60 - NUMERICAL AND EXPERIMENTAL STUDY OF BUCKLING OF...

NUMERICAL AND EXPERIMENTAL STUDY OF BUCKLING OF ADVANCED
FIBRE COMPOSITE CYLINDERS UNDER AXIAL COMPRESSION
R S PRIYADARSINI
1
, V KALYANARAMAN
2
Department of Civil Engineering, Indian Institute of Technology, Madras
Chennai 600 036, India
1
[email protected] ;
2
[email protected]
and
S M SRINIVASAN
3
Department of Applied Mechanics, Indian Institute of Technology, Madras
Chennai 600 036, India
3
[email protected]
ABSTRACT
Advanced lightweight laminated composite shells are increasingly being used in modern
aerospace structures, for enhancing their structural efficiency and performance. Such
thin-walled structures are susceptible to buckling when subjected to static and dynamic
compressive stresses. In this paper, details of a numerical (FEM) and an experimental
study on buckling of carbon fibre reinforced plastics (CFRP) layered composite cylinders
under displacement and load controlled static and dynamic axial compression are
reported. The effects of different types of loadings, geometric properties, lamina lay-up
and amplitudes of imperfection on the strength of the cylinders under compression are
studied. Accurate measurement of imperfections in the cylindrical surface is carried out
in the specimens tested. It is shown that the buckling behaviour of thin composite
cylindrical shells can be evaluated accurately by modeling measured imperfections and
material properties in FEM.
1. Introduction
Composite cylindrical shells, used in weight sensitive structures such as aircraft
fuselages, submarine hulls and space launch vehicles, are essentially subjected to
membrane stresses and are efficient due to the high strength to weight ratio and stiffness
to weight ratio.
1
However, they are vulnerable to instabilities (buckling) when subjected
to static or dynamic compressive stresses.
2
The introduction of faster supersonic
aircrafts, ballistic missiles and launch and re-entry vehicles has necessitated
investigations of dynamic buckling. The growing demand for safety of transport vehicles
has also had a strong impact on the increasing interest in dynamic buckling.
3
A cylindrical shell under compression in the meridional direction can fail by overall
buckling (global/Euler), local buckling or the material strength being reached. Various
failure mechanisms of composite cylindrical shells, as affected by initial geometric
imperfections, boundary conditions, lamina stacking sequence, anisotropic coupling
effects and load eccentricity, were identified by Weaver,
2
in terms of laminate
configurations and shell proportions. The buckling response of the shells is very
sensitive to changes in boundary conditions. A significant discrepancy between theory
and experiment is possible in the case of cylindrical shells unless the boundary and
loading conditions are accurately modeled and the initial geometric imperfections are
precisely taken into consideration in any theoretical model. Unlike shells made of

isotropic materials, composite cylindrical shells could experience failure due to a stronger
coupling between membranes and bending strains. Degradation of the buckling strength