Fatigue behaviour of wire ropes

This paper presents a model for the analysis of the fatigue behaviour of strands and cables. It is assumed that this behaviour may be derived from that of individual wires. The results of the model are compared to test results performed on wires and strands of different diameter, geometry, spin angle and chemical composition. Some recommendations based on the research performed are proposed for improving the fatigue behaviour of strands.     

Selecting and testing heavy-duty synthetic ropes

Synthetic fibre ropes — notably of nylon, polypropylene and polyester — are proving invaluable in industry. Particularly at sea, their qualities of flexibility, long life and resistance to damage have led to their wide adoption in place of steel and natural-fibre ropes. Consultant R.K. Evans looks at some of their characteristics, and at the tests carried out to determine these.     

Fatigue behaviour of aluminium matrix composites reinforced with continuous alumina fibres

Abstract

Alumina (N610) reinforced pure Al (A9) or Al–2 wt-%Cu alloy (AU2) unidirectional (UD) composites which combine a highly ductile matrix with a strong interface bonding, present high static and dynamic mechanical performances. In the present paper, the fatigue behaviour of quasi­UD N610+A9 and N610+AU2 composites is investigated. Notwithstanding the presence of the transverse bundles, the longitudinal behaviour in tension and fatigue of these quasi-UD composites is nearly equivalent to that of the pure UD. Only in the case of the N610+AU2 quasi-UD composite, the fatigue limit is about 30% lower than that of the pure UD. Acoustic emission (AE) monitoring correlated with microfractography and microstuctural examinations has enabled identification of different stages in the evolution of damage and the association of these with damage and failure mechanisms. In fatigue, three main damage mechanisms are activated in a sequential and/or superposed mode during a three stage evolution.     

Compressional behaviour of carbon fibres

The axial compressive strain to failure of various types of PAN-based carbon fibres was measured by applying small and defined compressive loads to single filaments which have been bonded to a rectangular polymer cantilever beam and parallel to its long edge. By monitoring the Raman frequencies along the fibre with the 2 m laser probe of a Raman microscope, the critical compressive strain required for first fibre failure could be assessed and the residual load that each type of fibre supported after first failure, could be measured. Estimates of the compressive moduli for all fibres could, also, be obtained by considering the dependence of the Raman frequency upon compressive strain in the elastic region. The critical compressive strain to failure was found to decrease with fibre modulus and its value was, approximately, equal to 50% of the tensile fracture strain. However, for some low-modulus fibres the compressive strain to failure was found to approach the tensile fracture strain. The initial compressive moduli of high-modulus fibres were estimated to decrease up to a maximum of 10% with respect to their tensile moduli, whereas more significant reductions were found in the case of intermediate and low-modulus fibres.     

Compressional behaviour of carbon fibres

Spectroscopic-mechanical studies have been conducted on a range of carbon fibres by bonding single filaments on the top surface of a cantilever beam. Such a loading configuration allows the acquisition of the Raman spectrum of carbon fibres and the derivation of the Raman frequency strain dependence in tension and compression. Strain hardening phenomena in tension and strain softening phenomena in compression were closely observed. The differences in the slopes of the Raman frequency versus applied strain curves in tension and compression respectively, have been used to obtain good estimates of the compression moduli. A method of converting the fibre Raman frequency versus strain data into stress-strain curves in both tension and compression, is demonstrated. Values of fibre stress and fibre modulus at failure in compression compare exceptionally well with corresponding estimates deduced from full composite data. The mode of failure in compression has been found to depend upon the carbon fibre structure. It is demonstrated that certain modifications in the manufacturing technology of PAN-based fibres can lead to fibres which show resistance to catastrophic compressive failure without significant losses in the fibre compressive modulus.     

Fatigue in low-strength silica optical fibres

Fatigue behaviour was investigated for low-strength silica fibres on which macroscopic flaws were forcibly introduced by abrading. Crack growth in silica glass was also examined on the CT specimen. Stable crack growth parameters, obtained from the static and dynamic fatigue tests for abraded fibres, were determined to be about 40 which is equal to that obtained from the CT specimen, indicating that the crack growth process in abraded fibres is quite the same as in the CT specimen. This leads to the conclusion that, for the optical fibre, the allowable stress condition wherein no breaks occur is given on the basis of some basic fracture mechanics parameters obtained from the CT specimen.     

Compressive and tensile behaviour of carbon fibres

Attempts have been made to discuss the fibre axial tensile and compressive behaviour of several carbon fibres prepared from different precursors, and surface- and/or sizing-treatments. With all fibres, the number of breaks increased with increasing tensile or compressive strain, and remained constant beyond a certain strain. The constant number of breakages based on the precursor differed remarkably in compression, whereas those based on the surface- and/or sizing-treatments differed remarkably in tension. In tension, the PAN-based fibre could be broken with a somewhat greater ease than the pitch-based fibre, while in compression, the pitch-based fibre could be broken with somewhat greater ease than the PAN-based fibre. © 1998 Chapman & Hall     

Fracture behaviour of cross-linked collagen fibres

Mechanical properties such as stress - strain, fracture behaviour and thermal behaviour were studied for cross-linked collagen fibres. The shrinkage temperature of cross-linked fibres shows increase in temperature when compared to the control. The results on measurements of breaking strength and strain show significant change when compared with that of the control. The morphological features of the fractured ends of cross-linked fibres were indicative of certain specific patterns. A critical observation of these patterns indicate the role played by the nature of cross-linking agents on the mechanism of failure of these fibres.     

Pull-out behaviour of hooked steel fibres

A programme of research is described that has investigated the fracture of steel fibre reinforced sprayed concrete under flexural load, with the aim of developing a stress-profile model to predict flexural behaviour in the form of a load-deflection response. This paper reports the work associated with establishing the pull-out characteristics of hooked end fibres. The effects of matrix strength, fibre embedment length and orientation are described, together with the interaction of these parameters. The relationships established can be used to model the tensile response of a beam at varying crack width and hence form a key part of the stress-profile for predicting residual flexural strength, which is an essential requirement of a much needed design rationale for steel fibre concrete.

---

Résumé Le programme de recherche décrit porte sur la rupture du béton projeté renforcé de fibres d'acier sous charge en flexion. Il a pour objectif de développer un modèle de profil de contrainte capable de prévoir le comportement en flexion sous la forme d'une réponse charge-déflexion. Cet article présente un travail lié à l'établissement des caractéristiques d'arrachement de fibres aux extrémités crochetées. Les effets de la résistance de la matrice, de la longueur d'enfoncement et l'orientation des fibres sont décrits, ainsi que l'interaction de ces paramètres. Les relations établies peuvent être utilisées pour modéliser la réponse en tension d'une poutre à une largeur de fissuration variable, et donc pour former la majeure partie du profil de contrainte visant à prévoir la résistance à la flexion résiduelle, qui est l'une des exigences essentielles d'une argumentation très attendue sur l'étude des bétons renforcés de fibres.

     

Birefringence behaviour of annealed silk fibres

Silk fibres were annealed at 140 ° C for different annealing times ranging from 2 to 10h. Refractive indices and birefringence of annealed fibres were measured by two different interferometric methods. An interference polarizing microscope and multiple-beam Fizeau fringes in transmission techniques were used. The scanning electron microscope was used to estimate the geometrical parameters of silk fibres. The behaviour of birefringence for annealed silk fibres showed that the birefringence reach a maximum value when silk was annealed for 5 to 6 h at 140 ° C. The isotropic refractive index of annealed silk is also slightly increased with increasing annealing time. The results obtained clarify the effect of annealing time on the optical behaviour of natural silk fibres. Microinterferograms are given for illustration.     

The oxidation behaviour of carbon fibres

The oxidation behaviour of carbon fibres has been studied in air at different temperatures from 550 to 860 °C. A linear relationship has been observed between the carbon fibre size and oxidation time. Experimental results show that the oxidation process is in a mixed control zone, i.e. controlled both by diffusion of the gaseous reactant and product within the boundary layer and by the chemical reaction. The activation energy of carbon burn-off is 140±5 kJ mol^–1. The uniform nature of the surface oxidation makes it possible to re-size the carbon fibres to smaller diameters.     

Tensile fatigue behaviour of PBO fibres

Poly(p-phenylene benzobisoxazole) (PBO) fibres are finding increasing applications on account of their exceptional stiffness and strength. This article presents results from tests on single PBO filaments, to characterize their intrinsic behaviour under quasi-static and cyclic tensile loading. Scanning electron microscopy is used to show the fibrillation mechanism leading to failure. Results are compared to data for polyester, aramid and high modulus polyethylene fibres. PBO fibres show shorter fatigue lifetimes than the other fibres when maximum stress is expressed as a percentage of quasi-static break load, but the absolute stress values applied are much higher for an equivalent lifetime.     

Bending fatigue behaviour of bearing ropes working around pulleys of different materials

Nondestructive quantitative detection and artificial detection were carried out to study bending fatigue behaviour and failure mechanisms of wire ropes. When working around nylon pulleys, wire ropes exhibit a slowly increasing of fracture rate and total damage in one lay length. The bending fatigue life of wire ropes is twice longer than that of ropes working around steel pulleys. The primary failure mode of wire ropes working around nylon pulleys is fatigue fracture and the fracture surfaces of wires exhibit a wide crack propagation zone and narrow tear zone.     

Fatigue behaviour of hybrid composites

A study has been made of the fatigue behaviour in repeated tension of unidirectional and [(±45, 0, 0)₂]_s hybrid laminates composed of XAS carbon fibres and E-glass fibres in the same 913 epoxy resin. The ordinary mechanical properties of these composites are close to those predicted by simple, conventional models of hybrid behaviour. For the unidirectional materials, the fatigue stress for a given life is not a linear function of composition, showing a substantial positive deviation from the rule of mixtures. This behaviour closely mirrors that of unidirectional carbon-Kevlar hybrids reported in Part 1 of this work. In terms of strain-life comparisons, results for all hybrid compositions and plain carbon fibre reinforced plastic fall within a single scatter-band. These features are also reflected in the fatigue behaviour of the more complex hybrid laminate.     

Fatigue behaviour of hybrid composites

A study has been made of the fatigue behaviour of carbon/Kevlar-49/epoxy hybrid composites. Stress-life data have been obtained for both unidirectional and [(±45, 0, 0)₂]_s laminates in repeated tension and compression-tension cycling tests at various values of the stress (or R) ratio. Goodman (constant life) diagrams are presented for the unidirectional composites which indicate that the fatigue resistance of hybrid mixtures varies linearly with composition. The presence of the Aramid fibre, whose natural resistance to compression loads is suspect, does not appear to exert any unexpected damaging influence on the response of the hybrids either in tensile or tension-compression loading. This is also true of the behaviour of hybrid laminates containing plies at an angle to the main loading direction.     

Fatigue behaviour of ribbon-reinforced composites

The fatigue behaviour of aluminium-based composites reinforced with high-strength steel ribbons has been examined. In the directions both parallel (longitudinal composites) and perpendicular (transverse composites) to the principal ribbon axis the development of the fatigue deformation is controlled by the matrix. The steel-matrix bond does not deteriorate during the initial stages of fatigue. The fatigue limit at 10⁷ cycles was arbitrarily defined in the case of the longitudinal composites as corresponding to approximately the half-destruction of the composite. In this way the limit for a composite with a volume fraction,V _r of 0.25 was around 25% of the fracture strength while with aV _r of 0.34, the limit was raised to about 33% of the fracture strength. The use of an alloy matrix increases the fatigue strength of the composite. The fatigue mechanism in both longitudinal and transverse composites initially involves matrix cracking; this leads to steel-aluminium or aluminium-aluminium debonding parallel to the principal stress axis in specimens fabricated from pre-coated steel ribbons, followed by ribbon fracture. In specimens fabricated by simply rolling together the steel ribbons and aluminium foils, little debonding is evident. The debonding results in a high fracture resistance.     

Fatigue behaviour of technical springs

Technical Springs belong to the components with the highest cyclic and superposed static load. Nevertheless they have to fulfill the requirements of lightweight constructions. This is only possible, if high strength materials with special properties are carefully manufactured to well designed springs and special additional treatments are carried out, which impose an advantageous residual stress profile in the surface layers of the springs. After a short historical view on the spring research activities in Professor Thums area, some aspects of the fatigue behaviour of hot formed parabolic leaf springs are presented. Then the fatigue properties of cold formed helical compression springs made of different steel spring wires are discussed. Finally some results on the fatigue behaviour of helical springs at a very high number of load cycles are reported.     

Tensile static and fatigue behaviour of sisal fibres

The work describes the quasistatic tensile and fatigue behaviour of as-received sisal fibres. Natural-based reinforced composites are gaining significant interest within the structural community, due to their interesting mechanical properties, recyclability and environmentally-sustainable production and use. Natural fibres such as sisal constitute an excellent reinforcement material, due to the low extraction costs from plants, and high level of recycling involved in their manufacturing process. In this work the diameter, Young’s modulus, strength and strain to failure over 15 different samples are measured and compared against data from open literature. Tensile cyclic fatigue loading at eight loading levels (from 0.6 to 0.95) has been carried out. The maximum forces involved (between 9 N and 22 N) are considerably higher than the ones used previously in open literature, and lead to significant dependence of the hysteresis loops, energy dissipation and S–N behaviour of the sisal fibres versus the cycle and loading ratio levels. The results obtained from this work can be used to predict from a fatigue and structural integrity point of view the behaviour of sisal-based reinforced composites with high load bearing capability, and extend the design envelope of this class of natural-reinforced materials.     

Fatigue behaviour of ATJ graphite

DetailedS-N curves are presented for two modes of fatigue testing characterized by different minimum-to-maximum stress ratios,R. The endurance limit, or maximum applied stress below which there were no failures, increased from 46% UTS for R = −1 to 64% UTS for R=0, or from 116 to 162 kg cm⁻². Thus, as the stress range narrowed for a given maximum stress, the endurance limit increased with mean stress. For ATJ specimens of a given tensile strengthσ _i, the smallest value of maximum applied stress, σ_A, at which fatigue cracks propagated was defined byσ _A/σ _i ratios of 0.60 and 0.85 for R=−1 and R=0, respectively. In addition, selected fatigue tests were conducted for several mean compressive stresses in order to complete the definition of a Goodman diagram for ATJ graphite.