Plate-like aerospace engineering structures are prone to mechanical/residual load during flight operation. The
mechanical/residual prestresses can cause significant changes in guided-wave (GW) propagation for structural
health monitoring (SHM) systems. The paper focuses on the characterization of the GW propagation using surfacebonded
piezoelectric wafer actuators in metallic spacecraft plates under prestresses. First, a new in-plane analytical
model with coupled piezo-elastodynamics is proposed to quantitatively capture the dynamic load transfer between a
thin piezoelectric actuator bonded onto an isotropic plate that is subject to prestresses. Based on the developed
model, effects of prestresses on the GW propagation generated by piezoelectric actuators are then analyzed and
demonstrated. It can be found that the both time-of-flight and amplitude of wave responses can be affected by the
presence of prestresses in plates. The results hopefully provide useful information for the real-time SHM.
Due to the complex nature of sandwich structures, damage detection in honeycomb sandwich structures inherently
imposes many challenges. In this study, leaky guided wave properties generated by piezoelectric wafer actuators/sensors
in honeycomb sandwich structures are first simulated by the finite element method. In the numerical model, the detailed
honeycomb core geometry is considered. Differential features due to presence of debonding are determined through an
appropriate damage index analysis of the signals at the normal and debonded conditions. The image of the debonding is
formed by using a probability analysis of the leaky guided wave at each frequency. The final image of the structure can
be fused from multi-frequency leaky guided waves. A new method for multi-debonding detection is proposed. Based on the analysis, information about the debondings in the honeycomb sandwich structures can be quantitatively characterized.
Piezoelectric wafer actuators (piezo-actuators) have been extensively used in integrated structural health monitoring
systems to generate ultrasonic guided waves (GWs) for structural damage interrogation. The big issue surrounding
precise characterization of piezoelectrically excited GWs is addressing the dynamic interfacial stress between the
piezo-actuator and the host structure. In this paper, an analytical actuator model is developed to quantitatively
describe the dynamic load transfer between a bonded thin piezo-actuator and an isotropic plate under in-plane
mechanical and electrical loading. The piezoelectrically induced GW responses are studied by coupling the actuator
dynamics with the Rayleigh-Lamb equations and solving the resulting integral equations in terms of the interfacial
shear stress. Typical examples are provided to show the capability of the current actuator model to capture the
effects of the geometry and the loading frequency upon the load transfer. The analytical prediction of transient GW
mode signals from the proposed model is compared with finite element simulation results for various excitation frequencies, and excellent agreement can be observed especially for high-frequency cases, which is a useful extension to the ultrasonic frequencies of most of existing analytical solutions for low frequency approximations.
Honeycomb composite structures have been widely used in aerospace and aeronautic industries due to their
unique characteristics. Due to the complex nature of honeycomb composite with the celled core, structural
health monitoring (SHM) of honeycomb composite panels inherently imposes many challenges, which
requires a detailed knowledge of dynamic elastic responses of such complex structures in a broad frequency
domain. This paper gives numerical and experimental analyses of elastic wave propagation phenomena in
sandwich panels with a honeycomb core, especially when the frequency domain of interest is relative high.
Numerical simulation based on the Finite Element (FE) method is first performed to investigate wave
generation and reception using piezoelectric actuators/sensors. The effectiveness of homogenized core
model is discussed, compared with the dynamic responses based on honeycomb celled core model. The
reliability of the simulated wave will be verified with the experimental results. Specific attention will be
paid on core effects on group wave velocity. This research will establish a solid theoretical foundation for
the future study of the structural health monitoring in the composites.
The design of nanosensor networks and systems encompass multiple areas of research, which include: Design of nanosensors and modeling; Design of wireless interfaces; Design of reliable sensor networks that sense and collect data reliably; Design of backbone networks capable of reliably transporting collected data to remote servers; Design of secure servers for data transfer. This paper provides a systems engineering framework and provides insights into the above design issues.
Concrete structures have been used widely in civil infrastructural systems especially in bridges. Due to the complex
nature of its microstructure, nondestructive testing (NDT) of concrete inherently imposes many challenges, which can
cause severe limitations to both the resolution and sensitivity of the observed signals. In this study, surface wave
propagation in concrete is examined and simulated by using a surface bonded active piezoelectric actuators/sensors
system experimentally and numerically, especially at high frequency. First, different experimental tests are conducted to
evaluate effects of the loading frequency upon the resulting surface wave propagation. Secondly, the numerical results
are compared with experimental data. The very good agreement shows the great feasibility and potential of surface wave
signals by using piezoelectric actuators/sensors to locate and characteristics of surface damages.
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