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Experimentally observed effects of edge conditions on the buckling behavior of cylindrical shells under axial compression impact are presented. Three effects are discussed, namely, those due to (1) inward radial displacement restraint of the shell wall, (2) asymmetry of the applied loading resulting from obliquity between the impact plate and the end cross section plane of the shell, and (3) impact velocity. It is shown that restraint of an initially free edge against inward radial displacement has two prominent effects: (a) to produce moderate increase in the buckling load, and (b) to force the formation of symmetrical buckling modes local to the restraint even for shells which tend to buckle in the asymmetrical mode. Another result is that although the initial response can be strongly influenced by the edge condition, the subsequent response can be virtually independent of it. Loading asymmetry results in a relatively lower stress response, depending on the degree of asymmetry, and has the effect of circumventing the initial buckling process. Results obtained from impacts at velocities up to 400 ft/sec show that the buckling stresses can be substantially higher at higher velocities. The data suggest, however, that the range of velocity over which this trend occurs may be limited by the particular mechanical, thermal, and geometrical properties of the structure. Also, at sufficiently high velocities, the preferred buckling and collapse mode is symmetrical, even for thin, unpressurized shells. Several experimental novelties are discussed such as a strain gage attachment fixture by means of which back-to-back pairs of strain gages can be accurately and conveniently positioned and fastened to thin shells. A semiautomatic system for mapping the initial geometrical imperfections of shells is also described.
test methods, compression members, buckling, shells (structural members), collapse, impact instability
Coppa, A. P.
Consulting engineer, Space Science Laboratory, Missile and Space Div., General Electric Co., King of Prussia, Pa