Monitoring of Buckling and Crack Growth in Delaminated Composites Using Fiber Optic Sensor

Buckling of composite cylinders under torsion has been analyzed using the geometrically nonlinear nine-node assumed strain shell element with six DOF per node. Buckling loads are pinpointed by finding the lowest torsion load that makes the determinant of the global tangent stiffness matrix zero in the course of the geometrically nonlinear analysis. Torsional buckling loads calculated from the present method agree well with the linear buckling loads obtained from various shell theories for most composite cylinders. For cylinders with [30/30/-60]s ply orientation, however, large discrepancy between the two buckling loads has been observed. Comparing the numerical test results with experimental data, we conclude that the present method can estimate the torsional buckling loads of composite cylinders with angle plies. The present paper may provide new reference solutions for torsional buckling loads of composite cylinders