Session: 01-01-02: General Topics of Aerospace Structures

Paper Number: 110637

110637 - Ultrasonic Guided Waves Sensitivity to Impact Damage Modes in Composite Stiffened Aerospace Panels 

Aerospace structures have been turning towards the use of composite materials for decades due to their light weight, high strength, and growing tailorability. Contrary to the isotropic materials often used in aerospace applications, the anisotropic multi-layered behavior of composite materials leads to complex stress-strain behaviors which can be engineered to provide higher strengths where they are needed. For this reason, these materials have been increasingly used in aircraft wings, fuselages, and many other structural components. However, complex materials lead to complex damage modes which may result in material failure even before and beyond the damage is visible to the naked eye. Impact damages are especially dangerous as damage modes in composite layups arise not only at the impact location but propagate into the layup around the impact center causing barely visible impact damages (BVID), which reduce laminate strength by up to 50 percent.

 

Inspecting and maintaining the structural health of composite aircraft components is crucial to extending their service life and preventing catastrophic failures. The slender design of composite laminates lends itself well to inspection by ultrasonic guided waves (UGWs), which are capable of involving the entire cross section of the structures, propagate over long distances and can be implemented in-situ without having to place the aircraft out-of-service. UGWs demonstrate high sensitivity to damages along their propagation path allowing the detection of subsurface and internal damages around the impact location. Since the UGWs are naturally supported by the geometry of the material, they are capable of inspecting complex curved components with multilayer composites and bonded stiffeners.

 

However, the gathered UGWs signals are very complex, due to the dispersive and multi-modal nature of UGWs, and require special implementation and post-processing techniques to interpret information. One such implementation technique uses a Single Input Dual Output (SIDO) technique to gather two signals on either side of the targeted inspection area. The two signals are then used to extract UGW transfer functions which carry the information corresponding to the targeted area of the composite laminate.

 

This work builds on experimental UGW data gathered from two composite aircraft fuselage panels impacted at different levels over a bonded hat stiffener, analyzing the data to identify three main damage modes and their locations in relation to the impact center. The gathered data is processed in the frequency domain to extract narrow and broad-band transfer functions, interacting at different sensitivities with the different damage modes. Transfer functions are gated in time domain to isolate wavemodes and features are extracted to be compared at locations along the stiffened composite panel.

 

Extracted feature data is compared for all feature-wavemode combinations using statistical Principal Component Analysis (PCA) and correlating the PCA scores with the feature data using the Pearson Correlation Matrix to reduce dimensionality of the large pool of extracted features. Results show that selected combinations are more sensitive to interference at locations on or around the impact location leading to characterization of the impact damage modes. Current work focuses on clustering PCA data from selected feature-wavemode combinations to correlate the unsupervised principal components with known damage modes extracted from higher resolution NDE data.

Presenting Author: Kalib Varela San Diego State University

Presenting Author Biography: Kalib Varela is a 3rd year Masters Student in Structural Aerospace Engineering at San Diego State University. He has previously received his bachelor's degree in Physics from Wesleyan University in 2019. He is currently completing research in the Non-Destructive Evaluation Clinic in preparation for his masters thesis using ultrasonic guided waves to detect damages in composite aircraft panels.

Authors:

Kalib Varela San Diego State University
Kyle Huynh San Diego State University Department of Aerospace Engineering
Margherita Capriotti San Diego State University Department of Aerospace Engineering
Hyungsuk Eric Kim NAVAIR Fleet Readiness Center Southwest
Andrew Ellison Matroid Inc.
Hyonny Kim UCSD Structural Engineering Department
Francesco Lanza Di Scalea UCSD Structural Engineering Department