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The influence of geometric imperfections of different tolerance levels on the buckling load of unstiffened cfrp cylindrical shells
Publikationstyp
Conference Paper
Date Issued
2019-01-01
Sprache
English
Author(s)
Volume
2019-August
Citation
International Conference on Composite Materials (ICCM 2019)
Contribution to Conference
Scopus ID
Unstiffened CFRP cylindrical shells under axial compression prone to buckle. For designing these shells a high discrepancy between the theoretical analytical and the real buckling load has to be handled. Responsible for this discrepancy are various imperfections, which influence the buckling load. One of the most important and historically first considered imperfections are the geometric or traditional imperfections, which describe the deviation from the ideal form. The extent of the geometric imperfections is largely determined by the manufacture of the cylindrical shells and the boundary conditions. The fact that these imperfections are not exactly known before manufacture makes the design difficult. Therefore, despite a multitude of already existing experiments with CFRP cylinders, knockdown factors are used for the design, which lead to very conservative designs. Therefore, the statistical data base has to be extended and imperfections have to be characterized. In this paper, geometric imperfections of eleven already tested CFRP cylinders are analysed and characterised. In addition, the influence of the clamping on the geometric imperfections is investigated. Furthermore, tolerance classes are defined based on the shape tolerances that occur. Artificial cylinders are generated for the individual tolerance classes and their buckling load is calculated. Before this, a study is carried out to determine how many Fourier coefficients are necessary to describe the cylinders and how the individual modes influence the buckling load. It is shown that a reduction of the geometric imperfections increases the buckling load slightly, but decreases it significantly if the existing geometric imperfections are increased. This is particularly caused by the increase in short-wave axial imperfection modes. Finally, the geometric imperfections of another newly manufactured cylinder are analysed and characterized. This cylinder is tested on the hexapod test rig of the Hamburg University of Technology and the test results are compared with the simulation results.
Subjects
Buckling
Composite Shells
Geometric Imperfection