Einfluss von Temperatur und Vorspannkraft auf elektromechanische Impedanzspektren am Beispiel von vorgespannten HV-Garnituren

The continuous and reliable monitoring of structures is becoming increasingly more important in engineering. The structures and elements to be monitored are as varied and diverse as their areas of application. A significant element in many constructions is the HV bolt, whose operational safety is significantly influenced by the level of preload force. For the safety and maintenance of functionality of structures with prestressed HV bolts, it is therefore important to know the current degree of prestressing in order to be able to intervene in time in case of critical reduction.
One possible method for continuous monitoring of pretensioning forces in HV sets is measurement by means of electromechanical impedance spectra. However, previous studies have shown that the development of the spectra is not only influenced by the level of the preload force, but also by the sample and ambient temperature present. Therefore, for an objective assessment of the prevailing preload force, a separation of the influences of temperature and preload force is essential.
The content of the paper deals with the influence of temperature and preload force on electromechanical impedance spectra using the example of preloaded HV sets according to DIN EN 14399. In the first part of the paper, important general physical principles for the measurement method are elaborated and presented. The content covers the compilation of essential physical phenomena from the fields of electrodynamics, piezo technology, and solid-state physics. In the following section, temperature- and preload-dependent parameters are separated and discussed. The knowledge gained is used to create a temperature- and preload-dependent numerical model, which, after prior validation by experimental findings, is used to explain and visualise essential physical relations. In the course of the work, the influences of temperature and prestressing force on electromechanical impedance spectra are
successively worked out with the help of theoretical principles, supported by experimental
findings, and illustrated with the help of numerical simulation. Towards the end of the thesis, some of the developed correlations are clarified by analytical calculations using examples. By separating the influences of temperature and prestressing force, an analytical compensation of the temperature in the electromechanical impedance spectra is finally possible.