| Περίληψη: | In the current thesis thin magnetoelastic ribbons of metallic glass alloy known as
Metglas 2826MB were investigated, characterized and applied as vibration-based
structural health monitoring sensors. Such materials have the property of changing their magnetic state (magnetization) when they are stressed mechanically (Villary effect), and vice versa they are stressed mechanically when they are magnetized by an external magnetic eld (magnetostriction effect). These materials were used in the form of thin ribbons in contact with a mechanical structure, such as a cantilever beam, as a vibration sensor, in order to monitor the structure's mechanically health state. The monitoring was established through the detection of the natural frequencies of the mechanical structure. The study of the thesis is divided into three main parts which are, the "proof of concept" of the work, the characterization procedure and the application process. As far as the first part is concerned, the ability of the ribbons in sensing and transmitting the vibrational state of a cantilever beam was investigated, as well as the accuracy of the recorded data in detecting the change of the vibrational state of the structure due to damages. To carry out this task, a number of different beam specimens, undamaged and damaged, of aluminum alloy 6063 material were used and the results were compared to computational ones using ANSYS modal analysis. The second part was the characterization of the ribbons as structural vibration sensors and the process involved seven different sensor parameters such as the frequency response, linearity, signal to noise ratio (SNR), quality factor, stability, repeatability and sensitivity. The experiment was accomplished using two different experimental setups, one to examine the frequency response parameter
and one to examine the rest of the parameters. The last part included the
application of the under consideration vibration sensors to detect and identify
cracks in cantilever beams, through a proposed crack identi cation methodology.
The methodology involved the use of a pattern matching process, through a minimization procedure, in order to identify the crack location and depth. Each one of the three parts was examined in detail and thoroughly, with the results of the experiments being properly presented and described.
|
|---|
