Unique Shape Memory Properties Research Articles

Study of chemically deposited magnetic materials of NiTi memory alloys and their magnetothermal properties

Abstract NiTi alloy has good mechanical properties and biocompatibility, as well as unique shape memory properties. Therefore, it is commonly used to make metal stents in clinical practice. In this study, the substrate used is a NiTi memory alloy, which has been coated with CoNiFeP magnetic material through an electroless plating. The morphology, composition, and magnetic properties of the coating were analyzed using SEM, XRD, and VSM. The magneto-thermal properties were studied by high-frequency alternating magnetic field (AMF) induction equipment. The results showed that after determining a reasonable plating application process, the prepared coatings had certain soft magnetic properties and could exceed 43°C in a short time at different field intensities (Happl×fappl=M×109 Aꞏm−1ꞏs−1, M=1.0, 2.0, 3.0, 4.0, and 5.0) to reach the temperature required for tumor ablation, which can be used to prepare magnetic scaffolds for magnetothermal therapy.

Toward the Development of a Shape Memory Polymer for Individualized Endovascular Therapy of Intracranial Aneurysms Using a 3D‐Printing/Leaching Method

Endovascular treatment of intracranial aneurysms (ICA) aims to occlude the aneurysm space to prevent ICA growth/rupture. Modern endovascular techniques are still limited by relatively low complete occlusion rates, frequently leading to aneurysm growth, rupture, and reoperation. Herein, shape memory polymer (SMP)‐based embolic devices are proposed to advance the effectiveness of ICA therapy by facilitating individualized ICA occlusion. Specifically, a 3D‐printing/leaching method for the fabrication of 3D‐SMP devices that can be tailored to patient‐specific aneurysm geometries obtained from computed tomography angiography is developed. It is demonstrated that this method allows the fabrication of highly porous, compressible foams with unique shape memory properties and customizable microstructure. In addition, the SMP foams exhibit great shape recovery, anisotropic mechanical properties, and the capability to occlude in vitro models with individualized geometries. Collectively, this study indicates that the proposed method will have the potential to advance the translation of coil‐ and stent‐free embolic devices for individualized treatment of saccular ICAs, targeting complete and long‐term durable aneurysm occlusion.

Numerical Investigation of Flexural Behavior of Reinforced Concrete (RC) T-Beams Strengthened with Pre-Stressed Iron-Based (FeMnSiCrNi) Shape Memory Alloy Bars

Shape memory alloy (SMA) is a material that can change shape in response to external stimuli such as temperature, stress, or magnetic fields. SMA types include nitinol (nickel-titanium), copper-aluminum-nickel, copper-zinc-aluminum, iron-manganese-silicon, and various nickel-titanium-X alloys, each exhibiting unique shape memory properties for different applications. Reinforced concrete (RC) T-beams strengthened and pre-stressed with Fe-SMA bars are numerically investigated for their flexural response under the influence of various parameters. The bars are embedded in a concrete layer attached to the beam’s soffit. Based on the numerical results, it was found that increasing the compression strength from 30 to 60 MPa slightly improves the beam’s strength (by 2%), but it significantly increases its ductility by approximately 45%. As opposed to this, the strength and ductility of the pre-stressed T-beam are considerably improved by using a larger diameter of Fe-SMA bars. Specifically, using 12 mm Fe-SMA bar over 6 mm resulted in 65% and 47% greater strength and ductility, respectively. Furthermore, this study examines the importance of considering the flange in the flexural design of pre-stressed beams. It is seen that considering a 500 mm flange width enhanced the ductility by 25% compared to the rectangular-section beam. The authors recommend further experimental work to validate and supplement the calculations and methodology used in the current numerical analysis.

Damage behavior analysis of unidirectional fiber reinforced shape memory polymer composites

Shape memory polymer composites (SMPCs) are gradually being used in space deployable structures due to their unique shape memory properties and variable stiffness characteristics. Currently, the damage behavior of SMPC has not been systematically investigated, which affects its structural design and application. In this study, the damage behavior analysis of unidirectional fiber-reinforced SMPCs was investigated. The buckling deformation and damage modes of SMPC were analyzed theoretically. The strain energy of the matrix cracking and fiber fracture damage system was developed considering the compressive strain of the matrix. Additionally, the analytical expressions of the key parameters during bending were determined and the law of evolution was revealed. The damage mode analysis showed that decreasing fiber volume content and increasing thickness were more likely to result in matrix cracking damage. The fiber fracture would occur in the stretching region if the fiber volume content was less than a certain value. Finally, the experiment was performed to demonstrate the validity of the theoretical method. This work is significant for the design and optimization of the SMPC-based structure.

On behaviors of porous shape memory polymer under different loading conditions

Shape memory polymer (SMP) has drawn much attention in the fields of aerospace, microsystems and biomedicine as a typical smart material with unique shape memory properties. The porous SMPs (P-SMPs) have been manufactured for the applications of reduce noise and insulate thermal. A constitutive model of P-SMPs that proposed based on phase transition theory has been investigated in this work. First, combining Mori–Tanaka method and phase transition theory, a modified micromechanics constitutive model of P-SMPs has been presented to describe the thermal-mechanical behavior of P-SMPs. Then, a series of experiments including uniaxial tension, stress relaxation and thermal cycling test have been conducted to determine the parameters of the modified constitutive model. Finally, the correctness of the proposed constitutive model has been verified by comparing the results of the thermodynamic cycle process including heating recovery and cooling loading stages obtained by the numerical simulation results and thermodynamic cycle experiment. The results show that with a porosity f = 0.1, the strain and stress mean square errors of the constitutive model based on the phase transition theory are 0.22 and 0.0102, respectively, which means that the constitutive model proposed based on phase transition theory can reflect the shape memory properties of P-SMP materials.

An investigation on Ni4Ti3 phase precipitation and its effects in laser directed energy deposition of TiC–NiTi composites

Abstract The failure of the NiTi alloys due to their low mechanical strength is the major problem inhibiting their further applications. Adding ceramic reinforcement materials could not only enhance the strength but also tribological characteristics of NiTi alloys. Among various adopted ceramic reinforcement materials including Al2O3, SiC, TiN, TiB2, TiO2, and TiC, TiC is preferred since it little affects the unique shape memory properties of NiTi. For the first time, this paper reports the fabrication of TiC–NiTi composites using laser DED process. Microstructural characterizations are presented to understand the Ni4Ti3 phase precipitation mechanisms with the addition of TiC particles. Nanoindentation tests are conducted to evaluate the mechanical properties. The addition of TiC particles could alter the phase formation since Ti atoms tend to migrate towards the TiC particles. The nucleation and growth of Ni4Ti3 precipitates are then effectively restricted. The typical thicknesses of the Ni4Ti3 precipitates are reduced by 20% (about 30 nm) at lower levels of laser power or eliminated at a higher level of laser power. The addition of TiC also leads to a reduction of about 10% in the volume fraction of the Ni4Ti3 precipitates and an increase of 6%–17% in the volume fraction of the NiTi2 phases. The refinement of the Ni4Ti3 precipitates improves the pseudoelasticity by about 10% (0.05 in recovery energy ratio). Besides, the nanohardness and Young's modulus are also strengthened. These experimental results indicate that TiC has the capability to refine the Ni4Ti3 precipitates, enhance the strength of NiTi, and improve the pseudoelasticity.

Effect of Coating Method on the Surface Characteristics of NiTi Shape Memory Alloy

Metallic materials including stainless steel, cobalt-chromium alloys, titanium and its alloys, and nickel-titanium (NiTi) shape memory alloys have been used in biomedical applications since the 1940s due to their favorable mechanical properties. Classified as a smart material, NiTi alloy has gained noticeable popularity in biomedical fields such as orthopedic, dental, and cardiovascular applications as it retains reasonable corrosion resistance and biocompatibility along with unique shape memory properties. However, several studies have shown their limits in medical applications due to the risk of Ni ions release from the NiTi implant surface. In order to prevent Ni release, ceramic-based surface coatings such as hydroxyapatite, alumina, and titanium dioxide have been proposed applied by various methods such as electrophoretic deposition, sol-gel, biomimetic and dip coating. In this work, HA coatings on NiTi wire samples were obtained by using biomimetic and dip-coating methods. The biomimetic coating consisted of immersing the NiTi wire samples into simulated body fluid for 24 and 48 h periods, whereas dip coating was accomplished by placing the NiTi wire samples into the HA suspension and retracting the sample with a controlled speed. The effects of the two coating methods on coating quality, surface characteristics and corrosion behavior of NiTi wire samples were investigated. Dip coating method was shown to be a more favorable technique for the NiTi wire samples used throughout this study.

Effects of types of polyols on thermal degradation behaviors of poly(benzoxazine-urethane) alloys

In this work, thermal stability of alloys of polybenzoxazine (PBA-a) / polyurethane (PU) which show unique shape memory properties has been investigated. This study aims to confirm the thermal stability under cyclic heat activation in shape memory performance. Thermal degradation kinetics of the system is evaluated as this behaviour has not been studied before. The degradation temperatures of the obtained alloys were determined by Thermogravimetric Analyzer (TGA) with various heating rates of 15, 20 and 25°C/min. Polybenzoxazine and polyurethane alloys at weight ratios of 80:20, 70:30 and 60:40 were examined.

OS1513 水素環境下における繰返し応力がTINI形状記憶合金の寿命に及ぼす影響

TiNi shape memory alloys (SMA) receive the great attention because of their unique shape memory properties and commercial potential. However, TiNi alloys are apt to absorb hydrogen and deteriorate in various hydrogen environments, and the behavior of TiNi alloy fatigue life under the hydrogen environment has not been elucidated yet. By comparing fatigue test in air and fatigue test in hydrogen environment, the fatigue life of later clearly decreased than the other. At this time, a brittle layer was not formed on the fracture surface of the specimen for fatigue test in hydrogen environment However, macroscopically fracture surface was showing signs of brittle fracture. Furthermore, by comparing fatigue test in hydrogen environment and constant stress test and SSRT, the relationship between maximum stress and charging time showed good agreement with each other in low stress area about 300 MPa. On the other hand, in high stress area about 1000 MPa, large difference can be seen in the life of each. Therefore, the destruction under high stress amplitude is controlled by the damage due to stress fluctuation. On the other hand, destruction under low stress amplitude is controlled by the hydrogen embrittlement and the maximum stress.

Phase Transformations of Nanocrystalline Martensitic Materials

AbstractThe physical phenomena and engineering applications of martensitic phase transformations are the focus of intense ongoing research. The martensitic phase transformation and functional properties such as the shape-memory effect and superelasticity are strongly affected by the crystal size at the nanoscale. The current state of research on the impact of crystal size on the phase stability of the martensite is reviewed summarizing experimental results of various nanostructured martensitic materials and discussing the corresponding theoretical approaches. The review outlines the effects of crystal size on the complex morphology of the martensite, leading to interface structures not encountered in coarse-grained bulk materials. The unique shape-memory properties of martensitic materials can persist even at the nanoscale. Nanocrystalline martensitic materials can be processed to obtain tailored functional properties in combination with enhanced strength. Structural changes of metallic nanowires are similar to those arising by martensitic phase transformations and also can lead to shape-memory effects, as predicted by atomistic simulations.

Shape memory characteristics of cold drawn Ti-Ni wires

With the aim of the applications for smart composite, the influence of cold drawing on the shape memory effect and mechanical properties of Ti-49.5at%Ni and Ti-50at%Ni was investigated systematically. It was found that the reverse transformation temperatures increased significantly, while the martensitic transformation temperatures decreased with increasing amount of cold drawing. Both the temperature range for reverse and martenistic transformations became larger with increasing amount of cold drawing. A recovery strain above 2% and a recovery stress up to 300MPa can be obtained in cold drawn wires. A two-way shape memory effect was observed in as-cold drawn TiNi wires. These results indicate that cold drawn TiNi wires have many unique shape memory properties which can be applicable for smart composites.