Bending Direction Research Articles

Novel uniplanar pedicle screw systems applied to thoracolumbar fractures: a biomechanical study.

Objective: In this study, the advantages of the internal fixation configuration composed of uniplanar pedicle screws in the treatment of thoracolumbar fractures were verified by biomechanical experimental methods, which provided the basis for subsequent clinical experiments and clinical applications. Methods: A total of 24 fresh cadaveric spine specimens (T12-L2) were utilized to conduct biomechanical experiments. Two different internal fixation configurations, namely, the 6-screw configuration and the 4-screw/2-NIS (new intermediate screws) configuration, were tested using fixed-axis pedicle screws (FAPS), uniplanar pedicle screws (UPPS), and polyaxial pedicle screws (PAPS) respectively. The spine specimens were uniformly loaded with 8NM pure force couples in the directions of anteflexion, extension, left bending, right bending, left rotation, and right rotation, and the range of motion (ROM) of the T12-L1 and L1-L2 segments of the spine was measured and recorded to access biomechanical stability. Results: No structural damage such as ligament rupture or fracture occurred during all experimental tests. In the 6-screw configuration, the ROM of the specimens in the UPPS group was significantly better than that of the PAPS group but weaker than those of the FAPS group (p < 0.01). In the 4-screw/2-NIS configuration, the results were identical to the biomechanical test results for the 6-screw configuration (p < 0.01). Conclusion: Biomechanical test results show that the internal fixation configuration with UPPS can maintain the stability of the spine well, and the results are better than that of PAPS. UPPS has both the biomechanical advantages of FAPS and the superiority of easy operation of PAPS. We believe it is an optional internal fixation device for minimally invasive treatment of thoracolumbar fractures.

Flexible, anisotropic strain sensor based on interdigital capacitance for multi-direction discrimination

The direction information of strain plays a pivotal role in practical applications such as soft robots and human-machine interfaces. However, most of the multi-directional strain sensors studied before are integrated devices, which accomplish the strain direction discrimination through the signal difference of independent sensing units when they are stretched, thus increasing the complexity of the detection system. In this article, a multi-directional flexible strain sensor based on an interdigital capacitance structure is reported. The structure enables opposite variation of the capacitance changes in the orthogonal direction because the device exhibits different structural deformation depending on the direction of strain, thus detecting multiple direction strain by a single device. This sensor is fabricated by a one-step transfer method, which takes advantage of the excellent electrical conductivity of silver nanowires and the extremely low surface adhesion of the release film. The strain range of this sensor can be up to 60%. The influence of the structural parameters of the sensor on the gauge factor (GF) is explored to optimize capacitance structure parameters. The device shows good stability dynamic response (0.1–1.0 Hz). When the angle of strain direction changes from 0° to 90°, the GF changes from 1.1 to -0.56. Furthermore, owing to the high sensitivity and excellent stability of the sensor, human motion such as the bending direction of the wrist, can be accurately detected by this sensor.

Wireless Power Transfer to Electrothermal Liquid Crystal Elastomer Actuators.

Wireless actuation of electrically driven soft actuators is of paramount importance for the development of bioinspired soft robotics without physical connection or on-board batteries. Here, we demonstrate untethered electrothermal liquid crystal elastomer (LCE) actuators based on emerging wireless power transfer (WPT) technology. We first design and fabricate electrothermal LCE-based soft actuators that consist of an active LCE layer, a conductive liquid metal-filled polyacrylic acid (LM-PA) layer, and a passive polyimide layer. LM can function not only as an electrothermal transducer to endow resulting soft actuators with electrothermal responsiveness but also as an embedded sensor to track the resistance changes. Various shape-morphing and locomotive modes such as directional bending, chiral helical deformation, and inchworm-inspired crawling can be facilely obtained through appropriately controlling the molecular alignment direction of monodomain LCEs, and the reversible shape-deformation behaviors of resulting soft actuators can be monitored in real-time through resistance changes. Interestingly, untethered electrothermal LCE-based soft actuators have been achieved by designing a closed conductive LM circuit within the actuators and combining it with inductive-coupling WPT technology. When the resulting soft actuator approaches a commercially available wireless power supply system, an induced electromotive force can be generated within the closed LM circuit, which results in Joule heating and wireless actuation. As proof-of-concept illustrations, wirelessly driven soft actuators that can exhibit programmable shape-morphing behaviors are demonstrated. The research disclosed herein can provide insights into the development of bioinspired somatosensory soft actuators, battery-free wireless soft robots, and beyond.

Printed Directional Bending Sensor with High Sensitivity and Low Hysteresis for Human Motion Detection and Soft Robotic Perception.

We present a high-performance flexible bending strain sensor for directional motion detection of human hands and soft robotic grippers. The sensor was fabricated using a printable porous conductive composite composed of polydimethylsiloxane (PDMS) and carbon black (CB). The utilization of a deep eutectic solvent (DES) in the ink formulation induced a phase segregation between the CB and PDMS and led to a porous structure inside the printed films after being vapored. This simple and spontaneously formed conductive architecture provided superior directional bend-sensing characteristics compared to conventional random composites. The resulting flexible bending sensors displayed high bidirectional sensitivity (gauge factor of 45.6 under compressive bending and 35.2 under tensile bending), negligible hysteresis, good linearity (>0.99), and excellent bending durability (over 10,000 cycles). The multifunctional applications of these sensors, including human motion detection, object-shape monitoring, and robotic perceptions, are demonstrated as a proof-of-concept.

Seismic behavior and modeling of elliptical concrete-filled FRP tubes with longitudinal steel rebars under lateral cyclic load and vertical constant load

Concrete-filled FRP tubes (CFFTs), which consist of a confining tube made of FRP, the internal concrete core and optional longitudinal reinforcements made of FRP or steel, are a novel type of structural member particularly attractive for new civil and industrial structures. Existing studies on CFFTs are mainly about specimens fabricated with a circular, a square or a rectangular FRP tube, while there are rather limited studies on CFFTs with an elliptical FRP tube. Similar to circular CFFTs, elliptical CFFTs have a cross-section with a continuous curved circumference, leading to effective confinement to the internal concrete. Elliptical CFFTs are attractive for engineering applications due to their appealing aesthetic appearance as well as different bending capacities around two symmetrical axes. This paper systematically investigated elliptical CFFTs reinforced with longitudinal steel rebars (ER-CFFTs) under combined lateral cyclic load and vertical constant load with special research attentions on the influences of elliptical aspect ratio (i.e., the ratio of the sectional major axis over the sectional minor axis, which was ranging from 1.0 to 2.5 with an interval of 0.5). The effects of the FRP thickness and the bending direction of lateral cyclic load were also investigated. Test results indicated that, the elliptical FRP tube had been effectively utilized to provide confinement during the cyclic loading process; ER-CFFTs exhibited generally rounded hysteretic curves with limited pinching, even for the specimen with a large elliptical aspect ratio of 2.5; the ductility of ER-CFFTs showed a general tendency to increase with the elliptical aspect ratio except the specimen with an elliptical aspect ratio of 2.5. A numerical model was established to simulate the seismic performance of ER-CFFTs, which was able to yield predictions with reasonable accuracy. In practical engineering, the elliptical aspect ratio for ER-CFFTs should be optimized according to the bending demand around two symmetrical axes.

A Locally Disordered Metamaterial for Directing and Trapping Water Waves

Manipulating the flow of water wave energy is crucial for ocean wave energy extraction or coastal protection, and the emergence of metamaterials paves a potential way for controlling water waves. In this work, by introducing a local disorder in a cavity-type metamaterial constructed by split-tube resonators, we show that water waves can be guided in an open channel with multiple energy flow paths formed merely by surrounded disconnected concurrent resonators that can serve as invisible walls without the requirement of a whole array system such as general periodic structures or waveguides. Specifically, we numerically and experimentally validate that a T-shaped metamaterial can achieve free guiding of water waves in a narrow band and a band-edge state along a distinct path. This open-space water waveguiding is found to be dominated by Fano-type interference and Fabry–Pérot resonance. Two distinct propagating modes, a low-frequency “trapping mode” and a high-frequency “following mode”, are identified. By simply rotating two configuration-dependent unit cells at the intersection of the metamaterial, we achieve a variety of water waveguiding paths tuning along rectilinear or bending (splitting or turning) directions, which rely on the two different propagating modes.

Towards the Effectiveness of 3D Printing on Tactile Content Creation for Visually Impaired Users.

We have conducted research on how tactile content is created for visually impaired individuals. From the data collected, an experiment was developed and applied. It investigated alternative materials to serve as a basis for the use of 3D printing to reduce production costs. It also evaluated the adherence of different values of width, height, and angles of the contour lines, as well as different geometric shapes and top/bottom fill patterns on these materials. The results show it is possible to use cellulose-based materials weighing between 120 g/m2 and 180 g/m2 to support the prints instead of making a base for the information, with gains up to 40 times in production time and up to 29 times in the consumption of materials if there is no need to fold the manufactured content. Based on visually impaired every-day activities such as locating and following a line (exploration), discerning different textures (tactile discrimination), identifying figures (picture comprehension), and locating copies of them (spatial comprehension), the ideal line widths for 3D printing adherence regarding tactile content creation were found to be between 0.8 mm and 1.2 mm, while 0.4 mm was the maximum height that did not compromise adherence. When bending the 3D printed material on the surface, we found that lines with angles between 0° and 20° from the bending direction could keep their adherence as well. The shapes must receive a small rounding at the corners and preferably align themselves with the mentioned angles. The top/bottom fill patterns did not affect adhesion. The infill can be used as a texture generator and should be adjusted to densities of 10% to 50%, or 10% to 90% when combined with other textures. In the first case, users were able to perceive differences in the tactile content whenever a single infill pattern was used. In the latter, combining two infill patterns leads to a more discriminating surface, resulting in a higher number of textures to be used in tactile content production (analogous to the number of colors used in an image for a person with no visual impairment).

Synthesis and properties of high-entropy CoCrFeNiMnWx alloys

Compact samples and coatings from CoCrFeNiMnWx high entropy alloys (HEAs) powders synthesized by mechanical alloying followed by plasma spheroidization (PS) were obtained by directed energy dssssseposition (DED). The microstructure of CoCrFeNiMnWx samples obtained by DED represents a cast dendritic structure. The phase composition of all samples represents a solid solution with FCC lattice. The increase in the lattice parameter in the samples by 0.33–0.47% compared to the spheroidized powder is characteristic of all obtained alloys after DED. The lattice parameter of CoCrFeNiMnWx samples increases with increasing W content, which is associated with the formation of a highly entropic solid replacement solution. The hardness of the samples increased by 4.6% and 12.9% with the addition of W in amounts of 0.125 and 0.25 at. % to the CoCrFeNiMn HEA, respectively. Tungsten-doped alloy coatings have a higher bending strength than the CoCrFeNiMn alloy. With relatively similar ductility values, the CoCrFeNiMn alloy has a lower strength, which is insufficient to resist cracking when bent to an angle above 20–45°, depending on the bending direction.

Is implant choice associated with fixation strength for displaced radial neck fracture: a network meta-analysis of biomechanical studies

The multitude of fixation options for radial neck fractures, such as pins, screws, biodegradable pins and screws, locking plates, and blade plates, has led to a lack of consensus on the optimal implant choice and associated biomechanical properties. This study aims to evaluate the biomechanical strength of various fixation constructs in axial, sagittal, and torsional loading directions. We included biomechanical studies comparing different interventions, such as cross/parallel screws, nonlocking plates with or without augmented screws, fixed angle devices (T or anatomic locking plates or blade plates), and cross pins. A systematic search of MEDLINE (Ovid), Embase, Scopus, and CINAHL EBSCO databases was conducted on September 26th, 2022. Data extraction was carried out by one author and verified by another. A network meta-analysis (NMA) was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Primary outcomes encompassed axial, bending, and torsional stiffness, while the secondary outcome was bending load to failure. Effect sizes were calculated for continuous outcomes, and relative treatment ranking was measured using the surface under the cumulative ranking curve (SUCRA). Our analysis encompassed eight studies, incorporating 172 specimens. The findings indicated that fixed angle constructs, specifically the anatomic locking plate, demonstrated superior axial stiffness (mean difference [MD]: 23.59 N/mm; 95% CI 8.12–39.06) in comparison to the cross screw. Additionally, the blade plate construct excelled in bending stiffness (MD: 32.37 N/mm; 95% CI − 47.37 to 112.11) relative to the cross screw construct, while the cross-screw construct proved to be the most robust in terms of bending load failure. The parallel screw construct performed optimally in torsional stiffness (MD: 139.39 Nm/degree; 95% CI 0.79–277.98) when compared to the cross screw construct. Lastly, the nonlocking plate, locking T plate, and cross-pin constructs were found to be inferior in most respects to alternative interventions. The NMA indicated that fixed angle devices (blade plate and anatomic locking plate) and screw fixations may exhibit enhanced biomechanical strength in axial and bending directions, whereas cross screws demonstrated reduced torsional stability in comparison to parallel screws. It is imperative for clinicians to consider the application of these findings in constraining forces across various directions during early range of motion exercises, taking into account the distinct biomechanical properties of the respective implants.

Clinical importance of imaging anatomical signs in predicting transverse sinus dominance using conventional magnetic resonance imaging

Background: Differentiating flow gaps associated with hypoplastic transverse sinus from venous thrombosis is a diagnostic challenge in brain magnetic resonance imaging with venography. Objectives: To assess the clinical benefit of anatomical signs to anticipate the side of the dominant transverse sinus. Patients and Methods: A total of 100 patients underwent brain magnetic resonance imaging with venography at the radiology department /medical city and were retrospectively reviewed for the direction of superior sagittal sinus flow void, inclination of sulcus for the superior sagittal sinus, angulation of the posterior falx and direction of occipital lobe bending in axial non-contrast T1 weighted image, then compare these findings with a side of the dominant transverse sinus in magnetic resonance venography. Results: Inclination of sulcus for superior sagittal sinus and superior sagittal sinus flow void direction toward the right side had high positive predictive values (95.5%) and (93.2 %) in proper matching with the right transverse sinus dominance, respectively. Right-sided angulation of the posterior flax and rightward direction of the occipital lobe had a positive predictive value of (90.9 %) in predicting transverse sinus dominance. Conclusion: The side of dominant transverse sinus can be anticipated by reviewing anatomical signs in T1 weighted image, which may help to differentiate hypoplastic transverse sinus from venous thrombosis that aid in better interpretation of brain MRI- MRV examinations.

Similarity Model Test on Stress and Deformation of Freezing Pipe in Composite Strata during Active Freezing

In order to prevent the problem of freezing pipe fracture in the process of artificial freezing construction, taking the main shaft freezing project of Shandong Yuncheng Mine as the background and based on the similarity theory, the similarity model test of freezing pipe in the composite stratum of the active freezing section is carried out. The test results show that the distribution of freezing temperature field in sand layer and clay layer is “W”-shape, and the temperature at the interface of outer ring pipe is slightly higher than that of the inner ring pipe. The change rate of freezing temperature can be divided into three stages: rapid decreasing section, slow decreasing section, and stable section. Compared with the clay layer, the sand layer has the shorter freezing closure time and the lower freezing average temperature. The frozen pipe is always in the state of vertical compression in the clay layer, while in the state of vertical compression first and then vertical tension in the sand layer. The maximum compressive strain in the clay layer is −305 με, which is equal to the vertical compressive stress of 64.1 MPa. The maximum tensile strain in the sand layer is 406 με, which is equivalent to the tensile stress of 85.2 MPa. The bending direction of different freezing pipes is different in the different soil layers. The maximum bending strain of the frozen pipe in the clay layer is 779 με, which is 2.6 times the vertical strain at the same location, corresponding to the bending stress of 163.4 MPa and reaching 0.69 times of the yield limit of frozen pipe, while the bending strain in the sand layer is very small. The vertical strain and bending strain of freezing pipes at the interface of soil layers are very small, but the bending strain is still dominant.

Asymmetric bending characteristics and failure mechanism of bamboo under different loading directions

Bamboo has a special microstructure, its fiber content decreases gradually from the outside to the inside. This kind of gradient distribution results in obviously asymmetric bending characteristics of bamboo, and shows different bending properties and failure modes in different bending directions. In this study, bending properties of moso bamboo (Phyllostachys pubescens) in three different directions (type A: outward bending, type B: tangential bending, type C: inward bending) were tested. Digital image correlation (DIC) and scanning electron microscopy (SEM) were used to analyze the failure process, strain field change and failure morphology of bamboo, and summarized the failure mechanism of bamboo bending in different directions. Results indicated that the tangential bending have the highest modulus of rupture (MOR) and modulus of elasticity (MOE), and the inward bending has the best flexural toughness. The failure mechanism of the three bending directions was different. For type A, the initial crack appeared in the parenchyma tissue in the tensile region where the fiber content was less, so the crack rapidly expanded inside the parenchyma tissue, forming a neat failure section, then led to low toughness of bamboo. For type B, the initial crack appeared in the parenchyma tissue in the tensile region. Due to the moderate fiber content in the tensile region, the fiber bridging phenomenon appeared in the fracture section, led to the higher elastic modulus and strength of the type B. For type C, the initial crack appeared in the parenchyma tissue in the compression region. Because of the more fiber content in the tensile region, the cracks in this part propagated transversely and formed the failure morphology of interlayer separation, which increased the toughness of the specimen. This study is helpful to understand the asymmetric bending characteristics of bamboo, and provide guidance for the use of bamboo as a structural material and the preparation of composite materials.

Highly Improved Acetone Gas Sensing Performance of Mesoporous Cobaltosic Oxide Nanoparticles and Physical Mechanism

Mesoporous Cobaltosic oxide nanoparticles are now widely employed in a variety of applications across the world. It is both environmentally and economically favorable. It was well prepared in this study using a cost-effective thermal stirring procedure. The X-ray diffraction method at ambient temperature was used to explain the formation of single spinel structure, purity, and cat-ion distribution of the material, and the lattice constant of mesoporous Cobaltosic oxide nanoparticles was 8.23 Å. SEM and EDX examination were used to investigate phase formation, elemental content, and surface morphology. The average particle size for primitive mesoporous Cobaltosic oxide nanoparticles is 17nm. DRS determined the band gap for mesoporous Cobaltosic oxide nanoparticles to be 1.48 eV for direct band bending and 2.19 eV for indirect band gap. The sensitivities of the sample are greater due to the mesoporous-structures with a large surface area. Mesoporous Cobaltosic oxide nanoparticles have a greater specific surface area (59.63m2 g− 1), resulting in good acetone gas sensing characteristics at the optimal working temperature of 150°C. Furthermore, the sample exhibits high stability and selectivity against acetone gas. The gas-sensing mechanism is determined by comparing the sensitivity of Mesoporous Cobaltosic oxide nanoparticles to surface oxygen and acetone gas adsorption. It is the best among the top other materials, according to the results.

Innervation of Sensing Microchannels for Three‐Dimensional Stimuli Perception

AbstractStimuli perception enables animals and robots to interact with unknown environments safely and predictably. For the sensing of soft robotics and wearable devices, although electronic skins have already been widely accepted and studied, their planar geometries are not applicable for multi‐direction volume sensing. Herein, the innervation of sensing microchannel networks into elastic matrices to mimic the exteroception and proprioception of the human bodies is employed. Soft actuators with interlaced actuating and sensing microchannels resembling the distribution of muscle fiber and proprioceptors are fabricated and the internal stimuli perception of deformation configurations (bending, elongating, and bending directions) and magnitudes (bending angle and elongation) of the soft actuators are demonstrated. It is also demonstrated that a soft cubic sensor containing 3D microchannels (diameter: 400 µm) is capable of identifying 3D external stimuli, including force types (pressing, squeezing, shearing, and twisting) and real‐time directions by measuring the resistance variation, and its application in the virtual reality field is exhibited.

Design of a Molecular Dynamics Model for High-Performance Computing of Conformational Changes in Microtubule Protofilaments Associated with the Anticancer Drug Taxol

Molecular dynamics models of tubulin tetramers in complex with the anticancer drug taxol were created based on high-resolution spatial structures (PDB ID 3J6G). We tested performance of various computational architectures in molecular dynamics calculations of tubulin tetramers. We revealed the optimal computer architecture and carried out three 1 μs molecular dynamic trajectories of taxol-bound tubulin tetramer. We analyzed the conformational flexibility of tubulin tetramers in a complex with taxol, calculated the Euler angles for intra- and inter-dimer interfaces of the protofilament, as well as the degree and direction of protofilament bending. The stiffness of protofilaments was studied using the energy equipartition theorem. The results allowed us to conclude that taxol binding reduces stiffness at both the inter- and intra-dimer interfaces, which may facilitate the process of microtubule assembly.

Dynamic Behavior of Concrete: A Review

Abstract: Concrete properties are the most essential and critical physical material property when reinforced concrete structures are designed. Considering potential catastrophic accidents, testing of dynamic mechanical properties of concrete is one of the most urgent stages of development. A large number of scientific experiments have shown that the dynamic mechanical properties of concrete are influenced by strain rate. This paper covers the existed researches on the dynamic mechanical characteristics of concrete. Review of the relationship between concrete's dynamic compressive strength, deformation properties, elastic modulus, and energy dissipation capacity with strain rate. The results may vary depending on the loading technique, test apparatus, specimen size, and other variables. The study of dynamic tensile behavior of concrete was uncommon due to the limitations of experimental tools and testing methods. The data returns so far have been inconsistent and even at conflict with one another. The most widely used test techniques to investigate the dynamic tensile behavior of concrete are the direct tensile test, splitting test, bending test and spalling test.

Positive and Negative Changes in the Electrical Conductance Related to Hybrid Filler Distribution Gradient in Composite Flexible Thermoelectric Films Subjected to Bending

P-type multiwalled carbon nanotubes (MWCNTs), as well as heterostructures fabricated by direct deposition of inorganic thermoelectric materials as antimony and bismuth chalcogenides on MWCNT networks are known as perspective materials for application in flexible thermoelectric polymer-based composites. In this work, the electrical response of three types of Sb2Te3-MWCNT heterostructures-based flexible films-free standing on a flexible substrate, encapsulated in polydimethylsiloxane (PDMS), and mixed in polyvinyl alcohol (PVA) is studied in comparison with the flexible films prepared by the same methods using bare MWCNTs. The electrical conductance of these films when each side of it was subsequently subjected to compressive and tensile stress during the film bending down to a 3 mm radius is investigated in relation to the distribution gradient of Sb2Te3-MWCNT heterostructures or bare MWCNTs within the film. It is found that all investigated Sb2Te3-MWCNT films exhibit a reversible increase in the conductance in response to the compressive stress of the film side with the highest filler concentration and its decrease in response to the tensile stress. In contrast, free-standing and encapsulated bare MWCNT networks with uniform distribution of nanotubes showed a decrease in the conductance irrelevant to the bending direction. In turn, the samples with the gradient distribution of the MWCNTs, prepared by mixing the MWCNTs with PVA, revealed behavior that is similar to the Sb2Te3-MWCNT heterostructures-based films. The analysis of the processes impacting the changes in the conductance of the Sb2Te3-MWCNT heterostructures and bare MWCNTs is performed. The proposed in this work bending method can be applied for the control of the uniformity of distribution of components in heterostructures and fillers in polymer-based composites.

Mesoscale modelling of SFRC based on 3D RBSM considering the effects of fiber shape and orientation

In this study, a mesoscale model of steel fiber reinforced concrete (SFRC) based on 3D RBSM (rigid body spring model), was proposed to take the fiber shapes (straight and hook end) and orientation into account in concrete. The steel fibers were distributed into the Voronoi mesh system of RBSM, and a zero-size spring was assigned at the interface of Voronoi mesh crossed by discrete fiber, to transfer the fiber pullout load to the nearest nodes of RBSM. The straight steel fiber was modeled based on proposed local bond-slip relationship and the mechanical hook action was proposed additionally to model the hook end fiber. The model can predict the macroscopic response and cracking of SFRC made with straight and hook end fibers under direct tensile and bending loads. The analysis results found the mechanical hook action as the governing parameter for hook end fiber then the bond-slip properties for straight fiber. The fiber orientation and matrix spalling due to friction induced pullout load component, were found prominent for steel fiber. The anisotropy induced by fiber shapes and orientations was headed by hook end fiber with superior macroscopic load capacity by delaying the crack propagation and transformation.

Overall stability capacity design of T-shaped irregularly concrete-filled steel tube columns considering axial compression and any directional moments

A slender T-shaped irregularly concrete-filled steel tube column (T-ICFSTC) may be subjected to overall instability failure under combined axial load and moment. But current research is not available about a complete design of T-ICFSTCs subjected to axial compression and any direction bending moments because of a complicated parameter study involved in the analysis. This paper investigates the overall stability capacity performance and design prediction of the T-ICFSTCs that are formed by I-shaped steel, U-shaped steel and several cell infilled concrete. First, the finite element model for analyzing the overall instability performance and failure is established and verified by the previously experimental tests carried out by the authours. Then, the overall stability capacity of T-ICFSTC around its symmetric axis is investigated numerically and accordingly design formulas of φy-λny are established. In particular, interaction influence between initial imperfection direction and applied bending moment direction is studied, thus resulting in a critical initial imperfection direction relatively to applied bending direction. Sequently, the load-bearing capacity and performance under any direction bending moments are explored numerically and the normalized design curves reflecting interaction of N-M and Mx-My at their limit states are formulated by fitting the FE results of examples. Finally, a complete set of overall stability prediction formulas of T-ICFSTCs under combined axial load and any directional bending moment are established and the results obtained agree well with FE numerical investigation results.

Bend-resistant stress-type segmented cladding large-mode-area single-mode fibers.

We propose a novel bend-resistant stress-type large-mode-area fiber with segmented cladding, to the best of our knowledge, in which a high refractive index stress rod is introduced at the core, to improve the loss ratio between the least high-order mode (HOM) and fundamental mode loss, and to reduce the fundamental mode loss effectively. The mode loss and effective mode field area with or without heat load, and mode field evolution between the straight and bending transition are investigated, by utilizing the finite element method and the coupled-mode theory. The results show that the effective mode field area and the loss of the fundamental mode can reach up to 1050.1 µm2 and 0.0055d B⋅m -1, respectively, and the loss ratio between the least loss HOM and fundamental mode loss is greater than 210. The coupling efficient of the fundamental mode in the straight-bending transition reaches 0.85 at a wavelength of 1.064µm and a bending radius of 24cm. In addition, the fiber is insensitive to the bending direction and has excellent single-mode performance in any bending direction; the fiber maintains single-mode operation under heat load from 0 to 8W/m. This fiber has potential application in compact fiber lasers and amplifiers.