Bending Tolerance Research Articles

A High-Performance and Flexible Electrothermal Heater with Bending Tolerance from Layer-by-Layer Self-Assembled Graphite Nanoplates and Carbon Black on Paper

A High-Performance and Flexible Electrothermal Heater with Bending Tolerance from Layer-by-Layer Self-Assembled Graphite Nanoplates and Carbon Black on Paper

Fundamental study on performances of fiber-superconducting composite CORC cable: electromagnetic, thermal, mechanical and quench behaviors

Abstract Common terminal voltage measurement can be hardly applied to detect quenches in long high temperature superconducting (HTS) conductor on round core (CORC) cable because not only the HTS normal zone propagation velocity (NZPV) is low but also immobilizing a large number of voltage leads is inconvenient. Distributed optical fiber sensing (DOFS) technology is a promising method for quench detection of long superconductors. To sense the thermal changes of CORC cables during quenches more directly and prevent optical fibers from damages by external stress, a fiber-superconducting composite (FSC) CORC cable was fabricated. For this cable, three optical fibers were placed in three grooves of the copper core respectively, then three HTS tapes were spirally wound on the copper core in sequence. Comparing to a traditional CORC cable, obviously, the FSC CORC cable structure has been changed. To promote FSC CORC cable engineering applications, it is necessary to study the fundamental performance of the cable. In this paper, we investigated the electromagnetic, thermal and mechanical properties of the FSC CORC cable by comparing those with a common one. The results demonstrated that, compared to the common one, the magnetic distribution of the FSC CORC cable hardly changed, but the current distribution of the copper core in the FSC CORC cable slightly changed which led to decreases of transport AC loss, in addition, the thermal characteristics of the FSC CORC cable was slightly changed and the bending tolerance ability of the cables reduced within a bending diameter range of 15 cm. What’s more, the embedded optical fibers combined with DOFS system are successfully used to detect the temperature changes of the cable surface. Finally, to study the quench behaviors of the cable, we built a quench detection platform, which equips with a voltage acquisition system, a thermocouple temperature acquisition system and the DOFS system. By using the platform to detect the quenches of the FSC CORC cable, minimum quench energy of the cable and NZPV of the tape and cable at different currents was tested.

Effect of nano-fluorapatite filler particles on surface microhardness and mineralization capacity of an experimental oral film

BackgroundThe objective of the study was to prepare and assess novel remineralizing oral films loaded with fluorapatite powder and composed of a combination of hydroxyethyl cellulose (HC) and cellulose nanofibers (CF).MethodsThree concentrations of the prepared nano-fluorapatite were tried and tested after loading in the cellulose blends and films were prepared using solvent cast technique. Along with SEM, measurements of thickness of film, bending tolerance, time of disintegration, surface pH and release of ions were made. The produced film’s ability to remineralize demineralized teeth in vitro was investigated.ResultsThe findings showed that the films’ thicknesses were uniform, their folding endurance exceeded 300, and their disintegration times exceeded 24 h. High amounts of fluoride and calcium ions were released, and nearly neutral pH values were observed. The distribution of fluorapatite powder particles was uniform, as demonstrated by SEM. The Vickers microhardness (VHN) of enamel and morphological analysis results showed that in comparison with the demineralized specimens, there was a substantial microhardness value increase following 15 and 30 days remineralization.ConclusionsNewly developed prepared films are a successful method for remineralizing early-stage demineralized tooth lesions.

Synergistic strategy of rigid-bridge and flexible-bridge achieving high-performance and mechanical robustness all-Polymer solar cells

As the great potential of the all-polymer solar cells (all-PSCs) for wearable devices, both excellent photoelectric conversion efficiency (PCE) and mechanical robustness are essential for commercial application. Unfortunately, the current photoelectric conversion efficiency and mechanical robustness of all-PSCs are always trade-off parameters. Here, a synergistic strategy of rigid-bridge and flexible-bridge in polymerized small molecular acceptors (PSMAs) affords four polymerized acceptors PY-IT, PY-IF1, PYF1-A and PYF1-B to simultaneously improve the PCE and mechanical property of the organic solar cells (OSCs). The different molecular structures from different bridges result in different molecular stacking, energy disorder, and mechanical robustness. The rigid-bridge PY-IT-based device yields a moderate PCE of 15.07% and flexible-bridge PY-IF1-based one shows a PCE of 11.73%. The terpolymer PYF1-A with the flexible-bridges partly replacing Y units also shows an unsatisfactory PCE of 13.60%. Interestingly, PYF1-B with the flexible-bridges partly replacing the rigid-bridges presents ordered molecular stacking, inducing the all-PSCs with PCE of 16.27%, which is the highest value in the flexible non-conjugated PSMAs-based devices. Besides, PM6:PYF1-B achieves an outstanding crack onset strain (COS) of 16.08% which is much better than 8.67% for PM6:PY-IT counterpart. Intrinsically flexibility enables the flexible device based on PYF1-B with preeminent bending tolerance. Besides, PM6:PYF1-B-based blend shows better comprehensive performance with an efficiency stretchability factor (ESF) of 2.16%, which is almost twice that of PM6:PY-IT counterpart. Our work provides a clear recognition of the rigid-bridges and flexible-bridges in the PSCs and promotes the development of all-PSCs in wearable electronic devices.

Design and Analysis of Multicore Fiber with High Bend Tolerance and Uniform Effective Area

Design and Analysis of Multicore Fiber with High Bend Tolerance and Uniform Effective Area

Dimerized small molecular acceptors: Regulation of dimer conformation realizes binary organic solar cells with highly comprehensive performance

Dimerized small-molecular-acceptors (DSMA)-based organic solar cells have gained much progress but insufficient flexibility of the rigid DSMAs limits application in wearable electronics. By regulating dimer conformation, a series of DSMAs (2BOHD-T, 2BOHD-TCxT (x = 4, 6)) are synthesized through microwave-assist-reaction. Conformation evolution from 2-dimension planarity to 3-dimension architecture evoked by linkage engineering from rigidity to flexibility precisely controls the electronic structures, intermolecular interactions, film-forming processes, and flexibility of DSMAs. The rigid terminal-linked 2BOHD-T performs best in small-area devices with efficiency of 17.68%. The 3-dimensional flexible terminal-linked 2BOHD-TC4T achieves a record efficiency of 16.50% with a notable VOC of 0.980 V among the reported flexible DSMAs. 2BOHD-TC4T-based large-area printing device obtains the best efficiency (14.53%) among these acceptors. Furthermore, PM6:2BOHD-TC4T not only improves thermal stability close to the all-polymer system but also achieves an excellent crack onset strain, producing the large-area flexible device with excellent bending tolerance. An updated evaluation parameter, efficiency-stretchability-thermal stability-factor (ESSTF), is proposed. 2BOHD-TC4T-based device yields the highest ESSTF, demonstrating the most balanced large-area device efficiency, thermal stability, and mechanical robustness.

Stretchable photosynaptic transistor with an ultralow energy consumption conferred using conjugated block copolymers/perovskite quantum dots nanocomposites

Emulation of photonic synapses offers a promising avenue for developing low-energy consumption of soft electronics, neurologically inspired robotics, and neuromorphic network computation. In this paper, a fully stretchable photosynaptic device with ultralow energy consumption using intrinsically stretchable poly(δ-decanolactone) (PDL)-based conjugated block copolymers (BCPs) with perovskite quantum dots (PeQDs) is first reported. The findings reveal that selectively choosing solvents for the PDL-based BCPs effectively regulates the assembly of P3HT and the accommodation of PeQDs, leading to improved self-aggregation of PeQDs, increased grain size, and optimized interfaces between P3HT and PeQDs The BCPs/PeQDs composite effectively emulates significant features of photonic synapses, such as paired-pulse facilitation (PPF), spike-dependent and short/long-term neuroplasticity, demonstrating excellent performance, including the fastest response time (1 ms), the highest current contrast (4.9 × 105), PPF (1.93) and ultra-low energy consumption (0.3 aJ) at an operating voltage of –0.1 mV. Furthermore, the BCP/PeQDs exhibit remarkable neuromuscular synapse characteristics, including high strain and bending tolerance and spike-dependent plasticity, enabling the devices to achieve high classification accuracy in artificial neural network simulations during tensile strain. The accommodation solvent selectivity of BCP/PeQDs suggests a promising strategy for advancing neurologically soft electronics, human-like pattern recognition, and neuromorphic computation.

Complex Neck Loading and Injury Tolerance in Lateral Bending With Head Rotation From Human Cadaver Tests.

Advancements in automated vehicles may position the occupant in postures different from the current standard posture. It may affect human tolerance responses. The objective of this study was to determine the lateral bending tolerance of the head-cervical spine with initial head rotation posture using loads at the occipital condyles and lower neck and describe injuries. Using a custom loading device, head-cervical spine complexes from human cadavers were prepared with load cells at the ends. Lateral bending loads were applied to prerotated specimens at 1.5 m/s. At the occipital condyles, peak axial and antero-posterior and medial-lateral shear forces were: 316-954 N, 176-254 N, and 327-508 N, and coronal, sagittal, and axial moments were: 27-38 N·m, 21-38 N·m, and 9.7-19.8 N·m, respectively. At the lower neck, peak axial and shear forces were: 677-1004 N, 115-227 N, and 178-350 N, and coronal, sagittal, and axial moments were: 30-39 N·m, 7.6-21.3 N·m, and 5.7-13.4 N·m, respectively. Ipsilateral atlas lateral mass fractures occurred in four out of five specimens with varying joint diastasis and capsular ligament involvements. Acknowledging that the study used a small sample size, initial tolerances at the occipital condyles and lower neck were estimated using survival analysis. Injury patterns with posture variations are discussed.

Structural analysis of REBCO coated conductors and quasi-isotropic strands under bending using continuum shell element

The electro-mechanical properties of Rare-Earth Barium Copper Oxide (REBCO) coated conductors (CCs) are crucial for practical structures such as power cables, magnet coils and so on. Many tests including tension and bending tests were conducted to estimate the critical current of REBCO CCs under different loadings. However, standard test method for the electro-mechanical properties of REBCO CCs has not been established, especially for bending tests. Therefore, finite element simulations of bending tests of REBCO CCs are still needed to further analyze the electro-mechanical behavior under loading. Structural responses of REBCO CCs and quasi-isotropic (Q-IS) strands under bending are analyzed using continuum shell element in this study. The numerical results indicate that bending strains obtained from finite element simulations match well with the analytical calculations in pure bending state. Furthermore, the influences of former shapes are also discussed to evaluate the bending tolerance of REBCO CCs in different cases. In addition, the mechanical properties and critical current degradation of Q-IS strands under bending are analyzed.

High-current-density Rutherford MgB2 cable sheathed by CuNi30 alloy

A Rutherford-type MgB2 cable has been fabricated from 12 six-core strands prepared by an internal magnesium diffusion (IMD) process with a resistive CuNi30 outer sheath. The uniformity of individual strands of diameter 0.448 mm prior to and after additional densification by rolling was studied by x-ray micro-tomography. The engineering current densities of the cable samples were measured at 4.2 K and external magnetic fields between 4.0 T and 8.0 T and compared with available published data. The presented Rutherford cable has the highest engineering current density with J e = 104 A cm2 measured in an external magnetic field of 5.73 T. The bending tolerance of the cable shows a critical diameter of 60 mm and less gradual critical current degradation in comparison to similar cables fabricated from single-core strands. The AC loss measurements of the present cable show lower coupling losses in comparison to monolithic multicore IMD conductors. The obtained results are promising for high-current-density and low-AC-loss MgB2 superconducting cables that are suitable especially for motors and generators.

Effects of bending and torsion behavior on Ic degradation and microstructure of ReBCO coated conductors

The performance degradation caused by bending and torsion is crucial for the application of superconducting coated conductors. In this study, we investigated the critical current (Ic) degradation of four kinds of conductors under bending and torsion. With 1 mm resolution, the critical bending radius of STT236μm (Shanghai Superconductor Technology) conductors is 6–7 mm, and that of STT380μm conductors is 4–5 mm, and that of SAMRI (Suzhou Advanced Materials Research Institute) conductors is 4 mm. With better bending tolerance, SAMRI conductors also have a less critical twist pitch of 82–87 mm. Considering the residual thermal stress during fabrication, the longitudinal strain corresponding to 5 % Ic degradation is 0.484 %. Further, to figure out the failure mechanism of coated conductors, the micromorphology of the ReBCO layer was observed after chemical etching. The crack distribution not only verified the cause of Ic degradation under mechanical behaviors, but also helps to develop a crack-based Ic prediction method.

Quantification of Bending Tolerance of the Cartilaginous Nasal Septum: Computer-Based Measurements

Objective: Nose deformity, including nasal deviation, is conspicuous since it locates in central face area. Regarding this and its prevention, nasal septum is one of the important supporting structures. Understand bending tolerance of the cartilaginous septum not only helps mitigate secondary deformity from surgical intervention, but also provides baseline information for further study regarding the nasal septum.Materials and Methods: Nineteen fresh cadavers were dissected to expose the cartilaginous nasal septum. It was connected with the set-up computer system for detection of electrical signal at 1-mm septal bending from the midline. Mechanical load (bending load) was applied over the dorsal septum to quantify its bending tolerance. The data of bending tolerance and Pearson’s correlation were reported.Results: The mean of septal thicknesses is 1.5 ± 0.4 with the average bending load of 19.0 ± 11.2 g. The majority of the septal thicknesses (15/19; 78.9%) of the dissections are within the range of 1.1 – 2.0 mm with bending load of 18.2 ± 8.9 g on average. There is a moderately positive association between septal thickness and bending load, the Pearson’s correlation coefficient is 0.602 (95%CI from 0.204 to 0.830) with p-value of 0.006.Conclusion: The overall nasal septum and the septum with thickness between 1.1 – 2 mm are able to tolerate loading over distal part of caudal septum about 19.0 and 18.2 g, respectively. Septal thickness shows moderately positive correlation with bending load.

Ultra-low loss polymer-based photonic crystal fiber supporting 242 OAM modes with high bending tolerance for multimode THz communication

A novel polymer-based ring-core circular photonic crystal fiber (C-PCF) is proposed and investigated. The solid core C-PCF structure is composed of Topas as background material, a high refractive index (RI) Kapton polymer as a ring material and four layers of air hole patterns. Numerical simulation is used to optimize the PCF geometry to support maximum stable modes with minimum losses. The proposed C-PCF supports 242 stable OAM modes near 1.9 THz with mode purity >0.9. The fiber exhibit low confinement loss (CL) ∼10-9 dB/cm, large effective mode area ∼ 10-2 mm2, low dispersion <1 ps/THz/cm and high effective mode index difference (Δneff) >10-3 in the range 1.5 THz to 3.5 THz. Attenuation, mode stability, material dispersion and fiber bending tolerance of PCF are analyzed to increase the transmission capacity. The detailed experimental feasibility and design sensitivity are theoretically addressed. The proposed PCF supports stable modes and works at a wider spectrum then the previously reported studies. The fiber has the potential to be employed for next-generation THz multimode communication systems.

Laboratory Investigation into the Flexural Behavior of Embedded Concrete Sleepers in Two-Stage Concrete with Preplaced Ballast Aggregate

The conversion of ballasted railway tracks into slab tracks using the preplaced aggregate concrete (PAC) technology over the bridges and in the tunnels has been introduced by many researchers but the flexural behavior of this composite system has not yet been studied. Therefore, in the first stage, a series of mortar and concrete mixture designs were proposed and evaluated. Subsequently, a concrete beam mold with dimensions of 3 * 0.6 * 0.5 m, which represented the track conditions, was developed and the bending behavior of the constructed beams in both conditions of the presence and absence of the concert B70 sleeper were investigated. The maximum bending force in the middle of the concrete beam without a sleeper (SE) equaled 177.5 kN. In addition, the average values of bending tolerance by the sleeper including a PAC beam for three specimens in the four modes of the positive moment of midspan (SPM), negative moment of midspan (SNM), positive moment of rail seat (SPR), and negative moment of rail seat (SNR) were 55.25 kN m, 32.5 kN m, 91.84 kN m, and 38.21 kN m, respectively, which met the requirements of the AREMA regulations.

Flexible Metal Halide Perovskite Photodetector Arrays via Photolithography and Dry Lift‐Off Patterning

Metal halide perovskites draw increasing attention as photodetector materials due to their strong visible light absorption and resulting photocurrent. The development of efficient fabrication routes to realize high‐resolution perovskite pixel arrays is critical to enable practical devices. Herein, a dry lift‐off process to fabricate methylammonium lead iodide (MAPbI3) pixels on different substrates is reported, with a resolution down to 5 μm. Accordingly, 8 × 10 photodetector arrays are fabricated on both glass and flexible polyethylene terephthalate (PET). These arrays show a sensitive photoresponse over a broad wavelength range from 320 to 760 nm. Moreover, when encapsulated by a Parylene‐C overlayer, the photodetector arrays on glass substrate show remarkable air stability, without noticeable performance loss after 10 days in ambient air, and the flexible photodetector arrays on PET substrate show excellent bending tolerance, retaining nearly 95% of the response after 170 bending cycles.

Bending and uniaxial tensile strain effects on the critical current of REBCO coated conductor tapes

Bending tolerance is one of the most fundamental mechanical properties of REBCO coated conductors for application to a superconducting coil. In this study, we investigated critical current degradation of REBCO coated conductors under bending and uniaxial tensile strain at 77 K and self-field with three different kinds of production from SuperPower Inc, Suzhou Advanced Materials Research Institute (SAMRI) and Shanghai Superconductor Technology (STT), respectively. All the tapes showed better bending tolerance under compressive strain than tensile strain, particularly for STT tapes, which showed no Ic degradation in compressive bending strain even with bending radius of 4.5 mm, but a 5% Ic degradation in tensile strain with bending radius of 6–6.5 mm. A uniaxial tensile strain test was also carried out to verify the dependence of Ic under tensile bending strain, the test results showed a good agreement between them. The tensile strain tolerance was 0.28–0.29% for STT tapes, 0.4–0.43% for SAMRI tapes, and 0.5–0.55% for SuperPower tapes.

A Dual-Crosslinked and Anisotropic Regenerated Cellulose/Boron Nitride Nanosheets Film With High Thermal Conductivity, Mechanical Strength, and Toughness.

The highly thermo-conductive but electrically insulating film, with desirable mechanical performances, is extremely demanded for thermal management of portable and wearable electronics. The integration of boron nitride nanosheets (BNNSs) with regenerated cellulose (RC) is a sustainable strategy to satisfy these requirements, while its practical application is still restricted by the brittle fracture and loss of toughness of the composite films especially at the high BNNS addition. Herein, a dual-crosslinked strategy accompanied with uniaxial pre-stretching treatment was introduced to engineer the artificial RC/BNNS film, in which partial chemical bonding interactions enable the effective interfiber slippage and prevent any mechanical fracture, while non-covalent hydrogen bonding interactions serve as the sacrifice bonds to dissipate the stress energy, resulting in a simultaneous high mechanical strength (103.4 MPa) and toughness (10.2 MJ/m3) at the BNNS content of 45 wt%. More importantly, attributed to the highly anisotropic configuration of BNNS, the RC/BNNS composite film also behaves as an extraordinary in-plane thermal conductivity of 15.2 W/m·K. Along with additional favorable water resistance and bending tolerance, this tactfully engineered film ensures promised applications for heat dissipation in powerful electronic devices.

Highly Flexible and Transparent Polylactic Acid Composite Electrode for Perovskite Solar Cells

Biomass substrates are urgently needed to develop green electronics. Herein, an ultra‐flexible and transparent biomass‐derived conductive substrate is originated from nature polylactic acid (PLA) with silver nanowires (AgNWs) modified by PH1000. The composite electrode exhibits low sheet resistance of 25 Ω sq−1, high transmittance (over 82% in the region of 400–800 nm), and excellent mechanical durability. After bending tests of 15 000 times at a curvature radius of 3 and 5 mm, the sheet resistances of the composite electrodes only increase to 89 and 51 Ω sq−1, respectively. Biomass electrode–based flexible perovskite solar cells are demonstrated with a champion power conversion efficiency (PCE) of 11.44% and high bending tolerance with preserving over 86% of the initial PCE after 1500 bending cycles at a curvature radius of 5 mm. The biomass electrode exhibits great potential for the development of green flexible devices.

Polycrystalline zirconium metal-organic framework membranes supported on flexible carbon cloth for organic solvent nanofiltration

Water-stable zirconium metal-organic frameworks (Zr-MOFs) such as the UiO-66 series have been recently identified as promising materials for polycrystalline membranes. However, the reliance of such membranes on rigid and expensive ceramic substrates with low packing density has greatly limited their wider applications. Herein, we report polycrystalline UiO-66(Zr)–NH2 membranes grown on cheap and flexible carbon cloth by in situ solvothermal synthesis. The membranes possess sub-micron thicknesses with a certain flexibility and angular bend tolerance up to 10°. In addition, these membranes exhibit great separation performance in organic solvent nanofiltration (OSN) because of their excellent solvent resistance, with above 99.8% dye rejection and high flux for dichloromethane (ca. 0.17 kg m−2 h−1 bar−1). Our study paves the way toward the development of polycrystalline Zr-MOF membranes for challenging liquid separations.

Rheological properties and screen printability of UV curable conductive ink for flexible and washable E-textiles

As a critical component for the realization of flexible electronics, multifunctional electronic textiles (e-textiles) still struggle to achieve controllable printing accuracy, excellent flexibility, decent washability and simple manufacturing. The printing process of conductive ink plays an important role in manufacturing e-textiles and meanwhile is also the main source of printing defects. In this work, we report the preparation of fully flexible and washable textile-based conductive circuits with screen-printing method based on novel-developed UV-curing conductive ink that contains low temperature and fast cure features. This work systematically investigated the correlation between ink formulation, rheological properties, screen printability on fabric substrates, and the electrical properties of the e-textile made thereafter. The rheological behaviors, including the thixotropic behavior and oscillatory stress sweep of the conductive inks was found depending heavily on the polymer to diluent ratio in the formulation. Subsequently, the rheological response of the inks during screen printing showed determining influence to their printability on textile, that the proper control of ink base viscosity, recovery time and storage/ loss modulus is key to ensure the uniformity of printed conductive lines and therefore the electrical conductivity of fabricated e-textiles. A formulation with 24 wt% polymer and 10.8 wt% diluent meets all these stringent requirements. The conductive lines with 1.0 mm width showed exceptionally low resistivity of 2.06 × 10−5 Ω cm Moreover, the conductive lines presented excellent bending tolerance, and there was no significant change in the sample electrical resistance during 10 cycles of washing and drying processes. It is believed that these novel findings and the promising results of the prepared product will provide the basic guideline to the ink formulation design and applications for screen-printing electronics textiles.