Analysis of a NiTi Shape Memory Alloy

2015 ◽  
Vol 812 ◽  
pp. 89-93 ◽  
Author(s):  
László Kálmán ◽  
István Mészáros
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Niti Shape Memory Alloy ◽  
Hysteresis Behavior ◽  
Niti Alloys ◽  
Basic Properties ◽  
Functional Mechanism ◽  
The One

This work demonstrates particularly the basic properties of shape memory alloys and gives a brief review about their basic crystallographic processes. The attributes of shape memory alloys will be presented through the NiTi alloys. The crystallographic principles of three unique properties were investigated and the functional mechanism described. One of the three essential mechanisms, the one-way effect was demonstrated through an experiment. The change of length depending temperature was tested and documented. The hysteresis behavior of shape memory alloys was recorded.

scholarly journals An analytical model for crack monitoring of the shape memory alloy intelligent concrete

2019 ◽  
Vol 31 (1) ◽  
pp. 100-116 ◽  
Author(s):  
Bingfei Liu ◽  
Qingfei Wang ◽  
Kai Yin ◽  
Liwen Wang
Keyword(s):  
Shape Memory Alloy ◽  
Constitutive Model ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
One Dimensional ◽  
Monitoring Model ◽  
Crack Monitoring ◽  
The One

A theoretical model for the crack monitoring of the shape memory alloy intelligent concrete is presented in this work. The mechanical properties of shape memory alloy materials are first given by the experimental test. The one-dimensional constitutive model of the shape memory alloys is reviewed by degenerating from a three-dimensional model, and the behaviors of the shape memory alloys under different working conditions are then discussed. By combining the electrical resistivity model and the one-dimensional shape memory alloy constitutive model, the crack monitoring model of the shape memory alloy intelligent concrete is given, and the relationships between the crack width of the concrete and the electrical resistance variation of the shape memory alloy materials for different crack monitoring processes of shape memory alloy intelligent concrete are finally presented. The numerical results of the present model are compared with the published experimental data to verify the correctness of the model.

A uniaxial constitutive model for NiTi shape memory alloy bars considering the effect of residual strain

2019 ◽  
Vol 30 (8) ◽  
pp. 1163-1177
Author(s):  
Canjun Li ◽  
Zhen Zhou ◽  
Yazhi Zhu
Keyword(s):  
Shape Memory Alloy ◽  
Constitutive Model ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Residual Strain ◽  
Hysteretic Behavior ◽  
Niti Shape Memory Alloy ◽  
Strain Effect ◽  
Proposed Model ◽  
Residual Strains

Super-elastic shape memory alloys are widely used in structural engineering fields due to their encouraging super-elasticity and energy dissipation capability. Large-size shape memory alloy bars often present significant residual strains after unloading, which emphasizes the necessity of developing a residual strain effect–coupled constitutive model to predict well the performance of shape memory alloy–based structures. First, this article experimentally studies the hysteretic behavior of NiTi shape memory alloy bars under quasi-static loading conditions and investigates the effects of cyclic numbers and strain amplitudes on residual strain. Second, a concept of cumulative transformation strain is preliminarily introduced into a phenomenological Lagoudas model. A uniaxial constitutive model for shape memory alloy bars including the residual strain is proposed. By using OpenSees platform, numerical simulations of shape memory alloy bars are conducted—the results of which indicate that the proposed model can accurately capture the hysteretic behavior of shape memory alloys. The predicted residual strains show a good agreement to experimental results, which demonstrates the desirable efficiency of the proposed model.

Preparation of High-Porosity NiTi Alloys by Powder Sintering with NaCl Pre-Forming

2010 ◽  
Vol 152-153 ◽  
pp. 1342-1345
Author(s):  
Hong Bo Sun ◽  
Xing Ke Zhao ◽  
Lan Lan ◽  
Ji Hua Huang ◽  
Hua Zhang
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Optical Microscope ◽  
Niti Shape Memory Alloy ◽  
High Porosity ◽  
Niti Alloys ◽  
Powder Sintering ◽  
On Line ◽  
Line Repair

High-porosity NiTi shape memory alloy has pseudo-elasticity and shape memory effect for energy absorption and convenient on-line repair without replace. In this paper, high-porosity NiTi alloys with interconnected and well distributed pores were fabricated successfully by sintering, using NaCl as temporary space-holders. Optical microscope, SEM and XRD have been used to investigate the porosity and pore structures. The results show that porosity can be up to 88%.The size and porosity of the pores depend mainly on the addition of salts in the compacts, and are also related to temperature and forming pressure.

scholarly journals Dissimilar Laser Welding of a NiTi Shape Memory Alloy to Ti2AlNb

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1578
Author(s):  
Fuguo Ge ◽  
Bei Peng ◽  
João Pedro Oliveira ◽  
Wenchao Ke ◽  
Fissha Biruke Teshome ◽  
...  
Keyword(s):  
Shape Memory Alloy ◽  
Laser Welding ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Niti Shape Memory Alloy ◽  
Dissimilar Joints ◽  
Lap Shear ◽  
Ti2alnb Alloy ◽  
Structural Applications ◽  
Potential Applications

NiTi-based shape memory alloys and the Ti2AlNb alloy have gained increasing importance in the aerospace field. The joining of these two materials can further increment the importance and usage of these relevant engineering materials and expand their potential applications. However, when joining NiTi-based shape memory alloys to Ti-based alloys, the formation of brittle Ti-rich intermetallic compounds often occurs, significantly limiting their functionality and use. Dissimilar joints between a NiTi shape memory alloy and Ti2AlNb alloy were obtained using a 0.1 mm thick Niobium (Nb) interlayer via laser welding. By process optimization, sound joints were obtained. The microstructure evolution was assessed by means of electron microscopy, whereas the mechanical strength of the joints was evaluated using lap shear tensile testing. The best performing joints were seen to fracture at maximum loads above 1230 N, thus allowing us to consider this dissimilar pair for structural applications.

The Influence of Hafnium Content, Cold Work, and Heat Treatment on the R-Phase Transformation of Niti Based Shape Memory Alloys

1996 ◽  
Vol 459 ◽  
Author(s):  
Chen Zhang ◽  
Paul E. Thoma ◽  
Ralph H. Zee
Keyword(s):  
Heat Treatment ◽  
Differential Scanning Calorimetry ◽  
Phase Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Cold Work ◽  
Niti Shape Memory Alloy ◽  
Scanning Calorimetry ◽  
Complex Manner

ABSTRACTThe R-phase transformation of a Ti-rich NiTi shape memory alloy (SMA) and two ternary SMAs having the compositions Ni49Ti51-XHfx with lat% and 3at% Hf, has been investigated. The influence of cold work (CW) and heat treatment (HT) on the R-phase transformation is analyzed thermally using Differential Scanning Calorimetry (DSC). Results show that the R-phase transformation depends on the SMA composition as well as the CW and HT conditions in a complex manner. For example, the formation of R-phase upon cooling from austenite (A) is increasingly suppressed with the substitution of Hf for Ti. For the ternary SMA with 3at% Hf, the A→R and R→A transformations are observed only at relatively large amounts of CW (above approximately 40%) and at a high HT temperature (450°C). DSC results also show that for the Ti-rich NiTi and the ternary SMA containing lat% Hf, the A→R and R→A transformation temperatures (TTs) are insensitive to cold work at a HT temperature of 450°C. However, at a lower HT temperature of 350°C, the TTs are found to decrease with increasing CW. For a given CW, the A→R and R→A transformations decrease with decreasing HT temperature and the effect is greatest at high CW (>50%) conditions. An effort is made to identify the factors responsible for the observed behavior in the R-phase transformation.

Thermomechanical Forming of NiTi Shape Memory Alloy Wire

2014 ◽  
Vol 939 ◽  
pp. 430-436 ◽  
Author(s):  
Kuang Jau Fann ◽  
Hau Chi Hsu
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Niti Shape Memory Alloy ◽  
Processing Temperature ◽  
Shape Memory Alloy Wire ◽  
Alloy Wire ◽  
Niti Shape Memory Alloys

Because of their smart characteristics with shape memory effect and superelasticity, NiTi shape memory alloys used in sensors and actuators are regarded as an emerging applied material with high added value by their additional biomedical compatibility for medical devices and implants. It is meaningful to pay more attention to study the production technique of NiTi shape memory alloys. For this reason, this article is aimed to investigate the results of a NiTi shape memory alloy wire in thermomechanical forming process regarding the processing temperature and duration. Thereafter a NiTi shape memory alloy wire of 0.63 mm in diameter is formed in a furnace at 450°C, 500°C, 550°C, and 600°C, respectively, by a semi cylindrical punch of 32 mm in diameter, then held together with the die set in the furnace for 10, 30, and 50 minutes long, respectively, and then quenched in the water. All of the formed wires have shape memory effect. That is, the wires returned their formed geometry once they were straightened below martensite transformation finishing temperature about room temperature and heated again above austenite transformation finishing temperature about 70°C. These thermomechanical forming processes were also investigated by commercial finite element software DEFORM. Both analytical and experimental results showed that the formed wires could not have the geometry precision as wanted because of stress relaxation found in process, which depends on the process temperature and the treatment duration. As a result, the lower the temperature and the shorter the duration is, the larger the springback is. That means that the higher the treatment temperature is and the longer the holding time is, the better the precision of the formed part is.

Superelastic Behavior in NiTi Shape Memory Alloy Wires and Ribbons

2016 ◽  
Vol 254 ◽  
pp. 278-282
Author(s):  
Roxana Sprincenatu ◽  
Madalin Condel ◽  
Sergiu Barbos ◽  
Andrei Novac ◽  
Ion Mitelea ◽  
...  
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Testing Machine ◽  
Ultimate Tensile Stress ◽  
Niti Shape Memory Alloy ◽  
Tensile Testing Machine ◽  
Fine Microstructure ◽  
Superelastic Behavior ◽  
Multiple Loading ◽  
The One

Shape memory alloy ribbons in austenitic state were studied in a tensile testing machine in order to assess their superelastic behavior. They were compared with conventional materials and hair wire. The shape memoy alloy ribbon shows a particular behavior, with an ultimate tensile stress of about 1450 MPa reached at 9.5 % strain. The superelastic plateau was recorded around 590 MPa on loading and around 350 MPa on the unloading branch. Following multiple loading and unloading cycles, the superelastic behavior was not affected, nor was affected the ultimate tensile strength, that remained in the same range as for the one tested before cycling. The advantages of the superelastic ribbon compared to the ones of conventional materials are discussed. The superelastic properties of the ribbon are in the range of single crystals on what concerns the recoverable strains. This is attributed to the particular fine microstructure of the NiTi ribbon.

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