Μέτρηση κατανεμημένων τάσεων σε χάλυβες με την χρήση των μαγνητοσυστολικών γραμμών καθυστέρησης (MDL)

Abstract

This work focuses on the study of magnetostrictive delay lines (MDLs) and their engineering applications. Initially, the generation, propagation, and detection of an elastic pulse in MDL arrangements are examined. This study enabled a deep understanding of the mechanisms and parameters affecting the generation and detection of the elastic pulse, such as the excitation and biasing fields, as well as the mechanical impact on the delay line. Understanding these parameters led to the development of various MDL configurations used as sensors. The fundamental properties of MDLs, including sensitivity, linearity, and hysteresis, were determined in detail, along with methods for tailoring these properties to meet the requirements of different applications. Additionally, the dependence of these properties on various factors such as field, frequency, stress, temperature, and time was analyzed. The work also introduces magnetoelastic uniformity, sound velocity, and MDL resolution—three properties that define the performance of these systems. Various magnetoelastic materials were investigated, concluding that amorphous ribbons and wires are particularly suitable for sensing applications, without excluding thin films. The properties of these materials can serve as a database for engineering applications, particularly in sensor development. The work focuses on presenting the main MDL sensors. For clarity, these sensors are categorized into three main types: position sensors, stress sensors, and field sensors. Several position sensors based on amplitude or time delay modulation were developed, capable of measuring either static or dynamic displacement. Various stress sensors, such as tensile stress sensors, pressure sensors, and force digitizers, were also developed, offering significant advantages over existing technologies. Additionally, MDL-based field sensors were presented, which offer distribution measurement capabilities with acceptable measurement uncertainty. Manufacturing technologies that allow for low-cost production with acceptable accuracy were also developed. In addition to technological applications, the work explores critical MDL applications in fields such as non-destructive testing, blood coagulation studies, and chemical composite materials, as well as in structural and mining engineering. As an additional application of the MDL technique, a method for measuring M(H) and λ(H) curves was presented, which allows for the determination of the magnetization and magnetostriction uniformity along the length of a magnetostrictive material. Finally, the thesis examines the challenges arising from the application of these techniques in real-world conditions, such as environmental effects and the need for high sensitivity and accuracy. The potential for improving measurement performance through further development of materials and data analysis methods is also discussed, thus enabling the broader application of MDLs in more demanding industrial uses.