STABILITY ANALYSIS OF LAMINATED COMPOSITE STIFFENED PANELS

Abstract

Laminated composite stiffened panels which are anisotropic and orthotropic in nature are gaining popularity in structural applications. The use of laminated composite provides flexibility to tailor different properties of the . structural elements to achieve strength and stiffness requirements. Laminated composite stiffened panels are generic structural elements in weight sensitive structure applications, which are made by adjoin of laminated composite plate and stiffeners. Some various shaped stiffening members commonly used for panel structural concepts are "T", "Z", "I", "C", "J", blade and hat. These panels are becoming increasingly used in structural applications because of their high specific stiffness (stiffness) per unit weight) and specific strength (strength per unit weight). The stiffened elements' representing a relatively small part of the total weight of the structure substantially influence their stiffness and stability. Accurate knowledge of critical buckling load and mode shapes are essential for reliable and lightweight structural design. In this dissertation, parametric studies have been carried out to understand the buckling characteristics of graphite epoxy hat and multicellular laminated composite stiffened panels for transverse loading actions. The effect of variation in fiber orientation and pitch length (number of stiffener) on buckling response has been examined in some detail using ANSYS. It is shown that variation in fiber orientation and pitch length can substantially improve the buckling capability of the stiffened panels sections. Buckling of the composite stiffened panels is indicated in this dissertation !foi~ increase in number of stiffener and constant dimensions of the panel as well as loading. n~ addition to this, nonlinear buckling analysis procedure is developed in this thesis ! fort laminated composite stiffened panels. The objective of the present work is to illustrate the capability of the implementation for buckling analysis of laminated composite stiffened panels. Post-buckling analysis for composite stiffened panels under realistic loading, including the effect of geometric nonlinearity, has been carried out using a small number of models. Buckling is the key design criterion for thin-walled structures. Since this type of structures typically exhibits post-buckling behavior, these structures are sensitive to geometric or load imperfections. Standard finite element based incremental-iterative iii nonlinear analysis of such panels are used but this type of process is computationally expensive and not suitable for repeated runs necessary for a design and optimization process, and often it is difficult to interpret the result and guarantee its correctness. Hence there is a strong need for fast tools that address these shortcomings and that can support the nonlinear, analysis so some of the models are compared with linear and. nonlinear buckling analysis; In this approach a load—displacement relation of nonlinear buckling analysis is used, with a corresponding of the linear buckling analysis. The presence of in-plane loading may cause buckling of stiffened panels. This! dissertation presents some parametric studies on simply supported laminated composite; stiffened panels subjected to in-plane shear loading. A number of models were analyzed using ANSYS and a database is prepared for different plate and stiffener combinations. Studies are carried out by changing the panel orthotropy ratio, stiffener depth, pitch length, smeared extensional stiffness ratio of stiffener to that of the plate and extensional stiffness to shear stiffness ratio of the plate. Based on the studies, few important parameters influencing the buckling behaviour are used and guidelines for better stiffener proportioning are developed, which will be helpful for the designer. This buckling study will not only help us to understand the performance of these thin walled structures but shall also help in creating a data base for further analysis and research on the subject.