[en] The friction-stir process (FSW) developed by England's TWI in the last decade is a new concept in solid phase friction welding that is particularly appropriate for soldering aluminum and its alloys. It offers interesting aspects and can advantageously replace the usual arch processes. It is an automatic process that solders together long pieces by butt or lap welding and, therefore, overcomes the greater limitation of the conventional friction process that can be applied only to pieces with revolution symmetry. FSW is based essentially on the use of a cylindrical tool with a special profile, which is inserted between the surfaces where the materials meet to join them together at a certain rotation speed and under a specific force. The pieces must be rigidly butt bonded or overlapped to prevent movement when the tool moves forward along the joint producing the dispersion of oxides, local plastisizing of the material and the weld. Since its creation FSW has been the subject of many international publications, but until the present work there was no technologically relevant data about tools and procedures. For this reason, when its promising and novel nature was noticed, the CNEA began its own development project in 1997. The main characteristics of the tool are reviewed here and the results of tests carried out to evaluate the influence of the feed velocity on the mechanical properties of the butt joining of a 6.25 mm thick AA6061 T6 plate. Different accumulated aspects of the experience are discussed as well (cw)

[en] The high cycle fatigue behaviour of friction stir welded AISi 10 Mg samples was investigated for a stress ratio R=0.1, ranging from 0.5 to 0.9 of the yield strength, in addition to tensile tests. The welds were produced with different tool rotation and travel speeds, and these welding parameters were correlated to residual stresses, measured by X-ray diffraction (sen''2Ψ method). Moreover, the residual stresses were measured during the fatigue testing, at fixed cycle intervals, being reported. It was observed that the residual (compressive)stresses within the nugget were smaller than in the interface regions (between the thermo-mechanically affected zone and the base metal) and stabilized above 4 x 10''5 cycles. Fatigue crack morphology and microstructural changes were characterized by optical and electron microscopy and the observations are discussed along with the fatigue results. (Author) 14 refs

[en] Two new models are proposed to determine the adhesion energy be means of the internal friction technique (IF) in thin films layered materials. for the first method is necessary to determine enthalpy by means of the IF technique, for which the adhesion work has been determined with experimental data. In the second method are necessary to perform IF tests at constant temperature. (Author)

[en] The friction and wear properties of mesocarbon microbeads-based graphite and siliconized graphite were investigated. At loads of 20–60 N, the graphite had low friction coefficient (0.15–0.26), while had high wear rate (0.039–0.50 × 10⁻³ mm³/m). Siliconized graphite had higher friction coefficient (0.375–0.40), while at higher loads of 40 N and 60 N, it had lower wear rates (0.15 and 0.18 × 10⁻³ mm³/m respectively). The main wear of ploughing resulted in low wear rate for siliconized graphite

[en] Nowadays, heat transfer enhancement plays an important role in improving efficiency of heat transfer and thermal systems for numerous areas such as heat recovery processes, chemical reactors, air-conditioning/refrigeration system, food engineering, solar air/water heater, cooling of high power electronics etc. The present work presents the experimental results of the heat transfer enhancement of TiO₂/water nanofluid in a heat exchanger tube fitted with double twisted tapes. The study covered twist ratios of twisted tapes (y/w) of 1.5, 2.0, and 2.5) while the concentration of the nanofluid was kept constant at 0.05% by volume. Observations show that heat transfer, friction loss and thermal performance increase as twist ratio (y/w) decreases. The use of the nanofluid in the tube equipped with the double twisted-tapes with the smallest twist ratio (y/w = 1.5) results in the increases of heat transfer rates and friction factor up to 224.8% and 8.98 times, respectively as compared to those of water. In addition, the experimental results performed that double twisted tapes induced dual swirling-flows which played an important role in improving fluid mixing and heat transfer enhancement. It is also observed that the TiO2/water nanofluid was responsible for low pressure loss behaviors. (paper)

[en] The ability to characterize tactile perception will be crucial to the effective use of tactile information in the next generation of information communication technology. Tactile perception depends on multiple properties of the surface being touched, including surface texture, stiffness, and temperature. To quantitatively evaluate the contribution of each individual property to tactile perception, our research group has used microfabricated tactile samples that have identical properties except for the one property under study. Until now, a separate sample has been needed for each level of each property of interest since the samples have lacked the capacity to vary property levels. In this research, we propose tactile samples that can change surface texture simply by being stretched. The proposed samples are made of PDMS and have grooves perpendicular to their length. In the initial state, the grooves are barely perceptible; however, when the sample is stretched lengthwise, the grooves open and surface texture appears. We first examined changes in the surface texture of the samples, together with Young’s modulus, the friction coefficient, and the mean deviation of the friction coefficient (MMD), under controlled conditions. We then conducted sensory experiments involving friction, moisture, roughness, stiffness, and warmness. Experimental results showed that the surface texture could be well perceived with grooves greater than 30 μm in width. Contrary to our intuition, the friction feeling did not increase with the friction coefficient but rather with the MMD of the coefficient. The perception of moisture was enhanced with the friction coefficient. The proposed tactile samples, with their ability to change their surface texture, will be of great help in future quantitative investigations of tactile perception. (paper)

No abstract available

[en] We present friction characteristics of sliding textured silicon surfaces at the submicrometre scale. A two-dimensional submicrometre dimple array on the Si surface is fabricated by femtosecond laser processing. Direct femtosecond laser nano-structuring of the Si (1 0 0) substrate by polystyrene particle-assisted near-field enhancement is used. In the investigated hole diameter domain from 229 to 548 nm, an increase in the friction coefficient with the decrease in the hole size is found experimentally. The fabricated submicrometre dimples act evidently as lubricant reservoirs to supply lubricants and traps to capture wear debris. The fluctuation of the friction coefficient is also increased by reducing the dimple size. The lowest friction coefficient of 1.41 x 10^-2 is achieved with the dimple array having a diameter of about 550 nm. This value is 2.6 times lower than that of non-structured substrates

[en] In this paper we have tried to present the influence of the metal surface wear and of the contact temperature on the evolution of the sliding speed, of the normal load and of the friction coefficient. We have performed numerous experimental trials that have highlighted the dependency between load and wear in relation to the friction coefficient. A dry linear friction couple was used with a large range of loads and speeds, simulating real-life working conditions: temperature, sliding speed, contact pressure. We have made a connection between the theoretical case and the experimental results arising from the use of the “wear imprint method” for the volume and depth of wear. (paper)

[en] When choosing a generalized interaction potential for ion-molecular systems and a radial distribution function, the friction coefficients and relaxation times of an aqueous NaCl solution are calculated numerically over a wide range of density ρ, concentration c, and temperature T. The results are presented in tabular form. (author)