Nudging Axially Compressed Cylindrical Panels Toward Imperfection Insensitivity

B S Cox,R M J Groh,A Pirrera

doi:10.1115/1.4043284

B S Cox, R M J Groh + Show 1 more

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https://doi.org/10.1115/1.4043284

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Abstract

Abstract Curved shell structures are known for their excellent load-carrying capability and are commonly used in thin-walled constructions. Although theoretically able to withstand greater buckling loads than flat structures, shell structures are notoriously sensitive to imperfections owing to their postbuckling behavior often being governed by subcritical bifurcations. Thus, shell structures often buckle at significantly lower loads than those predicted numerically and the ensuing dynamic snap to another equilibrium can lead to permanent damage. Furthermore, the strong sensitivity to initial imperfections, as well as their stochastic nature, limits the predictive capability of current stability analyses. Our objective here is to convert the subcritical nature of the buckling event to a supercritical one, thereby improving the reliability of numerical predictions and mitigating the possibility of catastrophic failure. We explore the elastically nonlinear postbuckling response of axially compressed cylindrical panels using numerical continuation techniques. These analyses show that axially compressed panels exhibit a highly nonlinear and complex postbuckling behavior with many entangled postbuckled equilibrium curves. We unveil isolated regions of stable equilibria in otherwise unstable postbuckled regimes, which often possess greater load-carrying capacity. By modifying the initial geometry of the panel in a targeted—rather than stochastic—and imperceptible manner, the postbuckling behavior of these shells can be tailored without a significant increase in mass. These findings provide new insight into the buckling and postbuckling behavior of shell structures and opportunities for modifying and controlling their postbuckling response for enhanced efficiency and functionality.

Highlights

In many engineering disciplines the onset of geometric nonlinearity is considered a form of structural failure
The response of two axially-compressed cylindrical shell panels was studied by means of a displacement-controlled finite element procedure
One panel was pinned on all four edges (PPPP) and the other was clamped at the two curved ends to prevent rotation on the loaded edges (CCPP)

Summary

Introduction

In many engineering disciplines the onset of geometric nonlinearity is considered a form of structural failure. White and Weaver [23] provide an interesting approach based on steering the fibre reinforcement along curvilinear paths over a cylindrical shell surface In this manner, curved shell structures with stable, plate-like post-buckling behaviour were designed. Their work draws attention to the fact that there exists a direct relationship between the critical buckling load and the geometry of the applied imperfection (amplitude, angular width, etc.) Both Finite Element (FE) simulations and a semi-analytical model were able to accurately predict the knockdown factors of these imperfect spherical shells, illustrating that their behaviour can be described with certainty once the initial geometry, including dominant imperfections, is defined precisely

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