Buckling of composite panels subjected to biaxial loading

Buckling loads and modes of flat composite laminates were measured and compared with theory. Laminates were subjected to simply supported boundary conditions and biaxial loading. Displacements were measured both mechanically using dial gages and optically using shadow moiré. Predictions were obtained numerically using the Galerkin method. Buckling loads were measured during 49 tests. Overall, measurements confirmed expected trends. Buckling loads increased with an increase in transverse tensile loading as predicted. Measured buckling modes were also well predicted, including an observed increase in mode number with an increase in transverse tensile loading. Measured buckling loads were not as well predicted, and substantial error was encountered during individual tests. Discrepancies between measurement and prediction are reported in terms of the percentage error in prediction. The average and standard deviation in percentage error for 49 measurements was 1.6 percent ±15.4 percent. These discrepancies are thought to be due to specimen imperfections, difficulties in simulating truly “simply supported” boundary conditions and/or nonuniform loading of the composite panels.