Large Tensile Strain Research Articles

AgNWs self-assembly along coaxially electrospun SEBS-PVP core-sheath fibers for stretchable conductive membranes with low interfacial losses

In this paper, core-sheath fibers with poly(styrene-ethylene/butylene-styrene) triblock copolymer (SEBS) as the core layer and polyvinylpyrrolidone (PVP) of different molecular weights as the sheath layer were prepared by coaxial electrospinning. Amphiphilic triblock copolymers were added to the SEBS core layer, and the fusion of incompatible SEBS-PVP at the core-sheath interface was further promoted by appropriate solvent post-treatment. Polydopamine (PDA) was in situ polymerized on the surface of SEBS-PVP fibers, so that silver nanowires (AgNWs) with high aspect ratios were conformally self-assembled along the fibers to form good interfacial bonding, so that the SEBS-PVP/AgNW composite membrane has high conductivity and exhibits good interfacial transfer effect in cyclic stretching under large strain. Based on core-sheath nanofibers and self-assembly, the excellent interfacial transfer gives SEBS-PVP/AgNW low viscoelastic loss, integrated large tensile strain sensing and stable Joule heating effect, which is conducive to the development and application of multifunctional stretchable electronics.

Both edge substitution effects on thermal conductivity of armchair graphene nanoribbons under tensile strain: From equilibrium molecular dynamics simulations

Thermal conductivity and phonon spectra change of graphene nanoribbon as function of both side edges substitution and strain is investigated using equilibrium molecular dynamics. Under small strain, the edge’s partial substitution by graphane plays effect role to change the phonon mode of GNR. Under large tensile strain, reduction ratio of thermal conductivity is the largest in case of fluorographane hybrid and the smallest in case of graphane hybrid. Especially, under 16 % strain, the thermal conductivity of GNR is reduced until 13 % by edges substitution of graphane. The phonon spectra shift peaks towards low frequency at high frequency range (>50 THz).

Monitoring data motivated health condition assessment of cement concrete pavements in field based on FBG sensing technology

Health condition of cement concrete pavements in field is difficult to characterize due to the random action of traffic loads and environmental variations. It is also difficult to accurately get the deformation merely based on theoretical or simulation analysis, for the heterogeneous material and complicated interfacial bonding properties of multilayered concrete pavements. Therefore, in situ health monitoring is particularly significant for structural condition assessment. To contribute this topic, improved fiber Bragg grating sensors have been designed and embedded in the two-layered pavement to measure the strain, deformation, and temperature. Deformation information of the cement concrete pavement under environmental action in about 3 years has been analyzed. Data analysis indicates that the longitudinal and transverse deformations of the pavement have behaved in nonuniform distribution, and local points suffered from the large tensile strains. The vertical measurement data declared that local interfacial micro void defects existed in the soil base and kept stable during the following 3 years. The temperature variation inside the pavement was highly correlated with the environmental temperature, and the variation amplitude was relatively smaller than the environmental temperatures, with the maximum amplitude smaller than 4°C. The load and temperature transfer principles in different layers have also been checked. Generally, the monitoring data in field from the year 2020 to year 2023 have declared that the concrete pavement has good performance to resist the combined action of traffic loads and environmental temperatures. The study can help to understand the actual structural performance of cement concrete pavements in field based on the optical fiber sensing system.

Tunicate cellulose nanocrystal reinforced multifunctional hydrogel with super flexible, fatigue resistant, antifouling and self-adhesive capability for effective wound healing

Hydrogels as skin wound dressings have been extensively studied owing to their good flexibility and biocompatibility. Nevertheless, the mechanical performance, adhesive capability, antifouling and antibacterial properties of conventional hydrogels are still unsatisfactory, which hinder the application of hydrogel for cutaneous healing. Here, we developed a novel biocompatible multifunctional hydrogel with super flexible, fatigue resistant, antifouling and self-adhesive capability for effective wound healing, where naturally rigid polymers including quaternized chitosan (QCS) and Tunicate cellulose nanocrystals (TCNCs) are used as bioactive cross-linkers and reinforcers to endow the hydrogel with excellent mechanical and antibacterial property, and the synergistic contributions from the poly(acrylic acid/methacrylate anhydride dopamine/sulfobetaine methacrylate) (poly(AA/DMA/SBMA)) chains and QCS endow the hydrogel with excellent adhesive property, antioxidant, antifouling and pH-responsive sustained drug release capabilities. The optimized hydrogel exhibited high tensile strength (77.69 KPa), large tensile strain (889.9 %), large toughness (307.51KJ.m−3), high adhesive strength (35.57 KPa) and ideal compressive property. The in vivo infected full-thickness skin model demonstrated that the hydrogel with vanvomycin sustained release ability efficiently improved the granulation tissue formation, facilitating collagen deposition and reducing inflammatory expression, thus effectively accelerating wound healing. This superiorly skin-adhesive antibacterial biocompatible hydrogel appears to be a promising candidate for wound therapy.

Skin-Conformable Flexible and Stretchable Ultrasound Transducer for Wearable Imaging.

Ultrasound imaging offers a noninvasive, radiation-free method for visualizing internal tissues and organs, with deep penetration capabilities. This has established it as a crucial tool for physicians in diagnosing internal tissue pathologies and monitoring human conditions. Nonetheless, conventional ultrasound probes are often characterized by their rigidity and bulkiness. Designing a transducer that can seamlessly adapt to the contours and dynamics of soft, curved human skin presents significant technical hurdles. We present a novel flexible and stretchable ultrasound transducer (FSUT) designed for adaptability to large-curvature surfaces while preserving superior imaging quality. Central to this breakthrough is the innovative use of screen-printed silver nanowires (AgNWs) coupled with a composite elastic substrate, together ensuring robust and stable electrical and mechanical connections. Standard tensile and fatigue tests verify its durability. The mechanical, electrical, and acoustic properties of FSUTs are characterized using standard methods, with large tensile strains (≥110%), high flexibility ( R ≥ 1.4 mm), and lightweight ( ≤ 1.58 g) to meet the needs of wearable devices. Center frequency and -6-dB bandwidth are approximately 5.3 MHz and 66.47%, respectively. Images of the commercial anechoic cyst phantom yielded an axial and lateral resolution (depths of 10-70 mm) of approximately 0.31 and 0.46, and 0.34 and 0.84 mm, respectively. The complex curved surface imaging capabilities of FSUT were tested on agar-gelatin-based breast cyst phantoms under different curvatures. Finally, ultrasound images of the thyroid, brachial, and carotid arteries were also obtained from volunteer wearing FSUT.

Experimental and constitutive model investigation on the tensile mechanical properties of polyurea at wide strain-rate range

Polyurea is extensively utilized as a protective coating material for structures under impact and blast loadings, owing to its significant large tensile deformation capability and strain hardening effect. In this study, the tensile performance of polyurea was experimentally and theoretically investigated. Firstly, rational geometric shapes and dimensions were designed, and a series of quasi-static and dynamic uniaxial tensile tests were conducted to obtain the nonlinear stress-strain curves at different strain rates. The results indicated a notable strain-rate effect in polyurea, with an increase in elastic modulus and tensile stress as the strain rate increased. Moreover, as the strain rate escalates, the strain hardening effect becomes more pronounced, thereby enhancing the protective capabilities of polyurea. Subsequently, an existing hyperelastic model, namely the Mooney-Rivlin (MR) model, was modified to incorporate the strain rate effect, resulting in a non-linear visco-hyperelastic constitutive model. Furthermore, the proposed constitutive model and parameters were validated by simulating existing tensile and blast tests using the finite element (FE) program LS-DYNA. This work could provide a reference for the design of structural protection.

Goldene: An Anisotropic Metallic Monolayer with Remarkable Stability and Rigidity and Low Lattice Thermal Conductivity.

In a recent breakthrough in the field of two-dimensional (2D) nanomaterials, the first synthesis of a single-atom-thick gold lattice of goldene has been reported through an innovative wet chemical removal of Ti3C2 from the layered Ti3AuC2. Inspired by this advancement, in this communication and for the first time, a comprehensive first-principles investigation using a combination of density functional theory (DFT) and machine learning interatomic potential (MLIP) calculations has been conducted to delve into the stability, electronic, mechanical and thermal properties of the single-layer and free-standing goldene. The presented results confirm thermal stability at 700 K as well as remarkable dynamical stability of the stress-free and strained goldene monolayer. At the ground state, the elastic modulus and tensile strength of the goldene monolayer are predicted to be over 226 and 12 GPa, respectively. Through validated MLIP-based molecular dynamics calculations, it is found that at room temperature, the goldene nanosheet can exhibit anisotropic tensile strength over 9 GPa and a low lattice thermal conductivity around 10 ± 2 W/(m.K), respectively. We finally show that the native metallic nature of the goldene monolayer stays intact under large tensile strains. The combined insights from DFT and MLIP-based results provide a comprehensive understanding of the stability, mechanical, thermal and electronic properties of goldene nanosheets.

Recyclable and leakage-suppressed microcellular liquid–metal composite foams for stretchable electromagnetic shielding

The metallic conductivity and high liquidity of liquid metal (LM) make LM-polymer composites exhibit high electrical conductivity, large stretchability, and excellent mechanical–electrical decoupling, which provide significant advantages in the fabrication of stretchable electromagnetic interference (EMI) shielding materials. However, problems such as undesired LM leakage, high density, and poor recyclability due to the frequent use of chemically cross-linked polymers limit the applications of LM-polymer composites. Herein, we report the fabrication of stretchable and recyclable microcellular thermoplastic polyurethane (TPU)/LM composite foams (TLFs) with controllable LM distribution through a water–vapor-induced phase separation (WVIPS) process. The sedimentation of LM droplets helps to improve the shielding effectiveness (SE) of TLF, while the microcellular structure enables TLF with more uniform LM dispersion to achieve high leakage resistance. Moreover, the stretch-activated TLF shows high electrical stability with only slight resistance changes during stretching and exhibits a strain-insensitive shielding behavior. As a stretchable joule heater, the sample has outstanding Joule-heating performance, with stable temperature dropping only slightly under large tensile strains. More importantly, the excellent solubility of TPU, combined with a solution-based WVIPS process, allows our TLFs to be easily recycled into new products with very similar structure and performance to those before recycling, indicating the ideal recyclability of such materials.

Stacking-dependent interlayer magnetic interactions in CrSe2.

Recently, CrSe2, a new ferromagnetic van der Waals two-dimensional material, was discovered to be highly stable under ambient conditions, making it an attractive candidate for fundamental research and potential device applications. Here, we study the interlayer interactions of bilayer CrSe2using first-principles calculations. We demonstrate that the interlayer interaction depends on the stacking structure. The AA and AB stackings exhibit antiferromagnetic (AFM) interlayer interactions, while the AC stacking exhibits ferromagnetic (FM) interlayer interaction. Furthermore, the interlayer interaction can be further tuned by tensile strain and charge doping. Specifically, under large tensile strain, most stacking structures exhibit FM interlayer interactions. Conversely, under heavy electron doping, all stacking structures exhibit AFM interlayer interactions. These findings are useful for designing spintronic devices based on CrSe2.

Superelastic and fluorine-free nanofiber membranes prepared by one-step electrospinning for waterproof and breathable applications

Waterproof and breathable membranes (WBMs) possessing high mechanical properties are widely sought after for a variety of applications. However, their manufacture still presents challenges in terms of environmental protection and process simplification. Herein, we present a facile way of developing fluorine-free and superelastic WBMs. The in-situ integration of poly(methylhydro-siloxane) and poly(styrene-butadiene-styrene) simultaneously satisfies the required mechanical properties, waterproofness, and breathability. The resultant membranes possess excellent tensile properties, exhibiting a breaking strain of 557.7 % and stress of 3.98 MPa. Further investigations reveal the membranes demonstrate excellent breathability (3303.7 g m−2 d−1) and hydrostatic pressure (70.9 kPa) while maintaining their comprehensive performance even under large tensile strains. The innovation of superelastic WBMs with stable properties holds promising application prospects in numerous fields.

MatrixCraCS: Automated tracking of matrix crack development in GFRP laminates undergoing large tensile strains

A novel image processing method for tracking development of matrix cracks in glass-fibre reinforced polymer (GFRP) laminates is presented. Images are acquired in a quasi-static tension test using transillumination white light imaging. These images show changes occurring due to developing damage. The method, called MatrixCraCS, tracks and quantifies matrix cracks while compensating for large specimen deformation and stitching threads, which obscure crack development and seriously impact crack detection. Matrix cracks are tracked via a sequential image difference and morphological filtering is used to detect cracks. MatrixCraCS is verified against synthetic images and shows an error of less than 7% in the quantified length of cracks and 0% detection failures. MatrixCraCS is validated against experimental results for a [±452°902°]S GFRP laminate, where microscopic analysis shows 5.92% error in crack detection. Error relative to manual crack tracking are quantified for detection failures and false positives as 3.3% and 1.57%, respectively. It is found that the method accurately quantifies cracks in GFRP laminates subject to large deformation and is robust against noise.

Cut layout optimization for design of kirigami metamaterials under large stretching

Kirigami metamaterials have gained increasing attention due to their unusual mechanical properties under large stretching. However, most metamaterial designs obtained with trial-and-error approaches tend to lose their desirable properties under large tensile strains due to occurrence of instability caused by out-of-plane buckling. To cope with this limitation, this paper presents a systematic approach of cut layout optimizing for designing kirigami metamaterials working at large tensile strains by fully exploiting their out-of-plane buckling behaviors. This method can also mitigate the local stress concentration issue at the hinges of conventional kirigami designs working at in-plane deformation modes. The effectiveness of the proposed method is demonstrated through several examples regarding metamaterial design with negative Poisson's ratio and specified flip angle pattern. It is shown that the proposed method is capable of addressing the highly nonlinear deformation impacts on the mechanical performance under large stretching, to meet the growing and diverse demands in the field of kirigami metamaterials.

Polyhydroxy structure orchestrates the intrinsic antibacterial property of acrylamide hydrogel as a versatile wound-healing dressing.

Hydrogel is considered as a promising candidate for wound dressing due to its tissue-like flexibility, good mechanical properties and biocompatibility. However, traditional hydrogel dressings often fail to fulfill satisfied mechanical, antibacterial, and biocompatibility properties simultaneously, due to the insufficient intrinsic bactericidal efficacy and the addition of external antimicrobial agents. In this paper, hydroxyl-contained acrylamide monomers, N-Methylolacrylamide (NMA) and N-[Tris (hydroxymethyl)methyl] acrylamide (THMA), are employed to prepare a series of polyacrylamide hydrogel dressings xNMA-yTHMA, where x and y represent the mass fractions of NMA and THMA in the hydrogels. We have elucidated that the abundance of hydroxyl groups determines the antibacterial effect of the hydrogels. Particularly, hydrogel 35NMA-5THMA exhibits excellent mechanical properties, with high tensile strength of 259kPa and large tensile strain of 1737%. Furthermore, the hydrogel dressing 35NMA-5THMA demonstrates remarkable inherent antibacterial without exogenous antimicrobial agents owing to the existence of abundant hydroxyl groups. Besides, hydrogel dressing 35NMA-5THMA possesses excellent biocompatibility, in view of marginal cytotoxicity, low hemolysis ratio, and negligible inflammatory response and organ toxicity to mice during treatment. Encouragingly, hydrogel 35NMA-5THMA drastically promote the healing of bacteria-infected wound in mice. This study has revealed the importance of polyhydroxyl in the antibacterial efficiency of hydrogels and provided a simplified strategy to design wound healing dressings with translational potential.

Zwitterionic liquid crystal elastomer with unusual dependence of ionic conductivity on strain and temperature for smart wearable fabric

Stretchable ionic conductors are appealing for soft electronics, yet frequently had their conductivities limited below the level desired by many applications, and also lack the ability of simultaneously actuating and sensing their own motions, resembling living organisms’ neuromuscular behaviors. In this study, by introducing a zwitterionic chain extender into liquid crystal elastomers (LCEs) backbones, a unique type of zwitterionic LCEs (iLCEs) fiber with ionic conductivity of 2.3 S m−1 and self-sensing properties was designed. By controlling the anisotropy solvent evaporation, the iLCEs fiber with certain degree of mesogenic alignment was easily obtained. The mesogenic alignment not only enabled a reversible actuation behavior, but also boosted the formation of ionic channels for an abnormal dependence of ionic conductivity on temperature and elongation. The resultant iLCEs fibers showed an increasing resistance at high temperatures, and a decreasing resistance at large tensile strain, in contrast to the liquid-like mechanism of ion transport for ionogel systems. This combination of actuation and ionic conductance promises great potential in applications of self-sensing actuation and self-perception of soft robots.

Superhydrophobic stretchable conductive composite textile with weft-knitted structure for excellent electromagnetic interference shielding and Joule heating performance

Conductive composite textiles (CCTs) as multifunctional integrated platform provide an effective path for developing flexible electromagnetic interference (EMI) shielding composites. However, conventional CCTs suffer from EMI shielding performance failure or the loss of textile's intrinsic properties under large tensile strain. Hence, in this work, a stretchable EMI shielding CCT that retains the inherent attributes of textile is proposed via weft-knitting and in-situ chemical Ag deposition. The complete and continuous silver nanoparticles (AgNPs) conductive networks bring excellent conductivity (38560 S/m) and ultrahigh EMI shielding performance (80.1 dB) in unstretched state. When tensile strain is applied, the fibers are gradually straightened from flexural state within 40 % strain, and then begin to be stretched at bigger strains, which benefits from the weft-knitting structure. Therefore, the conductive networks on the fiber surfaces are well protected from damage in the initial 40 % strain range, resulting in a stable EMI shielding performance (51.7 dB) even after 1000 cycles of 100 % tensile strain. Crucially, the CCT preserves good air permeability, softness and lightness even though a series of modifications and tensile strains are applied. Other than the EMI shielding perforamnce, the excellent superhydrophobicity (the contact angle of 158°) imparts the textile with the capability to tackle complex environments easily. Moreover, the textile can readily be heated to 73.4 °C at a low voltage of 0.5 V, showing outstanding Joule heating performance. Even after a long period of heating (3600 s), the textile maintains superior thermal stability, indicating potential applications in wearable heaters. In brief, this multifunctional CCT has excellent comprehensive properties and is expected to further expand the applications of EMI shielding textiles.

First-principles study on barrier height of silicon emission from interface into oxide during silicon thermal oxidation

Employing first-principles calculation, the detailed energy landscape of the path for Si emission from the interface into the oxide is studied. It is found that the barrier height almost reproduces the experimental values, indicating that Si emission surely corresponds to the diffusion of SiO interstitials. It is also found that the barrier height is microscopically rate-limited by the oxygen-vacancy transfer process, which temporarily and inevitably proceeds under a large local tensile strain induced by the diffusion of SiO interstitials.

The underlying mechanism of the strain-induced reversible magnetic state transition in MXene nanosheets

MXenes have emerged as one of the most promising members among the two-dimensional (2D) material family owing to their unique physical-chemical properties and outstanding application prospects. Here, we investigated the unique magnetic properties of Ti2C MXenes monolayer by means of the first-principles calculations combining with the Heisenberg spin Hamiltonian approach. A strain-induced reversible magnetic transition for the Ti2C monolayer could be found in our study. When the strain is applied to the Ti2C monolayer, the magnetic configuration of the Ti2C monolayer transforms from the A-type antiferromagnetic (A-AFM) phase to the ferromagnetic (FM) phase with the biaxial tensile strain larger than 6%. Furthermore, the transition from the A-AFM phase to the FM phase was found to be closely related with the change of the Ti and C atomic magnetic moments. The direct magnetic coupling between Ti and C atoms with the increased Ti and C magnetic moments is able to stabilize the structure due to the weakened superexchange interaction between Ti and C atoms under large tensile strain. This is the underlying driving force for the transition from the A-AFM phase to the FM phase. This work provides a promising pathway to better understand the existence of magnetic reversal behavior in the Ti2C MXenes monolayer and opens the door to future magnetic applications of MXenes.

Achieving high strength and pseudo-ductility in Bf/Cu composite enabled by 3D-Gr@B4C interface-modified layer

Improving wettability, interfacial mechanical and thermal compatibility between reinforced boron fiber and Cu are strongly desirable for developing continuous boron fiber reinforced Cu matrix (Bf/Cu) composite, which shows great potential for application in nuclear fusion reactor as a promising high-strength heat-sink material. Herein, a three-dimensional graphene network hybrid B4C (3D-Gr@B4C) coating was fabricated on B fiber by single filament chemical vapor deposition as the interface-modified layer of Bf/Cu composite. It is revealed that the 3D-Gr in 3D-Gr@B4C interface-modified layer can not only supply diffusion channel to Cu for enhancing interfacial thickness and strength, but also serve as high-thermal-conductivity network to increase TC of Bf/Cu composite from 322.3 W/m·K to 343.9 W/m·K. Meanwhile, modulus of 3D-Gr@B4C interface-modified layer lying between Cu and B can also improve the interfacial mechanical compatibility of composite. Accordingly, interface modification on B fiber using 3D-Gr@B4C layer enables tensile strength up to 1016 MPa at RT and 620 MPa at 300 °C, which are ∼1.3 and ∼1.5 times higher than the corresponding values of Bf/Cu composite, respectively. Furthermore, introducing 3D-Gr@B4C layer inhibits abrupt failure of Bf/Cu composite at small tensile strain and opens up fiber pull-outs and shearing of Cu matrix at large tensile strain, producing pseudo-ductile fracture.

Strain-controlled Néel temperature and exchange bias enhancements in IrMn/CoFeB bilayers

We propose a numerical method, where first-principles calculations are combined with modified Monte Carlo simulations, and study the Néel temperature of antiferromagnetic IrMn and exchange bias effect in antiferromagnet/ferromagnet IrMn/CoFeB bilayers manipulated by the applications of tensile and compressive strains. The results show that both tensile and compressive strains linearly change the magnetic moment of Mn and the magnetocrystalline anisotropy of IrMn, and meanwhile, the uniaxially easy-axis directions under tensile and compressive strains are perpendicular. The strain-triggered increase in antiferromagnetic exchange coupling between Mn–Mn pairs is revealed and induces an up to 1.5 times enhancement of the Néel temperature of IrMn. Furthermore, the spontaneous and conventional exchange bias effects can be both observed under large tensile strains, also sensitive to the cooling field, and strongly enhanced roughly by 800% under 8 T in the application of 1.5% strain, which can be interpreted by the strain-induced high magnetocrystalline anisotropies. Thus, the tensile strains are better for controlling and optimizing the Néel temperature of IrMn and further exchange bias properties in IrMn-based heterostructures. This work establishes the correlations between microscopically and macroscopically magnetic responses to strain, indicating that strain can be an intriguing means of extrinsic manipulation of exchange bias, which is of importance for spintronic device applications.

Strain engineering and strain measurement by spring tethers on suspended epitaxial GaN-on-Si photonic crystal devices

Suspended epitaxial gallium nitride (GaN) on silicon (Si) photonic crystal devices suffer from large residual tensile strain, especially for long waveguides, because fine structures tend to crack due to large stress. By introducing spring-like tethers, designed by the combination of a spring network model and finite element method simulations, the stress at critical locations was mitigated and the cracking issue was solved. Meanwhile, the tethered-beam structure was found to be potentially a powerful method for high-precision strain measurement in tensile thin films, and in this case, a strain of 2.27(±0.01)×10−3 was measured in 350 nm epitaxial GaN-on-Si.