The stability characteristics of laminated composite panels with cutouts.
Herein is contained details of a comprehensive finite element survey and experimental
investigation into the buckling and postbuckling characteristics of thin laminated square
Carbon-Epoxy panels with various cutout geometries, subjected to uniaxial compression.
The plate edges are considered to be fully fixed with constant edge displacement loading.
The panels were quasi isotropic in nature with a stacking sequence of (0/90/±45)2,.
Square, circular and elliptical centrally located cutouts were considered with cutout
dimension/panel widths ranging from 0.1 to 0.7 in increments of 0.1.
Eccentrically located circular and square cutouts were considered for cutout
dimension/panel width ratios ranging from 0.1 to 0.4 with vertical and horizontal
eccentricity varying from 0 to 20% of the panels width.
Multiple circular cutouts with cutout dimension/panel width ranging from 0 to 0.3 with
separation distance/panel width ratios ranging from 0.2 to 0.65.
A finite element eigenvalue analysis was adopted to determine the critical buckling loads
and buckle mode shapes for the panels. The postbuckling response of the panels were
investigated by adopting a non-linear finite element analysis approach using an
Incremental Newton-Raphson Iterative solution scheme.
A limited experimental test programme was undertaken to act as verification to the finite
element solutions. A purpose built buckling rig was designed and manufactured for the
purposes of the tests.
It has been confirmed that the critical buckling loads for centrally located circular and
square cutouts initially reduces as the cutout size increases. After reaching a minimum
value it thereafter increases with large cutout sizes, the exact changeover point being
dependant upon the shape of the cutout. The orientation of ellipse major axis significantly
affects the critical buckling load of a panel. A horizontally aligned ellipse exhibits similar
behaviour as that to a circular or square cutout. However when the major axis is rotated
relative to the horizontal axis its buckling capacity reduces monotonically till it has a
buckling load less than that for an unperforated panel when vertical aligned.
It has been shown when a circular cutout is eccentrically placed in a panel, for small
cutout sizes the buckling load reduces with horizontal eccentricity while a small increase
is experienced for vertical eccentricity.
Multiple circular cutouts significantly reduce the buckling capacity of the panel for all
cutout sizes and separation distances.
Initial geometric imperfection in the panel does not affect the critical buckling load
significantly. The postbuckled response of such panels are also insensitive to the
magnitude of imperfection.
Panels with circular, square and elliptical cutouts exhibit substantial postbuckled
strength. The post buckling response of such panels are insensitive to cutout geometry