©2012 Civil-Comp Ltd
G. Zamula and I. Kondakov
Central Aerohydrodynamic Institute (TsAGI), Zhukovsky, Moscow Region, Russia
Keywords: crippling, postbuckling, numerical, experimental, rods, panels.
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This paper is concerned with the crippling-postbuckling behaviour of aircraft structures; the primary objective is to analyse and compare the existing simplified methods, to consider new experimental data and to improve finite-element analysis of crippling of compression-loaded profiles and panels.
In the first part of the paper the semi-empirical methods for analysing crippling of roll-formed and extruded aluminum shapes have been studied in comparison with the methods developed at TsAGI. In the second part of the paper a number of analytical solutions have been obtained and the specialized high-precision experimental facility on the base of a universal test machine has been created in order to perform verification and development of the crippling analysis methods. The third part of the paper is devoted to the development of numerical methods for analyzing local buckling, postbuckling behaviour and the crippling or load-bearing capacity of plate systems based on the finite element method.
The study of the existing methods for crippling analysis has shown which method is the most suitable semi-empirical method developed to date. However, for application of this method for new materials and structural or manufacturing methods requires significant amount of additional experimental research. For a number of specimens the three-fold excess of the destructive crippling stresses over the local buckling stresses of the profile was experimentally obtained.
Development and parametrical research of the finite element modeling of crippling analysis has shown the following. As for the calculation of the critical stresses of local buckling, the solution using a bifurcational function usually makes little difficulties and the results correspond well with the experimental data as well as to the accurate analytical solution. This is also partly true for the finite element analysis of moderate postbuckling deformations of compressed rods and panels in the elastic regime. However, the assessment of the load-carrying capacity of structural elements with significant geometrical non-linear and plastic deformations requires further development, particularly for the problems of the crippling of stiffened panels with different boundary conditions and combined loading.