A review of shape memory alloy research, applications and opportunities

With the increased emphasis on both reliability and multi-functionality in the aerospace industry, active materials are fast becoming an enabling technology capturing the attention of an increasing number of engineers and scientists worldwide. This article reviews the class of active materials known as shape memory alloys (SMAs), especially as used in aerospace applications. To begin, a general overview of SMAs is provided. Their useful properties and engineering effects are described and the methods in which these may be utilized are discussed. A review of past and present aerospace applications is presented. The discussion addresses applications for both atmospheric earth flight as well as space flight. To complete the discussion, SMA design challenges and methodologies are addressed and the future of the field is examined.

https://journals.sagepub.com/doi/pdf/10.1243/09544100JAERO211

Aerospace applications of shape memory alloys

In this technical note we develop an adaptive tuned vibration absorber (ATVA) based on the unique characteristics of magnetorheological elastomers (MREs), whose modulus can be controlled by an applied magnetic field. The MRE used in the developed ATVA was prepared by curing a mixture of 704 silicon rubber, carbonyl iron particles and a small amount of silicone oil under a magnetic field. The ATVA works in shear mode and consists of an oscillator, smart spring elements with MREs, a magnet conductor and two coils. Natural frequencies of the ATVA under different magnetic fields were both theoretically analyzed and experimentally evaluated by employing a beam structure with two ends supported. The experimental results demonstrated that the natural frequency of the ATVA can be tuned from 55 to 82 Hz. The relative frequency change is as high as 147%. Furthermore, the absorption capacity of the developed ATVA can achieve as high as 60 dB, which was also experimentally justified.

https://iopscience.iop.org/article/10.1088/0964-1726/15/5/N02/pdf

Development of an adaptive tuned vibration absorber with magnetorheological elastomer

Filling an elastomeric material with magnetizable particles leads to mechanical properties -shear moduli, tensile moduli, and magnetostriction coefficients - that are reversibly and rapidly controllable by an applied magnetic field. The origin of the field dependence of these properties is the existence of field-induced dipole magnetic forces between the particles. These 'smart' composites, which are sometimes termed magnetorheological (MR) elastomers, have been explored for use in a number of components, including automotive suspension bushings. In these and other applications, the tunability of the stiffness can enhance the compliance-control or vibration-transfer performance of the complex mechanical systems in which they are used. In the present study, we have constructed a simple one-degree-of-freedom mass-spring system - an adaptive tuned vibration absorber - that utilizes MR elastomers as variable-spring-rate elements. This device was used not only to explore the performance of such tunable components, but also to extend measurements of the shear moduli of these materials to higher frequencies than has previously been reported. We find that the field-induced increase in moduli of these materials is effective to mechanical frequencies well above 1 kHz, and that the moduli are consistent with the behavior expected for filled elastomers.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Magnetorheological elastomers in tunable vibration absorbers

In this article, we have proposed a novel robotic finger design principle aimed to address two challenges in soft pneumatic grippers-the controllability of the stiffness and the controllability of the bending position. The proposed finger design is composed of a 3D printed multimaterial substrate and a soft pneumatic actuator. The substrate has four polylactic acid (PLA) segments interlocked with three shape memory polymer (SMP) joints, inspired by bones and joints in human fingers. By controlling the thermal energy of an SMP joint, the stiffness of the joints is modulated due to the dramatic change in SMP elastic modulus around its glass transition temperature (Tg). When SMP joints are heated above Tg, they exhibit very small stiffness, allowing the finger to easily bend around the SMP joints if the attached soft actuator is actuated. When there is no force from the soft actuator, shape recovery stress in SMP contributes to the finger's shape restoration. Since each joint's rotation can be individually controlled, the position control of the finger is made possible. Experimental analysis has been conducted to show the finger's variable stiffness and the result is compared with the analytical values. It is found that the stiffness ratio can be 24.9 times for a joint at room temperature (20°C) and at an elevated temperature of 60°C when air pressure p of the soft actuator is turned off. Finally, a gripper composed of two fingers is fabricated for demonstration.

Bioinspired Robotic Fingers Based on Pneumatic Actuator and 3D Printing of Smart Material

Controlled continuous tuning of the stiffness of shape memory alloy (SMA) spring elements of an adaptively tunable vibration absorber (ATVA) is a novel concept for adaptive-passive vibration control. Minimization of the vibration of a primary system is achieved indirectly via stiffness control of the SMA structural elements supporting a secondary mass. Stiffness control is further achieved via the heating of the SMA elements. In this paper a control law to achieve phase- tracking by controlling the heating of the SMA elements is developed and implemented. Successful analytical and experimental results demonstrate the feasibility of continuous control of the SMA ATVA. Performance of the SMA ATVA is compared to the performance of comparable passive tuned vibration absorbers (TVA). The comparison shows that substantial improvements in vibration attenuation can be achieved through the implementation of the SMA ATVA.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Controlled continuous tuning of an adaptively tunable vibration absorber incorporating shape memory alloys

The present invention relates to a vibration absorber in which an absorber end mass is coupled to a primary mass by means of a cantilevered beam, wherein at least a portion of the beam comprises a shape memory alloy (SMA). Preferably, the end mass is coupled to the primary mass with several discrete SMA wires which may be individually heated. When each of the SMA wires is heated above a predetermined temperature, the SMA material undergoes a phase change which results in a change in the stiffness of the SMA wire. Heating of the various wires in various combinations allows the operational frequency of the absorber to be actively tuned. The frequency of the absorber may therefore be tuned to closely match the current vibrational frequency of the primary mass, thereby allowing the absorber to be adaptively tuned to the frequency of the primary mass in a simple and straightforward manner.

Vibration absorber using shape memory material

The passive-adaptive approach to vibration control shows promise in its ability to combine the robust stability and low-complexity of passive tuned absorbers with the adaptability of active control schemes. Previous tunable vibration absorbers have been complex and bulky. Shape memory alloys (SMA) with their variable material properties, offer an alternative adaptive mechanism. Heating an SMA causes a change in the elastic modulus of the material by a factor as high as three. Incorporating SMA in parallel with traditional spring materials creates an absorber with a variable spring stiffness and a corresponding variable tuning frequency. Using on-off actuation of the SMA, discrete frequencies of tuning are obtained through the use of multiple SMA elements.

Passive-adaptive vibration absorbers using shape memory alloys

Stability Analysis of a Shape Memory Alloy Adaptive Tuned Vibration Absorber Under PI Control With Anti-Windup

The passive-adaptive approach to vibration control shows promise in its ability to combine the robust stability and low-complexity of passive tuned absorbers with the adaptability of active control schemes. Previous tunable vibration absorbers have been complex and bulky. Shape memory alloys (SMA) with their variable material properties, offer an alternative adaptive mechanism. Heating an SMA causes a change in the elastic modulus of the material by a factor as high as three. Incorporating SMA in parallel with traditional spring materials creates an absorber with a variable spring stiffness and a corresponding variable tuning frequency. Using on-off actuation of the SMA, discrete frequencies of tuning are obtained through the use of multiple SMA elements. An adaptive absorber of this type using 3 pairs of SMA wires and 1 pair of steel wires was constructed and tested. Characterization testing of the absorber showed tunability of the natural frequency of the absorber of approximately 15%. The absorber was applied to a beam system and the frequency response of the system at various states of absorber actuation was determined. Another experiment was done using manual tuning of the absorber during a stepped-sine input to the primary system. The resultant response showed a wider notch of attenuation than was possible with a non-adaptive absorber. Results of the tests indicate that an adaptive absorber incorporating SMA as a tuning element has potential as a simple, high-performance passive-adaptive technique for vibration control.

Keith A. Williams

Papers

Controlled continuous tuning of an adaptively tunable vibration absorber incorporating shape memory alloys

Vibration absorber using shape memory material

Passive-adaptive vibration absorbers using shape memory alloys

Stability Analysis of a Shape Memory Alloy Adaptive Tuned Vibration Absorber Under PI Control With Anti-Windup

Passive-adaptive vibration absorbers using shape memory alloys