Shape Memory Alloy Composites Research Articles

Enhanced internal friction and specific strength of porous TiNi shape memory alloy composite by the synergistic effect of pore and Ti2Ni

The contradictory relationship between the damping capacity and specific strength remains a challenge for developing metallic damping materials with high strength and stability for energy-absorbing and energy-saving applications. Porous TiNi shape memory alloy composite (SMAC) seems to be a valid strategy to solve this problem. The deformation and damping behaviors of porous SMAC (composed on a particle-like brittle Ti2Ni embedded in ductile TiNi shape memory alloy matrices) were studied and precisely determined using dynamic mechanical analyzer (DMA) and compressive testing in this study. The porous B2–TiNi and Ti2Ni composites exhibit a three-stage deformation character while only one-yielding phenomenon in the compressive stress-strain curves, which is ascribed to the synergistic effect of pore together with the interaction of TiNi and Ti2Ni phases which is different from dense SMAC. This is because porous SMAC with 37% porosity demonstrates exceptional damping property of at least 0.025 at relatively low strain amplitude in −100 to 200 °C temperature range, which resulted from modulus mismatch and the massive interfaces between pore/matrix and TiNi/Ti2Ni. Moreover, the high 113 MPa∙cm3/g compressive specific strength and 27% fracture strain in RT to 130 °C temperature range further dominate on dense SMAC.

Free vibration analysis of laminated composite conical shells reinforced with shape memory alloy fibers

In the present paper, for the first time the vibration behavior of hybrid composite conical shells reinforced with shape memory alloy (SMA) fibers is investigated. The temperature-dependent properties of SMA fibers and composite are accurately considered. Using the one-dimensional constitutive law of Brinson, thermo-mechanical properties such as recovery stresses, elasticity modulus and shear modulus with uniform temperature change are calculated for SMA fibers. Love’s first approximation classical shell theory with von-Karman type of geometrical nonlinearity is used in conjunction with Hamilton’s principle for deriving the equations of motion. A semi-analytical solution is presented so that trigonometric functions are applied in the circumferential direction, and the generalized differential quadrature method is used to discretize the equations of motion along the longitudinal direction. Finally, parametric studies are done to investigate the effects of volume fraction, pre-strain, location of SMA fibers, boundary conditions, semi-vertex angle of the cone, and temperature on the vibration characteristics of the SMA hybrid composite conical shells. It is shown that a proper utilization of SMA fibers significantly increases the fundamental frequency and vibration control of the SMA hybrid composite conical shells.

Stretchable electrochromic devices enabled via shape memory alloy composites (SMAC) for dynamic camouflage

Electrochromic device is a kind of device that can produce color change under the actuation of electric signal. It has attracted wide attention because of its dynamic color change properties, color diversity and convenience of driving signals. These properties highlight its potential application prospects in dynamic display, anti-counterfeiting treatment, biomedicine and other fields. In this study, stretchable photonic crystals are prepared by nano-imprint technology, soft actuators made by shape memory alloy composites (SMAC) were developed based on shape memory alloy (SMA). A stretchable electrochromic device is obtained by integrating the stretchable photonic crystal and SMAC. The electrochromic properties of the device is tested under different voltages. It is found that under the voltage of 1.0 V–1.5 V, it can achieve color changing in entire visible light range, and the total deformation required is less than 30%. The properties of stretchable electrochromic devices based on SMAC is comparative analyzed with that of other electrochromic devices or structures. The results show that the proposed stretchable electrochromic device has the characteristics of low driving voltage, good compliance, wide color changing range, short response time and large effective color changing area. Finally, the excellent soft dynamic display and camouflage functions of stretchable electrochromic devices are demonstrated in a special pattern, and the high impact resistance of the device is verified. The results indicates that the proposed structure is a promising stretchable electrochromic device, which may have great potential for applications of chameleon-like camouflage functional materials and devices.

Delamination analysis in bimaterials consisting of shape memory alloy and elastoplastic layers

Bimetallic shape memory alloy composites, consisting of an active layer of shape memory alloy and a metallic elastoplastic passive layer, are used for designing the sensors and actuators. Delamination analysis in SMA/elastoplastic bimaterial composites is numerically investigated in this study due to the important effects of interface cracks on failure and load bearing response of such composites. It is known that homogeneous elastoplastic material and shape memory alloy show different path-dependent behaviors for prediction of energy release rate near the crack tip. Therefore, evaluation of J-integral for an interface crack between SMA and elastoplastic layers remains a highly complex issue in fracture analysis of such bimaterials. Presuming small-scale phase transformation and yielding zones, path dependency of J-integral for this composite is investigated for a range of mixed-mode loading conditions, and the elastoplastic material properties including the Young’s modulus, hardening slope and yield stress. In addition, the maximum transformation strain within the framework of J2 plasticity for the elastoplastic material and the thermo-mechanical coupling model of Boyd and Lagoudas for the shape memory alloy are studied. Finally, the influence of mixed-mode loading rates on the crack tip fields is comprehensively assessed.

Optimal Design of Shape Memory Alloy Compositeunder Deflection Constraint.

Shape-adaptive or morphing capability in both aerospace structures and wind turbine blade design is regarded as significant to increase aerodynamic performance and simplify mechanisms by reducing the number of moving parts. The underlying bistable behavior of asymmetric cross-ply composites makes them a suitable candidate for morphing applications. To date, various theoretical and experiential studies have been carried out to understand and predict the bistable behavior of asymmetric laminates and especially the curvature obtained in their stable configurations. However, when the bi-stable composite plate is integrated with shape memory alloy wires to control the curvature and to snap from a stable configuration to the other (shape memory alloy composite, SMAC), the identification of the design parameters, namely laminate edge length, ply thickness and ply orientation, is not straightforward. The aim of this article is to present the formulation of an optimization problem for the parameters of an asymmetric composite laminate integrated with pre-stressed shape memory alloys (SMA) wires under bi-stability and a minimum deflection requirement. Wires are modeled as an additional ply placed at the mid-plane of the composite host plate. The optimization problem is solved numerically in MATLAB and optimal design variables are then used to model the SMAC in ABAQUS™. Finite element results are compared against numerical results for validation.

On thermomechanical behaviors of the functional graded shape memory alloy composite for jet engine chevron

This study presents a theoretical work for a novel adaptive jet engine chevron concept based upon embedding the functionally graded shape memory alloy actuators in a composite laminate, termed a functionally graded shape memory alloy actuator composite. The constitutive models of the functionally graded shape memory alloy actuator composites including the monolayer shape memory alloy composites and multilayer shape memory alloy composites with different volume fractions of the shape memory alloy were first given. An example using such models was discussed on a published finite element work on a shape memory alloy hybrid composite jet engine chevron concept to prove the validity of the theoretical work. The thermomechanical behaviors of the functionally graded shape memory alloy actuator composite with different volume fractions of the shape memory alloy subjected to the thermal loading were then discussed using the obtained constitutive model. The tip deflections of the jet engine chevron with different embedding patterns of the shape memory alloy were finally obtained.

Finite element analysis of Al 2024/Cu-Al-Ni shape memory alloy composites with defects/cracks

In this work, a numerical approach to predict the stress field behaviour of defect/crack in shape memory alloy (SMA) particles reinforced composite known as the adaptive composite is presented. Simulation is based on the finite element method. The critical stress field approach was used to determine the stresses around defect/crack. Thereby stress amplification issue is being resolved. In this paper, the effect volume % of shape memory alloy and shape memory effect of reinforcement for as-cast and SME trained composites are examined and discussed. Shape memory effect known as training is achieved by pre-straining of reinforcement particles by equivalent changes in their expansion coefficients.

Microstructure design of the excellent shape recovery properties in (Ti,Hf)2Ni/Ti-Ni-Hf high temperature shape memory alloy composite

The microstructure, martensitic transformation behaviors, mechanical and shape recovery properties of the (Ti,Hf)2Ni/Ti-Ni-Hf composite fabricated by SPS were investigated. The microstructure of the (Ti,Hf)2Ni/Ti-Ni-Hf composite consisted of B19′ martensite matrix interspersed with (Ti,Hf)2Ni phases. The larger (Ti,Hf)2Ni phases distributed at the surface of the original alloy powders and formed network structure, while the fine (Ti,Hf)2Ni phases was also observed in the interior of the original alloy powders. The distribution and the amount of the (Ti,Hf)2Ni phases contributed to the lower transformation temperatures of the (Ti,Hf)2Ni/Ti-Ni-Hf composite. In addition, the strengthening of larger (Ti,Hf)2Ni phases with the network structure at the macro level and precipitation strengthening of fine (Ti,Hf)2Ni phases at the micro level played an important role in the better mechanical and shape recovery properties in the sintered Ti-Ni-Hf composite.

High Damping of Lightweight TiNi-Ti2Ni Shape Memory Composites for Wide Temperature Range Usage

A bimodal porous TiNi-Ti2Ni shape memory alloy composite (SMAC) with 59% porosity was fabricated by sintering Ti-46at.%Ni elemental powders with pore-forming agent. The porous TiNi-Ti2Ni SMAC contains two irregular pores of about 400 and 120 μm. We investigated the microstructure and pore morphology correlated with the mechanical properties and damping capacities of the SMAC. Ti2Ni intermetallic phases with size of 1-3 μm were homogeneously distributed in the TiNi matrix. The porous TiNi-Ti2Ni SMAC exhibits exceptionally high inverse mechanical quality factor (Q −1) of ~0.25 at < 40 °C, which is among the highest value reported for porous/dense shape memory alloys or composites to best of our knowledge, and it shows very high compressive fracture strain of about 25%. Moreover, the fabricated porous SMAC at relatively low strain amplitude can exhibit considerable high Q −1 of 0.06 ~ 0.11 for a wide range of temperature between − 90 and 200 °C, which is attributed to the stress concentration distribution provided by the bimodal structure of pores and the massive interfaces between pore/matrix and TiNi/Ti2Ni. These porous SMACs can be an ideal candidate for using as a lightweight damping material in the energy-saving applications.

Fatigue behavior of glass-fiber-reinforced epoxy composites embedded with shape memory alloy wires

The tensile fatigue behavior of glass-fiber-reinforced epoxy (GF/epoxy) composites embedded with shape memory alloy (SMA) wires prepared by vacuum assisted resin infusion (VARI) processing was investigated. The experiments were performed under cyclic tensile load. The damage mechanism of SMA composites under different stress levels of cyclic loadings was revealed. The fracture surface and fatigue failure modes of the specimens were examined and analyzed according to the damage mechanism under different stress levels. The stress-number (S-N) curves, the residual strength and residual stiffness of specimens were calculated after the experiment. The results show that the fatigue life of SMA composites is more than twice higher than GF/epoxy composites. Microstructural analysis using the scanning electron microscopy (SEM) technique was conducted on fractured surfaces to fully understand the failure mechanism. The fatigue failure modes in SMA composite laminates were revealed.

Improved adhesion between nickel–titanium SMA and polymer matrix via acid treatment and nano-silica particles coating

Shape memory alloy (SMA) composites are the desirable candidate for smart materials that used in intelligent structures. However, the overall mechanical performance of SMA composites depends immensely on the quality of the interaction between SMA and polymer matrix. Therefore, it is necessary to find out an approach to enhance the interfacial property of this composite. In this paper, we modified nickel–titanium SMA wire with nano-silica particles before and after acid treatment. The modification effect on the interfacial strength between SMA and epoxy resin was evaluated. Contact angle analysis, scanning electron microscopy (SEM) observation, and single fiber pull-out test were carried out. The bonding characteristics between modified wire and liquid/cured resin were investigated. We then embedded SMA wire into woven glass fabric/epoxy composite laminates, and manufactured this hybrid composites via vacuum assisted resin transfer molding processing. Three-point-bending test of the hybrid composites was performed to validate the modification effect. Fiber pull-out experiment demonstrates that the interfacial shear strength increases by 6.48% by nano-silica particles coating, while it increases by 52.21% after 8 h acid treatment and nano-silica particles coating simultaneously. For hybrid composites, flexural strength of the two specimens increases by 19.8 and 48.2%, respectively. In SEM observation, we observed large debonding region in unmodified composites, while interfacial adhesion between modified wire and epoxy keeps strong after flexural damage.

Interfacial characteristics and fracture behavior of spark-plasma-sintered TiNi fiber-reinforced 2024Al matrix composites

Embedding of shape memory alloy (SMA) fibers into materials to fabricate SMA composites has attracted considerable attention because of the potential applicability of these composites in smart systems and structures. In this study, 2024Al matrix composites reinforced by continuous TiNi SMA fibers were fabricated using spark plasma sintering (SPS). The interface between the fibers and matrix consisted of a bilayer. The layer close to the fiber consisted of a multiple phase mixture, and the other layer exhibited a periodic morphology resulting from the alternating phases of Al3Ti and Al3Ni. In addition, a small quantity of TiO2 phases was also observed in the interface layer. Based on detailed interface studies of the orientation relationships between the Al3Ti, Al3Ni, and TiO2 phases and the atomic correspondence at phase boundaries, the effects of the interface phases on the fracture behavior of the composites were demonstrated.

Closed-form solution for thermal, mechanical, and thermo-mechanical buckling and post-buckling of SMA composite plates

In this paper, an analytical study on thermal, mechanical, and thermomechanical buckling and post-buckling of symmetric laminated composite plates reinforced with shape memory alloy (SMA) fibers are presented. The closed-form solution used in this study is developed based on the FSDT incorporated with the Von-Karman non-linear strains. The effect of SMA fibers is captured by adding a tensile recovery, stress term that determined using 1-D simplified Brinson’s model, in the constitutive equations of the SMA composite plate. Galerkin technique is implemented for solving the nonlinear partial differential equations of motion to obtain buckling load and post-buckling path. The influence of several parameters such as SMA activation temperature, SMA fiber volume fraction, SMA pre-strain, biaxial ratio, etc., are studied in this work. Due to the generation of recovery force, significant improvement in buckling load is attained by increasing each of the SMA fiber volume fraction, activation temperature or SMA pre-strain.

Enhancement of interfacial bonding strength of SMA smart composites by using mechanical indented method

Abstract Shape memory alloy (SMA) wire reinforced polymer-based composites have been recognized as a new type of smart materials. However, their weak interfacial bonding strength between the wire and its surrounding matrix limits its applications in many engineering industries. In this paper, a new method called “mechanical indentation” is introduced to effectively enhance the interfacial bonding strength of SMA composites. According to the results from a wire pullout test, the interfacial bonding strength of an indented SMA wire composite increased by 4.48–8.58 times as compared with a hand-sanded SMA wire composite at a room temperature condition. Two different sizes of indentations, sparse and dense indentations were studied in detail and the results indicated that the dense indented SMA wire had a better performance in terms of tensile and recovery properties, than that of the sparse indented wire. Furthermore, the interface between the dense indented wire and vinyl-ester (VE) matrix demonstrated a better restoration performance during a repeated loading-and-unloading process at room temperature condition.

Bimetallic shape memory alloy composites produced by explosion welding: Structure and martensitic transformation

The aim of the present work was a study of the influence of explosion welding on the grain structure, chemical composition, phase composition and phase transitions in bimetallic shape memory composites containing the TiNi shape memory alloy as an active layer and one of four alloys having different abilities to react with TiNi alloys as passive layer. Stainless steel was chosen as a non-reacted material, TiNi alloy was used as the alloy with close chemical composition, and Ti6Al4V alloy and copper beryllium (C17200) alloy were chosen as materials which might react with TiNi alloy to form new phases. The results of the study showed that variations in the grain structure and properties of the layers in the bimetal composite depended on the ability of the alloys used for the production of these composites to react with TiNi alloys. If the alloys did not react with TiNi alloy, as in the case of stainless steel, the explosion welding resulted in significant plastic deformation of the layers. This led to a change in the grain morphology, a deep decrease in transformation temperatures and a suppression of the martensitic transformation (a decrease in the volume fraction undergoing phase transformation). In this case, annealing at high temperatures had to be used for recovery of the grain structure and properties of the composite before application. If the alloys were able to react with TiNi alloy to form the intermediate phases, for instance Ti6Al4V alloy, the explosion energy was then expended for the formation of the intermediate layer and the plastic deformation of the basic layers was small. This composite retained the parameters of the martensitic transformation and grain structure and should be subjected to annealing at low temperature to decrease the internal stresses appeared during welding.

On Behaviors of Functionally Graded SMAs under Thermo-Mechanical Coupling

An analytical solution is obtained for the Functionally Graded Shape Memory Alloy (FG-SMA) composites subjected to thermo-mechanical coupling. Young's modulus and thermal expansion coefficient of the material are assumed to vary in different forms of power function through the thickness, with the Poisson's ratio being constant. An SMA constitutive model is combined with the averaging techniques of composite to determine the mechanical properties of the FG-SMA composites. Different phase transformation steps and the corresponding stress distributions through the thickness direction are given. The results show that the average stresses decrease as the transformations proceed.

Numerical simulations and experimental results of tensile behaviour of hybrid composite shape memory alloy wires embedded structures

The shape memory alloys (SMA) possess both sensing and actuating functions due to their shape memory effect, pseudo-elasticity, high damping capability and other remarkable properties. Combining the SMA with other materials can create intelligent or smart composites. The epoxy resin composites filled with Ti-Ni alloys wires were fabricated, and their mechanical properties have been investigated. In this study, stress/strain relationships for a composite with embedded SMA wires are presented. The paper illustrates influence of the SMA wires upon changes in mechanical behaviour of a composite plate with the SMA components, firstly and secondly, the actuating ability and reliability of shape memory alloy hybrid composites.

Review and perspectives: shape memory alloy composite systems

Following their discovery in the early 1960s, there has been a continuous quest for ways to take advantage of the extraordinary properties of shape memory alloys (SMAs). These intermetallic alloys can be extremely compliant while retaining the strength of metals and can convert thermal energy to mechanical work. The unique properties of SMAs result from a reversible diffussionless solid-to-solid phase transformation from austenite to martensite. The integration of SMAs into composite structures has resulted in many benefits, which include actuation, vibration control, damping, sensing, and self-healing. However, despite substantial research in this area, a comparable adoption of SMA composites by industry has not yet been realized. This discrepancy between academic research and commercial interest is largely associated with the material complexity that includes strong thermomechanical coupling, large inelastic deformations, and variable thermoelastic properties. Nonetheless, as SMAs are becoming increasingly accepted in engineering applications, a similar trend for SMA composites is expected in aerospace, automotive, and energy conversion and storage-related applications. In an effort to aid in this endeavor, a comprehensive overview of advances with regard to SMA composites and devices utilizing them is pursued in this paper. Emphasis is placed on identifying the characteristic responses and properties of these material systems as well as on comparing the various modeling methodologies for describing their response. Furthermore, the paper concludes with a discussion of future research efforts that may have the greatest impact on promoting the development of SMA composites and their implementation in multifunctional structures.

Modeling and analysis of laminated shape memory alloy composite plates

In the present work, static deformation, dynamic characteristic, and time response of laminated composite plates with surface-bonded shape-memory alloy (SMA) sheets are modeled. A modified higher order shear deformation theory with Ritz method is utilized. The energy balance equations are used to formulate the nonlinear heat transfer governing equations. The time response of the SMA/elastomer plate and the deflection as well as dynamic characteristics before and after activation of the SMA is computed. A Mathematica code is developed to analyze different plate problems. Parametric studies are performed for proposed structure system to demonstrate the effect of thickness ratio, aspect ratio, material properties, thermal expansion coefficient, electric input power, and thickness of SMA sheet on the transverse deflections, natural frequencies, and response time of the SMA layer. The obtained results are compared to the available studies solved by different theories.

Research on Mechanical Properties of TiNi Shape Memory Alloy Wires Reinforced Al Matrix Composite Material

TiNi/Al shape memory alloy (SMA) composite was fabricated by a vacuum hot-pressing method to investigate the phase , microstructure and mechanical properties. Phase analysis was conducted by XRD . Interface bonding between TiNi wire and Al matrix was observed by using SEM and EDS. Quasi-static and dynamic compressive mechanical properties of the composite were investigated by using electronic universal testing machine (INSTRON5985) and Split-Hopkinson Pressure Bar (SHPB),respectively. The experiment results show that new phases Ni4Ti3 and Ti2Ni precipitined from TiNi wire. Interfacial reactions occurred at the bonding between matrix and TiNi wire, creating a diffusion layer about 2μm thick. Both quasi-static and dynamic compressive mechanical properties are anisotropic , and the degree of the anisotropy increased with the increase of TiNi volume fraction.