Bending Performance Research Articles

An Experimental Study on the Flexural Performance of a Steel-ECC Composite Bridge Deck Sheet in the Negative Moment Zone

This paper seeks to solve the problem of orthotropic anisotropic steel deck pavement being prone to damage and fatigue, and to study the negative moment performance of steel-ECC concrete composite deck slabs. In this work, four groups of eight specimens were designed for the negative moment four-point bending test study, which included four variables of two ECC slab thicknesses and two bolt spacings. By analyzing the damage mode, crack distribution characteristics, bending load capacity, load-deflection curve, and load-strain curve, the effects of different ECC slab thicknesses and bolt spacings on the bending performance, deformation capacity, and cracking behavior of the steel-ECC composite bridge deck were investigated. The test showed that the combined structure of the ECC and steel plate showed good integrity and good ductility under a negative bending moment, and the damage mode of the member was pure bending of a section of the ECC with concrete cracking damage. When the thickness of the ECC plate increased from 50 mm to 75 mm, the ultimate flexural load capacity of the specimen increased by 92.6%, and when the distance between bolts was reduced from 200 mm to 150 mm, the ultimate flexural load capacity of the specimen increased by 13.4%. The increase in the ECC layer thickness increases the ultimate bearing capacity of the specimen significantly, and the decrease in the bolt spacing increases the ultimate bearing capacity of the specimen less.

Dielectric characterization of Mg–Zn ferrite-based high permittivity flexible substrate for SNG metamaterial

This article reports the preparation of MgxZn(1-x)Fe2O4 ferrite-based flexible substrate using the sol–gel synthesis method. A stove-shaped metamaterial unit cell is designed and fabricated on a flexible substrate, and the microwave performance of the structure is investigated. The developed flexible composite substrate is built using PVA glue and a micro-scale of Mg–Zn ferrite nanoparticle powder, while this powder is used as filler. The structural (XRD) and morphological (FESEM) investigation allows for being used as a flexible substrate. The dielectric and loss tangent properties of the substrate are manipulated using different weight ratios of filler, while PVA keeps the flexibility features. The substrate achieved a dielectric constant (Td), and loss tangent (T) of 6.101 and 0.00899 are measured using DAK 3.5 Kit while the bending performance is investigated for 0°, 30°, 60°, and 90°, respectively. The suggested structure exhibited SNG properties within the frequency range of 4.77–5.65 GHz, 8.75–10.60 GHz, and 16.86–17.66 GHz, respectively, and near-zero index is exhibited within the frequency range of 5.216–6.388 GHz, 9.626–12.617 GHz, and 17.277–18.276 GHz, respectively. The measured response of S21 achieved a bandwidth of 4.88–5.76 GHz, 8.26–10.69 GHz, and 15.87–17.93 GHz with a maximum magnitude of −40.57 dB, −39.41 dB, and −27.63 dB at 5.31 GHz, 9.77 GHz, and 17.123 GHz resonance frequency. The proposed flexible substrate-based MTM structure can be a potential candidate for wireless communications in the S-, C-, and Ku-bands, especially as the SNG material that can increase the antenna bandwidth and gain enhancement.

Research on the Microstructure and Properties of a Flux-Cored Wire Gas-Shielded Welded Joint of A710 Low-Alloy High-Strength Steel

In this study, a 16 mm thick A710 low-alloy high-strength steel was welded by using flux-cored wire gas-shielded welding with an E81T1-Ni1M flux-cored wire. The microstructure characteristics and mechanical properties of the joints were systematically studied. The results showed that the joint was well formed without obvious welding defects. The center of the weld was mainly needle-like ferrite, the coarse grain area was mainly slat-like and granular bainite, and the fine grain area was mainly ferrite and pearlite. The lowest hardness in the weld area was the weakest area of the joint. The average tensile strength of the joint was 650 MPa, reaching 95% of the base metal; the samples were all fractured in the weld area, and the fracture morphology showed typical plastic fracture characteristics. The low-temperature (−40 °C) impact energy of the joint weld area and the heat-affected zone were 71 J and 253 J; the fracture morphology was characterized by a ductile–brittle mixed fracture, and the ductile area of the specimen fracture in the heat-affected zone was larger. The bending performance was good. Under the specified life of 2 × 106 cycles; the median fatigue limit and the safety fatigue limit were 520 MPa and 492 MPa, and the fatigue cracks germinated on the surface of the priming weld.

Bending performance of carbon fiber–reinforced polymers/aluminum sandwich structure with different forming process and analysis of failure mode

This paper aims to study the failure response of carbon fiber–reinforced polymers (CFRP)/aluminum honeycomb sandwich structures facing three-point bending test by combining the experiments and numerical models. The theoretical model of three-point bending is established by the finite element software ABAQUS to predict the damage, and then verified by experiments. In order to study the bending performance of sandwich structures made by different forming processes, the test was carried out on sandwich panels with two different molding processes, which are secondary bonding and co-curing. The failure mode and failure mechanism of sandwich structures were also studied by testing specimens with different panel thicknesses and core heights. The results shows that the specimens of the secondary bonding molding process are more prone to damage, most of the samples were observed to be debonded after the test, and the peak load is lower than that of the co-curing. Three different failure modes, closely related to the damage length of the core, which are greatly influenced by different parameters, were observed for the co-cured specimens during the test and parametric studies were carried out for the co-cured specimens. The results showed that small damage length makes it easier to form type I failure mode, while the type II failure mode is more likely to form in situations when the damage length is larger.

Improve wind gears bending performance by means of IGS (Improved gear surface)

Gearbox power density plays a decisive role in wind energy competitiveness. As wind turbines become larger to reduce the levelized cost of energy (LCOE), bending fatigue plays a higher role in gearbox design. Shot peening (SP) has been introduced frequently as a technique to increase wind gearbox bending capacity, but other techniques, such as root grinding (RG) and superfinishing (SF), remain insufficiently explored. This paper investigates the tooth root bending strength of the case-carburized gears of a normal modulemn = 10 with different root finishing conditions. The results show no relevant influence of SF after SP. In contrast, RG prior to SP shows a potential capacity increase. However, high cycle subsurface failures must be considered for this potential capacity increase.

ANALYSIS OF BENDING MECHANICAL PERFORMANCE OF WELDING JOINTS WITH THE ADDITION OF DIAMOND AND CIRCULAR PLATES

The design and analysis of welded joints are very useful for the safety of steel-based structures. The effect of welded joints meeting at one point on the resulting stress is a critical factor in constructing steel joints. The main objective of this research is to analyze the mechanical performance and microstructure of the welding process on diamond and circular plate joints. The analysis was carried out through experiments and finite element simulations to find out how much influence the addition of a diamond plate and circular plate had on the plate connection. The method used is to analyze the strength, hardness, and micro and macrostructure testing to determine the strength and structural changes of the metal after welding. The results of the test are then used to create an inhomogeneous model of weld joint, then the model is applied to the FEA software to be analyzed by the bending test simulation. The experimentally bending testing was carried out to examine bending performance of the test objects. From the simulation and experimental results, it is found that the shape of a circular plate measuring a diameter of 60 mm with a thickness of 6 mm is appropriate for a flat plate joint, and the flat-diamond plate measuring 60x60 mm with a thickness of 6 mm is proper for application to un-flat (cornered) plate joints. The structural integrity of a flat plate joint with a circular plate is greater than that of a diamond plate.

Comparative study of the negative bending behaviour of corrugated web steel–concrete composite beams using NC, ECC and UHPC

Engineered cementitious composites (ECC) and ultra-high performance concrete (UHPC) could significantly enhance the cracking performance of the negative bending regions of composite beams. In this study, the negative bending behaviour of corrugated web composite beams using normal concrete (NC), ECC and UHPC was comparatively discussed. Firstly, the negative bending test was performed for three composite beams using different concrete. The results showed that the failure modes of the corrugated web composite beams were characterized by local buckling of the steel beam compressed flanges and severe cracking of the concrete slabs. The negative bending capacity of the composite beams using UHPC increased by 17.9% and 14.4% compared to those using NC and ECC, respectively. Besides, finite element simulation indicated that the negative bending performance of steel-ECC composite beam was particularly affected by steel strength and reinforcement strength, and that of steel-UHPC composite beam showed the most significant response to steel strength. Furthermore, the negative bending capacity formula in the code was found conservative in predicting corrugated web composite beams, especially for those using UHPC. With the consideration of the tensile strength of concrete and the omission of the contribution of corrugated webs, a reasonable formula for predicting the corrugated web composite beams using different concrete was proposed and proved to have satisfactory accuracy.

Development and performance evaluation of self-healing concrete railway sleepers using different size PU tubes

The rail seats and middle are the main critical zones in railway concrete sleepers wherein the damage normally occurs due to high positive and negative bending moments, respectively. To address this issue, self-healing concrete railway sleepers (SHCRS) were developed by reinforcing the sleepers with polyurethane (PU) filled glass tubes, and their bending performance was subsequently investigated. A total of sixteen full-scale reinforced concrete railway sleepers with different diameters of glass tubes (4 mm and 9 mm) and lengths (50 mm and 200 mm) were manufactured and tested under three-point bending at the rail seat up to 440 kN for intact and 220 kN for damaged sleepers, as well as in the middle of the sleepers at 160 kN for intact and 70 kN for damaged sleepers. The digital image correlation (DIC) method was used to study the fracture behavior of SHCRSs, evaluating the crack strains and crack width openings, and their behavior was compared with conventional reinforced concrete sleepers. Short tube sleepers perform better in the rail seat where they have a further distance to the maximum flexural zone than the middle does, almost 60 mm. Meanwhile, long tube sleepers have a better performance in the middle of the sleeper, with a distance of 40 mm from the maximum flexural zone due to the greater slenderness of long tubes as opposed to short tubes. A FE model was developed to measure different slenderness ratios for long and short tube sleepers. The results show that the slenderness ratio and surface area to volume ratios (sa/vol) of the PU tubes have a significant effect on the healing of damaged sleepers. Decreasing the slenderness ratio from 250 to 200 on the short tubes increases the applied stress by 11 % in the rail seat and 450 % in the middle of the sleeper.

Bamboo slivers with high strength and toughness prepared by alkali treatment at a proper temperature

Despite bamboo slivers having long been used to manufacture bamboo weaving products, the flexibility is still well below satisfactory, especially for those split from inner layer of bamboo culm. Here, a facile approach was reported to obtain strong and flexible bamboo slivers, in which the slivers from the outer and inner layer of bamboo culm were processed with 5 wt% alkali treatment at various temperatures (23, 40, 60, and 80 °C), respectively. Compared with untreated bamboo slivers, the treated ones were investigated in terms of the microstructure, chemical composition, morphology, tensile and bending performances. The results showed that tensile and bending properties of all treated bamboo slivers were significantly improved, especially for those from inner layer of bamboo culm. The tensile strength of outer bamboo sliver treated at 60 °C and the inner ones treated at 40 °C increased up to the maximum, respectively, increasing by 86.6% and 132.0% compared with the untreated ones. The highest flexibility of the outer- and inner bamboo sliver can be achieved at 80 °C and 60 °C alkali treatment, respectively. The slivers can be completely wound around a nylon rod with a diameter of 10 mm without fracture. The excellent tensile and bending performance of bamboo slivers alkali-treated at proper temperature was largely attributed to tightly cellulose molecule aggregating induced by substantially increasing hydrogen bonding after the partial removal of lignin and hemicellulose. A denser and interlocking cellular structure due to the collapse of parenchyma cells after alkali treatment at proper temperature also partly contributed to the increased tensile and bending strength. The results suggest that strong and flexible bamboo slivers can be prepared by one-spot alkali treatment at a proper temperature, which may widen the application scope of bamboo slivers.

Ultimate Bending Performance and Fatigue Life of Single-layer and Multi-layer Bellows

Ultimate Bending Performance and Fatigue Life of Single-layer and Multi-layer Bellows

Study of the Key Mechanical Properties of Welded Hollow Spherical Joints after Uniform Corrosion

The welded hollow spherical joint is the most common form of the spatial grid structure, but the corrosion treatment at the joint is difficult. There are many corrosion problems of the welded hollow spherical joint in the actual structure, which brings hidden problems to structural safety. To study the effects of uniform corrosion on the key mechanical properties of welded hollow spherical joints, the joint refinement FEM in one typical size is built considering the effect of uniform corrosion through the method of the element birth and death, and the tensile, compressive, and bending performance of the FEM has been analyzed. Based on the analysis results, the relation curves between the three bearing capacities of the welded hollow spherical joint and the uniform corrosion degree are given. The results show that the influence of early corrosion on the joint tensile and compressive performance is not obvious. After corrosion to a certain extent, the loss of tensile and compressive capacity has a significant linear relationship with the degree of corrosion, and the loss of bending capacity has a significant quadratic curve relationship with the degree of corrosion from the initial stage. This study can provide a theoretical reference for a better understanding of the mechanical properties of welded hollow spherical joints in one typical size after corrosion to evaluate structural safety.

Mechanical properties and macro–meso coupled damage behavior of three-dimensional four-directional braided composites under bending loading

A hierarchical coupled multiscale method is developed to capture the onset and propagation of damage within the three-dimensional four-directional (3D4D) braided composites subjected to bending loading. Using a directly two-scale coupled scheme, the macroscopic nonlinear behavior at the structural dangerous region could be iteratively solved, combined with the progressive damage response of the realistic mesoscale architecture. The continuum damage model is merely defined at the mesoscale and considers failure in each of constituents with the well-established Hashin failure criteria and the Bažant crack band damage model. To accelerate finite element computation in two scales, a parallel numerical implementation is presented alongside the commercial software ABAQUS/Standard. Besides the good agreement between the experimental and the predicted values, the results also show a significant effect of the braiding angle on the bending performance of 3D4D braided composites. With the increase of braiding angle, the bending stiffness and strength of 3D4D braided composites decreases, but the fracture toughness increases. This phenomenon was numerically investigated by identifying the different fundamental failure mechanism and damage development process at both the scales.

Multivariate regression approaches to predict the flexural performance of cellulose fibre reinforced extruded earth bricks for sustainable buildings

Regression analysis is commonly used to predict the compressive strength of soil-based materials to reduce the time and cost of construction projects. This study presents the results of multivariate regression analysis on the prediction of modulus of rupture and specific energy of cement-stabilised earth bricks reinforced with bamboo cellulose fibres as a function of cellulose fibre percentage, curing temperature and curing time. Statistical modelling is carried out on the experimental data of the four-point bending test of clay brick stabilised with 10 wt% Ordinary Portland Cement reinforced with 0, 5, 7.5 and 10 wt% organosolv bamboo pulp fibres. The water content of the unreinforced specimen was adopted at 25 wt% of the solid materials based on the plastic limit value of the soil, while the value of the water content of the samples with cellulose fibres was 35 wt% due to the affinity of the cellulose with water as well as to allow good extrudability of the pulp. The bricks were cured under different conditions (23 °C, 60% RH and 60 °C, 100% RH) and at different ages (14 and 28 days). Regression analysis and two-way ANOVA were studied to assess the accuracy, correlation and effect of each variable on the prediction of the random response variable. The results showed that non-linear regression analysis provides the best-fitting statistical model with an accuracy of 96%. In addition, the curing temperature and the percentage of cellulose fibres significantly affect the bricks bending performance, while the effect of curing time is the least visible. This non-linear model can be adopted as a suitable model to predict the flexural properties of cellulose pulp fibre-reinforced earth bricks for a sustainable building solution in developing countries. For better generalization and practical application of this method to predict the flexural performance of cellulose pulp fibre-reinforced earth bricks, a large data set of a broader range should be explored.

Investigation of bending properties of continuous fiber reinforced resin T-beams made by 3D printing

In the study, method of 3D printing is adopted to make continuous fiber reinforced resin T-beams, presenting a new approach to the fabrication of beam structure for building, aviation, shipbuilding and other fields. The effects of the height of the rib as well as deposited space on the bending performance of printed T-beam were investigated. Specifically, bending damage modes were analyzed, and the bending process was monitored through acoustic emission. The results show that, the bending strength and modulus increase distinctly with the decrease of the deposited space. The bending strength and modulus can reach a maximum of 315 MPa and 16 GPa respectively. The bending damage mode of the 3D printed T-beam is the fracture of the outer part of the middle part of the rib followed by delamination of the rib. Principal component analysis (PCA) was used to reduce the multidimensional variables to three principal components. Furthermore, the three principal components were classified into 5 categories based on the k-means clustering algorithm to analysis bending damage process of T-beam.

Study on mechanical properties and application in communication pole line engineering of glass fiber reinforced polyurethane composites (GFRP)

Reinforced concrete poles, wooden poles and steel poles are commonly used in communication pole line engineering, but there are numerous shortcomings, which can’t be ignored. In this paper, a scheme of applying glass fiber reinforced polyurethane composites (GFRP) instead of traditional materials to manufacture poles in communication pole line engineering is proposed. The technical properties and bending moment of GFRP poles were studied through material test and bending performance test. Furthermore, Abaqus was used to carry out finite element analysis on GFRP pole, and physical and mechanical properties of GFRP and traditional materials were compared. Referring to GB/T 51421–2020 and DL/T 5219–2014, structural design of GFRP pole and foundation was carried out, respectively. Finally, economic benefit of GFRP pole was analyzed, then an innovative installation method of GFRP pole was proposed. Results show that GFRP has high stiffness, light weight, high strength and durability. Besides, GFRP pole has sufficient flexural bearing capacity, and foundation has excellent overturning stability, which lays a foundation for the application of GFRP in communication pole line engineering.

Experimental and numerical studies on bending characteristics of woven CFRP reinforced aluminum thin-walled automotive structures

Metal/composite hybrid thin-walled structure is the most preferential approach to achieve dual contradictive objectives of high crashworthiness and lightweight of auto body. Its collapse with regard to different fiber layup patterns is one of the governing mechanisms of energy dissipation, which is yet to be explored. Especially, the effect of different fiber layup angles and layup sequences on bending collapse, which is one of the most significant performance indicators, has received little attention. To this gap, this study investigates experimentally and numerically the bending characteristics of aluminum/carbon fiber reinforced plastic (Al/CFRP) hybrid structures with different layup angles and layup sequences. To start with, three-point bending tests are carried out on specimens to derive the bending failure behavior and crashworthiness, and the internal section damage is observed by CT scan. Finite element model is then constructed and benchmarked against the test results to be proficient. On this basis, the effects of Al thickness, number of CFRP layers and CFRP wrapping range on the bending performance of hybrid tube are analyzed numerically. The simulation results show that layup angle has greater effect on the bending performance than layup sequence. Increasing Al thickness and the number of CFRP layers can effectively improve the bending resistance of structure, and appropriate partial wrapping of CFRP can increase the specific energy absorption (SEA) by 10.92% compared with that of complete wrapping. The revelation from this study provides sound reference for the crashworthiness design of metal/composite hybrid thin-walled structure.

Influence of steel fibre on bending behaviours of RPC based on X-ray CT and mesoscopic numerical simulation

The mechanical properties and fracture mechanism of quasi-brittle materials are considered to be largely reliant on the mechanical properties of meso-components and the structure formed when these components are combined. In recent numerical simulation practice, a trend has developed whereby the real structure of materials is considered in as accurate a way as possible. In this paper, the macroscopic and mesoscopic bending behaviours of steel fibre-reinforced reactive powder concrete (RPC) slabs with fibre volume content between 0.0% and 2.5% were investigated using both experimental tests and numerical simulations. Images obtained from X-ray computed tomography (CT) were input into a program named RFPA3D-CT to build a modified three-dimensional finite-element method model. The results indicate that the steel fibres can help to convert a brittle failure pattern of RPC into a ductile one. Compared with specimens without fibres, the crack tortuosity and bending strength of specimens with fibre content of 2.5% are increased by 20.25% and 308.80%, respectively. The bending performance according to numerical results obtained by the modified model are in good agreement with the experimental results. Moreover, the acoustic emission (AE) parameters and AE curves obtained in RFPA3D-CT can be used to reveal the initiation and propagation process of cracks in RPC.

Key Design Parameters Analysis and Calculation Theory Research on Bending Performance of Steel–UHPC Lightweight Composite Deck Structure

This paper aims to study the influence of key design parameters (e.g., reinforcement ratio, cover thickness, stud spacing, and thickness of the ultra-high-performance concrete (UHPC) layer) on the longitudinal and transverse bending performance, as well as the cracking load and ultimate bearing capacity calculation theory of steel–UHPC lightweight composite deck (LWCD) structure. Four transverse bending tests and four longitudinal bending tests on steel–UHPC composite plates and steel–UHPC composite beams were conducted, respectively. The refined finite element models of components with different key design parameters based on ABAQUS were established. The influences of different key design parameters on the transverse and longitudinal flexural behaviors (e.g., load-mid-span displacement curve, cracking stress, stiffness, elastic limit load, critical slip load, ultimate bearing capacity and ductility) were compared and analyzed in detail. The ultimate bearing capacity can be improved by increasing the thickness of UHPC layer and the reinforcement ratio of longitudinal reinforcement, and reducing the cover thickness and the spacing of studs. According to the longitudinal bending characteristics of the steel–UHPC lightweight composite deck structure, the calculation formulas for the cracking load and the ultimate bearing capacity of the steel–UHPC composite beam are proposed, and the calculated values are in good agreement with test results (the errors are basically within 10%), which is convenient for practical engineering applications.

Development of the hardness, three-point bending, and wear behavior of self-lubricating Cu-5Gr/Al2O3-Cr3C2 hybrid composites

This research aims to assess the mechanical characteristics of high-performance copper composites made utilizing powder metallurgy. The composites were produced by adding reinforcement elements (Al2O3-Cr3C2) at different rates (3-6–9 wt.%) into copper-graphite (Cu-5Gr) via hot pressing technique. The microstructure, hardness, three-point bending and wear performance were analysed. The results determined that hybrid reinforced composites exhibited higher density, hardness and bending strength compared to Cu-Gr composites. The highest hardness of 73.02 HB was found in the CG-4 (copper graphit-4) sample. The maximum bending stress of 151.06 MPa occurred in sample CG-2. In addition, it was observed that the wear resistance increased significantly with the addition of the hybrid reinforcements. The lowest specific wear rate of 7.961 × 10−7 mm3/N.m occurred in sample CG-6. As a result, 15.92%, 58.16% and 83.21% improvements were achieved in hardness, bending strength and wear performance, respectively. The current work indicates that certain mechanical properties of copper can be improved via the powder metallurgy process and the addition of reinforcements which could expand the applications and use of this metal in different industries.

Effect of retained austenite on the fracture behavior of a novel press-hardened steel

• Effect of RA on both the tensile and bending properties of the PHS has been studied. • RA with various mechanical stabilities and volume fraction are obtained via tuning the degree of auto-tempering of martensite during die quenching. • The tensile performance is improved with increasing of volume fractions of RA in the novel PHS. • The mechanical stability, rather than volume fraction of RA, has significant impact on the bendability of the PHS. Tensile and bending properties are two critical attributes of press hardened steels (PHSs) for automotive body structural components. However, the research on these properties of PHSs with retained austenite (RA), which is introduced to improve the mechanical properties, has not been well reported. In this study, the effect of RA on the quasi-static uniaxial tensile and three-point bending behaviors has been systematically investigated for a newly developed Cr and Si alloyed PHS. RA with various degrees of mechanical stabilities was obtained by tuning the auto-tempering of martensite through the control of the die contact pressure during the press hardening process. Mechanically stable RA provides the optimal combination of tensile and bending performance, while the PHS with RA of poor mechanical stability has a deteriorated bending toughness as manifested by a reduction of bending angle from approximately 61.6° to 56.8°. However, its tensile properties, in contrast, are the best in terms of the product of ultimate tensile strength and total elongation (15.9 GPa %). This is mainly attributed to the unstable RA on the outermost surface of the bending sample. The unstable RA can easily transform into brittle martensite under local plane strain and strain gradient conditions in the bending test compared with uniaxial stress in the tensile test, promoting crack initiation and propagation. Furthermore, the effect of martensitic auto-tempering or contact pressure on the quantity and stability of RA are also discussed. This study would provide a useful reference to guide hot stamping process optimization for the newly developed Cr and Si-containing press-hardened steel.