1,720,982 research outputs found
Study of pseudoelastic systems for the design of complex passive dampers: Static analysis and modeling
Get PDFThis work presents an experimental and numerical analysis of several parallel systems of NiTi pseudoelastic wires. Standard tensile tests were accomplished to evaluate the global damping capacity, the energy dissipated per cycle and the maximum attenuated force in a static condition. Besides, a numerical model was implemented to predict the damping response of more complex pseudoelastic arrangements. It was found a damping capacity upper limit of 0.09 regardless the number and the length of the NiTi components. In addition, it was found that the energy dissipated per cycle is related to the strain and to the number of the NiTi components; furthermore, the system composed of NiTi wires with different length allows for an elastic region that is related to the numbers of wires and that presents a modulation of the stiffness. Finally, the proposed numerical model allows a precise design of complex pseudoelastic combinations as it is able to represent the rhombohedral characteristic
Static and dynamic response of SS316L thin-wall Origami and Auxetic structures fabricated through laser powder bed fusion
No full textIn many engineering applications, vibrations are a constant concern, and mitigating their effects is crucial to preserve structural integrity, functionality, and overall safety. With their distinct geometry and material distribution, lattice structures are an intriguing solution to vibrational issues and additive manufacturing represents a production process that can meet the challenge of fabricating such geometries. This work represents a preliminary investigation of novel metal lattice specimens fabricated through additive manufacturing aiming at providing further insights into the field of damping of lattice structures. To this end, a laser powder bed fusion technique is used to fabricate SS316L thin-wall Origami and Auxetic structures. Defects analysis along with quasi-static and dynamic mechanical tests have been carried out. A numerical model to predict the stress distribution in the two structures have been developed as well. It was found that the mechanical response is influenced by defects resulting from the production process, such as porosity and dimensional errors. Furthermore, the results of the static tests show a notable decrease in the elastic modulus when compared to the bulk specimen, indicating that the thin-walled construction exhibits the scale effect. Dynamic tests have been carried out through the study of the Tan Delta parameter at different deformation and frequency amplitudes. The mechanical response presented by the two geometries is similar. For both structures, results indicate that Tan Delta decreases with the mean force, increases with frequency and stabilizes at high solicitation amplitude to approximately 0.02. The highest Tan Delta was registered for the Auxetic structure measuring 0.073 at a mean force of - 20 N, 0.006% deformation and 5 Hz
Design and optimization of a new NiTi-based shape memory alloy structures for damping applications via additive manufacturing
Get PDFShape Memory Alloys (SMA), such as NiTi-based systems, are functional materials suitable for damping applications due to their pseudoelastic effect. This property allows to obtain simple, lightweight structures capable of absorbing energy through a mechanical hysteresis and able to recover significant deformations. For this reason, SMA are attractive candidates for the development of novel devices in many fields, such as the biomedical one or in aerospace and in automotive. Recently, the development of Additive Manufacturing (AM) of metals has considerably expanded the design and production possibilities of SMA-based devices, potentially overcoming the limited workability of these materials through conventional manufacturing techniques, which is one of the main limitations to their wider adoption. This study presents a preliminary investigation of a NiTi octahedral cell structure fabricated via Laser Powder Bed Fusion (L-PBF) starting from a NiTi powder with Ni content of 50.8 at. %. C..
An in-depth study of a thin-wall origami-inspired NiTi structure fabricated through laser powder bed fusion
Get PDFThis study aims to advance the field of additive manufacturing of NiTi shape memory alloys by providing a comprehensive functional analysis of a complex NiTi structure fabricated using laser powder bed fusion. While most of the literature on additive manufacturing of NiTi has been focused on the pseudoelastic effect, this research explores both pseudoelastic and shape memory effect. The selected geometry is origami inspired with wall thickness of 0.45 mm. Samples were fabricated through an AM400 of Renishaw starting with a NiTi powder with 50.8 at. % of Ni and followed a double-stage heat treatment, at 950 °C for 5.5 h and 450 °C for 15 min. The heat-treated cells were characterized to assess at first the phase transformation temperatures through thermal analysis and then both the pseudoelastic and the shape memory effects (analyzing both free and under load shape recovery), with maximum load ranging from 600 to 1500 N for pseudoelasticity, from 600 to 1000 N for free shape recovery an..
Preliminary design and modeling of mini channels to enhance heat transfer in a millimetric catalytic combustor
Get PDFMini channel solution is used in devices that require a high density of transmitted thermal power as a very large-scale integration design in computer systems and compact exchangers. Furthermore, the mini channels are extensively investigated in the literature for turbulent and laminar regimes. In this project, different configurations of mini channels have been studied to enhance heat transfer, using simulations with a commercial multi-physics code. Thanks to the results of the models, more promising configurations with 3D printing technique may be built. The project challenge is improving convective thermal power extracted by the exhaust gases of a mini-catalytic combustor. The combustor feeds six modules for thermoelectric power production (TEMs). As the first step, three different mini channel geometries have been chosen; the first one with 19 channels with rectangular cross-section, the second one with 6 channels with a convergent profile, and the latter with 2 channels with a fractal branching geometry. Simulations started from studying fluid dynamic to investigate the velocity field at the exit of the mini channels. The analysis has been extended by adding the conjugate heat exchange between fluid and combustor wall. The results show an increase in heat exchange compared to the base case for all configurations, with a maximum value for the 19 mini channels configuration
Processing and surface treatments for pseudoelastic wires and strands
No full textThe 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 multiwire Ni-Ti strand has been prepared, characterized and thermally treated in this research. The pseudoelastic strands have not been widely investigated in the literature to date, 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 (scanning electron microscopy [SEM], X-ray photoelectron spectroscopy [XPS], Energy Dispersive X-ray Spectrometry [EDS], dynamic wettability), of a single wire and multiwire strand was 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 were treated by mechanical roughening and different chemical modifications (acid and peroxide etching) and characterize
Towards an understanding of the functional properties of NiTi produced by powder bed fusion
Get PDFIn this work, near fully dense NiTi components have been fabricated using a 55.2Ni-Ti (wt.%) powder through selective laser beam melting. The effect of the manufacturing process on mechanical and functional properties of the selected NiTi alloy has been systematically investigated by tuning the hatching distance, h, and the scanning speed, v, in order to define a set of 12 NiTi families. The as-built NiTi parts present phase transformation temperatures higher than those of the feedstock, ascribed to the depletion of Ni during the process. Pseudoelasticity and shape memory responses have been evaluated through uniaxial compression and bending measurements, respectively. Both quasi-static and dynamic analyses have been considered. It is shown that the resulting material may exhibit distinct damping and strain recovery responses depending on the used process parameters
Additive manufacturing for orthopedic implants: morphological and material characterization of SLM thin Ti6Al4V samples
Get PDFLaser and surface processes of NiTi shape memory elements for micro-actuation
Get PDFIn the current microtechnology for actuation field, shape memory alloys (SMA) are considered one of the best candidates for the production of mini/micro devices thanks to their high power-to-weight ratio as function of the actuator weight and hence for their capability of generating high mechanical performance in very limited spaces. In the microscale the most suitable conformation of a SMA actuator is given by a planar wavy formed arrangement, i.e., the snake-like shape, which allows high strokes, considerable forces, and devices with very low sizes. This uncommon and complex geometry becomes more difficult to be realized when the actuator dimensions are scaled down to micrometric values. In this work, micro-snake-like actuators are laser machined using a nanosecond pulsed fiber laser, starting from a 120-μm-thick NiTi sheet. Chemical and electrochemical surface polishes are also investigated for the removal of the thermal damages of the laser process. Calorimetric and thermo-mechanical tests are accomplished to assess the NiTi microdevice performance after each step of the working process. It is shown that laser machining has to be followed by some post-processes in order to obtain a micro-actuator with good thermo-mechanical properties
A Study of a Cryogenic CuAlMn Shape Memory Alloy
No full textIn extreme temperature environments, a newly emerging engineering application involves both the active and passive control of structures using cryogenic shape memory alloys, which are smart materials able to recover high deformation below the freezing point. With the objective of carrying out new advances in this area, the present work aims to investigate the Cu-7.5Al-13.5Mn (wt.%) shape memory alloy. Thermal, microstructural, and thermomechanical analyses of as-cast and hot-rolled specimens were performed, taking into account the effects of annealing and solubilization. It was observed that the phase transition occurs at temperatures below 120 K and changes according to the thermo-mechanical path. Specifically, hot-rolling lowers the phase transition temperature range with respect to the as-cast condition–from 34 K to 23 K for Mf, and from 89 K to 80 K for Af. Additionally, when the annealing temperature rises, the phase transformation temperature increases as well, and the alloy loses its cryogenic features when heat treated above 473 K. Finally, loss factors of 0.06 and 0.088, which were respectively found in dynamic and static settings, validate the material’s good damping response
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