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Effect of face sheet flexural stiffness on buckling of elastic curved plates and cylindrical shells of sandwich construction in axial compression
Combined compressive and shear buckling analysis was conducted on flat rectangular sandwich panels with the consideration of transverse shear effects of the core. The sandwich panel is fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that the square panel has the highest combined load buckling strength, and that the buckling strength decreases sharply with the increases of both temperature and panel aspect ratio. The effect of layup (fiber orientation) on the buckling strength of the panels was studied in detail. The metal matrix composite sandwich panel was much more efficient than the sandwich panel with nonreinforced face sheets and had the same specific weight.
A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked flat plate and beam elements. Plates are idealized as multilayered orthotropic elements; structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections and stiffened plates is investigated. Buckling loads are found as the lowest of all possible general and local failure modes and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections and stiffened plates including boron-reinforced structures are discussed. In general, correlations are reasonably good.
The longitudinal compression behavior of unidirectional fiber composites is investigated using a modified Celanese test method with thick and thin test specimens. The test data obtained are interpreted using the stress/strain curves from back-to-back strain gages, examination of fracture surfaces by scanning electron microscope, and predictive equations for distinct failure modes including fiber compression failure, Euler buckling, delamination, and flexure. The results show that the longitudinal compression fracture is induced by a combination of delamination, flexure, and fiber tier breaks. No distinct fracture surface characteristics can be associated with unique failure modes. An equation is described which can be used to extract the longitudinal compression strength knowing the longitudinal tensile and flexural strengths of the same composite system.
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A parametric study of the buckling behavior of infinitely long symmetrically laminated anisotropic plates subjected to combined loadings are presented. The loading conditions considered are pure inplane bending, transverse tension and compression, and shear. Results obtained using a special purpose analysis are presented for clamped and simply supported plates. An important finding of the study is that the effects of anisotropy are much more pronounced in shear-loaded plates than in axial compression-loaded plates and plates loaded by pure inplane bending.
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The infinitely long cylindrical shell under axial compression with axisymmetric sinusoidal imperfections is considered. The bifurcation problem is formulated exactly, and a complete family of buckling modes is identified. Koiter's (1963) upper bound pertains to the critical stress associated with one restricted set of modes, and the critical stress for a set of long wavelength modes reproduces some numerical results obtained by Almroth (1966). The initial postbuckling analysis is also formulated exactly. An exact analytical solution is obtained for the limiting case of modes with infinitely long wavelengths, and numerical analysis is used to solve the equations for the other cases. An appendix gives the details of the analysis.
The fundamental equations for the plastic buckling of a rectangular plate under edge thrusts are developed on the basis of a new set of stress-strain relations for the behavior of a metal in the plastic range. These relations are derived for buckling from a state of uniform compression. The fundamental equation for the buckling of a simply compressed plate together with typical boundary conditions is then developed and the results are applied to calculating the buckling loads of a thin strip, a simply supported plate, and a cruciform section. Comparisons with the theories of Timoshenko and Ilyushin are made. Finally, an energy method is given which can be used for finding approximate values of the critical load.
The static post-buckling of simply-supported flat panels exposed to a stationary nonuniform temperature field and subjected to a system of subcritical in-plane compressive edge loads is investigated. The study is performed within a refined theory of composite laminated plates incorporating the effect of transverse shear and the geometric nonlinearities. The influence played by a number of effects, among them transverse shear deformation, initial geometric imperfections, the character of the in-plane boundary conditions and thickness ratio are studied and a series of conclusions are outlined. The influence played by the complete temperature field (i.e., the uniform through thickness and thickness-wise gradient) as compared to the one induced by only the uniform one, is discussed and the peculiarities of the resulting post-buckling behaviors are enlightened.
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Buckling loads of thick-walled orthotropic and anisotropic simply supported circular cylinders are predicted using a higher-order transverse-shear deformation theory. A comparison of buckling loads predicted by the conventional first-order transverse-shear deformation theory and the higher-order theory show that the additional allowance for transverse shear deformation has a negligible effect on the predicted buckling loads of medium-thick metallic isotropic cylinders. However, the higher-order theory predicts buckling loads which are significantly lower than those predicted by the first-order transverse-shear deformation theory for certain short, thick-walled cylinders which have low through-the-thickness shear moduli. A parametric study of the effects of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 45 degree plies are most sensitive to transverse-shear deformation effects. Interaction curves for buckling loads of cylinders subjected to axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are as sensitive to transverse-shear deformation effects as buckling loads due to axial compressive loadings. The effects of anisotropy are important over a much wider range of cylinder geometries than the effects of transverse shear deformation.
This paper evaluates analytically the structural integrity of discretely-loaded, graphite-epoxy, corrugated adapters for the Centaur-in-Shuttle, where combined compression and shear are the critical loads involved. With normal build-ups in the thickness at load introduction boundaries, the structural integrity for both compression and shear buckling was little (or not al all) affected by the discrete load introductions. The analytical tool employed was the STAGSC computer code, and both bifurction buckling and nonlinear collapse options were used; the latter option was limited to shear since postbuckling strength in compression for plate-type structures is governed by crippling strengths, which is not attainable by existing computer codes.
Buckling loads of thick-walled, orthotropic, simply-supported right circular cylinders are predicted using a new higher-order transverse shear deformation theory. The higher-order theory shows that, by more accurately accounting for transverse shear deformation effects, the predicted buckling load may be reduced by as much as 80 percent compared to predictions based on conventional transverse shear deformation theory. A parametric study of the effect of ply orientation on the buckling load of axially compressed cylinders indicates that laminates containing 0 deg plies are the most sensitive to transverse shear deformation effects. Interaction curves for buckling of cylinders with axial compressive and external pressure loadings indicate that buckling loads due to external pressure loadings are much less sensitive to transverse shear deformation effects than those due to axial compressive loadings.