Research On Piezoelectric Smart Aggregate Signal Stability

Currently, the concrete structure as the most common structure is widely used in various construction projects. In the course of their service, reliability reducing issues would inevitably happen because of the material damage by aging which has been widespread concerned by the academic and engineering. Structural health monitoring (SHM) is become to have priority to solve these problems by previously obtaining the related information of structurally, timely monitoring the situation and making the structure safety warning. The SHM technology based on piezoelectric ceramic is widely used in concrete structural health monitoring with its high sensitivity, fast response, sensitive to the advantages of damage, etc. Currently, the technology through efforts of scholars has made a number of achievements, but there are still some unresolved technical problems to restrict its wide application in actual projects. The issues of the signal stability affected by conditions and engineering environmental is prominent increasingly, and based on this, this dissertation will focus on the work of signal stability subjected to different environmental conditions, to analyze the root cause of signal stability changing, and propose appropriate solutions to enhance the signal stability. This dissertation specifically focuses on the follows:(1)The current advantages and weaknesses concerning concrete health monitoring, piezoelectric ceramics, piezoelectric smart aggregates (PSAs) and other related issues are analyzed in summary to propose research objectives of this dissertation.(2)The production methods of new packaged PSAs which increase the capabilities of the temperature acquisition are proposed, and new packaged PSAs have higher signal stability and sensitivity than original package one through experimental verification.(3)Based on the theory of piezoelectric wave method, signal propagation of PSAs in concrete beams is simplified as the acoustic wave propagation of circular piston sound source in the limited size of the solid medium. By considering the driver model, the piston sound source model, sensor model together and add vibration coupling coefficient, acoustic attenuation coefficient and size effect coefficient, the physical model is established to simulate the property of signal propagation. By compare of results calculated by the physical model and the experimental data, the error level is less than 10%, indicating its feasibility in practical engineering.(4)The PSAs signal exhibits nonlinear changes with ambient temperature change measured by tests, because of the elastic constant change of piezoelectric ceramic material with ambient temperature and the signal stability is affected by ambient temperature changes using physical models. The temperature compensation algorithm based on least squares method and cubic spline function method is proposed, respectively, to effectively enhance the signal temperature stability.(5)The influence law of signal stability by size of piezoelectric ceramics, spacing of smart aggregate and cross-sectional dimensions of the specimen is validated by testing. The dimension of piezoelectric ceramic impacts the area of the PSAs excitation end (circular piston sound source) and vibration coupling coefficient resulting in affecting the signal propagation process, waveform characteristics and strength,The impact of smart aggregate distance, concrete specimen size for signal stability is relatively limited, and their influence on the signa stability is coupleding together.