ANALYSIS OF LAMINATED COMPOSITE FOLDED PLATES

Abstract

Laminated composite materials are being widely used in many recent civil engineering applications such as roof of buildings, bridge decks, structural panels, beams etc. Using laminated composite materials in construction gives many advantages such as high strength/stiffness to weight ratio, serviceability in extreme weather conditions, durability, fatigue resistance and design flexibility (three-dimensional forms moulded in place), easy to install in structure replacement. It is anticipated that in coming days composite materials are going to replace the present day construction materials in many applications. However, composite materials are relatively weak in shear compared to extensional rigidity. Hence, the shear deformation has to be modelled very efficiently in laminated composite structures. Folded plates are a very useful form of structure which has many advantages. Several methods are available for the analysis of this type of structure. Conventional methods are simple and easy, but they have the limitations of generality of application and precision. The combination of Laminated Composites as the construction material and Folded Plates as the structural form can be very advantageous for the construction industry. Some of the main parameters for the analysis and design of composite folded plates are deflection and stresses. This dissertation work presents static analysis of composite folded plates by developing a Co finite element (FE) model based on higher order shear deformation theory (HSDT). Many commercial software packages (e.g., Ansys, Abaqus etc.) are developed based on FE method for the analysis of laminated composite structures. However, almost all of these software packages have the capability of modelling the transverse shear deformation using 2D elements up to a certain extent based on FSDT. On the other hand, the laminated structures can also be modelled by using three-dimensional solid elements. But a large number of elements will be required to model the multi-layered laminates since each layer will require at least one element in the thickness direction and the element size in the other directions cannot be made large in order to maintain its aspect ratio. Thus it will require a huge computational effort which may not be encouraged in practical applications. Therefore, a computer code is developed for the mathematical formulation based on HSDT for present problem. FORTRAN 90 language has been used to develop a computer code for the mathematical formulation explained in previous section for the analysis of laminated composite folded plates. iv In the present theory the transverse shear stresses are taken as zero at the top and bottom surfaces. A realistic parabolic variation of transverse shear strains through the thickness is assumed and the use of shear correction factor is avoided. The Co finite element formulation has been done quite efficiently to overcome the problem of C1 continuity associated with the HSDT. The isoparametric FE used in the present model consists of nine nodes with nine nodal unknowns per node. Many problems of laminated composite folded plates are solved using the present finite element model based on HSDT for different geometries of folded plates having several variations in the material like cross ply, angle ply etc. Studies have been done by varying various parameters such as thickness ratios, different boundary conditions and different ply orientations. The results obtained are presented in the form of tables. For the purpose of validation of the proposed model, a large number of these results are compared with the ABAQUS results as well as with the published results. It has been found in the literature that so far there is no result available on the present problem of laminated composite folded plates based on HSDT. Actually, very few results are available for composite folded plates based on FSDT. Hence, HSDT theory for composite folded plates can be very useful for analysis and future research.