Outer Wire Research Articles

Cellular Automata-Based Experimental Study on the Evolution of Corrosion Damage in Bridge Cable Steel Wire

Cable-stayed bridges have become the preferred bridge type for large-span bridges due to their unique advantages, and the long-term performance of the cable under the extreme conditions has been facing great challenges. An accelerated corrosion test was carried out using in-service cable, and the evolution model of the etch pit was established based on cellular automata to study the evolution law of corrosion damage to steel wire. This study showed that with the increase in the number of dry-wet cycles in the electrified accelerated corrosion, the macro- and micromorphology of the steel wire showed more serious corrosion damage, the tensile strength decreased, the ductility index decreased, and the tensile strength of the steel wire after corrosion decreased by nearly 5%; the geometric dimension of the steel wire etch pits all met a right-skewed distribution with a broader range of etch pit depth, mainly consisting of shallow spherical etch pits and deep ellipsoidal etch pits. The length, width, and depth sizes were mainly distributed in the range of 0.005 mm to 0.015 mm, 0.005 mm to 0.02 mm, and 0 mm to 0.04 mm; at the early stage of corrosion, the etch pits were first developed along the longitudinal direction. As the corrosion process progressed, the iron matrix participated in the electrochemical reaction, leading to the rapid expansion of the etch pits’ dimensions. The stress concentration effect at the bottom of the etch pit caused the maximum stress to approach 1800 MPa, with a stress concentration coefficient of more than 3.0; when the cable anchorage system was located in the connecting sleeve and the threaded splice seam, where corrosion protection was prone to failure, the outer steel wire bore most of the corrosive effects, and the internal cable was less eroded by the corrosive medium.

Analysis of the bending performance of unbonded flexible risers

ABSTRACT As the key equipment for offshore oil and gas production systems, the unbonded flexible riser (UFR) is subjected to extensive interlayer and intralayer non-linear contact and slip that make it difficult to analyse its bending performance. In this paper, by combining the theoretical model of bending of the UFR with the finite element model, the influence of the number, width, external pressure and coefficient of friction of tensile armour wires on its bending performance was studied. The results showed that the non-slip bending stiffness of the UFR decreased by 3.20 and 23.35 kN·m2 every time one of the outer tensile armour wires was removed and the width of the wires was reduced by 0.3 mm, respectively. The external pressure and coefficient of friction did not influence its bending stiffness in the non-slip and complete slip stages, and were linearly related to the curvature of the critical slip.

Comparative performance analysis of straight and harped prestressing seven-wire strands: High-strength stainless steel vs. conventional carbon steel

This paper presents an experimental investigation into the utilization of high-strength stainless steel (HSSS) strands systems in prestressed bridges. The study delves into the effects of localized bent and harping of seven-wire HSSS strand systems under various harping angles and curvatures produced by the deviators. For comparison purpose, conventional carbon steel (CS) strands were also studied using the same experimental parameters. It was anticipated that CS strands would exhibit better performance due to its superior post-yied ductility. To closely mimic the state of practice in the precast plant, two types of deviators were designed and used in this investigation. A comparable harping capacity was observed for HSSS strands relative to CS strands, despite the CS strands exhibiting higher strain compared to the HSSS strands. Upon reaching their breaking load, necking of all seven wires was predominantly observed for HSSS, whereas the CS strands failed due to the fracture of only one or two outer wires. Due to the lack of ductility in the HSSS stand, it was expected to have the lower bent capacity, especially at higher harping angles. Despite the significant difference in post-yied ductility, the study revealed that both HSSS and CS strands exhibit similar performance. To further understand the similarity and difference in behaviour of these two materials, scanning electron microscopy (SEM) examinations were conducted on both HSSS and CS wires to visualize the bending effects on the microstructure level after bending the center wire at different angles.

Analysis of the quality of aluminum overhead conductors after 30 years of operation

Overhead power conductors (OHL), which are installed in transmission and distribution lines, are designed for a service life of min. 30–50 years. During this time, the OHL conductors should work in a safe and fault-free state with the highest current capacity. This article refers to the testing of aluminum conductors after 30 years of operation. The mechanical properties and structural characteristics of the conductor were tested. The analysis of the quality of the supplied wire samples carried out with a scanning microscope allowed us to distinguish three types of wire damage, namely: corrosion on the surface of the outer layer, wires, local melting, and loss of cross section and wire breakage. On the basis of a detailed analysis of the areas of damage to wires from the tested OHL conductors, it can be stated that the main cause of their breakage is local smelting areas caused by an electric arc.High temperatures affect local material melting, leading to a large reduction and the consequence of strength decreasing. This situation leads to the loss of the conductor's carrying capacity and ultimately to its destruction. During 30 years, conductors had to be subjected to frequent short circuits caused by changing weather conditions, i.e., high wind or storms. The paper dealt with the results of the mechanical properties test, which showed that the aluminium wires are lower than those required by the standard. The greatest degradation of the strength properties occurs on the wires of the outer layer of conductor. The center wires show a negligible reduction in tensile strength.

Study on method of controlling interaction between wires of Galfan spiral strands

This paper presents a method of controlling the interaction between the wires of Galfan spiral strands. Axial tensile tests were carried out on 1 × 7, 1 × 19, 1 × 37, and 1 × 61 strands. The material properties of the wire, the bearing capacity of the strand, and the surface strain of the outer wire were measured. The wear of the wire after loading was observed by cutting open the 1 × 7 strand and the 1 × 19 strand. The initial contact state between the wires was then determined by calculation and modelling. The contact state between the wires under load was analyzed by ABAQUS. Finally, the contact pressure caused by the interaction was investigated. The method of controlling the maximum contact pressure was developed. A formula for the complete elimination of the maximum contact pressure was also proposed.

Mechanical Behavior of Cross-Winding Steel-Wire–Reinforced Thermoplastics Pipe under Internal Pressure

Cross-winding steel-wire–reinforced thermoplastic pipes (CSWRTPs) have been widely applied in oilfield gathering environments in China because of their excellent physical properties. In this study, the failure mode, short-term burst pressure, and strain for a CSWRTP with an external diameter of 75 mm and a wall thickness of 10 mm under internal pressure are investigated through experimental measurements conducted with a burst test system and simulations completed with ANSYS software. A new three-dimensional finite-element burst failure model of CSWRTPs is proposed. Simulation results are in good agreement with the measurements. An axial ductile crack was found on the tested pipe with an uneven circumferential expansion deformation. The simulated short-term burst pressure is in a good agreement with the measured value (19.7 MPa) with an error of +8.7%. The growth of the strain is initially zero, followed by a linear growth, rapid growth, and a clifflike drop when the crack is generated. The effective plastic strain within the inner polyethylene liner is greater than that within the outer polyethylene sheath, and the effective stress within the inner steel wire is greater than that within the outer steel wire. The ultimate pressure–bearing capacity decreases linearly as the strength of the steel wire decreases. Therefore, reduction of the ultimate pressure–bearing capacity of CSWRTP results from the decrease of steel wire strength from corrosion when applied in oilfield gathering systems. This finite-element analysis method can provide a reference to optimize the structural design of CSWRTP.

Corrosion Damage Evolution Study of the Offshore Cable-Stayed Bridge Anchorage System Based on Accelerated Corrosion Test

The cable-stayed bridge anchorage system is prone to serious corrosion problems in the offshore environment, threatening its service safety. Based on the copper accelerated salt spray (CASS) test, the anchorage system was subjected to accelerated corrosion and then dissected along the axial direction to study the corrosion damage evolution of the internal structure. This revealed the evolution of corrosion damage in the anchorage system of offshore cable-stayed bridges. The results show that in the offshore environment, a large number of corrosion factors enter the interior of the cable anchorage system through the splicing seam at the junction of the anchor cup and the connecting barrel, and spread to both ends, thus causing corrosion damage to the anchor cup, connecting barrel, filling medium and cable steel wires. Inside the cable of the anchorage system, cross-sections with a higher corrosion level on the outer circle steel wires will also have a higher overall corrosion level. The outer circle steel wires are less able to meet the strength requirements, because they withstand most of the corrosion effects, and the corrosion pits on the surface of the steel wires will render them much weaker than the design tensile strength and fracture. After the CASS test, the ductility of cable steel wires decreases from the inner circle to the outer circle, and the higher the corrosion level of steel wires, the more obvious the brittle indications; the steel wires tend to undergo brittle failure. In the design and manufacture of the cable-stayed bridge anchorage system, special attention should be paid to the corrosion protection of the splicing seam, as well as the corrosion condition and residual strength of steel wires in the outer circle of the cable, to delay the degradation of the mechanical properties and brittle damage of the anchorage system.

Low-cycle tensile fatigue performance of a wire rope strand with an internal flaw in varied position and direction

Taking into account the effects of mean stress, elastic-plasticity and nonlinear contact, the finite element model of the tensile fatigue performance of an internal flawed wire rope strand is built by using the local stress strain method in the present study. A mesh model of the strand with a high-precision feature is established through a block-based method and refinement in the flaw region. The strand with a flaw is investigated to explore its fatigue life distribution, and the effects of the flaw’s position and direction on the strand’s fatigue and bearing performances are analyzed. The numerical results demonstrate that the low-cycle fatigue life zone occurs at the interwire contact region of the intact wire rope strand, while is located at the flaw region of the wire rope strand with an internally flawed wire. The minimum fatigue life of the wire rope strand decreases due to the occurrence of the internal flaw. Moreover, as the internal flaw’s direction angle decreases, the strand’s minimum fatigue life is reduced, and the internal flaw with the major axis perpendicular to the strand axis is the most dangerous. The internal flaw in the outer wire has a more severe influence on the fatigue property of the wire rope strand than a core wire flaw with the same dimension and direction. The wire rope strand is more prone to stress yielding due to the internal flaw, and the effect is getting more significant as the internal flaw’s direction angle decreases.

Алгоритмизация задачи видеоскопического контроля состояния стальных канатов

The paper considers the problem of monitoring the technical state of steel ropes used in industrial and civil installations, such as elevators, cable cars, lifts, etc. To date, the assessment of the state of steel ropes and the safety of their operation is carried out mainly through visual-instrumental control, which is long in time and subject to the influence of the human factor, which determines the relevance of the task of automating this process using computer technology and artificial intelligence methods in order to improve the quality of the assessment, reducing the check interval, detecting defects in steel ropes at an early stage. The article proposes two approaches to the algorithmizing of the problem of videoscopic control of the state of steel ropes using computer vision technologies, based on software modeling of the logic of visual analysis and machine learning methods, such as deep learning artificial neural networks. The authors have developed algorithms for automatic detection of the main types of defects in images of the surface of steel ropes: increase/decrease in diameter, deformation in the form of rope, breaks in the outer wires, thermal and electric damage. The paper presents the results of preliminary testing of the developed algorithms and programs, the composition and methods for determining the main indicators for evaluating their effectiveness are proposed.

Tensile failure behavior of unbonded flexible riser with damaged tensile armor wires

Unbonded flexible risers (UFRs) connect surface production platforms to subsea production systems, and are therefore vital for tasks such as the transportation of oil and gas and the injection of water. The tensile armor layer is the main load layer of UFRs. Once this layer is partially broken, the safety of offshore oil and gas gathering and transportation is seriously threatened. In this study, an 8-layer UFR model is developed to calculate the effects of damaged inner and outer armor wires and boundary conditions on the tensile stiffness, ultimate load capacity, and stress distribution and load ratio of the inner and outer tensile armor layers. Broken inner tensile armor wires are found to have a greater impact on the tensile properties and produce the same torsional buckling failure mode as observed in the field. The influence of the pressure load on the ultimate load capacity of the UFRs is analyzed, and the results demonstrate that the outermost pressure increases the interlayer action between the tensile armor layers and the adjacent layers, thereby reducing the torsional angle of the UFRs under the ultimate tension. Additionally, the innermost pressure is found to have a negligible effect on the ultimate load.

Reliability assessment of parallel wire suspender components considering interlayer corrosion variance

The suspenders bear the repeated stress caused by various cyclic actions during the bridge operation while the stress amplitude under dynamic load is smaller than under dead load. The steel wire degradation process is a typical corrosion fatigue degradation, in which the initial defects caused by surface corrosion are the main source of fatigue cracks and the crack development under operating load leads to the failure of the steel wire. The steel wires of the suspender are considered as a co-deformed parallel structural system. The corrosion process of steel wires in different layers are different for the diffusion paths of corrosion medium, which makes the bearing capacity of steel wires differs from each other. The suspender strength depends on the wire of lowest strength due to the Daniels effect, interlayer corrosion variance should be considered in the evaluation of suspender reliability. This paper investigates the interlayer corrosion variance of parallel steel wire suspenders on the basis of neutral salt spray test. It proposes a corrosion variance coefficient, and considers the stochastic degradation process of suspender. Combined with the daily traffic model, it establishes a sophisticated reliability evaluation method of suspender. The results are shown: The steel wires in each layer of test specimens are all severely corroded when the corrosion time reaches a certain degree. For the specimens with different damage types, the overall corrosion condition of the annular damaged specimen is the most severe; whereas that of the vertical damaged specimen is the least. Under experimental environment, the corrosion variance coefficients of sheath damaged specimens follow normal distribution. In the application of suspender evaluation, the service lifespan of wires varies obviously with the corrosion variance coefficient. The distribution of steel wire lifespan under different corrosion variance coefficients also follows normal distribution. The service lifespan of outer layer wires is longer than inner layer wires, and the overall reliability lies between the reliability of outer and inner layers.

A New Detection Method Based on Magnetic Leakage Theory and BP Neural Network for Broken Steel Strands in ACSR Conductor

Aluminum conductor steel-reinforced (ACSR) conductor is characterized by inner tensile body of steel core and outer twisted aluminum wire strands, which is obviously different from common steel wire ropes (SWRs) or cables. However, the existing studies are mainly focused on the magnetic flux leakage (MFL) testing of the SWR defects, few or not related to broken steel strands in ACSR conductors. Thus, the leakage magnetic field distributions of SWR and ACSR defects are compared and analyzed by the theoretical and numerical calculations. By considering the nonconductivity characteristics of aluminum wire strands, the steel-air model is established to calculate the effects of fracture width and the number of broken steel strands on the MFL signal for ACSR conductors. Based on the spatial distribution characteristics of ACSR leakage field with low intensity, weak lifting-off effect, and weak circumferential correlation, a single-channel signal processing method with time–frequency domain coupling is proposed. Multiple sets of characteristic values of MFL signal both in time and time–frequency domains are extracted to construct a back propagation (BP) neural network for broken steel strand identification. The results have shown that the improved single-channel time–frequency analysis method has higher accuracy in identifying the ACSR fracture width and the number of broken steel strands compared to the image processing method with multichannel leakage data fusion. With the improved method, the detection error of the fracture width is less than 2 mm, and the accuracy of the number of broken strands can reach 91.67%.

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).

Bending Behavior of a Frictional Single-Layered Spiral Strand Subjected to Multi-Axial Loads: Numerical and Experimental Investigation

Bending deformation gives rise to interwire slippage for spiral strands subjected to multi-axial loads, and further induces wear or fatigue phenomena in practice. The interwire friction would resist bending deformation and lead to uneven tension distribution of individual constituent wires but little research has quantified these effects. To figure out this issue, a beam finite element (FE) is established, into which a penalty stiffness algorithm and a Coulomb friction model are incorporated. A series of free bending simulations are developed for parametric study on deflection near the terminations and tension distribution of individual wire for strands with different levels of length and friction coefficient as well as external loads. Based on the simulation results, it is found that strand length has little influence on bending deformation and tension distribution if the strand length exceeds six times the pitch length. A deflection formula extended from the classical Euler beam model well predicts the sag deflections and the relative error with respect to experimental measurements is less than 10%. Furthermore, additional axial tension induced by the friction is clearly characterized and an approximate expression is proposed to estimate tension distribution for outer layer wires. Its predictions are encouraging for longer strands.

Improvement in rotational performance by periodic tensile change of a torque transmission wire: basic experimental verification using a single straight wire

A parallel-wire driven system has the drawback of a narrow rotation range. To overcome this problem, this paper focuses on a ‘torque wire’, which consists of inner and outer wires and can transmit the inner wire rotation; the utilization of torque wires is effective in increasing the rotational range. However, significant degradation of the rotational transmission-accuracy is observed when a constant tension is applied to a torque wire. This degradation is attributed to the load in the tensile direction, which causes an increase in Coulomb friction at the sliding parts and an increase in the elastic torsion of the inner wire. Collectively defining the Coulomb friction and elastic torsion as a ‘disturbance’, this paper proposes a technique to suppress the disturbance and improve the rotational accuracy. This method applies a periodic change in tension to the torque wire. However, periodic tension induces lateral vibration due to parametric excitation. Thus, the amplitude and frequency of the torque wire are applied in several combinations for periodic tension as a preliminary experiment; the best combinations of amplitude/frequency with small lateral vibration are selected. The lateral vibration results are evaluated after Strutt-diagram-analysis. By using selected combinations, the usefulness of the method is experimentally confirmed.

Effect of time-varying corrosion on the low-cycle fatigue mechanical properties of wire rope

In this study, we investigate the macroscopic mechanical behaviour of wire rope corroded by seawater by analyzing the monotonic tensile and hysteretic behaviour of 6 × 19 S + IWR round strand steel wire ropes with different corrosion degrees. First, the wire rope samples were subjected to a full immersion accelerated electrochemical corrosion experiment, which revealed that the corrosion distribution is uneven, and that corrosion progresses from the outer wires to the inner wires through crevices in the wire rope. Scanning electron microscopy revealed that an increase in corrosion increases the number, length, and depth of microscopic cracks on the surface of the wire rope. The degradation effect of corrosion on the mechanical properties of wire rope differs significantly. As corrosion increases, the bearing and deformation capacities decrease substantially, and the fracture mode changes from ductile to brittle fracture. Based on the mechanical characteristics and the influence factors of a steady stress–strain cycle of a corroded wire rope, we proposed a hysteretic mechanical model consisting of a loading and unloading curve. The proposed model was verified using the experimental data, and can accurately reflect the influence of the corrosion degree and loading amplitude on the hysteretic characteristics of a wire rope.

Study on bending fatigue failure behaviors of end-fixed wire ropes

Torsional fatigue always exists after a wire rope is put into use, which results in damage aggravation and lifespan reduction. This study is aimed at exploring the comprehensive tribo-fatigue behaviors of wire rope considering torsional fatigue. To achieve this aim, a new type of self-made fatigue testing machine was introduced, and the bending fatigue tests were carried out. Furthermore, the diameter shrinkage ratio, the number and distribution of broken wires under different fatigue times were studied by means of manual detection and non-destructive testing. Moreover, the fractures and wear scars were investigated with the aid of the LW200-4JT optical microscope system. For the thicker outer wire of spiral strand (SS), the influences of bending fatigue times on the evolution of wear parameters were comparatively analyzed. The research results are as follows. With the increase of bending fatigue times, the diameter shrinkage ratio increases, and the increase decelerates gradually. The artificial statistical results agree well with the non-destructive testing results. To be specific, the broken wire develops slowly in the early stage of fatigue, whereas it develops rapidly when the fatigue times exceed 60,000. The broken wire is highly concentrated in the thicker outer wire of SS 1. The maximum width and depth of wear scars of the thicker outer wire of SS 1 increase with the increase of cycles. The values of the two parameters at different contact positions follow the order: contact with the pulley > contact with the adjacent SS 1 > contact with the SS 2 > contact with the wire in the adjacent layer in the same strand. This study is expected to find the fatigue failure rules of end-fixed hoisting wire rope, thus providing a basis for improving the safety of mine hoisting.

Effect of the thickness of polyethylene insulation on flame spread over electrical wire with Cu-core under AC electric fields

Effect of the thickness of polyethylene (PE) insulator on flame spread over electrical wire with high thermal conductivity of Cu-core is experimentally investigated by varying the applied AC voltage (VAC) and frequency (fAC) in the ranges of 0 – 5 kV and 0 – 1000 Hz, respectively. Three outer wire diameters (Dout= 0.8, 1.1, and 1.5 mm) with the same core diameter (Dc= 0.5 mm) are used. For the baseline cases without applying electric field, the flame spread rate (FSR) decreases with an increase in the outer wire diameter. When AC electric fields are applied to the wires, flame shapes and FSRs are appreciably influenced. The FSR behaviors with AC electric fields are classified into four sub-regimes as the frequency increases: a decreasing FSR (Regime I) having a leaning flame toward the burnt wire side, an increasing FSR (Regime II) showing a splitting phenomenon from a single-peak flame to a double-peak one due to a dielectrophoresis phenomenon, a decreasing FSR again (Regime III) generating a globular molten PE near the flame front and forming a liquid film of molten PE via continuously migrating a part of molten PE toward the burnt wire side, and an increasing FSR again (Regime IV) showing vortex flames at the front and rear flame edges along with an electrospray of molten PE. These emphasize diverse effects of the dynamic behaviors of molten PE. The onset condition for the formation of the vortex structure is identified as fAC,cr∼VAC−2Dout, supporting that such phenomenon is generated by induced magnetic field. An intermittent rotation of secondary (main) molten PE around the wire is a new observation. The mechanism is suggested by a dielectrophoretic force. Excluding the cases experiencing an intermittent leaning flame toward the burnt wire side and an irregularly splitting flame, FSR under the influence of such complex dynamic-behaviors of molten PE could reasonably be characterized with the gradient of electric field intensity taken at the outer surface of PE insulator, the area ratio between insulator and core, and AC frequency in all the regimes.

Design and Micro-Nano Fabrication of a GaAs-Based On-Chip Miniaturized Bandpass Filter with Intertwined Inductors and Circinate Capacitor Using Integrated Passive Device Technology.

In this study, we propose a miniaturized bandpass filter (BPF) developed by combining an approximate circular (36-gon) winding inductor, a circinate capacitor, and five air-bridge structures fabricated on a gallium arsenide (GaAs) substrate using an integrated passive device (IPD) technology. We introduced air-bridge structures into the outer metal wire to improve the capacitance per unit volume while utilizing a miniaturized chip with dimensions 1538 μm × 800 μm (0.029 λ0 × 0.015 λ0) for the BPF. The pattern was designed and optimized by simulating different dimensional parameters, and the group delay and current density are presented. The equivalent circuit was modeled to analysis various parasitic effect. Additionally, we described the GaAs-based micro-nano scale fabrication process to elucidate the proposed IPD technology and the physical structure of the BPF. Measurements were conducted with a center frequency of 1.53 GHz (insertion loss of 0.53 dB) and a 3-dB fractional bandwidth (FBW) of 70.59%. The transmission zero was located at 4.16 GHz with restraint of 35.86 dB. Owing to the benefits from its miniaturized chip size and high performance, the proposed GaAs-based IPD BPF was verified as an excellent device for various S-band applications, such as satellite communication, keyless vehicle locks, wireless headphones, and radar.

Degradation mechanism of the superconducting performance of a Bi2212 cable under magnetic fields

In magnetic confinement fusion reactors, superconducting magnet systems are essential for generating and controlling high magnetic fields. To increase the magnetic field, new superconducting materials such as Bi2212 (Bi2Sr2CaCu2O8+x ) have been selected in the design of magnet systems. However, the stability of the Bi2212 superconductor under magnetic fields must be studied for the routine and safe operation of magnet systems. In this work, the stability and degradation mechanism of a Bi2212 cable under magnetic fields were investigated. With a magnetic field of 5.8 T, the cable carrying 29 kA was exerted with a force of ∼168.2 kN m−1. In the core area of the cable, moved wires were detected by computed tomography. The macroscopic movement of the wires would vary with the axial position, which could be related to the twist structure. Then, the cable was decomposed, and the acquired wires were tested under 12 T at 4.2 K by four-probe method. The results indicated that the inner wires had relatively lower critical currents, which should be the reason for the degradation of cable performance. Scanning electron microscope images of the superconducting phase within the wires confirmed that cracks existed in the superconducting phase of the inner wires, while intact crystals were found in that of the outer wires. The variation in microstructures gave rise to changes in the wire performance.