Browsing by Author "Varol, R"

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    The effect of surface hardening treatments on the mechanical properties of iron based P/M specimens
    Yilmaz, SS; Varol, R
    In this study, boronizing and/or shot peening surface treatments were applied individually or in combination to the P/M steel specimens. The composition of specimens was 3% Cu + 0.2% C + balance Fe%. Tensile strength, hardness values and surface properties of treated specimens were determined. Boronizing + shot peening surface treatment was found to be the most convenient surface treatment for P/M steel materials based on test results. However, it is important to avoid high peening intensities for shot peening of boronized surfaces because shot peening deteriorates the boronized surface of P/M steel specimens. As a result. surface hardness values such as 1800-2500 HV were achieved after boronizing, the difference between the matrix materials with a hardness of 200 HV was quite high. (c) 2010 Elsevier B.V. All rights reserved.
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    Evaluation of female athlete triad and gynecological complaints in young Turkish female athletes
    Hasdemir, PS; Oral, O; Calik, E; Ulusoy, M; Varol, R; Ozcakir, HT
    Purpose: Female athlete triad (FAT) is a serious healthcare concern in the young female population. The aim of this study was to determine the prevalence and clinical characteristics of FAT and its relationship with gynecologic complaints of young Turkish female athletes. Materials and Methods: This was a cross-sectional survey and included 87 female athletes involved in a variety of sports as a case group and 85 sedentary female university students from Ege and Celal Bayar Universities. All subjects completed a questionnaire consisting of 32 separate questions assessing eating behavior, menstrual status, gynecologic and systemic complaints, psychological problems, and sexual history. SPSS 21.0 was used for statistical analysis. Results: This survey involved 172 females in between to 30 years of age. The age of menarche was found to be significantly lower in the sedentary group (p = 0.00). Late menstruation and oligo-amenorrhea were notable complaints among the athletes, and body mass index (BMI) was found to be statistically lower in the athletic group (p = 0.00). Cold hands and hair loss were seen more often in the sedentary group compared to the athletic group (p < 0.05). According to a logistic regression analysis, independent variables (BMI, menstrual status, and bone fractures) were found to be statistically insignificant (p > 0.05). Conclusions: Excessive sports activity can be hazardous in young female population. Lower BMI might be related to menstrual irregularity. Young female population should be informed about this relationship, especially athletes who are particularly at risk. Certain precautions should be taken into consideration in this population in order to get benefits of sports activity.
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    Effect of shot peening on the oxidation behavior of thermal barrier coatings
    Karaoglanli, AC; Doleker, KM; Demirel, B; Turk, A; Varol, R
    A conventional thermal barrier coating (TBC) system is made up of a multilayered coating system that comprises a metallic bond coat including oxidation-resistant MCrAlY and a thermally insulating ceramic top coat including yttria stabilized zirconia (YSZ). In this study, in order to improve the oxidation behavior in conventionally produced TBC systems, shot peening process is applied for modification of surface layer structure of atmospheric plasma spray (APS) bond coats. The oxidation behavior of TBCs, produced by the APS process and subjected to shot peening, was investigated. Oxidation tests were performed under isothermal conditions at 1000 degrees C for different time periods. The coatings produced by the APS process include high porosity and oxide content due to atmospheric production conditions as well as exposure to very high temperature. In this study, the coatings, produced by the APS process, subsequently subjected to shot-peening, were compared with the ones which were not shot peened. Following the application of the shot peening process, a dense structure is obtained due to the plastic deformation effect in the metallic bond coating structure at a certain distance from the surface. To this end, the effects of the shot-peening on the high temperature oxidation behavior of the coatings are investigated and evaluated. (C) 2015 Elsevier B.V. All rights reserved.
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    The effects of various strength training intensities on blood cardiovascular risk markers in healthy men
    Akyüz, M; Dogru, Y; Nalcakan, GR; Ulman, C; Tas, M; Varol, R
    Objectives Regular physical exercise, especially aerobic exercise, is known to have a protective effect on cardiovascular health. The aim of this research is to look at the impact of two separate resistance training programs on blood biomarkers that are associated with the early detection of cardiac risk. Methods Forty-five male participants (mean 41 years) were randomly divided into three groups: The low-intensity resistance exercise group (LIEG), the moderate-intensity resistance exercise group (MIEG), and the control group (CG). The programs were implemented three times a week and in two sets. MIEG consisted of 8-10 repeats at 70-80% density of one repetition maximum load (1RM), while LIEG consisted of 15-17 repeats at 50-60% density of 1RM. CG did not participate in any exercise program. Two-factor mixed-design ANOVA assessed the data. Results Before, fourth week, and after the exercise program in repeated measurements, there was a significant decrease in body mass (-1.7%), body mass index (-1.7%), apelin (-44%), and pentraxin 3 (-39%) levels in MIEG (p < 0.05). Additionally, our study noted a decrease in pentraxin 3 (-25%, p < 0.05) and interleukin 6 (-21%) levels, while there was an increase in creatine kinase (18%), and lactate dehydrogenase (7.4%) levels in LIEG. Strength levels improved significantly in exercise groups. Conclusions Eight weeks of moderate-resistance training can potentially reduce the cardiovascular risk in healthy men.
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    Effect of Boronizing and Shot Peening on the Fatigue Properties of an Iron Based FeCu-Graphite P/M Material
    Yilmaz, SS; Ünlü, BS; Kurgan, N; Varol, R
    Iron based materials manufactured by powder metallurgy (P/M) method are widely used in industry. These materials are very important in applications where no machining is required, they can also be used as journal bearing material due to their self-lubricated property, and can be used for applications in the medical industry. In this study, powder metal parts were manufactured from composites based on FeCu-graphite by P/M method. Fatigue test was carried out on manufactured samples, which were only treated by boronizing or boronizing and shot peeing. The fatigue properties of these parts were investigated by a rotating bending fatigue test rig.
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    Effect of boronizing and shot peening in ferrous based FeCu-Graphite powder metallurgy material on wear, microstructure and mechanical properties
    Yilmaz, SS; Ünlü, BS; Varol, R
    Ferrous based materials manufactured by powder metallurgy (P/M) method are widely used in industry. These materials are very important because they do not require machining, have self-lubricated properties as journal bearing material, find applications in medical industry. In this study, powder metal parts were manufactured from ferrous based FeCu-Graphite composites by P/M method. Wear and mechanical test samples were manufactured and boronizing and boronizing + shot peening was applied to samples. Wear properties of these parts were investigated by wearing at 17 N load and 50 rpm on pin-on-disc wear test rig under dry conditions. Moreover, mechanical properties of powder parts were investigated in detail. (C) 2010 Elsevier Ltd. All rights reserved.
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    Tribological properties of boronized ferrous based PM journal bearings
    Ünlü, BS; Yilmaz, SS; Kurgan, N; Varol, R
    Ferrous based PM (powder metallurgical) materials are widely used in journal bearings since they provide a good tribological performance. These bearings are self-lubricating and can be used in places where lubricating is not possible. This also applies to the shaft material which shows adhesive wear. Tribological properties can be improved and adhesive wear can be decreased by boronizing. In this study, tribological properties of ferrous based boronized and non-boronized Fe-graphite, FeCu-graphite and CuSnFe-graphite bearings manufactured by PM method have been determined and compared. Boronizing treatment was carried out at 950 degrees C for 4 hours. The SAE 1050 steel shaft was used as counter abrader. Experiments were carried out at 20 N loads and 1500 rpm every 30 minutes for 2.5 hours.