Design, Analysis, and Tests of a Structural Prototype Viking Aeroshell

Abstract

A design procedure and test results for a lightweight, ring-stiffened, 140° conical shell having structural proportions and loadings appropriate for the Viking aeroshell are reported. Objectives were to develop a rational design procedure for establishing the buckling strength of a structurally efficient aeroshell and to demonstrate the reliability of the design procedure by the acquisition of test data from full-scale models. Part I describes the computerized design procedure which iterates between a design program based on approximate equations to determine skin and ring gages and ring spacings, and a sophisticated system of shell-of-revolution programs for more accurate analysis as a basis for redesign. Part II discusses fabrication techniques, test procedures, and test results. Two aeroshells which differed only in base ring stiffness were fabricated and tested. Measured prebuckling strains in skin and rings agreed well with theoretical predictions for both models. Each aeroshell appeared to buckle in the general instability mode at approximately the ultimate design pressure. Appropriate buckling knockdown factors for this type of construction are identified. A r b\ C D d E Nomenclature = cross-sectional area of ring, in. 2 L I. M n R T 19 T 2 T, t I z a r n V°c r (a cr /E r )(l/h) n correlation factor for general instability [see Eq. (Al)] shell flexural rigidity, Ib-in. local value of ring spacing, in. Young's modulus for shell wall material, lb/in. 2 Young's modulus for ring material, lb/in. 2 eccentricity of centroid of ring-shell composite wall from the middle surface of shell skin, in. thickness of interior ring cross section, in. interior ring section moment of inertia about centroid of composite wall, in. 4 interior ring section moment of inertia about ring centroid, in. 4 meridional.length of truncated shell (see Fig. 17), in: characteristic length of ring cross section, in. number of shell segments exponent [see Eq. (A8)] (critical) pressure, lb/in. 2 average circumferential radius of curvature [Eq. (A4)] local radius of shell, in. shell stress resultants in meridional and circumferential directions, respectively, lb/in. (positive in compression) ring hoop force, Ib (positive in compression) shell wall thickness, in. effective thickness [Eq. (A2)], in. eccentricity of ring centroid, in. cone half angle (see Fig. 17), deg hl/td ratio of bending stiffness of composite ring-skin combination . to bending stiffness of skin Poisson's ratio allowable stress for ring local buckling [Eq. (A8)], lb/in. 2