Fretting Wear Rate Research Articles

The influences of normal load and displacement amplitude on fretting wear behavior of M50 bearing steel

This study aims to obtain key parameters such as the fretting wear coefficient and wear rate of M50 bearing steel through fretting wear experiments. By integrating the Umeshmotion subroutine, a validated 3D ball-plane energy dissipation fretting wear model was established. The research explores wear behavior and transition mechanisms under different normal loads and displacement amplitudes. Experimental and finite element analyses show that fretting wear rate is negatively correlated with normal load and positively correlated with displacement amplitude. These variables influence contact stress, shear stress, and slip distance, affecting wear morphology. Results indicate that increasing normal load transitions fretting wear from gross slip to partial slip, while increasing displacement amplitude shifts it from partial slip to gross slip.

Comparative study on the fretting and sliding wear properties of micro-arc oxidation-treated aluminum alloy at different temperatures

Micro-arc oxidation is an effective method to enhance surface wear resistance. This paper comparatively studies the fretting and sliding wear properties of micro-arc oxidation-treated 7075 aluminum alloy at different temperatures. Research indicates that both the untreated and MAO-coated samples exhibit peak friction coefficient values due to adhesion at elevated temperatures. At both room temperature and 150 °C, the fretting wear rate of the MAO-coated sample is lower than that of the sliding wear rate, which can be attributed to distinct surface damage mechanisms and third body behavior under different wear modes. Adhesive wear is more prominent in MAO-coated samples during high-temperature fretting compared to room temperature, while abrasive wear and spalling are more prevalent during high-temperature sliding.

Thermal hydraulic design and evaluation of the solid microencapsulated fuel in light water reactors

Solid Microencapsulated Fuel (SMF) is a kind of solid fuel rod design that disperses TRISO coated fuel particles directly into a kind of matrix. Without cladding tube and associated failure mechanisms, this type of new fuel design is expected to provide improved performance under normal and even accident conditions. The purpose of this paper is to analyze the thermal hydraulic performance of SMF based on a single channel, compared to the traditional fuel in the 200 MW Nuclear Heating Reactor (NHR200-II). Two kinds of specific SMF by dispersing TRISO particles into Zirconium or SiC matrix were investigated. Thermal margin to DNB was assessed and confirmed by determining the heat transfer capacity under normal condition. Two-phase pressure drop was evaluated by using the homogeneous equilibrium boiling assumption. The centerline temperature of SMF rod was calculated by using effective thermal conductivity of two-phase composite. The analysis of flow instability and flow-induced vibration were also included and compared. This study showed that SMF has a better thermal transfer capacity, a higher margin from vortex shedding and fluid-elastic instability, and a lower fretting wear rate, while a higher sliding wear rate because of a higher Young’s modulus and fundamental frequency, which is compensated by a higher hardness for SiC matrix.

Modeling contact size effect on fretting wear: a combined contact oxygenation - third body approach

This study investigates the effect of the contact size and the gross-slip sliding amplitude on the fretting wear rate of a steel flat-on-flat interface. Results confirm an asymptotic decrease of the wear rate with the contact size. This evolution is induced by an easier oxygen access to the interface favoring abrasive wear according to the Contact Oxygenation Concept (COC) and by a faster ejection of the protective debris particles from the interface according to the Third Body Theory (TBT). To decouple these COC and TBT contributions, the effect of the sliding amplitude and the contact orientation with respect to the sliding direction is assessed using an original macro-texturation test strategy. Wear rate evolutions as well as SEM-EDX fretting scar analyses suggested that COC is mainly driven by the minimum distance between the contact center and the open air contact edges (LCOC), whereas TBT wear process is chiefly controlled by the ratio of the collinear contact length to the sliding amplitude (LTBT/δg). Assuming a weighted influence of the contact oxygenation process on the TBT wear process, a simple power-law formulation is introduced to quantify the contact size effect on the energy wear rate fluctuation. A very good correlation with the experiments confirms the stability of the proposal.

Fretting wear behaviour and frictional force mapping of Al2O3 based thermal barrier coatings

Efficiency and structural stability of gas-turbine engines were acheived with compliant thermal barrier coatings (TBCs) on structural components. In TBCs, top ceramic coatings encountered with other structural parts in a relative motion (amplitude of 100–500 μm and frequency of 1–5 Hz) was leading to failure, namely fretting wear. So, a high hardness material, Al2O3 based ceramic matrix composite (CMC) coatings were utilized to improve the tribological properties of the engineered surface. At this juncture, fretting wear behaviour of atmospheric plasma sprayed Al2O3–3 and 8 mol% Y2O3 stabilized ZrO2 (3YSZ and 8YSZ)‑carbon nanotube (CNT) based CMC coatings were investigated. The fretting wear rate of Al2O3 based CMC coatings against WC ball was observed as 0.97–1.87 × 10−6 mm3N−1 m−1. The least in wear resistance of Al2O3-CNT (1.87 × 10−6 mm3N−1 m−1) among the composite coating is attributed to low hardness and high Hertzian contact pressure (1.65 GPa) on the coatings. Among the composite coatings, Al2O3-3YSZ and Al2O3-8YSZ-CNT showed an improved wear resistance (~40.1% and ~34.5%, respectively) with wear rate of 0.97 × 10−6 mm3N−1 m−1 and 1.06 × 10−6 mm3N−1 m−1, respectively. It is attributed to improved mechanical properties, altered surface by reciprocating motion and the presence of wear debris, which reduces the wear rate by acting as a third body. So, there is an overestimation of wear rate (4.1–6.6 times) compared to that of experimentally calculated wear rate. Further, the Al2O3-YSZ-CNT composite showed fatigue crack on the fretting wear surface due to low plasticity index (62.0–109.3 MPa) of the coating. Also, the gradual change of running-in regime to the steady-state regime is achieved in the CNT reinforced composite coatings due to high resistance by the coatings which possess commendable mechanical properties. The frictional force mapping during the reciprocating motion confirms the rapid and gradual transition of two different regimes in the composite coatings.

Contact Corrosion of Metals under Low Amplitude Fretting

This article discusses fretting corrosion of different friction couples with the consideration of mechanical properties, chemical activity of contacted materials, effect of gaseous environment composition, and external electric current. It has been demonstrated that the fretting wear rate of materials of a friction couple depends on the difference of their electrode potentials. On the basis of the electron theory of adsorption and catalysis on semiconductors (oxides), the physical and chemical formation of a corrosive medium in the area of frictional contact, promoting development of electrochemical processes, have been analyzed. It is mentioned that the catalytic action of an oxide interlayer in fine dispersion is exposed in chemosorption acceleration of oxygen and moisture in a reactive radical in ion radical forms. It has been demonstrated that the existence of cathodic impurities in the alloy and an increase in cathodic depolarizer content (oxygen) in the friction area increases corrosion loss stipulated by electrochemical processes. Relative contribution of chemical and electrochemical corrosion of the friction contact is estimated during the progress of fretting. It is mentioned that the factors delaying the electrochemical processes are efficient for minimization of the fretting wear rate. Opportunities of application of cathodic and anodic electrochemical protection against fretting corrosion are considered.

Theoretical Study of Fretting Wear Rate Evolution in Axi-Symmetrical Elastic Contact Using the Method of Dimensionality Reduction

We carried out a simulation of wear in elastic tangential contact in partial-slip mode using the method of dimensionality reduction. The obtained numerical dependencies of wear rate on the number of loading cycles were approximated with existing analytical dependencies, at that, the estimated values of parameters of approximating equations are close to analytical estimates given before. The present results demonstrate the possibility of application of the method of dimensionality reduction to theoretical study of fretting wear rate evolution.

Fretting wear rate evolution of a flat-on-flat low alloyed steel contact: A weighted friction energy formulation

Fretting wear resulting from micro-displacement oscillatory movements is considered a serious impediment to many industrial applications like gears, turbo engines, etc. Large conformal contact configurations of industrial components are very complicated to reproduce at laboratory scale. As a result, simple non-conformal contact geometries including sphere-on-flat and cylinder-on-flat are usually adopted in research laboratories. Yet, few are the researches that examined fretting wear using flat-on-flat geometry due to its high sensitivity to alignment issues although this contact configuration allows the analysis of quasi-constant pressure condition. In the current study, fretting wear of flat-on-flat dry contact made of a steel alloy (35NCD16) is investigated experimentally by varying several parameters including test duration, contact pressure, sliding amplitude and frequency. A power law formulation is introduced providing reliable prediction of the wear rate. The analysis of test results confirms a high dependency of the wear kinetics on the loading condition regarding the transition from abrasive to adhesive wear.

Influence of humidity on the endurance of silver-plated electrical contacts subjected to fretting wear

The use of connectors in electrical devices for automotive has significantly increased during the last decades. These connectors need to keep a low and stable electrical contact resistance (ECR) otherwise disconnects may occur, inducing critical failures. Close to the engine, these connectors are subjected to vibrations inducing fretting in the contact (i.e. wear damage induced by small oscillating sliding).This phenomenon induces surface wear and the formation of oxide debris (third body) which, being trapped within the interface, can drastically increase the electrical contact resistance.The aim of this study is to investigate the effects of the relative humidity (RH) on the fretting wear rate and the Electrical Contact Resistance (ECR) of a silver plated electrical contact. The analyses show that an increase of RH tends to increase the ECR fretting endurance Nc related to the failure condition (ΔR > ΔRth = 4 mΩ). However, a discontinuous evolution is observed. Below a RH threshold, RH = 50%, the endurance increase is rather slow and can be related to a decrease of the friction work at the interface. Above RH = 50%, the high humidity conditions modify the rheological properties of the debris layer. The wear rate is becoming smaller and a larger wear volume is required to reach the ECR failure. This induces a fast linear increase of Nc. Whatever the wear processes, the investigation confirms that ECR failure is reached when the silver concentration in the inner part of the contact is becoming lower than [Ag]th = 5%.

Torsional fretting and torsional sliding wear behaviors of CuNiAl against 42CrMo4 under dry condition

Many wear failures are caused by a combination of fretting wear and sliding wear. In this study, the torsional fretting and torsional sliding wear properties of CuNiAl against 42CrMo4 were comparatively investigated under dry condition using a flat on flat contact tester. Experimental results showed that the sliding friction coefficients declined more dramatically than the fretting friction coefficients when the normal load increased. The fretting wear rate was lower than the sliding wear rate, which was partly due to the solid lubrication effect of the wear debris and strain hardening of the worn surfaces. The dominant wear mechanisms for the fretting tests were oxidation, cracks and delamination, while for the sliding tests were abrasion combined with plastic deformation.

Fretting wear response of a nitrided 316L SS/304L SS interface: Effect of lithium/bore liquid environment

In nuclear power plants (NPP), rod cluster control assembly (RCCA) tubes undergo impact under low-pressure contact against guides, leading to specific wear on the contact surfaces. To focus on this industrial issue, an experimental layout was designed to perform reciprocating fretting in different environments.A representative tube interface (nitrided AISI 316L)/plane (AISI 304L) was investigated in air and in a solution composed of 1000ppm of bore and 130ppm of lithium to be closed to a NPP primary water chemistry at atmospheric pressure and room temperature. Wear regimes were identified in terms of variation in parameters such as sliding amplitude (from ±40μm to ±160μm), normal loads (from 2N/mm to 5N/mm) and test duration (from 100,000 to 1.5millioncycles).Surface damage evolution was followed by 3D profilometry and several analyses (SEM, EDX, optical observation) were conducted on surfaces and cross-sections. Based on these results, fretting-wear mechanisms in the 304L SS plate and nitrided 316L SS tube were investigated. The first results in dry environment showed that, for δg⁎ <±120μm, plane profiles had a “W-shape” whereas for δg⁎ >±120μm there was a U-shape. Thus, a W-shape morphology parameter Mw was defined, taking into account the third-body wear volume. Moreover, the worn surfaces of the plane were smoother in solution, and wear was no longer detected on the tube specimens. A modified energy wear approach was then implemented to quantify reciprocating fretting wear rate according to ambient conditions. Finally, two wear mechanisms are proposed.

An elastic–plastic investigation of third body effects on fretting contact in partial slip

In this investigation, the third body effects in fretting contact is modeled using the commercially available ABAQUS finite element (FE) software. A two dimensional Hertzian line contact model is simulated in the presence of third bodies at the contact interface. The third bodies are modeled using simplified geometry like cylinders. Elastic–plastic material properties are used to model both the first bodies and third bodies. The FE model is used to investigate fretting phenomena under different displacement amplitudes and the influence of third body particles on contact stress and contact slip. In addition, the effects of different factors such as material properties of the third bodies and number of third body particles on fretting are investigated. Fretting loops obtained from the model show notable differences in shear stress distribution when compared to smooth Hertzian line contacts in the absence of third body particles. The results indicate that the third bodies deformed to platelet like structures as observed in experiments. The obtained results also indicate that contact stress decreases with the increase in the number of third bodies. As the number of third bodies in contact is increased, the contact shear force between the first bodies decreases while the contact slip increases. Due to this phenomenon, the dissipated energy is not affected and therefore does not influence fretting wear rate significantly. Although fretting wear rate is not directly influenced by the presence of third bodies, plastic deformation of the first body surfaces influences contact parameters which in turn impacts fretting wear.

Prediction of the electrical contact resistance endurance of silver-plated coatings subject to fretting wear, using a friction energy density approach

Electrical connectors need to display low and stable electrical contact resistance (ECR). However, subjected to vibrations (engines, heat, etc.), fretting wear damages promotes the formation of insulating oxide debris and a sharp ECR increase decaying the information transmission. Noble plated coatings like silver layers are usually applied to delay the ECR failure. However, to predict such ECR endurance, it appears essential to determine the fretting wear rate. In the present study, a homogeneous crossed-cylinders Ag/Ag interface was investigated under gross slip conditions imposing various loading parameters (±2µm<δg<±16µm, 1N<P<6N, RH=10% and f=30Hz) for Ag layers from 1.7µm to 4.8µm. A global chemical investigation of the fretting scars confirms that ECR failure is reached when most of the silver is removed from the interface and an oxide debris layer is trapped in the contact. ECR endurance (Nc: ΔR>4mΩ) can be formalized, using a power law function of the mean friction energy density dissipated during a fretting cycle taking into account the contact area extension. Finally, a simple ECR endurance expression is derived as a function of the fretting loading parameters and the thickness of the silver plated layer. A very good correlation between experimental and predicted ECR endurances is achieved.

Experimental Validation of Fretting Fatigue Strength and Fretting Wear Rate at Contact Surface of Turbine-Blade-Shroud Cover

In continuously coupled blade structures, fretting fatigue and wear have to be considered as supposed failure modes at the contact surface of the shroud cover, which is subject to steady contact pressure from centrifugal force and the vibratory load of the blade. We did unique fretting tests that modeled the structure of the shroud cover, where the vibratory load is only carried by the contact friction force, i.e., a type of friction. What was investigated in this study are fretting fatigue strength, wear rate, and friction characteristics, such as friction coefficient and slip-range of 12%-Cr steel blade material. The friction-type tests showed that fretting fatigue strength decreases with the contact pressure and a critical normal contact force exists under which fretting fatigue failure does not occur at any vibratory load. This differs from knowledge obtained through pad-type load carry tests that fretting fatigue strength decreases with the increase of contact pressure and that it almost saturates under a certain contact pressure. Our detailed observation in the friction-type tests clarified that this mechanism was the low contact pressure narrowing the contact area and a resulting high stress concentration at a local area. The fretting wear rate was explained by the dissipated energy rate per cycle obtained from the measured hysteresis loop between the relative slip range and the tangential contact force. It was found that the fretting wear rate is smaller than the wear rate obtained by one-way sliding tests, and the former is much smaller than the latter as the dissipated energy decreases. Finally, to prevent fretting fatigue and wear, we propose an evaluation design chart of the contact surface of the shroud cover based on our friction-type fretting tests.

On the Necessary but Sufficient Amount of Grease to Obtain Fully Lubricated Fretting Regime in Moist Air for SUJ2 Bearing Steel against S15C Carbon Steel

Influence of the moist air humidity (10-70%) on the fretting characteristics of steels under grease lubrication is experimentally investigated. Ball (bearing steel, JIS SUJ2) on disk (carbon steel, JIS S15C) type fretting tests for 0-20 mg of grease supplied before each test at the punctual contact between ball and disk were conducted at 50 μm slip amplitude and 6.7 Hz frequency. From the shape of the friction hysteresis one calculates the slip index, and based on it, determines the type of fretting regime against the number of fretting cycles. Influence of the grease amount and relative humidity on the friction coefficient, slip index and wear rate is interpreted based on the occurrence of the grease film breakdown. Fretting wear rate appears as unaffected by variation of the environmental humidity for an amount of grease exceeding 3 mg, this representing the minimum amount necessary to avoid the grease film breakdown. Results obtained are useful to find the amount of grease necessary but sufficient for proper lubrication, and hence to protect the environment by grease saving. In order to generalize the results obtained for ball- bearings, screws, joints, guide-ways, etc., a tribological analysis based on the Stribeck curve was performed and then, the amount of grease necessary but sufficient to obtain fully lubricated fretting regime in moist air for ball bearings was discussed in detail.

프레팅 마멸계수 및 마찰계수 측정에 관한 연구

The prediction of fretting wear is a significant issue for the design of contacting mechanical components such as flexible couplings and splines, jointed structures and so on. In our earlier study, we developed a numerical model to predict the fretting wear using boundary element method. The developed algorithm needs experimental fretting wear coefficients and friction coefficients between two moving materials to get more reliable results. In this study, therefore, we demonstrated the measurement method of the fretting wear coefficients and friction coefficients using disk on plate tribometer with piazo actuator and gap sensor. For four different material combinations, the fretting wear coefficients and friction coefficients are acquired through the fretting wear experiment and the analysis of the measured values. Thess results are useful to predict the quantative fretting wear rate in the developed algorithm.

Characteristics of Fretting Wear in a Press-Fitted Shaft Subjected to Bending Load

This paper presents the results of an experimental investigation of fretting wear characteristics on the contact surface of press-fitted shaft subjected to a cyclic bending load. A series of interrupted fretting wear tests with press-fitted specimens were carried out by using a rotating bending fatigue test machine. The evolution of contact surface profile of press-fitted shaft due to fretting wear were measured with a profilometer. The local wear coefficient during the running-in period is discussed from experimental results and FE analysis. It is found that the maximum depth of fretting wear by repeated slip between shaft and boss occurred at the close of contact edge at the early stage of fatigue life and the regions of worn surface are expanded to the inner side of contact edge as increasing number of fatigue cycles. The initial fretting wear rate at the early stage of fatigue life increased rapidly at all loading condition. After steep increasing, the increase of wear rate is nearly constant in the low bending load condition. The local wear coefficient in running-in period decrease dramatically at the early stage of fretting wear.

The study on grid-to-rod fretting wear models for PWR fuel

The fretting wear is found to be generated at grid-to-rod contact areas by flow-induced vibration. This flow-induced grid-to-rod fretting wear may be initiated at a certain critical grid-to-rod gap that strongly depends on the extent of flow-induced vibration and grid spring designs. Three fretting wear excitation mechanisms acting on the grid-to-rod fretting wear are summarized. In order to examine the impact of grid spring designs on the fretting wear rate, the fretting wear tests for three kinds of grid spring designs were carried out for 500 h, simulating the reactor flow conditions. In parallel, three grid-to-rod fretting wear models that include constant work rate model, constant work density rate model and linear work density rate model have been developed. The three fretting wear models were used to predict the fuel rod perforation times with the use of the fretting wear test results. It is said that the constant work density rate model or the linear work density rate model is quite effective in predicting the grid-to-rod fretting-induced rod failure time observed in commercial nuclear power plants.

Friction and wear properties of steel backed Al–10Sn–4Si–1Cu metallic strips prepared via spray atomization–deposition-rolling route

In various load bearing structural applications related to automotive industries, steel backed aluminum alloy strips are considered. For such applications, it is desired to design appropriate alloy composition for metallic strip so that good tribological properties can be achieved. In our ongoing efforts to accomplish this aim, we have recently fabricated a steel backed Al–10Sn–4Si–1Cu bearing strip, which is prepared by spray depositing the molten bearing alloy on a steel substrate, followed by warm rolling of the resulting laminated strip to different thickness reductions up to 80%. The tribological performance of the steel backed Al–10Sn–4Si–1Cu strips is evaluated against the bearing steel. While the recorded steady state coefficient of friction (COF) does not show any noticeable difference (varying in the range of 0.6–0.7) with respect to difference in warm rolling conditions, the fretting wear rate (10–26 × 10 − 5 mm 3 N − 1 m − 1 ) of the steel backed and warm rolled strips exhibits a systematic decrease in wear rate with increase in amount of warm rolling. SEM-EDS analyses reveal the oxidative wear and the extensive cracking of alumina rich tribolayer as the dominant material removal mechanisms. The tribological properties of the spray deposited and 80% rolled steel backed Al–10Sn–4Si–1Cu bearing strip is compared with those of a commercially available Al–Sn based sleeve bearing under identical fretting conditions.

Fretting fatigue and wear damage of structural components in nuclear power stations—Fitness for service and life management perspective

Fretting fatigue and wear problems have major economical and safety impact on the nuclear industry. This keynote paper provides examples of the fretting problems encountered in nuclear power stations and an overview of the methodologies used to assess their root cause, their potential effect on the integrity of structural components and the future damage projection for risk management. The limitations of existing models that are commonly used to predict fretting wear rate are discussed. A system approach to the fretting wear/fatigue problem allowed us to significantly improve the capability of predicting fretting damage through the recognition of the problem nonlinearity, and the effect of self-induced changes. The application of linear elastic fracture mechanics principles for predicting the fretting wear and fretting fatigue strength is demonstrated. The paper underlines the critical roles of the following two factors. First, the validation of the above mentioned methodologies, through experimental investigation of the long-term fretting wear and fatigue behavior of structural components under realistic operating conditions. Second, the qualification of in -situ measurements of fretting wear damage using nondestructive evaluation NDE and inspection methods.