Constituent Wires Research Articles

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.

Витягування циліндричних деталей із не суцільного матеріалу

A new method for drawing cylindrical parts from a flat metal mesh netting with square openings has been proposed, developed and investigated. According to this method, drawing is carried out from a square workpiece, whose sides are parallel to the diagonals of the netting mesh. A new method of drawing parts with flange clamping of a sheet workpiece has been proposed and experimentally tested, which differs in that the workpiece is pre-perforated; perforation of the workpiece is performed only in the flange area, whose inner diameter is equal to the average diameter dc of the cylindrical part obtained; perforation of the workpiece is performed so that the sum  of all jumpers by the width ai on each concentric circle of the location of the perforation holes is equal to the circumference at the average diameter dc of the cylindrical part obtained, i.e. formula is valid. The use of the proposed method, in comparison with the known one, creates such conditions for drawing, under which the limiting drawing ratio becomes significantly lower (< 0,46), which makes it possible to conduct a deeper drawing of parts in one press run. The scientific novelty of this research is as follows. Usually, when manufacturing parts such as caps or box shapes, stamping is used in several runs to avoid the phenomenon of tearing- off of the bottoОдержаноm. However, the use of stamping in several runs leads to a complication of the process equipment and an increase in the cost of the product, which is justified only for cases of obtaining a high-quality product and provided that the integrity of the part is intact at a considerable depth. When trying to draw parts of considerable depth, objective difficulties arise associated with breaking-off of the bottom, which are due to exceeding by the tensile stresses in the critical section of the workpiece (between the bottom and lateral surfaces) of the ultimate tensile strength в of the latter. As part of the research described in this article, a way to overcome those difficulties has been proposed. It is based on the fact that when implementing the stamping process at lower values of the drawing ratio than the critical one, a metal mesh netting or perforated workpiece is used, and tearing-off of the bottom is therefore no longer observed. This method made it possible to obtain an integral shape of the part while using a significant depth of drawing due to the prior perforation of the workpiece, which significantly reduces the cost of the product. That means that the obtained scientific result in the form of a proposed kinetic description of the stamping process compared to the known one creates such drawing conditions, under which the unevenness of the height of the cylindrical portion of the part is significantly reduced, which in turn reduces by 35-40% the cost of stamping cylindrical parts from a flat metal mesh netting with square openings. This result is interesting from a theoretical point of view. As far as the practical point of view is concerned, a mechanism of transition of plastic bending of netting meshes into cold volumetric expanding of its constituent wires has been revealed, which makes it possible to determine the conditions for using the process of manufacturing parts from metal mesh netting or perforated workpieces. Consequently, an applied aspect of using the scientific result obtained is the possibility of improving the typical technological process of stamping, where the stamping force will be significantly reduced and hence the stress in the critical section, which will make it possible to reduce significantly the limiting drawing ratio and increase the depth of stamping. This constitutes prerequisites for the transfer of the obtained technological solutions of the process of drawing from a metal mesh netting or a perforated workpiece.

On the model building for transmission line cables: a Bayesian approach

ABSTRACTThis work is aimed at building models to predict the bending vibrations of stranded cables used in high-voltage transmission lines. The present approach encompasses model calibration, validation and selection based on a statistical framework. Model calibration is tackled using a Bayesian framework and the Delayed Rejection Adaptive Metropolis (DRAM) sampling algorithm is employed to explore the posterior probability of the unknown model parameters. Two model classes are proposed to predict the bending vibrations of a typical high-voltage stranded cable. Both model classes account for the aerodynamic damping with the surrounding medium and the bending stiffness of the cable. The difference between the two relies on the damping model chosen to quantify the energy dissipation due to friction among the constituent wires of the cable. Model ranking is rigorously quantified by means of a Bayesian model class selection approach, in which both the data-fitting capability and complexity of each model class are simultaneously taken into account. Experimental tests are performed on a laboratory span with a typical high-voltage stranded cable. The measured frequency response functions are the observable quantities employed in the Bayesian model updating for the two model classes proposed. Both model classes provide comparable and accurate predictions for the cable’s frequency response functions within the range [5, 25] Hz, with the fractional derivative-based model class providing the most accurate predictions. Nonetheless, both model classes failed to accurately reproduce the measured cable’s dynamic response within the frequency range [25, 30] Hz.

Fatigue and fracture of wires and cables for biomedical applications

Fine wires and cables play a critical role in the design of medical devices and subsequent treatment of a large array of medical diagnoses. Devices such as guide wires, catheters, pacemakers, stents, staples, functional electrical stimulation systems, eyeglass frames and orthodontic braces can be comprised of wires with diameters ranging from 10s to 100s of micrometres. Reliability is paramount as part of either internal or external treatment modalities. While the incidence of verified fractures in many of these devices is quite low, the criticality of these components requires a strong understanding of the factors controlling the fracture and fatigue behaviour.1,2 Additionally, optimisation of the performance and reliability of these devices necessitates characterisation of the fatigue and fracture properties of its constituent wires. A review of cable architecture and stress states experienced during testing is followed by an overview of the effects of changes in material composition, microstructure, processing and test conditions on fracture and fatigue behaviour of wire and cable systems used in biomedical applications. The review concludes with recommendations for future work.

Analysis of the tensile response of a stranded conductor using a 3D finite element model

A 3D finite element modelling approach is proposed to investigate the axial force-elongation behaviour of a stranded conductor used for high voltage overhead lines. An all aluminium alloy conductor (AAAC), a four-layer conductor, is analysed based on the stress-strain response measured for individual wires. The aim of the model is to reproduce the complex deformation mechanisms and non-linearities associated with the helical shape of the wires, their contact interactions and the residual stress state from the manufacturing process. The latter is included in the model through a simulation of the stranding procedure. Simulations of the tensile response are compared to corresponding measurements. The results demonstrate improved predictive capabilities of the finite element model when compared to analytical formulae, and show that inelastic elongation at load levels significantly below the nominal yield strength of the constituent wires can be rationalized when residual stresses from the manufacturing process are included in the calculation.

Analysis of Pearlitic Cold Drawn Steel Wire

The effect of microstructure on the mechanical properties of cord steel wires was investigated. Material properties and damage behaviours were identified. Metal cord, for reinforcing articles of an elastomeric material, such as tires, conveyor belts and so on of the single strand type, in particular made up of a plurality of 3, 4 or 6 wires, where in the said wires are twisted together loosely. The metal cord characterized by the fact that the diameter of the individual constituent wires varies between 0.12 and 0.30 mm. Rm tested cord wire was max. 2 946 MPa. Fracture surfaces cords steels were observed.

DESIGN OF A WIRE GRID INVERTED-F ANTENNA WITH ULTRA WIDEBAND CHARACTERISTICS

In this paper, a new wire inverted-F antenna (IFA) is proposed, which is structured by grids of thin wires. This novel wire grid IFA is » 0:3‚ long and » 0:14‚ high and renders 41% fractional bandwidth which is nearly 5 times higher than the bandwidth of a classic IFA. In addition to the novel structure and high bandwidth, the distinguishing feature of the design process employed is its computational e-ciency. While the constituent wires of the wire grid (WG) model are one-dimensional (1D) thin wires, they can indirectly form very thick arms leading to bandwidth enhancement. The thin- wire structure of the WG-IFA provides the opportunity to carry out the analysis and design accurately and fast in a 1D MoM-based software like NEC.

Yield Characteristics of a Twill Dutch Woven Wire Mesh Via Experiments and Numerical Modeling

Woven structures are steadily emerging as excellent reinforcing components in composite materials. Metallic woven meshes, unlike most woven fabrics, show high potential for strengthening via classical methods such as heat treatment. Development of strengthening processes for metallic woven materials, however, must account not only for behavior of the constituent wires, but also for the interactions between contacting wires. Yield behavior of a 325 × 2300 stainless steel 316L (SS316L) twill dutch woven wire mesh is analyzed via experimental data and 3D numerical modeling. The effects of short dwell-time heat treatment on the mechanical properties of this class of materials is investigated via uniaxial tensile tests in the main weave orientations. Scanning electron microscopy (SEM) is employed to investigate the effects of heat treatment on contacting wire interaction, prompted by observations of reduced ductility in the macrostructure of the mesh. Finally, the finite element method (FEM) is used to simulate the accumulation of plastic deformation in the mesostructure of the mesh, investigating how this wire level plasticity ultimately affects global material yielding.

Measurement of Strain/Load Transfer in Parallel Seven-wire Strands with Neutron Diffraction

The elastic strains induced in the constituent wires of parallel wire strands under tensile loading were measured using neutron diffraction. The elastic strains carried by the individual wires depended very strongly on the boundary conditions at the grips and on radial clamping forces. The friction forces between the wires were quite significant and should not be neglected in analytical or numerical formulations of strain partitioning in parallel wire cables.

Mechanical modeling of self-expandable stent fabricated using braiding technology

The mechanical behavior of a stent is one of the important factors involved in ensuring its opening within arterial conduits. This study aimed to develop a mechanical model for designing self-expandable stents fabricated using braiding technology. For this purpose, a finite element model was constructed by developing a preprocessing program for the three-dimensional geometrical modeling of the braiding structure inside stents, and validated for various stents with different braiding structures. The constituent wires (Nitinol) in the braided stents were assumed to be superelastic material and their mechanical behavior was incorporated into the finite element software through a user material subroutine (VUMAT in ABAQUS) employing a one-dimensional superelastic model. For the verification of the model, several braided stents were manufactured using an automated braiding machine and characterized focusing on their compressive behavior. It was observed that the braided stents showed a hysteresis between their loading and unloading behavior when a compressive load was applied to the braided tube. Through the finite element analysis, it was concluded that the current mechanical model can appropriately predict the mechanical behavior of braided stents including such hysteretic behavior, and that the hysteresis was caused by the slippage between the constituent wires and their superelastic property.

Evaluation of Tensile Strength of Multistrand Conductors—Part II: Experimental Results

Tension-torsion measurements were made with applied strain on ACSR, AACSR,ACAR, aluminum and aluminum alloy conductors, as well as on groundwires. Results were compared with predictions of a model based on mechanical properties of constituent wires and the geometry of the multistrand cable. True tensile strength of each cable was predicted accurately. Deviations were found in the torque values of cables containing galvanized steel strands. Interstrand friction, not considered in the model, is thought to be responsible for the deviation. Frictionless interaction of strands was found to be a reasonable approximation for aluminum and aluminum alloy stands.

Localized effect of clamp or socket end connections on helical wires in multilayered cables

A complete theory of helical thin elastic rods is applied to analyze the effect of constraint due to clamp or socket end connections on changes to the lay angles of the constituent wires in multilayered cables. While the effect on stresses in the wires is small, the end connection causes slipping to occur between the wires which could contribute to wear or fretting damage near the end connection.

A theory of thin rods with application to helical constituent wires in cables

Based on the direct approach of Green and Laws [A general theory of rods. Proc. R. Soc. A283, 145–155 (1966)], a theory of thin rods is derived and applied to the analysis of helical constituent wires in cables. Uniform extension, twisting and bending of cables are considered. The present theory predicts a new effect in the bending of cables when friction restrains relative movement of the constituent wires.

Frequency analysis of the signals generated by the failure of constituent wires of wire rope

Frequency analysis has been applied to the acoustic emission signals resulting from the failure of steel wire ropes and individual wires taken from the ropes. These preliminary tests were performed on notched and unnotched specimens under rising and cyclic loads; the signals were digitized and analysed using a fast Fourier transform program. Failure of the wires generated signals with frequencies between 0 and 100 kHz; the average peak to peak amplitude values of the signals from individual wires were greater than those from the failure of notched wires within the rope. The signal duration also increased in the rope specimens.

Theoretical Estimation of the Response of Helically Armored Cables to Tension, Torsion, and Bending

This paper concerns the mechanical behavior of ACSR (aluminum conductor steel-reinforced) conductors under static-loading conditions, which may comprise any combination of tension, torsion, and bending. The model described is quite general and can be applied to other types of helically armored cables. A stiffness matrix is developed and relations are given for axial, torsional, and flexural rigidities and for coupling parameters. For small curvatures, the flexural rigidity is comparable to the upper limit accepted in current practice by ACSR users. As the curvature increases, however, frictional forces develop between the outer layers and sliding of wires may occur, with the result that the flexural rigidity decreases. The tension level also influences the flexural rigidity of the conductor. Actually the model does not consider the flexural rigidity of the system as a fixed entity but as directly influenced by local compressive forces and internal radial and tensile forces. The analysis can also apply to situations where a given number of initial constituent wires have failed and the load is transferred to neighboring wires, leaving the conductor unbalanced; it will be seen how internal arrangements manage to accommodate the local perturbation.

Differential blood cell separation using a high gradient magnetic field.

A technique for the separation of erythrocytes from whole blood is described which exploits the magnetic property of haemoglobin in the reduced state. The technique is characterized by the use of a filter consisting of a cylinder, containing stainless steel wire mesh, placed between the jaws of an electro magnet. When activated, the electromagnet induces a magnetic field gradient in the vicinity of each of the constituent wires, sufficient to attract and trap erythrocytes in suspension. The number of erythrocytes captured varies with the applied field (0-1.4 Tesla in these experiments) and flow rate (1.9-12.9 x 10(-4) m s-1). The capture process does not cause haemolysis or observable surface damage to the erythrocytes and neither leucocytes nor platelets are retained by the filter.