Fretting Fatigue Mechanism Research Articles

Cumulative fretting fatigue damage model for steel wire ropes

AbstractFretting fatigue contributes significantly to the fatigue failure process in steel wire ropes at the wire‐to‐wire trellis contact region with partial slip conditions. In this respect, this work demonstrates a new damage‐based fretting fatigue model for the prediction of such a failure process. The model is based on Lemaitre's damage equations for quasi‐brittle material with a damageable micro‐inclusion embedded in an elastic meso‐element. It incorporates the cyclic degradation of the elastic modulus of the drawn steel wire material. The fatigue life model acknowledges the mean stress effect. The constitutive and damage equations are formulated into user material (UMAT) subroutine for integration with Abaqus finite element analysis code. The localized fretting fatigue damage mechanism is simulated with an isolated two‐wire model. The effect of the contact condition with the coefficient of friction of 0.2 and 0.8 on the contact mechanics of the drawn wires is considered. The fretting fatigue mechanism map is established for each simulation case. The simulated results of N0 (no of cycles to initiate damage) and damage variable, D, confirm the fretting fatigue condition as the damage occurs in the slip region of the contact area for both the frictional conditions. The results were found in agreement with the previously establish Ruiz fretting parameter. This study will provide a base for the onward reliability assessment of steel wire ropes.

Improved fretting fatigue mechanism of surface-strengthened Ti-6Al-4V alloy induced by ultrasonic surface rolling process

Surface plastic deformation methods are prevalently applied to improve the fretting fatigue (FF) property of titanium alloys. Understanding the intrinsic relation between surface plastic deformation severity and the FF property is of great significance to the application of these methods. Here, the influence of surface plastic deformation severity on the FF behavior of Ti-6Al-4V alloy is investigated. Two different levels of surface plastic deformation severity are prepared at the surface of Ti-6Al-4V alloy by employing ultrasonic surface rolling process. Uniaxial FF tests illustrate that both of the deformed samples have improved FF properties and although their fatigue life is comparable, the influences of their refined microstructures and compressive residual stresses are different. Pre- and post-mortem microstructural analyses reveals that the grains are coarsened or crystallized from amorphous material at the topmost surface under the multiaxial stresses to accommodate the plastic strain for the high surface deformation severity, while the grains are refined at the subsurface for the low surface deformation during FF loading.

A Review of Research Progress on the Fretting Fatigue Mechanism and Protection Measures of Metal Matrix Composites

The performance characteristics of metal matrix composites (MMCs) and the need to study their fretting fatigue and wear during service are discussed. Four main elements of the study of fretting fatigue wear of MMCs (aluminum, copper, titanium, iron, magnesium, nickel, etc.) are discussed. These are factors influencing fretting fatigue, mechanism research, life prediction, and the development process of protection methods, respectively. Factors such as internal crack nucleation and development, loading conditions, and working environment are analyzed and discussed. The development trend of fretting fatigue research is outlined from several perspectives such as the fretting fatigue mechanism, research methods, and protection methods. In particular, the current state of research and the results achieved are highlighted, and some of the issues that remain to be studied are illustrated. The combined effects of fretting, fatigue and wear, the accuracy and applicability of fretting fatigue life prediction, the dispersion of the strengthening phase, and interface problems of MMCs themselves, etc., are all issues that need further research. The review summarizes some of the existing results and provides some reference help for subsequent developments.

Fretting fatigue mechanism of 40CrNiMoA steel subjected to the ultrasonic surface rolling process: The role of the gradient structure

In this research, a gradient nanostructure (GNS) of 40CrNiMoA steel prepared by the ultrasonic surface rolling process (USRP) is investigated. The results show that the USRP sample surface is equiaxial nanocrystalline and has a high-density nanolamellar gradient structure, and excellent compressive residual stress (CRS) and hardness gradient distribution are observed. In this study, the fretting fatigue (FF) limit of the USRP-treated specimen is 550 MPa, which is about 67 % higher than that of the untreated specimen. It is found that the equiaxed nanocrystalline top layer can effectively delay FF crack initiation. The high-density nanolamellar martensite structure is almost parallel to the surface, reduces the FF crack initiation angle, and increases the crack propagation path. High-strength CRS increases the crack growth resistance and changes the crack growth path. In addition, the improvement in surface hardness, CRS, and surface quality enhances the resistance to fretting wear and FF crack initiation. It is concluded that these factors effectively improve the FF limit of the material.

Failure analysis of a parabolic spring belonging to a railway wagon

This paper describes the study of three fractured parabolic springs belonging to a two-axle wagon suspension system. In order to determine the causes of the failures, a material analysis was performed, followed by a detailed study of the fracture’s surface both visually and using optical and scanning electron microscopy. The observations of fracture surfaces of the three springs revealed that the fractures began in the contact zones between the leaf springs, suggesting a fretting fatigue mechanism. The mechanism of failure of the springs fracture was a fatigue process. The propagation of fatigue cracks is more pronounced and extensive in one of the leaf springs. Finite element analyses were also performed taking into account the service conditions in order to determine the stress and strain distribution along the leaf springs. From the numerical simulations it can be concluded that the maximum stresses occur in two different zones: in the central section of the leaf spring and along the distance to the central section, in the sections where the relationship between the thickness reduction of the leaf spring and the resulting bending moment is most unfavourable. The Goodman's criterion shows a safety factor of approximately 1 and it can be concluded that this value is not enough to prevent the fatigue failure.

Fretting fatigue experiment and simulation of WC-12Co coating taking into account the wear effects

WC-12Co coating can be used to improve the wear resistance of mechanical connectors, but due to the fretting behavior between the contact interfaces during service, the problem of fretting fatigue cannot be ignored. Through the fretting fatigue experiment and simulation study of the WC-12Co coating, the fretting fatigue mechanism of the coating was investigated under the premise of considering the competitive or coupling relationship between fretting wear and fretting fatigue. Based on Smith-Watson-Topper (SWT) fatigue damage parameter and Miner-Palmgren (M-P) linear cumulative fatigue damage theory, a prediction model for fretting fatigue crack initiation life of WC-12Co coating was established, and the stress redistribution caused by fretting wear was analyzed by Archard wear theory. The analysis results show that the fretting fatigue cracks of the WC-12Co coating mainly initiate at the edge of the wear pits and gradually extend to the substrate; the increase of external load and friction coefficient will accelerate the fretting fatigue process of WC-12Co coating and reduce its fretting fatigue crack initiation life; the change of fretting fatigue crack initiation life and position of WC-12Co coatings caused by fretting wear depends on the change of contact state between contact interfaces.

The effect of phase difference and stiffness ratio on fretting fatigue behavior under variable normal load conditions

This paper investigated the effect of variable normal load on the fretting fatigue mechanism. A kinetics-based Q- P curve analysis method was proposed to assist testing system design and experiment result analysis. Based on this method, a biaxial fretting fatigue testing system was designed. Experimental and numerical investigation was carried out to discuss the effect of biaxial loading phase difference (the phase difference between bulk load and cyclic normal load) and stiffness ratio (the stiffness ratio between pad fixture and flat specimen) on the fretting fatigue mechanism. Based on the critical plane approach and proposed Q- P curves analysis method, it is found that the fretting status is partial slip regime under small stiffness ratio conditions. The stress/strain which is influenced by phase difference is the main factor of fretting fatigue damage in this condition. Furthermore, the mean stress of the normal load on the critical plane is compressive stress. It directly influences the fatigue damage under partial slip regime. With the increase of stiffness ratio and phase difference (from 0° to 90°), the fretting status changes from partial slip regime to gross slip regime, which means that the influence of wear increases. Wear inhibits the initiation of fatigue cracks, which has a positive influence on fretting fatigue life. As a result, the fretting failure mode gradually changes from fatigue to wear.

Fretting Fatigue Experiment and Finite Element Analysis for Dovetail Specimen at High Temperature

The dovetail attachment between the turbine blade and disk for an aero-engine operates under varying centrifugal load and vibration at elevated temperatures. The fretting fatigue is prone to occur at the contact surface of the dovetail attachment. This paper investigated the fretting fatigue behavior of the dovetail specimen at 630 °C through experiment and numerical simulation, in which the blade-like dovetail specimen is nickel-based single crystal superalloy DD10 while two fretting pads in contact with the dovetail specimen simulating the mortise of the disk are made of powder metallurgy FGH99. It is revealed from all the tests that the fracture induced by the fretting wear occurs at the upper edge area of the contact surface. The contact surface near the upper edge is more severely worn; hence, the phenomenon of partition on the worn contact surface can be observed, which is consistent with the fretting fatigue mechanism. Moreover, the calculated area of maximum contact pressure gradient through finite element method is in good agreement with the experimental position of the initial fretting fatigue cracks.

Fretting fatigue damage mechanism of Nickel-based single crystal superalloys at high temperature

A novel high temperature fretting fatigue test apparatus was developed to investigate the fretting fatigue mechanism of Nickel-based single crystal (NBSX) superalloys at elevated temperature. The fretting fatigue tests were carried out under 5 loading conditions at 600°C. Results showed that the fretting fatigue life decreased with the increase of axial load and normal load. Metallographic observations revealed that surface peeling, delamination occur at the contact area. Energy dispersive spectrum (EDS) analysis showed that the surface material was oxidized, and the oxides will be compacted onto the contact surface and form a glazed layer. Besides, many micro cracks are observed at the contact surface that are nearly perpendicular to the fretting direction. These micro cracks would either be eliminated due to the large relative displacement or grow into the main crack, which are supposed to be the dominant source of fretting fatigue failure. Multiple fretting fatigue cracks initiate at the contact leading edge area and grow along the (100) plane that is nearly perpendicular to the fretting direction. Then the crack propagation direction will deflect from (100) plane to a series of {111} planes and the specimen eventually failed. The combined effect of fretting wear and crystallographic slip is the cause of fretting fatigue failure.

On the diversity in design for different bending fretting fatigue mechanism

Fretting fatigue has emerged as the center of interest for research in recent decades due to its high importance in real application field. Despite this advancement, comparatively few experiments as well as studies have been accomplished on bending fretting fatigue. Researchers either developed new test rigs or accepted a conventional concept since there exists no specific, standalone and standard test rig. However, as it is difficult to compare each work with others, the increasing number of test rigs are not suitable to ensure the justified results under conditional circumstance. This article classified the existing bending fretting fatigue test rigs depending on the variable parameters like fretting and loading actions. It can be mentioned that reciprocating fretting fatigue test rigs have more diversities as compared to rotary fretting fatigue test rigs due to the advantages of variable loading values, displacement controlling, fretting damage pre-determination and other desirable purposes. This article might be useful as a state of art for future contributions of the modern technology in industrial applications.

Study of the variation of contact state near the contact boundary in a dovetail attachment under different loads

It is very important to characterize the variation of cyclic parameters near the contact edge in dovetail attachments for understanding the fretting fatigue mechanism. In this paper, the variation of contact state in a dovetail attachment was studied by using the finite element method (FEM), which is affected by two key factors i.e. the relative slip and the mutual compaction. When the flank angle and the coefficient of friction are constant, the influence of compaction seems much more obvious under centrifugal loads, and the edge of contact zone would move up along the contact surface. However, the influence of relative slip becomes much more obvious under tensile loads, and the edge of contact zone would move down. The movement of contact edge shows a similar trend under cyclic loads, which may result in the movement of position where the high stress gradient locates, and the numerical results show that the negative stress ratio would occur near the contact edge.

Fretting Fatigue Mechanism Research of the Aluminum Alloy Clinched Joints

Fretting Fatigue Mechanism Research of the Aluminum Alloy Clinched Joints

Observation of fretting fatigue cracks of Ti6Al4V titanium alloy

Using a test system developed in laboratory, the fretting fatigue mechanism of Ti6Al4V alloy has been studied, with analyses of fracture morphology and composition. The results show that fretting fatigue source area is semi-elliptical and occupies a small proportion of the total fracture surface. The area is relatively flat and smooth and shows traces of friction. With the increase of contact pressure, the depth of the source region first increases rapidly and then stabilizes, but the fatigue strength decreases rapidly and then stabilizes. Fretting causes severe oxidation of the surface. In the interface between the source and the fatigue propagation zone, the contents of O and Fe drop sharply.

Fretting fatigue on thread root of premium threaded connections

Identification of the fatigue failure mode of the premium threaded connection for Oil Country Tubular Goods pipes was conducted via full-scale fatigue tests. A through-wall crack was found at the imperfect thread root of the male embodiment, but the crack initiation site depended on the stress level. At relatively higher stress amplitude region, the crack originated from the thread rounded corner by stress concentration. At relatively lower stress amplitude region, the crack originated at the middle of the thread root because of fretting fatigue. To investigate the fretting fatigue mechanism in the threaded connection, a fundamental fretting fatigue test was conducted. This test achieved the fretting fatigue failure at the middle of the contact surface under large gross slip condition.

An investigation on fretting fatigue mechanism under complex cyclic loading conditions

In this paper, a methodology was proposed and an experimental configuration was designed to investigate the fretting fatigue mechanism under complex cyclic loading condition. This condition is common and highly influences the fretting fatigue behavior. However, it is barely studied at present. A series of fretting fatigue tests shown that cyclic normal load will enlarge the slip region of contact interfaces, making the crack nucleation location moves toward the middle range of contact region. It is demonstrated that complex cyclic loads have a positive effect of fretting damage, making the fatigue life shorter than those in constant normal loading conditions.

A fretting related damage parameter for fretting fatigue life prediction

As the mechanism of fretting fatigue is very complex, there is not a satisfactory fretting fatigue damage criterion at present. In this paper, a fretting related damage (FRD) parameter was proposed based on fretting fatigue mechanism and experimental results. Analysis result proves that tangential force can be used to quantify the effect of fretting. The fatigue lives predicted by FRD parameter are in close agreement with the experimental data. This parameter is succinct and has a determinate physical meaning. The proposed method can make full use of the plain fatigue research results for fretting fatigue life prediction.

An investigation into failure analysis of interfering part of a steam turbine journal bearing

Journal bearings as so sensitive parts of steam turbines are very susceptible to failure through different mechanisms of wear, fatigue and crush during service conditions. Failure occurring through these mechanisms lead to turbine completely shut down as a result of interfering in working conditions of bearing different parts. In this research, failed interfered part of a journal bearing related to a 320,000kW steam turbine was examined. Failure analysis investigations were performed by utilizing of stereographic, optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) analysis and hardness test. Surface crush, large amounts of surface cracks, no noticeable changes of failed surface chemical composition and microstructure with significant hardness improvement were the main obtained results. The studies were revealed that the bearing part loosing and inappropriate clearance can produce relative displacements under cyclic gradient loading. This condition was detrimental for the service life of turbine journal bearing via failure through fretting fatigue mechanism.

Fretting fatigue mechanism of bearing cap bolted joints.

Fretting fatigue is a common type of failure of the bearing cap bolted joints. This paper proposes a methodology to analyze the fretting fatigue mechanism of the bearing cap bolted joint. A biaxially loading system was designed to simulate fretting fatigue failure under typical engine working condition. Meanwhile, a submodel was developed in the finite element calculation to analyze the contact status and stress distribution of the structural models. The test result shows that long inclined cracks (about 650 μm long, orientation at 17°-34°) initiate at the middle region of the contact interface. As the increase of the bolt pretension load (from 6000 N to 10,000 N), the crack initial location is getting away from the bolt screw, and the fretting fatigue lives is increasing (from 7.8 × 10(5) to 6.0 × 10(6)). With the fatigue phenomenon and the stress field analysis result, it concludes that the crack initiation is governed by the maximum shear stress; the bolt pretension load and the additional rotate torque caused by the bearing load are the two main factors which affect the fretting fatigue mechanism of the bearing cap bolted joints. It is beneficial to fretting fatigue lives of the bearing cap joints by increasing the bolt pretension load and restraining the oscillation of the bearing cap.

Review and classification of fretting fatigue test rigs

There is no standard or generally accepted test rig for fretting fatigue experiments. Therefore,researchers adopt an existing concept, or build a new test rig that meets their specific requirements.However, too many different test rigs may be disadvantageous because the results of two different test rigsare hard to compare. The increasing amount of diversity is mainly caused by the lack of a recent literaturesurvey on fretting fatigue test rigs. In 1994, Hills and Nowell described a few test rigs in Mechanics OfFretting Fatigue. In this study, the authors made a classification of test rigs based on the contact geometry,which is determined by the test specimens, not by the test rig itself.Ghent University, Laboratory Soete, BelgiumThe authors of this article present a review of the available literature, and present a classification based onthe properties of test rigs. Fretting fatigue test rigs are first divided in two categories based on the geometryof the test specimen: full scale and coupon scale test rigs. The latter are mostly used to perform researchand are subdivided in categories based on increasing functionalities. This is the ability to apply a fatigueload, a constant normal force, and an alternating slip in the range of some micrometers. In time, from thefifties until now, progress has been seen in the design of fretting fatigue test rigs. More parameters can becontrolled during experiments and more measuring techniques are incorporated. State of the art test rigsare classified in the last category with most functionalities, but still have imperfections. Future designerscan use this article to classify their needs, or help to design a better test rig knowing the imperfections ofthe state of the art test rigs.

Fracture of Cementless Femoral Stems at the Mid-Stem Junction in Modular Revision Hip Arthroplasty Systems

Mechanical failure of femoral stems at the modular junction of revision hip arthroplasty systems has been reported only infrequently. In the current study, the cause of six stem fractures, which occurred in vivo, was analyzed with use of clinical data and failure analysis. Six patients with a fracture at the mid-stem junction of a modular revision hip implant were identified in our database of patients who had undergone revision arthroplasty. The characteristics of the patients with a fractured stem were compared with those of 165 patients from the same prospective database who had a modular stem implanted, had at least two years of follow-up, and had not had a fracture of the stem. Failure analysis of three implants (six fracture surfaces) was carried out, with use of microscopic, chemical, and microhardness characterization techniques. Patients with a fractured stem had significantly higher body mass indices than patients without a stem fracture. Radiographs demonstrated that these femoral implants lacked adequate osseous support of the junction area of the stem. All stems failed approximately 1 to 2 mm proximal to the body-stem junction, thus indicating the presence of a bending moment. The chemical composition and microhardness matched those of Ti-6Al-4V. Evidence of wear and fatigue were found on the fracture surface. A wear strip was also observed along the circumference of the stem near the junction. We concluded that the stem failure was initiated by a fretting fatigue mechanism and was propagated by a pure bending fatigue mechanism. Risk factors for fractures of the modular junction include excessive body weight and inadequate proximal osseous support because of trochanteric osteotomy, reduced preoperative bone stock, osteolysis, loosening, and/or implant undersizing. Surgeons should consider the use of implants with strengthened junctions when using modular stems in such patients.