Optimal design of clamped laminated composite plates

The characteristics of composite materials are of high importance to engineering applications; therefore the increasing use as a substitute for conventional materials, especially in the field of aircraft and space industries. It is a known fact that researchers use finite element programs for the design and analysis of composite structures, use of symmetrical conditions especially in complicated structures, in the modeling and analysis phase of the design, to reduce processing time, memory size required, and simplifying complicated calculations, as well as considering the response of composite structures to different loading conditions to be identical to that of metallic structures. Finite element methods are a popular method used to analyze composite laminate structures. The design of laminated composite structures includes phases that do not exist in the design of traditional metallic structures, for instance, the choice of possible material combinations is huge and the mechanical properties of a composite structure, which are anisotropic by nature, are created in the design phase with the choice of the appropriate fiber orientations and stacking sequence. The use of finite element programs (conventional analysis usually applied in the case of orthotropic materials) to analysis composite structures especially those manufactured using angle ply laminate techniques or a combination of cross and angle ply techniques, as well considering the loading response of the composite structure to be identical to that of structures made of traditional materials, has made the use of, and the results obtained by using such analysis techniques and conditions questionable. Hence, the main objective of this paper is to highlight and present the results obtained when analyzing and modeling symmetrical conditions as applied to commercial materials and that applied to composite laminates. A comparison case study is carried out using cross-ply and angle-ply laminates which concluded that, if the composition of laminate structure is pure cross-ply, the FEA is well suited for predicting the mechanical response of composite structure using principle of symmetry condition. On the other hand that is not the case for angle-ply or mixed-ply laminate structure.

Response of a cylindrical panel made of layers of composite material and subjected to in-plane loads is investigated. Prebuckling deformations are determined for antisymmetric angle-ply and cross-ply panels having simply supported boundary conditions. Buckling solutions are obtained via the Rayleigh-Ritz method. Nonlinear programming is used to optimize the designs. Design variables are taken as fiber orientations and/or thicknesses of different layers. Numerical results are presented for different materials and different geometrical parameters, including aspect ratio and curvature-to-length ratio.

Buckling and free vibration analysis of piezoelectric laminated composite plates using various plate deformation theories

In the present study, the thermal buckling analysis of thick anisotropic laminated composite plates is carried out using the finite strip method based on the higher-order shear deformation theory. This theory accounts for the parabolic distribution of the transverse shear strains through the thickness of the plate and for zero transverse shear stresses on the plate surfaces. Therefore, this theory yields improved results over the Mindlin plate theory and eliminates the need for shear correction factors in calculating the transverse shear stiffness. The critical temperatures of simply supported rectangular cross-ply and angle-ply composite laminates are calculated. The effects of several parameters, such as the aspect ratio, the length-to-thickness ratio, the number of plies, fibre orientation and stacking sequence, are investigated.

Composite materials are believed to be materials of future with potential application in high performance structure. Composites being light weight and having higher strength to weight ratio proves very efficient and economical. The static strength of laminated composite materials can be calculated easily but it’s analysis under cyclic loading is a quite complicated phenomenon. Continuous degradation of material occurs under cyclic loading which causes redistribution of the stresses within the laminate hence failure of single lamina does not indicate failure of entire laminate which in turn increases the complexity of the analysis. Also laminated composite materials being nonhomogeneous and anisotropic its fatigue analysis involves a lot of calculations; this can be reduced with the help of finite element-based software. Plenty of work has been carried out for fatigue analysis of laminated composite materials subjected to axial loading but the flexural fatigue analysis needs some attention. Here, the attempt has been made to perform the flexural fatigue analysis of laminated composite material using finite element-based software ANSYS. The results are presented for cross ply and angle ply laminates with two material combinations, namely, E-Glass epoxy and Carbon epoxy for different aspect ratios. KeywordsLaminated compositeFlexural fatigue analysisANSYSE-glass epoxy

A method for optimally designing laminated plates subject to fatigue loads for minimum weight using a cumulative damage constraint

Effects of nonuniform boundary conditions on the buckling load optimization of laminated composite plates

Disappearance of free-edge stress singularity in composite laminates

A mono tiltrotor (MTR) design which combines concepts of a tiltrotor and coaxial rotor is presented. The aerodynamic modeling of the MTR based on blade element momentum theory (BEMT) is conducted, and the method is fully validated with previous experimental data. An automated optimization approach integrating BEMT modeling and optimization algorithms is developed. Parameters such as inter-rotor spacing, blade twist, taper ratio and aspect ratio are chosen as design variables. Single-objective (in hovering or in cruising state) optimizations and multi-objective (both in hovering and cruising states) optimizations are studied at preset design points; i.e., hovering trim and cruising trim. Two single-objective optimizations result in different sets of parameter selections according to the different design objectives. The multi-objective optimization is applied to obtain an identical and compromised selection of design parameters. An optimal point is chosen from the Pareto front of the multi-objective optimization. The optimized design has a better performance in terms of the figure of merit (FM) and propulsive efficiency, which are improved by 7.3% for FM and 13.4% for propulsive efficiency from the prototype, respectively. Further aerodynamic analysis confirmed that the optimized rotor has a much more uniform load distribution along the blade span, and therefore a better aerodynamic performance in both hovering and cruising states is achieved.

This paper deals with an efficient optimization method of combining fiber orientation and topology for constant-stiffness composite laminated plates. The optimal topology and fiber orientation can be simultaneously obtained, using the proposed method. To overcome the non-monotonous behaviors derived from directly optimizing fiber orientation, the lamination parameters are selected as design variable. The proposed method mainly includes two steps. Initially, lamination parameters and density are taken as the design variables for determining the fiber orientation and topology shape. A combined optimization model is built based on the penalization theory. The optimal lamination parameter and topology shape can be achieved simultaneously in this step. Then, solving nonlinear equations is transformed into a least squares optimization problem. The optimal fiber orientation is obtained and matched with the optimal lamination parameter. Finally, numerical examples of designing short cantilever beam and compliant inverter are performed to illustrate the validity of this method.

The effective thermal conductivity of coated/uncoated fiber-reinforced composites with different fiber arrangements

Optimization of FRP composites against impact induced failure using island model parallel genetic algorithm

This paper presents a semianalytical method for the prediction of interlaminar stresses and displacements near the free edges and ply cracks in general angle-ply laminates subjected to biaxial extensions and/or in plane shear deformation. The method is based on a state space representation of the three-dimensional equations of elasticity. Numerical solutions are obtained by using layer refinement in the through thickness direction and Fourier series expansion in the other directions. By this approach, an angle-ply laminate may be composed of an arbitrary number of monoclinic layers and each layer may have different material property and thickness. This method guarantees continuous fields of all interlaminar stresses across interfaces between material layers. Numerical results are compared with those obtained from other methods. It is found that the theory provides a satisfactory approximation to the stress singularities near the free edges and ply cracks. Numerical solutions for antisymmetric laminates under extension and general laminates under shearing are new in the literature and can be used as benchmarks for validating new models.

This paper is concerned with a theoretical treatment of thermal stress and thermal bending problems for a multi-layered anisotropic laminated plate due to partially distributed heat supply. As an analytical model, we consider a laminated rectangular plate consisting of a diagonal pile of layers having orthotropic material properties, i. e. an angle-ply laminate. We obtain the three-dimensional temperature in a transient state and thermal deformation of a simply supported plate using the higher-order shear deformation theory. As an example, numerical calculations are carried out for a 2-layered angle-ply laminate, and the numerical results are examined precisely.

A thermoplastic angle-ply AS4/PEEK laminate with a hole is considered. The interlaminar stresses along the hole edge at different interfaces under uniaxial extension are investigated. According to the symmetries of the structure and loading, a suitable finite-element model is developed. Utilizing a three-dimensional elastic-plastic finite-element procedure elaborated previously, a finite-element modeling of the interlaminar stresses in a thick angle-ply composite laminate is carried out. Based on the interlaminar stresses obtained, the dangerous locations of delamination initiation are predicted. The results obtained indicate that there is some relationship between the dangerous locations and fiber orientations in the adjacent layers, and it maybe inferred that the critical locations are near the regions where the hole edge is tangent to the fiber orientation in the layers adjacent to the interface. The interlaminar stresses at the same interfaces are not sensible to distances from the midplane of the laminate. Very high interlaminar tensile stresses are found to exist on the hole edge at the +25°/+25° or -25°/-25° interfaces, and delaminations can initiate there first.