Experimental Research Of Structural Damage Detection Based On EMI Technique

Electro-mechanical impedance(EMI) technique as one kind of non-destructive testing(NDT) methods develops in recent 20 years, which can realize online monitoring. At present, many domestic and foreign scholars had studied on this method and acquired certain achievements. The current research mainly focused on the qualitative analysis on the structure damage, i.e., the difference of electrical impedance spectrums before and after the damage occurred is analyzed to identify whether the structure damage occurred. EMI could identify the damage severity basically and depict damage severity through quantitative index. Without combining with other detective methods, the damage location identification mainly based on its local detective properties, to improve its recognition accuracy remained to be further research. Through specifically studying and referring to the theory and test methods from those scholars studied in this field, further experimental research on the structure damage detection based on EMI technique was studied. The specific research works were as follows:1. A overview of the development of piezoelectric ceramic material was showed, its direct and converse piezoelectric effect and piezoelectric equations were analyzed, coupling impedance of the piezoelectric ceramics and structure was deduced, the basic principles of applying EMI technique to structure damage detection was illustrated.2. The feasibility of applying EMI technique to one-dimensional(1D) beam and two-dimensional(2D) plane damage identification was specifically analyzed, the simulated location and test analysis of self-made holes and cracks damages were completed, According to the relationship between the impedance curve change and damage location in references, many experiments were carried out around a fairly wide frequency band, finally feasible frequency bands applying to damage localization were found, and the experiment of the 1D damage localization in aluminum beam was conducted accordingly, and then 2D damage localization, the processed results can meet the requirements of damage localization in general.3. The relevant experiments on the effects of different parameters on the detective sensitivity were carried out, the factors that likely affect damage index such as frequency bands, excitation voltage, the distance from piezoelectric ceramic to damage, etc. were discussed separately, ultimately the influence law of each influence factor on damage quantitative indicators were determined, the testing condition that possessed relatively high detective sensitivity was found, which can be used for the damage detection of corresponding materials, particularly suited to find the structure whether the damage had occurred or detect damage initiation.4. The local detective property of EMI technique was discussed by experiments, and the experimental research on the aluminum beams and composite beams was carried out, the size of damage was quantified by the two kinds of quantitative indicators, the results showed that EMI technique can identify local damage through the change of the quantitative indicators, and detect the damage propagation, two kinds of quantitative indicators can both meet the corresponding requirements.