Bent Portion Research Articles

Visualization of Hydrogen in Stress and Strain Fields Using SIMS

In order to clarify the mechanism of hydrogen embrittlement in high strength steel, it is necessary to evaluate local hydrogen concentration in stress and strain fields where hydrogen embrittlement is considered to occur. There are several ways to visualize hydrogen, but SIMS is advantageous in that it can detect hydrogen directly without reaction. In this study, visualization of hydrogen accumulated in stress and strain field was tried using SIMS. Hydrogen flux intensity in the bent portion of the U-bend specimen, where the stress gradient exists, changed according to the stress gradient, and the hydrogen flux intensity was higher on the outside of the bending than on the inside, with the center of the plate thickness at the boundary. On the shearing surface with strain field, the hydrogen flux intensity had a positive correlation with the stress. On the other hand, it remained constant with respect to the strain. From these observations, the hydrogen partitioning behavior in steel could be visualized semi-quantitatively by using the isotope labeling method with SIMS.

A practical macro-mechanical model for the bend capacity of fibre-reinforced polymer bars

Bent fibre-reinforced polymer (FRP) bars embedded in reinforced concrete elements resist lower forces than straight counterparts due to strength losses at the bend, and such losses are difficult to calculate. This paper reports on an investigation into the effect of section geometry and bond, which led to a new macro-mechanical model to calculate the bend capacity of FRP bars. The proposed model uses the Tsai–Hill failure criterion and accounts for factors known to influence the bend capacity of bars. A section factor, ignored in existing models, also accounts for the strength degradation due to the change in geometry at the bent portion of the bar. The model was calibrated using a set of 80 tests found in the literature and tests performed by the authors. The results indicated that, compared with existing equations, the proposed model predicts the bend strength of bars more accurately, with an average prediction to experiment ratio of 1·0 and a standard deviation of 0·25. Following validation and verification, appropriate values for the model parameters are recommended for design. The proposed model can lead to more economical design, by up to 15%.

Analytical springback assessment in flexible stretch bending of complex shapes

Stretch bending is commonly used in the fabrication of profile-based shapes. However, one of the challenges in many bending-type forming processes is controlling springback upon unloading. Springback appears sensitive to upstream and in-process parameters, making prediction and control difficult. The springback problem is particularly important in forming processes where stringent control strategies are needed to assure product dimension, process flexibility and overall equipment effectiveness. In this research, we present an analytical framework for springback assessment in a stretching-controlled bending process. A new, flexible rotary stretch bending machine is designed and built, which allows the manufacture of complex-shape profiles with varying curvatures, including straight portions, with low tool investments. Furthermore, a Full Moment (FM) analytical model is developed for springback assessment. The modeling strategy employs a full moment distribution along the entire profile upon bending, introducing a stretching-controlled moment transition between different curvature portions such that the springback contribution from the plastic moment outside the theoretically bent portions is considered. Additionally, the influential factors related to material, geometry and process, including the applied stretching strains, are comprehensively considered. In this way, the modeling strategy enables accurate evaluation of springback in the flexible stretch bending process. Moreover, the proposed forming process is validated by a series of experiments conducted for a wide range of stretching levels using rectangular hollow aluminum alloy profiles. This forming strategy demonstrates high capability for controlling springback and dimensional accuracy. By comparing experiments, numerical simulations and analytical calculations, this proves that the developed FM model provides accurate and efficient assessment of springback. The average relative error provided by the FM model is 2.2%, as compared to 10.5% for a classical method used for comparison. Using the analytical model combined with numerical simulation, the crucial deformation characteristics, including stretching-dependent evolution of strain transition, are revealed. Overall, the FM analytical strategy has proven its capability as an effective tool, which can make springback knowledge more explicit, generic and reuseable for stretching-controlled bending processes.

Crash Characteristics of Partially Quenched Curved Products by Three-Dimensional Hot Bending and Direct Quench

Recently, improvement of hybrid and electric vehicle technologies, equipped with batteries, continues to solve energy and environmental problems. Lighter weight and crash safety are required in these vehicles body. In order to meet these requirements, three-dimensional hot bending and direct quench (3DQ) technology, which enables to form hollow tubular automotive parts with a tensile strength of 1470 MPa or over, has been developed. In addition, this technology enables to produce partially quenched automotive parts. In this study, the crash characteristics of 3DQ partially quenched products were investigated as the fundamental research of the design for improving the energy absorption. Main results are as follows: (1) for partially quenched straight products in axial crash test, buckling that occurs at nonquenched portion can be controlled; (2) for the nonquenched conventional and overall-quenched curved products, buckling occurs at the bent portion at the initial stage in axial crash tests, and its energy absorption is low; (3) by optimizing partially quench conditions, buckling occurrence can be controlled; and (4) In this study, the largest energy absorption was obtained from the partially quenched curved product, which was 84.6% larger than the energy absorption of the conventional nonquenched bent product in crash test.

Strength Degradation in Curved Fiber-reinforced Polymer (FRP) Bars Used as Concrete Reinforcements.

Steel reinforcements in concrete tend to corrode and this process can lead to structural damage. Fiber-reinforced polymer (FRP) reinforcements represent a viable alternative for structures exposed to aggressive environments and have many possible applications where superior corrosion resistance properties are required. The use of FRP rebars as internal reinforcements for concrete, however, is limited to specific structural elements and does not yet extend to the whole structure. The reason for this relates to the limited availability of curved or shaped reinforcing FRP elements on the market, as well as their reduced structural performance. This article presents a state-of-the art review on the strength degradation of curved FRP composites, and also assesses the performance of existing predictive models for the bend capacity of FRP reinforcements. Previous research has shown that the mechanical performance of bent portions of FRP bars significantly reduces under a multiaxial combination of stresses. Indeed, the tensile strength of bent FRP bars can be as low as 25% of the maximum tensile strength developed in a straight counterpart. In a significant number of cases, the current design recommendations for concrete structures reinforced with FRP were found to overestimate the bend capacity of FRP bars. A more accurate and practical predictive model based on the Tsai–Hill failure criteria is also discussed. This review article also identifies potential challenges and future directions of research for exploring the use of curved/shaped FRP composites in civil engineering applications.

Torsion in concrete beams reinforced with GFRP spirals

Abstract Current FRP guidelines do not have enough evidence on the torsional performance of beams reinforced with glass fiber-reinforced polymer (GFRP) reinforcement due to the lack of research and complexity of the problem. A review of the past work was presented in the state-of-the-art section to stand on mile-stone prospective considering the variety and development of GFRP manufacturing. This study examined the rectangular spirals and rectilinear stirrups to reinforce concrete beams in the transverse direction under pure torsion loading. The test parameters included four levels of transverse reinforcement ratio and the type of transverse reinforcement in terms of rectilinear stirrups vs. spirals. The test results demonstrated that rectangular GFRP spirals provided superior tensile resistance required to develop high ultimate torsional moments after cracking and hence can be effectively used. The failure of the tested beams was attributed to the rupture of GFRP rectangular spirals at bent portions. The test results of the spiraled specimens were discussed and compared with predictions from a developed analytical model and based on CSA equations. Two values of failure plane angle and stress levels were considered. The 45-degree inclination angle provided safe predictions with an average experimental-to-practiced result of 1.16 compared to 0.99 using the 37.5-degree. Design equations were proposed and validated for the ACI code for a probable future incorporation.

Concrete beams with different arrangements of GFRP flexural and shear reinforcement

This paper presents experimental research on the flexural and shear behaviour of concrete beams reinforced with glass fibre reinforced polymer (GFRP) composite reinforcement. Three-point bending tests on shear critical concrete beams reinforced with GFRP longitudinal bars and GFRP stirrups are presented. The test variables were the size and spacing of closed loop stirrups as well as the size, amount, and arrangement of longitudinal reinforcement. Twelve beams were tested with four different stirrup arrangements and three different longitudinal reinforcement arrangements. Longitudinal bars were instrumented at mid-span and stirrups were instrumented at the straight and bent portions. The beams had a shear-span-to-effective-depth ratio of 2.5 and behaved like deep beams. The beams without stirrups failed in shear-tension while the beams with stirrups failed in shear-compression with no ruptured stirrups. Longitudinal reinforcement strains showed evidence of a tied arch mechanism. The analysis found diminishing increases in shear strength with increasing shear reinforcement ratio when failure occurred as a result of crushing of confined concrete.

Shear behavior of concrete beams reinforced with CFRP sheet strip stirrups using wet-layup technique

Fiber-reinforced polymers (FRP) are being used in reinforced concrete structures featuring their lightweight, high tensile strength, nonmagnetic, and corrosion resistance properties, contrasting conventional steel reinforcement. However, low bend strength, anisotropic and non-plastic nature of FRP composites are the major concerns for their assertive applications in construction industry. Pultruded FRP bar stirrups are characterized by premature failure either due to slippage at overlapping region or rupture at bend portion due to kinking of fibers. In this experimental study, close-type direct wound rectangular cross-section CFRP sheet strip stirrups (CSS) were proposed to mitigate the shortcomings of pultruded CFRP bar stirrups (CP). Total of seven full-scale beam specimens reinforced with steel longitudinal bars and CFRP stirrups were cast and tested to investigate the performance of proposed stirrups. The main study parameters include shear reinforcement material type, the cross-sectional geometry of CFRP stirrups, and the inclination angle of CSS stirrups with the beam axis. Specimens reinforced with CSS stirrups provided better shear capacity and crack control ability compared to steel and CP stirrups for same shear reinforcement ratios. Shear capacity of beam corresponding to serviceability limit state was improved up to 13% by changing the inclination of CSS stirrups from 90° to 45°.

Shear behavior of large-scale concrete beams reinforced with CFRP bars and handmade strip stirrups

To obviate the premature failure of pultruded FRP stirrups due to low bent portion strength and slippage at overlapping region, this study fabricated handmade strip stirrups with a rectangular cross-section and investigated the shear behavior of concrete beams reinforced with handmade CFRP strip stirrups and CFRP longitudinal bars. Five large-scale concrete beams with the cross-section of 200 mm × 500 mm and the shear span ratio of 2.26 were tested under three-point loading. The effects of stirrups inclination and stirrups spacing were studied. Test results showed that inclined stirrups improved both the shear capacity and the serviceability performance. The beams reinforced with inclined stirrups exhibited 1.19–1.26 times higher shear capacities than the beam reinforced with vertical stirrups. Inclined stirrups not only increased the load corresponding to the maximum allowable crack width to 1.10–1.89 times higher, but also improved the ratio of the load corresponding to allowable crack width to the peak load. Moreover, inclined stirrups are more effective in improving the serviceability performance even compared with vertical stirrups with a halved spacing. The shear provisions in CSA S806-12 produced the most accurate predictions of the experimental shear capacities, while the predictions of ACI440.1R-15 and CSA S6-14 were relatively conservative.

Modulation of flexible filaments dynamics due to attachment angle relative to the flow

This paper describes experiments carried out in a wind tunnel with three flexible silicone filaments (length to diameter ratio L/D = 50, 100, 150) hanging in crossflow in the range of reduced velocities of 7 <U* < 150 and at various attachment angles (0 ≤ α ≤ 90°) with respect to the flow direction. At low reduced velocities, due to the negligible bending stiffness, the filaments were statically reconfigured but remained mostly rectilinear along their lengths, except for the relatively small bent portion of the filaments close to the upstream fixed end. As the reduced velocity was further increased the filaments started vibrating, but in certain cases large-amplitude flapping motions were observed. Despite of the negligible role of the attachment angle at the fixed end on the static reconfiguration of the filaments, it was found that it plays a crucial role on the dynamics of the flapping motions, as it determines whether the filaments exhibit large-amplitude limit-cycle oscillation dynamics or noisy small-amplitude vibrations.

3D Simulation of Dean Vortices at 30° Position of 180° Curved Duct of Square Cross-Section under Opposing Buoyancy

3D numerical simulations are performed to analyze correctly the effect of opposing thermal buoyancy and Dean number on Dean vortices, fluid flow and heat transfer through 180° curved duct of square cross-section. Due to tremendous found results, this works emphasizes only at the position 30° of the bend portion. The governing equations involving momentum, continuity and energy are solved in three dimensions under these assumptions: the flow is laminar, steady-state and incompressible. The present study is investigated in the range of these conditions: Dean number of De = 125 to 150, Richardson number of Ri = 0 to 2 at Pr = 1. The principal obtained results are represented in forms of streamlines and isotherms to analyze and to discuss the found physical phenomena. The local Nusselt number along the wall of square cross-section is also computed and presented. The main found point is that the opposing thermal buoyancy has a tendency to eliminate the effect of centrifugal force at the position 30° of bend portion of 180° curved duct.

Residual wall thickness of water‐powered projectile‐assisted injection molding pipes

Water‐powered projectile‐assisted injection molding (W‐PAIM) is an innovative molding process for the production of hollow shaped polymer parts. The W‐PAIM utilizes high pressure water as a power to drive a solid projectile to displace the molten polymer core to form the hollow space. The residual wall thickness (RWT) and its distribution are the important quality criteria. The experimental and numerical investigations were conducted. Experimental specimens showed that the RWT of a W‐PAIM pipe was much thinner than that of a water‐assisted injection molding pipe. The cross‐section size of the projectile defined the basic penetration section size. The software FLUENT was used to obtain the instantaneous distributions of the flow field, which revealed the forming mechanism of the RWT. The experiments indicated that the processing parameters, such as melt temperature, melt injection pressure, mold temperature, and water injection delay time had obvious effects on the RWT, while the water pressure had little effect on it. The RWT of curved pipes was thin at the inner concave side while thick at the outer convex side. The RWTs at the bend portion are influenced by the deflection angle and bending radius, which is due to the pressure difference between the two sides. POLYM. ENG. SCI., 59:295–303, 2019. © 2018 Society of Plastics Engineers

Bend sprinting performance: new insights into the effect of running lane

Athletes in inner lanes may be disadvantaged during athletic sprint races containing a bend portion because of the tightness of the bend. We empirically investigated the veracity of modelled estimates of this disadvantage and the effect of running lane on selected kinematic variables. Three-dimensional video analysis was conducted on nine male athletes in lanes 8, 5 and 2 of the bend of an outdoor track (radii: 45.10, 41.41 and 37.72 m, respectively). There was over 2% (p < 0.05) reduction in mean race velocity from lane 8 (left step 9.56 ± 0.43 m/s, right step: 9.49 ± 0.41 m/s) to lane 5 (left step: 9.36 ± 0.51 m/s, right step: 9.30 ± 0.51 m/s), with only slight further reductions from lane 5 to lane 2 (left step: 9.34 ± 0.61 m/s, right step: 9.30 ± 0.63 m/s). Race velocity decreased mainly because of reductions in step frequency as radius decreased. These unique data demonstrate the extent of the disadvantage of inner lane allocation during competition may be greater than previously suspected. Variations in race velocity changes might indicate some athletes are better able to accommodate running at tighter radii than others, which should have implications for athletes’ training.

Effect of martensitic transformation on springback behavior of 304L austenitic stainless steel

The present paper studies the effect of martensitic transformation on the springback behavior of 304L austenitic stainless steel. Martensite volume fraction was determined at the bent portion under various strain rates after bending test. Martensitic transformation has a significant effect on the springback behavior of this material. The findings of this study indicated that the amount of springback was reduced under a situation of low strain rate, while a higher amount of springback was obtained with a higher strain rate. The reason for this phenomenon is that higher work hardening occurs during the forming process with the low strain rate due to the higher martensite volume fraction, therefore the formability of the sheet is enhanced and it leads to a decreased amount of springback after the bending test. Dependency of the springback on the martensite volume fraction and strain rate was expressed as formulas from the results of the experimental tests and simulation method. Bending tests were simulated using LS-DYNA software and utilizing MAT_TRIP to determine the martensite volume fraction and strain under various strain rates. Experimental result reveals good agreement with the simulation method.

Barracudia australiensis n. g., n. sp. (Nematoda: Philometridae) from the obtuse barracuda Sphyraena obtusata Cuvier (Perciformes: Sphyraenidae) off eastern Australia.

Based on light and scanning electron microscopical studies, a new nematode parasite, Barracudia australiensis n. sp. (Philometridae), is described from the gall-bladder of the marine fish (obtuse barracuda) Sphyraena obtusata Cuvier (Sphyraenidae, Perciformes) from off the eastern Pacific coast of Australia, for which a new genus Barracudia n. g. is established. This new genus is mainly characterised by features found in the male: sickle-shaped, ventrally curved spicules, a gubernacum with a broad, dorsally bent distal portion and a markedly dorsoventrally elongated cloacal aperture. Based on these features, Barracudia spp. conspicuously differ from representatives of all other philometrid genera with known males. Philometra philippinensis Quiazon & Yoshinaga, 2013 is transferred to Barracudia as B. philippinensis (Quiazon & Yoshinaga, 2013) n. comb. Barracudia australiensis is the third nominal species of philometrids described from the Sphyraenidae and the 19th species of the Philometridae recorded from fishes in Australian waters.

TH‐CD‐206‐11: An Ellipsoid Convex Enhancement Filter Based Computer‐Aided Diagnostic Framework of Intracranial Aneurysms in MRA Images

Purpose:For early detections of asymptomatic intracranial aneurysms, computer aided diagnostic (CAD) frameworks of intracranial aneurysms in magnetic resonance angiography (MRA) images were developed with various enhancement filters. However, discrimination between aneurysms and false positive structures, such as bending or branching portions of vessels could still be a challenging task for the enhancement filters. Therefore, we focused on developing an ellipsoid convex enhancement (ECE) filter based CAD framework, which is capable of enhancing aneurysms while reducing the effect on bending and branching portions of vessels, for detection of intracranial aneurysm candidate.Methods:The proposed ECE filter was designed for selectively enhancing aneurysms with certain ellipsoid convex shapes, whose ratios of the shortest to longest diameters correspond to the ratio of reciprocals of the square roots of the first and third eigenvalues of Hessian matrices. This filter was applied to artificial images with Gaussian ellipsoid models and clinical MRA images of 30 patients (Male: 10, Female: 20; age: 48 to 86 years, mean: 69.2) with 31 unruptured aneurysms (longest diameter: 2.0 to 5.5 mm, mean: 3.7 mm) based on a leave‐one‐out‐by‐patient test.Results:The proposed ECE filter reduced the average contrast for false positive Gaussian ellipsoid models by 51.4%. The number of false positives per patient decreased from 41.1 to 22.8 at a sensitivity of 87% by using the ECE filter.Conclusion:The ellipsoid convex enhancement filter based CAD framework of intracranial aneurysms in MRA images would be useful by providing a higher contrast between aneurysms and false positive structures such as bending or branching portions of vessels.

An ellipsoid convex enhancement filter for detection of asymptomatic intracranial aneurysm candidates in CAD frameworks.

Various kinds of enhancement filters have been developed in computer-aided diagnostic (CAD) frameworks for asymptomatic intracranial aneurysms in magnetic resonance angiography (MRA). However, many bending or branching portions on vessels are also enhanced by the conventional filters as false positives in 3.0 T MRA, which can visualize smaller vessels compared with 1.5 T MRA. To overcome this problem, this study focused on developing an ellipsoid convex enhancement (ECE) filter, which can selectively enhance aneurysms while reducing false positive contrasts on bending or branching portions on vessels, for detection of asymptomatic intracranial aneurysm candidates in CAD frameworks. The ECE filter was mathematically designed to enhance various convex regions in the intensity space such as convex aneurysms, in which the ratio of the shortest and longest diameters for aneurysms corresponds to the ratio of reciprocals of the square roots of the first and third eigenvalues of a Hessian matrix. The proposed ECE filter was evaluated by measuring an average contrast for false positive models and free-response receiver operating characteristic curves between two simple CAD frameworks using the ECE and conventional filters based on a leave-one-out-by-patient test. MRA images for thirty patients (male: 10, female: 20; age: 48-86 yr, mean: 69.2) with 31 unruptured aneurysms (longest diameter: 2.0-5.5 mm, mean: 3.7 mm) were selected for this study. The average contrast for false positive models was reduced by 51.4% using the ECE filter, compared with the conventional filter for the convex regions with ratios of the shortest and longest diameters less than 0.4. The number of false positives per case was decreased from 41.1 to 22.8 on average at a sensitivity of 87% by using the ECE filter. The ECE filter would be useful for boosting the performance of the CAD framework of asymptomatic intracranial aneurysms by providing higher contrast aneurysms and lower contrast false positives such as bending or branching portions on vessels.

Comparative Analysis of Hydrodynamics Behavior of Microalgae Suspension Flow in Circular, Square and Hexagonal Shape Photo Bioreactors

Microalgae based biofuel is an emerging natural source of energy alternative to the fossil fuel. As microalgae are photosynthetic microorganisms, light is one of the limiting factors for its culture. Though many researches have been carried out for findings behind suitable culture system for the proper growth of microalgae, those are confined only to tubular Photo-bioreactor (PBR). This paper aims to make comparison among the horizontal loop photo bioreactors with different cross sections based on the analysis of hydrodynamics behavior. Three different geometrical shapes having vertical cross sections of circular, square and hexagonal PBR, have been proposed taking into account light intensity for microalgae culture. In this study, we simulate the flow dynamics of three types of PBRs and discuss the velocity, pressure and shear stress properties as microalgae endurance capacity depends on them. For the dimension of the three PBRs we considered here, each of them have radius of about 0.05 m while the length together with bending portion is approximately 20.5 m for a single loop. From the study, the hydrodynamic behaviors are observed to be quite dissimilar in case of three PBR’s. In the straight portion the velocity profile is quite parabolic in tubular but distorted minimally in case of square and hexagonal PBRs. In the middle of the U-loop, a haphazard fluid distribution is noticed. The velocity magnitude and agitation of microalgae cells are higher in hexagonal than in square and tubular. The shear rate is less in case of tubular compared to square and hexagonal. A linear pressure drop is found from the inlet to the outlet for three PBR’s. From this comparison, it can be said that the tubular one would be the best option for microalgae culture in case of industrial purposes.

A foldable OLED display with an in-cell touch sensor having embedded metal-mesh electrodes

A foldable organic light-emitting diode display integrating a touch sensor is fabricated. The touch sensor has an in-cell structure where metal-mesh sensor electrodes are formed in a counter substrate. It is demonstrated that touch on the entire panel surface, including a bent portion, is detected and that the touch panel operates correctly after 100,000 folding operations with a radius of curvature of 5 mm.

Tube Glass Waveguides Modified With Gold Nanoparticles for Application as a Simple Chemical and Biological Sensor

A low-cost, simple, and stable optical chemical and biological sensor was prepared using a U-shaped glass tube, whose 200-μm-thick wall coated with a colored layer serves as a sensitive waveguide. Light from a LED is launched into the glass wall of the tube from an endface and emits from the other endface to be detected with a silicon photodetector. The refractive-index (RI) sensitivity of the sensor is mainly attributed to the clad-RI-induced enhancement of evanescent field that results in the increased absorption of the colored layer. The sensor's sensitivity can be effectively improved by hydrofluoric acid etching of the bent portion of the U-shaped tube before deposition of the colored layer. The gold-nanoparticle (GNP) monolayer was used as the colored layer in this paper, and the GNP self-assembly process that took more than 12 h was in situ monitored with the sensor. The resulting sensor can easily detect a small change of 1 wt% in sucrose concentration, and is also applicable for real-time detection of bimolecular adsorption and immunoreaction.