This work investigates the effect of abnormal microstructure on rolling contact fatigue (RCF) damage of high-speed railway wheels under service and the formation mechanism of abnormal microstructure by optical microscopy, scanning electron microscopy, transmission electron microscopy, nano indentation and laser-induced break down spectroscopy. Results show that there are large amounts of upper bainite in the wheel tread, which destroyed the uniformity of the microstructures of the wheel matrix. The bainite is composed of ferrite with high density of dislocations and short bar-shaped cementite. The bainite exhibited higher hardness and elasticity but lower plasticity than the matrix microstructure. The incongruity of plastic deformation between upper bainite and matrix microstructures will lead to stress concentration at boundary of the microstructures, thus accelerating the RCF crack initiation and propagation. The formation of upper bainite is caused by carbon segregation. Segregation of carbon element will make the continuous cooling transformation (CCT) curve shift to the right significantly, thus increasing the probability of bainite transformation in segregation zone at higher cooling rate. Therefore, large amounts of upper bainite were formed at wheel tread.

The wear characteristics of the trapezoidal fin against high-speed rotor were experimentally investigated at different final incursion depths, incursion rates, and sliding velocities. To characterize the geometrical effect, a small specimen (SS) and a large specimen (LS) were selected to analyze the mass loss, wear geometry, contact forces, and frictional temperature distributions under different conditions. The results show that the contact-separation is most likely to occur between the trapezoidal fin and rotor. In the rubbing process, the plastic deformation is dominating, and the abrasive and adhesive wears have pronounced effects on the wear behavior of the rubbing interface. The wear performance of the SS is sensitive to the structure imbalance, which induces the combined mushrooming and bending damage in the trapezoidal fin. However, the symmetrical mushrooming damage is generated in the LS. For both SS and LS, the mass loss is decreased with increasing incursion rate and sliding velocity, and the mass loss percentage is pronounced at the early stage of rubbing. The averaged friction coefficient is 0.1–0.16 for the LS whereas 0.1–0.19 for the SS. The peak frictional temperature is 560–640 °C for the LS, while 360–400 °C for the SS. The contact-separation significantly reduces the effects of final incursion depth, incursion rate, and sliding velocity on the wear geometry, contact forces, and temperature rise in the trapezoidal labyrinth fin.

This paper presents a finite element model (FEM) to investigate the effect of prior austenite grain refinement on rolling contact fatigue (RCF). RCF life was determined using continuum damage mechanics (CDM), which simulated material deterioration as a function of cycle. Continuum damage mechanics calculations in this investigation considered the subsurface shear (orthogonal) reversal to be responsible for RCF failure. To establish the CDM critical parameters—resistance stress (σ r ) and damage rate exponent (m)—torsion stress-life data from open literature of three different grain sizes for the same material was used. It was observed from the torsion S-N (stress-life) data that the resistance stress exhibits a linear relationship with grain diameter. As grain diameter was refined, the resistance stress was found to increase. The damage rate exponent (m) displayed no relation to grain diameter; hence, the average value from the three torsion S-N curves was used in this investigation. In order to assess the effect of grain refinement on RCF life, a series of unique material microstructures were constructed using the Voronoi tessellation process at eight mean grain diameters. Finite element (FE) simulations were devised at three contact pressures, typical of heavily loaded lubricated contacts, and the RCF life was determined for each set of microstructures of a given mean grain diameter. The RCF results at the eight grain diameters indicate that fatigue performance is improved exponentially with finer grain diameter. The observed life improvements from the RCF simulations resulting from grain refinement exhibit good corroboration with existing experimental results found in open literature. A single predictive fatigue life equation was constructed from this investigation’s RCF simulations to evaluate the stochastic RCF performance, given grain diameter and contact pressure, of non-conformal contacts.

In this paper, the mechanism of energy transfer from cavitation bubbles to solids is demonstrated as shock waves. To identify this mechanism, cavitation bubble structures, the corresponding damaged surface, and the wear particles in vibratory erosion tests on pure aluminum Al-99.999 using high-speed and scanning electron microscope photography were observed. The eroded surface morphology was in the form of large swellings (hundreds of micrometers), which embodies the plastic flow. Results indicate that large swelling regions formed in a few seconds are caused by shock pressure waves and not by a microjet only several micrometers in size. The observed surface erosion and falling particles make it clear that the mechanism of cavitation wear is fatigue failure.

Stepwise cavitation erosion is used to study pits formed by microjets. The aim is to determine the role of the pit in the development of cavitation erosion damage, including geometrical features of the pitted area and pit counting. The study also identified the dominant feature in the development of cavitation damage. We used a vibratory cavitation apparatus to perform cavitation erosion damage on a stainless steel, SUS 304, in tap water with scanning electron microscopy (SEM) at 5-min intervals from t = 0 min to t = 45 min. We then analyzed and characterized the pits formed by impacting the surface with a microjet. These results showed that individual pits and clusters of pits are characterized by a black spot surrounded by plastic deformation, and both are irregular in shape. This suggests that the microjet is hitting the wear surface in an oblique direction. Over the course of the test time, neither the shape nor the size of the microjet pits and their clusters change; pit diameters approximately 2 μm or less. The area of pits and their clusters does not exceed 1% of the worn surface. All these features demonstrate that the pit and its clusters do not impact the evolution of cavitation damage. Our results also indicated that slip bands were caused by a shock wave. Slip bands are large (>10 μm) and account for about 30% of the wear surface. This confirms that slip bands are predominantly responsible for the development of cavitation; the predominant cavitation mechanism is fatigue due to multiple shock waves.

Surface fatigue resulting from cyclic contact loading is a main reason for the rough surface wear. Since a rough surface consists of many asperities, the fatigue in one asperity is investigated. The multiaxial Fatemi–Socie fatigue criterion is adopted to study the contact fatigue in a spherical asperity subjected to cyclic elastic-plastic normal loading. The fatigue damage in the asperity is predicted. The maximum fatigue damage occurs at the edge of the maximum contact area. Two typical patterns are found for the fatigue damage distribution. Locations and orientations of fatigue microcrack initiation are also identified. Finally, future research directions are discussed.

Usually, rail materials are exactly affected by the erosion of windblown sand in the desert environment. For this reason, the influence of impact angle, particle velocity, and particle size on the erosion wear behavior of the U75V heat-treated rail steel, a material frequently employed in Chinese railways, were studied in this work. The results showed that, with increasing impact angle, the erosion rate increased between 15 deg and 45 deg, decreased between 45 deg and 75 deg, and then increased again between 75 deg and 90 deg. The highest erosion rate occurred at about 45 deg. When the particle velocity increased, the erosion rate increased approximately in a quadratic way. As the sand particle size increased, the erosion rate presented a decreasing trend. During the initial stage of erosion, shear craters, indentation craters, and ploughing craters were the main surface damage features. The shear craters predominated at the impact angle of 45 deg whereas the indentation craters predominated at 90 deg. During the steady-state of erosion, the rail damage was mainly composed of craters, platelets, and cracks. Both the length and depth of craters increased almost linearly with increasing particle velocity, whereas the increased rate of length was significantly higher than that of depth. The length and depth of craters increased with increasing particle size at 90 deg, whereas only the length increased with increasing particle size at 45 deg. The microstructure evolution and the formation mechanism of platelet at low impact angles were different from those at high impact angles. Platelet formation was the main erosion wear mechanism.

Metallic materials usually contain some amounts of inclusions which are known to affect their mechanical properties since the bonding strength of the matrix–inclusion interface is relatively low, voids or cracks are thus easily formed under a tensile loading. However, under a contact loading, the effects of subsurface inclusions on the sliding wear of metallic materials are not thoroughly understood. In this work, a micromechanical model is proposed to study the shear fracture and wear of metallic materials containing random inclusions. With the model, crack branching and crack aggregation during contact loading are simulated, and the formation process of sheet-like wear particles is clarified. It is demonstrated that the subsurface micro-cracks, particularly those near inclusions, and their subsequent evolution play a major role in the adhesive wear. This investigation is helpful in understanding the adhesive mechanism of wear, and the proposed model could be a promising approach for the prediction of adhesive wear.

Fretting is a damaging phenomenon, generally observed when a mating pair is subjected to a small amplitude of oscillatory motion. The contact behavior in fretting is governed by a complex interaction between mechanical properties of mating pair, contact geometry, and loading conditions. In most of the practical applications, dissimilar materials are chosen for a contacting pair with one of the materials having superior material properties than other so as to replace the worn-out or unfit component during the maintenance. In the literature, many researchers have studied the effect of dissimilar materials on fretting behavior but mainly in the context of hardness. As experimental methodology has been adopted in these studies, the effect of dissimilar material properties has been reported in terms of global variables like wear volume or fretting fatigue life, but its influence on underlying local contact tractions could not be studied. In the present work, a two-dimensional finite element analysis has been carried out for a cylinder-on-plate configuration. The effect of dissimilar materials for the mating pair has been studied by modeling elastic–plastic behavior for combinations of three different materials, namely, SS 304, ASTM A302-B, and aluminum. The validation of the finite element model is carried out by comparing the results of elastic analysis with the analytical solutions available in the literature. The pertinent contact parameters in the context of fretting wear, namely, contact pressure, contact slip, and contact stresses are extracted. A frictional dissipation energy density-based approach is used for the qualitative comparison of the fretting damage for different cases and validated with the literature data.

This paper presents a partitioned strongly coupled fluid–solid interaction (FSI) model to solve the 2D elastohydrodynamic (EHD) lubrication problem. The FSI model passes information between a control volume finite-difference discretized Reynolds equation and abaqus finite element ( fe ) software to solve for the fluid pressure and elastic deformation within heavily loaded lubricated contacts. Pressure and film thickness results obtained from the FSI model under a variety of load and speed conditions were corroborated with open published results. The results are in excellent agreement. Details of the model developed for this investigation are presented with a focus on the simultaneous solution of the Reynolds equation, load balance, and the coupling of the solid abaqus fe with the finite-difference fluid (Reynolds) model. The coupled FSI model developed for this investigation provides the critical venue needed to investigate many important tribological phenomena such as plasticity, subsurface stress, and damage. The current FSI model was used to explore and demonstrate the efficacy of the model to investigate the effects of microstructure inhomogeneity, material fatigue damage, and surface features on heavily loaded lubricated contacts as can be found in a wide range of industrial, automotive, and aeronautical drive systems.

Solid particle erosion (SPE) as a common damage mechanism in industrial applications can reduce the effective operation of components or contribute to failure. However, it has beneficial usages in manufacturing processes, especially in abrasive sandblasting and waterjet cutting. The aim of this paper is an investigation of erosive behavior of Ti-6Al-4V alloy through numerical and experimental approaches. A three-dimensional finite element (FE) model is developed using the representative volume element (RVE) to simulate multiple particles impact on Ti-6Al-4V target. Failure and plastic behavior of the target surface due to particles impact is described by Johnson-Cook constitutive equations. Furthermore, erosive behavior of the alloy is experimentally researched by multiple SPE tests. Verification of the implemented approach is studied by comparing the results of the FE model and the SPE experiments. Effects of particles impact angle considering Johnson-Cook coefficient values and particles velocity on erosive behavior of Ti-6Al-4V are also studied. Both numerical and experimental results show a maximum erosion rate of the alloy at an impact angle of 45 deg for spherical sand particles with a diameter of 100 µm. According to the scanning electron microscopy (SEM) images, the erosion process involves both ductile and brittle mechanisms at this angle.

In this study, friction and evolution of cohesive failures (cracks and spallations) in CoB/Co 2 B layers were analyzed. Thermochemical treatment was carried out at 950, 975, and 1000 °C during 6, 8, and 10 h of exposure time, respectively. The characterization techniques include scanning electron microscopy (SEM) for morphology inspection of layers and thickness measurement, X-ray diffraction for the investigation of phases formed, and instrumented indention to obtain hardness, Young’s modulus, and residual stresses. The practical adhesion of the boride layers was evaluated by a progressive load scratch test (PLST), and the critical loads of cracking, chipping, and spallation were calculated. Later, unidirectional multipass scratch tests (MPSTs) were performed by applying subcritical loads selected from the lower spallation load (54 N); these tests were conducted for a different number of scratch passes. The results show that the coefficient of friction (COF) and coating damage depend on the applied load, the number of passes, and coating thickness. In multipass scratch, the mechanical properties, residual stress state, and thickness play a significant role in the evolution of the coating damage that manifests in the form of cracks and cohesive spallations. Considering the scratch and multipass scratch results, it was found that the sample with 10 h of exposure time presents a better performance among the samples.

A coupled multibody elastic–plastic finite element (FE) model was developed to investigate the effects of surface defects, such as dents on rolling contact fatigue (RCF). The coupled Voronoi FE model was used to determine the contact pressure acting over the surface defect, internal stresses, damage, etc. In order to determine the shape of a dent and material pile up during the over rolling process, a rigid indenter was pressed against an elastic plastic semi-infinite domain. Continuum damage mechanics (CDM) was used to account for material degradation during RCF. Using CDM, spall initiation and propagation in a line contact was modeled and investigated. A parametric study using the model was performed to examine the effects of dent sharpness, pile up ratio, and applied load on the spall formation and fatigue life. The spall patterns were found to be consistent with experimental observations from the open literature. Moreover, the results demonstrated that the dent shape and sharpness had a significant effect on pressure and thus fatigue life. Higher dent sharpness ratios significantly reduced the fatigue life.

Frictional and fretting wear behaviors of Inconel X-750 alloy against GCr15 steel ball were investigated in dry contact condition with ∼60% air humidity. Fretting tests were run at the high frequency tribosystem SRV 4 in room temperature and ball-on-flat contact configuration were adopted with the relative oscillatory motion of small displacement amplitude (40 μ m). Sliding regimes, wear volumes, frictional properties, and material damage mechanisms were studied with regard to different normal loading and test durations. After the tests, the worn surface morphologies were analyzed by three-dimensional (3D) optical surface profiler, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to distinguish fretting running conditions and material responses for different test cases. It was found that the material removals by abrasive and adhesive wear, debris formation and oxidization, and wear delamination were the main damage mechanisms under the lower normal load where the full slide or gross slip regime (GSR) was dominant between the contact surfaces. On the other hand, fretting regime was found to be a stick-slip or a partial slip at greater loads where damage mechanisms were correlated with deformed asperities, fatigue cracks, and thick layer removal due to highly concentrated cyclic stresses. Time dependence was crucial during GSR where the wear volume increased substantially; however, the wear volumes and scars sizes were consistent over time because of stick-slip effects under the higher normal load.

In this study, a new approach has been developed to simulate three-dimensional (3D) experimental rolling contact fatigue (RCF) spalls using a two-dimensional (2D) finite element (FE) model. The model introduces a novel concept of dividing the 3D Hertzian pressure profile into 2D sections and utilizing them in a 2D continuum damage mechanics (CDM) RCF model. The distance between the two sections was determined by the size of the grains in the material microstructure. The 2D RCF model simulates characteristics of case carburized steels by incorporating hardness gradient and residual stress (RS) distribution with depth. The model also accounts for the topological randomness in the material microstructure using Voronoi tessellation. In order to define the failure criterion for the current model, sub-surface stress analysis was conducted for the Hertzian elliptical contact. It was predicted that the high shear stress region near the end of the major axis of the contact is the cause of catastrophic damage and spall formation. This prediction was validated by analyzing the spalls observed during RCF experiments using a surface profilometer. The model was implemented to predict RCF lives for 33 random material domains for different contact geometry and maximum Hertzian pressures. The model results were then compared to the RCF experiments conducted on two different test rigs, a three-ball-on-rod and a thrust bearing test apparatus (TBTA). It was found that the RCF lives obtained from the model are in good agreement with the experimental results. The results also demonstrated that the spalls generated using the analytical results resemble the spalls observed in experiments.

This paper presents mathematical expressions to identify the existence of localized surface defects on the raceways of the deep groove ball bearings. For the formulation of the mathematical expressions, matrix method of dimensional analysis based on force, length, time, and temperature (FLTϴ) system of unis is used. The model is based on the complete set of physical dimensions and operating parameters of the deep groove ball bearing in that the spall size is directly allied with vibration responses. The formulated governing model equations are solved numerically by applying a scheme of empirical modeling through multiple factorial regression analysis. Experiments are performed on the laboratory test rig to verify the results obtained from the developed model equations. For the experiments, deep groove ball bearings designated as SKF 6307 are used. These bearings are having artificially induced square-shaped surface defects of different sizes on the outer and inner races and are analyzed for different operating speeds. A good similarity between the predicted numerical values and the experimental results is noticed. This study showed that the proposed methodology can be successfully used for the characterization of the localized surface defects on the raceways of the deep groove ball bearings.

The torsional fretting wear behaviors of artificial cervical disk were studied under different loads (50, 100, and 150 N) and angular displacement amplitudes (±2 deg, ±5 deg, and ±7 deg). The cervical prosthesis was simplified and designed as a ball-on-socket contact with the material configuration of ultrahigh molecular weight polyethylene (UHMWPE) and thermally oxidized titanium alloy. The fretting running regime changed from mixed regime (MR) to slip regime (SR) when the angular displacement increased from 2 deg to 7 deg. The frictional torque became larger with an increasing load at all of the angular displacement amplitudes. Larger load and angular displacement amplitude also led to more severe wear for UHMWPE ball. The damage patterns for titanium socket were only slight scratches and polished tracks on the raised oxide scales. However, the dominant wear mechanism was abrasive and adhesive wear as well as deformation for UHMWPE ball. Hence, titanium socket revealed less severe damage than UHMWPE ball due to the protection of oxide film. Arc-shaped wear scars and scratches appeared in both the central and edge zones of the ball and socket component, which were rather different with that of ball-on-flat. In addition, a new damage pattern, annular stress concentration damage, occurred on the edge of UHMWPE ball characterized by severe abrasive and adhesive wear.

Titanium alloys are widely used in the field of artificial joints, but their poor wear resistance limits their clinical application. Therefore, in this paper, the diamondlike carbon (DLC) film deposited on Ti6Al4V alloy surface by unbalanced magnetron sputtering technology to improve its wear resistance. Swinging tests are conducted on a self-refit multifreedom degree friction tester, and their coefficient of friction, wear loss, and wear morphology were analyzed. Results show that there are no evident scratches on the socket surface with small axial load and angular displacement. The worst wear scratches appear under the largest load and swing angular displacement. A spot of scratches with different depths are found on the edge of the socket, which reveals the characteristic of swinging friction. The friction coefficient increases from 0.134 to 0.206 as the axial load increases, and increases from 0.11 to 0.186 as the swing angular displacement increases. Therefore, the swing angular displacement has greater influence on the wear degree. The wear mechanisms of DLC film involved a combination of fatigue, adhesive, and abrasive wear.

With a subscale rolling-sliding apparatus, the objective of this study is to explore the adhesion and rolling contact fatigue characteristics of wheel/rail rollers with sanding under water condition. Sanding improves adhesion coefficient but aggravates the surface damage of wheel and rail materials. With the particle diameter and feed rate increasing, the adhesion coefficient is further improved. However, the surface damage (spalling and pits) becomes severer as well as the surface roughness. Note that pitting is a special damage type when sanding is used to improve the adhesion. Big pits and fatigue cracks appear on subsurface under larger particle diameter and feed rate conditions. Severe cracks initiate from big pits and develop into material to a depth, which results in bulk material breaking.