Behavior Of Shape Memory Alloys Research Articles

Effects of residual stress on the isothermal tensile behavior of nanocrystalline superelastic NiTi shape memory alloy

The residual stress greatly affects the mechanical behavior of a material. In this work, the effect of residual stress on the isothermal tensile behavior of a NiTi shape memory alloy is studied. The focused ion beam and digital image correlation are combined to measure the two-dimensional residual stress in nanocrystalline NiTi plates processed with prestrain laser shock peening. A four-point bending experiment verified the accuracy of this measurement method. The FIB-DIC method is an attractive tool for measuring the two-dimensional residual stress in phase transition nanocrystalline materials. The internal residual stress significantly decreases the phase transition stress, and the mechanism is studied via finite element and theoretical analyses. This work implies that the mechanical behavior of NiTi shape memory alloys can be tailored via residual stress engineering.

Optimizing laser parameters and exploring building direction dependence of corrosion behavior in NiTi alloys fabricated by laser powder bed fusion

The microstructure and materials performance of Laser Powder Bed Fusion-fabricated (LPBFed) NiTi shape memory alloys (SMAs) varies depending on the laser parameters and building directions. This study initially optimized the laser processing parameters (laser power and scanning speed) for LPBFed NiTi SMAs to enhance their printing quality and mechanical properties. We determined that with fixed hatch spacing of 80 μm and layer thickness of 30 μm, the laser power of 105 W, and scanning speed of 600 mm/s produced the best results. Subsequently, the corrosion behavior of LPBFed NiTi SMAs built in three different building directions (0°, 45°, 90°) was investigated in 0.9 wt.% NaCl solution at 37 °C. The electrochemical data revealed that the corrosion current density (Icorr) decreased with increasing building direction angle (Icorr-90° <Icorr-45° <Icorr-0°). The corrosion resistance followed the order of 0° sample ˂ 45° sample ˂ 90° sample. These findings were attributed to the difference in the grain size and boundary density. Higher boundary densities enhanced the electron activity capacity and the element diffusion rates, facilitating the rapid formation of a protective film and thus improving the corrosion resistance. This new insight into the anisotropy of corrosion behavior relative to building directions can inform the design of NiTi-SMA products and improve their reliability in tissue engineering applications.

Effect of Laser Surface Texturing Process on Dry Sliding Wear Behavior of NiTi Shape Memory Alloy Used in Airplane

In this study, the effect of laser surface texturing (LST) applied to NiTi Shape Memory Alloy (SMA) on the dry sliding wear behavior of the material was investigated. After polishing and cleaning the material surface, a pitted surface texturing process was performed using a femtosecond laser under atmospheric conditions. After the surface texturing process, dry sliding wear tests were performed at room temperature. When the wear behavior of the laser-applied and non-laser-applied test samples was evaluated comparatively, it was determined that the coefficient of friction (COF) of the laser-applied samples under 1N load was approximately 17% lower. It was determined that the decrease in the COF value decreased with increasing load. However, the wear amount of the LSD-applied NiTi SMA was higher than the untreated sample. It was evaluated that this situation was due to thermal softening that occurred depending on the ablation geometry and dimensions.

Mechanical behavior of shape memory alloys considering the effects of body fluids corrosion for biomedical applications

Abstract Shape memory alloys (SMAs) are widely used in biomedical engineering, including cardiovascular stents, artificial skeletons, and orthodontic implants. For the above applications, the body fluids corrosion processes will inevitably cause deterioration in the mechanical properties of the SMAs actuator during its service life, which will threaten the safety of human health. To analyze such problems, experimental measurements have been carried out to investigate the influence of body fluid corrosion on the mechanical properties of SMAs. Changes in the mechanical properties, such as Young’s modulus and phase transformation temperatures of SMAs under body fluids corrosion were tested firstly in the simulated body environment with the 0.9 wt. % NaCl solution at 37. With an increase of the immersion time, the results show that the Ti (titanium) percentage, austenitic (reverse) transformation start temperature, austenitic (reverse) transformation finish temperature, and maximum residual strain all increase, the Ni (nickel) percentage, martensitic transformation finish temperature, tensile strength, and yield strength decrease, and the martensitic transformation start temperature first decreases and then increases. The research in this work can provide an experimental basis for further study of the SMAs materials in biomedicine applications.

Crack monitoring and repair model of SMA composite material based on strain transfer

In the process of using composite materials, crack damage is unavoidable. These cracks may cause a decrease in the structural performance of the material and may even pose a threat to the safety of the entire structure. In this paper, the shape memory alloy (SMA) is embedded into the composite material, and the strain transfer effect of the interface layer is considered. The crack monitoring and repair model of SMA composite material based on strain transfer are established using SMA resistance-sensing characteristics and SMA constitutive model. Based on this monitoring and repair model, the crack monitoring behavior of SMA under different initial states and temperature conditions is discussed, and the crack repair behavior of SMA under specific initial states and temperature conditions is also discussed. The research results show that the change in SMA resistance and the strain of the composite material crack are linearly segmented, and as the temperature increases, the composite material crack is gradually repaired. This study can provide theoretical guidance for the further engineering application of SMA composite material crack monitoring and repair theory.

A study on interactive fiber rubber composite structures subjected to bend-twist coupling

Abstract This paper investigates the deformation behavior of shape memory alloy (SMA)-integrated fiber-reinforced composites, with an emphasis on how different fiber orientations influence bend-twist coupling. The study combines experimental analysis, finite element simulations using Ansys, and analytical modeling via Classical Laminate Theory (CLT) to assess the mechanical response of these composites. The experiments revealed that composites with higher fiber angles (60°) exhibited dominant twisting behavior, while those with lower angles (30° and 45°) showed more pronounced bending deformation. The simulations corroborated these trends, offering detailed insights into the displacement behavior. The CLT model further predicted a decrease in deflection with increasing fiber angles, which was consistent with experimental results, although some deviations in Z-deformation were attributed to material and manufacturing factors. This research highlights the critical role of fiber orientation in achieving desired deformations in SMA-integrated composites, offering valuable insights for the design of adaptive structures. The findings demonstrate the potential for optimizing fiber configurations to tailor bend-twist coupling in advanced composite applications.

Elevated Temperature Deformation Behavior of Novel NiTiAg Shape Memory Alloys: A Comparison Between Various Constitutive Models and Experimental Flow Curves

Elevated Temperature Deformation Behavior of Novel NiTiAg Shape Memory Alloys: A Comparison Between Various Constitutive Models and Experimental Flow Curves

The effect of Nb additions on the passive behavior of NiTi shape memory alloys

This study explores the passivity and localized corrosion behavior of Ni(100-x)/2Ti(100-x)/2Nbx shape memory alloys (where x = 3, 6, and 9 at.%) through potentiodynamic and potentiostatic polarization tests in 3.5 wt% NaCl solution. The results reveal a significant dependence of the surface passive film’s stability on the Nb concentration. Using X-ray photoelectron spectroscopy (XPS), the chemical composition of the passive films formed on the NiTiNb alloys was characterized. Microstructural analysis showed that increasing Nb content affects the volume fraction of the eutectic microconstituent, leading to the suppression of martensite and secondary Ni-Ti phases in the microstructure with higher Nb additions. The findings demonstrate that localized corrosion resistance improves with Nb additions, attributed to the incorporation of Nb2O5 into the TiO2 passive film, enhancing its protective capacity. Remarkably, the NiTi shape memory alloy exhibits immunity to localized corrosion when 9 at.% Nb is added.

Simultaneous position and force control of a SMA-actuated continuum robotic module

Continuum manipulators with controllable shape and exerting force are attractive devices. Utilizing great features of shape memory alloys (SMAs), thin continuum modules are developed. SMAs are embedded around an elastic rod and activated through a control algorithm to set a desired shape. However, complex behavior of SMAs in such a multi-input multi-output system, make the control challenging. Additionally, simultaneous control of position and the force applied by the module, as a challenging problem, has not been investigated so far. Handling this problem may increase the application of continuum robots when utilized as manipulators or when pass through narrow and complex canals with sensitive wall. In this research, position and force control of such continuum module is under focus for achieving a more practical tool for better non-invasive medical devices. Further to the position control, the amount of force applied to the environment is adjusted in different locations of the workspace through a novel fuzzy controller. The results indicate the possibility of simultaneous control of the position and force using fuzzy controller with a reasonable accuracy of 0.5° for angle and 0.05 N for the force. The concluded results may be utilized in developing smarter soft robots.

Combined Effect of Annealing Temperature and Pre-deformation on the Superelastic Behaviors of NiTi Shape Memory Alloys

Combined Effect of Annealing Temperature and Pre-deformation on the Superelastic Behaviors of NiTi Shape Memory Alloys

Advancements in shape-memory alloys: Properties, applications, challenges, and future prospects

Shape-memory alloys (SMAs) are advanced engineering materials that have gained significant attention in recent years due to their unique properties and potential applications. SMAs have the remarkable ability to recover their original shape after deformation, making them invaluable in various fields, from biomedical devices to aerospace engineering. Despite their many advantages, SMAs also face several challenges, including the need for improved processing techniques and the development of more efficient actuation systems. To address these challenges, researchers have adopted various approaches, including using advanced fabrication methods and developing novel actuation systems. Recent research has yielded several notable achievements in the field of SMAs. For example, researchers have developed new processing techniques that allow the production of SMAs with improved properties, such as higher strength and better fatigue resistance. Additionally, researchers have developed new actuation systems that allow for more precise and efficient control of SMA behavior. Looking ahead, the future of SMAs looks promising. With continued research and development, SMAs have the potential to revolutionize various fields, from aerospace engineering to biomedical devices. However, further work is needed to overcome the remaining challenges and fully realize the potential of these remarkable materials. This article provides a comprehensive overview of SMAs, including their properties, fabrication methods, and various applications. It also discusses the challenges facing the field, the approaches to address them, and recent achievements.

Effect of laser energy density on the phase transformation behavior and functional properties of NiTi shape memory alloy by selective laser melting

NiTi shape memory alloy (SMA) was prepared via selective laser melting (SLM). Orthogonal tests were conducted with varying laser power and scanning speeds to explore the influence of laser energy density on microstructure, phase transformation behavior, mechanical properties and functional properties (superelasticity and shape memory effect). As energy density increases from 24.3 to 106.3 J/mm³, microstructure transforms from fine to columnar grains. Ni consumption intensifies, boosting transformation temperature and B2 content at room temperature. Post cyclic stretching, B2 content in alloy escalates further at room temperature. Tensile strength peaked at 53.6 J/mm³, while the elongation rate significantly increases with increasing energy density. During cyclic stretching, low or high energy densities in SLM NiTi induce high-density dislocations and stable residual martensite, respectively, significantly inhibiting martensitic transformation and resulting in extremely poor functional properties. The alloy produced at 53.6 J/mm³ boasts exceptional superelasticity due to stress-induced martensitic transformation and phase inversion post-unloading. Following heating past the critical transition, it nearly fully recovers (97.78 % recovery rate). Despite multiple shape memory fatigue tests, it maintains a recovery rate above 90 %. This study provides crucial theoretical insights for optimizing NiTi SMA phase transformation behavior and enhancing the performance.

Post-fire mechanical behavior of iron-based shape memory alloy used for structural damping

This study sheds light on the post-fire mechanical behavior of Fe-SMA by conducting a series of tests at material level, with a particular focus on the low-cycle fatigue (LCF) performance. Three temperatures (500 °C, 750 °C, 1000 °C) and three cooling methods (air cooling, water spray quenching, water quenching) are considered to simulate different fire-cooling scenarios. After the heating-cooling cycle, 10 monotonic tensile specimens and 20 LCF specimens are tested. Essential material parameters for Manson-Coffin model and combined hardening model are also calibrated based on the experimental data. The failure mechanism and possible factors affecting the post-fire LCF performance of Fe-SMA are further explored by scanning electron microscope (SEM), metallographic observation (MO), electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) analysis. Results show that Fe-SMA could exhibit even better LCF resistance after undergoing the considered fire-cooling procedure, especially those heated up to 750 °C and 1000 °C. Even under rapid cooling, no signs of brittle fracture are observed, which is superior to traditional structural steels. Different heating temperatures and cooling methods affect the grain sizes and microstructure of Fe-SMA, leading to variations in its post-fire LCF behavior.

Multi-doping effect on the martensitic transformation behavior of shape memory alloys

Incorporating various elements into host shape memory alloys (SMAs) has proven to be an effective strategy for optimizing their functional properties. However, modeling the complex multi-doping effect is challenging. In the present study, we introduced a phenomenological model based on Ginzburg–Landau theory, wherein each doping element is conceptualized as an internal dilatational stress. This internal stress is represented as a spatial Gaussian distribution characterized by two influential parameters: potency (h) and range (σ). The interaction between doping elements arises from the superposition of these stresses. Utilizing a time-dependent Ginzburg–Landau simulation based on our proposed model, diverse combinations of h and σ replicate the varied experimental outcomes associated with multi-doping effects. This model offers insight into the understanding of the doping impact on martensitic transformation and may contribute to the development of SMAs with tailored properties.

Modeling the interaction between instabilities and functional degradation in shape memory alloys

Localization of the stress-induced martensitic phase transformation plays an important role in the fatigue behavior of shape memory alloys (SMAs). The phenomenon of return-point memory that is observed during the subloop deformation of a partially-transformed SMA is a clear manifestation of the interaction between localized phase transformation and degradation of the functional properties. The present study aims to demonstrate this structure–material interaction in the modeling of return-point memory. It seems that this crucial aspect has been overlooked in previous modeling studies. For this purpose, we developed a gradient-enhanced model of pseudoelasticity that incorporates the degradation of functional properties in its constitutive description. The model is employed to reproduce the hierarchical return-point memory in a pseudoelastic NiTi wire under isothermal uniaxial tension with nested subloops. Additionally, a detailed analysis is carried out for NiTi strip with a more complex transformation pattern. Our study highlights the subtle morphological changes of phase transformation under different loading scenarios and the resulting implications for return-point memory.

Investigation of bio-corrosion behavior, structural and thermal properties of Ni20Ti50Sn30 high-temperature shape memory alloy

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.

Test, design, and parametric analysis of a prefabricated industrial building with shape memory alloy (SMA) cable-restrained bearings for seismic resilience

This paper presents an in-depth discussion on the behavior and design of a novel shape memory alloy (SMA) cable-restrained natural rubber (hereinafter denoted as SMA-NR) bearing used for multi-stage seismic protection of an industrial building equipped with critical facilities. The study commences with a brief illustration of the working mechanism of the bearing, followed by an individual SMA cable test and a full-scale quasi-static test on an SMA-NR bearing specimen. The SMA cable specimen exhibits a unique flag-shaped hysteretic behavior with large recoverable strain. The SMA-NR bearing test results present a double-stage hysteretic behavior, i.e., initial horizontally flexible performance and cable-restrained state for structural safety. Through a verified numerical modelling, and taking three structural responses into consideration, i.e., peak absolute acceleration, peak bearing deformation, and residual bearing deformation, an extended parametric study is conducted, covering different bearing types and restraining elements (SMA or steel cables). The system-level analysis results highlight the benefit of the SMA cable-restrained strategy in seismic isolation performance, and show a favorable efficiency of this strategy in trade-off of critical responses. Furthermore, a representative single-degree-of-freedom (SDOF) model is developed and well validated, with a satisfactory agreement to the overall structural model. Seismic fragility analyses are finally conducted considering both far-field and near-fault ground motions, indicating that the SMA cable restrainer, serving as the last-defense strategy, could effectively balance the various dynamic responses of the superstructure.

Effect of Nb Content on Behavior of (Ti-Nb) Shape Memory Alloys for Biomedical Applications

Effect of Nb Content on Behavior of (Ti-Nb) Shape Memory Alloys for Biomedical Applications

Experimental-Numerical Assessment of Mechanical Behavior of Laboratory-Made Steel and NiTi Shape Memory Alloy Wire Ropes

The mechanical behaviors of laboratory-fabricated steel and superelastic shape memory alloy (SMA) wire ropes are assessed in this study through a comprehensive approach encompassing both experimental investigations and finite element (FE) numerical simulations. The assessment of steel wire ropes involves experimental scrutiny under sinusoidal cyclic loading and natural earthquake loading conditions. In parallel, SMA wire ropes’ behaviors are analyzed utilizing FE simulations employing the widely acknowledged ABAQUS software version 2020. The validation of all numerical simulations is undertaken against the experimentally observed behaviors. Moreover, full-scale steel wire ropes are subjected to shaking table tests to validate the simulations, facilitating a comparative analysis between the mechanical responses of SMA and steel wire ropes. The findings demonstrate that SMA wire ropes exhibit superelastic behavior akin to SMA wires, with marginal variations in overall response observed across distinct configurations, akin to steel wire ropes. Furthermore, augmenting the helix angle of SMA wire ropes results in reduced stress and increased strain when exposed to the El Centro earthquake scenario. Nevertheless, the mechanical response of SMA wire ropes closely mirrors that of a single wire.

Finite strain modelling of Shape Memory Alloys in the logarithmic strain space: A comparative study with other finite strain approaches

Finite strain models for Shape Memory Alloys (SMAs) offer significant advantages over small strain models in that they excel in their ability to characterize SMA behaviour under large strain and finite rotations while eliminating the inherent assumptions associated with the small strain framework. The paper at hand presents a numerical model for SMAs at finite strain, employing the logarithmic strain measure to obtain an additive split of the total strain into its elastic and inelastic (transformation) parts. Notably, the model maintains the thermodynamic consistency validated using the Clausius–Duhem inequality. Additionally, we compare this model with two other finite strain SMA models employing logarithmic strain measures: a hypoelastic model, which splits the rate of deformation tensor additively, and a hyperelastic model, which decomposes the deformation gradient multiplicatively. The numerical formulation for the three finite strain models is specifically tailored to address superelasticity in SMAs. It is derived from the established small strain model and seamlessly extended into the domain of finite strain framework. Several numerical examples are carried out to showcase the logarithmic strain space approach applied to SMAs and to compare its response with that of the other aforementioned finite strain models in SMAs. The meticulous examination reveals that the logarithmic strain space approach aligns well with the existing finite strain models, demonstrating its effectiveness and compatibility.