Steel Core Research Articles

Analysis on the crimping quality of overhead transmission line conductors considering equivalent cross-sectional stiffness

Approximately 58% of wire failures are caused by slippage and fracture of electrical connectors, and the crimping quality analysis of connectors is based on equivalent cross-sectional stiffness. First, a JL/GLA 400/35 steel cord aluminum strand and NY-400/35 strain clamp are selected to fabricate 26 groups of specimens with different pipe penetration depths, opposite edge distances, inner diameters of the aluminum tube, and die widths. Then, through crimping tests on the aluminum tube and conductor and the steel core and steel anchor, five main crimping failures, namely, the slip at the outlet of the clamp, the slip at the outlet of the clamp with some broken aluminum strands, fracture of the aluminum tube in the non-pressure area, wire fracture at the outlet of the clamp, and separation of steel anchors, are observed. Finally, a failure analysis method for conductor crimping is proposed based on equivalent cross-sectional stiffness. Through the analysis of grip force and crimping quality, four failure modes and simplified curves of the load–displacement curve are obtained, and the failure principle of the conductor crimping is further elaborated. The results show that the stress release caused by the steel core and steel anchor of the crimping wire and the crimping aluminum tube and wire is the main reason for the slippage and fracture of the transmission line conductors and that it is also the key to improve the installation quality of the transmission line.

Calculation and analysis of ampacity and stress of overhead transmission line

To ensure the safe operation of a transmission line, it is necessary to study the radial temperature rise and the stress and strain distribution of the transmission line under on-load state. A three-dimensional solid finite element model of reinforced aluminum conductor steel was established, and the temperature and stress distribution of the conductor were calculated. The effects of operating tension, wind speed, and radial temperature difference on the temperature and stress distribution were analyzed. The radial temperature difference increases about 1.40–3.16 °C with the rise of the mean temperature of the conductor. When the ambient temperature decreases from 20 to −40 °C, the mean temperature of the conductor decreases from 50.34 to −9.31 °C, and the external layer stress increases from 44.59 to 60.19 MPa. At the same time, the external layer stress of the conductor increases with the increase in wind speed and operating tension. The stress of the outermost aluminum conductor of the conductor under the radial temperature difference load increases with the rise in the temperature difference, and the stress of the inner aluminum conductor and the inner steel core decreases with the rise in the temperature difference.

Theoretical analysis and design of fire protection and thermal insulation of parallel wire or strand cables

In this study, a transient heat flow model has been established for parallel wire or strand cables at high temperature by employing the lumped thermal mass approach, and the numerical solution of the surface temperature as a function of time in each layer of the steel wire or strand inside the cable was calculated. Accuracy of the theoretical method is verified through uniform heating test of 73Φ15.7 mm steel strand cable. The results calculated show that temperature field inhomogeneity of cable section is overestimation on the condition that heat conduction inside the cable is not considered. Considering heat conduction or not, the maximum temperature difference of the core steel stand at the same time point is 373 . Unprotected 73Φ15.7 mm cable is damaged in only 12 min in UL1709 fire, and arrangement of fire protection layer around cable can effectively retard the temperature rise of cable surface. The experimental results are in good agreement with the theoretical calculation values in early stage of fire, and the temperature difference between the two is within 10%. Besides, the numerical calculations were analyzed in accordance with the fire protection requirements limiting the surface temperature of cables. It was observed that the minimum thickness of the fire protection layer required to meet the PTI DC45.1-12 standard was linearly related to the numerical value of the section factor of the outermost layer of steel wires or steel strands in the equivalent model, and the slope of the function was approximately equal to the conduction coefficient of fire protection layer, as the cable was subjected to fire for 30 min. Further, based on this, a simple method was proposed to calculate the minimum thickness of the fire protection layer for parallel wire or strand cables.

Experimental and numerical investigations on large‐section rectangular CFT columns with distributive beam under axial compression

SummaryIn order to improve the co‐working performance between the core concrete and steel tube for large‐section rectangular concrete‐filled steel tubular (LSCFT) columns when a vertical load is directly applied to the steel tube, a distributive beam is proposed as a load transferring measure. Four scaled LSCFT column specimens with different details were tested under axial compression to investigate the mechanical behavior and load transferring mechanism of the LSCFT columns with a distributive beam. The experimental results indicated that the bearing capacity of the LSCFT columns without a distributive beam was close to the yield capacity of the steel tube and the load shared by the core concrete was negligible. In contrast, the specimen with a distributive beam and inner stiffeners could bear a much higher load. In addition, refined nonlinear finite element models were developed to further analyze the load‐transferring mechanism of LSCFT columns with different details. The numerical results showed that the ultimate load of the specimen with a distributive beam and inner stiffeners was much closer to the theoretical value calculated from Chinese code CECS159:2004. Setting a distributive beam and inner stiffeners simultaneously in LSCFT columns could ensure the cooperation between the core concrete and steel tube.

Design of a New Puncture Needle for Trocar

To develop a new type of puncture needle for indwelling needle, which can overcome the performance problems of the existing puncture needle, reduce producing cost, and enhance clinical operability. In this design, solid needle thread is used to replace the traditional hollow pipe thread, three cutting edges are used to replace the existing two cutting edges, and the shaft edge form (the needle tip is on the needle thread's axis) is used to replace the original back blade or edge blade; the slot on the side of the solid core wire is used to replace the hollow and side hole on the traditional pipe. Finally, a new solid core puncture needle is formed by a section of solid core steel wire with a spiral groove, the cross-section of which is a circular slotted needle with a triangular shape at one end. Through the comparative analysis of stiffness mutation and puncture force in the experiment, the characteristics and advantages of new puncture needle are reflected. The new solid core needle can meet the need of puncture in the course of treatment, and can avoid the potential risk caused by the rigidity mutation of the needle used in the traditional indwelling needle, at the same time, it also has the space to reduce the demand of needle diameter, that means it has the potential to develop smaller needle products. The new type of trocar puncture needle, from hollow to solid core, can not only meet the basic requirements of puncture and observation of blood return, but also can avoid the risk of traditional puncture needle due to stiffness mutation, the utility model also has the advantages of better performance (less puncture force) and larger expansion space.

Study on buckling-restrained braces using multiple round steel core bars

This study proposes a novel buckling-restrained brace (BRB) using multiple round steel core bars to increase the feasible strength of BRBs utilizing steel bars with roll-threaded screw ends. The buckling restraining members of the proposed BRB consists of multiple primary tubes and a secondary tube. The primary tube directly restrains the buckling of each core bar, and the secondary tube restrains the buckling of the primary tube through spacers. This paper first describes the configuration of the proposed BRB and the design method of buckling restrainers, in which the spacer spacing is assumed to be the buckling length of the primary tube. Subsequently, cyclic loading tests of three specimens with different spacer spacing are presented to demonstrate the mechanical behavior of the proposed BRB, such as the hysteresis behavior, axial force, and bending moment of the primary tubes. The test results indicated that fulfilling the requirement of spacer spacing is essential for achieving stable behavior of the primary tubes and steel core bars. Finally, finite element analyses of buckling-restrained units of the proposed BRB with different combinations of primary tubes and spacer spacing are presented to verify the design method. The results of the parametric analyses indicated that the proposed design formula can provide a conservative evaluation of the stability of the primary tube.

The Effect of Drawing in Conventional and Hydrodynamic Dies on Structure and Corrosion Resistance of Hot-Dip Galvanized Zinc Coatings on Medium-Carbon Steel Wire.

The paper presents the impact of the drawing method on the microstructure and corrosion resistance of galvanized steel wires. The microstructural tests confirmed that, in the drawing speed range v = 5–20 m/s, the use of hydrodynamic dies creates more favorable conditions for the deformation of the soft zinc coating on the hard steel core. The increase in friction at the wire/die interface in the conventional method, as compared to the hydrodynamic method, contributed to the decrease in coating thickness and the increase in the diffusion layer, and the higher the drawing speed, the greater the differences between the analyzed drawing methods. In the conventional method, while drawing at high speeds v = 20 m/s, there was a two-way diffusion and complete remodeling of the ζ phase in δ1. In the hydrodynamic method, at the speed of 20 m/s, in the analyzed micro-areas, places showing the presence of the ζ phase, partially dispersed in the layer with pure zinc, were observed. A corrosion tests comparison between conventionally and hydrodynamically drawn wires showed an improved behavior of the latter. The greater mass in the surface layer of pure zinc, a substrate for the corrosion product in hydrodynamically drawn wires, reacted, creating insulation from the white corrosion produced. The compressive stresses in the hydrodynamic dies caused by the high pressure of the lubricant on the circumference of the wire closed the microcracks on its surface, which additionally sealed the zinc coating.

Experimental investigation of effect of changing gap size in buckling restrained braces

This experimental study investigates the effect of changing the debonding gap between the core and the mortar filler on the global stability of BRBs using different cross-section restrained members. A total of eight mortar-filled BRBs were produced using a rectangular cross-section steel core and two different restraining members, a circular hollow cross-section (BRB-C series) and a square hollow cross-section (BRB-S series). In choosing the gap sizes, the gap limit formulas in the literature were considered. Not exceeding the limits of the gap, 2.8 mm, 5.6 mm, 8.4 mm, and 11.2 mm gaps were left as the multiples for the radius of inertia of the rectangular cross-section core in the BRBs. All specimens were subjected to displacement-controlled axial cyclic loading. As a result, failure modes, hysteretic performance, energy dissipation, and ductility were summarized and analysed for each specimen. The results showed that the specimens had a better structural performance with a 2.8-mm gap size, which is the radius of inertia of the core. Furthermore, the local buckling modes throughout the core increased in number as the size of the gap decreased, thus raising the members' axial load capacity and energy dissipation. It was concluded that the best structural behaviour of the tested series was provided with the smallest gap of 2.8 mm, better behaviour in energy dissipation may be obtained with smaller gap sizes. However, in this case, it is more likely to increase buckling at the gusset plates and cause local deformations with the end of the restraining members.

New Self-Repairing System for Brittle Matrix Composites Using Corrosion-Induced Intelligent Fiber.

Brittle matrix composites such as concrete are susceptible to damage in the form of cracks. Most of the current self-repair and self-healing techniques have repair limits on crack widths or high costs of an external stimulator, or have an unfavorable effect on the composite’s strength. This paper proposes a new concept of corrosion-induced intelligent fiber (CIF) and a new self-repairing system that uses the CIFs to close cracks in brittle matrix composites within a corrosive environment without external help, and without compromising the strength. The CIF comprises an inner core fiber and an outer corrodible coating that are in equilibrium, with the core fiber in tension and the corrodible coating in compression. The preparation steps and shape recovery mechanism of the CIF and the self-repair mechanism of the CIF composites are explained. Based on these concepts, this paper also describes several mechanical models built to predict the magnitude of pre-stress stored in the core fiber, and the maximum pre-stress released to the matrix composites, and the minimum length of the reliable anchor ends of CIF. The sample calculation results show that the recovery strain was 0.5% for the CIF with the steel core fiber and 12.7% for the CIF with the nylon core fiber; the maximum crack closing force provided by the CIF to concrete can be increased by increasing the amount of the CIFs in concrete and the initial tensile stress of the core fiber. This paper provides some suggestions for enhancing the self-repair capability of brittle composites in complex working environments.

Localized magnetic properties measurement of interlocking core laminations

PurposeIn rotational alternating current machines, interlocking is a commonly used manufacturing method to fix laminated silicon steel cores. The purpose of this study is to measure the localized magnetic properties more comprehensively and to analyze the deteriorated magnetic properties caused by interlocking more accurately.Design/methodology/approachA movable B–H sensor is designed in this paper. The localized magnetic properties measurement was performed to investigate the magnetic properties around the interlocks with various sizes, various orientations and various numbers of laminations. Then, the damaged area caused by the interlocking was quantified, and the magnetic degradation of different degrees is layered.FindingsThe measurement results have shown that the interlocks with larger sizes, along the transverse direction and on 10-layer laminate, will lead to more serious magnetic degradation, and the maximum loss increment can reach up to 70%.Originality/valueThis work is an improvement and optimization based on the previous overall magnetic measurement of the interlock. The quantitative results of the localized magnetic measurement will have a certain significance for the accurate modeling and simulation of the electrical machines and provide valuable guidance for the optimization of the actual production process of the motor.

Comparison of Structural, Microstructural, Elastic, and Microplastic Properties of the AAAC (A50) and ACSR (AC50/8) Cables after Various Operation Periods in Power Transmission Lines

In modern economic infrastructure, Al cables of overhead power transmission lines are used both without and with a steel core (respectively, all aluminum alloy conductor (AAAC) and aluminum conductor steel reinforced (ACSR) cables). In this article, the changes in structural, microstructural, and elastic-microplastic properties have been analyzed for the outer wires of the AAAC (A50) and ACSR cables (AC50/8 cables with a steel core of ~8 mm2 cross-section, hereinafter referred to as AC50) with the cross-section of the stranded conductor of ~50 mm2, which were in operation for 0–20 years in the Volgograd region of Russia. Using the techniques of X-ray diffraction, electron backscattered diffraction, densitometry, and the acoustic method, the structural and microstructural features of the wires have been compared and found to be correlated with their elastic-microplastic properties. It has been ascertained that the presence of a steel core in AC50 leads to a decrease in the defectiveness of the near-surface layer of their aluminum wires. Compared with A50 cables, the development of void defects in the near-surface layer of Al-wires of AC50 cables slows down (by ~1 year with a service life of ~10 years and by ~3 years with a service life of ~20 years).

Mechanical Behavior of Concrete-filled Steel Tubular Space Intersecting Nodes in High-rise Oblique Diagrid Tube Structures

In recent years, the researches on concrete-filled steel tubular (CFST) intersecting nodes mainly focused on the plane intersecting nodes, while that on space intersecting nodes with off-plane angles was relatively less. In this study, the nonlinear analyses of CFST space intersecting node models established in ABAQUS were performed under the monotonic axial compression and reciprocal axial tension-compression loads, respectively. The stress distributions of steel tubes and core concrete were analyzed, and the hysteresis characteristics and stiffness degradation of the node were studied. The in-plane angle, off-plane angle, out-of-plane constraint effect, steel tube diameter-to-thickness ratio, and core concrete strength were used as control parameters to analyze their effects on the mechanical behavior of the nodes. The results show that the bearing capacity of the nodes meets the design requirements, the hysteresis loop is full, the initial stiffness is large and the stiffness degrades slowly. The off-plane angle, out-of-plane constraint effect, steel tube diameter-thickness ratio and core concrete strength have significant effects on the bearing capacity and lateral stiffness of the nodes. In order to reduce the adverse effect of out-of-plane displacement, the space intersecting nodes in practical engineering can use reinforced floor beams or prestressd cables to impose out-of-plane constraint, and the recommended value of out-of-plane constraint effect is 10–30 kN/mm.

Performance of Bolt-Welded CFST Short Columns with Different Initial Imperfections: Experimental and Numerical Studies

Gap between the steel tube and core concrete of Concrete-Filled Steel Tube (CFST) members is regarded as an initial imperfection, which may exist in the CFST arch bridge due to construction process problems. In this paper, based on the design scheme of the bolt-welded joints in arch rib columns of an extra-long span CFST arch bridge, the effects of two types of initial imperfections, interfacial gap and spherical-cap gap, on the mechanical properties of Bolt-Welded CFST (BWCFST) short column under axial compression were investigated. Axial compression tests were conducted on three column specimens with spherical-cap gap, three specimens with interfacial gap, and one normal specimen without imperfection. A Finite Element Analysis (FEA) model was developed to further investigate the behavior of the BWCFST short columns, and was validated by the experiment.

Multiple ballistic damage of segmented SiC/BN laminated ceramic composite armor

This article investigated the structure of the laminated ceramics to improve the multiple ballistic performance of segmented ceramic composite armors. The multiple ballistic experiments were conducted with 5.8 mm caliber steel core bullets at the impact velocity of about 920 m/s. The experiments verified that two laminated SiC/BN structures (GLC and ULC) exhibit higher residual ballistic performances than the monolithic SiC structure (MC). Moreover, through damage evolution analysis, two laminated SiC/BN structures (GLC and ULC) exhibit less sensitivity to the multiple ballistic impacts damages, and possess more energy absorption mechanisms than the monolithic ceramics. The structure design of the laminated of ceramics is beneficial for improving the multiple ballistic performances of composite armors and reducing the crater deformation.

A Study on Multi-Objective Optimization of Large Deformable Elastic Plates

Metallic yielding dampers are damaged early before the main frame during earthquakes and take over the damage of the main frame. Under the assumption of the main frame elasticity, both maximum and residual deformation are expected to be reduced. However, the main frame may be damaged, and the assumption of the main frame elasticity may not hold under major earthquakes. However, large deformable elastic plates have larger yielding deformation than standard steel core plates of the damper and can be used as braces to reduce the seismic response of buildings. This study presents a simple definition of design variables for a topology optimization problem involving large deformable elastic plates with rectangular shapes. As bi-objective functions, yielding deformation and yielding force capacity maximization were used. The optimization results were compared with the findings of a previous study. Finally, the efficacy of the braces was verified by experimental tensile tests. The obtained results are as follows. (1) A distinct trade-off relationship was obtained between tensile yielding deformation and tensile yielding load through muti-objective optimizations using the proposed formulation. (2) The Pareto fronts using the proposed formulation were almost identical to the findings of the previous study. (3) While the experimental test results of yielding tensile load are overestimated by the analysis results by the 10 mm rough grid elements, the test results almost correspond to reanalysis results with the 2.5 mm fine grid elements.

Effect of the Microsand Fraction on the Ballistic Resistance of UHP-SFRC

This work investigates the effect of various sand fractions on the ballistic resistance of ultra-high-performance steel-fibre-reinforced concrete (UHP-SFRC) samples. We specifically investigated replacing expensive and generally inaccessible microsands with commonly available sands. The tests and the measured values show that replacing part of the microsand with the more commonly and economically acceptable 0/2 mm aggregate fraction minimises the resulting mechanical properties and ballistic resistance. The most common type of ammunition was used to test all sample bodies, which is a 7.62 × 39 mm calibre with an all-metal jacket and a mild steel core. The damage’s extent and mode were determined using a 3D scanner operating on photogrammetry.

Analysis of ACCC failure of composite core glass transition temperature reduction due to brittle damage

The failure analysis of the Aluminum Conductor Steel Reinforced (ACSR) was often based on conventional failure methods such as strength and fracture, and the failure analysis of the Aluminum Conductor Composite Core (ACCC) usually followed the analysis methods of the ACSR. This research proposed a new ACCC failure mode based on the glass transition temperature (Tg) of composite materials. In this paper, a fracture accident of a 500 kV overhead transmission line was discussed. Firstly, impact test found that composite core of the ACCC was more brittle than steel core of the ACSR, and the brittle damage of the composite core was inferred as the cause of the accident in combination with fracture analysis. Then, thermal-structural coupling analysis showed that the axial stress of aluminum wires increased to 33 MPa after the brittle damage of the composite core. Subsequently, thermoelectric coupling analysis showed that the operating temperature (T) of conductor was raised to 151 °C after the increment of the axial stress of the aluminum wires. Finally, in dynamic mechanical analysis, it was shown that the Tg of faulty composite core was reduced to 146.3 °C. According to investigation, the T of conductor was greater than the Tg of epoxy resin in the faulty composite core, resulting in a decrease in the tensile strength of the composite core, which eventually led to the ACCC failure. The failure mechanism proposed in this paper can provide a reference for the prevention and maintenance of ACCC lines in power grid system.

ЗАХИЩЕНІ ІЗОЛЯЦІЄЮ ПРОВОДИ ДЛЯ ПОВІТРЯНИХ ЛІНІЙ ЕЛЕКТРОПЕРЕДАЧІ НА СЕРЕДНЮ НАПРУГУ: ПЕРЕВАГИ, КОМПЬЮТЕРНІ РОЗРАХУНКИ

The paper presents the advantages of protected insulated wires for medium-voltage (up to 35 kV) overhead power lines compared to the lines with traditional non-insulated wires. The mathematical model is developed and the computer calculations are realized for a 20 kV protected insulated wire with a steel-aluminum core. For such design, the distributions of the magnetic field and current density in three wires of overhead power line are analyzed, their resistance is determined taking into account the nonlinear properties of the steel core within the frequency range of 50–10000 Hz. This makes it possible to compute the electrical losses in the conductors of the power lines under the transient conditions and at high harmonics in the power network. References 8, figures 4.

Nondestructive Testing of Local Incomplete Brazing Defect in Stainless Steel Core Panel Using Pulsed Eddy Current.

Stainless steel core panel is a novel structure for fast modular building, but its brazing foils are susceptible to defects due to the difficulty of precisely controlling the brazing process. An automated, nondestructive testing technique is highly desirable for quick inspection of the brazing defects buried in the stainless-steel core panel. In this paper, pulsed eddy current testing (PECT) was employed to inspect local incomplete brazing defects. Finite element simulation and experiment verification were conducted to investigate the feasibility and effectiveness of the proposed method. The peak value of the PECT signal was found to be sensitive to the presence of the defect. With the aid of an industrial robotic arm, line and two-dimensional scans were performed of the PECT probe above the panel specimen. The prefabricated incomplete brazing foil was successfully imaged as a notched ring, whose opening coincides with the physical length of the missing brazing. The proposed method shows potential to serve as an effective tool for in-line or off-line automated nondestructive testing of the brazing defects in stainless steel core panels.

Study on ballistic impact behavior of Al alloys against two different shapes of steel core projectiles

In this study, a relation between the quasi-static, dynamic compressive and ballistic impact of 7055 and 7075 Al alloys was made. The results showed that the ultimate tensile strength, hardness and absorption capacity were considerably higher in 7055 Al alloy compared to 7075 Al alloy. Consequently, 7055 Al alloy exhibited superior ballistic impact resistance (low depth of penetration) against different shapes of 7.62 mm soft steel core projectiles. The microstructure evolution after ballistic impact revealed gradient variation of strain rate away from the crater which assists in the nucleation of different deformation zones, i.e., fine grain zone (FGZ), high-density deformation zone (HDZ) and low-density deformation zone (LDZ). These zones were confirmed through optical micrographs, hardness, stress-strain and XRD analysis. The strong texture {111} component was changed to the {111} and {200} component in HDZ and LDZ, which also assists in understanding that the deformation was more complex in these regions. Therefore, a model was proposed for the nucleation of fine grains near the crater. In addition, fracture morphology was different under each loading condition and a transitional effect is observed from quasi-static loading to ballistic impact loading. These interesting features can further enhance the understanding and the development of Al alloys in aerospace and military applications.