@article{wang_abbott_fong_xu_yuan_2023, title={Vibration-based hidden damage imaging using stereo cameras with digital image correlation}, volume={8}, ISSN={["1741-3168"]}, url={https://doi.org/10.1177/14759217231191102}, DOI={10.1177/14759217231191102}, abstractNote={ This paper explores a full-field non-contact optical sensing technique using a stereo camera for imaging hidden damage based on vibration-based damage detection methodology in structural health monitoring. The technique utilizes a pair of digital cameras to capture dynamic operational deflection shapes (ODSs) over the region of interest (ROI) of a structure’s surface via digital image correlation (DIC) when subjected to vibrational excitation. This research overcomes bottlenecks in using high vibration modes for imaging the hidden damage area by (1) applying DIC to operational modal analysis with simple pick-peaking techniques to gather natural frequencies and operational mode shapes in plate structures, while (2) using wavelet analysis to reveal the image of the damage region as a means for baseline-free global damage quantification. In the feasibility study, four cases with two aluminum plates with large damage regions were investigated with a vibration shaker generating a frequency sweep up to 1 kHz. The stereo camera imaged the speckled surface of the plate with white light. Once the dynamic ODSs in the ROI were observed using DIC, the natural frequencies and associated operational mode shapes were extracted using a peak-picking technique in the frequency spectrum. Natural frequencies and operational mode shapes from finite element analysis correlated well with the experimental observations from three-dimensional DIC for all 12 vibration modes respectively. A wavelet transform mode shape curvature (WT-MSC) technique to obtain the modal shape curvature via a two-dimensional continuous wavelet transform with a Mexican Hat analyzing wavelet was then implemented on each of the first 12 vibration mode shapes. A damage image condition that incorporates all weighted wavelet coefficients is proposed to image the damage region. The hidden damage was visualized clearly with WT-MSC, as the technique is much less sensitive to noise than the use of MSC alone, and the use of high vibration modes exhibiting larger mode shape curvatures provided a greater sensitivity for imaging the damage region. Hidden damage regions were successfully visualized in all four cases. }, journal={STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL}, author={Wang, Shaohan and Abbott, Trenton Bryce and Fong, Rey-Yie and Xu, Cheryl and Yuan, Fuh-Gwo}, year={2023}, month={Aug} }
 @article{welzen_yuan_fong_2022, title={Hidden damage visualization using laser speckle photometry}, volume={131}, ISSN={["1879-1174"]}, url={http://dx.doi.org/10.1016/j.ndteint.2022.102700}, DOI={10.1016/j.ndteint.2022.102700}, abstractNote={This paper exploits laser speckle photometry (LSP), a full-field non-contact optical-based image analysis technique, for effectively and rapidly imaging hidden damage in structures, rather than with the complex setups in digital speckle pattern interferometry (DSPI) or shearography (SG)-based interferometry. This technique will demonstrate a promising potential for large-area inspection of composite structures in near real time to unearth barely visible impact damage (BVID) which would typically go unnoticed during routine inspections. Three image (processing) algorithms for localizing and then imaging the BVID area were explored: conventional mean squared error (MSE), normalized cross-correlation (NCC), and an index-centered algorithm known as structural similarity index measure (SSIM). When implementing these algorithms in LSP, a pre-processing step of selecting a window size (subregion size) for locally correlating the images to localize the damage and estimate its size was performed as an advancement on the previous pixel-by-pixel correlations made with LSP. A trade-off strategy between two perceptual-based metrics, image fidelity and image sharpness/blurriness, was implemented to evaluate an appropriate range for window sizes followed by the image algorithms for creating high contrast imaging of damage regions. From the correlation map, the strategy was carried out to mitigate image noise caused by the camera (image) sensors and speckle patterns dictated by the overall root-mean-square deviation (RMSD) while maintaining a high level of sharpness characterized by the magnitude of the third-level discrete wavelet transform. The proposed image algorithms in conjunction with the appropriately selected window size served as imaging conditions in the context of laser speckles for the first time and were tested on BVID in an impacted honeycomb composite panel under thermal excitation. A low coherence (high-power) laser for fast screening of a large area, if required, followed by a high coherence (low-power laser) for detailed imaging were used to demonstrate the efficacy of LSP. The damage image region agreed well with a baseline image from the well-established point-by-point CT-scan with all the three image algorithms. Overall, NCC and SSIM performed slightly better than MSE, with SSIM generally being the better of the two. Nevertheless, MSE has its merits with ease of interpretation and implementation. LSP with the proposed imaging conditions shows enormous potential as a real-time non-destructive inspection (NDI) technique not only in the aerospace industry but also in industries such as additive manufacturing where on-line in-situ monitoring is desired for prevalent defects. The real-time inspection using LSP will further allow immediate feedback for process controls.}, journal={NDT & E INTERNATIONAL}, publisher={Elsevier}, author={Welzen, J. and Yuan, F. G. and Fong, R. Y.}, year={2022}, month={Oct} }
 @article{fong_yuan_2022, title={Phase estimation via riesz transform in laser speckle interferometry for large-area damage imaging}, volume={132}, ISSN={["1879-1174"]}, url={https://doi.org/10.1016/j.ndteint.2022.102711}, DOI={10.1016/j.ndteint.2022.102711}, abstractNote={A direct phase estimation (DPE) via Riesz transform from a speckle pattern (images) for visualizing barely visible impact damage (BVID) occurring in layered composites is proposed in this paper. Rather than complex optical hardware setup for phase extraction in commercial digital speckle pattern interferometry (DSPI) or shearography (SG) systems, the proposed numerical (software) DPE implementation via Riesz transform with a log-Gabor filter enables a compact, portable, and cost-effective system for large-area real-time nondestructive inspection (NDI) due to its simplicity, stability, and efficiency. Using speckles in laser speckle interferometry (LSI) speckle pattern is intrinsically noisy; the correlation-based phase signatures derived from Riesz transform followed by the log-Gabor filter is implemented to supplant the conventional phase-difference algorithm to localize damage regions, especially in the case where the high-power diode laser (low coherence) can cause serious phase drift. By enveloping the monogenic signal through Riesz transform for direct phase retrieval is more intuitive than TPS or SPS. This yields visualization of the damage feature with higher fidelity. Consequently, a phase-correlation algorithm becomes a more robust operation to cope with speckle images from the interferometry. This full-field optical SG system was demonstrated and verified in an impacted damaged honeycomb composite panel using the proposed phase-correlation algorithm under thermal stress loading for large-area inspection in near real-time. The visualized damage images enhanced by principal component analysis (PCA) agreed with images from pulse laser/LDV and X-ray CT scan. The DPE algorithm has a promising potential to apply on any optical metrology for instantaneous phase estimation and can combine with selected imaging conditions for multi-damage detection.}, journal={NDT & E INTERNATIONAL}, publisher={Elsevier}, author={Fong, Rey-Yie and Yuan, Fuh-Gwo}, year={2022}, month={Dec} }
 @article{fong_yuan_2021, title={An In-situ Real-time Hidden Damage Inspection on C-17 Globemaster III Composite Aileron using LSP Technique under Thermal Excitation}, volume={11591}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85108636709&partnerID=MN8TOARS}, DOI={10.1117/12.2585247}, abstractNote={A non-contact, full-field vision-based non-destructive inspection (V-NDI) system was developed with multiple damages detection capabilities in composite structures under thermal excitation. In contrast to point-based nondestructive inspection (P-NDI) systems employing laser Doppler vibrometer (LDV) with discrete wavefield captured by pointwise scanning, the V-NDI system captures higher spatial resolution wavefield by a CMOS camera for every time instance without repeating the experiment tens of thousand times to reassemble the wavefield like P-NDI. An Advanced Damage Processing Network (ADPNet) was proposed with laser speckle photometry (LSP) employed in a V-NDI system for hidden damages inspection. The LSP/ADPNet system relies on observing the variation of speckle clouds in time sequence without a baseline and is very insensitive to ambient noise with statistics-based image processing where traditional holography/ESPI suffers greatly. Other advances of LSP/ADPNet system are its robust tolerance of laser coherence, larger illumination area, flexible choice of correlation functions, and more advanced post-processing techniques such as Bayesian updating/inference or unsupervised image segmentation that can be readily applied. Thermal excitation can have very large power throughput in hundreds of watts compared to traditional PZT actuator, merely in a few watt ranges. Laser speckle itself is the result of self-interference scatter field reflected from a rough surface, and each speckle can be treated as a sensing point from a randomly distributed speckle cloud. By observing the variation of speckle cloud on the structure surface, displacement related quantities in higher dimensions (e.g. hypercomplex envelope, phase between real-valued signal and its quadrature, phase congruency, etc.) can be deduced by the Riesz bp transform and correlated in time sequence to highlight the location of hidden damages in a very effective way. Another novelty of this paper is to make a super compact real-time LSP system on LabVIEW FPGA by applying ADPNet comprised of the Riesz bp transform, non-linear filter bank and unsupervised image segmentation to quantify/characterize barely visible impact damages (BVID) on a C-17 Globemaster III composite aileron. To conclude, the images processed by LSP/ADPNet of a V-NDI system show a very good agreement with ultrasonic C-scan and pulse laser/LDV wavefield reconstruction results. It is also demonstrated to be more accurate and robust than Digital Image Correlation (DIC) for minute deformation (sub-nano to nano meter) measurement and large area (meter by meter) inspection under industrial environment.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2021}, author={Fong, Rey-Yie and Yuan, Fuh-Gwo}, year={2021} }
 @article{welzen_yuan_fong_2021, title={Comparison of Image Correlation Algorithms for Hidden Damage Laser Speckle Photometry}, volume={11591}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85108612487&partnerID=MN8TOARS}, DOI={10.1117/12.2585921}, abstractNote={This paper explores laser speckle photometry (LSP), a recent optical-based image analysis tool, as a method for detecting barely visible impact damage (BVID) in composite structures. This non-contact optical-based method provides the potential for large-scale scanning of aircrafts in real time to unearth BVID which would typically go unnoticed during routine inspections. In exploring LSP, various image correlation algorithms were tested to determine the most effective. The typical error-based correlation algorithm of mean squared error (MSE) was compared to two more advanced algorithms, normalized cross-correlation (NCC) and structural similarity (SSIM) index. Thermal LSP was conducted on a composite honeycomb panel with a surface dent of maximum depth 0.5 mm. The underlying damage was around 30 mm in diameter. When compared to the baseline experiments conducted using C-Scan and a laser Doppler vibrometer (LDV), it was found that only with limited cooling (around 2 seconds) did the algorithms produce consistently accurate results. Among the three imaging conditions, MSE and certain configurations of SSIM provided results that aligned the best with the baselines. Upon extended cooling, LSP produces too many false positives to be useful regardless of correlation algorithm used. Nevertheless, LSP shows great promise as a real-time non-destructive inspection tool not only in the aerospace industry but also in industries such as additive manufacturing where defects are prevalent.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2021}, author={Welzen, J. and Yuan, F. G. and Fong, R. Y.}, year={2021} }
 @article{fong_grimes_yuan_2021, title={Real-time Inspection with Advanced Damage Processing Network (ADPNet) for Laser Speckle Interferometry (LSI) | Poster}, url={http://rgdoi.net/10.13140/RG.2.2.13532.92803/1}, DOI={10.13140/RG.2.2.13532.92803/1}, journal={Unpublished}, publisher={Unpublished}, author={Fong, Rey-Yie and Grimes, Jack Archer and Yuan, G.}, year={2021} }
 @article{wang_fong_yuan_2021, title={Vibration-based Damage Imaging via High-Speed Cameras with 3D Digital Image Correlation using Wavelet Transform}, volume={11591}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85108648763&partnerID=MN8TOARS}, DOI={10.1117/12.2585246}, abstractNote={Advances in computer prerformance, optical devices and digital imaging technology have allowed digital image correlation methods to measure the shape and deformation of the vibrating structures. This paper presents a novel vision-based damage detection framework which can eliminate the sinusoidal shaker step along with a magnified, precise modal shape data especially for higher modes that typical DIC algorithm can hardly detect. For this, an aluminum plate has been selected to make a comparative study on the performance of serval vibration-based damage detection techniques, namely, curvature mode shapes , Gapped smoothing techniques Generalized Fractal Dimension, Modal Strain Energy and Wavelet Transform.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2021}, author={Wang, Shaohan and Fong, Rey-Yie and Yuan, Fuh-Gwo}, year={2021} }
 @phdthesis{fong_2021, title={Vision-based Large-area Damage Inspection via Ultrasonic Phase Estimation in Laser Speckle Interferometry}, school={PhD Dissertation, Mechanical and Aerospace Engineering, North Carolina State …}, author={Fong, Rey Yie}, year={2021} }
 @article{yuan_fong_2020, title={Recent Advances in Non-contact Full-field Damage Visualization for Composite Structures}, author={Yuan, Fuh-Gwo and Fong, Rey-Yie Abel}, year={2020} }
 @article{fong_tsai_lin_ou_2014, title={Demonstration Software Modeling Exercise Aids Taiwan’s Yachtbuilding Community}, volume={22}, number={3}, journal={High-Performance Composites}, author={Fong, Rey-Yie and Tsai, Ray and Lin, Yu-Chieh and Ou, Chia-Chuan}, year={2014}, pages={68–69} }
 @article{fong_chang_2014, title={Finite Element Analysis Project Proposal}, author={Fong, Rey-Yie Abel and Chang, Huan-Yu Tony}, year={2014} }
 @article{fong_chang_2014, title={Finite Element Analysis Project Proposal for Yacht Hydrodynamic Quantification}, author={Fong, Rey-Yie Abel and Chang, Huan-Yu Tony}, year={2014} }
 @article{fong_tsai_lin_ou_2014, title={Luxury Yacht Design Takes a New Tack}, journal={Maritime Reporter and Engineering News}, author={Fong, Rey-Yie and Tsai, Ray and Lin, Yu-Chieh and Ou, Chia-Chuan}, year={2014} }
 @inproceedings{fong_tsai_lin_ou_2013, title={High Performance Yacht Design with Abaqus}, booktitle={SIMULIA Community Conference}, author={Fong, Rey-Yie and Tsai, Ray and Lin, Yu-Chieh and Ou, Chia-Chuan}, year={2013} }
 @inproceedings{chin_hwang_tu_chang_fong_2012, title={The Coupled Hydrodynamic and Structure Analysis of the Trans-Velocity Propellers in Inclined Shaft Conditions}, booktitle={Proceedings of the 26th Assian-Pacific Technical Exchange and Advisory Meeting on Marine Structure}, author={Chin, Shang-Sheng and Hwang, Jeng-Li and Tu, Jing-Ching and Chang, Kuan-Kai and Fong, Rey-Yie}, year={2012} }
 @inproceedings{ou_fong_lin_2011, title={95' Planning Yacht Structure Strength and Stiffness Analysis}, booktitle={Abaqus Taiwan Users’ Conference}, author={Ou, Chia-Chuan and Fong, Rey-Yie and Lin, Yu-Chieh}, year={2011} }
 @inproceedings{fong_2011, title={A Comparison Study between ALE and SPH for Yacht Structure Design under Slamming Impact Loads}, booktitle={Abaqus Taiwan Users’ Conference}, author={Fong, Rey-Yie}, year={2011} }
 @inproceedings{lin_fong_2010, title={95' Planning Yacht Deck Structure Arrangement and Parameter Optimization}, booktitle={Abaqus Taiwan Users’ Conference}, author={Lin, Yu-Chieh and Fong, Rey-Yie}, year={2010} }
 @inproceedings{fong_cheng_2010, title={Human Injury Evaluation on Production 125cc. Scooter under Side Slip Impact}, booktitle={Abaqus Taiwan Users’ Conference}, author={Fong, Rey-Yie and Cheng, Jung-Ho}, year={2010} }
 @phdthesis{fong_cheng_2009, title={Design and Failure Prediction of Insert for Composite Sandwich Structures}, school={National Taiwan University}, author={Fong, Rey-Yie and Cheng, Jung-Ho}, year={2009} }
 @inproceedings{fong_cheng_2009, title={Fuel Cell Stack Damage Evaluation for Hybrid Fuel Cell Scooter under Road Vibration Bumping Impact}, booktitle={Abaqus Taiwan Users’ Conference}, author={Fong, Rey-Yie and Cheng, Jung-Ho}, year={2009} }
 @inproceedings{fong_cheng_2009, title={Inclination and Crash Analysis for Hybrid Fuel Cell Scooter}, booktitle={Abaqus Taiwan Users’ Conference}, author={Fong, Rey-Yie and Cheng, Jung-Ho}, year={2009} }
 @article{fong_chang_2008, title={Cohesive Analysis and Applications for CADesigner}, journal={CADesigner}, author={Fong, Rey-Yie and Chang, Jung-Ho}, year={2008}, pages={117–125} }
 @inproceedings{fong_cheng_2007, title={Experimental Verification and Application for Cohesive Element}, booktitle={Abaqus Taiwan Users’ Conference}, author={Fong, Rey-Yie and Cheng, Jung-Ho}, year={2007} }