Nanomechanical properties of friction stir welded AA6082-T6 aluminum alloy

Lightweight alloys are of major concern, due to their functionality and applications in transport and industry applications. Friction stir welding (FSW) is a solid-state welding process for joining aluminum and other metallic alloys and has been employed in aerospace, rail, automotive and marine industries. Compared to the conventional welding techniques, FSW produces joints which do not exhibit defects caused by melting. The objective of the present study is to investigate the surface hardness (H) and elastic modulus (E) in friction stir welded aluminum alloy AA6082-T6. The findings of the present study reveal that the welding process softens the material, since the weld nugget is the region where the most deformations are recorded (dynamic recrystallization, production of an extremely fine, equiaxial structure), confirmed by optical microscopy and reduced nanomechanical properties in the welding zone. A yield-type pop-in occurs upon low loading and represents the start of phase transformation, which is monitored through a gradual slope change of the load-displacement curve. Significant pile-up is recorded during nanoindentation of the alloy through SPM imaging.     

Efficient frequency-doubling in a poled PVDF copolymer guest/host composite

We describe the linear and nonlinear properties of a new polymer composite, which uses a ferroelectric PVDF copolymer host in which an optically nonlinear low-molecularweight guest is dissolved and subsequently aligned using a room-temperature poling process. We have measured the frequency-doubling coefficient d33 of these poled composites at 1-064/mi to be as high as 2-6 × 10?12m/V. In addition, we have shown that this material may be formed into waveguiding structures with an acceptable optical loss (?5dB/cm), as is needed in many signal processing systems.     

Radiation doses in common X-ray examinations carried out in two dedicated paediatric hospitals

In this study, the entrance surface dose (ESD) and the respective effective dose (E) were determined for paediatric patients undergoing various common radiological examinations in two dedicated paediatric hospitals. Measurements of ESD were carried out in 289 examinations using thermoluminescent dosemeters. The patients were categorised according to their age and the mean ESD and E values were determined for each examination and age category. These ESD values were compared with the existing diagnostic reference levels (DRLs). In both hospitals there were cases where the DRLs were exceeded but in one of them this was rather the general rule, since additionally to the routine use of grid and low tube potential settings, occasional use of fluoroscopy for positioning check was also observed. While the remedial actions required to appropriately reduce the doses were clearly identified, this cannot be achieved without the cooperation of medical physicists with operators and radiologists.     

Impact of water activity and temperature on growth and ochratoxin A production of two Aspergillus carbonarius isolates from wine grapes in Greece

The aim of this study was to determine the effects of water activity (a(w); 0.85 to 0.98) and temperature (10 to 40 degrees C) on the radial growth rate and ochratoxin A (OA) production of two Aspergillus carbonarius isolates in vitro. The isolates were obtained from wine grapes cultivated in Greece, and the trial was conducted with a synthetic grape juice medium similar in composition to grapes between veraison (beginning of color change) and ripeness. Fungal growth and OA production data were collected for 55 days. Response surface curves and cardinal values for a(w) and temperature were obtained using multiple regression analysis. The lag phase lasted from less than 1 to 10 days. Both isolates grew optimally at 30 to 35 degrees C and 0.96 a(w), but maximum OA production occurred under suboptimal growth conditions (15 to 20 degrees C and 0.93 to 0.96 a(w)). Growth also was observed at 0.85 a(w) and 25 degrees C, however at this same a(w) the fungus failed to produce mycelium at any other temperatures tested. The isolates produced OA at 15 to 30 degrees C and 0.90 to 0.98 a(w). Maximum OA production was detected after 25 days of incubation at 20 degrees C and 0.96 a(w) and was 3.14 and 2.67 microg g(-1), respectively, for the two strains. The isolated strains used in this study were more xerotolerant than others from the Mediterranean basin. These data will allow producers to identify and thus monitor critical environmental conditions effectively in wine grapes. These data also increase the knowledge base concerning the ability of A. carbonarius to grow and produce toxin under different ecological conditions and can contribute to the development of secondary models for the prediction and risk assessment of OA in wine production.     

Hydrogen effect on fracture toughness of pipeline steel welds, with in situ hydrogen charging

The API 5L X70 and X52 pipeline steel weld fracture toughness parameters are measured in a hydrogen environment and compared to the ones in air. The hydrogen environment is created by in situ hydrogen charging, using as an electrolyte a simulated soil solution, with three current densities, namely 1, 5 and 10 mA/cm². A specially designed electrolytic cell mounted onto a three-point bending arrangement is used and hydrogen charging is performed during the monotonic loading of the specimens. Ductility is measured in terms of the J₀ integral. In all cases a slight change in toughness was measured in terms of K_Q. Reduction of ductility in the base metal is observed, which increases with increasing current density. A more complex phenomenon is observed in the heat affected zone metal, where a small reduction in ductility is observed for the two current densities (1 and 5 mA/cm²) and a larger reduction for the third case (10 mA/cm²). Regarding microstructure of tested X70 and X52 base and HAZ metal, it is observed that the hydrogen degradation effect is enhanced in banded ferrite-pearlite formations. The aforementioned procedure is used for calculating the fracture toughness parameters of a through-thickness pipeline crack.     

Titanium Alloys Thin Sheet Welding with the Use of Concentrated Solar Energy

The present study deals with the welding of titanium alloys thin sheets 1.3 mm thick, with the use of concentrated solar energy. The experimental part of the work took place at a medium size solar furnace at the installation of the Centre National de la Recherche Scientifique, at Odeillo, in Southern France, where similar and dissimilar defect-free welds of titanium Grades 4 and 6 were achieved, in the butt joint configuration. After the determination of the appropriate welding conditions, the optimum welded structures were examined and characterized microstructurally, by means of light optical microscopy, scanning electron microscopy, and microhardness testing. In addition, test pieces extracted from the weldments were tested under uniaxial tensile loading aiming to the estimation of the strength and the ductility of the joint. The analysis of the experimental results and the recorded data led to the basic concluding remarks which demonstrate increased hardness distribution inside the fusion area and severe loss of ductility, but adequate yield and tensile strength of the welds.     

Occupancy‐based decision support system for building management: From automation to end‐user persuasion

In this paper, an intelligent occupancy‐based, automated building control system is initially introduced, which has the capability of reducing energy consumption while respecting the occupants' comfort and actions inside building areas. Data stemming from a multisensorial network is combined with implicitly extracted information, since no direct feedback is expected by the users, towards unsupervised monitoring and control of building operation. However, due to significantly higher costs of actuating equipment and the reluctance that some end users show in accepting fully automated solutions, a new hybrid approach is conceptualized and presented; the automated decision support system is supplemented with a persuasion mechanism aimed at increasing energy savings, through raising user awareness. The persuasive methodology employs a continuous feedback mechanism in order to select the optimal incentive strategy by taking into account user success rates, in terms of requested actions, as well as available mechanisms, and daily harassment.     

Development of lithographic techniques for metallisation of organic substrates

A wide range of applications which involve organic crystalline materials require the metallisation of low-molecular-weight compounds. Conventional lithographic techniques used in silicon fabrication technology use high-temperature processing methods which are unsuitable for organic materials. Gold/titanium bilayer and shadow-masking techniques were found to provide suitable solutions to the problem of metallisation of these materials and allowed fabrication of a surface acoustic wave (SAW) device with (–)-2-α-methylbenzylamino-5-nitropyridine (MBANP) as substrate.     

Polyamide 6 Filled with Melamine Cyanurate and Layered Silicates: Evaluation of Flame Retardancy and Physical Properties

The efficiency of melamine cyanurate and a clay filler for improving the flame retardancy and other physical properties of polyamide 6 was examined. Partially intercalated‐exfoliated morphologies were obtained. Nanocomposites suffered from polymer degradation during compounding, while the molecular weight was enhanced in the case of the flame retarded samples. Silicates were shown to restrain crystallization, whereas melamine cyanurate induced heterogeneous nucleation. Both additives positively influenced the tensile modulus of the prepared samples, decreasing their ability to elongate. With respect to the UL94 flammability test, melamine cyanurate was proved to be not sufficiently capable of increasing the tendency of nanocomposites to drip, negatively affecting flammability.