B2 Intermetallic Compounds of Zr. New Class of the Shape Memory Alloys

A new class of shape memory alloys, based on near-equiatomic compositions of Ta-Ru and Nb-Ru, was recently discovered at the Naval Research Laboratory. These alloys exhibit transformation temperatures ranging up to 1400 °C for Ta-Ru and 1100 °C for Nb-Ru, making them the highest transition temperature shape memory alloys yet discovered. Other shape memory alloys typically have transition temperatures within a couple hundred degrees of room temperature. These two alloy systems are quite similar in their transformation behavior. Near the equiatomic composition, the high temperature β phase of both systems has a B2-ordered cubic crystal structure. During cooling, the cubic lattice of β undergoes a slight tetragonal distortion to form the β' phase. Continued cooling of the tetragonal β'(within specific composition ranges) causes a transformation to β'', which is reported to have an orthorhombic crystal structure. The effect of alloy composition on the temperatures, hysteresis, and strains of these transformations was determined by dilatometry.

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Tensegrity Structures Incorporating Actuator and Pseudoelastic Shape Memory Alloys

Volume 4: Advances in Aerospace Technology ◽

10.1115/imece2020-24645 ◽

2020 ◽

Author(s):

Gavin M. Butler ◽

Edwin A. Peraza Hernandez

Keyword(s):

Shape Memory Alloys ◽

Shape Memory ◽

Large Deformations ◽

External Disturbances ◽

Active Materials ◽

Tensegrity Structures ◽

Shape Morphing ◽

New Class ◽

Potential Applications ◽

Accumulated Error

Abstract Tensegrity structures are networks of tensile and compressive truss members that have pre-stressability and shape-morphing capabilities. Potential applications of tensegrities in the aerospace, civil, and robotics fields require them to have actuation capabilities and adjustable stiffness. An approach to infuse these properties into tensegrities is to employ active materials. Shape memory alloys (SMAs) are active materials with the ability of exchanging mechanical and thermal energies. They have actuation capabilities enabled by the shape memory effect and large recoverable deformations enabled by the pseudoelastic effect. This paper presents a study on the integration of actuator and pseudoelastic SMAs into tensegrities to create a new class of stifftruss structures that exhibit controlled large deformations. A model for tensegrities that incorporates mechanical equilibrium, thermal equilibrium, and an SMA constitutive model is first developed. The tensile members in the tensegrities may be comprised of actuator or pseudoelastic SMA wires. The actuator wires can be manipulated through Joule heating to change the shape of the tensegrity structure on demand. The pseudoelastic wires provide high stiffness under moderate external disturbances, and become compliant and allow for large deformations as their stress is increased by the actuator wires. This unique combination of actuator and pseudoelastic SMA members in tensegrities is demonstrated through examples of controlled morphing of a tensegrity beam and a tensegrity plate. The results show that using pseudoelastic members antagonistic to the actuators, as opposed to elastic members, reduces the accumulated error and the energy required to control the tensegrities.

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