Metodologie e set-up di misura per l’esecuzione di test non distruttivi su materiali metallici

In this thesis, the methodologies and measurement set-up for the execution of non-destructive tests with the eddy currents technique (ECT) and ultrasound technique (UST) are examined and implemented. Any industrial product, made from metallic and non-metallic materials, can present numerous varieties of defects, inside or on its external surface, which differ both in type and shape. These discontinuities can be caused by the manufacturing processes and by the stresses that the various components undergo during their use. The presence of these defects or their development and increase, especially in working conditions, can cause both a reduction in the useful life and an unexpected breakage of the same, with results that can be harmful from an economic viewpoint and of the safety of the people. For this reason, in the industrial sector (aeronautics, automotive, construction, etc.), each product of critical importance must be checked for the verification of its integrity and compliance with current regulations ensuring its quality and safety of use. In this scenario, the development of techniques and tools for non-destructive diagnostics is moving towards new frontiers, capable of facing the current needs of the industrial sector. In particular, the eddy current and ultrasound inspection techniques offer a good compromise in terms of ease of use, speed of inspection and reliability of the test. Although technologically advanced, the methods and tools for non-destructive testing with eddy current and ultrasound techniques currently in use are not without problems and limitations. For example, as regards the ECT, the most important limitations are related to the applicability only to the conductive materials, to the possibility of locating only the surface discontinuities or to limited depths, to the use of different probes according to the defect to be analysed (superficial or sub-superficial) or to the difficulty in identifying the specific typology of the defect. As for the UST instead, the most important limitations are related to the need to use couplers for the probes, to the loss of sensitivity towards thin defects and parallel to the direction of propagation of the ultrasonic beam, to the calibration procedures of the instrument to obtain a response to the easily recognizable defect, to the need to use high energy excitation signals and to the difficulty in correctly identifying the result of the measurement. In this thesis, as regards the non-destructive method of eddy current investigation, solutions of low energy consumption probes assisted by the use of magnetic field sensors are analysed and implemented, with the aim of increasing the sensitivity of the method at depths greater than those of the current solutions available in the literature. In particular, the prototype of the realized probe is presented, with all the steps of the design, implementation and realization. The innovative detection system created is highlighted, which allows to improve the probe performance. The experimental configuration for the probe characterization and the results of the numerous tests are illustrated. Finally, it is shown how the realised probe improves the detection of defects compared to the cutting-edge solutions available in the literature. Regarding the line of research, concerning the non-destructive ultrasound investigation methods, the attention was paid to the analysis of structures such as metal bars. This type of investigation is currently absent in the literature. Starting therefore from the different types of excitation signals, from the different digital conditioning methods and from the different signal processing methods proposed in the literature, which allow a better accuracy of the measurement process, a higher inspection speed and a greater sensitivity compared to various types of defects, an experimental comparison is performed to identify the better combination that allows the best detection and location of the defects. The designed measurement station for the execution of non-destructive ultrasound tests is presented, which allows a real-time analysis of the examination performed, using a developed ad-hoc software, and finally, the experimental results are presented, to identify the best combination of the different types of excitation signals, digital conditioning and data processing considered, for the detection and localization of defects in structures such as metal bars.