Journal of Aerospace Engineering

Circular bars under distributed torque are formulated based on the linear theory of elasticity, and analysis is presented for bars under a single Fourier term of distributed torque. As the motivation of the study is to examine the extent of adequacy of the conventional technical torsion theory to bars under distributed torques, stress distribution in solid bars is first investigated. Stress distribution for hollow bars under three different loading conditions is then analyzed. Results indicate that the conventional theory is adequate when the region of distributed torque is large. In small regions, the conventional theory may substantially be in error resulting in underestimating the maximum shear stress and misidentifying the location of maximum shearing stress.

Several nonclassical stability problems dealing with simple cantilever columns of practical engineering importance are comprehensively presented. The salient feature of these rather peculiar problems is that column instability with a tubular cross section filled with a liquid or subjected to gas pressure may occur while its cross section remains axially unstressed. Interesting subcases are also discussed where the static stability criterion of existence of two adjacent equilibria fails to predict the actual critical load. This leads to the erroneous conclusion that the undeformed configuration is the only equilibrium position, being stable irrespective of the level of external loading. Hence, the dynamic stability criterion which is of general validity must be employed for establishing the critical load. It has also been clarified that the hydrostatic pressure load, although nonconstant-directional, cannot be identified as nonconservative.

The filament-winding process introduces inherent geometric defects into thin-shell cylinders in the form of fiber-bundle, or tow, crossovers. This research identified the micromechanical geometry in the fiber crossover regions of filament-wound cylinders. A stiffness model was developed for the crossover regions based on a modified classical lamination theory. The local stiffness-coupling values predicted by this model were incorporated into a global finite-element model of thin-shell, filament-wound cylinders. Eigenvalue buckling analyses performed using this enhanced finite-element model are compared to eigenvalue analyses performed without incorporating the influence of the stiffness couplings at the fiber crossover regions. Experiments were carried out in which 16 filament-wound cylinders with four different surface patterns were fabricated and tested. The results showed that the accuracy of a finite-element analysis improved significantly when the stiffness coupling effects due to fiber undulations were properly accounted for in the analytical model.

This paper describes a method for improving the accuracy of buckling predictions of thin-shell, filament-wound cylinders under axial compression loads using enhanced finite-element models. This is accomplished by incorporating the out-of-plane displacements due to residual strains, in addition to realistic stiffness coupling due to fiber undulations, into finite-element models. The out-of-plane displacements of filament-wound cylinders were scanned mechanically and incorporated into the finite-element models using a computer program. An eigenvalue buckling analysis was performed on these models. Results show that the accuracy of the buckling load prediction of the model with stiffness coupling and out-of-plane displacements due to residual strains is significantly improved compared to the case when only the stiffness coupling is incorporated into the model.

On the basis of 3D elasticity, asymptotic solutions for buckling analysis of multilayered anisotropic conical shells under axial compression are presented. By means of proper nondimensionalization, asymptotic expansion, and successive integration, the classical shell theory is derived as a first-order approximation to the 3D theory. Because the governing equations for various orders consist of partial differential equations with variable coefficients, the use of analytical techniques is restricted. The method of differential quadrature is adopted in the present study. The modifications of the buckling loads and associated buckling modes can be determined in a consistent and hierarchic manner by considering the solvability and normalization conditions for various orders. The critical loads of cross-ply conical shells with simply supported–simply supported boundary conditions are studied to demonstrate the performance of the present asymptotic theory.