scholarly journals Crystallographic Attributes of a Shape-Memory Alloy

1999 ◽  
Vol 121 (1) ◽  
pp. 93-97 ◽  
Author(s):  
Kaushik Bhattacharya
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Nickel Titanium ◽  
Potential Applications

Shape-memory Alloys are attractive for many potential applications. In an attempt to provide ideas and guidelines for the development of new shape-memory alloys, this paper reports on a series of investigations that examine the reasons in the crystallography that make (i) shape-memory alloys special amongst martensites and (ii) Nickel-Titanium special among shape-memory alloys.

scholarly journals Behaviour of Superelastic Nickel Titanium Shape Memory Alloy Material under Uniaxial Testing and its Potential in Civil Engineering

2018 ◽  
Vol 203 ◽  
pp. 06005
Author(s):  
Azmi Mohammad Hassan ◽  
Raizal Saifulnaz Muhammad Rashid ◽  
Nazirah Ahmad ◽  
Shahria Alam ◽  
Farzad Hejazi ◽  
...  
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Structural Characteristics ◽  
Nickel Titanium ◽  
Life Extension ◽  
Structural Safety ◽  
Structural System ◽  
Finish Temperature

Smart structures are defined as structures that able to adapt and maintain structural characteristics in dealing with changes of external disturbance, environment and unexpected severe loadings. This ability will lead to improve structural safety, serviceability and structural life extension. Shape memory alloys is one of the smart materials which has potential to be integrated in structural system to provide functions such as sensing, actuation, self-adapting and healing of the structures. The unique characteristic of shape memory alloys material is the ability to ‘remember’ its original shape after deformation. Nickel Titanium superelastic shape memory alloy wire is popular and widely used in many engineering fields and owned fully recovery of maximum strain of 6%-13.5% which is among the best shape recovery limit in alloy materials. The austenite finish temperature plays important role in stress-strain behaviour of superelastic shape memory alloys where higher stress required to complete martensite transformation with the increase of austenite finish temperature. The similar behaviour also is observed in the case of higher strain rate. The behaviour of superelastic shape memory alloys need to be studied before implementing in the structural system, so the targeted improvement for the structural system can be achieved.

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.

scholarly journals Rigidity of Branching Microstructures in Shape Memory Alloys

2021 ◽  
Author(s):  
Theresa M. Simon
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Differential Inclusion ◽  
Linearized Strain ◽  
Weak Limits ◽  
All Solutions ◽  
Rank One ◽  
Branched Structures ◽  
Habit Planes

AbstractWe analyze generic sequences for which the geometrically linear energy $$\begin{aligned} E_\eta (u,\chi )\,{:}{=} \,\eta ^{-\frac{2}{3}}\int _{B_{1}\left( 0\right) } \left| e(u)- \sum _{i=1}^3 \chi _ie_i\right| ^2 \, \mathrm {d}x+\eta ^\frac{1}{3} \sum _{i=1}^3 |D\chi _i|({B_{1}\left( 0\right) }) \end{aligned}$$ E η ( u , χ ) : = η - 2 3 ∫ B 1 0 e ( u ) - ∑ i = 1 3 χ i e i 2 d x + η 1 3 ∑ i = 1 3 | D χ i | ( B 1 0 ) remains bounded in the limit $$\eta \rightarrow 0$$ η → 0 . Here $$ e(u) \,{:}{=}\,1/2(Du + Du^T)$$ e ( u ) : = 1 / 2 ( D u + D u T ) is the (linearized) strain of the displacement u, the strains $$e_i$$ e i correspond to the martensite strains of a shape memory alloy undergoing cubic-to-tetragonal transformations and the partition into phases is given by $$\chi _i:{B_{1}\left( 0\right) } \rightarrow \{0,1\}$$ χ i : B 1 0 → { 0 , 1 } . In this regime it is known that in addition to simple laminates, branched structures are also possible, which if austenite was present would enable the alloy to form habit planes. In an ansatz-free manner we prove that the alignment of macroscopic interfaces between martensite twins is as predicted by well-known rank-one conditions. Our proof proceeds via the non-convex, non-discrete-valued differential inclusion $$\begin{aligned} e(u) \in \bigcup _{1\le i\ne j\le 3} {\text {conv}} \{e_i,e_j\}, \end{aligned}$$ e ( u ) ∈ ⋃ 1 ≤ i ≠ j ≤ 3 conv { e i , e j } , satisfied by the weak limits of bounded energy sequences and of which we classify all solutions. In particular, there exist no convex integration solutions of the inclusion with complicated geometric structures.

The electron beam freeform fabrication of NiTi shape memory alloys. Part I: Microstructure and physical–chemical behavior

2020 ◽  
pp. 146442072097505
Author(s):  
RPM Guimarães ◽  
F Pixner ◽  
G Trimmel ◽  
J Hobisch ◽  
T Rath ◽  
...  
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Nickel Titanium ◽  
Freeform Fabrication ◽  
Austenitic Transformation ◽  
Columnar Grains ◽  
One Step ◽  
Niti Shape Memory Alloys

Nickel–titanium alloys are the most widely used shape memory alloys due to their outstanding shape memory effect and superelasticity. Additive manufacturing has recently emerged in the fabrication of shape memory alloy but despite substantial advances in powder-based techniques, less attention has been focused on wire-based additive manufacturing. This work reports on the preliminary results for the process-related microstructural and phase transformation changes of Ni-rich nickel–titanium alloy additively manufactured by wire-based electron beam freeform fabrication. To study the feasibility of the process, a simple 10-layer stack structure was successfully built and characterized, exhibiting columnar grains and achieving one-step reversible martensitic–austenitic transformation, thus showing the potential of this additive manufacturing technique for processing shape memory alloys.

Shape memory alloy–actuated prestressed composites with application to morphing automotive fender skirts

2018 ◽  
Vol 30 (3) ◽  
pp. 479-494 ◽  
Author(s):  
Venkata Siva C Chillara ◽  
Leon M Headings ◽  
Ryohei Tsuruta ◽  
Eiji Itakura ◽  
Umesh Gandhi ◽  
...  
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Smart Materials ◽  
Design Procedure ◽  
Building Blocks ◽  
Smart Composite ◽  
Thermally Induced ◽  
One Dimensional ◽  
Flat Shape

This work presents smart laminated composites that enable morphing vehicle structures. Morphing panels can be effective for drag reduction, for example, adaptive fender skirts. Mechanical prestress provides tailored curvature in composites without the drawbacks of thermally induced residual stress. When driven by smart materials such as shape memory alloys, mechanically-prestressed composites can serve as building blocks for morphing structures. An analytical energy-based model is presented to calculate the curved shape of a composite as a function of force applied by an embedded actuator. Shape transition is modeled by providing the actuation force as an input to a one-dimensional thermomechanical constitutive model of a shape memory alloy wire. A design procedure, based on the analytical model, is presented for morphing fender skirts comprising radially configured smart composite elements. A half-scale fender skirt for a compact passenger car is designed, fabricated, and tested. The demonstrator has a domed unactuated shape and morphs to a flat shape when actuated using shape memory alloys. Rapid actuation is demonstrated by coupling shape memory alloys with integrated quick-release latches; the latches reduce actuation time by 95%. The demonstrator is 62% lighter than an equivalent dome-shaped steel fender skirt.

Design of Shape Memory Alloy Springs With Applications in Vibration Control

1993 ◽  
Vol 115 (1) ◽  
pp. 129-135 ◽  
Author(s):  
C. Liang ◽  
C. A. Rogers
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Vibration Control ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Design Method ◽  
Control Area ◽  
Spring Constant ◽  
Damping Capacity

Shape memory alloys (SMAs) have several unique characteristics, including their Young’s modulus-temperature relations, shape memory effects, and damping characteristics. The Young’s modulus of the high-temperature austenite of SMAs is about three to four times as large as that of low-temperature martensite. Therefore, a spring made of shape memory alloy can change its spring constant by a factor of three to four. Since a shape memory alloy spring can vary its spring constant, provide recovery stress (shape memory effect), or be designed with a high damping capacity, it may be useful in adaptive vibration control. Some vibration control concepts utilizing the unique characteristics of SMAs will be presented in this paper. Shape memory alloy springs have been used as actuators in many applications although their use in the vibration control area is very recent. Since shape memory alloys differ from conventional alloy materials in many ways, the traditional design approach for springs is not completely suitable for designing SMA springs. Some design approaches based upon linear theory have been proposed for shape memory alloy springs. A more accurate design method for SMA springs based on a new nonlinear thermomechanical constitutive relation of SMA is also presented in this paper.

Cold Bending a Ni-Ti Shape Memory Alloy Wire

2015 ◽  
Vol 661 ◽  
pp. 98-104 ◽  
Author(s):  
Kuang-Jau Fann ◽  
Pao Min Huang
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Room Temperature ◽  
Aging Treatment ◽  
Treatment Temperature ◽  
Bending Test ◽  
Solution Treatment Temperature

Because of being in possession of shape memory effect and superelasticity, Ni-Ti shape memory alloys have earned more intense gaze on the next generation applications. Conventionally, Ni-Ti shape memory alloys are manufactured by hot forming and constraint aging, which need a capital-intensive investment. To have a cost benefit getting rid of plenty of die sets, this study is aimed to form Ni-Ti shape memory alloys at room temperature and to age them at elevated temperature without any die sets. In this study, starting with solution treatments at various temperatures, which served as annealing process, Ni-rich Ni-Ti shape memory alloy wires were bent by V-shaped punches in different curvatures at room temperature. Subsequently, the wires were aged at different temperatures to have shape memory effect. As a result, springback was found after withdrawing the bending punch and further after the aging treatment as well. A higher solution treatment temperature or a smaller bending radius leads to a smaller springback, while a higher aging treatment temperature made a larger springback. This springback may be compensated by bending the wires in further larger curvatures to keep the shape accuracy as designed. To explore the shape memory effect, a reverse bending test was performed. It shows that all bent wires after aging had a shape recovery rate above 96.3% on average.

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