Shape Memory Alloy Elements Research Articles

Vision-based support in the characterization of superelastic U-shaped SMA elements

The authors investigate the feasibility of applying a vision-based displacement-measurement technique in the characterization of a SMA damper recently introduced in the literature. The experimental campaign tests a steel frame on a uni-axial shaking table driven by sinusoidal signals in the frequency range from 1Hz to 5Hz. Three different cameras are used to collect the images, namely an industrial camera and two commercial smartphones. The achieved results are compared. The camera showing the better performance is then used to test the same frame after its base isolation. U-shaped, shape-memory-alloy (SMA) elements are installed as dampers at the isolation level. The accelerations of the shaking table and those of the frame basement are measured by accelerometers. A system of markers is glued on these system components, as well as along the U-shaped elements serving as dampers. The different phases of the test are discussed, in the attempt to obtain as much possible information on the behavior of the SMA elements. Several tests were carried out until the thinner U-shaped element went to failure.

Biological Cell Investigation of Structured Nitinol Surfaces for the Functionalization of Implants.

Expandable implants including shape memory alloy (SMA) elements have great potential to minimize the risk of implant loosening and to increase the primary stability of bone anchoring. Surface structuring of such elements may further improve these properties and support osteointegration and bone healing. In this given study, SMA sheets were processed by deploying additive and removal manufacturing technologies for 3D-printed surgical implants. The additive technology was realized by applying a new laser beam melting technology to print titanium structures on the SMA sheets. The removal step was realized as a standard process with an ultrashort-pulse laser. The morphology, metabolic activity, and mineralization patterns of human bone marrow stromal cells were examined to evaluate the biocompatibility of the new surface structures. It was shown that both surface structures support cell adhesion and the formation of a cytoskeleton. The examination of the metabolic activity of the marrow stromal cells on the samples showed that the number of cells on the laser-structured samples was lower when compared to the 3D-printed ones. The calcium phosphate accumulation, which was used to examine the mineralization of marrow stromal cells, was higher in the laser-structured samples than in the 3D-printed ones. These results indicate that the additive- and laser-structured SAM sheets seem biocompatible and that the macrostructure surface and manufacturing technology may have positive influences on the behavior of the bone formation. The use of the new additive technique and the resulting macrostructures seems to be a promising approach to combine increased anchorage stability with simultaneously enhanced osteointegration.

Development of Smart Textile Materials with Shape Memory Alloys for Application in Protective Clothing.

The latest directions of research on the design of protective clothing concern the implementation of smart materials, in order to increase its protective performance. This paper presents results on the resistance to thermal factors such as flames, radiant heat, and molten metals, which were obtained for the developed smart textile material with shape memory alloys (SMAs). The laboratory tests performed indicated that the application of the designed SMA elements in the selected textile material system caused more than a twofold increase in the resistance to radiant heat (RHTI24 = 224 s) with an increase of thickness of 13 mm (sample located vertically with a load), while in the case of tests on the resistance to flames, it was equal to 41 mm (sample located vertically without a load) and in the case of tests on the resistance to molten metal, it was 17 mm (sample located horizontally).

Experimental tests and finite element simulations of a new SMA-steel damper

Owing to their outstanding recentering capability, shape memory alloy (SMA) dampers are emerging as promising passive dampers for seismic applications. However, compared to typical seismic dampers, the inherent energy dissipation capability of SMAs is often deemed barely satisfactory. To enhance the damping capacity of SMA dampers, this study suggests combining SMA elements with steel dampers based on bending steel plates. In this new SMA-steel damper, the steel dampers are mainly responsible for absorbing seismic energy, whereas the SMA bars primarily play the role of recovering inelastic deformation. Experimental tests were conducted at room temperature to verify the cyclic behavior of the proposed damper. The hysteretic parameters, such as strength, stiffness, equivalent damping ratio, and residual deformation, are of particular interest and quantified as a function of the loading amplitude. According to test results, the new damper is confirmed to possess desirable recentering capability and high damping. To further understand the damper, numerical simulations were carried out in the finite element (FE) analysis software ABAQUS. The numerical results validated the experimental data. Based on the calibrated FE model, the thickness of the bending steel plate of the steel damper and the diameter of the SMA bars were varied in the parametric analysis to examine its effect on the recentering tendency and damping mechanism.

A macroscopic description of shape memory alloy functional fatigue

Shape memory alloys (SMAs) are smart materials employed in several applications including medical devices, aerospace components, robotics, among others. In many of these applications, devices are subjected to cyclic loading conditions. Based on this, a proper comprehension of fatigue phenomenon is essential for suitable design of systems involving SMA elements. In general, SMAs exhibit two kinds of fatigue: functional fatigue, related to the decrease of the functional properties; and structural fatigue, associated with the nucleation and growth of microcracks that lead to fracture. This paper presents a macroscopic three-dimensional constitutive model to describe functional fatigue on shape memory alloys considering continuum damage perspective. Numerical simulations are compared with experimental results showing the capabilities of the proposed model. In addition, numerical simulations are presented in order to explore the general thermomechanical aspects of SMA functional fatigue, allowing a proper comprehension of phenomenological aspects.

Influence of shape memory alloy brace design parameters on seismic performance of self‐centering steel frame buildings

This paper investigates the seismic and collapse performance of shape memory alloy (SMA) braced steel frame structures considering the effects of various brace design parameters and ultimate state of SMAs. An SMA-braced steel frame building is designed to have comparable strength and stiffness with a steel-moment resisting frame selected as case study building. Then, the stiffness and ultimate deformation capacity of the SMA braces in the initially designed reference SMA-braced frame are systematically varied. First, the static pushover analysis and incremental dynamic analysis are employed to illustrate the significance of SMA brace failure consideration in seismic performance assessment of steel frames with SMA elements. Then, the influence of SMA brace initial stiffness and ultimate deformation capacity on the seismic and collapse performance of SMA braced frames are studied through pushover analyses, nonlinear response history analyses, and incremental dynamic analysis. The results show that the SMA brace initial stiffness does not affect the interstory drift and floor absolute acceleration response at design and maximum considered earthquake level seismic hazard or collapse capacity of the frame. However, it has considerable influence on post-event functionality of the frame. It is also found that the SMA brace ultimate deformation capacity should be at least 80% of maximum interstory drift demand at maximum considered earthquake level for satisfactory seismic performance, whereas larger values provide higher collapse capacity for the SMA-braced frame.

F(1H‐Pyrazol‐4‐yl)methylene‐Hydrazide derivatives: Synthesis and antimicrobial activity

AbstractThis paper investigates the seismic and collapse performance of shape memory alloy (SMA) braced steel frame structures considering the effects of various brace design parameters and ultimate state of SMAs. An SMA braced steel frame building is designed to have comparable strength and stiffness with a steel‐moment resisting frame selected as case study building. Then, the stiffness and ultimate deformation capacity of the SMA braces in the initially designed reference SMA braced frame are systematically varied. First, the static pushover analysis and incremental dynamic analysis (IDA) are employed to illustrate the significance of SMA brace failure consideration in seismic performance assessment of steel frames with SMA elements. Then, the influence of SMA brace initial stiffness and ultimate deformation capacity on the seismic and collapse performance of SMA braced frames are studied through pushover analyses, nonlinear response history analyses, and IDA. The results show that the SMA brace initial stiffness does not affect the interstory drift and floor absolute acceleration response at design and maximum considered earthquake (MCE) level seismic hazard or collapse capacity of the frame. However, it has considerable influence on post‐event functionality of the frame. It is also found that the SMA brace ultimate deformation capacity should be at least 80% of maximum inter‐story drift demand at MCE level for satisfactory seismic performance, while larger values provide higher collapse capacity for the SMA braced frame.

A novel shape memory alloy damping inerter for vibration mitigation

Various shape memory alloy (SMA) dampers have been developed to reduce structural vibration responses. However, the application of SMA dampers has been restricted by the high material costs of SMAs. Therefore, this study developed and tested an innovative SMA damping inerter (SDI) in which an SMA element and an inerter element were arranged in parallel and deployed in series with a supporting spring element. A single-degree-of-freedom structure with an SDI was employed to analyze the effect of vibration mitigation. A theoretical analysis was conducted via an equivalent linearization method, and parameter studies were then used to evaluate the performance of the SDI-fitted structure from perspectives of structural displacement, acceleration, and energy dissipation as well as the most efficient frequency tuning bandwidth. The performances of the SDI and a conventional SMA damper were compared by using a time-domain analysis with recorded and simulated ground motions, revealing clearly superior results for the SDI with respect to structural response mitigation, and seismic energy dissipation. The system proposed here took advantage of the full potential of combining SMA and inerter elements, making the SDI a robust system for mitigating structural vibration with more economical SMA material costs.

A Novel Self-Deployable Solar Sail System Activated by Shape Memory Alloys

This work deals with the feasibility and reliability about the use of shape memory alloys (SMAs) as mechanical actuators for solar sail self-deployment instead of heavy and bulky mechanical booms. Solar sails exploit radiation pressure a as propulsion system for the exploration of the solar system. Sunlight is used to propel space vehicles by reflecting solar photons from a large and light-weight material, so that no propellant is required for primary propulsion. In this work, different small-scale solar sail prototypes (SSP) were studied, manufactured, and tested for bending and in three different environmental conditions to simulate as much as possible the real operating conditions where the solar sails work. Kapton is the most suitable material for sail production and, in the space missions till now, activated booms as deployment systems have always been used. In the present work for the activation of the SMA elements some visible lamps have been employed to simulate the solar radiation and time-temperature diagrams have been acquired for different sail geometries and environmental conditions. Heat transfer mechanisms have been discussed and the minimum distance from the sun allowing the full self-deployment of the sail have also been calculated.

Wave-induced vibration control of offshore jacket platforms through SMA dampers

Since permanent wave-induced vibrations of offshore jacket platforms reduce the service life of the jacket structure and deck equipment and increase the fatigue failure of the welded connections, this research has used SMA (shape memory alloy) dampers to control the jacket platform oscillations. Superelasticity, high durability, and energy dissipation capability make SMA elements good nominees for the design of vibration control devices. In this research, to model the force-displacement hysteretic behavior of SMA elements their idealized multi-linear constitutive model has been implemented and the time history responses of vibration equations have been evaluated by direct integration method. To analyze the SMA damper effects on the vibration suppression of the jacket platforms, a 90 (m) high jacket located 80 (m) deep in water has been selected as a case study. Numerical results have shown that optimized SMA dampers with constant-geometry SMA bars will improve the dynamic behavior of the jacket platform under the action of an extreme regular wave. However, under the action of two irregular waves, SMA dampers with varying-geometry SMA bars will cause significant reduction in the dynamic responses of the jacket platform. The power spectral density function of the deck displacements have shown that the previously mentioned SMA dampers avoid resonance by shifting the natural frequencies of the jacket structure away from the excitation frequencies.

Numerical study of patient-specific ankle-foot orthoses for drop foot patients using shape memory alloy

Drop foot is a nerve-muscle disorder that affects the muscles that lift the foot. The two main side effects of drop foot are slapping/kicking the foot after heel strike (foot) and dragging the foot during the swing (toe drag). Treatment methods such as ankle-foot orthoses (AFO) have some biomechanical benefits, but are not applicable to all walking conditions and cannot mitigate significant gait complications. This study introduces the design of a passive AFO system, which combines an ordinary AFO and a shape memory alloy (SMA) element. OpenSim was used to simulate patients with muscle weakness and to calculate the torque needed to imitate normal ankle joint stiffness. The calculated torque was then reproduced for different levels of muscle weakness by the superelasticity of SMAs. The study showed that the normal joint stiffness profile for each patient with a certain level of muscle weakness can be restored by designing a patient-specific orthosis.

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.

Chaos control of a shape memory alloy structure using thermal constrained actuation

Shape memory alloys (SMAs) have been widely used in smart structures due to their adaptive properties. Their thermomechanical coupling can provide vibration attenuation or actuation providing a desired dynamical response. Chaos control methods can provide the stabilisation of unstable periodic orbits allowing one to choose a convenient response. Besides, it can promote bifurcation control that can avoid undesirable responses. This work investigates the chaos control of smart structures employing time-delayed feedback control to perform orbit stabilisation. A two-bar truss is of concern using thermal actuation of SMA elements. Thermal constraints defined by energy equation are investigated, showing the real possibilities of this kind of control. Numerical results show situations related to controller constraints, defining its range of applicability. Control strategy potentialities are discussed showing unstable periodic orbit stabilisation, exchangeable target control and bifurcation control.

Adaptive vortex generators based on active hybrid composites: from idea to flight test

In this contribution, we present a system of adaptive vortex generators (VGs) enabling an on-demand optimization of the airflow for high angles of attack. The generated vortices enhance the boundary layer with kinetic energy and prevent flow separation. The maximum cruise efficiency is ensured as VGs are stowed. The system presented uses active hybrid composites, where the actuation is initiated by shape memory alloys (SMA). By the direct integration of SMA elements in flat fiber-reinforced polymer (FRP) parts, the components turn into active hybrid composites. A well-selected amount of SMA wire is integrated in a composite layup and allows small elements of about 25 × 30 mm2 and a thickness of only 1.8 mm to deflect up to 8 mm upwards into the airflow. These small active VG with a weight of 1.5 g each can easily be integrated in the wing structure, since only an electrical connection is required. This contribution will highlight the actuation performance of these elements under airflow in the laboratory, illustrate the required system architecture and will give a first look on results of flight tests with functional setup equipped on a glider for measuring the aerodynamic impact on the flight behavior.

A Superelastic Retrofitting Method for Mitigating the Effects of Seismic Excitations on Irregular Bridges

Irregularities in bridge pier stiffness concentrate the ductility demand on short piers; while not operating on the longer and more flexible ones. The existence of non-uniform, ductility demand distribution in bridges significantly influences seismic response. As such, this paper proposes a new approach for balancing the ductility demand in irregular bridges by utilizing shape memory alloys (SMAs). An irregular, single column bent viaduct with unequal pier heights is modeled and used as a reference bridge. To enhance seismic behavior of the bridge, a fixed bearing at the top of the short pier is replaced by a sliding bearing and two groups of SMA bars. SMAs are designed to keep their maximum strain within the super-elastic range. The seismic response of the controlled bridge is compared with a reference bridge through parametric studies using a set of suitable ground motion records. Study parameters include SMA lengths, short pier reinforcement ratios, design strain of SMA elements, and the heights of the medium and long piers. The proposed method successfully reduced the response of the short pier and, hence, improved the overall seismic behavior.

Connected and Doubly Connected Buckling Problems for Shape Memory Alloys

The models and methods of studying the buckling of shape memory alloy (SMA) elements that is caused by a forward thermoelastic phase transformation under a constant load are analyzed. The singly and doubly connected formulations of the corresponding problems are considered in terms of the concepts of a fixed load and a variable load concept. The critical parameters are shown to be minimal for the singly connected formulation at a variable load. The conclusions are illustrated by the example of solving the problem of buckling the Shanley column on SMA rods.

Chaos control of an SMA–pendulum system using thermal actuation with extended time-delayed feedback approach

Chaos control has been applied to a variety of systems exploiting system dynamics characteristics that present advantages of low energy consumption when compared with regular controllers. This work deals with the chaos control of a smart system composed of a pendulum coupled with shape memory alloy (SMA) elements. SMAs belong to smart material class being employed in several applications due to their adaptive behavior. The basic idea is to apply the extended time-delayed feedback control on an SMA–pendulum system by exploring the SMA temperature-dependent behavior. Actuation constraints are considered based on heat transfer equations. Controller parameters are estimated using Floquet theory employed to analyze controlled unstable periodic orbits (UPOs). Results show the capability of the thermal controller to perform UPO stabilization. Energy consumption and stabilization time are discussed establishing a comparison with an ideal controller, without heat transfer constraints.

A novel methodology for solar sail opening employing shape memory alloy elements

Solar sails exploit the radiation pressure as propulsion system. Sunlight is used to propel space vehicles by reflecting solar photons from a large and lightweight material, so that no propellant is required for primary propulsion. Kapton seems to be the most suitable material for the sail production and in the space missions till now activated booms as deployment systems have always been used. In this work, an innovative self-deploying system based on NiTi shape memory wires has been designed and manufactured in a small-scale prototype. As kapton has always been employed with a thin Al coating on the surface of the sail, commercial pure Al thin sheets with thin adhesive kapton have been used in order to simulate the sail. The attention has been focused, in the deployment experiments performed in the laboratory, on the effect of different heating methods and different pressure conditions on the activation times. The folded configuration chosen has been deployed in atmospheric condition and in low pressure condition (0.05 bar) inside a oven connected to a rotary pump. For what concerns the heating methods, the attention has been focused on low-pressure oven ISCO NSV 9035 (1.3 kW) and on halogen lamp (1 kW) in order to obtain the self-deployment of the sail. Some comparisons between the two configurations in the different environmental conditions have been performed. In all cases, the full self-activation of the sail has been achieved.

Effects of Heating and Cooling Cycle on the Shape Memory and Mechanical Characteristics of Tape-shaped Shape Memory Alloy Element

Effects of Heating and Cooling Cycle on the Shape Memory and Mechanical Characteristics of Tape-shaped Shape Memory Alloy Element

Developing a semi-analytical model for thermomechanical response of SMA laminated beams, considering SMA asymmetric behavior

In this study, thermomechanical behavior of a beam reinforced with Shape Memory Alloy (SMA) elements is investigated (an elastic core with upper and bottom SMA layers). The improved Brinson constitutive model is used in order to account for the asymmetric behavior of SMA in tension and compression. Assuming a plane stress model for the beam reinforced with SMA layers, a semi-analytical formulation is proposed. This formulation has two parts: the first part consists of a linear distribution of strain along the cross section and the second part is an iterative numerical procedure to satisfy classical equilibrium equations. For the numerical procedure, bisection method is used. Moreover, the semi-analytical results are compared with a 2D Finite Element (FE) solution. The proposed model is applicable for Euler–Bernoulli beams with any material and geometric features. For example, for a composite beam including both superelastic and shape memory SMA layers the proposed model can be employed. Regarding the results, there is more than 95% agreement between the present numerical solutions and those of 2D FE method. Also, for the numeric examples discussed in this paper, it is shown that considering the asymmetry between the tension and compression behavior of SMA, leads to at least 25% change in the force–displacement plot with respect to the cases when considering symmetric behavior and also, there is 8% (of the width of the structure) shift in the location of the neutral axis from the centerline. In addition, hysteresis inner loops are investigated, using the asymmetric proposed model and compared against 2D FE solution, where results show a good agreement between two solutions.