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Shape memory alloys are well known to be used as a ring element for connect coupling two pipes in various fields. In the case of structural and functional designs for a coupling ring of shape memory alloy, we have considered the shape memory effects in multi-axial stress and strain using volumetric strain in each element, so as to make FEM analysis more effective for optimizing the shape and the amount of pre-deformation. Using some uni-axial fundamental test results, as property parameters for FEM, the modeling method simulating the deformation behavior of a coupling ring has been eveloped in order to optimize the configuration and size of a coupling ring. The validity of this FEM modeling method was confirmed by verification experiments.

A new constitutive equation is proposed based on the series combined model, considering the generation of slip deformation, due to the recovery stress in heating under constraint strain, as well as external stress in loading. The martensite volume fractions in the constitutive equation were distinguished into three kinds: un-reoriented martensite, reoriented martensite and plastic damaged martensite. And the critical stress for the slip deformation, generated through the reverse transformation, in a constraint strain-heating process, was clarified experimentally and introduced into the constitutive equation. Moreover, the validity of our constitutive equation has been confirmed by experimentation conducted under various constraint strain-heating conditions in the recovery process.

This paper investigates the microstructure, martensitic transformation and shape memory effect of Co-16Al alloy. The optical micrographs of Co-16at.%Al alloy quenched from 1200°C show that the ε martensite occurs at room temperature, while some remaining γ phase can also be observed. This microstructure analysis can be supported by XRD pattern. It is shown that the alloy undergoes a martensitic reverse transformation at about 220°C during heating. However, no transformation from the fcc phase to hcp phase is detected by DSC measurement upon cooling. It is thought that the precipitation of β phase by aging at high temperature may suppress the martensitic transformation. The tension strain is 12% and the fracture strength is above 800MPa. No obvious yield deformation is observed from the stress-strain curve. SEM images exhibits many dimples on the fracture surface, which means the fracture mechanism is ductile rupture. Bending test show that only 25% deformation can be recovered due to shape memory effect when the pre-strain is 5%.

The purpose of the study was to comparatively investigate two NiTi orthodontic wires. It is valuable to determine the phase transformation temperature and corrosion characteristics of the orthodontic wires to further study the shape memory effect and corrosion resistance properties. Optical microscope and EDX analysis were used for microstructure characteristics and composition analysis. Differential scanning calorimetry (DSC) was carried out to identify the phase transformation behavior of the two wires. Electrochemical tests in artificial saliva at 37 ±1^°C including polarization and electrochemical impedance spectroscopy (EIS) were used to assess the corrosion resistance and corrosion mechanism of the wires. It was found that the transformation temperature range of A-wire (imported) is narrower while the A_s and A_f are close to the body temperature, which is more suitable in the orthodontic operation at early stage. The corrosion current density of A-wire is lower than that of B-wire (domestically made) while the corrosion potential is higher. EIS test results indicated that the corrosion mechanism was the same. However, the oxide layer formed on the surface of A-wire is more protective.

In this paper, first we investigate the heating-responsive shape memory effect in an acrylonitrile butadiene styrene (ABS). Subsequently, after surface treatment (via dipping in acetone/water solution of different concentrations and for different dipping time) of pre-stretched samples, we demonstrate the feasibility to form strip shaped wrinkles atop the surface upon heating of pre-stretched ABS for shape recovery. The influential factors, such as acetone concentration and dipping time in surface treatment, are revealed and discussed.

NiTinol Shape Memory Alloys (SMA) are becoming one of the ideal choices for biomedical industries due to their unique properties such as Shape Memory Effect (SME), Super Elasticity (SE) and Biocompatibility. In the process of making complicated biomedical implants, welding processes play a vital role. In this work, an attempt was made to study the effect of heat input and Post Weld Heat Treatment (PWHT) on the TIG-welded NiTinol SMA. TIG welding was carried out on 1-mm thick NiTinol sheets. With increase in heat input, there was a significant variation in Phase Transformation Temperature (PTT) of welded samples. The variation in PTT is attributed to the formation of intermetallic phases such as Ti₂Ni, Ni₃Ti and NiTiO₃ and coarse grain formation. Electron Back Scattered Diffraction (EBSD) analysis on the weld revealed that the average grain size of parent material was increased from 9.92851$\mu$m to 48.292345$\mu$m after the welding process. The PWHT was carried out on the best weld characteristic sample. PWHT did not produce significant effect on PTT. Austenite start and finish temperature slightly decreased after PWHT, whereas slight drift towards the positive side was noticed in martensite start and finish temperature.

This study aims to analyze the surface pattern created on a shape memory polymer (SMP; thermoset polystyrene) after indentation by a spherical indenter, polishing off the top surface and recovery through the shape memory effect (SME) using the finite element method (FEM) and other computational techniques. Depending on how to polish, three different types of patterns are generated, namely the lens-type protrusion, flat-top protrusion and groove. The actual dimensions of the surface patterns are determined by the polishing depth and the coefficient of friction during indentation. The influence of the latter can be fixed if the coefficient of friction is over a certain value. All the lengths in this study are normalized with the respective indent depth. Hence the results can be scaled. The trends obtained here should be applicable to other shape memory polymers.

Biocompatible stent implants that have been made of shape memory alloys (SMA) are being used in arteries which are restoring normal blood flow. A high failure rate of stent implants in femoral artery causes the investigation of the mechanical behavior of stent implants, and its design and manufacturing, a necessity study. In this paper, two different stent designs, with different geometries, have been simulated. One is a Diamond-shaped profile stent and the other one is a V-shaped profile stent. These stents have been simulated under different loadings such as tensile and bending loadings that are very similar to the loading environment imposed by the arterial wall and blood flow. Two different temperatures have been selected to investigate superelasticity as well as shape memory effect of NiTi stents. During unloading for the shape memory case, the residual strains are recovered by heating the stents. The verified model based on microplane model is numerically considered for simulation of the stents. Numerical results show that the V-shaped stent design stretches more than the Diamond-shaped stent design under tensile loading. In addition, the V-shaped stent bends more than Diamond-shaped stent under the same bending loading, which shows more flexibility.

SMPU (shape memory polyurethane) non-ionomers and ionomers, synthesized with poly(ε-caprolactone) (PCL), 4, 4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BDO), dimethylolpropionic acid (DMPA) were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content.

Ni₂MnAl Heusler alloy is one of the promising materials for the shape memory effect. It has been reported in literature that the magnetic shape effect is observed only when this alloy is in L2₁phase. The appropriate processing parameters to achieve this phase in this alloy, is the subject of our study in this report. The results of our investigations of the structural and magnetic property changes at various stages of processing are reported here. Differential Scanning Calorimeter and dc magnetization measurements have been used to probe structural and magnetic phase transformation of the material after the heat treatment. The structural analysis has been carried out by X-ray diffraction mehod.

The evolution of the ultrafine structure, obtained at thermal treatment below recrystallization, and its effect onto shape memory characteristics in NiTi alloy was under study. It was shown that low temperature annealing (< 0.5 Tmelt) of the hot rolled NiTi leads to the structure refinement accompanied by the growth in accumulated martensite deformation. It was suggested that this is possible due to the increase of the volume fraction of martensite crystals properly oriented in respect to external stress.

High-temperature shape memory alloys are promising candidates for actuator applications at elevated temperatures. Ternary nickel–titanium-based alloys either contain noble metals which are very expensive, or suffer from poor workability. Titanium–tantalum shape memory alloys represent a promising alternative if one can avoid the cyclic degradation due to the formation of the omega phase. The current study investigates the functional fatigue behavior of Ti–Ta and introduces a new concept providing for pronounced fatigue life extension.

Laser welding is a suitable joining technique for shape memory alloys (SMAs). This paper reports the existence of shape memory effect (SME) on laser welded NiTi joints, subjected to bending tests, and correlates this effect with the microstructural analysis performed with X-ray diffraction (XRD). All welded samples were able to recover their initial shape after bending to 180°, which is a remarkable result for industrial applications of NiTi involving laser welding.