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NASA Technical Note
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Vibration Characteristics of Z-ring-stiffened 600 Conical Shell Models of a Planetary Entry Spacecraft
An experimental investigation of the vibration characteristics of a 60 deg conical shell model of a planetary entry vehicle is described and the results presented. Model configurations include the shell with or without one or two Z-ring stiffeners and with or without a simulated payload. Tests were conducted with the model clamped at the small diameter and with the model suspended at the simulated payload. Additionally, calculated results obtained from application of several analytical procedures reported in the literature are presented together with comparisons between experimental and calculated frequencies and meridional mode shapes. Generally, very good frequency agreement between experi...
Analytical and Experimental Studies of Natural Vibration Modes of Ring-stiffened Truncated-cone Shells with Variable Theoretical Ring Fixity
Experimental and analytical investigations of the vibratory behavior of ring-stiffened truncated-cone shells are described. Vibration tests were conducted on (1) 60 [degree] conical shells having up to four ring stiffeners and for free-free and clamped-free edge constraints and (2) 90 [degree] conical shells, for two thicknesses, each with two angle rings and for free-free, free-clamped, and clamped-clamped edge constraints. The analytical method is based on linear thin-shell theory, employing the Rayleigh-Ritz method. Discrete rings are represented as composed of one or more segments, each of which is a short truncated-cone shell of uniform thickness. Equations of constraint are used to join a ring and shell along a circumferential line connection. Excellent agreement was obtained for comparisons of experimental and calculated frequencies.
Influence of Programing Techniques and of Varying Limit Load Factors on Maneuver Load Fatigue Test Results
Variable-amplitude axial-load fatigue tests were conducted on 7075-T6 aluminum-alloy edge-notched specimens having a theoretical elastic stress concentration factor of 4. The load programs were designed to approximate maneuver load spectra. Fatigue life was found to be shorter for random form tests than for block form tests having the same load spectrum. The greatest change in life occurred when the test program contained negative loads. Life for variable-amplitude tests was found to increase as much as 60 percent above the original test life after preloading with a program having a higher limit load factor. The summations of cycle ratios were approximately 2 for tests without negative loads but were approximately 1 for tests with negative loads.
