Multiscale Deformation Leveraging Multispectral Speckle Patterns (16/289842)
Inventors: Melvin Mathew, Andrew Ellenberg, Antonios Kontsos, Ivan Bartoli, Matthew McCarthy. Issued March 01, 2019 in United States
A Bio-inspired Frequency-Based Approach for tailorable and Scalable Speckle Pattern Generation
Published by (Experimental Mechanics)
Authors: M. Mathew, B. Wisner, S. Ridwan, M. McCarthy, I. Bartoli, A. Kontsos. Published July 20, 2020
Digital Image Correlation (DIC) is a length scale independent surface pattern matching and tracking algorithm capable of providing full field deformation measurements. The confident registration of this pattern within the imaging system becomes key to the derived results. Practically, conventional speckling methods use non-reliable, non-repeatable patterning methodologies including spray paints and air brushing leading to increased systematic and random errors based on the user’s experience.
A methodology to develop a speckle pattern tailored to the imaging and experimental conditions of the given system is developed in this paper.
In this context, a novel bio-inspired speckle pattern development technique is introduced, leveraging spatial imaging parameters in addition to frequency characteristics of speckle patterns, enhancing the results obtained through DIC. This novel technique leverages gradient parameters in the frequency spectrum obtained from patterns fabricated using a bio-templating manufacturing technique.
The analysis presented shows that optimized gradient features alongside tailored spatial characteristics reduce errors while increasing the usefulness of DIC results across the entire region of interest. With this new approach, gradient information is derived from the bio-templated pattern, extracted, optimized and then convolved with spatial properties of a numerically generated 2D point clouds which can then be transferred onto actual specimens. Numerical error analysis shows that the optimized patterns result in significant reduction in root mean square error compared to conventional speckling methods.
Physical experiments show the scalability of this optimized pattern to allow for varying working distances while consistently maintaining a lower error threshold compared to conventional speckling techniques.
Experimental Investigation of the Multiscale Mechanical Behavior of Knitted Textiles.
Published by (Material Design and Processing Communications)
Authors: E. Tekerek, D. Liu, B. Wisner, M. Mathew, N. Castaneda, M. Oncul, A. Kontsos. Published September 03, 2019
The nonlinear, anisotropic, and multiscale mechanical behavior of knitted textiles is investigated experimentally in this article. The approach is motivated by recent computational work by the authors that revealed, for the first time to their best knowledge, local‐global mechanical behavior effects related to the hierarchical, three‐dimensional structure of this type of materials. The investigation is carried out on single jersey knitted textile specimens. Mechanical testing consisting of tensile loading along the two principal directions was coupled with a noncontact, optical metrology method capable of providing deformation measurements. The effect of globally applied loading on yarn‐to‐yarn interactions was explored using measured data. The results validate the previously obtained computational findings that include the anisotropic behavior between course and wale directions, the pronounced out‐of‐plane motion observed when in‐plane loading is applied, as well as the characteristic nonlinear mechanical behavior of knitted textiles. These effects were linked to direct observations of the loop structure that demonstrated the coupling between local kinematics and kinetics with global mechanical behavior.
Multiscale Deformation Measurement using Multispectral Sensing
Published by (Structural Control Health Monitoring)
Authors: M. Mathew, A. Ellenberg, S. Esola, M. McCarthy, I. Bartoli, A. Kontsos. Published March 25, 2018
Remote measurements using images are particularly useful in structural health monitoring cases in which the installation of contact sensors is difficult. Some limitations, though, associated with photogrammetry‐type optical metrology involve the application of speckle patterns, which become even more important with variable working distance or when the required resolution and sensitivity are not a priori known which are both very practical common issues. In this context, multispectral sensing can circumvent some of the challenges of acquiring data at different working distances. The objective of this investigation is therefore to use multispectral imaging combined with the method of digital image correlation to demonstrate an approach for remote sensing related to deformation measurements at the structural level. To demonstrate this novel approach, two speckle patterns were designed for measurements at specified working distances; one was set to work in the visible and the second in the ultraviolet spectrum. The results show that the spectral specific reflectivity of the speckle patterns can be used for spatial overlay without affecting imaging in either spectral range considered, which allows the extraction of multiscale deformation information.
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