Results Of Four-point Bending Tests Research Articles

Determination of elastic moduli and Poisson’s ratios of bi-modulus materials based on the results of four-point bending test

Determination of elastic moduli and Poisson’s ratios of bi-modulus materials based on the results of four-point bending test

Upcycling use of red mud-based solid waste in engineered cementitious composites: Properties, activation mechanism, and life-cycle assessment

In this study, a low-carbon engineered cementitious composite (ECC) was produced by combining alkali-activated red mud (RM)/ground granulated blast-furnace slag (GGBS) with polyvinyl alcohol (PVA) fibers as the reinforcement. Both calcium aluminosilicate hydrate (C-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H) gels are detected in the reaction products. A higher modulus of sodium silicate in the activator results in a higher degree of reaction of silicates in the samples, but not promising a higher mechanical property. The potential mechanism of iron activation in the alkali-activation RM-based ECC system was revealed. The four-point bending test results indicate a large deflection ability and multiple cracking characteristics of the composite. Life cycle assessment of this system is also presented by calculating energy consumption and carbon emissions. This study not only sheds light on the feasibility of using RM in the preparation of high-toughness alkali-activated ECC but also provides a promising method to upcycle industrial solid wastes in a highly effective way.

Out-of-plane flexural behavior of autoclaved aerated concrete block masonry walls strengthened with high-ductility concrete

Masonry walls are susceptible to out-of-plane failures during seismic events. Therefore, this study investigated the out-of-plane flexural behavior of autoclaved aerated concrete (AAC) blocks masonry walls, strengthened with high-ductility concrete (HDC) and HDC with built-in textile grid (TR-HDC), to improve the flexural behavior of AAC block masonry walls. Nine groups of specimens, one group of reference walls, four groups of HDC-based strengthened walls, three groups of TR-HDC-based retrofitted walls, and one group of mortar-based retrofitted walls were built and tested using four-point loadings. The experimental parameters included the thickness of the strengthening layer, retrofitting configuration, shear-to-span ratio, and reinforcing textile ratio. The effects of these parameters on the failure mode, bearing capacity, deformability, and strength index were discussed based on four-point bending test results. The results demonstrated that the HDC and TR-HDC overlays improved the failure mode of the specimens from brittle to ductile fracture and increased their bearing capacity, ductility, and absorbed energy. The loading capacity of the strengthened walls further improved with an increase in the strengthening layer thickness and reinforcing textile ratio. Finally, based on the failure mode of the strengthened specimens, equations for estimating their out-of-plane bending and shear capacities were proposed.

Effect of NiAl Bond Layer on the Wear Resistance of an Austenitic Stainless Steel Coating Obtained by Arc Spray Process

<div>The present investigation has been conducted to study the tribological and adhesion properties of X10CrNi18-8 austenitic stainless steel (ASTM 301) coatings deposited on aluminum alloys such as AU4G by using the arc-spraying process. These coatings were made with and without a bond-coat layer, which is constituted by NiAl. The structure of the phases that are present in coatings was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The measurements of microhardness and tribological behavior at different loads were also performed on the surface of the coatings. Adherence test was also carried out using four-point bending tests. The SEM showed that the dense microstructures of coatings have a homogeneous lamellar morphology with the presence of porosities and unmelted particles. The main phase of coating corresponds to a solid solution as a face-centered cubic (fcc). The microhardness of coatings is nearly four times that of the two substrates of aluminum alloys. The four-point bending test results showed that the NiAl bond layer increases the critical interfacial fracture energy <i>G</i> <sub>IC</sub>, the force to share the multilayer is more important.</div>

Flexural and compressive performance of BFRP-reinforced geopolymer sea-sand concrete beams and columns: Experimental and analytical investigation

The combination of geopolymer sea-sand concrete (GSSC) and basalt fiber reinforced polymer (BFRP) reinforcement has the potential to optimally exploit the advantages of both materials, resulting in superior structural durability and environmental friendliness. The resulting structure is called a BFRP-reinforced GSSC structure, which has broad application prospects in marine engineering construction. This paper presents a recent experimental and analytical investigation into the flexural and compressive performance of BFRP-reinforced GSSC structures to verify the expected benefits of such a material combination. In particular, a type of GSSC that uses MgO as an expansion agent to reduce concrete shrinkage was used in this study. The results of four-point bending tests on nine rectangular beams, where longitudinal reinforcement ratios and reinforcement types were key parameters, and monotonic axial compression tests on seven columns, where concrete types and transverse reinforcement ratios were key parameters, are reported in this paper. The test results initially confirmed the advantages of using GSSC in combination with BFRP reinforcement and showed that: (1) the ultimate carrying capacity of BFRP-reinforced GSSC beams and columns was higher than that of conventional steel-reinforced counterparts for the same reinforcement configurations; (2) the flexural and compressive capacity of BFRP-reinforced concrete beams and columns could be enhanced by an appropriate increase in reinforcement ratio and the addition of expansion agents. Finally, this paper presents design equations for the flexural and compressive capacity of BFRP-reinforced GSSC structures.

Determining the fracture toughness of quasi-brittle materials with notched four-point bending tests

Fracture is common failure mode of quasi-brittle materials when suffering tensile loads, the accurate determination of the fracture toughness becomes extremely vital. Notched four-point bending (4-p-b) test is one of main fracture test methods, but is rarely applied in evaluating the fracture behavior of quasi-brittle materials. In this study, on the basis of relevant standards, the specific requirement of 4-p-b fracture test is proposed. Then the closed-form solution is used to establish the relation between the four-point bending test results and fracture toughness on the basis of the Boundary Effect Model. The influence of test conditions, boundary effect and distribution characteristics of fracture properties are discussed in detail. After that, two types of hard rock and concrete are utilized to verify the reliability of proposed methods. The results show that four-point bending test and corresponding analytical solution are suitable for determining the fracture toughness of quasi-brittle materials, regardless of the different initial notch length and material categories.

Flexural capacity enhancing of notched steel beams by combining shape memory alloy wires and carbon fiber-reinforced polymer sheets

Combining shape memory alloy (SMA) and carbon fiber-reinforced polymer (CFRP) sheet can achieve a self-stressing SMA-CFRP composite, providing an innovative prestressing method for steel elements. This study applied SMA(Ni–Ti–Nb) wires and CFRP sheets to achieve composite strengthening for notched steel beams. The effectiveness of SMA-CFRP composite for flexural strengthening of notched steel beams was evaluated, and the formula for the maximum allowable moment of the strengthened beams with SMA-CFRP composites was proposed. The four-point bending test results showed that the ultimate load and flexural stiffness of the strengthened beams with SMA-CFRP composites increased by 79.2% and 57.9% more than those of the unstrengthened beams. By comparison, the CFRP-only and SMA-only strengthened beams merely achieved half the ultimate load and flexural stiffness over the strengthened beams with SMA-CFRP composite. Besides, compared to the unstrengthened beams, the notch tip yield load for the strengthened beam with SMA-CFRP composite was increased by 230%, while the notch tip yield load for strengthened beams with CFRP-only and SMA-only just increased by 70% and 125%. These indicate that the SMA-CFRP composite strengthening can significantly delay crack propagation and improve the load capacity and stiffness of notched steel beams. Moreover, the analytical results of the maximum allowable moment were in good agreement with experimental results, indicating the accuracy of the proposed analytical equations.

Biocompatibility, Degradation Behavior, and Mechanical Properties of Magnesium Alloy Plates In Vivo

The magnesium alloy was made into orthopedic steel plates to repair tibial fractures of New Zealand white rabbits and to explore the biocompatibility, degradation behavior, and mechanical properties of the magnesium alloy plates in repairing fractures in vivo. Fifty-four rabbits were randomly divided into experimental, control, and sham-operated groups. Tibial fractures in the experimental and the control groups were fixed with magnesium alloy and titanium alloy plates, respectively, and only bone tunnels were established without any implants in the sham-operated group. The concentrations of serum alanine transaminase, creatinine (CREA), creatine kinase (CK), and magnesium ion were measured before and 1 day, 1, 2, 4, 8, and 16 weeks after operation, respectively, to evaluate the biocompatibility of magnesium alloy plates. The corrosion products and components were observed using a scanning electron microscope with an energy-dispersive spectroscopy system, and the corrosion rate was observed by weight loss testing. Then the degradation behavior of magnesium alloy plate was analyzed. Analysis of mechanical properties of magnesium alloy plates was done by four-point bending tests. There were no statistically significant differences in serum alanine transaminase, CREA, or CK at each time point among the three groups ( P > 0.05 ). The degradation behavior of the magnesium alloy plates increased with the longer implantation time. The four-point bending test results indicated that the mechanical properties of magnesium alloy plates decreased gradually during the degradation. The results showed that magnesium alloy plates implanted into rabbit tibias degrade gradually with the implantation time, and the mechanical properties of the magnesium alloy weaken gradually during the degradation. Meanwhile, the magnesium alloy plate had excellent biocompatibility and biosafety in the process of degradation in vivo.

Characterization of chemically treated waste wood fiber and its potential application in cementitious composites

In recent years, the utilization of various fibers in cementitious composites gained remarkable popularity worldwide. Unlike well-known fibers, this study focused on examining the incorporation of waste wood fiber (WWF) assorted from construction and demolition sites into the cementitious matrix. In the first stage of the study, alkali-treatment of the WWF was carried out with different concentrations of sodium hydroxide (NaOH) solution (i.e., 1.0 M, 2.0 M, 2.5 M, 5.0 M, 10.0 M) and treatment durations (i.e., 2 h, 4 h, 6 h, 12 h) to eliminate impurities and enhance fiber properties and fiber-matrix compatibility through surface treatment. To investigate alkali-treatment efficiency, microstructural analyses were conducted on the untreated and alkali-treated WWFs by Scanning Electron Microscopy and Fourier Transform Infrared Spectrophotometer measurements. Afterward, physical and mechanical performance assessments were conducted by water absorption test, compressive and four-point bending tests on the WWF-incorporated cementitious composites to monitor the compatibility behaviour of the WWF-matrix interface. Microstructural examinations showed that after the alkali treatment, impurities (i.e., painting, hemicellulose, lignin, etc.) on the WWF surface were successfully removed; however, higher alkali concentrations (beyond 5.0 M) and longer treatment duration (after 6 h) lead to deterioration, fragmentation, and a more heterogeneous structure due to the degradation of long cellulosic chains of WWF. Four-point bending test results showed that the flexural strength capacity of 2.5M-2 h-WWF-composite was 7.9 MPa, which was higher than untreated WWF-composite and plain mortar by 34.7% and 39.8%, respectively. Furthermore, the 2.5M-2 h treated WWF composite had the highest compressive strength of 46.3 MPa, which was higher than plain mortar, and the untreated WWF composite by 6.4% and 21.5%, respectively. The elimination of impurities such as painting, lignin, hemicellulose, and other inorganic compounds at the optimal alkali treatment concentration and time increases the WWF surface area and strengthens the fiber-matrix interface adhesion, resulting in a stronger matrix-WWF interface connection and an increase in load-carrying capability. The study's findings are believed to encourage the usage of alkali-treated WWF in cementitious matrix with improved mechanical performance and high waste upcycling.

Numerical Analysis of Structural Performance of Concrete-GFRP Composite I-Beam

The concrete-GFRP composite beams have received extensive attention in civil engineering. However, the ambiguity of the fracture, debonding of the interface, and the GFRP profile limit the precise design of the composite beam. This article presents a comprehensive numerical study for the structural performance of composite pultruded GFRP beams to provide a better understanding of the mechanism of interfacial debonding and GFRP matrix fracture. The failure and delamination process of pultruded GFRP for anisotropy of materials is modeled using the Hashin criteria. The bond–slip behavior between the concrete slab and the top flange of the GFRP I-beam is simulated by the bilinear cohesive interface element. The availability and accuracy of the finite element model are verified by comparison with the four-point bending test results of the pure GFRP I-beam and composite beams as well. Based on the proposed comprehensive finite element model, the effects of the strength, thickness, and width of the concrete slab and the shear-span ratio of the beam on the structural behavior of the composite beam are studied. According to the parametric analysis, the excessive high strength of concrete, the width, and/or thickness of the concrete slab would lead to shear failure of the slab rather than significantly increasing the ultimate load of the composite beam. When having a small shear-span ratio, the matrix fracture and delamination will occur in the web of the GFRP profile. In addition, the height of the I-profile web has a significant effect on the stress and strain distribution of the composite beam. These parametric analyses could provide the numerical basis for the design of the GFRP composite beams.

Digital Concrete Production With Vertical Textile Reinforcement

One major challenge preventing widespread introduction of digital concrete production is the integration of reinforcing materials. Textile grid structures offer a possible solution for this challenge.
 Textile reinforced concrete (TRC) has been researched for approximately 20 years and is currently being commercialized, initially in pre-cast elements for facades and bridges. TRC enables the construction of thin-walled, strong structures with a high freedom of design, properties well suited for the integration in digital concrete production.
 First trials for this integration have been performed and published. However, these studies only use short fibres mixed into the concrete matrix or textile reinforcement within the printing plane, which limits the transferred loads.
 This study shows the results of preliminary tests of vertical, out-of-plane textile reinforcements for digital concrete production. The textile reinforcement is fixed vertically and the concrete printing process is performed diagonally, “through” the textile. The results of four-point bending tests are presented.

Experiment and Research on Calculation Methods on Flexural Mechanical Behaviors of Non-Metallic Reinforced ECC Beams

Engineered cementitious composites (ECC) has high tenacity and the characteristics of strain hardening. In the bending test, ECC beams equipped with carbon fiber reinforced polymer (CFRP) in the tensile region show good deformation ability and bending ability. In this paper, the constitutive models of ECC and CFRP materials are established by uniaxial tensile compression test. Based on the plane section supposition, the analysis theory of bending capacity of cross section for ECC beams with non-metallic reinforcement is proposed. The calculation results are compared with the four-point bending test results. The results show that: (1) ECC beams with non-metallic reinforcement reflect the advantages of the two materials, and have strong deformation capacity before bending failure. (2) The calculation results based on the theory of flexural capacity of normal section are in good agreement with the experimental results, and the maximum error is less than 4%. The research results can provide the basis and reference for the calculation analysis and practical application of non-metallic reinforced high toughness material structure.

Co-cured manufacturing of multi-cell composite box beam using vacuum assisted resin transfer molding

Co-curing holds great promise to minimize assembly weight, time, and cost for stiffened aerospace structures, which are conventionally fabricated separately and then integrated either through mechanical fastening or adhesive bonding—also known as secondary bonding. This study presented a low-cost co-curing process using VARTM to fabricate stiffened shells, particularly composite box beams. The experimental investigation was performed and the co-curing process was improved by scrutinizing the critical process parameters, such as foam strength and coating, and curing cycle. This work was also intended to present the demonstration of the proposed co-curing method and its comparison with the conventional secondary bonding technique for three-cell carbon fiber-reinforced polymer (CFRP) composite box beams. Fiber volume fraction measurements were carried out to the specimens extracted from the various section of the co-cured part, namely top skin, web, and bottom skin and as a result, around 60% of fiber volume fraction was measured, which was in good agreement with the results obtained from optical microscopy-based image analysis. Structural-level four-point bending test results showed that the weight normalized maximum and the ultimate load of the part increased by 44% and 45% with the use of the co-curing process, respectively. The improved mechanical properties indicated that stronger structural integration can be achieved by integrally curing structures. SEM micrographs revealed a favorable fiber-matrix interface, bolstering the superior integration of the co-cured part. These findings suggest that the low-cost co-curing process can be a potential candidate for the fabrication of stiffened aerospace structures, such as composite box beams.

Experimental and Numerical Analyses of Steel-concrete Composite Floors

Background: The performances of composite steel-concrete slabs are strongly influenced by the connection between the concrete and the steel decking, which is essentially assured by bonding, interlocking, and adhesion. The connection can be continuous or localized by means of connectors. In order to increase the bonding between steel and concrete elements and to allow their collaboration, typically, a continuous connection with indentations or embossings is realized. Objective: In this study, the simulation of the concrete-steel bond interaction of a typical composite decking is analyzed. In particular, the objective is the investigation of the role of the main geometric parameters of the indentations or embossings that determine the effective functionality of the connection. Methods: To this scope, the results of four-point bending tests on five specimens of a typical layout of a composite floor are reported and discussed. Then, the obtained results are used to determine the shear bond strength according to the partial interaction method, by following the procedure provided by the Eurocode 4. Successively, the experimental results are exploited in order to calibrate a FE model in Abaqus software to be able to account for the basic effects involved in the shear bonding mechanism, i.e. interlocking, friction, and adhesion. Results & Conclusion: Finally, the obtained results are discussed, and the FE model is used to evaluate the geometrical and mechanical parameters influencing the longitudinal shear bonding resistance.

Experimental investigation on shear behavior of RC beams strengthened by CFRP grids and PCM

This paper presents the experimental results of four-point bending tests for reinforced concrete (RC) beams strengthened by carbon fiber reinforced polymer (CFRP) grids and sprayed polymer-cement-mortar (PCM). The reinforced arrangements of CFRP grids, stirrups and longitudinal steel rebars were selected as changing parameters. The maximum loads, mid-span deflections and strains for the PCM, longitudinal steel rebars, stirrups and CFRP grids were obtained. The mechanical behavior of CFRP grids and the cooperation work performance between CFRP grids and steel rebars were investigated emphatically. The research results indicated that the shear strengthening effect of the CFRP grid-PCM reinforcing layers bonded along both sides of RC beams was sufficient. The shear contribution of the vertical CFRP grid was similar to that of the stirrup, but the stress distribution of vertical CFRP grid was not uniform due to the resistant action of grid points. Moreover, the vertical CFRP grids bore the lateral extruding action with opposite directions in tension and compression zones due to the compressive and tensile behavior of horizontal CFRP grids, resulting in the complex stress state of the vertical grid which differs from the stirrup. There exists the cooperation work between CFRP grids and steel rebars in shear strengthening RC beams. So as to clarify the shear mechanism of RC beams strengthened by CFRP grids and PCM, the complex stress state of vertical CFRP grid, influence of the horizontal CFRP grid and the preconditions for the normal work of CFRP grid should be taken into account. The proposed shear capacity calculation formula based on truss-arch model could satisfy the design requirements.

Experimental determination of residual flexural strength and critical buckling load of impact-damaged glass/epoxy laminates

The main objective of this research is to find experimentally the effect of impact damage on the flexural strength of glassfiber/epoxy laminated composite materials at two different test conditions. The other objective is to determine the criticalbuckling load of laminated composite material after impact loading. Thus, the loss of flexural and buckling performances ofthe damaged material has been established by comparison with the undamaged material. Initially, angle-ply laminatedcomposite plates with rectangular shaped have been subjected to impact load at different energy levels by using a dropweighttesting machine and impact damage has been created. To find the residual flexural strength, four-point bending testshave been carried out. Four-point bending specimens have been cut from the damaged area of the middle of the laminatedplates and have been positioned in two different ways according to the face subjected to the impact. For buckling tests, aunidirectional compression load has been applied to the impacted specimens with the size of 100 mm x150 mm. Accordingto the four-point bending test results, the flexural strengths of the specimens subjected to impact at 10 J and 30 J havedecreased approximately 25 and 42%, respectively. Similarly, the reductions in critical buckling loads of specimenssubjected to impact at 10 J and 40 J are approximately 16 and 32%, respectively. Consequently, the impact load significantlyreduces the flexural and buckling performances of laminated glass/epoxy composites. Furthermore, the positioning of thefour-point bending test specimen affects the flexural strength.

Experimental study on the flexural behaviour of notched steel beams strengthened by prestressed CFRP plate with an end plate anchorage system

Strengthening deficient steel structures using prestressed bonded Carbon Fibre Reinforced Polymer (CFRP) plate could be a promising technology, but has not been well developed yet due to the lack of a proper CFRP prestressing device. In this study, notched steel beams strengthened with prestressed CFRP plate with end anchorage systems were designed and experimentally studied. The prestress loss and flexural behaviour of the strengthened steel beams were investigated. With the aid of strain gauges and Fibre Bragg Grating (FBG) sensors, the prestress loss in specimens with prestress levels of 20% and 40% were monitored during tensioning, release and a mid-long period after release. There is almost no prestress loss for specimens after 30 days of release, which indicates that the end anchorage system can effectively impede prestress loss. From the four-point bending test results, the bearing capacity and utilization ratio of the CFRP plate, effect of prestress on the flexural performance and failure modes were discussed. The prestressed strengthening can improve the bearing capacity and ductility of deficient steel beams, and increases the utilizationrate of CFRP plate, while the enhancement of the stiffness is not obvious. Additionally, the bearing capacity of the specimens and utilization rate of the CFRP increase with the prestress level. More importantly, the prestressed strengthening can delay debonding propagation of the strengthened beams, preventing premature failure.

Numerical analysis of reinforced concrete structures with oriented steel fibers and re-bars

In this study, a new strength and stiffness numerical analysis approach of fiber reinforced concrete with oriented fibers and re-bars is proposed. The model is based on discrete lattice simulation that is obtained from standard tetrahedron mesh. Area of cross section of lattice members is obtained by homogenization of each tetrahedron finite element. A non-linear material constitutive model that takes into account fiber orientation, concrete damage and plasticity of re-bars is proposed. Re-bars are embedded in fiber concrete lattice by using a special joint elements that are consistent with re-bar’s surface pattern. The numerical model is validated by using four-point bending test results of high performance fiber concrete with oriented fibers. Moreover, the model showed a good agreement with re-bar pull-out test results for ultra-high performance concrete with oriented fibers. The proposed model is used to analyze a ribbed concrete panel with oriented fibers and best optimal fiber orientation for three-point bending is proposed.

Gradient Elastic–Plastic Properties of Expanded Austenite Layer in 316L Stainless Steel

The gradient mechanical properties, variation of stress with strain and surface cracking behavior of expanded austenite developed on 316L austenitic stainless steel were investigated by nanoindentation tests, X-ray residual stress analysis and scanning electron microscope observation in four-point bending tests. The results show that the plastic properties of the carburizing layer including true initial yield strengths and strain hardening exponents increase significantly from substrate to surface, while the true elastic modulus just improves slightly. Due to the onset of plastic flow, the residual stresses are almost equivalent to the true initial yield strengths from surface to the depth of ~ 10 μm. The results of four-point bending tests show that surface stress increases linearly with the increase in strain until the strain reaches ~ 1.0%, after that the plastic yield happens. The expanded austenite surface layer is brittle, and the cracks will be created at the strain of ~ 1.4%. The cracking stress is about ~ 2.4 GPa.

Bending behaviors of 3D-printed Bi-material structure: Experimental study and finite element analysis

This paper investigates the bending behaviors of a bi-material structure (BMS) using both experimental and numerical methods The BMS is a composite material built by a 3D-printed, open-cellular brittle plaster structure filled with a silicone elastomer. The composition and configuration of the two materials determine the overall mechanical properties. Four-point bending test results show a non-linear elastic property, enhanced strength and toughness of BMS samples compared to either material phase alone. Such behavior is believed to be a result of delayed microcrack propagation in the brittle phase and a hardening effect of elastomer. In the numerical study, finite element analysis (FEA) is employed to verify these hypotheses. The FEA incorporates a brittle cracking material model for the plaster and a hyperelastic model for the silicone. The brittle cracking model enables the estimation of element degradation as a result of crack development and thus eliminates the need for the extremely refined mesh. Simulation result confirms the non-linear elastic transition and crack-induced material degradation and visualizes the silicone strengthening mechanism that can avoid rapid structural rupture.