Bending Performance Research Articles

Experimental investigation on mechanical properties of Chinese fir composites as cross-laminated timber

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is a significant plantation species in South China. However, this plantation species is primarily utilized to produce low-value wood products. This study evaluated the feasibility of manufacturing cross-laminated timber using fast-grown small-diameter Chinese fir by investigating its bending performance and exploring the contribution of the lamination effect to the load capacity. Through bending tests and theoretical analysis, three different lay-ups with the same cross-laminated timber thickness (105 mm) but varying lamination thicknesses (35 mm, 21 mm, 15 mm) were examined. The results revealed that the 5-layer and 7-layer CLT, with the average bending strength of 37.4 MPa and 33.9 MPa, showed the significantly higher mean values than the 3-layer CLT (23.2 MPa). Moreover, the predicted ultimate loads and failure modes aligned with the experimental observations. Additionally, all mechanical criteria met the mechanical performance requirements for the 105 mm thick cross-laminated timber according to the ANSI/APA PRG 320 standard, except for bending stiffness. These findings provide valuable insights for improving the performance of Chinese fir cross-laminated timber made from small-diameter timber by optimizing lamination thickness and underscore the viability of producing cross-laminated timber using Chinese fir.

Experimental Investigation of the Three-Point Bending Property of a Sandwich Panel with a Metal Rubber Core

Sandwich structures and porous materials have been applied widely in various fields due to their excellent mechanical performance, and multifunctional composites will have a significant engineering demand in the future. Studying damped composites’ mechanical properties and failure forms has significant engineering value and significance. However, the current connecting processes for sandwich panels and porous materials must be improved. Therefore, to explore the ambiguity of the connection interface between the core material and panel in sandwich panels, as well as the mechanical properties of such structures, a sandwich panel with a metal rubber core material was prepared using vacuum brazing and cementing processes. Microscopic examinations using scanning electron microscopy and energy-dispersive spectroscopy were conducted to observe the physical bonding mechanism at the interface of the sandwich panel. The results indicate that the brazed sandwich panels exhibited a more uniform and continuous interface than the cemented sandwich panels. This work designs three-point bending compression experiments to investigate the effects of core material thickness, density, and preparation process on the bending mechanical properties of the sandwich panel. Failure modes of the sandwich panel during the experiments are analyzed. The experimental results show that the failures of the brazed sandwich panels are attributable to the bending deformation of the panel and the shear failure of the metal wire core material. The cemented sandwich panels exhibit separation failures in the area below the indenter and at both ends of the panel. The core material’s thickness and density significantly influence the bending performance of the sandwich panels. An increase in the core material’s thickness and density effectively enhances the sandwich panels’ peak load and energy absorption capacity.

Stable production of dissimilar steel joints in construction machinery by narrow gap oscillating laser welding

Narrow gap oscillating laser welding with filler wire is a promising technique for joining high-strength steels in construction machinery. In order to investigate the influence of beam oscillation on the surface morphology and microstructure of weld joints of two types of commonly-used high-strength steels, a comparative study between oscillation welding and non-oscillation welding was conducted. High-speed photography technique was employed to reveal the microstructure and mechanical properties of the dissimilar joints. The results showed that laser beam oscillation produces two effects: one was to enlarge the heated surface of molten pool, while the other was to stir the liquid metal in molten pool periodically. Under the first effect, the fusion between sidewall and weld bead layers was promoted, while under the latter, coarse columnar grains ceased to appear, but finer grains were formed. The weld joints between Q355 and 35 steels exhibited excellent tensile impact bending performance, which was attributed to the grain refinement effect. The results also demonstrated that the oscillation welding with a contact angle less than 50° could avoid lack of fusion in multi-pass wire-filling laser welding. The influence of the oscillation welding process on the quality of welding was further discussed.

Fabric handling evaluation of woven shirting fabrics by the fabric touch tester

A fabric touch tester is a novel instrument with fabric handling properties. Its principal advantage is that the device has integrated modules for compression, surface friction, and thermal and bending properties. This module integration simplifies the testing process, and provides an efficient measurement method, and a comprehensive physical index. This study focused on woven fabrics for dress shirts. The fabric samples comprised three groups with various yarn compositions – that is, cotton, polyester, and wool. Sample group 1 was composed of cotton, polyester, and blended yarns; sample group 2 mainly compared the effect of twist yarns on the fabric touch; and sample group 3 was composed of wool and blended yarns with polyester. The handling properties were assessed by compression work and the compression recovery rate for the compression attributes. The results revealed that fabric (T100p1) with high twist-level yarns had a higher value of compression work (242.56 gf*mm2), and the texture type may affect the compression characteristics more significantly than the blending ratio. The fabric touch tester can also distinguish small changes in the compression properties of samples (0.43–0.71), the maximum heat flux and surface roughness amplitude for the thermal and surface roughness properties. The results revealed that the maximum heat flux value of all the samples in this study was 1109 Wm−2, the sample C100 using pure cotton yarn had the highest maximum heat flux value (1270 Wm−2). Moreover, the sample W100 with 100% wool fiber yarn had the highest surface roughness amplitude in the warp direction (81 μm) and surface roughness amplitude in the weft direction (67 μm). Finally, the bending average rigidity was used to assess the bending performance of the fabric samples. These fabric touch tester indicators were applied to analyze the fabric handling characteristics of woven shirting fabrics, and perform cross-analysis among samples.

Development of self-sensing engineered cementitious composite sensors for monitoring flexural performance of reinforced concrete beam

In this paper, self-sensing engineered cementitious composite (ECC) was prepared and post-processed to obtain self-sensing ECC sensors. The sensor piezoresistive effect was modified considering the constraint of concrete. Then the sensor was embedded in the reinforced concrete beam to analyze the sensing performances under different conditions. The results show that the modified piezoresistive effect formulas were obtained by introducing correction coefficients, the formulas can describe the relationship between strain and impedance well. Sensors embedded in concrete beams cannot affect the bending performance and the development of cracks. The sensor can be used to monitor the strain in the compression under loading and unloading process of the beam and its sensing performance has good linearity, repeatability and accuracy. In the tension, when cracking, the sensors maintain the monitoring ability, but the accuracy needs to be improved. The gauge factor of the sensor applied in the beam is above 130.

Experimental and numerical study of the flexural behaviour of semi-precast slab reinforced with prestressed FRP bars

The performance of semi-precast slabs with prestressed basalt fibre-reinforced polymer (BFRP) bars under load is explored in this paper, using both experiments and computer simulations. The semi-precast slabs consist of precast concrete panels and cast-in-situ layers. The Precast panels are reinforced with BFRP bars prestressed at varying levels from 0% to 50% of their ultimate tensile strength. The experimental programme encompasses four-point bending tests conducted on five semi-precast slabs. For the numerical study, an ABAQUS model was used to perform finite element (FE) analysis, which aimed to simulate how the semi-precast slabs bent and to study how different factors affected their bending performance. The study parameters in this study were the grade of concrete and the reinforcement ratio. The results of this study show that prestressed BFRP bars significantly enhance load capacity and stiffness, while steel offers superior ductility. The computer models and the experiments matched well, as the average error between the two sets of data was less than 10%. Additionally, the parametric study reveals that enhancing the concrete grade or the reinforcement ratio can effectively enhance the flexural capacity and stiffness of the semi-precast slabs. In conclusion, this paper advocates for the utilisation of prestressed BFRP bars as an efficient and long-lasting reinforcement solution for semi-precast concrete slabs.

Fabrication and bending performance of ultra-low-density all-composite honeycomb sandwich shell based on stretching process

A sandwich shell with an ultra-low-density honeycomb core was designed and manufactured from a carbon-fibre prepreg via a stretching process. Subsequently, the bending bearing limits of the sandwich shell corresponding to five possible failure modes (shear buckling, shear fracture, intracellular dimpling, face fracture, and core debonding) were obtained through theoretical predictions. Failure mechanism maps were generated to reflect the possibility of each failure mode intuitively. In addition, three-point bending tests were performed on specimens with different shell thicknesses to acquire as many of these typical failure modes as possible. Moreover, the competition mechanism between different failure modes was revealed. The research results provide theoretical guidance for parameter optimisation and applications in advanced engineering fields for ultra-low-density carbon-fibre honeycomb sandwich shells.

A numerical study on bending behavior of sandwich beam with novel auxetic honeycomb core

To further improve the load-bearing capability and anti-impact properties of the auxetic structure, a novel enhanced auxetic honeycomb core (NEH) was introduced, and the bending resistance and crashworthiness of this sandwich beam (NEH-SWB) were analyzed through numerical simulation. First, bending tests on sandwich beams under different loading situations revealed that NEH-SWB was more susceptible to impact damage in three-point bending situations than those under four-point bending, and the influence of structural parameters were more pronounced. In addition, the impact of load position and structural parameters on the bending response and deformation pattern of NEH-SWB were investigated. NEH-SWB exhibited superior bending resistance when the punch was located in the S position. Furthermore, increasing the panel thickness and altering the panel thickness configuration both contributed to improving the flexural resistance of NEH-SWBs. At a certain mass, the configuration with T f / T b > 1 exhibited better bending resistance. Meanwhile, increasing both the cell angle (θ) and wall thickness-to-length ratio (t/l) enhanced load-carrying capability and energy absorption of NEH-SWB. Subsequently, further analysis showed that NEH had better bending performance compared to cell structures with reentrant (RH), star-shaped (SSH), and reentrant-star (RSH) honeycombs. Finally, the complex proportion assessment method was employed to examine the significance of structural parameters regarding the flexural behavior of the NEH-SWB. It was concluded that increasing the t/l value could be the best solution to enhance the bending performance of the NEH-SWB.

A soft wearable exoglove for rehabilitation assistance: a novel application of knitted shape-memory alloy as a flexible actuator

We developed the knitted shape-memory alloy (SMA) as a flexible actuator and applied it to a soft wearable exoglove for rehabilitation assistance. Based on user needs and anthropometric data, we custom-designed the exoglove for three hemiplegic patients using the knitted-SMA actuator and evaluated its bending performance, gripping force and wearability under the four simulation conditions (S1–S4). To address the specific needs, both SMA plain- and double-knit modules were applied to the exoglove based on the patients’ finger joint range of motion (ROMs). The joint ROMs of all fingers increased by 13.71% and the skin temperature increased by 2.21 °C after actuating the glove (p = 0.006). The gripping force increased as much as 55.01%, when compared to the baseline. All patients were able to don and doff the developed glove independently, and positively evaluated their subjective satisfaction and thermal perception. The findings suggested the potential of the knitted SMA for the future development of soft wearable robots.

Harmonizing Efficiency and Bending Performance in Flexible Perovskite Solar Cells through Annealing Duration Optimization

Perovskite materials are promising candidates for flexible photovoltaic applications due to their high light absorption and low‐temperature processability. However, achieving high‐efficiency flexible perovskite solar cells (FPSCs) typically requires annealing the films for extended periods at elevated temperatures to enhance crystalline quality. This poses a challenge, as prolonged or high‐temperature heating can cause deformation or cracking when using conventional flexible substrates for FPSCs. Overcoming the thermal instability of the substrate is essential for ensuring the high performance and stability of FPSCs. To address this issue, a feasible strategy to minimize the annealing duration is explored. The research unveils that a reduced annealing time of only 3 min can yield a perovskite film of comparable high quality to that achieved with conventional 15‐minute annealing, leading to an optimized power conversion efficiency of 21.97%. Moreover, the shortened annealing duration significantly enhances the bending performance of FPSCs, enabling them to maintain 90% of the original efficiency even after undergoing 5000 bends with a radius of 5 mm. These findings offer a practical and straightforward pathway to harmonize the exceptional efficiency and resilience properties of FPSCs.

Effect of selective enhancement on the bending performance of fused deposition methods 3D-printed PLA models

The top and bottom shells of fused deposition 3D-printed PLA models are exposed to the highest stresses. To improve the bending performance of PLA models under three-point bending conditions, the models were strengthened by a selective enhancement method. Several sets of PLA models were fabricated using FDM technology, and three-point bending experiments were conducted to compare the bending strength of PLA models when the layer height, top/bottom shell thickness, and extrusion rate were varied. The bending strength of the PLA models increased as the layer height of the top/bottom shell decreased, the thickness increased, and the extrusion rate increased. The average bending strength of the PLA models after selective enhancement was 84.4 MPa, and the average bending modulus of elasticity was 0.816 GPa, which were higher than the average bending strength of 68.6 MPa and the average bending modulus of elasticity of 0.736 GPa of the conventional groups. These results indicated that the selective enhancement method improved the bending performance of 3D-printed PLA models, and it also provided a reference for the improvement of the mechanical properties of the 3D-printed models with cellulose composite reinforced materials.

Distribution of coarse aggregate and steel fibers in ultra-high performance concrete containing coarse aggregate (UHPC-CA) and their effect on the flexural performance

The addition of coarse aggregate in ultra-high performance concrete offers several benefits, including the reduction of self-shrinkage, cost reduction, and increased modulus of elasticity. However, it also affects the dispersion space of steel fibers, resulting in a combined effect that both enhances and limits their respective advantages. An image method was used to describe the dispersion of steel fibers and coarse aggregate in the specimens along their length, width and height directions, respectively. The impact of dispersion of steel fibers and coarse aggregate on bending performance was investigated by four-point bending tests using various surfaces as the bottom tensile zone. Furthermore, the damage occurrence mode and crack development process are discussed using micro-morphology and cross-sectional graphs. The results show that the combined effect of steel fibers and coarse aggregate is not conducive to dispersion in the length direction but prevents settling due to gravity during vibration. Differences in bending properties among various surfaces in the bottom tension zone was significant, but the synergy between steel fibers and coarse aggregate reduced these differences by 1.5–2.4 times. Steel fibers in ultra-high performance concrete containing coarse aggregate act as crack arrestors, resulting in ductile damage. Cracks develop partly through the coarse aggregate and partly along the interface transition zone, indicating that the addition of coarse aggregate does not compromise flexural strength.

A structural optimization analysis of cable-driven soft manipulator

Cable-driven soft robots hold significant potential for surgical and industrial applications, yet their performance and maneuverability can be further enhanced through design optimization. By optimizing the design, factors such as bending angles, manipulator deformation, and overall functionality can be directly influenced, leading to improved interaction with the environment and more accurate task performance. This article presents a physics-based design optimization approach for cable-driven soft robotic manipulators, aiming to enhance bending performance through structural design enhancements. Four design criteria, namely, cross-sectional shape, material, gap shape, and gap size, are considered in the optimization process. Given the inherent nonlinearity of soft materials, finite element modeling techniques are employed to analyze the effects of modifying each design parameter on displacement and bending angle. The manipulator’s design is evaluated using ABAQUS/CAE, and an analysis of variance test is conducted to identify significant performance differences among the design parameters. The results reveal that material variation has the most substantial impact, followed by gap shape and gap size. Based on subsequent parameter optimization, Dragon Skin 10 is determined to be the optimal material for bending motion, while a trapezoidal gap shape is preferred. In addition, a genetic algorithm is utilized to select a maximum gap size of 8.87 mm. These findings provide valuable insights into key design principles for cable-driven soft manipulators, aiming to enhance flexibility and reduce actuation forces. By establishing a fundamental understanding of the relationship between morphology and motion capability, this methodology demonstrates an effective simulation-driven optimization approach that incorporates the nonlinear elastic behavior of materials to improve performance. Overall, this work establishes a framework for optimizing cable-driven architectures to suit various applications in the field of soft robotics.

Experimental and numerical study on flexural properties of glass fiber reinforced plastic sandwich plates

Due to their high specific strength and stiffness, glass fiber reinforced plastic (GFRP) sandwich plates are widely used in various fields such as construction, aerospace, shipbuilding, and military. This paper studies the bending performance of FRP sandwich plates with reinforcement through experimental and numerical simulation methods. The study shows that the bending performance of unidirectional and bidirectional reinforced plates under the same concentrated load is similar, and bidirectional reinforcement cannot significantly reduce the bending deformation of the sandwich plate. Under uniform load, the four-sided supported bidirectional reinforced sandwich plate can significantly reduce the deformation of the plate, and the deformation can be reduced by 40% compared to the unidirectional reinforced plate.

Research on the Influence of Yarn Reduction on the Bending Performance of Three-dimensional Woven Composites

Research on the Influence of Yarn Reduction on the Bending Performance of Three-dimensional Woven Composites

Assessment of damping and flexural behaviour of hybrid fibre-particulate composites

Hybrid composites are an advanced solution that offers multifunctional capabilities, including exceptional strength-to-weight ratios, vibrational damping and impact absorption. This work describes the damping capacity and flexural behaviour of a hybrid fibrous-particulate system composed of glass/carbon fabrics and three distinct micro-inclusions: silica particles, carbon waste microfibres, and cement. A statistical methodology based on the full factorial design is applied to identify the effects of fibre stacking sequence, including carbon-C5, glass-G5, C2G3, G3C2, GCGCG and CG3C, microparticle inclusions and matrix/fibre volume fraction (40/60 and 60/40) on damping and bending responses. A non-linear finite element (FE) analysis is conducted to explore the stress distribution based on the stacking sequence and predict the failure mechanisms of the hybrid laminate. The results indicate significant interaction effects, with hybrid architectures showcasing approximately 33% higher performance compared to glass fibre composites. A greater dependence on the fibre layup sequence is found for the damping factor, flexural modulus and strength. Notably, the incorporation of silica microparticles leads to an increase in flexural strength. Furthermore, a greater volume fraction of the matrix phase enhances the rheological efficiency in terms of the fibre-particle interface. Carbon fibre layers placed symmetrically on both beam sides (CG3C) and bottom layers (G3C2) significantly enhance the bending performance of hybrid composites.

Bending performance analysis of variable stiffness composite laminates

AbstractFor fiber‐reinforced polymer structures, the out‐of‐plane stiffness is much lower than the in‐plane stiffness and is extremely prone to damage and instability. The potential of variable stiffness (VS) laminates was explored to enhance the stiffness in the thickness direction. Based on the finite strip method (FSM), a semi‐analytical solution for bending problems of laminates was derived, which is called the variable‐stiffness discrete strip (VSDS) method. By comparing with traditional constant stiffness (CS) laminates, the influence of design parameters of VS laminates on the bending shape and stress distribution of laminates under two load cases were studied. Combining the results of FE models, the accuracy of VSDS has been verified, and the strategy of VS layout configuration design to improve the bending resistance was proved.Highlights Variable stiffness discrete strips (VSDS) method was presented based on FSM. Bending performances of VS laminates under two load conditions were studied. The method has the ability to reduce the computation cost of bending problems. The solutions of VSDS agree well with the results of FE models. The improvement mechanism of VS laminates on bending resistance was explored.

Enhancing bending performance of ultrathin flexible glass through chemical strengthening

AbstractFlexible glass with high bending strength is a remarkable component of flexible electronic displays. However, as a brittle material, its bending properties often do not meet requirements of application. To address this challenge, the application of chemical strengthening stands out as a viable approach to significantly bolster scratch resistance and bending strength in flexible glass. This study focuses on a conventional one‐step chemical strengthening method, employing molten potassium nitrate, to reinforce ultrathin aluminosilicate glass produced through the secondary down‐drawing thermoforming process. Effects of ion‐exchange temperature and time on mechanical properties of strengthened 110 µm flexible glass were investigated, and moreover, properties of strengthened ultrathin flexible glass with various thicknesses were compared. The results indicate that, after chemical strengthening at 380°C for 1 h, the compressive stress (CS) of 110 µm glass reaches 864.60 MPa, and the depth of layer is 15.86 µm, at which time the glass has the best bending performance and scratch resistance, and half of the faceplate spacing during glass breakage can be enhanced from 38.02 ± 2.7 to 8.40 ± 0.62 mm. For ultrathin flexible glass from 40 to 110 µm, after treatment at 380°C for 1 h, the CS of thick glass is higher than that of thin glass, and the enhancement of bending performance is better.

The Influence of Treatment Methods on Bending Mechanical Properties of Bamboo Strips

This study aimed to obtain a comprehensive understanding on bamboo as a curve-member manufacturing material by comparative analysis of how different treatment methods on bending properties improve the effect on bamboo strips. In order to achieve this purpose, bamboo strips were subjected to water boiling, 15% NaOH, and 25% NH3 impregnation; the impact of physical, mechanical and chemical properties were explored. The results revealed that: (1) Water boiling significantly affected crystallinity, cellulose, and lignin content, with a treatment duration of 10 h showing the most favorable results for flexibility and plasticity, greatly improving bending performance. (2) An amount of 15% NaOH treatment significantly increased bending MOE and plastic displacement by 73% and 122.7%. However, it led to a noticeable decrease in bending strength (MOR). A treatment above 8 h could cause irreversible damage to bamboo strips. (3) The improvement of 25% NH3 on bamboo bending ability was lower than water boiling. The effects of chemical composition were obvious in the initial five days and changed little after five days. Generally, water boiling for over 10 h is suitable for applications with significant bending requirements. While for maintaining bamboo color, original strength, and bending performance, 25% NH3 for five days was recommended, and 15% NaOH was not advised for improving bamboo bending performance and its applications.

Flexural behavior of LVL made from Australian radiata pine

As a commonly used engineering wood in modern timber constructions, laminated veneer lumber (LVL), produced from small-diameter wood, short-dimension wood, or fast-growing wood, significantly enhances material properties to meet the mechanical and physical requirements in structural engineering. This study aims to investigate the feasibility of utilizing fast-growing Australian radiata pine to produce structural LVL, providing essential theoretical support for its application in civil engineering. The investigation focuses specifically on Australian radiata pine LVL (RP-LVL) and involves a systematic experimental study to assess the bending performance of RP-LVL under various bending directions and specimen sizes. The findings reveal that the edgewise bending strength of RP-LVL is comparatively lower than its flatwise bending strength. Nevertheless, RP-LVL exhibits superior bending strength compared to conventional glulam and dimensional lumber, rendering it an attractive and suitable building material for achieving enhanced bending performance in flexure members. Moreover, the study identifies significant influences of height and width on the bending strength of RP-LVL. Consequently, prediction method is proposed to calculate the bending strength of RP-LVL, considering these size influences. Importantly, the size influences on bending strength are quantified to provide a comprehensive evaluation of the bending capacity of RP-LVL flexure members.