Avaliação da aplicação de ancoradores por soldagem em laminados metal-fibra visando a indústria aeronáutica

Abstract

Fiber-metal laminate panels are modern and efficient alternatives for obtaining light and high strength structures applicable in the transport industry, especially in aeronautics. Traditionally, these panels are formed interlaying thin metal and composite components, combining the best properties of both materials into a single structure. Thus, the adhesion between the metal and the composite layers is critical for the good performance of the structure. Anchorages fixed to the metal sheet surfaces have proved to be beneficial for the adhesion. Typically, sophisticated manufacturing processes, such as LASER, are used for this purpose producing micro-edging or texturing. However, such techniques are usually applied for metal-composite joints rather than for laminate panels. The aim of this work was to propose and evaluate a new concept of anchorages for laminate panels, which consists of the deposition of metallic mini pins by arc welding to act as anchorages of the metal-composite interface. For this, the CMT PIN welding process, already successfully tested in hybrid metal-composite joints, was used. Initially the CMT PIN process was studied in order to produce the best type of pin geometry for the intended application. Then, miniaturized panels were fabricated with different arrangements and pin densities and then evaluated by comparing to conventional panels of the same material and similar dimensions by means of quasi-static mechanical loading tests (three-point bending, buckling and shearing), low- and high-speed impact and modal analysis. In order to evaluate the panels against flexure, compression and shear stresses (which are typical stresses suffered by the aircraft structure in operation), appropriate mechanical tests were carried out. Impact tests were intended to simulate the behavior of these structures in collisions with objects in their trajectory, or even when being the target of projectiles launched on them. The modal analysis assay was aimed to determine the pins ability to impart damping to the panels. Finally, an evaluation of the surface quality of the panel outer walls was implemented in order to avoid cosmetic limitations of the panels manufacturing by welding. The panels with anchorages were found to have similar strength to buckling, but lower bending strength, as compared to the conventional laminate panel. However, these panels presented a less catastrophic behavior after failure and a higher resistance to shear. The Drop-Weight Test showed that the pins did not make the panels more fragile nether altered their ability to absorb the impact energy, moreover when subjected to the high-speed (Ballistic) impact test, panels with pins exhibited a greater energy absorption capacity. It was verified by modal analysis that the pins did not change the natural vibration frequency but they considerably increased the damping factor of the panels, giving them a greater capacity to absorb vibration and noise. These positive features are related to a better anchoring between the metal and the composite promoted by the pins, which accompanied by a slight increase of mass and without significant surface alterations of the panel external walls. Thus, anchoring achieved from composite layers through pins deposited by welding has proved to be able of improving the performance of fiber-metal laminate panels.