定、变载弯曲疲劳钢丝绳失效机理对比研究

为对比揭示定、变载弯曲疲劳钢丝绳断裂机理及磨损演化特性,运用自制钢丝绳弯曲疲劳试验机开展钢丝绳定载、变载弯曲疲劳试验,通过人工拆股统计法和VW-9000系列高速度数码显微系统对比研究钢丝绳断丝分布、断丝数、断口和磨痕形貌等断裂机理,对比分析钢丝绳未断钢丝和断丝的磨痕尺寸演化特性. 结果表明:与钢丝绳定载弯曲疲劳相比,变载弯曲疲劳钢丝绳断丝出现较晚,芯股、螺旋股外层断丝数分别较多、较少,芯股外层钢丝断口挤压变形较大,芯股各层钢丝断口裂纹扩展区占比较低,芯股和螺旋股的各层钢丝磨痕尺寸总体较小,钢丝绳更易达到报废水平.      

The mechanical behavior of a wire rope with an independent wire rope core

A new model for simulating the mechanical response of a wire rope with an independent wire rope core is presented. The rope is subjected to both an axial load and an axial torque. In contrast with previous models that consider the effective response of wound strands, the present model fully considers the double-helix configuration of individual wires within the wound strand. This enables to directly relate the wire level stress to the overall load applied at the rope level. The model assumes a fiber response of individual wires. Two alternative kinematics of the wires are considered, and are used to predict the elastic response of the rope. The postulated kinematics are theoretically validated and the predicted rope response is in agreement with new experimental data. The new model enables the extraction of the stress at the wire level that can be used in turn to estimate global features of the rope such as force interaction between wires, rope stiffness, strength, and fatigue life.     

Statically indeterminate contacts in axially loaded wire strand

This paper is concerned with the analysis of simple wire strands made from one layer of circular wires helically wrapped around a circular straight core wire. The undeformed configuration is the special case in which each of the surrounding helical wires touches its two adjacent neighbouring helical wires as well as touching the core wire. This forms a statically indeterminate contact problem. A simple finite element model is developed to analyse this situation. Numerical results show that contacts can occur simultaneously at all possible contact points when the strand is subjected to extension with both ends fixed against rotation.     

PROPAGATION CHARACTERISTICS OF HIGH ORDER LONGITUDINAL MODES IN STEEL STRANDS AND THEIR APPLICATIONS

Propagation characteristics of high order longitudinal modes of ultrasonic guided waves in seven-wire steel strands are investigated theoretically and experimentally. According to these analysis results, proper longitudinal modes are selected for defect detection in steel strands. Dispersion curves for helical and central wires in a 17.80 mm nominal diameter seven-wire steel strand are numerically obtained firstly, and propagation characteristics of high-order longitudinal modes, such as wave structures, attenuation and dispersion, are analyzed. In experiments, the signals of ultrasonic guided wave at different high frequencies are excited and received at one end of a steel strand by using the same single piezoelectric transducer. The identification of longitudinal modes in the received signals is achieved based on short time Fourier transform. Furthermore, appropriate L（0, 5） mode at 2.54 MHz is chosen for detecting an artificial defect in a helical wire of the steel strand. Results show that high order longitudinal modes in a high frequency range with low dispersion and attenuation whose energy propagates mainly in the center of the wires can be used for defect detection in long range steel strands.     

Wave propagation in multi-wire strands by wavelet-based laser ultrasound

Methods based on guided ultrasonic waves are gaining increasing attention for the non-destructive inspection and condition monitoring of multi-wire strands used in civil structures such as prestressing tendons and cable stays. In this paper we examine the wave propagation problem in seven-wire strands at the level of the individual wires comprising the strand. Through a broad-band, laser ultrasonic setup and a time—frequency wavelet transform processing, longitudinal and flexural waves are characterized in terms of dispersive velocity and frequency-dependent attenuation. These vibrating frequencies propagating with minimal losses are identified as they are suitable for long-range inspection of the strands. In addition, the wave transmission spectra are found to be sensitive to the load level, suggesting the potential for continuous load monitoring in the field.     

Some dynamic properties of axially loaded wire ropes

Results are presented on the transverse damping, the transverse fundamental natural frequency as well as the longitudinal fundamental natural frequency for axially loaded wire ropes. Twelve different wire ropes are tested. During the test, a mass is centrally attached to the rope. The results indicate an increasing transverse damping with an increasing axial load. This damping is primarily attributed to a Coulomb damping. Although core material and construction influence the transverse damping of the wire rope, no relationships are found when comparing this damping with the structural strength, the number of wires used in the rope, the alloy composition or the heat treatment of the rope materials. The transverse and longitudinal fundamental natural frequencies of the axially loaded wire ropes with a mass centrally attached has been satisfactorily modeled.     

Neutron Diffraction Measurement of Stress Redistribution in Parallel Seven-Wire Strands after Local Fracture

We report results from neutron diffraction experiments where partitioning of applied tensile load between the inner and outer wires of seven-wire parallel and quasi-parallel wire strands were measured while 1-all wires were undergoing elastic deformation, 2-where one wire within the bundle was undergoing plastic flow and, 3-when one or more wires fractured under load. The results indicate that mechanical interference and friction mechanisms have similar contributions to the load transferred to fractured wires, and both mechanisms should be included in analytical or numerical formulations of strain partitioning in quasi-parallel wire cables.     

Effect of interfacial contact forces in radial contact wire strand

A new mathematical model has been developed to predict the behaviour of a stranded cable assembly under the influence of interfacial radial contact forces and radial contraction of the core. A single layered cable assembly with six helical wires and a straight cylindrical core, all made with the same material, Steel has been chosen to explain this phenomenon when the assembly is under the influence of core–wire radial contact. An attempt is made in this paper to model the strand with a radial (core–wire) contact and deduce its equations of equilibrium. Numerical analysis of strand force, twisting moment, strand stiffness, contact force and contact stresses is carriedout based on the equilibrium of thin rods, and the results are compared with the earlier research work. The importance of the inclusion of interfacial forces at the contact locations and their associated effects of axial and twist slip of the helical wires on the core, is highlighted. The behaviour of the stranded cable assembly due to the contact force in the radial direction and its associated effects on the axial strain of the core due to Poisson’s effect is one more additional feature incorporated in the present work.     

Ultrasonic Wave Propagation in Progressively Loaded Multi-Wire Strands

In recent years methods based on guided ultrasonic waves gained increasing attention for the nondestructive evaluation and the health monitoring of multi-wire strands used in civil structures as prestressing tendons and stay cables. The study of wave propagation properties in such components has been challenging due to the load-dependent inter-wire contact and the helical geometry of the peripheral wires. The present paper addresses an experimental investigation on the ultrasonic wave propagation in seven-wire strands loaded at different stress levels. Wafer piezoelectric sensors are employed in a through transmission configuration for the generation and detection of stress waves. The response of the lowest-order longitudinal mode is studied at different levels of load. Those ultrasonic features, associated with the transmitted ultrasonic energy, sensitive to the variation of applied load are identified and discussed as possible means of a load monitoring.     

Investigation of characteristics of hard x-rays produced during implosions of wire array loads on 1.6 MA Zebra generator

Experimental study of the characteristics of hard x-ray (HXR) emission from multi-planar wire arrays and compact-cylindrical wire arrays (CCWA) plasmas on the 1.6 MA Zebra generator at UNR has been carried out. The characteristics of HXR produced by multi-planar wire arrays such as single, double, and triple planar as well as compact-cylindrical wire arrays made from Al, Cu, brass, Mo, and W were analyzed. Data from spatially resolved time-integrated and spatially integrated time-gated x-ray spectra recorded by LiF spectrometers, x-ray pinhole images, and signals from fast x-ray detectors have been used to study spatial distribution and time history of HXR emission with different loads. The dependence of the HXR yield and power on the wire material, geometry of the load and load mass is observed. Both HXR yield and power are minimum for Al and maximum for W loads. The HXR yield increases with the rise of the atomic number of the material for all loads. The presence of aluminum wires in the load with the main material such as Cu, Mo, or W in combined wire arrays decreases HXR yield. For W plasma, the intensity of cold L-shell spectral lines (1–1.5 Å) correlates with corresponding amplitude of HXR signals which may suggest the evidence of generation of electron beams in plasma. It is found that HXRs are generated from different plasma regions by the interaction of electron-beam with the plasma trailing mass, with the material of anode and due to thermal radiation from plasma bright spots. The theoretical assumption of thermal mechanism of HXR emission predicts the different trends for dependency of HXR power on atomic number and load mass.     

Experimental investigation of the impaction of water droplets on cylindrical objects

The impaction of water droplets on isothermal cylindrical wires has been investigated experimentally in the present study. Mono-size droplets of 110, 350 and 680 μm in diameter were generated using piezoelectric droplet generators. The effects of droplet velocity and wire size were varied parametrically to reveal the impacting phenomena. Typical modes of the impaction outcome are disintegration and dripping. For droplets impacting on small wires, finer drops are disintegrated if the impacting droplet velocity is high, and larger dripping drops are observed if the velocity is low. For droplets impacting on large wires, bigger pendent drops are gradually formed which would eventually detach from the wires under the influence of gravity. In addition, droplets impacting on wires with waxy surface generate smaller dripping drops than that of the non-waxed wires. A non-dimensional regime map and new formulations in terms of the droplet Weber number, the wire Bond number and the size ratio of the wire diameter to incoming droplet diameter have been established to identify the regime for each mode of outcome and to predict the size of the dripping drops within the experimental limits.     

An experimental study of wire strains in an undamaged and damaged steel strand subjected to tensile load

Wire stráins in a wire-rope strand subjected to static and quasistatic tensile load are experimentally examined both before and after the cutting of one of the external wires. These tests are carried out with electrical-resistance strain gages. Significant differences between the most accepted Italian regulations and the measured values, obtained with the strand with one external wire severed, were noted.     

服役导线的力学性能退化研究

为更清楚地了解阳江35kV服役导线的运行状态,从分析导线断线原因出发,通过对老旧导线的单丝断裂强度、弹性模量、应力应变曲线、拉断力、抗拉强度等综合指标的测试与分析,研究服役导线的力学性能,由试验结果得出:35kV老旧导线钢芯的直径变化对于架空导线的外径变化有直接的影响,老旧导线的铝线直径变化较小,其外径增大1.67%~4.24%;钢单线的拉断应力仍能达到标准中规定值的106%,且伸长率也满足要求;部分铝线的抗拉强度低于95%;绞线拉断力仍能达到95%的计算拉断力。但是相同规格下的老旧导线的抗拉强度比新导线的抗拉强度低2%~18%。结果表明:阳江地区服役三十年以上的老旧导线在力学性能上仍能继续承载。     

基于ASME应变限制准则的小冲杆试验等效断裂应变

为更清楚地了解阳江35kV服役导线的运行状态,从分析导线断线原因出发,通过对老旧导线的单丝断裂强度、弹性模量、应力应变曲线、拉断力、抗拉强度等综合指标的测试与分析,研究服役导线的力学性能,由试验结果得出：35kV老旧导线钢芯的直径变化对于架空导线的外径变化有直接的影响,老旧导线的铝线直径变化较小,其外径增大1.67％~4.24％;钢单线的拉断应力仍能达到标准中规定值的106%,且伸长率也满足要求;部分铝线的抗拉强度低于95%;绞线拉断力仍能达到95%的计算拉断力。但是相同规格下的老旧导线的抗拉强度比新导线的抗拉强度低2%~18%。结果表明：阳江地区服役三十年以上的老旧导线在力学性能上仍能继续承载。     

Response of epoxy oversized models of strands to axial and torsional loads

As part of an extensive investigation on strand and cable properties, epoxy oversized models of strands have been manufactured using a newly developed technique. Axial and torsional loadings have been applied to the models. Strains, stresses and displacements have been determined using mechanical and electrical strain gages, dial gages and brittle coatings. The results obtained are compared with calculations using a previously developed theory. The response of a reference structure in which each wire is assumed to act independently is also compared with the response of the strand. Several discrepancies with theory are pointed out. It is believed that these are the first systematic measurements taken on strands.     

General axial response of stranded wire helical springs

The large static deflection of an axially loaded helical spring formed of a twisted strand of smooth circular wires is considered. Contact between the wires in the strand may or may not be maintained upon loading, depending upon the type of construction and the type of loading. It is found that the making or breaking of wire contact within the strand has a drastic ettect upon the extension and twist of a wire and upon the extension of the strand, but has practically no effect upon the twist of the strand, and only a moderate effect upon the overall response of the spring. Limited experimental data tend to verify the theory. It is found that a good engineering approximation for the axial stiffness of a twisted m-wire spring in which contact is maintained can be made by treating the spring as m untwisted helical wires acting independently, provided the strand twist is not too severe.     

Superelastic shape memory alloy cables: Part II – Subcomponent isothermal responses

This paper constitutes the second part of our experimental study of the thermo-mechanical behavior of superelastic NiTi shape memory alloy cables. Part I introduced the fundamental, room temperature, tensile responses of two cable designs (7 × 7 right regular lay, and 1 × 27 alternating lay). In Part II, each cable behavior is studied further by breaking down the response into the contributions of its hierarchical subcomponents. Selected wire strands were extracted from the two cable constructions, and their quasi-static tension responses were measured using the same experimental setup of Part I. Consistent with the shallow wire helix angles in the 7 × 7 construction, the force–elongation responses of the core wire, 1 × 7 core strand and full 7 × 7 cable were similar on a normalized basis, with only a slight decrease in transformation force plateaus and slight increase in plateau strains in this specimen sequence. By contrast, each successive 1 × 27 component (1 × 6 core strand, 1 × 15 strand, and full cable) included an additional outer layer of wires with a larger number of wires, greater helix radius, and deeper helix angle, so the normalized axial load responses became significantly more compliant. Each specimen in the sequence also exhibited progressively larger strains at failure, reaching 40% strain in the full 1 × 27 cable.Stress-induced phase transformations involved localized strain/temperature and front propagation in all of the tested 7 × 7 components but none of the 1 × 27 components aside from the 1 × 27 core wire. Stereo digital image correlation measurements revealed finer features within a global transformation front of the 1 × 7 core strand than the 7 × 7 cable, consisting of an staggered pattern of individual wire fronts that moved in lock-step during elongation. Although the 1 × 27 multi-layer strands exhibited temperature/strain localizations in a distributed pattern during transformations, the localizations did not propagate and their cause was traced back to contact indentations (stress concentrations) arising from the cable’s fabrication. The normalized axial torque responses of the multi-layer 1 × 27 components during transformation were distinctly non-monotonic and complex, due to the alternating handedness of the layers. Force and torque contributions of individual wire layers were deduced by subtracting 1 × 27 component responses, which helped to clarify the transformation kinetics within each layer and explain the unusual force and torque undulations seen in the 1 × 27 cable response of Part I.     

Analytical modeling of synthetic fiber ropes. Part II: A linear elastic model for 1 + 6 fibrous structures

In part I of this study it was shown that, to model synthetic fiber ropes, two scale transition models can be used in sequence. The first model (continuum model) has been presented in the part I and the present paper examines the behavior of a fibrous structure consisting of 6 helicoidal strands around a central core (1 + 6 structure). An analytical model will be presented which enables the global elastic behavior of such a cable under tension–torsion loading to be predicted. In this model, first, the core and the strands are described as Kirchhoff–Love beams and then the traction–torsion coupling behavior is taken into account for both of them. By modeling the contact conditions between the strands and the core, with certain assumptions, it is possible to describe the behavior of the cable section as a function of the degrees of freedom of the core. The behavior of the cable can thus be deduced from the tension–torsion coupling behavior of its constituents. Tensile tests have been performed on the core, the strands and then on a full scale 205 ton failure load cable. Finally, predicted stiffness from the analytical models is compared to the test results.     

Analytical solutions for bending and flexure of helically reinforced cylinders

There has been a great deal of interest in the problems of modelling cables and ropes. A recent review by Cardou and Jolicoeur [Appl. Mech. Rev. 50 (1997) 1] considers the modelling of a cable which consists of a central core surrounded by one or several helically wound wire layers. One approach has been to consider the deformations of an individual helical wire and to synthesise the model of a cable by using contact conditions between the various wires. Other authors have adopted a continuum approach regarding each layer as a transversely isotropic material whose principal direction is along a helix surrounding the central axis of the cable. In each layer the helix angle is constant so that, when referred to cylindrical polar co-ordinates, the cylinder has a constant stiffness matrix in each layer. The intention in this paper is to use the continuum approach and describe the analytical solutions that govern the simple bending, flexure, or bending under a uniform load, of an anisotropic elastic cylinder consisting of a single material of this type. The extension of this work to a composite cylinder consisting of several concentric layers, surrounding a central core, which are either bonded together or make a frictionless contact, is briefly described.     

Tensile behaviors of pre-twisted composite strands

In this paper, we address the tensile behaviors of pre-twisted composite strands, which consists of a pre-twisted single core filament surrounded by n-helical side filaments. Based on the extensible rod with zero bending and small twisting moduli for the core filament and inextensible rod for the side filaments, we develop the analytical method of the tensile behaviors of pre-twisted composite strands. Using a numerical continuation scheme, we elucidate the effects of microscopic factors such as initial helical angle, pre-twist of core filament, ratio of elastic modulus of core to that of side filament, and the number of the side filaments on the macroscopic tensile behavior of the strand as a whole structure. As a result, we show that the behavior is not trivial, even though the filament is a linear elastic due to the interplay of both geometrical constraint and finite deformation of the strand.