Phased array filters using piezoelectric sensors are presented as an approach to detect
damage in isotropic plates. Plate dynamics can be described in terms of wave propagation.
Boundaries and other discontinuities, such as damage, produce reflections from incident
wavefronts. Phased arrays, acting as a directional filter, can be used along with a wave
propagation approach to look in different directions on a plate. Damage to the plate can be
inferred if there is a significant change in the transient response of the plate. The
location of this damaged area can be determined using the phased sensor array
response. This paper presents results from simulated damage on an isotropic
plate. A piezoelectric sensor array is used to actively interrogate the plate to
determine the presence and location of damage using low frequency Lamb waves.
In this paper, a numerical simulation technique based on the local interaction simulation approach (LISA)/sharp interface model (SIM) is used to study the propagation of Lamb waves in aluminum and orthotropic plates and wave interactions with damage. The LISA/SIM model allows for accurate and fast simulations of sharp changes in material properties across interfaces associated with damage or specimen boundaries. Damage in the form of holes and changes in density and/or stiffnesses are studied for three different plates. These local changes in density and stiffness have dimensions not exceeding the wave length of the interrogating wave form. Wave scatter from these damage sites is shown at different time instants and at specific spatial locations. Multiple site damage cases are studied for all the plate structures. The different scatter patterns associated with intersecting and nonintersecting surface cracks are also studied. Results obtained from a combination of single site damage cases are compared with the composite multiple site damage case to study the usability of commonly applied algorithms for identifying damage. The benefits of observing multiple directions of the displacement field are demonstrated. It is shown that the out-of-plane measurements give a clearer indication of damage sites than the in-plane measurements.
In this study, beamformers consisting of phased sensor or actuator arrays are used in the nondestructive evaluation of homogeneous and heterogeneous structural components. Beamforming can be used to detect, locate, and quantify damage by suitably applying weights and time or phase delays to the tapped signals from a sensor array and/or actuator array in a narrow frequency band to obtain the desired directional sensitivities and optimal array gains. Some aspects about beamforming and wave propagation are discussed as a prelude to the experimental investigation. Design considerations for the phased arrays are also examined. The advantages of using adaptive over conventional beamforming are demonstrated with Frost constraint- and pilot signal-based adaptive techniques. Data from steel and composite plates are analyzed using propagating elastic waves and phased arrays of sensors and/or actuators. Damage, which can be characterized as a local change in impedance, is diagnosed by using propagating elastic waves as they are sensitive to small changes in impedance and do not require a large number of input/output transducers. Beamforming of sensor and/or actuator arrays is carried out to characterize damage in steel and composite plates by comparing the directivity patterns associated with the damage and baseline data.
Guided waves are utilized in structural health monitoring for identifying damage in material components. Simulations can be used to examine how elastic waves propagate in components to help in selecting measurement and data analysis techniques. In this work, the influence of grid size and the frequency sample rate on the amplitude accuracy and convergence of local interaction simulation approach/sharp interface model (LISA/SIM) numerical simulations are studied as they pertain to guided wave propagation in structural materials. These issues are studied in all three dimensions, and amplitude distortion with respect to the Courant–Friedrich–Lewy criterion is explored. The LISA/SIM enables accurate and fast modeling of localized and sharp changes in material properties across interfaces associated with heterogeneities and/ or boundaries. The validity of the simulation is demonstrated by comparing simulated responses with experimentally measured data. Additionally, Lamb wave dispersion curves are extracted through the course of the convergence study using a broadband pulse and the two-dimensional fast Fourier transform method.
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