Shape Memory Alloy Ring Research Articles

Efficacy of the shape-memory alloy ring hugger and microplate in proximal clavicle fractures

The efficacy and safety of shape-memory alloy (SMA) ring hugger and microplate in the treatment of proximal clavicle fractures were compared to better improve the quality of patient rehabilitation and minimize complications. The mechanical properties of Ni-Ti alloy and Ti64Al4V (compressive strength and elastic modulus) were examined in the physicochemical property tests, while, mouse osteoblasts were cultured to test their biocompatibility. Subsequently, clinical data of patients with clavicle fractures treated at our hospital from January 2012 to January 2022 were retrospectively analyzed. The patients were divided into microplate and SMA groups based on the surgical methods, and the follow-up period was 1 year post-surgery. Clinical treatment, mobility and functional recovery (DASH score and Constant score) of the affected upper limb, numbness, and adverse effects were compared between the two groups. SMA exhibited a compressive strength similar to that of Ti6Al4V, but its modulus of elasticity was significantly lower. Meanwhile, the results of the cellular experiments suggested that the addition of SMA and Ti6Al4V would not markedly decrease the osteoblast activity, suggesting that both internal fixation implants had good biocompatibility. In addition, SMA ring hugger was effective in reducing operative time, intraoperative bleeding, wound size, fracture end healing time, and residual fracture shortening. In terms of postoperative assessment of affected limb mobility, SMA ring hugger better improved the mobility of the affected shoulder in supination, abduction, adduction, and forward flexion, and was more effective in decreasing the DASH score and increasing the Constant score. Meanwhile, SMA ring hugger effectively reduced numbness in the affected area and decreased the incidence of delayed wound healing, exercise restrictions, proliferative scars, and vegetative stimulus. Therefore, SMA ring hugger demonstrates favorable mechanical performance and biocompatibility, meanwhile, it can better promote postoperative functional recovery of the affected limb in clavicle fracture patients with guaranteed safety.

Seismic mitigation performance of shape memory alloy flexible circumferential joint in shield tunnel

AbstractThe circumferential joint of a shield tunnel is prone to damage under strong earthquakes, affecting the safety of the tunnel. This paper adopts an innovative shape memory alloy (SMA) flexible circumferential joint for longitudinal seismic mitigation of the tunnel. The SMA joint is composed of SMA ring springs and ordinary bolts. The SMA joint design is performed for a shield tunnel, and a simplified model of the SMA joint is proposed. Based on the generalised response displacement method, the longitudinal seismic mitigation analysis of the tunnel is conducted, the arrangement of SMA joints is discussed, and the seismic mitigation performance is evaluated. Results show that the SMA joint design method can efficiently complete the joint design, and the SMA joint model can accurately reflect the joint performance. SMA joints can reduce the stiffness of tunnel joints and have a good energy dissipation effect, which is suitable for shield tunnel seismic mitigation. An appropriate SMA joint arrangement can concentrate the tunnel joint deformation and effectively reduce the opening width between the tunnel segment rings. It can also dissipate energy and reduce the internal force of the tunnel joint, thus enhancing the seismic safety of the tunnel.

On the performance of a smart hybrid damper consisting of shape memory alloy and steel rings

This study investigated the performance of hybrid rings used as a smart damper made by shape memory alloy (SMA) as well as steel rings. The aim of the SMA ring was to provide recentering capacity, while the steel ring may provide sufficient damping capacity for fabricated hybrid rings. To this end, two types of hybrid rings were studied: 1) An SMA ring with an outer steel ring and 2) an SMA ring with an inner steel ring. The experimental data during cyclic loading tests were compared to those of pure SMA rings. The results indicated that pure SMA rings showed an almost perfect recentering capacity, and hybrid cases with an outside steel ring increased the energy dissipation when there was a small reduction in the recentering capacity. However, in the case of hybrid dampers with an inner steel ring, the recentering capacity was almost lost, and the damping capacity had a large increase. From finite element (FE) models, it was found that the connection between the two rings was so strong that the hybrid ring became similar to a damping device, regardless of the location of the steel ring. Therefore, the loose connection between the SMA and steel rings is critical to maintain the recentering capacity of SMA rings.

An innovative shape memory alloy flexible circumferential joint for tunnel seismic mitigation

Under strong ground motion, shield tunnels passing through uneven soil layers are easily damaged. Based on the concept of elastic washers, a shape memory alloy (SMA) flexible circumferential joint for longitudinal seismic mitigation of shield tunnels is proposed to achieve seismic mitigation with minimal impact; it is composed of SMA ring springs and ordinary joint bolts. The test performance and influencing factors of SMA ring springs are discussed. Then, based on the analytical solution of the SMA ring spring, the design method of the SMA flexible circumferential joint is proposed. The mechanical properties of the SMA flexible circumferential joint under different loads are studied through the numerical simulation of tunnel joints. Test, analysis and simulation results indicate that SMA ring springs have good energy dissipation and self-recovery effects and can satisfy the mechanical performance requirements of elastic washers. The joint design method can conveniently and efficiently design suitable SMA flexible circumferential joint. Numerical simulations show that under various loads, the joints can reduce the longitudinal stiffness of the tunnel and dissipate energy. The joint can improve the ability of the tunnel to adapt to the soil deformation under earthquakes, reduce the internal force of the structure and at the same time achieve energy dissipation effect, thereby enhancing the seismic safety of the tunnel.

A simplified analytical model to simulate martensite reorientation and plasticity in shape memory alloy ring couplers

Recent studies on Shape Memory Alloy rings have been undertaken at the European Organization for Nuclear Research (CERN) to develop smart and leak-tight couplers for Ultra High Vacuum systems of particle accelerators. A special thermo-mechanical process (training) is needed to provide SMA rings with proper functional properties, that is to allow thermal mounting, dismounting, and leak tight coupling within a given service temperature window. Low temperature ring expansion is a crucial part of the training process as it gives suitable size, shape recovery properties, and thermal stability range to the SMA element. An analytical model, based on simplified elastic-plastic axisymmetric concepts, has been developed and implemented in a commercial software to simulate isothermal SMA rings expansions. It is particularly useful to predict the final size of a martensitic SMA coupler as a function of the initial dimensions and of the pre-deformation parameters. The effectiveness of the model has been demonstrated by analyzing the stress/deformation field occurring in a wide range of ring geometries for different load cases including martensite reorientation and plasticity. The predictions of the analytical model have been systematically compared with those obtained by axisymmetric finite element (FE) analyses based on elastic-plastic constitutive models and experimental measurements.

Inverse problems with the digital image correlation: approach and applications

A viable approach to solve inverse problems in elasticity is proposed. It is based on regression algorithms to estimate materials and/or loading parameters by fitting the experimentally-evaluated displacement field to representative analytical solutions. Displacements are measured by the digital image correlation (DIC) technique and they are used as input for numerical procedures able to minimize the estimation errors of the unknowns and to quantify the unavoidable rigid body motions of the samples/components. In addition, thanks to ad-hoc developed iterative algorithms, non-linear phenomena related to high and localized stress/strain states, can be captured successfully. This latter represents a relevant novelty of the methodology as it allows to investigate plasticity-induced mechanisms in solid mechanics which are impossible to analyze with more traditional DIC-based approaches. Three different case studies are considered: 1) estimation of the stress intensity factor in fracture mechanics problems, 2) estimation of the elastic properties of a material by the Brazilian tests, 3) estimation of the contact pressure generated by thermally activated shape memory alloy (SMA) rings used for pipe coupling. The reliability and the accuracy of the method is demonstrated through systematic comparisons of the results with conventional techniques in experimental mechanics.

Experimental and numerical studies on self-centring beam-to-column connections free from frame expansion

In this study, a new type of self-centring beam-to-column connection is proposed, which is free from frame expansion and therefore causes minimal damage to the slab system. The connection rotates about the top flange, with shape memory alloy (SMA) ring spring-based devices installed underneath the beam. An experimental investigation on a proof-of-concept connection specimen was first carried out, followed by a comprehensive numerical study looking at a variety of parameters that may affect the connection behaviour. The test specimen showed typical flag-shaped hysteretic response with excellent self-centring capability under both positive and negative moments. Moderate energy dissipation with an equivalent viscous damping ratio of up to 15% was exhibited. The subsequent numerical study revealed that the friction and precompression of the SMA ring spring system critically affect the overall connection behaviour. In addition, extra energy dissipation can be reliably provided by the web bolts, and a “partial self-centring” connection with fully tightened high-strength web bolts is recommended. The cover plate design and the influence of concrete slab were also discussed. Considering a prototype building frame, an illustrative connection design example was finally presented, with some preliminary design recommendations briefly outlined. The design example clearly demonstrates the feasibility of the proposed connection in a “full-scale” structure.

Behavior and Design of Self-Centering Energy Dissipative Devices Equipped with Superelastic SMA Ring Springs

AbstractThis paper presents a novel type of self-centering energy dissipative device equipped with superelastic shape memory alloy (SMA) ring springs. The fundamental mechanical behavior and analyt...

Self-centering and damping devices using SMA dual rings

Cyclic tests have been conducted on five shape memory alloy (SMA) rings, i.e. single superelastic ring (SE), single martensitic SMA ring (MA), two superelastic SMA rings (SE–SE), two martensitic SMA rings (MA–MA), and martensitic–superelastic SMA rings (MA–SE). Experimental results show that while the single SMA ring systems in this study showed better symmetrical behaviors than those in a previous study, the dual ring systems show perfectly symmetrical behaviors. The use of martensitic SMA could increase the damping ratios of the ring systems while the use of superelastic SMA could enhance the self-centering capacity. In addition to experimental studies, a numerical model of the superelastic SMA ring systems was also developed using ANSYS software. The verification of experimental results showed that the analytical results are acceptable. Furthermore, to examine the effect of SMA ring thickness on the symmetrical behavior of the single SMA systems, a thickness ratio and a hardening stiffness ratio (HSR) are introduced. The thickness ratio is the ratio between the thickness and outer diameter of the rings, while the HSR is the ratio between the stiffnesses in hardening phase of the ring in pulling action and that in pushing action. The analysis results obtained through ANSYS demonstrate that an increase in the thickness ratio leads to a decrease in the stiffness ratio. Therefore, the ring could behave symmetrically when the thickness of the ring reaches a critical value. However, due to the p-delta effect when large displacement is applied, unsymmetrical behavior still occurs. Thus, to ensure symmetrical behavior, it is recommended to use dual SMA ring systems or 2 rings in symmetrical structures.

Behavior and design of top flange-rotated self-centering steel connections equipped with SMA ring spring dampers

Existing self-centering steel connections developed based on either posttensioned (PT) tendons or shape memory alloy (SMA) elements are usually symmetric ones, in which case the connections rotate via a gap-opening mechanism over the beam-to-column interface and as a result causes unwanted “frame-expansion” (also called beam growth) effect and severe slab damage. This paper presents a novel type of asymmetric self-centering steel connection, which rotates around the top flange of the beam. The bending moment capacity and restoring force are provided by a couple of SMA dampers attached beneath the bottom flange of the beam. The working principles of the damper devices and the beam-to-column connections are discussed in detail, and a comprehensive experimental study on individual SMA rings, individual SMA damper devices, as well as two proof-of-concept beam-to-column steel connections, is conducted. The test results show that this type of connection generally exhibits typical flag-shaped hysteretic behavior with satisfactory energy dissipation and excellent self-centering capability. An extra ‘training’ process with an adequate pre-deformation to the SMA ring spring system can be adopted to effectively mitigate the degradation effect of the connections under repeated loading. Based on the test observations, a preliminary design recommendation is also proposed.

Manufacturing and performance of a novel self‐centring damper with shape memory alloy ring springs for seismic resilience

This paper discusses the manufacturing process and mechanical performance of a novel self-centring damper equipped with a group of kernel elements, namely, shape memory alloy (SMA) ring springs. The study commences with an experimental investigation on individual SMA ring spring specimens, enabling a fundamental understanding of their working principle and mechanical performance. Some technical issues related to manufacturing process, low-temperature heat treatment (annealing), quenching, and cyclic training are also discussed. Subsequently, the fabrication steps and working mechanism of the dampers incorporating the SMA ring springs are elaborated, and a further experimental study on a large-scale prototype damper specimen is carried out. The test results show that the damper specimen exhibits satisfactory mechanical behaviour with a stable flag-shaped load–displacement hysteretic response. A high initial stiffness and an adequate level of “yield” resistance are exhibited due to a relatively high preload applied to the SMA ring spring group. Excellent self-centring capability with no residual displacement is observed, and satisfactory energy dissipation with an equivalent viscous damping ratio of up to 18.5% is shown. No failure to any component of the damper is observed by the end of the test. The proposed damper is expected to resist strong earthquakes and offer self-centring driving action effectively for engineering structures without the need for repair.

Optimization of thin-walled sealing structure based on mechanical simulation

In the hydraulic and gas pipelines, even thin-walled cylinder device, the built-in elastomeric O-rings are widely used to ensure their sealing. Unfortunately, a case of excessive radial contact pressure will lead to leakage risk. At the same time, the aging of elastomeric O-ring will result in decrease of radial contact pressure, which can also bring about leakage risk. To increase the life of the seal structure, the external shape memory alloy (SMA) sealing ring is subsequently developed for the actual product. However, excessive contact pressure will cause the leakage risk with the lateral deformation at the outside of the sealing interface of the thin-walled cylinder. Based on mechanical simulation, a proposal for the optimization design of seal structure with thin-walled cylinder is given. That is, the radial contact seal on the inner and outer side of the thin-walled cylinder can simultaneously made by SMA. Results gained show that the theoretical value of the resultant force from the SMA at the inside and outside of the sealing interface of the thin-walled cylinder is zero. The bilateral seal structure with SMA ring can avoid the leakage risk caused by the unilateral force and deformation on the thin-walled cylinder, and effectively prolong the service life of the sealing device.

Application of an Innovative SMA Ring Spring System for Self-Centering Steel Frames Subject to Seismic Conditions

AbstractThis paper presents an innovative shape memory alloy (SMA) ring spring system used for high-performance steel beam-to-column connections. The ring spring system, which includes a series of ...

A Proof-of-Concept Study on Self-Centering Column Feet Equipped with Innovative Shape Memory Alloy Ring Springs

This paper presents a feasibility study on a self-centering steel column foot equipped with innovative shape memory alloy (SMA) ring springs. The ring spring system includes a series of SMA outer rings and high-strength alloy inner rings stacked in alternation with mating taper faces, and the system is used in conjunction with high-strength bolts in a typical extended end-plate connection to achieve favorable self-centering and energy dissipation performances while ensuring ease of construction. An experimental investigation was first conducted looking into the basic mechanical performance of individual SMA ring springs under cyclic loading. Driven by the superelastic behavior of SMA, excellent self-centering ability with satisfactory energy dissipation is exhibited. Subsequently, a further experimental study on a proof-of-concept column foot specimen is conducted, where the key properties, including ductility, self-centering ability, and energy dissipation capability, are discussed in detail in this paper.

Innovative use of a shape memory alloy ring spring system for self-centering connections

This paper presents superelastic shape memory alloy (SMA) ring spring systems for seismic applications. The study commences with an experimental investigation looking into the mechanical performance of individual SMA ring springs under cyclic loading. The strength, self-centering ability, and energy dissipation capacity are shown to be dependent on the ring size as well as the treatment of the contacting taper face. Subsequently, a proof-of-concept beam-to-column self-centering connection is physically tested, shedding further light on the practical application of the ring spring systems for high-performance seismic resisting steel frames. The connection shows favorable cyclic behavior, with the majority of the deformation demand resisted by the SMA ring spring systems. The remaining structural components generally stay undamaged. Driven by the superelastic behavior of SMA, excellent self-centering ability with satisfactory energy dissipation is exhibited. A numerical investigation is then conducted to gain a further understanding of the load resistance mechanism of the proposed connection. The numerical model is validated against the experimental results with good agreement observed, enabling a further parametric study to be conducted taking a more in-depth look into the influence of ring pre-compression, taper face friction, ring size, and shear tab bolt preload on the overall performance of the connection. Based on the test and numerical data, some design comments are also made.

Shape-memory alloy rings as tight couplers between ultrahigh-vacuum pipes: Design and experimental assessment

The ultrahigh-vacuum (UHV) coupling performance of NiTiNb shape memory alloy (SMA) rings was investigated by finite element (FE) simulations and experimental measurements. The contact pressure at the interface between the SMA ring and the vacuum pipe was measured and good agreements with the FE results were obtained. Furthermore, a design method was proposed that involves the FE results and a vacuum sealing model. Finally, leak rate measurements were carried out to assess the sealing performance of selected coupling configurations. The main result found was that the leak rate constraints for UHV applications could be easily satisfied (leak rate <10−10 mbar l s−1), which opens the possibility of remotely clamping/unclamping the tight couplers by well-defined changes in their temperature. Possible applications in the field of particle accelerators and, in particular, in restricted access areas were considered.

Beam-pipe coupling in particle accelerators by shape memory alloy rings

Shape Memory Alloy (SMA) rings have been studied for possible applications as beam-pipe connectors in particle accelerators. The rings were analyzed by both experimental tests and finite element simulations. In particular, the tightening performance of NiTiNb rings, in terms of contact pressure and clamping/unclamping mechanisms, was studied for different values of the initial clearance between ring and vacuum pipe. The results have revealed that the contact pressure is not significantly affected by the assembly clearance due to the plateau in the stress-strain response of the material. In addition, thermal dismounting and subsequent re-clamping is obtained by exploiting the two way shape memory recovery capabilities of the SMA rings. Thanks to these features, these connectors can be used in high-energy particle accelerators, especially in radioactive areas, where thermally induced mounting and dismounting operations can be activated remotely.

An innovative seismic bracing system based on a superelastic shape memory alloy ring

Shape memory alloys (SMAs) have great potential in seismic applications because of their remarkable superelasticity. Seismic bracing systems based on SMAs can mitigate the damage caused by earthquakes. The current study investigates a bracing system based on an SMA ring which is capable of both re-centering and energy dissipation. This lateral force resisting system is a cross-braced system consisting of an SMA ring and four tension-only cable assemblies, which can be applied to both new construction and seismic retrofit. The performance of this bracing system is examined through a quasi-static cyclic loading test and finite element (FE) analysis. This paper describes the experimental design in detail, discusses the experimental results, compares the performance with other bracing systems based on SMAs, and presents an Abaqus FE model calibrated on the basis of experimental results to simulate the superelastic behavior of the SMA ring. The experimental results indicate that the seismic performance of this system is promising in terms of damping and re-centering. The FE model can be used in the simulation of building structures using the proposed bracing system.

A micro-coupling for micro mechanical systems

The error motions of micro mechanical systems, such as micro-spindles, increase with the increasing of the rotational speed, which not only decreases the rotational accuracy, but also promotes instability and limits the maximum operational speed. One effective way to deal with it is to use micro-flexible couplings between the drive and driven shafts so as to reduce error motions of the driven shaft. But the conventional couplings, such as diaphragm couplings, elastomeric couplings, bellows couplings, and grooved couplings, etc, cannot be directly used because of their large and complicated structures. This study presents a novel micro-coupling that consists of a flexible coupling and a shape memory alloy (SMA)-based clamp for micro mechanical systems. It is monolithic and can be directly machined from a shaft. The study performs design optimization and provides manufacturing considerations, including thermo-mechanical training of the SMA ring for the desired Two-Way-Shape-Memory effect (TWSMe). A prototype micro-coupling and a prototype micro-spindle using the proposed coupling are fabricated and tested. The testing results show that the prototype micro-coupling can bear a torque of above 5 N • mm and an axial force of 8.5 N and be fitted with an SMA ring for clamping action at room temperature (15 °C) and unclamping action below–5 °C. At the same time, the prototype micro-coupling can work at a rotational speed of above 200 kr/min with the application to a high-speed precision micro-spindle. Moreover, the radial runout error of the artifact, as a substitute for the micro-tool, is less than 3 μm while that of turbine shaft is above 7 μm. It can be concluded that the micro-coupling successfully accommodates misalignment errors of the prototype micro-spindle. This research proposes a micro-coupling which is featured with an SMA ring, and it is designed to clamp two shafts, and has smooth transmission, simple assembly, compact structure, zero-maintenance and balanced motions.

SMA를 이용한 공구홀더의 자동공구교환장치 개발

Micromanufacturing is a useful system for reducing energy consumption. For micromanufacturing, tool clamping and workpiece clamping are important components to realize the machining process. Therefore, a shape memory alloy (SMA) ring type tool holder is developed. In addition, this holder needs cooling and heating processes to execute the tool clamping process. This study suggests a cooling/heating device based on peltier elements. The device will be applied to the heating/cooling process of an automatic tool changer (ATC) for the SMA tool holder. This study introduces the configuration and operating principle of the proposed ATC system. The description and prototype evaluation of this system were given. Plastic bolt and aluminum block were selected to enhance the cooling performance, and the installed tool was changed in 17 s during the experiments.