Moire interferometry provides contour maps of in-plane displacement fields with high sensitivity and high spatial resolution. It has matured rapidly as an invaluable tool for engineering analyses, proved by many industrial and scientific applications. With the typical reference grating frequency of 2400 lines/mm, the contour interval is 0.417 μm displacement per fringe order. For microscopic moire interferometry, sensitivity corresponding to 17 nm per contour has been achieved. Reliable normal strains and shear strains are extracted from the displacement data for bodies under mechanical, thermal and hydrostatic loading. The characteristics and basic concepts of moire interferometry are reviewed. Significant examples from the fields of composite materials, fracture mechanics, electronic packaging and biomechanics are presented.
The Fourier transform moiré and grid method, which we previously presented, is extended to analyze strain distributions from the image of a fringe pattern with carrier fringes obtained by moiré interferometry. The characteristics of the carrier fringes and the procedure of obtaining strain distributions are explained in the spatial frequency domain. The fringe pattern without carrier fringes is obtained from the fringe pattern with carrier fringes by extracting the first harmonic of the spectrum of the fringe pattern with carrier fringes and shifting it. The strain distribution is obtained by analyzing the phase of the image obtained from the inverse Fourier transform of the shifted first harmonic. Strain distributions of a composite material with a wavy ply under compressive loading are analyzed.
The Fourier transform moiré and grid method (FTMGM) which we have previously presented is extended to analyze strain distribution from the image of a fringe pattern with carrier fringes obtained by moiré interferometry. The characteristics of the carrier fringes are explained in the frequency domain. The fringe pattern without carrier fringes is obtained from the fringe pattern with carrier fringes by extracting the first harmonic of the spectrum of the fringe pattern with carrier fringes and shifting it. The strain distribution is obtained by analyzing the phase of the image obtained from the inverse Fourier transform of the shifted first harmonic. Strain analysis of composites under compressive loading are shown.
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