Knockdown factors for cylindrical shells caused by torsional Mode-I type geometric imperfections under axial compression

Year 2021, Volume: 5 Issue: 3, 419 - 425, 15.12.2021

İbrahim Kocabaş , Haluk Yılmaz

https://doi.org/10.35860/iarej.891791

Abstract

Geometrical imperfection, which is generally a result of manufacturing process and service conditions, plays a crucial role in load-bearing capacity of shell structures. This study presents a numerical study on knockdown factors of cylindrical shells as a result of torsional Mode-I type of geometric imperfections under compressive loads. The deformation patterns obtained from liner bifurcation analysis (LBA) for torsional Mode-I shape are used as a source of geometric imperfection. Then, geometrically nonlinear buckling analysis with imperfect model (GNIA) is incorporated with LBA in ANSYS Workbench to obtain limit loads of imperfect structures. A parametric study is thus performed to investigate the influence of imperfection depth on the load-bearing capacity considering a wide range of cylindrical shell configurations. Local and global buckling characteristics of the imperfect shells are examined and knockdown factors are characterized by three distinct regions as a basis of normalized imperfection depth. For a large number of shell configurations, a scattering of knockdown factors against normalized imperfection depth is given with mathematical expressions evolving lower and upper bounds. These expressions provide the minimum and maximum values of knockdown factors for a given imperfection depth, which can be treated as a design tool to ensure safety of the shell structure.

Keywords

Axial compression, Cylindrical shell, Finite element method, Geometric imperfection, Knockdown factor

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