scispace - formally typeset
Search or ask a question

Showing papers in "Fatigue & Fracture of Engineering Materials & Structures in 2003"


Journal ArticleDOI
TL;DR: An overview of rail defects and their consequences from the earliest days of railways to the present day can be found in this paper, where the authors present an overview of the rail defects in the early days of railway systems.
Abstract: For about 150 years, the steel rail has been at the very heart of the world's railway systems. The rail works in a harsh environment and, as part of the track structure, it has little redundancy; thus, its failure may lead to catastrophic derailment of vehicles, the consequences of which can include death, injury, costs and loss of public confidence. These can have devastating and long-lasting effects on the industry. Despite the advances being made in railway permanent way engineering, inspection and rail-making technology, continually increasing service demands have resulted in rail failure continuing to be a substantial economic burden and a threat to the safe operation of virtually every railway in the world. This paper presents an overview of rail defects and their consequences from the earliest days of railways to the present day.

372 citations


Journal ArticleDOI
TL;DR: In this article, a total of 128 fillet welded specimens were re-analysed by using an energy-based Notch Stress Intensity Factor (N-SIF) approach and the local weld toe geometry, characterised by its angle and radius, was measured with accuracy for the actual test series.
Abstract: In the Notch Stress Intensity Factor (N-SIF) approach the weld toe region is modelled as a sharp V-shaped corner and local stress distributions in planar problems can be expressed in closed form on the basis of the relevant mode I and mode II N-SIFs. Initially thought of as parameters suitable for quantifying only the crack initiation life, N-SIFs were shown able to predict also the total fatigue life, at least when a large part of the life is spent as in the propagation of small cracks in the highly stressed region close to the notch tip. While the assumption of a welded toe radius equal to zero seems to be reasonable in many cases of practical interest, it is well known that some welding procedures are able to assure the presence of a mean value of the weld toe radius substantially different from zero. Under such conditions any N-SIF-based prediction is expected to underestimate the fatigue life. In order to investigate the degree of conservatism, a total of 128 fillet welded specimens are re-analysed in the present work by using an energy-based N-SIF approach. The local weld toe geometry, characterised by its angle and radius, has been measured with accuracy for the actual test series. The aim of the work is to determine if the N-SIF-based model is capable of taking into account the large variability of the toe angle, and to quantify the inaccuracy in the predictions due to the simplification of setting the toe radius equal to zero.

184 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a universal fracture diagram for finite size components by simply introducing the shape factor a commonly used in fracture mechanics, where the obtained critical defect size was termed a D, which is a material and geometry dependent parameter, in order to distinguish it from a 0, which was a material parameter.
Abstract: A diagram valid for the analysis of the fatigue limit of cracks and notches centred in an infinite plate was recently proposed by the authors of the present work with the aim to make explicit the bridging at the fatigue limit between defect sensitivity (correlated to the length parameter a 0 , according to El Haddad-Topper-Smith's definition) and notch sensitivity (correlated to a*, where a* is a particular notch depth corresponding to the intersection between the ΔK th and Δσ 0 /K t curves). The expression a* = K 2 t .a 0 being valid, defect sensitivity and notch sensitivity were seen as two sides of the same medal. Such a diagram is now extended to finite size components by simply introducing the shape factor a commonly used in fracture mechanics. The obtained critical defect size is termed a D , which is a material and geometry dependent parameter, in order to distinguish it from a 0 , which is a material parameter. As a consequence the critical notch depth aN is introduced, such that. aN = K 2 t .a D This results in the proposal of a 'universal' diagram able to summarize experimental data related to different materials, geometry and loading conditions. The diagram, the validity of which is checked by means of several results available in the literature, is applied both to the interpretation of the scale effect and to the surface finishing effect.

172 citations


Journal ArticleDOI
TL;DR: In this paper, a stress-based method for low/medium-cycle fatigue assessment was proposed by considering the plane of maximum shear stress amplitude coincident with the microcrack initiation plane, which requires the calculation both of the maximum normal stress relative to the same plane.
Abstract: This paper extends to low/medium-cycle fatigue a stress-based method recently proposed by the same authors for high-cycle multiaxial fatigue assessments. By considering the plane of maximum shear stress amplitude coincident with the microcrack initiation plane, the method requires the calculation both of the maximum shear stress amplitude and the maximum normal stress relative to the same plane. Multiaxial fatigue life estimates are made by means of bi-parametric modified Wohler curves, which take into account the mean stress effect, the influence of the out-of-phase angle and the presence of notches by using a generalization to multiaxial fatigue of the fatigue strength reduction factor K f . Approximately 700 experimental data taken from the literature are used to demonstrate that the method is a useful tool to summarize fatigue strength data of both smooth and notched components, subjected to either in-phase or out-of-phase loads. Finally, a simple practical rule for the calculation of the multiaxial fatigue strength reduction factor is proposed.

148 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a two-dimensional finite element model in connection with the three-layer technique in order to reduce the computational effort and showed that the application of carbon fibre reinforced plastic (CFRP) strips and the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life.
Abstract: Pre-stress bonded composite patch is a promising technique to reinforce steel member damaged by fatigue. ifhe effectiveness of this technique was verified by fatigue tests on notched steel plates. Results showed that the application of carbon fibre reinforced plastic (CFRP) strips and, eventually, the introduction of a compressive stress by pretension of the CFRP strips prior to bonding produced a significant increment of the remaining fatigue life. In this paper, the stress intensity factor in the notched plates is computed by a two-dimensional finite element model in connection with the three-layer technique in order to reduce the computational effort. Due to high stress concentration at the plate crack tip, debond is assumed at the adhesive-plate interface. The goal is to illustrate the influence of some reinforcement parameters such as the composite strip stiffness, the pre-stress level, the adhesive layer thickness and the size of the debonded region on the effectiveness of the composite patch reinforcement.

145 citations


Journal ArticleDOI
TL;DR: In this paper, a multiaxial fatigue criterion for random loading is proposed, where the orientation of the critical plane, where fatigue life estimation is carried out, is determined from the weighted mean position of the principal stress directions.
Abstract: A multiaxial fatigue criterion for random loading is proposed. Firstly, the orientation of the critical plane, where fatigue life estimation is carried out, is determined from the weighted mean position of the principal stress directions. Then, the scalar value of the normal stress vector N(t) perpendicular to the critical plane is taken as the cycle counting variable since the direction of such a vector is fixed with respect to time (conversely to the time-varying direction of the shear stress vector C(t)), and a nonlinear combination of normal and shear stress components acting on the critical plane is used to define an equivalent stress amplitude. Finally, a damage accumulation model is employed to process such an equivalent stress amplitude and to determine fatigue endurance. This criterion is herein applied to some relevant random fatigue tests (proportional bending and torsion).

114 citations


Journal ArticleDOI
TL;DR: In this article, the problem of multiaxial fatigue limit estimation of sharply notched components has been addressed using two different methods: a critical distance method and a method involving modified Wohler curves.
Abstract: In this paper the problem of the multiaxial fatigue limit estimation of sharply notched components has been addressed using two different methods: a critical distance method and a method involving modified Wohler curves. These two methods had been previously developed by the authors, but required modification for use in conjunction with finite element stress analysis of sharply notched specimens subjected to multiaxial loadings. Initially, it was demonstrated mathematically that these methods are equivalent in terms of multiaxial stresses near the notch tip. Subsequently, by employing some well-known uniaxial notch fatigue concepts, some assumptions have been made in order to extend the use of these methods to in-phase multiaxial notch fatigue situations. Experimental data were obtained from tests conducted on V-notched specimens subjected to in-phase mixed Mode I and Mode II loadings. Both methods were successful in giving fatigue limit predictions with an error usually less than 15%. This is interesting because the two methods make quite different assumptions about the nature of fatigue crack growth in the vicinity of the notch.

111 citations


Journal ArticleDOI
TL;DR: In this paper, the fracture-toughness of the inorganic polymeric cement called geopolymer or PSS has been studied in recent years as a binder for mortar and concrete.
Abstract: The inorganic polymeric cement called geopolymer or PSS, has been studied in recent years as a binder for mortar and concrete. The present work reports the fracture toughness studies in mortars made of PSS cement matrix reinforced by wollastonite microfibers (Ca(SiO 3 )). K 1 -curves for PSS cement composites were determined according to the superposition asymptotic assumption and compared with reference Portland cement (PC) composites. The maximum toughness gain occurs in both composite systems with V f = 2%. For higher fibre volumes (3 and 5%), K I values decrease, due to an increase in porosity. Microstructural analyses showed that toughening mechanisms, as debonding and pullout of the fibers, are more common in PSS cement composites than in the reference PC composites. The difference of toughness between PSS and PC cement (0% of fibers) is about 80%. This demonstrates the high performance of these geopolymeric materials.

109 citations


Journal ArticleDOI
TL;DR: In this paper, the authors summarized the forces that develop in the contact patch between the wheel and rail in a railway vehicle and explained the ways that these forces govern the behaviour of a vehicle running on straight and curved track.
Abstract: This paper summarizes the forces that develop in the contact patch between the wheel and rail in a railway vehicle. The ways that these forces govern the behaviour of a vehicle running on straight and curved track are explained and the methods commonly used to calculate and utilize the forces summarized. As an illustration, the results from a computer simulation of a typical UK passenger train are presented and certain aspects examined.

95 citations


Journal ArticleDOI
TL;DR: In this article, the authors explored the nucleation and growth of cracks in filled natural rubber and found that a small positive R ratio can have a significant beneficial effect on fatigue life and crack growth rate, particularly at low strain range.
Abstract: Rubber components subjected to fluctuating loads often fail due to nucleation and the growth of defects or cracks. The prevention of such failures depends upon an understanding of the mechanics underlying the failure process. This investigation explores the nucleation and growth of cracks in filled natural rubber. Both fatigue macro-crack nucleation as well as fatigue crack growth experiments were conducted using simple tension and planar tension specimens, respectively. Crack nucleation as well as crack growth life prediction analysis approaches were used to correlate the experimental data. Several aspects of the fatigue process, such as failure mode and the effects of R ratio (minimum strain) on fatigue life, are also discussed. It is shown that a small positive R ratio can have a significant beneficial effect on fatigue life and crack growth rate, particularly at low strain range.

87 citations


Journal ArticleDOI
TL;DR: In this paper, a unified analysis to both high and low cycle fatigue based on elastic shakedown theories and dissipated energy is presented, with a presentation of the fatigue phenomena at different scales (microscopic, mesoscopic and macroscopic).
Abstract: The purpose of this paper is to present a unified analysis to both high and low cycle fatigue based on shakedown theories and dissipated energy. The discussion starts with a presentation of the fatigue phenomena at different scales (microscopic, mesoscopic and macroscopic) and of the main shakedown theorems. A review of the Dang Van high cycle fatigue criterion shows that this criterion is essentially based on the hypothesis of elastic shakedown and can therefore be expressed as a bounded cumulated dissipated energy. In the low cycle fatigue regime, recent results by Skelton and Charkaluk et al. show that we can speak of a plastic shakedown at both mesoscopic and macroscopic scale and of a cumulated energy bounded by the failure energy. The ideas are also justified by infrared thermography tests permitting a direct determination of the fatigue limit.

Journal ArticleDOI
TL;DR: In this paper, a finite element (FE) model was proposed to predict short crack growth conditions for rolling contact fatigue (RCF) loading on a railway line with a cylinder on a semi-infinite half space, with a short surface breaking crack.
Abstract: Recent accidents involving railway rails have aroused demand for improved and more efficient rail maintenance strategies to reduce the risk of unexpected rail fracture. Numerical tools can aid in generating maintenance strategies: this investigation deals with the numerical modelling and analysis of short crack growth in rails. Factors that influence the fatigue propagation of short surface-breaking cracks (head checks) in rails are assessed. A proposed numerical procedure incorporates finite element (FE) calculations to predict short crack growth conditions for rolling contact fatigue (RCF) loading. A parameterised FE model for the rolling-sliding contact of a cylinder on a semi-infinite half space, with a short surface breaking crack, presented here, is used in linear-elastic and elastic-plastic FE calculations of short crack propagation, together with fracture mechanics theory. The crack length and orientation, crack face friction, and coefficient of surface friction near the contact load are varied. The FE model is verified for five examples in the literature. Comparison of results from linear-elastic and elastic-plastic FE calculations, shows that the former cannot describe short RCF crack behaviour properly, in particular 0.1-0.2 mm long (head check) cracks with a shallow angle; elastic-plastic analysis is required instead.

Journal ArticleDOI
TL;DR: In this paper, a review of the models used to predict the cumulative fatigue damage in FRP composites is presented, in terms of fatigue strength and damage growth and are compared with those in the literature.
Abstract: A brief review of the models used to predict the cumulative fatigue damage in FRP composites is presented. Two-stage fatigue loading of a [0/90, ± 45 2 ,0/90] s quasi-isotropic woven carbon fibre/epoxy resin laminate was evaluated at stress ratio R = 0.05 and the failure mechanisms investigated using x-radiography after each loading stage. The results are presented in terms of fatigue strength and damage growth and are compared with those in the literature. A low-to-high loading sequence is more damaging than a high-to-low one and the Palmgren-Miner linear damage rule may no longer be valid for this kind of material, as previously reported.

Journal ArticleDOI
TL;DR: In this paper, the authors used a modified linear-elastic fracture mechanics (LEFM) approach to examine the mechanistic basis for these correlations, including consideration of the endurance limit rather than the threshold level as a factor controlling fatigue crack growth in the very short crack growth range, consideration of elastic-plastic behaviour, and consideration of crack closure in the wake of a newly formed crack.
Abstract: Murakami and Endo have used the √area parameter to successfully predict the endurance limits and the threshold levels for components, which contain small defects or cracks. The present paper uses a modified linear-elastic fracture mechanics (LEFM) approach to examine the mechanistic basis for these correlations. The modifications include consideration of the endurance limit rather than the threshold level as a factor controlling fatigue crack growth in the very short crack growth range, consideration of elastic-plastic behaviour, and consideration of the role of crack closure in the wake of a newly formed crack. Predictions based upon the modified LEFM behaviour are found to be consistent with the earlier predictions of Murakami and Endo.

Journal ArticleDOI
TL;DR: In this article, a hybrid crack element (HCE) is introduced which is powerful and convenient not only for directly determining the SIF but also the coefficients of higher order terms in the plane linear elastic crack tip asymptotic field.
Abstract: An improvement to the extended finite element method (XFEM) and generalised finite element method (GFEM) is introduced. It enriches the finite element approximation of the crack tip node as well as its surrounding nodes with not only the first term but also the higher order terms of the linear elastic crack tip asymptotic field using a partition of unity method (PUM). Numerical results show that together with a reduced quadrature rule to the enriched elements, this approach predicts accurate stress intensity factors (SIFs) directly (i.e. without extra post-processing) after constraining the enriched nodes properly. However, it does not predict accurately the coefficients of the higher order terms. For that a hybrid crack element (HCE) is introduced which is powerful and convenient not only for directly determining the SIF but also the coefficients of higher order terms in the plane linear elastic crack tip asymptotic field. Finally, the general expressions for the coefficients of the second to fifth terms of the linear elastic crack tip asymptotic field of three-point bend single edge notched beams (TPBs) with span to depth ratios widely used in testing are extended to very deep cracks with the use of the HCE.

Journal ArticleDOI
TL;DR: In this paper, a bainitic rail steel with potential additional resistance to rolling contact fatigue damage is described. But, the performance of the bainite steel is not fully understood, although a number of hypotheses exist.
Abstract: Rails are a major capital and maintenance cost for railways in North America. While manufacturers produce clean steels with high quality, most rails made today retain the basic carbon-manganese chemistry of traditional pearlitic rails. This paper describes the development of a bainitic rail steel with potential additional resistance to rolling contact fatigue damage. It is shown that rails can be produced in bainitic steel without the need for complex heat treatments after rolling, and that bainitic rails can have higher hardness and fracture toughness than pearlitic rails. Although small- and full-scale tests indicate that the wear performance of bainitic steel depends considerably on test conditions, the indication is that bainitic steel rails can have significantly better rolling contact fatigue performance compared to pearlitic rails. Reasons for the superior fatigue performance are not fully understood, although a number of hypotheses exist. A conclusion is that continued research would be useful to understand quantitatively the physics and metallurgy of wheel/rail contact.

Journal ArticleDOI
TL;DR: In this article, a crack growth induced debonded region in the adhesive-plate interface was observed using an optical technique, and the size of the debond region significantly influences the efficiency of the crack repair.
Abstract: Prestressed composite patch bonded on cracked steel section is a promising technique to reinforce cracked details or to prevent fatigue cracking on steel structural elements. It introduces compressive stresses that produce a crack closure effect. Moreover, it modifies the crack geometry by bridging the crack faces and so reduces the stress intensity range at the crack tip. Fatigue tests were performed on notched steel plate reinforced by CFRP strips as a step toward the validation of crack patching for fatigue life extension of riveted steel bridges. A crack growth induced debonded region in the adhesive-plate interface was observed using an optical technique. Moreover, the size of the debonded region significantly influences the efficiency of the crack repair. Debond crack total strain energy release rate is computed by the modified virtual crack closure technique (MVCCT). A parametric analysis is performed to investigate the influence of some design parameters such as the composite patch Young's modulus, the adhesive thickness and the pretension level on the adhesive-plate interface debond.

Journal ArticleDOI
TL;DR: In this article, a new model for three-dimensional progressive failure analysis of adhesive joints is presented, which uses interface elements and includes a damage model to simulate progressive debonding, which allows the simulation of the initiation and growth of damage at interfaces without considering the presence of initial flaws.
Abstract: The paper presents a new model for three-dimensional progressive failure analysis of adhesive joints. The method uses interface elements and includes a damage model to simulate progressive debonding. The interface finite elements are placed between the adherents and the adhesive. The damage model is based on the indirect use of fracture mechanics and allows the simulation of the initiation and growth of damage at the interfaces without considering the presence of initial flaws. The application of the model to single lap joints is presented. Experimental tests were performed in aluminium/epoxy adhesive joints. Linear elastic and elastoplastic analyses were performed and the predicted failure load for the elastoplastic case agrees with experimental results.

Journal ArticleDOI
TL;DR: A review of the literature on crack closure/opening load and crack tip shielding effects determination methods is presented in this paper, where commonly used "subjective" (visual) and non-subjective approaches have been included.
Abstract: In this paper a review of the literature on crack closure/opening load and crack tip shielding effects determination methods is presented. Commonly used ‘subjective’ (visual) and ‘non-subjective’ approaches have been included. Procedures associated with the determination of an effective crack driving force for both Elber type and that of partial (or incremental) crack closure models have been covered. Comparison among different methods of analyses based on compliance and fatigue crack growth rate measurements is discussed together with their implications and difficulties in fatigue crack growth correlations.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the crack growth behavior of 0.47% carbon steel under mode II and III loadings and found that crack branching started from small semi-elliptical cracks nucleated by shear at the tip of the original circumferential crack.
Abstract: The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔK IIth . The relationship ΔK IIth >ΔK Ith caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory-roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both node II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory-roofs were formed by crack branching into mode I. Crack branching started from small semi-elliptical cracks nucleated by shear at the tip of the original circumferential crack.

Journal ArticleDOI
TL;DR: In this article, the problem of modeling the specific effects of brittle fracture in high loading rate conditions is discussed, and an approach based on the system of fixed material constants describing macro-strength properties of the material is considered.
Abstract: Discrete features of the dynamics of fracture of solids are analyzed. The problem of modeling of some of the specific effects of brittle fracture in the high loading rate conditions is discussed. An approach based on the system of fixed material constants describing macro-strength properties of the material is considered. New principles of material testing are analyzed. The corresponding incubation time criterion allows one to manage without the a priori given rate dependences of dynamic strength and fracture toughness. An application of the incubation time criterion to the problem of erosion is considered.

Journal ArticleDOI
TL;DR: In this article, a 3D finite element study of mode I fatigue crack growth in the small-scale yielding (SSY) regime under a constant amplitude cyclic loading with zero T-stress and a ratio K min /K max = 0.
Abstract: Plasticity induced closure often strongly influences the behaviour of fatigue cracks at engineering scales in metallic materials. Current predictive models generally adopt the effective stress-intensity tractor (ΔK eff =K max -K oP ) in a Paris law type relationship to quantify crack growth rates. This work describes a 3D finite element study of mode I fatigue crack growth in the small-scale yielding (SSY) regime under a constant amplitude cyclic loading with zero T-stress and a ratio K min /K max = 0. The material behaviour follows a purely kinematic hardening constitutive model with constant hardening modulus. Dimensional analysis suggests, and the computational results confirm, that the normalized remote opening load value, K op /K max at each location along the crack front remains unchanged when the peak load (K max ), thickness (B) and material flow stress (σ 0 ) all vary to maintain a fixed value of K = K max/σ0 √B. Through parametric computations at various K levels, the results illustrate the effects of normalized peak loads on the through-thickness opening-closing behaviour and the effects of σ 0 /E, where E denotes material elastic modulus. The examination of defamation fields along the fatigue crack front provides additional insight into the 3D closure process.

Journal ArticleDOI
TL;DR: In this paper, a hypothesis on the basis of local normal and shear stresses in the critical plane has been developed and applied to aluminium weldings, which reveals no influence of changing principal directions on fatigue life compared to multiaxial loading with constant principal stress directions.
Abstract: Multiaxial stress states occur in many welded constructions like chemical plants, railway carriages and frames of trucks. Those stresses can have constant and changing principal stress directions, depending on the loading mode. Latest research results on welded steel joints show a loss of fatigue life for changing principal stress directions simulated by outer-phase bending and torsion compared to constant directions given by in-phase loading. However, aluminium welds reveal no influence of changing principal directions on fatigue life compared to multiaxial loading with constant principal stress directions. This behaviour is not predictable by any conventional hypothesis. A hypothesis on the basis of local normal and shear stresses in the critical plane has been developed and applied to aluminium weldings.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a procedure for estimating the total fatigue life in fretting fatigue and separately analyzed the fatigue crack initiation and propagation lives, considering a non-arbitrary crack initiation length provided by the model.
Abstract: This paper proposes a procedure for estimating the total fatigue life in fretting fatigue. It separately analyses the fatigue crack initiation and propagation lives. The correlation between crack initiation and propagation is made considering a non-arbitrary crack initiation length provided by the model. The number of cycles to initiate a crack is obtained from the stress distribution beneath the contact zone and a multiaxial fatigue crack initiation criterion. The propagation of the crack is considered using different fatigue crack propagation laws, including some modifications in order to take the short crack growth into account. The results obtained by this method are compared with the fatigue lives obtained in various fretting fatigue tests under spherical contact with 7075-T6 aluminium alloy.

Journal ArticleDOI
TL;DR: In this article, a progressive fatigue damage model has been developed for predicting damage accumulation and life of carbon fiber-reinforced plastics (CFRP) laminates with arbitrary geometry and stacking sequence subjected to constant amplitude cyclic loading.
Abstract: A progressive fatigue damage model has been developed for predicting damage accumulation and life of carbon fibre-reinforced plastics (CFRP) laminates with arbitrary geometry and stacking sequence subjected to constant amplitude cyclic loading. The model comprises the components of stress analysis, fatigue failure analysis and fatigue material property degradation. Stress analysis of the composite laminate was performed by creating a three-dimensional finite element model in the ANSYS FE code. Fatigue failure analysis was performed by using a set of Hashin-type failure criteria and the Ye-delamination criterion. Two types of material property degradations on the basis of element stiffness and strength were applied: a sudden degradation because of sudden failure detected by the fatigue failure criteria and a gradual degradation because of the nature of cyclic loading, which is driven by the increased number of cycles. The gradual degradation of the composite material was modelled by using functions relating the residual stiffness and residual strength of the laminate to the number of cycles. All model components have been programmed in the ANSYS FE code in order to create a user-friendly macro-routine. The model has been applied in two different quasi-isotropic CFRP laminates subjected to tension–compression (T–C) fatigue and the predictions of fatigue life and damage accumulation as a function of the number of cycles were compared with experimental data available in the literature. A very good agreement was obtained.

Journal ArticleDOI
TL;DR: In this article, a computer model is presented to simulate the wear of ductile material subject to repeated loading, and the model is used to study the effect of partial slip on wear rate.
Abstract: A computer model, which simulates the ratcheting wear of a ductile material subject to repeated loading, is presented and discussed in detail. Variation of material properties is a feature of the model, failure by ductility exhaustion occurring at isolated points or extending regions of failure. Such regions form crack-like features. Mechanisms for removal of weakened material from the surface as wear debris are described. The wear process causes a degree of surface roughness. The simplicity of the model enables simulation of millions of load cycles in only a few hours' computer time. The computer model is used to study the effect of partial slip on wear rate. When creepage is relatively low, the wear rate increases sharply with creepage. When creepage is relatively high, the wear rate is largely insensitive to the creepage.

Journal ArticleDOI
TL;DR: In this paper, the predictive tools for rail fatigue and profile deterioration have been developed and applied to the process of rail grinding, and these models are substantiating the past practices and providing a pathway towards the development of improved predictive tools.
Abstract: Modern rail grinding practices have developed largely through a combination of field experience and intuitive speculation. Many theories related to crack initiation and growth have been proposed through the decades, and those concepts have been cleverly extended to the field of rail grinding to form the basis of the practice known as ‘preventive grinding’. But only recently have practical models emerged from the laboratory and theoretical environment and been applied to the process of rail grinding. These models are substantiating the past practices and providing a pathway towards the development of improved predictive tools for rail fatigue and profile deterioration.

Journal ArticleDOI
TL;DR: In this article, 10 10 -cycle fatigue tests were conducted at 100 Hz for three years and at 20 kHz for one week on 1800 MPa-class JIS-SUP7 spring steel.
Abstract: 10 10 -cycle fatigue tests were conducted at 100 Hz for three years and at 20 kHz for one week on 1800 MPa-class JIS-SUP7 spring steel. Uniaxial tests up to 10 8 cycles were also conducted at 120 and 600 Hz. The 120 Hz tests had larger control volumes. The fatigue limit at 10 10 cycles was lower than at 10 8 cycles, and any frequency effect was shown to be negligible. A size effect was found; the tests with larger control volumes showed results of lower fatigue strength.

Journal ArticleDOI
TL;DR: In this article, a crack-like Notch Analogue model is proposed for finite-life fatigue design in the presence of a geometrical notch, and the model is shown to be asymptotically correct if friction is infinitely high or the contact area is very small.
Abstract: Various analogies have recently been proposed for comparing the stress fields induced in fretting fatigue contact situations, with those of a crack and a sharp or a rounded notch, resulting in a degree of uncertainty over which model is most appropriate in a given situation. However, a simple recent approach of Atzori–Lazzarin for infinite-life fatigue design in the presence of a geometrical notch suggests a corresponding unified model also for fretting fatigue (called Crack-Like Notch Analogue model) considering only two possible behaviours: either 'crack-like' or 'large blunt notch.' In a general fretting fatigue situation, the former condition is treated with a single contact problem corresponding to a Crack Analogue model; the latter, with a simple peak stress condition (as in previous Notch Analogue models), simply stating that below the fatigue limit, infinite life is predicted for any size of contact. In the typical situation of constant normal load and in phase oscillating tangential and bulk loads, both limiting conditions can be readily stated. Not only is the model asymptotically correct if friction is infinitely high or the contact area is very small, but also remarkably accurate in realistic conditions, as shown by excellent agreement with Hertzian experimental results on Al and Ti alloys. The model is useful for preliminary design or planning of experiments reducing spurious dependences on an otherwise too large number of parameters. In fact, for not too large contact areas ('crack-like' contact) no dependence at all on geometry is predicted, but only on three load factors (bulk stress, tangential load and average pressure) and size of the contact. Only in the 'large blunt notch' region occurring typically only at very large sizes of contact, does the size-effect disappear, but the dependence is on all other factors including geometry.

Journal ArticleDOI
TL;DR: In this article, the impact of contact pressure, stress amplitude, stress ratio, and contact geometry on the degradation process of fretting fatigue crack nucleation in Ti−6Al−4V when fretted against itself is investigated to determine the influence of contact pressures, stress amplitudes, stress ratios, and contacts geometry on degradation process.
Abstract: Fretting fatigue crack nucleation in Ti−6Al−4V when fretted against itself is investigated to determine the influence of contact pressure, stress amplitude, stress ratio, and contact geometry on the degradation process. For the test parameters considered in this investigation, a partial slip condition generally prevails. The resulting fatigue modifying factors are 0.53 or less. Cycles to crack nucleation, frictional force evolution, crack orientations and their relationship to the microstructure are reported. The crack nucleation process volume is of the same order as the microstructural length scales with several non-dominant cracks penetrating 50 μm or less. The effective coefficient of friction increases during early part of fretting. Observations suggest that cyclic plastic deformation is extensive in the surface layers and that cyclic ratchetting of plastic strain may play a key role in nucleation of the fretting cracks. A Kitagawa–Takahashi diagram is used to relate the depth of fretting damage to the modifying factor on fatigue life.