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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.

The present paper concerns an approach to the structural identification of tall buildings. The identification is based on a large number of experimental data obtained on a scaled model. The procedure consists in steps of system identification by means of a refined finite element model which is the base for the evaluation of a simplified one dimensional scheme. The parameters accuracy of this last one has been determined with reference to a refined schematization. The approach is model updating, based on the first three experimental natural frequencies and modes. The case study is a structure in Naples, made by two reinforced concrete towers, linked at the top by a steel girder with suspended storeys, while the foundation slab is based on a reinforced concrete piled group.

This paper deals with a mechanical model for the analysis of the railway track behaviour built by exploiting the periodicity of the track-structure. The starting point of this study is the analysis of the inner forces transferring modes. They have been determined by the unit principal vectors analysis of the base cell transfer matrix. The proposed model is able to reproduce accurately the track behaviour in transferring its inner forces. However, solutions that are equilibrated but not kinematically admissible are obtained from it when transversal loads are applied. In additions, only boundary conditions compatibles with the track transferring modes can be satisfied. This inconsistency is eliminated by superposition of a corrective deformed shape. This is derived from the eigenvectors of the transfer matrix pertaining to self-equilibrated systems of bending moments decaying along the track. The application field of the proposed track model is also discussed and the results of a validation study carried out by F.E. analysis are finally presented.

In this paper an homogenization procedure of a Vierendeel girders with elastic joints is shown. The method is based on the Stephen transfer matrix analysis and employs as substitute continuum a polar Timoshenko beam. The polar character of the equivalent beam arises quite naturally from the analysis of the pure bending eigenvector components of the girder force transfer matrix. Through the girder unit cell, two bending moments are transmitted: one is generated by the couple of axial forces acting on each nodal section of the beam, the other is produced by the moments applied at the nodes of every ones by the adjacent cells and is modelled as the resultant of the micro-polar moments. Transfer force eigenvector analysis reveals that the unit cell bends maintaining the webs undeformed, a property that allows evaluating both the bending stiffnesses and the equivalent material micro-polar scale parameter by means of straightforward equations. The accuracy of the proposed method is verified by comparing the predictions of the homogenized model with literature data and with the results of the analysis of a series of girders carried out by the finite element method.

Several prototypes of mechanical fingers composing anthropomorphic prosthetic hands have been developed using underactuated mechanisms. These mechanisms require specific experimental procedure to measure their properties. Due to their low weight, the addition of further sensors for measurement purposes could modify the trajectory of the single parts and the overall prosthetic device behaviour. Vision system methods represent a route to overcome these drawbacks. In this study, an experimental methodology to acquire the dynamics of an underactuated prosthetic finger is presented due to the employment of a vision-based technique, the Digital Image Correlation. The experimental characterization aids the development of a dynamical model of the finger behaviour.

The recent diffusion of wind turbines has evidenced problems about their vulnerability in different site conditions, as shown by recent collapse of wind towers after severe actions. The analysis of structures subjected to variable actions can be carried out by means of several methods with different levels of accuracy, among which the nonlinear dynamics is generally recognized as the most reliable one. This paper develops a numerical procedure to obtain approximate solutions for rigid-plastic response of structures subjected to base harmonic pulse. The model is applied to a wind turbine tower subjected to inertia forces generated by an harmonic ground acceleration, in which the failure is assumed depending on the formation of shear hinges. The approach presents the advantages of rigid-plastic procedures, in particular an efficient representation of the post-elastic behaviour of the structure, low computational competence and limited number of mechanical parameters.

The global interest in renewable energy sources has increased the attention to the manufacturing of wind turbine towers, since they are largely diffused in seismic areas too. Different types of towers have been produced in recent years. Among them, the truss structures assure a reduced mass and the modular characteristics necessary for easy transportation. Reduced costs of production, installation and maintenance are typical of these structures. Nonlinear dynamics is an efficient framework to analyze structures subjected to variable actions, i.e. to assess the seismic safety of wind turbine towers in case of earthquake actions. This study outlines a procedure to evaluate the post-elastic behavior of truss towers for wind turbines. Rigid-plastic behaviour is taken into account to develop approximate solutions for the problem of a tower modeled as a vertical cantilever beam and subjected to harmonic base motion. A comparison with the results of a finite element model is proposed.

To homogenize lattice beam-like structures, a direct approach based on the matrix eigen- and principal vectors of the state transfer matrix is proposed and discussed. The Timoshenko couple-stress beam is the equivalent continuum medium adopted in the homogenization process. The girders unit cell transmits two kinds of bending moments: the first is generated by the couple of the axial forces acting on the section nodes, the other one is due to the moments directly applied at the node sections by the adjacent cells. This latter moment is modelled as the resultant of couple-stress. The main advantage of the method consists in to operate directly on the sub-partitions of the unit cell stiffness matrix. Closed form solutions for the transmission principal vectors of the Pratt and X-braced girders are also attained and employed to calculate the stiffnesses of the related equivalent beams. Unit cells having more complex geometries are analysed numerically. As a result, the principal vector problem is always reduced to the inversion of a well-conditioned ( 3 × 3 ) matrix employing the direct approach. Hence, no ill-conditioning problems, affecting all the known transfer methods, are present in the proposed method. Finally, comparing the predictions of the homogenized models with the finite element (f.e.) results of a series of girder, a validation of the homogenization method is performed.

The seismic protection of objects contained within museums is a topic of great interest, especially with reference to how they are displayed or stored. This problem is the same as that of a large class of non-structural components, such as mechanical and electrical hospital and laboratory equipment that could lose their functionality because of earthquakes. Statues and ceramics simply supported on the floor represent a significant set of case. In some cases, like the Bronzes of Riace, isolation systems have been developed. However, in general museum exhibits are not equipped with devices capable of mitigating the oscillations induced by possible earthquakes. The case study of a marble statue placed on a freestanding squat rigid pedestal is examined. The system of algebraic differential equations governing the problem has been derived and included in an ad-hoc numerical procedure. It is shown that the insertion of a squat rigid body with low frictional resistance at the lower interface with the floor, and high frictional resistance at the upper interface with the artifact significantly reduces the amplitude of the rocking response. As a result the artifact rocks without sliding on the rigid base that slides without rocking with respect to the floor. The numerical analysis performed can be a tool to help in the choice of the optimal friction values in the surfaces of the flat block, designed as a simple isolation system.

Over the past few years, foam materials have been increasingly used in the passive safety of sport fields, to mitigate the risk of crash injury. Currently, the passive safety certification process of these materials represents an expensive and time-consuming task, since a considerable number of impact tests on material samples have to be carried out by an ad hoc testing apparatus. To overcome this difficulty and speed up the design process of new protective devices, a virtual model for the low-velocity impact behaviour of foam protective mats is needed. In this study a modelling approach based on the mesh-free Element Galerkin method was developed to investigate the impact behaviour of ethylene-vinyl acetate (EVA) foam protective mats. The main advantage of this novel technique is that the difficulties related to the computational mesh distortion and caused by the large deformation of the foam material are avoided and a good accuracy is achieved at a relatively low computational cost. The numerical model was validated statistically by comparing numerical and experimental acceleration data acquired during a series of impact events on EVA foam mats of various thicknesses. The findings of this study are useful for the design and improvement of foam protective devices and allow for optimizing sports fields&rsquo, facilities by reducing head injury risk by a reliable computational method.

A homogenization method for periodic beam-like structures that is based on the unit cell force transmission modes is presented. Its main advantage is that to identify the principal vectors of the state transfer matrix corresponding to the transmission modes it operates directly on the sub-partitions of the unit cell stiffness matrix and allows to overcome the problems due to ill-conditioning of the transfer matrix. As case study, the Pratt girder is considered. Closed form solutions for the transmission modes of this girder are achieved and used into homogenization. Since the pure bending mode shows that the Pratt unit cell transmits two kinds of bending moments, one given by the axial forces and the other originated by nodal moments, the Timoshenko couple-stress beam is employed as substitute continuum. Finally, a validation of the proposed procedure is carried out comparing the predictions of the homogenized models with the results of a series of girder f.e. analyses.

This paper deals with a mechanical model for the analysis of the railway track behaviour built by exploiting the periodicity of the track-structure. The starting point of this study are the inner forces transferring modes. They have been determined by the unit principal vectors analysis of the base cell transfer matrix. The main outcome on bending moments is that they are transferred through the track without deforming the sleepers and fasteners and are composed of two parts: the first one, referred as primary bending moment, is generated by the couple of axial forces acting on each nodal section while the second is due to the curvature changes of the rails. Shear forces are engendered by two independent mechanisms that are associated respectively with the unit changes of the total and primary bending moments. The constitutive properties of the equivalent medium are derived by an averaging and limiting process of the transferring modes strain energies, avoiding any a priori assumption on the kinematics of the substitute medium. Finally, the equilibrium equations are achieved by the virtual work principle. The proposed model is able to reproduce accurately the track behaviour in transferring its inner forces. However, solutions that are equilibrated but not kinematically admissible are obtained from it when transversal loads are applied. In additions, only boundary conditions compatibles with the track transferring modes can be satisfied. This inconsistency is eliminated by superposition of some corrective deformed shapes. These are derived by the eigenvectors of the transfer matrix pertaining to self-equilibrated systems of bending moments decaying along the track. The application field of the proposed track model is also discussed, and the results of a validation study carried out by F.E. analysis are finally presented.

The paper deals with a direct approach to homogenize lattice beam-like structures via eigen- and principal vectors of the state transfer matrix. Since the girders unit cells transmit two bending moments, one given by the axial forces, the other originated by nodal moments, the Timoshenko couple-stress beam is employed as substitute continuum. The main advantage of the method is the possibility of operating directly on the sub-partitions of the unit cell stiffness matrix. Closed form solutions for the Pratt and X-braced girders are achieved and used into the homogenization. Unit cells with more complex geometries are numerically addressed with direct approach, showing that the principal vector problem corresponds to the inversion of a well-conditioned matrix. Finally, a validation of the procedure is carried out comparing the predictions of the homogenized models with the outcomes of f.e. analyses performed on a series of girders.

The analysis of structures subjected to earthquake actions can be carried out by means of several methods with different levels of accuracy, among which the nonlinear dynamics is generally recognized as the most reliable one. This paper presents a general treatment to develop approximate solutions for rigid-plastic response of structures subjected to base harmonic pulse, by means of a numerical procedure on purpose developed. The case study is a vertical cantilever beam, with base support, constant mass and inertia distribution, subjected to only ground acceleration. The failure is assumed depending on the formation of a single shear hinge and the results are expressed in general terms. As a result, the motion proceeds through successive spreading and contractions of the plastic front and related elastic returns. Possible applications of the method to real structures can be envisaged. © 2020 European Association for Structural Dynamics.