Complex Buckling Modes Of Sandwich Panels Subjected To Combined Loads

Sandwich materials, mainly used as the wing surfaces and fuselage panels, are playing an increasingly important role in modern aircraft design due to the performance of high-strength in unit weight. These structures are usually subjected to tension and compression, shear and bending loads simultaneously, which situation is complex. Buckling is one of the possible failure modes. Therefore, the in-depth study of the sandwich stability has an important practical significance to its further application in the engineering field.As a part research work of Eleventh Five-Year Project, which is new structural design and strength verification of an aircraft, this paper first introduced the load path in sandwich structures and some basic concepts of stability as well as classical theoretical method to solve the buckling issue - Ritz method. Then, MSC.Patran / Nastran finite element software was used to analyze buckling eigenvalue of sandwich panels under shear, compression load alone and the combination of the both. Furthermore, some conclusions of different load cases summarized. In order to verify the credibility of calculations, the calculated results with ESAComp software were compared with the results obtained in Patran/Nastran and satisfactory results were obtained. According to the results above, curves of the buckling stress under combined loads were drawn, providing the basic information for design.Wrinkling, a kind of short-wave buckling mode of sandwich usually occurs when the core is thick or soft. Limited by model scale sandwich panel is usually modeled using shell element during finite element buckling analysis. This approach ignores the interactions of the face sheet and the core in the thickness direction and can not calculate the wrinkling modes. This paper developed a two-dimensional cross-section finite element model of the sandwich panels to analysis overall buckling and wrinkling together. The analytical results of sandwich structures were compared with the theoretical solutions. Then the ply angle effect of composite face sheet on buckling was discussed. The result getting from this paper was compared with the result getting from the conventional modeling method. At last some suggestions were presented to the analysis about sandwich buckling and wrinkling.In addition, this paper also investigated the buckling behavior of perforated sandwich plates. The effects of the cutout dimensions, the boundary conditions and laminate sequences on buckling were discussed. The results showed that an increase in cutout dimension will not necessarily reduce the buckling load in specific situations. In the end Riks method in ABAQUS was applied to investigate the buckling and postbuckling paths of sandwich plates and regulations on sandwich buckling were proposed.