Experimental studies of the vibrations and dynamic stability of laminated composite shells

Abstract

The paper discusses the results of systematic experimental studies of vibrations and dynamic instability of thin shells of revolution made of laminated composite materials (glassfiber-reinforced plastics). The basic patterns in the dynamic deformation of shells during natural, forced, and parametric vibrations are considered. The damping parameters of natural vibrations are analyzed. The wave deformation modes of shells subject to periodic excitation are studied. The effect of long-term vibratory loading (torsion) on the dynamic characteristics of three-layer glassfiber-reinforced plastic shells is examined Keywords: composite, shell of revolution, frequencies and modes of vibration, dynamic instability, amplitude-frequency characteristic, running wave 1. Introduction. The unusual word "composite" came into use in the materials-science literature in the mid-1950s. It refers to then absolutely new, artificial anisotropic materials consisting of several components with different physical properties. The resulting material has properties qualitatively and quantitatively different from those of the components.The most popular structural composites are materials with oriented high-strength reinforcement (reinforced composites [1,3,4,13,25,26,32,34]) of which so-called glassfiber-reinforced plastics lead in practical use. These materials are produced by combining glass fibers or fabrics with polymeric resin as a matrix. Such materials are advantageous due to high mechanical strength at relatively low weight, corrosion resistance, relatively high thermal resistance, radio transparency, electric stability, etc. An exceptional value of fiberglass is that it makes it possible to influence the parameters of structural members being created. Glassfiber-reinforced plastic materials and structures with prescribed stiffness, weight, and other physical constraints are created in a single process cycle. This is very important because a not very complex process allows creating, in a relatively short time, mechanical objects of quite complex geometry, high strength, and low cost.It is therefore no wonder that the scope of application of fiberglass constantly extends. Nowadays glassfiber-reinforced plastic materials and structural elements are used in aircraft and rocket technology, transport space systems, chemical engineering, automotive industry, shipbuilding, pipeline construction, etc. This list could be extended.The basic stages in the development of the mechanics of composites and structures and results obtained to date are well reflected in many publications ([1, 4, 17, 25, 26, 32, etc.]) and in the multivolume collective monographs Mechanics of Composite Materials and Structural Members [in Russian] (1982-1983) and Mechanics of Composite Materials (1993Materials ( -2003 edited by academician A. N. Guz and issued by the S. P. Timoshenko Institute of Mechanics. Modern areas of research on the mechanics of composite materials and structures are indicated in the reviews [38,[40][41][42].In the former USSR, the S. P. Timoshenko...

Dynamic deformation of a cylindrical composite shell with filler subject to radial two-frequency excitation

“…As is seen, when the amplitude g v is low, the radial vibrations with maximum amplitude 2A of the shell's free end are excited at the resonant frequencies of conjugate modes with wave numbers n = 3, 4 corresponding to the minimum frequencies, which was mentioned earlier [13,16].…”

“…If g v = 2-4g 0 , vibrations with n = 3 are excited only in one of the two conjugate modes. As indicated earlier [13,16], the second mode is excited by a vibration load of high amplitude. In the dry shell, the second conjugate mode with n = 3 is excited when g v = 5g 0 .…”

“…These loads cause beating w b = 1.2-2.4 Hz with minor alteration in both g v and 2A. For example, g v = (4.5-5.0)g 0 and 2A = 9-11 mm when the wave number n = 3, the deformation mode being a standing wave with diffuse nodes [13,16].…”

“…It is revealed that such processes can be accompanied (especially at the lowest resonant frequencies) by the cyclic variation in the amplitude and deformation mode between traveling and standing circumferential wave Introduction. An important task of solid mechanics is to study the nonlinear vibrations (with large (of the order of the thickness) deflections) of thin-walled shells made of laminated composites among which glass-reinforced plastics are most popular [16]. Many publications [1-3, 5-9, 11-16, etc.]…”

Nonlinear vibrations of cylindrical shells filled with a fluid and subjected to longitudinal and transverse periodic excitation

“…An analysis of the above results reveals a qualitative difference between the cases of K 0 0 = and K 0 0 ¹ . As follows from (2.4), the former case takes place when u 30 = u 40 = 0, which corresponds to the steady-state dynamic deflection w (1.3) in the form of a standing wave [12] with the axisymmetric term w 11 ¹ and corresponds to a generalized (with variable amplitude and phase) circumferential traveling wave [13,19]. Figure 1a demonstrates that as the external excitation frequency W is slowly varied, the deformation mode of the shell in the resonance zone changes between a standing wave and a traveling wave.…”