Öner, Erdal

This paper presents a semi-analytical method to investigate the frictionless contact mechanics between a\rfunctionally graded material (FGM) coating and an orthotropic substrate when the system is indented by a\rrigid flat punch. From the bottom, the orthotropic substrate is completely bonded to the rigid foundation. The\rbody force of the orthotropic substrate is ignored in the solution, while the body force of the FGM coating is\rconsidered. An exponential function is used to define the smooth variation of the shear modulus and density\rof the FGM coating, and the variation of Poisson’s ratio is assumed to be negligible. The partial differential\requation system for the FGM coating and the orthotropic substrate is solved analytically through Fourier\rtransformations. After applying boundary and interface continuity conditions to the mixed boundary value\rproblem, the contact problem is reduced to a singular integral equation. The Gauss–Chebyshev integration\rmethod is then used to convert the singular integral equation into a system of linear equations, which are\rsolved using an appropriate iterative algorithm to calculate the contact stress under the rigid flat punch. The\rparametric analyses presented here demonstrate the effects of normalized punch length, material\rinhomogeneity, dimensionless press force, and orthotropic material type on contact stresses at interfaces,\rcritical load factor, and initial separation distance between FGM coating and orthotropic substrate. The\rdeveloped solution procedures are verified through the comparisons made to the results available in the\rliterature. The solution methodology and numerical results presented in this paper can provide some useful\rguidelines for improving the design of multibody indentation systems using FGMs and anisotropic materials.

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Ates, Sevket; Ergün, Mustafa

The aim in this study is to numerically present some characteristic features of the rectangular finite elementusing the matrix displacement method and to show the utility of this element in plane stress problemscompared to the finite element method. The paper consisted of three parts. In the first part, all of the finiteelement formulation steps from choosing the convenient coordinate system to creating element stiffnessmatrix are presented respectively. In the second part of the study, a static finite element analysis of the shearwall is also made by ANSYS Mechanical APDL. In the final part, the results (displacements, strains andstresses) obtained from the previous parts are compared with each other by the help of tables and graphics.The results show that this method is effective and preferable for the stress analysis of shell structures. Furtherstudies should be conducted in order to indicate the efficiency of the matrix displacement method for thesolution of different types of plane stress problems using different finite elements.

İncele

Altunışık, Ahmet Can; Ergün, Mustafa; Doğan, Umut Ufuk

In this study, it is aimed to be searched the effect of the rebar on the structural behavior of reinforced concretebridges formed with the finite element method. For this purpose, the numerical model of the bridge withknown dimensions, material properties and rebar configuration was modeled using ANSYS finite elementanalysis program. In the first model, it was thought that the bridge was constructed using only concrete, rebarwas not taken into consideration. Then the same bridge was modelled without changing the boundaryconditions as if it was built by reinforced concrete material in which rebar and concrete were together andthe modal analyses were carried out on this model again. The dynamic characteristics of the two differentbridge models were determined using numerical methods and the effect of the rebar on these characteristicswas presented by comparing them with each other. When the results obtained were examined, it was foundthat the rebar had no significant effect on the modal behavior of the bridge. Thus, not taking into account therebar will provide a great convenience during the modeling stage. In addition, linear and nonlinear dynamicanalyzes were performed on the reinforced and unreinforced finite element models of the bridge using theeffective earthquake acceleration record of the Erzincan earthquake of 1992 and structural behavior wasevaluated. The results are presented in comparison with the graphs and tables in this paper.

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