KEYWORDS: Finite element methods, Structural health monitoring, Sensors, Wave propagation, Optical simulations, Active sensors, Chemical elements, 3D modeling, Semiconducting wafers, Wave plates
Crack detection with piezoelectric wafer active sensors (PWAS) is emerging as an effective and powerful
technique in structural health monitoring (SHM). Modeling and simulation of PWAS and host structure play an
important role in the SHM applications with PWAS. For decades finite element method has been extensively applied
in the analysis of piezoelectric materials and structures. The advantage of finite element analysis over analytical
solutions is that stress and electrical field measurements of complex geometries, and their variations throughout the
device, are more readily calculated. FEM allows calculation of the stress and electric field distributions under static
loads and under any applied electrical frequency, and so the effect of device geometry can be assessed and optimized
without the need to manufacture and test numerous devices. Coupled field analysis taking both mechanical motions
and electrical characteristics into account should all be employed to provide a systemic overview of the piezoelectric
sensors/actuators (even arrays of them) and the host structures.
This use of PWAS for SHM has followed two main paths: (a). Wave propagation (b). Electromechanical
impedance; Previous research has shown that PWAS can detect damage using wave reflections, changes in wave
signature, or changes in the electromechanical (E/M) impedance spectrum. The primary goal of this paper is to
investigate the use of finite element method (FEM) to simulate various SHM methods with PWAS. For the
simulation of Electro-mechanical (E/M) impedance technique, simple models, like free PWAS of different shapes
and 1-dimmension beam with PWAS are investigated and the simulated structural E/M impedance was presented.
For the wave propagation SHM technique, a long beam with several PWAS installed was studied. One PWAS is
excited by tone burst signals and elastic wave will propagate along the beam. The existence of a crack will affect the
structure integrity and the echo reflected by crack can be observed through the simulations. By using the coupled
field elements, direct simulation of electro-mechanical interaction of the PWAS and the host structure was made
possible. The electrical potential generated on the PWAS surface by the stimulation of elastic wave can be examined
in our FEM analysis. The simulation results are then compared to analytical calculation and experimental data.
KEYWORDS: Structural health monitoring, Finite element methods, Sensors, Wave propagation, Optical simulations, Active sensors, 3D modeling, Semiconducting wafers, Chemical elements, Wave plates
Crack detection with piezoelectric wafer active sensors (PWAS) is emerging as an effective and powerful technique in structural health monitoring (SHM). Modeling and simulation of PWAS and host structure play an important role in the SHM applications with PWAS. For decades finite element method has been extensively applied in the analysis of piezoelectric materials and structures. The advantage of finite element analysis over analytical solutions is that stress and electrical field measurements of complex geometries, and their variations throughout the device, are more readily calculated. FEM allows calculation of the stress and electric field distributions under static loads and under any applied electrical frequency, and so the effect of device geometry can be assessed and optimized without the need to manufacture and test numerous devices. Coupled field analysis taking both mechanical motions and electrical characteristics into account should all be employed to provide a systemic overview of the piezoelectric sensors/actuators (even arrays of them) and the host structures. This use of PWAS for SHM has followed two main paths: (a). Wave propagation (b). Electromechanical impedance; Previous research has shown that PWAS can detect damage using wave reflections, changes in wave signature, or changes in the electromechanical (E/M) impedance spectrum. The primary goal of this paper is to investigate the use of finite element method (FEM) to simulate various SHM methods with PWAS. For the simulation of Electro-mechanical (E/M) impedance technique, simple models, like free PWAS of different shapes and 1-dimmension beam with PWAS are investigated and the simulated structural E/M impedance was presented. For the wave propagation SHM technique, a long beam with several PWAS installed was studied. One PWAS is excited by tone burst signals and mechanical wave will propagate along the beam. The existence of a crack will affect the structure integrity and the echo reflected by crack can be observed through the simulations.
This paper describes work performed in the development of a set of specification for the construction of an integrated electronic system for piezoelectric wafer active sensor (PWAS). The paper starts with a comprehensive review of the PWAS material properties, dimensions, and electrical characteristics. PWAS of various shapes and sizes are considered. Two boundary conditions were examined: free PWAS and PWAS attached to actual structures. For both, the PWAS immittance and the allowable dc and ac voltages were considered. The predicted values were compared with measurements performed over a wide frequency range (10 kHz to 2 MHz). Next, the electronic-equipment specifications were considered. The PWAS can be used in a number of different ways to actively detect damage in structures. Our aim was to develop electronic-equipment specifications that would extract the optimum performance from the PWAS, i.e., maximize the coupling with the structure and obtain large-amplitude Lamb wave transmission and reception. Analytical predictions were compared with measurements made using current laboratory equipment. The comparative analysis revealed that the current electronic equipment does not fully exploit the PWAS capabilities. Hence, the PWAS equipment specifications were divided into two categories: “existing” and “desired”. The former category designates integrated electronic equipment that would offer the same PWAS performance as the existing lab equipment, but be of a lower volume/weight/cost. The latter category refers to advanced electronic equipment that will exploit the full potential of PWAS transducers while being of lower volume/weight/cost than the lab equipment. Both categories are presented and discussed in the paper.
Crack detection with piezoelectric wafer active sensors (PWAS) is emerging as an effective and powerful technique in structural health monitoring (SHM). Because of the piezoelectric properties of the PWAS, they act as both transmitters and receivers of guided Lamb waves for such applications. With arrays of PWAS attached to the structure, excitation signals are sent to one of the PWAS and wave signals from the structure are received at all the PWAS. The signals are analyzed to detect the position of cracks. One important issue associated with the PWAS-assisted SHM is the connectivity between the PWAS arrays and the measurement instruments. An automatic signal collection unit is necessary to send the excitation signals to PWAS and acquire the response signal from another PWAS. Such a program-controlled switching unit can quickly and precisely execute the data collection in a way which is more efficient and reliable than the manual switching operations. In this paper, we present an innovative design of a LabVIEW controlled automatic signal collection unit (ASCU) for PWAS-assisted SHM. The hardware circuit construction and the control LabVIEW program are discussed. As a conduit between the phase array of PWAS and the signal instruments (signal generators, oscilloscopes etc.), the ASCU provides a convenient way to switch excitation and echo signals automatically to the selected PWAS transducers with the help of GUI in the LabVIEW control program. The control program is easy to implement and can be integrated into an upper level program that executes the whole task of signal acquisition and analysis. Because of the concise design of the hardware, the ASCU concept of the auto signal switch has been extended to other application cases such as the electromechanical (E/M) impedance measurement for SHM.
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