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The problem of creep induced instability in structures is discussed. A linearization procedure proposed by Onat and Wang (Creep in Structures, Springer-Verlag, 1962, p. 125) and generalized by Carlson (Recent Progress in Applied Mechanics - The Folke Odgvist Volume, Almqvist and Wiksell, Gebers, Stockholm, 1966) is applied to the problem of the creep buckling of circular cylindrical shells under uniform, axial compression. Solutions for axisymmetric creep buckling of semi-infinite and infinite cylinders are obtained and a comparison with experimental data is made. In accordance with expectations based on the criterion for instability, the theoretically predicted critical times are smaller than the experimentally observed critical times.
Experimental results obtained with 31 nickel circular cylindrical shell specimens are evaluated in the light of the theory. The test results have already been reported in SUDAAR No. 415. The experimental creep buckling times obtained in axial compression at a temperature of 650F were found to be in reasonable agreement with the theoretical formulas. (Author).
The use of electroforming to produce circular cylindrical shells is described. Examples are cited for which the use of electroforming provides opportunities for the development of unique specimen designs and test procedures. The use of a tapered creep specimen to generate isochronous stress-strain curves is described. The procedure developed provides a method for deriving basic creep relationships form data obtained from a small number of tests. The results of creep buckling tests on circular cylindrical shells under axial compression are presented. The basic features described are the end-shortening history, the variation of buckling load with time, and the post-buckling pattern which is developed. (Author).
The purpose of the investigation described in this paper is the study of the effect of very small nonaxisymmetric initial deviations from the exact shape upon the deformations and the critical time of a thin-walled circular cylindrical shell which was manufactured with larger initial deviations of an axisymmetric type. The calculations are carried out in a manner similar to that of a recent paper by the senior author. It is assumed that all the deformations are due to nonlinear steady creep governed by Odqvist's law. In consequence of the nonlinearity of the constitutive equation and the use of three terms in the expressions for the deformations and the stresses the trigonometric calculations become so complicated that they must be carried out by means of the high-speed digital computer. For this purpose use is made of the 'REDUCE' program. It is found that in a particular case the critical time of the shell is reduced to about one-half the original value when one adds to the small axially symmetric component of the initial deviations a nonaxisymmetric component which is ten orders of magnitude smaller. The reduction in critical time is represented by a factor of about 1/15 when the amplitudes of the axisymmetric and nonaxisymmetric initial deviations are equal. (Author).