Guided wave based nondestructive inspection (NDI)/structural health monitoring (SHM) is aimed at using the excitation source to interrogate the structure. Through interaction of the wave with the damage, signal or image processing algorithms are employed from the sensors to locate or visualize the damage. The excitation source includes thermal load, mechanical vibration shaker, air-coupled transducer (ACT), piezoelectric transducer (PZT), pulse laser, etc. and sensors could be ACT, PZT, optical fibers, EM transducer, photo detector (PD), camera (CCD or CMOS), etc. In aerospace industry, several optical-based imaging modalities to assess the damage have been developed. This keynote will focus on two recently developed non-contact full-field optical-based techniques for visualizing the barely visibly impact damage (BVID) in composite structures.   
An integrated system comprised of the image acquisition device (high-speed camera), digital image correlation (DIC), and an imaging processing software system can be termed as GWSHM-IC (Guided Wave based SHM using digital Image Correlation). This study is viewed as the first attempt at using a high-speed camera together with DIC using white light to capture the scattered guided wavefield on the surface of a structure (caused by the wave-damage interactions from the damage underneath the surface) in the near ultrasonic frequency range. A phase-based damage imaging condition, wavenumber index (WI), was employed to image the BVID. While guided waves have the ability to interrogate the entire thickness of plate-like structures over large areas, the digital camera (camera sensor), where each pixel is considered to effectively act as a sensor, can provide extremely high spatial resolution by measuring these guided waves simultaneously at all the points within the field of view. As such, the use of high-speed digital cameras has promising potential to provide an effective and reliable means for non-contact, large area monitoring in order to identify hidden damage within the structure.   
The second non-contact full-field damage image technique is to use coherent light to visualizing the BVID in composite structures through speckle interferometry using CCD or high-speed camera. The system comprises two sub-systems (1) laser speckle photometry (LSP) and (2) shearography. Both sub-systems rely on observing the variation of laser speckles in time series without reference arm and are very insensitive to ambient noise where traditional holography/ESPI suffers greatly. Other advantages of LSP/shearography are their robust tolerance of laser coherence, larger illumination area, flexible choice of correlation functions, and more advanced post-processing techniques such as Bayesian updating and inference can be readily applied where holography/ESPI do not possess.  These two non-contact, full-field techniques for damage image are believed to be a significant first step towards that goal of using an integrated high-speed camera system to visualize hidden damage in structures via ultrasonic guided wavefields.  
 


Recent Advances in Optical-Based Non-Contact Full-Field Damage Visualization for Composite Structures

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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