Optimisation des performances d'une structure de composite actionnées par des fils en alliages à mémoire de forme

Abstract

Morphing structures have gained a lot of attention lately; these structures have the ability to change their geometry in order to optimise their performances. One of the most promising field of applications is the aerospace, where their implementation could result in a significant performance gain. Recent developments in the fields of intelligent materials as well as advent of composites materials in aerospace structural components give new opportunities for the development of such structures. Indeed, many research projects have focussed on developing shape morphing wings, which could optimise their geometry in response to a variation of flight conditions in order to reduce fuel consumption. The project described in this document focuses on the development of a morphing composite surface that can be applied to a wing extrados. It is an effort in pursuing the CRIAQ 7.1 project, which demonstrated that adapting the profile of a wing extrados could successfully promote the laminar flow over the surface and thus, improve fuel consumption. Specific objectives are formulated in this project in order to solve some drawbacks of the solution proposed in the CRIAQ 7.1 project. As a result, a methodology is propose to develop a composite surface actuated by intelligent materials that can be deformed without a continuous actuation in order to minimize the energy consumption of the solution. It is done considering the lifetime of the surface as well as the manufacturing process. The two composite manufacturing processes considered here were the infusion as well as out of autoclave molding from pre-impregnated composite. The starting point of the proposed methodology is to identify the nominal geometry as well as the deformed geometry that optimises the laminar flow region over the extrados by a CFD analysis. These elements were already known from the CRIAQ 7.1 project and are identical for the present project. In order to obtain the proper morphed geometry, the composite’s layup is optimised. A model of the morphing surface is implemented in ANSYS Mechanical APDL as well as an optimisation sub routine to identify the lay-up that best match the targeted deformed geometry. The loading corresponds to a case where the leading edge of the extrados is fixed and the shape change is performed through the imposition of a tangent displacement at the trailing edge of the morphing surface. The model was validated through mechanical testing on a servo-hydraulic traction machine MTS 858 Mini-Bionix using GOM ARAMIS, a digital image correlation device. The same machine was used to perform fatigue tests on 50 mm wide section of the extrados manufactured with the two processes studied. After 1 000 000 cycles, none of the sample shown evidence of fatigue degradation. However, a better repeatability in the general quality of the composite and a better repeatability of the results was observed for the pre impregnated composite, it was therefore selected for this application. An actuation mechanism featuring a locking device was designed. The mechanism uses a camshaft located at the trailing edge of the extrados surface to apply the displacement, thus, freeing most of the space under the extrados. The locking device consists of a torsion spring wrapped around the camshaft and shape memory alloys wires are used to generate the rotation. The selected shape memory alloy is Nitinol (Ni 50,26%Ti). Thermo mechanical treatments were performed and a training routine was developed in order to develop the two way shape memory effect, which allows the mechanism to return to its nominal position without the use of external work. A prototype of the mechanism designed to morph the extrados was manufactured and tested. The locking capable mechanism allowed to successfully morph the composite, however, full actuation was not reached. This is mainly due to the difficulty regarding the adjustment of the pre-tension in the actuators. While the desired displacement was 2,1 mm, only 1,7mm could be obtained. The controller developed for the application allowed a precise control of the temperature of the actuators as well as the position of the camshaft. The temperature was kept within 2oC from the command and the angular position was maintained within 1o.

Date	16 May 2016
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Patrick Terriault (Supervisor) & Martine Dubé (Co-supervisor)