Results Of Four-point Bending Tests Research Articles

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.

Flexural behavior and a modified prediction of deflection of concrete beam reinforced with a ribbed GFRP bars

This study experimentally investigated the flexural capacity of a concrete beam reinforced with a newly developed GFRP bar that overcomes the lower modulus of elasticity and bond strength compared to a steel bar. The GFRP bar was fabricated by thermosetting a braided pultrusion process to form the outer fiber ribs. The mechanical properties of the modulus of elasticity and bond strength were enhanced compared with those of commercial GFRP bars. In the four-point bending test results, all specimens failed according to the intended failure mode due to flexural design in compliance with ACI 440.1R-15. The effects of the reinforcement ratio and concrete compressive strength were investigated. Equations from the code were used to predict the deflection, and they overestimated the deflection compared with the experimental results. A modified model using two coefficients was developed to provide much better predictive ability, even when the effective moment of inertia was less than the theoretical Icr. The deformability of the test beams satisfied the specified value of 4.0 in compliance with CSA S6-10. A modified effective moment of inertia with two correction factors was proposed and it could provide much better predictability in prediction even at the effective moment of inertia less than that of theoretical cracked moment of inertia.

Experimental and numerical investigation of short-term behaviour of CLT-steel composite beams

This paper concerns the short-term behaviour of innovative steel-timber composite (STC) floors comprising of cross-laminated timber panels connected to steel girders by various mechanical fasteners and/or glue. The results of four-point bending tests performed on full-scale STC beams are reported and the structural behaviour (the load-deflection response, short-term stiffness, peak load capacity, and failure modes) of the proposed STC system is studied. In addition, extensive non-linear 1D and 2D finite element (FE) analyses of STC beams are carried out and the numerical results are verified against the test results. It is shown that 1D and 2D FE models are adequate in capturing the structural response of the STC beams. Using the FE and experimental results, the composite efficiency of STC beams that can significantly influence their structural behaviour beams is determined and reported in the paper.

Cement Composite Reinforced with Synthetic Fibers: Comparison of Three-Point and Four-Point Bending Test Results

Presented article deals with the influence of PET fiber production on the bending strength of cement-based composite when incorporated into the fresh mortar, and comparison of results of 3-point and 4-point bending test. Cement paste samples were reinforced with 2 wt. % of primary or recycled PET fibers. The bending test was performed on prismatic samples with dimension of 40 × 40 × 160 mm. It was found that samples with recycled PET fibers, compared to primary ones, exhibit a decrease in bending strength. In the case of 4-point bending tests, the samples with recycled PET fibers exhibited higher bending strength than reference samples without any fibers. However, in the case of 3-point bending tests, the samples with recycled PET fibers had lower bending strength than the reference ones. The results suggest that recycled PET fibers could be used as an alternative to reinforce cement-based composites.

Manufacturing and investigation of steel-CFRP hybrid pillar structures for automotive applications by intrinsic resin transfer moulding technology

Automotive lightweight design can be achieved by the combination of sheet metal and carbon fibre-reinforced plastic (CFRP). The hybrid structure enables a simultaneous usage of the specific advantages of both materials. This paper is focused on basic technological investigations in the field of manufacturing of hybrid structures by utilising the intrinsic RTM technology. Initially, the production process of automotive pillar structures in a steel-CFRP hybrid design is exemplified by an omega profile. Further, the viscosity measurement is carried out to identify the curing properties of the deployed epoxy matrix system used. Finally, the results of four-point bending tests and crash tests on hybrid omega profiles are presented, analysed and evaluated. It could be shown that the mechanical properties in the bottom area and the flank area are consistent. Additionally, hybrid materials exhibit a satisfying weight-saving potential for automotive structural components comparing pure steel structures.

Flexural behaviour of glulam timber beams reinforced with FRP cords

Glued laminated timber (glulam) is widely used as a construction material to make up lightweight and large span structures. The basic principle of this material consists in bonding together a number of layers of dimensioned timber with structural adhesives, in order to increase strength and stiffness of the member, and allowing to make up sustainable structures with great visual impact. Recent applications showed the effectiveness of fibre-reinforced polymer (FRP) composites in enhancing the structural performances of glulam beams, with particular reference on their flexural and shear strength. In fact FRP reinforcements could be used to strengthen existing structures or to reduce the dimensions of new structures to be designed. Considering the importance of the latter application, the present work shows the results of four-point bending tests on fifteen small scale glulam specimens, reinforced with glass (GFRP) or carbon (CFRP) cords, varying the kind of adhesive (epoxy resin or melamine glue). Eight further large-scale beams were tested in order to evaluate the role of the scale effect. Finally, an analytical model was developed, able to predict the behaviour of multilayer heterogeneous wood sections and which takes into account the effect of the reinforcements.

Experimental research on flexural toughness of green high performance fibre reinforced cementitious composites

Engineered cementitious composites (ECCs) have recently demonstrated excellent mechanical performances in civil engineering, thanks to their significant strain hardening behaviour under tension. As a new class of cement based composite materials, green high performance fibre reinforced cementitious composites (GHPFRCCs) have the optimised mixing proportion of ECC with high volume fly ash based on the orthogonal experiment method. In this study, the flexural toughness of GHPFRCC was carefully examined by inspecting the influences of fly ash content, water/binder ratio, sand/binder ratio, polyvinyl alcohol (PVA) fibre and water reducing agent. The results of four-point bending tests indicated that GHPFRCC beam can effectively disperse large cracks into harmless ones with ultrahigh energy dissipation capacity. The flexural toughness of GHPFRCC can retain a higher value with the fly ash content of 65% and PVA fibre content of 2%.

Planar copper-tin inter-metallic film formation on strained substrates

This paper presents the results of four-point bending tests investigating the effects of substrate strain on the growth ɛ of interfacial Cu–Sn inter-metallic compounds (IMCs). Test specimens were cut into strips, 27.5mm in length and 5mm in width, from 4in. double polished silicon wafers. A very thin adhesion layer (Ta) was deposited on the silicon substrate by sputtering followed by a 10μm thick layer of copper using electroplating. Finally, a 30μm tin layer was deposited over the copper film also by electroplating. Samples were then placed in a furnace at 200°C to undergo bending in order to introduce in-plane strain under tension or compression. Control samples also underwent the same treatment without applied strain. Our aim was to investigate the influence of substrate strain and aging time on the formation of IMCs (1.54×10−4, 2.3×10−4 and 3.46×10−4). The thickness and separation of each phase (Cu3Sn) and η (Cu6Sn5) are clearly visible in scanning electron microscope images. Compressive strain and tensile strain both increased the thickness of the IMC layer during the aging process; however, the effects of compressive strain were more pronounced than those of tensile strain. We hypothesize that the increase in IMC thickness is related to the strain enhanced out-diffusion of Cu towards the solder as well as strain in the underlying lattice at the diffusion interface.

Aminosilanization Nanoadhesive Layer for Nanoelectric Circuits with Porous Ultralow Dielectric Film

An ultrathin layer is investigated for its potential application of replacing conventional diffusion barriers and promoting interface adhesion for nanoelectric circuits with porous ultralow dielectrics. The porous ultralow dielectric (k ≈ 2.5) substrate is silanized by 3-aminopropyltrimethoxysilane (APTMS) to form the nanoadhesive layer by performing oxygen plasma modification and tailoring the silanization conditions appropriately. The high primary amine content is obtained in favor of strong interaction between amino groups and copper. And the results of leakage current measurements of metal-oxide-semiconductor capacitor structure demonstrate that the aminosilanization nanoadhesive layer can block copper diffusion effectively and guarantee the performance of devices. Furthermore, the results of four-point bending tests indicate that the nanoadhesive layer with monolayer structure can provide the satisfactory interface toughness up to 6.7 ± 0.5 J/m(2) for Cu/ultralow-k interface. Additionally, an annealing-enhanced interface toughness effect occurs because of the formation of Cu-N bonding and siloxane bridges below 500 °C. However, the interface is weakened on account of the oxidization of amines and copper as well as the breaking of Cu-N bonding above 500 °C. It is also found that APTMS nanoadhesive layer with multilayer structure provides relatively low interface toughness compared with monolayer structure, which is mainly correlated to the breaking of interlayer hydrogen bonding.

UHPFRC tensile behavior characterization: inverse analysis of four-point bending test results

The tensile stress–strain response of ultra-high performance fiber reinforced concrete (UHPFRC) is a fundamental constitutive property, and reliable knowledge of this response is necessary for appropriate application of the tensile-carrying capacity of such advanced cement-based materials. Flexural test methods, whose implementation is well established, present a test procedure capable of assessing this property. Nevertheless, these methods provide indirect information and need to be complemented by inverse analysis in order to quantify the intrinsic tensile behavior of tested materials. Moreover, bias or scatter can be induced when simplified constitutive laws are assumed for the analysis. Flexural tests have been completed on multiple types of commercially available UHPFRC. A new inverse analysis method is presented and qualified, compared with existing methods, and also compared with results from direct tensile tests. Advantages and limitations of the experimental and analysis methods have been derived.

Experimental and finite-element analysis of the anisotropic response of high-purity α-titanium in bending

In this paper, we present results of four-point bending tests performed on beams of high-purity α-titanium material. These tests have been performed at room temperature for different beam configurations and loading orientations with respect to the orthotropy axes of the material. Digital image correlation was used to determine local strains in the deformed beams. Experimental results compare very well with the predictions of finite-element simulations obtained using the elastic/plastic model developed by Nixon et al. (2010) [12]. Specifically, we compare local deformations and the cross-sections of each beam for all loading configurations. We show that the model predicts with great accuracy the tension–compression asymmetry and the evolving anisotropy of the material. The experimentally observed upward shift of the neutral axis, as well as the rigidity of the response along the hard to deform c-axes are very well described by the proposed model.

An experimental investigation of free vibration response of curved sandwich beam with face/core debond

The aim of this research was to investigate the curvature and face/core debond influence on the vibration behavior of curved composite sandwich beams made up of carbon/epoxy laminate skins over a polyurethane foam core. Flat and curved sandwich beams with debond were prepared by keeping the arc length of the sandwich beams equal to the length of the flat sandwich beams. Sandwich specimens with three different curvatures and debond between the top and bottom face/core were manufactured. Systematic vibration and static experiments were carried to determine the response and to study the effect of curvature and debond. Flexural stiffness and strength of the sandwich beams were determined by four-point bending tests. The natural frequencies and damping loss factors of the sandwich beams were determined using impulse frequency response technique under free—free boundary conditions. Four-point bending test results indicate that stiffness of the beams decrease with presence of debond. Vibration test results show that face/core debond causes reduction of the natural frequencies whereas damping loss factor values increase with presence of debond. The effects of debond and curvature on damping loss factor is higher than that on natural frequency.

Modeling the Structural Response of Reinforced Glass Beams using an SLA Scheme

This paper investigates whether a novel computational sequentially linear analysis (SLA) technique, which is especially developed for modeling brittle material response, is applicable for modeling the structural response of metal reinforced glass beams. To do so, computational SLA results are compared with experimental results of four-point bending tests. The results show similarities in loaddisplacement curves and to some extent also in cracking behaviour. Overall, it is concluded that the SLA scheme is a very promising technique to model the structural response of reinforced glass beams, which will be even further improved in future research.

Flexural properties of sandwich beams consisting of air plasma sprayed alloy 625 and nickel alloy foam

Sandwich structures are considered as viable engineering constructions due to their unique structural, physical, and mechanical properties. An investigation of the mechanical characteristics of sandwich structures suitable for high temperature application is presented. A process has developed to produce high temperature sandwich structures by depositing alloy 625 skins on Ni alloy foam cores using air plasma spraying (APS). The experimental investigation consisted of fabrication of sandwich structures and testing of mechanical performance of sandwich specimens under flexural loading conditions. The responses of the as-fabricated sandwich structure to heat treatment were investigated. The strength of the sandwich structure was significantly increased after heat treatment. The influence of skin thickness on mechanical behavior of sandwich structures was examined by performing four-point bending test on sandwich samples with skin thicknesses of 0.5 and 0.1 mm. The larger the skin thickness, the higher the strength of the sandwich beams. Comparison between the results of four-point bending tests on sandwich structures with different skin thicknesses will help us to understand the effect of skin thickness on the failure mechanism of sandwich structures.

Debonding failure modes of flexural FRP-strengthened RC beams

In this paper, different types of debonding failure modes are described. Then, experimental results of four-point bending tests on FRP strengthened RC beams are presented and debonding failure mechanisms of strengthened beams are investigated using analytical and finite element solutions. Reasonable results could be obtained for modelling of debonding failure load of tested beams. Existing international codes and guidelines from organizations such as ACI, fib, ISIS, JSCE, SIA, TR55, etc. are presented and compared with the results from the experiments and calculations. A discrepancy of up to 250% was seen between different codes and guidelines for predicting the debonding load. Furthermore, a new recommendation for debonding control is given.

Concrete Beams Strengthened with Externally Bonded Glass Fiber Reinforced Plastic Plates

In this work, the flexural behavior of reinforced concrete beams strengthened by epoxy bonded glass fiber reinforced plastic plates is investigated through the finite element method. The finite element models based on the widely used package ABAQUS are employed in simulating the behavior of reinforced concrete beams strengthened by externally bonded glass fiber reinforced polymer. The numerical results of four-point bending test of reinforced concrete beams strengthened by externally bonded glass fiber reinforced plastic plates in comparing with the experimental results show satisfactory agreement. The results indicate that the flexure strength of reinforced concrete beams can be significantly increased by externally bonded glass fiber reinforced plastic plates. The dynamic behavior of reinforced concrete beams strengthened by epoxy bonded glass fiber reinforced plastic plates is investigated through the differential quadrature method. In this approach, only eleven sample points are required to obtain convergence.

Modification of fracture toughness of isotactic polypropylene with a combination of EPR and CaCO 3 particles

The main goal of this study is to investigate the role of both ethylene–propylene rubber (EPR) and calcium carbonate (CaCO 3) on fracture toughness and fracture mechanism of isotactic polypropylene (iPP). For this purpose, several hybrid composites with different ratio of EPR/CaCO 3 were examined. Three and four-point bending test were carried out as well as microscopic evaluation. The results of three-point bending test show that plane strain fracture toughness ( K IC) of PP–CaCO 3 can be improved by addition EPR content. Since the trend of the fracture toughness values is nearly similar to what expected by the rule of mixtures, thus one may conclude that the existence of both CaCO 3 and EPR have not significant effect on synergistic toughening. The results of four-point bending test show that the dominant mechanism of fracture in PP–CaCO 3–EPR studied in this work can be a craze-like type damage which is included with both highly localised dilatational shear bands due to EPR particles and some crazes owning to CaCO 3.

Influence of filler particles on deformation and fracture mechanism of isotactic polypropylene

This study is focussed on the role of calcium carbonate particles on the deformation and fracture mechanism in PP/CaCO3 composites. Several composites with different amounts of calcium carbonate were examined. Tensile test, three- and four-point bending test were conducted. The results of tensile tests show that the addition of CaCO3 to PP decreases yield strength and elongation at break while causes to promote modulus. Optical microscopy taken from the polished surfaces of tensile test illustrates presence of the damage zones in all specimens. Looking at in more details via scanning electron microscope (SEM) show the damage zone included some crazes and some voids owing to poor adhesion between filler and matrix. Briefly the dominant mechanism of deformation in PP/CaCO3, observed in this work, appears to be a craze type of damage, propagating via repeated cavitation. The results of three-point bending tests show that the fracture toughness of PP decreases with increasing of CaCO3 content. The results of four-point bending tests display that a wide spread damage zone in front of the pre-crack while SEM photographs appears that the damage zone including craze which is followed by repeated cavitation and debonding.

Collapsing process simulations of timber structures under dynamic loading II: simplification and quantification of the calculating method

In a previous paper we presented the efficacy of the extended distinct element method (EDEM) on the collapsing process simulation of timber-frame structures. The results obtained were qualitative, and the need for quantitative simulation was pointed out. In this report, we improved our simulating programs with the aim of establishing a quantitative simulation by EDEM. For this purpose, the parameters of the frame members (beam or column) were determined by comparing the simulated results of four-point bending tests with experimental results. Other parameters of plywood and joint members were determined by simulations of two rail shear and slip tests of joint parts, respectively. Using these parameters we made simulations of the collapsing process of an actual-size plywood-sheathed wall and at the same time carried out the experiments under similar conditions. Simulated load–displacement curves of the plywood-sheathed wall were similar to those obtained in the experiments, and the sequence of failure at nailed joints of the simulation model gave good agreement with that of the experimental collapsing processes. Using these processes, we believe that we established a basic quantitative simulation method to test the collapsing process of timber-frame structures.

Liquid-phase bonding of silicon nitride ceramics using Y 2O 3–Al 2O 3–SiO 2–TiO 2 mixtures

Hot-pressure sintered β-Si 3N 4 ceramic was bonded to itself using Y 2O 3–Al 2O 3–SiO 2–TiO 2 mixtures. Reactive behavior at interface between Si 3N 4 and Y 2O 3–Al 2O 3–SiO 2–TiO 2 mixtures during silicon nitride ceramic joining was studied by means of scanning electron microscopy (SEM), electron probe microanalyses (EPMA), X-ray diffraction (XRD) and auger electron spectroscopy (AES). The joint strength under different bonding conditions was measured by four-point bending tests. The results of EPMA, AES and XRD analyses show that the liquid glass solder reacts with silicon nitride at interface, forming the Si 3N 4/Y–Si–Al–Ti–O–N glass/TiN/Y–Si–Al–O glass gradient interface. From the results of four-point bending tests, it is known that with increase of bonding temperature and holding time, the joint strength increased reaching a peak, and then decreased. The maximum joint strength of 200 MPa measured by the four-point bending tests is obtained for silicon nitride bonded at 1823 K for 30 min.