Aplication of the Electro-mechanical (e/m) Impedance Method to Machinery Failure Prevention

A short review of current methods for damage detection and failure prevention in complex machinery is first presented. Two main classes are identified: (a) detailed inspection through machinery strip-down and minute examination with a variety of scanning methods, and (b) in-situ health monitoring using passive and active sensors. The emergence of new in-situ sensor techniques based on the active material approach is highlighted. In this context, the electro-mechanical impedance technique is identified as an emerging new technology with high potential for in-situ health monitoring and NDE of complex machinery. The fundamental principles of the electro-mechanical impedance methods are presented and its practical implementation is highlighted. The piezoelectric material response equations are given. The coupled electro-mechanical impedance of a wafer-transducer affixed to on an elastic structure is presented. A number of demonstration experiments are presented. These experiments were conducted on a variety of applications: precision machinery parts, real-life aircraft junction, composite patch repairs, etc. From these experiments, the importance and benefits of this method for on-line health monitoring and damage detection of complex machinery become apparent. Further investigation of the electro-mechanical impedance method is warranted. A deeper understanding is needed of the complex interaction between wave propagation, drive-point impedance, structural damage and electro-mechanical impedance of the wafer transducer. Thus the method could be developed in a widely used technique and its applicability can be extended to other engineering areas.