Papers by Author: Nai Zhi Zhao

Abstract: PZT-based ultrasonic guided wave has played an important role in health monitoring of pipeline structures. By using the PZT-based ultrasonic guided wave energy method and finite element software ABAQUS, the numerical simulation is performed to analyze various corrosion damaged pipeline structures, emphasizing on the damage identification, sensitivity analysis and longitudinal energy attenuation of the guided wave along various corrosion damaged pipelines. The preliminary analysis of the echo signals shows that the grass-like clutter wave belongs to echoes of the corrosion damage of the pipeline, and the wave energy spreads faster here. At the same time, by frequency spectrum analysis of the echo signal, the relationship between the reflection coefficient and the radial depth of defection is made which can be used to approximately evaluate geometrical dimension of the damage.

Abstract: A dynamic mechanical model for actuating performance of piezoelectric material bonded on the surface of structures was established based on the second class of piezoelectric equation and continuum dynamics. Piezoelectric patches such as lead zironate titanate (PZT) to be used as an actuator were pasted on the surface of structures by bonding layers. An electrically and mechanically coupled model based on the piezoelectric equation and Newton's second law was set up and the dynamic equations of the coupled system were theoretically solved under the harmonic effect of the alternating voltage. Moreover, the effect of physical properties and the layer thickness of the PZT actuator were determined. The theoretical and experimental results showed that the proposed model was reasonable and precise to a certain extent.

Abstract: In this paper, a mechanical model for bonded PZT actuator is presented. By analysis (analyzing) and researching principles of the bonded PZT drive combined with the second class of piezoelectric force - electric coupled constitutive equations based on continuum dynamics established along the length of PZT-driven model to the mechanical vibration. In (during) the modeling process, the impact of the bonding layer was mainly considered between the PZT and the structure.

Abstract: Damage detection in composite materials can be divided into active and passive approaches. The active approach is usually based on various non-destructive techniques utilizing actuators and/or receivers. Simple laser scans, revealing the change in Lamb wave response amplitudes, have been used to locate delamination and estimate its severity in a composite plate. The validity of the proposed method is demonstrated through experimental studies in which input signals exerted at piezoelectric (PZT) patches on a composite plate are successfully reconstructed by using the time reversal method. The ultimate goal of this study is to develop a reference-free damage diagnosis technique based on the time reversal process so that defects can be identified without relying on any past baseline data.