Analysis of the influence of damage on flutter speed in CFRP structures

Abstract

The companies' incessant search for lighter aircraft has led to the use of several new technologies and design solutions in new aircraft models. Two of them have been the use of composites and more flexible structures, mainly in the wings. However, such structures lead to two main problems: (i) difficulty in identifying damage and defects in composite structures and (ii) very flexible aircraft are more subject to flutter. In view of the new challenges imposed, the present work seeks to assess the influence of structural reduction caused by damage/defects in the flutter speed. As the wing is the structure most subject to such a phenomenon, a laminated composite panel was used to simulate it. To study the effects of the damage, the Design of Experiments methodology was used, where with the aid of the Minitab software, 3 factors of influence of the damage were evaluated: location, damage size and severity. Then the designs were modelled in the FEMAP software, considering the damage as a reduction of the material properties, and using the aerodynamic model present in it. Two different elongation configurations and stiffness were evaluated using the P-K method for flutter solution. Aiming at a greater application of the study, a commercial wing was also evaluated. With the results obtained for the panels, a static analysis was made to evaluate the most influential factors in the flutter speed as well as its combination, such analysis was performed in the Minitab software. Using the surface response method present in the DoE tool, it was found that the damage location was the most influential factor in all panel configurations.