Mechanical Properties Of Shape Memory Alloys Research Articles

Dissecting the influence of nanoscale concentration modulation on martensitic transformation in multifunctional alloys

Nanoscale concentration modulation (CM) is a novel and effective approach of manipulating martensitic transformations (MTs) for developing next-generation high-performance shape memory alloys (SMAs). Spinodal decomposition is one of the most economic methods to obtain bulk compositionally modulated materials for practical applications. The wavelength, amplitude, and statistical distribution of CM generated by spinodal decomposition are tunable via adjusting the aging temperature, or the aging time. However, how these features influence the effect of CM on MTs still remains largely unexplored. In this study, theoretical analyses and computer simulations are combined to dissect the influence of these features on the kinetic process of MTs and mechanical properties of SMAs. The findings of this study provide insights and guidance on the design of SMAs for desired mechanical properties via CM engineering. Moreover, the findings are applicable to not only SMAs but also other materials that have MTs, e.g. steels and high-entropy alloys.

Corrosion Assessment of Coupled Steel Reinforcement with Ni-Ti–Based Shape Memory Alloy in Simulated-Concrete Pore Solution

AbstractThough the mechanical properties of shape-memory alloys (SMAs) make them a promising material for reinforcement in concrete structures, their electrochemical behavior in concrete environments has not previously been studied. This study investigated the influence of galvanic coupling between a nickel-titanium (Ni-Ti)–based SMA and a low-carbon steel on their corrosion performance in simulated concrete pore solution. Three measurement cells were considered: SMA alone, low-carbon steel alone, and one with the coupled SMA and carbon steel. The specimens were immersed in the chloride-free pore solution for 20 days and then 3% by weight of NaCl was added to the solution. The specimens were then kept in the chloride-contaminated solution for 70 days. The corrosion resistances of the specimens were assessed by different electrochemical measurement techniques. The results of the electrochemical experiments showed a significant increase in corrosion activity of the coupled specimens compared with that for o...

Structure and Mechanical Properties of Shape-Memory Alloys of the Ti – Ni – Cu System

The effect of copper additives in an amount of up to 35 at.% on the structure and phase transformations in ternary Ti – Ni – Cu alloys in conventional microcrystalline, submicrocrystalline and nanocrystalline states is studied. Complete diagrams of thermoelastic martensitic transformations B2↔B19′, B2↔B19↔B19′ and B2 ↔ B19 are plotted as a function of the copper content. Special features of variation of the microstructure are determined. Tensile mechanical properties including the parameters of the shape memory effect are measured.

Investigation of Mechanical Properties in Welding of Shape Memory Alloys

Shape-memory alloys (SMA) are increasingly used due to the exceptional properties such as shape memory effect (SME), Pseudo elasticity and super-elastic effect (SE). However, mechanical properties of SMA are scantly studied in the field of welding technology. In this study, effect of laser welding on SMA is considered through investigation of mechanical properties as well as microstructure of the weldments. The specimens have been manufactured from NiTi, one of the most popular SMA alloys in the industry, in order to evaluate tensile strength and microstructure before and after the laser welding process. Based on the results, higher ultimate tensile strength and elongation are achieved in the specimens for which the tensile test was carried out in same direction as manufacturing rolling direction. Furthermore, microstructure investigations show that the behavior of solidification is changed from planar to volumetric and/or to dendritic. Due to this evolution, the joint tensile strength and strain reached to 118MPa and 8%, respectively.

形状記憶複合材料の電気的・機械的特性

We clarified experimentally electrical and mechanical properties of SMA (Shape; Memory Alloy) in diameter 0.2mm and SMP (Shape Memory Polymer) in thickness 1.15mm. In addition, SMC (Shape Memory Composite) composed of these SMA and SMP, was also investigated to clarify the electrical and mechanical properties required to actuators. Main results obtained in this study are as follows; (1) When SMA was heated electrically over 0.4A, recovery time until the original figure was under 5 seconds. (2) When SMC was heated electrically over 0.3A, the surface temperature of SMC reached approximately T_g after 120 seconds. (3) We confirmed that application of 0.4A and 120 seconds to SMC was the most suitable condition as an actuator controlled electrically.

Shape Memory Alloy in Tension and Compression and its Application as Clamping Force Actuator in a Bolted Joint: Part 2 — Modeling

The mathematical modeling of a bolted joint with a Shape Memory Alloy (SMA) actuator ring is presented. In this way, phase transformation, constitutive and displacement compatibility equations are used. The obtained model is utilized to show how the application of the SMA actuator ring in the bolted joint can help the joint to recover a significant amount of its lost clamping force. The model is run using the experimental data obtained for the Ni-55.7%wt Ti SMA in the companion paper (Part 1). The mechanical properties of SMA are calculated using the mentioned equations and compared to the experimental findings. It is observed that the final clamping force obtained theoretically is close to the measured value. The proposed method can, therefore, be a starting point in order to perform the analysis and design of bolted joints with SMA actuator rings.

Structural modification of simply-supported laminated plates using embedded shape memory alloy fibers

Shape memory alloy (SMA) fibers, and in particular Nitinol fibers, have been embedded in advanced composite materials to demonstrate numerous structural control/modification concepts. A large number of control concepts have been postulated, formulated and demonstrated by using the unique control parameters available from Nitinol fiber actuators. Several new paradigms for structural design and control have resulted from the unusual behavior and mechanical properties of SMA. A brief introduction to SMA, laminated composite plates with embedded SMA fibers and a description of some of the available control parameters is presented. A linear analysis for a simply-supported symmetrically laminated composite plate embedded with SMA fibers using the Rayleigh-Ritz method is presented. Results of deflection, free vibration, buckling, and structural acoustic control are discussed. Two novel structural control techniques, active strain energy tuning (ASET) and active property tuning (APT), are highlighted and the authority of each technique demonstrated.