Shape Memory Alloy Sheet Research Articles

Experimental study of characterization and optimization of shape memory alloy sheet for enhanced mechanical actuation performance for microelectromechanical systems (MEMS)

In this paper, a shape memory alloy (SMA), NiTiNOL, zigzag sheet is used and experimental method is developed using programmable power supply, laser displacement sensor, and K-type thermocouple to investigate actuation and thermo-mechanical behavior of trained SMA zigzag sheet under three different weights, 2.5 N, 3.5 N, and 4.5 N, along with three distinct voltage levels 2.0 V, 3.0 V, and 4.0 V and hysteresis curves are comprehensively examined to get optimum value of load and voltage to achieve better life cycle and actuation as per the requirement of the design. The displacement and temperature data of the zigzag sheet is recorded for every 200 ms for the entire operating life, utilizing heating and cooling processes, of the zigzag sheet and the value of constant displacement for each cycle is optimized which can be used for the development of microelectromechanical systems (MEMS).

Effect of Annealing on the Microstructure, Texture, and Properties of Cold-Rolled Ti50Ni47Fe3 Shape Memory Alloy Sheets

A systematic study was conducted on the impact of annealing treatments on the microstructure and properties of cold-rolled Ti50Ni47Fe3 alloys using optical microscopy, scanning electron microscopy, electron backscattered diffraction, and an electronic universal testing machine. It was found that, during low-temperature annealing (400 °C and 500 °C), the annealing time had no significant effect on the microstructure or properties of the Ti50Ni47Fe3 alloy. Only elongation (δ) increased with the increase in the annealing time, and the grain orientation of the Ti50Ni47Fe3 alloy was <111>//RD (rolling direction). When annealing at medium–high temperature (600 °C), as the annealing time increased, recrystallization and grain growth processes occurred, resulting in a continuous decrease in strength and an increase in δ. Meanwhile, it was found that the grain orientation of the cold-rolled Ti50Ni47Fe3 alloy changed from <111>//RD during the recovery and recrystallization processes to <101>//RD after the grain growth process. The orientation distribution function cross-section φ2 = 45° results indicate that the texture was mainly distributed along the γ orientation line (φ1 = 0~90°, Φ = 54.7°, φ2 = 45°). When annealed at 400 °C and 500 °C, the texture of the Ti50Ni47Fe3 alloys was (111)[uvw]. When the annealing treatment was 600 °C for 120 min, a (110)[uvw] texture occurred. Additionally, ductile fracture occurred in all specimens, and the crack origin was located on one side of the fracture surface, with obvious “Y”-shaped propagation. This article studied annealing treatments of cold-rolled Ti50Ni47Fe3 alloys, providing corresponding theoretical guidance for subsequent production applications.

Laser deposition of titanium layer to enhance two-way shape memory behavior of Nitinol sheet

One of the long-standing mechanical challenges associated with shape memory alloys (SMAs) is achieving and stabilizing an evolving two-way shape memory effect (TWSME) through thermomechanical training/cycling. In most martensitic NiTi SMAs that exhibit zero TWSME at room temperature, the TWSMEs typically require hundreds of cycling repetitions to track trivial values. This demonstrates a promising solution to overcome this challenge. The surface of NiTi SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers on the NiTi surface using a laser beam. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 cycles when the optimum number of five Ti layers was deposited, which was much higher than that of the NiTi sheet (0.3% TWSME) and the sample with a single-time laser path irradiation (1.8%). This was attributed to the low coefficient of thermal expansion of the Ti vs. NiTi sheet, which prevented reverse bending during heating, and the formation of Ti-rich intergranular Ti2Ni(Ox) precipitates, which hindered dislocation movement. Meanwhile, in this sample, owing to the generation of a large residual tensile stress and a large heat-affected zone that led to a reduction in plastic zones, the one-way shape memory effect (OWSME) was retained at values above 90% with good stability over cycling. However, the introduction of additional Ti layers can cause problems in terms of oxygen accumulation within the NiTi sheet, which should be considered when designing a product.

Abnormal Grain Growth and Pseudoelasticity of Industrially Processed Fe–Mn–Al–Ni Shape Memory Alloy Joined by Metal Inert Gas Welding

The effect of metal inert gas welding on the microstructure, abnormal grain growth and the pseudoelastic properties of industrially processed Fe–Mn–Al–Ni shape memory alloy sheets were studied. Square-butt welds were manufactured using similar filler material. The influence of alternating mean arc linear energy on the microstructure of the individual zones is shown. A correlation between the process parameters, the associated heat input, the grain morphology and the α/γ-ratio could be deduced. As the mean arc linear energy increases, the α/γ-ratio in the fusion zone and the heat-affected zone increases. To evaluate the influence of the welding process on abnormal grain growth, a post-weld cyclic heat-treatment was carried out. Although no loss of major alloying elements in the fusion zone was observed after welding, metal inert gas welding has a significant effect on grain growth upon cyclic heat treatment. While abnormal grain growth occurred in the base material, a polycrystalline microstructure characterized by significantly smaller grain sizes was visible in the former fusion zone. Incremental strain tests revealed severe plastic deformation near the grain boundaries in the former fusion zone. However, the grain boundaries of the bamboo-like grown grains in the base material turned out to be more critical for structural failure.

Multi-Response Optimization of Abrasive Waterjet Cutting on r-GO-Reinforced Fibre Intermetallic Laminates through Moth–Flame Optimization Algorithm

Laminated metal-composite structures, also known as fibre metal laminates (FMLs), have emerged as prominent engineering materials in various industries, particularly in the domains of aircraft and automobile manufacturing. These materials are sought after due to their enhanced impact and fatigue resistance capabilities. The machining of FMLs plays a crucial role in achieving near-net shapes for the purpose of joining and assembling components. Delamination is a prevalent issue encountered during the process of conventional machining, thus rendering FMLs are challenging materials to machine. This study aims to investigate the cutting process of novel fibre intermetallic laminates (FILs) using the abrasive water jet (AWJ) cutting technique. The FILs consists of carbon and aramid fibers that are adhesively bonded with a resin matrix filled with reduced graphene oxide (r-GO) nano fillers. Moreover, these laminates contain embedded Nitinol shape memory alloy sheets as the skin materials. Specifically, the study aims to investigate the impact of different factors, such as the addition of reduced graphene oxide (r-GO) in the laminates (ranging from 0 to 2 wt%), traverse speed (ranging from 400 to 600 mm/min), waterjet pressure (ranging from 200 to 300 MPa), and nozzle height (ranging from 2 to 4 mm), on the material removal rate (MRR), delamination factor (FD), and kerf deviation (KD). ANOVA was used in the statistical analysis to determine the most influential parameters and their effects on the selected responses. The optimal AWJC parameters are determined using a metaheuristic-based moth–flame optimization (MFO) algorithm in order to enhance cut quality. The efficacy of MFO is subsequently compared with similar well-established metaheuristics such as the genetic algorithm, particle swarm algorithm, dragonfly algorithm, and grey-wolf algorithm. MFO was found to outperform in terms of several performance indices, including rapid divergence, diversity, spacing, and hypervolume values, among the algorithms compared.

Structural and superelastic properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on industrial process routes by hot rolling

In the present study the structural and functional properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on an industrial process route focusing on hot rolling were investigated. The as-processed condition is characterized by a high fraction of the non-transforming γ-phase, which ensures good workability, but is associated with poor superelasticity. The alloy shows good structural properties with a yield strength of about 600 MPa, which is well above the usual transformation stress related to the martensitic phase transformation for the investigated alloy composition. After solution annealing, a microstructure showing no preferred orientation being characterized by distinctly larger grains is present. The results obtained reveal that the previous thermo-mechanical processing had no impact on the subsequent texture, however, provided a sufficient amount of driving force for abnormal grain growth. Imposed by a cyclic heat treatment, oligocrystalline structures with grain sizes above 10 mm can be achieved in the industrially processed material, which show superelastic properties similar to material processed in small batches in the laboratory.

Effects of thermomechanical treatments on Cu–Al–Mn Shape Memory Alloys

In this paper, the authors, building on the established state-of-the-art knowledge, explore the effects of thermomechanical treatments on the Shape Memory Effect (SME) and damping performance of the Cu–Al–Mn Shape Memory Alloys (SMA). Specifically, to explore the potential of application of this SMA in the form of sheets, for the purpose of designing lightweight structures with high damping performance. The casting and the thermomechanical treatment process were fully laid out in the paper. The characterization of the material in terms of chemical composition and microstructure was performed through optical microscopy and SEM coupled with EDX analysis. The temperature-induced phase transformation behavior of the alloy was explored using DSC. The damping performance was quantified through the loss factor which was measured at different levels of static tensile preload using a DMA machine. The alloy has shown significant workability which permits the fabrication of sheets. However, the material displays high sensitivity to oxidation due to a combined effect of impurities and the hot-rolling process necessary for obtaining thin SMA sheets. Nonetheless, the alloy shows competitive damping performance with respect to commercially available NiTi SMA.

Flexural capacity enhancing of notched steel beams by combining shape memory alloy wires and carbon fiber-reinforced polymer sheets

Combining shape memory alloy (SMA) and carbon fiber-reinforced polymer (CFRP) sheet can achieve a self-stressing SMA-CFRP composite, providing an innovative prestressing method for steel elements. This study applied SMA(Ni–Ti–Nb) wires and CFRP sheets to achieve composite strengthening for notched steel beams. The effectiveness of SMA-CFRP composite for flexural strengthening of notched steel beams was evaluated, and the formula for the maximum allowable moment of the strengthened beams with SMA-CFRP composites was proposed. The four-point bending test results showed that the ultimate load and flexural stiffness of the strengthened beams with SMA-CFRP composites increased by 79.2% and 57.9% more than those of the unstrengthened beams. By comparison, the CFRP-only and SMA-only strengthened beams merely achieved half the ultimate load and flexural stiffness over the strengthened beams with SMA-CFRP composite. Besides, compared to the unstrengthened beams, the notch tip yield load for the strengthened beam with SMA-CFRP composite was increased by 230%, while the notch tip yield load for strengthened beams with CFRP-only and SMA-only just increased by 70% and 125%. These indicate that the SMA-CFRP composite strengthening can significantly delay crack propagation and improve the load capacity and stiffness of notched steel beams. Moreover, the analytical results of the maximum allowable moment were in good agreement with experimental results, indicating the accuracy of the proposed analytical equations.

A two-scale thermo-mechanically coupled constitutive model for grain size- and rate-dependent deformation of nano-crystalline NiTi shape memory alloy

In this paper, a two-scale thermo-mechanically coupled constitutive model is established to predict the grain size (GS)- and rate-dependent deformation of nano-crystalline super-elastic NiTi shape memory alloy (SMA). At the mesoscopic scale, the polycrystalline representative volume element (RVE) is considered as an aggregation of individual grains. Owing to the relatively large volume fraction (VF) of grain boundary in nano-crystalline NiTi SMA, an individual grain is further considered as a composite containing the grain interior (GI) and grain boundary (GB) phases. For the GI phase, a crystal plasticity-based model accounting for the internal heat generation is developed through the fundamental laws of irreversible thermodynamics. The constraint of GB phase on the martensite transformation in the GI phase is considered by introducing a scaling law between the transformation hardening modulus (THM) and GS. Owing to its un-transformable nature and relatively high yielding stress, the GB phase is assumed to behavior constitutively linear thermo-elasticity. To evaluate the thermo-mechanical interactions among the grains, GI phase and GB phase, and obtain the overall response of the polycrystalline RVE, a double inclusion self-consistent homogenization scheme involving the material nonlinearity and thermo-mechanical coupling effect is developed in an incremental form. At the macroscopic scale, the overall thermo-mechanical responses for the specimen of nano-crystalline NiTi SMA are obtained by solving the equations of force balance, deformation compatibility, and thermodynamic equilibrium through an approximation method. Finally, considering the specific texture measured in experiments, the proposed model is validated by predicting the GS- and rate-dependent deformation of nano-crystalline NiTi SMA sheet. Furthermore, the anisotropic thermo-mechanical responses of the sheet caused by the texture are predicted and discussed.

On the characterization of the compressive response of shape memory alloys using bending

Determination of material parameters of metals/polymers under compressive loadings has been sometimes an onerous issue especially for thin sheets and wires. In the present paper, an approach is presented to determine the compressive material constants of the shape memory alloy (SMA) sheets by employing four-point bending tests. A three-dimensional (3D) asymmetric model is presented and implemented in COMSOL software. An SMA strip showing pseudoelasticity at the ambient temperature is trained under tensile loading, and the experimental results are used together with the model to determine the tensile material parameters of the specimen. On the other hand, a sample is subjected to four-point bending, and, after training, the strain distribution at the lateral surface of the sample is captured by using digital image correlation method. The empirical results for bending are utilized along with 3D simulations to determine the compressive material parameters of the specimens. The approach is finally validated by experimental data, and it appears to provide a reliable procedure for the compressive characterization of SMAs. The present research enables users to avoid performing susceptible compression tests and also empowers them to study the compressive mechanical response of a material during training cycles under quasi-static/adiabatic conditions.

Synchrotron-based multiscale study on phase transformation in a cold-rolled NiTi shape memory alloy: Effects of preexisting defects

Deformation and phase transformation of a cold-rolled, textured, shape memory alloy sheet Ni50.6Ti49.4 are investigated via real-time, in situ synchrotron X-ray diffraction and digital imaging correlation. The specimens are subjected to tensile loading along two orthogonal directions. Bulk stress–strain curves (macroscale), strain fields (mesoscale) and X-ray diffraction patterns (microscale) are obtained simultaneously. Martensite nucleation is highly correlated with the preexisting defects. Different from the widely observed Lüders bands within defect-free NiTi, uniform martensite phase transformation occurs in the cold-rolled alloy as a result of the relatively widely distributed preexisting defects, giving rise to progressive growth of martensite, relatively uniform strain fields, the sigmoidal stress–strain curves and increased strain hardening rate. Different favorably oriented martensite variants are induced due to the initial texture, and the martensite phase transformation is more active for loading along the less favorable orientation, giving rise to the anisotropy in the phase transformation.

Fatigue behaviour of notched steel beams strengthened by a self-prestressing SMA/CFRP composite

Integrating a NiTiNb-based shape memory alloy (SMA) and carbon fibre-reinforced polymer (CFRP) sheet can achieve a self-stressing SMA/CFRP composite, providing an alternative active (or prestressing) strengthening technology for steel elements. In this study, the effects of retrofitting methods and fatigue load amplitudes on the fatigue behaviour of notched steel beams were experimentally investigated. The retrofitting methods included SMA patch bonding, CFRP sheet bonding, and SMA/CFRP composite bonding. Test results showed that, compared with strengthening methods of CFRP sheets or SMA patches, SMA/CFRP composite strengthening can greatly increase the fatigue lives and slow down the fatigue crack growth rate of steel beam web cracks and interfacial debonding. Besides, the strengthening effect of the SMA/CFRP composite becomes increasingly significant on notched steel beams as the fatigue load amplitude decreases. Additionally, the fatigue life of the SMA/CFRP composite repaired beams was greater than that of the sum of the fatigue life of repaired beams with SMA or CFRP alone. Moreover, SMA/CFRP composite strengthening can effectively reduce the stiffness degradation rate compared with the other two strengthening methods.

AWJC of NiTi interleaved r-GO embedded carbon/aramid fibre intermetallic laminates: Experimental investigations and optimization through BMOA

ABSTRACT Laminated metal-composite structures or fiber metal laminates (FMLs) are advanced engineering materials currently being utilized in several distinct applications, especially in aircraft and automobile manufacturing industries where an improved impact and fatigue resistance are required. Machining of FMLs is an important task in obtaining near-net shapes for joining and assembly of the components. However, the delamination occurs during conventional machining making FMLs as difficult-to-machine materials. Therefore, the present study will look into the abrasive water jet cutting (AWJC) of novel fiber intermetallic laminates (FILs) made of with alternatively stacked carbon/aramid fiber adhesively bonded with r-GO filled epoxy resin matrix and Nitinol shape memory alloy sheet embedded laminates. The AWJC experiments were performed on fabricated FILs to investigate the cut quality features including kerf taper (K t ), surface roughness (Ra) and kerf deviation (KD) by varying addition of r-GO from 0-2 wt% in the laminates, traverse speed (400-600 mm/min), waterjet pressure (200-300MPa) and nozzle height (2-4 mm), respectively. Statistical results obtained through ANOVA reveals that the traverse speed and nozzle height are the utmost significant variables which influencing the cut quality characteristics followed by waterjet pressure. Surface morphology analysis shows the wear and erosion mechanism of FILs at varying AWJC conditions. For an improved cut quality, the optimal AWJC parameters are achieved through a metaheuristic-based Barnacles Mating Optimization Algorithm (BMOA).

케블라가 보강된 고분자 복합 재료와 형상 기억 합금 시트가 보강된 케블라 에폭시 고분자 복합재료에 대한 탄도충격테스트를 이용한 실험적/수치적 조사

In the present study, the ballistic impact resistance of kevlar reinforced polymer composites and shape memory alloy sheet reinforced kevlar epoxy polymer composites have been compared numerically and experimentally. The test specimens have been fabricated by the hand layup method, and the ballistic impact test has been conducted according to NIJ Level IIIA. In the current research, a new method has been proposed to measure the ballistic impact resistance of the material by using Image J software. From the test results, it has been observed that reinforcement of shape memory alloy in kevlar epoxy polymer composites has increased the ballistic impact resistance by 89-145% for the damaged area compared with plain kevlar reinforced epoxy polymer composite. Also, the damaged area observed in the numerical and the experimental results is almost the same.

Stress concentration in shape memory alloy sheets with circular cavities: Effects of transformation, saturation, and plasticity

The analysis of stress concentration in geometrically heterogeneous smart structures is of great importance. In this study, by utilizing a recent constitutive model which considered both transformation and plasticity of shape memory alloys (SMAs), the stress concentration factor (SCF) in plates with circular cavities is investigated and the effect of phase transformation, saturation, and plasticity which may occur locally is studied. The results show that the conversion of the austenitic phase to the martensite leads to a reduction in SCF. After saturation of phase transformation at the stress concentration point, the SCF increases until the entire sheet enters the martensite phase. In the example under study, the SCF reaches 5.8 which is greatly higher than the elastic SCF. By entering the plastic region locally, the SCF reduces. Also, the modeling of sheets with more than one cavity has been done. It is concluded that extra hole, as a stress relief method, has a stronger effect on decreasing maximum stress concentration of shape memory alloys (considering transformation and plasticity) compared to purely elastic stress concentration studies.

Shape Memory Behaviour of PMMA-Coated NiTi Alloy under Thermal Cycle.

Both poly(methyl methacrylate) (PMMA) and NiTi possess shape memory and biocompatibility behavior. The macroscale properties of PMMA–NiTi composites depend immensely on the quality of the interaction between two components. NiTi shape memory alloy (SMA) and superelastic (SE) sheets were spin coated on one side with PMMA. The composite was prepared by the spin coating method with an alloy-to-polymer-thickness ratio of 1:3. The bending stiffness and radius of curvature were calculated by using numerical and experimental methods during thermal cycles. The experimental radius curvatures in actuation have good agreement with the model. The change in shape results from the difference in coefficients of thermal expansion between PMMA and NiTi. Actuation temperatures were between 0 and 100 °C for the SMA–PMMA composite with a change in curvature from 10 to 120 mm with fixed Young’s modulus of PMMA at 3 GPa, and a change in Young’s modulus of NiTi from 30 to 70 GPa. PMMA–NiTi composites are useful as actuators and sensor elements.

Resistance spot welding of NiTi shape memory alloy sheets: Microstructural evolution and mechanical properties

Resistance spot welding was used for welding superelastic NiTi shape memory alloy sheets. The microstructure of the welded sample showed a fully austenitic NiTi nugget without any visible weld defect due to the insignificant change in the transformation temperature during the welding process. Additionally, the fusion zone has a homogenous microhardness distribution with an average hardness value of ~340 HV, which is below the average hardness value for NiTi base material (~410 HV) because of the large grain size in the weld nugget. The perseverance of the superelastic response as a main functional property of NiTi alloy after the RSW procedure is significant. The welded sample failed via pullout failure mode during tensile shear loading conditions. Face digital image correlation imaging confirmed that strain is localized in the area around the nugget. The dominant fracture mode of the sample during tension-shear loading was ductile, and the EBSD results of the fracture area revealed the excessive deformation around the HAZ resulted in a transgranular fracture. Therefore, resistance spot welding is highly capable of providing a sound, straightforward and reliable joint between NiTi sheets.

A flexible carbon fibre-based electrothermal film for fast actuation of shape memory alloy sheets

Two-dimensional shape memory alloy (SMA) structures have great potential in intelligent and highly flexible robots. However, they have challenges in direct electric heating. This paper proposes a solution to heat SMA sheets using carbon fibres as surface heat sources and indirectly transmits Joule heat generated by the carbon fibres to the SMA sheets. The preparation process of the carbon fibre-based thermoelectric composite film is illustrated in this study. The effect of heat source (carbon fibre) distribution on heat transfer characteristics and the temperature field of the SMA surface is simulated. Then, a functional prototype integrated thermoelectric film and flexible SMA is fabricated, and its effectiveness is verified by local and global activation, respectively. The results show that the composite structure can recover deformation rapidly in 2 s with only 0.7 A running current (applied to each carbon fibre). In addition, the local temperature control method can also realize distributed (spatial dimension) and sequential (temporal dimension) control of the structure. The proposed solution is expected to expand further the design and control of complex, intelligent structures with the development of 4D printing technology.

Finite element simulation and experimental investigation on the effect of temperature on pseudoelastic behavior of perforated Ni–Ti shape memory alloy strips

In the present study, the temperature-dependent pseudoelastic behavior of shape memory alloy (SMA) sheets is studied experimentally and by finite element (FE) modeling. For this purpose, temperature-dependent mechanical properties for Ni–Ti alloy materials are first obtained by using direct tensile and three-point bending experiments at 23 °C, 50 °C, and 80 °C temperatures, respectively. The structure of these materials is examined at different temperatures using SEM images and the XRD test. Furthermore, using the FE model, the pseudoelastic behavior and the effect of temperature on the residual deflection of the prose-shape memory strips with a circular hole under three-point bending loads are studied. After validating the results of the FE model with the results of experimental tests, the effects of various parameters such as the diameter and number of holes on residual deformation and residual strains are investigated. The results show that with increasing temperature, the mechanical properties including the tensile strength, Young’s modulus, yield stress, and flexural strength of SMA strips increase significantly. For solid strips, although increasing the temperature increases the maximum flexural force, in contrast, it reduces the flexural stiffness. In solid strips, flexural stiffness decreases by 5.5% with increasing temperature from 23 °C to 80 °C.

Structural material with designed thermal twist for a simple actuation

Abstract Materials with desired thermal deformation are very important for various engineering applications. Here, a material with the combination of chiral structure and TiNi shape memory alloy (SMA) sheets that performs a twist during heating is proposed. The thermo-mechanical properties of these materials are experimentally investigated. Inspired by this, a car-like material performing translational and rotational motion is designed, which illustrates the potential applications for the next-generation soft robotic devices. Based on this method, one can design remotely manipulated artificial muscles, nanorobots, revolute pairs, and thermal sensors or actuators in a noncontact fashion.