Abstract
Background. The concept of functionally graded materials (FGMs)
was first introduced as ultrahigh temperature resistant materials for
aircrafts. FGMs are non-homogeneous composites characterized by a smooth and
continuous change of material properties from one surface to the other. This
is achieved by gradually varying the volume fractions of the constituent
materials according to certain power law through desired direction(s) in
contrast with classical composite materials whose properties vary abruptly
form one lamina to the other. FGMs can survive environments with high
temperature gradients, while maintaining structural integrity.
Method of Approach. The response of FGM panels will be
investigated under the combined effect of elevated temperature conditions
and aerodynamic loading using a finite element model based on the thin plate
theory and von Karman strain-displacement relations. The aerodynamic
pressure is modeled using the quasi-steady first order piston theory. The
governing equations are obtained using the principal of virtual work
adopting a marching method in temperature to account for temperature
dependent material properties. This system of nonlinear equations is solved
by Newton-Raphson numerical technique.
Results. The buckling temperature, post buckling deflection, and
flutter boundaries are presented under the combined effect of thermal and
aerodynamic loadings, illustrating the effect of volume fraction exponent
and boundary conditions on the FGM panel response.
Conclusions. It is found that the temperature increase has an
adverse effect on the FGM panel flutter characteristics through decreasing
the critical dynamic pressure. Decreasing the volume fraction enhances
flutter characteristics but this is limited by structural integrity aspect.
The presence of aerodynamic flow results in postponing the buckling
temperature and in suppressing the post buckling deflection. The clamp
boundary condition is found to have better response than the simply
supported one.
