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Experiments have been conducted to investigate the buckling and postbuckling behavior of aluminum alloy 7050-T7651 integrally stiffened panel under a combined compression-shear load. A new combined-load test fixture was designed and used in these experiments. There were a total of six large rectangular stiffened panels in the size of960 by 850 mm, which were classified in two groups according to the cross section and layout of their stiffeners. Three panels, named J panels, were designed in four parallel J-shaped stiffeners. Another three panels, named X panels, were designed in eight orthogonal blade-shaped stiffeners. Strain rosettes bonded back-to-back on the skin were used to measure the strains of skin at their locations in three directions (0,45, and 90 deg), whereas the strain gauges installed on the stiffeners were used to measure the strains of stiffeners in a single direction. The integrally stiffened panels were loaded up to a sudden drop of the applied load and an accompanying harsh noise caused by the stringers splitting from skins. All the test panels failed in the same modes of global flexural buckling and the spitting of the stiffeners from skins. The mean value of the first buckling loads of X panels is 11.6% higher than that of the J panels. The mean value of the failure loads of X panels is 1.5% less than that of the J panels. All experimental results will be employed for the validation of finite element models and optimization method on the buckling and postbuckling analyses of integrally stiffened aluminum panel in further studies. [ABSTRACT FROM AUTHOR]

The focus of this paper is the application of the recently introduced extended high-order sandwich panel theory to the global buckling of a sandwich beam/wide panel. Three different solution approaches using the extended high-order sandwich panel theory are presented to investigate the effects of simplifying the loading case by applying loads just on the face sheets and by including or excluding nonlinear axial strains in the core. The results are also compared with results from a benchmark elasticity solution and, furthermore, from the simple sandwich buckling formula by the earlier extended high-order sandwich panel theory. It is found that all three theories are close to the elasticity solution for "soft" cores with Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed.. However, for "moderate" cores, i.e., with Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., the theories diverge and the extended high-order sandwich panel theory is the most accurate. [ABSTRACT FROM AUTHOR]

A meshless approach is developed and used to predict buckling loads of discretely assembled composite panels made from skin and stiffeners. Particular emphasis is given to stringer run-outs within a stiffened panel, where abrupt eccentricity can trigger very large transverse displacements of the skin in front of the run-out tip and perturb the internal in-plane loads distribution. The effect of load eccentricity is included in the formulation. The final set of nonlinear equations is obtained by combining von Kármán's formulation for moderately large deflections in plates with an extended Timoshenko approach for small initial perturbations. Solutions are calculated by means of a Rayleigh-Ritz method in conjunction with a Galerkin technique. Orthogonal eigenfunctions are employed to expand the variables of interest in generalized Fourier series. An iterative algorithm is proposed to calculate buckling loads. Limits of applicability, convergence of results, and further potential exploitations are discussed. Numerical results are compared with those from finite element analysis and other numerical approaches. [ABSTRACT FROM AUTHOR]

A truss-lattice panel is modeled under shear loading, up to and beyond the critical buckling load. Nondimensional buckling loads and corresponding buckling mode shapes are obtained for such panels with increasing numbers of diagonally placed internal struts. A method for minimum-mass optimization of the truss lattice is given, based upon simultaneous in-plane and out-of-plane buckling. The finite element method is applied to examine the buckling performance and postbuckling stability. The postbuckling response of the optimized truss lattice is shown to be stable in all cases. The advantages of using the truss-lattice structure are demonstrated by comparing the volume requirements with those of a conventional continuous shear panel, based on the load carried and the buckling capabilities. It is shown that although the continuous shear panel is more efficient for heavy load applications, the truss lattice offers potential weight savings when lighter loads are applied. [ABSTRACT FROM AUTHOR]

The article discusses a study on the use of intuitive approach to examine thermal postbuckling behavior of circular plates. Knowledge of the linear buckling load and the tension developed is said to be required in the intuitive formulations. The functional form of radial displacement was evaluated in the study by using Berger's approximation. Also explained is a proposed methodology to obtain tension value induced in the plate because of large axisymmetric lateral displacements.

Most aerospace structural designs are complex assemblies of a large number of panel components. In designing such a structure, it is customary to divide the structure into many regions and design them independently/semi-independently. A coarse finite element model of the entire structure is first used to determine loads in each component, and subsequently the components are designed using local constraints and performance requirements for these fixed loads. This two-level approach works well if a linear static behavior is considered. For cases in which local components display postbuckling behavior, the internal load distribution in the structure is altered requiring nonlinear global analysis, which is computationally expensive. This paper focuses on developing a computationally efficient approximate methodology for predicting internal load distribution in a structure considering some or all panels to be buckled. In this paper, a semi-analytical approach based on the Rayleigh-Ritz method and the perturbation approach is developed to compute the postbuckled stiffness of buckled panels. An iterative procedure is suggested to predict the internal load distribution with successive buckling during loading. Three different examples are presented. A simply supported flat composite panel subjected to different edge compression is used to verify the perturbation approach used for the calculation of the postbuckled panel stiffness. A two-panel arrangement with different thicknesses subjected to end compression and a 48-panel composite wing structure subjected to bending load are used as cases for structures with buckled panel components. In all cases, the present approach agrees with full nonlinear analysis in predicting the internal load distribution. [ABSTRACT FROM AUTHOR]

The article presents a formulation that aims to obtain the thermal postbuckling behavior of uniform thin circular plates with immovable edges. It states that the literature for circular plates served as the source of values of the corresponding linear buckling loads. It mentions that an equivalent uniform compressive radial edge load is developed in the plate if the circular plate radius is heated to a temperature from the stress free state.

This paper presents a new method for the sensitivity analysis of membrane wrinkling based on the tension-field theory. This method can be applied to design membrane structures to reduce the occurrence of wrinkles. In this method, the wrinkle intensity in a partly wrinkled membrane is evaluated from an apparent strain energy resulting from the deformation through wrinkling. This wrinkle intensity is used as an objective function for wrinkle-reduction membrane design. Further, the sensitivity of the wrinkle intensity with respect to an arbitrary design parameter is derived by employing a semi-analytical differentiation technique and is used to resolve the minimization problem of the objective function. Some design examples show that this minimization problem can be effectively resolved by the proposed sensitivity analysis method and the occurrence of membrane wrinkles can be considerably reduced by minimizing the wrinkle intensity. [ABSTRACT FROM AUTHOR]