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This is Fig. 28 from the 1995 p2stags paper. This slide shows the STAGS model of the deformed panel at load steps (a) 7, (b) 19, (c) 29, (d) 44.
PA is the load factor (PA = 1.0 is the design load factor), and
W(max) is the maximum normal deflection in inches.
The “pillowing” between stringers is caused by the normal pressure. The presence of the initial buckling modal imperfection shown in the previous figure gives rise to the axial non-uniformity of the “pillowing” in (a).
Note that the load factor, PA, does not increase monotonically (see the next slide) and that the post-locally-buckled deformation pattern develops an additional axial half-wave from states (b) to (c) to (d).
In a load-controlled test this panel would experience a “mode jump” from state (c) at load factor, PA = 0.177 to state (d) at PA = 0.167.
(from Computers & Structures, Vol. 55, No. 5, pp. 819 – 856, 1995)
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