Boundaries Of Instability Regions Research Articles

Dynamic instability characteristic of damped laminated composite conical shell panel under periodic axial compression

The static and dynamic instability behavior of a simply supported damped composite conical shell panels subjected to periodic axial compression is studied. Bolotin method is adopted to trace the boundaries of instability regions. Influences of semi-vertex angles, symmetric and antisymmetric laminate, length to radius ratios, thickness to radius ratios, and static load factors on the instability regions are studied. Moreover, the time history responses and corresponding phase plots from the unstable and stable region are studied to bring out the various features of instability problem such as existence of beats, effect of damping, and forcing frequency on the response.

Dynamic Instability of Laminated-Composite and Sandwich Plates Using a New Inverse Trigonometric Zigzag Theory

A structure with periodic dynamic load may lead to dynamic instability due to parametric resonance. In the present work, the dynamic stability analysis of laminated composite and sandwich plate due to in-plane periodic loads is studied based on recently developed inverse trigonometric zigzag theory (ITZZT). Transverse shear stress continuity at layer interfaces along with traction-free boundary conditions on the plate surfaces is satisfied by the model obviating the need of shear correction factor. An efficient C0 continuous, eight noded isoparametric element with seven field variable is employed for the dynamic stability analysis of laminated composite and sandwich plates. The boundaries of instability regions are determined using Bolotin's approach and the first instability zone is presented either in the nondimensional load amplitude–excitation frequency plane or load amplitude–load frequency plane. The influences of various parameters such as degrees of orthotropy, span-thickness ratios, boundary conditions, static load factors, and thickness ratios on the dynamic instability regions (DIRs) are studied by solving a number of problems. The evaluated results are validated with the available results in the literature based on different deformation theories. The efficiency of the present model is ascertained by the improved accuracy of predicted results at the cost of less computational involvement.

Fonksiyonel Değişimli Çekirdeğe Sahip Üç Tabakalı Silindirik Kabukların Parametrik Titreşimi

In this study, the parametric vibration of three-layered cylindrical shells with functionally graded (FG) core is investigated. Firstly, analytical models of an FG core, which uses the intermediate member and outer sheath layers of the cylindrical shell formed from metal-rich and ceramic-rich represented as ternary systems. The governing equations of three-layered cylindrical shells with an FG core are derived and are reduced Mathieu-Hill equation by using Galerkin method. The expressions for non-dimensional frequency, critical axial load and boundaries of instability regions of three-layered cylindrical shell with an FG core are found. The expressions for non-dimensional frequency parameter, critical axial load and boundaries of instability regions are obtained for the monolayer FGM, pure metal and pure ceramic cylindrical shells, as a special case. Finally, the effects of variations of volume fractions, shell characteristics and variations of the thickness of a core on the values of critical parameters of three-layered cylindrical shells made of different types of FG core are studied numerically. Comparisons are made with the available studies in the open literature to validate this study

Parametric instability of delaminated composite plates subjected to periodic in-plane loading

This paper deals with the study of the parametric instability characteristics of delaminated composite plates subjected to periodic in-plane load. A first order shear deformation theory based on finite element method is developed for studying the instability region of mid-plane delaminated composite plate. A detailed parametric investigation is carried out to study the influence of the delamination area, number of layers, degree of orthotropy, aspect ratio and static in-plane load on the dynamic stability characteristics of delaminated cross-ply plates. The results of vibration and buckling of delaminated composite plates are compared with previous numerical studies in the literature and the authors’ experimental investigations. The boundaries of instability regions are obtained by using Bolotin’s method and are represented in the non-dimensional load amplitude-excitation frequency plane. It is observed that the natural frequencies and the critical buckling load of the plates decrease with an increase in delamination size. The increase in delamination size also causes dynamic instability regions to be shifted to lower excitation frequencies.