Keywords: combined stability, shear load, external pressure, concentric cylinders, elliptic cylinders.

The paper provides details about tests on elastic buckling of circular cylindrical shells due to external pressure, horizontal edge force and combined action of both. The latter pattern of loading was chosen in order to obtain envelopes of combined stability domains. Additional tests were carried out on buckling of concentric cylindrical shells subjected to horizontal edge force. Final set of experiments treats buckling of elliptic cylinders, again under the horizontal edge force and external pressure. In total, test results on nineteen shells are given.

The experimental data is benchmarked against the finite element (FE) predictions. Good agreement has been obtained between experimental results and numerical predictions for all tested shells except for buckling of concentric cylinders by horizontal edge force. Possible reasons for discrepancies are discussed and suggestions for modifications of test arrangements are given.

For circular cylinders, experimental results on buckling shear force, and on buckling pressure, compare well with the FE predictions. In the experiment, it was found that under edge shear force, buckling occurs gradually in the form of appearance of wrinkles on cylinder. However, under external pressure cylinder buckles suddenly. Numerical results on buckling of concentric cylinders under edge shear force indicate that critical shear displacement plays an important role in deciding the buckling pattern. For optimal design, the inner and outer cylinder should have the same critical shear displacement. Experimental results on the buckling of concentric cylinders under edge shear force do not compare as well with the FE predictions, as experimental results for all other shell configurations. It is felt that this was due to difficulties in making specimens of concentric cylinders. While fixing the top flange, some pre-stressing was induced into the inner cylinder and this probably made it weaker under edge shear and hence experimental results were on a lower side.

Experimental results on elliptic cylinders under edge shear force show favourable comparison with the FE calculations. During these experiments position of vertical joint in the Mylar cylinders was found to have an influence on the buckling force. To minimise this influence, joints should be positioned below the point of application of force. Like in circular cylinders, here too buckling occurs gradually. For elliptic cylinders under external pressure, experimental results compare well with those of the FE. Under external pressure, buckling occurs suddenly and there was no difficulty in identifying the buckling pressure. In previous studies on elliptic cylinders under external pressure (Yao and Jenkins [1], Bushnell [2], and Marlowe and Brogan [3]) failure occurred due to collapse. But these cylinders were comparatively thick ones. Some further calculations showed that indeed thin cylinders failed by bifurcation buckling and thick ones failed by collapse with transition occurring between b/t = 150 and 100 (where b = semi-axis, t = wall thickness).

1

J.C. Yao, W.C. Jenkins, "Buckling of elliptic cylinders under normal pressure", AIAA J., 8(1), 22-27, 1970. doi:10.2514/3.5600

2

D. Bushnell, "Stress, buckling and vibration of prismatic shells", AIAA J., 9(10), 2004-2013, 1971. doi:10.2514/3.50008

3

M.B. Marlowe, F.A. Brogan, "Collapse of elliptic cylinders under uniform external pressure", AIAA J., 9(11), 2264-2266, 1971. doi:10.2514/3.50030

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