CLASSIFICATION OF BUCKLING MODES IN STIFFENED FUNCTIONALLY GRADED COMPOSITE TUBES SUBJECT TO BENDING

2021 ◽  
Author(s):  
LUAN TRINH ◽  
PAUL WEAVER
Keyword(s):  
Wall Thickness ◽  
Functionally Graded ◽  
Geometric Parameters ◽  
Mode Shapes ◽  
Local Mode ◽  
Buckling Mode ◽  
Global Mode ◽  
Local Modes ◽  
Linear Discriminant ◽  
Finite Element Software

Bamboo poles, and other one-dimensional thin-walled structures are usually loaded under compression, which may also be subject to bending arising from eccentric loading. Many of these structures contain diaphragms or circumferential stiffeners to prevent cross-sectional distortions and so enhance overall load-carrying response. Such hierarchical structures can compartmentalize buckling to local regions in addition to withstanding global buckling phenomena. Predicting the buckling mode shapes of such structures for a range of geometric parameters is challenging due to the interaction of these global and local modes. Abaqus finite element software is used to model thousands of circular hollow tubes with random geometric parameters such that the ratios of radius to periodic length range from 1/3-1/7, the ratio of wall thickness to radius varies from 1/4-1/10. The material used in this study is a type of bamboo, where the Young’s and shear moduli are point-wise orthotropic and gradually increase in magnitude in the radial direction. Under eccentric loads with varying eccentricity, the structures can buckle into a global mode or local modes within an internode, i.e. periodic unit. Moreover, the local modes may contain only one wave or multiple waves in the circumferential direction. As expected, numerical results show that the global mode is more likely to occur in small and thick tubes, whereas the local modes are observed in larger tubes with a smaller number of circumferential waves present in thicker walls. Also, greater eccentricity pushes the local mode domains towards smaller tubes. An efficient classification method is developed herein to identify the domains of each mode shape in terms of radius, wall thickness and eccentricity. Based on linear discriminant analysis, explicit boundary surfaces for the three domains are defined for the obtained data, which can help designers in predicting the mode shapes of tubular structures under axial bending.

Experimental Verification of Decentralized Approach for Modal Identification Based on Wireless Smart Sensor Network

2011 ◽  
Vol 291-294 ◽  
pp. 3-11 ◽  
Author(s):  
Xi Jun Ye ◽  
Tian Feng Zhu ◽  
Quan Sheng Yan ◽  
Wei Feng Wang
Keyword(s):  
Mode Shape ◽  
Experimental Verification ◽  
Large Scale ◽  
Modal Identification ◽  
Least Square ◽  
Mode Shapes ◽  
Local Mode ◽  
Smart Sensor ◽  
Global Mode ◽  
Modal Test

This paper provides an experimental verification of decentralized approach for modal test and analysis of a 30 meters long railway overpass bridge. 11 Imote2 smart sensor nodes were implemented on the WSSN. In order to compare the identification precision of different topologies, acceleration responses were obtained under centralized and 3 different decentralized topologies. Local modal parameters were estimated by NExT/ERA within each local group; true modes were then distinguished from spurious modes by EMAC and finite-element analysis. In order to estimate global mode shape, a least square method was used for calculating the normalization factor. Then the global mode shapes were determined by normalization factors and local mode shapes. The result demonstrates that the more overlapping nodes in each group, the more accurate the global mode shape will be; the decentralized approach is workable for modal test of large-scale bridge.

Torsional Buckling of Functionally Graded Multilayer Graphene Nanoplatelet-Reinforced Cylindrical Shells

2019 ◽  
Vol 20 (01) ◽  
pp. 2050005 ◽  
Author(s):  
Jiabin Sun ◽  
Yiwen Ni ◽  
Hanyu Gao ◽  
Shengbo Zhu ◽  
Zhenzhen Tong ◽  
...  
Keyword(s):  
Cylindrical Shells ◽  
Functionally Graded ◽  
Mode Shapes ◽  
Multilayer Graphene ◽  
Distribution Profile ◽  
Torsional Buckling ◽  
Buckling Mode ◽  
Reinforced Composite ◽  
Bifurcation Buckling ◽  
Slope Factor

Exact solutions for the torsional bifurcation buckling of functionally graded (FG) multilayer graphene platelet reinforced composite (GPLRC) cylindrical shells are obtained. Five types of graphene platelets (GPLs) distributions are considered, and a slope factor is introduced to adjust the distribution profile of the GPLs. Within the framework of Donnell’s shell theory and with the aid symplectic mathematics, a set of lower-order Hamiltonian canonical equations are established and solved analytically. Consequently, the critical buckling loads and corresponding buckling mode shapes of the GPLRC shells are obtained. The effects of various factors, including the geometric parameters, boundary conditions and material properties on the torsional buckling behaviors are investigated and discussed in detail.

BUCKLING AND WRINKLING OF A FUNCTIONALLY GRADED MATERIAL (FGM) THIN FILM

2012 ◽  
Vol 04 (02) ◽  
pp. 1250012 ◽  
Author(s):  
MASOUD NOROOZI ◽  
LIYING JIANG
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Functionally Graded Material ◽  
Functionally Graded ◽  
Mode Shapes ◽  
Winkler Foundation ◽  
Bending Rigidity ◽  
Free Standing ◽  
Buckling Mode ◽  
Graded Material

The instability of a functionally graded material (FGM) strip as a free standing film or a substrate-bound film is studied in this work, in which the stiffness of the film is assumed to change exponentially along the length. The buckling load and the buckling mode shapes for the free standing FGM film are determined analytically. For the substrate-bound film, the substrate is modeled as a Winkler foundation and the wrinkling load and wrinkling pattern are determined numerically by using a finite difference method and a series solution. In contrast with the wrinkling of homogenous thin films in which the wrinkles propagate in the entire domain, the wrinkles of the FGM films accumulate around the location with the least bending rigidity. The results of this work show that the sensitivity of the wrinkle accumulation around the weak locations of the system with lower stiffness is very high. This work is expected to provide a better understanding for localization of wrinkles around a region of substrate-bounded thin films in thin film technology.

Delamination Buckling of Composite Cylindrical Panels Under Axial Compressive Load

Volume 1 ◽  
2004 ◽  
Author(s):  
Tim Leigh ◽  
Azam Tafreshi
Keyword(s):  
Finite Element ◽  
Service Use ◽  
Computing Time ◽  
Compressive Load ◽  
Shear Deformation Theory ◽  
Local Mode ◽  
Global Mode ◽  
Local Modes ◽  
Cylindrical Panels ◽  
Delamination Buckling

Composite cylindrical shells and panels are widely used in aerospace structures. Delaminations within the composite structure reduce the compressive strength of laminates, and often result because of damage incurred during manufacturing and in-service use. This paper investigates the buckling behaviour of laminated cylindrical panels loaded in axial compression using the finite element method. The use of three-dimensional finite elements for predicting the delamination buckling of these structures is computationally expensive. Here the analysis has been carried out using a layerwise shell finite element based on the first-order, shear deformation theory. Contact elements were placed between the delaminated regions to avoid physical interpenetration of the elements. It is shown that through-the-thickness delamination can be modelled and analysed effectively without requiring a great deal of computing time and memory. Delamination shapes considered in this study were square and rectangular — extended longitudinally over the entire length or extended along the entire circumference of the panel. Some of the results were compared with the corresponding analytical results which were in good agreement. The most influential parameters for a given laminated panel were the size of the delamination and its through-the-thickness position. The effect of the curvature on the global buckling strength of a delaminated panel was also studied. Depending on the size and through the thickness position of delaminations, three different modes of buckling behaviour occur. The local mode occurs when the delamination is near the free surface of the laminate and the area of the delamination is large. The global mode occurs when the delamination is deeper within the laminate and has a small area. The mixed mode is a combination of global and local modes.

Solar sail structural analysis via improved finite element modeling

2016 ◽  
Vol 231 (2) ◽  
pp. 306-318 ◽  
Author(s):  
Luisa Boni ◽  
Giovanni Mengali ◽  
Alessandro A Quarta
Keyword(s):  
Finite Element ◽  
Structural Analysis ◽  
Solar Sail ◽  
Mode Shapes ◽  
Solar Sails ◽  
Element Analysis ◽  
Global Mode ◽  
Local Modes ◽  
Global Buckling ◽  
Stabilization Technique

Despite the existence of many studies about the structural analysis of a square solar sail, the need for obtaining reliable numerical results still poses a number of practical issues to be solved. The aim of this paper is to propose a new method that improves the existing analysis techniques. In this sense, the solar sail is modeled using distributed sail-boom connections, and its structural behavior in free flight is studied, using the inertia relief method, at different incidence angles of the incoming solar radiation. The proposed approach is able to circumvent the onset of numerical convergence problems by means of suitable strategies. A nonlinear analysis is carried out starting from an initial geometrical configuration in which the whole solar sail is perturbed using a linear combination of the first global buckling modes, obtained with a static eigenvalue analysis. Key points of the procedure are the application of a correct sail pre-stress, a clever choice of the type of elements to be used in the finite element analysis and the use of a suitable mesh refinement. The performance of the new approach have been successfully tested on square solar sails with side length varying from relatively small to medium-to-large sizes, in the range of 10–100 m. A detailed analysis is presented for a reference 20 m × 20 m square solar sail, where the paper shows that the suggested procedure is able to guarantee accurate results without the need of additional stabilization technique. In particular, the vibration global mode shapes and frequencies of the solar sail are correctly described even in presence of unsymmetrical loading conditions. In other terms, the numerical analysis is completed without any convergence problem and any disturbing local modes.

Modal and Local Modal Analysis of High Speed Train Car-Body

2012 ◽  
Vol 215-216 ◽  
pp. 800-803
Author(s):  
Tian Li Chen ◽  
Yao Hui Lu ◽  
Jing Zeng ◽  
Li Min Zhang
Keyword(s):  
Modal Analysis ◽  
Structural Design ◽  
High Speed ◽  
Ride Comfort ◽  
Side Wall ◽  
Local Mode ◽  
Analysis Method ◽  
Local Modes ◽  
Car Body ◽  
Finite Element Software

with the speed rising of railway train and the weight lightening of car-body, the frequency range of car-body is widened and the natural frequency is decreased. Especially, the local modes of car-body are caused by suspension device under the car-body bottom, which lead to large vibration response, influence the ride comfort and fatigue failure of structure. In this paper, the whole mode of car-body was analyzed through finite element software. The local mode of car-body bottom and side wall were computed by method of equivalent stiffness constrain. The results show that the local mode of car-body is mainly caused by asymmetry suspension device. The modal analysis method and local modal analysis method adopted in this essay provide the reference and guide the dynamic structural design.

Effect of crack on free vibration of a pre-stressed curved plate

2021 ◽  
pp. 095440622199486
Author(s):  
Can Gonenli ◽  
Hasan Ozturk ◽  
Oguzhan Das
Keyword(s):  
Finite Element ◽  
Free Vibration ◽  
Natural Frequency ◽  
Present Model ◽  
Mode Shapes ◽  
Load Parameter ◽  
Flexible Plate ◽  
Cantilever Plate ◽  
Finite Element Software ◽  
Aspect Ratios

In this study, the effect of crack on free vibration of a large deflected cantilever plate, which forms the case of a pre-stressed curved plate, is investigated. A distributed load is applied at the free edge of a thin cantilever plate. Then, the loading edge of the deflected plate is fixed to obtain a pre-stressed curved plate. The large deflection equation provides the non - linear deflection curve of the large deflected flexible plate. The thin curved plate is modeled by using the finite element method with a four-node quadrilateral element. Three different aspect ratios are used to examine the effect of crack. The effect of crack and its location on the natural frequency parameter is given in tables and graphs. Also, the natural frequency parameters of the present model are compared with the finite element software results to verify the reliability and validity of the present model. This study shows that the different mode shapes are occurred due to the change of load parameter, and these different mode shapes cause a change in the effect of crack.

Torsional vibration of functionally graded carbon nanotube reinforced conical shells

2018 ◽  
Vol 25 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Yaser Kiani
Keyword(s):  
Torsional Vibration ◽  
Conical Shell ◽  
Volume Fraction ◽  
Differential Quadrature Method ◽  
Functionally Graded ◽  
Mode Shapes ◽  
Coupled Equations ◽  
Parametric Studies ◽  
Torsional Frequency ◽  
Generalized Differential

AbstractThe present study deals with the free torsional vibration of a composite conical shell made of a polymeric matrix reinforced with carbon nanotubes (CNTs). Distribution of CNTs across the thickness of the conical shell may be uniform or functionally graded. Five different cases of functionally graded reinforcements are considered. First-order shear deformable shell theory compatible with the Donnell kinematic assumptions is used to establish the motion equations of the shell. These equations are two coupled equations which should be treated as an eigenvalue problem. The generalized differential quadrature method is used to obtain a numerical solution for the torsional frequency parameters and the associated mode shapes of the shell. After validating the results of this study for the cases of isotropic homogeneous cone and annular plates, parametric studies are carried out to analyze the influences of geometrical characteristics of the shell, volume fraction of CNTs, and grading profile of the CNTs. It is shown that volume fraction of CNTs is an important factor with regard to torsional frequencies of the shell; however, grading profile does not change the torsional frequencies significantly.

A Study on the Design Curves for Pultruded Composite Columns

2007 ◽  
Vol 26-28 ◽  
pp. 337-340 ◽  
Author(s):  
Seung Sik Lee ◽  
Soo Ha Chae ◽  
Soon Jong Yoon ◽  
Sun Kyu Cho
Keyword(s):  
Local Mode ◽  
Design Equation ◽  
Global Mode ◽  
Buckling Loads ◽  
Steel Columns ◽  
Short Columns ◽  
Theoretical Approaches ◽  
Interaction Mode ◽  
Column Design ◽  
Thin Walled

The strengths of PFRP thin-walled columns are determined according to the modes of buckling which consist of local mode for short columns, global mode for long columns, and interaction mode between local and global modes for intermediate columns. Unlike the local and global buckling, the buckling strength of interaction mode is not theoretically predictable. Refined theoretical approaches which can account for different elastic properties of each plate component consisting of a PFRP thin-walled member are used. Based on both the analytical buckling loads and the experimentally measured buckling loads from literatures, the accuracies of Ylinen’s equation and modified AISC/LRFD column design equation for isotropic steel columns were compared. From the comparison, it was found that the modified AISC/LRFD column design equation is more suitable for the prediction of the buckling loads of PFRP thin-walled members than Ylinen’s equations.

Distortional buckling of compressed cold‐formed lipped C channels via buckling mode shapes

ce/papers ◽  
2021 ◽  
Vol 4 (2-4) ◽  
pp. 2535-2541
Author(s):  
Bálint Vaszilievits‐Sömjén
Keyword(s):  
Mode Shapes ◽  
Distortional Buckling ◽  
Buckling Mode
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