Search Results (302)

Laser powder bed fusion (LPBF) technology offers an effective approach for fabricating high-performance superelastic NiTi alloys. This study achieved Ni_51.9Ti_48.1 alloys with outstanding superelastic properties through a triple optimization design of the initial powder composition, printing process parameters, and post-processing. The phase transformation behavior and microstructure of the alloys were systematically investigated. The results indicate that as energy density increases, the size and quantity of pore defects in LPBF-fabricated Ni_51.9Ti_48.1 alloys increase, phase transformation temperatures rise, and hardness conversely decreases. Ni_51.9Ti_48.1 alloys produced at lower energy densities exhibit fewer dislocations. After annealing at 600 °C, Ni₄Ti₃ and R phases form internally, resulting in a maximum superelasticity of 6.64%. Conversely, Ni_51.9Ti_48.1 alloys produced at higher energy densities exhibited a large number of dislocations and formed subgrains after annealing at 600 °C. Additionally, due to the high void volume fraction, they demonstrated deteriorated superelasticity. Full article

Flexible polyurethane foam (FPUF) is widely used in buffer protection, biomedical, and wearable fields due to its light weight, high resilience, and adjustable mechanical properties. However, the traditional water foaming system is often accompanied by bottleneck problems such as cyclic fatigue attenuation, insufficient thermal stability, and surface hydrophilicity while achieving low density. In this study, a dense Si-O-Si cross-linked layer was in situ constructed on the surface of the foam by systematically regulating the water content of the foaming agent (1.5~2.5 wt%) and coupling with methyltrimethoxysilane (MTMS) chemical vapor deposition. Experiments show that the foam foamed with 2 wt% water content still maintains 0.0466 MPa compressive strength and 0.0532 MPa compressive modulus (modulus loss is only 16.6%) after 500 cycles of compression at 90% strain after MTMS deposition. MTMS modification drives the surface wettability to change from hydrophilic (70.4°) to hydrophobic (128.7°), and significantly improves thermal stability (the carbon residue rate at 800 °C increased to 25.5%, an increase of 59.4%). This study not only improves the resilience, but also endows the FPUF surface with hydrophobicity and thermal protection ability, which provides the feasibility for its wide application. Full article

NiTi alloys are widely used in biomedical applications due to their shape memory and superelastic properties. However, their surface reactivity requires protective, biofunctional coatings. To enhance NiTi performance, its surface was modified with an Ag-SiO₂-TiO₂ nanocoating containing small amounts of silica and silver. The coating’s primary phase was rutile with structural defects and a silver solid solution. It showed good adhesion, high scratch resistance, and improved corrosion behavior in Ringer’s solution, as demonstrated by EIS and cyclic polarization. EIS revealed high low-frequency impedance and two time constants, suggesting both barrier protection and slower electrochemical processes. Despite low breakdown and repassivation potentials, the coating effectively limited uniform corrosion. SEM/EDS confirmed localized degradation and partial substrate exposure, while elemental mapping showed well-dispersed silica and silver in a TiO₂-rich matrix. The proposed pitting mechanism involves chloride-induced depassivation and galvanic effects. Surface potential mapping indicated electrostatic heterogeneity, mitigated by silica. The coating offers a balanced combination of corrosion protection and biofunctionality, supporting its potential for implant use. Full article

Shape memory alloy (SMA) materials are valued for their shape memory effect, superelasticity, and biocompatibility, making them an ideal choice for applications in biomedical, aerospace, and actuator fields. Nickel–titanium (NiTi) SMA is a promising biomedical material. It is widely used in the manufacture of biomedical instruments, devices, implants, and surgical tools. However, its complex thermo-mechanical behavior and poor machinability pose challenges for conventional machining. To manufacture high-quality nitinol parts, traditional machining processes are being replaced by advanced machining technologies. Electric discharge machining (EDM) is an advanced machining technique whose mechanism of material removal involves erosion caused by plasma formation and spark generation. It has proven effective for processing difficult-to-machine materials. This review summarizes EDM and its variants, including hybrid EDM, with a focus on machining NiTi-SMA materials for biomedical, aerospace, microelectromechanical systems, and automotive applications, and systematically explores key factors such as process parameters, material removal mechanisms, surface integrity, tool wear, and optimization strategies. This review begins with an introduction to nitinol (i.e., NiTi-SMA) and its variants, followed by an in-depth discussion of plasma formation, spark generation mechanisms, and other key aspects of EDM. It then provides a detailed analysis of notable past research on the machining of NiTi SMA materials using EDM and its variants. This paper concludes with insights into future research directions, aiming to advance EDM-based machining of SMA materials and serve as a valuable resource for researchers and engineers in the field. Full article

Incorporating Nitinol (NiTi) shape memory alloy (SMA) into concrete structures has gained significant attention in recent years due to its ability to enhance the properties of concrete. This review paper illustrates the history of NiTi SMA and its use in various civil engineering structural applications. A detailed analysis of the existing literature and case studies offers perspectives on the possible applications, benefits, and prospects of utilizing NiTi SMA to reinforce and strengthen elements in concrete structures. The study examined publications on the internal usage of NiTi SMA in concrete and cement-based matrices as an embedded element, including fibers, bars, cables, wires, powder, and strands. In addition, superelastic and shape memory forms of NiTi were considered. It was concluded that the superelasticity of NiTi aided in energy dissipation from impact or seismic events. It also improved the re-centering performance and deformation capacity and reduced residual stresses, strains, and cracks. Conversely, the SMA effect of NiTi helped bridge cracks, recover the original shape, and induced prestressing forces under thermal activation. Full article

Objectives: The aim of this study is to demonstrate the efficacy of the modified technique of radical organ-preserving surgery of invasive cervical cancer (CC) in patients of reproductive age. Methods: This study included 118 patients of reproductive age (34.9 ± 4.8 years) with a morphologically verified diagnosis of invasive CC (T1a-1bNxM0). All patients underwent organ-preserving surgery in the scope of radical trachelectomy. A shape memory mesh implant woven in the form of a stocking from superelastic nickelide titanium thread with subsequent fixation with separate sutures around the perimeter was used to form the uterine closure apparatus and to strengthen the utero-vaginal anastomosis. The mesh implant was made of superelastic thin nickelide titanium threads with a diameter of 60–40 microns on a metal knitting machine. All patients were prospectively followed up for a mean of 120 months. Results: No intraoperative or postoperative complications were revealed when using a shape memory implant made of titanium nickelide during radical trachelectomy to form a locking apparatus and strengthen the anastomosis zone. No cervical stenoses or mesh failures were noted in any case. The 5-year overall and recurrence-free survival rates were 100% and 98%, respectively. Two patients indicated recurrence; it occurred in 3 and 36 months. There were 42 spontaneous pregnancies, and 29 resulted in full-term delivery, whereas 2 and 11 ended in miscarriage and early abortion, respectively. Currently, 18 patients are at different stages of the use of assisted reproductive technologies. Conclusions: The shape memory implant made of titanium nickelide integrates well into the surrounding tissues and successfully imitates the effect of the cervix. The use of this sparing-surgery technique has shown reasonably good results in carrying the pregnancy to term and good reproductive outcomes. Full article

To address the limitations of traditional buckling-restrained braces (BRB), which feature a single-stage yielding and inadequate energy dissipation under small earthquakes, this study proposes a novel double-stage yielding buckling-restrained brace (DSY-BRB). The proposed design integrates a sliding friction damper with shape memory alloy (SMA) bolts and conventional BRB components, enabling effective energy dissipation at small deformations and adaptive performance across varying displacement amplitudes compared with traditional BRBs. Leveraging SMA superelasticity, the DSY-BRB also exhibits self-centering capability that distinguishes it from prior DSY-BRB configurations. Experimental investigations were conducted on DSY-BRB specimens with varying core plate widths under cyclic quasi-static loading to evaluate hysteresis behavior, energy dissipation capacity, and self-centering performance. Results demonstrate that DSY-BRBs exhibit symmetric flag-shaped hysteresis curves with enhanced energy dissipation and excellent self-centering capabilities, achieving minimal residual deformation compared to traditional BRBs. Complementary finite element modeling with parametric analysis was performed to establish design guidelines for optimal double-stage buckling behavior. The findings reveal critical stiffness ratio requirements between BRB and SMA bolt-based friction damper components, providing valuable design criteria for engineering applications. This hybrid approach offers significant advantages in seismic energy dissipation and structural resilience compared to existing DSY-BRB systems. Full article

Shape memory alloy dampers (SMADs) are widely applied in structural vibration control due to their excellent superelastic properties. However, there has been no research on the random wind-induced vibration control of transmission tower-line (TTL) systems with added SMADs. To address this gap, this paper proposes an analytical framework for the wind-induced vibration control of TTL systems with SMADs under random wind loads. An analytical model for the coupled TTL system is developed. The constitutive relationship of the SMAD is derived using the statistical linearization method, and a vibration control approach for the TTL-coupled system with SMADs is proposed. The vibration response of the TTL–SMAD system under random wind loads is derived, and an extreme response analysis framework based on the first exceedance failure criterion is established. The results show that the optimal installation scheme for the SMAD achieves a vibration reduction of more than 30%. When the damper’s stiffness coefficient is approximately 1, the SMAD effectively controls the vibrations. Moreover, a service temperature of 0 °C is found to be the optimal control temperature for the SMAD. These findings provide important references for the application of SMADs in the vibration control of TTL systems. Full article

Growing environmental concerns have driven increased interest in solid-state thermal technologies based on the elastocaloric properties of shape memory alloys (SMA). This work examines the elastocaloric effect (eCE) in Ni-Ti SMA sheets subjected to cyclic bending, providing quantitative thermal characterization of their behavior under controlled loading conditions. The experimental investigation employed passive thermography to analyze the thermal response of Ni-Ti sheets under two deflection configurations at 1800 rpm loading. Testing revealed consistent adiabatic temperature variations (ΔT_ad) of 4.14 °C and 4.26 °C for the respective deflections during heating cycles, while cooling phases demonstrated efficient thermal homogenization with temperature gradients decreasing from 4.13 °C to 0.13 °C and 4.43 °C to 0.68 °C over 60 s. These findings provide systematic thermal documentation of elastocaloric behavior in bending-loaded Ni-Ti sheet elements and quantitative data on the relationship between mechanical loading parameters and thermal gradients, enhancing the experimental understanding of elastocaloric phenomena in this configuration. Full article

A Cu-11.85Al-3.2Mn-0.1Ti shape memory alloy (SMA) with excellent superelasticity and shape memory effect was successfully fabricated via selective laser melting (SLM). Increasing the energy density enhanced grain refinement, achieving a 90% refinement rate compared to cast alloy, with an average width of ~0.15 µm. Refined martensite lowered transformation temperatures and increased thermal hysteresis. Nanoscale Cu₂TiAl phases precipitated densely within the matrix, forming a dual strengthening network combining precipitation hardening and dislocation hardening. This mechanism yielded a room-temperature tensile strength of 829.07 MPa, with 6.38% fracture strain. At 200 °C, strength increased to 883.68 MPa, with 12.26% strain. The maximum tensile strength represents a nearly 30% improvement on existing laser-melted quaternary Cu-based SMAs. Full article

Loading and clamping schemes significantly influence the behavior of shape memory alloys, specifically, the course of their solid-state transformations. This paper presents experimental and numerical findings regarding the nonlinear response of samples of the above-mentioned type of smart materials observed during tensile tests. Hysteretic properties were studied to elucidate the superelastic behavior of the tested and modeled samples. The conducted tensile tests considered two configurations of grips, i.e., the standard one, where the jaws transversely clamp a specimen, and the customized bollard grip solution, which the authors developed to reduce local stress concentration in a specimen. The characteristic impact of the boundary conditions on the solid phase transformation in shape memory alloys, present due to the specific clamping scheme, was studied using a thermal camera and extensometer. Martensitic transformation and the plateau region in the nonlinear stress–strain characteristics were observed. The results of the numerical simulation converged to the experimental outcomes. This study explains the complex nature of the phase changes in shape memory alloys under specific boundary conditions induced by a given clamping scheme. In particular, variation in the martensitic transformation course is identified as resulting from the stress distribution observed in the specimen’s clamping area. Full article

The incorporation of advanced smart materials, such as shape memory alloys (SMAs), in civil engineering presents significant challenges, particularly in modeling their complex behavior. Traditional numerical SMA models often require material parameters that are difficult to estimate and validate. The objective of this paper is to introduce an equation-based approach to modeling the superelastic behavior of SMAs based on rheological models. The proposed phenomenological model accurately captures SMA superelasticity under isothermal conditions, with each material parameter directly correlated to data from standard mechanical experiments. Four modifications to the baseline rheological model are proposed, highlighting their impact on superelastic characteristics. The resulting constitutive relationships are expressed as non-linear ordinary differential equations, making them compatible with commercial finite element method (FEM) software through user-defined subroutines. The practical application of this modeling approach is demonstrated through the strengthening of a historical masonry wall subjected to seismic activity. Comparative analysis shows that ties incorporating SMA segments outperform traditional steel ties by reducing the potential damage and enhancing the structural performance. Additionally, the energy dissipation during the SMA phase transformation improves the damping of vibrations, further contributing to the stability of the structure. This study underscores the potential of SMA-based solutions in seismic retrofitting and highlights the advantages of equation-based modeling for practical engineering applications. Full article

This study addresses the clinical requirements of a transoral surgery-assisting continuum robot. This application requires both high bendability and stiffness in order to ensure precise positioning and stable fixation of surgical tools. To meet these needs, we developed a tendon-driven discrete continuum robot unit featuring a ball–socket joint and superelastic Nitinol rods. One to three serially connected robot units were tested by applying proximal tendon tension ($T_l$) in the range of 100–1000 g while distal tension ($T_s$) was continuously increased to induce bending. During bending, the curves were interpolated using third-order to fifth-order polynomials at discrete $T_l$ levels. The interpolated inverse statics were validated experimentally and compared with finite element simulations using ANSYS. Furthermore, we propose a planar path planning algorithm and numerically evaluate it for a three-unit robot following an arc-shaped trajectory. The inverse statics successfully captured the nonlinear bending behavior of the tendon-driven robot. Validation experiments showed average angular errors of 2.7%, 6.6%, and 5.3% for one, two, and three connected units, respectively. The proposed path planning method achieved an average positional deviation from the reference trajectory ranging from 0.95 mm to 19.77 mm. This work presents a practical and generalizable experimental mapping framework for the inverse statics of tendon-driven discrete continuum robots, avoiding the need for complex analytical models. Full article

In this study, the effect of aging heat treatment on the superelastic properties and microstructure of [001]-oriented Fe₄₁Ni₂₈Co₁₇Al_11.5Ti_1.25Nb_1.25 (at.%) single crystals was investigated using the cyclic superelastic strain test and a transmission electron microscope (TEM). The TEM results reveal that the average precipitate size is around 3–5 nm in the 600 °C/24 h samples, 6–8 nm in the 600 °C/48 h samples, and 10–12 nm in the 600 °C/72 h samples. The results indicate that precipitate size increases as aging time increases from 24 to 72 h. EDS analysis results show decreased Fe and increased Ni when the analyzed line crosses the precipitate region. The diffraction pattern results show that the precipitate has an L1₂ crystal structure. The thermo-magnetization curves of single crystals under the three aging conditions (600 °C/24 h, 600 °C/48 h, and 600 °C/72 h) show that the values of the transformation temperatures increased from 24 to 72 h. Magnetization was saturated at 140 emu/g under the magnetic field of 7 Tesla. When increasing the magnetic field from 0.05 to 7 Tesla, the transformation temperatures rose. The results indicate that magnetic fields can activate martensitic transformation. From the results of the superelasticity test at room temperature, [001]-oriented FeNiCoAlTiNb single crystals aged at 600 °C for 24, 48, and 72 h presented recoverable strains of 3%, 5.1%, and 2.6%, respectively. Digital image correlation (DIC) results of the aged samples show that two martensite variants were activated during the superelasticity test. The two variants form corresponding variant pairs (CVPs) and improve the recoverable strain of superelasticity. Although maximum recoverable strain was obtained for the 600 °C/48 h samples, the samples show poor cyclic stability at room temperature after applying the 6% strain. According to the DIC results, the retained martensite, which is pinned by dislocations, was observed after the test. The irrecoverable strain was attributed to the residual martensite. For the 600 °C/72 h samples, the large size of the precipitates poses an obstacle to dislocation transformation and formation. The dislocations increase the stress hysteresis width and stabilize the martensite, causing poor recoverability. Full article

Three-Dimensional Concrete Printing (3DCP) is transforming the construction industry by offering faster, more cost-effective, and sustainable building solutions. However, a major challenge that hinders its full potential is the low tensile strength of concrete, which, as in conventional methods, necessitates reinforcement. Unlike traditional construction, integrating reinforcement into the automated 3D printing process is complex and remains a critical research gap. In this study, zigzag-reinforcing method, that could be classified as an in-process interlayer reinforcement in 3DCP, is proposed. To investigate the effect of the proposed reinforcement technique, an analytical study was conducted using Abaqus finite-element software. Four beam models with different reinforcement configurations were considered: an unreinforced control specimen, two Nitinol-reinforced beams (one exhibiting superelastic behavior and the other the shape memory effect), and a steel-reinforced beam. Three-point bending tests were simulated using a displacement-controlled, centrally applied load. The results showed that zigzag reinforcement improved flexibility and prevented sudden failure. The Nitinol-reinforced sample with superelastic behavior failed at a displacement of 2.67 mm, approximately 37 times greater than the 0.07 mm failure displacement of the unreinforced beam. Unlike the unreinforced specimen, where cracks propagated vertically, the zigzag reinforcement redirected crack propagation horizontally, allowing the beams to carry more load. Additionally, the steel-reinforced sample demonstrated a 68% increase in maximum flexural moment and a 286% increase in flexibility compared to the control specimen. Overall, zigzag reinforcement significantly enhanced the mechanical performance of the samples, and if its durability and other practical parameters are validated through experimental studies, it could be considered a promising reinforcement technique for use in 3D concrete printing. Full article