Imperfection-Insensitive Axially Loaded Cylindrical Shells

Researchers and Collaborators

Xin Ning
Sergio Pellegrino

Description

The high efficiency of monocoque cylinders in carrying axial loads is curtailed by their extreme sensitivity to geometric imperfections, boundary conditions, loading, etc. which has been alleviated by introducing closely stiffened shells, i.e., cylindrical shells reinforced by stringers/corrugations and rings. This type of architecture is currently established as the premiere efficient aerospace structure and is widely used for lightness and extreme efficiency. However, closely stiffened shells usually require complex manufacturing process, resulting in very expensive structures.

In this research, we have designed symmetry-breaking wavy cylindrical shells that avoid imperfection sensitivity. Their cross-section is formulated by NURBS interpolation on control points whose positions are optimized by evolutionary algorithms. Both perfect and imperfect structures are used to evaluate the value of objective function in our optimization. This is fundamentally different from conventional structural optimization in which usually only perfect structures are considered.

We have applied our approach to both isotropic and orthotropic shells and have also constructed optimized composite wavy shells and measured their imperfections and experimental buckling loads. Through these experiments we have confirmed that optimally designed wavy shells are imperfection-insensitive. We have studied the mass efficiency of these new shells and found them to be more efficient than even a perfect circular cylindrical shell and most stiffened cylindrical shells.

Buckling analyses of heavily corrugated and stiffened cylindrical shells based on detailed full finite element models are computationally intensive. This high computational effort has been the major constraint of the use of finite element analysis in the optimization of corrugated/stiffened shells. To address this issue, we have proposed a computational method which is a modification of the traditional Bloch wave method. It was found that our method can obtain highly accurate results and is much more efficient than detailed full finite element models.

Publications:

  • Ning, X. and Pellegrino, S., Imperfection-Insensitive Axially Loaded Thin Cylindrical Shells, International Journal of Solids and Structures, in press.
  • Ning, X. and Pellegrino, S., Buckling Analysis of Axially Loaded Corrugated Cylindrical Shells. 56th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, Jan. 5-9, 2015, Kissimmee, FL. (pdf)
  • Ning, X. and Pellegrino, S., Imperfection-Insensitive Axially Loaded Cylindrical Shells. 54rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, April 8 - 11, 2013, Boston, Massachusetts. (pdf)