Large Strain Range Research Articles

Generating two-dimensional ferromagnetic charge density waves via external fields

Two-dimensional (2D) ferromagnetic charge density wave (CDW), an exotic quantum state for exploring the intertwining effect between correlated charge and spin orders in 2D limit, has not been discovered in the experiments yet. Here, we propose a feasible strategy to realize 2D ferromagnetic CDWs under external fields, which is demonstrated in monolayer VSe$_2$ using first-principles calculations. Under external tensile strain, two novel ferromagnetic CDWs ($\sqrt{3}$$\times$$\sqrt{3}$ and 2$\times2\sqrt{3}$ CDWs) can be generated, accompanied by distinguishable lattice reconstructions of magnetic V atoms. Remarkably, because the driving forces for generating these two ferromagnetic CDWs are strongly spin-dependent, fundamentally different from that in conventional CDWs, the $\sqrt{3}$$\times$$\sqrt{3}$ and 2$\times2\sqrt{3}$ CDWs can exhibit two dramatically different half-metallic phases under a large strain range, along with either a flat band or a Dirac cone around Fermi level. Our proposed strategy and material demonstration may open a door to generate and manipulate correlation effect between collective charge and spin orders via external fields.

Soft Capacitive Force Sensors With Low Hysteresis Based on Folded and Rolled Structures

Force sensors made of a polymer material with soft characteristics have application potential in the fields of soft robotics, exoskeletons, and human motion measurement. However, the hysteresis of soft force sensors is generally large because their sensing materials are rubbers with large dynamic viscoelasticity. The problem of large hysteresis caused by this dynamic viscoelasticity needs to be solved to improve the dynamic measurement precision of these force sensors. In this article, we have tested and found that the hysteresis of silicone rubber is significantly reduced when it operates in a large strain range. Therefore, we propose a design idea to allow the silicone rubber to work at large strain ranges involving a folded and rolled capacitive sensor structure based on large prestretching. Compared with previously reported silicone rubber force sensors, this sensor has a lower hysteresis error of 4.73% and a lower repeatability error of 3.42%. In addition, the folded and rolled sensor exhibits quick response, long-term stability, and durability under periodic dynamic load.

Large dynamic strain range slope-assisted Brillouin optical time domain reflectometry based on a graded-index multi-mode fiber.

A slope-assisted Brillouin optical time domain reflectometry system with large dynamic strain range was proposed and demonstrated using graded-index multi-mode fiber (GI-MMF) as sensing fiber. Analysis of the simulated and experimental results indicated that the Brillouin gain spectrum in GI-MMF could be broadened by controlling the coupling efficiency of optical and acoustic modes. The coupling efficiency could be controlled by adjusting lateral offset between single mode fiber (SMF) and GI-MMF. The system realized the maximum strain dynamic measurement of 3000 µɛ with the spatial resolution of 5 m along ∼1 km GI-MMF, and exhibited significant linear relationship between signal intensity and strain at vibrational frequency of 7.83 and 15.47 Hz. The measured error of vibration frequency was less than 0.2 and 1.5 Hz, respectively. The measured strain range of this system was more than three times that of traditional systems based on SMF and could be achieved at relatively low cost.

Quantum spin Hall effect in two-dimensional transition-metal chalcogenides MX5 (M = Zr, Hf and X = S, Se, Te)

Based on first-principles calculations, we have found a family of two-dimensional (2D) transition-metal (TM) chalcogenides MX5 (M = Zr, Hf and X = S, Se, Te) can host quantum spin Hall (QSH) effect. The molecular dynamics (MD) simulations indicate that they are all thermal-dynamically stable at room and high temperature. We have investigated MX5’s electronic properties and found their properties are very similar. The single-layer MX5 are all gapless semimetals without consideration of spin–orbit coupling (SOC). With consideration of SOC, they are all insulators with maximum band gap of 0.187 eV. The evolution of Wannier charge centers (WCC) and edge states confirm they are all QSH insulators. The mechanisms for QSH effect in MX5 originate from the special nonsymmorphic space group features. In addition, the QSH state of MX5 survives at a large range of strain as long as the interchain coupling is not strong enough to reverse the band ordering. Monolayer MX5 expand the TI materials based on TM chalcogenides and may open up a new way to fabricate novel low power spintronic devices.

The relationship between austenite morphology and continuous TRIP effects in forged 4Mn steel

In this study, we developed forged medium-Mn steel (4Mn-3Al-0.38C) with a high product of tensile strength and elongation (PSE) (68.5 GPa·%). The PSE initially increased and then decreased with the quenching temperature. Austenite with various morphologies (including lath, block, flake, and equiaxed types) was obtained in the sample quenched at 730 °C (F730), and it continuously transformed into martensite (67%) during the tensile process. The different austenite morphologies exhibited different stability. The lath and block austenites transformed into martensite in the early deformation stage, followed by the flake and equiaxed austenites. Therefore, transformation induced-plasticity (TRIP) effects occurred continuously in a large strain range to reduce strain localization and stabilize the change of the work hardening rate, providing theoretical guidance for controlling the microstructure of high-PSE medium-Mn steels.

A Hollow Core‐Sheath Composite Fiber Based on Polyaniline/Polyurethane: Preparation, Properties, and Multi‐Model Strain Sensing Performance

AbstractFlexible strain sensors are gradually developing toward being textile‐shaped and multifunctional. Here, a microfluidic spinning strategy with special designed coaxial‐like needles is developed to fabricate conductive fibers with multi‐model strain sensing properties. The coaxial‐like needle can regulate the fiber's structure and characteristics by adjusting the meeting point of core and sheath solution. First, a polyaniline (PANI)/thermoplastic polyurethane (TPU)‐based blended composite fiber (PTBF) with unique hollow‐porous morphology is prepared. The PTBF fibrous sensors with 30 wt.% PANI obtain a large strain range (50% strain), while the PTBFs with 50 wt.% PANI possess a high sensitivity (gauge factor of 160). On this basis, a PANI/TPU‐based core–sheath composite fiber (PTCF) is fabricated by changing the core and sheath solutions. PTCFs exhibit satisfactory multi‐model strain sensing capabilities, including tensile, bending, and pressure. The results show that the resistance of PTCF is extremely sensitive to tensile deformation. The PTCF‐based fibrous sensor can also detect 0–180° bending strains and 0.1–2 N pressure strains. The multi‐model strain sensor can be used in motion monitoring, gesture discrimination, finger‐pressure recognition, and flexible circuit switches. This work may provide a foundation for the direct integration of fiber‐based strain sensors into smart clothing.

Improved Stretchable and Sensitive Fe Nanowire-Based Strain Sensor by Optimizing Areal Density of Nanowire Network.

Flexible strain sensors, when considering high sensitivity and a large strain range, have become a key requirement for current robotic applications. However, it is still a thorny issue to take both factors into consideration at the same time. Here, we report a sandwich-structured strain sensor based on Fe nanowires (Fe NWs) that has a high GF (37–53) while taking into account a large strain range (15–57.5%), low hysteresis (2.45%), stability, and low cost with an areal density of Fe NWs of 4.4 mg/cm2. Additionally, the relationship between the contact point of the conductive network, the output resistance, and the areal density of the sensing unit is analyzed. Microscopically, the contact points of the conductive network directly affect the sensor output resistance distribution, thereby affecting the gauge factor (GF) of the sensor. Macroscopically, the areal density and the output resistivity of the strain sensor have the opposite percolation theory, which affects its linearity performance. At the same time, there is a positive correlation between the areal density and the contact point: when the stretching amount is constant, it theoretically shows that the areal density affects the GF. When the areal density reaches this percolation threshold range, the sensing performance is the best. This will lay the foundation for rapid applications in wearable robots.

Physicochemical effects of pore fluid on the dynamic behavior of reconstituted marine clay

An experimental investigation was conducted to study the effect of pore fluid chemistry on the dynamic behavior of reconstituted marine clay. Sodium chloride solution of 0.4 M and 1 M concentrations was used to induce the physicochemical changes. Strain-controlled undrained cyclic triaxial tests were carried out to evaluate the most important parameters such as shear modulus and damping ratio at a large strain range. The results showed that the effect of pore fluid was more pronounced on cyclic shear modulus values at a strain amplitude of 0.3–1%. Tests were also conducted to study the effect of physicochemical factors on the degradation of normalized modulus G N/G 1 of marine clay specimens reconstituted with distilled water and salt solutions.

Superhydrophobic, biocompatible and durable nanofiber composite with an asymmetric structure for anisotropic strain sensing and body motion detection

Anisotropic strain sensors show multi-directional sensing that can be used to monitor complex human motions. Aligned electrically conductive nanofiber membranes have been candidates for anisotropic strain sensors. Challenges remain for developing nanofiber composite strain sensors with a large workable strain range, corrosion resistance, excellent durability and biocompatibility. Here, we propose a facile vacuum filtration method to prepare an asymmetric nanofiber composite for the anisotropic strain sensing. The carbon nanofibers (CNF)/polydimethylsiloxane (PDMS) are deposited onto an aligned thermoplastic polyurethane (TPU) nanofiber membrane surface, forming a two layered structure. The PDMS ensures strong interfacial adhesion between the TPU nanofibers and the CNF layer, which endows the nanofiber composite with excellent surface stability and durability. The superhydrophobic CNF/PDMS constructs the conductive network, while the aligned nanofiber layer provides the anisotropic mechanical deformation. The nanofiber composite is cytotoxicity-free and exhibits excellent biocompatibility and biosafety. The asymmetric nanofiber composite shows anisotropy in the mechanical property and sensing behavior. The nanofiber composite demonstrates a large working strain range and outstanding sensing durability, and can be used for monitoring the multidirectional body joint motions even under corrosive conditions. Furthermore, the conductive CNF/PDMS exhibits excellent photothermal conversion performance and a negative temperature coefficient (NTC) behavior, and is hence suitable for isotropic temperature sensing. The asymmetric structure opens a new avenue for multifunctional and anisotropic strain sensing.

Novel stretchable fiber-shaped fluidic nanogenerators fabricated from carbonized lignin/thermoplastic polyurethane

Harvesting energy from water flow using fiber-shaped fluidic nanogenerators (FFNGs) based on liquid-solid contact electrification has practical significance. Challenges remain in the fabrication of conformal FFNGs with favorable durability and a large strain range. Herein, a robust, flexible, and stretchable FFNG is fabricated using carbonized lignin and thermoplastic polyurethane via wet-spun approach. A maximum output direct current voltage of 420 mV is generated when the saline solution flows over a 6-cm-long FFNG. The output voltage of the FFNG shows excellent stability and repeatability in multiple cyclic tensile tests. Furthermore, the excellent mechanical properties and high stretchability of FFNG enable it to be woven into fabric, proving its tremendous potential for use in conformal electronics. The robust FFNG can also act as a self-powered wave sensor, which provides basic information on the wave conditions.

Constructing conductive titanium carbide nanosheet (MXene) network on natural rubber foam framework for flexible strain sensor

Sensors, as one of the crucial components of wearable electronics, have attracted much attention due to their extensive application in healthcare, human–machine interfaces, electronic skins (E-skins), rehabilitation, and internet of things. However, there is still a challenge to fabricate flexible strain sensors with both good sensitivity and large working strain range. Herein, a facile, scalable, and low-cost strategy is developed to prepare highly sensitive strain sensors based on natural rubber foam and Ti3C2Tx nanosheeets (MXene/NR) by dip-coating method. The fabricated MXene/NR composite exhibits excellent strain sensitivity and large strain range. The gage factor of the MXene/NR composite reaches 14 in the strain range of 0–5% with a low pressure limitation of detection (435 Pa). Additionally, the sensing range is as large as 0–80% of strain and shows good stability during the pressing and relaxing cycles. It is demonstrated that the MXene/NR composite could be used to detect motions, such as finger pressing and step monitoring, suggesting it is a promising candidate for fabricating wearable electronics.

Breathable and Wearable Strain Sensors Based on Synergistic Conductive Carbon Nanotubes/Cotton Fabrics for Multi-directional Motion Detection.

Flexible strain-sensitive sensors have been receiving intensive attention in many aspects ranging from human motion capture to health-related signal monitoring. However, the fabric strain sensor with multi-directional sensing capability, besides having a wide strain range and high response sensitivity, is still very challenging and deserves further exploration. Here, we have prepared a wearable cotton fabric strain sensor uniformly decorated with single-walled carbon nanotubes through a facile solution process. The unique hierarchical architecture of the cotton fabric woven from twisted yarns combined with the conductive carbon nanotube network endows the fabric strain sensors with attractive performance, including low detection limit, large workable strain range, fascinating stability and durability, excellent direction-dependent strain response, and good air permeability. The strain sensor without polymer encapsulation can not only monitor subtle and large multi-directional motions but also fit well to the human body with satisfactory comfort, demonstrating its potential application in wearable electronics and intelligent clothing.

A silanized MCNT/TPU-based flexible strain sensor with high stretchability for deformation monitoring of elastomeric isolators for bridges

Laminated elastomeric bearings are widely used in large bridges for adjusting the deformation and ensuring the safety of the bridge structure. Interestingly, the bridge bearing’s deformation contains rich information that reflects the complex load conditions of the bridge structure. Nevertheless, the structural health monitoring (SHM) of the bridge bearings has not been carried out effectively due to the special characteristics of bridge bearings’ deformation, including the large range and the existence of varied forms such as shear, compressive and rotation. Along these lines, a novel conductive polymer composite-based flexible strain sensor was fabricated by employing a simple solution-blending method. Specifically, the proposed strain sensor was composed of thermoplastic polyurethane (TPU), multiwall carbon nanotubes (MCNTs), and silane coupling agent KH550. The utilization of the KH550 not only promoted the dispersion of MCNTs within the TPU matrix but also enhanced the interfacial bonding between the MCNTs and the TPU matrix, resulting in the large strain range (∼150%) of the silanized MCNT/TPU strain sensor. The silanized strain sensor with 3.0 wt% MCNTs demonstrated extraordinary linearity, promising gauge factor (∼8.26), and great durability under a tensile strain up to the value of 150% through the application of consecutive stretch–release tests. Furthermore, the compressive bending sensing tests proved the stable and repeatable bending sensing capability of the proposed silanized strain sensor. Moreover, the silanized strain sensor could effectively monitor the shear and the compressive deformation of the laminated elastomeric bridge bearings. This work provides a new way for fabricating flexible strain sensors with enhanced strain range, which validates the feasibility of the strain sensor for monitoring the bearing’s deformation and provides an experimental basis for developing the SHM of laminated elastomeric bridge bearings.

Study on the mechanical properties of CFRP composite auxetic structures consist of corrugated sheets and tubes

In recent years, auxetic (negative Poisson's ratio) structures have attracted great attention because of their non-conventional behaviour. However, auxetic structures are usually characterized by low stiffness, which limits their application. Once, their stiffness can be improved, their application field will be significantly broadened. In addition, most auxetic structures are difficult to be produced due to their complex geometries. To solve these two problems, high-performance carbon fibre reinforced polymer (CFRP) composites are used to manufacture an auxetic structure consist of corrugated sheets and tubes. The mechanical properties of the composite auxetic structure consist of corrugated sheets and tubes (CorTube) are studied by experiments, finite element simulation and theory analysis. The results show that, the composite CorTube structures display obvious negative Poisson's ratio effect in large compression strain range, and the auxetic characteristics of the composite CorTube structures become more notable with the increase of the compression strain. The stiffness of the structure depends on the thickness of the corrugated sheets in small strain stage, while the material parameters of the tubes plays determining role in large strain stage. Finally, the deformation characteristics and failure modes of the CorTube during the compression process are discussed.

Strain-modulated electronic transport in two-dimensional carbon allotropes

Carbon has various allotropes showing rich physical properties. Here, we take net C and net W as the research objects. They are all composed of carbonic squares C4, hexagons C6, and octagons C8, but with different compositions. Using the combination of density functional theory calculations and non-equilibrium Green’s function method, we study the significant changes in electronic structures and transport behaviors in response to external strain. For net C, tunable negative differential resistance (NDR) is observed. The NDR bias region can be moved and widened, while its peak-to-valley ratio can be increased from the original 1.14 to largest 2.67. The electrical conductivity of net W exhibits a very good linear relationship within a large strain range from −4% to +4%, and it can be increased to 219.9%. By analyzing their band structures, the effective regulations of strain on both the NDR and linear conductivity are explained. These results show not only the differences from deformation for various carbon rings under strain but also a certain guiding significance for applications in electronic devices.

Stabilization and microstructural network of pickering emulsion using different xanthan gum/lysozyme nanoparticle concentrations

In this paper, xanthan gum/lysozyme nanoparticles (XG/Ly NPs) were used to prepare Pickering emulsion, and the effect of particle concentration was investigated from the aspects of stability, rheology, and microstructure. Creaming index (CI) decreased along with the increase of XG/Ly NPs concentration and oil content until the particle concentration exceed 2%. At this time, the stratification disappeared, and the emulsion was more stable. Confocal laser scanning microscope showed that XG/Ly NPs form a three-dimensional network in the aqueous phase serving as a physical barrier, which can enhance the viscosity and shear resistance of the emulsion and have the maximum contribution to the emulsions’ solid-like elastic properties. Increasing the particle concentration was favorable to enhancing the solid-like property and reducing the droplet size, and the stability of the emulsion was improved. Rheological analysis showed that Pickering emulsions exhibited shear-thinning behavior and good structural stability within a large strain range in a particle concentration dependent manner. The exponent n decreased from 0.70 to 0.39 as the particle concentration and oil content increased. The endeavor confirmed that microstructure and rheological performance of Pickering emulsions could be regulated by particle concentration, which might provide feasible strategy for development functional emulsion systems with controllable structures.

Multi-objective shape optimization of large strain 3D helical structures for mechanical metamaterials

The need for mechanical metamaterials with large strain range and lightweight properties are evidenced to engineering applications. In this regard, novel helical structures are proposed as suitable unit cell’s components of mechanical metamaterials. Three-dimensional helical structures composed of varying coil numbers, defined in a cylindrical spatial domain are shape optimized through genetic algorithm in a finite element script for conflicting objectives of minimum mass and maximum tensile range. The superior performance of the shape optimized helical structure is highlighted in terms of structural rigidity, large deformation capability, buckling and vibrational modal analysis in compare to equivalent coil springs of identical weight and comparable domain. Deformation mechanism is analyzed carefully to justify the improved performances of proposed structure. Tensile and compressive experimental analysis are undertaken to validate the enhanced strain ranges. One dimensional metamaterials implementations with various tessellation arrangements are simulated. Results show that the proposed design can effectively generate lightweight substitutes of metamaterials unit cells ligaments to improve the strain range performance. Planar and lattice metamaterial concepts employing shape optimized helical structure are illustrated to demonstrate the possibilities of promoting lightweight structural integrities in the design of mechanical metamaterials.

U-shape core-offset fiber sensor with submicrostrain resolution over a 35 millistrain range.

Large strain with submicro resolution is essential for steel structural monitoring; however, the fiber base sensors are limited by the glass extension to be less than 1%. Here, we propose a U-shape core-offset fiber sensor including four fiber segments to realize a large strain sensor. Four fiber segments with slight length differences in between are core-offset fused together to achieve U-shape spring-like microstructure fiber for large transverse bending radius. The reflected high-order modes at three silica/air interfaces interfere to give a broad spectrum due to unequal segment length, which enables continuous strain detection over 35 mɛ. The air and glass hybrid structure of the device enables the large bending, and hence compression and tension measurement can be achieved simultaneously. The strain sensitivity is up to 20.75 pm/µɛ with the strain accuracy of 0.5 µɛ. This novel, to the best of our knowledge, core-offset fiber has high strain sensitivity and large strain range for compression and tension strain measurement. Furthermore, the proposed strain sensor can be fabricated easily for practical applications where large strain with high strain accuracy is needed.

Improving strength–ductility synergy in medium Mn steel by combining heterogeneous structure and TRIP effect

The deformation mechanisms of a novel medium Mn steel (Fe–0.14C–7.8Mn–1.65Al–0.11Zr, wt%) were investigated through mixed multiphase preservation-intercritical annealing route. A heterogeneous duplex microstructure consisting of plate-like and equiaxed austenite and ferrite with multiple morphologies and multiscale and Mn inhomogeneous distribution was obtained after intercritical annealing at 680 °C for 10 min. The heterostructured sample exhibited excellent strength–ductility synergy with a yield strength of 1022 MPa, an ultimate tensile strength of 1280 MPa, and a total elongation of 53%. Comparative analysis revealed that hetero-deformation-induced (HDI) stress was generated during tensile deformation. This stress was primarily responsible for the superhigh yield strength of the heterostructured sample. In addition, the HDI stress could initially trigger premature martensitic transformation of austenite in the grain or phase boundary region and delay the martensite transformation of untransformed austenite to a large strain range due to the shielding effect of the formed core–shell structure, which comprised an untransformed core austenite and a shell α'-martensite. Multiple strengthening and ductility-enhancing mechanisms involving transformation-induced plasticity effect, twin-induced plasticity effect, HDI synergistic hardening, and dislocation strengthening occurred sequentially during deformation, leading to the extraordinary strength–ductility combination of the heterostructured medium Mn steel.

Mechanical properties of C60 at finite temperature from first-principles calculations

C60 has been the focus of many studies since its discovery, but the mechanical properties of this unique molecule remain poorly known. To remedy that, we performed density functional theory molecular dynamics calculations of the compression of C60 at finite temperature, within a large strain range. The possible recovery of the molecule after unloading was also investigated with first principles accuracy, for two different modes. We found that the behavior of C60 follows three regimes depending on the compression strain. Up to 0.48 ± 0.02, the deformation is elastic with a small but distinct influence of the compression orientation. A relation between the electronic gap and the orientation is also revealed. The second regime starts for larger strains up to 0.75 ± 0.02, after a 30–32 nN force plateau. It is characterized by stochastic carbon bond breakings. Although bonds rupture is generally the fingerprint of plastic deformation in materials, we found that the C60 structure can be dynamically recovered in a significant fraction of cases, following a fast unloading. This mode also yields defected structures with low energies compared to a slow unloading mode. Finally, the third regime corresponds to irreversible deformation of the molecule, for strains larger than 0.75 ± 0.02.