Shape Memory Alloy Composites Research Articles

Interface stress transfer model and modulus parameter equivalence method for composite materials embedded with tensile pre-strain shape memory alloy fibers.

The constitutive model and modulus parameter equivalence of shape memory alloy composites (SMAC) serve as the foundation for the structural dynamic modeling of composite materials, which has a direct impact on the dynamic characteristics and modeling accuracy of SMAC. This article proposes a homogenization method for SMA composites considering interfacial phases, models the interface stress transfer of three-phase cylinders physically, and derives the axial and shear stresses of SMA fiber phase, interfacial phase, and matrix phase mathematically. The homogenization method and stress expression were then used to determine the macroscopic effective modulus of SMAC as well as the stress characteristics of the fiber phase and interface phase of SMA. The findings demonstrate the significance of volume fraction and tensile pre-strain in stress transfer between the fiber phase and interface phase at high temperatures. The maximum axial stress in the fiber phase is 705.05 MPa when the SMA is fully austenitic and the pre-strain increases to 5%. At 10% volume fraction of SMA, the fiber phase's maximum axial stress can reach 1000 MPa. Ultimately, an experimental verification of the theoretical calculation method's accuracy for the effective modulus of SMAC lays the groundwork for the dynamic modeling of SMAC structures.

Plate end debonding strength model for RC beams strengthened with FRP/SMA composites

Plate end debonding is a common failure mode for fiber reinforced polymer (FRP) strengthened beams. FRP sheets and shape memory alloy (SMA) composites can effectively slow down plate end debonding and improve beam ductility owing to the anchorage effect of SMA wires on the FRP ends. This work aims to comprehensively study the anchorage performance of FRP/SMA composite strengthened beams through both model analysis and experimental investigation. The plate end debonding strength models of existing FRP strengthened beams were initially summarized and analyzed, and an improved model was proposed to predict the debonding strength of FRP/SMA composite strengthened beams at the plate end. Moreover, the anchorage performance and flexural behavior of beams strengthened with carbon fiber reinforced polymer (CFRP) and SMA composites were studied through experiments. The failure mode of the FRP sheet strengthened beams was plate end debonding failure, while the plate end debonding failure of the CFRP/SMA composite strengthened beams occurred at the strengthening zone end, and the peeling failure was delayed owing to the anchorage effect of SMA wires on the ends of the strengthening CFRP sheets. The recovery effect of SMA wires could successfully introduce prestress into CFRP sheets. Moreover, the CFRP strain corresponding to plate end debonding increased because of the anchorage of SMA wires on the CFRP sheet in the strengthening zone. The strength and ductility of the CFRP/SMA composite strengthened beam significantly improved. The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments.

Achieving high strength and large recoverable strain by designing honeycomb-structural dual-shape-memory-alloy composite

Developing shape memory alloys (SMAs) with high strength and large recoverable strain is meaningful to broaden their application in extreme scenarios. In this work, a dual-SMA composite with bio-spired honeycomb structure, which consists of NiTi SMA matrix and NiTiZrCu SMA reinforcement, was designed and fabricated through the combination of 3D printing and hot extrusion. The utilization of honeycomb structure ensures uniform stress transmission and reducing the likelihood of stress concentration. The resulting microstructure, martensite transformation, and superelasticity were studied systematically. The dual-SMA composite exhibited a superior superelasticity with a remarkable recoverable strain higher than 5% and good recovery rate of 96% under a high external stress of 1.4 GPa. Fundamentally, the honeycomb structure in the dual-SMA composite facilitates the occurrence of progressive phase transformation process. The large recoverable strain and good recovery rate were attributed to the coupling effect of superelasticity and linear-elasticity throughout the whole loading process, which enables the dual-SMA composite to sustainably bear the load without undergoing plastic yielding. These findings make it available for designing and fabricating SMA composites with superior performance.

Variable stiffness mechanism of flexible composite laminates implanted with modular SMAHC

In this study, a new flexible hybrid shape memory alloy composites (SMAHCs) with a polydimethylsiloxane (PDMS) matrix containing a shape memory alloy (SMA) of a hybrid Basalt/Kevlar fiber 3D woven composite is developed. The SMAHC is implanted into a glass fiber/PDMS composite laminate in a modular manner to study the stiffness of composite plates in response to temperature. The variable stiffness theory of the SMAHC is derived, and the influence of SMA parameters on the stiffness of the SMAHC is analyzed. A three-point bending test is performed to determine the stiffness of the composite plates at multiple temperature points in the form of Joule heat driving the composite plates. The stress and temperature distributions of the composite plate are analyzed in Abaqus under a temperature-displacement coupling setting. The results shows that the SMAHC stiffness is negatively correlated with SMA fiber diameter and positively correlated with SMA fiber volume fraction. With an increase in driving temperature, the stiffness of the composite plates tends to decrease. When the end temperature of the austenitic phase transformation is reached, the high-modulus austenitic SMA slightly increase the stiffness of the composite plate. The stiffness improvement is more significant when the SMAHC is placed in the middle area of the laminate and the SMA is located in the tension area. This study may provide a reference for the design of variable stiffness SMAHC for plate composite structures.

Experimental study on flexural behavior of RC beams strengthened with FRP/SMA composites

Fiber reinforced polymer (FRP)/shape memory alloy (SMA) composites are disclosed that can be used to repair cracked members and improve the mechanical behavior of concrete structures. This work aims to synthetically investigate the flexural behavior of reinforced concrete (RC) beams strengthened with FRP/SMA composites through both experimental study and finite element analysis. Five beam specimens are prepared to investigate the effect of important parameters on the flexural behavior of RC beams strengthened with FRP/SMA composites, including the different strengthened materials (i.e., SMA wires, CFRP sheets, and FRP/SMA composites) and different types of FRP/SMA composites (i.e., CFRP/SMA composites and BFRP/SMA composites). The test results showed that the flexural stiffness and capacity improvement of the beam strengthened with only SMA wires were not significant, but the ductility was not reduced. The flexural capacity of the beam strengthened with CFRP sheets was effectively improved, but the stiffness improvement was limited. However, the flexural stiffness and capacity of the beam strengthened with FRP/SMA composites significantly increased. At the same time, the service performance was also improved, FRP/SMA composites could effectively reduce the strain of longitudinal rebars and constrain crack development. Compared to the control beam, the capacity of the beam strengthened with the FRP/SMA composites improved from 17.52% to 40.23%, and the stiffness improved from 9.95% to 17.65%. In addition, the CFRP/SMA composites could more effectively improve the capacity and stiffness of strengthened beams than the BFRP/SMA composites because of the higher elastic modulus of CFRP sheets. The strength of BFRP sheets of the BFRP/SMA composites can be fully utilized after reinforcement. Finally, an iterative method for calculating the recovery stress of SMA wires for reinforcement was proposed and incorporated with finite element method for simulation, which was verified by experimental results.

Deformation mechanism and load transfer in an in-situ NiTi–Nb composite

In this study, the cyclic deformation behaviours of an in-situ Nb nanowire reinforced NiTi shape memory alloy composite were studied by in-situ synchrotron X-ray diffraction measurements. Localized hardening in Nb nanowire and the corresponding localized relaxation in NiTi matrix were detected in the Lüders band front upon stress-induced martensitic transformation, indicating a phase load transfer from the transformed NiTi to Nb nanowire. Based on the load transfer, a self-propagating transformation process performing under an average phase stress lower than the critical transformation stress was proposed, which should be responsible for the Lüders-like deformation of the composite. The change of deformation mode from Lüders-like localized deformation to homogeneous deformation after the first tensile cycle was attributed to the plastic deformation in Nb nanowire and the formation of internal stress gradient field in NiTi upon pseudoelastic cycling.

Microstructure, martensitic transformation, mechanical properties and shape memory effect of (TiBw+TiCp)/Ti-V-Al shape memory alloy composites

In the present investigation, the effect of the volume fraction of B4C ceramic particles on the microstructure, martensitic transformation, mechanical properties and strain recovery characteristics of Ti-V-Al shape memory alloy composites was explored. The results revealed that the addition of B4C ceramic particles resulted in the formation of in-situ TiB whiskers and TiC particles as well as grain refinement. Based on the introduction of in-situ reinforcement and grain refinement, the martensitic transformation temperature of Ti-V-Al shape memory alloy composites gradually increased, as the B4C ceramic particle content increased from 0.5 vol.% to 10.0 vol.%. In summary, a lightweight Ti-V-Al shape memory alloy composite with high performance, including a higher martensitic transformation temperature, improved thermal cycling stability, higher strength and larger elastic modulus, can be obtained by adjusting the volume fraction of B4C ceramic particles.

Revealing the interface structure of {111} type I twin in Ti-Ni-Hf shape memory alloy composite

• The interface of martensite twins in Ti-Ni-Hf shape memory alloy composite was studied. • The formation mechanisms of {111} type I twins in Ti-Ni-Hf alloy was revealed. • The lattice dislocations and misfit dislocations of the interface of martensite variant are identified. In the present study, the interface of martensite twins in Ti-Ni-Hf shape memory alloy composite was studied by high resolution transmission electron microscopy in terms of atomic structure. The results reveal that two varieties of interface structure for {111} type I twins are observed, which is determined by the interior substructure (001) compounds twin. The formation of {111} type I twins can be attributed to the interaction between the misfit dislocations on (001) plane and ( 1 ¯ 11) twin boundary. In addition, the corresponding characteristic parameters of misfit dislocation were calculated in theory. The theoretical value of disregistry factor and average spacing for the misfit dislocations are well in good agreement with the experimental results.

Modeling the role of phase boundaries on the pullout response of shape memory wire reinforced composites

Shape memory alloy (SMA) wire-reinforced composites are being widely adopted in several applications. The interactions of the SMA wires with the matrix are quite complex due to heterogeneous strain distributions arising from phase transformations in SMA wires. There have been few studies of the role of the phase boundaries and their effect on debonding of the SMA wire. In this work, a discrete particle approach is used to model the effect of microstructure on the debonding of SMA composites. The force versus displacement response is studied under pullout loading conditions and the microstructure is found to have a strong effect.

Static analysis of shape memory alloy (SMA) reinforced composite

Many engineering applications are using Shape Memory Alloy (SMA) composites as smart structures. The actuators, aircraft, smart bridges, and civil structures are some applications of SMA composites. SMA materials can alter the stress-strain distribution within structures in a controlled manner. The effective response of the composite depends on the SMA fiber as load transfer occurs through this medium. Due to this, there is a need to understand the relationship between the variation of mechanical properties and the static behavior of SMA reinforced composite. In this paper, the effect of SMA tuning on static deformation and equivalent stress of the composite has been analyzed with the help of Finite Element Analysis (FEA). The results obtained from finite element analysis are presented, and the selective case is validated by suitable experimentation. The experimental and numerical results were found to be comparable.

Augmentation of low frequency damping via hydrogen-doping in a hybrid shape memory alloy composite

Carbon fiber reinforced polymer (CFRP) composites hybridized with hydrogen-doped NiTi wires can be used to design structures requiring high stiffness and high damping in the low frequency range, such as helicopter blades. The current work investigates aging and hydrogen-doping for high damping without hydrogen embrittlement. We establish a hydrogenation treatment that (i) results in a response that is repeatable in the martensitic phase and after exposure to composite processing temperatures and (ii) increases the loss factor in NiTi wires by nearly 470%. By embedding H-doped wires exhibiting the highest damping into the interlayers of a [0/±45]s carbon/epoxy laminate at a volume fraction of 0.1, the hybrid NiTi-CFRP composite loss factor increases by 170%. The measured dynamic properties were found to be close to micromechanical predictions based on the properties of the NiTi and CFRP.

Conceptual design and numerical studies of active flow control aerofoil based on shape-memory alloy and macro fibre composites

ABSTRACTActive flow control for aerofoils has been proven to be an effective way to improve the aerodynamic performance of aircraft. A conceptual hybrid design with surfaces embedded with Shape-Memory Alloy (SMA) and trailing Macro Fibre Composites (MFC) is proposed to implement active flow control for aerofoils. A Computational Fluid Dynamics (CFD) model has been built to explore the feasibility and potential performance of the proposed conceptual hybrid design. Accordingly, numerical analysis is carried out to investigate the unsteady flow characteristics by dynamic morphing rather than using classical static simulations and complicated coupling. The results show that camber growth by SMA action could cause an evident rise of Cl and Cd in the take-off/landing phases when the Angle-of-Attack (AoA) is less than 10°. The transient tail vibration behaviour in the cruise period when using MFC actuators is studied over wide ranges of frequency, AoA and vibration amplitude. The buffet frequency is locked in by the vibration frequency, and a decrease of 1.66–2.32% in Cd can be achieved by using a proper vibration frequency and amplitude.

Thermoelastic and vibration response analysis of shape memory alloy reinforced active bimorph composites

In this paper, thermoelastic and free vibration responses of hybrid Shape Memory Alloy (SMA) and E-glass fiber-reinforced composites are investigated using finite element analysis. We consider four composites for analysis and comparison of performances, (1) single layer SMA fiber-reinforced hybrid composite (unimorph SMAHC), (2) a two-layer (cross-ply) SMA fiber-reinforced hybrid composite (bimorph SMAHC), (3) single layer SMA fiber-reinforced with a honeycomb core, and (4) single layer SMA fiber-reinforced with reentrant-honeycomb or auxetic core. We analyze the bending response of all the aforementioned composite structures, focusing on the bimorph anticlastic and synclastic bending with negative and positive Gaussian curvatures, respectively. The uniqueness of this work is utilizing the shape memory effect of the SMA fibers to achieve active shape control of low-stiffness and lightweight auxetic composite structures. We investigated the free vibration response and analyzed the effect of the fiber volume fraction and the fiber orientation angle on the natural frequency of the system. Further, the role of the reentrant angle and stiffness of honeycomb struts on the overall effective mechanical properties of the ply is also studied. Results confirm the non-linearity of the parametric combination and the importance of optimization of these parameters for improved Gaussian curvature. The findings are envisaged to be useful for the design of lightweight rigidizable space structures and tensairity structures.

Fabrication and characterization of aluminum - magnetic shape memory alloy composites

Smart composites, manufactured with embedded functional materials, hold the potential for a new type of structural health monitoring systems. The work herein focuses on how embedding Ni 43 Co 7 Mn 39 Sn 11 metamagnetic shape memory alloy (MMSMA) sensory particles into pure aluminum matrix modifies the chemical constitution and mechanical properties of both materials. Martensitically transforming particles in pure Al or Al alloys can interact with crack tip stress fields and undergo stress-induced martensitic transformation. This process emits acoustic signals and changes the magnetic state of the particles, which can then be exploited using acoustic monitors and/or magnetic sensors to determine the crack locations. Fabrication of these composites consisted of consolidation of homogeneously mixed powder precursors containing 10 vol% of Ni 43 Co 7 Mn 39 Sn 11 MMSMA particles. Elemental composition, hardness, and elastic modulus of the embedded particles and resulting diffusion region between the particles and the matrix were determined using wavelength dispersive spectrometry and instrumented nanoindentation. Elastic constants of the sintered bulk composites were also experimentally determined using resonant ultrasonic spectroscopy (RUS). Compositional analysis revealed that the diffusion region contained a diverse group of intermetallics. Nanoindentation results demonstrated that the diffusion region exhibits a high hardness value of 10.0 ± 0.3 GPa and an elastic modulus of 163 ± 5 GPa, as compared to the embedded particles having a hardness of 4.5 ± 0.4 GPa, and elastic modulus of 127 ± 6 GPa. Poisson's ratio and the stiffness tensor components (C 11 , C 12 , and C 44 ) were found to be 0.34, 214 GPa, 111 GPa, and 52 GPa, respectively, through RUS. The important material properties determined in the present study, especially the interface properties, can be used to model the composite system to optimize the particle size, distribution, and the size of the interfaces for desired bulk mechanical properties and damage sensing ability.

Experimental and numerical investigation on the low-velocity impact response of shape memory alloy hybrid composites

The impact response of shape memory alloy hybrid composite (SMAHC) prepared by vacuum-assisted resin infusion was investigated experimentally and numerically. The impact properties of shape memory alloy composites under three impact stages were characterized. A numerical simulation method is used to simulate the impact damage evolution process of SMAHCs. The experimental results are consistent with the numerical results, which further verified the effectiveness of the laminate against impact load after embedding SMA. The impact threshold energy value of impact damage of SMAHCs was found by numerical simulation. The results show that the impact failure of SMAHC laminates requires more energy than GF/epoxy composites due to the excellent energy absorption capacity of SMA.

Nonlinear dynamics of earthquake-resistant structures using shape memory alloy composites

Earthquake-resistant structures have been widely investigated in order to produce safe buildings designed to resist seismic activities. The remarkable properties of shape memory alloys, especially pseudoelastic effect, can be exploited in order to promote the essential energy dissipation necessary for earthquake-resistant structures. In this regard, shape memory alloy composite is an idea that can make this application feasible, using shape memory alloy fibers embedded in a matrix. This article investigates the use of shape memory alloy composites in a one-story frame structure subjected to earthquakes. Different kinds of composites are analyzed, comparing the influence of matrix type. Both linear elastic matrix and elastoplastic matrix with isotropic and kinematic hardening are investigated. Results indicate the great energy dissipation capability of shape memory alloy composites. A parametric analysis allows one to conclude that the maximum shape memory alloy volume fraction is not the optimum design condition for none of the cases studied, highlighting the necessity of a proper composite design. Despite the elastoplastic behavior of matrix also dissipates a considerable amount of energy, the associated residual strains are not desirable, showing the advantage of the use of shape memory alloys.

Ductile–Brittle Variation Phenomenon and a Special Transformation-Induced Plasticity Effect in NbTi-NiTi Composite

In order to study the transformation-induced plasticity (TRIP) effect in a NiTi shape-memory alloy composite, an in situ NbTi-NiTi composite was prepared by vacuum arc melting, hot forging and wire drawing. An unusual ductile–brittle variation phenomenon was observed by means of a series of tensile tests. The composite was brittle in the absence of transformation at 200 °C, and the fracture strain was about 2%. With lowering the tensile temperature, the composite became ductile when stress-induced martensitic transformation occurred, and the elongation increased to about 18% (a ninefold increase) during tensile test at room temperature. This ductile–brittle variation phenomenon indicates that the stress-induced martensitic transformation of NiTi alloy helps to improve the ductility of the composite, which is just the exhibition of TRIP effect in the NbTi-NiTi composite. Different from conventional TRIP steels, the TRIP behavior in NiTi induces only an increase in the elongation, but not any increase in fracture strength.

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

In the present paper, vibration behavior of hybrid laminated composite cylindrical shells reinforced with shape memory alloy fibers is investigated. Material properties of shape memory alloy fibers and composites are accurately considered temperature dependent. Thermo-mechanical properties of shape memory alloy fibers with uniform temperature change are calculated using Brinson’s one-dimensional constitutive law. Love’s first approximation and first-order shear deformation theory of shells with the von Kármán type of geometrical non-linearity are used in conjunction with Hamilton’s principle for deriving the equations of motion. The generalized differential quadrature method is employed to solve the coupled partial differential equations. The effects of pre-strain, volume fraction, phase transformation, location of shape memory alloy fibers, boundary conditions and temperature on the fundamental frequency of the hybrid laminated composite cylindrical shells are studied. Results indicate that a small amount of shape memory alloy fibers significantly increases the fundamental frequency and vibration control of the hybrid laminated composite reinforced with shape memory alloy hybrid laminated composite cylindrical shells.

Microstructure evolution and superelasticity behavior of Ti-Ni-Hf shape memory alloy composite with multi-scale and heterogeneous reinforcements

In the present study, the in-situ TiB whisker was introduced into the Ti-Ni-Hf shape memory alloy composite by the in-situ reaction of the Ti-Ni-Hf alloy powder and TiB2 powders. The (Ti,Hf)2Ni phase also precipitated, accompanied with the formation of TiB phase. Moreover, the residual TiB2 particles can be observed, as the TiB2 content was higher than 0.7 wt%. Thereinto, the larger scale reinforcements constituted the quasi-continuous network structure. The smaller scale reinforcements distributed in the interior of the network structure. The two-scale reinforcements showed the uniform distribution at macroscopic level and inhomogeneous distribution at microscopic level. The single stage B19′↔B2 martensitic transformation occurred in the Ti-Ni-Hf composites. In addition, the martensitic transformation temperatures continuously decreased with the increased TiB2 content owing to the compositional and mechanical effect. The moderate TiB2 addition not noly enhanced the matrix strength, but also significantly improved the superelasticity. The excellent superelaticity with the completely recoverable strain of 4 % can be obtained in the Ti-Ni-Hf composite containing 0.7 wt% TiB2.

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.