Fretting Fatigue Conditions Research Articles

Investigating the effect of cold expansion on frictional force evolution during fretting fatigue tests of AL2024-T3 plates

In this paper, fretting fatigue experiments are conducted on cold expanded holed plates using fretting test configuration which is designed to simulate fretting fatigue condition around the holes. Two values of normal contact force and longitudinal cyclic load are applied on the specimens, and the evolution of friction force is measured during the tests. Finite element simulation is performed for better understanding of the cold expansion process and its effect on the contact configuration. The obtained results show that a high degree of cold expansion does not increase fretting fatigue life. Moreover, the value of frictional force is low at the early cycles of tests and increases to reach a stabilized value. The stabilized value of frictional force on the entrance and exit planes of low degree cold expanded specimens is almost the same, while it is lower on the exit plane of high degree cold expanded specimens in comparison to the entrance plane of the same specimen. It is revealed that the geometrical change that occurs on the plate during the high degree cold expansion process is the main cause of this phenomenon, while the increased hardness around the hole is the subsidiary factor.

Stress intensity factor solutions for fretting fatigue using stress gradient factor

This paper presents stress intensity factor (SIF) solutions for fretting fatigue conditions by including a stress gradient factor (SGF) to correct the classic geometry factor for tension semi-infinite strip (TSIS) specimen. This gradient factor considers the stress gradient due to the pressure of the pad on the surface of the specimen, which creates a high concentration of stresses around the contact of the bodies. To obtain these solutions, 2D finite element model simulations were performed varying important fretting parameters, namely: coefficient of friction, bulk stress intensity, pad radius and material. All configurations respected a partial slip contact condition and the results obtained show agreement with the ones obtained analytically. Weight functions were used to obtain stress intensity factors under mode I, then to compute the SGF, which were fit into equations with a unique structure, varying only coefficients. To consider real problems, a 3D correction factor was introduced. The final SGF presented a general form to compute SIF under fretting conditions when applied in suggested methods, such as: Strain-based Fracture Mechanics, Theory of Critical Distances (TCD) and Stress Gradient.

Numerical investigation of contact stresses for fretting fatigue damage initiation

Fretting fatigue phenomena occurs due to interaction between contacting bodies under application of cyclic and normal loads. In addition to environmental conditions and material properties, the response at the contact interface highly depends on the combination of applied loads. High stress concentration is present at the contact interface, which can start the damage nucleation process. At the culmination of nucleation process several micro cracks are initiated, ultimately leading to the structural failure. In this study, effect of ratio of tangential to normal load on contact stresses, slip amplitude and damage initiation is studied using finite element analysis. The results are evaluated for Ruiz parameter as it involves the slip amplitude which in an important factor in fretting fatigue conditions. It is observed that tangential to normal load ratio influences the stick zone size and damage initiation life. Furthermore, it is observed that tensile stress is the most important factor that drives the damage initiation to failure for the cases where failure occurs predominantly in mode I manner.

Methodology for reliability assessment of steel wire ropes under fretting fatigue conditions

This paper describes a newly-developed damage-based fatigue life model for the long-Term reliability assessment of drawn steel wires and wire ropes. The methodology is based on the computed local stress field in the critical trellis contact zone of a stranded wire rope by FE simulations and the estimated fretting damage of the drawn wire material. A case study using a single strand (1x7) steel wire rope with 5.43 mm-dia. drawn wires is employed to demonstrate the damage-based fatigue life prediction procedures. Under applied tensile loading with peak stress corresponding to 50%MBL (ΔP = 145 kN, R = 0.1), the von Mises stress cycles in-phase and with an identical stress ratio to the applied axial load. The damage initiation life at the trellis contact along the core wire is No = 673 cycles with an additional 589 load cycles to reach the first separation of the material point. The threshold load cycle for the fretting fatigue damage is predicted to be 12.3%MBL. An improved data set of the damage model parameters of the drawn steel wires is indispensable in achieving an accurate and validated life prediction model.

Lifetime prediction methodology for variable fretting fatigue loading: Plasticity effect

Both experimental and numerical approaches were developed to follow cracking damage in steel cylinder/plane fretting fatigue contact subjected to variable loading conditions.For the experimental approach, the potential drop technique was implemented on the fretting fatigue test device to observe on-line crack propagation. A calibration curve relating crack length and potential provided direct knowledge of cracking status.Numerically, total life was separated between crack nucleation and crack propagation. To formalize crack nucleation prediction, Crossland multiaxial fatigue behavior was applied at a critical distance to take into account the severe fretting fatigue gradients. The crack propagation rate was formalized using Kujawski’s fatigue crack driving force parameter, K‾∗, and coupling the Paris law of the material.Using this combined crack-nucleation/crack-propagation analysis, constant fretting fatigue conditions and variable fretting fatigue sequences were investigated. Good correlations were observed.Finally, the influence of different plastic laws was investigated. Both monotonic and cyclic approximations provided good correlation with experimental data, the cyclic description being closer.

Crack initiation and propagation under fretting fatigue of inconel 600 alloy

The purpose of the study is to experimentally investigate the fatigue crack initiation and propagation characteristics of nuclear power plant steam generator tube materials, Inconel 600 alloy, under fretting fatigue conditions. In addition, this study aims to enhance the overall reliability of nuclear power plant equipments by developing fretting fatigue life and integrity evaluation methods. In order to achieve these purposes, a fretting fatigue experiment apparatus is developed and fatigue crack growth experiments are conducted to evaluate the characteristics of Inconel 600 alloy under various stress conditions. Finally, microstructures are observed in accordance with fretting fatigue and contact pressure conditions and fretting fatigue crack initiation mechanism is examined.

Experimental and numerical study on crack initiation under fretting fatigue loading

Press-fitted railway axles and wheels are subjected to fretting fatigue loading with a potential hazard of crack initiation in press fits. Typically, the resistance against crack initiation and propagation in press fits is investigated in full-scale tests, which procedure is both costly and time consuming. In this context, combined experimental and numerical approaches are of increasing practical importance, as these may reduce the experimental effort and, moreover, provide a basis for the transferability of experimental results to different axle geometries and materials. This study aims at evaluating stress–strain conditions under which fretting fatigue crack initiation is likely to occur. Experiments on small-scale specimens under varying fretting fatigue load parameters and their finite-element modelling to characterize the resulting stress–strain fields are performed. Subsequently, different multiaxial fatigue parameters are applied to predict crack initiation under fretting fatigue conditions.

Multi-scale approach for the analysis of the stress fields at a contact edge in fretting fatigue conditions with a crack analogue approach

This paper describes a novel method to model the stress gradient effect in fretting-fatigue. The analysis of the mechanical fields in the proximity of the contact edges allows to extract nonlocal intensity factors that take into account the stress gradient evolution. For this purpose, the kinetic field around the contact ends is partitioned into a summation of multiple terms, each one expressed as the product between nonlocal intensity factors, Is, Ia, Ic, depending on the macroscopic loads applied to the mechanical assembly, and spatial reference fields, ds, da, dc, depending on the local geometry of the part. This description is obtained through nonintrusive post-processing of FE computation and is conceived in order to be easily implementable in the industrial context. By using as input the macroscopic load, the procedure consists in computing a set of nonlocal stress intensity factors, which are an index of the severity of the stress field in the proximity of the contact edges. This description has two main advantages. First, the nonlocal stress intensity factors are independent from the geometry used. Secondly, the procedure is easily applicable to industrial scale FE model..

Analysis of edge crack behaviour influenced by non‐symmetrical contact tractions and bulk tension

AbstractThis paper analyses a crack growth behaviour, which is initiated from the contact edge between a square punch with rounded edges and a half plane. Investigated are the influences of the contact profile, magnitude of the bulk tension and, crack obliquity, in particular, misalignment between the punch and half plane on the variation of the stress intensity factors KI and KII during the crack growth. The misalignment is simulated by a tilting of the punch. A partial slip regime is considered for the contact shear force to accommodate a general fretting fatigue condition. It was found that a crack closure occurs if only the contact forces are applied. The crack grows longer before it is closed if the punch is tilted (clockwise, in this paper) such that it initiates at the opposite site with respect to the direction of tilting. The closure phenomenon disappears when the bulk tension is added and exceeds a certain magnitude, which significantly depends on not only the contact profile but also the degree and direction of tilting. Provided are the lowest values of the bulk tensile stress due to a fatigue load necessary to extend the crack without a closure for each condition of the contact profile and misalignment. This may be used as a design guideline to restrain the contact‐induced failure.

Comparison of the cracking energy density and the Smith–Watson–Topper parameters in predicting fretting fatigue lifetime of a steel/aluminum alloy contact

ABSTRACTMany multiaxial fatigue parameters are available to estimate the onset of the crack initiation in mechanical components subjected to fretting fatigue conditions. This study focuses on the ability of the cracking energy density parameter to predict the fretting fatigue life. To estimate this, obtained predictions are compared with those given by another commonly used parameter, namely the Smith–Watson–Topper parameter. First, fretting fatigue experiments were achieved using a new designed setup with a mono‐contact configuration (aluminum/steel). A finite element model was used to compute the stress/strain fields around the contact zone. Because of the high stress gradient in the contact zone, the estimates of the two fatigue parameters, when using the mechanical quantities on the most loaded material point, lead to too conservative predicted values. It was therefore necessary to define a kind of process zone in which crack nucleation takes place. Using an averaging method to compute stress and strain in this zone, the obtained results show a quite good agreement between the estimated fatigue life and experimental data, whatever the used fatigue indicator. The size of this zone was then compared with the material microstructure and seems to be in the same magnitude that the average grain size.

Effect of fretting on fatigue performance of Ti-1023 titanium alloy

The plain fatigue and fretting fatigue tests of Ti-1023 titanium alloy were performed using a high-frequency push-pull fatigue testing machine. Both σmax versus number of cycles to failure curves were obtained for comparative analysis of the fretting effect on fatigue performance of the titanium alloy. Meanwhile, by analyzing the fracture of plain fatigue and fretting fatigue, the fretting scar and the fretting debris observed by scanning electron microscopy (SEM), the mechanism of fretting fatigue failure of Ti-1023 titanium alloy is discussed. The fretting fatigue strength of Ti-1023 titanium alloy is 175MPa under 10MPa contact pressure, which is 21% of plain fatigue strength (836MPa). Under fretting condition, the Ti-1023 titanium alloy fatigue fracture failure occurs in a shorter fatigue life. When it comes to σmax versus number of cycles to failure curves, data points in the range of 106–107cycles under plain fatigue condition moved to the range of 105–106 under fretting fatigue condition. The integrity of the fatigue specimen surface was seriously damaged under the effect of fretting. With the alternating stress loaded on specimen, the stress concentrated on the surface of fretting area, which brought earlier the initiation and propagation of crack.

Experimental Analysis and Modeling of the Crack Arrest Condition Under Severe Plastic Fretting Fatigue Conditions

The fretting-fatigue crack arrest condition is formalized as the condition for which a crack nucleates but stops propagating and so the sample never fails. Usually this domain is small as the fatigue loading greatly promotes the crack propagation. The aim of this research work is to investigate the crack arrest condition for severe plastic condition (maximal pressure is 2.5 times greater than the yield stress) and high fatigue stress ratio (R=0.94) thus for not much propagating conditions.A low alloyed industrial steel flat specimen (IS) fretted against a 35NCD16 steel cylinder pad was studied in order to identify the crack arrest condition for various fretting loadings (shear amplitude). An original experimental monitoring has been implemented on a fretting-fatigue test device to observe on-line the crack arrest using the potential drop technic. To rationalize these results, a fretting-fatigue map concept which consists to plot the crack arrest boundary as a function of the applied maximum fatigue stress and the fretting tangential force amplitude is applied [1].A 2D plain strain FEM modelling has been implemented to simulate the complex contact stressing including the contact plasticity. This plastic deformation promotes a significant extension of the contact and a proportional reduction of contact pressure and cyclic shear stresses. One consequence is that for a given contact and fatigue loading, this plastic accommodation of the interface tends to reduce the effective stress imposed to the material.The crack arrest boundary was formalized applying a pure mode I effective intensity stress range approximation [2]. It is shown that combining elastic-plastic FEM modelling, weight function and an adequate estimation of the effective intensity stress range, it is possible to predict with accuracy the fretting fatigue crack arrest boundary.

Contact mechanics in fretting fatigue

This paper studies the contact mechanics in a line contact during fretting fatigue conditions. Inliterature one can find numerical and analytical solutions of normal and tangential stresses for a variety ofloading cases. However, a unified solution valid for all loading cases during fretting fatigue conditions is notavailable. We present in this paper a strategy to combine existing contact mechanics theories into a unifiedcalculation procedure. Therefore, the relevant contact mechanics theories for an idealized cylinder-on-flatcontact are selected and bundled. Two clear flowcharts group the existing theories, which results in aunified strategy that can easily be implemented in a programming language. A Matlab script wasprogrammed and calculates the normal and tangential stress distribution based on the applied forces, thegeometry of the contact, the coefficient of friction and the material properties. The present theory can beused to automate the calculation of the stress distributions, or as validation of new numerical techniques.The script is modular and can be extended to calculate the lifetime of a component, by adding lifetimecriteria.

Numerical Investigation into the Effect of Contact Geometry on Fretting Fatigue Crack Propagation Lifetime

Fretting fatigue is a phenomenon in which two contact surfaces undergo a small relative oscillatory motion due to cyclic loading. There is a need to analyze the effects of contact geometry on crack propagation under fretting fatigue conditions. In this investigation, a finite element modeling method was used to study the effects of different contact geometries along with crack–contact interaction on crack propagation lifetime. Different contacts geometries—that is, cylindrical on flat and flat on flat—along with different contact span widths were analyzed. In addition, the effects of different contact spans on stress distribution at the contact interface were investigated. The computed crack propagation life was compared with experimental results. It was found that the crack initiated near the contact trailing edge for all contact geometries, which agreed with experimental observations. In terms of crack propagation for different contact spans, the fretting fatigue life for a two-based cylindrical pad was shorter than that for a two-based flat pad. By increasing the contact span width for both flat and cylindrical pads, the crack propagation lifetime increased. A comparison between the experimental and numerical results demonstrated a difference of about 18% in crack propagation lifetime.

FINITE ELEMENT MODELLING OF DAMAGE FRACTURE AND FRETTING FATIGUE

This paper summarises the research carried out to develop Finite Element (FE) modelling and predictive techniques for damage, fracture, fatigue and fretting fatigue problems. A damage model is developed based on Continuum Damage Mechanics and integrated within FE code. It is then used to predict the number of cycles to crack initiation in adhesively bonded joints. Furthermore, crack propagation algorithm is programmed within FE code using the principles of Fracture Mechanics and Paris law. The effect of mode mixity on crack propagation is taken into account using a Double Cantilever Beam (DCB) test specimen. Moreover, FE model of fretting fatigue aluminium test specimen is carried out in order to study the stress distribution and predict the crack propagation fatigue lifetime. Fretting fatigue problems involve two types of analyses; namely contact mechanics analysis and damage/fracture mechanics analysis. Both analyses are performed in FE code and the stress distribution along the contact surface between the two bodies is obtained and analysed. Furthermore, crack propagation analysis under fretting fatigue condition is presented. In most cases, the numerical results are compared to experimental ones.

Life prediction of titanium and aluminum alloys under fretting fatigue conditions using various crack propagation criteria. Part 2. Application of the technique to cylindrical specimens with semi-elliptical crack and account of the residual stresses

In order to simulate the operating fretting-fatigue conditions in cylindrical structural components, we have performed experimental studies on fretting fatigue of cylindrical specimens with clamped concave cylindrical pads of bridge type. Using the known solutions for stress intensity factors in the semi-elliptical cracks growing in cylindrical specimens, we predict the kinetics of propagation of fretting-fatigue cracks according to the two-parameter model described in Part 1. A close correlation of calculated and experimental fretting-fatigue life values is observed for AMg6N alloy for varied experimental fretting conditions (contact load, slip amplitude and friction coefficient). For alloy VT9 we have provided approbation of the technique, which takes into account distribution of the residual stresses in the material subsurface during calculation of stress-strain state and life under fretting-fatigue conditions.

A13 フレッティング疲労条件下の微小き裂進展に及ぼす接触面圧の影響(A1材料力学I)

A13 フレッティング疲労条件下の微小き裂進展に及ぼす接触面圧の影響(A1材料力学I)

A study on the prediction of fretting fatigue behavior

Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. The critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations.

Life prediction of titanium and aluminum alloys under fretting fatigue conditions using various crack propagation criteria. Part 1. Experimental and calculation techniques

Using the analysis of state-of-the-art techniques of fretting fatigue studies and results of description of multi-stage fatigue crack propagation in fretting zone within fracture mechanics framework, we have refined the calculation-and-experimental technique earlier proposed by the author. This technique allows one to predict current values of the angle and rate of inclined crack propagation in the subsurface layers of material under fretting conditions using calculated stress intensity factors KI and KII for contact and bulk loads, as well as experimental crack resistance diagrams by KI and/or KII types. We have performed comparative analysis of various techniques for construction of crack resistance diagrams by KI and KII types and obtained the results for AMg6N and Al 7075-T6 aluminum alloys and VT9 titanium alloy. It is shown that the initial stage of crack propagation in the above alloys can occur in the maximal shear stress plane by shear mechanism or in the maximal tensile stress plane by cleavage mechanism according to the Otsuka two-parameter criterion or to the Richard empirical criterion.

Characterization of crack nucleation in TA6V under fretting–fatigue loading using the potential drop technique

Crack initiation in a Ti–6Al–4V alloy was investigated experimentally in fretting fatigue conditions. A cylinder–plane geometry was used for the contact, and partial slip conditions were considered. The experiments were conducted on a new bi-actuator fretting fatigue machine and an original interrupted test expertise methodology was proposed. The potential drop technique is used to monitor crack nucleation. The careful calibration procedure used in this study and presented in this paper allowed the detection of cracks as small as 50 μm. Three experimental campaigns were conducted: fretting tests (optical expertise), fretting fatigue tests up to a lifetime of 100,000 cycles (optical expertise) and fretting fatigue interrupted tests (potential drop technique). The experiments have shown that the addition of a fretting–fatigue to conventional fretting conditions can induce a drop off of 45% of the tangential threshold for crack nucleation. Two mechanisms were shown to promote this drop off: increasing the fatigue load leads to a decrease of the tangential force nucleation threshold whereas raising the fretting load leads to a decrease of the nucleation and fracture fatigue lifetime.