used to produce deformed images, making this framework suitable for performance analysis of speckle-based displacement/strain measurement techniques, such as Digital Image Correlation, widely used in experimental mechanics.