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IssuesArchive of Issues2005-6pp.81-94

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V. A. Ivanov, V. N. Paimushin, and V. I. Shalashilin, "Linearized neutral equilibrium equations for nonthin sandwich shells with transversely soft filler and related problems of nonlinear elasticity," Mech. Solids. 40 (6), 81-94 (2005)
Year 2005 Volume 40 Number 6 Pages 81-94
Title Linearized neutral equilibrium equations for nonthin sandwich shells with transversely soft filler and related problems of nonlinear elasticity
Author(s) V. A. Ivanov (Kazan)
V. N. Paimushin (Kazan)
V. I. Shalashilin (Moscow)
Abstract For sandwich shells with nonthin transversely soft filler, we construct refined linearized stability equations, which are intended for describing buckling modes with both zero (purely shear modes) and large (mixed bending modes) variability of parameters of the perturbed stress-strain state in the tangential directions. These equations comprise six neutral equilibrium equations for the outer layers (which are constructed on the basis of the geometrically nonlinear equations in Kirchhoff-Love theory of moderate bending of thin shells and allow for the force interaction with the filler on the interface) and equations describing the stress-strain state of the transversely soft filler in the perturbed state. The latter equations are obtained by integration, with respect to the transverse coordinate, of the linearized elasticity equations describing the neutral equilibrium of the transversely soft filler in the perturbed state and subject to the kinematic matching conditions with the outer layers. If in the original unperturbed state we accept the assumption of finiteness of the in-plane shear strain and retain the terms nonlinear in all three displacement components in the expression for the transverse compression strain, then the constructed relations prove to be integro-differential equations for two two-dimensional functions characterizing the transverse tangential stresses in the undeformed axes and two three-dimensional filler displacement functions (the complete model). The relations of this model are simplified and reduced to the above-mentioned two two-dimensional differential equations for the characteristics of transverse tangential stresses if we introduce the assumption of small variation of the filler deflection along the thickness in the original state (the simplified model). The equations of the partially simplified model, intermediate between the equations of the complete and simplified filler models, have the same structure and complexity. We show that the equations of the complete model, as well as those of the partially simplified model, are inadequate, since so are the underlying well-known geometrically nonlinear kinematic elasticity relations, which are recommended for using at small extension strains in the scientific literature. The latter become adequate if one omits the terms nonlinear in the displacement components in whose direction the extension strains are to be determined. In view of the preceding, only the simplified model is adequate for sandwich shells. All these conclusions are based on the results obtained by solving the problem on all possible buckling modes of a sandwich ring subjected to external (or internal) pressure and also the elementary problem on the longitudinal extension-compression of a rod with rectilinear axis in the exact and approximate settings for the cases of arbitrary and small strains.
References
1.  V. N. Paimushin, "Theory of stability for three-layer plates and shells: stages of development, state-of-the-art, and prospects," Izv. RAN. MTT [Mechanics of Solids], No. 2, pp. 148-162, 2001.
2.  V. A. Ivanov, V. N. Paimushin, and V. I. Shalashilin, "Refined geometrically nonlinear theory and buckling modes of sandwich shells with transversely-soft core," Izv. RAN. MTT [Mechanics of Solids], No. 3, pp. 167-177, 2005.
3.  V. A. Ivanov and V. N. Paimushin, "Refined stability theory of sandwich structures (the nonlinear equations of subcritical equilibrium of shells with transversely soft filler)," Izv. Vuzov. Matem., No. 11, pp. 29-42, 1994.
4.  V. A. Ivanov, V. N. Paimushin, and T. V. Polyakova, "Refined stability theory of sandwich structures (the linearized equations of neutral equilibrium and elementary one-dimensional problems)," Izv. Vuzov. Matem., No. 3, pp. 15-24, 1995.
5.  V. N. Paimushin and S. N. Bobrov, "Refined geometrically nonlinear theory of sandwich shells with transversely soft filler of medium thickness for the analysis of mixed buckling modes," Mekh. Kompoz. Mater., Vol. 36, No. 1, pp. 95-108, 2000.
6.  V. V. Bolotin and Yu. N. Novichkov, Mechanics of Multilayered Structures [in Russian], Mashinostroenie, Moscow, 1980.
7.  V. N. Paimushin, V. A. Ivanov, S. N. Bobrov, and T. V. Polyakova, "Stability of a sandwich circular ring under uniform external pressure," Mekh. Kompoz. Mater., Vol. 36, No. 3, pp. 317-328, 2000.
8.  V. N. Paimushin and V. R. Khusainov, "Refined theory of sandwich plates and shells for the analysis of dynamic deformation processes with large variability exponents," Mekh. Kompoz. Mater. i Konstr., Vol. 7, No. 2, pp. 215-235, 2001.
9.  V. N. Paimushin, "Classical and nonclassical problems of dynamics of sandwich shells with transversely soft filler," Mekh. Kompoz. Mater., Vol. 37, No. 3, pp. 289-306, 2001.
10.  V. N. Paimushin, "Shear buckling mode of a sandwich circular ring under uniform external pressure," Doklady RAN, Vol. 378, No. 1, pp. 58-60, 2001.
11.  V. V. Novozhilov, Fundamentals of Nonlinear Elasticity [in Russian], Gostekhizdat, Moscow, 1948.
12.  V. N. Paimushin and V. A. Ivanov, "Buckling modes of homogeneous and sandwich plates under pure shear in tangential directions," Mekh. Kompoz. Mater., Vol. 36, No. 2, pp. 215-228, 2000.
Received 30 May 2003
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