Effect of heat treatment on the bending behavior of aluminum alloy tubes

Quasistatic experiments and numerical simulations were performed to investigate the three-point bending behavior of different temper AA6082 tubes in this study. The effect of heat treatment on the samples was investigated by microstructural analyses. Temper designations of T6, T4 and O were applied to the samples to study the load-carrying capacity and bendability of AA6082 tubes. The samples with T4 and O tempers show appropriate bendability of up to the punch travel distance of 60 mm under low-punch forces. However, the samples with T6 temper require three times more punch force than the other temper samples. Furthermore, the T6 temper samples cannot hold their structural integrity. Therefore, crack formation occurred at the enhanced bending angle stages. Experimental results were compared with the numerical simulation outputs, and the deformation mechanism was observed with finite element method. In addition, various element formulations in the numerical simulations were compared in terms of bending force and computational time. Based on the numerical results, element formulations exhibit different performances with respect to temper conditions.     

Treatability studies on domestic wastewater using UV/H2O2 process

Advanced oxidation processes (AOPs) are emerging and promising technology both as an alternative treatment to conventional wastewater treatment methods and enhancement of current biological treatment methods especially dealing with highly toxic and low biodegradable wastes. In this paper, the results of domestic wastewater treatment using H₂O₂/UV process in both batch and continuous mode are presented. Over 95% reduction in COD was achieved in less than 60 min of reaction time. Optimum conditions for pH and H₂O₂ dosage for this process was found to be 3 and 50 mg L⁻¹, respectively. A pretreatment in the form of removal of turbidity is recommended for the success of the process in the long run. Electric energy required is estimated to be 10 kWh kg⁻¹ COD on the average.     

On handshakes in random graphs

In [Y. Métivier, N. Saheb, A. Zemmari, Analysis of a randomized rendezvous algorithm, Inform. and Comput. 184 (2003) 109-128], the authors introduce and analyze a randomized procedure to implement handshakes in graphs. In this paper, we investigate the same problem in random graphs. We prove results on the probability of success and we study the distribution of the random variable which counts the number of handshakes in the graph.     

Exfoliation targeted toughness enhancement in polypropylene‐blend‐ montmorillonite nanocomposites

BACKGROUND: Both exfoliated and toughened polypropylene‐blend‐montmorillonite (PP/MMT) nanocomposites were prepared by melt extrusion in a twin‐screw extruder. Special attention was paid to the enhancement of clay exfoliation and toughness properties of PP by the introduction of a rubber in the form of compatibilizer toughener: ethylene propylene diene‐based rubber grafted with maleic anhydride (EPDM‐g‐MA). RESULTS: The resultant nanocomposites were characterized using X‐ray diffraction, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis and Izod impact testing methods. It was found that the desired exfoliated nanocomposite structure could be achieved for all compatibilizer to organoclay ratios as well as clay loadings. Moreover, a mechanism involving a decreased size of rubber domains surrounded with nanolayers as well as exfoliation of the nanolayers in the PP matrix was found to be responsible for a dramatic increase in impact resistance of the nanocomposites. CONCLUSION: Improved thermal and dynamic mechanical properties of the resultant nanocomposites promise to open the way for highly toughened super PPs via nanocomposite assemblies even with very low degrees of loading. Copyright © 2008 Society of Chemical Industry     

Hydro-abrasive erosion of concrete incorporating ground blast-furnace slag and ground basaltic pumice

In this research work, an attempt has been made to find the suitability of the ground blast-furnace slag (GBS) and ground basaltic pumice (GBP) as a possible substitute for conventional crushed fine aggregate. The main purpose of this investigation is to determine the hydro-abrasive erosion (HAE) characteristics of concrete with GBS and GBP as fine aggregates.The results create perspectives of forecasting HAE of concrete structures depending on the types and amount of additives. It was found that the HAE characteristics of concrete had improved when some of the fine aggregates were replaced by GBS and GBP. As the amount of these additives increased, the mass loss of the concrete incorporating GBS + GBP decreased. This improvement can be explained partly by the decrease in the permeability and partly by the HAE resistance of the additives. In addition to these results, the HAE of concrete was strongly influenced by its compressive strength. Furthermore, the increase in the percentage of additives increased the chloride penetration depths, sharply. The results of this investigation suggest that a joint incorporation of GBS and GBP could conveniently be used to improve its HAE characteristics of concrete.     

The normal approach between rough flat surfaces in contact

The relationship between the normal approach and load for a variety of rough flat surfaces has been considered experimentally and theoretically. The experimental values of normal approach measured by a capacitance technique correlate well with the theoretical values based on the measured surface parameters. For smooth surfaces the texture deformation is essentially elastic whilst the rough surfaces behave plastically. Linearity between the normal approach and the surface roughness at any given load is established and is thereby in agreement with theoretical expectation.     

Renewable energy market conditions and barriers in Turkey

Decentralized wind, hydropower, biogas and biomass, geothermal, solar thermal and solar electricity energy systems are the most commonly found renewable energy technologies promoted for rural energy supply within sustainable developments programs. They are, therefore, seen to have a central place in the practice of sustainable development and in allowing less development countries to bypass the environmentally damaging fossil fuel intensive paths made by industrialized countries. On the political front, many less development countries are critical of pressure on them to adopt environmental energy technologies.Turkey is situated the meeting point of three continents (Asia, Europe and Africa) and stands as a bridge between Asia and Europe. The country is located in southeastern Europe and southwestern Asia. As Turkey’s economy has expanded in recent years, the consumption of primary energy has increased. Presently in order to increase the energy production from domestic energy resources, decrease the use of fossil fuels as well as reduce of green house gas emissions different renewable energy sources are used for energy production in Turkey. The share of energy production from renewable energy sources has increased during the last 10 years. Turkey must import most of the energy to meet her needs. Turkey also has a large potential for renewable energies. The lack of knowledge about renewable energy technologies by most policy-makers, potential consumers, and energy firm managers has played against renewable energy developments. The paper presents renewable energy used in Turkey and Europe Union and evaluation of the market conditions and barriers of renewable energy use in Turkey.     

Room-temperature aging of manganese-alloyed high nitrogen duplex stainless steels

The room-temperature aging behavior of two duplex stainless alloys with different austenite stability was investigated. Both alloys readily aged at room temperature. Even for aging times as short as 30 seconds, the originally continuous yielding behavior becomes discontinuous upon reloading after prestraining. The magnitude of the stress increase due to aging was higher in the presence of strain-induced martensite, even though it was shown that aging also occurred in the austenite phase. The aging response was shown to be thermally activated, with increasing age hardening associated with increasing aging times. The results could be explained by the combination of aging phenomena in the bcc phases by interstitials and the aging by interstitial-vacancy complexes in the fcc phase, where the interstitials are thought to be immobile during the short aging times used and aging would occur due to short-range migration of vacancies instead.     

Application of new techniques for characterization of non-metallic inclusions in steel

This research, aiming at a new approach to the characterization of non-metallic inclusions in steel, has revealed how to measure and specify them quantitatively. Inclusions to be measured are the ones near the surface or the center of continuously cast low carbon steel, and also those in two sorts of bearing steel after rolling. The specimens are prepared for microscopic observation of the sectioned inclusions, and SEM observation of the inclusions floating up on the surfaces after electron beam remelting of the specimens. Two new methods, which have been proposed in consideration of not only the particle sizes but also the shapes, are applied for the measurement. For the low carbon steel, the inclusions, as a whole or as limited only to alumina, are larger and more spherical in the central zone than those in the surface-near areas. Morphological differences between the inclusions in these bearing steels can be statistically clarified. The new approach shows that even the overlapping information can be individually separated and quantified by using approximate functions through the suitable choice of variable conversion. Examination and discussion on the present quantitative results can be enriched with various combinations of the specimens and the methods. The achievement can also suggest several remarks for further investigation on inclusions.     

An investigation for usage of graphite powder-helium suspension as reactor coolant in a HTGR

This study's aim is to perform a numerical experiment to examine the enhancement of heat transfer in high-temperature gas-cooled reactors (HTGR) by using gas-particulate (graphite powder-helium) suspension as reactor coolant. At very high temperatures, the radiative heat can be profoundly improved compared to gas alone because of the large absorptivity of the cloud of fine particles. For every high-temperature flow situation where radiation is a significant mode of heat transfer, there exists an optimum loading ratio (mass of graphite to that of He) and particle size for which maximum heat-transfer rates are achieved. The study uses typical HTGR data to examine the heat-transfer phenomena and determine the mass of graphite, optimum particle size, and the influence of other parameters which will result in maximum heat transfer.