8 February 1999 Advanced electronic phase stepped interferometry (EPSI) for detection and characterization of early-stage damage in aerospace materials
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Abstract
An advanced electronic phase stepped interferometry (EPSI) system is described for quantitative out-of-plane displacement and surface topography measurements for NDE applications. Image processing algorithms were developed using novel techniques to extend the sensitivity of EPSI and provide near real-time measurement capability. EPSI is known to provide out-of-plane displacement and surface topography measurements on the order of 1/20-1/100 microns. Noise can be a limiting factor, however, and robust phase unwrapping, which is required, remains an open and active research area. A prototype EPSI system was developed and tested using simulated and real data sets of known displacement fields. A robust maximum-likelihood binary-tree (MLBT) phase unwrapping technique was developed, providing greater robustness in the presence of noise than standard techniques. In addition, the MLBT algorithm lends itself to efficient and fast parallel implementations for near-real time implementation. The use of these advanced algorithms improves the capabilities of existing EPSI techniques, providing more robustness and near real-time measurements. Results are provided for deformations in Ti-6Al-4V and Al2024-T3 aerospace materials.
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James L. Blackshire, Russell C. Hardie, M. I. Younus, "Advanced electronic phase stepped interferometry (EPSI) for detection and characterization of early-stage damage in aerospace materials", Proc. SPIE 3585, Nondestructive Evaluation of Aging Materials and Composites III, (8 February 1999); doi: 10.1117/12.339841; https://doi.org/10.1117/12.339841
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