Results Of Bending Tests Research Articles

Biaxial flexural response of Strain-Hardening UHPFRC circular slab elements

The biaxial flexural response of strain-hardening UHPFRC circular slab element is investigated experimentally and analytically using the ring-on-ring test. The Digital Image Correlation (DIC) technology is applied to capture the 3D full-field of strain and deflection of the tensile surface through the whole loading process. Based on DIC analysis, a quasi-elastic limit is determined additionally to characterize the flexural response of UHPFRC under biaxial stress condition. The random and uniform distribution of matrix discontinuities in UHPFRC in the quasi-elastic domain, as well as multiple fictitious crack formation in hardening domain, is highlighted. In addition, ring-on-ring test and Four-Point Bending Test (4PBT) results are compared with special emphasis on flexural strength and characteristics of matrix discontinuity development. The results show higher ultimate flexural strength and energy absorption capacity at ultimate limit from the ring-on-ring test, and almost same flexural strength at the quasi-elastic limit for both tests. Finally, a simplified inverse analysis is proposed for the ring-on-ring test based on the elastic slab bending and yield line theories. The calculation results indicate a 19% lower tensile elastic limit stress of the UHPFRC, while an almost equivalent value of tensile strength is obtained from the ring-on-ring test, compared with the 4PBT results.

Effect of salt solution wet-dry cycling on the bond behavior of FRP-concrete interface

The strengthening of concrete structures with externally bonded fiber reinforced polymer (FRP) was increasingly being used in marine exposure environments. Marine environment exposure may significantly affect the bonding behavior of FRP externally bonded to concrete. This paper is intended for studying the effect of tidal-like condition such as salt solution wet-dry cycling on the behavior of FRP-concrete interface. Exposure tests and analytical approach are carried out on specimens externally bonded with carbon fiber reinforce polymer (CFRP) and basalt fiber-reinforce polymer (BFRP). Test variable include the types of fiber and the environmental exposure periods (0, 90, 180, 270, 360 cycles). From the bending test results, the bilinear bond stress-slip relationships for different exposure periods are derived. Based on these bond stress-slip relationships, the full-range behavior of shear stress along the bond length and debonding load can be obtained through the analytical solution. The test and numerical results show that salt solution wet-dry cycling can greatly affect the bond behavior of CFRP-concrete and BFRP-concrete interface with the increase of exposure periods. With the increase of exposure periods, the position of maximum shear stress tend to move backward, which indicates the behavior of FRP-concrete interface is weakened due to the salt solution wet-dry cycling. Compared with CFRP-concrete interface, salt solution wet-dry cycling exposure has greater influence on the bond behavior of the BFRP-concrete interface.

Experimental Evaluation of the Influence of Aggregate Strength on the Flexural Cracking Behavior of Epoxy Asphalt Mixtures.

The flexural cracking resistance of an asphalt concrete mixture used in a steel bridge deck pavement needs to be higher than that of one used in ordinary pavement. In this study, mechanical experimental tests were used to evaluate the influence of the aggregate strength on the flexural cracking behavior of epoxy asphalt concrete (EAC). The aggregate fracture area of beam cross sections was quantitatively analyzed by digital image processing, and crack propagation in the mixture was analyzed using fracture mechanics theory. The bending test results showed that the EAC containing high-strength aggregates exhibited the highest flexural cracking resistance among all of the aggregate mixtures under the same conditions. The use of high-strength aggregates led to a reduction in the aggregate fracture area, thereby improving the flexural cracking resistance of the mixture. The aggregate strength had a significant influence on the flexural cracking propagation behavior of the mixture. Fatigue test results at strain-controlled levels of 600–1200 με and 15 °C showed that the aggregate strength had no evident influence on the fatigue properties of the EAC. It is recommended that high-strength aggregates are used to increase the fracture resistance of aggregates and the flexural crack resistance of EACs.

Comparison of methods of evaluating materials’ tendency to brittle fracture

This article concerns different methods of evaluating material’s tendency to brittle fracture. It includes results of impact bending tests of cold-resistant metastable austenitic steel 12Cr18Ni10Ti (AISI 321) and ferritic steel 0Ni9A in a broad temperature range. The article shows that evaluation of the effectiveness of the material should be carried out in consideration of numerous factors, especially the specific exploitation conditions of the materials.

Mg–1Zn–1Ca alloy for biomedical applications. Influence of the secondary phases on the mechanical and corrosion behaviour

An as-cast Mg–1Zn–1Ca alloy has been soundly characterized to be used as a biodegradable material in biomedical applications. Ca and Zn additions have a great influence in the microstructure, mechanical properties and corrosion behaviour of Mg alloys. SEM examinations revealed that most of the Ca and Zn atoms form Mg 2 Ca and Ca 2 Mg 6 Zn 3 precipitates, which distribute preferentially along the grain boundaries forming a continuous network of secondary phases. The results of nanoindentation tests show differences in hardness and elastic modulus between the α-Mg matrix and the secondary phases. The results of three-point bending tests shows that cracks propagate following the network formed by the intermetallic compounds at the grain boundaries (GBs). The evolved hydrogen after immersion in Hank’s solution of the alloy has been also estimated, showing a change in the corrosion mechanism after 160 h. The intermetallic compounds act as a barrier against corrosion, so that it progresses through the α-Mg matrix phase. • Mg–1Zn–1Ca alloy is formed by α-Mg matrix and Mg 2 Ca and Ca 2 Mg 6 Zn 3 secondary phases. • Fracture mechanism occurs along the continuous secondary phases in a brittle way. • Mg–1Zn–1Ca alloy shows proper mechanical properties for biomedical applications. • Mg 2 Ca and Ca 2 Mg 6 Zn 3 secondary phases act as barriers for corrosion progress. • Immersion in Hank’s solution produces Mg(OH) 2 and HA as corrosion products.

Fly ash-based geopolymer with self-heating capacity for accelerated curing

Geopolymers has gained increasing attentions in recent decades because of its potential for CO2 emission reductions. In order to further increase the curing efficiency and save energy, the self-electrical heating fly ash based geopolymer was developed in this paper. In this work, carbon black and steel fibers were added into the fly ash based geopolymer to increase its electrical property. The feasibility of curing fly ash based geopolymer by using self-electrical heating was investigated. Calorimetry measurements were performed to quantify the effect of curing temperature on geopolymerization process of fly ash-base geopolymer. The three-point bending tests were conducted to investigate the influences of electric-heating on the flexural behaviours of geopolymer specimens. The results showed that the maximum surface temperature of geopolymer specimens under electric-heating reached 67 °C, which proved the feasibility of making conductive geopolymer with self-electrical behaviors. The three-point bending test results showed that the flexural strength for specimen significantly increased after self-electrical heating. With the proper addition of carbon black and steel fiber, the fly ash based geopolymer specimen cured after electrical heating possesses a denser micro-structure and therefore exhibits higher strength and better ductility. Besides, self-electrical heating method can significantly increase the eco-efficiency of geopolymer.

Adhesion enhancement of conductive graphene/PI substrates through a vacuum plasma system

Flexible electronics is regarded as a promising solution to stretchable/wearable devices given its light weight and high deformation ability. As a conducting layer, a widely utilized transparent conducting film, namely, indium tin oxide (ITO), is approaching its limitation on flexible applications given its high stiffness and brittle characteristics. Thus, this study proposes a highly flexible bi-layered architecture composed of polyimide (PI) substrate and coated graphene ink. This architecture is considered to replace the foregoing ITO film. A vacuum plasma system with different treatment parameters is taken into account to enhance the interfacial adhesion of graphene/PI substrates. Furthermore, a fracture-based finite element model of patterned graphene/PI substrates with various line widths are constructed to ensure the applicability of the presented stacked structure to actual flexible applications. This model aims to analyze the interfacial cracking energy under several designed bending radii of curvature through a modified virtual crack closure technique. To determine the fractured criterion of graphene/PI interfacial adhesion, a series of pull-off and lap shear tests are performed while requiring a comparison with simulated predictions. Results show that the peeling mode dominates the interfacial delamination of graphene/PI substrates, and the critical pull-off energy is appropriated to judge the fractured occurrence in accordance with the corresponding results of experimental bending tests. The adoption of vacuum plasma treatment contributes to enhancing the interfacial adhesion of the concerned interface and preventing the delamination failure occurrence during operating flexural loads.

INFLUENCE OF PANDANUS TECTORIUS LEAF FIBER ON MECHANICAL PROPERTIES AND MORPHOLOGY OF POLYPROPYLENE COMPOSITE

Natural fiber reinforced polymer composites are widely developed because of their relative low price and eco-friendly. One of natural fiber sourches is pandanus tectorius leaf. This study aimed to determine the effect of variations in fiber volume fraction on tensile strength, impact strength, bending strength and morphological on sea pandanus fibers- polypropylene composites.Tensile test spesimen refer to ASTMD 638, impact test spesimen refes to ASTMD 5942-96, bending test spesimen refer to ASTMD 790 -02. The increasing of the volume fraction increased the tensile strength and impact strength. The tensile test results showed the highest tensile strength results for composites with a volume fraction of 35% was 25.82 MPa. The impact test results showed that the highest impact strength was obtained in the 35 % volume fraction of 0.0062 Joule/mm2. The bending test results showed that the highest bending strength was obtained in the 20% volume fraction of 24.96 MPa. Based on SEM test results, there were voids, cracks, fibers pull out on the composite.

Local and global response of sandwich beams made of GFRP facings and PET foam core in three point bending test

In the paper behaviour of laminated sandwich beams (FRP face sheet – PET foam core – FRP face sheet) subjected to three point bending is studied. The paper aim is to find practical descriptions enabling effective and accurate estimation of the elastic response, damage and failure of the beams, basing on experiments and static calculations. Therefore a number of tests are described, that were done on laminated coupons and foam specimens in order to choose appropriate material models and find their constants. Experimental results of three-point bending tests of sandwich beams with three types of PET cores are analysed to evaluate the chosen material laws. The beam responses are predicted in numerical static simulations. The equations of problem are solved by means of finite element method (FEM). In the end the experimental and FEM results are compared. They are similar in terms of both their quantity and quality.

Modelling and simulation of the straw-grain separation process based on a discrete element model with flexible hollow cylindrical bonds

The grain separation process in a combine harvester is nonlinear and full of uncertainty. To study the process of separating grains from straw-grain mixtures (SGMs) in a combine harvester, a bonded-particle straw model (BSM) with flexible hollow cylindrical bonds was proposed. The mechanical properties of the BSM were simulated and compared with analytical predictions and experimental results. The maximum relative error between the BSM cantilever deflections and bending analytical predictions was 4.04%, and that between the normal displacements and stretching analytical predictions was 0.28%. Similarly, the maximum relative errors of the BSM cantilever deflections from bending test results and the normal displacements from stretching test results were 12.87% and 4.78%, respectively. Then, separation experiments with different straw area densities (SADs) were simulated using the BSM, and the simulation results were compared with experimental data. The coefficients of determination of the separation curve over time exceeded 0.995 for SADs of 2 and 3 kg/m2. Good agreement was achieved with maximum relative errors of 6.69% and 7.06% for the separation fraction results with SADs of 2 and 3 kg/m2, respectively. The BSM could accurately describe the separation process of grain from straw and quantify the interference of the straw and equipment.

Skeletal integrity of a marine keystone predator (Asterias rubens) threatened by ocean acidification

The current increase in atmospheric CO2 concentration induces changes in the seawater carbonate system resulting in decreased pH and calcium carbonate saturation state, a phenomenon called ocean acidification (OA). OA has long been considered as a major threat to echinoderms because their extensive endoskeleton is made of high‑magnesium calcite, one of the most soluble forms of calcium carbonate. Numerous studies addressed this question in sea urchins, but very few questioned the impact of OA on the sea star skeleton, although members of this taxon do not compensate their extracellular pH, contrary to most sea urchins. In the present study, adults of the common sea star, Asterias rubens from Kiel Fjord, a site experiencing natural acidification events exceeding pCO2 levels of 2500 μatm, were chronically exposed to different levels of simulated ocean acidification (pHT-SW 8.0, 7.4, 7.2), encompassing present and future conditions, for the duration of 109 days. Corrosion and mechanical properties of skeletal elements were studied using scanning electron microscopy, three-point bending tests as well as nanoindentation. The spines were significantly corroded at pHT-SW 7.4 and below while the ambulacral plates were only affected at pHT-SW 7.2. Nanoindentation of newly formed spines and ambulacral plates did not reveal significant CO2-induced differences in skeleton hardness or elasticity across treatments. Results of three-point bending tests revealed significantly reduced characteristic strength and fracture force of ambulacral plates from the median arm segment at pHT-SW 7.4 and below. These plates are those supporting the tube feet involved in the opening of bivalves during feeding and in the animal attachment to the substrate. Under reduced seawater pH, this might result in fracture of sea star plates during predation on mussel. The present results predict a possible impact of ocean acidification on the skeletal integrity of a marine keystone predator.

Accuracy of beam theory for estimating bone tissue modulus and yield stress from 3-point bending tests on rat femora

Mechanical analysis of animal long bones often makes use of beam theory to estimate tissue properties from bending tests. An earlier study (van Lenthe et al., 2008) found that beam theory leads to a considerable underestimation of the Young's modulus of mice femora. However, we hypothesized that beam theory might still be an accurate tool for the determination of bone strength from experimental data. The first goal was to test this hypothesis, along with checking if the underestimation of the tissue modulus is also valid for rat femurs. The second goal was to investigate if micro-FE and beam theory would yield similar increases in Young's moduli and yield stress during aging. Twelve rat femurs (12 and 16 weeks old) were scanned using micro-CT and subjected to a three-point bending test from which the bending stiffness and the yield force were obtained. The Young's modulus and yield stress then were calculated by regressing the experimental results with results obtained from beam theory and micro-FE analysis based on the micro-CT scans. It was found that bone strength calculated using beam theory overestimated that calculated from micro-FE by 8.0%. The Young's modulus did not significantly differ. When comparing age groups, similar increases in tissue modulus and yield strength were found for beam theory and micro-FE, with significant differences only for the micro-FE yield stress. We concluded that the use of beam theory to calculate bone yield strength from 3-point bending test results of rat femurs leads to its overprediction.

A study of fracture behaviour of gamma lamella using the notched TiAl micro-cantilever

ABSTRACT Microcantilevers were machined from a single γ(TiAl)-α2(Ti3Al) lamellae colony of a polycrystalline commercial Ti-45Al-2Mn-2Nb sample using the focussed ion beam. The long axis of the microcantilevers is perpendicular to the lamellar interface with the notch prepared in the same γ lamella. Bending test results demonstrated good repeatability and the fracture stress intensity factor of individual γ lamella was measured to be 3.1 ± 0.2 MPa m1/2. twinning ahead of the notch (crack) tip plays a key role in the crack initiation. TEM analysis shows that the interaction of twinning with the lamellar interface leads to interfacial cracking and contributes to the work-hardening observed.

Delamination behavior analysis of steel/polymer/steel high-strength laminated sheets in a V-die bending test

Steel/polymer/steel laminated sheets were fabricated by inserting three types of adhesive layers between two 590-MPa grade high-strength steel sheets. V-die bending tests of the laminated sheets were conducted and the results showed that the delamination behaviors depended on the inserted adhesive type. To investigate the mechanical behaviors of the adhesive layers, delamination tests for each adhesive layer along normal and shear directions were performed. Based on the results of the delamination tests, an inverse parameter characterization using an iterative finite element simulation with interface elements was successfully conducted to characterize the cohesive properties for mixed-mode bilinear cohesive zone model that clearly described the measured load–displacement curves. The results of the V-die bending tests were predicted through simulations using the characterized cohesive properties; the delamination patterns, punch force drop, and entire level of punch force agreed well with the experimental results. Delamination mechanisms were deduced based on parametric studies conducted to elucidate the direct effect of cohesive properties on delamination.

Microstructures and mechanical properties of stainless steel clad plate joint with diverse filler metals

Thick stainless steel clad plate is used widely in the petroleum and petrochemical industries because of its low cost and good corrosion resistance. It is generally welded by the multilayer and multipass welding process with stainless steel filler metal matched with the clad layer. In this research, the base metal of stainless steel clad plates was filled with carbon steel filler metal, and the microstructures and mechanical properties of joints with diverse filler metals were analysed and compared. The results indicate that a local hardening zone (LHZ) forms in the weld filled with the filler metals of stainless steel and carbon steel because of the formation of martensite phase in the first layer of weld with filler metal of carbon steel. The microhardness value in LHZ reaches up to 425 HV1, which is significantly higher than that of the base metal. However, the tensile strength value of joints filled with carbon steel filler metal is equivalent to that of the joints with stainless steel filler metal. The results of the side bending test indicate that the LHZ protrudes from the weld, and the crack occurs near the LHZ if the area of the LHZ on the cross section of joint is larger than 17 % of that of the whole cross section of the joint. The studied results show that it is feasible to use carbon steel filler metal to fill the base metal of carbon steel in welding of stainless steel clad plate.

An experimental investigation of novel hybrid epoxy/glass fibers nanocomposite reinforced with nanoclay with enhanced properties for low velocity impact test

The application of nanoparticles in order to enhance the composites properties has been recently attracted many researchers' attentions. To increase the mechanical and physical properties of the composites, the nanoparticles have no significant effect on the weight and nanostructure of composites. One of the well-known nanoparticles is the Nanoclay (NC) that have been widely used in industries due to its unique geometric shape and some specific chemical properties. In this research, the effect of NC on the mechanical behavior of epoxy hybrid/glass fibers composite has been investigated. Samples containing (1, 2, 3, 5 and 7) wt% of NC with constant amount of epoxy hybrid /glass fibers composite were produced. Samples with 3 wt% NC has shown proper impact, tensile properties. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique were used to analysis the morphology and phase characterization of the samples. The results of tensile, bending and impact tests on hybrid samples showed improvement in these properties compared to the primary sample without nanoparticles incorporated. On the other hand, the energy absorbed by the target was increased, due to the sensitivity of the glass fiber to the strain rate. The novel hybrid epoxy/glass fibers composite reinforced with 3 wt% NC present proper mechanical properties compared to another specimen.

Flexural and shear behavior of large diameter PHC pile reinforced by rebar and infilled concrete

The purpose of this paper is to provide an experimental and analytical study on the reinforced large diameter pretensioned high strength concrete (R-LDPHC) pile. R-LDPHC pile was reinforced with infilled concrete, longitudinal, and transverse rebar to increase the flexural and shear strength of conventional large diameter PHC (LDPHC) pile without changing dimension of the pile. To evaluate the shear and flexural strength enhancement effects of R-LDPHC piles compared with conventional LDPHC pile, a two-point loading tests were conducted under simple supported conditions. Nonlinear analysis on the basis of the conventional layered sectional approach was also performed to evaluate effects of infilled concrete and longitudinal rebar on the flexural strength of conventional LDPHC pile. Moreover, ultimate strength design method was adopted to estimate the effect of transverse rebar and infilled concrete on the shear strength of a pile. The analytical results were compared with the results of the bending and shear test. Test results showed that the flexural strength and shear strength of RLDPHC pile were increased by 2.3 times and 3.3 times compared to those of the conventional LDPHC pile, respectively. From the analytical study, it was found that the flexural strength and shear strength of R-LDPHC pile can be predicted by the analytical method by considering rebar and infilled concrete effects, and the average difference of flexural strength between experimental results and calculated result was 10.5% at the ultimate state.

Optimization of cooling time for polyethylene fusion joints

The objective of this research is to optimize cooling time for polyethylene fusion joints which will lead to higher output and cost savings to the industry. Conventionally, the butt fusion joints are prepared as per DVS standard with the following sequence: (i) preparation (alignment and facing of pipe & heating of plate) (ii) bead build up and heat soaking (iii) change over (iv) joining and cooling time. Among these stages cooling time is the most significant part as it governs the strength of the joint as well as the productivity. Higher is the cooling time lower is productivity. To the best of the authors’ knowledge, no study has been reported so far to address cooling time for the polyethylene fusion joints. Therefore, this work intends to study the cooling time and its effect on the joint integrity for these joints. Commonly used size of High Density Polyethylene (HDPE) pipes, OD 160 and OD 315 mm are used for the study. Sample joints are prepared as per the standard, with 100%, 80% and 60% cooling time. The samples are tested - tensile and bending tests. The comparison of the tensile properties and bending test results of the joints with different cooling time as well as with the parent material are analyzed to reach an optimum cooling time.

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.

DSC analysis and evaluation of forces released on deactivation of 0.40-mm (0.016") orthodontic thermo-activated NiTi wires: An in vitro study.

Background. This study evaluated the phase transformation of NiTi orthodontic wires and forces they release on deactivation. Methods. The structural phase transformations of the following five thermo-activated nickel-titanium (NiTi) wires were evaluated using differential scanning calorimetry (DSC): Flexy Thermal Sentalloy® (GAC International), NiTi (35ºC) (Eurodonto), Thermo-Plus® (Morelli), FlexyNiTi® Flexy Thermal (35ºC) (Orthometric) and Damon® CuNiTi (35ºC) (ORMCO Corp.). The wires had a cross-section of 0.40 mm (0.016"). In addition, the forces they released were investigated using the three-point bending test. Five arches of each wire were tested using DSC (-20/80ºC at 10ºC/min), and six arches from each wire were sectioned for bending tests. The data were analyzed with ANOVA and post hoc Tukey tests. Pearson’s correlation test was performed between the results yielded by the DSC tests and those by three-point analyses (P=0.05). Results. The DSC analysis showed differences between the NiTi alloys from all the manufacturers, with no differences between the lots of the same brand. ORMCO and Orthometric wires exhibited similar TTR values in cooling (P=0.49), and statistically similar TTR values in heating (P=0.056). The three-point bending test showed different patterns in releasing forces. A correlation was found between the DSC analysis and the three-point bending test results. Conclusion. The higher the temperature transformation was, the larger was the variation of force. All the wires presented higher forces at 3-mm deflection from 155 (±12.3) to 168.1 (±8) cN. The DSC analysis and the three-point bending test showed differences between the NiTi alloys from all the manufacturers.