The general solution for the stress problem of circular cylindrical shells with an arbitrary cutout

I.IntroductionIncircularcylindricaIsheIls.likeaircraftfuselages,deep-diving\-ehicles.pressurevesselsandoiIlines,openingsareinvariabl}'necessaryforavarietyoffunctionalrequirements.Stressconcentrationsonthecontourofcircularornon-circu1arcutoutsreducebearing…     

On reductions of the differential equations for circular cylindrical shells

Summary The paper begins with a statement of the differential equations of equilibrium and compatibility for circular cylindrical shells in the form first given in a pioneering work by Schaefer, and with constitutive equations incorporating transverse shear deformations and moment components normal to the shell surface as stated earlier by the present author. It is then shown that this system of equations may be reduced, for a rather general class of orthotropic shells, to four simultaneous third-order equations for two stress functions and two displacement variables. Subsequent to this it is shown that for the case that transverse shear deformations and shell surface normal moment components are absent the four simultaneous equations degenerate in such a manner that a further reduction to two simultaneous fourth order equations, for one stress function and one displacement variable, becomes possible. For the case of the isotropic shell these are equivalent to results by Morley, Simmonds, and Wan which were obtained by somewhat different reduction procedures.

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Übersicht Es werden die Differentialgleichungen für Gleichgewicht und Verträglichkeit von kreiszylindrischen Schalen in der von Schaefer angegebenen Form besprochen, zusammen mit den vom Verfasser früher bereits aufgestellten Stoffgleichungen, bei denen Querschubdeformationen sowie Momentenkomponenten normal zur Schalenoberfläche berücksichtigt sind. Dieses System von Gleichungen kann für eine ziemlich allgemeine Klasse von orthotropen Schalen auf ein System von vier Gleichungen dritter Ordnung für zwei Spannungsfunktionen und zwei Verschiebungsvariable zurückgeführt werden. Bei Abwesenheit von Querschubdeformationen und von Momentenkomponenten normal zur Schalenoberfläche ist eine weitere Reduktion auf ein System von zwei Gleichungen vierter Ordnung für eine Spannungsfunktion und eine Verschiebungsvariable möglich. Für isotrope Schalen sind diese Gleichungen äquivalent zu den auf anderem Wege abgeleiteten Ergebnissen von Morley, Simmonds und Wan.

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Dedicated to Professor Dr. U. Wegner on the occasion of his 70th birthday.

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Supported by the Office of Naval Research and by the National Science Foundation, Washington, D.C.     

Buckling behavior of compression-loaded composite cylindrical shells with reinforced cutouts

Results from a numerical study of the response of thin-walled compression-loaded quasi-isotropic laminated composite cylindrical shells with unreinforced and reinforced square cutouts are presented. The effects of cutout reinforcement orthotropy, size, and thickness on the non-linear response of the shells are described. A high-fidelity non-linear analysis procedure has been used to predict the non-linear response of the shells. The analysis procedure includes a non-linear static analysis that predicts stable response characteristics of the shells and a non-linear transient analysis that predicts unstable dynamic buckling response characteristics. The results illustrate the complex non-linear response of a compression-loaded shell with an unreinforced cutout. In particular, a local buckling response occurs in the shell near the cutout and is caused by a complex non-linear coupling between local shell-wall deformations and in-plane destabilizing compression stresses near the cutout. In general, reinforcement around a cutout in a compression-loaded shell can retard or eliminate the local buckling response near the cutout and increase the buckling load of the shell. However, results are presented that show how certain reinforcement configurations can cause an unexpected increase in the magnitude of local deformations and stresses in the shell and cause a reduction in the buckling load. Specific cases are presented that suggest that the orthotropy, thickness, and size of a cutout reinforcement in a shell can be tailored to achieve improved buckling response characteristics.     

Non-linear oscillation of circular cylindrical shells

The method of multiple scales is used to analyze the non-linear forced response of circular cylindrical shells in the presence of a two-to-one internal (autoparametric) resonance to a harmonic excitation having the frequency Ω. If ω_r and a_r denote the frequency and amplitude of a flexural mode and ω_b and a_b denote the frequency and amplitude of the breathing mode, the steady-state response exhibits a saturation phenomenon when ω_b ≈ 2ω_r, if the excitation frequency Ω is near ω_b. As the amplitude ƒ of the excitation increases from zero, a_b increases linearly whereas a_r remains zero until a threshold is reached. This threshold is a function of the damping coefficients and ω_b−2ω_r. Beyond this threshold a_b remains constant (i.e. the breathing mode saturates) and the extra energy spills over into the flexural mode. In other words, although the breathing mode is directly excited by the load, it absorbs a small amount of the input energy (responds with a small amplitude) and passes the rest of the input energy into the flexural mode (responds with a large amplitude). For small damping coefficients and depending on the detunings of the internal resonance and the excitation, the response exhibits a Hopf bifurcation and consequently there are no steadystate periodic responses. Instead, the responses are amplitude- and phase-modulated motions. When Ω ≈ ω_r, there is no saturation phenomenon and at close to perfect resonance, the response exhibits a Hopf bifurcation, leading again to amplitude- and phase-modulated or chaotic motions.     

Fracture of cylindrical shells with cracks in tension

In practice, cracks may frequently be introduced in structural components during the course of the technological manufacturing and service. Studies concerning the strength prediction of structures with cracks are therefore of considerable importance. During the fracture process of thin-walled structure elements, material local to the crack may buckle. The fracture characteristics may be affected considerably. Both theoretical and experimental studies of this problem were made for plates [1]. In this work, experimental results are presented for the deformation and fracture of cylindrical shells with cracks.     

Buckling behaviour of elliptical cylindrical shells and tubes under compression

This paper presents several issues that characterize the buckling behaviour of elliptical cylindrical shells and tubes under compression. First, a formulation of Generalised Beam Theory (GBT) developed to analyse the elastic buckling behaviour of non-circular hollow section (NCHS) members is presented. Since the radius varies along the cross-section mid-line, the main concepts involved in the determination of the deformation modes are adapted to account for the specific aspects related to elliptical cross-section geometry. After that, two independent sets of fully orthogonal deformation modes are determined: (i) local-shell modes satisfying the null membrane shear strain but exhibiting transverse extension and (ii) shell-type modes satisfying both assumptions of null membrane shear strain and null transverse extension. In order to illustrate the application, capabilities and versatility of the formulation, the local and global buckling behaviour of elliptical hollow section (EHS) members subjected to compression is analysed. In particular, in-depth studies concerning the influence of member length on the variation of the critical load and corresponding buckling mode shape are presented. Moreover, the GBT results are compared with estimates obtained by means of shell finite element analyses and are thoroughly discussed. The results show that short to intermediate length cylinders buckle mostly in local-shell modes, exhibiting only transverse extension, while intermediate length to long cylinders buckle mostly in shell-type modes (distortional and global modes), which are characterized by transverse bending and primary warping displacements. It is also shown that the present formulation is very efficient from the computational point of view since only three deformation modes (one local-shell, one distortional and one global) are required to evaluate the buckling behaviour of EHS cylinders for a wide range of lengths.     

Stresses around elliptic holes in circular cylindrical shells

The stress state around an elliptic hole in a circular cylindrical shell under axial loads is measured. The test cylinders which are made of aluminum are loaded both in tension and compression. Stress-concentration factors around the hole for different eccentricities of the ellipse and different curvature parameters are evaluated. Stress-concentration factors away from the edge of the hole are also determined. The results obtained are compared with theoretical results available in the literature. The effect of bending on the stress concentration as related to the eccentricity of the elliptic hole and to the curvature parameters of the shell is discussed. The results from tension test and those from compression test are also compared, and the sensitivity of the shell to any imperfection and possible local buckling at the hole in the case of compression test are demonstrated.     

On the analyses of vibration and stability for orthotropic circular cylindrical shells conveying fluid

Based on flügge's thin orthotropic shell equations and a linear potential flow theory, buckling instability and flutter-type instability of orthotropic circular cylindrical shells conveying fluid are studied. By means of the expansion in beam-mode functions and Galerkin's method they can be reduced to solving a generalized complex eigenvalue problem. In calculating the generalized forces defined as Eq. (23), a direct numerical integration technique, which has proven to be more efficient than others, is used. For clamped-clamped orthotropic shells several numerical examples show that the effects of axial elastic modulus on the dynamic behaviors are quite different from those of circumferential elastic modulus.     

Nonobvious features of dynamics of circular cylindrical shells

In the framework of the nonlinear theory of flexible shallow shells, we study free bending vibrations of a thin-walled circular cylindrical shell hinged at the end faces. The finite-dimensional shell model assumes that the excitation of large-amplitude bending vibrations inevitably results in the appearance of radial vibrations of the shell. The modal equations are obtained by the Bubnov-Galerkin method. The periodic solutions are found by the Krylov-Bogolyubov method. We show that if the tangential boundary conditions are satisfied “in the mean,” then, for a shell of finite length, significant errors arise in determining its nonlinear dynamic characteristics. We prove that small initial irregularities split the bending frequency spectrum, the basic frequency being smaller than in the case of an ideal shell.     

On the stress concentration in thick cylindrical shells with an arbitrary cutout

1.IntroductionThefocusofmuch'researcllforalongtimehasbeenontheinvestigationofstressconcentrationsofthincylindricalshellsll--41.Thestressproblemisdiscussedinreferences[5,6].Whentheratioofthicknesshofshellstothecutoutsizeroisnotrathersmall,thegoverningequationofReissuer'sshallowshellincludingtheeffectoftransversesheardeformationsmustbeusedl7-sl.Thethickshelltheorymakesupweaknessesoftheclassicaltheoryofthinshells.Thetheoryofthickshellscanbeusedforanalyzingstressconcentrationsofcircularcylindrica…     

Postbuckling behavior of circular cylindrical shells under torsion

Summary Applying the Galerkin procedure to the Donnell basic equations, fairly accurate solutions are obtained for the postbuckling behavior of clamped circular cylindrical shells subjected to torsion. Through detailed calculations, main postbuckling characteristics, i.e., connections of the angle of twist, axial shortening and deflection with applied torque, are clarified for a wide range of shell geometrics. The results here obtained are ascertained to be in good agreement with the corresponding experimental results.

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Übersicht Durch Anwendung des Verfahrens von Galerkin auf die Donnellschen Grundgleichungen werden praktisch genaue Lösungen für das Nachbeulverhalten von eingespannten Kreiszylinderschalen gewonnen, die einer Torsion unterworfen sind. Über detaillierte Rechnungen für einen weiten Bereich von Schalengeometrien wird geklärt, wie Verdrehung, Stauchung und Nachbeulverformung mit dem gegebenen Torsionsmoment zusammenhängen. Die Ergebnisse stimmen mit experimentell ermittelten Werten gut überein.

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The authors wish to express their thanks to Mr. T. Watanabe at the Sumitomo Heavy Machinery, Ltd., and Mr. T. Sato at the Institute, for their help in computations and drawings.     

Postbuckling behavior of circular cylindrical shells under compression

Applying the Galerkin procedure to the Donnell basic equations, reasonably accurate solutions are obtained for the postbuckling behavior of clamped circular cylindrical shells under axial compression. To make a distinct comparison with the previous experimental results, calculations are carried out for shells with the same elastic and geometric parameters and the relations between the waveform, axial shortening and maximum deflections with applied loads are clarified. The results here obtained are found to be in reasonable agreement with experimental ones throughout the regions with fairly large deformations.     

Solution of the problem of the stress state of noncircular cylindrical shells of variable thickness

A procedure is proposed for solving two-dimensional boundary-value problems on the stress-strain state of open and closed noncircular cylindrical shells of variable thickness under surface loads. The solution is based on the use of the spline-collocation method along the directrix and the method of discrete othogonalization along the generatrix. Examples of solutions for ellipsoidal shells of variable thickness are given. Translated from Prikladnaya Mekhanika, Vol. 34, No. 12, pp. 26–33, December, 1998.