Search

In this work, we studied the nature and dilemma of the inverse magnetocaloric effect using Ni50Mn36In14 magnetic shape memory alloy. In this context, the inverse magnetocaloric effects of Ni50Mn36In14 magnetic shape memory alloy polycrystalline samples were investigated as a function of annealing heat treatments by the thermo-magnetometry method. Two forms of Ni49TiMn36In14 magnetic shape memory alloy were studied: one that predominantly undergoes a magnetic phase transition and the other that exhibits both a magnetic and martensitic phase transition. The magnetic behaviors and magnetocaloric properties of these alloys were analyzed to investigate the competition between magnetic and lattice contributions to the total entropy change. Finally, the mutually contradictory role of magnetic and lattice contributions was demonstrated. [ABSTRACT FROM AUTHOR]

In this work, we propose a variation of Miura origami which, different from the existing out-of-plane bending Miura origami, has an in-plane bent configuration due to its graded crease pattern. By combining with the one-way shape memory alloy spring, we show that the proposed graded Miura origami can serve as a smart actuator and can be applied to drive crawling robots or grippers. First, we constructed a physical model of the graded Miura origami, from which a curvature-programmable geometric equation is proposed. Then, in addition to providing a mechanical model that can capture the mechanical behavior of the initial force–displacement relationship of the curved beam, we show that the proposed curved origami has a different mechanical behavior compared to the corresponding simple flexible arch, specifically if realized by silicon rubbers. By arranging anisotropic friction to the feet, the origami robot can crawl with an omega-elongation/compression motion like an inchworm. With a closed-loop current source control system using a high-frequency pulse width modulation-based topology, where the strain state of the arched origami is detected by a demodulator-free fiber Bragg grating sensor, the average speed of the origami crawling robot can reach 2.72 mm/s. In addition, by arranging three graded Miura origami, a gripper capable of lifting a weight of 518.5 g can be formed, where the carried load is over 4.5 times its own weight. [ABSTRACT FROM AUTHOR]

Utilizing molecular dynamics simulation, this study aims to explore the phase transformation behavior of porous nanocrystalline (NC) NiTi shape memory alloys (SMAs) when subjected to cyclic deformation. The influences of porosity and cyclic deformation on the phase transformation of NC NiTi SMAs are examined and discussed. The simulation results show that the increase in the porosity and number of cycles leads to a decrease in both the critical phase transformation stress and peak stress whereas an increase in the residual martensite, phase boundary, and interstitial atoms; the related results can be supported by previous experiments. After cyclic deformation, the reduction in the potential energy for the entire system during the tensile phase occurs at an earlier stage, indicating that the martensitic transformation occurs earlier as the number of cycles increases. Notably, the dissipated energy demonstrates a decrease with an increasing number of cycles, and the potential energy during the austenite elastic unloading stage undergoes a transition from a decreasing to an increasing trend due to the presence of residual martensite increasing with the number of cycles. [ABSTRACT FROM AUTHOR]

Intermetallic compounds were applied widely in the fields of automotive and aerospace because of its excellent shape memory effect. In this work, the structural, mechanical, and thermodynamic properties of Ni–Ti intermetallic compounds are studied by first-principle calculation. The results show that Ti, NiTi3, NiTi2, NiTi, Ni4Ti3, Ni3Ti, Ni4Ti, and Ni are stable based on Born stable criterion. On the mechanical aspect, the bulk modulus of Ni–Ti intermetallic compounds increases with the rising electron density. Their ductility is ranked as follows: NiTi3 > Ni4Ti3 > NiTi2 > Ni4Ti > NiTi > Ni3Ti. And when the ratio of Ni and Ti is 3:1, it is the hardest. In addition, the Ni–Ti intermetallic compounds in this work are anisotropy, except NiTi2. On the thermodynamic aspect, the Debye temperature θD, melting point Tm, and minimum thermal conductivity kmin of Ni–Ti intermetallic compounds increase first and then decrease with the rising content of Ni. The θD and kmin of NiTi3 are the minimum among the Ni–Ti ICs mentioned above, and θD of Ni3Ti and kmin of NiTi are both the maximum. The melting point of Ni3Ti is 1940 K, it is the highest temperature. [ABSTRACT FROM AUTHOR]

Due to its numerous practical applications and intriguing phase transformation behavior, shape memory alloys (SMAs) have garnered significant research and development interests. In the past, most studies on the mechanical behavior of SMAs have been conducted under uniaxial stress loadings. Limited research on SMAs under shock loading has not provided conclusive results regarding their transformation behavior and transformation stress under such loading. Additionally, there is a lack of comprehensive understanding regarding the effects of different stress states on transformation behavior. The main objectives of this study are to address these issues. To achieve these objectives, a series of shock wave experiments were designed and conducted. Additionally, quasi-static and dynamic uniaxial stress experiments were carried out to establish a baseline for comparison. The results revealed that the transformation stress under dynamic uniaxial strain shock loading was approximately 1.92 GPa in contrast to 0.5 GPa (quasi-static) to 0.8 GPa (dynamic) observed in uniaxial stress loading. The transformation behavior exhibited noticeable rate sensitivity for both types of loading. There appeared to be a critical strain rate above which the austenite phase was driven to a metastable state. This estimated critical axial strain rate along the loading direction was approximately 2 × 103/s–4 × 103/s for uniaxial stress loading and approximately 2 × 106/s for uniaxial strain loading. The apparent high transformation stress for uniaxial strain loading can likely be attributed to a combination of high-pressure confinement and high strain rate. However, determining their relative contributions remains an open issue. [ABSTRACT FROM AUTHOR]

Four-dimensional scanning transmission electron microscopy, coupled with a wide array of data analytics, has unveiled new insights into complex materials. Here, we introduce a straightforward unsupervised machine learning approach that entails dimensionality reduction and clustering with minimal hyperparameter tuning to semi-automatically identify unique coexisting structures in metallic alloys. Applying cepstral transformation to the original diffraction dataset improves this process by effectively isolating phase information from potential signal ambiguity caused by sample tilt and thickness variations, commonly observed in electron diffraction patterns. In a case study of a NiTiHfAl shape memory alloy, conventional scanning transmission electron microscopy imaging struggles to accurately identify a low-contrast precipitate at lower magnifications, posing challenges for microscale analyses. We find that our method efficiently separates multiple coherent structures while using objective means of determining hyperparameters. Furthermore, we demonstrate how the clustering result facilitates more robust strain mapping to provide immediate and quantitative structural insights. [ABSTRACT FROM AUTHOR]

Electro-chemical machining (ECM) can safely be categorized as being a unique unconventional machining technique, in which the role of thermal defects are not involved. The NiTiCo shape memory alloy has high yield strength coupled with good resistance to aggressive aqueous environments, which makes it a potential candidate for use in several bio-medical applications. This research concentrates on electro-chemical machining of a NiTiCo alloy. Taguchi's Design of Experiment (DOE) containing three-parameters and three-factors was used to conduct the experimental study. The influence of concentration of the sodium chloride electrolyte, voltage, and frequency on output characteristics, such as (i) material removal rate (MRR), (ii) surface roughness (SR), and (iii) over-cut (OC), was analyzed. Experimental outputs revealed the voltage (45.29%) to be the most influential among the three controlling parameter. Grey relational analysis (GRA) was utilized to discover the ideal parametric relation and optimize machining characteristics. [ABSTRACT FROM AUTHOR]

This paper presents an experimental examination of the compression demeanor of lightweight corrugated core composite (CCC) sandwich panel and corrugated core smart composites (CCSC) sandwich panels subjected to quasi‐static edgewise compression loading. The existence of shape memory alloy (SMA) wires and pre‐strain percentages of SMA are the indicators studied in this article. The fabrication procedure presented and the appraisement of the mechanical properties of the CCC and CCSC sandwich panels are expressed. The core geometry of samples is trapezoid corrugated made of aluminum. The facesheets are four layers of woven glass fiber/ epoxy laminated composite. For evaluation of the efficacy of the presence of SMA wires on mechanical specifications of sandwich panels, three SMA wires with various pre‐strain percentages (0%, 3%, and 6%) are embedded in each composite facesheet. Mechanical properties of all types of CCC and CCSC sandwich panels such as maximum force, critical damage force, specific strength, absorb energy, specific toughness, Young's modulus, and specific stiffness were evaluated. Results showed that the CCC sandwich panel has higher mechanical specifications than the CCSC sandwich panels with 0% and 3% pre‐strain. Also, increasing pre‐strained SMA wires improves all mechanical parameters of CCSC sandwich panels. CCSC sandwich panel with 6% pre‐strain has the highest compression properties than other sandwich panels. Maximum Force, Critical Damage Force, Specific Strength, Absorbed Energy, Specific Toughness, Young's Modulus, and Specific Stiffness of CCSC sandwich panel with 6% pre‐strain are 14.73 kN, 13.6 kN, 9.55 MPa/g, 26.61 kJ, 0.346 MJ/m3g, 4395 MPa and 0.61 kN/mm g, respectively. Highlights: Lightweight CCC sandwich panel and CCSC sandwich panel manufactured.Compression behavior of CCC sandwich panel and CCSC sandwich panel evaluated.Pre‐strained SMA wires improves energy absorption of CCSC sandwich panels.Higher specific toughness was obtained with 6% pre‐strain SMA.Presence of SMA wires with no pre‐strain cannot improve the specific strength. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are the key components of actuators and sensors due to their shape memory effect and superelasticity. However, the thermal hysteresis associated with martensitic phase transformation limits their use in the long-duration precise control. We report a strategy that obtains SMAs with low hysteresis by constructing a composition-temperature pseudo phase diagram. This strategy is inspired by the physically parallel ferroelectric system where the hysteresis is minimized at the multiple phase coexistence point, due to the absence of energy barrier across different phases. Following this, an alloy in the phase diagram with a low hysteresis of about 5 K is synthesized. In contrast, those alloys compositionally different from the optimal one have large hysteresis. Microstructures characterization and diffraction analysis are employed to identify the multiple phase coexistence. The proposed strategy should be general and can shed light on the rational design of SMAs with low hysteresis. [ABSTRACT FROM AUTHOR]

Highlights A high filling load (62% weight) printable magnetic composite has been elaborated from the dispersion of magnetocaloric Ni45Mn36.7In13.3Co5 metamagnetic shape memory alloy microparticles into a PCL polymer matrix. The composite material has been prepared by solution method, resulting in a very homogeneous particles dispersion into the matrix. The structural transitions in the polymer are not affected by the addition of the metallic microparticles, which in turn results in a significant increase of the mechanical consistency. The good ductility of the elaborated composite allows its extrusion in flexible printable filaments, from which 3D pieces with complex geometries have been grown. The heat transfer of the composite material has been assessed from finite element simulation. In spite of the achievable magnetocaloric values are moderated with respect to the bulk, numerical simulations confirm that, in terms of heat transference, a PCL/Ni‐Mn‐In‐Co wire is more efficient than a bulk Ni‐Mn‐In‐Co cubic piece containing the same amount of magnetic active material. The quite good magnetocaloric response of the composite and the possibility to print high surface/volume ratio geometries make this material a promising candidate for the development of heat exchangers for clean and efficient magnetic refrigeration applications. 3D printable magnetic composites developed from dispersion of MSMA in PCL. High filling factor and uniform dispersion characterized by SEM. Inclusion of microparticles does not affect polymeric structural transitions. Metallic fillers improve DMA response of 3D printed pieces. FEM simulations endorse PCL/MSMA composites for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

ABSTRACT The influence of various heat treatments on the corrosion behavior of a novel iron‐based shape memory alloy (Fe‐SMA), Fe‐17Mn‐6Si‐10Cr‐4Ni‐1(V,C), used as prestressing elements in civil engineering was examined through electrochemical corrosion methods. SMAs were subjected to two different electrolytes: saturated Ca(OH)2 solutions with and without chlorides to mimic the conditions in concrete. Two specific heat treatments were applied to the Fe‐SMA, which resulted in a change in grain size and precipitation of secondary phases. Furthermore, conventional structural steel, B500B, was utilized as a reference material. The results reveal that the heat treatments did not significantly change the corrosion rates of these alloys in Ca(OH)2 solution compared to B500B when chlorides were absent. However, the presence of chloride ions suppressed the passivity of B500B and promoted the localized corrosion (pitting and intergranular) of the Fe‐SMAs, among which the solutionized alloy showed significantly higher resistance to the pitting. It was demonstrated that the heat treatments and, consequently, microstructural characteristics influence the pitting behavior of these alloys. [ABSTRACT FROM AUTHOR]

In this study, Ni20Ti50Sn30 (atomic %) sample was prepared using the arc melting method. Some thermodynamic parameters (phase transformation temperatures, PTT; enthalpy, ΔH; and phase transformation hysteresis, H) obtained from the phase transformations of the alloy were determined using differential scanning calorimetry (DSC). The sample exhibited high-temperature shape memory alloy (HTSMA) properties. X-ray (XRD) analysis was performed to determine the crystal structure properties at the alloy. The presence of B2, B19′, Ti2Ni, β-Ti, Ni3Sn4, TiNiSn and Ti3Sn phases was identified through X-ray analysis of the alloy. Scanning electron microscopy (SEM) was used to examine the pre- and post-corrosion surface morphologies of the sample, with EDX analysis being performed to reveal chemical structure determinations (matrix phases, precipitates and weathering zones). The presence of dendritic arms was observed, while martensite plates were absent in all SEM images. Particularly in the SEM image taken after corrosion, it was noted that the TiO2 layer placed on the surface of the matrix rich in Ti elements altered the surface morphology of the alloy. The presence of Ti and O elements in the post-corrosion EDX analysis confirmed the existence of this layer. Biocompatibility studies of the alloy were conducted using potentiodynamic corrosion tests and electrochemical impedance spectroscopy (EIS) methods. It was determined that the NiTiSn sample was in the excellent stability class according to corrosion standards. [ABSTRACT FROM AUTHOR]

The corrosion behavior of two different Cu–Al–Mn–Ni alloys, pseudoelastic and pseudoplastic, was studied in a 0.6 M sodium chloride aqueous solution by monitoring the open circuit potential for 100 h and characterizing the resulting corrosion products. Electrochemical impedance spectroscopy analysis detected three processes related to the electrochemical double layer, a passive film and a diffusive contribution associated with the dissolution/precipitation of corrosion products. Potentiodynamic scans revealed a cathodically controlled corrosion mechanism and the presence of active–passive behavior at anodic potentials for both alloys studied. Polarization of the samples at selected potentials in the anodic branch allowed the investigation of the reactions involved, highlighting an improved corrosion resistance of the pseudoelastic alloy. The corrosion rates of the pseudoelastic and pseudoplastic alloys, after 100 h of immersion, were determined to be 0.007 and 0.011 mmpy, respectively. The post‐experiment characterization was carried out by means of scanning electron microscopy, micro‐Raman spectroscopy and X‐ray diffraction, supporting the electrochemical results. [ABSTRACT FROM AUTHOR]

At present, Fe–Mn–Si shape memory alloy with high corrosion resistance has become the focus of attention because of its special requirements in some fields. On the basis of Fe–Mn–Si shape memory alloy, a corrosion‐resistant shape memory alloy was designed by adding Cr and other alloy elements. The microstructure characteristics and phase ratio control mechanism of the annealed alloy and the influence mechanism of the second phase (ferrite) and ratio on the alloy memory effect are emphatically studied. The results show that ferrite and austenite are evenly distributed at low annealing temperature, and there is thermal‐induced ε‐martensite at the same time. Appropriate thermal‐induced ε‐martensite can strengthen the austenite matrix, and the shape recovery rate is high at this time. With the increase of annealing temperature, the volume fraction and grain size of ferrite increase, the volume fraction of thermal‐induced ε‐martensite and austenite decreases, and the shape recovery rate decreases, but it is beneficial to improve the corrosion resistance. [ABSTRACT FROM AUTHOR]

Current standardized in vitro bending experiments for orthodontic archwires cannot capture friction conditions and load sequencing during multi-bracket treatment. This means that clinically relevant forces exerted by superelastic wires cannot be predicted. To address these limitations, this study explored a novel test protocol that estimates clinical load range. The correction of a labially displaced maxillary incisor was simulated using an in vitro model with three lingual brackets. Deflection force levels derived from four different protocols were designed to explore the impact of friction and wire load history. These force levels were compared in nickel-titanium (NiTi) archwires with three commonly used diameters. The unloading path varied between protocols, with single or multiple sequences and different load orders and initial conditions. Deflection forces from the new protocol, employing multiple continuous load/unload cycles (CC incr), consistently exceeded those from the conventional protocol using a single continuous unloading path (CU decr). Mean differences in plateau force ranged from 0.54 N (Ø 0.014" wire) to 1.19 N (Ø 0.016" wire). The CC inr protocol also provided average force range estimates of 0.47 N (Ø 0.012" wire), 0.89 N (Ø 0.014" wire), and 1.15 N (Ø 0.016" wire). Clinical orientation towards CU decr carries a high risk of excessive therapeutic forces because clinical loading situations caused by friction and load history are underestimated. Physiological tooth mobility using NiTi wires contributes decisively to the therapeutic load situation. Therefore, only short unloading sequences starting from the maximum deflection in the load history, as in CC incr , are clinically meaningful. • Friction and load history affect deflection forces of orthodontic NiTi wires. • Conventional in vitro 3-bracket bending tests underestimate clinical force levels. • Physiological tooth movement must be considered to derive clinically relevant loads. • Reactive forces from wire deflection may vary because of physiological conditions. • Sequential short unloading sequences allow characterization of clinical load range. [ABSTRACT FROM AUTHOR]

Background: The behavior of shape memory alloys that admit large reversible deformations in response to thermal excitation has been extensively studied in recent years. Yet, the number of works dealing with springs made from these alloys is rather limited in spite of their attractiveness in various applications. Objective: To bridge this gap we designed and constructed an experimental system for characterizing the behavior of the springs. It enables precise control of the three state variables: temperature, elongation, and force. Methods: Control of the sample temperature is achieved by immersing it in a water-filled thermal bath, where the water temperature is adjusted using a thermoelectric Peltier device. A tension-compression motorized unit sets the spring elongation and a force gauge is used for measuring the force exerted on the spring. The data is continuously monitored and acquired with a self-coded LabVIEW program. An important aspect is the calibration procedure developed for identifying the spring load-free state and ensuring the repetitiveness of the measurements. Results: Experiments in which the elongation or the force were measured as a function of the temperature demonstrate the role of the phase transformations. Isothermal experiments enabled to characterize the variations of the force versus the elongation at different temperatures. Conclusions: The proposed system facilitates the execution of highly accurate experiments through which the complex history-dependent behavior of shape memory springs can be revealed and studied. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were conducted to explore nanoindentation-induced martensitic transformation in NiTi shape memory alloys. Three atomic compositions and two indenter sizes were considered. During loading, the B2 structure underwent martensitic transformation to the B19' structure, accompanied by atomic rearrangement in the form of bands. After unloading, a portion of the B19' phase underwent reversible transformation, while the remainder remained in the form of bands, resulting in residual strain. This effect was accentuated by the more localised deformation promoted by the smaller indenter. The influence of atomic composition was observed not to play a key role in the mechanical and structural properties, contrary to previous reports on tension and compression tests. Our findings shed light on the intricate interplay of factors influencing the mechanical performance of NiTi shape memory alloys at the atomic scale, providing crucial insights for the design and understanding of such materials. [ABSTRACT FROM AUTHOR]

Thermomechanical coupling effects, which are almost inevitable in materials processing, are particularly notable in NiTi shape memory alloy (SMA). Understanding the dynamic mechanical properties of NiTi SMA at high temperatures and high strain rates is important to reveal its cutting mechanism. In the present work, the split Hopkinson pressure bar experiments under different temperatures and strain rates are carried out. The dynamic mechanical behaviors are discussed from both macro- and microperspectives. The results indicate that nonlinear deformation behaviors of Ni50.8Ti SMA strongly depended on strain rates and temperatures. The influence mechanisms of temperature and strain rate on the nonlinear deformation of Ni50.8Ti SMA are clarified in detail. Moreover, a constitutive model for nonlinear deformation of Ni50.8Ti SMA is established to depict the dynamic characteristics. This is helpful to study the thermomechanical effects on the Ni50.8Ti SMA during machining. [ABSTRACT FROM AUTHOR]

We report unique two-step strain glass transition toward different local strain states in NiTi, i.e. R and B19′ strain glasses. This unique transition is evidenced by dynamic mechanical analysis and in-situ HR-TEM. A comprehensive phase diagram is established to illustrate diverse transition pathways and corresponding tunable superelastic properties. This pathway exploits the integrated transition of different phases, lowering the transition energy barrier, yielding superelasticity with large recoverable strain (6%), ultralow modulus (24 GPa) and robust cyclic and wide-temperature stability. Our investigation provides fresh insights into continuous transition pathways among different strain glass states to achieve exceptional properties in shape memory alloys. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are potential materials in various areas such as engineering and medicine, and their applications are being studied for practical use. SMAs show competence in their main material properties in response to their working environment or external stimuli. Machining of NiTiCu10 SMAs is difficult using traditional machining because of their wide-ranging mechanical properties like high toughness, strength, and sensitivity to phase transformation temperature. Nonconventional machining methods such as electro-discharge machining (EDM) are suitable for effective machining SMAs. The work material NiTiCu10 SMA has been used in this study, and processed using the vacuum induction melting (VIM) technique. The addition of copper leads to increase in the martensitic transformation temperatures. This paper focuses on the electro-discharge drilling (EDD) of NiTiCu10 SMA using copper tool electrode. Experimental analysis of performance criteria has been evaluated by conducting experiments following one factor at a time (OFAT) approach. Machining features such as material removal rate (MRR), tool electrode wear rate (TEWR), and surface roughness (SR) have been studied by considering pulse current ( I p ), gap voltage ( V g ), pulse on time ( T on ), pulse off time ( T off ), and rotational speed of tool electrode (N). Experimental results have shown that machining at the highest I p of 12 A yields the highest MRR with the value of 4.077 mm3/min, whereas mcahining at T on of 15 μ s yields the lowest TEWR with the value of 0.031 mm3/min. The lowest SR is 2.8 μ m achieved at the lowest T on of 15 μ s. Surface morphology is significant in quality evaluation in the manufacturing, and building industries because it directly determines the mechanical performance of parts, and the service life of products. Morphological investigation via scanning electron microscope (SEM) has confirmed the formation of craters, debris, microcracks, and resolidified layers. The benefit of this study has been that we have been able to select the range of significant control factors, and predict their levels, for decisive experimentation. [ABSTRACT FROM AUTHOR]

The effect of Ru addition on the martensitic transformation and mechanical properties of Zr50Pd50−xRux SMAs shape memory alloys has been studied. Strain–temperature experiments, differential scanning calorimeter, and scanning electron microscope analyses were performed to validate the theoretical predictions by DFT calculation regarding the influence of the C′ parameter on martensitic stability. Despite the absence of an observed shape memory effect under the tested conditions, the findings suggest that ZrPdRu alloys hold promise for high-temperature applications. [ABSTRACT FROM AUTHOR]

Widening the martensitic hysteresis ( T Dhys ) in NiTiNb shape memory alloys (SMAs) holds potential for broadening their working temperature range while enabling the room-temperature storage. In this study, the T Dhys is divided into two parts: the thermal-induced hysteresis ( T hys ) and the deformation-induced hysteresis ( T hys ′ ). In addition to decreasing the martensitic transformation start temperature ( M S ), it is found that grain refinement is an effective method for widening both T hys and T hys ′ of the Ni47Ti44Nb9 alloy, a commercial SMA widely used for shape memory couplings. According to thermodynamic analysis, grain refinement increases the dissipation energy ( Δ E dis ) (caused by thermal friction at martensite/austenite interface), thereby widening T hys . Moreover, the Ni47Ti44Nb9 alloy with finer grains has the potential to release more elastic strain energy ( Δ E el ) after deformation, thereby exhibiting a wider T hys ′ . When deforming a large strain, the alloy with finer grains generates more dislocations which stabilize the martensitic phase, thus further widening T hys ′ . [ABSTRACT FROM AUTHOR]

Copyright of Cuadernos del Centro de Estudios de Diseño y Comunicación is the property of Cuadernos del Centro de Estudios de Diseno y Comunicacion and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To construct resilient structures, systems and sustainable buildings, capable of enduring fatigue, inclement weather, and seismic activity, researchers are actively seeking effective solutions to minimize vibrations and cyclic loading. Although these factors may not have immediate effects, they contribute to residual deformation in structures that gradually grows over time. For this reason, shape memory alloy (SMA) can be used as a perfect damper to dissipate the mechanical load in structures construction and buildings. The SMA actuators characterized by several thermo-mechanical functions, they are generally used in different applications as Mechatronics, Biomedical, Mechanical engineering and building systems. This study aims to adapt SMA actuator with structures for construction and buildings, in order to ensure a high displacement and vigilance taking into account fatigue phenomena to repulse mechanical fatigue and fretting. Accordingly, a thermomechanical analysis has been developed using finite element techniques to describe shape memory alloys' behavior and can integrate these material as a thermomechanical actuator dampers in building engineering systems. Furthermore, the suggested model elucidates the actuator's thermomechanical response, showcasing its adaptable behavior to both superelasticity and the shape memory effect within the desired structure in the building. Thus, the numerical findings affirm the efficacy of the proposed design that based on shape memory materials in addressing thermomechanical fatigue within buildings, concurrently enhancing structural resilience against mechanical fatigue. The primary outcome of this study is the successful preservation of the Ni-Ti superelastic response within the proposed system. This preservation is validated through cycling variations of up to 7.6% strain, significantly surpassing the requirements typically mandated for applications in earthquake engineering. [ABSTRACT FROM AUTHOR]

Dry sliding wear tests on Cu-Al-Mn Shape Memory Alloys (SMAs) were performed in this study. The alloy was synthesised with the amount of manganese content varied as 5, 7, and 9 wt.% and the amount of aluminium was kept constant at 10.5 wt.% with the remaining copper. Dry sliding wear tests were carried out at different conditions of sliding speeds, sliding distances, and various load conditions. Experiments were carried out using Taguchi's technique to obtain an experimental design. The data were analysed using an L27 orthogonal array. The wear rate (WR) and coefficient of friction (COF) were evaluated using the 'smaller is better' method approach. The main parameters affecting WR and COF were determined using ANOVA. The effects of applied load, sliding speed, sliding distance, and material on WR and COF are determined. The optimum combinations of parameters were set to achieve the lowest wear rate and highest COF. Finally, confirmation tests were conducted to ensure that the experimental results were accurate. After the wear test, the sample texture was observed and analysed using a Scanning Electron Microscope (SEM). [ABSTRACT FROM AUTHOR]

The author aimed to enhance the functional characteristics of the proposed Ti–Ni shape memory alloy (SMA) with a functionally graded property by ultrasonic shot peening (USP) treatment. To the author’s knowledge, this was the first study in which USP treatment was utilized for manufacturing functionally graded SMAs; previous studies relied on powder metallurgy and hot rolling techniques. By examining the various properties of the specimens, the author confirmed the effects of hot rolling and USP treatment. Hot rolling and USP treatment led to an increased Vickers hardness. Hot rolling primarily contributed to densification, while USP treatment induced work hardening, resulting in increased hardness. The surface of TiNi SMA sintered bodies experienced compressive residual stress up to 300 MPa because of the USP treatment. The transformation peaks in differential scanning calorimetry curves shifted toward lower temperatures as the Ni content increased. Therefore, the transformation properties of the functionally graded shape memory alloys were unaffected by the USP treatment. The USP treatment work-hardens the sintered TiNi SMA produced through hot rolling. The effect was more pronounced in the high-Ni-concentration region, resulting in the development of a functionally graded behavior of deformation resistance. [ABSTRACT FROM AUTHOR]

Objective Methods Results Conclusion Arthrodesis, usage of metallic implants for internal fixation, is commonly employed as the primary treatment modality for Müller‐Weiss disease (MWD). Nevertheless, the efficacy of the current methods of fixation leaves room for improvement. Inadequate fixation strength and the risk of fixation failure are both critical concerns requiring attention. This study explored the clinical effects of implementing a modified fixation technique in talonavicular arthrodesis for the treatment of MWD.A total of 14 cases diagnosed with MWD undergoing talonavicular (TN) arthrodesis from January 2021 toMarch 2023 were included in the retrospective study. The fixation method for fusion involved the use of screws, with additional support from the shape‐memory alloy (SMA) staple. Relevant clinical outcomes and complications were evaluated preoperatively and postoperatively. Paired‐samples t‐test was used for all data comparisons.Radiographic evidence confirmed solid fusion, and follow‐up evaluations showed satisfactory results in all cases. The American Orthopedic Foot and Ankle Society (AOFAS) scores were elevated from 32.21 ± 4.0 (range: 22–38) preoperatively to 86.5 ± 2.7 (range: 81–90) postoperatively (p < 0.001). The visual analog scale (VAS) scores declined from 7.40 ± 0.8 (range: 6–8.5) preoperatively to 1.21 ± 1.1 (range: 0–3) postoperatively (p < 0.001). The lateral Meary's angle changed from 13.50 ± 5.2 (range: 8–24) preoperatively to 4.14 ± 2.9 (range: 1–11) degrees postoperatively (p < 0.001). The calcaneal pitch angle increased from 10.07 ± 4.0 (range: 5–19) preoperatively to 14.35 ± 4.0 (range: 8–21) degrees postoperatively (p < 0.001). The talar‐first metatarsal angle decreased from 11.71 ± 3.8 (range: 8–18) preoperatively to 4.28 ± 3.1 (range: 0–9) degrees postoperatively (p < 0.001). One patient was observed to experience delayed wound healing and wound infection. No nerve damage, malunion, pseudoarthrosis, or fixation failure were observed.The results indicated that the fusion of the TN joint using a combination of screws and shape memory alloy staples, could lead to favorable clinical outcomes and significantly enhance the quality of life for patients with MWD. This technique is not only safe and effective but also straightforward to perform. [ABSTRACT FROM AUTHOR]

Research into the processability of NiTiHf high-temperature shape memory alloys (HTSMAs) via laser powder bed fusion (LPBF) is limited; nevertheless, these alloys show promise for applications in extreme environments. This study aims to address this limitation by investigating the printability of four NiTiHf alloys with varying Hf content (1, 2, 15, and 20 at. %) to assess their suitability for LPBF applications. Solidification cracking is one of the main limiting factors in LPBF processes, which occurs during the final stage of solidification. To investigate the effect of alloy composition on printability, this study focuses on this defect via a combination of computational modeling and experimental validation. To this end, solidification cracking susceptibility is calculated as Kou's index and Scheil–Gulliver model, implemented in Thermo-Calc/2022a software. An innovative powder-free experimental method through laser remelting was conducted on bare NiTiHf ingots to validate the parameter impacts of the LPBF process. The result is the processability window with no cracking likelihood under diverse LPBF conditions, including laser power and scan speed. This comprehensive investigation enhances our understanding of the processability challenges and opportunities for NiTiHf HTSMAs in advanced engineering applications. [ABSTRACT FROM AUTHOR]

General derivation of the well-known Ren–Otsuka relationship, 1 α d T o d x = − α β (where T o , x, α and β (> 0) are the transformation temperature and composition, as well as the composition and temperature coefficient of the critical shear constant, c′, respectively) for shape memory alloys, SMAs, is provided based on the similarity of interatomic potentials in the framework of dimensional analysis. A new dimensionless variable, t o x = T o x T m x , describing the phonon softening (where Tm is the melting point) is introduced. The dimensionless values of the heat of transformation, ΔH, and entropy, ΔS, as well as the elastic constants c′, c44, and A = c 44 c ′ are universal functions of to(x) and have the same constant values at to(0) within sub-classes of host SMAs having the same type of crystal symmetry change during martensitic transformation. The ratio of d t o d x and α has the same constant value for all members of a given sub-class, and relative increase in c′ with increasing composition should be compensated by the same decrease in to. In the generalized Ren–Otsuka relationship, the anisotropy factor A appears instead of c′, and α as well as β are the differences between the corresponding coefficients for the c44 and c′ elastic constants. The obtained linear relationship between h and to rationalizes the observed empirical linear relationships between the heat of transformation measured by differential scanning calorimetry (DSC) (QA⟶M) and the martensite start temperature, Ms. [ABSTRACT FROM AUTHOR]

The objective of this research is to forecast the impact of alternating non-uniform temperature distributions on the deformation and internal stress within the thin film of a solar photon sail, as well as to assess how stress variations affect the sail's characteristics. To maintain the internal stress amplitude within the film during extreme temperature fluctuations, the solar sail employs an innovative pre-tensioning technique utilizing shape memory alloy (SMA) springs. A thermal-structural model is formulated specifically for a hexagonal solar sail. Subsequently, thermal-structural analyses are conducted to quantify deformations and stresses within the sail during its operation on the Earth-Moon L1 halo orbit. Incorporating the prestress factor, the out-of-plane deflection of the film under solar pressure is computed. Furthermore, prestressed modal analyses are performed to determine mode shapes and natural frequencies, taking into account both the prestress and the solar pressure acting on the film. Finally, numerical results are used to compare the performance of the solar sail in hot and cold environments. [ABSTRACT FROM AUTHOR]

The construction of mechanically responsive materials with reversible shape‐shifting, shape‐locking, and stretchability holds promise for a wide range of applications in fields such as soft robotics and flexible electronics. Here, we report novel thermoelastic one‐dimensional organic–inorganic hybrids (R/S‐Hmpy)PbI3 (Hmpy=2‐hydroxymethyl‐pyrrolidinium) to show mechanical responses. The single crystals undergo two phase transitions at 310 K and 380 K. When heated to 380 K, they show shape‐shifting and expansion along the b‐axis by about 13.4 %, corresponding to a larger deformation than that of thermally activated shape memory alloys (8.5 %), and exhibit a strong actuation force. During the cooling process, the stretched crystal shape maintains and a shape‐locking phenomenon occurs, which is lifted when the temperature decreases to 305 K. Meanwhile, due to the introduction of chiral ions, the thermal switching shows a 10‐fold second‐order nonlinear switching contrast (common values typically below 3‐fold). This study presents a thermoelastic actuator based on shape‐shifting and ‐locking of organic–inorganic hybrids for the first time. The dielectric and nonlinear optical switching properties of organic–inorganic hybrids broaden the range of applications of mechanically responsive crystals. [ABSTRACT FROM AUTHOR]

Recent advancements in machine learning (ML) have revolutionized the field of high-performance materials design. However, developing robust ML models to decipher intricate structure-property relationships in materials remains challenging, primarily due to the limited availability of labeled datasets with well-characterized crystal structures. This is particularly pronounced in materials where functional properties are closely intertwined with their crystallographic symmetry. We introduce a self-supervised probabilistic model (SSPM) that autonomously learns unbiased atomic representations and the likelihood of compounds with given crystal structures, utilizing solely the existing crystal structure data from materials databases. SSPM significantly enhances the performance of downstream ML models by efficient atomic representations and accurately captures the probabilistic relationships between composition and crystal structure. We showcase SSPM's capability by discovering shape memory alloys (SMAs). Amongst the top 50 predictions, 23 have been confirmed as SMAs either experimentally or theoretically, and a previously unknown SMA candidate, MgAu, has been identified. [ABSTRACT FROM AUTHOR]

To improve the energy dissipation and self-resetting ability of bridge structures under strong earthquakes, a new buckling-restrained SMA bar-based friction damper (SFD) is proposed. The damper is composed of buckling-restrained super-elastic SMA bars, friction pads, and a steel frame. The buckling-restrained SMA bars provide self-reset capability, while the friction pads provide additional energy dissipation capacity. Firstly, the configuration, working mechanism, and restoring force model of the SMA bar-based friction damper are introduced. Secondly, a specimen of the damper is made, and the pseudo-static test is carried out. Finally, the experimental results are analyzed based on the Abaqus finite element model. The results indicate that the damper has better self-resetting ability and energy dissipation capacity. [ABSTRACT FROM AUTHOR]

The checkerboard constitutes the best pattern for full‐field strain measurement because it maximizes image gradient. In the experimental mechanics community, employing this pattern is currently strongly limited because depositing it on the surface of specimens raises practical difficulties. A recent study shows, however, that it is technically possible by using a laser engraver. The present paper aims to push this solution forward by printing a checkerboard pattern on a thin polymeric film and then gluing the resulting laser‐engraved film on the specimen surface. The underlying idea is to separate the manufacturing process of this optical strain gauge on the one hand and its use on the other hand to help spread this strain measuring tool in the experimental mechanics community. The polymeric film employed here is the same as that used in the manufacturing process of classic electrical gauges, so one can rely on the know‐how of classic strain gauge bonding to glue this optical strain gauge on the specimen surface. The main difference between the proposed tool and classic electrical gauges is that the strain field beneath the polymeric support is measured instead of localized strain values. The paper is a proof of concept for this strain field measuring tool. The manufacturing and bonding processes are described in the paper. The localized spectrum analysis, a spectral technique developed for processing images of periodic patterns, is used to retrieve the strain fields from checkerboard images. Through two complementary examples, we show the ability of this new type of strain gauge to detect and quantify local details in the strain field beneath. A simplified 1D model is also proposed to assess the minimum width of the strain peak that can reliably be measured with this technique. [ABSTRACT FROM AUTHOR]

Crystal size engineering allows tailoring of flexible metal–organic frameworks (MOFs) to achieve new properties. The gating type flexibility of the DUT-8(Zn) ([Zn2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane) compound is known to be extremely particle size sensitive. Here, the physisorption of ethanol vapor gives rise to so-called shape-memory effect, leading to rigidification and flexibility suppression. According to powder X-ray diffraction and nitrogen physisorption experiments, the open pore phase is retained selectively after desorption of alcohols, which could be attributed to the nano-structuring and surface deformation of the crystals as a result of exposure to alcohols. [ABSTRACT FROM AUTHOR]

This study introduces a one‐dimensional phenomenological constitutive model designed to describe two‐way shape memory effect (TWSME) and its associated cyclic degradation. The model utilizes the logistic function to formulate the phase transformation equation, incorporates the expansion of key parameters into their respective fatigue functions to characterize the fatigue phenomenon, and integrates a phase transformation rate regulation function into the differential form of the phase transformation equation. This integration facilitates the control over the entire phase transformation process and the simulation of incomplete transformations. The model is distinguished by its comprehensive functionality, simple form, ease of calculation, and the clear and direct influence of key parameters. Furthermore, it offers a degree of flexibility because each function within the framework is replaceable. The simulation of the TWSME strain and recovery stress hysteresis loop deformation has been successfully conducted, enabling the description of internal hysteresis loops caused by incomplete transformation. The validity of the model is corroborated by comparing it with existing experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a new artificial detrusor system is proposed to achieve continuous control over the urination process and realize the normal voiding process of human (NVPH). The system is powered by a wireless power transfer (WPT) module, controlled by a control module and actuated by a shape memory alloy (SMA) spring. The design method of the SMA springs is proposed. Two control strategies are proposed to achieve NVPH. The first strategy is an open-loop control strategy based on the result of finite element analysis (FEM) simulation results and calculation of the derived system governing equations. The second strategy is a closed-loop control strategy based on the collection of feedback data and algorithmic processing. Both strategies are verified by experiments. The results show that the proposed system is feasible and both strategies can achieve NVPH. It can provide reference and guidance for the design of artificial detrusor system and formulation of control strategies. [ABSTRACT FROM AUTHOR]

This document provides information on various training courses offered by ASM International. The courses cover topics such as fractography, metallography, failure analysis, corrosion, heat treating, and the properties and applications of specific materials like stainless steels, superalloys, Nitinol, and aluminum. The courses are designed for individuals involved in industries that rely on materials science and engineering, and they provide practical knowledge and skills in these areas. The document also includes contact information for registration and further inquiries. [Extracted from the article]

In recent years, accelerated bridge construction has led to the substantial application of precast post-tensioned segmental (PPS) bridge piers. However, PPS piers are not widely used in high-seismicity regions due to their low energy-dissipation capacity (EDC). To address this deficiency, a series of shape memory alloy (SMA)–concrete composite PPS piers were examined in this work. Non-linear static and dynamic analyses were performed on experimentally validated finite-element models of the SMA–concrete composite piers and the results were compared with those of piers without SMA bars. It was found that the length, area and post-tensioning ratio of the SMA bars affected the EDC of the piers, and an optimal design of the bars is required to reach the highest EDC possible. The effects of SMA bars on the frequency response functions of piers were investigated for the first time in this study and it was found that, unlike the piers without SMA bars, sub-harmonics and super-harmonics were not seen in the responses of the SMA–concrete composite piers, mainly the drift responses. Furthermore, the SMA–concrete composite piers experienced a significant reduction in drift responses compared with piers without SMA bars. [ABSTRACT FROM AUTHOR]

SMA actuators are a group of lightweight actuators that offer advantages over conventional technology and allow for simple and compact solutions to the increasing demand for electrical actuation. In particular, an increasing number of SMA torsional actuator applications have been published recently due to their ability to supply rotational motion under load, resulting in advantages such as module simplification and the reduction of overall product weight. This paper presents the conceptual design, operating principle, experimental characterization and working performance of torsional actuators applicable in active rudder in aeronautics. The proposed application comprises a pair of SMA torsion springs, which bi-directionally actuate the actuator by Joule heating and natural cooling. The experimental results confirm the functionality of the torsion springs actuated device and show the rotation angle of the developed active rudder was about 30° at a heating current of 5 A. After the design and experiment, one of their chief drawbacks is their relatively slow operating speed in rudder positioning, but this can be improved by control strategy and small modifications to the actuator mechanism described in this work. [ABSTRACT FROM AUTHOR]

In practical applications, TiNi shape memory alloys (SMAs) exhibit behavior that can pose a challenge with current constitutive models and their implementations in finite element method (FEM) software. TiNi SMA devices typically operate in the forward or reverse martensitic transformation regime, which is known as subloop loading. During such cyclic loading–unloading, the hysteresis stress–strain loop changes because of material damage, which can be considered the fatigue of TiNi SMAs. During both the loading and unloading processes, the stress plateau decreases. At the same time, the accumulated (residual) martensitic transformation strain increases. In this study, the experimental investigation results and observations of the aforementioned phenomena are presented. Next, the phase-field damage model is employed, along with a modified Lagoudas constitutive model, to simulate the change in stress–strain hysteresis. Furthermore, a fatigue function is used to simulate the accumulation of martensitic transformation strain. The experimental stress–strain response is compared with the simulation results, and good quantitative and qualitative agreement is obtained. The damage and martensitic volume fraction with respect to strain are discussed for full-loop and subloop loading. The observations and conclusions, as well as open questions, are presented. Possible directions for future research are provided. [ABSTRACT FROM AUTHOR]

In this research, experimental and theoretical results for bending and buckling of a five-layer sandwich plate with composite face sheets reinforced by carbon nanotubes (CNTs), carbon nanorods, graphene platelets (GPLs), or nitinol shape memory alloy (SMA) wire and foam core are studied. The equations of equilibrium for this sandwich plate based on RFSDT and the principle of minimum total potential energy are derived, and then, the transverse displacement and buckling load are obtained. Using the rule of mixture and the Halpin–Tsai equation, the mechanical properties of the reinforced composite face sheets are calculated and also, and the constitutive equations of the SMA are presented according to the Brinson model. As well as, the influence of various parameters including thickness ratio, aspect ratio, the volume fraction of CNTs, GPLs, and nitinol SMA wire, fiber placement angle, and temperature changes are investigated on transverse deformation and dimensionless critical buckling load. Finally, tensile and buckling experimental tests were performed according to the standard tests ASTM D 3039 and ASTM C 364, respectively. [ABSTRACT FROM AUTHOR]

Shape Memory Alloys (SMA) are materials used to design smart structures with intrinsic functional properties and improved efficiency. This is a key aspect of aerospace industry and makes SMA good candidates in this field. One of the most widespread SMA is the equiatomic NiTi alloy which, however, has the strong limitation of poor machinability, so only simple shapes can be obtained. Additive Manufacturing processes allow to overcome this limit and to design complex shapes. Compared to other metallic materials, the optimization of the process for NiTi alloy is complicated because, beside mechanical properties and presence of defects, considerable attention needs to be dedicated to the material functionality. The high temperatures involved in the additive process significantly affect the material properties due to possible evaporation of Ni and formation of precipitates that enable a shift of the phase transformation temperatures. This paper is focused on the optimization of the process parameters of the NiTi alloy printed through the Laser Powder Bed Fusion (L-PBF) to ensure optimal pseudo-elastic behaviour, which is essential for the design of structural dampers. This was accomplished starting from simple structures and then designing a damper that couples the pseudoelasticity of NiTi with load support capacity. The L-PBF is a powder-bed technique that selectively melts layers of micrometric metal powder. A pseudoelastic NiTi powder with 50.8 at. % of Ni content was selected and characterized through scanning electron microscope (SEM) and observations connected to an Energy Dispersive X-ray Spectroscopy (EDX) probe. After that, some cubic samples were manufactured, with the dimension of 3 × 3 × 15 mm3. A set of different laser powers and scanning speeds were used to find the set of process parameters that optimize the functional properties of the printed parts. Near fully dense specimens with density higher than 99.5 % were selected for further investigations. Differential scanning calorimetry (DSC) and mechanical tests were performed on as-built and heat-treated samples. Quasi-static mechanical tests were accomplished in compression mode, at different strains, up to 8 %. It was observed that the residual strain for cyclic loading at 4 % is lower than 1 %, so good recovery of the deformation was shown. Moreover, numerical analyses that mimic the pseudoelastic behaviour in compression tests were implemented. Finally, the best set of parameters was selected on the basis of the material's ability to recover deformations and its loss factor. • Optimization of process parameters for functional behaviour of SMA. • Design of damping structure using pseudoelastic effect of Nitinol. • Internal defects observation of manufactured specimens. • Compression tests on as built and thermal treated specimens with strain up to 8 %. • Numerical simulation of compression tests with experimental correlation. [ABSTRACT FROM AUTHOR]

This study proposed a novel type of self-centering (SC) timber beam–column connection utilizing shape memory alloy (SMA) bars and investigated its cyclic behavior through experimental and numerical studies. In this SC connection, anchor bars consisting of SMA bars, steel bars, and couplers were utilized to connect the beam and column and achieve SC and energy dissipation capabilities. The configuration of the SC timber beam–column connection and material properties of the SMA bars were first introduced. The cyclic behavior of the SC timber beam–column connection was systematically investigated through experimental and numerical studies. A series of cyclic loading tests were conducted on the SC timber beam–column connection to evaluate its stiffness, SC, and energy dissipation capabilities, and the effect of multiearthquake loading. A detailed finite element model of the timber connection was also built and validated using the experimental results. Results indicated that the timber connection could exhibit a desirable flag-shaped hysteretic behavior, indicating favorable SC and moderate energy dissipation capabilities. The connection remained functional without any repair work after experiencing two consecutive cyclic loads up to 4% drift ratios, demonstrating its potential to withstand multiple seismic events. [ABSTRACT FROM AUTHOR]

In realistic applications, shape memory alloys are mostly under cyclic loading and, thus, fatigue failure is the major mode of failure in these components. Fatigue mainly starts from a nano- or micro-defect studying which is not feasible using experiments. Thus, Molecular Dynamics (MD) simulations are useful for obtaining understanding of the underlying mechanisms leading to failure of the part. In this study, MD simulations were performed on single crystal NiTi models containing a middle crack subjected to cyclic tensile loading in different crystallographic orientations (i.e., [100], [110] and [111]) at two austenitic temperatures. The orientation dependence of the fatigue behavior of NiTi was observed to be significant. The crack did not propagate significantly under [100] and [110] loading due to the stress-induced martensitic phase transformation at the crack tip. The formation of the martensite at the crack tip acted as a barrier to crack propagation. On the other hand, the crack grew significantly in the model loaded along [111] crystallographic orientation. The crack growth was accelerated when the crack met the {110}<111> slip system which is favorable for austenite with B2 crystal structure. In addition, the effect of temperature on the fatigue crack growth of NiTi was studied at 500 K and 550 K, both being above the austenite finish temperature. The results indicated a slower crack growth rate in NiTi at a higher temperature. [ABSTRACT FROM AUTHOR]