Yazar "Adiyaman, Gokhan" seçeneğine göre listele

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    ANALYSIS OF A LONG STRIP CONTAINING AN INTERNAL OR EDGE CRACK USING FEM
    (Yildiz Technical Univ, 2016) Yaylaci, Murat; Birinci, Ahmet; Adiyaman, Gokhan; Oner, Erdal
    This paper presents the elastostatic plane problem of a long strip containing an internal or edge crack perpendicular to its boundaries. The plane problem consists of an infinitely long strip of thickness h. The infinitely long strip is loaded by uniformly distributed load and rests on two simple supports. It is assumed that the effect of gravity is neglected. The finite element model of the problem is constituted using ANSYS software and the two dimensional analysis of the problem is carried out. Normalized stress-intensity factors for the cases with internal and edge crack, and normal stress (sigma(x)) for uncracked layer case are obtained for various dimensionless quantities. Finally, the results obtained from the finite element analysis are verified by comparing with analytical ones and it is seen that the results from finite element analysis indicate a good agreement with the analytical solution.
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    Analyzing of continuous and discontinuous contact problems of a functionally graded layer: theory of elasticity and finite element method
    (Taylor & Francis Inc, 2024) Yaylaci, Murat; Oner, Erdal; Adiyaman, Gokhan; Ozturk, Sevval; Yaylaci, Ecren Uzun; Birinci, Ahmet
    Contact mechanics analysis is crucial because such problems often arise in engineering practice. When examining contact mechanics, the material property of the contacting components is a crucially significant aspect. It is more complex to solve the contact mechanics of systems that are composed of materials that do not have a homogenous structure compared to materials that have homogeneous qualities throughout. While many studies on contact problems with homogeneous materials exist, those involving non-homogeneous materials are scarce in the literature. As material technology improves fast, there will be a greater need to solve such problems. In this respect, analytical and finite element method (FEM) solutions of the continuous and discontinuous contact problems of a functionally graded (FG) layer are carried out in this article. The FG layer in the problem rests on a rigid foundation and is pressed with a rigid punch. From the solutions, the contact length, contact stress, initial separation distance, and beginning and ending points of separation were determined, and the results were compared. It has been concluded that the FEM findings are consistent with the analytical results to a satisfactory degree. This study analyzes contact problem using different approaches and accounts for the influence of body force in a contact geometry that has yet to be reported.
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    Assessment of different solution methods for receding contact problems in functionally graded layered mediums
    (Elsevier, 2021) Yaylaci, Murat; Eyuboglu, Aysegul; Adiyaman, Gokhan; Yaylaci, Ecren Uzun; Oner, Erdal; Birinci, Ahmet
    This paper presents a comparative study of different methods, such as the analytical method, finite element method (FEM), and multilayer perceptron (MLP) for analyzing a frictionless receding contact problem. The problem consists of two layers resting on a Winkler foundation. The top layer is functionally graded (FG) along the depth and pressed using a rigid cylindrical stamp, whereas the bottom layer is homogeneous. We assumed that the contact between the two layers, and that between the FG layer and the rigid cylindrical stamp are frictionless; additionally, compressive normal tractions can be transmitted through the interface. First, the problem was solved analytically using the theory of elasticity and integral transform techniques. Second, the finite element solution of the problem was obtained using ANSYS software. Finally, the problem was extended based on the MLP, which an artificial neural network used for different problem parameters. The results of this study showed that the variations in the contact lengths at the interface between the rigid cylindrical stamp and the FG layer, those between the homogeneous layer and the FG layer, and the maximum contact pressures at these interfaces depended on various dimensionless quantities such as the stamp radius, stiffness parameter, shear modulus ratio, and elastic spring constant ratio. We observed that the results obtained with the three different methods, namely the analytical method, FEM, and MLP, are extremely compatible with each other, thus proving the accuracy of these results.
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    The contact problem of a functionally graded layer under the effect of gravity
    (Wiley-V C H Verlag Gmbh, 2023) Adiyaman, Gokhan; Oner, Erdal; Yaylaci, Murat; Birinci, Ahmet
    This paper considers the continuous and discontinuous contact problems of a functionally graded (FG) layer under the effect of gravity. A finite distributed load is applied to the beam from the top and the beam is placed to the top of a rigid foundation. It is assumed that the shear modulus and mass density of the beam vary exponentially whereas Poisson's ratio remains constant. The problem is solved for both continuous and discontinuous cases. In each case, the governing equations and boundary conditions of the problem are reduced to an integral equation by the help of Fourier integral transform. In the continuous contact, the integral equation solved analytically and critical load that causes initial separation between the layer and the rigid foundation, separation distance and contact pressures are investigated for various non-homogeneity parameters that presents the change in the shear modulus and density and loadings. The singular integral equation in case of discontinuous contact is numerically solved by using corresponding Gauss-Chebyshev quadrature and an iterative scheme. The effect of non-homogeneity parameters and loading on the separation distance between the layer and the foundation and contact pressures are analyzed. All the results are shown in tables and figures. It is seen that increasing stiffness and decreasing density at the top of the layer reduce maximum pressures but increase separation distances. This study aims to fill the deficiency in the mechanical behavior of the coatings under gravity.
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    Free Vibration and Buckling Analysis of Porous Two-Directional Functionally Graded Beams Using a Higher-Order Finite Element Model
    (Springer Heidelberg, 2024) Turan, Muhittin; Adiyaman, Gokhan
    A new type of functionally graded material (FGM) with material properties varying in two or three directions is needed to obtain materials with better mechanical properties and high-temperature resistance for use in the military, aerospace, automotive, and engineering structures. Considering the porosity that occurs during the production of these materials, it has become necessary to examine the free vibration and buckling behaviors. Therefore, this study investigated free vibration and buckling analysis of porous two-directional functionally graded (2D FG) beams subject to various boundary conditions. A high-order finite element based on parabolic shear deformation theory (PSDT) is proposed to solve this problem. Three types of porosity distributions were used in the study (FGP-1, FGP-2, and FGP-3). The governing equations are derived from Lagrange's principle. The material change in the beam volume in both directions is defined by a power-law rule. The dimensionless fundamental frequencies and critical buckling loads are obtained for various boundary conditions, gradation exponents (p(x), p(z)), porosity coefficient (e), porosity distribution, and slenderness (L/h). The numerical results obtained with the proposed higher-order finite element are compatible with the literature.
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    THE GENERAL SOLUTION OF A LAYERED MEDIUM RESTING ON A RIGID FOUNDATION
    (Yildiz Technical Univ, 2018) Adiyaman, Gokhan; Oner, Erdal; Birinci, Ahmet
    In this study, the general solution of a receding contact problem of layered medium resting on rigid foundation is considered. The layered medium consists of N homogeneous layer with varying material properties and heights. The contact surfaces can be receding or attached. The problem may include M receding contact surfaces. The layered medium is loaded with n concentrated loads transmitted by circular stamps and r distributed loads. The problem is reduced to integral equation system using elasticity theory and Fourier integral transform. The numerical solution of the system is done by using Matlab. A program is written to solve the problem given by the user with any geometry and loading. The program is tested with two studies from the literature and it was shown that the results are compatible.
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    Investigation of continuous and discontinuous contact cases in the contact mechanics of graded materials using analytical method and FEM
    (Techno-Press, 2021) Yaylaci, Murat; Adiyaman, Gokhan; Oner, Erdal; Birinci, Ahmet
    The aim of this paper was to examine the continuous and discontinuous contact problems between the functionally graded (FG) layer pressed with a uniformly distributed load and homogeneous half plane using an analytical method and FEM. The FG layer is made of non-homogeneous material with an isotropic stress-strain law with exponentially varying properties. It is assumed that the contact at the FG layer-half plane interface is frictionless, and only the normal tractions can be transmitted along the contacted regions. The body force of the FG layer is considered in the study. The FG layer was positioned on the homogeneous half plane without any bonds. Thus, if the external load was smaller than a certain critical value, the contact between the FG layer and half plane would be continuous. However, when the external load exceeded the critical value, there was a separation between the FG layer and half plane on the finite region, as discontinuous contact. Therefore, there have been some steps taken in this study. Firstly, an analytical solution for continuous and discontinuous contact cases of the problem has been realized using the theory of elasticity and Fourier integral transform techniques. Then, the problem modeled and two-dimensional analysis was carried out by using ANSYS package program based on FEM. Numerical results for initial separation distance and contact stress distributions between the FG layer and homogeneous half plane for continuous contact case; the start and end points of separation and contact stress distributions between the FG layer and homogeneous half plane for discontinuous contact case were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio and load factor for both methods. The results obtained using FEM were compared with the results found using analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.
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    A New Higher-Order Finite Element for Static Analysis of Two-Directional Functionally Graded Porous Beams
    (Springer Heidelberg, 2023) Turan, Muhittin; Adiyaman, Gokhan
    A new higher-order finite element for the static analysis of two-directional functionally graded (2D FG) porous beams subjected to various boundary conditions based on parabolic shear deformation theory (PSDT) is presented. The main purpose of this study is to predict the deflections and stresses of 2D FG porous and non-porous beams with the help of the proposed finite element. Since a higher-order finite element with a third order polynomial is used, the deflections and stresses can be accurately and rapidly obtained even for short beams. In addition, the new higher-order element is free of shear locking phenomenon without requiring any shear correction factors. Three types of distribution functions were used for porosity in this study. To the author's knowledge, the sinusoidal uneven distribution function (FGP-3) is presented for the first time. The governing equations are derived by Lagrange's principle using a parabolic shear deformation theory that considers normal and shear deformations. According to a power-law rule, the material change in the beam volume in both directions is defined. The dimensionless maximum transverse deflections, normal stresses, and shear stresses are obtained for various boundary conditions, gradation exponents (p(x), p(z)) in the x- and z-directions, porosity coefficient (e), porosity distribution (FGP-1, FGP-2, FGP-3), and the slenderness (L/h). This study's new higher-order finite element gives results compatible with the literature and it can be used to accurately find the deflections and stresses for the 2D FG non-porous or porous beams subjected to various boundary conditions.
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    On the plane receding contact between two functionally graded layers using computational, finite element and artificial neural network methods
    (Wiley-V C H Verlag Gmbh, 2022) Oner, Erdal; Sengul Sabano, Bahar; Uzun Yaylaci, Ecren; Adiyaman, Gokhan; Yaylaci, Murat; Birinci, Ahmet
    The frictionless double receding contact problem for two functionally graded (FG) layers pressed by a uniformly distributed load is addressed in this paper. The gradation in the layers is assumed to follow an exponential variation through the height with constant Poisson's ratios. The lower layer rests on a homogeneous half-plane (HP). There is no adhesion between the FG layers or between the lower layer and the HP. The body forces of the FG layers and HP are ignored. First, the governing equations are reduced to a system of two singular integral equations with contact pressures and contact lengths as unknowns using Fourier transform techniques and boundary conditions. The integral equations are solved numerically using the Gauss-Chebyshev integration formula. Then, a parametric finite element analysis is performed using the augmented contact method. Finally, the problem was extended based on the multilayer perceptron (MLP), an artificial neural network used for different problem parameters. The effects of stiffness parameters, the normalized load length, the ratio of shear moduli, the ratio of FG layer heights to the normalized contact lengths, and normalized maximum contact pressures are explored. The results of finite element analysis and the MLP approach are used to validate the normalized maximum contact pressures and contact lengths obtained from an analytical method based on elasticity theory, and finally, good agreement between these three methods results is obtained. The obtained results could help in designing multibody indentation systems with FGMs.
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    A STUDY ON THE CONTACT PROBLEM OF A LAYER CONSISTING OF FUNCTIONALLY GRADED MATERIAL (FGM) IN THE PRESENCE OF BODY FORCE
    (Mathematical Science Publ, 2023) Adiyaman, Gokhan; Oner, Erdal; Yaylaci, Murat; Birinci, Ahmet
    One of the most important components of the early design process for layered systems is gaining a knowledge of the behavior of materials under varied contact situations. Functionally graded materials (FGMs) have grown in popularity in layered systems as a result of their numerous benefits, such as permitting the reduction of local stress concentrations and thermal stresses often experienced in traditional composites. This paper suggests an analytical approach to solving the continuous and discontinuous contact problems of a functionally graded (FG) layer subjected to a distributed load. Elasticity theory and integral transform methods provide the basis of the aforementioned analytical approach. The FG layer rests on a half-plane that is homogeneous, and there is no adhesion or bonding at the contact surface. For this problem, we assume an exponentially varying shear modulus and mass density in the FG layer. In the solution, the body force of the FG layer is considered. The problem is solved analytically by applying boundary conditions for both continuous and discontinuous contact cases. The presented results show the effects of load factor, amplitude of distributed load, inhomogeneity parameters, and interface material property mismatch on contact stress distributions, initial separation load (critical load), initial separation distance, starting and end point of separation, and separation interval.