Advanced composite structures, such as foam core carbon fiber reinforced polymer composites, are increasingly being
used in applications which require high strength, high in-plane and flexural stiffness, and low weight. However, the
presence of in situ damage due to manufacturing defects and/or service conditions can complicate the failure
mechanisms and compromise their strength and reliability. In this paper, the capability of detecting damages such as
delaminations and foam-core separations in X-COR composite structures using non-destructive evaluation (NDE) and
structural health monitoring (SHM) techniques is investigated. Two NDE techniques, flash thermography and low
frequency ultrasonics, were used to detect and quantify the damage size and locations. Macro fiber composites (MFCs)
were used as actuators and sensors to study the interaction of Lamb waves with delaminations and foam-core
separations. The results indicate that both flash thermography and low frequency ultrasonics were capable of detecting
damage in X-COR sandwich structures, although low frequency ultrasonic methods were capable of detecting through
thickness damages more accurately than flash thermography. It was also observed that the presence of foam-core
separations significantly changes the wave behavior when compared to delamination, which complicates the use of wave
based SHM techniques. Further, a wave propagation model was developed to model the wave interaction with damages
at different locations on the X-COR sandwich plate.
Physics-based wave propagation computational models play a key role in structural health monitoring (SHM) and the
development of improved damage quantification methodologies. Guided waves (GWs), such as Lamb waves, provide the
capability to monitor large plate-like aerospace structures with limited actuators and sensors and are sensitive to small
scale damage; however due to the complex nature of GWs, accurate and efficient computation tools are necessary to
investigate the mechanisms responsible for dispersion, coupling, and interaction with damage. In this paper, the local
interaction simulation approach (LISA) coupled with the sharp interface model (SIM) solution methodology is used to
solve the fully coupled electro-magneto-mechanical elastodynamic equations for the piezoelectric and piezomagnetic
actuation and sensing of GWs in fiber reinforced composite material systems. The final framework provides the full
three-dimensional displacement as well as electrical and magnetic potential fields for arbitrary plate and transducer
geometries and excitation waveform and frequency. The model is validated experimentally and proven computationally
efficient for a laminated composite plate. Studies are performed with surface bonded piezoelectric and embedded
piezomagnetic sensors to gain insight into the physics of experimental techniques used for SHM. The symmetric
collocation of piezoelectric actuators is modeled to demonstrate mode suppression in laminated composites for the
purpose of damage detection. The effect of delamination and damage (i.e., matrix cracking) on the GW propagation is
demonstrated and quantified. The developed model provides a valuable tool for the improvement of SHM techniques due
to its proven accuracy and computational efficiency.
Physics-based computational models play a key role in the study of wave propagation for structural health monitoring
(SHM) and the development of improved damage detection methodologies. Due to the complex nature of guided waves
(GWs), accurate and efficient computation tools are necessary to investigate the mechanisms responsible for dispersion,
coupling, and interaction with damage. In this paper, a fully coupled electromechanical elastodynamic model for wave
propagation in a heterogeneous, anisotropic material system is developed. The final framework provides the full three
dimensional displacement and electrical potential fields for arbitrary plate and transducer geometries and excitation
waveform and frequency. The model is validated theoretically and proven computationally efficient. Studies are
performed with surface bonded piezoelectric sensors to gain insight into the physics of experimental techniques used for
SHM. Collocated actuation of the fundamental Lamb wave modes is modeled over a range of frequencies to demonstrate
mode tuning capabilities. The effect of various actuation types commonly used in numerical wave propagation models
on Lamb wave speed are studied and compared. Since many studies, including the ones investigated in this paper, are
difficult to perform experimentally, the developed model provides a valuable tool for the improvement of SHM
techniques.
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