Papers by Author: Mojtaba Sadighi

Abstract: The orientation of fibers in the layers is an important factor that must be obtained in order to predict how well the finished composite product will perform under real-world working conditions. In this research, a five-layer glass-epoxy composite truncated cone structure under buckling load was considered. The simulation of the structure was done utilizing finite element method and was confirmed comparing with the published experimental results. Then the effect of different orientation of fibers on the buckling load was considered. For this, a computer programing was developed to compute the buckling load for different orientations of fibers in each layer. These orientations were produced randomly with the delicacy of 15 degrees. Finally, neural network and genetic algorithm methods were utilized to obtain the optimum orientations of fibers in each layer using the training data obtained from finite element simulation. There are many parameters such as the number of hidden layers, the number of neurons in each hidden layer, the training algorithm, the activation function and so on which must be specified properly in development of a neural network model. The number of hidden layers and number of neurons in each layer was obtained by try and error method. In this study, multilayer back-propagation (BP) neural network with the Levenberg-Marquardt training algorithm (trainlm) was used. Finally, the results showed that the truncated cone with optimum layers withstand considerably more buckling load.

Abstract: This paper presents a vibration analysis of sandwich beams with functionally-graded skins containing edge cracks. Finite Element models of FGM sandwich beams are created with different depths and locations of the edge-cracks, and the first four natural frequencies of the beam are obtained for each crack configuration. The integrity of the data is validated for the FGM skins in comparison to a previously published reference. Finally, an inspection is conducted on the data to show the influences of the location and depth of cracks and material properties on the flexural vibration characteristics of cracked FGM sandwich beams.

Abstract: In this paper, to investigate energy absorption capability of hybrid (metal-composite) square tubes under axial loading, a new theory is proposed based on collapse mode of metal square tubes and considering off-axis strength of each layer of composite. An expression is derived for mean crushing load and folding wave length in terms of mechanical properties and geometrical dimensions of metal tube and composite prepregs wrapped around it. To validate the theoretical model, predicted values for mean crushing load are compared with experimental and numerical results that show reasonably good agreement.

Abstract: New Reddy-type elements based on Reddy’s higher-order theory are used in the analysis of composite sandwich plates with viscoelastic core, which is achieved by considering independent transverse displacements on two faces and linear variations through depth of plate core. In addition, Young modulus, rotational inertia, and kinetic energy of core are considered and core is assumed as 3D elastic structure with the properties of an orthotropic viscoelastic material. To improve the Reddy’s higher-order theory, a rectangular element with four nodes, which each node has seven degrees of freedom, is proposed. Hamilton’s principle has been used to obtain the equations of motion. A finite element code for structural response analysis of the free vibration is developed. The obtained results are compared with existence researches. The influence of material properties, lamination schemes, and fiber angle on natural frequencies of composite plates are investigated.