Bending Mechanical Properties Research Articles

Alterations to the bending mechanical properties of Pinus sylvestris timber according to flatwise and edgewise directions and knot position in the cross-section

Given the heterogeneity of the material, the behaviour of a timber beam may differ depending on which of its sides is subjected to tension and which one is subjected to compression. An analysis is undertaken in the present work of the behaviour in non-destructive bending tests on the four sides of 57 samples of Pinus sylvestris (scots pine) of structural size (2000 × 100 × 70 mm3). A study is additionally performed of the influence of the size and position of knots in the cross-section. The modulus of elasticity in flatwise direction was found to be 3 % higher than in edgewise direction. This difference could be attributable to the shear effect. While the introduction of knottiness variables did not improve modulus of elasticity prediction, it did decrease the error in the prediction of the modulus of rupture. The margin knot area ratio corresponding to the outer eighth of the cross-section’s width occupied by knots was the knottiness variable with the lowest error in modulus of rupture prediction.

Mechanical characterization of lining under three-dimensional complex load during shield posture adjustment

The shield tunneling method is widely used in urban underpass construction. However, research on the mechanical characteristics of segments during construction is insufficient. Throughout the shield tunneling construction process, segments undergo a diverse range of loads, and their modes become complex. During the adjustment of the posture of the shield machine along a curved path, segments must withstand three-dimensional uneven loads from the shield tail brush and extrusion of the shield shell, in addition to conventional loads. Thus, this study delves into the mechanical characterization of the lining during shield posture adjustment. First, three-dimensional refined models of the longitudinal and circumferential joints were established to investigate their bending and shear mechanical properties. Using the joint and shield tail brush stiffness models, a nonlinear spring-connector-shell model was developed for the mechanical analysis of segments during posture adjustment. Subsequently, a three-dimensional segment load model was formulated for the construction period. The segment response under the influence of different posture adjustments was examined using a numerical model of a tunnel subjected to a complex three-dimensional load. Furthermore, a multistage model of the segment response under various posture adjustments was established. This model serves as a valuable reference for engineering applications.

Research on the bending and tensile mechanical properties of ceramic yarns

Research on the bending and tensile mechanical properties of ceramic yarns

Investigation of the fracture behavior of cemented waste rock-tailing backfill by digital image correlation technique and discrete element modeling

Cemented waste rock-tailing backfill (CWTB), as an artificial false roof in the downward-filling mining method, with its fracture mechanical properties, directly affects the safety of workers. However, few studies have been conducted on CWTB. Therefore, in this study, three-point bending tests and digital image correlation were used to systematically investigate the effects of waste rock aggregate content (10, 20, 30, 40, and 50 %) on the bending mechanical properties (bending strength, post-peak toughness, and fracture toughness) and deformation characteristics (crack extension length and crack opening length) of CWTB. In addition, based on the partition modelling method, a mesoscopic DEM model of CWTB was proposed to reveal the crack extension mechanism and contact force evolution trends of CWTB beams. The results showed that increasing the waste rock aggregate content decreased the flexural strength and increased the post-peak toughness of CWTB. The waste rock aggregate content affected the contact force distribution characteristics and contact force variation was the mesoscopic reason for the evolution of the mechanical properties of CWTB. This study provided important experimental data and simulation basis for the engineering application of CWTB.

Static Bending Mechanical Properties of Prestressed Concrete Composite Slab with Removable Rectangular Steel-Tube Lattice Girders

In recent years, with the development of building technology, the Chinese construction industry has begun to gradually promote the prefabricated buildings to save on construction costs. Among them, composite slabs, as essential components of prefabricated buildings, have been widely used by designers mainly in favor of their low cost. However, is it possible to further reduce the cost without affecting the quality? Researchers think so if the operation cycle of support from the bottom of composite slabs can accelerate and the mechanical properties of their bottom plate can be optimized. To prove this hypothesis, researchers proposed a new type of prestressed concrete composite slab with removable rectangular steel-tube lattice girders (referred to as CDB composite slabs), whose bottom plate consists of a temporary structure composed of a prestressed concrete prefabricated plate and removable rectangular steel-tube lattice girders. Through static bending performance tests on three prefabricated bottom plates and one composite slab, researchers measured corresponding load-displacement curves, load-strain curves, crack development, and distribution, etc. The test results show that the top chord rectangular steel tubes connected to the bottom plate concrete through web reinforcement bars significantly improve the rigidity, crack resistance, and load-bearing capacity of the bottom plate and possess better ductility and out-of-plane stability. The number of supports at the bottom of the bottom plate is effectively reduced, with the maximum unsupported span reaching 4.8 m. Beyond 4.8 m, only one additional support is needed, and the maximum support span can be up to 9.0 m, which provides space for cost reduction. The cooperative load-bearing performance of the prefabricated bottom plate and the post-cast composite layer concrete is good. The top chord rectangular steel tubes are easy to dismantle and can be reused, which reduces the steel consumption by about 24% compared to that used for the same size of ordinary steel-tube lattice-girder concrete composite slabs. It can greatly decrease the cost. In conclusion, the results have shown that the new method researchers proposed here is practically applicable and also provides great space to save on financial costs.

Entire mechanical analysis of prestressed CFRP strengthened RC beams under different prestressed introduced methods

In order to clarify the effect of mechanical tensioning and SMA wire heating recovery on introducing prestress into CFRP sheet strengthened reinforced concrete (RC) beams, an experimental research on the bending performance of prestressed CFRP sheet strengthened RC beams was conducted. Based on the test results, a bending carrying capacity model for RC beams externally strengthened with prestressed CFRP sheets was proposed. The model provides calculation methods for the decompression moment, cracking moment, yielding moment, and ultimate moment, corresponding to different failure modes of the RC beams strengthened with externally bonded prestressed CFRP sheets. Four experimental beams were designed to verify the accuracy of the model with the prestresses of 100 MPa and 200 MPa. The results show that during the yield stage and strengthening stage, the loading-unloading stress-strain relationship curves of SMA wire under different prestrains are basically consistent. When the prestrain of SMA wire is 10%, the maximum recovery stress reaches 448.5 MPa. Under the same prestrain conditions, the maximum recovery stress of CFRP sheets was reduced by 37.8–39.5% when the prestress was introduced through heating recovery of SMA wires. The failure mode of mechanically tensioned prestressed CFRP sheet strengthened beams is the CFRP sheet debonding caused by mid-span bending cracks, while the failure mode of strengthened beams with prestressed CFRP sheet by SMA wire heating recovery is the CFRP sheet end debonding. The cracking moment and yield moment of the strengthened beams are significantly increased by two methods of introducing prestressing. The stiffness improvement of mechanically tensioned prestressed CFRP sheet strengthened beam is relatively large. While, the prestressed CFRP sheet strengthened beam by SMA wire heating recovery gradually experience end peeling failure of the CFRP sheet, and the prestressing effect does not effectively limit the development of cracks, resulting in limited stiffness improvement. The calculation results are in good agreement with the experimental results, proving that the proposed method for analyzing the entire bending process can be used to predict the bending mechanical properties of the prestressed CFRP sheet strengthened beams.

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.

Examining the bending test properties of bio-composites strengthened with fibers through a combination of experimental and modeling approaches

This study explores the relationship between natural fiber filling density (10%, 15%, 25%) and its impact on the bending properties of polymer compounds reinforced with Diss, Sisal and Luffa fibers. Using advanced techniques like fiber analysis and Fourier transform infrared spectrometry (FTIR), the research reveals that a 25% filling density results in the highest stress values (25.61 MPa, 22.21 MPa and 20.88 MPa) for Diss, Sisal and Luffa compounds, respectively, fostering robust bonds in Diss-reinforced polymers. The Artificial Neural Network (ANN) model demonstrates superior predictive capability with correlation coefficients exceeding 0.99 for stress and displacement, outperforming Response Surface Methodology (RSM). Analysis of Variance (ANOVA) underscores the impact of sample section parameters and fiber rate on stress, establishing the significance of type parameters and fiber rate on displacement. This integration of ANN and RSM represents a paradigm shift in predicting bending mechanical properties, advancing our understanding of composite materials for innovative applications.

Bending performance of wet joints in negative moment zone of prefabricated small-box girder bridges: Experimental and numerical study

The prefabricated small-box girder (PSBG) structure adopts the construction method of simple supporting beam transforming to continuous beam, which results in negative bending moment on the box girder supports and large tensile stress on the top of the longitudinal wet joints. Due to the relatively low tensile strength of concrete, the top plate of the bridge in the negative bending moment zone is susceptible to cracking under the load of vehicles, as well as due to the shrinkage and creep of concrete. This poses a risk to the safety, applicability, and durability of the bridge structure and may lead to a reduction in these aspects. Ultra-high performance concrete (UHPC) has excellent tensile performance and stronger crack control capability, which can effectively improve the anti-cracking and durability of the wet joints of the PSBG. In the present study, the research focused on the negative bending moment zone of a three-span continuous small–box girder bridges. This zone was selected as the research object and served as the basis for designing a stepped wet joint girder, where UHPC is partially cast on the top plate. By conducting three-point bending tests, we compared the bending mechanical properties of the joint girders when poured with normal concrete (NC) and UHPC in the joint top area. Further, the key factors affecting the anti-cracking performance and bearing capacity, including the length and thickness of the UHPC layer and the width of the wet joint, were analyzed by finite element simulation. The results show that the contribution of the top plate UHPC to tensile stress cannot be ignored. Compared with the NC joint girder, the UHPC joint girder has better toughness and plasticity, and the cracking load and bearing capacity increased by 28.6% and 9.7%, respectively. According to the simulation results, as the increase of the length and thickness of the UHPC layer and the width of wet joint, the anti-cracking and bearing capacities of the PSBG with the wet joint were enhanced. The thickness and length of the UHPC layer had a significant effect on improving the anti-cracking performance of the wet joint, and the joint width only needed to meet the transfer length of rebar bond stress.

An Equivalent Linear Method to Predict Nonlinear Bending Mechanics of Dredging Floating Hose String

Dredging hoses are flexible and are particularly suitable for slurry transportations for mud or sand in dredging projects. To achieve sufficient bending stiffness and to prevent the pipe body from collapsing, this type of hose segment is a composite structure that is embedded with several cord reinforcement layers and steel wires in its rubber layer. To quickly evaluate the nonlinear bending mechanical properties of rubber hoses, this study proposes the equivalent stiffness method of linear superposition, which is verified by test data and numerical results. The results show that the equivalent bending stiffness method proposed in this study is in good agreement with numerical and experimental results. Then, by comparing the calculation results of the hose string, it was demonstrated that the linear stiffness superposition method proposed in this study can also accurately predict the bending mechanical behavior characteristics of string hose, and provide reliable guidance for hose design in practice.

Cracking characteristics evaluation for reinforcement basalt fiber reactive powder concrete beam using acoustic emission

New types of fibers such as basalt fibers are gradually being used to reinforce cement-based concrete materials. To provide a basis for the further popularization of basalt fibers and basalt fiber reinforced reactive powder concrete (BFRPC) materials, the bending mechanical properties and fracture properties of BFRPC beams were investigated by innovatively applying four-point bending test and multiple acoustic parameter analysis methods. On the one hand, the load vs. displacement curve and crack pattern of reinforcement BFRPC beam were obtained from the four-point bending test. On the other hand, Acoustic emission (AE) technology was used to monitor the cracking process of reinforcement BFRPC beam under four-point bending load, and the AE signal was analyzed to illustrate the cracking characteristics of reinforcement BFRPC beam. The results revealed that AE hits, amplitude, counts, duration, and energy have a similar changing trend with bending load. Cumulative hits and cumulative energy are positively linearly related to the displacement and quadratically related to the sum of crack widths, and the correlation coefficients are all above 0.95. Besides, the cracking process of reinforcement BFRPC beam can be divided into four stages by the variation of AE basic parameters with bending load. The main rebars yielding is an important turning point of the crack characteristic of reinforcement BFRPC beam. AE signal data varies greatly in different locations, and it has an obvious advantage to detect the formation of invisible cracks. The results of predicting concrete damage and cracking by AE signal data are consistent with the experimental phenomenon. The low-stress brittle fracture caused by tensile fracture was reduced, and the tensile resistance and flexural bearing capacity of the reinforcement BFRPC beam were increased. The results obtained in this paper support the damage assessment and structural health monitoring for cement base concrete materials under bending load.

Experimental study of dynamic mechanical properties and damage mechanism of textile reinforced concrete

The flexural characteristics of alkali-resistant (AR) glass textile reinforced concrete slabs (GTRC) at static-to-dynamic loading rates are investigated in the present study. The fabricated GTRC slabs were manufactured with four and six textile layers as reinforcement. Static flexural testing is conducted at 0.5 mm/min, while dynamic flexural tests are conducted at five loading velocities of 1, 2, 3, 4, and 4.5 m/s. The corresponding strain rates at selected impact velocities are 4, 8, 12, 16, and 18 s-1. Two separate mechanical setups, including (i) the MTS load frame and (ii) Instron drop-weight impact system, are used for distinct experimental testing. Furthermore, the mechanical properties of flexural strength, maximum strain, ultimate strain, flexural modulus, and toughness are calculated by using mathematical relations. In addition, failure patterns and the load-bearing intrinsic mechanisms of GTRC samples are analyzed in detail. Flexural experiments at various loading rates revealed that the loading rate and the number of reinforcing layers significantly influence the bending characteristics and mechanical properties of GTRC samples. In addition, the mechanical response is comparatively reduced at six layers of reinforcement than GTRC with four layers, proving better mechanical properties in flexural load at static and dynamic loading conditions.

Performance of painted and non-painted non-woven nickel-coated carbon fibers for lightning strike protection of composite aircraft

This study investigates the performance of non-woven nickel-coated carbon fibers with varying sheet resistivity as potential solutions for lightning strike protection of composite aircraft, with a focus on the influence of the paint layer on top of the protection. Carbon/epoxy laminates protected by nickel-coated carbon fibers were subjected to lightning strike tests (modified A-waveform), and the heat transfers in the composite were observed using an infrared camera. The damages were analyzed with C-Scan and CT-Scan, and the retention of mechanical properties in bending was characterized via 4-point bending tests. The sheet resistivity, depth and area of damages, retention of mechanical properties, additional cost and weight were then compared to the expanded copper foil currently used in the aerospace industry, with and without a paint layer. With an additional weight of at most 140 gm−2, nickel-coated carbon fibers are lighter than expanded copper foil (325 gm−2), while providing 100% of retention of flexural strength after lightning strike, better than the expanded copper foil (90%). However, adding a paint layer decreases the retention of flexural strength to at best 87% when the composite is protected by nickel-coated carbon fibers, but has a very small effect on composites protected by an expanded copper foil.

Bending behavior of 3D printed continuous fiber reinforced composite sandwich cylindrical shells

Continuous carbon fiber reinforced composite sandwich cylindrical shells (CFRCSs) have been widely used in aerospace and automotive fields due to their excellent load-bearing performance. However, traditional manufacturing methods involve complex processes and expensive molds. This study uses 3D printing technology to manufacture CFRCSs with sinusoidal, triangular, and trapezoidal core. The sample surface and inside fiber distribution is inspected by the optical microscope and X-ray microscope, respectively. It is found that the samples have the defects of uneven resin distribution, fiber breaking, and fiber waviness. The bending behaviors of CFRCSs are investigated by the three-point bending test. The results show that the CFRCSs with sinusoidal core have the maximum ultimate load of about 3094 N, while those with the triangular core structure have the minimum ultimate load of about 1774 N. The triangular and sinusoidal structures mainly undergo debonding at the junction of the core and the panel and fracture at the core because of the small contact area between the core and panel. In contrast, the trapezoidal structure is mainly brittle fracture with fiber pull-out at the bottom panel and fracture at the top panel. The core type greatly influences the bending mechanical properties of the printed CFRCSs. 3D printing technology can be used to manufacture CFRCSs with required mechanical properties by flexibly designing the core shape.

Study on the Effect of Free-edge Conditions on Bending Properties of Composite Materials

The glass fiber is selected as the reinforcement, and the structural design of the composite is carried out to enhance the continuity of the edge fiber of the laminate. The influence of the width of the edge fiber on the bending mechanical properties is discussed. It is found that when the edge fiber of the laminate is continuous, the failure mode of the laminate bending can be changed to a certain extent, and the strength of the reinforcement and the matrix bonding is strengthened. The width of the laminate is not the influence factor in improving the bending strength.

Mechanical properties test of plant fiber reinforced cementitious composites

In this paper, a new type of plant fiber-reinforced cementitious composite (PFRCC) is developed. Compared with ordinary cement-based materials, its toughness is greatly improved. To investigate the tensile and bending mechanical properties of PFRCC, four kinds of PFRCC panels with different thicknesses were developed, and the axial tensile test and bending test of the PFRCC panel were designed. The results show that with the increase in the thickness of the PFRCC panel, the bearing capacity increases gradually. The peak tensile strain is about 0.022 %, which is 1.47-2.2 times that of the matrix cement mortar. The average tensile strength is about 2.52 MPa, which is slightly higher than that of the matrix cement mortar. The bending failure load of the PFRCC panel increases with the increase in thickness, but its peak displacement decreases gradually. The bending strength of the PFRCC panel is about 13.5 MPa, which is 2.7 times that of the matrix cement mortar. It shows that the addition of plant fiber can not only increase the toughness of cement mortar but also improve its tensile and bending strength. The above research provides a theoretical basis for the application of PFRCC panels in practical engineerings such as permanent formwork of foundation beams and light-gauge steel stud concrete composite external wall panels.

Volumetric Printing across Melt Electrowritten Scaffolds Fabricates Multi-Material Living Constructs with Tunable Architecture and Mechanics.

Major challenges in biofabrication revolve around capturing the complex, hierarchical composition of native tissues. However, individual 3D printing techniques have limited capacity to produce composite biomaterials with multi-scale resolution. Volumetric bioprinting recently emerged as a paradigm-shift in biofabrication. This ultra-fast, light-based technique sculpts cell-laden hydrogel bioresins into three-dimensional structures in a layerless fashion, providing enhanced design freedom over conventional bioprinting. However, it yields prints with low mechanical stability, since soft, cell-friendly hydrogels are used. Herein, for the first time, the possibility to converge volumetric bioprinting with melt electrowriting, which excels at patterning microfibers, is shown for the fabrication of tubular hydrogel-based composites with enhanced mechanical behavior. Despite including non-transparent melt electrowritten scaffolds into the volumetric printing process, high-resolution bioprinted structures were successfully achieved. Tensile, burst and bending mechanical properties of printed tubes were tuned altering the electrowritten mesh design, resulting in complex, multi-material tubular constructs with customizable, anisotropic geometries that better mimic intricate biological tubular structures. As a proof-of-concept, engineered tubular structures were obtained by building tri-layered cell-laden vessels, and features (valves, branches, fenestrations) that could be rapidly printed using this hybrid approach. This multi-technology convergence offers a new toolbox for manufacturing hierarchical and mechanically tunable multi-material living structures. This article is protected by copyright. All rights reserved.

Bending mechanics test and parameters calibration of ramie stalks

Research and development of ramie harvesting equipment is a key link to revitalize ramie industry, problems such as the tendency of stalks to tangle and clog the machine are very problematic, seriously affect the quality and fluency of the harvester. The structure of ramie stalk is complex, and the mechanical properties of each component vary greatly, collision between stalk and machine creates complex stress relationship. By building a finite element model, it is possible to analyze the stress state of the stalk during bending from a microscopic perspective, and to analyze the complex stress–strain situation within the stalk. The purpose of this paper is to establish a standard ramie stalk bending finite element model to provide a theoretical basis for the subsequent kinematics and dynamics. Firstly, material experiments were carried out on ramie straw. The structural and mechanical parameters of the straw components were obtained through measurement and calculation tests, and the force–deformation curves for straw bending were obtained. Bending finite element simulations were carried out on the basis of mechanical tests, and the parameters such as dynamic friction coefficient, wood Poisson's ratio and bast Poisson's ratio were determined by the central combination design. Then established an accurate bending finite element simulation model of ramie stalk, the accuracy of the model was verified at the end. In this paper, the key parameters of the ramie stalk model were calibrated through a combination of material tests and simulations. All parameters of the ramie stalk model were finally obtained, and the bending mechanical properties of the ramie stalk were analysed by applying finite element analysis. This bending mechanics simulation model can be used for kinematic and dynamics simulation analysis of conveying and baling to provide a theoretical basis for the structural design of the harvester. The methods explored here can be applied to other slender straw crops.

Effect of hydrostatic pressure on multilevel structure and bending progressive damage of 3D braided composites under simulated deep-sea environment

Compared to metal materials and laminated composites, three-dimensional (3D) braided composites are showing innovatively great potential in deep-sea pressure shell applications owing to their light-weight, excellent out-of-plane mechanical properties and near-net forming capacity. In this paper, three-dimensional six-directional (3D6D) braided composites with different epoxy resins are designed and fabricated. The samples are put in a deep-sea pressure simulator at 10 MPa pressure for 80 h and experimentally test via the three-point bending method. A multi-level evaluating approach, namely nano-scale, micro-scale, meso-scale and macro-scale, is proposed. The effect of the hydrostatic pressure on multilevel structure and progressive failure behaviours are analyzed. Results indicate that, although the moisture absorption does not lead to the generation of new chemical bonds on the nanoscale in the carbon/epoxy composites, the moisture absorption has significant effects on the bending mechanical properties and damage initiation of 3D6D braided composites. Moreover, after deep-sea hydrostatic pressure, the strength of 3D6D braided composites decrease by 15.64–30.93 %, and the damage volumes increase by 0.039–0.405 %. Furthermore, the final failure mechanism of 3D6D braided composites after deep-sea hydrostatic pressure are largely governed by the fiber-matrix debonding and matrix cracking.

An Experimental and Numerical Analysis of Glued Laminated Beams Strengthened by Pre-Stressed Basalt Fibre-Reinforced Polymer Bars

Damage often develops in glued laminated timber members under high bending loads due to natural defects in the timber, which results in their low load-bearing capacity and stiffness. In order to improve the bending mechanical properties of glulam beams, a new type of longitudinal glulam reinforcement with pre-stressed basalt fibre-reinforced polymer composites (BFRP) was developed using the Near Surface Mounted (NSM) technique. The strengthening method consisted of two pre-stressed BFRP bars glued into the grooves at the bottom side of the beam; meanwhile, for the second strengthening alternative, the third BFRP bar was embedded into the groove at the top side of the beam. Therefore, an experimental study was carried out to verify this strengthening technique, in which fifteen full-size timber beams were tested with and without bonded BFRP bar reinforcement in three series. According to the results of this experimental study, it can be seen that the effective load-bearing capacity of the reinforced beams increased up to 36% and that the stiffness of the beams increased by 23% compared to the unreinforced beams. The tensile stresses in the wooden fibres were reduced by 11.32% and 25.42% on average for the beams reinforced with two and three BFRP bars, respectively. On the other hand, the compressive stresses were reduced by 16.53% and 32.10% compared to the unreinforced beams. The usual failure mode saw the cracking of the wood fibres at the defects, while for some specimens, there were also signs of cracks in the epoxy adhesive bond; however, the crack propagation was, overall, significantly reduced. The numerical calculations also show a good correlation with the experimental results. The difference in the results between the experimental and numerical analysis of the reinforced and unreinforced full-sized beams ranged between 3.63% and 11.45%.