1,721,098 research outputs found
Design and characterization of a small-scale solar sail deployed by NiTi Shape Memory actuators
Full text linkAbstractSolar sails exploit the radiation pressure as propulsion system for the exploration of the solar system. Sunlight is used to propel space vehicles by reflecting solar photons from a large and light-weight material, so that no propellant is required for primary propulsion. Kapton seems to be the most suitable material for the sail production and in the space missions till now activated booms as deployment systems have always been used. In this work a self deploying system based on NiTi Shape Memory wires has been designed and manufactured in a small-scale prototype. As kapton has always been employed with a thin Al coating on one or both surfaces of the sail, for the first experiments commercial pure Al thin sheets have been used in order to simulate the sail. In the small-scale prototype manufactured, three different configurations have been studied for bending the sail while two different Nitinol wires have been used as active materials for the self-deployment of the sail. Infrared lamps have been employed in order to warm the solar sail and obtain the activation of the shape memory active elements
Dynamic and static compressive behaviour of aluminum foam
No full textCompressive behavior of closed-cell Al foams with different density and pore size has been investigated under two different loading condition, static and dynamic. The effect of the TiH2 amount and consequently the foam density is fundamental for the mechanical behavior, not only in terms of energy absorption but particularly for the acceleration peak. Low density Al foams are promising for structural applications in which high energy absorption, high damping and lightness are required
Lead and lead alloys foams production
Full text linkLow-cost techniques for the manufacturing of lead and lead-alloys foams have been investigated in this work. In particular the “sintering and dissolution process” (SDP) and “replication process” (RP) have been focused and discussed. The effects of some process parameters have been investigated too: powder compacting pressure, composition of the base metal, granulometry, sintering time and temperature. Spherical urea and NaCl have been employed in the SDP method. In the replication process the melt viscosity has been found the main parameter. Furthermore melt infiltration in the NaCl particles has been found much easier if external pressure is applied. Lead recovery and recycling of exhaust batteries into foam-based electrodes has been examined too with a novel method for the direct conversion of Pb scrap into lead foam
Weldability of austenitic stainless steel by metal arc welding with different shielding gas
Full text linkAbstractDuring fusion welding the molten metal is shielded from contact with the atmospheric gas by means of a gaseous flux. The shielding gas prevents weld embrittlement, affects welding quality, because of its influence on filler metal transfer, and has a direct impact on welding costs as well. Argon is the most common shielding gas, often used with some adds of other gases that can be inert, as helium, or active, as CO2, O2 or H2. In this work the effects of mixtures with different composition have been considered for the arc welding of austenitic steels. Metallographic samples of welded sections have been undergone to visual and optical microscopy observations, microhardness, indentations and tensile tests
Optimization of the process parameters for the manufacturing of open-cells iron foams with high energy absorption
Full text linkAbstractIn this work the main results of the experimental research aimed to manufacture iron foams are reported. Iron powders (base metal) have been mixed with urea (filler agent) in different relative amounts (60% Fe- 40% urea, 50-50, 40-60 and 30-70) and then compressed in a cylindrical die in order to obtain a compact precursor. After compaction, the filler agent has been removed from each precursor in boiling water. The successive manufacturing step has been sintering and for this operation the optimum temperature has been found at 950 °C. Finally such foams have been subjected to compressive tests. Different amounts of Fe and urea match with different density and mechanical behavior in compressive tests. Energy absorbed during deformation has been calculated from the stress-strain compressive curve. Plateau stress, total strain and absorbed energy during deformation have been found strictly dependent from the iron/urea ratios
A novel methodology for solar sail opening employing shape memory alloy elements
No full textSolar sails exploit the radiation pressure as propulsion system. Sunlight is used to propel space vehicles by reflecting
solar photons from a large and lightweight material, so that no propellant is required for primary propulsion. Kapton
seems to be the most suitable material for the sail production and in the space missions till now activated booms as
deployment systems have always been used. In this work, an innovative self-deploying system based on NiTi shape memory
wires has been designed and manufactured in a small-scale prototype. As kapton has always been employed with a
thin Al coating on the surface of the sail, commercial pure Al thin sheets with thin adhesive kapton have been used in
order to simulate the sail. The attention has been focused, in the deployment experiments performed in the laboratory,
on the effect of different heating methods and different pressure conditions on the activation times. The folded configuration
chosen has been deployed in atmospheric condition and in low pressure condition (0.05 bar) inside a oven connected
to a rotary pump. For what concerns the heating methods, the attention has been focused on low-pressure oven
ISCO NSV 9035 (1.3 kW) and on halogen lamp (1 kW) in order to obtain the self-deployment of the sail. Some comparisons
between the two configurations in the different environmental conditions have been performed. In all cases, the full
self-activation of the sail has been achieved
Effetto trattamento superficiale con letto fluido sul comportamento a fatica della lega AA6082 T6
No full textNel presente lavoro si è investigato sul miglioramento del comportamento a fatica della lega Al 6082 T6 dopo lavorazione a letto fluido con Al2O3. Il trattamento a letto fluido è una tecnica relativamente nuova, semplice da attuare grazie al fatto che agisce in maniera puramente meccanica. A seguito dei ripetuti impatti a bassa velocità (dell’ordine di qualche m/sec) il metallo base viene ricoperto e si modificano le proprietà superficiali. Le prove di fatica, eseguite con macchina a flessione rotante e campione a sbalzo, evidenziano come i campioni dopo il trattamento mostrino un notevole aumento del numero di cicli a rottura a parità di carico oltre che del limite di fatica. Il riporto è stato studiato e caratterizzato in termini di spessore, durezza, rugosità e adesione. Una maggiore durezza unitamente a una più bassa rugosità superficiale è stata ottenuta grazie alla capacità dell’Al2O3 di coprire le microvalli e smussare i micropicchi, derivanti dalle precedenti operazioni di tornitura, a seguito dei ripetuti impatti. A livello microstrutturale sono stati rilevati con diffrattometria RX stress residui di compressione. Questi ultimi rappresentano un ostacolo al processo di nucleazione della cricca che si configura in una maggiore vita a fatica superiore anche di un ordine di grandezza a parità di condizioni di prova tra campioni trattati e non trattati
Mechanical and surface properties of Ti sputtered thin films
No full textThe mechanical behaviour of the film and the thickness influence on
the surface morphology have been studied in detail for Ti-sputtered coatings
deposited at room temperature on AA6082 T6 and AA2618/20% Al2O3 flat
samples. The intrinsic hardness and surface roughness of Ti thin films ranging
from 0.5 μm to 2 μm have been investigated. The higher the coating thickness
(up to 2 μm), the lower the surface roughness and the higher the intrinsic
hardness of the film. The improvement of surface roughness has been achieved
by Ti-sputtered clusters able to cover the micro-valleys
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