Embedded Shape Memory Alloy Wires Research Articles

Fatigue behavior of laminated composites with embedded SMA wires

Embedding pre-strained shape memory alloy (SMA) wires within laminated composites can enhance their fatigue performance due to pseudoelastic and shape memory effects. In the present research, an experimental program was conducted to investigate the fatigue behavior of carbon/epoxy laminated composites with/without embedded SMA wires. Moreover, a novel fatigue model was proposed to predict the behavior of laminated composites with embedded SMA wires. The model is an integration of three parts. The first part is the progressive fatigue damage model to simulate the fatigue behavior of composites. The second part is the self-heating model for the prediction of the self-temperature rise in laminated composites subjected to cyclic loading. The third part is the thermomechanical constitutive model of the mechanical behavior of the SMA wire. Effects of the stacking sequence, the applied stress level, and the pre-strain level of SMA on fatigue behavior of laminated composites were studied. Good agreement between theoretical and experimental results revealed the ability of the present model.

Experimental analysis of fiber-reinforced laminated composite plates with embedded SMA wire actuators

Shape memory alloy (SMA) wires are effective smart actuators since they provide relatively large actuation force and strain in a very limited space. Embedding SMA wires in flexible laminated composite plates or shells allows for creating active structures for morphing applications. However, the design of such structures is challenging due to the nonlinear thermomechanical coupling of SMA materials, the adhesion of the SMA actuators to the resin, the effect of temperature on the adhesion strength, the heat transfer between the SMA wires and the surrounding laminate, and the convection boundary conditions. This paper presents an experimental analysis of smart fiber-reinforced composite laminated plates with embedded SMA wires, focusing on the relationship between the applied electric current, measured temperature of the SMA wires, and the resulting tip deflection. A temperature-based control method was developed to achieve the required wire temperature and tip deflection as quickly as possible. Results showed that the fiber-orientation angle of the composite plies and the convection boundary conditions have significant effects on the structure’s actuation. With cyclic actuation, damage starts around the heated SMA wires and can grow to cause delamination at areas between neighboring SMA wires and yielding of the matrix material, resulting in permanent deformation.

Flutter performance of shape memory alloy-embedded 3D woven flexible composite plate under subsonic flow

Recently, 3D composites have gained prominence over 2D composites due to their remarkable through-the-thickness reinforcement that enhanced performances of structures subject to multi-directional stress conditions. However, it is at the expense of reduced in-plane properties. 3D composites also increased damage tolerance due to their high impact and delamination resistance properties, which are susceptible in 2D composites. In aeronautics, both are major concerns in primary structures such as lifting and control surfaces due to high vibrational loads from the airflow. Advancements in the aeroelasticity of aircraft structures show an increasing trend in using smart materials with composite structures for improved aeroelastic performance. An example is combining shape memory alloys (SMAs) with composites for improving damping, stiffness, and vibrational characteristics by utilizing stress generation and strain accommodation properties of SMAs in response to temperature and load, respectively. Published works are mostly numerical in nature, and experimental research is noticeably lacking as aeroelasticity is multidisciplinary and involves both structural and aerodynamic methodology. In this work, 3D composites with embedded SMA wires (for improved in-plane properties) are evaluated in terms of flutter performance in wind tunnel flutter testing under low airspeed conditions. Three 3D orthogonal interlock configurations with a different interlocking pattern of yarns with SMA wire were considered. These 3D configurations are layer-to-layer (L2L), through-the-thickness (TT), and a modified interlock (MF) structure that provides the strongest grip to SMA wire than L2L and TT. The effect of SMA positioning, at mid and near to trailing and leading edges of the cantilevered composite plate, on the aeroelastic flutter properties is also investigated. Results showed that activating SMA wires embedded in 3D structures have significantly improved post-flutter properties while there is a decrement in flutter speed and flutter frequency due to increased flexibility of deflected plate in the airflow by SMA-induced stresses. Among 3D structures, L2L with SMA near to trailing edge showed significant improvement in post-flutter properties by decreasing 22.2% in twist limit cycle oscillation (LCO) amplitude while L2L with SMA at mid showed a decrement of 9.5% for bending LCO amplitude. Hence, this work showed that embedding SMA is beneficial for mitigating the post-flutter vibrations but at the consequence of reduced flutter speed and frequency of flexible composite plate.

A nonlinear aerothermoelastic model for slender composite beam-like wings with embedded shape memory alloys

This paper reports the formulation of an aerothermoelastic tool developed to investigate the behavior of flexible beam-like wings made of a hybrid adaptive material. Here, hybrid materials are defined as laminated composites additionally reinforced with embedded shape memory alloy wires. As main novelties, the proposed model couples geometrical, material, and aerodynamic nonlinearities to the thermal dynamics of SMA wires undergoing Joule’s effects, thereby establishing a multi-physical nonlinear problem. Geometrical nonlinearities were taken into account via an FE model of a 2D Timoshenko’s beam experiencing large deformations. Material nonlinearities were incorporated by a semi-empirical micro-mechanical model that computes the properties of hybrid laminates. To complement, nonlinear aerodynamic effects were introduced via an unsteady strip theory method in the time-domain, along with a nonlinear stall model and an assumption of follower aerodynamic forces. A set of numerical aerothermoelastic cases was performed by assuming various layups and SMA temperatures, with the objective of tailoring the aeroelastic response of hybrid wings. These cases were shown to lead to a considerable reduction in both post-flutter oscillations and post-divergence amplitudes as the SMA temperature increases. The outcomes have indicated compelling evidences on the applicability of embedded SMAs for structural, shape or aeroelastic control of flexible wings.

A unified modeling method for dynamic analysis of GPLs-FGP sandwich shallow shell embedded SMA wires with general boundary conditions under hygrothermal loading

In this research, the dynamic analysis of graphene platelets (GPLs) reinforced functionally graded porous (FGP) sandwich shallow shell embedded shape memory alloy (SMA) wires with general boundary conditions under hygrothermal loading is conducted. Four different porosity distributions of FGP reinforced with four various GPLs dispersion patterns are considered. Based on the Brinson formulation, the constitutive equation of the SMA is established. The energy functional of the sandwich shallow shell is constructed by employing the Hooke’s law and the first-order shear deformation theory (FSDT). Ultimately, the dynamic characteristics of the sandwich shallow shell are obtained by solving the energy functional with the Rayleigh-Ritz method. After the verification of accuracy and reliability, parametric studies on the effects of material properties, geometrical parameters, and boundary conditions are investigated.

Development of a constitutive model considering functional fatigue and pre-stretch in shape memory alloy wires

Shape memory alloy (SMA) wires integrate functionality into composites and encourage the design and creation of adaptable smart structures. Upon the application of cyclic loading, however, the functional properties of SMA wires can decrease significantly resulting in functional fatigue. To simulate this cyclic behavior, an SMA material model with logarithmically evolving and temperature dependent functional fatigue is developed. Pre-stretch is also considered to simulate structures with embedded pre-stretched SMA wires. The material model is fit to a set of tests (constant strain, isobaric, isothermal tension, isothermal cyclic tension) performed on SMA wires. The fit demonstrates an excellent agreement with the experimental results with minor discrepancies. The simulations show the capabilities of the model to evolve the residual strains, residual stresses, hysteresis and hardening in the presence of cyclic loading. Additionally, the isobaric actuation behavior and the reorientation response of the model are validated using experiments from the literature. The fitted and validated model is then used to simulate the response of a rubber specimen with two embedded SMA wires subjected to cyclic thermal loading. The simulated rubber specimen illustrates the loss of functionality after the applied cyclic loading and highlights the importance of not exceeding design temperature loads. Furthermore, the complex thermomechanical loading in the SMA wires displays the importance of including temperature or stress dependence for defining functional fatigue.

Shape memory alloy based 3D printed composite actuators with variable stiffness and large reversible deformation

Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft polymer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufacturing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators.

Experimental investigation of sandwich panels with hybrid composite face sheets and embedded shape memory alloy wires under low velocity impact

AbstractThis experimental study was conducted to investigate the behavior of hybrid composite sandwich panels with superelastic shape memory alloy (SMA) wires under low velocity impact (LVI). Square‐shaped sandwich panels were made few of a foam core and hybrid composite structures with carbon fiber and glass fiber, in which prestrained superelastic SMA wires were embedded between the layers. The sandwich panels had symmetrical and asymmetrical lay‐ups and SMA wires were placed between the layers with different states. LVI tests were performed by drop weight impact testing machine. Moreover, damaged areas of the panels were estimated using thermography. The experimental results showed that the impact performance of the panels improved after embedding SMA wires. The presence of the SMA within the composite sandwich structure prevented the full perforation of the samples and reduced the internal delamination area. The utilization of SMA wires embedded in front face sheet, which is subject to the direct impact, is more effective than the utilization of wire in the back face layer. It was also found that increasing the layers of the back face and asymmetrication of the structure were more effective than the use of SMA wires in the symmetric structure in improving the panel impact resistance.

Tensile behavior of multilayer 3D smart woven composites embedded with shape memory alloy (SMA) wires

Shape memory alloys (SMA) are reputable for their capability of regaining shape at certain temperatures even after large deformations. In the martensite phase, when a load is applied on SMA wire, it accommodates strain rather than breakage by unfolding its lattice that results in improving damping and stiffness. Also, SMA generates stresses due to phase transformation from martensite to austenite at higher temperatures. This coupling effect of SMA in response to load and temperature makes its use for improving properties of composites by embedding in composite structures. The major factor considered during embedding SMA wires into composite structures is the compatibility between SMA and matrix. SMA wires should have excellent adhesion with matrix otherwise, cracking and delamination in the composite will occur. Therefore, different techniques are carried out for surface modification of SMA wire to improve the bonding between matrix and SMA wire. These techniques are expensive, time-consuming and sometimes give undesirable results. An alternative approach used in this research is to weave SMA wires in 3D structures for providing better grip to these wires before composite fabrication. 3D structures have higher through-the-thickness properties and delamination resistance, but their in-plane properties are lower than 2D laminated composites. Due to the weaving of SMA wires into 3D structures, binder yarns provide a better grip to SMA wire that ultimately increases the interfacial strength of composite while SMA wire improves the tensile properties of 3D structures. Results show that a single SMA wire embedded in three different 3D configurations contributes in improving the tensile properties of each 3D structure depending on the interlocking behavior of fibers with SMA wire. The layer-to-layer 3D configuration loosely grips SMA wire, hence SMA wire faces less resistance upon activation and improves Young’s Modulus to 34.9%. The modified 3D structure provides a strong grip to the SMA wire, hence limitise the increment of Young's Modulus to 16.06%. Tensile behavior along with structural failures of SMA embedded 3D woven composites are discussed in detail.

Vibration Analysis Of Nitinol Shape Memory Alloy In Carbon Fibre Reinforced Polymer Composites

Owing to high specific strength and stiffness, composites find wide applications in automobile and aerospace industry. In this paper, an attempt has been made to study the vibration characteristics of embedded shape memory alloy wire (SMA). Earlier, experimental modal analysis was carried out on the carbon fiber reinforced epoxy composite beams (CFRP beam) embedded with shape memory alloy wire manufactured by hand lay-up process. Increased levels of pre-strain up to 4% on shape memory alloy wire resulted in maximum increment in natural frequency when activated at 75°C. The experiment also investigates change in modal frequencies in CRPF plates embedded with the SMA wires. The selected pre-strain for experimentation was 4% pre-strain actuated at 75°C.

Effect of embedded shape memory alloy wires on the mechanical behavior of self-healing graphene-glass fiber-reinforced polymer nanocomposites

In this paper, the effect of embedded shape memory alloy (SMA) wires on the mechanical behavior of glass fiber-epoxy polymer composite reinforced with graphene nanoplatelets (GnPs) was studied. Composites with different GnPs contents, SMA wires number and pre-strain levels were prepared by hand lay-up method. Then, the composite samples were subjected to the bending tests to evaluate the bending strength, bending elastic modulus and healing efficiency. The fracture surface of samples was also characterized by SEM observations. The results showed that the bending behavior of samples was improved to 13.3% by adding 0.2 wt% GnPs. In contrast, the bending strength was decreased by 24.9% with increasing the number of SMA wires in the composite sample. However, the healing efficiency was increased by 57.4% with increasing the number of SMA wires and pre-strain levels. Furthermore, an improvement in the bending strength and healing efficiency can be achieved using GnPs and SMA simultaneously. Moreover, the polymer composite containing GnPs and SMA wires exhibited better interfacial adhesion between the resin and glass fibers.

Effect of Shape Memory Alloy Wires on the Buckling Behavior of Fiber Metal Laminates

Buckling behavior of shape memory alloy (SMA) reinforced fiber metal laminates (FML) was experimentally investigated. The SMA reinforced FML specimens with three different pre-strain levels (1, 2 and 3 %) and different number of the embedded wires (2, 4 and 6 wires) were prepared by a specific mold and hydraulic pressure. The effects of the applied pre-strains in the SMA wires, as well as the stacking sequence of the laminate, SMA volume fraction and the location of the wires were studied on the axial and lateral force-displacement diagrams for the specimens during buckling tests. According to the results, 53 % enhancement in the buckling load was obtained for 2 SMA wires reinforced FML specimens in comparison with the specimens without embedded SMA wires. In constant volume fraction of the SMA, pre-straining the wires by 3 % led to 25 % improvement in the buckling load, in comparison with the specimens reinforced with 1 % pre-strained wires. The influence of the FML stacking sequence on the results was also discussed.

Numerical simulation of buckling behavior of thin walled composite shells with embedded shape memory alloy wires

In this research, the buckling behavior of thin walled composite shell with embedded shape memory alloy (SMA) wires is examined numerically. To model the SMA wire properties, constitutive equation of Brinson is used and a UMAT subroutine is developed to link with ABAQUS finite element (FE) model performed to simulate the buckling behavior of composite shells. To validate the FE modeling, some experimental specimens are fabricated by filament winding process and tested under axial compressive loading to analyze the buckling behavior of the structure. The results show that the numerical model has sufficient accuracy and the effect of tensile pre-strain and the number of embedded SMA wires on the buckling capacity of the cylindrical composite shell are investigated. As the results obtained, by embedding 4 SMA wires without pre-strain in composite shell, the critical buckling load increases about 35%. Also, by increasing the pre-strain and the number of SMA wires (more than 4), the stiffness of the structure and the magnitude of the critical buckling load are decreased.

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.

Experimentation of the Bilinear Elastic Behavior of Plain-Woven GFRP Composite with Embedded SMA Wires.

In this paper, a plain-woven glass-fabric-reinforced polymer (GFRP) composite with embedded shape memory alloy (SMA) wires is investigated by means of experiments. The vacuum-assisted resin injection (VARI) method is utilized to fabricate the composite specimens. Quasi-static uniaxial tensile tests are then carried out to evaluate the influence of SMA reinforcement on the stress–strain behavior of the composite. Only the elastic behavior of the composite is considered in the present study. The tensile strain in all the experiments is kept below 2.5% to avoid debonding of the SMA-resin interface, which would lead to failure of the composite. Stress–strain curves are obtained and shown to present a bilinear behavior due to phase transformation taking place in the SMA wires beyond a certain stress threshold.

Static analysis of sandwich plates embedded with shape memory alloy wires using active strain energy tuning method

In this study, static analysis of sandwich plates with flexible core and composite face sheets embedded with shape memory alloy (SMA) wires in the face sheets is conducted. Third-order plate theory is used to model face sheets, and quadratic and cubic functions are assumed for transverse and in-plane displacements of the flexible core. Continuity conditions of transverse shear stresses at the interfaces between face sheets and core and the zero transverse shear stresses conditions on the upper and lower face sheets are satisfied. Also, transverse flexibility and transverse normal strain and stress of the orthotropic core are noted. The SMA wires are placed in the laminated composite face sheets. Constitutive equation of the SMA wires is employed for modeling their behavior. Nonlinear equations of motion and boundary conditions of sandwich plates are derived using Hamilton’s principle. The nonlinear governing equations of the simply supported sandwich plates under uniform and sinusoidal transverse loads are solved based on Navier’s method. The effect of activating embedded SMA wires on bending behavior of composite sandwich plates are investigated using the active strain energy tuning method. The Liang’s constitutive model is employed to obtain the SMA wires recovery force. The obtained results show that activating SMA wires causes a decrease in the deflection and stresses in these plates.

Damping capacity in pseudo-elastic and ferro-elastic shape memory alloy-reinforced hybrid composite beam

Reinforcing a composite beam with shape memory alloy wires may have several benefits such as reduction of buckling risks or elimination of unwanted oscillations. In this paper, the vibration damping of a typical shape memory alloy-reinforced composite or hybrid beam is explored. To formulate the thermo-mechanical behavior of embedded shape memory alloy wires, three-dimensional Panico–Brinson model is employed and tailored to one-dimensional model. This material model can simulate pseudo-elastic and ferro-elastic forms of martensite transformations which occurs in cyclic loadings. Besides, unlike the former studies which rely on classical beam theories, the first-order shear deformation beam theory is used to obtain more accurate estimations of shape memory alloy-wire hysteresis loops and their decaying characteristics. In order to explore the effects of a transient concentrated load applied in the middle of a beam, the governing equations are developed and discretized by differential quadrature–integral quadrature combined method. Incremental time marching solution of the problem is accomplished using the Newmark technique. Results are assessed by comparing with available literature. Considering different types of boundary conditions, the influence of pseudo-elastic and ferro-elastic hysteresis loops on the material damping effects, shape memory alloy volume fraction, and resonance phenomenon is studied in detail.

Strategies for modelling and optimization of bi-stable composite laminates actuated by embedded Shape Memory Alloy wires

Shape-adaptive or morphing capability is regarded as significant to increase aerodynamic performance of airfoils employed in aerospace, wind turbines or race cars, while at the same time reducing the number of moving parts. The inherent bistable behavior of asymmetric cross-ply composites makes them as a suitable candidate for morphing applications with a small energy input, and an efficient way to switch between the two equilibrium configurations is given by embedded shape memory alloy (SMA) wires. However, when a bi-stable composite plate is integrated with SMA wires (Shape Memory Alloy Composite, SMAC), the identification of design parameters, namely laminate size and layup, composite elastic constants, SMA wires number and thermomechanical behavior, SMAC manufacturing cycle, is not straightforward. The present work described the strategies developed by the authors to model and optimize a SMAC subjected to bi-stability and post-manufacturing deflection requirements.

A Biomimetic Flexible Fishtail Embedded With Shape Memory Alloy Wires

In this paper, a biomimetic flexible fishtail actuated by shape memory alloy (SMA) wires is presented. The detailed structure of the fishtail propeller is designed to mimic the muscle and bone structure of a Carassius auratus. The mechanical modeling of the biomimetic fishtail is built; then, constitutive equations and thermal models of embedded SMA wires are described. Next, experiments are carried out to analyze the propulsive performance of the fishtail. Its maximum bending angle is 50° under the conditions of a heating voltage of 14.8 V and a heating time of 175 ms at a water temperature of 24.5°C. The symmetrical characteristic of both sides of the biomimetic fishtail is good, and different fluctuation can be adjusted by changing the heating time. The bending time and recovery time are recorded, and the effect of heating time on oscillation frequency is analyzed. Finally, the propulsive forces of three different heating modes at frequencies of 0.4 Hz, 0.5 Hz and 0.6 Hz are tested and compared. A relatively good heating mode is discovered for controlling the biomimetic fishtail during the experiments. The biomimetic fishtail obtains the largest average propulsive force of 0.041 N at a frequency of 0.8 Hz with a heating time of 80 ms and a bending angle of 22°.

A review of techniques for embedding shape memory alloy (SMA) wires in smart woven composites

Metallic structures, in various industrial fields such as transport and aerospace, are mostly replaced by composite structures having less weight and good strength. There is also a need of intensification of the operational dynamic environment with high durability requirements. So a smart composite structure is required that can manifest its functions according to environmental changes. One method of producing smart composite structures is to embed shape memory alloys in composite structures. Shape memory alloys (SMAs) have significant mechanical and thermodynamic properties and are available in very small diameters less than 0.2mm. These SMAs are embedded into composites for obtaining smart composites having tunable properties, active abilities, damping capacity and self-healing properties. Shape memory alloys are available in different shapes as wires, sheets, foils, strips, etc. For smart composites, mostly SMA embedded are in wire shape. Different techniques are used for embedding SMA wires in composites. SMA wires can be embedded between layers of laminates of composites, or embedded directly as reinforcement in matrix and can be woven into fabrics and used as a reinforcement. This paper reviews the different techniques of embedding SMA wires in composite structures, their pros and cons and their applications.