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    Biosourced polymeric cryogels for future biomedical applications with remarkable antimicrobial activities and tribological properties
    (Elsevier, 2024) Gurel, Cansu Meltem; Bozbeyoglu, Naime Nur; Yardimci, Berna Kavakcioglu; Sarkaya, Koray; Mutlu, Dogukan; Akincioglu, Sitki; Dogan, Nazime Mercan
    Cryogels, known as a subclass of hydrogels, are promising biomaterials to use in various biotechnological fields. In recent years, applications of antimicrobial hydrogels with improved antimicrobial activities, high biocompatibility, and physicochemical stability have attracted attention as an alternative to using antimicrobial drugs against microbial interactions that may threaten human health, which may even result in death. In this paper, we investigated in detail the biological activities and tribological performances of the previously characterized 2hydroxyethyl methacrylate (HEMA)-based amphiphilic cryogels (PHEMA-PLinaOH) (HC series) that contain hydroxylated polymeric linoleic acid (PLinaOH) as biosource. The biocompatibilities of these cryogels were examined against human embriyonic kidney (HEK293) cell line with MTT assay and acridine orange/ethidium bromide (AO/EB) dual staining. The antimicrobial activities of the materials were extensively investigated against Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa PA01 besides four different strains of the yeast Saccharomyces cerevisiae BY4741 by using biofilms eradication, antibiofilm activity and colony forming unit assays. Additionally, the possible morphological changes in microbial cells were evaluated by taking FESEM images. The tribological performances of the cryogels were evaluated in terms of their applicability for future biomedical applications such as artificial articular cartilage or tissue scaffold. Our results showed that while the cryogels did not show significant inhibition on HEK293 cell viability and intensive live cell population was observed after AO/EB staining, they exerted remarkable antimicrobial activities against all studied bacterial and fungal strains. The morphological deformations including the decrease in EPS density and formation of holes were recorded for bacteria and yeast cells with FESEM images, respectively. Finally, it was determined that the increase in the fatty acid ratio contributes positively to tribological properties of the cryogels. All the results indicate that these polymeric cryogels might be considered potential biomaterials for future tissue-engineering studies.
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    Evaluation of the tribological performance of the green hBN nanofluid on the friction characteristics of AISI 316L stainless steel
    (Emerald Group Publishing Ltd, 2021) Akincioglu, Sitki; Sirin, Senol
    Purpose The purpose of this study is to investigate the effect of new green hexagonal boron nitride (hBN) nanofluid on AISI 316L stainless friction coefficient, wear resistance and wear using a ball on disc tester. Design/methodology/approach Nanofluids were prepared by adding hBN nanoparticles with two-step method to the vegetable-based oil at 0.50 vol%. Before the experiments, hBN nanofluid viscosity, pH and thermal conductivity specifications were determined. Friction tests of AISI 316L stainless steel were performed under 2 N, 5 N and 8 N loads at 400 rpm using a ball-on-disc test device under dry, oil and hBN conditions. Coefficient of friction, wear profile, surface integrity and wear mechanisms were chosen as performance criteria. Findings The friction coefficient values obtained under the oil and hBN test conditions with the 8 N load were, respectively, 72.46% and 77.64% lower than those obtained under dry test conditions. hBN nanofluid performed better on surface topography, and especially wear, compared to the dry and oil test conditions. Practical implications The aim of this study was to determine the best tribological performance of the hBN nanofluid on AISI 316L stainless steel used in orthopedic applications. Originality/value The paper is a study investigating the effect of hBN nanoparticle additive in vegetable-based oil on friction and wear performance of AISI 316L stainless steel. It is an original paper and is not published elsewhere.
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    Friction-wear performance in environmentally friendly brake composites: A comparison of two different test methods
    (Wiley, 2021) Akincioglu, Gulsah; Uygur, Ilyas; Akincioglu, Sitki; Oktem, Hasan
    In this study, an eco-friendly brake composite sample (EFP) was produced with 3.5% hazelnut shell dust as a natural additive material. Friction tests were performed on the manufactured pad sample and on a commercial pad (CP) using both a Chase-type test machine and a specially designed device. A different approach is presented with the evaluation of the two different test device results. The experimental results were compared using the Taguchi method and it was concluded that the braking performance of the sample with hazelnut shell dust was in accordance with international standards. As a result of the study; the nominal friction coefficient value was found to be 0.505 mu. The shearing force of the EFP and CP samples was measured at 607.3 and 850.5 N, respectively. The friction coefficient values obtained from the EFP and CP samples were in accordance with the SAE J-661 standard and are in the F letter class.
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    Investigation of effect of abrasive water jet (AWJ) machining parameters on aramid fiber-reinforced polymer (AFRP) composite materials
    (Emerald Group Publishing Ltd, 2021) Akincioglu, Sitki
    Purpose The purpose of this study was to optimize the surface roughness (Ra), delamination damage at the hole entrance (FdT) and at the hole exit (FdB) and kerf angle (K) in the drilling of aramid fiber-reinforced polymer (AFRP) composite material using abrasive water jet (AWJ) machining. Design/methodology/approach The AFRP composite was produced by the vacuum infusion method. The drilling experiments were performed on an AWJ machine using a three-axis computerized numerical control system. Machine processing parameters were determined as water pressure (2,000, 3,000 and 4,000 bar), stand-off distance (2, 4 and 6 mm) and traverse feed rate (150, 250 and 350 mm/min). Optimization of processing parameters in the drilling experiments was carried out according to the Taguchi L27 (33) orthogonal array. In addition, gray relational analysis (GRA) was used to analyze the complex uncertainty affecting the results. Findings Results of the drilling operations demonstrated that water pressure (P) was the most effective parameter, with 65.3%, 65.2%, 49.8% and 52.1% contribution rates for Ra, FdT, FdB and K, respectively. Practical implications Reliable results have been obtained with Taguchi-based GRA while drilling AFRP composite material using AWJ. Significant results have been achieved to increase the hole quality in the drilling of AFRP composite material. Originality/value The new approach is to present more detailed analysis by using Taguchi method and multi-decision Taguchi-based gray relation analysis in AFRP composite material drilling using AWJ. Thus, time and experiment costs are saved.
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    Investigation of the Effect of Deep Cryogenic Process on the Tribological Properties of X153CrMoV12 Mold Steel
    (Springer, 2021) Akincioglu, Sitki
    This study investigated the effect of deep cryogenic treatment (-140 degrees C) on the wear resistance, hardness, wear rate and electrical conductivity of X153CrMoV12 steel. The results showed that with deep cryogenic treatment, the friction coefficient was increased by 64.67% compared to that of traditional heat treatment. In addition, it was observed that fine carbide was formed, the carbide rate increased, and the particles were homogeneously dispersed by the deep cryogenic treatment. The difference in the wear rate of deep cryogenic treatment 2 (Cry-2) and deep cryogenic treatment 1 (Cry-1) sample was 33.6 and 29.6% higher than that of the conventional heat treatment (CHT) sample, respectively. The microhardness value of Cry-2 and Cry-1 sample was 9.9 and 8.3% higher than that of the CHT sample, respectively. With Cry-2, the wear rate was reduced by 50.7% compared to CHT samples.
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    A novel study of hybrid brake pad composites: new formulation, tribological behaviour and characterisation of microstructure
    (Taylor & Francis Ltd, 2021) Oktem, Hasan; Akincioglu, Sitki; Uygur, Ilyas; Akincioglu, Gulsah
    In the production of brake pad composites, a well-designed new composition formulation plays a key role in improving performance. The purpose of this study; was to investigate the effectiveness of a specifically developed formulation under brake-test conditions. The composition of the brake lining consists of 18 powder materials. As the friction adjuster, Petro-coke powder was used instead of Cashew, which is cheaper and more readily available. The wear tests were carried out in a special design test device simulated close to the real environment. The results obtained have been compared with commercial brake pads. The friction coefficient values decrease with increasing disc temperatures. Brake tests showed that as a friction modifier, petro-coke provided a more effective stabilizer for the friction coefficient and improved the specific wear rate. Also the study can be utilized effectively in determining the friction coefficient and the specific wear rate of designed brake composites.
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    Taguchi optimization of surface roughness in the turning of Hastelloy C22 super alloy using cryogenically treated ceramic inserts
    (Sage Publications Ltd, 2020) Akincioglu, Sitki; Gokkaya, Hasan; Akincioglu, Gulsah; Karatas, Meltem A.
    Cryogenic treatment has been used in recent years to improve the performance of cutting tools. This study evaluated the machinability of a nickel-molybdenum-based super alloy using cryogenically treated (-80 celcius and -145 celcius) ceramic inserts under dry turning conditions. Three cutting speeds (350, 400, and 450 m/min), three feed rates (0.1, 0.2, and 0.3 mm/rev), and a 1-mm fixed cutting depth were used in the turning tests. Experiments were conducted using the Taguchi orthogonal array L(27)design. The factors affecting the surface roughness (Ra) were determined via analysis of variance. The effect of cryogenic treatment type (shallow and deep), cutting speed, and feed rate on surface roughness was investigated. Results of the analysis determined that the feed rate was the major parameter that affected surface roughness and that the deep cryogenic treatment was more effective. The regression analysis confirmed that the experimental results and the predicted values were within the 95% confidence interval. The most effective parameter affecting the surface roughness was feed rate at a contribution of 57.9%. The contribution of the cutting tool type to the surface roughness was 28.5%. The results obtained showed that the surface roughness can be optimized for turning the Hastelloy c22 super alloy with the Taguchi method.
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    Wear response of non-asbestos brake pad composites reinforced with walnut shell dust
    (Springer, 2020) Akincioglu, Gulsah; Akincioglu, Sitki; Oktem, Hasan; Uygur, Ilyas
    With automobile numbers continuing to increase, competition among manufacturers of brake pads is also increasing along with the search for additives to serve as alternatives to the materials presently being used. In addition to the cost of the additives used, another important consideration in choosing materials is that they should be safe for the environment and human health. This study investigated the effect on braking performance of brake pads produced using walnut shell powder as a natural additive material. Two different types of brake pad samples were produced using 3.5 (2A) and 7% (2B) walnut shell dust in the contents. A commercial Clio brake tip was used as the reference (CO). The produced brake pads were subjected to thermal conductivity, friction wear, density, hardness and water and oil absorption tests and microstructure analysis. A Chase type device was used for wear friction tests, and the results were obtained according to SAE-J661(Brake Lining Quality Test Procedure) standards. The experimental data were compared with those of the commercial brake pads, and the performances of the natural additive brake pads were evaluated. The addition of walnut shell was shown to be compatible within the composition and exhibited a positive effect on the friction coefficient.