Hard Bending Research Articles

Research on dynamic analysis and maintenance strategy for hard bending of high-speed turnout switch rail

Plastic deformation occurs in the turnout switch rail during loading, unloading, transportation, and storage, resulting in hard bending of the switch rail. The hard bending of the switch rail will lead to an abnormal increase in insufficient displacement, resulting in the geometric size exceeding the limit and the potential risk in the train operation. However, the dynamic simulation of the turnout area has not fully explored the potential impact of the insufficient displacement caused by the hard bending of the switch rail on driving safety. Therefore, this paper establishes a high-speed railway EMU-turnout dynamics model to evaluate the influence of the hard bending of the switch rail on the safety and stability of the train. The results show that the influence of theoretical and measured switch rail hard bending amplitude on the vehicle dynamics index is limited when it is 4 mm or less. However, when the hard bending amplitude of the switch rail increases to 8 mm, the relevant vehicle dynamics indexes increase significantly. The maximum derailment coefficients under the theoretical and measured hard bending of the 8 mm working conditions are 4.42 times and 6.71 times the normal working conditions, respectively. The wheelset lateral force is 4.55 times and 6.86 times the normal working conditions, but they are all within the safety limit. The on-site verification also confirms that there is no significant change in the vertical and lateral acceleration of the car body under the 4 mm hard bending of the switch rail. Finally, a maintenance strategy for the insufficient displacement caused by the hard bending of the switch rail is proposed and the effectiveness of the maintenance strategy is verified in the case study.

Highly hard modified Novikov gears for special purpose drive gearboxes

A comparison of the technical and economic characteristics of the drive gearbox of oil pumping units with different versions of modified Novikov gears with thermally improved and highly hard teeth is considered. The advantages of the latter are shown. Keywords: Novikov gearing, thermally improved teeth, highly hard teeth, contact endurance, bending endurance, technical and economic characteristics of the gearbox. vkorotkin@sfedu.ru

Bending Strain Sensitivity of Critical Current in REBCO Coated Conductor Winding for Coil Application at 77 K

High-temperature superconducting (RE)Ba₂Cu₃ O_7-x (REBCO)-coated conductor (CC) tapes are known for their capacity to tolerate high tensile stress under uniaxial tension, which is typically in the range of 600-700 MPa at 77 K. However, when used in a coil, there is a limit to the allowed strain before degradation of the critical current (<i>I</i>_c) occurs. This is attributed to the combined strain due to bending and axial tension which was caused during fabrication, cool down, and operation of coils and magnets and corresponds to the irreversible strain limit of <i>I</i>_c degradation. Applied strain along the CC tape&#x0027;s edgewise direction (hard bending strain) also affects the irreversible strain limits of <i>I</i>_c considerably. With such conditions, degradation of the REBCO coil performance can be expected. Therefore, the current study aims to systematically investigate the mechanism for such <i>I</i>_c degradation in REBCO coils. Linear superposition of strains induced in different modes of easy and hard bending were studied analytically and experimentally. The <i>I</i>_c degradation behaviors were examined in IBAD&#x002F;REBCO CC tapes in windings with different pitches on mandrels with different diameters. The investigation was done at 77 K and in self-field conditions using an apparatus designed for coil testing. The bend strain parameters in coils were analyzed, including the radius of curvature and pitch between CC tape turns. Through the linear superposition of strains induced in the REBCO coils, an appropriate approach is suggested to effectively handle the <i>I</i>_c degradation under winding including edgewise bending.

Analysis of incremental die bending of wires and tubes

The use of bent wires, tubes, and profiles has a broad application in the industry as it is based on a great number of possible applications. Both structures with a high light-weight construction potential as well as functional and aesthetic geometry can be realised expediently. Known processes are often limited in case of tight radii and complex bending contours that cut each other or that are similar to a loop. The so called incremental die bending provides the remedy. It is an innovative process for the production of complexly shaped workpieces in the form of bent wires, tubes, or profiles. The bending process in case of incremental die bending is different to conventional processes, since a die is reshaped. With this process the semi-product is put into a hard bending shape by a moving feeding unit. The process is very accurate and at the same time cost-effective, since almost any bending contours can be produced form-based in one working stage. Furthermore, the die geometry enables the manufacture of contours that were previously very work-intensive or not producible at all.

Out-of-plane bending characteristics of second generation high temperature superconducting tapes

REBCO tapes, known as second generation (2G) high temperature superconducting (HTS) tapes, are promising for their application in high field magnets and high current cables. However, in practical applications 2G HTS tapes always need to be bent, which causes the degradation of critical current. Therefore, it is necessary to study the bending characteristics of 2G HTS tapes. Studies have been carried out regarding easy bending and hard bending characteristics, but there has been no research into the characteristics of out-of-plane bending with different bending angles. This paper theoretically analyzes the out-of-plane bending with different bending angle characteristics of 2G HTS tapes and deduces the strain formula of different bending modes. Experiments on the bending characteristics of 2G HTS tapes were performed in liquid nitrogen. The experiments verified the theoretical calculation, and the results have significance for the applications of 2G HTS tapes.

Large-scale plasma patterning of transparent graphene electrode on flexible substrates.

Graphene, a two-dimensional carbon material, has attracted significant interest for applications in flexible electronics as an alternative transparent electrode to indium tin oxide. However, it still remains a challenge to develop a simple, reproducible, and controllable fabrication technique for producing homogeneous large-scale graphene films and creating uniform patterns with desired shapes at defined positions. Here, we present a simple route to scalable fabrication of flexible transparent graphene electrodes using an oxygen plasma etching technique in a capacitively coupled plasma (CCP) system. Ascorbic acid-assisted chemical reduction enables the large-scale production of graphene with solution-based processability. Oxygen plasma in the CCP system facilitates the reproducible patterning of graphene electrodes, which allows controllable feature sizes and shapes on flexible plastic substrates. The resulting graphene electrode exhibits a high conductivity of 80 S cm(-1) and a transparency of 76% and retains excellent flexibility upon hard bending at an angle of ±175° and after repeated bending cycles. A simple LED circuit integrated on the patterned graphene film demonstrates the feasibility of graphene electrodes for use in flexible transparent electrodes.

Mechanical analysis of organic flexible devices by finite element calculation

In recent years, organic flexible devices have been investigated extensively and sub‐millimeter bending stability of organic thin film devices has been achieved by placing the active layer of the transistor on a neutral strain surface. Around the neutral strain surface, an organic thin film has a high bending durability because the in‐plane tensile and compressive strain cancel each other. However, this type of highly flexible device is also destroyed or undergoes irreversible degradation when subjected to hard bending, and the breaking point is very difficult to detect experimentally. Therefore, we performed a finite element analysis of a flexible device and found a possible breaking point at the boundary between the contact electrode and the organic layer. This was the result of a strain concentration at the boundary due to the difference in Young's modulus of the organic semiconductor and Au. In addition, the shear stress is concentrated around the edge of the Au electrode. These results indicate that the most likely breaking point for this type of flexible transistor is a rupture of the organic layer at the interface with the Au electrode.

Preliminary investigation of Ic homogeneity along the longitudinal direction of YBCO coated conductor tape under tensile loading

In this study, the homogeneity of critical current, , along the lengthwise direction in the coated conductor (CC) tape under uniaxial tension was investigated using a multiple voltage tap configuration. Initially, a gradual and homogeneous degradation occurred in all subsections of the tape up to a certain strain value. This was followed by an abrupt degradation in some subsections, which caused scattering in values along the length with increasing tension strain. The degradation behaviour was also explained through n-value as well as microstructure analyses. Subsections showed scattering corresponding to damaged areas of the CC tape revealed that transverse cracks were distributed throughout the gauge length. This homogeneous degradation behaviour under tension is similar with the case under torsion strain but different with the case under hard bending which were previously reported. This behaviour is also different with the case using Bi-2223 HTS tapes under tension strain.

Determination of winding diameter based on bending strain analysis for REBCO coated conductor tapes

In order to recognize the allowable bending diameter in coils, the strain as function of diameters is evaluated. The irreversible strain limits of <TEX>$I_c$</TEX> in the easy and hard bending modes were measured. Strains were calculated at the coating film in the easy bending and at outer edge or inner edge in the hard bending of the CC tape, respectively. The tape geometry subjected to bending procedures is considered from the current industrial spool winding operation. Through the linear superposition of strain induced in different bending modes regarding the expressions, the appropriate design for critical bending diameter is suggested. Results proved that the existence of buckling resulting from bending in hard direction when applied strain exceeded 0.6% is possible. The depicted results showed that the strain limit as a viable parameter should be considered for future purposes.

MARS, a new beamline for radioactive matter studies at SOLEIL

MARS (Multi Analyses on Radioactive Samples) beamline is the hard X-ray bending magnet beamline dedicated to the study of radioactive matter of the new French synchrotron SOLEIL. The beamline, which has been built thanks to a close partnership and support by the CEA, has been designed to provide X-rays in the energy range of 3.5 keV to 35 keV. This allows to encompass M and L absorption edges of actinides, as well as K edges of transition metals (that are present in alloys and fuel claddings) up to heavy halogens, rare gases and alkalis (fission products in nuclear fuels). The MARS project aims to extend the possibilities of synchrotron based X-ray characterizations towards a wider variety of radioactive elements and a wider variety of techniques than what is currently available at other facilities. Thus, its specific and innovative infrastructure has been optimized in order to carry out analyses on materials with activities up to 18.5 GBq per sample for α and β emitters and 2 GBq for γ and n emitters. So, today, more than 70 different elements and more than 350 different isotopes have been proposed for studies on the beamline by the involved user community. The arrangement of the different elements in the optics hutch is based on an original scheme which permits to have two alternative optical configurations (monochromatic or dispersive) depending on the nature of experiments to be performed. At least three main techniques are progressively being proposed on the three complementary end-stations located in the experimental hutch: transmission and high resolution powder diffraction (TXRD and HRXRD), standard and dispersive X-ray absorption spectroscopy (XAS and EDXAS) and X-ray fluorescence (XRF). In addition, by using the KB optics, a micro-focused beam will be available on the second station of the monochromatic branch. The beamline is currently under commissioning. The first two experimental stations, using the monochromatic branch, are scheduled to be operational at the end of the year.

Bending Strain Characteristics of the Transport Property in Lap-Jointed Coated Conductor Tapes

The electro-mechanical properties of lap-jointed ReBCO coated conductor (CC) tapes have been investigated. Different contact configurations considering its geometry were adopted in this study. The configuration where the YBCO layer is in close proximity showed much less joint resistance. In all joint configurations, the electrical resistance decreased as the joint length increased. For HTS tapes, the joint resistance-joint length behavior could be explained by parallel circuit analysis. In easy and hard bending modes, the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> degradation behaviors in lap-jointed HTS tapes were examined. The critical radius for 95% I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> retention in each bending mode were determined.

Bending strain characteristics of critical current in REBCO CC tapes in different modes

The influences of bending strain on the critical current, I c in stabilized YBa 2Cu 3O 7− δ (YBCO) and SmBCO coated conductor (CC) tapes in different modes of easy and hard bending were investigated at 77 K and self-field. Under easy bending, the influences of the compressive and tensile bending strains on the I c in REBCO (rare earth element, Barium and Copper oxide) CC tapes were investigated. Under tensile bending strain, when the I c was plotted against the strain on the YBCO film layer, the 95% I c retention strain limit under bending was comparable to the value obtained in the axial-tension test. Under the hard bending of YBCO CC tape, I c started to degrade when the bending strain exceeded 0.6% and the recovery of I c did not occur when the bending strain applied was released. This might be a result of the generation of a new type of damage such as local buckling during hard bending which is different from the damage type experienced in Bi-2223 tapes. The n-value behavior showed a good agreement with the I c degradation behavior. On the other hand, the SmBCO CC tape showed a superior strain tolerance under hard bending resulted from its flexibility to in-plane deformation due to thin geometry compared to other copper stabilized YBCO CC tapes.

Stretching an anisotropic DNA

We present a perturbation theory to find the response of an anisotropic DNA to the external tension. It is shown that the anisotropy has a nonzero but small contribution to the force-extension curve of the DNA. Thus an anisotropic DNA behaves like an isotropic one with an effective bending constant equal to the harmonic average of its soft and hard bending constants.

Dynamic scattering of semirigid macromolecules

The polarized (VV) and depolarized (VH) dynamic light scattering functions of dilute solutions of semirigid macromolecules are calculated assuming that the scattering wave vector [under q] is high compared to the chain Kuhn segment l : ql>>1. The terminal relaxation rate is Gamma proportional to q8/3. Dynamics of both uniaxial and biaxial wormlike macromolecules (filaments) are considered. Biaxial macromolecules are characterized by two persistence lengths proportional to elastic constants for bending in two perpendicular directions (easy and hard bending). We showed that biaxiality may result in a significant broadening of the relaxation spectrum. A nonmonotonous q dependence of the depolarized scattering intensity is predicted. Analyzing the short-time behavior of the dynamic structure factor for t<<1/Gamma, we show that it is characterized by two additional characteristic times: t perpendicular proportional to q(-4) and t parallel proportional to q(-8) reflecting the transverse and the longitudinal dynamics of polymer chains. The longitudinal motions (along the chain contour) increase the initial relaxation rate of the structure factor by a factor of 2. The longitudinal contribution to the dynamic structure factor is significant even for t>>t parallel.

Critical current degradation behaviour in Bi-2223 superconducting tapes under bending and torsion strains

In this paper, we have investigated the Ic degradation behaviours in Ag alloy sheathed Bi-2223 superconducting tapes under bending and torsion strains. In particular, we have examined the homogeneity of Ic degradation along the longitudinal direction of tapes by adopting multiple voltage terminals. The bending modes influenced the Ic degradation behaviour in Bi-2223 tapes. A gradual and consistent decrease of Ic could be observed at all sections, which was a different behaviour from that under tensile loading. Up to εirr, Ic showed a nearly similar degradation at each section, due to a simultaneous initiation of cracks from defects indicating that uniform deformation occurred in tapes with bending. Over εirr, some variations in the Ic degradation occurred due to the difference of crack growth rates at each section. In particular, the behaviour appeared significantly with hard bending. The degradation of Ic in Bi-2223 tapes by torsion occurred gradually when the torsion angle exceeded 150°. However, the Ic degradation by torsion strain was small compared with other types of loading. Also, the Ic degradation behaviour at each section along the longitudinal direction of tapes was gradual and consistent, representing a uniform torsional deformation in the tapes.

A comparison of strain effect on critical current in Bi-2223 superconducting tapes in different bending modes

The influence of the bending strain on the critical current (I/sub c/) in Ag alloy/Bi-2223 superconducting tapes was investigated at 77 K. The strain effect on I/sub c/ degradation in the different bending modes is discussed in terms of sample geometry and n-value. The I/sub c/ degradation behavior with bending occurring across the tape's width direction called 'hard bending' is discussed in particular, and compared with results under conventional bending tests known as 'easy bending'. It was found that I/sub c/ degraded with increases in the bending strain. In the case of hard bending, greater degradation in I/sub c/ occurred than under easy bending. This might be a result of the difference in the filaments cross-section of the tape and the generation of a new type of damage, such as local buckling, expected during hard bending. The n-value also decreased as the bending strain increased and its behavior was similar to the I/sub c/-bending strain relationship.

Abbiegungen und Abknickungen von Insektenflügeln beim Flug ohne und mit zusätzlicher Beutelast

Wing bending around preformed bending lines due to hitting a hard object and wing bending due to aerodynamic forces are differentiated. After analysing approximately 10h of video recordings, the maximum bendings found in 22 specimens from 6 insect orders, during short distance flights or hovering in a flight chamber (exposure time 1 / 4000 -1 / 8000 s), and in the bees wool during landing in free nature (1 / 1000s) are described and demonstrated in video prints. A scheme for classifying bending effects is given. The latter are generally much higher in flights under load [Hymenoptera: Sphecidae: Cerceris quadrifasciata Panzer (+ sandbees), Oxybelus uniglumis Linnaeus (+ flies), Philanthus triangulum Fabricius (+ honeybees) than in free flight, thus signalling higher aerodynamic wing loads. Especially the latter morphological changes should be taken into account when calculating wing statics under extreme loading conditions.

The chevron folding instability in thermoplastic elastomers and other layered materials

When thermoplastic elastomers (TPEs) such as styrene-isoprene-styrene or styrene-butadiene-stryrene copolymers in an aligned lamellar or hexagonal morphology are stretched perpendicularly to the plates or rods, then above a critical stress the lamellae or cylinders buckle to form a chevron or zig-zag structure. We examine this instability both analytically and using finite element analysis. In the analytic work we treat the elastomer as if it were a homogeneous anisotropic material and describe the chevron formation in terms of strain fields at length scales larger than that of the microphase pattern. We find that in order to do this one must respect the underlying microphase structure in two respects: (i) in terms of a statement as to how the material anisotropy rotates with the material; and (ii) in terms of additional `material moduli' which represent couplings between the macroscopic strain fields and deformations that occur at the microphase length scale. We define moduli which relate to hard phase bending and to displacement of the soft phase relative to the hard phase. The analytical results are tested by comparison with finite element models which solve for the microscopic strain field, and which allow the examination of post-buckling behaviour. We find that for perfectly aligned TPEs there is a geometric instability towards a sinusoidal buckling profile, which evolves into the chevron shape on further strain beyond the instability. The buckling is associated with a sharp turnover in the stress-strain curve. We also set our work in the context of treatments of similar buckling instabilties found in the fields of structural geology and liquid crystals.

Work environment and low back pain: the influence of occupational activities.

OBJECTIVES: To find associations between the prevalence of low back pain and occupational activities. METHODS: Interviews of a random sample of 5185 19-59 year old Danish employees analysed by logistic...