6, a and 6, b shows the variation of the first natural frequency of the sandwich beam versus the thickness ratio, with various fiber orientations.
For both Models I and II, it can be indicated that the frequency of the sandwich beam with fiber orientation [theta] = 0[degrees] is relatively high compared with the others cases.
As seen from the results, it is clear that the natural frequency and mode shapes of the beam with coating layer composite can be controlled by choosing the proper fiber orientation, the laminate thickness and the boundary conditions imposed on the sandwich beam.
The following conclusions can be drawn from the present study: (1) the natural frequencies obtained by the FEM are in good agreement with those of the method analytical, (2) the natural frequency increases generally with the increase in the thickness ratio, (3) when the stiffness of the face layers is higher than that of the core layer, a linear relation is observed between frequency and thickness ratio and the amplitude of the mode increases when the thickness ratio increases, (4) the frequencies are larger with a fiber orientation of 0[degrees] and this for any thickness of the reinforcing layer, This is explained by the fact that the fibers are the direction of the sandwich beam, (5)the boundary conditions clamped-clamped (C-C) give the maximum natural frequency value.
DESIGN MAP OF A SANDWICH BEAM LOADED IN THREE-POINT BENDING
EXPERIMENTAL ANALYSIS OF THE SANDWICH BEAM LOADED IN THREE-POINT BENDING
In most cases, for sandwich beams loaded in three-point bending, the following failure modes can occurs, Fig.