Reducing sensitivity to initial imperfections by changing bifurcation diagrams

An approach to the construction of equilibrium state diagrams is presented in order to reduce the sensitivity to initial imperfections for the problem of stability for reinforced plates (transfer of the bifurcation point corresponding to the wave formation of ribs and cladding). New ratios of geometric parameters for two variants of strengthened plates have been obtained, where the first critical load of the general form of stability loss is the first by value, and the next critical load corresponds to the local form of wave formation of ribs or cladding. The finite element complex MSC PATRAN - NASTRAN was used to solve the stated above problems. Flat four-node finite elements were applied for modeling. The calculations were performed with account of geometric nonlinearity. The material was considered to be absolutely elastic. Curves of critical load sensitivity to the amplitudes of the initial imperfections were generated. The results demonstrate that transposition of bifurcation points of wave formation in the plate or ribs enabled to obtain curves with less significant decrease of critical load as compared to the initial ones. Consequently, the presented algorithm for changing the geometric parameters of reinforced plates obtained in accordance with new equilibrium state diagrams implements the possibility of rational design of the specified thin-walled systems.