Explicit Local Buckling Analysis Of FRP Composite Honeycombs Under Out-of-plane Compression

Composite honeycomb sandwich structures have extensive application in structural engineering because of its low specific weight, relative great bending stiffness, excellent impact absorption ability, good thermal and noise insulation properties, etc. Honeycomb material is also the first choice as the sandwich core in aerospace. Honeycomb material is also applied in the automobile industries and civil engineering. A lightweight core such as honeycomb or foam between two tough skins makes up the typical sandwich construction. When the honeycomb structures made up of fiber-reinforced plastic sustain the axial compressive load, local buckling always comes first before the other kinds of fa ilure mode take place. Owing to the complicated geometric features and self-periodic honeycomb cells, there are few studies for local buckling predictions of FRP honeycomb structures.The local buckling of FRP honeycomb structures is studied by the Rayleigh- Ritz method and discrete plate theory. The new formulas of rotational restraint stiffness(k) of orthotropic composite plates are primarily derived using the bending deformation equations of the isotropic plates. The local buckling explicit analys is expressions of FRP honeycomb structures can be obtained in terms of the new rotational restraint stiffness formula. It also provides design analysis for the local buckling load of FRP honeycomb structures when they are under the axial compressive load. The main tasks of the research consist of the following three parts:First, based on the equation of bending deformation when the orthotropic plates under specific boundary conditions, the new explicit formulas of rotational restraint stiffness(k) for restrained orthotropic plates are derived, and they are more accurate than the previous ones which are directly approximated from the isotropic cases. The new formulas of the rotational restraint stiffness(k) are used to the local buckling explicit analys is of box-section using the discrete plate analysis technique, and the effects of plate aspect ratio, the material orthotropy ratio and section dimensions of box-section on the rotational restraint stiffness(k) are considered in the new formula. The explicit formulas can calculate the critical local buckling loads, and they are compared with the results by the numerical finite element analysis. The present formulas are demonstrated to be effective in determining the local buckling loads of composite box-sectional structures.Second, the explicit formulas of the critical local buckling load of composite plate with the rotational restraint along both unloaded edges( RR) subjected to axial uniformly distribute load are obtained by the Rayleigh- Ritz method. Assuming that the principle of superposition is suitable for the local buckling analysis of the honeycomb structure, the new formulas of rotational restraint stiffness are applied to local buckling analysis of FRP honeycomb structures under the axial compressive loads. The explicit expressions of the critical local buckling load of three different FRP honeycomb shapes.Finally, considering the effects of sectional aspect ratio, thickness and orthotropic parameters of three different FRP honeycomb shapes on the critical local buckling load a parametric study is conducted. The present results by the explicit formulas of the critical local buckling load are compared with those of the numerical finite element analysis, and the present explicit formulas can be used to be effective in determining the critical local buckling load of any sectional aspect ratio FRP honeycomb structures under axial compression.