Author

Hanfei Mei

Date of Award

Summer 2020

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Victor Giurgiutiu

Abstract

The extensive use of composites in aerospace structures has posed new challenges for implementing effective structural health monitoring (SHM) and nondestructive evaluation (NDE) techniques due to the general anisotropic behavior and complex damage scenarios in composites. This dissertation addresses the SHM and NDE of composites using ultrasonic guided waves, with an emphasis on theoretical modeling and experimental validation of guided-wave propagation and interaction with damage in composites. A semi-analytical finite element (SAFE) approach is presented to calculate guided-wave dispersion curves in composites. The theoretical framework is formulated using the finite element method (FEM) to describe the material variation along the thickness direction and assuming analytical solutions in the wave propagation direction. The dispersive curves are obtained in terms of phase and group velocities, the skew angle between them, and modeshape across the thickness. A user-friendly software ‘LAMSS COMPOSITES’ is developed to retrieve and display the dispersion curves from the guided wave database. To predict guided waves generated by a surface-mounted piezoelectric wafer active sensors (PWAS) transmitter in composites, the SAFE approach is employed to model one-dimensional (1D) and two-dimensional (2D) wave propagation using normal mode expansion (NME) and stationary phase method. Damping effects on guided wave propagation are also considered, including improved tuning model with damping, energy velocity calculation, and 2D guided wave propagation in damped composites. For wave-damage analysis in composites, a numerical and experimental investigation is conducted for the characterization of multilayer delaminations in a 3-mm quasi-isotropic [-45/90/45/0]3s composite plate in which two different delamination scenarios, one delamination and two delaminations, are considered. The wavefield data are analyzed using wavenumber analysis to study the wave trapping phenomenon and to characterize the wave behaviors at the delamination regions. Moreover, a novel angle beam NDE methodology for guided-wave detection and sizing of wrinkle, delaminations, and actual impact damage is developed. A hybrid global local (HGL) approach is developed to model guided wave interaction with damage in composites, in which a local FEM discretization only in the damage regions is deployed to capture wave-damage interaction coefficients (WDIC) while guided wave propagation in the global domain is solved using the very efficient SAFE approach. The WDIC is extracted from the harmonic analysis of local small-size FEM with non-reflective boundaries (NRB). A predictive tool WFR-2D-Composites is developed as a general description of wave generation, propagation, interaction with damage. The HGL simulations of guided propagation and interaction with damage were carried out and compared with experiments using scanning laser Doppler vibrometer (SLDV). The dissertation finishes with summary, conclusions, major contributions, and suggestions for further work.

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