Experimental Investigation of Creep Buckling of Circular Cylindrical Shells Under Axial Compression and Bending

The results are presented of an experimental investigation of creep buckling of circular cylindrical shells. The test specimens, manufactured from an aluminum alloy similar to 24S, had radius to thickness ratios between 30 and 150 and length to radius ratios greater than 2. They were subjected to axial compression or bending at a temperature of 225 deg C (430 deg F) and at various stress levels. The critical time under a constant load was determined as a function of the stress level, the shell geometry, and the type of loading. It was found that the shells subjected to pure compression had a substantially shorter lifetime than those subjected to pure bending with the same maximum applied stress. The thickest test specimens failed through collapse into a “wrinkling” mode which for the pure compression case is axisymmetric, whereas the thinner cylinders buckled into a typical diamond pattern. In all cases, buckling occurred at one of the edges. The postbuckling configuration was found to depend not only on the geometry of the shell but also on the load level. For very low stress levels, even the thinner cylinders buckled in the short wave pattern (symmetric for compression). A comparison between the present experimental results and theoretical values of the critical time presented in earlier works showed that a fairly good estimate may be obtained for the case of axial compression, whereas the approximate theory for creep buckling under pure bending gives an unduly conservative result.