Daniel Post

Bio: Daniel Post is an academic researcher from Virginia Tech. The author has contributed to research in topics: Interferometry & Moiré pattern. The author has an hindex of 28, co-authored 95 publications receiving 2901 citations.

High Sensitivity Moiré: Experimental Analysis for Mechanics and Materials

Abstract: Moire patterns (which form when two regular patterns of comparable frequency interfere) are sensitive indicators of changes of shape as objects rotate, heat up, or are otherwise affected by external forces Applications include non-destructive testing and evaluation, and quality and process control This text explains the theory and practice of physical measurements by high-sensitivity moire - principally moire interferometry, focusing on the mechanics and micromechanics of materials and structural elements Moire interferometry is unique in providing maps of in-plane displacements from which can be derived normal and shear strains Typical moire sensitivities are on the order of 2-4 fringes per fm displacement, but sensitivities of 17 nm per fringe contour can be reached The applications discussed include: advanced composite materials, thermal stresses, electronic packaging, fracture, metallurgy, time-dependence, and strain gage calibration The methods discussed in the text can be applied for whole-field measurements on nearly solid and solid bodies

Developments In Moire Interferometry

Abstract: Recent progress in high-sensitivity moire interferometry is reviewed. Interference patterns reveal full-field contour maps of in-plane displacements. Sensitivity corresponds to moire with 1200 lines/mm (30,480 //in.) for most examples, but approaches the theoretical limit of X/2 displacement per fringe in one demonstration. Techniques for producing cross-line phase gratings on specimens are described, as well as use of real and virtual reference gratings. Carrier patterns and optical filtering are used to cancel initial or no-load patterns. Diverse applications are illustrated.

Moiré interferometry for engineering mechanics: Current practices and future developments

Abstract: In the past decade, the optical method called moire interferometry has matured rapidly to emerge as an invaluable tool, proved by many industrial and scientific applications. It has been applied to numerous problems in engineering mechanics. It measures in-plane displacement fields with high sensitivity and high spatial resolution. This paper reviews current practices of moire interferometry and its extensions. Applications in diverse fields are addressed to demonstrate the wide applicability of the method, especially the recent applications for thermal deformation analyses of microelectronics devices. Speculation on future developments and practices is presented.

High-sensitivity moiré interferometry—A simplified approach

Abstract: High-quality moire-interferometry patterns were obtained with the following conditions: specimen of graphite-polyimide composite material; reflective cross-line specimen grating of 600 l/mm (15,000 l/in.); virtual reference grating of 1200 l/mm (30,000 l/in); fringe-multiplication factor of 2; carrier pattern of 10 fringes/mm (250/in.); carrier eliminated by optical filtering. The phase-type specimen grating was cast onto the composite material with silicone rubber, using a ‘homemade’ mold. The virtual grating was formed with a plane mirror in a collimated field. Precision-quality optical elements are not required.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Depth mapping using projected patterns

Abstract: Apparatus for mapping an object includes an illumination assembly, which includes a single transparency containing a fixed pattern of spots. A light source transilluminates the single transparency with optical radiation so as to project the pattern onto the object. An image capture assembly captures an image of the pattern that is projected onto the object using the single transparency. A processor processes the image captured by the image capture assembly so as to reconstruct a three-dimensional (3D) map of the object.

Advances in Two-Dimensional and Three-Dimensional Computer Vision

Abstract: The foundations of two- and three-dimensional image correlation, as well as recent developments, are described in detail. The versatility and robustness of these methods are illustrated through application examples from diverse areas including fracture mechanics, biomechanics, constitutive property measurement in complex materials, model verification for large, flawed structures and nondestructive evaluation. A detailed description of experimental and data-reduction procedures is presented for the application of the two-dimensional image-correlation method to thin-sheet mixed-mode I/II fracture studies, local crack-closure measurements using optical microscopy and the measurement of constitutive properties. Application examples using three-dimensional image correlation include profiling of components for reverse engineering and manufacturing and the measurement of full-field surface deformation during wide cracked panel tensile tests for verification of buckling and crack-growth models. Results from nearly sixteen years of use have demonstrated that both two-dimensional and three-dimensional image-correlation methods are robust and accurate tools for deformation measurements in a variety of applications. The range of uses for the two-and three-dimensional image-correlation methods is growing rapidly as scientists and engineers begin to understand their true capabilities.

I The Self-Imaging Phenomenon and its Applications

Abstract: Publisher Summary This chapter describes the self-imaging phenomenon and its applications. The self-imaging phenomenon requires a highly spatially coherent illumination. It disappears when the lateral dimensions of the light source are increased. When the source is made spatially periodic and is placed at the proper distance in front of the periodic structure, a fringe pattern is formed in the space behind the structure. The chapter discusses the theoretical and applicational aspects of the self-imaging phenomenon—that is, the property of the Fresnel diffraction field of some objects illuminated by a spatially coherent light beam. The applications of self-imaging are summarized in four main groups—namely, (1) image processing and synthesis, (2) technology of optical elements, (3) optical testing, and (4) optical metrology. The chapter describes the double diffraction systems using spatially incoherent illumination. The first periodic structure plays the role of a periodic source composed of a multiple of mutually incoherent slits. Depending on whether the periods of two periodic structures are equal, the Lau or the generalized Lau effect is discussed. Various applications of incoherent double-grating systems are described in the fields of optical testing, image processing, and optical metrology. After examining some cases of coherent and incoherent illumination, the general issue of spatial periodicities of optical fields and its relevance to the replication of partially coherent fields in space is discussed.