A finite element program is developed for the nonlinear structural analysis of the laminated composite shell structure. The formulation is based on updated Lagrangian description with the Green-Lagrangian strain and the second Piola-Kirchhoff stress. The eight-node degenerated shell element is utilized for the finite element modeling of the laminated shell structure.
The buckling behavior of $[0/±θ/90]_s$ laminated cylindrical composite panels under axial compression is investigated by a parametric study on fiber angles and panel widths. The shape of the buckled panel and the buckling mode are influenced by the change of fiber angles. When the fiber angle is not 0 or 90 degrees, panels are deformed into the twisted shape due to the bending-twisting coupling even for symmetric laminates. The fiber angle for the maximum buckling stress of the laminated cylindrical panel depends upon the panel width.
The transverse displacement parameter is defined to estimate the degree or the magnitude of the initial imperfection on the finite element model. Geometrical imperfections which have buckling mode shapes of perfect panels are imposed on finite element models to investigate the imperfection sensitivity of the buckling load.
Cylindrical composite panels exhibited the great imperfection sensitivity of the buckling load. Buckling loads of imperfect panels are reduced to 60%-80% of those of perfect panels due to the initial imperfection of the magnitude of 10% of the wall thickness. The choice of the shape of the initial imperfection is found to be very important for the conservative estimation of the buckling load of the imperfect composite shell structure.
