Prestrained Shape Memory Alloy Research Articles

Deformation Behavior of Shape-Control Plate Using NiTi Shape Memory Alloy Wire

This study deals with deformation behavior of a shape-control plate which consists of an aluminum alloy plate and a pre-strained NiTi shape memory alloy (SMA) wire. The shape-control plate exhibits reciprocating bending deformation by heating and cooling. Deformation behavior of the plate is examined by electric heating and natural cooling of the SMA wire. Experimental results exhibit that the bending deformation of the plate is considerably stable over more than two thousand heating-cooling cycles and can be well controlled by electric current. Furthermore, the deformation behavior of the plate is analyzed by a simple beam theory for the aluminum alloy plate and Brinson’s one-dimensional constitutive model for the SMA wire taking account of not only martensitic transformation but also rhombohedral-phase transformation. Numerical results describe well the deformation behavior of the shape-control plate observed in the experiments.

RANDOM RESPONSE OF SHAPE MEMORY ALLOY HYBRID COMPOSITE PLATES SUBJECT TO WHITE-GAUSSIAN NOISE AND THERMAL ENVIRONMENT

The random response and thermal buckling of a traditional composite plate impregnated with pre-strained shape memory alloy (SMA) fibers subjected to combined thermal and acoustic loads are investigated using a finite element model based on the first order shear deformable plate theory and von Karman strain-displacement relations to account for moderately large deflection. The thermal load is assumed to be steady state constant temperature distribution, and the acoustic excitation is considered to be a stationary Gaussian pressure with zero mean and uniform magnitude over the plate surface. The governing nonlinear equations are obtained using the principal of virtual work adopting an approach based on the thermal strain being an integral quantity of the thermal expansion coefficient with respect to temperature to account for temperature dependent material properties. The static nonlinear equations are solved by Newton-Raphson numerical technique to get the thermal post-buckling deflection. The dynamic nonlinear equations of motion are transferred to modal coordinates to reduce the computational efforts. The Newmark implicit integration scheme is employed to solve the second order ordinary differential equations of motion. Finally, the buckling temperature, post-buckling deflection and the random response of a SMA hybrid composite plate panel are presented, illustrating the effect of SMA volume fraction, pre-strain, sound pressure level and temperature rise on the panel response.

Thermomechanically micromechanical modeling of prestressed concrete reinforced withshape memory alloy fibers

Concrete is a very popular material in civil engineering, although it exhibits somelimitations. The most crucial limitation is its low tensile strength, compared to itscompressive strength, which results from the propagation of micro-cracks. This may beprevented by using prestrained shape memory alloy wires that are embedded in theconcrete matrix. Upon activation, these wires regain their original shape, and consequentlyinitial compressive stresses are transmitted to the concrete matrix. In this study, athermomechanically micromechanical model of prestressed concrete reinforced by shapememory alloy fibers is presented and examined for different reinforcement aspects. Itwas found that there is a strong relation between the activation temperaturedeviation and the behavior of the prestressed concrete. The relation between thefiber’s volume fraction and the composite response and the effect of the shapeof the reinforcing fibers and residual strain orientations is examined in detail.

Investigation of the phase transformation behaviour of constrained shape memory alloywires

Adaptive or smart hybrid composites consisting of a polymer matrix reinforced by aramid fibres and incorporating pre-strained Shape Memory Alloy (SMA) wires are able to tune some of their properties, such as their shape, the natural vibration frequency or the damping coefficient, in response to an external stimulus. The functional properties of these systems are directly related to the reversible martensitic transformation in the SMA elements. In this work the transformational behaviour of both free SMA wires and SMA wires embedded in polymer matrix is investigated by means of DSC. The martensitic transformation of the constrained wires is impeded by the polymer matrix, while the interface integrity plays a crucial role.

W05K Tailored damping and self-repair of composite materials(International Workshop on "New Frontiers of Smart Materials and Structural Systems")

Composite materials are currently developed not only for their structural properties, but also because they are good candidates to integrate other materials or devices, which bring added functions to the part. Several examples are presented based on recent work performed at LTC, which cover the areas of damping and self-repair. Tailored damping has been addressed following two different routes: (i) active damping using Shape Memory Alloys (SMA) is made possible by embedding pre-strained SMA wires into a host material ; (ii) another route to damp some unwanted frequencies in a composite beam is to introduce a layer with shear thickening properties, which stiffens when the local shear exceeds a given level, without the need for an external energy source. Finally, recent research on self-repair of composites using embedded resin micro-capsules and SMA wires for closing cracks and heating the resin will be presented. In all these examples, manufacturing issues are addressed to bring these concepts closer to practical applications.

Flutter and Thermal Deflection Suppression of Composite Plates Using Shape Memory Alloy

An efficient finite element method for predicting critical temperature, postbuckling deflection and flutter response is developed for composite plates embedded with prestrained shape memory alloy (SMA) fibers. The large panel deflection and the temperature-dependent material properties of SMA and composites are considered in the formulation. The finite element formulation and solution procedure of the incremental updated Lagrangian method for nonlinear temperature-dependent material properties are presented briefly. Flow yaw angle at supersonic speed is also considered. For the static solution, the system equations are solved by using the Newton-Raphson iteration method to determine aerothermal postbuckling deflection under the combined aerodynamic and thermal loads. For the dynamic flutter response, the modal method and time-domain numerical integration are employed. Results show that the critical buckling temperature can be raised high enough so that buckling deflection can be eliminated, and the desired flat and stable region in the temperature-dynamic pressure operating domain can be enlarged greatly for composite surface panels embedded with SMA for supersonic vehicle applications. Weight savings based on critical temperature when SMA is used are also presented.

Interfacial debond of shape memory alloy composites

A theoretical model for the prediction of interfacial behaviour is successfully developed forcomposites with pre-strained shape memory alloy (SMA) fiber. A two-cylindermodel with a thin SMA fibre surrounding by epoxy matrix is employed for apull-out test. The material constants and thermomechanical properties of theconstituents were determined from a series of tensile tests, stress-recovery testsand strain-constrained tests. All this information is then substituted into thenewly developed model so as to predict the debonding behaviour, initial debondstress and critical bonded fibre length. The maximum debond stresses at differentactivation temperatures are predicted and compared with the experimental resultsobtained from the fiber pull-out test. The good agreement between experimentalfindings and theoretical results warrants the application of this new developedtheoretical model on the design of SMA-reinforced composites and structures.

A Basic Study of CFRP Laminates with Embedded Prestrained SMA Foils for Aircraft Structures

This paper presents some basic research results for the application of the smart materials and structural systems to aircraft structure. The authors conducted quasi-static load-unload tests and fatigue tests on several kinds of quasi-isotropic carbon fiber-reinforced plastic (CFRP) laminates with embedded prestrained shape memory alloy (SMA) foils. The damage behavior and the fatigue behavior were evaluated based on the effects of the recovery stress of SMA, and the relationship between the applied strain and the transverse crack density is discussed. It was found that the developed smart materials achieved a maximum improvement of 34% in the onset strain of the transverse cracks and a maximum improvement of 60% in the onset strain of delamination as compared with the standard CFRP laminates in the static condition. However, the fatigue properties of the smart material were not improved due to the material degradation of the 90°-ply at 80°C. The fatigue test by the multistep strain method using a structural element specimen was used to verify the results of coupon tests. The results indicate the possibility of using coupon data as a design database.

Modeling of thermo-mechanical behavior of Ti-Ni shape memory alloy foils embedded in carbon fiber reinforced plastic laminates

Ti-Ni shape memory alloy (SMA) foils are embedded into carbon fiber reinforced plastic (CFRP) cross-ply laminates in order to suppress the occurrence and progress of the transverse cracks in the laminates. When the pre-strained SMA foil is heated, the shape memory effect produces appropriate recovery compressive stress in the direction to suppress transverse cracks. However, Ti-Ni SMA foil has these specific characteristics due to the existence of a rhombohedral phase (R-phase). Thus, in this research, in order to use this SMA foil as an actuator, an extended Brinson model was proposed to clarify complicated behaviors of SMA. Then, for the determination of the parameters in the constitutive equation in this model, experimental tests were performed for the SMA foils. Using this model, several simulations were conducted and compared with experimental results. The agreement indicated that this model could express the thermo-mechanical behavior of the Ti-Ni SMA foil adequately. Finally, the behavior of the SMA foil during the CFRP manufacturing process was calculated on the basis of this model. The calculation results proved that the recovery stress already existed after the manufacturing process and the embedment of 4% pre-strained SMA into CFRP cross-ply laminate had the effect of suppressing the occurrence of transverse cracks.

Evaluation of the damage suppression effect of Ti-Ni shape memory alloy foils embedded in carbon fiber reinforced plastic laminates

In this research, shape memory alloy (SMA) foils were embedded into carbon fiber reinforced plastic (CFRP) cross-ply laminates. When the tensile pre-strained SMA foil is heated, the SMA produces appropriate compressive stress (recovery stress) to suppress the transverse cracks in the laminates. In order to investigate the damage suppression effect, tensile loading–unloading tests were conducted for the CFRP cross-ply laminates. The test results implied that the recovery stress of embedded SMA foil suppressed the occurrence and the progress of the transverse crack. Then, to confirm that the damage suppression effect was caused by the embedded SMA foil, the one-dimensional (1D) shear-lag model considering the behavior of SMA was newly derived. Using this model, the progress of transverse crack density was predicted probabilistically. The simulation results showed the same tendency as the experimental results. As a result, it was proved that the embedment of SMA foils into CFRP laminates is effective to suppress the occurrence and growth of the transverse cracks.

Thermal Buckling Suppression of Supersonic Vehicle Surface Panels Using Shape Memory Alloy

An efficient finite element method for the prediction of critical temperature, postbuckling deflection, and vibration characteristics is presented for traditional composite plates embedded with prestrained shape memory alloy (SMA) wires. The temperature-dependent material properties of SMA and composites and the large deflections are considered in the formulation. An iterative eigensolution is presented to determine the critical temperature, the Newton-Raphson method is employed to obtain postbuckling large deflection, and the eigensolver is used to predict free vibration frequencies about the thermally buckled equilibrium positions. Results show that the critical buckling temperature can be raised high enough and that the postbuckling deflection can be completely suppressed for surface panels of supersonic vehicle applications by the proper selection of SMA volume fraction, prestrain, and alloy composition. Weight savings based on critical temperature in the use of SMA as compared with the traditional composite and titanium plates are demonstrated.

Design of pull-out stresses for prestrained SMA wire/polymer hybrid composites

Shape memory alloy (SMA) materials possess many unique mechanical, thermal and thermal-mechanical properties that govern their temperature-dependent shape memory, superelastic and pseudoelastic effects. SMA actuators, in the forms of wire or strip embedded into polymer-based composite structures are able to control the structures' shape and stiffness in order to accommodate any environment impacts. Due to an intrinsic shape memory effect (SME) of prestrained SMA wires, additional recovery forces, which are able to alternate the dynamic and buckling properties of the structures, are generated upon heating. This heat is usually induced by a means of externally applied current. To fully use the benefit of the SME in SMA composite structures, understanding the interfacial bonding behaviour and stress transfer properties between the embedded SMA wires and matrix is crucial. In this paper, the wire pull-out properties of prestrained SMA wire/polymer composites subjected to different temperatures were experimentally studied. The results indicated that the critical debonding stress, that initiates fully debond at a bond interface between the SMA wire and matrix increased with increasing the externally applied current, and thus changing the phase condition in the wire. This phenomenon was due to the SME of the prestrained wires and can be interpreted by using a newly developed phase–stress–displacement diagram.

Damage suppression in CFRP laminates using embedded shape memory alloy foils

This paper presents an overview of the damage growth suppression effects in CFRP laminates using embedded SMA foils, and was conducted to technically verify the application to aircraft structures. In previous studies, the authors confirmed the damage growth suppression of CFRP laminates with embedded pre-strained shape memory alloy (SMA) foils through both coupon testing and structural element testing. Through detailed observation of the damage behavior, we determined that these effects occurred due to the suppression of the strain energy release rate based on the suppression of the crack opening displacement caused by the recovery stress of SMA foils. These results were verified in this study using a demonstrator test article, which was a 1/3-scaled model of a commercial airliner's fuselage structure (B737 class). To demonstrate the damage growth suppression, the lower panel, which was dominated by tension load, was selected as the evaluation area. The evaluation area was an integrated panel including both the 'smart area' (CFRP laminate with embedded pre-strained SMA foils), and the 'conventional area' (standard CFRP laminate), for direct comparison of the damage behavior. The demonstration was conducted at 80°C in the smart area, and room temperature (RT) in the conventional area using a quasi-static load-unload test method. The demonstrator test article identified that the damage onset strain in the smart area was improved by 30% over that in the conventional area.

Vibration characteristics of SMA composite beams with different boundary conditions

Recently, the development of shape memory alloy (SMA) actuators, in the forms of wire, thin film and stent have been found increasingly in the fields of materials science and smart structures and engineering. The increase in attraction for using these materials is due to their many unique materials, mechanical, thermal and thermal-mechanical properties, which in turn, evolve their subsequent shape memory, pseudo-elasticity and super-elasticity properties. In this paper, a common type of SMA actuator, Nitinol wires, were embedded into advanced composite structures to modulate the structural dynamic responses, in terms of natural frequency and damping ratio by using its shape memory and pseudo-elastic properties. A simple theoretical model is introduced to estimate the natural frequency of the structures before and after actuating the embedded SMA wires. The damping ratios of different SMA composite beams were measured through experimental approaches. The natural frequencies changed slightly at a temperature above the austenite finish temperature of composite beams with embedded non-prestrained SMA wires. However, the increase of the natural frequencies of the beams with embedded prestrained SMA wires were found in both the theoretical prediction and experimental measurements. The damping ratios of SMA composite beams increased with increasing the temperature of the embedded wires with and without being pre-strained. Compressive and local failures of the beams with high wire content are a possible explanation.

Debond induced by strain recovery of an embedded NiTi wire at a NiTi/epoxy interface: micro-scale observation

Rapid development in smart structures has enhanced the great efforts in understanding the mechanical and thermo-mechanical behaviour of shape-memory alloy (SMA) materials. SMAs, in the form of wires and strips, have been embedded into advanced composite structures to control the shape and residual stress of the structures. It is well recognised that the mechanical properties of embedded SMA composites are highly dependent on the integrity of the interface, particularly by the existence of high thermal-induced shear stress at the SMA wire/epoxy interface. This paper discusses the debonding failure mechanism of embedded pre-strained SMA wires in an epoxy matrix environment using the scanning electron microscopy (SEM) technique. It was found that debonds occurred at the SMA wire/matrix interface for a wire with a pre-strained level of 8% at a temperature above A f. Several cracks in the matrix were found around the wire-end region and arrayed along the circumferential direction. A sharp crack, which was propagated towards the radial direction of the wire, was induced in a matrix with high air-bubble content during the wire/matrix debonding process. The effect of high-temperature treatment of SMAs was also studied. It was found that the surface layer of the wire peeled off when the wire was heated at 773 K for 10 min.

806 形状記憶合金箔の回復応力を利用した損傷抑制効果の評価

The focus point of this paper is if Recovery Stress of SMA (Shape Memory Alloys) foil could be used as Damage Suppression system. Recovery Stress is the stress generated owing to SMA's shape memory effect when Pre-strained SMA is restricted and risen in temperature. If Recovery Stress is effective in Damage Suppression, Cross-ply laminates with embedded Pre-strained SMA foils in hot air must be suppressed Transverse Crack Density in 90° ply. According to loading-unloading test, not only the first cracking strain and the crack density of the specimens with Pre-strained SMA foils were suppressed but also the ultimate strain was larger than the specimens without them. In conclusion, that is the hopeful way Pre-strained SMA foils are used as Damage Suppression system.

Non-linear Supersonic Panel Flutter And ControlUsing Shape Memory Alloy

Due to aerodynamic heating, flight vehicles at supersonic speeds are subjected to surface panel temperatures that can potentially reach several hundred degrees. This paper will present the temperature effect on large-amplitude flutter of composite panels, and the suppression of flutter by embedding prestrained shape memory alloy (SMA) in composite panels. The finite element formulation and the two-step solution procedure in conjunction with the incremental method for temperature-dependent nonlinear material properties of SMA are presented briefly. Results are obtained for a laminated composite panel to demonstrate the effectiveness of SMA in control of nonlinear panel flutter.

Enhancing the post-buckling response of a composite panel structure utilising shape memory alloy actuators – a smart structural concept

Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of a laminated panel structure. An extensive experimental and numerical programme has been conducted, of which, results will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy panel is outlined. The panel specimen features 0.3 mm diameter shape memory alloy wires embedded and partially consolidated to the host matrix at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminate. Structural finite element (FE) analysis has been employed to determine the hybrid panel's adaptive response while under the influence of the uniaxial compressive load in excess of its pseudo-critical buckling value. It is shown that, utilising the control authority generated from the small SMA actuator volume fraction employed, the out-of-plane displacement of the post-buckled laminated panel can be reduced. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.

Realization of higher-mode deformation of beams using shape memoryalloy wires and piezoceramics

In this study, shape memory alloy wires and piezoceramic actuatorswere employed in order to generate higher modes on the beam deformationswithout intermediate supporting points. Compressive force was generated andapplied to the beam by the prestrained shape memory alloy wires attached atboth ends of the beam. The piezoceramic actuators applied concentrated momentsto several locations on the beam. Combinations of the compressive force andconcentrated moments were investigated in order to understand the higher-modedeformation of cantilevered and simply supported beams.The first mode shape was obtained by applying heat to the shape memory alloywires so that the wires generated and applied a compressive force to the beam.First and third mode shapes of deformation of the cantilever beam have beengenerated as well as first and second modes of the simply supported beam.

The control of the post-buckling response in thin composite plates using smart technology

Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of various laminated plate structures. An extensive experimental and numerical programme has been conducted, the results of which will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy plates is outlined. Such specimens feature 0.4-mm diameter shape memory alloy wires located within tubing at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminates. Structural finite element analysis has been employed to determine the hybrid plates' adaptive response while under the influence of a uniaxial compressive load in excess of its critical buckling value. It is shown that, utilising the considerable control authority generated, even for a small actuator volume fraction, the out-of-plane displacement of the post-buckled laminates can be significantly reduced. Such displacement alleviation allows for load redistribution away from the specimens' unloaded edges. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.