Daisuke Narita

Analysis for Vibration of Laminated Shallow Shells with Non-Uniform Curvature

Despite a large number of technical papers on vibration of composite shallow shells, all the previous papers have dealt with shallow shells with uniform curvature to avoid difficulty in the analysis. Recent composite products, however, require various surface designs of thin panels from the viewpoint of industrial design, for example, in the fender and door panel designs of commercial vehicles. The present study proposes an analytical method to deal with vibration of shallow shells with non-uniform curvature. An interpolating function is introduced to represent the required surface shape and the corresponding curvature is derived as a function of the position (x,y). The obtained curvature is substituted into the total potential energy of the shell, and the procedure is shown to derive a frequency equation in the Ritz method. Numerical examples clarifies the effects of non- uniform curvature on the natural frequencies and mode shapes.

Analysis and Design of Curved Laminated Composite Panels under External Pressure

Curved panels can bear more lateral load than flat plates because they can transmit the external load along curved surface in addition to load-carrying capacity by the bending stiffness. For curved panels, however, there is a critical point of the lateral load that structure can endure before it buckles. On the other hand, composites are known to have more advantages in specific strength and stiffness than conventional metal materials. The present paper proposes a semi-analytical method to predict the initial buckling loads of slightly curved panels composed of thin orthotropic composite layers under general boundary conditions. Based on the Donnell type theory, the potential strain energy is evaluated as a sum of stretching energy, stretching-bending coupling energy and bending energy, and the external work done by uniform external pressure is included in the functional. The eigenvalue equation is derived by the Ritz method to yield such initial buckling load parameters as eigenvalues. Numerical examples include a list of buckling loads and the corresponding buckling patterns for typical panels with simply supported and clamped edges.