Fretting Fatigue Damage Research Articles

Crack failure behaviors of Ti–6Al–4V dovetail joints subjected to fretting fatigue and effect of laser shock dimple-textured surface coated with diamond-like carbon film

Fretting damage can lead to a reduction in fatigue strength by more than half, due to the increased stress on the fretting surface, which accelerates crack initiation and propagation. Laser shock peening (LSP) technology is an advanced method for protecting against fretting fatigue, which reduces the effective stress on the fretting surface of components by introducing a deeper compressive residual stress field. In this work, LSP was utilized to create regularly arranged dimples on the surface of titanium alloy dovetail joints, and followed by diamond-like carbon (DLC) coating to alter fretting friction. Five surface treatment samples including as-machined, conv-LSP, LSP dimple-textured, DLC, LSP dimple-textured + DLC, were prepared for fretting fatigue tests on dovetail joints. The experimental results showed that the fatigue performance of specimens treated with LSP dimple-textured + DLC is better. Furthermore, it is found that wear debris from fretting surface was discharged into crack source area during fretting fatigue, leading to the formation of a fracture debris area forms in the crack initiation zone. The crack initiation zone displays the protrusion morphology characteristics due to the friction effect induced by contact loads. There is an internal correlation between the size of fracture debris area and surface wear resistance. Fracture debris area and the protrusion morphology vary with surface treatments and applied load. This research further reveals that the variation characteristics of the crack initiation area including the fracture debris area, have a positive influence on observing and analyzing failure behavior of fretting fatigue damage.

Fretting fatigue fracture behavior of Ti6Al4V dovetail joint specimens at 500°C treated with nanosecond stacked femtosecond laser impact strengthening

AbstractThe high‐temperature fretting fatigue damage characteristics of dovetail specimens strengthened by nanosecond laser (NL) and nanosecond combined femtosecond laser (F‐NL) were investigated. The results show that the fretting fatigue life of the NL strengthened sample (NL sample) is improved by 211.2% compared to the base metal samples (BM sample). The lifetime of the nanosecond combined femtosecond strengthened sample (F‐NL sample) was increased by 319.6%. It was attributed to the strengthening introducing hardened layers, residual compressive stress field, and high density of dislocations. The combined strengthening process reduces the surface roughness of the NL strengthened surfaces, while the strengthening influence layer is further increased. The fracture morphology shows that the crack source of the strengthened specimen has changed from multi‐source sprouting to single‐source sprouting, and the crack source sprouted on the subsurface. The fatigue strip morphology similarly confirms that a reduction in the crack propagation rate occurs.

Fretting fatigue damage mechanism of Ti6Al4V dovetail joint specimens at high temperature treated with salt layer

Salt layer preparation on the contact surface of Ti6Al4V dovetail joint specimens using solid NaCl and Na2SO4 deposition, the effect of hot salt layer on fretting fatigue properties of Ti6Al4V alloy at high temperature was studied. The maximum stress load and temperature are 10 kN and 500 °C, respectively. The results show that the average fatigue life of the base metal dovetail joint sample (BM sample) is 9.93×104, and the average fatigue life of the hot salt dovetail joint sample (HS sample) is increased to 69.9×104. The increase in fatigue life stems from the fact that the hot salt layer promotes the generation of thicker loose oxides on the surface of the Ti6Al4V alloy, besides, the lubricating effect of the oxide with higher hardness and the wear debris alleviates the fretting damage between the dovetail joint sample and the contact surface of the fretting pad. Fracture analysis shows that the hot salt layer does not change the crack initiation mechanism, and all of them show single crack source propagation and ductile fracture mechanism. Analysis of crack formation zone by electron back-scattered diffraction (EBSD), it is found that the presence of less dislocation distribution in the HS sample relative to the BM sample. The dislocations are more concentrated on the crack propagation paths and the fretting fatigue contact surfaces. This indicates that the BM sample produced more significant plastic deformation in the crack formation zone, accelerating crack initiation. The contact surface plastic deformation of the HS sample is small and the fretting fatigue life is enhanced.

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.

A comparative study of several life prediction models based on the critical plane approach for fretting fatigue crack initiation

AbstractTo reasonably forecast the crack initiation characteristics of fretting fatigue, this study evaluates the accuracy of several damage models. The existing experimental and simulation investigations are compared, noting the similarities and differences in the crack initiation location, crack orientation angle, and crack initiation life predicted by various damage models. It is crucial to employ a reasonable and reasonable damage prediction model of fretting crack initiation life, as fretting fatigue, a phenomenon of mechanically fastened connecting parts, can considerably reduce the fretting fatigue life of the components. This paper compares the fatigue damage prediction models of fretting fatigue specimens under partial slip conditions, and it will help researchers understand the benefits and drawbacks of various damage models and give them the knowledge and foundation to select the more reasonable fretting fatigue damage model.

Experimental and numerical study on the multi‐site fretting fatigue crack initiation of press‐fitted axles

AbstractIn this study, fretting fatigue tests were conducted to gather information on both fretting fatigue and fretting wear. Subsequently, an evaluation methodology that combined the Modified Wöhler Curve Method (MWCM) with the theory of critical distance (TCD) was established to investigate multi‐site fretting crack initiation. The results showed that the fretting fatigue damage could be reasonably evaluated using the MWCM equivalent stress σMWCM. σMWCM is greatly influenced by both bulk stress and fretting wear‐induced stress concentration. The stress field close to the wear boundary increased due to the continuous fretting wear, leading to an increase in σMWCM; meanwhile, the bulk stress near the wear boundary decreased as the crack propagated, resulting in a decrease in σMWCM. The combined effect of the fretting crack propagation and wear caused σMWCM, which was located within an annular strip of the axle, to exceed the critical value, causing the multi‐site fretting crack initiation.

Experimental and numerical study on press-fitted railway axles: Competition between fretting and plain fatigue

To investigate the competitive relationship between plain and fretting fatigue in press-fitted railway axles, the plain fatigue limit and fretting fatigue strength were tested, respectively, by changing the depth of the stress relief groove. Next, detailed information on fretting and plain fatigue, as well as on fretting wear, was gathered. Finally, an evaluation methodology integrating the finite element (FE) simulation with the Modified Wöhler Curve Method (MWCM) was established to evaluate the damage in both fretting and plain fatigue scenarios. It was found that as the groove depth increased, the plain fatigue limit decreased while the fretting fatigue strength increased. The optimal groove depth, hopt, that equalized the anti-fatigue capabilities of the groove and wheel seat, was affected by the number of test cycles. For this press-fitted railway axle, hopt was 0.2 mm < hopt < 0.4 mm for 107 test cycles, and hopt > 0.6 mm for 108 cycles. The calculated critical local stress condition, σCri, required for initiating a crack, was 161.8 MPa, which almost agreed with the theoretical value. The calculated σMWCM values can be used to characterise the fretting and plain fatigue damage. The local stress condition for determining an optimal groove depth was: σMWCM in the wheel seat and groove root simultaneously reached σCri.

Finite Element Analysis of the Influence of the Assembly Parameters on the Fretting Phenomena at the Bearing/Big End Interface in High-Performance Connecting Rods

Fretting fatigue is a well-known and dangerous damage mode that occurs on the mating surfaces of mechanical components, mainly promoted by a combination of stress distribution, contact pressure distribution, and relative sliding (micro)motion between the surfaces. However, predicting this mechanism is challenging, necessitating specific studies for each assembly due to variable influences. This article presents a methodology for evaluating fretting fatigue damage at the contact between a titanium connecting rod big end and the bearing, adopting the Ruiz parameter as a quantifying damage index. For this purpose, a thermal-structural finite element model is prepared. In particular, the machining and assembly of the split conrod big end are simulated, considering thermal effects. A full engine cycle is first simulated, and results are used for identifying critical instants to be considered for accurate yet computationally efficient calculations. The dependence of fretting fatigue on three factors is studied: bearing crush, bolts tightening torque, and friction coefficient between the big end and the bearing. In summary, the damage increases with a higher crush and friction, while tightening torque has marginal effects. Following a 20% increase in crush height, a corresponding 10% rise in the Ruiz parameter is observed. Conversely, reducing the crush height by 20% leads to an approximately 8% decrease in the Ruiz parameter. When the influence of the bolt preload is taken into account, only a marginal 1% increase of the Ruiz parameter is recorded despite a 30% rise in preload. Evaluating the impact of the friction coefficient on the Ruiz parameter reveals an almost linear relationship. These findings suggest that adjusting the screw preload can enhance the hydrodynamic behavior of the bearing without exacerbating fretting. Furthermore, exploiting the linear correlation between Ruiz and the friction coefficient allows for the generalization of results obtained with specific coefficient values. This methodology can, therefore, serve as a valuable reference for adjusting different variables during the initial design phases of a four-stroke internal combustion engine’s dismountable connecting rod.

On monitoring fretting fatigue damage in solid railway axles by acoustic emission with unsupervised machine learning and comparison to non-destructive testing techniques

Railway axles are safety-critical components of the rolling stock and the consequences of possible in-service failures can have dramatic effects. Although this element is traditionally designed against such failures, the initiation and propagation of service cracks are still occasionally observed, requiring an effective application of non-destructive testing and structural health monitoring approaches. This paper investigates the application of structural health monitoring by acoustic emission to the case of solid railway axles subject to fretting fatigue damage. A full-scale test was performed on a specimen in which artificial notches were suitably manufactured in order to cause the initiation and evolution of fretting fatigue damage up to the stage of relevant propagating fatigue cracks. During the test, both periodical phased array ultrasonic inspections and continuous acquisition of acoustic emission data have been carried out. Moreover, at the end of the test, the specimen was inspected, analyzed and evaluated by visual inspection and magnetic particles testing, while acoustic emission raw data were post-processed by a special unsupervised machine learning algorithm based on an Artificial Neural Network. It is demonstrated that the proposed methodology is very effective to detect the onset of crack initiation in a non-invasive and safe way.

A hybrid analytical-FEM 3D approach including wear effects to simulate fretting fatigue endurance: Application to steel wires in crossed contact

Fretting fatigue causes failures in steel wire ropes. A crossed wires set-up was used to investigate the influence of displacement amplitude on fretting fatigue damage. The analysis confirms previous literature results, showing a beneficial effect of wear in gross slip regime, which extends the contact area and thus decreases the contact stresses. The computation of such combined cracking and wear processes is very expensive using a classical FEM strategy, particularly for 3D contact geometries. To palliate such limitations, a hybrid analytical-numerical strategy was developped. It consists in estimating pressure and shear stress surface fields using analytical formulations, then to transpose these fields to an FEM model. This allows to simulate contact geometry modifications in a fast and efficient way.

Predicting fretting-fatigue endurance of rotating bending shrink-fitted assemblies using a sequential RUIZ-SWT approach: The effect of entrapped debris layer

Fretting-fatigue damage often appears in shaft shrink-fitted assemblies submitted to rotating bending. This paper focuses on the influence of the sleeve edge geometry on such damage. Rotating bending tests have been performed and broken and unbroken specimens have been expertized confirming fretting-fatigue phenomena. A 3D finite element method model was developed to evaluate the sliding and opening lengths. A sequential tribological - fatigue stress analysis strategy allowed the prediction of the maximum crack location ( Ruiz criterion) then the estimation of the fatigue endurance of the assembly using the SWT criterion. The last step of this σSWTXΓmaxapproach considers the presence of a debris layer within the contact to improve the consistency of the service life prediction.

Frictional half plane contacts subject to varying normal load and bulk tension under various load paths with application to fretting fatigue experiments

In many fretting fatigue experiments the loads applied to the contact are sinusoidal and in phase, creating a straight line path through load space. Although this form of loading is a good representation of many of the load histories present in engineering assemblies, the usefulness of this form of load cycle when investigating the causes of fretting fatigue damage is limited. In this paper we first review solutions for uncoupled half plane contacts under bulk tension and normal loading, then develop some novel load paths with properties that are desirable in fretting fatigue experiments. Throughout this paper the results are illustrated via application to a Hertzian contact, although the principles apply to any contact capable of representation using half-plane theory.

Numerical simulation of damage evolution of bolted connectors considering fretting fatigue effect

ABSTRACT In engineering, the failure of bolted connector is mainly caused by multi-axis non-proportional fretting fatigue damage. A three-dimensional finite element model of bolted connector is established in this paper, and a damage constitutive model suitable for multi-axial fatigue analysis is established based on the critical plane SWT (Smith Watson-Topper) method and continuous damage mechanics theory. A material subroutine UMAT is developed to describe the damage model and realizes the visualization of the damage evolution process caused by the fretting fatigue effect. Based on the test, the validity of the program is verified, the fretting fatigue characteristics and damage evolution characteristics of the bolted connector are analyzed. The results show that (i) the damage evolution analysis method can make up for the deficiency that the critical plane SWT method is only used for simple components and can be applied to the damage evolution analysis and fatigue life evaluation of three-dimensional complex structures. (ii) The crack initiation position of the connecting plate does not change with the magnitude of the tensile load and pre tightening force. In the process of losing the bolt preload from 1 to 0.8 times, the connected parts will be damaged faster as the preload 20 decreases.

Two-Scale analysis of fretting fatigue crack initiation in heterogeneous materials using Continuum Damage Mechanics

The phenomenon of fretting fatigue damage is related to tribological behaviour and commonly occurs at the contact interface between two bodies that sustain oscillation loads. Based on the complicated mechanical situation, several methods have been developed to predict the crack initiation location and life. The Continuum Damage Mechanics (CDM) approach in conjunction with Finite Element Method (FEM) is used in this paper. The fretting fatigue lifetime includes two parts, crack initiation lifetime and crack propagation lifetime, and this paper focuses on the crack initiation phase. Homogeneous materials are usually studied in fretting fatigue problems, and the influence of defects is necessary to be considered. In this study, the authors proposed several models to consider the effect of heterogeneity on crack initiation location and lifetime. The numerical model is a 2D one with plane strain assumption. To get more accurate numerical results with low computational cost, a Two-Scale Analysis approach is developed in this paper. Two macroscopic models and three microscopic models are proposed, including a Macroscopic homogeneous model (Macro-HOMO), a Multiscale Homogenization model with Direct Numerical Simulation (MH-DNS), a Microscopic homogeneous model (Micro-HOMO), a Microscopic Model with equivalent material properties by using Mean Field Homogenization method (Micro-MFH), and a microscopic model with Direct Numerical Simulation (Micro-DNS). The results obtained by using the CDM approach with different microscopic models are compared, and show that the prediction accuracy of the Micro-DNS is the best. In addition, in terms of computational cost, the Micro-DNS model shows great advantages as well comparing to the Macro-DNS model.

Numerical Simulation of Fretting Fatigue Damage Evolution of Cable Wires Considering Corrosion and Wear Effects

In this paper, a numerical model of fretting fatigue analysis of cable wire and the fretting fatigue damage constitutive model considering the multi-axis effect were established, and the user material subroutine UMAT was written. Then, the constitutive model of wear morphology evolution of cable wire and the constitutive model of pitting evolution considering the mechanical-electrochemical effect were established, respectively. The corresponding subroutines UMESHMOTION_Wear and UMESHMOTION_Wear_Corrosion were written, and the fretting fatigue life was further predicted. The results show that the numerical simulation life obtained by the program in this paper has the same trend as the tested one; the error is only about 0.7% in the medium life area; When the normal contact force increases from 120 to 240 N, the fretting life of cable wire decreases by 25%; When the evolution of wear morphology and corrosion effect are considered simultaneously, the depth of the wear zone exceeds 0.08 mm after 600,000 loads, which is much larger than 0.04 mm when only the evolution of wear morphology is considered. When the evolution of wear morphology and corrosion morphology is considered simultaneously, the damage covers the whole contact surface after 300,000 loads, and the penetrating damage zone forms after 450,000 loads, which is obviously faster than that when only the wear morphology evolution is considered. The method proposed in this paper can provide a feasible numerical simulation scheme for the visualization of the damage process and accurate life prediction of cable-supported bridges.

Fretting fatigue of interference fitted joints: development of a novel specimen for four-point rotating-bending tests and experimental results

Interference-fitted joints are widely used to join a shaft and a hub. The contact pressure produced by the interference induces stress concentration on the shaft at the hub end. FEA can be helpful in evaluating the related stress concentration factor. However, fretting damage may be generated and may arise from micro-sliding between the mating surfaces. It is currently not feasible to take this occurrence into account and to properly and reliably address this phenomenon by a standard numerical simulation. In order to tackle this question, an ad hoc specimen was designed for four-point rotating bending fatigue testing. The new specimen has three main advantages: the first one is the reduced dimensions with respect to the usually tested shafts, the second is the possibility of controlling the average contact pressure, and the third is the capability of easily dismounting the specimen without damaging the coupled surfaces. The specimen has been then tested. The study focused on C40 normalized steel, whose fretting fatigue limit was experimentally evaluated by the aforementioned device. The mating surfaces could also be carefully analyzed for fretting damage detection after cycling. The fatigue limit retrieved was 254 MPa and fretting damage and induced cracks were detected in the specimens, which proves the effectiveness of the introduced testing rig at reproducing fretting fatigue damage.

Experimental and numerical study on press-fitted railway axles: Fretting fatigue behaviour in the very high cycle regime

Fretting fatigue cracks at the press-fitted part of railway axles are commonly observed in the very high cycle (VHC) regime. However, most studies concerning the fretting fatigue behaviour of railway axles have been limited to the high cycle (HC) regime, which cannot provide sufficient knowledge to ensure the safe operation of railway axles over a service life of 30 years. In this study, fretting fatigue experiments for scaled railway axles were extended from the HC regime to the VHC regime. The fretting wear and fretting fatigue damage were observed and measured. Finally, based on the finite element simulation, an evaluation method coupled with the Modified Wöhler Curve Method (MWCM) and the theory of critical distance (TCD) was developed to investigate the fretting fatigue damage. The experimental investigation found that the fretting fatigue strength of railway axles in the VHC regime decreased with an increase in the number of test cycles, which can be described by the Basquin equation. This suggests that the fretting fatigue strength in the VHC regime can be predicted to provide data for the design of safer railway axles. The numerical study showed that the developed evaluation method can provide a reasonable estimation of the occurrence of fretting crack initiation in the VHC regime, and that the fretting fatigue damage can be described by the MWCM equivalent stress. The stress concentration at the press-fitted part gradually increased due to the continuous fretting wear, which resulted in the disappearance of the fretting fatigue limit of the press-fitted railway axles in the HC regime, and VHC fretting fatigue occurred.

Experimental study on fretting damage in the interference fit area of high-speed train wheels and axles based on specimen

Taking the high-speed train axles as the object, this paper designs and produces fretting fatigue specimens that simulate the interference fit of the high-speed train axles and conducts the fretting damage test on the interference fit area of the axles under rotating bending loads. The interrupted fretting fatigue tests were conducted based on the fretting fatigue limit to study the distribution, the damage of the wear debris and the characteristics of crack initiation of the specimen shaft in the contact area of the interference fit. Research shows that the fatigue limit of high-speed train axle materials is significantly reduced due to fretting damage in the interference fit area. The closer to the outer edge of the contact slip zone, the more concentrated the wear debris, the more severe the fretting fatigue damage. When the amount of wear debris reaches its maximum, the load cycle occurs 1 million cycles. Fretting wear and fretting fatigue coexist in the interference fit specimen under rotating bending loads, accompanied by the formation of third-body oxides between the contact surfaces.

Estimation Method of Relative Slip in Fretting Fatigue Contact by Digital Image Correlation

An experimental method that can quantify relative slip was developed using digital image correlation (DIC) in order to evaluate the sliding portion. The bridge-type test setup was designed to establish the fretting contact condition. The relative displacements between the contact surfaces were determined by DIC methods. Based on the evolution and distribution of relative slip, the transitions from gross slip to partial slip on the contact surface were found throughout all tests. This result indicated that the fretting scar was closely correlated to relative slip. The variation of relative slip corresponding to the stick-slip state was consistent with the tangential force coefficient. Besides, the load amplitude was an important factor for fretting fatigue damage, which can affect the stick-slip state.

Fretting fatigue behaviours of SiC reinforced aluminium alloy matrix composite and its monolithic alloy

This study presents the experimental and FEA (finite element analysis) investigations on the fretting fatigue behaviours of the metal matrix composite, 2124 Al–Cu–Mg alloy reinforced with 17 vol% of 3 μm SiC particles by a powder metallurgical route and its equivalent monolithic alloy, 2024. The predicted stress concentration and orientation from the nonlinear FEA stress analyses are aligned with the experimental observation including fretting wear damage and crack initiation and propagation. Compared with its equivalent monolithic alloy, the composite in the naturally aged condition (T4) demonstrates similar subsurface degradation but the crack propagation life is much shorter. In general, the composite has shown superior fretting fatigue performance in the low cycle regime (104 to 4x105 cycles) but not in the high cycle regime (4x105 to 107 cycles). Its fretting fatigue behaviour is interpreted in terms of higher wear resistance, delayed crack initiation, superior tensile strength in the low cycle regime. The reported fretting fatigue performance of the composite suggest the different material behaviours in low and high cycle regimes should be considered when developing a fretting fatigue damage model and assessing an engineering design.