Bending Performance Research Articles

The Influence of Foam Density on the Flexural Properties of Structural Insulated Panels

Abstract The effect of foam core density on the strength of structural insulated panels (SIPs) was investigated herein as part of a larger study to determine the creep performance of SIPs. Two depths (16.5 cm and 31.1 cm [6.5 in. and 12.25 in.]) of SIPs were tested in 1/3rd-point flexure according to the American Society of Testing and Materials standard ASTM D6815. Parent SIP panels, each approximately 122 cm (48 in.) wide, were manufactured by a SIPA member in accordance with ESR 4698 and sawn into beam, type elements, each approximately 29.8 cm (11.8 in.) wide, for mechanical testing. All specimens had discontinuities in the foam core in a location that was subject to high shear stress, i.e., between the reaction support and the load head, during the bending tests. The foam density in half of the specimens was approximately 0.016 g/cm3 (1.0 lb/ft3) and in the other half of the specimens, it was approximately 0.019 g/cm3 (1.2 lb/ft3). The flexural properties of these specimens based on the maximum load, Pmax and deflection at failure Δymax (two different depths and two different foam densities) were statistically compared by 2-tailed t test. The results showed that foam density affects the bending performance of SIPs. In both depths, beams with heavier foam cores were stronger for the specific test conditions used in this study. It is noted that results may not be applicable to other design situations such as SIPs subjected to uniform loading with randomly placed foam core joints.

Pneumatic Bending Soft Actuator Coupling With Revolute Joint With Different Boundary Constraints

This article presents a study on pneumatic bending soft actuator (SA) coupling with revolute joint (RJ) with different boundary constraints (BCs), aimed to discover the bending performance of SA wearing on physical joint of human body as body joint actuators with different installation methods. First, a new pneumatic bidirectional bending SA is designed and fabricated, and its mechanical characteristic is obtained by experimental tests and fitting methods. Then, the mechanical characteristic is applied to the discrete bending model that approximates the continuous bending of the SA, and the kinetostatic analysis based on the principle of virtual work is conducted on the SA-RJ coupling system (SA-RJ CS) with fixing BC (FBC), hinging BC (HBC), and sliding BCs (SBCs). The kinetostatic equations are solved numerically, and thus the bending performance of the SA-RJ CS with different BCs is obtained. Results show the SA-RJ CS with SBCs performs better in bending angle and actuating torque than that with FBC or HBC. Therefore, it is suggested to install the SA of joint actuator on human body by SBCs. This study guides the application of pneumatic bending SA in rehabilitation exoskeleton. At present, we have used the axial SBC in rehabilitation exoskeleton.

A novel isogeometric scaled boundary finite element method for bending and free vibration analyses of laminated plates with rectilinear and curvilinear fibers constrained or free from elastic foundations

In this paper, a novel numerical approach based on isogeometric analysis and the scaled boundary finite element method is performed, focusing on improving the computing performance (such as accuracy, efficiency and flexibility) of bending and free vibration analyses for laminated composite plates with rectilinear and curvilinear fibers constrained or free from elastic foundations. The non-uniform rational B-splines are used as shape functions for both the construction of exact geometry and the approximation of field variables. The governing formulations are derived from the 3D theory of elasticity, while only discretization for the 2D in-plane dimension is required, with the displacement and stress fields expressed analytically along the thickness direction. Compared to traditional methods, the proposed method possesses the following major advantages: a) The powerful calculation accuracy and less computation consumption due to the higher-order continuity of non-uniform rational B-splines and the intrinsic semi-analytical property from the scaled boundary finite element method; b) The geometric exact description encapsulated in the non-uniform rational B-splines basis ensures the excellent adaptability of the present approach to arbitrary free-form geometries; c) Interaction between laminated plates and elastic foundations can be easily constructed by using the proposed formulations due to discretizations are restricted only to the 2D in-plane; d) Outstanding capability of the presented formulation for the mechanical analysis of variable stiffness laminated composite plates with curvilinear fibers; e) The robust flexibility of the non-uniform rational B-splines in handling curved boundaries makes a strong adaptability of the present method to irregular meshes. Numerical examples on both static and free vibration analyses demonstrate the excellent performance of the present approach.

Bending and shear performance of a cross-laminated composite consisting of flattened bamboo board and Chinese fir lumber

Bamboo-wood composites are effective for utilizing the mechanical properties of bamboo and fast-growing wood resources. Investigation the application of flattened bamboo in engineering structures provides added value to bamboo resources. This paper analyzes the flatwise bending and shear properties of cross-laminated bamboo and timber (CLBT) panels consisting of flattened bamboo boards and Chinese fir lumber. A three-layer cross-laminated timber (CLT) panel made from Chinese fir lumber was used for comparison. The mechanical properties of the CLBT and CLT panels in the major strength direction were obtained through experimental tests, and theoretical and finite element models were developed to predict the panels’ bending stiffness and strength. The calculated values were compared with the experimental data. The results showed that the failure modes of the three groups of CLBT panels were similar to those of the CLT panel and were predominantly rolling shear and bonding delamination. The bending strength and modulus of the CLBT were higher than that of the CLT. Increasing the number of layers of the flattened bamboo board improved the maximum bending moment and bending stiffness of the CLBT. The bending stiffness and strength of the CLBT/CLT obtained from the finite element model were in better agreement with the static test values than the theoretical model values. The results of this study provie new information for future engineering applications and the structural design of CLBT.

Bending performance of 3D re-entrant and hexagonal metamaterials

Auxetic structures have theoretically superior bending resistance that was previously inaccessible. Compared with the planar two-dimensional (2D) auxetic structures, the three-dimensional (3D) counterparts may exhibit auxetic behavior in multiple directions. Recently, increasing studies have been devoted to studying the mechanical properties of 3D auxetic structures. In this paper, two 3D honeycomb structures were proposed, namely 3D re-entrant honeycomb and 3D hexagonal honeycomb. Subsequently, the mechanical properties, deformation modes, and deformation mechanisms of these two honeycomb structures under three-point bending were investigated experimentally and numerically. Compared with the 3D non-auxetic hexagonal honeycomb, the 3D auxetic re-entrant honeycomb exhibits higher ductility and fracture resistance. In addition, unlike the conventional honeycomb structure, the mid-span section of the 3D auxetic honeycomb exhibits a trapezoidal deformation mode under bending. Finally, the influence of the number of unit cells and geometric parameters on the mechanical properties of the 3D honeycomb structure were systematically studied by parametric analysis. The excellent bending performance provides a basis for the application of auxetic honeycomb in the fields of biomedicine, soft robots, and buffer devices.

Interfacial Modification and Bending Performance of 3D Orthogonal Woven Composites with Basalt Filament Yarns.

To improve their interfacial properties, 3D orthogonal woven fabrics with basalt filament yarns were modified with functionalized carboxylated carbon nanotubes (KH570-MWCNTs) and polydopamine (PDA). Fourier infrared spectroscopy (FT-IR) analysis and scanning electron microscopy (SEM) testing were used. It was demonstrated that both methods could successfully modify basalt fiber (BF) 3D woven fabrics. The 3D orthogonal woven composites (3DOWC) were produced with epoxy resin and 3D orthogonal woven fabrics as raw material by the VARTM molding process. The bending properties of the 3DOWC were tested and analyzed by experimental and finite element analysis methods. The results showed that the bending properties of the 3DOWC modified by KH570-MWCNTs and PDA were significantly improved, and the maximum bending loads were increased by 31.5% and 31.0%. The findings of the finite element simulation and the experiment results were in good agreement, and the simulation error value was 3.37%. The correctness of the finite element simulation results and the model's validity further reveal the material's damage situation and damage mechanism in the bending process.

Printable Silver Nano Ink for Bendable Ultrawideband Antenna with Triple-Notch Characteristics

Flexible antennas based on the printed flexible electronic technology are of great interest for important applications in wireless communication systems due to their distinctive features over traditional rigid-based antennas. The ultrawideband (UWB), notch characteristics, and bending capabilities of such antennas are crucial for flexible and wearable applications. Currently, only a few are focused on the printed flexible electronics technology with printable ink materials for UWB antenna applications. In addition, flexible UWB antennas with triple-notch characteristics and good bending performance are rarely reported. Thus, there is a need to make advances in this area. Here, we describe the application of a printable silver nanoparticle-based ink for rapidly fabricating an antenna with bendable and triple-notch characteristics designed for UWB communication systems. The ink, composed of monodisperse silver nanoparticles, isopropanol, and ethyl glycol, can easily produce favorable conductive patterns at a sintering temperature below 130 °C after inkjet printing. The antenna is designed on a flexible polyethylene terephthalate (PET) substrate and has a moderate size of 27 mm × 38 mm × 0.12 mm. It operates at a frequency range of 1.9–10.75 GHz, which covers the desired UWB frequency band. By loading a “U”-like slot and two “C”-like slots on the radiating patch, band rejections were generated at 3.2–3.8, 5.3–6.2, and 7.8–8.5 GHz, shielding the interference from world interoperability for microwave access, wireless local area networks, and X uplink bands. The bending results show that the antenna retains good UWB and triple-notch performance even after bending along the Y- or X-axis for different degrees. An antenna prototype was finally fabricated by inkjet printing of the silver nano ink on the PET substrate, exhibiting the desired notch characteristics and excellent bendability. The fabricated antenna prototype proved the feasibility of use as a flexible device at an ultrawide frequency band. The research provides a design guide for flexible antennas with notch features toward flexible and wearable electronics.

Impact of Joint Parameters on Performance of Self-Opening Dual-Matrix Composites

Origami-based structures have expanded in recent years due to new mathematical formulations along with materials that can achieve the bending requirements, often in the form of composites. While current methods of manufacturing can produce complex structures, they lack the ability to scale efficiently. A novel manufacturing technique is discussed in this work that allows for a simpler and lower cost fabrication that can scale to larger structures through robotic deposition. Samples made from this technique are investigated to understand the mechanical bending performance and effect on the tensile properties. Results show an orientation-dependent response for the material with the 45° samples having a direct impact on the tensile response. However, their bending response proved to be stiffer compared to the samples, holding more consistent bend radii. Joint stacking was also investigated, where discrete layers were not bonded together and showed an increase in force required to bend compared to the completely bonded samples. The results provide insight into how integrated composite hinges can perform in complex structures. The advancement of composite origami technology additionally works to reduce the overall number or parts and fasteners that are needed to achieve detailed deployable structures.

Bending performance of nail laminated timber: Experimental, analytical and numerical analyses

Nail laminated Timber (NLT) is a kind of mass timber product becoming popular in recent years. To further understand the bending performance of NLT and motivate its utilization in engineering, experimental, analytical and numerical analyses were conducted in this study. Spruce-pine-fir (SPF) dimension lumber was used as the lamination to fabricate the NLT and four-point bending test was conducted on ten NLT specimens. The failure modes, modulus of elasticity and load-carrying capacity of the NLT were investigated. Results showed that the dominant failure mode of specimens was tension failure at the bottom of the laminations. The bending strength of the NLT corresponding to the occurrence of the first lamination failure was about 11.4% lower than the ultimate bending strength. The average modulus of elasticity and the average ultimate bending strength of the NLT were close to those of the laminations. Considering the property difference of the laminations, an analytical method was proposed to analyze the internal force of NLT. Then, the finite element model of NLT was established and further calibrated by the experimental and analytical results. The comparison proved that both the analytical and numerical methods could effectively predict the bending performance of NLT.

Multi-nested antiresonant hollow-core fiber with ultralow loss and single-mode guidance.

We propose an antiresonant hollow-core fiber design that exhibits ultralow loss and exceptional single modedness at 1.55 µm. In this design, the confinement loss of less than 10-6 dB m-1 can be obtained with excellent bending performance even at a tight bending radius of 3 cm. At the same time, a record-high higher-order mode extinction ratio of 8 × 105 can be achieved in the geometry by inducing strong coupling between the higher-order core modes and cladding hole modes. These guiding properties make it an excellent candidate for applications in hollow-core fiber-enabled low-latency telecommunication systems.

Effects of the molecular weight of soft segment of polycaprolactone polyurethane prepolymer on the properties of polyurethane composites with high wood content

Developing green composite with high biomass content is one crucial way to realize the strategy of ‘carbon reduction’. The type of polyurethane prepolymer and its soft segment’s structure have an important influence on the structure and properties of composite materials. This work focused on preparing different kinds of wood powder-polyurethane prepolymer (WCLPU) composite with high biomass content to study the effects of the molecular weight of the soft segment of the polyurethane prepolymer (PCLPU) on the structure and properties of the composites. The results showed that the composite materials with 70 wt% wood content exhibited high strength and good bending performance. Specifically, with decreasing molecular weight of the PCLPU soft segment, the bending strength and bending modulus of the modified WCLPU composite also increased. This work has laid a foundation for studying the effects of the molecular weight of the PCLPU soft segment on the structure and properties of composite materials.

Performance of corrugated steel plate flange joint under combined compression and Bending: Experimental and numerical investigations

Prefabricated corrugated-steel-plate (CSP) structures have been increasingly applied in tunnel maintenance. In practice, the varying stiffness of bolted joints can change their mechanical characteristics and failure mechanism. This paper presents experimental and numerical investigations of the joint behavior and bending resistance of CSP flange joints under combined compression and bending forces. Full-scale tests were conducted on CSP flange joints with and without axial forces, and the deformation characteristics and failure modes were analyzed and discussed. Numerical simulations were then conducted to simulate the test joint responses and applied to conduct parametric studies. The influence of the axial force, CSP thickness, flange plate thickness, and bolt preload on bending performance was evaluated based on the test and numerical data. The results revealed that the flange joint specimen under combined axial and bending load exhibited superior integrity, less flange plate deformation, and less vertical midspan displacement, compared with the pure bending condition. An increase in the axial force, CSP thickness, and flange plate thickness greatly improved the bending stiffness of the joint, with the flange plate thickness having the greatest effect and the bolt preload having no obvious effect on the bending performance. Comprehensive structural economy and safety considerations suggested that the CSP thickness should exceed 6 mm and the flange plate thickness should be between 10 and 15 mm. Additionally, for practical purposes, a backpropagation neural network was developed. The proposed neural network model accurately and effectively predicted the joint rotation angle using the joint geometric parameters and load conditions. This paper provides a reference for the flange-joint design of corrugated-steel structures.

Study on the influence of bending curvature on the bending characteristics of unbonded flexible pipes

Unbonded flexible pipes are widely used in offshore oil and gas development as key equipment for offshore oil and gas transportation. Their biggest advantages are their flexibility and easy bending, making them more adaptable to the complex marine environment and the movement of offshore floating oil and gas platforms. These platforms also bring challenges to the structural design and analysis of flexible pipes. The mechanical response of each spiral strip layer used to construct the flexible pipe is the most complex response in the bending process. To analyze the bending performance of flexible pipes, this study focuses on the derivation of the explicit relationship between the bending curvature and the minimum critical curvature of a flexible pipe in the partial slip process of a spiral strip layer. An interlayer friction coefficient is introduced in the theoretical derivation, and complete expressions of the bending moment and bending stiffness for the non-slip, partial slip, and complete slip stages of the spiral strip layer are established. The expressions explain the hysteresis phenomenon of the bending characteristics of flexible pipes under a bending load. The results show that the hysteresis present when analyzing the bending moment-curvature relationship and the bending stiffness-curvature relationship of flexible pipes is mainly caused by the nonlinearity of the bending moment-curvature relationship of the tensile armor layer, while the bending moment-curvature relationship of all other layers is linear and the bending stiffness remains constant. The contribution of the carcass layer, pressure armor layer and anti-wear layer to the bending moment and bending stiffness is very small. The minimum critical curvature is the key variable affecting the slippage of the spiral strips of the tensile armor layer. The minimum critical curvature has a linear relationship with the interlayer friction coefficient and a nonlinear relationship with the helix angle.

Finite Element Analysis of Bonding Property and Flexural Strength of WUHPC-NC Gradient Concrete.

Ultra-high-performance concrete (UHPC) has greater mechanical and durability performance than normal concrete (NC). Using a limited dosage of UHPC on the external surface of NC to form a gradient structure could significantly improve the strength and corrosion resistance of the concrete structure and avoid the problems caused by bulk UHPC. In this work, white ultra-high-performance concrete (WUHPC) was selected as an external protection layer for normal concrete to construct the gradient structure. WUHPC of different strengths were prepared, and 27 gradient WUHPC-NC specimens with different WUHPC strengths and interval times of 0, 10, and 20 h were tested using splitting tensile strength to reveal the bonding properties. Fifteen prism gradient specimens with the size of 100 × 100 × 400 mm and a WUHPC ratio of 1:1, 1:3, and 1:4 were tested using the four-pointed bending method to study the bending performance of the gradient concrete with different WUHPC thicknesses. Finite element models with different WUHPC thicknesses were also built to simulate the cracking behaviors. The results showed that the bonding properties of WUHPC-NC were stronger with less interval time and reached the maximum of 1.5 MPa when the interval was 0 h. Moreover, the bond strength first increased and then decreased with the decline in the strength gap between WUHPC and NC. When the thickness ratios of WUHPC to NC were 1:4, 1:3, and 1:1, the flexural strength of the gradient concrete improved by 89.82%, 78.80%, and 83.31%, respectively. The major cracks rapidly propagated from the 2 cm position to the bottom of the mid-span, and the thickness of 1:4 was the most efficient design. The results simulated by finite element analysis also proved that the elastic strain at the crack propagating point was the minimum and was easier to crack. The simulated results were in good accordance with the experimental phenomenon.

Flexural properties of porcupine quill-inspired sandwich panels

This paper presents the bending behaviour of the porcupine quill and bioinspired Voronoi sandwich panels, aiming to explore the effect of geometrical design on the bending performance of the inspired structures. Through the x-ray micro-computed tomography, the internal morphology of the quill is explored. The longitudinal cross-section of the porcupine quill revealed a functionally graded design in the foam structure. Based on this observation, Voronoi sandwich panels are designed by incorporating the Voronoi seed distribution strategy and gradient transition design configurations. Porcupine-inspired sandwich panels with various core designs are fabricated via material jetting technique and tested under three-point bending condition. Results show that the sample failed at the bottom face panels for uniform sandwich panels, whereas graded samples failed in the core panel. The bending behaviour developed via simulation software shows a good agreement with the experimental results. The parametric study provides insights into structural designs for engineering applications, particularly in the aerospace and automobile industries.

Self-Powered Sterilization System for Wearable Devices Based on Biocompatible Materials and Triboelectric Nanogenerator

Wearable electronics with multifunction and convenience are entering a period of rapid development. However, the longer people wear electronic devices, the easier it is for bacteria to infect the skin. Sterilization of wearables has received little research, partly because mature high-voltage sterilization systems require energy sources, which will greatly restrict the large-scale applications of wearable devices. Therefore, a self-powered sterilization system with high comfort and safety is strongly appealing. To solve the above problem, we design a wearable, self-powered sterilization system with a biocompatible nano/microporous fiber triboelectric nanogenerator (NMF-TENG) as the energy source and an interdigital electrode for better bactericidal performance. Ag nanowires (AgNWs) and carbon nanotube (CNT) are added to the indium tin oxide (ITO)-based interdigital electrode to improve the conductivity, bending performance, and local electric field strength. Due to the tip effect, the local electric field of the electrode can be improved as high as 1 MV m–1, which can kill the bacteria. The system can achieve a long-term sterilization rate of up to 90%, which has great application potential in the sterilization direction of wearable electronic devices.

High performance electro-active artificial muscles based on 3D dendritic nickel cobalt sulfide nanorods-graphene electrodes

As the desire for biomimicry that utilizes the advantages of natural organisms, increases, electroactive artificial muscles, an emerging technology, have been phasing-in to bioinspired applications in medicine, electronics, and soft robotics. However, it remains challenging to simultaneously obtain stable response characteristics and high bending displacement, considering the instability of electrode materials in open air environments. Here, 3D dendritic nickel cobalt sulfide nanorods grown on graphene electrodes, exhibiting stable electrochemical reactivity owing to their structural and material advantages, are employed to realize high-performance artificial muscles. Importantly, the significant influence of the phase transition of nickel-cobalt metals and graphene template in the synthesis steps on tuning the electrical and electrochemical properties is reported. The resulting artificial muscles show an almost 98 % enhanced bending performance and stable response to both AC and DC input signals without significant phase delay or distortion. These substantial improvements in the performance of artificial muscles enable the demonstration of bioinspired soft locomotive robots; these artificial muscles will thus expand the soft electronics industry in the field of next-generation human-machine interfaces.

Development of a Novel Ball-and-Socket Flexible Manipulator for Minimally Invasive Flexible Surgery

This work proposes a novel flexible manipulator consisting of a series of 2-DOF vertebrae based on a ball-andsocket joint that is connected by a ball-shaped surface and a cupshaped socket and constrained by pins for circumferential rotation. This manipulator can demonstrate outstanding torsional stiffness since the circumferential rotation between the vertebrae is constrained by four ball pins. The point contact between ball pins and guideways effectively reduces the friction between the vertebrae, thus allowing the designed manipulator to yield a smooth bending shape with constant curvature. This manipulator features high axial and torsional stiffness, excellent bending performance, sufficient loading capacity, and convenient integration with surgical instruments. Moreover, the excellent torsional stiffness enables this manipulator to efficiently transfer torque and be applied in in-situ torsional motion, effectively addressing the typical issue of limited dexterity for torsional motion. The kinematic modeling of the proposed manipulator under in-situ torsional motion has been derived, and its workspace has been analyzed. A robotic system has been assembled, and experiments have verified the proposed design and modeling validity. The results show that the maximum position errors in bending motion are 2.39% (horizontal direction) and 1.98% (vertical direction), and its torsional stiffness is 21.13N∙mm/deg, which is 46 times higher than that of a typical spherical flexible manipulator (SFM). Such merits support this manipulator excellently performing the in-situ torsional motion with a maximum average position error of 3.58%. Furthermore, a phantom test of the larynx has been performed to verify the potential of clinical feasibility.

Temperature Influence on the Bending Performance of Laminated Bamboo Lumber

Temperature Influence on the Bending Performance of Laminated Bamboo Lumber

A Novel Rectangular-Section Combined Beam of Welded Thin-Walled H-Shape Steel/Camphor Pine Wood: The Bending Performance Study

At present, the development of green building materials is imminent. Traditional wood structures show low strength and are easy to crack. Steel structures are also prone to instability. A novel rectangular-section composite beam from the welded thin-walled H-shape steel/camphor pine was proposed in this work. The force deformation, section strain distribution law, and damage mechanism of the combined beam were studied to optimize the composite beam design, clarify the stress characteristics, present a more reasonable and more efficient cross-section design, and promote green and environmental protection techniques. Furthermore, the effect of different factors such as steel yield strength, H-type steel web thickness, H-type steel web height, H-type steel flange thickness, H-type steel upper flange covered-board thickness, and combined beam width was investigated. The ABAQUS simulation with the finite element software was also performed and was verified through empirical experiments. According to the results: (1) the damage process of the composite beam was divided into three steps, namely elastic stage, elastic–plastic step, and destruction stage, and the cross-middle section strain met the flat section assumption; (2) additionally, the bond connection was reliable, the two deformations were consistent, and the effect of the combination was significant. The study of the main factors showed that an increase in the yield strength, the H-type steel web height, the steel H-beam upper flange thickness, and the combined beam width caused a significant enhancement in the bending bearing capacity. The combined beam led to high bending stiffness, high bending bearing capacity, and good ductility under bending.