Comportamento strutturale di isolatori elettrici in alta tensione per l'esperimento MITICA: modelli numerici e prove sperimentali

The objective of this thesis is the experimental validation of particular structural components of the MITICA Beam Source prototype, made of Polyetheretherketone (PEEK), an engineering thermoplastic with high mechanical and electrical insulation properties. The components are named "post-insulators" due to their double-function of mechanical support and of electrical insulator and are subjected to high mechanical strengths since they sustain the whole weight of the cantilevered structure of the MITICA Mock-Up Beam Source, as properly described later. The thesis has been carried out at “Consorzio RFX” during the months between March and December 2023 under the supervision of Prof. Giuseppe Chitarin and Dr. Sylvestre Denizeau. In a first phase, the stress distribution and deformation of the PEEK post-insulators is simulated using two FEM models, so as to evaluate the behavior during operation and to support the interpretation of the results to be obtained during subsequent tests. A first model used accurate geometry, including also screws, helicoils and bolts connections used to fasten the PEEK insulator to the stainless-steel flanges. The second model was a simplified version of the same post-insulators model, where connections by screws, helicoils and bolts were replaced with bonded contact type connection. Experimental tests were then carried out on 4 post-insulator samples, using a specific set-up, so as to measure the force-deformation characteristic of the insulators, while subjected to a pre-determined tensile force and bending moment combination. The results indicated that, the stiffness calculated by either numerical simulation procedure was overestimated with respect to the experimental data. Such discrepancy has consequences in terms of total deformations, equivalent stress and natural frequencies of the MITICA Mock-Up Beam Source. The differences have been quantified by calibrating the numerical models of the tensile test with the experimental results. Lastly, an explanation of this discrepancy is given by making an accurate sub model of the M14 screw, helicoil and PEEK bulk material. This model shows how the replacing real-case screw-helicoil connections with standard bonded connections causes an increased stiffness of the model compared to the real-case scenario.

Studio del comportamento meccanico-strutturale degli isolatori elettrici portanti (denominati "post-insulators") costituiti di polimeri ad alte prestazioni (PEEK) utilizzati nell'esperimento mock-up di MITICA. Analisi di dati ottenuto da prove sperimentali a trazione e simulazione numerica di viti Helicoil a contatto tra l'isolatore e la flangia da implementare nel modello completo ANSYS di MITICA.