Prestrained Shape Memory Alloy Wires Research Articles

Self-healing performance of a microcapsule-based structure reinforced with pre-strained shape memory alloy wires: 3-D FEM/XFEM modeling

Combination of microcapsules and shape memory alloys (SMAs) is one of the promising self-healing mechanisms. Although there are several parameters which affect the performance of such structures, limited studies are performed on this combined healing mechanism. In this work, we study the performance of such a composite structure using a 3-D finite element and extended finite element model consisting of matrix, glass microcapsule, healing agent, and Ni-Ti SMA wire. After examining the results, the effect of shape memory alloy wires on increasing the maximum fracture stress was observed. Moreover, the effect of radius of shape memory alloy wires, initial crack location, thickness ratio and volume fraction of microcapsules, and interface strength on ultimate fracture stress are investigated. Also, as a key parameter in self-healing performance, the crack opening distance decreased from 5 to 0.008 μm using 0.5% volume fraction of shape memory wires without pre-strain. In the case that the wires have a pre-strain of 1%, this value reaches almost zero and a compressive stress is induced between fracture surfaces which can enhance the healing process and adherence of healing agent.

Study on a Fault Mitigation Scheme for Rub-Impact of an Aero-Engine Based on NiTi Wires.

The aim of this study was to solve the frequently occurring rotor-stator rub-impact fault in aero-engines without causing a significant reduction in efficiency. We proposed a fault mitigation scheme, using shape memory alloy (SMA) wire, whereby the tip clearance between the rotor and the stator is adjusted. In this scheme, an acoustic emission (AE) sensor is utilized to monitor the rub-impact fault. An active control actuator is designed with pre-strained two-way SMA wires, driven by an electric current via an Arduino control board, to mitigate the rub-impact fault once it occurs. In order to investigate the feasibility of the proposed scheme, a series of tests on the material properties of NiTi wires, including heating response rate, ultimate strain, free recovery rate, and restoring force, were carried out. A prototype of the actuator was designed, manufactured, and tested under various conditions. The experimental result verifies that the proposed scheme has the potential to mitigate or eliminate the rotor-stator rub-impact fault in aero-engines.

Development and actuation analysis of shape memory alloy reinforced composite fin for aerodynamic application

In this investigation, a shape memory alloy (SMA) based aerodynamic composite Fin has been developed. In general, the missile fins play a crucial role in changing the direction of a conventional missile using motor arrangement. Therefore, SMA-based composite Fin might be a promising alternative to control the direction without using the motor. The composite Fin is made of laminated fiber polymer and SMA wire. Initially, rectangular composite structures have been developed with different wire prestraining percentages, lengths, diameters, and configurations to understand their electrical actuation behavior. Based on the experiments, optimized parameters have been derived and applied to the composite fin. Adaptive composite actuation was performed via selective joule heating on the composite fin. Under optimized conditions, SMA-based composite structure shows maximum displacement of 65 mm with a maximum angle of 60 degrees before failure, where the diameter of 5 % pre-strained SMA wire was 0.5 mm at 6 % of SMA to Composite ratio (volume of SMA/volume of composite). Maximum displacement and failure analysis of the composite structure has been analyzed at optimized parameters.

Sound Radiation of Orthogonal Antisymmetric Composite Laminates Embedded with Pre-Strained SMA Wires in Thermal Environment

The interest of this article lies in the sound radiation of shape memory alloy (SMA) composite laminates. Different from the traditional method of avoiding resonance sound radiation of composite laminates by means of structural parameter design, this paper explores the potential of adjusting the modal peak of the resonant acoustic radiation by using material characteristics of shape memory alloys (SMA), and provides a new idea for avoiding resonance sound radiation of composite laminates. For composite laminates embedded with pre-strained SMA, an innovation of vibration-acoustic modeling of SMA composite laminates considering pre-stain of SMA and thermal expansion force of graphite-epoxy resin is proposed. Based on the classical thin plate theory and Hamilton principle, the structural dynamic governing equation and the frequency equation of the laminates subjected to thermal environment are derived. The vibration sound radiation of composite laminates is calculated with Rayleigh integral. Effects of ambient temperature, pre-strain, SMA volume fraction, substrate ratio, and geometrical parameters on the sound radiation were analyzed. New laws of SMA material and pre-strain characteristics on sound radiation of composite laminates under temperature environment are revealed, which have theoretical and engineering functional significance for vibration and sound radiation control of SMA composite laminates.

Innovative prestressing technique using curved shape memory alloy reinforcement

Concrete prestressing techniques have been widely used in various structural applications. However, the application of local prestressing has been limited due to complexities related to the on-site implementation of anchorage devices and mechanical jacking systems. In this work, a novel method is introduced to apply local prestressing using curved Shape Memory Alloy (SMA) reinforcement. The experimental part of the study involves casting and prestressing a mortar plate with embedded curved prestrained SMA wire. The prestressing of the SMA wire is conducted by applying temperature using electrical resistivity. Next, an experimental study is carried out to explore the feasibility of using a mortar plate with embedded SMA as a precast prestressing plate (PPP) for existing concrete. A comparison is carried out between different installation methods to ensure effective connection between the PPP and concrete. Digital Image Correlation (DIC) and strain gage measurements are adopted to monitor the value and distribution of prestress in specimens. The experimental results are used to validate a Finite Element (FE) model of the SMA-reinforced PPP. The model is used to conduct a parametric study to explore the effect of SMA geometric configuration on the prestressing level. The experimental and numerical results show that the proposed prestressing technique is valid and can be used effectively for local prestressing.

Thermal vibration analysis of SMA hybrid composite double curved sandwich panels

This work analyses the thermal vibration of a double curved sandwich panel (DCSP) with embedded pre-strained shape memory alloy (SMA) wires hybrid composite face sheets and soft core. The von Karman nonlinear displacement–strain relationships are here applied to handle large deflections due to a thermal loading. The equations of motion are derived by applying the Hamilton’s principle and the first order shear deformation theory (FSDT) for the composite face sheets and core layer. This last one features the displacement field of the Frostig's second model here, used to model the DCSP. The material properties of the DCSP are assumed to be both temperature-dependent (TD) and/or temperature-independent (TI). The effect of the SMA wires is captured by adding a stress recovery within the formulation. This term is determined by using a one-dimensional Brinson’s model in the constitutive equations of the SMA composite face sheets during the phase transformation of the pre-strained SMA wires. It is verified that SMAs can play a key role within DCSPs subjected to a thermal loading condition, whereby the proposed formulation is validated comparatively against the available literature. We also explore the sensitivity of the vibration response for a varying SMA activation temperature, volume fraction, and pre-strain, as well as for different curvature ratios, thickness ratios and different sequences in composite layers.

A novel self-healing composite made of thermally reversible polymer and shape memory alloy reinforcement

A novel self-healing polymer composite made of the thermally reversible polymer matrix and shape memory alloy reinforcement is introduced. The healing system is designed in such a way that by heating the structure, activation of shape recovery in shape memory alloy and chemical reversible reactions in polymer occur simultaneously. In the present healing method, the required crack closure force is provided by activating the embedded shape memory alloy wires in the polymer. Both superelastic and shape memory effects of shape memory alloy are considered on the fracture behavior of composites by investigating the passive and active reinforcement methods, respectively. Double cleavage drilled compression tests are utilized in order to study the fracture behavior and healing efficiency of composites. In the case of passive reinforcement, embedding 2% prestrained shape memory alloy wires caused 15% enhancement in the fracture toughness of composites. In this prestrain level, results of the micromechanical model are in good agreement with experiments. Promising results are also obtained for healing efficiency of composites in the case of active reinforcement. The average healing efficiency of 92% is achieved for shape memory alloy-reinforced thermally reversible epoxy composites. The excellent healing performance, without the necessity of external force and pressure, makes the present healing method as an ideal candidate for utilizing self-healing composite structures.

Shape Memory Alloy Based Dampers for Earthquake Response Mitigation

This paper describes the development process and initial tests performed with a new energy dissipation damper based on Shape Memory Alloy (SMA) wires. The aim of this study was to develop a new iteration of this type of devices, and eventually develop a methodology to properly design them for any type of application. The underlying concept of our device is the use of a double counteracting system of pre-strained SMA wire sections as the dissipating component. By using pre-strained wires, this design focuses on maximizing energy dissipation, partially relinquishing the re-centering capabilities of the device.The experimental part was performed on a downscaled prototype based on this design methodology. The goal of this study was to validate the basic mechanical concepts. The device was subjected to a considerable number of load cycling tests, in order to better characterize the SMA wire behavior when used in this arrangement and to improve our understanding of their influence on the device's capabilities.

Characterization and modeling of three-dimensional self-healing shape memory alloy-reinforced metal-matrix composites

In this work, three-dimensional metal-matrix composites (MMCs) reinforced by shape memory alloy (SMA) wires are modeled and simulated, by adopting an SMA constitutive model accounting for elastic deformation, phase transformation and plastic behavior. A modeling method to create composites with pre-strained SMA wires is also proposed to improve the self-healing ability. Experimental validation is provided with a composite under three-point bending. This modeling method is applied in a series of finite element simulations to investigate the self-healing effects in pre-cracked composites, especially the role of the SMA reinforcement, the softening property of the matrix, and the effect of pre-strain in the SMA. The results demonstrate that SMA reinforcements provide stronger shape recovery ability than other, non-transforming materials. The softening property of the metallic matrix and the pre-strain in SMA are also beneficial to help crack closure and healing. This modeling approach can serve as an efficient tool to design SMA-reinforced MMCs with optimal self-healing properties that have potential applications in components needing a high level of reliability.

Mechanical properties of potentially-smart carbon/epoxy composites with asymmetrically embedded shape memory wires

Embedding Shape Memory Alloy (SMA) wires in composite structures enables controlling of their mechanical properties. The main aim of this study is to characterize experimentally the mechanical properties of two-layer smart composite structures which are made of one layer of carbon fibers epoxy laminate and one layer of epoxy embedded with SMA wires. A carbon/epoxy layer was first fabricated using vacuum infusion method. Then a SMA/epoxy layer was prepared separately and then laid over the completely cured carbon/epoxy layer using the hand lay-up process. The final structure is smart and has potential of being specifically bent under controlled thermal loading, due to the embedded pre-strained SMA wires. However the temperature was kept constant and there was no thermal excitation of the SMA wires in this experimental study. The configuration of the material constituents through the thickness of the structure renders the cross-section to be unsymmetrical. The specimens were tested in a specially developed unsymmetrical tensile testing machine. From the readings of force from the testing machine and strain gages, the tensile and shear stress–strain relations of the composite materials were obtained. The elastic and shear moduli and also Poisson’s ratio of the composite materials were defined and it was observed that, the effective moduli increased with increasing density of SMA wires in the layer. It is concluded that, due to the asymmetrical material variation, finding the mechanical properties via conventional testing machine is not accurate and a special testing machine is needed.

The Post-Buckling Behavior of the Composite Plates with Embedded Shape Memory Alloy Subjected to Combined Loading Using Finite Element Method

Thin composite structures that are used in aerospace applications can be subjected to buckling failure due to combined mechanical and thermal loadings. This paper presents the work on the thermal post-buckling improvement of composite plates previously subjected to mechanical loading. Pre-strained shape memory alloy wires were embedded within laminated composite plate so that the recovery stress that can improve strain energy of the plate can be induced when the wires were heated. A geometric non-linear finite element formulation of the shape memory alloy composite plate and its source codes were developed. The formulation is based on total strain for the case of mechanical loading and incremental strain for the case of thermal loading. Using the codes, post-buckling paths were determined for quasi-isotropic and anti-symmetric cross-ply composite plates. It was found that by embedding shape memory alloy wires within composite plates, thermal post-buckling paths can be improved significantly even after the degradation of the thermal buckling resistance of composite plates due to the application of the mechanical loading.

Vibration analysis of a beam with embedded shape memory alloy wires

In this study, analytical relations for evaluating the exact solution of natural frequency and mode shape of beams with embedded shape memory alloy (SMA) wires are presented. Beams are modeled according to Euler-Bernoulli, Timoshenko and third order beam (Reddy) theories. A relation is obtained for determining the effect of axial load generated by the recovery action of pre-strained SMA wires. By defining some dimensionless quantities, the effect of different mechanical properties on the frequencies and mode shapes of the system are carefully examined. The effect of axial load generated by SMA wires with buckling load and frequency jump is accurately studied.

The post-buckling behavior of the composite plates with embedded shape memory alloy subjected to combined loading using finite element method

Thin composite structures that are used in aerospace applications can be subjected to buckling failure due to combined mechanical and thermal loadings. This paper presents the work on the thermal post-buckling improvement of composite plates previously subjected to mechanical loading. Pre-strained shape memory alloy wires were embedded within laminated composite plate so that the recovery stress that can improve strain energy of the plate can be induced when the wires were heated. A geometric non-linear finite element formulation of the shape memory alloy composite plate and its source codes were developed. The formulation is based on total strain for the case of mechanical loading and incremental strain for the case of thermal loading. Using the codes, post-buckling paths were determined for quasi-isotropic and anti-symmetric cross-ply composite plates. It was found that by embedding shape memory alloy wires within composite plates, thermal post-buckling paths can be improved significantly even after the degradation of the thermal buckling resistance of composite plates due to the application of the mechanical loading.

A high-rate shape memory alloy actuator for aerodynamic load control on wind turbines

This article discusses the development of a high-rate shape memory alloy–driven actuator. The concept of the actuator was developed to act as aerodynamic load control surface on wind turbines. It was designed as a plate or beam-like structure with prestrained shape memory alloy wires embedded off its neutral axis. Moreover, the shape memory alloy material was embedded in channels through which air was forced to actively cool the wires when the recovery load was to be released. Wires were implemented on both sides of the neutral axis to deflect the beam in both directions. Thermal analysis of the cooling channels showed that they increased the cooling rate up to 10-fold in comparison to the same set-up without forced convection. Subsequently, a fuzzy logic controller was designed to control the thermo-mechanical system. The inputs were the error between the deflection and the set point, the value of the set point and the time derivative of the set point. The output consisted of two signals to the valves that controlled the flow through the channels and a signal heating signal that was split into both sets of wires, depending on its sign. The controller was tested on an antagonistic set-up, through which a similar thermo-mechanical behaviour as with the actuator was obtained, but eliminating the beam dynamics. The results were satisfactory; an actuation bandwidth of 1 Hz was attained. Subsequently, the controller was tested on the actuator. With increasing actuation frequency, until 0.6 Hz, a relatively small error between the set point and the actual deflection was observed. Above that frequency, the error increased, but the sinusoidal response was lost. This is believed to be due to snap-through behaviour around the neutral position of the actuator. This was substantiated by the apparent inability of the actuator to track the set point around the neutral position in tracking a composite sinusoidal set point.

Robust actuation of silicon MEMS using SMA wires integrated at wafer-level by nickel electroplating

This paper reports on both the wafer-level fixation and electrical connection of pre-strained SMA wires to silicon MEMS using electroplating, and on the fabrication of the first Joule-heated Shape memory alloy (SMA) wire actuators on silicon. The integration method provides both high bond strength and electrical connections in one processing step, and it allows mass production of microactuators having high work density. SEM observation showed an intimate interconnection between the SMA wires and the silicon substrate. The variation of the actuators’ performance across the wafer was evaluated on three 4.5mm×1.8mm footprint devices, proving repeatable results. The actuators showed a mean hot state deflection of 536μm and a mean stroke of 354μm at a low power consumption (less than 70mW). One actuator was tested for m150×103 cycles, and it demonstrated a highly reliable long-term performance, showing neither material degradation, nor failure of the nickel anchors.

Analysis of nonlinear free vibration and damping of a clamped–clamped beam with embedded prestrained shape memory alloy wires

Nonlinear free vibration and damping of a clamped–clamped composite beam containing shape memory alloy wires with different prestrains embedded in the midsurface are investigated. The constitutive relations of shape memory alloy are considered in the large deflection response of the elastic Euler–Bernoulli beam, and Hamilton’s principle is used to derive differential equation of the beam motion with extensible midplane. Considering midplane stretching due to tension in the shape memory alloy wires provides an ability to model damping in a nonlinear analysis although there is no distinct damping expression in the governing equation of motion. The results show a gradual decrease in the free vibration amplitude of the beam until it reaches a fully elastic response while this cannot be seen in linear models. Free vibrations of the beam are investigated, and time response, phase diagram, state of stress and strain in the wires, and variations of loss factor are studied. The effect of prestrain in the shape memory alloy wires on the final stable vibration amplitude and loss factor in free vibrations of the beam is also investigated.

The Strain Energy Tuning of the Shape Memory Alloy on the Post-Buckling of Composite Plates Using Finite Element Method

This paper presents a geometric non-linear finite element model of shape memory alloy composite plates and its source code in order to determine critical loads and to trace post-buckling paths of the composite plates. A numerical study was conducted on symmetric and anti-symmetric angle-ply and cross-ply composite plates. Buckling and post-buckling improvements of composite plates due to the shape memory effect behaviour of shape memory alloy were carried out. The pre-strained shape memory alloy wires were embedded within laminated composite plates so that recovery stress could be induced with the heated wires. The methods of active property tuning and active strain energy tuning were applied to show the various effects of the shape memory alloy on the studied behaviour. The result showed that significant improvements occurred in the critical loads and the post-buckling paths of the symmetric and anti-symmetric angle-ply and the symmetric cross-ply composite plates due to the active strain energy tuning method. In the case of the anti-symmetric cross-ply composite plate where bifurcation point did not exist, the post-buckling path was substantially improved.

The Strain Energy Tuning of the Shape Memory Alloy on the Post-Buckling of Composite Plates Using Finite Element Method

This paper presents a geometric non-linear finite element model of shape memory alloy composite plates and its source code in order to determine critical loads and to trace post-buckling paths of the composite plates. A numerical study was conducted on symmetric and anti-symmetric angle-ply and cross-ply composite plates. Buckling and post-buckling improvements of composite plates due to the shape memory effect behaviour of shape memory alloy were carried out. The pre-strained shape memory alloy wires were embedded within laminated composite plates so that recovery stress could be induced with the heated wires. The methods of active property tuning and active strain energy tuning were applied to show the various effects of the shape memory alloy on the studied behaviour. The result showed that significant improvements occurred in the critical loads and the post-buckling paths of the symmetric and anti-symmetric angle-ply and the symmetric cross-ply composite plates due to the active strain energy tuning method. In the case of the anti-symmetric cross-ply composite plate where bifurcation point did not exist, the post-buckling path was substantially improved.

Active shape change of an SMA hybrid composite plate

An experimental study was carried out to investigate the shape control of plates via embedded shape memory alloy (SMA) wires. An extensive body of literature proposes the use of SMA wires to actively modify the shape or stiffness of a structure; in most cases, however, the study focuses on modeling and little experimental data is available. In this work, a simple proof of concept specimen was built by attaching four prestrained SMA wires to one side of a carbon fiber laminate plate strip. The specimen was clamped at one end and tested in an environmental chamber, measuring the tip displacement and the SMA temperature. At heating, actuation of the SMA wires bends the plate; at cooling deformation is partially recovered. The specimen was actuated a few times between two fixed temperatures <TEX>$T_c$</TEX> and <TEX>$T_h$</TEX>, whereas in the last actuation a temperature <TEX>$T_f$</TEX> > <TEX>$T_h$</TEX> was reached. Contrary to most model predictions, in the first actuation the transformation temperatures are significantly higher than in the following cycles, which are stable. Moreover, if the temperature <TEX>$T_h$</TEX> is exceeded, two separate actuations occur during heating: the first follows the path of the stable cycles; the second, starting at <TEX>$T_h$</TEX>, is similar to the first cycle. An interpretation of the phenomenon is given using some differential scanning calorimeter (DSC) measurements. The observed behavior emphasizes the need to build a more comprehensive constitutive model able to include these effects.

The confining effectiveness of NiTiNb and NiTi SMA wire jackets for concrete

The purpose of this study is to assess the confining effectiveness of shape memoryalloy (SMA) wire jackets for concrete. The performance of SMA wire jackets wascompared to that of steel jackets. A prestrained martensitic SMA wire was wrappedaround a concrete cylinder and then heated by a heating jacket. In the process,a confining stress around the cylinder was developed in the SMA wire due tothe shape memory effect; this jacketing method can increase the strength andductility of the cylinder under an axial compressive load. In this study, NiTi andNiTiNb SMA wires of 1.0 mm in diameter were used for the confinement. Recoverytests were conducted on the wires to assess their recovery and residual stress.The confinement by SMA wire jackets increased the strength slightly and greatly increasedthe ductility compared to the strength and ductility of plain concrete cylinders. TheNiTiNb SMA wire jacket showed better performance than that of the NiTi SMA wirejacket. The confining effectiveness of the SMA wire jackets of this study was estimated tobe similar to that of the steel jackets. This study showed the potential of the SMA wirejacketing method to retrofit reinforced concrete columns and protect them from seismicrisks.