Natural fibre composite have a potential to be widely applied in the alternative to a fibreglass composites in sustainable energy impact absorption structures. In this study, the behaviour of hemp ...fibre epoxy composites subjected to a low-velocity impact loading, using an instrumented falling weight impact equipment, is presented. Two types of hemp reinforcements were used: unidirectional and bi-directional fabric and three balanced laminates (0 degree /90 degree ) different in thickness were studied: 4 plies, 8 plies, 12 plies. The results were compared. The laminates were fabricated by RIFT process using a common epoxy matrix. The reached volumetric fibre percentage Vf was not too high. It assumed a value of 34% for the unidirectional reinforcement and an average value of 30% for the bidirectional one. Some laminates were impregnated by PLA resin at the aim to obtain a completely natural system. The impact behaviour was analysed carrying out tests impacting square specimens, 100100mm, with a hemispherical tup geometry with a diameter of 19.8mm and a velocity of 4.0m/s. Both penetration and indentation tests were performed at the aim to investigate about the damage start and evolution. The impact induced damage, characterised by an optical microscope, includes matrix cracking, delamination, fibre breakage and fibre pullout. An interesting compressed central zone of the laminate under the impact point was noted.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Aluminum foams are becoming potential materials for applications in several industrial fields, due to an intriguing combination of physical and mechanical properties. Their performances can be ...enhanced by using them as core of reinforced systems, like sandwich structures. Traditional reinforced foams usually present metal sheets or composite materials as skins, but these solutions are in contrast with some requirements of industrial applications, like lightness and high-temperature resistance. This work proposes an innovative single-step process, based on the powder compact melting technique, for the manufacture of aluminum foam panels reinforced by a steel wire mesh-grid, also acting as a mold. In doing so, problems of cost-effectiveness and flexibility typical of the conventional in-mold processes can be overcome on one hand and light-weight, high-temperature resistant aluminum foam sandwiches can be made on the other. A manufacturing campaign yielded the optimal foaming temperature for the production of the sandwich panels. In addition, mechanical tests highlighted the effectiveness of the mechanical coupling between the core and skin and a significant improvement of the bending load carrying capacity, compared with plain foam panels, of these innovative sandwiches.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Metal foams are attracting interest in both aerospace and automotive industries due to their intriguing properties such as high stiffness coupled with low specific weight, good absorbing energy ...capabilities and flame resistance. To date, many researchers are trying to develop innovative solutions for the improvement of the mechanical properties of metal foams keeping the light-weight condition, with the scope to extend their potential application field. In this scenario, an advanced solution was here proposed; in particular, an innovative manufacturing process was presented for the production of steel grid–reinforced closed-cell aluminium foam cylinders in one single step by using the powder compact melting technique. The bending properties of plain, as well as reinforced, foam systems were experimentally tested and extensively discussed. An original finite element model was developed and validated for the analysis of the bending behaviour and the synergistic action of each component constituting the hybrid system, with a special focus on the failure mechanisms occurring under specified load conditions. The outcomes showed an increase of the mechanical properties of the reinforced systems due to the action of the light-weight mesh grid reinforcement that delays the failure of the structure. The solution proposed shows promises of being a useful method to expand the industrial applications of metal foams.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this paper, AA 2024 T3-rolled sheets were joined in butt joint configuration through the friction stir welding process. Different joints were carried out varying the principal process parameters ...(i.e., tool welding speed and tool rotational speed). The aim of this work was the study and the experimental characterization of the influence of the process parameters on the forces acting on the tool during the FSW process. Furthermore, it was studied the correlation between the forces and the grain size, in particular with the extension of the heat-affected zone. Forces acting along the axis parallel to the tool are actually greater than those acting along welding direction. All the recorded forces are strictly dependant on the process parameters adopted. No correlation has been found between the grain dimension within the weld bead and the recorded forces, while the greater the forces, the narrower the extension of the heat-affected zone.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
2024 aluminium alloy is used for parts and structures which demand high-strength/weight ratio. In particular, Al2024 is, for its high specific strength and good chemical stability, a suitable ...material for aerospace application. Aluminium alloys are involved in corrosive phenomena when they are used in critical applications, such as the aeronautic ones. The solution commonly adopted to solve corrosive problems is to paint aluminium alloy surface including 2024 aluminium alloy which is the subject of this study. The applied paint film protects the aluminium alloy from corrosion. In order to improve the adhesion of the paint film it is necessary to pre-treat the manufactured surface. The objective of the pre-treatment is to develop a cleaned, uniform, wettable surface. Cold plasma is an efficient, economic and environmentally attractive alternative to the use of the traditional pre-treatment. This work aims to study the relationship between cold plasma and 2024 aluminium alloy wettability and cleaning. Surface samples have been analysed by: (i) standard procedure to measure the quantitative wettability; (ii) Energy Dispersive X-ray Spectroscopy or EDS to determine a quantitative measure of organic contaminant.
This work demonstrates that air cold plasma treatment improves significantly wettability and cleaning of 2024 aluminium alloy surfaces both associated with pre-cleaning by MEK
® and without pre-cleaning by MEK
®: the wettability reducing has been greater than 70% and the contaminants reducing greater than 65%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
2024 aluminium alloy is widely used in aeronautical applications because it provides a high mechanical strength and low weight. Aeronautical critical environmental conditions cause corrosion on the ...surface in part, due to the Cu present in Al2024. To solve problems associated with corrosion, the aluminium alloy surface is commonly covered by paint; it is important to guarantee the adhesion of the paint coating to the aluminium alloy and the stability of the coating in the course of time. To achieve this aim the surface must be prepared before applying a protective coating. Cold plasma treatment represents an efficient, non-polluting and economical alternative to clean and activate aluminium surfaces. In particular, it has been demonstrated that an oxygen cold plasma treatment improves wettability and adhesion of the Al2024 surface.
The aim of this work has been to value the wettability ageing time of Al2024 surfaces treated with oxygen cold plasma. The evaluation of the ageing time represents a fundamental step to plan the insertion of the plasma process inside an industrial process. In fact, once the ageing time has been determined, it is possible to establish how much time has to pass between the surface activation of a body, obtained by cold plasma treatment, and the following paint process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Cemented carbides, also known as Widia, are hard metals produced by sintering process and widely used in mechanical machining. They show high cutting capacity and good wear resistance; consequently, ...they result to be excellent materials for manufacturing cutting tools and sandblast nozzles. In this work, the wear resistance of WC-Co carbides containing Eta-phase, a secondary phase present in the hard metals when a carbon content deficiency occurs, is analyzed. Different mixtures of carbide are prepared and sintered, with different weight percentages of carbon, in order to form Eta-phase and then analyze how the carbon content influences the wear resistance of the material. This characterization is carried out by abrasive wear tests. The test parameters are chosen considering the working conditions of sandblast nozzles. Additional information is gathered through microscopic observations and the evaluation of hardness and microhardness of the different mixtures. The analyses highlight that there is a limit of carbon content below which bad sintering occurs. Considering the mixtures without these sintering problems, they show a wear resistance depending on the size and distribution of the Eta-phase; moreover, the one with high carbon content deficiency shows the best performance.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper presents an original algorithm, with a finite-element interface capability, that can calculate, for superplastic forming processes, the load curve to be applied during forming. The ...algorithm makes it possible to maintain the maximum strain rate as near as possible to the optimum characteristic value of the material thereby reducing forming time. The proposed algorithm was validated by calculating the optimum pressure curve to be assigned in the case of both a conical-bulging process and a cap-forming one. Parallel experimental activity was carried out using a Pb/Sn-based metallic alloy that is superplastic at room temperature. For both geometries examined, comparison between numerical and experimental results proved to be acceptable. In particular, the relative error was less than 6% for measurements of both the strain–time relationship and the thickness distribution. Different measurements were carried out during each process: the shift in the sheet centre-point for the conical-bulging process and the thickness distribution corresponding to a particular sheet configuration for the cap-forming one.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The use of hard metals, in particular for cutting tools, is becoming wider. Their manufacturing cost, higher than traditional steel, is compensated by an increased lifetime. This work involves the ...rheological characterization of a WC–Co compound, in order to evaluate its viscosity for different values of strain rate. Following this characterization, the data are implemented in a FEM code, in order to simulate the extrusion processes of such compounds to manufacture hard metal bars. This study highlights the importance of an accurate viscosity evaluation of these mixtures and the correct setting of FEM parameters in order to predict successfully extrusion processes. As an example, an analysis is presented for the case of cutting tools with helical holes for the passing of fluid coolant.
•The rheological characterization of a WC–Co compounding is proposed.•The viscosity for different values of strain rate is evaluated.•An extrusion process to manufacture hard metal bars is simulated.•Bars for cutting tools with helical holes are realized.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
