Bending Performance Research Articles

Multi-rings modulation and hole-assisted fiber under single-mode operation

In this paper, we propose a novel air-hole-assisted step refractive index fiber. Air holes located in the cladding can ensure the single-mode operation of the proposed fiber. The triangular refractive index ring structure further enlarges large mode field area. Bending performance of the proposed fiber is analyzed by the finite element method with perfectly matched layers, and the influence rule of each structure parameter on bending performance is summarized. Numerical results show that the proposed fiber can achieve stable single-mode operation over a wide wavelength range from 1.5 μm to 1.9 μm at a tight bending scale of 10 cm. Effective mode field area can reach 1002.73 μm2, and the bending loss of fundamental mode (FM) is only 0.000827 dB/m at the working wavelength of 1.55 μm; meanwhile, the loss ratio between higher-order mode (Homs) and fundamental mode is 7240. The proposed fiber is more stable compared to photonic crystal fibers. The change in bending angle does not affect the single-mode operation, and this novel fiber has potential applications in high-power lasers.

Experimental Study on Double-Joint Soft Actuator and Its Dexterous Hand.

In this paper, we propose a pneumatic double-joint soft actuator based on fiber winding and build a dexterous hand with 11 degrees of freedom. Firstly, soft actuator structural design is carried out according to the actuator driving principle and gives the specific manufacturing process. Then, an experimental analysis of the bending performance of a single soft actuator, including bending angle, speed, and force magnitude, is carried out by building a pneumatic control experimental platform. Finally, a series of dexterous robotic hand-grasping experiments is conducted. Different grasping methods are used to catch the objects and measure the objects' change in height, length, and rotation angle during the experiment. The results show that the proposed soft actuator is more consistent with the bending rule of human fingers, and that the gestures of the dexterous hand are more imaginable and flexible when grasping objects. The soft actuator can carry out horizontal and vertical movements, and rotation of the object in the dexterous hand, thus achieving better human-computer interaction.

Drip molding process of PCM for improving thermal and moisture comfort of thermal protective clothing

The application of phase change materials (PCMs) in thermal protective clothing can effectively adjust the heat transfer through thermal storage, thus providing extra thermal protection to firefighter. However, the incorporation of PCMs resulted in lower thermal and moisture comfort, and greater weight bearing for firefighter. To solve the above deficiencies, a new method (drip molding process) was used to prepare the PCM thermal protective clothing with phase change temperatures (PCTs) of 25 °C and 42 °C. The effects of diameter and interval of droplet on physical and mechanical properties, were analyzed. A dynamic hotplate system was used to calculate total heat loss (THL) for evaluating the thermal and moisture comfort. The results showed that the drip molding process can effectively improve the air permeability and bending performance of the PCM fabrics compared with dry coating process. The weight of dripped fabrics was decreased by 50.99–257.76 g/m2. In addition, the thermal insulation for the dripped fabric systems had a minor change compared to the coated fabric systems (−14.02 %∼16.88 %), while there was a significant decline for the moisture resistance (65.3 %∼89.9 %). The THL for the dripped fabric systems increased by 88.7 %∼182.5 %, indicating that the thermal and moisture comfort of thermal protective clothing was significantly improved by the new method. The findings obtained by the study can be used to engineer thermal protective clothing that provide better wearing comfort for firefighter.

Mechanical properties of hybrid cross-laminated timber with wood-based materials

In this study, four wood-based materials (plywood, laminated veneer board (LVB), oriented strand board (OSB), and particle board (PB)) were proposed as layered materials for CLT to improve its shear performance. The fabricated hybrid CLT exhibited better bending, shear performance, and compressive strength than that of traditional CLT. The out-of-plane bending performance, in terms of modulus of elasticity and modulus of rupture, improved by 2912–5836 MPa and 1.89–18.54 MPa compared with that of traditional CLT. The out-of-plane shear modulus and strength of the LVB CLT and PLY CLT improved by 31.19–76.15 MPa and 0.5 MPa, respectively, compared with that of traditional CLT. The compressive strength of the hybrid CLT improved by 6.86–24.6 MPa. The cross-arranged veneer with the LVB and plywood exhibited rolling shear failure. The ratio of tensile and shear failure of LVB CLT and PLY CLT increased compared to traditional CLT. The failure mode of the hybrid CLT with OSB and PB exhibited shear failure in the middle of the panel thickness of the OSB and PB. This study confirmed an improvement in the mechanical properties of hybrid CLTs with wood-based materials. LVB and plywood hybrid CLTs exhibited the best results. Additional studies are required on the mechanical properties of hybrid CLTs in the arrangement direction of wood-based materials and in the minor direction of the hybrid CLT.

Bearing capacities and failure behaviors of bolt fasten wedge (BFW) active joints used in prestressed internal supports

In this paper, the bearing capacities and failure behaviors of bolt-fastened wedge active joints used in prestressed internal supports are studied. A thorough exploration of the design of the bolt-fastened wedge active joint is elaborated, and an overview, working mechanism, stiffness analysis, parameters, and strength checking are provided. Then, loading tests are conducted on four full-scale specimens. One test is an axial compression test, while the other three tests are performed to analyze the long-axis (Y-axis) eccentricity, short-axis (X-axis) eccentricity, and biaxial (XY-axis) eccentricity. The load–displacement curve, load–strain curve, bending moment-rotation curve, and failure mode of each specimen are obtained. The experimental results show that the samples have good compressive properties and bending resistance. The impact of the X-axis and Y-axis eccentricities on the compressive ultimate bearing capacity is investigated, revealing a significant reduction in the former, while the latter has a minimal effect. Under bidirectional eccentricity, the weakening of the axial bending performance is most apparent. Bidirectional eccentric loads lead to a reduction in the yield load and initial compression stiffness to approximately 90% of those observed under unidirectional eccentricity. Finally, a field test is carried out to compare the constructability and load-holding performances of bolt-fastened wedge active joints with those of commonly used steel wedge active joints. It is demonstrated that the bolt-fastened wedge active joint effectively maintains prestress through bolt fastening, substantially enhancing the safety of foundation pit excavation construction.

Interface failure identification of argon/nitrogen double plasma modified hybrid laminated para‐aramid composites

AbstractThis work reveals the synergistic effect of argon/nitrogen double plasma alteration on the mechanical properties of para‐aramid fiber/epoxy resin composites with various laminating sequences. Acoustic emission monitored interface failure during tensile, bending and fracture testing. A comparative analysis was conducted on the bending performance of the composites modified by argon/nitrogen double plasma and single plasma. The results showed that the synergistic effect of nitrogen and high‐energy molecule argon optimized the modifying effect of argon/nitrogen double plasma. The optimal modification parameters obtained through fiber extraction testing analysis are power 200 W, time 120 s, and Ar/N2 double gas flow rate of 12 sccm. After plasma treatment, twill weave modifies better than plain weave. The AE signal amplitude of PX1 is minimized during stretching. Due to the difference in internal bending stiffness of PX2, interface delamination failure is more likely to occur. The PX5 had greater fiber and matrix debonding failure between mode‐II fracture tests due to the weak modification effect of plain weave and its difficulty in deformation. In ballistic testing, PX1 blocks impact force through fiber bundle stretching deformation, while PX4 is more brittle.Highlights Prepare para‐aramid/epoxy resin composites with various laminating sequences. Study on the interfacial properties of composites treated with double plasma. The composites with different gas sources treatment were analyzed. Acoustic emission analysis was used to identify interface failure modes. The bonding strength between plain and plain interfaces is the lowest.

Crack propagation and failure mechanism of 3D printing engineered cementitious composites (3DP-ECC) under bending loads

Engineered cementitious composites (ECC), as a self-reinforcing material featuring the characteristic of multiple cracking and strain hardening, provides a feasible solution to overcome the dependence on steel reinforcement in 3D concrete printing (3DCP). Nevertheless, interlayers in 3D printing ECC (3DP-ECC) create potential paths for crack propagation under bending load, which is expected to result in different failure mechanisms for bent 3DP-ECC. Different from the conventional multiple cracking behaviors of cast ECC, the test results reveal that 3DP-ECC exhibits two new crack propagation modes depending on the interface bond strength. In the first mode, bending cracks deflect into the interlayer, leading to the splitting of two adjacent filaments, while the filaments in the upper part of the interface crack countinue to exhibit multiple cracking behavior and bear loads. In the second mode, the localized shearing cracks became dominant when the interlayer bond strength was excessively low. This study comprehensively discusses the bending performance and failure mechanisms of 3DP-ECC exhibiting different crack propagation modes. The findings are valuable for enhancing the ductility design of 3DP-ECC beam components, ultimately contributing to the improvement of 3D concrete printing technology.

Fabrication of thin-walled hat-shaped beams from ultrahigh strength steel by laser-assisted robotic roller forming

Laser-assisted robotic roller forming (LRRF) can be applied to forming ultrahigh strength sheets to products with high geometrical accuracy. In this study, the geometrical profiles and three-point bending performance of thin-walled hat-shaped beams formed by LRRF and robotic roller forming (RRF, i.e., without laser heating) were experimentally investigated. It is found that the geometrical distortion resulted from the accumulation of longitudinal tension during multi-pass roller forming is significantly alleviated by LRRF. In addition, the bending performance of LRRF beam assembly is ameliorated at the initial deformation stage of three-point bending. The improvement is ascribed to a smaller bending radius and the alter of mechanical properties at the laser heat-affected zone. The lower geometrical precision of beams formed without laser heating results in early failure of spot welds of the beam assembly during three-point bending. LRRF beam assembly exhibits larger displacements at failure, and the failure mode is cracking at the edge of the laser-irradiated region. The pronounced microstructure differences on both sides of the crack suggest that the obvious laser-induced mechanical property gradients are responsible for the failure of LRRF beam assembly during three-point bending.

Batch fabrication of the smooth-surfaced and tailored-diameter microfiber Bragg grating sensors using hydrothermal method and its characteristics

Microfiber Bragg grating sensors hold great promise given their compactness and large evanescent field effect. The fabrication method of the sensors plays a pivotal role in determining the performance. In this study, a novel approach for batch manufacturing microfiber Bragg grating sensors was proposed using a NaOH solution under hydrothermal conditions. Compared to other methods, it is simpler, safer, and more efficient. Through precisely controlling the reaction time, 50 microfiber Bragg grating sensors were produced with smooth surfaces, exhibiting a surface roughness of about 87 nm, and achieved tailored fiber diameters with an error of only ± 1.2918 μm. In addition, the sensors with different diameters produced by the method to systematically investigate the effects of diameter reduction on various aspects, including spectral characteristics, temperature, strain, refractive index sensing, and bending performance, accompanied by theoretical explanations.

Characterization and Prediction of Plane Strain Bendability in Advanced High-Strength Steels

The rapid development of new classes of automotive steels such as the 3rd generation of advanced high-strength steels has created the need for the efficient characterization of their mechanical properties in loading scenarios other than uniaxial tension. The VDA 238-100 tight radius bend test has gained widespread acceptance in recent years for characterizing performance in plane strain bending, but there is uncertainty surrounding the use of the bend angle and its interrelation with the test parameters. The objective of the present study is to investigate the intertwined effects of the sheet thickness, bend radius, and tensile properties upon the bendability of seven advanced high-strength steels in different thicknesses for a total of 83 conditions. Practical correlations are developed to predict the bend angle and plane strain fracture strain as functions of the bending conditions and tensile mechanical properties. An extensive dataset comprising 26 additional advanced high-strength steel test cases was compiled from the literature to evaluate the proposed correlation for the plane strain fracture strain.

Unbonded Pre-Tensioned CF-Laminates Mechanically Anchored to HSC Beams as a Sustainable Repair Solution for Detachment of Bonded CF-Laminates

The present article outlines a Finite Element Model (FEM) that was created and validated by comparing it to prior experimental investigations to estimate the flexural performance of HSC beams strengthened with exterior bonded, unbonded, and unbonded pre-tensioned Carbon Fibre Reinforced Polymer (CFRP) sheets in several patterns. Nonlinear analysis was performed on three-point-loaded beams using ANSYS software, incorporating the constitutive characteristics of various components (concrete, CFRP, and steel). The comparison of FE-models and experimental data, namely for load-deflection curves, crack patterns, and failure modes, revealed that the developed numerical FE-models and experimental outcomes are in good accord. There has been numerous prior research on the behavior of beams strengthened with externally bonded CFRP sheets, but few on those reinforced with externally unbonded CFRP laminates, and even fewer on HSC beams reinforced with externally unbonded pre-tensioned CFRP laminates. Therefore, the major contribution of this article is to investigate the flexural behavior of HSC beams strengthened utilizing externally unbonded pre-tensioned CFRP laminates. The analysis revealed that the bending performance of RC-beams strengthened using external unbonded pre-tensioned CFRP-laminates is quite similar to that of bonded CFRP-strengthened beams, indicating a high potential for tackling the durability issues caused by detachment of bonded CFRP-strips in such structural elements. The existence of a fully wrapped CF sheet forced the beam to develop diagonal shear cracks in the region between the wrapped CF sheet and beam supports while also enhancing the flexural cracked zone at mid-span to change from smeared to discrete fractures. The flexural fractures spread over a deeper and wider area of the beam as a result of the incorporation of a half-wrap CF laminate. Externally unbonded CFRP-sheets pre-tensioned with 45% of the CFRP ultimate strength utilizing various patterns (straight and U-wrap) performed similarly to bonded CFRP-sheets, with a slight boost in load capacity of around 4.5% and notable reduces in deflection ranging from 9.7% to 16.24%. Using exterior unbonded CFRP laminates to strengthen RC-beams resulted in a flexural capacity increase ranging from 22.3% for NC beams to 71.6% for HSC beams.

Study on mechanical properties of poplar timber bending members of ancient buildings strengthened with CFRP sheets embedded

The reduction of the section area of timber beams in ancient buildings leads to the decline of their flexural mechanical properties. In order to study the effect of the reinforcement method with near-surface mounted CFRP sheets, three groups of 14 scaled poplar timber beam specimens were designed for static loading tests, and the strengthening effects of the new members replacing the damaged members and the concealed CFRP sheets strengthening the damaged members were compared. The results show that the ultimate flexural capacity and flexural stiffness of the strengthened timber beams are significantly improved compared with the simulated damaged beams; the bending performance of the optimum strengthened timber beam is equivalent to that of the undamaged beam. The distribution of the section strain of the strengthened timber beam along the height of the beam section basically conforms to the plane section assumption. A formula for calculating the ultimate flexural capacity of poplar timber beams strengthened with CFRP sheets is proposed. The calculated results are in good agreement with the experimental results.

A Novel Extensible Continuum Robot with Growing Motion Capability Inspired by Plant Growth for Path-Following in Transoral Laryngeal Surgery.

This article presents a novel extensible continuum robot (ECR) with growing motion capability for improved flexible access in transoral laryngeal procedures. The robot uses an extensible continuum joint with a staggered V-shaped notched structure as the backbone, driven by the pushing and pulling of superelastic Nitinol rods. The notched structure is optimized to achieve a wide range of extension/contraction and bending motion for the continuum joint. The successive and uniform deflection of the notches provides the continuum joint with excellent constant curvature bending characteristics. The bidirectional rod-driven approach expands the robot's extension capabilities with both pushing and pulling operations, and the superelasticity of the driving rods preserves the robot's bending performance. The ECR significantly increases motion dexterity and reachability through its variable length, which facilitates collision-free access to deep lesions by following the anatomy. To further exploit the advantages of the ECR in path-following for flexible access, a growing motion approach inspired by the plant growth process has been proposed to minimize the path deviation error. Characterization experiments are conducted to verify the performances of the proposed ECR. The extension ratio achieves up to 225.92%, and the average distal positioning error and hysteresis error values are 2.87% and 0.51% within the ±120° bending range. Compared with the typical continuum robot with a fixed length, the path-following deviation of this robot is reduced by more than 58.30%, effectively reducing the risk of collision during access. Phantom experiments validate the feasibility of the proposed concept in flexible access procedures.

Structural performance of a novel combined nested bolted joint for aluminum alloy mega-latticed structures

A novel steel-aluminum joint system is first presented for aluminum alloy mega-latticed structures. This joint can be effectively applied to the connection of large-diameter tube members with complex spatial locations in space structures. The joint's finite element model is examined and validated, followed by a case study of one joint, including static analysis and an analysis of the bending moment-rotation curve. According to the moment-rotation curve, the joint is classified as a type of semi-rigid joint. Furthermore, the analysis considers key parameters that impact the joint's bending, axial, and torsional performance, such as the number of bolts per ring, the rings of bolts, and the thickness of the joint zone. Two simplified formulas for joint stiffness are proposed to evaluate the overall structural stability. Finally, a stability analysis of an aluminum alloy mega-latticed structure is conducted, incorporating this joint and the proposed simplified formulas. The ultimate load of the mega-latticed structure with the joints is found to be about 0.7 of that with ideal rigid joints with the same parameters. This paper presents a potential solution for appropriate connections in large-span aluminum alloy mega-lattice structures, thereby serving as a reference for the design of the joints in related space structures.

Bending performance and failure mechanisms of hybrid and regular sandwich composite structures with 3D printed corrugated cores

The effect of core geometry and hybridization on the bending performance and failure mechanisms of carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) corrugated sandwich composite structures (SCS) were experimentally investigated using a three-point bend test. The CFRP and GFRP corrugated cores and facesheets were produced using Fused Filament Fabrication (FFF) and vacuum-assisted infusion processes, respectively. Three types of corrugated SCSs were built: SCSs with different core geometries (circular, square, trapezoidal, sinusoidal, and triangular), hybrid SCSs with different CFRP and GFRP cores and facesheets, and fully 3D-printed CFRP and GFRP SCSs. The corrugated SCS with square core geometry outperformed due to the presence of vertical walls and a large bonding area. The hybrid SCSs with a CFRP core showed a significant load drop due to shear failure in the 3D-printed core caused by weak inter-layer bonding. In contrast, the hybrid SCS with a GFRP core deformed plastically and absorbed more energy without failure due to strong inter-layer bonding. In fully 3D printed SCSs, the GFRP specimen failed catastrophically due to higher bending stress at the bottom facesheet, while the CFRP undergoes plastic deformation without failure. Results elucidate that the hybrid corrugated SCS with a GFRP top facesheet and 3D-printed core is an appropriate configuration for superior bending performance. The proposed 3D-printed SCS enables optimising complex shapes and material distribution in the core, resulting in improved strength-weight ratios. These findings will make an important contribution to the design and development of fibre-reinforced 3D-printed SCS for lightweight and high-performance applications.

Analysis of epoxy composites reinforced with jute, banana, and coconut fibers and enhanced with Rubik's layer: Tensile, bending, and impact performance evaluation

This research paper presents a comprehensive analysis of epoxy composites fortified with natural fibers such as jute, banana, and coconut, further augmented by the incorporation of Rubik's layer, aimed at evaluating their mechanical performance in terms of tensile, bending, and impact properties. As sustainable alternatives to traditional reinforcement materials, these natural fibers offer the advantage of low environmental impact, renewability, and biodegradability. The Rubik's layer, known for its three-dimensional interlocking structure, holds promise in enhancing composite properties due to its unique geometry and material characteristics. The study involves the fabrication of composite specimens through a systematic layering process, varying the composition of natural fibers and Rubik's layer. A comprehensive experimental campaign is conducted to assess the tensile strength, bending modulus, and impact resistance of the resultant composites. The results are systematically compared against those of pristine epoxy composites to ascertain the influence of the added reinforcements and enhancement layer. The findings reveal distinctive trends in mechanical behavior based on the type and proportion of natural fibers employed. Notably, the jute-reinforced composites exhibit commendable tensile and bending properties, while banana and coconut reinforcements contribute to improved impact resistance. The introduction of the Rubik's layer further refines these properties, with discernible variations based on its placement within the composite structure. This paper offers valuable insights into the multifaceted impact of natural fiber reinforcements and Rubik's layer incorporation on epoxy composites. The systematic evaluation of mechanical attributes provides a comprehensive understanding of the synergistic effects among these constituents. As the demand for sustainable and high-performance materials escalates, this research contributes to the growing body of knowledge on composite design, catering to diverse engineering applications that prioritize mechanical excellence and ecological responsibility.

Bending performance of the CORC cable with flexible interlocked stainless steel former

The high temperature superconducting cable on round core (CORC) is a kind of cable that could be used in fusion projects. Nevertheless, conventional copper former CORC cables require a large external force to allow the cable to endure plastic deformation and be tightly wound into solenoids. In this case, the superconducting tape will be affected by concentrated stress, resulting in a risk of critical current degradation. Therefore, this paper proposes a new CORC cable with flexible interlocked stainless steel former, which can be wound into a solenoid by applying a small external force. To verify the bending performance of this interlocked former CORC cable, a double-layer and a ten-layer interlocked stainless steel former CORC cable, as well as a double-layer traditional copper former CORC cable, are fabricated. And these three CORC cables are used to wind solenoids of various radius sizes respectively. The experimental results show that the critical bending radius of the double-layer interlocked stainless steel former CORC cable is less than 20 mm, the critical bending radius of the ten-layer interlocked stainless steel former CORC cable is less than 50 mm, and the critical bending radius of the double-layer traditional copper former CORC cable is larger than 55 mm. A self-consistent finite element model for the critical current of the CORC cable solenoid is also established. And the critical current experimental results are in good agreement with the simulation results. The results of this paper verify the excellent bending performance of the interlocked former CORC cable, which provides a good option for the preparation of insert magnets for future fusion projects.

Bending Performance of Timber Beam Strengthened with Passive Prestressing

Prestressing technology and its application is common in concrete design and construction particularly in Malaysia and most parts of the world. However, prestress strengthening in timber is rare and not widely applied especially in Malaysia. Application of prestressing in timber has the potential to allow the use of longer span with reduced cross-sectional size and simultaneously exhibiting some level of ductility through the prestressing rod since timber material is susceptible to brittle tensile failure. This paper highlights exploratory research into the extent of bending performance enhancement in Malaysian Kempas species timber beam strengthened by way of passive prestressing. The research was conducted to investigate the change in bending strength and moment capacity of timber beam with passive prestressing rods installed at different lever arm positions, and the enhancement of moment capacity of timber beam with and without passive prestressing. Five Kempas timber specimen configurations with size of 40 mm (b) × 90 mm (d) × 900 mm (l) were prepared for four-point bending tests, and their bending behaviours were evaluated. The timber beam with passive prestressing steel rods applied at tension side bottom fibre of timber beam exhibited the greatest enhancement in bending performance and stiffness. The improvement of bending performance ranges from 1.1 to 1.5 times greater compared to the timber beam without prestressing steel rods. The improvement of stiffness in prestressed timber beam is up to 11% at service limit state and a reduced rate of stiffness degradation is prominent.

Study of flexible metasurface with gold rod resonators on ploymide substrate in terahertz waveband

A flexible metasurface based on gold rod resonator arrays on a polyimide substrate in the terahertz band is presented. Four different resonator structures with various azimuth angle were designed and investigated. Experimental results demonstrate that the azimuth angle of the gold rod resonators have a significant impact on the terahertz waves under different polarization conditions. Experimental studies on the bending performance reveal that the spectral modulation characteristics of the flexible metasurface is robust within a degree of bending. In addition, the effect of the incident angle on the resonant peaks was investigated, and the redshift of the high-frequency resonant peak was found as the incident angle increases.

Ablation properties of SiC-reinforced PBI resin matrix composites under high-energy continuous laser ablation

In this work, poly-p-phenylene benzobisoxazole (PBO) fibers reinforced polybenzimidazole (PBI) resin-based laser ablation composites (thickness = 5 mm) with different SiC contents were prepared. SiC/PBI/PBO composites exhibited good mechanical properties, excellent thermal stability and laser ablation properties. The laser ablation properties and ablation mechanism of the composites were investigated using a high-energy continuous-wave laser (30 MW·m−2). Increasing the SiC content led to increase in composites density, while decreasing the bending performance of the composites. However, it improves the mass and linear ablation rates, resulting in an overall improvement in ablation properties. At a SiC content of 70 %, the composite exhibited a mass loss of 8.2 %, a mass ablation rate of 9.2 mg·s−1, and a linear ablation rate of 0.11 mm·s−1. The ablation process of SiC/PBI/PBO composites was delineated into pre-ablation and post-ablation stages, with the ablated composites divided into the ablation center, transition region, and outer region based on morphological characteristics. After ablation, numerous white hollow SiO2 spheres and SiO2 protective layers were formed in the ablation centers, the transition regions were deformed and cracked, while the outer region remained unscathed.