Nonlinear behavior of circular plates with work hardening

Tests were performed on two simply supported plates of aluminum alloy 2024-0, under a central concentrated load, with peak deflections up to 2.6 times the thickness. The load was provided by a small-diameter hard-steel rod. The plates had diameter-to-thickness ratios (D/h) of 20 and 41. Measurements were made of load, deflections and strains; membrane and bending strains were calculated from the test data. The test data are presented in comparison with theoretical predictions generated by the Grumman-developed finiteelement-computer code PLANS, which includes material and geometric nonlinearities. The theoretical prediction was excellent for deflections, and generally good for strains, when the central force was represented by a line load around the loading rod's contact circle. Using a uniform pressure as the central force caused the theory to slightly overpredict the peak deflections and greatly overpredict the peak strains at the plate center. The plates exhibited initial loss of stiffness under the plastic-bending behavior, followed by a restiffening when the large deflections caused a rapidly increasing membrane action that provided much additional resistance to the applied load.