Thesis defense of Ander Domínguez - Macaya Lopez

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Thesis defense of Ander Domínguez - Macaya Lopez

THESIS

Thesis defense of Ander Domínguez - Macaya Lopez

Title of the thesis: “Air-coupled ultrasonic inspection of fiber reinforced composite materials”. Obtained the SOBRESALIENTE qualification and he has received the DOCTOR INTERNACIONAL mention

2020·05·20

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  • Title of the thesis: “Air-coupled ultrasonic inspection of fiber reinforced composite materials”
  • Court:
    • President: António Torres Marques (Universidade do Porto)
    • Vocal: Gerardo Aranguren Aramendía (UPV/EHU)
    • Vocal: Idurre Saez de Ocariz Granja (Centro de Tecnologías Aeronáuticas)
    • Vocal: Jorge Jaime Camacho Sosa (Consejo Superior de Investigaciones Científicas)
    • Secretary: Laurentzi Aretxabaleta Ramos (Mondragon Unibertsitatea)

Abstract

The increase in the use of composite materials in recent years has led the industry into the development of new composite manufacturing processes, like the 3D ultraviolet pultrusion. These new manufacturing processes usually reduce manufacturing costs, cycle time or both. Ensuring the quality of the parts manufactured with these new processes is critical. Therefore, it is necessary to gain knowledge on these manufacturing processes, especially on the behavior of the material during the cure. To monitor these processes, the development of new non-destructive inspection techniques is required. For the 3D ultraviolet pultrusion, the use of non-contact non-destructive testing is necessary. Moreover, for structural parts, ensuring the required mechanical properties gives added value to the part.

In this thesis, the viability of air-coupled ultrasonics for plate-like fiber reinforced parts manufacturing is evaluated. At first, isotropic materials are evaluated, considering the ultraviolet cure of a vinyl ester resin. Air-coupled ultrasonics has proved to be fast enough to follow the ultraviolet cure, with quasi-normal ultrasonic spectroscopy. Then, the mechanical properties in fiber reinforced polymers with air-coupled ultrasonics are evaluated. The optimal set-up to generate leaky Lamb waves in plates with different properties is defined. Air-coupled ultrasonics showed that is what difficult to generate Lamb modes with different velocities, although it was possible with a mixed air-coupled laser ultrasonics set-up. Last, leaky Lamb waves where used with air-coupled ultrasonics to evaluate the properties of a fiber reinforced polymer during the thermal cure. The stiffness tensor of the composite was measured during the cure observing the largest variation at the last stages of the cure.

The main conclusion of this thesis is that the potential of air-coupled ultrasonics to monitor the fiber reinforced manufacturing processes is elevated. It can presents both the speed required to monitor fast curing processes like ultraviolet cure, with single measurements in less than a second; and the ability to characterize the full matrix of an orthotropic fiber reinforced polymer, through the use of micromechanical models. Air-coupled ultrasonics can be used to characterize the properties of materials with different geometries, like curves or hollow.