ESDU Engineer

Buckling of Composite Panels and Struts

ESDU 03001 accompanies ESDUpac A0301 which provides a Fortran computer program that calculates initial compressive buckling loads for long, flat, stiffened, rectangular panels and struts made of composite materials. The method on which the program is based is the finite strip method (FSM), which is particularly well-suited to the analysis of prismatic structures that show periodic deformation patterns under loading.

Although the program is based on FEM-like discretization procedures, it possesses significant advantages in speed compared to a full-scale finite element approach. The buckling analysis is applicable to models of panels or struts constructed from composite laminates that fall into the category of balanced, or mid-plane symmetric, laminate lay-ups, that is, generally orthotropic laminates of the AsBoDf type. The types that are allowable is dictated by the requirement that a uniform pre-buckling state of stress exists, together with satisfaction of given boundary conditions. In addition, the panels are presumed to behave within the realm of classical laminate thin plate theory.

Thus, ESDUpac A0301 is able to compute the compressive buckling stresses and – if relevant – the associated modes for local, flexural and torsional or torsional-flexural buckling for panels and struts made of composite materials and subjected to pure compressive loading.

One of the features of the program is a pre-processor routine which simplifies the input of data for 12 commonly–used skin–stringer sections by generating the strip model data file for a panel consisting of a skin and a number of stringers. This option frees the user from the need to generate a usually large strip model data file. Detailed geometrical and model information for these skin-stringer sections is provided in Appendix A of the Data Item.

The user may, of course, still generate the strip model data file for a panel or strut of completely arbitrary cross-section, without utilization of the predefined sections mentioned above.

An added option for use with a predefined skin-stringer section consisting of specially orthotropic laminates is the possibility of representing a wide panel having many stringers by a special single skin-stringer model with predefined boundary conditions. The predefined boundary conditions have been selected in such a way as to give complete freedom in the z - direction whilst not allowing lateral in-plane displacements and rotations in the buckling mode of the outer edges of the skin section. This option allows quick exploration of the variation of compressive buckling loads for ranges of geometrical and physical parameter values that may occur in a new design.

Detailed descriptions of the input required by the program and the output data it provides are given, along with example input and output files.

Adam Quilter is Head of the Strength Analysis Group. He can be contacted at aqui@esdu.com