NiTi Shape Memory Alloy Fibers Research Articles

Microstructure characterization and mechanical properties of the 304SS-(NiTif/FeAl) metal-intermetallic laminate composites

In this work, a novel continuous NiTi Shape Memory Alloy Fiber Reinforced (SMAFR) B2-FeAl based metal-intermetallic laminate (MIL) composite was prepared via two-step vacuum hot pressing combined with “multi-thin foils” stacking configuration. The microstructure characterization of the composite was conducted by using X-ray diffractometer, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. The compressive and tensile properties of the composites were measured. Results indicated that the SMAFR MIL composite exhibits multi-layer structure consisting of residual stainless steel layer, newly-formed intermetallic layer and intermediate transition layer. The intermetallic layer is composed of several sublayers with the boundaries of centerlines, and B2-FeAl phase is the main phase in this layer. NiTi fibers locate at the centerlines in the intermetallic layer and show a uniform distribution. A metallurgical interfacial bonding between NiTi fiber and FeAl matrix was obtained through the inter-diffusion of Ni, Ti and Al elements across the interface. In the intermediate transition layer, B2 phase was also the dominant phase, and a large amount of fine Al-rich precipitates dispersed in the matrix. Compared with the MIL composite without NiTi fibers, the SMAFR MIL composite possesses superior compressive and tensile properties, which are mainly attributed to (Ⅰ) high tensile properties of NiTi fiber, (Ⅱ) a good interfacial bonding of NiTi/B2-FeAl, (Ⅲ) strong interfacial reaction products, and (Ⅳ) pullout effect of NiTi fibers.

Displacement recovery and energy dissipation of crimped NiTi SMA fibers during cyclic pullout tests

Abstract This study examines the cyclic pullout behavior of two types of cold-drawn NiTi shape memory alloy fibers, such as paddled and crimped fibers. For this, two diameters of 1.0 and 0.7 mm are considered. The experimental cyclic pullout results show that the deep crimped fibers produce a higher maximum pullout resistance than the shallow crimped fibers. When heated, the shallow crimped fiber increases the diameter more significantly than the deep crimped fiber, whereas the fiber wave depth decreases more than the deep crimped fiber. Thus, the maximum pullout resistance increases for the heated shallow crimped fiber and decreases for the heated deep crimped fiber. The displacement recovery ratio (DRR) reduction with an increasing slip is significant for the fiber with a low anchoring bond. The high anchoring bond fiber also introduces a higher average DRR than the fiber with a relatively low anchoring bond. Under heating treatment, the average DRR increases due to the prestressing in the fiber due to the shape memory effect. However, the anchoring bond of the fiber is enough to produce prestressing in the fiber. The anchoring bond of the fiber and the prestressing also influence the energy dissipation (ED). The higher anchoring bond results in a higher ED value, and the prestressing in the fiber contributes more to the increased ED values.

Effect of heat treatment and end-hook geometry on pullout behaviour of heavily cold worked superelastic NiTi shape memory alloy fibres embedded in concrete

In this study, superelastic fibres were fabricated from heavily cold worked shape memory alloy (SMA) wire followed by heat treatment, with the goal of enhancing fibre pullout performance and simplifying the fibre production process. The effects of annealing at 350 °C, 450 °C, and 550 °C for 20, 40, and 60 min on the tensile properties of the cold worked SMA were studied. Monotonic and cyclic single fibre pullout tests were conducted using an embedment length of 30 mm. The fibres had straight, 3D, 4D, and 5D end-hook geometries and were embedded in normal strength (NS), high performance (HP), and ultra-high-performance (UHP) concrete. The results demonstrated that heat treatment at 350 °C for 20 and 40 min produced significantly higher peak load, pullout energy, average bond strength, and equivalent bond strength values as compared to the properties of fibres exposed to other temperatures and durations. Heat treatment at 350 °C for 40 min showed the highest re-centring and cumulative energy dissipation under cyclic pullout. Pullout performance significantly increased when either mechanical anchorage or concrete strength were increased. Among the SMA fibre geometries, 5D in NS concrete, 4D and 5D in HP concrete, and 3D and 4D fibres in UHP concrete generated sufficient resistance for martensitic transformation that resulted in a significantly higher re-centring ratio and cumulative pullout energy under cyclic loading than was observed for their steel counterparts.

Uniaxial compressive behaviour of mortar cylinders reinforced with crimped NiTi shape memory alloy fibres

This study investigated the axial compressive behaviours of cement mortar reinforced with crimped shaped memory alloy (SMA) fibres produced by cold drawing. The performance of the crimped fibre was investigated in term of tensile behaviour, deformation recovery, recovery stress and pullout behaviour. After that, compressive tests of mortar reinforced with two types of SMA fibres, namely, dog-bone-shaped fibres and crimped fibres, were conducted to compare their compressive behaviours. The results showed that both types of SMA fibres increased the compressive strength of mortar, and a 1.0% volumetric ratio of SMA fibres is effective to increase the compressive strength of mortar, whereas a 0.5% volumetric ratio did not significantly increase the compressive strength. The recovery stress of the SMA fibres induced by the shape memory effect does not significantly increase the compressive strength of mortar. However, when crimped SMA fibres with a 1.0% volumetric ratio were heated and recovery stress was induced, they controlled volume expansion more effectively after cracking than crimped SMA fibres without recovery stress. The findings indicate that crimped SMA fibre with recovery stress can provide crack-bridging capacity.

Flexural and toughness properties of NiTi shape memory alloy, polypropylene and steel fibres in self-compacting concrete

Self-compacting concrete presents good workability to fill complicated forms without mechanical vibrations. This concrete is often reinforced with fibres to improve the strength and toughness. This study investigated the use of nickel -titanium (NiTi) shape memory alloy fibres in comparison with polypropylene and steel fibres in self-compacting concrete. The performances of the fresh fibre–reinforced self-compacting concrete are explored by slump flow and J-ring experiments. Meanwhile, the static and cyclic flexural tests are conducted to estimate the bending resistance strength performance, residual deformation and recovering capacity of shape memory alloy, polypropylene and steel fibre–reinforced self-compacting concrete. Moreover, the flexural toughness of the shape memory alloy, polypropylene and steel fibre–reinforced self-compacting concrete is calculated using four different codes. The shape memory alloy fibre–reinforced self-compacting concrete with 0.75% volume fraction presents the largest flexural strength, re-centering ability and toughness in comparison with polypropylene and steel fibre–reinforced self-compacting concretes. The experimental results demonstrated the beneficial influence of the shape memory and superelastic properties of NiTi in postponing initial crack formation and restricting the crack widths.

Interfacial characteristics and normal mechanical strength of a NiTi shape memory alloy fiber reinforced Mg3AlZn (SMAFR-AZ31) composite sheet

In this paper, a novel NiTi shape memory alloy fiber reinforced Mg3AlZn (SMAFR-AZ31) composite sheet was successfully fabricated by laminate structure design combined with hot pressing method using Mg3AlZn (AZ31) foils and continuous NiTi shape memory alloy fibers. The interfacial microstructure of the SMAFR-AZ31 composite sheet was systematically characterized by a high resolution transmission electron microscopy (FEI-TEM Talos F100) combined with an FEI Helios 600i focused ion beam/scanning electron microscopy (FIB/SEM) system. The normal tensile strength of the SMAFR-AZ31 composite sheet was tested using a novel direct tensile sample configuration with the tensile direction perpendicular to prior AZ31 foils. Results showed that a well-densified AZ31 matrix and uniformly distributed NiTi fiber reinforcements were obtained in the SMAFR-AZ31 composite sheet after hot pressing. A continuous interfacial reaction layer consisting of nanocrystalline-amorphous mixture and a few intermetallic phases were formed around the NiTif/AZ31 interface. The nanocrystalline was identified as dual phase coexistence grains of MgO and TiO2, and the amorphous phase was a mixture of Mg–Ti–O and Mg–O. A newly Ti2Ni intermetallic phase that obeys a specific orientation relationship with NiTi fiber ([4‾21‾] NiTi// [1‾12] Ti2Ni, (132) NiTi// (11‾1) Ti2Ni with an angle difference of 6.27°) precipitated adjacent to the interface reaction layer. A Ni-rich intermetallic phase identified as AlNi formed at the NiTif/AZ31 interface. Furthermore, it is found that large plastic deformation occurred near the interface reaction region in the AZ31 matrix, which is responsible for the successful embedding of NiTi fibers. Compared with the AZ31 laminate sheet without NiTi fibers, the SMAFR-AZ31 composite sheet possessed a superior normal tensile strength, which is attributed to the formation of the amorphous phase at the NiTif/AZ31 interface.

Fabrication, microstructure characterization and mechanical property of the Ti6Al4V-(NiTif/Mg3AlZn) laminate composite

In this paper, an innovative NiTi shape memory alloy fiber reinforced Ti6Al4V-(NiTif/Mg3AlZn) metal-metal laminate composite (SMAFR-MML) was successfully fabricated by vacuum hot pressing method using Ti6Al4V (TC4) foils, Mg3AlZn (AZ31) foils, commercial pure Al foils and continuous NiTi shape memory alloy fibers. The phase constituent analyses of the composites were conducted by X-ray diffractometer (XRD). The microstructure characterizations and elemental analyses of the composites were examined by a field emission scanning electron microscopy (FE-SEM) equipped with an energy dispersive spectroscopy (EDS). The tensile mechanical properties of the composites were comparatively investigated with those of the MML composite without NiTi fibers and as-received AZ31 foils. Results showed that a continuous Mg-Ti elements diffusion layer with a thickness of ∼2.0 μm was formed at the TC4/AZ31 interface, and Mg2Al3 as well as Al8Mn5 phases discontinuously precipitated in the AZ31 matrix near the interface. Similarly, a continuous ∼1.7 μm thick Mg-Ni-Ti elements diffusion layer was formed at the AZ31/NiTi fiber interface, and Al3Ni2 phases precipitated adjacent to the NiTi fiber at the interface. Compared with the AZ31 foils and the MML composite without NiTi fibers, the SMAFR-MML composite possessed a superior comprehensive mechanical properties, which are attributed to the high strength and toughness of TC4 layers, good interfacial bonding at AZ31/NiTif interface and the plastic deformation and fracture of NiTi fibers during tensile process.

Crack-closing performance of NiTi and NiTiNb fibers in cement mortar beams using shape memory effects

This study evaluated the crack-closing performance of NiTi and NiTiNb shape memory alloy (SMA) fibers in cement mortar beams. In addition, the effects of the geometry and number of SMA fibers were evaluated. For this purpose, material tests were performed to assess the mechanical and thermal properties of the SMA fibers, as well as the components and shape recovery ratios. Three-point bending tests were then carried out to generate a crack approximately 0.5 mm wide in cement mortar beams with the SMA fibers, which were placed along an artificial crack in the bottom of the beam at mid-span. The crack-closing performance of the SMA fibers was evaluated with the increase in temperatures and the number of fibers. The crack-closing ratios were more efficient in straight-shape and NiTi fibers.

Influence of Embedding SMA Fibres and SMA Fibre Surface Modification on the Mechanical Performance of BFRP Composite Laminates.

In this paper, a new shape memory alloy (SMA) hybrid basalt fibre reinforced polymer (BFRP) composite laminate was fabricated and a new surface modification method with both silane coupling agent KH550 and Al2O3 nanoparticles was conducted to enhance the interface performance. The mechanical performance of BFRP composite laminates with and without SMA fibres and the influence of SMA surface modification were studied in this paper. Different SMA fibre surface treatment methods, including etching with both H2SO4 and NaOH, modification with the silane coupling agent KH550 and new modification method with both KH550 and Al2O3 nanoparticles, were conducted to enhance the bonding between the SMA fibres and polymer matrix. Scanning electron microscopy (SEM) was used to observe the micromorphology of the SMA fibre surfaces exposed to different treatments and the damage morphology of composite laminates. The mechanical performance of the composites was investigated with tensile, three-point bending and low-velocity impact tests to study the influence of embedded SMA fibres and the different surface modifications of the SMA fibres. The results demonstrated that the embedded Ni-Ti SMA fibres can significantly enhance the mechanical performance of BFRP composite laminates. SMA fibres modified with both the silane coupling agent KH550 and Al2O3 nanoparticles illustrate the best mechanical performance among all samples.

Improved fracture toughness of NiTi shape memory alloy fiber-reinforced Ti-Al metal-intermetallic-laminate composite

In this paper, the fracture toughness of Ti-Al metal-intermetallic-laminate (MIL) composite with and without NiTi shape memory alloy fibers was comparatively investigated via a three-point bending test. The results indicated that the fracture toughness of the NiTi shape memory alloy fiber-reinforced (SMAFR) Ti-Al MIL composite was almost twice as much as that of the Ti-Al MIL composite without NiTi fibers. The improved toughness of the SMAFR MIL composites is mainly attributed to the plastic deformation and breakage of the NiTi fibers. In addition, the debonding of NiTi fibers, the repeated deflection of the main crack in the intermetallic layers, and the grain refinement of the intermetallic contribute to the toughening of the SMAFR MIL composite through absorption of energy.

Effect of enhancement of interface performance on mechanical properties of shape memory alloy hybrid composites

Effect of enhancement of interface performance on mechanical properties of shape memory alloy hybrid composites (SMAHCs) was investigated in this work. Composite laminates without Ni-Ti shape memory alloy (SMA) fibers, with Ni-Ti SMA fibers polished, corroded and modified by silane coupling agent KH550 were taken into comparison to investigate the effect of surface treatments. Surface morphology of Ni-Ti fibers under different treatments were observed with scanning electron microscope. The mechanical performance of specimens without Ni-Ti fibers and with Ni-Ti fibers under different treatments were investigated through tensile, three-point bending and low-velocity experiments. The morphology and micromorphology were observed to study the effect of different surface treatment methods. The conclusion shows that embedded Ni-Ti SMA fibers can enhance the mechanical performance of composite laminates. However, the performance of Ni-Ti SMA fibers was restrained by the poor interface performance. After surface treatments, SMAHCs illustrate better mechanical performance owing to the enhanced interface performance. Among all the surface treatment methods, modification with silane coupling agent KH550 shows the best effect.

Prestressing effect of cold-drawn short NiTi SMA fibres in steel reinforced mortar beams

This study investigated the prestressing effect of cold-drawn short NiTi shape memory alloy (SMA) fibres in steel reinforced mortar beams. The SMA fibres were mixed with 1.5% volume content in a mortar matrix with the compressive strength of 50 MPa. The SMA fibres had an average length of 34 mm, and they were manufactured with a dog-bone shape: the diameters of the end- and middle-parts were 1.024 and 1.0 mm, respectively. Twenty mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B × H × L) were prepared. Two types of tests were conducted. One was to investigate the prestressing effect of the SMA fibres, and the beams with the SMA fibres were heated at the bottom. The other was to assess the bending behaviour of the beams prestressed by the SMA fibres. The SMA fibres induced upward deflection and cracking at the top surface by heating at the bottom; thus, they achieved an obvious prestressing effect. The beams that were prestressed by the SMA fibres did not show a significant difference in bending behaviour from that of the SMA fibre reinforced beams that were not subjected to heating. Stress analysis of the beams indicated that the prestressing effect decreased in relation to the cooling temperature.

Deformation Mechanisms in NiTi-Al Composites Fabricated by Ultrasonic Additive Manufacturing

Thermally active NiTi shape memory alloy (SMA) fibers can be used to tune or tailor the effective coefficient of thermal expansion (CTE) of a metallic matrix composite. In this paper, a novel NiTi-Al composite is fabricated using ultrasonic additive manufacturing (UAM). A combined experimental-simulation approach is used to develop and validate a microstructurally based finite element model of the composite. The simulations are able to closely reproduce the macroscopic strain versus temperature cyclic response, including initial transient effects in the first cycle. They also show that the composite CTE is minimized if the austenite texture in the SMA wires is 〈001〉B2, that a fiber aspect ratio >10 maximizes fiber efficiency, and that the UAM process may reduce hysteresis in embedded SMA wires.

Phase transition induced interfacial debonding in shape memory alloy fiber–matrix system

This paper investigates the phase transition induced interfacial debonding of an embedded superelastic NiTi shape memory alloy (SMA) fiber in an epoxy matrix. In situ interfacial debonding morphology and the stress–strain responses of the fiber are obtained for different fiber diameter and surface roughness. It is shown that, depending on these fiber parameters, a ductile or a brittle debonding can occur. The ductile debonding is caused by the phase transition of the fiber and took place together with the propagating necking front of the martensite domain. Compared with the tension of a free-standing fiber, the fiber–matrix bonding can lead to an increase in the front propagating force (plateau) of the fiber. By using Griffith’s energy balance approach, the crack surface energy is derived and the predictions of crack driving force agree well with the experimental data.

Crack-closing of cement mortar beams using NiTi cold-drawn SMA short fibers

In this study, crack-closing tests of mortar beams reinforced by shape memory alloy (SMA) short fibers were performed. For this purpose, NiTi SMA fibers with a diameter of 0.965 mm and a length of 30 mm were made from SMA wires of 1.0 mm diameter by cold drawing. Four types of SMA fibers were prepared, namely, straight and dog-bone-shaped fiber and the two types of fibers with paper wrapping in the middle of the fibers. The paper provides an unbonded length of 15 mm. For bending tests, six types of mortar beams with the dimensions of 40 mm × 40 mm × 160 mm (B×H×L) were prepared. The SMA fibers were placed at the bottom center of the beams along with an artificial crack of 10 mm depth and 1 mm thickness. This study investigated the influence of SMA fibers on the flexural strength of the beams from the measured force- deflection curves. After cracking, the beams were heated at the bottom by fire to activate the SMA fibers. Then, the beams recovered the deflection, and the cracks were closed. This study evaluated crack-closing capacity using the degree of crack recovery and deflection-recovery factor. The first factor is estimated from the crack-width before and after crack-closing, and the second one is obtained from the downward deflection due to loading and the upward deflection due to the closing force of the SMA fibers.

Pullout resistance of straight NiTi shape memory alloy fibers in cement mortar after cold drawing and heat treatment

In our study, we found cold drawing to be an effective method for enhancing the pullout resistance of NiTi shape memory alloy (SMA) fibers in concrete. The pullout resistance was observed to be dependent on the contact pressure and friction coefficient at the interface between the fibers and the mortar matrix. The drawing process increased the stiffness and yield stress of the fibers and consequently increased the contact pressure at the interface between the fibers and the mortar matrix. Moreover, heat treatment of the fibers after cold drawing was found to noticeably recover the fiber diameter, thereby significantly enhancing the pullout resistance. The enhancement of the interfacial bond strength by heat treatment verified the crack-closing capabilities of SMA-fiber-reinforced cement composites.

An Experimental Investigation of Mechanical Strength of Knotted NiTi SMA Fiber Composite

The paper presents a new design concept for evaluating the mechanical strength of unidirectional composite material with shape memory alloy (SMA) fiber in the presence of matrix crack. NiTi SMA fiber with both ends knotted is used to actively control the composite strength instead of straight fiber for purpose of better ensuring stress transfer from the matrix to the fiber. Experiment is conducted to verify the effectiveness of this new design concept.

A nanometre-scale fibre-to-matrix interface characterization of an ultrasonically consolidated metal matrix composite

Future ‘smart’ structures have the potential to revolutionize many engineering applications. One of the possible methods for creating smart structures is through the use of shape memory alloy (SMA) fibres embedded into metal matrices. Ultrasonic consolidation (UC) allows the embedding of SMAs into metal matrices while retaining the SMA's intrinsic recoverable deformation property. In this work, NiTi SMA fibres were successfully embedded into an Al 3003 (0) matrix via the UC layer manufacturing process. Initially the plastic flow of the Al matrix and the degree of fibre encapsulation were observed using optical microscopy. Then microstructural grain and sub-grain size variation of the Al 3003 (0) matrix at the fibre—matrix interface, and the nature of the fibre—matrix bonding mechanism, were studied via the use of focused ion beam (FIB) cross-sectioning, FIB imaging, scanning electron microscopy, and mechanical peel testing. The results show that the inclusion of the NiTi SMA fibres had a significant effect on the surrounding Al matrix microstructure during the UC process. Additionally, the fibre—matrix bonding mechanism appeared to be mechanical entrapment with the SMA surface showing signs of fatigue from the UC embedding process.

Mechanical behavior of NiTi shape memory alloy fiber reinforced Sn matrix “smart” composites

The detrimental effects of Pb on the environment and human health have provided the driving force for replacement of Pb–Sn solders with Pb-free alternatives. Sn-rich Pb-free solder alloys with silver and copper alloying additions have higher strength but lower elongation-to-failure than Pb–Sn solders. Thus, these alloys are more susceptible to failure under mechanical shock, drop, and thermal fatigue conditions. In this article, mechanical tensile testing of NiTi–Sn3.5Ag single fiber composites demonstrates superelastic behavior of the composite with 85% strain recovery. Fatigue experiments show an evolution in damage over cycles, and an S–N curve shows sharp transition between a nearly vertical low-cycle fatigue behavior and the high-cycle fatigue regime. The solder composite exhibits constant fatigue strength over the superelastic range of the NiTi fiber.

Effect of Hot-Forging on NiTi Shape Memory Alloy Fibers Reinforced Mg Alloy Composite

The composite used in this paper was prepared by hot-pressing ball-milled Mg alloy powders, in which NiTi shape memory alloy fibers in a row were sandwiched. The microstructure were examined by an optical microscope, scanning electron microscope, X-ray diffraction, and transmission electron microscope to measure its microhardness and density. It is shown that the composite consisted of a homogenous matrix with uniformly distributed NiTi shape memory alloy fibers, where recrystallization took place in the Mg alloy matrix that was subjected to plastic deformation. It is known that plastic deformation is beneficial to the refinement of the grains, that is an adequate bonding forms between the matrix and fibers, the density of the composite increases after the hot-forging; its tensile strength increases significantly because of the grain refinement; the hot-forging process improves the properties of the NiTi shape memory alloy fibers reinforced Mg matrix composite.