Tensile Bending Tests Research Articles

Experimental research of the tensile strength of concrete reinforced with basalt fiber

Non-metallic composite fittings are increasingly used in modern construction due to their high mechanical characteristics, corrosion resistance, durability in concrete and aggressive external environments, and other properties. At the sametime, usually, non-metallic composite reinforcement is used in the form of rods with the main supporting element in the form of basalt, glass, aramid or roving made of other materials, which is thin fibers with a diameter of 7...20 mm.The specified roving, as an element of reinforcement of concrete structures, will be used in the form of fiber to a much lesser extent, although it is a real alternative to traditional steel fiber with all the advantages of fiber reinforcement, to which corrosion resistance is also added. The limited number of experimental explains the current situation andtheoretical studies of non-metallic fiber reinforcement, in particular, tensile strength, which is one of the main advantages of fiber reinforcement of concrete.This article presents the results of experimental studies of the tensile strength of concrete reinforced with fiber from basalt roving with a diameter of 16 μm and a length of 24 mm, which included bending tensile tests of three series of concrete samples with a strength class of compression, respectively, C20/25, C25/30, C30/35 and percentage of fiber reinforcement within 2.0...8%.As a result of the conducted research, it was established that the fiber reinforcement from the baseboard roving leads to an increase in the axial tensile strength of concrete. At the same time, the most intensive increase in tensile strength took place when the percentage of reinforcement was increased in the range of 2.0...4.0%. With a further increase in the percentage of reinforcement in the range of 6.0...8.0%, this growth stopped, which indicates that fiber reinforcement in the range of 2.0...4.0% is the most effective, regardless of the class of concrete in terms of compressive strength.Other things being equal, the increase in axial tensile strength of concrete with an increase in the percentage of fiber reinforcement within the limits of 2.0...8.0% is 15...20% compared to concrete without reinforcement.

Experimental Investigations on the Application of Natural Plant Fibers in Ultra-High-Performance Concrete.

Due to its high strength, the use of ultra-high-performance concrete (UHPC) is particularly suitable for components subjected to compressive loads. Combined with its excellent durability, UHPC can be used to produce highly resource-efficient components that represent a sustainable alternative to conventional load-bearing structures. Since UHPC fails in a brittle manner without the addition of fibers, it is typically used in conjunction with micro steel fibers. The production of these steel fibers is both expensive and energy-intensive. Natural plant fibers, due to their good mechanical properties, cost-effective availability, and inherent CO2 neutrality, can provide a sustainable alternative to conventional steel fibers. Thanks to the low alkaline environment and dense matrix of UHPC, the use of natural plant fibers in terms of durability and bond is possible in principle. For the application of natural plant fibers in UHPC, however, knowledge of the load-bearing and post-cracking behavior or the performance of UHPC reinforced with natural plant fibers is essential. Currently, there are no tests available on the influence of different types of natural plant fibers on the load-bearing behavior of UHPC. Therefore, five series of compression and bending tensile tests were conducted. Three series were reinforced with natural plant fibers (bamboo, coir, and flax), one series without fibers, and one series with steel fibers as a reference. Under compression loads, the test specimens reinforced with natural plant fibers did not fail abruptly and exhibited a comparable post-failure behavior and damage pattern to the reference specimens reinforced with steel fibers. In contrast, the natural plant fibers did not perform as well as the steel fibers under bending tensile stress but did show a certain post-cracking bending tensile strength. A final life cycle assessment demonstrates the superiority of natural plant fibers and shows their positive impact on the environment.

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

Highly Robust Flexible Poly-Si Thin Film Transistor Under Mechanical Strain With Split Active Layer for Foldable Active Matrix Organic Light Emitting Diode Display

We report a novel active split structure of low-temperature polysilicon (LTPS) thin film transistor (TFT) on polyimide (PI) substrate showing robust electrical performance under mechanical strain. The compressive and tensile bending tests were carried out with cylinders of radii 3, 2 and 1 mm respectively. The active split TFT exhibits much more stable electrical performance than the conventional TFT. The conventional LTPS TFT shows electrical failure due to the crack generation during tensile or compressive bending test carried out with 1 mm radius cylinder. The split poly-Si islands could resist crack formation/propagation, resulting in a robust electrical performance.

Testing and Evaluation of Flexural Tensile Strength of Prestressed CFRP Cables.

To expand the application scope of prestressed carbon fiber-reinforced polymer (CFRP) cables in civil engineering, the ultimate tensile strength of these cables was tested and evaluated under bending conditions. First, the study analyzed the tensile failure mechanism of CFRP cables under bending conditions based on elastic bending analysis theory. Thereafter, the ultimate stress state of individual tendons and cables was derived and a calculation model for the tensile strength of bent CFRP cables was established. Second, 14 sets of test conditions were created for CFRP cables under bending angles of 20–40° and bending radii of 1.5–3 m. Then, bending tensile tests were conducted to evaluate the effects of the above factors on the ultimate tensile strength, and the correctness of the computational model was verified using experiments. Finally, the ultimate performance of CFRP cables was theoretically predicted using the established model. The results showed that the cable bending tensile strength was associated with the radius r, tensile strength f, and elastic modulus E of the reinforced material and the bending radius R, but was not correlated with the interface buffer material or the bending angle of the steering system. Moreover, the flexural tensile residual strength was only affected by R/r and E/f. When E/f involved conventional material parameters, the residual strength increased nonlinearly with increased R/r. When R/r ≥ 600, the residual strength reached more than 80%. Therefore, R/r at 600 could be used as the design basis for a safe critical radius.

A Multiscale Study of Moisture Influence on the Crumb Rubber Asphalt Mixture Interface

In order to study the influence of moisture on the interface of crumb rubber–asphalt (CR) mixture, the interface bonding performance and crack resistance of a crumb rubber–asphalt mixture under dry and wet conditions were studied at three scales. At the macroscale, the characteristics of medium temperature fatigue cracking and low temperature fracture were studied by semi-circular bending tensile test (SCB) on the example of digital image correlation (DIC) technique. At the microscale, the surface energy of CR with basalt and limestone was measured using the contact angle measurement test, and then the adhesion work was calculated and analyzed. At the molecular scale, the model of CR, the model of basalt representative mineral (augite) and limestone representative mineral (calcite) were studied by molecular dynamics simulation. The relationship between these three scales was further explored to reveal the mechanism of the damage of moisture on the interface deterioration of the CR mixture. The results show that moisture has a certain effect on the interface of the CR mixture, which is characterized by macroscopically reducing the crack resistance of the asphalt mixture, microscopically reducing the adhesion ability between the asphalt and the aggregate and weakening the interaction between the asphalt and aggregate molecules at the molecular scale. Molecular dynamics can accurately simulate the deterioration of micro asphalt-aggregate adhesion under the damage of moisture. The decrease in microadhesion leads to the decrease in the crack resistance of the macro-CR mixture.

Numerical Modeling and Diagnostic of FRC Slab under Centric and Eccentric Load

Abstract The solved area of research is the slab in interaction with the subsoil, where the goal is numerical modeling of the problem using a 3D computational model and nonlinear analysis. Specifically, the case of two experiments with a slab with centric and eccentric loading is solved. The performed experiments are used after for numerical modelling when a comprehensive set of laboratory tests of mechanical properties of fiber-reinforced concrete is also performed. Specifically, compressive strength, modulus of elasticity, splitting tensile test and bending tensile test were performed. The performed experiments are evaluated using 2D sections and 3D approximation surfaces, which are then used for load-displacement diagrams. Numerical modeling is based on nonlinear analysis and the use of the finite element method. The computational model use isoparametric finite elements. Based on the performed experiments and numerical modeling, the evaluation of the solved task is performed.

Tests Regarding the Effect of Dispersed Reinforcement Made with a Prototype Device from PET Beverage Bottles on the Strength Properties of Concrete

Currently, waste generation is a huge problem all over the world. The largest source of generated waste is plastics from plastic packaging made of polyethylene and polypropylene, including PET bottles. Modern ecology aims to reduce the carbon footprint by recycling plastics or by producing biodegradable plastics that are completely broken down by microorganisms into simple particles that occur naturally in nature. Polyethylene terephthalate (PET) has good mechanical properties but is resistant to microorganisms. As a result, it cannot be classified as a biodegradable plastic, but when it is reused for the production of utility products, it becomes a bioplastic. A good way to dispose of PET is to use it for the production of utility products, in which its good mechanical properties can be used. Concrete is a basic material, the consumption of which in the construction industry is enormous. One of the negative features of concrete is its low tensile strength, which can be improved with continuous or dispersed reinforcement. This paper presents the results of compressive and tensile-bending tests of concrete reinforced with dispersed “fibres” of a different length and width, which were produced by a prototype device from PET beverage bottles. The prototype device enables repeatable fibres with a width of 2 mm, and lengths of 38 mm, 62 mm, and 93 mm to be obtained. The highest flexural tensile strength of the concrete was achieved in the case of the PET fibres with a length of 62 mm. It turned out that concrete with such reinforcement has a higher bending tensile strength by 15 % in relation to the tensile bending strength of the concrete without the dispersed reinforcement. The PET fibres also improve compressive strength. PET fibres, in order not to deteriorate in the alkaline environment of concrete, must be secured with an appropriate chemical agent. The effect of concrete reinforcement with the recycled PET fibres was compared to the effect of dispersed reinforcement made of polypropylene and steel fibres. The highest bending tensile strength was obtained in the case of the concretes with the scattered PET reinforcement. However, the differences in the bending tensile strength of concrete are not big and are equal to 0.64 MPa for polypropylene fibres and only 0.09 MPa for steel fibres.

Large-scale characterisation of cemented rock fill performance for exposure stability analysis

A novel large-scale geomechanical laboratory testing program is developed to provide full characterization of the strength and deformational response of cemented rockfill (CRF) material for use in exposure stability analyses. Uniaxial compressive strength (UCS), direct shear, and three-point bending tensile tests are performed on large-scale samples that require the use of novel processes and laboratory equipment. For the first time, the shear properties of large-scale CRF samples have been investigated using direct shear tests under constant normal stiffness (CNS) boundary conditions. Large-scale three-point bending tests are also conducted to obtain true tensile strengths without having to infer them from UCS test results. For up to 28 days curing time, the effects of particle size distribution and binder quantity are experimentally examined for each compression, tension, and shear failure mode through a study of the full stress–strain response. In order to obtain accurate laboratory results, findings are compared against published large-scale tests from various mine sites. The results show that the large-scale samples completed herein provide a reliable UCS estimate with standard deviations of less than one. It is also found that the direct shear responses are substantially larger for simulated CRF: Sidewall contacts than CRF: CRF contacts, and tensile strength responses are higher than previously estimated at 10% of the UCS strength. The effect of particle size distribution on the geomechanical response of the CRF material is highlighted through the large-scale sample testing. The findings of this research study provide increased technical understanding for the development of CRF structures in underground mines that are cost-effective, safe, and durable. Additionally, this research study establishes a practical testing methodology that overcomes the challenges that occur in collecting quantitative geomechanical data from large-scale CRF samples for design purposes.

Влияние рецептурных факторов на прочностные характеристики базальтофибробетонов

Today, dispersed-reinforced concrete is a promising structural building material. In order to improve the strength characteristics of basalt fiber reinforced concrete, authors studies the effect of prescription factors, namely the percentage of fiber reinforcement and the percentage of coarse aggregate fractions. In total, 18 series of basic samples of standard size are manufactured and tested: 27 cubes with dimensions of 100x100x100 mm for compression tests; 27 prisms with dimensions 100x100x400 mm for tensile bending tests. Also, calculations of strength characteristics are carried out depending on recipe factors, the calculations are made by the method of mathematical planning of the experiment - a full-factor experiment (FFE 22). According to the results of the study, the basic regression equations are obtained by the least squares method, which are presented in the form of polynomials of the 2nd degree. It is concluded that the most effective would be the use of basalt fiber in the amount of 4.5 % of the mass of the concrete mixture and the use of a coarse aggregate with a fraction of 5-10 mm in the amount of 40 %, and fractions of 10-20 mm in the amount 60 %.

Molecular dynamics study on thermal and mechanical properties of AOO modified DGEBA‐anhydride insulating materials for high voltage GIS

AbstractIncreases in rated voltage and power density of high voltage gas insulated switchgears (GIS) impose stringent requirements on the diglycidyl ether of bisphenol A (DGEBA)‐anhydride thermoset, which is widely used as insulation materials for high GIS, for higher mechanical and heat‐resistant properties. In this paper, 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexanecarboxylate (AOO) was copolymerized with DGEBA ‐anhydride system to increase the mechanical and thermal properties of the thermosets. Based on the molecular dynamics simulation method, the coefficient of thermal expansion, glass transition temperature (Tg), and modulus of AOO copolymer‐modified DGEBA‐anhydride thermosets were calculated. The AOO copolymer‐modified DGEBA‐anhydride thermosets specimens were further experimentally prepared and subjected to differential scanning calorimeter test, TGA test, tensile bending test, and dielectric test. The results of simulation and experiment simultaneously indicated that the Tg and modulus of the DGEBA‐anhydride thermoset are enhanced after AOO modification. This is mainly due to the decrease in free volume percentage and mean square displacement of the epoxy cross‐linked network structure after the introduction of AOO molecules, which makes the structure more compact and the cross‐link density increased. Additionally, the dielectric performances of the thermoset was enhanced by AOO. The excellent thermal, mechanical and dielectric properties of AOO modified DGEBA‐anhydride thermoset make it a promising application in the field of high voltage GIS.

FRACTURE ENERGY OF ILLITIC RAMMED EARTH WITH HIGH WATER-CLAY RATIO

The article is focused on design of mixture of rammed earth, producing, testing and determination of fracture energy of unfired rammed earth and its stress-strain curve in tensile bending test. Three different mixtures of rammed earth were designed and tested. The amount of water and binder is one of the key properties of the rammed earth, the amount of the water is expressed by the water-clay ratio. Mechanical properties of the earth material highly depend on the composition of sand, clay and water. The prescription AGL III with 80 % of sand, 20 % of clay and 0.400 water-clay ratio reached the maximum value of fracture energy 4.858±0.002 J/m2 and set AGL V had the minimum value 1.934±0.310 J/m2.

Fast sputter deposition of MoOx/metal/MoOx transparent electrodes on glass and PET substrates

Dielectric/metal/dielectric (DMD) transparent electrodes emerged as a compelling alternative to the widely used indium-tin-oxide (ITO) for solar cells and optoelectronic devices. DMD electrodes are especially attractive for flexible substrates, as, in contrast to ITO, they retain their low electrical resistance upon substrate bending and they do not require deposition at elevated temperatures. In a DMD, the choice of the dielectric is mainly dictated by the device architecture. Owing to its high work function, MoO3 is a commonly used hole-selective dielectric layer. The present work investigates MoOx/metal/MoOx (with 2 < x < 3) DMD electrodes, with Ag and Au as metals, fabricated by direct current, magnetron sputtering, at industry-relevant, high deposition rates. This was possible with a properly engineered MoOx target, providing high electrical conductivity and compactness. The sputtered electrodes on polyethylene terephthalate (PET) substrates show higher figure-of-merit than similar, evaporated electrodes in the literature. It is shown that the DMD electrodes with amorphous MoOx layers have low stability in water, but they are stable to other solvents, such as toluene, dimethylsulfoxide (DMSO), dimethylformamide (DMF), chlorobenzene or chloroform, allowing their implementation in devices like organic light-emitting diodes or perovskite solar cells. Further, it is shown that the electrodes show dramatically enhanced mechanical stability compared to ITO, when subjected to tensile bending tests.

Analysis of the Crack Evolution Process in Crumb Rubber Concrete Based on Acoustic Emission Technology

In this study, the crack evolution process of crumb rubber concrete (CRC) in a four-point bending tensile test was monitored using the acoustic emission (AE) technique. The peak frequency, distribution characteristics of the AE source, and the damage process based on the AE ring count during the crack evolution were analyzed. The test results revealed that the addition of rubber particles decreased the brittleness of cracks and improved the ductility of the concrete during the macro-cracking process. The AE positioning method could effectively monitor the evolution process of micro-cracks inside the concrete. Additionally, based on the statistical results of the AE source events and energy distribution, the position of macroscopic cracks could be predicted, and the random distribution of micro-cracks could be characterized. By introducing the Weibull distribution to describe the random growth process of micro-cracks, the damage inside the concrete could be qualitatively predicted. As the rubber particle content increased, the inherent micro-cracks inside the concrete also increased. The damage inside the concrete was biased toward the crack nucleation stage.

Comparative study on the results of different tensile test methods of artificial frozen soil

Tensile strength of frozen soil is an important index for frozen soil engineering design. It is found that uniaxial tensile strength, three-point bending and four-point bending tensile strength values of frozen soil are inconsistent in the test. For this reason, the meso-level numerical method is adopted, assuming that the meso-level material parameters conform to Weibull distribution, and the damage model is adopted, and the macro-level material properties conform to linear elasticity assumption. Uniaxial tensile test, three-point bending tensile test and four-point bending tensile test are respectively simulated. The results show that the difference comes from the non-uniformity of materials. The results of this paper provide effective guidance for frozen soil strength design.

Quantitative Research by Non-local Fracture Criterias Difference of Frozen Soil Strength in Different Tensile Test

Frozen soil strength is an important index in practical engineering design, but different test methods can get different strength values. Non - localization theory characterizes material properties by describing the characteristic length of non-uniform materials. In this paper, the non-localized theory of mesoscopic materials is introduced into frozen soil, explaining that the difference of different test strengths of frozen soil comes from the non-uniformity of frozen soil. The relationship between non-uniformity and strength and the relationship between uniaxial tensile strength and bending tensile strength are described quantitatively through uniaxial tensile test and bending tensile test.

Identification of moisture affected mechanical properties of polymer matrix materials by the employment of samples with moisture gradients

The article explores the possibility to identify the moisture affected mechanical properties of polymer matrix materials by the employment of samples with moisture gradients. The identification is based on the use of a weakly coupled diffuso-mechanical model. A coupled tensile-bending test configuration is considered. It is shown that tensile and bending tests can be decoupled when the elastic properties of the matrix are polynomial functions of the moisture content. Tensile and bending tests in samples with moisture gradients are compared in terms of identification times, leading to a significant reduction of the identification time compared to moisture-saturated samples.

Theoretical development of suitable test scenarios for the determination of the bending tensile strength of thin glass with or without influence of edges and their experimental implementation

ABSTRACTThe use of thin glass in the field of electrical engineering for screens of mobile phones or laptops is well known and the necessary material requirements such the scratch resistance has been sufficiently researched. For applications in the building sector, however, the determination of the bending tensile strength of such thin glass necessary for structural design represents a new research topic. The test scenarios described in the standard series EN 1288 relevant for the determination of the bending tensile strength, such as the ring‐on‐ring test or the four‐point‐bending test, are not applicable for glass with a thickness of less than 3 mm. One reason is e.g. the high flexibility of the glass in case of four‐point‐bending tests. As a consequence, these test scenarios have to be adapted or new test scenarios have to be developed. The double‐ring bending tensile test was adapted in that the loading ring, e.g. was replaced by a pressure pad of soft elastomer. Thus, a constant stress distribution in the area under the pressure pad necessary for the determination of the probability of failure could be achieved. The four‐point‐bending test was replaced by test set‐ups in which the force is introduced in‐plane – parallel to the glass surface – as a membrane force in the glass and the glass is thereby deformed or bent until breakage analogous to a stability test. Another variant is bending with a constant bending radius. In this test set‐up, a circular arc is created by precise adjustment of the distance of the supported smaller straight edges and their rotation. Thus, the length of the edge, at which sets a constant bending moment can be increased. These alternative test scenarios were theoretically developed and analysed or partially experimentally investigated by means of test series. These experimental series serve to validate the theoretical development of suitable experimental scenarios and are intended to provide a first approach for a necessary adaptation of EN 1288.

Bending Mechanical Behavior of Epoxy Matrix Reinforced with Buriti Fiber

Environmentally correct composites, made from natural fibers, are among the most investigated and applied today. In this paper, the mechanical behavior of epoxy matrix composites reinforced with continuous buriti fiber, through bending tensile tests was investigated. Specimens containing 0, 10, 20 and 30% in volume of buriti fiber were aligned along the entire length of a mold to create plates of these composites. The plates were cut following the ASTM standard to obtained bending test specimens. The test was conducted in an Instron Machine and the fractured specimens were analyzed by SEM. The results showed an increase in the materials flexural properties with the increase in volume fraction of buriti fiber.

Experimental Investigations on New Characterization Method for Giant Piezoresistance Effect and Silicon Nanowire Piezoresistive Detection

This paper presents a novel and effective characterization method for giant piezoresistive properties of silicon nanowires by using the reference structures. This contrast detection approach investigates the influences of quantum size effect and surface defects effect on piezoresistive coefficients of silicon nanowires by direct comparison of the resistivity change ratio of silicon wires with nanoscale-to-microscale width under the same applied stress conditions. The characterization experiments based on four-point bending tensile test demonstrate that piezoresistive coefficient of small nanowidth silicon nanowire can be significantly increased to about five times higher levels than that of bulk silicon under the same impurity concentration, which indicates that the silicon nanowire can have giant piezoresistive effect. On the other hand, to solve the problem on nanowires pick-up, we proposed a nanowire piezoresistive detection approach, whose validity is confirmed by the dynamic LDV resonance test. Meanwhile, to investigate the influence of undercut arising from the wet chemical release process of the suspended silicon nanowire, a three-dimensional finite element simulation is also carried out for the fundamental resonant frequency using ANSYS software. The numerical and experimental results show that our piezoresistive detection is accurate and effective and the undercut should be carefully considered in the design of the high frequency resonator and mixer. The findings of this paper provide some useful references for the piezoresistive effect measurement and the piezoresistive pick-up in nanoelectromechanical system.