Application Of Active Multi-Actuator Structural Health Monitoring System On Composite

Structural Health Monitoring(SHM) system is an essential part for smart materials, concluding two major diagnostic processes, that is passive sensing diagnosis(PSD) and active sensing diagnosis(ASD).The SHM basing on Piezoelectric transducer(PZT) is an ASD, because using such transducer ,piezoelectric effect and inverse of piezoelectric effect can take place. Any transducer can be an actor or a sensor. Comparing to other SHM, this method based PZT will use less money, use unheavy equipment, and will be very easy to use.The research using Active SHM in this thesis is mainly .about the detecting on composite laminate including damage detecting and evaluating of performance. Damage detecting is required to determine the existence of damage, to locate the damage and to estimate the extent of damage. Aim to this result, three conditions must be satisfied: (1) choose a fit PZT to be actor and also sensor; (2)generating a good acting signal. It can drive PZT to generate stress waves propagating in the plate easily. (3)use a signal processing scheme to process the collection data from sensor.Firstly, in the research, transducers of different sizes were used for different composite laminate. Secondly, a tone-burst, narrowband modulated sinusoidal signal is applied as acting signals waveform. With high central frequency for the acting signal, ultrasonic stress waveform will be generated and spread all directions, the ultrasonic stress waveform propagating in thin plate is also called as Lamb wave. The phase velocity of Lamb waves depend on the central frequency of itself, and while propagating in anisotropy plate such as composite laminate, the phase velocity is also a function of the propagation direction. Lamb waves propagating in composite laminate is sensitive to damage including delamination, hole,crack etc. when It come to the boundary of damage, Lamb waves would reflect and scatter every directions. This scatter signal contains the information of damage.In this thesis, experiments have been done to detect the delamination damage in beam and plate of composite laminate. Two characteristic parameters named DI(damage index of signal energy ) and AI(attenuation index of signal energy) have been introduced. And by the two parameters, expecting conclusion of damage detection can be found. Detecting of hole damage in the beam and plate laminate and impact on laminate are also mentioned is this paper.