Investigations On Damage Location Using Metal Core Piezoelectric Fibers

With paying more and more attention to that the integrity of in-service structures, Structural Health Monitoring (SHM) has attracted more attention. SHM is an effective way to get the condition of the structures in-situ and real-time. This thesis is focus on the application of Piezoelectric Fibers with Metal Core (MPF) in structural health monitoring. Making use of directivity of MPF, passive and active damage location were mainly studied.Firstly, Sensors which are fit for using in SHM were discussed , and the advantages and disadvantages of the sensors used in SHM were also listed. Specially, The characteristic of piezoelectric component and the piezoelectric formula which describes the piezoelectric effect were introduced in detail. MPF (Metal Core Piezoelectric Fibers) is a new kind of piezoelectric device, which was fabricated of 150μm to 250μm in diameter with metal cores of 50μm in diameter. Since the metal core can be used as an electrode, a single fiber can be used as sensor or an actuator after the other electrode is coated on the outer surface of the fiber. After being poled, the fiber can be used as a sensor or an actuator. Therefore , MPF is so compact that it is more fit for SHM.Secondly, for the impact loading conditions that structure suffers, the directivity of MPF was mainly investigated. And a new method based on relative signal peak for impact location has been developed. Experiments have also been carried out to calibrate the feasibility.Finally, active damage location based on diagnostic Lamb wave was studied . The basic theory of Lamb wave was firstly discussed. Secondly, experiments have been carried out to calibrate the Lamb wave active monitoring system. Some results show the feasibility for sensing ultrasonic Lamb waves with MPF. Further more, the directivity of the MPF response to Lamb wave is also strongly obvious. By calculating the relative signal peak or signal energy with wavelet transform of the disperse signal aroused by damage, damage position can be detected.