Irfan Kaymaz

Deposition and Adhesion Characterization of Ti(BN:MoS2) Based Composite Thin Films Prepared by Closed-Field Unbalanced Magnetron Sputtering

Composite structured solid thin films were deposited on 52100 tool steel by co-sputtering from BN, TiB2, MoS2 and Ti targets using a closed-field unbalanced magnetron sputtering process (CFUBMS). The structural and mechanical properties of the composite structured coatings were investigated. The composition and morphology of the films were investigated using X-ray diffraction and scanning electron microscopy (SEM). The adhesion properties of the films were characterized by the use of a Revetest-scratch tester. The adhesion test results indicated that bias voltage was the most effective coating parameter related to the critical load.

CHARACTERIZATION OF TiB2 COATING ADHERENCE BY A MULTI-PASS SCRATCH TESTING

TiB2 films deposited using various deposition techniques are used to increase the wear lifetime of industrial components. The performance of TiB2 films is dependent on the coating–substrate adhesion. In this study, the fatigue behavior of TiB2 films was investigated using the multi-mode scratch method. Films of TiB2 were deposited on silicon wafers and AISI M2 steel substrates at different frequencies by pulsed-dc closed field unbalanced magnetron sputtering (CFUBMS). The microstructures of the films were investigated using SEM techniques, and the hardness was measured using a microhardness tester. A multi-mode operation was used for sliding-fatigue, like multi-pass scratching in the same track at different fractions of critical load (bidirectional sliding) and a standard mode using progressive load operation. It was observed that the films deposited at low frequencies had higher adhesion strength and microhardness, and a denser microstructure.

Numerical investigation of mechanical effects caused by various fixation positions on a new radius intramedullary nail

Fracture of the radius diaphysis is an unusual injury in adults. Open reduction and plate osteosynthesis has been recommended by most of the authors. However, this trend has started to change with the recent introduction of newly designed interlocking intramedullary (IM) nails. New generation of IM nails are developed in order to utilise the advantages of IM nails against plates. Because of its anatomical structure, the radius bone has a complex geometry. Therefore, the callus structure, which forms during the healing period, should not be affected from external effects, such as excessive loads or motion. In this study, effects of radial styloid process (RSP), dorsal side and ulnar notch edge fixations of a new design radius IM nail on the healing period were numerically investigated. A three-dimensional solid model of radius was obtained from computed tomography images of a volunteer and callus structure model, was placed accordingly and different fixations of implants were performed. The models were analysed under axial loads transferring from the wrist to the radius bone using finite element method. As a result of the analysis, fixation of IM nail from RSP was found to be beneficial on healing period in terms of both callus motion and emerging stresses.

An Analysis of Mandibular Symphyseal Graft Sufficiency for Alveolar Cleft Bone Grafting

Abstract The purpose of this study was to evaluate the sufficiency of the mandibular symphysis as a donor site for unilateral and bilateral alveolar grafting, measuring both the alveolar cleft volume and maximum bone graft volume that can be harvested from the mandibular symphysis using 3-dimensional computed tomography (CT) and software in children and adults. Computed tomography data obtained from 20 unilateral and bilateral cleft lip palates patients in the preoperative period were used in this study. The patients were divided into 2 groups: children (female, n = 5; male, n = 5) and adults (female, n = 5; male, n = 5). The required bone graft volume for grafting and the maximum bone graft volume that can be harvested from the mandibular symphysis were measured based on cone beam CT data and software. The average required bone graft volume (cleft volume) for unilateral alveolar grafting was 963.51 ± 172.31 mm3 in the children and 1001.21 ± 268.16 mm3 in the adults. The average required bone graft volume for bilateral alveolar grafting was 1457.82 ± 148.18 mm3 in the children and 2189.59 ± 600.97 mm3 in the adults. The average the mandibular symphysis bone graft volume was 819.29 ± 330.85 mm3 in the children and 2164.9 ± 1095.86 mm3 in the adults. The results demonstrated that the mandibular symphysis region provided an adequate bone volume for alveolar grafting in adults with unilateral alveolar clefts. However, it is difficult to standardize these results, due to cleft volume and graft volume that could be harvested from the mandibular symphysis are highly variable among individuals.

The Effect of Residual Stresses Induced by Prestraining on Fatigue Life of Notched Specimens

The effect of tensile prestraining-induced residual stress on the fatigue life of notched steel parts was investigated. The study was performed on AISI 4140 steel. Rotating bending fatigue tests were carried out on semicircular notched specimens with different notch radii in the as-quenched and tempered conditions. Metallography of the specimens was performed by means of light optical microscopy. The finite-element method was used to evaluate the residual stress distribution near the notch region. Fatigue tests revealed fatigue life improvement for notched specimens, which changes depending on the notch radii and applied stress. Scanning electron microscopy was used to examine the fracture surfaces of the specimens.

Corrosion behavior of 90%Cu-10%Ni alloy at different rotation speeds

In this study, the corrosion behavior of 90%Cu-10%Ni (C70600) cupronickel alloy in artificial seawater was investigated. The corrosion tests were conducted using a rotating cylindrical electrode at different speeds. In the experiments, free corrosion potential tests, electrochemical impedance spectrum (EIS) analysis, weight loss tests, and optic microscope observation were performed. The corrosion rate of 90%Cu-10%Ni alloy in artificial seawater increased with increasing rotation speed and time. Damage period was changed with rotation speed. It was also determined that the damage to the protective film began after 3 hours at the rotation speed of 1600 rpm, and after 3 hours at 2000 rpm, and increased with increasing time. It was determined that 1200 rpm rotation speed is better than both 1200 rpm and 1600 rpm for working conditions.

A New Design for Maximum Conformity of Total Knee Prosthesis to Femur and Tibia

Total knee arthroplasty (TKA) is a common procedure for treating patients with excessively arthritic knees. Nonetheless, early failure of TKA may occur in the first 5 yr, and up to 20% of TKA procedures can fail after 20 yr. In this study, a new anatomic prosthesis was designed to provide maximum conformity to knee bones and produce less stress and strain, in an effort to avoid possible failure of the prosthesis. Anatomical and conventional knee models were compared on the basis of both geometric conformity and stress and strain results obtained from finite element analysis. To compare geometric conformity, anatomic prosthesis components were manufactured by laser melting, and conventional prosthesis components were fixed to sawbone knee models. The anatomical model yielded up to 50% less contact pressure at the insert, which may indicate potential for reduced wear between insert and femur components. This model also resulted in less principal strain value at the tibial component, considered to be an important parameter to indicate loosening. The anatomical model with a new femur component in the anterior cortex design also yielded less stress at the femoral cortex, when compared to the conventional model. The findings in this study suggest that the anatomic prosthesis model may be a better design alternative to conventional knee prostheses in terms of wear, aseptic loosening, and normal joint biomechanics.

Failure analysis of the cement mantle in total hip arthroplasty with an efficient probabilistic method

Accurate prediction of long-term behaviour of cemented hip implants is very important not only for patient comfort but also for elimination of any revision operation due to failure of implants. Therefore, a more realistic computer model was generated and then used for both deterministic and probabilistic analyses of the hip implant in this study. The deterministic failure analysis was carried out for the most common failure states of the cement mantle. On the other hand, most of the design parameters of the cemented hip are inherently uncertain quantities. Therefore, the probabilistic failure analysis was also carried out considering the fatigue failure of the cement mantle since it is the most critical failure state. However, the probabilistic analysis generally requires large amount of time; thus, a response surface method proposed in this study was used to reduce the computation time for the analysis of the cemented hip implant. The results demonstrate that using an efficient probabilistic approach can significantly reduce the computation time for the failure probability of the cement from several hours to minutes. The results also show that even the deterministic failure analyses do not indicate any failure of the cement mantle with high safety factors, the probabilistic analysis predicts the failure probability of the cement mantle as 8%, which must be considered during the evaluation of the success of the cemented hip implants.

Çift Katmanlı Kemik Modeli İle Diz Protezi Dizilimi Eldesi Ve Sonlu Elemanlar Analizi İle Değerlendirilmesi

Basarili protez tasarimlari, vucudun gercek anatomisine en yakin kemik modeli ile elde edilebilir. Bu amacla, tasarimlarin dogrulugunu artirmak icin kisiye ozel protez tasarimlarinda kortikal ve trabekukler kemik katmanlari dikkate alan modeller kullanilmalidir. Bu calismada 65 yasindaki bir hastanin diz eklemine ait bilgisayarli tomografi (BT) goruntuleri ile kemik yapisinin uc boyutlu (3B) modeli literaturde bulunan pek cok calismadan farkli olarak kortikal ve trabekuler kemik katmanlari dikkate alinarak modellenmistir. Metal protez bilesenleri ile kemigin fiksasyonu icin kemik cimentosu kullanilarak diz protezi dizilim modeli elde edilmistir. Sonlu elemanlar yontemi ile dize en fazla yuk geldigi 45° acida normal kuvvetler etki ettirilerek analizler gerceklestirilmistir. Calisma sonucunda anatomiye en yakin kemik modeli icin elde edilen bulgular degerlendirilmistir.

Fatigue behavior of X40CrMoV 51 at high temperatures

The fatigue characteristics of the hot work tool steel X40CrMoV 51 (UNS number T20811) at high temperatures is presented. The temperatures for the experiments were chosen between 50–600 °C. The experiments used B-type cylindrical specimens machined from X40CrMoV in an R.R. Moore rotating bending type fatigue test machine obeying the high cycle principle. The temperature intervals for the experiments were chosen as 50, 100, 200, 300, 400, 500, and 600 °C, for which the fatigue limit for each interval at 2 × 106 cycles was determined. The fatigue limit of the material at room temperature (RT) is observed as 432 MPa, whereas it drops to 383 MPa at 400 °C. On the other hand, it stays almost constant between 400–600 °C, indicating that the material includes the elements forming strong carbides such as V, Mo, and Cr, which prevent the decrease of the fatigue limit due to higher temperatures.