Development of curing and self-healing methodologies of polymeric composites and study of the fiber-matrix interphasial interactions developed

• Κύριος συγγραφέας: Κονταξής, Λυκούργος
• Άλλοι συγγραφείς: Kontaxis, Lykourgos C.
• Γλώσσα: English
• Έκδοση: 2024
• Θέματα: Epoxy resin curing; Self-healing; PET (polyethylene terephthalate); Resistance heating; Joule heating; Electrothermal curing process; Self-resistance electric (SRE); Embedded resistance heating; Epoxy floor curing; Carbon fibers; Πολυμερισμός της ρητίνης; Θέρμανση Joule; Θερμοκρασία σκλήρυνσης; Θερμοκρασία αυτοθεραπείας; Επούλωση θερμοπλαστικών πολυμερών; Αυτοΐαση

In the current dissertation the possibility of using Joule’s heating effect to completely cure a thermosetting resin as well as heal thermoplastic polymers, is explored. The Joule heating effect is the process by which the passage of an electric current through a conductor produces heat. The proposed method in this dissertation is to insert resistive wiring into the polymer material, and via the Joule heating method, to ensure that the desired curing or self-healing temperature will be achieved uniformly throughout the polymer. However, a major concern is that the introduction of wiring may compromise the integrity of the bulk material. Initially, the viability of the method when curing bulk epoxy resin was tested and a comparison was drawn between Joule-cured and oven-cured specimens. Kanthal resistance wires were used, embedded in a resin plate, acting as the heating elements. Accurate temperature-time and temperature-position diagrams for fixed positions and times were created based on these experimental findings. By investigating the three-point bending mechanical behaviour of the cured resin and comparing it to the equivalent behaviour of the same resin cured at the same temperature in a traditional oven, the impacts of curing using this method were assessed. Also, specimens manufactured with both curing methods were characterized in single-fiber pull-out experiments in order to study the wire-matrix adhesion which, in turn, affects the heat transmission from the wire to the resin. The experimental results from the pull-out tests were studied through respective theoretical modelling. The next natural step was to replace the Kanthal wires with carbon fibers. The Kanthal resistance fibers were used as reference heating elements and subsequently, they were replaced by a Torayca Carbon Tow of the same radius. Specimens cured in a conventional oven were also manufactured, to compare the resistance heating method, for both types of fibers/wires to the conventional one. All specimens were mechanically characterized in a quasi-static three-point bending. Additionally, a preliminary financial study concerning power consumption needed for the application of both the traditional oven curing and the embedded heating elements method used for the manufacturing of the same amounts of materials is presented, showing a maximum financial benefit that can be achieved, on the order of 68%. Lastly, when concerning the resin curing part, the spatial limit of this method had to be established, thus, the degree of curing, and the dynamic viscoelastic behaviour of the epoxy resin, were studied as a function of both the curing time and the point distance from the heating element. For the degree of curing, DSC experiments were carried out, while for the dynamic-mechanical behaviour of the epoxy resin, DMA experiments were carried out over a frequency sweep mode. Thermal images were captured during the Joule heating curing process, to describe the temperature distribution variation with location and time, simultaneously. Consequently, the experimentally obtained temperature distribution was next predicted and compared with respective numerical results. After the numerical model was validated the Kanthal wire separation distance was parametrized in Abaqus in order to obtain an optimal distance between Kanthal wires. Finally, the last chapter presents the application of the embedded resistance wires technique, for the healing of thermoplastic polymers. In this investigation, the self-healing mechanism used was diffusion, and thermoplastics such as PET support this type of healing mechanism. PET specimens with artificial notch and abrasion damage were manufactured, and their ability to heal after internal heating was investigated. The specimens were evaluated optically and through three-point bending testing. The dissertation ends with the global conclusions of the entire work and future scientific avenues on this subject, while Appendices with supplementary material, are provided. At this point it is important to stress that both the subject and the methodology followed in the present dissertation comprise a prototype approach to the said problem, providing new knowledge to the relatively small number of relevant publications that currently exist in the literature.