Embedded Shape Memory Alloy Research Articles

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. Â

Investigation of shape memory alloy embedded wind turbine blades for the passive control of vibrations

This paper investigates hybridized architectures of large wind turbine blade material with the aim to passively suppress uncontrolled vibration. The laminate composite layup of the blade was hybridized by embedding shape memory alloy (SMA) layers, in areas which are recognized as having a major role in the dissipation of energy. The embedded SMA thin sheet was laser patterned in order to improve the interface adhesion and to tailor the flexural stiffness requirement. The response of the blade with new architecture has been investigated in the time domain, to find an optimal composite layup in which the smallest amount of SMA is used while system damping is being maximized.

Enhancement of vibration characteristics in filament wound FRP composite shafts using nitinol wires

PurposeThe purpose of this paper is to investigate the use of embedded Shape Memory Alloy (SMA) nitinol wire for the enhancement of vibration and damping characteristics of filament-wound fiber-reinforced plastic composite hollow shafts.Design/methodology/approachThe plain Glass Fiber-Reinforced Plastic (GFRP) and plain Carbon Fiber-Reinforced Plastic (CFRP) hollow shafts were manufactured by filament winding technique. Experimental modal analysis was conducted for plain hollow shafts of C1045 steel, GFRP and CFRP by subjecting them to flexural vibrations as per ASTM standard C747, with both ends clamped (C-C) end condition to investigate their vibration and damping behavior in terms of first natural frequency, damping time and damping ratio. Nitinol wires pre-stressed at various pre-strains (2, 4 and 6 per cent) were embedded with CFRP hollow shafts following same manufacturing technique, and similar experimental modal analysis was carried out by activating nitinol wires. The first natural frequencies of all the shaft materials were also predicted theoretically and compared with experimental measurements.FindingsAmong the three materials C1045 steel, plain GFRP and plain CFRP, the vibration and damping behavior were found to be the best for plain CFRP. Hence, CFRP shafts were considered for further improvement by embedding nitinol wires at pre-stressed condition. For CFRP shafts embedded with nitinol wires, the damping time decreased; and damping ratio and first natural frequency increased with increase in percentage of pre-strain. In comparison with plain CFRP, 7 per cent increase in first natural frequency and 100 per cent increase in damping ratio were observed for nitinol embedded CFRP shafts with 6 per cent pre-strain. Theoretical predictions of the first natural frequencies agree well with the experimental results for all the shaft materials.Originality/valueThe effect of nitinol on vibration and damping characteristics of filament wound hollow CFRP composite shafts with different pre-strains has not been studied extensively by the previous researchers. This paper addresses the effect of embedded nitinol wires pre-stressed at three varied pre-strains, that is, 2, 4 and 6 per cent on the vibration and damping characteristics of composite hollow CFRP shafts manufactured by filament winding technique.

Studies on shape memory alloy-embedded GFRP composites for improved post-impact damage strength

ABSTRACT Embedding shape memory alloys (SMAs) in composites is a promising method resistance against impact loading.In the present paper, an attempt is made to quantify the improvement in damage mitigation properties of FRP (fibre reinforced plastic)composites by embedding SMA.Numerical modelling of low velocity impact was carried out topredict the delamination in composites and composites embedded with SMA and steel wires. Through modelling, effect of location and quantity of SMA material in decreasing the impact induced delamination size was also studied.Compression after impact (CAI) tests were carried out on pristine and SMA hybrid composite (SMAHC)specimens to quantify the change in damage resistance. Experimental results show an improvement in compressive load-carrying capacity after impact in SMAHC as compared to pristine composites.Experimental results match well with numerical findings in terms of; location of placement of SMA wire and optimum quantity of SMA wires.

Vibration Control of a Flexible Beam with Embedded Shape Memory Alloy Wire

Structural vibrations can damage systems and lead to high cycle fatigue, excess noise or even catastrophic failure. The research presented herein aims to quantify the effect of embedded shape memory alloy (SMA) wire as an active suppression system to mitigate such vibrations in a flexible clamped-free beam. A silicone beam with embedded SMA wire was designed. Natural frequencies were calculated using a frequency response function (FRF) at varying temperatures. Experiments resulted in an average natural frequency shift of 44.7% and an amplitude decrease of 34% at the tip of the beam. Control samples were created using the same dimensions and silicone material. One control sample contained embedded aluminum wire while the other sample contained no embedded material. The addition of the unactuated SMA wire resulted in an average natural frequency shift of 160% and amplitude decrease of 44.6% while the actuated SMA wire resulted in a shift of 258% and amplitude decrease of 63.6%. The natural frequency of the embedded aluminum wire sample remained the same at low and high temperatures, leading to the conclusion that the frequency shift of the SMA sample was a result of the shape memory effect.

Compact Modular Cycloidal Motor With Embedded Shape Memory Alloy Wires

In this study, we develop a rotary motor using embedded shape memory alloy (SMA) wires, with the aim of realizing a novel compact and modular motor that can generate high-torque bidirectional continuous rotation. Thus, we focus on designing the motion transmission mechanism and torque amplifier of the motor. The designed motion transmission mechanism that functions to convert the contraction/expansion of the SMA wires to rotational motion enables the motor to generate continuous rotation with relatively short-length SMA wires. Additionally, a double-disc cycloidal speed reducer designed as the torque amplifier allows the motor to reliably generate high torque with a compact structure due to its simple configuration, size variability, and torque amplification functionality. One of the advantages of the motor is that an actuating module could be additionally incorporated into the motor to achieve higher torque. In this case, the overall size and weight of the motor are marginally increased although the output torque capacity almost doubles. Hence, the energy density of the motor significantly increases. The study describes the main concept, operating principle, design, and experimental results of the output torque capacity, positioning characteristics, and frequency response of the proposed motor.

Natural Frequency Analysis of Composite Skew Plates with Embedded Shape Memory Alloys in Thermal Environment

In this study, free vibration analysis of laminated composite skew plates with embeddedshape memory alloys under thermal loads is presented. The plates are assumed to be made of NiTi/Graphite/Epoxy with temperature-dependent properties. The thermo-mechanical behavior of shape memory alloywires is predicted by employing one-dimensional Brinson’s model. The governing equations are derivedbased on first-order shear deformation theory and solved using generalized differential quadraturetechnique as an efficient and accurate numerical tool. Some examples are provided to show the accuracyand efficiency of the applied numerical method by comparing the present results with those availablein the literature. A parametric study is carried out to demonstrate the influence of skew angle, pre-strainand volume fraction of shape memory alloys, temperature, and stacking sequence of layers on the naturalfrequencies of the structure. Results represent that shape memory alloys can change the vibrationalcharacteristics of shape memory alloy hybrid composite skew plates by a considerable amount. Thenumerical results also reveal that the effect of shape memory alloy wires on natural frequencies ofcomposite plates with simply supported boundaries is higher than those with clamped boundaries.

Mitigation of flutter vibration using embedded shape memory alloys

Aeroelastic flutter is a major concern for designers of planes, boats, turbines and other systems that experience aerodynamic loading. The typically undesirable phenomenon can cause aircraft instability, high cycle fatigue, excess noise, and in some cases catastrophic failure. This research aims to quantify the effect of embedded shape memory alloys (SMA) as an active suppression system to mitigate vibrations induced by aeroelastic flutter through an experimental investigation. A silicone plate with embedded SMA wire was designed. A subsonic wind tunnel was utilized to actuate flutter vibration. Control samples were created using the same dimensions and silicone material. One control sample contained embedded aluminum wire while the other sample contained no embedded material. Frequencies at the tip of the fluttering plates were calculated using a Fast Fourier Transfer (FFT) at varying temperatures. Experiments resulted in an average natural frequency shift of 44.6% at the sample tip upon actuation of the SMA material. Two dimensional vibrational scanning tests revealed three vibration modes in the fluttering flags. A first bending mode revealed a tip amplitude decrease of 34.4% upon actuation of the embedded SMA material. A second bending mode revealed a tip amplitude decrease of 33.6%. A torsional mode revealed a tip amplitude decrease of 60.7%. The frequency of the embedded aluminum wire sample remained relatively constant at low and high temperatures, leading to the conclusion that the frequency shift of the SMA sample was a result of the shape memory effect.

Enhancement of thermal buckling strength of laminated sandwich composite panel structure embedded with shape memory alloy fibre

The present article reported the thermal buckling strength of the sandwich shell panel structure and subsequent improvement of the same by embedding shape memory alloy (SMA) fibre via a general higher-order mathematical model in conjunction with finite element method. The geometrical distortion of the panel structure due to the temperature is included using Green-Lagrange strain-displacement relations. In addition, the material nonlinearity of SMA fibre due to the elevated thermal environment also incorporated in the current analysis through the marching technique. The final form of the equilibrium equation is obtained by minimising the total potential energy functional and solved computationally with the help of an original MATLAB code. The convergence and the accuracy of the developed model are demonstrated by solving similar kind of published numerical examples including the necessary input parameter. After the necessary establishment of the newly developed numerical solution, the model is extended further to examine the effect of the different structural parameters (side-to-thickness ratios, curvature ratios, core-to-face thickness ratios, volume fractions of SMA fibre and end conditions) on the buckling strength of the SMA embedded sandwich composite shell panel including the different geometrical configurations.

Mechanical characterization of pseudoelastic shape memory alloy hybrid composites

Shape memory alloys (SMAs) are embedded in fiber reinforced plastic (FRP) composites material to achieve properties like higher toughness, shape morphing, variable stiffness etc. Pseudoelastic SMAs are mostly used in improving the energy absorbing capability of composites subjected to impact loading. Pseudoelastic SMA material has the property of absorbing higher strain energy without failure as compared to other engineering materials. Embedding SMA in FRP composites may affect its in-plane properties. This paper deals with study on SMA hybrid GFRP (Glass Fiber Reinforced Plastic) composites to find out the effect of embedding SMA in composites on the mechanical properties such as longitudinal tensile and compressive strength, transverse tensile strength and compressive strength and in-plane shear strength. Experimental results show that longitudinal compressive strength of shape memory alloy hybrid composites (SMAHCs) increases by approximately 30% over pristine composites. There is a marginal change in values of longitudinal tensile strength and in-plane shear strength in SMAHCs as compared to pristine composites whereas there is reduction observed in transverse tensile and compressive strength in SMA hybrid GFRP composites as compared to pristine GFRP composites.

Effect of shape memory alloy wires on the enhancement of fracture behavior of epoxy polymer

The effect of embedded shape memory alloy (SMA) wires on the fracture behavior of epoxy resin was studied. A micromechanical model was developed to predict the double cleavage drilled compression (DCDC) test results for SMA reinforced epoxy specimens. The DCDC tests were performed on SMA reinforced epoxy and the fracture behavior of specimens with different crack lengths was investigated. The experimental tests were conducted on the specimens with 1%, 2% and 4% pre-strain levels in order to investigate the enhancement of crack growth resistance (KR) in the epoxy polymer. The effects of SMA wire diameter, temperature change and applied pre-strain level on the fracture behavior of SMA reinforced epoxy were studied using the present model. The results showed a 67% increase in the changes in the crack growth resistance (KR) in 1% pre-strained SMA reinforced epoxy subjected to temperature change from 25 °C to 65 °C. This improvement was 38% and 16% for the 2% and 4% SMA pre-strained reinforced epoxy, respectively. The results also revealed that, at constant temperature (T = 65 °C), 2% and 4% pre-strains improved (KR) of epoxy by 2 and 4 times, respectively, in comparison with the case of 1% pre-strained wires. The effect of the interface region between SMA wires and epoxy was also discussed in the present study.

Dynamic response of laminated composite beam reinforced with shape memory alloy wires subjected to low velocity impact of multiple masses

The response of laminated hybrid composite beam with embedded shape memory alloy wires subjected to impact of multiple masses is analytically investigated. Two degree of freedom spring-mass system and Fourier series are used in order to study the low velocity impact phenomenon on the resulting hybrid composite beam. A linearized contact law is chosen to calculate the contact force history. The effect of pseudo elasticity of wires as well as the recovery stresses generated in shape memory alloy wires due to shape memory effect is investigated. The beam is subjected to impactors with various masses, radii, and initial velocities. Impacts are occurred on the top and/or bottom surface of the beam. The effects of volume fraction of shape memory alloy wires, location of embedded wires, location of impacts and pre-strain in shape memory alloy wires on the contact force history and the deflection curve of the beam are investigated. The obtained results illustrated that embedding shape memory alloy wires in the laminated composite beam caused the deflection of the beam to occur more local at the points of impact, in comparison with the beams without shape memory alloy wires. Moreover, embedding 0.2 volume fraction of the shape memory alloy wires reduced the maximum deflection of the beam subjected to impact of 2 impactor masses by 57% and 3 impactor masses (on both sides) by 12%. Pre-straining the wires caused more reduction in deflection of the beam under impact loading.

An Experimental Platform for Surface Embedded SMAs in Morphing Applications

This article will address the modeling and control of surface embedded shape memory alloys (SMAs) for the camber modification of a hybrid morphing airfoil. An analytical model will be derived. The results of this models will be discussed and compared to the experiments. The advantages of this modeling approach will be highlighted and alternatives will be briefly revisited. This discussion will figure into the utility of these models in the sizing of a full scale prototype of a SMA actuated active trailing edge of an airfoil. Throughout this article the prototype specifications are detailed and the design choices will be discussed. Performance improvements stemming from the inherent nature of the SMAs will be analyzed. It will be shown in this article that through the use of forced convection the overall cycle time can be reduced.

Implementation of a Hybrid Electro-Active Actuated Morphing Wing in Wind Tunnel

Amongst current aircraft research topics, morphing wing is of great interest for improving the aerodynamic performance. A morphing wing prototype has been designed for wind tunnel experiments. The rear part of the wing - corresponding to the retracted flap - is actuated via a hybrid actuation system using both low frequency camber control and a high frequency vibrating trailing edge. The camber is modified via surface embedded shape memory alloys. The trailing edge vibrates thanks to piezoelectric macro-fiber composites. The actuated camber, amplitude and frequency ranges are characterized. To accurately control the camber, six independent shape memory alloy wires are controlled through nested closed-loops. A significant reduction in power consumption is possible via this control strategy. The effects on flow via morphing have been measured during wind tunnel experiments. This low scale mock-up aims to demonstrate the hybrid morphing concept, according to actuator capabilities point of view as well as aerodynamic performance.

An Experimental Study on the Structural Behaviors of HIRC Beams Using Nickel-Titanium SMA Wires

This paper deals with structural behavior of highly intelligent reinforced concrete (hereinafter, HIRC) beams actuated by embedded shape memory alloy wires through an extensive experimental program. The experiments were conducted under the monotonic loading condition. Based on the structural experiments involving HIRC, load-temperature deflection curve, ductility-effective depth, recovery, crack patterns, and failure mode comparison were made for investigative purposes. The results of the experiments confirmed that the ductility, recovery rates, and other properties of the HIRC specimens reinforced with SMA, wire mesh, fiber, and admixtures were superior to those of the unreinforced RCBs. The experimental results indicate that a good recovery rate in the HIRC beams could be obtained when the SMA wires were heated. Accordingly, the SMA wires could be potentially used for structural self-rehabilitation capability and deformation monitoring in architecture and civil structures.

Numerical Investigation of the Macroscopic Mechanical Behavior of NiTi-Hybrid Composites Subjected to Static Load–Unload–Reload Path

Shape memory alloys (SMAs) are a type of shape memory materials that recover large deformation and return to their primary shape by rising temperature. In the current research, the effect of embedding SMA wires on the macroscopic mechanical behavior of glass–epoxy composites is investigated through finite element simulations. A perfect interface between SMA wires and the host composite is assumed. Effects of various parameters such as SMA wires volume fraction, SMA wires pre-strain and temperature are investigated during loading–unloading and reloading steps by employing ANSYS software. In order to quantify the extent of induced compressive stress in the host composite and residual tensile stress in the SMA wires, a theoretical approach is presented. Finally, it was shown that smart structures fabricated using composite layers and pre-strained SMA wires exhibited overall stiffness reduction at both ambient and elevated temperatures which were increased by adding SMA volume fraction. Also, the induced compressive stress on the host composite was increased remarkably using 4% pre-strained SMA wires at elevated temperature. Results obtained by FE simulations were in good correlation with the rule of mixture predictions and available experimental data in the literature.

Thermal buckling analysis and stacking sequence optimization of rectangular and skew shape memory alloy hybrid composite plates

Abstract This paper deals with analysis and optimization of rectangular and skew composite plates with embedded Shape Memory Alloy (SMA) wires with respect to thermal buckling. The governing equations are derived based on First Order Shear Deformation Theory (FSDT) and the critical buckling temperatures are calculated using Generalized Differential Quadrature (GDQ) method. The influences of SMA volume fraction, lay-up orientation, pre-strain of SMA fibers, dependency of material properties on temperature, and geometrical parameters like skew angle on thermal buckling of the structure are examined. Results demonstrate that SMAs can play a significant role in delaying buckling when the structure is under thermal loads. Then, in the second part of results, optimization of shape memory alloy hybrid composite (SMAHC) plates is presented in order to maximize critical buckling temperatures. A four-layer composite plates with two SMA-reinforced layers is considered for the optimization problem in which the orientations of fibers are the optimization variables. As the critical buckling temperatures cannot be obtained through a closed-form solution, the optimization process takes a lot of time. Therefore, a powerful meta-heuristic algorithm called Firefly Algorithm (FA) is implemented to find the best answers. A comprehensive verification study is also performed to indicate the accuracy and efficiency of both GDQ solution and optimization process.

Simulation-based development of adaptive fiber-elastomer composites with embedded shape memory alloys

Fiber-reinforced composites are currently being used in a wide range of lightweight constructions. Function integration, in particular, offers possibilities to develop new, innovative products for a variety of applications. The large amount of experimental testing required to investigate these novel material combinations often hinders their use in industrial applications. This paper presents an approach that allows the layout of adaptive, fiber-reinforced composites by the use of numerical simulation. In order to model the adaptive characteristics of this functional composite with textile-integrated shape memory alloys, a thermo-elastic simulation is considered by using the Finite Element method. For the numerical simulation, the parameters of the raw materials are identified and used to generate the model. The results of this simulation are validated through deflection measurements with a specimen consisting of a glass fiber fabric with structurally integrated shape memory alloys and an elastomeric matrix system. The achieved experimental and numerical results demonstrate the promising potential of adaptive, fiber-reinforced composites with large deformation capabilities.

Modeling and control of a flexible continuum module actuated by embedded shape memory alloys

Continuum manipulators as a kind of mechanical arms are useful tools in special robotic applications. In medical applications, like colonoscopy, a maneuverable thin and flexible manipulator is required. This research is focused on developing a basic module for such an application using shape memory alloys (SMA). In the structure of the module three wires of SMA are uniformly distributed and attached to the circumference of a flexible tube. By activating wires, individually or together, different rotation regimes are provided. SMA model is used based on Brinson work. The SMA model is combined to model of flexible tube to provide a composite model of the module. Simulating the model in Matlab provided a platform to be used to develop controller. Complex and nonlinear behavior of SMA make the control problem hard especially when a few SMA actuators are active simultaneously. In this paper, position control of the two degree of freedom module is under focus. An experimental control strategy is developed to regulate a desired position in the module. The simulation results present a reasonable performance of the controller. Moreover, the results are verified through experiments and show that the continuum module of this paper would be used in real modular manipulators.

Mechanical characterization of a shape morphing smart composite with embedded shape memory alloys in a shape memory polymer matrix

This article presents a smart composite that shows a reversible bending deformation from an initial flat configuration into a 90° angle controlled by local thermal activation. The novelty lies within the structural fixation of the deformation at room temperature without continuous energy input. The new structural architecture of antagonistic performing shape memory alloy actuators embedded in a shape memory polymer matrix is presented. The shape memory polymer is locally heated from the rigid glassy state to the easily deformable rubbery state by integrated heating wires. By subsequent activation of the different shape memory alloy actuators by resistive heating, the reversible performance can be realized. By deactivation of the heating wires in the shape memory polymer, the shape memory polymer fixates the deformation in its rigid condition. The actuation characteristics of the smart composite are investigated by thermo-mechanical experiments. The performance of the smart composite was investigated by thermo-mechanical experimentation of the individual components. The results show that a 90° bending deformation is feasible with the current material dimensions, but repeated deformation is restricted due to fatigue of the alloy. By superposition of the bending forces of the individual components, it is possible to estimate the bending angle of the composite material.