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291.
Musa Doğruer Cabir Terzioğlu Gürcan Yildirim Osman Gorur 《Journal of Superconductivity and Novel Magnetism》2014,27(3):755-761
Mechanical behavior of YBa2Cu3O7?x (Y123) superconductors exposed to Sn nanoparticles diffusion is determined by the way of Vickers microhardness (H v ) conducted at different applied loads (0.245N≤F≤2.940 N). Load dependent microhardness, load independent microhardness, elastic modulus, and yield strength values are estimated from the microhardness curves. Unpredictably, the findings of the H v values reveal that the undiffused sample and Sn diffused sample prepared at 500 °C exhibit reverse indentation size effect (RISE) behavior while the other samples obey indentation size effect (ISE) nature. Further, we extract the load independent (true) microhardness using the Meyer’s law, proportional specimen resistance (PSR), elastic/plastic deformation (EPD), Hays–Kendall (HK) approach and indentation-induced cracking (IIC) model, and compare the true hardness with the apparent hardness. 相似文献
292.
Gadipelli Srinivas Jamie Ford Wei Zhou Taner Yildirim 《International Journal of Hydrogen Energy》2012
We report controllable and enhanced hydrogen release kinetics at reduced temperatures in ammonia borane (AB) catalyzed by Zn-MOF-74. AB is loaded into the unsaturated Zn-metal coordinated one-dimensional hexagonal open nanopores of MOF-74 (ABMOF) via solution infiltration. The ABMOF system provides clean hydrogen by suppressing the release of detrimental volatile byproducts such as ammonia, borazine and diborane. These byproducts prevent the direct use of AB as a hydrogen source for polymer electrolyte membrane fuel cell applications. The H2 release temperature, kinetics, and byproduct generation are dependent on the amount of AB loading. We show that nanoconfinement of AB and its interaction with the active Zn-metal centers in MOF are important in promoting efficient and clean hydrogen generation. 相似文献
293.
Piping network design of geothermal district heating systems: Case study for a university campus 总被引:1,自引:0,他引:1
Geothermal district heating system design consists of two parts: heating system and piping network design. District heating system design and a case study for a university campus is given in Yildirim et al. [1] in detail. In this study, piping network design optimisation is evaluated based on heat centre location depending upon the cost and common design parameters of piping networks which are pipe materials, target pressure loss (TPL) per unit length of pipes and installation type. Then a case study for the same campus is presented. 相似文献
294.
This article sets forth two different computational methods developed to evaluate fracture parameters for inclined cracks lying in orthotropic functionally graded materials, that are under the effect of thermal stresses. The first method is based on the J k -integral, whereas the second entails the use of the J 1-integral and the asymptotic displacement fields. The procedures introduced are implemented by means of the finite element method and integrated into a general purpose finite element analysis software. Numerical results are generated for an inclined edge crack in an orthotropic functionally graded layer subjected to steady-state thermal stresses. Comparisons of the mixed-mode stress intensity factors computed by the use of the proposed methods to those calculated by the displacement correlation technique point out that both approaches lead to numerical results of high accuracy. Further results are provided in order to illustrate the influences of inclination angle, material property gradation, and crack length upon the thermal fracture parameters. 相似文献
295.
Vebil Yildirim 《先进材料力学与结构力学》2013,20(3):205-217
The first six resonance frequencies of unidirectional composite noncylindrical helical springs (barrel and hyperboloidal types) made of carbon-epoxy (T300/N5208) material are determined theoretically based on the transfer matrix method. The rotary inertia, shear, and axial deformation effects are considered with the first-order shear deformation theory. The overall transfer matrix is obtained by integrating the 12 scalar ordinary differential equations with variable coefficients governing the free-vibration behavior of noncylindrical helical springs made of an anisotropic material. Numerical results are verified with the reported values for isotropic noncylindrical helices. A parametric study is performed to investigate the effects of the number of active coils (n = 5-10), the helix pitch angle ( f = 5° and 25°), the ratio of the minimum to maximum cylinder radii ( R min/ R max = 0.1 and 0.9), and the ratio of the maximum cylinder diameter to the wire diameter ( D max/ d = 5 and 15) on the free-vibration frequencies of constant-pitch composite barrel and hyperboloidal helical springs with circular sections and fixed-fixed ends. 相似文献
296.
The effects of quenching air temperature, quenching air speed and winding speed in the melt spinning process of poly(ethylene terephthalate) fibres with a titre of 147 dtex and 96 filaments on dye uptake were investigated. The ranges used for quenching air temperature, quenching air speed and winding speed were 17–27 °C, 0.3–0.7 m/s and 2600–3800 m/min, respectively. Specimens were dyed and their colour strengths (K/S values) were measured using a spectrophotometer. The results were statistically analysed. 相似文献
297.
298.
299.
Mustafa Ulutan M. Mustafa Yildirim Osman N. Çelik Soner Buytoz 《Tribology Letters》2010,38(3):231-239
The present study evaluates the tribological properties of boride layers on the surface of AISI 4140 steel, formed using the pack-boriding method. Commercial EKabor®2 was used as the boronizing agent and the treatment was carried out at 900, 950, 1000, and 1050 °C for 2, 4, and 6 h, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), and microhardness tests were used to characterize the phase composition, microstructure, and local hardness, respectively, of the borided steel samples. Block-on-disc tests were used to investigate tribological properties. Abrasive wear tests were carried out using emery paper at a fixed sliding speed and three different loads. Adhesive wear tests were executed against AISI 52100 steel at a fixed load and distance. The coefficient of friction values (COF) of the samples were determined simultaneously during the tests. The weight loss and COF of the borided samples were compared with untreated samples and the results suggest that both wear resistance and friction properties of the AISI 4140 steel improve with boriding. 相似文献
300.
Conclusion Through metallurgical SEM analysis, it was found that 42% of failures occurred due to corrosion plus erosion-corrosion, 16.5%
were due to inclusions and stress gaps that could be correlated oto fatigue, 16.5% had traces of production impurities, and
25% showed fatigue via ductile-type failures. The results/reasons correlation can be summarized as follows:
As a result of the analysis of various implant materials, the main reasons for failure are corrosive attack, manufacturing
defects, and nonstandard-caused failures. Biocompatible inorganic materials, such as hydroxy-apatite coating with some binders,
would make the dissolution of metal ions difficult and so may delay corrosion and wear and also minimize the loosening of
implants from bone. 相似文献
– | • In the investigation of a total hip prosthesis, the fracture was multiorigined, probably due to the presence of manufacturing defects in both surfaces of the device; was associated with poor design of the component; and introduced points of high stress concentration. |
– | • The study revealed that the failure of the stainless steel femoral compression plates occurred by a fretting-fatigue mechanism under the action of low nominal stresses and unidirectional bending. |
– | • The failure of femoral compression titanium plates occurred by corrosion fatigue promoted by the presence of intense localized corrosion and intergranular cracking. |
– | • The failure of hollow spinal rods occurred by overload caused by the intense formation of pitting corrosion during service. The pitting was associated with the presence of superficial manufacturing routes. |