In this paper, a cost effective design procedure for laminated composite structure using GA (Genetic Algorithms) is proposed. Design variables considered to enhance the rigidity of the laminated composite structure are the number of laminae, the fiber orientation and the stacking sequence. The fiber orientations are chosen among some prepared angles. In the proposed design procedure, a rigidity function is defined to determine which angle to reinforce by means of weighing coefficients and transformed elastic constants in the prepared angles. The weighing coefficients are defined to represent the distribution of principal stress in the structure. Then, the orientation of reinforcements can be found according to the weighing coefficients such that the defined rigidity function takes maximum. Futhermore, to find a global optimum solution, the weighing coefficients are adjusted. In this paper, the detail of our developed procedure and some applications are shown.
Dynamic characteristics as natural frequencies and modal damping ratios of laminated composite materials are influenced by the fiber orientations and the stacking sequence. Since the transfer functions of laminated composite structures are determined by these characteristics, we pay attention to the relations between the fiber orientations (including the stacking sequence) and transfer functions in order to minimize the vibrational response of structures. This paper presents an optimum design method of laminated composite structures to minimize the vibrational response. The optimization program evaluates the frequency response functions as an objective function of the genetic algorithm. With this evaluate function, the proposed method can minimize the vibrational response against the various vibrational forces in any frequency domains. As numerical examples, the proposed method is applied to the design of a rectangular plate and a cylindrical cantilever of CFRP.
The aim of our study is to develop a conventional method to estimate a fatigue life of textile composite based on damage propagation analysis. The textile composite is treated as heterogeneous bodies with anisotropy for fiber bundles and isotropy for matrix, respectively. The stress distribution in unit cell model of textile is estimated by FEM and damage in each element is evaluated. At the same time, material properties of each element under cyclic loading are estimated from fatigue test results carried out for UD composite. The proposed method is applied to the plain woven CFRP and it is confirmed that the proposed method is applicable to estimation of fatigue life of textile composites. Moreover, it is revealed that the fatigue life distributions are also estimated by considering the scatter of fatigue strength of UD composite.
This paper proposes a novel design methodology of graded microstructures of functional composites for the emergence of macroscopic function. Micro-macro correlation is analyzed by the homogenization theory. That is, the homogenized properties such as elastic moduli and coefficients of thermal expansion and thermal conductivity are calculated for arbitrary complex microstructures. Then, the functional composites with graded microstructures can be replaced by a homogenized model. Also because it is impossible to design all of the numerous graded microstructures, a discretized model is adopted. To determine the optimum graded arrangement of the microstructures in the discretized model, the genetic algorithm is adopted in this paper. Next, the design of continuously graded microstructures is completed using a feature-based 3D-CAD system. In addition, a solid model is produced by the stereolithography to help the understanding of the designed complex microstructures. Brief description of the formulation of the homogenization method for heat conduction and thermal stress problems are shown. An example of the design of a plate with graded microstructures in its thickness direction to control the macroscopic temperature distribution, thermal strain distribution and deflection is shown.
A personal computer program of Finite Element Method was developed in the past in order to analyze the stresses in composite materials. Although the mechanical behavior of composite materials can be analyzed by such a developed computer program, the component construction of laminates can not be obtained because it is very difficult to optimize the computational results by using an ordinary F.E.M.. On the other hand, the ratio of layer components can be calculated by the method of optimization, but not the lay-up sequence of laminates.In this paper, the personal computer program of intelligent F.E.M. with a new concept has been developed in order to analyze the component and lay-up sequence of laminates which satisfy the design objects. As an example of analysis, the material for each layer of a laminated panel under bending condition was selected and the thickness of laminae under combined loads of bending and tension was determined. The computational results were very reasonable for the composite structure. Therefore, it was recognized that the proposed intelligent F.E.M. is very useful for the structure design of composite materials.
In recent years active researches have been made of nondestructive testing of Fiberglass Reinforced Plastics (FRP), and the following methods have so far been employed for the purpose.(1) The use of X-Rays(2) The use of Ultrasonic Waves(3) The utilization of Temperature(4) The transmission of Light Waves (Infra-Red Rays)(5) KnockOf these the X-ray and the ultrasonic wave methods have been found as respectively useful, and the light wave method, though its practical application has been but little known, has been found as equipped with the following advantages.(1) That it requires simple apparatuses.(2) That it is of easy procedure.(3) That it permits good transmission.These advantages will recommend the light wave method to recognition as most suitable in our present experiment. That was the way the light wave method was adopted for the nondestructive besting of FRP, and the results of its measurements with respect to its strain, glassfiber direction and the number of layers are reported hereunder.The diffraction patterns that were recorded as they took place under stress were given out as the strain of the FRP. The light wave transmission method has given due to the glassfiber direction in the FRP and to the number of its layers by making the light pass through the material. The light wave transmission method is thus confirmed by these results of the experiment as an effective device for nondestructive testing of FRP.
