Thermomechanical postbuckling of composite laminated cylindrical shells with local geometric imperfections

The effect of local geometric imperfections on the buckling and postbuckling of composite laminated cylindrical shells subjected to combined axial compression and uniform temperature loading was investigated. The two cases of compressive postbuckling of initially heated shells and of thermal postbuckling of initially compressed shells are considered. The formulations are based on a boundary layer theory of shell buckling, which includes the effects of the nonlinear prebuckling deformation, the nonlinear large deflection in the postbuckling range and the initial geometric imperfection of the shell. The analysis uses a singular perturbation technique to determine buckling loads and postbuckling equilibrium paths. Numerical examples are presented that relate to the performances of cross-ply laminated cylindrical shells with or without initial local imperfections, from which results for isotropic cylindrical shells follow as a limiting case. Typical results are presented in dimensionless graphical form for different parameters and loading conditions.     

Multiple geometric defects: Their effect on stability of cylindrical shells

Thin isotropic circular cylindrical shells of near perfect quality were tested in axial compression with multiple local geometric defects imposed on them. The defects were in the form of diamond-shaped Yoshimura-facet-type dimples, with large amplitudes, of the same order of magnitude as that of the facets in a cylinder buckled in axial compression. This investigation was performed in continuation of a previous study on the effect of single local defects on the stability of axially loaded cylinders. Apart from establishing the changes in load-carrying capacity with increasing number of defects, the present set of experiments reveals certain behavioral aspects of the defects, providing insight into how they affect the overall shell stiffness and its stability. Based on the test results, an empirical formula relating the reduction in buckling load to the number and size of the local defects is developed.     

Buckling analysis of cylindrical shells with random geometric imperfections

In this paper the effect of random geometric imperfections on the limit loads of isotropic, thin-walled, cylindrical shells under deterministic axial compression is presented. Therefore, a concept for the numerical prediction of the large scatter in the limit load observed in experiments using direct Monte Carlo simulation technique in context with the Finite Element method is introduced. Geometric imperfections are modeled as a two dimensional, Gaussian stochastic process with prescribed second moment characteristics based on a data bank of measured imperfections. (The initial imperfection data bank at the Delft University of Technology, Part 1. Technical Report LR-290, Department of Aerospace Engineering, Delft University of Technology). In order to generate realizations of geometric imperfections, the estimated covariance kernel is decomposed into an orthogonal series in terms of eigenfunctions with corresponding uncorrelated Gaussian random variables, known as the Karhunen-Loéve expansion. For the determination of the limit load a geometrically non-linear static analysis is carried out using the general purpose code STAGS (STructural Analysis of General Shells, user manual, LMSC P032594, version 3.0, Lockheed Martin Missiles and Space Co., Inc., Palo Alto, CA, USA). As a result of the direct Monte Carlo simulation, second moment characteristics of the limit load are presented. The numerically predicted statistics of the limit load coincide reasonably well with the actual observations, particularly in view of the limited data available, which is reflected in the statistical estimators.     

Axial compression buckling of conical and cylindrical shells

Experiments on the axial compression buckling of high-quality epoxy cylindrical shells with imposed dimpletype defects are described. Additionally, a technique for the manufacture of high-quality epoxy conical shells which buckle at loads approaching the classical critical load is presented. For both types of shells, prebuckling deformations have been monitored optically. The sizes of defects determined from the optical examination when applied in the space-frame approach to shell buckling have led to predicted knock-down factors which are remarkably consistent with measured knock-down factors (i.e., the ratio of actual collapse to classical critical load).     

Dynamic carrying capacity of elasto-visco-plastic cylindrical shells

Summary We consider axially-compressed thin cylindrical shells, which deform elasto-visco-plastically under high intensity external impulsive loading and in which volume damage can occur. The shell carrying capacity is determined in accordance with deformation, stability and strength criteria. Our purpose is introducing special dimensionless parameters, to obtain the relation between the geometrical sizes and the material characteristics of the shell-on one hand and the dynamic impulse parameters (amplitude and duration) on the other, when the shells lose their carrying capacity.

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Dynamische Tragfähigkeiten von elasto-visko-plastischen zylindrischen Schalen

Übersicht Untersucht werden dünne zylindrische Schalen unter Einwirkung eines dynamischen axialen Druckes. Die Schalen weisen elastische und visko-plastische Verformungen sowie Schädigung auf. Die Tragfähigkeit wird durch die Verformung, die Festigkeit und die Stabilität bestimmt. Unser Ziel ist es, durch Einführung von speziellen dimensionslosen Parametern die Abhängigkeit zwischen den geometrischen Abmessungen und den Materialcharakteristiken einerseits und den Beanspruchungsparametern der dynamischen Belastung (Amplitude und Dauer der Pulsbelastung) andererseits beim Versagen der Schalen festzustellen.

     

Load-carrying capacity of thin-walled shells with local imperfections

The load-carrying capacity of axially compressed thin-walled shells of revolution with a circular cut is studied. The problem is solved by using the numerical version of an experimental-theoretical method. The numerical experiment is performed by using the finite-element software ANSYS/LS-DYNA 11.0. The size effect of a circular cut on the load-carrying capacity of a compressed cylindrical shell is investigated.     

Free vibrations of ribbed cylindrical shells with local axisymmetric deflections

The paper proposes a method to calculate the natural frequencies of ribbed cylindrical shells with local axisymmetric deflections. The influence of initial imperfections of two types on the minimum frequencies of vibration is analyzed Translated from Prikladnaya Mekhanika, Vol. 44, No. 9, pp. 63–72, September 2008.     

Dynamical response of hyper-elastic cylindrical shells under periodic load

Dynamical responses, such as motion and destruction of hyper-elastic cylindrical shells subject to periodic or suddenly applied constant load on the inner surface, are studied within a framework of finite elasto-dynamics. By numerical computation and dynamic qualitative analysis of the nonlinear differential equation, it is shown that there exists a certain critical value for the internal load describing motion of the inner surface of the shell. Motion of the shell is nonlinear periodic or quasi-periodic oscillation when the average load of the periodic load or the constant load is less than its critical value. However, the shell will be destroyed when the load exceeds the critical value. Solution to the static equilibrium problem is a fixed point for the dynamical response of the corresponding system under a suddenly applied constant load. The property of fixed point is related to the property of the dynamical solution and motion of the shell. The effects of thickness and load parameters on the critical value and oscillation of the shell are discussed.     

The dynamic responses of cylindrical shells including geometric and material nonlinearities

The methods of finite-element analysis are applied to the problem of large deflection elastic-plastic dynamic responses of cylindrical shells to transient loading. Assumeddisplacement quadrilateral finite-elements of a cylindrical panel are used to idealize the cylindrical shell structure. The formulation is based upon the Principle of Virtual Work and D'Alembert's Principle. A direct numerical integration procedure is employed to solve the resulting equations of motion timewise. The present predicted dynamic responses of an explosively-loaded clamped cylindrical panel are compared with other independent predictions and with experimentally measured responses; very good agreement is observed.     

Stress-strain analysis of elliptic cylindrical shells under local loads

The stress-strain state of elliptic cylindrical shells under local loads is analyzed.Translated from Prikladnaya Mekhanika, Vol. 40, No. 10, pp. 113–121, October 2004.     

On the timoshenko buckling load of thin walled cylindrical shells

Summary A technique is presented for simulating simply supported boundary conditions in axial cylinder buckling experiments. An internal mandrel is employed. The geometric and material constants of the mandrel can be carefully selected allowing it to expand, through a Poisson effect, at the same rate as the shell. The mandrel provides an expansion mechanism for the edges of the shell which allows the shell's generators to remain straight until buckling occurs. In addition, the mandrel can also be used to limit buckle deformations to the elastic region.