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Öğe Fatigue crack growth behaviour in ferritic ductile iron with surface crack under reverse bending(ELSEVIER SCIENCE BV, 2007) Akdemir, Ahmet; Tekeli, Mehmet; Ataberk, NecatiIn this paper, fatigue crack growth behaviour of ferritic ductile cast iron containing 3.26%C and 4.18%Si was studied. Materials were produced and reverse bending fatigue test specimens were cut from the casting with the thickness of 24 mm. Process annealing heat treatment was applied to the specimens. Semi-elliptical surface cracks were formed and reverse bending fatigue tests were carried out. Fatigue crack growth rates were determined. Stress intensity factors (Delta K) were obtained by Newman-Raju's equations. Fatigue crack growth material constants (n and c) were determined in Paris-Erdogan's equation. Fractured surfaces of the specimens were examined by using SEM. (C) 2007 Elsevier B.V. All rights reserved.Öğe Friction and wear properties of friction materials containing nano/micro-sized SiO2 particles(EMERALD GROUP PUBLISHING LTD, 2016) Sugozu, Kezban Banu; Daghan, Behcet; Akdemir, Ahmet; Ataberk, NecatiPurpose - Among the components used for a car brake lining, the chemical and structural properties of the abrasives, jointly with the morphology and size of the particles influence the friction parameters and stability of the composite. This paper aims to investigate the effect of nano SiO2 particles in brake pads on friction and wear properties. Design/methodology/approach - In this paper, the effects of SiO2 (Silica) particles of varying size on the friction-wear properties of polymeric friction composites are investigated. Four friction composites were prepared containing (5, 10 Wt.%) micro silica (MS) particles and (5, 10 Wt.%) nano silica (NS) particles. The samples were produced by a conventional procedure for a dry formulation following dry-mixing, pre-forming and hot pressing. Friction and wear characteristics of the specimens against to a disk made of cast iron were studied. Friction coefficient, specific wear rate and hardness of specimens were obtained. Detailed examinations on the worn surface were analyzed using a scanning electron microscope. Findings - The results of test showed that the inclusion of nano silicon carbide (SiC) powder improved the wear performance significantly. Friction coefficient (mu) of NS samples was higher than the MS samples. Micro-SiC showed poor performance and mu. High wear performance was exhibited in materials containing 5 Wt.% NS and 10 Wt.% NS. Originality/value - This paper emphasizes the importance of nano-composites in the automotive industry and helps to industrial firms and academicians working on wear of materials.Öğe Improving electrical and mechanical properties of a conductive nano adhesive(TAYLOR & FRANCIS LTD, 2017) Ekrem, Mursel; Ataberk, Necati; Avci, Ahmet; Akdemir, AhmetIn this experimental study, lap shear strength and electrical conductivity of nanohybrid adhesives containing multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles were investigated. Ag nanoparticles were produced via arc-discharge method in liquid nitrogen. For characterizing the Ag nanoparticles, X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy (SEM) were performed. Tensile lap shear properties were determined in accordance with ASTM D 1002-10 standard. Mechanical and the electrical properties of nanohybrid adhesives were compared with neat epoxy adhesive. The best electrical conductivity of nanohybrid adhesive was obtained for the 1% wt MWCNT-2% wt Ag-contained sample. However, the samples which contain 0.5% wt. MWCNT-0.5% wt. Ag nanoparticles reached the highest lap shear strength. The results showed that Ag nanoparticles enhance the conductivity in the presence of MWCNT. It is concluded that the MWCNT act as conductivity bridges among epoxy adhesive and facilitate the electron transfer. As seen in the tensile test results, the ductility of the adhesive was improved by adding the nanoparticles in to the epoxy resin.Öğe Plastic Zones for a Penny-shaped Crack in a Transversely Isotropic Layer Bonded Between Two Isotropic Half Spaces(GAUTHIER-VILLARS/EDITIONS ELSEVIER, 2002) Uyaner, Mesut; Ataberk, Necati; Avcı, A.In this paper, a problem in an elastic-perfectly plastic dissimilar layered medium is considered. It is assumed that a transversely isotropic layer is sandwiched between two isotropic semi-infinite half spaces, and contains a penny-shaped crack located in its mid-plane. The problem is formulated by using integral transform technique under uniform load and reduced to a singular integral equation. This integral equation is solved numerically by using Gaussian Quadrature Formulae. The plastic zones are evaluated by using the plastic strip model. They are plotted for various penny-shaped crack sizes and transversely isotropic materials. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.Öğe Stress Intensity Factors for a Penny-shaped Crack in a Transversely Isotropic Layer Bonded Between Two Isotropic Half Spaces(Wiley-v C H Verlag Gmbh, 2003) Ataberk, NecatiIn this paper, a problem in an elastic-perfectly plastic dissimilar layered medium is considered. It is assumed that a transversely isotropic layer is sandwiched between two isotropic semi-infinite half spaces, and contains a penny-shaped crack located in its mid-plane. The problem is formulated by using integral transform technique under uniform load and reduced to a singular integral equation. This integral equation is solved numerically by using Gaussian Quadrature Formulae. Stress intensity factors are given for various penny-shaped crack sizes and transversely isotropic materials.Öğe Stress Intensity Factors for a Ring- Shaped Crack in a Transversely Isotropic Thick Layer(2003) Ataberk, Necati; Uyaner, Mesut; Avcı, AhmetThe problem of a ring-shaped crack in an infinitely long thick layer was considered in this study. The problem was formulated for a transversely isotropic material by using integral transform technique under uniform load. Due to the geometry of the configuration, Hankel integral transform technique was chosen and the problem was reduced to a singular integral equation. This integral equation was solved numerically by using Gaussian Quadrature Formulae and the values were evaluated for discrete points. Stress intensity factors were obtained by using these values. They were tabulated for various ring-shaped crack sizes and transversely isotropic materials.Öğe Thermal buckling behavior of cross-ply hybrid composite laminates with inclined crack(ELSEVIER SCI LTD, 2006) Avci, Ahmet; Sahin, Omer Sinan; Ataberk, NecatiThermal buckling analysis of symmetric and antisymmetric cross-ply laminated hybrid composite plates with an inclined crack subjected to a uniform temperature rise are presented in this paper. The first-order shear deformation theory in conjunction with variational energy method is employed in the mathematical formulation. The eight-node Lagrangian finite element technique is used for obtaining the thermal buckling temperatures of hybrid composite laminates. The effects of crack size and lay-up sequences on the thermal buckling temperatures for symmetric and antisymmetric plates are investigated. The results are shown in graphical form for various boundary conditions. (c) 2006 Elsevier Ltd. All rights reserved.Öğe Yüzük şeklinde çatlağı olan enine izotrop bir levhada gerilme şiddet faktörü ve plastik bölgelerin bulunması(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2001-11-02) Ataberk, Necati; Avcı, AhmetBu çalışmada yüzük şeklinde çatlağı olan enine izotrop bir levhada gerilme şiddet faktörü ve plastik bölgelerin büyüklüğü bulunmuştur. Problem analitik olarak çözülmüştür. Bunun için silindirik koordinatlarda Love tipi gerilme fonksiyonu cinsinden gerilmelerin ifade edilmesinden sonra ele alınan problemin geometrisine uygun olarak Hankel dönüşümü uygulanmıştır. Gerilme ve şekil değiştirmelere ait denklemler elde edildikten sonra sınır şartları uygulanarak problem, tekil integral denklemine indirgenmiştir. Bu integral denklemi sayısal olarak çözülerek çatlak uçlarındaki gerilme şiddet faktörü değerleri bulunmuştur. Bulunan gerilme şiddet faktörü değerleri kullanılarak verilen bir yük etkisi altında kalıcı şekil değişimine uğramış bölgelerin büyüklüğü bulunmuştur. Birkaç değişik malzeme için, analitik yöntem ile sayısal çözümleme tekniklerinin bir arada kullanılması sonucunda geliştirilen bir bilgisayar programı aracılığı ile problem çözülmüş ve sonuçlar eklerde sunulmuştur.
