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

Paper Number: 110705

110705 - Ultrasonic Guided Waves Scattering Spectra by Hybrid Global-Local Method for Quantitative Non-Destructive Evaluation 

Guaranteeing safety and cost-effective use of aerospace structures involves improving their inspections, in terms of sensitivity, accuracy, and reliability. Recently, Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) of complex structures, such as composite aerospace assemblies, have been widely approached with Ultrasonic Guided Waves (UGWs). Compared to traditional ultrasonic testing, UGWs preserve great sensitivity to even small flaws and defects while providing a larger monitoring range and deeper penetration. These advantages make UGWs a valuable tool for a variety of applications and defect cases. However, modeling the propagation of UGWs in complex structures with discontinuities, to both design and interpret UGW inspections, can be a major challenge. Fully theoretical solutions are difficult or impossible to obtain due to the complexity of the problem, and conventional numerical methods such as Finite Element Method (FEM) are very time-consuming and computationally expensive, especially when a broad frequency analysis is required.

To overcome this challenge, a hybrid numerical method has been developed and improved by the authors, that provides a more efficient and effective manner of modeling UGWs propagation in arbitrary waveguide cross-sections and varying material discontinuities, over a wide frequency range. Considering that Semi Analytical Finite Element method (SAFE) enables to model structures with uniform and arbitrary cross-sections, and Finite Element method (FE) allows for the study of complex damages, the proposed approach, Global-Local (GL) method, divides the waveguide into “local region” and global region”. The “local region” contains any discontinuity and/or defect of the structure, and the “global region” represents the pristine waveguide.

The global and local solutions are then coupled at the boundaries. The complex solutions are found in terms of wavenumbers and corresponding mode shapes from a generalized eigenproblem. The scattering (reflection and transmission) spectra, due to different incident modes interacting with the discontinuity, are computed and can be used to optimize the design of NDE testing and perform prognostics on the structural inspection.

In this study, the GL method is used to analyze UGWs scattering in defected aluminum and composite plates. Parametric analyses including material degradation, defect location, defect size, and defect shape are conducted over a broad range of frequencies, to study the effect of various features of defects. The scattering (reflection and transmission) energy spectra for various incident modes are calculated. Evaluation of energy balance is computed to assess the accuracy of the obtained solutions while minimizing the computational costs, and the accuracy of the simulation test results is assessed by comparison with known independent data from previous literature. Results will also be presented as forced time-domain solutions and utilized in a direct comparison with experimental tests.  

Presenting Author: Margherita Capriotti San Diego State University

Presenting Author Biography: Dr. Capriotti is currently an Assistant Professor in the Department of Aerospace Engineering at San Diego State University, focusing on Non-Destructive Evaluation (NDE) and wave propagation. She received her Ph.D. in Structural Engineering from University of California San Diego in 2019, pursuing research in the Experimental Mechanics & NDE Lab. She previously graduated with her B.S. and M.S. in Mechanical Engineering at the University of Parma (Italy). She has been a postdoctoral Research Fellow at Mayo Clinic in the Department of Radiology, within the Ultrasound Research Lab.

Her research aims at developing noninvasive techniques for defect detection, material characterization and structural assessment of composite aerospace structures, using ultrasonic guided waves and heat diffusion. She is also interested in noninvasive techniques for biomedical applications, specifically shear wave elastography. She is currently setting up her NDE Research Clinic at SDSU.

Authors:

Mingyue ZHANG San Diego State University
Luis Escalona San Diego State University
Antonino Spada The University of Palermo (UNIPA)
Margherita Capriotti San Diego State University