Fretting Fatigue Life Research Articles

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.

Effect of faying surface treatments and bolt tightened levels on fretting fatigue performance of slip critical connections with high strength bolts

The experimental investigation focuses on the fretting fatigue performance of M24 high-strength bolt slip critical connections (SCC) under shear load, taking into account the influence factors of faying surface treatments and bolt tightened levels. A novel extensometer supporting device for measuring micro-displacement between connection plates is proposed. The μ-N curves are obtained. Three-dimensional surface morphology scanning and fracture morphology analysis are conducted on the specimens. The results showed that the SCC contact area can be divided into stick, partial slip, and gross slip, with distribution ranges determined for each zone. Meanwhile the fretting fatigue life decreases with the increase of μ and pre-tension. Finally, a prediction of fretting fatigue life is made based on a multiaxial fatigue critical plane model.

Fretting fatigue life of galvanized bridge support cable wire: Experimental study and strain-based fracture mechanics analysis

The galvanized wires used in cable bridges can fail due to fretting fatigue. Experimental results have shown that defects resulting from the galvanization process are a possible source of initiation for fatigue cracks and make the life shorter than that of a wire without a galvanized layer. The investigation presented in this paper uses strain-based fracture mechanics to analyze the influence of these defects on the fatigue life of galvanized wire. The presented analysis considers nonlinear material behaviour. A 3D finite element model is used to compute the required stress field. Stress intensity factors are obtained by a proposed numerical point load weight function, and shape factors are found for the surface and deepest points of the semielliptical crack. Plain fatigue tests of galvanized wires are performed to calibrate key model parameters. The calibrated model is then shown to provide reasonably accurate but systematically conservative estimates of the fatigue life under fretting conditions typical of bridge stay cable saddle supports.

A modified critical distance method for estimating fretting fatigue life of dovetail joints

AbstractIn this paper, a modified theory of critical distance (TCD) method (i.e., Gradient‐TCD method) is proposed, which combines fatigue parameter gradient and the TCD, to estimate fretting fatigue life of dovetail joints. The advantage of Gradient‐TCD method lies in utilizing the gradient parameters to effectively characterize the local effect zone caused by fretting, thereby enabling the determination of a suitable critical distance length independent of material fatigue parameters. The reliability and predictive capability of the method is validated through experimental results. Furthermore, this method demonstrates insensitivity to mesh size, resulting in an 83.6% reduction in computational time while maintaining the predictions within the two‐times scatter band. The novel Gradient‐TCD method may provide an efficient and reliable approach for fretting fatigue life prediction, which holds promise for evaluating complex full‐scale fretting problems.

Nonlocal multiaxial fatigue model based on artificial neural networks for predicting fretting fatigue life of dovetail joints

Fretting fatigue of dovetail joints is of paramount importance for ensuring equipment safety, where the swift and precise estimation of their fatigue life is crucial. In this study, we present a nonlocal multiaxial fatigue model based on artificial neural networks (ANN) to tackle these challenges. Initially, the damage parameters were calculated using critical plane approaches (CPA) and theory of critical distance (TCD) analysis, and the fretting fatigue stress was computed. Subsequently, these parameters were integrated as input features in the ANN model to predict the fretting fatigue life of dovetail joints. The predicted results demonstrate that this proposed model can accurately predict the fretting fatigue life of dovetail samples within a 1.5× limit band. Furthermore, a comparative analysis with other ANN models inspired by previous researchers also supports this viewpoint. This capability stems from its integration of ANN representation capabilities with physics and domain knowledge, such as CPA/TCD methods and fretting fatigue stress analysis. This approach not only establishes a theoretical foundation for predicting the fretting fatigue life of dovetail samples but also showcases promising practical applications.

Fretting fatigue life prediction of full-scale dovetail joints using the theory of critical distances with mesh control

The fretting fatigue life of full-scale dovetail joints in two contact configurations was estimated using the theory of critical distance with the area method (TCD-AM) and the mesh control method (TCD-MC). The TCD-MC method demonstrated prediction accuracy comparable to the traditional TCD-AM method, while improving computational efficiency by 85 %. By incorporating a calibration strategy with the TCD-MC method, the predicted fatigue life was within the scatter band of factor 3 when compared with the experimental data, indicating its reliability. The proposed parameter-fitting method for TCD-MC yielded results nearly identical to the conventional method, while reducing the workload by 75 %. The TCD-MC method is expected to provide a potentially novel and convenient approach for fretting fatigue life prediction in full-scale specimen.

Fretting fatigue in dovetail assembly and bridge-flat model: Verification of a life prediction model based on stress gradient

The dovetail assembly and the bridge-flat model are two typical fretting fatigue tests. This article concentrates on the fretting fatigue of the dovetail assembly, utilizing a sub-scaled specimen tested under cyclic loading. Simultaneously, fretting tests on the bridge-flat and combined high and low cycle fatigue tests on the dovetail assembly were conducted. These tests were analyzed in conjunction with the dovetail assembly to understand the stress state characteristics in the contact region. The results from both tests and finite element analysis highlight that fretting leads to a significant reduction in fatigue life, primarily attributed to stress concentration at the edges of the contact area. Building upon the method of stress gradient correction, a life prediction model for fretting fatigue is proposed, demonstrating good accuracy in predicting fretting fatigue life.

Numerical investigation to the effect of wear on fretting fatigue life using CDM and fracture mechanics

Fretting fatigue is a common type of problem in the engineering fields. Due to its multiaxial characteristics, it leads to a shorter overall fatigue life compared to plain fatigue. Fretting fatigue is caused by the micro slip at the contact surface, which is always accompanied by interface wear. This paper presents a refined elastic numerical simulation method combining interfacial wear with continuum damage mechanics (CDM) and fracture mechanics to predict fatigue life. The crack initiation life is determined by damage evolution law and the initiation position is determined by the total dissipated energy. Crack propagation life and path can be predicted using stress intensity factor. The stress redistribution and geometric change of contact surface caused by wear are considered in the whole fatigue process. Results indicate that the fretting fatigue simulation method incorporating wear has higher accuracy compared with the experimental results in the literature. It is noteworthy that wear retards nucleation damage process and crack propagation. As stress amplitude decreases, fatigue life increases, and delay effect of wear becomes more obvious. Additionally, wear causes the crack initiation position to move out, but crack initiation region is still near the slipping zone and propagation path does not change.

Study of the Point Method for fretting fatigue life prediction

With the improvement and success of the Theory of Critical Distances (TCD) in notch fatigue problems, the TCD, especially the Point Method (PM), combined with multiaxial fatigue criteria, has been used over the last few years to predict the fretting fatigue life. However, little attention is paid to the effect of different damage mechanisms, especially stress distribution, between the two conditions on the application of the PM. This paper aims to select a suitable path for the PM, considering various stress distributions, for the fretting fatigue life prediction of complete contacts. A new method is developed to select the suitable path of the PM for fretting fatigue life prediction. To validate the analysis, corresponding tests were carried out using an improved proving ring-like rig in a Ti-6Al-4V alloy. Predicted lives on all paths were calculated using the PM combined with different multiaxial fatigue criteria, without incorporating wear effects, and compared with experimental lives using an error bar graph. Results indicate that when the fretting wear is not considered, the minimum predicted life path is more suitable for the PM than the perpendicular and maximum predicted life paths. This suitable path is compared to the path selection in the uniaxial symmetric V-notch fatigue condition. Analysis shows that the conventional path (the notch bisector) of the PM produces the maximum predicted life for the notch fatigue condition. The cause of this different path selection of the PM in the two fatigue conditions is assumed to be the effect of the asymmetric stress distribution and fretting wear damage in the fretting fatigue condition.

Assessment of critical parameters affecting fretting fatigue life of bridge stay cables at saddle supports

Saddle systems are a popular solution for supporting cables in cable-stayed bridges. Fretting fatigue failure of cables at saddle supports is a primary design consideration for these systems. Critical parameters that affect the fretting fatigue life of the cables are the contact forces and the slip displacements at the contact points between the cables and the saddle. Determining these critical parameters is the first step in evaluating the fretting fatigue life of the cables. Wear in the contact points between the cables and the saddle can affect the load distribution in saddle systems and consequently affect these critical parameters. However, the effect of wear has not been studied in the previous works. This paper first discusses the methods proposed in the literature for evaluating contact forces and slip displacements in the contact points between a cable and a saddle. Then, a finite element model of the problem and a framework for modelling the wear are presented. Finally, fretting fatigue life is determined based on the different studied approaches. The main highlights of the current study are considering the effect of wear in the simulation and employing an enhanced FE model for slip displacement calculations. The results of the basic model without wear effects showed that the first contact point between the cable and the saddle is critical for fatigue failure. However, by incorporating wear in the model, the contact force at the first point dropped and the second contact point became critical; this is in line with the observations in large-scale fatigue tests of saddle systems.

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.

Enhanced fretting fatigue strength of TC11 titanium alloy using laser-assisted ultrasonic surface rolling process

In this paper, ultrasonic surface rolling (USRP) and laser heating-assisted USRP (Laser-USRP) techniques are employed to enhance the fretting fatigue strength of TC11 titanium alloy. Furthermore, the surface deformation mechanism and fretting fatigue behavior are investigated. The properties of the reinforced surfaces were observed using transmission electron microscope (TEM), microhardness test, residual stress test and fretting fatigue experiments. The results showed that laser-USRP led to a remarkable enhancement in the fretting fatigue life of TC11 titanium alloy compared to traditional USRP. This was mainly due to the fact that laser heating improved the plasticity of TC11 titanium alloy, contributed to the formation of a smoother surface and increased the degree of surface oxidation, which could improve surface lubrication. Under high temperature, more slip systems were activated and more stable dislocations were formed, which resulted in larger compressive residual stress (CRS) with higher stability. The superposition of the elevated temperature field and the kinetic energy of the ultrasonic vibration produced an annealing effect in localized regions, resulting in the formation of more stable gradient nanograins. This study demonstrated the immense potential of laser-assisted plastic deformation in improving the surface properties of titanium alloys.

Fretting Fatigue Life Prediction for Aluminum Alloy Based on Particle-Swarm-Optimized Back Propagation Neural Network

Fretting fatigue is a specific fatigue phenomenon. Due to the complex mechanisms and multitude of influencing factors, it is still hard to predict fretting fatigue life accurately, despite there being many works on this topic. This paper developed a particle-swarm-optimized back propagation neural network to predict the fretting fatigue life of aluminum alloys using the test data gathered from the published literature. A commonly used critical plane model, the Smith, Watson, and Topper criterion, was used as a contrast. The analysis result shows that the proposed fretting fatigue life prediction neural network model achieves a higher prediction accuracy compared to the traditional SWT model. Experimental validation demonstrates the effectiveness of the model in improving the accuracy of fretting fatigue life prediction. This research provides a new data-driven methodology for fretting fatigue life prediction.

Experimental research on mechanical, material, and metallurgical properties of Inconel 600: Application in elevated temperature environment

Experimental research on mechanical, material, and metallurgical properties of Inconel 600: Application in elevated temperature environment

Finite element analysis of fretting fatigue properties of GH4169 superalloy considering the surface treatments

In the present work, the fretting fatigue properties of GH4169 superalloy at 650℃ were investigated through numerical simulation considering the influences of the surface treatments. As a detrimental phenomenon, fretting fatigue involves fatigue and wear simultaneously, where the coefficient of friction and residual stress fields induced by the surface coating or modification techniques may affect the fretting fatigue lifetimes by changing the complex stress state between the two contacting surfaces. The numerical solutions were implemented to compare the crack initiation angles and paths under different surface conditions. The simulation results indicated that fretting fatigue cracks in residual stress fields were tendentiously parallel to the surface resulting in crack retardation and debris peeling, as verified by experimental observations. Additionally, three propagation models were compared to study the effect of compressive loading on the driving force of crack propagation rates, especially where compressive residual stresses was present. The combination of the linear superposition model with the Harter-T method was proven to be more accurate in the fretting fatigue life prediction, which may provide a modeling basis for service life prediction of engineering components in many practical applications.

Fretting fatigue tests on 6201-T81 aluminum alloy conductor wires at room temperature and 75 °C

The aim of this work was to conduct a test campaign to investigate the effect of temperature on the fretting fatigue life of aluminum alloy 6201-T81 wires taken from All Aluminum Alloy Conductors (AAAC) 900 MCM. To this end, fretting fatigue tests were conducted at room temperature (25 °C) and 75 °C. A three actuators fretting fatigue rig was upgraded with a heating system to allow the tests at elevated temperatures with an accuracy of ±2 °C. A methodology to ease the control of the temperature within the contact region was proposed and the details of the wire-against-wire fretting fatigue test were described. Two S–N curves were then obtained under the same load conditions, but each one at a different temperature. The results showed that at higher temperature the fretted wires could face up to 72 % reduction in fatigue life. Failure analysis of the fracture surfaces proved that the fatigue phenomenon in both conditions, i.e., at 25 °C and 75 °C, were very similar even though fatigue lives are quite different.

Study of the shot peening surface roughness in fretting

Fretting fatigue manifests in mechanical systems exposed to contact forces that vary over time, resulting in premature cracks that can lead to component failure. Shot peening treatment is one of the palliatives to mitigate fretting fatigue problems. Recent studies have noted that the fretting fatigue is also extended by exclusively applying SP to the contact pad surface. This suggests that the improvement in the fatigue live produced by SP comes not only from the compressive residual stresses but also due to the characteristic surface roughness from the SP treatment. For this reason, the main goal of this work is to analyse how the shot peened roughness affects the fretting fatigue life. To do so, a confocal microscope was used to measure various profiles of shot peened pads. Using these profiles, and under fretting loads combination, the contact stress and strain field are calculated, followed by the application of a fatigue model. Finally, the estimated fatigue life is contrasted with empirical data derived from a research published by the authors. The study reveals that the fretting fatigue life is influenced by the surface roughness, although to a lesser extent with respect to residual stresses. Besides, the Smith-Watson-Toper parameter and stress intensity factor were analysed, suggesting that the rough surface primarily affects the initiation phase rather than the propagation phase, as it was expected.

Improvement in fretting fatigue life of GH4169 dovetail joint component by bonded solid lubricant coating at 500 ℃

In this work, GH4169 dovetail specimens were coated on both sides with a bonded solid lubricant coating. Fretting fatigue tests were carried out at 500 °C and compared with untreated dovetail specimens. The results showed that the fretting fatigue life of the coated specimens was increased by about 41.4% compared to the untreated specimens. This is attributed to the inherent shear properties of the two-dimensional material and its uniform adsorption at the friction interface, which provides excellent lubrication, significantly reduces the interfacial shear, effectively inhibits early crack initiation, and to a certain extent promotes crack closure to slow down the crack propagation rate. This study further demonstrates that interfacial lubrication has a positive effect on the enhancement of fretting fatigue life.

Influence of various contact-materials on the fretting fatigue life of P91 steel

Fretting-induced damage is an important failure mechanism in steam generator (SG) tubes in which there will be continuous contact and relative motion between tube and tube-support structures. In this work, the influence of various contact-materials on the fretting fatigue (FF) behavior of modified 9Cr-1Mo (P91) steel, a widely used SG material has been studied. The test setup has been configured as a flat-on-flat contact between the fatigue specimen made of P91-steel and contact-pad. The three different bridge type contact-pads namely, P91-steel, Inconel-718 (IN-718) and aluminized IN-718 were employed. The contact-pad applies constant pressure on the specimen while it is undergoing fatigue cycle. All the tests were carried out at a frequency of 10 Hz, with maximum cyclic stresses ranging from 250 to 525 MPa and a stress ratio of R = 0.1 at a constant contact pressure of 100 MPa. The FF life of the alloy with the contact material made of aluminized IN-718 alloy was observed to be lower in comparison with the IN-718 and P91 contact-materials. The life reduction in the former case was investigated through a comparative analysis of the formation and distribution of debris on fretted surfaces, surface roughness, and the fracture surface of the steel. The formation of the oxide phase such as Fe2O3 (hematite) and Fe3O4 (magnetite) was found on the fretted surface of the specimens.

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.