New applications for shape memory alloys in angular - contact ball bearings preloading systems

SMA(Shape memory alloys) are unique materials with many excellent properties, such as excellent wear resistance, corrosion resistance, high power/weight ratio and biocompatibility, high damping, shape memory effect, super elasticity, etc. In civil engineering, scientists try to use the advantages of SMA by making it into different components and they have already made some types of components that are SMA bracing, SMA constrains RC columns, SMA ring springs and base isolation bearing. All of these components can make contributions to seismic resistance, therefore, this article mainly focuses on the the contribution of SMA bracings and SMA constrains RC columns to the seismic resistance of the structure and the relationship between the improvement of their own performance and SMA.

To unlock the lock of futuristic developments, nowadays shape memory alloys (SMAs) are acting as key by outnumbering the existing smart materials in view of new design competence, innovative techniques, enhanced technologies, and meeting the dire need according to the demand of ongoing scientific and industrial progress. Undoubtedly, it can be worthy to associate SMAs with the term polymorphism, as they possess unique capability to encapsulate multitudinous inherent characteristics under their name. Shape memory effect, superelasticity, and damping are there to name a few among many others, as prime indicators. The exhibition of these characteristics of SMAs is due to the transformation that takes place between austenite phase and martensite phase which is achieved either by temperature or stress variation. The fascinating characteristics they possess enable them to attract researchers and designers toward their potential applications in diverse domain as smart and multi-functional materials. The present work focuses on the review of research works accomplished in the recent 5 years pertaining to modeling and applications of shape memory alloys in distinct domains. Under the topic of modeling, a look into the research carried out on a variety of SMA structures—like functionally graded SMAs, SMA springs, porous SMAs, novel SMA actuators—is presented. In addition to this, the work carried out to represent SMAs with large strains and large rotations and to model polycrystalline SMAs is also covered. This is supplemented by application-oriented domains, each of which disseminates the attributes of SMAs that are self-sufficient to express what factors make SMAs more prominent. It is believed that the foregoing works comprehensively detailed in this review article will certainly lay a solid platform for the future investigations that are going to take place in time to come.

In this paper, a kind of shape memory alloy (SMA) model based on hysteretic nonlinear theory and data mining was developed and applied in vibration control on rotor system with SMA bearing. Nonlinear difference item was introduced to interpret the hysteretic phenomenon of SMA. Arctangent function was introduced to describe the variation of SMA stiffness with temperature. Based on above, all of possible items in the model were found and stepwise multiple regression method was applied in finding the final relationship among strain, stress and temperature. Finally the stability and the bifurcation characteristic of rotor system with SMA bearing were analyzed. The result of significance test shows that the effects of all of the items in the final model are remarkable, which means that the model can describe the strain-stress curves of SMA in different temperatures well. The new SMA model broadens the region of controlling temperature, admits the existence of control error, and is easy to be analyzed in theory, which is helpful to vibration control.

Shape memory alloys (SMAs) are often used in smart materials and structures as the active components. Their ability to provide a high force and large displacement has been useful in many applications, including devices for damage control, active structural acoustic control, dynamic tuning, and shape control. The paper presents a macroscopic mathematical model which captures the thermomechanical behaviors and the two-way shape memory effect (TWSME) of SMAs, and SMA applications as an actuator to control the shape of a circular composite cylinder. The radial displacement control of an externally pressurized circular composite cylinder where a thin SMA layer actuator is bonded inside the cylinder is investigated numerically. The circular composite cylinder with the thin SMA layer was designed and analyzed to determine the feasibility of such a system for the removal of stiffeners from externally pressurized stiffened composite structures. SMAs start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the composite cylinder to expand in the radial direction. The externally pressurized composite cylinder with the SMA actuators was analyzed using the 3-D finite element method.

This study used two forms of shape memory alloy (SMA) wires, nickel–titanium–niobium (NiTiNb) and nickle–titatanium (NiTi), to retrofit reinforced concrete (RC) columns with lap splices. NiTiNb shape memory alloys are considered to show a wider temperature window compared with NiTi shape memory alloys and thus may be beneficial for applications in the area of civil structures. The goals of this study are to assess the mechanical behaviour of the two shape memory alloy wires and investigate the seismic performance of the shape memory alloy wire jackets for reinforced concrete columns with lap splices. First, the study investigates the recovery and the residual stress of NiTiNb and NiTi shape memory alloy wires. This study also evaluates the behaviour of the NiTiNb shape memory alloy wire under residual stresses. The results indicate that the shape memory alloy wire jackets show good performance for reinforced concrete columns with lap splices. The shape memory alloy wire jackets increase the ductile behaviour of the lap-spliced columns without strength degradation. The results show that their performance is superior to that of the RC column with continuous reinforcements. The study shows that the NiTiNb shape memory alloy wire jackets are more adaptive for retrofit of RC columns than the NiTi shape memory alloy wire jackets since the NiTiNb shape memory alloy shows more appropriate temperature windows for the applications of shape memory alloys in civil structures.

The use of shape memory alloys (SMAs) in aerospace engineering

Advances in smart materials and structures technology, especially in applications of Shape Memory Alloys (SMA) as actuators and vibration isolation devices require understanding of the nonlinear hysteretic response found in SMAs. SMA hysteresis can be modeled either through constitutive models based on physical material parameters or through models based on system identification. In this work, a simplified material model for the pseudoelastic response of SMAs is presented, suitable for vibration isolation applications. Response obtained from the simplified model is compared with the response obtained from an existing thermodynamic constitutive SMA model and the results from the two models are found to match well. The computation time required by the simplified model was approximately seven times faster compared with the thermodynamic constitutive model. The simplified model is utilized to simulate a single degree of freedom mass-SMA system where the SMA acts as a passive vibration isolation device, showing a substantial reduction in displacement transmissibility.

Shape Memory Alloys (SMAs) are unique materials with a paramount potential for various applications in bridges. The novelty of this material lies in its ability to undergo large deformations and return to its undeformed shape through stress removal (superelasticity) or heating (shape memory effect). In particular, Ni-Ti alloys have distinct thermomechanical properties including superelasticity, shape memory effect, and hysteretic damping. SMA along with sensing devices can be effectively used to construct smart Reinforced Concrete (RC) bridges that can detect and repair damage, and adapt to changes in the loading conditions. SMA can also be used to retrofit existing deficient bridges. This includes the use of external post-tensioning, dampers, isolators and/or restrainers. This paper critically examines the fundamental characteristics of SMA and available sensing devices emphasizing the factors that control their properties. Existing SMA models are discussed and the application of one of the models to analyze a bridge pier is presented. SMA applications in the construction of smart bridge structures are discussed. Future trends and methods to achieve smart bridges are also proposed.

This study presents the utilization of shape memory alloys in steel structures for retrofitting purposes in order to bring them to the state of the current specifications. Shape memory alloys with the super-elastic behavior can be exploited in order to operate as a suitable passive seismic control device in structural systems. This article presents the results of a numerical study in which the seismic behavior of a damaged steel moment resisting frame is improved using shape memory alloy braces. Super-elastic model of shape memory alloy and plasticity model of steel are incorporated into the nonlinear finite element program particularly developed for this research. Also, to compare the behavior of the proposed energy dissipative system, the behavior of the steel frame with shape memory alloy braces is compared with the behavior of the buckling restrained bracing system which is to date considered to possess the best performance among the existing concentrically braced frames. Results proved that using shape memory alloy braces for the retrofitting purposes is preferred to buckling restrained braces; particularly in high levels of seismic damage.

The application of shape memory alloy (SMA) thin films in optical devices is introduced and explored for the first time. Physical and optical properties of Titanium-Nickel (TiNi) SMA thin films change as these films undergo phase transformation upon heating. An optical beam can be modulated either mechanically using a TiNi actuator or by the changes that occur in TiNi's optical properties upon heating and phase transformation. Reflection coefficient of TiNi films were measured in their so called martensitic (at room temperature) and austenitic (elevated temperature) phases. The reflection coefficient of the austenitic phase were higher than those of the martensitic phase by more than 45% in the wavelength range between 550 - 850 nm. Also, a microfabricated TiNi diaphragm with a 0.26 mm diameter hole was used as a prototype light-valve. The intensity of the transmitted light through the hole was reduced by 10 - 17% when the diaphragm was heated. A novel TiNi light-valve fabricated using silicon micromachining techniques is also proposed and discussed. We present both optical data and structural data obtained using transmission electron microscopies.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Re-tuning an off-tuned tuned mass damper by adjusting temperature of shape memory alloy: Exposed to wind action

In many applications of Shape Memory Alloys, the most appropriate means and sometimes the only one to measure temperature is thermography, which relies on knowing the emissivity of the material. This paper aims to evaluate experimentally the behavior of the emissivity of a NiTi shape memory alloy as a function of temperature in order to investigate how the emissivity behaves during phase transformation and how it may impact the measured temperature. The emissivity of a Ni55Ti45 shape memory alloy was measured by means of active and passive infrared sensors in a spectral band of 8-14 µm in the temperature range from 25 to 100oC under a vacuum of 3 x 10 -3 Pa. The results show that the emissivity of the Ni55Ti45 shape memory alloy varied approximately 9% between fully martensitic and fully austenitic states.

Shape Memory Alloy in Various Aviation Field

Shape memory alloys are unique materials, capable of returning to their original shape after deforming. Due to their characteristics, Shape Memory Alloys have proven suitable for use in various fields, including aerospace, medicine and marine. One of the biggest challenges facing the practical application of Shape Memory Alloys is corrosion, which can significantly degrade its mechanical characteristics and performance. This paper presents the corrosion analysis of alloys Cu (copper), CuAl (copper, aluminum), and two samples of NiTi (nickel, titanium) using advanced information technologies. Furthermore, Focused Ion Beam analysis was used to analyze the corrosion process of the shape memory alloys which were exposed to different sea and atmospheric conditions for one month.

Low hysteresis and high cyclic stability in a Ti50Ni45.2Cu1Fe3.8 shape memory alloy