Volume 55, Issue 3

The climate change necessitates measures to reduce carbon dioxide (CO 2 ) emissions in the atmosphere, one of which is carbon dioxide capture and storage (CCS). Transmission of pressurized liquid or supercritical CO 2 containing residual flue gas constituents in pipelines is an important component of CCS systems. Material testing under conditions as close as possible to real conditions is a prerequisite for reliable and safe implementation of CCS. A novel pipeline corrosion test facility was developed, accounting for major mechanical, physical and chemical influencing factors: elastic deformation, pressure, temperature, gas composition and flow velocity can be independently adjusted. Radial and tangential stress distributions on a round sample were experimentally investigated, indicating a good accordance with expected theoretical values. In this contribution the idea of the novel corrosion test facility and the assembled equipment as well as first results are presented and discussed.

In this study, commercial hot work tool steels were selected and their wear behaviour under dry sliding condition was investigated after heat treatment applications. In the first stage of the study, solution annealing, quenching, and finally tempering treatments were applied to the experimental steels. All samples were examined by light microscopy after metallographic preparations. In the second stage, hardness values (HRC) of the steels were determined to evaluate the surface resistance to wear. Finally, wear tests were carried out using ‘ball-on-disc’ type tribometer under dry sliding condition and all worn surfaces were characterized using both light and scanning electron microscopy. It is concluded that (i) the steels had typical tempered martensite matrices, (ii) alloy content affected the final microstructure and a finer matrix was obtained due to vanadium addition, (iii) hardness levels directly affected the coefficient of wear of steels, and (iv) worn surfaces exhibited abrasive and adhesive wear tracks.

Constant amplitude data obtained from smooth specimens have been used for many years to evaluate the fatigue life of components. However, most of the loadings used in real applications are variable or random. In this research, three types of loading were applied – constant, low–high (LH), and high–low (HL) loading sequences. This paper presents an assessment of the fatigue behaviour under these three types of loading, and the effects of each loading on the fatigue behaviour as well as on life are highlighted. Fatigue tests were performed according to ASTM E466-96 standard with a strain gauge attached to the specimen being tested. AISI 1045 carbon steel was used as material for this tests due to its wide applications in the automotive industry. Fatigue tests were carried out at a constant, LH, and HL loading stresses at a sampling frequency of 8 Hz. A set of data acquisition system was used to collect the fatigue strain signals. All signals obtained were analyzed using two signal-processing approaches – the power spectral density (PSD) method and the integrated Kurtosis-based algorithm for Z-filter (I-kaz) technique. Fatigue behaviour was observed from the initial until the last stage of the fatigue test. The PSD peak values and I-kaz coefficients were determined to explain and describe the behaviour of fatigue damage. Both results are comparable in the fatigue damage assessment.

The improvements in physical and mechanical properties of industrial adhesives show that adhesive bonding techniques can be successfully applied to the most engineering fields. Due to some of their advantages in comparison to fastening methods, adhesively bonded joints have been researched by many researchers. In this study, the effect of the inverse Z joints angle (IZJs) was both experimentally and numerically analyzed. Vinylester Atlac 580 and Flexo Tix were used as adhesives. Two different composite materials were the adherends. In order to identify the mechanical properties of the adhesives, the bulk specimen method was used. Finite Element Analysis (FEA) was performed with software Ansys (V.10.0.1). Experimental results were compared with numerical results and the comparisons were found to be reasonable. The results showed that angle of the specimen with the increase of the stresses increase as well. The stresses in the middle of the overlap length were also higher than those at the edge of the overlap length.

The present paper focuses on two techniques, namely regression and neural network techniques, for predicting surface roughness in ball burnishing process. Values of surface roughness predicted by the two techniques were compared with experimental values. Also, the effects of the main burnishing parameters on surface roughness have been determined. Surface roughness (R a ) was taken as response (output) variable and burnishing force, number of passes, feed rate, and burnishing speed were taken as input parameters. Relationship between the surface roughness and burnishing parameters was found out for direct measurement of the surface roughness. Results showed the application of the regression and neural network models to accurately predict the surface roughness.

Expandable polystyrene (EPS) foam has been a well-known pattern material for a long time in the investment casting process, however it always suffers from insufficient surface finish compared to wax patterns. In this study, EPS foam patterns were coated with waxes and the effects of such coating on the surface quality were investigated. Cubic shaped EPS patterns were coated with liquid ordinary candle wax (c-wax) and commercial pattern wax (p-wax). These patterns and an uncoated pattern were used to prepare plaster bonded solid investment casting moulds and a A319 aluminium alloy was casted into these moulds. Average surface roughness (Ra) of the patterns, moulds internal surfaces and cast parts were measured, cross sections of the coated patterns were investigated by optical microscopy and the coating thicknesses were measured with an image analyser. As an obvious result, wax coating significantly increases the surface quality and the p-wax creates smoother, while the c-wax creates more uniform coating films.

In this study, X-ray radiographic tests of Ti6Al4V alloys welded by plasma tungsten arc welding (PTA) were investigated. PTA welding experiments were carried out under argon shielding gas atmosphere, at 1400–1600 W and 1800 W welding powers as well as 1 m/min, 0.75 m/min, and 0.50 m/min welding speeds. After this process, radiography of the welded joints was performed by X-ray diffraction. The result of the radiographic tests indicated that by increasing welding power the widths of deep penetration increased in all specimens. On the contrary, increasing welding speeds decreases the widths deep penetration. The best properties of Ti6Al4V joints were observed for specimens welded at 1800 W welding power and at 0.50 m/min welding speed.

Green phosphor of Y(BO 3 , PO 4 ): Ce, Tb was synthesized by means of sol-gel and conventional solid state methods. The thermal formation process was characterized by thermogravimetric analysis (TG) and differential thermal analysis (DTA). The effects of synthesis conditions on the crystalline and morphological structures were investigated using the X-ray diffraction (XRD) and Scanning Electronic Microsocpy (SEM). The results revealed that Y(BO 3 , PO 4 ): Ce, Tb phosphors with the monocline structure and high purity were successfully prepared by the sol-gel method. Furthermore, the products synthesized by the sol-gel method showed a well developed crystal structure, small particle size, narrow size distribution, and high luminescent performance. The product synthesized at 1050 °C in 2 h had better emission intensity than the others.

Kurzfassung Aufgrund des hohen Wirkungsgrades und der vielfältigen Einsatzmöglichkeiten können Brennstoffzellen einen wichtigen Beitrag zur zukünftigen Energieversorgung leisten. Für die Optimierung der Brennstoffzellentechnik ist es erforderlich, die während des Zellbetriebs ablaufenden Prozesse zu verstehen und exakt zu charakterisieren. Ein ausbalanciertes Wassermanagement ist die Grundlage für die optimale Leistungs­fähigkeit einer wasserstoffbetriebenen Zelle. Das während des Betriebs entstehende Wasser muss die Membran ausreichend befeuchten, um deren Protonenleitfähigkeit aufrechtzuerhalten. Andererseits behindern zu große Wasseransammlungen in der Zelle die Gaszufuhr durch die porösen Materialien sowie in den Kanälen der Gasverteilerstrukturen. Alterungsphänomene einzelner Zellkomponenten können die Verteilung der Wasseransammlungen und somit das Wassermanagement empfindlich stören und so die Leistungsfähigkeit der Brennstoffzelle herabsetzen. Zur Analyse der Wasserverteilung werden zerstörungsfreie, bildgebende Methoden, wie die Ex-situ-Neutronentomografie und die In-situ-Synchrotronradiografie, eingesetzt. Diese Methoden können während des Brennstoffzellenbetriebs mit weiteren Messverfahren, beispielsweise der ortsaufgelösten Stromdichtemessung, kombiniert werden. Auf diese Weise werden einzelne Komponenten, wie zum Beispiel die Gasdiffusionsschichten, charakterisiert.

This study aimed to produce self-compacting normal weight concrete by the use of lightweight aggregate, which has become more widespread, as Turkey has many natural lightweight aggregate sources. Nevşehir pumice aggregate was used in the tests. The characteristics of fresh concrete incorporating additives as fly ash and super plasticizer were determined via self-compacting concrete tests such as slump flow, V-funnel and L-box flow. Compression, flexure and split tests were conducted on cube, cylinder and girder samples produced with the concrete. The test results and strength data showed that self-compacting lightweight concrete could be produced by the methods used in this study.

Most of the marine phosphate deposits are calcareous phosphates. Calcination process is one of the famous processes used for upgrading sedimentary calcareous phosphate ore. In this study, evaluation of the calcination process performance in terms of its operating parameters was carried out. The effect of operating parameters and their significance on calcination of calcite as a main phosphate ore impurity was studied using statistical design of experiments. A statistical model was developed to correlate the studied parameters with the phosphate grade in the calcined product. The studied parameters were temperature, time, and particle size. The analysis of the design results showed that the tempe­rature is the most significant parameter. The higher the temperature is the higher the calcite conversion to calcium oxide and release of carbon dioxide. In addition, the particle size plays a significant role in contact area between particles as well as the voids among them that help to release the CO 2 faster. Moreover, a phosphate concentrate, suitable for phosphoric acid production, containing ∼32 % P 2 O 5 can be achieved at optimum values of studied parameters, i. e., at a temperature of 850 °C, after a calculation time of 40 minutes and with a particle size of 0.074 mm, respectively. Furthermore, quenching and slacking of calcined products increased the grade by 2–3 % to reach 34 % to 35 % P 2 O 5 in the final concentrate.