mohammadjavad kazemzadeh-parsi

This paper analyzes the nonlinear dynamic response of truncated conical shells reinforced with carbon nanotubes with functional graded ceramic-metal matrix subjected to harmonic excitation. Carbon nanotubes are distributed with three different patterns along the length and thickness of the conical shell. The matrix material of the shell is considered to be a combination of metal and ceramic, whose properties change as a power function along the thickness of the shell. In order to analyze the dynamic of this system, firstly, the nonlinear dynamic equations of the conical shell are derived based on the first order shear deformation theory and von Karman's strain-displacement relations. Then, with the help of Galerkin discretization method, partial differential equations of the system are converted into time-dependent ordinary differential equations. Adams-Bashforth numerical method is used to solve the system of nonlinear differential equations. Finally, a parametric study is presented to investigate the effects of some parameters of the system, such as the power index, volume fraction and distribution pattern of carbon nanotubes, the geometric characteristics of the shell, and amplitude of the excitation force on the nonlinear dynamic response of the conical shell. In order to validate, the results of this article are compared and presented with the results of previous valid references.

In this paper, the free vibrations of functionally graded porous beams with simple boundary conditions on an elastic foundation in a thermal environment were studied using the theory of third-order shear deformation. The properties of the material are temperature dependent and continuously change in the direction of the thickness of the beam and according to the power law distribution of the volume fraction of the material constituents. The uniform porosity distribution at the cross section is examined. Hamilton's principle was used to obtain the governing equations of motion. In order to discretize these equations, the generalized differential quadrature method has been used. Here, the effect of various parameters such as heat field type, temperature difference, power law index, porosity volume fraction, slenderness ratio and elastic foundation parameters on the natural frequencies of a functionally graded porous beam was studied for simple boundary conditions. The results, in addition to showing these effects on the thermomechanical behavior of the beam, also confirm the accuracy of the numerical method used.

Bolt connections often loosen under environmental loading conditions and system vibrations, which can lead to disaster risks during its operation. In this study, the behavior of nonlinear vibrations of an aluminum single-lap joint has been studied analytically and experimentally. Accordingly, considering the effects of nonlinear behavior at the bole joint, a nonlinear two-degree of freedom model for this type of connection is proposed. Then, in order to determine the unknown parameters of the proposed model, the vibrational and dynamic properties of this structure have been estimated using experimental modal analysis and model updating method. Finally, the effect of amplitude of the excitation force and the preload force of the bolts on the dynamic behavior of these systems has been studied analytically. Examination of amplitude-frequency curves shows that reducing the preload force of the bolts reduces the natural frequency and also distorts the amplitude-frequency curve to the left side, which indicates the softening nonlinear behavior of the system with decreasing applied bolt preload force. In addition, the comparison of the theoretical and experimental natural frequencies shows that the proposed model predicts the vibrational characteristics of these systems with a good accuracy and using the proposed model can study the dynamic behavior of these systems for different parameters.

In this paper, Frequency analysis of cracked porous functionally graded beams which are resting on elastic foundation based on reddy third order shear deformation theory is studied. Mechanical property gradients defined in accordance with model of exponential law. Governing equations obtained with the aid of third order shear deformation theory and by considering elastic foundation effects within hamilton’s principle. Due to complicating closed form solution of equations, differential equations solved utilizing Generalized Differential Quadrature Method by considering various end conditions. In order to validate the results, comparisons are made with solutions which are available for other papers. This study shows that the difference between the results of this paper and the results of others is negligible. Finally the effects of geometrical parameters, exponential law indexes, crack location and depth, elastic foundation and porosity on natural frequencies of functionally graded beams are studied. The results of this paper and effects of these parameters can be used in the optimum design of functional graded beams and crack prediction, detection and monitoring techniques.

In the deep drawing process, the optimal design of the initial blank shape has many advantages such as reducing the cost of production and waste and improving the quality of the process and thickness distribution. The deep drawing process is highly nonlinear due to the large deformation, plastic deformation of the material and the contact phenomenon. Therefore, the general solution to such problems is to use iterative methods based on numerical simulation. The present study implements a similar approach and presents a new algorithm to make geometrical corrections to the external boundaries of a blank, as well as its internal boundaries, in several iterations. A computer program was developed to automatically run these iterations to study the features of the proposed algorithm. Next, an example problem was solved, and the results are compared with other studies. The results showed that the proposed algorithm is sufficiently robust against the initial guesses for the blank, which is an advantage of the present algorithm over those from other algorithms. Because in other algorithms presented in the articles, if the appropriate initial guess is not selected, the algorithm will not converge to the answer. The proposed algorithm also has a higher convergence speed in achieving optimal blank.

Deep drawing is a popular process in sheet metal forming. The goal of shape optimization of the initial blank which is considered in the present work is to find the shape of the blank in a manner in which after a deep drawing process the contour of the edges of the produced part meets a target contour.  Such problems are highly nonlinear because the simulation consists of large deformation, plastic deformation, and contact.  Therefore, the general approach to solving such problems is using iterative methods which are based on numerical simulation.  Such an approach is also followed in the present work and a new algorithm for geometry modification of initial blank in each iteration is proposed.  In the proposed algorithm, the normal distance between the final contour and target contour is used as a criterion to modify the initial blank.  To evaluate the proposed algorithm a computer program is developed and to automatically execute the iterative process.  One numerical example solved and the results are compared with those reported in the literature.  One of the benefits of the proposed algorithm is its insensitivity to the initial guess.  Therefore, to evaluate the effect of the initial guess on its performance the example was solved using different initial guesses. The results show that the proposed algorithm is robust regarding the initial guess and convergence to the optimum shape will be achieved by starting from an initial guess.

Today, metal forming is considered one of the essential methods of manufacturing and producing parts. Therefore, the more accurate knowledge of it leads the industrialists to produce higher quality parts. Deep drawing is one of the most important methods in metal forming processes used to produce cup-shaped products. In this paper, numerical simulation of the deep drawing process based on the finite element method is performed using Abaqus software for a cylindrical cup. Then, the results obtained from numerical simulation are compared with the experimental results in the sources, and the validation of the simulation is performed. In the deep drawing process, effective parameters such as circumferential strain distribution, thickness strain distribution, and radial force distribution are extracted from numerical simulations and compared with experimental results in the sources. The effect of friction coefficient, blank holder force, and punch radius on the deep drawing process has also been investigated. Because experimental methods based on trial and error are time-consuming and costly to achieve the shape of the primary blank, researchers use numerical methods to simulate and design metal sheet forming processes such as deep drawing. It is necessary to compare the results with experimental works to validate the simulations performed by numerical methods.

In the standard finite element method, the edges of the adjacent elements are aligned to each other, and the corner of an element does not located on the edges of another one. If this constraint is violated it is said that the mesh is non-conforming and the use of such meshes in the finite element method requires specific techniques. In the present paper, a new method is suggested for the use of non-conforming meshes which are generated using quadtree algorithm. Quadtree is a data structure that has a very fast recursive algorithm and can be used to divide a two-dimensional domain into sub-regions or elements. The elements produced by this method are non-conforming and are not usable in the standard finite element method. In general, six types of elements with different arrangement of nodes may be appeared in a quadtree mesh and the conventional methods which are using the polynomials cannot be used to derive the shape functions. In the present paper, a new idea is proposed to obtain the shape functions of such elements. In this method, a boundary value problem is defined and its solution is used as the shape functions of the non-conforming elements. To evaluate the applicability and accuracy of the proposed method, two numerical examples are solved and the results are presented. The results show that the proposed method can be used to effectively apply the non-conforming meshes in the finite element method.