Advanced composite materials such as carbon fiber reinforced plastics (CFRP) possess higher specific strength (strength-to-density ratio) and higher specific stiffness than the other metallic materials. They are widely used for aerospace applications, for instance aircraft and space structures, where a severe weight saving is required, because designers can tailor materials depending on their purposes.
On the other hand, composite laminated structures are very susceptible to external impacts and internal damages such as delaminations which denote that two laminae at an interface in the plate are debonded locally. In aircraft structures, delamination can be caused by some reasons during manufacturing, service, and maintenance operations, for example impact damage due to the impact of external objects, such as hail or bird, which is comparatively light weight. The existence of delaminations can cause severe reductions in the mechanical properties of laminates, such as the compressive buckling strength. Also, it is often pointed out that they cause more serious damages in the structures leading to various accidents, especially under aerodynamic, elastic, and inertia forces repeatedly while the aircraft is in operation.
Generally, such a coupled motion caused by the interaction of aerodynamic, elastic, and inertia forces is the well-known aeroelastic phenomenon, and the aeroelastic problem results in the strength degradation of aircraft structures or fatal damage to the structural performance. In general, aeroelastic phenomena might appear remarkably due to large aerodynamic forces acting on aircraft structures of insufficient stiffness properties. It means that the demand for high speed flight results in the increase of structural weight of aircrafts for avoiding aeroelastic instabilities. Consequently, the increase of structural weight may degrade the performance of aircrafts. Therefore, the understanding and the improvement of structural aeroelastic characteristics are some of significant issues in the aircraft structure design. Up to date, there have been many works on the characteristics of composite laminates with internal damages, however, the studies on the effect of delaminations on 'panel flutter characteristic,' which is one of aeroelastic properties, are still limited.
The present research treats a supersonic panel flutter problem for composite laminates with a delamination, and the effect of the delamination on panel flutter characteristics of laminated beams and plates is investigated by using a finite element method (FEM) and a quasi-steady aerodynamics theory.
edited by Tatsuya HANAWA