Il Rapporto descrive le attività e i risultati ottenuti nel periodo gennaio 2022 - aprile 2022: realizzazione preserie dispositivo

Il Rapporto descrive le attività e i risultati ottenuti nel periodo maggio 2021 - gennaio 2022: (i) studio di fattibilità, (ii) studio, progettazione e ingegnerizzazione del prototipo

Background: Childhood dyskinesia (CD) is a complex movement disorder with components of dystonic and hyperkinetic nature, characterized by involuntary, sometimes stereotypical postures and gestures that are often impossible to control and hinder the execution of willful motion. The standard orthoses for the treatment of neurological diseases, including CD, are generally poorly differentiated for functional characteristics. The application of similar devices for movement disorders is far less generalized because of the very different symptoms, including the incapacity to control rather than initiate movement.

Herein, a new torsional device based on shape memory alloy elements and operating as torque limiter is presented. It consists of a set of pseudoelastic NiTi tapes working in series configuration. The tapes are assembled radially with respect to the rotational direction and work sequentially in beam-like bending mode. The trend of the resulting torque may span from pulsating to continuous by changing the number of tapes. Furthermore, the use of NiTi material enables a temperature-dependent response. Due to the particular mounting, the flag-shaped pseudoelastic mechanical behavior typical of NiTi is partially hidden; however, the use of pseudoelastic elements provides a stable cyclic response and enables the possibility to tune the output torque.

High temperature (550 °C) and short duration (10, 15, 20 s) heat treatments were performed on pseudoelastic NiTi alloy in addition to the conventional aging process in order to increase the mechanical hysteresis of the material. Pre-treated and aged samples were compared with plain aged ones through mechanical testing, powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The introduction of the pre-treatment, in combination with the aging process, was shown to increase the mechanical hysteresis of the aged samples up to ~30% after stabilization. XRD analysis showed how the introduction of the pre-treatment introduces a recovery of the residual stresses in the material microstructure, as well as the nucleation of different sets of metastable precipitates (such as TiNi3). We thus observe that the combination of pre-treatment and aging affects the alloys microstructure, causing a series of effects that synergise in increasing the material hysteresis.

Thanks to their functional properties, NiTi and NiTi-based shape memory alloys (SMAs) exhibit both pseudo-elastic and intrinsic damping ability finding applications in several fields. The use of these alloys in damping devices or systems allows the attenuation of different kinds of vibration such as noise or more intense oscillations. In this work, the damping behaviour of different NiTi semifinished products has been evaluated by means of dynamic thermomechanical measurements in order to have a preliminary indication for the integration of these SMA elements in damper demonstrators. The evolution of the internal friction parameter with respect to temperature, frequency and strain extent is evaluated. Moreover, some possible demonstrators' concepts, i.e. a cladding panel, some dampers and a shock absorber, are proposed and characterized. The investigated SMA elements are a plain-woven mesh made of NiTi and steel thin wires, wave-shaped NiTi ribbons and NiTi single-turn wave springs. The elements have been thermally treated in order to achieve the required shapes and thermomechanical conditions. The perspectives and potential of these semifinished products in the field of damper devices are investigated by a preliminary characterization and discussed.

Herein, a new torsional device based on shape memory alloy elements and operating as torque limiter is presented. It consists of a set of pseudoelastic NiTi tapes working in series configuration. The tapes are assembled radially with respect to the rotational direction and work sequentially in beam-like bending mode. The trend of the resulting torque may span from pulsating to continuous by changing the number of tapes. Furthermore, the use of NiTi material enables a temperature-dependent response. Due to the particular mounting, the flag-shaped pseudoelastic mechanical behavior typical of NiTi is partially hidden; however, the use of pseudoelastic elements provides a stable cyclic response and enables the possibility to tune the output torque.

In this work, the effect of the Al content (x = 5, 10, and 15 at. %) on the martensitic transformation (MT) and microstructure and mechanical properties of CuZrAl alloys was studied. The microstructure of the alloys was characterized at room temperature by means of scanning electron microscopy and X-ray diffraction. An increase in Al content reduces the amount of transforming CuZr phase, and consequently the secondary phase formation is favored. The evolution of the MT upon thermal cycling was investigated as a function of the Al content by differential scanning calorimetry. MT temperatures and enthalpies were found to be decreased when increasing the Al content. Al addition can induce a sudden, stable MT below 0C, while the binary alloy requires ten complete thermal cycles to stabilize. Finally, the mechanical properties were investigated through microhardness and compression testing. No linear dependence was found with composition. Hardness lowering effect was observed for 5-10 at. % of Al content, while the hardness was increased only for 15 at. % Al addition with respect to the binary alloy. Similarly, compressive response of the alloys showed behavior dependent on the Al content. Up to 10 at. % Al addition, the alloys indicate a superelastic response at room temperature, while higher Al content induced untimely failure.

Among NiTi-based alloys, one of the most promising and exploited alloys is NiTiCu, since the addition of Cu in substitution of Ni in the binary equiatomic NiTi has a significant influence on the martensitic transformation and the thermomechanical properties of the system. A high content of Cu improves the damping properties at the expense of phase homogeneity and workability. The present study focuses on an alloy with a high copper content, i.e., 20 at.%. For this specific composition, the correlation between the thermal treatments, microstructure, formation of secondary phases, and damping properties are investigated by several analyses. The microscopic observation, together with the compositional analysis, allowed the determination of four different phases in the alloy. Both the calorimetry and dynamic thermo mechanical measurements, which confirmed the high damping ability of the alloy, provided a characterization of the martensitic transition. Finally, the electron backscatter diffraction (EBSD) analysis detected the different crystallographic structures (i.e., cubic austenite, orthorhombic martensite, and cubic (face-centered) NiTi2) and their orientation in the different phases. Therefore, the present work aims to improve the knowledge of the role of secondary phases in the optimization of the NiTiCu20 alloy as a valuable alternative to typical alloys used for damping purposes.

This work presents a comparison between two dampers based on conventional NiTi pseudoelastic elements, wires and tapes, and a NiTi pseudoelastic component realized through additive manufacturing. The first case study is a linear damper consisting in parallel groups of pseudoelastic NiTi wires with different length. This device achieves high level of dissipated energy during one working cycle and permits the control and the modulation of the elastic domain. The second case study is a torsional damper composed by a set of pseudoelastic NiTi tapes assembled radially with respect to the direction of rotation. With this configuration, the flag-shaped pseudoelastic behavior is completely hindered. The output torque has a peak-like trend; each peak is related to the bending of a single tape and at the maximum deflection, the corresponding registered torque is null. The third case study is an "A-shaped" auxetic complex structure to use as damper, produced with additive manufacturing technology (Selective Laser Melting). Results show that additive manufacturing permits the fabrication of devices with complex geometries and superior specific damping properties.

This paper presents the design, manufacturing and experimental assessment of a morphing element consisting of a composite corrugated panel that hosts a diffused actuation system based on Shape Memory Alloy (SMA) actuators. The characterisation of the SMA actuators is reported and the system performance is predicted through an analytical model and finite element analyses. Two versions of the actuated system are proposed, with different methods for the physical integration of the SMA wires into the composite part. Manufacturing and testing of specimens with different wire densities are reported. Correlation with experiments validates the analytical and numerical approaches adopted for the design and analyses. The results confirm the potential of the concept proposed for developing corrugated panels that can be contracted in a predefined direction by a load-bearing actuation system, but still retain high stiffness and strength properties in other directions.

Nowadays, additive manufacturing (AM) permits to realize complex metallic structural parts, and the use of NiTi alloy, known as Nitinol, allows the integration of specific functions to the AM products. One of the most promising designs for AM is concerning the use of lattice structures that show lightweight, higher than bulk material deformability, improved damping properties, high exchange surface. Moreover, lattice structures can be realized with struts, having dimensions below 1 mm-this is very attractive for the realization of Nitinol components for biomedical devices. In this light, the present work regarded the experimental characterization of lattice structures, produced by selective laser melting (SLM), by using Ni-rich NiTi alloy. Differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD), and compression testing were carried out for analyzing microstructure, martensitic transformation (MT) evolution, and superelasticity response of the SLMed lattice samples. The lattice microstructures were compared with those of the SLMed bulk material for highlighting differences. Localized martensite was detected in the nodes zones, where the rapid solidification tends to accumulate solidification stresses. An increase of martensitic transformation temperatures was also observed in lattice NiTi.

This work is focused on the study of Ni41-xTi50Cu9Yx (x = 1, 3, 5 at%) alloys prepared setting different temperatures of the annealing process: 900°C, 950°C and 1000°C for one hour with quenching at room temperature. Morphology and chemical composition of annealed specimens were investigated by optical and electronic microscopy observations, together with the energy dispersive X-ray analysis. In addition, calorimetry was useful in determining the path and the product of the phase transition as a function of the annealing temperature. These techniques highlight the peculiar multi-phase structure that characterizes the presented alloys, which result to be principally compound by a double-matrix based on NiTiCu and NiTi alloys, by YCu-based areas, and by few Y-based and Cu-based particles. Optical microscopy helped in detecting the presence of the orthorhombic B19 phase in x = 1 at% and x = 3 at% samples, and it revealed to be more precise with respect to the differential scanning calorimetry. Besides, scanning electron microscopy pointed out the polygonal morphology of the Y-based particles that take origin inside the YCu zones; some star-like inclusions, seemingly related to the nucleation points of such Y particles, were also observed. Image processing helped in studying the average size of YCu areas: it was found that these zones have dimension that increases both with Yttrium content and with the annealing temperature. Finally, scanning electron microscopy was also advantageous in detecting some cracks around and across the YCu areas.

Martensitic transformations in Ni50Ti40Cu10 are well known to proceed with a two-step process, from B2 austenite to monoclinic B19? with intermediate orthorhombic B19. These transformations can be readily followed by X-ray diffraction especially in solution heat-treated materials through split and distribution of the main diffraction lines, while peaks broadening and overlap make the transformations more difficult to be described in highly defective materials. The present study addresses the effect of defects and chemical inhomogeneities on the martensitic transformation, placing particular emphasis on the crystallography of the low temperature B19 to B19? phase transition. Lattice strains proved to be a powerful tool to monitor the martensitic transformations: whereas a clear discontinuity is observed for the solution heat-treated sample, defects promote a continuous progressive distortion from B19 to B19?. Calorimetry and internal friction investigations were added as a reference to verify the occurrence of the transformations and define the corresponding temperatures.

Magnetic shape memory Ni55Fe16Ga29 and Ni50Mn40Sn10 melt spun ribbons have been characterized by thermomechanical and mechanical analysis. Martensitic transformation temperatures show an abnormal tendency to decline under low stress followed by a conventional increase above a threshold stress, related to the internal compressive stress generated in the fabrication process. The shrinkage of the samples during the forward martensitic transformation gives rise to an inverse elastocaloric effect. A conventional contribution in the total elastocaloric response is observed when applied stress overcomes the internal one. The conventional and inverse elastocaloric effects are attributed to the stress-induced forward and reverse martensitic transformation, respectively.

The aim of this work is a preliminary investigation of the manufacturing process of Ni-Ti and Ni-Ti-Cr wires and strands to be applied in mechanical applications. The diamond wires for stone cutting were used as a case study. A prototype of multi-wire Ni-Ti strand has been prepared, characterized and thermally treated in this research. The pseudoelastic strands have not been widely investigated in literature until now and they are not available in the market with this size (final diameter in the 1-2 mm range). A mechanical characterization (tensile and three-point bending tests), as well as surface analysis (SEM, XPS, EDS, dynamic wettability), of a single wire and multiwire strand has been performed. Moreover, different surface treatments to be used during the manufacturing process have been tested for improving the adhesion of a polymeric coating (polyurethane) as protection against abrasion and as the binding element of the diamond beads assembled on the strand. The surfaces have been treated by mechanical roughening and different chemical modifications (acid and peroxide etching) and characterized.

Introduction: We designed and built customised orthotic devices able to provide a non-linear corrective force for the repositioning of the elbow joint. The purpose of this study is to evaluate if those orthoses with pseudoelastic characteristics can improve posture and increase functional movement abilities in stroke patients. On-board sensors were used to investigate the dynamic interaction of patients and orthoses during standardised motor tasks. Methods: Six chronic hemiplegic patients (age 56.16±7.22 years) were enrolled for the study and were prescribed to wear a custom-made orthosis for at least 6 hours a day for a month. Patients were evaluated before and after this period using several scales, including Fugl-Meyer (F-M), Modified Ashworth Score (MAS), and WOLF Motor Function Test (WMFT). Furthermore an accelerometer and an analogic potentiometer on-board the orthosis were used to evaluate quantitatively the performances of patients during the execution of motor tasks such as Reaching Foreward, Hand to Mouth and Timed Upand- Go. Results: The present orthotic treatment produced mild improvements in several articular and functional parameters. For instance MAS (Elbow) decreased by 1±0.89 (p=0.02), F-M (items A-D) improved by 1.66±1.13 (p=0.01) and WMFT increased by 4±4.35 (p=0.05). Improvement in movement speed in the hand-to-mouth task (from onboard sensor) seems to be greater for patients with high pre-treatment MAS (Pearson R2=0.82). Reaching Foreward times decrease by 19.1±20.5% (p=0.035). Spectral analysis of measured accelerations can separate movement uncertainties from cloni. Conclusions: This pilot study showed that a pseudoelastic orthotic treatment can promote moderate reacquisition of segmental mobility of the upper limb in chronic hemiplegic patients. The parameters collected by on-board unit are a promising tool for identifying patterns of movement in evaluation tasks and monitoring variations during the therapy; this resource could be used in future for implementing home-based tele-rehabilitation.

An unconventional method for shape setting of NiTi shape memory alloy wires is proposed. A laser beam was used to induce straight shape, superelasticity and shape memory effects to thin NiTi wires. Laser treatment revealed to be a suitable and reliable alternative to the conventional final thermal treatment of NiTi wires, which is normally carried out in annealing furnaces. Thermo-mechanical and calorimetric tests showed that the laser heat treatment confers optimal functional properties, analogous to those of commercially available NiTi wires.

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Shape memory alloys (SMAs) are active materials able to recover large strains over several thermo-mechanical cycles. In the actuation field, this strain recovery is principally exploited on the mini and micro scales at which SMAs exhibit their highest power density with respect to common lightweight technologies. During the repetitive actuation of a SMA element, certain events occur: strain drift at the beginning of cyclic testing, the accumulation of plastic deformation, and strain stabilisation. In this study, these events as well as the overall mechanical response of an articulated NiTi element were monitored through calorimetry and scanning electron microscopy. Fatigue and cyclic stability were tested under different loads and under different aging conditions. In addition, the surface morphology was continuously observed via scanning electron microscopy to monitor crack growth and propagation during the fatigue test. Finally, before and after the fatigue test, samples were tested through calorimetry to investigate the overall microstructural homogeneity. Results confirm the high potential of the proposed geometry for the development of NiTi non-conventional active elements in the miniature actuation field.