24 Stability Analysis of Curved Panels 263 Fig. 24.5 Orthogrid and constant thickness panel geometry and material properties Fig. 24.6 Loading sequence for the orthogrid and constant thickness panel 0 2 4 6 8 10 -20 -15 -10 -5 0 5 10 15 20 Displacement [mm] a b Point load [N] Primary path (stable) Primary path (unstable) Secondary path C Secondary path B Secondary path L 0 2 4 6 8 10 -20 -15 -10 -5 0 5 10 15 20 Displacement [mm] Point load [N] Primary path (stable) Primary path (unstable) Secondary path L Fig. 24.7 Equilibrium paths for constant thickness panel and orthogrid panel that were buckled to a rise of 3.5 mm. (a) Constant thickness panel; (b) Orthogrid panel that the degree of instability for the constant thickness panel is higher than for the orthogrid. Also, the value at which the loss of stability occurs is lower for the constant thickness panel. The loss of stability occurs at a bifurcation point for the constant thickness panel and at a limit point for the orthogrid panel. For the orthogrid panel, the loss of stability will eventually move from a limit point to a bifurcation point, but this happens at higher rises than for the constant thickness panel. Figure 24.8 shows with solid line the load values at which loss of stability occurs for the constant thickness panel, and with dashed line the load values for the orthogrid panel. The figure also illustrates the rise at which the loss of stability switches from a load corresponding to a limit point to a load corresponding to a bifurcation point. This switch takes place at lower rises for the constant thickness panel. Although at lower rises both the orthogrid and the constant thickness panels have similar critical force values, as the rise increases the load at which loss of stability happens increases significantly faster for the orthogrid panel.
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