Search

Additive manufacturing technologies have several well-known advantages; however, the surface quality of the printed parts is poor, compromising the corrosion and mechanical properties. Thus, surface finishing treatments are necessary. The most post-processing treatments proposed in the literature are mechanical or chemical. The formers are contact techniques and cannot be suitable for complex geometry, while the latter use strong and dangerous reagents. This paper is aimed to investigate the effect of the electropolishing treatment, a contactless technique, using an eco-friendly electrolytic solution in reducing the roughness and improving the fatigue properties of Ti6Al4V specimens produced by electron beam melting technology. Several parameters affecting the effectiveness of the electropolishing treatment have been investigated, as interelectrode distance, stirring rate and duration time. An optimal combination of them allowed a uniform surface treatment and a significant roughness reduction (64% of Sa reduction for cylindrical specimens). Under sinusoidal loading conditions with a maximum stress of 378 MPa and a stress ratio equal to R = 0.1, the mean fatigue life of electropolished dog-bone specimens was 250% longer than that of as-built specimens.

The homogenization of a Vierendeel girders with elastic jointsis is treated in the paper. The starting point of the proposed method is the Stephen transfer matrix analysis and the polar Timoshenko beam is adopted as equivalent continuum of the Vierendeel girder. The polar character of the homogenized beam raises by the analysis of the pure bending eigenvector components of the girder force transfer matrix. Two bending moments are transmitted by the unit cell of the girder: one is caused by the couple of axial forces applied on each nodal section of the beam, the other is due to the moments present at the nodes of each ones by the adjacent cells and is modelled as the resultant of the micro-polar moments. The Transfer force eigenvector analysis bring out that the unit cell bends maintaining the webs undeformed. This property allows evaluating both the bending stiffnesses and the equivalent material micro-polar scale parameter with straightforward equations. The results of the homogenization procedure proposed are tested by comparison with litera-ture data and with the the outcomes of the analysis of a series of girders carried out by the finite element method.

It refers to the use of a graphical technique in combination with the experimentation standardized by ASTM G99 to identify a parameter that characterizes and quantifies the wear behavior of a steel thermally and/or chemically variously treated, such as those used to build tools for working hard materials or moulds for the powder metallurgy. In particular, the experimental procedure adopted, the data acquisition modes of the tests, the processing mode and interpretation of these latter are described. Finally, the precision with which the wear parameter is evaluated by the graphical technique and the possibility to distinguish - with only one test - the wear behavior of the treated surface layer from that of the base metal are pointed out. The material used for the creation of the various specimens' samples is the sintered Vanadis 4 Extra. Each sample was subjected preliminarily to one or two of the following treatments: quenching, cryogenization, nitrogenization and coating with the PVD coating technique.

Planted articular joints replace bone articulation allowing the transfer of loads and articular displacements. However, hip prosthesis cannot guarantee the same dynamic friction coefficients of natural joints. The present study analyses the main design solutions for hip prosthesis, in terms of geometries and materials and an in-depth bibliographic research was performed to identify the load spectra corresponding to the different operation conditions of the planted joint. The final aim of this study is to analyze the stress state induced in the prosthesis by the mounting effect as well as under the action of loads deriving from ambulation in order to perform a structural optimization which guarantees the needed life time. In order to optimize the chosen prosthesis, the geometry of the three elements constituting the prosthesis was reconstructed through the reverse engineering technique: femoral head, acetabular cup and insert. The geometries obtained were used to implement a finite element 3D model in ANSYS® environment. The results obtained with the finite element 3D model were used as a reference to study the effects of some geometrical parameters of the prosthesis with a simplified model which takes advantage of the geometric axisymmetrical properties of the prosthesis.

Si analizza il comportamento a fatica di pistoni per motori ad accensione comandata, alimentati con miscela alcool-benzina, mediante prove full-scale al banco e con una macchina universale adeguatamente attrezzata per simulare il carico di esercizio sull'articolo di prova. I primi risultati ottenuti mostrano un'ottima resistenza del tipo di pistone esaminato all'innesco di cricche di fatica ed alla propagazione dei difetti, anche severi, appositamente introdotti sulla superficie di testa

This paper describes the redesign activities of lightweight rail vehicle component using advanced composite materials. The activities have been carried out in the framework of the SCILLA-M National Project funded by Ministry of Research in collaboration with AnsaldoBreda. By exploiting the lightweighting and design integration benefits of composites, an innovative solution has been developed, which provides significant savings in mass, cost and part count compared to conventional designs. Several solutions have been evaluated among those reported in literature and related to the several transport systems. On the basis of the information acquired composite structure seems to be the ideal candidate for the design of lightweighting railway components. The current metallic design has been compared with the new proposed solutions in terms of weight saving, stiffness and strength. An innovative flatwise composite panel solution, which has been selected among those analyzed, seems to be applicable for the structural optimization of the railway vehicle carbody roof. The study underlines that the sandwich structure made of composite materials and polyurethane foam confirms to give good results in terms of weight and flexural stiffness. Consequently, the proposed sandwich structure can be adopted in the design of an innovative railway vehicle carbody roof.

In the paper a study on an underactuated finger for a robotic hand is presented. The mechanical hand, of which the finger is a part, is an underactuated device made of five fingers, each one having three phalanxes, operated by non-extendible tendons; thus it can be used both as robot grasping end-effector and as human prosthesesis. The mechanical behavior of the finger was studied by means of an energetic or variational approach. The latter model permits an easier computing of the constraint reaction applied to the tendon end when the displacement is imposed. Results are presented obtained both by the proposed model and by a simulation multilink code. Finally an early experimental prototype is also shown.

On the basis of what established by the Product Technical Specifications - Specifiche Tecniche di Prodotto RFI (STP) - regarding the performance requirements that fastening systems between sleepers and rails should meet to be homologated, a test plant was designed and a procedure to determine the capabilities of the above-mentioned systems to lessen the effects of impact loads was defined. Moreover, specific guidelines concerning the ways in which impacts are generated are not supplied by the same STP. Issues arise in designing the test plant due to the need of guarantee a certain adjustment margin on the drop height as well as on the determination of the weight of the drop mass. Before building the plant, to check that it could perform impact tests in compliance with the Norms specifications, a massive numerical simulation campaign have been carried out. Numerical results allowed to solve optimally the design problem of the test apparatus here proposed.

This paper describes the design of composite shock absorber mounting for an innovative rail vehicle end in which structural, crash and aerodynamic functionalities are realized in a single integrated element. An experimental activity has been conducted in order to characterize the basic stiffness and strength parameters of the selected composite material. Results of the material characterization have been used for the laminate composite material card of the FE software. The computational analysis has been performed to optimize the sandwich configuration of the composite component and to assess the structural requirements. The final configuration of the composite sandwich shock absorber mounting exhibits strength and stiffness that are very close to the existing metallic one with a significant weight saving. The activities have been performed in the context of the Italian research project “SCILLA-M” (Structures, Innovative Components, Light Applications for Metro) funded by the MIUR (Ministry of Education, University and Research).

The present experimental work analyses the impact behaviour of thermosetting composite materials for aeronautic applications. The main goal of the experimental activity was to identify the energy level in correspondence of which penetration occurs. The initial values of the impact energy were estimated according to analytical correlations found in literature. Tests were performed on three types of composite panels: carbon fibre laminated panels, fibreglass laminated panels and hybrid panels. The technology of lamina is that of prepeg fabric with twill sequence and fibres weaving at 0°-90° and ± 45°. The fixture used for tests is a Charpy impact test machine, which was conveniently equipped to evaluate the angular variation and the acceleration of the impacting mass. Preliminarily, non-destructive ultrasonic controls were performed to check that the specimens were not damaged before impacts tests. The interesting results of the tests were identification of the energy absorbed and the impact force for each specimen. Moreover, for each energy and force level, it was possible to associate a different fracture state. Comparisons among the results obtained for specimens made up of just one type of reinforcement (glass or carbon) and the results obtained with hybrid specimens were performed.

In the present paper a model of an underactuated tendon driven mechanical hand is proposed. The aim of the activity was to study the possibility of realization of a mechanical hand five fingers, the movement of which is realized by the use of one only actuator. The mechanism is conceived as an hand prosthesis. The main particularity of the device essentially consist in that it is based on an adaptive scheme. In this way it is possible to obtain that the three phalanxes of each of the fingers adapt their rotation to the grasped object shape. This will be obtained by non-extendible tendons. So each finger will grasp the object surface independently on the configuration of the finger itself and independently on the configuration of the other fingers.

The results of an experimental inquiry regarding damping properties of alternative materials for rail-to-ground fastening components are presented and discussed. The examined materials are an high porosity sintered steel and a composite material obtained by infiltrating the steel with a viscoelastic resin. Fatigue tests were carried out with a resonance vibrofore under various fluctuating compressive loads of constant amplitude. The tests were periodically interrupted to acquire the load decay curves from which material damping properties were derived by a new procedure. Finally, damping data obtained from both materials were compared and discussed on the basis of information gained from static tests and literature results.

A method is presented for evaluating the axial critical loads and deformed shapes of a Vierendeel periodic girder. They are obtained by solving the large-deflections equilibrium problem of a micro-polar equivalent model. The elastic properties of this model have been derived from those of an ideal girder whose cells may deform only according to the inner forces transferring modes of the unit cell. In particular, the strain energy density of the equivalent medium is obtained by evaluating the limit of the girder elastic energy for the cell to girder size ratio tending to zero. To solve Engesser/Haringx discord, the large deflections equilibrium equations are deduced by the virtual work principle, without any a priori assumption on the shear force. For this aim, also the external work of the substitute medium is evaluated by the same procedure as the strain energy density. Actually, it is first written for the ideal girder under the assumption of negligibility of the axial effects at the cell-scale, then specialized for the continuous medium by examining the limit value for cell to girder size ratio going to zero. Closed form solutions for the critical deformed shapes are given, together with an accurate formula for the girder buckling load

In this study the mechanical properties of parts 3D printed with virgin polylactic acid (PLA) to those printed with recycled PLA were compared. Using an entry level 3D printer and commercially available PLA, tensile specimens were produced and then tested. The specimens were then ground up and re-extruded into filament, and a second set of specimens were produced and tested using this recycled PLA filament. Mechanical testing showed that 3D printing with recycled PLA is a viable option. However, although the average mechanical properties before and after recycling were similar, there was more variability in the results of the recycled filament. Additionally, when printing with the recycled filament there was some nozzle clogging, while none occurred with the virgin filament. Overall, the mechanical properties of specimens 3D printed from recycled PLA filament were similar to virgin properties, encouraging further development in the area of recycling 3D printed filament.