Ekrem Tufekci

Istanbul Technical University · Department of Mechanical Engineering

This study evaluates the accuracy and computational demands of Mean Field Homogenisation (MFH) and Finite Element Method-Based Homogenisation (FEMBH) for composites. FEMBH requires generating a Representative Volume Element (RVE) to capture the essential microstructural characteristics. The focus is on nanoparticle-reinforced composites, considerin...

Lattice structures have significant potential in engineering, allowing for material and weight reduction while maintaining desired mechanical properties. This versatility is crucial in applications ranging from aerospace to medical implants, where customisability and efficiency are essential. This study investigates the mechanical performance of fo...

The use of lattice structurses is becoming more common day by day. Limitations such as being expensive and time-consuming have led to a search for new solutions in the industry. In light of these limitations, the widespread use of 3D printing technology methods is evaluated. 3D printing technology has advantages in terms of design flexibility, quic...

This research investigates various damage models for predicting intralaminar failures and interface delamination in ceramic matrix composite (C/C SiC) with cohesive zone modelling (CZM) at the interface of DCB (Double Cantilever Beam). This study utilises the cohesive zone model to forecast the onset and propagation of delamination. In the finite e...

The composite material modelling methods aim to predict the mechanical behaviour and properties of composite materials consisting of two or more different materials, such as fibres and matrices. Using and designing composite materials aims to reach specific mechanical, thermal, and electrical properties that cannot typically be achieved with a sing...

The focus of this study is the experimental assessment of the mechanical behaviour of balsa wood and its sandwich structures, where balsa serves as the core, supported by carbon fibre-epoxy skin layers. A comprehensive characterisation is conducted on the mechanical behaviour of balsa wood and carbon fibre-epoxy balsa core sandwich structures subje...

This article presents the bending behavior of carbon nanotubes (CNTs) based on doublet mechanics (DM) and Euler–Bernoulli beam theory to analyze how deflection changes with higher-order boundary conditions and the coupling, which have not been previously investigated. The governing equations and associated boundary conditions are obtained using the...

Structural identification and health monitoring based on dynamic response has found a great area of application due to its easy application compared to local detection techniques and sensitivity of modal quantities to damage. It has been shown in the literature that the accuracy of the identification procedure depends strongly on the mathematical d...

This study analytically handles the three-dimensional free vibrations of spatial frames using the initial values method, considering the axial and shear deformations alongside rotary inertias, namely, torsional, in-plane bending and out-of-plane bending. To handle the spatial geometry, the direction cosine matrices are used. Validation is performed...

Applications of foam materials are becoming more common in recent years. Especially in the industry, due to their lightweight, tailorable/improvable thermal, electrical and mechanical properties, the need for porous materials/foams is increasing. Thus, research focusing on foams is also accelerated. Hence, this study deals with the theoretical mode...

This study aims to propose a manufacturing procedure for syntactic epoxy foams, in which the volume fraction of the micro balloons can go up to 80%, as well as characterise and numerically investigate their mechanics. The characterisation focuses on the mechanical and thermal properties of the foams. In order to visualise the morphology of the foam...

In this study the static behaviour of two-dimensional (2D) elastic porous materials are investigated by using finite element models. The porous material is modelled using a 2D representative element (RE) which includes two quarter circular holes at diagonal corners and analysed under plane stress assumptions. The REs are prepared with different por...

This study focuses on the dynamic modelling and analysis of the wind turbine blades made of multiple layers of fibre reinforced composites and core materials. For this purpose, a novel three-dimensional analytical straight beam model for blades is formulated. This model assumes that the beam is made of functionally graded material (FGM) and has a v...

This study investigated the failure of the roof, with steel truss construction, of a factory building in Tekirdag in the northwestern part of Turkey. The failure occurred under hefty weather conditions including lightning strikes, heavy rain, and fierce winds. In order to interpret the reason for the failure, the effects of different combinations o...

This study investigates the failure of a roof with steel truss construction of a factory building in Tekirdag in North-western part of Turkey. The failure occurred under hefty weather conditions including thunderbolt, lightning strikes, heavy rain and fierce winds. In order to interpret the reason for the failure, the effects of different combinati...

In this study, forced vibration of a rotating disk is investigated. The disk is clamped at the inner and free at the outer circumferences. A time varying excitation force is applied to a spacefixed point on the disk surface perpendicularly. The presence of multiple excitation forces is also considered in the paper. These forces can be applied to an...

We study natural vibration of elastic parabolic arches, modeled as plane curved beams susceptible to elongation, shear, and bending, exhibiting small concentrated cracks. The crack is simulated by springs between regular chunks, with stiffness evaluated following stress concentration in usual crack opening modes. We evaluate and compare the linear...

This study aims to derive approximate closed-form solutions for critical loads of straight beams with variable cross-section. The governing equations are derived for purely flexible beam for small displacements and rotation and turned into non-dimensional form. Approximate solutions to the set of equations for stability problems are searched by Var...

This study aims to derive a new finite element formulation for in-plane free vibrations of curved beams with arbitrary curvature, and cross-section variation. The stiffness matrix presented in this study are obtained from the exact solution of the static problem, considering the effects of axial extension, shear deformation. Using the exact solutio...

Nanobeams are widely used as a structural element for nanodevices and nanomachines. The development of nanosized machines depends on proper understanding of mechanical behavior of these nanosized beam elements. In this chapter, the static and dynamic behavior of a curved planar nanobeam having variable curvature and cross-section is investigated. T...

Abstract. Dynamic behavior of rotating annular disks is the main focus of this study. Solution of governing differential equations of the system is obtained by Galerkin method that includes proposing an approximate function for displacement that satisfies the boundary conditions. Two displacement functions are selected for the solution and the boun...

Rotating disks are frequently used applications of engineering problems. They are used in rotating machinery, turbines, grinding wheels, gears, hard disk drives etc. The rotation has a significant impact on the mechanical properties of rotating disks so the effects of rotation must be included into calculations in order to make more accurate pre...

With the help of advancing technology, rotating discs which are used in many industrial fields occupy wider application areas that require speed day by day. Vibrations of these discs which are used from informatics to automotive industry are one of the profound topics of engineering discipline. In literature, most of analytical studies about rotat...

In this study, a systematic approach to study small-amplitude vibrations of large deflected straight beams is presented. The differential equation system of small-amplitude free vibrations about the deflected configuration is presented considering the effects of axial extension, shear deformation, and rotatory inertia. It is shown that in the absen...

Rotating annular plates are the major components of a wide range of engineering applications including space structures, automotive parts, and generally rotating machineries such as turbine rotors, industrial fans, circular saws, engine flywheels, gears, rail wheels, grinding wheels, brake systems, and computer hard disk drives. Since the rotation...

In this study, damage identification in planar curved beams is studied. Transfer matrix method is used to obtain the exact solution to the free vibration problems of curved beams. Crack is modelled using the concepts of linear elastic fracture mechanics. Due to the coupling between the axial force and bending moment in curved beams, the transition...

The purpose of this study is to analytically investigate the out-of-plane static behavior of curved nanobeams with non-uniform distributed loads. Nonlocal constitutive equations are implemented into the governing equilibrium equations in cylindrical coordinates. Use of these equations enables revealing the scale effect on static response of curved...

Despite being one of the simplest structural elements, beams are used in many engineering structures. One of the most common methods to analyze and design such structures is the finite element method. Even though many different shape functions for finite beam elements have been offered, still there is a need for a beam formulation that does not suf...

In this paper, a procedure based on the transfer matrix method for obtaining the exact solution to the equations of free vibration of damaged frame structures, considering the effects of axial extension, shear deformation, rotatory inertia, and all compliance components arising due to the presence of a crack, is presented. The crack is modeled by a...

In this study, a new finite element formulation is presented for straight beams with an edge crack, including the effects of shear deformation, and rotatory inertia. The main purpose of the study is to present a more accurate formulation to improve the beam models used in crack detection problems. Stiffness matrix, consistent load vector, and mass...

In this paper, out-of-plane static behavior of circular nanobeams with point loads is investigated. Inclusion of small length scales such as lattice spacing between atoms, surface properties, grain size etc. are considered in the analysis by employing Eringen’s nonlocal elasticity theory in the formulations. The nonlocal equations are arranged in c...

Nanobeams are widely used as a structural element for nanodevices and nanomachines. The development of nano-sized machines depends on proper understanding of mechanical behavior of these nano-sized beam elements. Small length scales such as lattice spacing between atoms, surface properties, grain size etc. are need to be considered when applying an...

This paper presents the derivation of the nonlocal equations for curved beams with varying curvature and cross-section. Eringen’s nonlocal constitutive equations are rewritten in cylindrical coordinates and implemented into the classical beam equations considering the effects of axial extension and the shear deformation. Varying distributed loads a...

Exact analytical solutions of in-plane static problems of circular beams with uniform cross-section made of functionally graded material (FGM) are obtained. Material properties are assumed to be varying arbitrarily through the thickness. Governing differential equations are derived using static equilibrium of an infinitesimal circular beam element...

Advanced lightweight laminated composite shells are increasingly being used in all types of modern structures, for enhancing their structural efficiency and performance. Such thin-walled structures are susceptible to buckling when subjected to various loading. This paper focuses on the buckling of cylindrical shells under axial compression and tors...

The in-plane free vibration of circular arches with continuously varying cross-sections is studied by means of the exact solution. The exact solution can be obtained only for a circular arch with constant cross-section. As an approximation, the circular arch with varying cross-sections is divided into a number of arch elements with constant cross-s...

In-plane free vibrations of circular beams with stepped cross-sections are investigated by using the exact analytical solution. The axial extension, transverse shear deformation and rotatory inertia effects are taken into account. The stepped arch is divided into a number of arches with constant cross-sections. The exact solution of the governing e...

In this study, free in-plane and out-of-plane bending vibrations of frame structures have been analyzed together with torsional vibration. Axial extension, rotational inertia and shear effects have also been considered. The frame structure has been constructed as having two beams with doubly symmetric cross-sections and connected at any angle to ea...

The value of the contact stress between a band saw blade and the driving wheel is modeled using the theory of an elastic Cosserat surface. Specifically, we use nonlinear Cosserat theory to model the bending of an elastic plate into a rotating right circular cylindrical tube with associated end moments. The resulting equations are then linearized, t...

This paper investigates the free in-plane vibration of stepped circular arches. The effects of axial extension, transverse shear deformation and rotatory inertia are included in the governing equations. The solution is obtained exactly by using the initial value method. The solution procedure is also applied to cases in which only one effect is con...

This paper deals with the exact solution of the differential equations for the out-of-plane behavior of an arch with varying curvature and cross section. The differential equations include the shear deformation effect. The cross section of the arch is doubly symmetric. Due to the double symmetry, in-plane and out-of-plane behavior will be uncoupled...

In this study, free out-of-plane vibrations of a circular arch with uniform cross-section are investigated by taking into account the effects of transverse shear and rotatory inertia due to both flexural and torsional vibrations. The governing differential equations for out-of-plane vibration of uniform circular beams are solved exactly by using th...

Exact analytical solutions for in-plane static problems of planar curved beams with variable curvatures and variable cross-sections are derived by using the initial value method. The governing equations include the axial extension and shear deformation effects. The fundamental matrix required by the initial value method is obtained analytically. Th...

Small deformation three-dimensional free vibrations of a circular arch with uniform rectangular cross-section have been investigated by using different theoretical approaches and by experimental verification. Special emphasis has been focused on a numerical formulation which models each element of the arch using the theory of a Cosserat point. Comp...

The main purpose of this study is to investigate the free vibrations of curved beams, both theoretically and experimentally. Three different geometries for the curved beams are considered in the experiments; circular beam with uniform cross-section, parabolic beams with uniform and varying cross-section. The exact solution of in-plane vibration can...

The free out-of-plane vibration of a circular beam with uniform cross-section is investigated. The study takes into account the effects of transverse shear deformation and rotatory inertia. The governing differential equations for the out-of-plane vibrations of uniform circular beams are solved exactly by using the initial value method. The solutio...

The free in-plane vibration of a shallow circular arch with uniform cross-section is investigated by taking into account axial extension, shear deformation and rotatory inertia effects. The exact solution of the governing differential equations is obtained by the initial value method. By employing the same solution procedure, the solutions are also...

Exact solution of free in-plane vibrations of circular arches of uniform cross-section is given by considering axial extension, transverse shear and rotatory inertia effects. In contrast with Kirchhoff's beam theory the restrictions of perpendicular cross-section and inextensible arc length are removed. The principal axes of the cross-section are a...