Bending Performance Research Articles

Laboratory evaluation on performance of Polyurethane Porous Elastic Mixture

Poroelastic road surface (PERS)has high rubber particle content and air void, and its noise reduction performance is excellent. However, the performance of Polyurethane Porous Elastic Mixture (PUPEM) prepared with different contents of rubber particles and different types of polyurethane (PU) are rarely studied. This study aims to evaluate the comprehensive and functional performance of PUPEM and to analyze the influence of rubber particle content and PU type on PUPEM. PUPEM was prepared using different types of PU and different rubber particle content. The high-temperature performance, low-temperature bending performance, water stability performance, and skid resistance performance of PUPEM were evaluated by rutting test, low-temperature bending test, freeze–thaw splitting test, immersion Cantabro loss test, pendulum friction coefficient tester and sand patch method. The effects of air void content, rubber particle content, and thickness on the noise reduction performance of PUPEM were also studied by impedance tube test and dynamic modulus test. The results indicate that the PUPEM has excellent high-temperature performance, favorable low-temperature bending performance and skid resistance, and its water stability can meet the specification requirements. PUPEM also has favorable sound absorption and noise reduction performance through voids and noise reduction performance through elastic damping. In addition, the maximum sound absorption coefficient of PUPEM corresponds to a frequency that is influenced by the thickness. In order to balance the road performance and noise reduction of PUPEM mixture, it is recommended that the rubber particle content is 10%, and the polyurethane PU-Ⅰ with larger isocyanate index is used.

Fiber optic detection method for intrinsic defects in carbon fiber composite core overhead conductors considering bending performance

Carbon fiber composite core wire in the carbon fiber core rod bending strength is low, easy to break, and thus affects the detection effect. In this regard, it is proposed to consider the bending performance of carbon fiber composite core overhead wire intrinsic defects fiber detection method. The overhead wire is X-ray scanned, and the image is bent compensated by the filtering algorithm. The image is reconstructed using an iterative reconstruction algorithm, and the Tamura texture feature operator is used to extract the roughness feature parameters in the texture feature enhancement map of each conductor to achieve the identification of defects. In the experiments, the proposed method is verified for detection accuracy. The analysis of the experimental results shows that the proposed method has a high correct defect recognition rate and has a more excellent detection accuracy when the proposed method is used to detect the inherent defects of overhead conductors.

Calculation Method for the Cracking Resistance and Bearing Performance of SFRAC Beams.

The utilization of recycled aggregate (RCA) in preparing recycled concrete (RAC) is an effective measure to solve the increase in construction waste. Furthermore, applying RAC to flexural members is a viable practice. The addition of steel fiber to RAC to prepare steel fiber recycled concrete (SFRAC) solves the performance deterioration caused by the recycled aggregate, so it is necessary to study the effects of the recycled aggregate replacement rate and fiber-volume ratio on the crack resistance and bending performance of SFRAC beams. In this study, 13 beams were designed and manufactured, with the water-cement ratio, recycled aggregate replacement rate, and fiber-volume ratio as the primary variables, and the cracking moment and ultimate moment of the SFRAC beams were systematically studied. The results show that the cracking and ultimate moments of the SFRAC beams increased with decreases in the water-cement ratio or with increases in the fiber-volume ratio and were unaffected by the replacement rate of recycled aggregates. Based on the experimental results and theoretical analysis, a calculation model and formula for the cracking moment were established. The ultimate bearing capacity of SFRAC beams can be accurately determined using the ACI 318 and ACI 544 standards. The research results serve as a valuable reference for the design of SFRAC beams, effectively address the issue of performance degradation in RAC structural members, and promote the use of green building materials.

Experimental and Theoretical Studies on Bending Performance of Hot Press GFRP Composite Panels

Bu çalışmada, sıcak pres yöntemi ile üretilmiş CETP (Cam elyaf takviyeli polimerler) kompozit panellerin eğilme performansları araştırılmıştır. Bu amaçla cam elyaf ve reçine ile hazırlanmış kompozit plakalar belli bir sıcaklık ve basınç altında preslenerek panellere çevrilmiştir. Üretilen paneller değişken yükler altında çalışan malzemeler olması nedeni ile eğilme testine tabi tutulmuştur. Panellerden 14×150×6 mm3 ebatlarında numuneler alınarak üç nokta eğilme testi uygulamıştır. Deneyin doğrulanması ve gerilme dağılımının görsel olarak incelenebilmesi amacıyla sonlu elemanlar analizi (SEA) yapılmıştır. Çalışma sonunda deneysel ve teorik sonuçlar karşılaştırılmış ve uygulanan yüklerin etkileri tartışılmıştır. Deneylerde en yüksek eğilme gerilmesi 150.39 MPa, SE analizinde ise 164.31 MPa şeklinde gerçekleşmiştir. Malzemenin hasar öncesi deplasmanı deney ve SEA için sırasıyla 4.92 mm ve 5.46 mm’dir. Deney ve SEA sonuçlarının birbirine yakın sonuçlar verdiği görülmüştür. Elde edilen sonuçlar CETP kompozit malzemelerin farklı alanlarda kullanımı öncesi boyut ve mekanik özelliklerin belirlenmesi çalışmalarına destek olacak niteliktedir.

Design, Modeling and Experiments of a Variable Stiffness Soft Robotic Glove for Stroke Patients With Clenched Fist Deformity

Soft wearable devices for hand rehabilitation can assist activities of daily living. While existing soft robotic gloves can help with finger flexion, they are less suitable for patients who cannot extend their fingers due to poststroke increased muscular tension. In this letter, we proposed a variable stiffness pneumatic actuator that effectively increases the elasticity of the actuator to facilitate finger extension. The actuator consists of a fiber-reinforced actuator and a multi-stage articulated elastomer. It bends and extends by pneumatic actuation, with multi-stage articulated elastomer providing stiffness adjustment to accommodate varying joint resistance. The variable stiffness mechanism was achieved by the multi layered discrete metal plates which can gracefully fit the unique structure of human fingers. Analysis models were established to quantify the actuator's air pressure, vacuum pressure, and bending angle, also to predict the actuator's stiffness under different vacuum pressures. Experiments and finite element simulation were carried out to evaluate the bending performance of the actuator. Meanwhile, the output force and variable stiffness characteristic of the actuator were tested. The results show that the actuator can achieve 1.54 N fingertip output force and 2.4 times stiffness change, which satisfy the requirement of stroke patient. In addition, a clenched artificial hand with similar damper forces to human hand was applied to further verify the extending effect of the variable stiffness actuator. Finally, a rehabilitation glove integrated with multiple actuators was tested to assess typical rehabilitation gestures and the ability to grasp daily objects.

Bending Analysis of Stepped Rectangular Plates Resting on an Elastic Half-Space Foundation

In this paper, the bending behavior of rectangular plates with stepped thickness resting on an elastic half-space foundation is investigated through an analytic method. Combined with the bending theory of the rectangular thin and moderately thick plate, the stepped rectangular plate is divided into upper and lower plates, and the Fourier series is used to obtain the analytical solution of the deflection of the plate and the interaction force between the plate and foundation. The influence of the elastic modulus of the plate, plate theory, and the dimension of the plate on the deflection of the stepped rectangular plate is also discussed. The results show that the analytical solution is basically the same as the existing research results, and it is also verified by the analysis results of the models established by ABAQUS software. The deflection at the center of the stepped rectangular plate increases with the increase of the elastic modulus of the upper plate and the decrease of the side length of the upper plate, while the plate theory has little effect on the deflection of the plate. This method not only overcomes some of the disadvantages of numerical methods but also eliminates the assumptions of the Winkler foundation model and the two-parameter foundation model, thus obtaining a more reasonable and accurate bending performance of the stepped rectangular plate resting on the elastic half-space foundation.

Interfacial toughening and bending performance of the CFRP/aluminum-honeycomb sandwich

CFRP / honeycomb sandwiches often fail prematurely due to interface debonding when subjected to bending loads. In this paper, three kinds of toughening interfaces were designed, and their effects on the sandwich’s three-point bending performances (including peak force and energy absorption) were studied. The results showed that the peak force and energy absorption of the sandwich were increased by 43.6% and 141.3%, respectively by adding a multi-scale toughening film (short aramid fiber (AF) film grafted with polydopamine (PDA) and graphene oxide (GO)) at the interface. The toughening interface affected the deformation process and failure mode of the sandwich by changing the competition mechanism between the facesheet, interface, and honeycomb strength. The short fibers of toughening film formed bridges at the toughened interface, and the crack propagation mechanism changed from interface debonding to a combination of interface debonding and matrix fracture. In addition, the test results revealed that the wettability, tensile strength, surface roughness, and specific surface area of the fiber could be significantly improved by treating with PDA and GO, which lead to crack deflection at the interface. Thus, the interface debonding is effectively delayed or prevented.

Effect of triaxial woven fabric on bending properties of unidirectional composites

AbstractThis study investigates the impact of incorporating a triaxial woven fabric (TWF) into a unidirectional ply structure on the bending performance of the structure. The failure processes of the different ply structures were recorded using video analysis and acoustic emission. The experimental results indicated that incorporating a layer of carbon fiber TWF between the second and third layers (GGTGG) or between the third and fourth layers (GGGTG) of the four‐layer unidirectional fabric significantly improved the flexural strengths by 79.5% and 213.7%, respectively, and the flexural toughness by 480.3% and 324.8%, respectively. In addition, the incorporation of TWF in the structure resulted in a shift in the overall failure mode from brittle to ductile. When the TWF was closer to the lower surface of the sample, the crack was more uniform and the distribution range was wider. In contrast when the TWF was in the middle, the range of cracks generated by the sample was narrower. However, some of these cracks affected the stability of the material structure. Furthermore, the damage process was confirmed using images of crack growth and acoustic emission during the destruction process. This study provides valuable insights into enhancing the bending performance of unidirectional fiber layup in the non‐load direction.

Fiber reinforced sulphoaluminate cementitious composites: Mechanical properties and comprehensive evaluation method

The rapid repair of concrete structures is an important research subject, which has attracted the attention of engineers at home and abroad. Here, an early-strength and strain, fast-setting and fast-hardening cementitious composite named as fiber reinforced sulphoaluminate cementitious composites (FRSACC)was developed. The mechanical properties of FRSACC were investigated through a series of experiments, including compressive strength, flexural strength, uniaxial tensile performance, four-point bending performance, three-point bending fracture, and microstructure analysis. The results indicated that these properties were influenced by the curing age, water to binder (W/B) ratio, sand to binder (S/B) ratio, and fly ash (FA) dosage. To be specific, the W/B ratio plays a vital role in achieving desirable mechanical properties at early curing stage, followed by the FA dosage and the S/B ratio. In addition, a facile six-dimensional representation was proposed to assess the overall performance of FRSACC. This comprehensive evaluation method can also be used for other cementitious composites to evaluate and select the better mixture ratio based on mechanical properties, bending toughness and fracture toughness.

Flexural property of steel reinforced bamboo scrimber composite beam

To improve the bending performance of long-span bamboo scrimber beams, a new method of prepressing-cold pressing-hot forming was used to produce steel-reinforced bamboo scrimber composite beams. For steel-RBSC beams, four-point bending experiments were performed to study the failure mode, bending performance, load-displacement relationships, and strain history curves of composite beams. Based on cohesive zone model theory, finite element models of steel-RBSC beams were established and the bonding stress of the adhesive layer in steel-RBSC beams revealed. The results indicated that the failure mode of composite beams was fracture failure of the bamboo scrimber at the bottom between the loading rollers. Steel reinforcement had a significant effect on the strength and stiffness of bamboo scrimber beams. The maximum static stiffness of composite beams was increased by 70.15%, compared with that of bamboo scrimber beams. The load-displacement curves, mechanical properties, and section strains predicted by finite element models were consistent with the test results, verifying that these finite element models were correct. The main influence factors for the peeling of the adhesive layer were normal stress, shear stress, and mixed stress in the areas of pure bending section, bending-shear section, and loading roll area, respectively.

Study on the Bending Behaviors of a Novel Flexible Re-Entrant Honeycomb

Abstract In order to further improve the bending performance of the traditional re-entrant (RE) honeycomb, a novel auxetic honeycomb architecture, called RE-L honeycomb, was proposed by adding an additional link-wall structure to the RE cell. The bending behaviors of the novel RE-L honeycomb, including the properties under linear elastic deformation and the bending behaviors under large deformation, were comprehensively investigated by the analytical, numerical, and experimental models. Results show that the proposed RE-L honeycomb significantly improves the bending compliance in the x-direction due to the highly flexible performance of the additional structure, where the bending rigidity and the maximum bending force are only 23% and 29.4% of those of the RE honeycomb, respectively. Besides, the additional structure obviously improves the designability and orthotropic properties of the original auxetic honeycomb. In conclusion, the proposed RE-L shows improved bending performance, which deserves more attention in future research and related applications.

Experimental investigation and analytical prediction of flexural behaviour of reinforced concrete beams with steel fibres extracted from waste tyres

In recent years, studies on the use of car tyre wastes in concrete have gained momentum. Especially, the effect of recycled waste steel wires (RWSWs) from tyres to be mixed into concrete for using in newly designed reinforced concrete buildings on the performance of construction elements is a fairly new research area. In this study, the bending behaviour of 12 reinforced concrete beams was investigated having 1/3 geometric scale, 100 × 150 × 1000 mm in size, and produced with RWSWs additive in different volumetric ratios (1%, 2%, and 3%) under vertical loads. Another main parameter selected in the study was the amount of varying tension reinforcements (2ϕ12, 2ϕ10, and 2ϕ8). The load-carrying, stiffness, ductility, and energy dissipation capacities of the RWSW reinforced bending beams were compared with the primary aim of this study which was to examine and present the contribution of RWSWs on the improvement of the bending performance of the reinforced concrete beams. The results revealed that the mechanical properties of the hybrid beams with RWSWs vary depending on dosages but are comparable with those of the beams-only with the same fibre dosage. A positive effect was obtained for the hybrid beams containing 2–3% RWSWs. Besides, RWSWs were found to be highly well mobilised at larger crack widths, and the post-cracking strength of RWSW mixes was significantly higher. Considering both mechanical properties of the beams and fresh properties such as the workability, 2% of RWSWs is recommended to be utilised in the reinforced concrete beams. On the other hand, the results were compared with the predictions of the methods given in the literature and standards. Moreover, an equation was derived to better predict the capacity of the hybrid beams using RWSWs.

Bending properties of carbon fiber reinforced composite multilayer damping structures with different types of stiffeners

Carbon fiber reinforced composite multilayer damping structures with different types of stiffeners demonstrate excellent mechanical properties. This paper deals with the bending properties analysis of carbon fiber reinforced composite multilayer damping structures with different types of stiffeners for the first time. A theoretical model was constructed to investigate the bending performance of the structure under static loading based on structural stress transfer mechanism between stiffener and composite plate. Moreover, the theoretical solution was compared with the numerical simulation results to confirm their validity. Finally, structural parameters were considered to discuss the change law of the structural center deflection.

Highly hydrostable and flexible opal photonic crystal film for enhanced up-conversion fluorescence sensor of COVID-19 antibody

Efficient detection of related markers is significant for the early screening of COVID-19. Near infrared (NIR) light excited up-conversion fluorescence probes are ideal for biosensing but limited by the low luminescence efficiency. In this work, a novel highly stable opal photonic crystal (OPC) structure was designed to provide an OPC effect for up-conversion fluorescence enhancement, and sensitive Novel Coronavirus IgG up-conversion FRET-based sensor was further constructed. For the problems of water stability and mechanical stability of polymer OPC which cannot be solved for a long time, polymer spray combined with a flipped OPC film strategy is presented. Fragmented size OPC film was firmly fixed by polymer modification layer, which gave large size OPC film great water stability, mechanical stability and bending performance without affecting the fluorescence enhancement property. On this basis, the up-conversion emission intensity was enhanced significantly, and fluorescence resonant energy transfer (FRET) based Novel Coronavirus IgG antibody sensor was constructed. Monolayer up-conversion nanoparticles (UCNPs) on the surface of the polydopamine (PDA)/OPC film can make the fluorescent signal more sensitive, and effectively reduce the detection limit. The test device integrating NIR excitation and mobile phone realized the visual fast detection, showing remarkable sensing performance for COVID-19 antibodies with the limit of detection (LOD) of 0.1 ng mL−1. This detection platform will provide a more effective tool for early detection of the novel coronavirus.

Static, dynamic and buckling responses of random functionally graded beams reinforced by graphene platelets

This work proposes a multiscale numerical method that can be used to study the static, dynamic and buckling behavior of functionally graded (FG) beams reinforced with graphene platelets (GPLs), whose random gradation is achieved through tailoring the internal porosity and GPLs reinforcement, either along the transverse or the longitudinal direction. The multiscale numerical method consists of microscale homogenization and structural analysis: micromechanics homogenization methods are introduced to predict the elastic moduli of nanocomposite layers with finite thickness along the transverse direction; Explicitly-expressed composite finite elements are then developed through the proposed variational principle and Hamilton principle. In the meantime, the corresponding governing equations are derived for FG beams with Timoshenko theory. On this basis, the static bending deflection, fundamental frequency and critical buckling load of the FG beams are obtained through the proposed FG finite elements. The effectiveness and accuracy of the proposed method are verified against the numerical results in the existing literature and experimental results in 3D printing with good agreement. Based on the credence of the present method, the effects of boundary conditions, gradient distributions of GPLs and pores, microscopic parameters of GPLs and structural geometric dimension on the static and dynamic performance of the FG beams are systematically analyzed, where the bi-directional gradient distribution pattern corresponding to the GPLs along the thickness direction and the pore along the axial direction demonstrates the best improvement of both bending and dynamic performance.

Flexural property study of multiaxial fiber reinforced polymer sandwich panels with pultruded profile cores

This study investigates the bending performance of a new type of composite sandwich panels with pultruded profile cores, and multiaxial glass fiber reinforced polymer (GFRP) facial sheets and webs between the profile cores. The influences of the position and number of fiber cloth layers on the bending properties of the sandwich panel are also studied. The failure modes, load–deflection behavior, and load–strain relationships are compared using four-point bending tests. The results show that wrapping multiaxial fiber cloth can change the brittle failure characteristics of the pultruded profiles, and that the multiaxial FRP surface and uniaxial pultruded profiles can operate effectively. The completely wrapped fiber cloth method improves the bending performance of the sandwich plate.

Study on Bending Performance of Tightly Spliced Truss-Reinforced Plate-Honeycomb Flat Beam

The tightly spliced truss-reinforced plate-honeycomb flat beam is a novel type of composite beam, with the advantages of high rigidity, high bearing capacity, and ease of construction. In this study, on the basis of the performance in bending tests, the numerical analysis method is used to study the influence of the honeycomb hole–height ratio, and section height on the bearing capacity of the honeycomb composite flat beam. On this basis, the simplified method to calculate the ultimate bending capacity of the new honeycomb composite flat beam was proposed. The research results show the failure modes of the specimens are mainly divided into two states, including the deflection exceeding the limit and the concrete flange plate separating from the steel beam. The tightly spliced truss-reinforced plate-honeycomb flat beams have good ductility, of which the average value reaches 8.2. The simplified method proposed in this article for calculating this type of honeycomb composite beam has an error of less than 10% in terms of bending bearing capacity, which has advantages over the double T-shaped steel method. The calculation method and design suggestions proposed in this study provide a basis for the research and application of this type of composite flat beam.

Finger Joint Stiffness Estimation with Joint Modular Soft Actuators for Hand Telerehabilitation

In a telerehabilitation environment, it is difficult for a therapist to understand the condition of a patient’s finger joints because of the lack of direct assessment. In particular, not enabling the provision of spasticity evaluation significantly reduces the optimal performance of telerehabilitation. In a previous study, it has been proposed that finger stiffness could be estimated using an analytical model of a whole-finger soft actuator. However, because the whole-finger soft actuators require high air pressure for high bending performance and are costly to customize for each patient, using joint modular soft actuators for telerehabilitation turns to be a necessity, though stiffness estimation with joint modular soft actuators has not been studied yet. Another problem is caused by using a marker-based joint angle measurement, which requires the markers to be attached to the exact positions, and limits its application in telerehabilitation. In this study, we proposed a procedure of finger joint stiffness estimation that combines information acquired from a joint modular soft actuator and a marker-less hand joint position acquisition device. Correction parameters were added to the previous analytical model for -the bending analysis of a joint assisted using a joint modular soft actuator. Moreover, a multi-variate regression model was implemented for correcting joint angles obtained from the hand joint position acquisition device. As a result, a reasonable accuracy of stiffness estimation was achieved for rehabilitation with the joint modular soft actuators, which suggests the possibility of using the proposed method to evaluate the finger spasticity in a telerehabilitation environment. This is a big step forward towards optimal hand telerehabilitation.

Posterior intra-articular fixation stabilizes both primary and secondary sacroiliac joints: a cadaveric study and comparison to lateral trans-articular fixation literature

BackgroundPosterior and lateral techniques have been described as approaches to sacroiliac joint arthrodesis. The purpose of this study was to compare the stabilizing effects of a novel posterior stabilization implant and technique to a previously published lateral approach in a cadaveric multidirectional bending model. We hypothesized that both approaches would have an equivalent stabilizing effect in flexion–extension and that the posterior approach would exhibit better performance in lateral bending and axial rotation. We further hypothesized that unilateral and bilateral posterior fixation would stabilize both the primary and secondary joints.MethodsRanges of motion (RoMs) of six cadaveric sacroiliac joints were evaluated by an optical tracking system, in a multidirectional flexibility pure moment model, between ± 7.5 N-m applied moment in flexion–extension, lateral bending, and axial rotation under intact, unilateral fixation, and bilateral fixation conditions.ResultsIntact RoMs were equivalent between both samples. For the posterior intra-articular technique, unilateral fixation reduced the RoMs of both primary and secondary joints in all loading planes (flexion–extension RoM by 45%, lateral bending RoM by 47%, and axial RoM by 33%), and bilateral fixation maintained this stabilizing effect in both joints (flexion–extension at 48%, lateral bending at 53%, and axial rotation at 42%). For the lateral trans-articular technique, only bilateral fixation reduced mean RoM of both primary and secondary sacroiliac joints, and only under flexion–extension loads (60%).ConclusionDuring flexion–extension, the posterior approach is equivalent to the lateral approach, while producing superior stabilization during lateral bend and axial rotation.

Effect of Interlayer Bonding Temperature on the Bending Properties of Asphalt Concrete Core Wall.

In the construction process of an asphalt concrete impermeable core wall, the interlayer bonding of the core wall is the weak link of the core wall structure and also the focus of construction, so it is important to carry out research on the influence of interlayer bonding temperature on the bending performance of an asphalt concrete core wall. In this paper, we study whether asphalt concrete core walls could be treated with cold-bonding by fabricating small beam bending specimens with different interlayer bond temperatures and conducting bending tests on them at 2 °C. The effect of temperature variation on the bending performance of the bond surface under the asphalt concrete core wall is studied through experimental data analysis. The test results show that the maximum value of porosity of bituminous concrete specimens is 2.10% at lower bond surface temperature of -25 °C, which does not meet the specification requirement of less than 2%. The bending stress, strain, and deflection of bituminous concrete core wall increase with the increase of bond surface temperature, especially when the bond surface temperature is less than -10 °C. If the lower bonding surface temperature is less than 10 °C, the upper layer of asphalt mixture with large grain size aggregate cannot be effectively buried in the low bond surface, resulting in flat fracture and brittle damage to the specimen, which is detrimental to construction quality; therefore, the bonding surface should be heated so that the temperature of the bottom bonding surface is 30 °C. If the lower bonding surface temperature is 10 °C or above, no heating is required.