Line Contact Condition Research Articles

CO2 tribocorrosion of CVD W/WC coatings and performance against internally epoxy coated pipes: A benchmark against HVOF WC-Cr3C2-NiCr and electroless Ni-P coatings

CO2 anoxic environments are often found in the energy sector in applications comprising oil and gas, geothermal energy or carbon capture and utilization, among others. These environments are highly corrosive, resulting in material degradation and ultimately component failure. A widely used option for mitigating degradation in CO2 corrosive environments relies on the use of corrosion resistant coatings. However, these coatings are often exposed simultaneously to wear in many applications such as in sucker rods for the oil and gas industry, resulting in tribocorrsion. The separate corrosion or wear behavior of many industrial relevant corrosion resistant coatings has been previously widely reported in many works. However, knowledge about their tribocorrosion behavior is scarce and limited to atmospheric conditions, being the knowledge on their CO2 tribocorrosion behavior inexistent. The present work shows under well-controlled electrochemical conditions that the specific wear rate of chemical vapor deposited W/WC and thermal spray WC-Cr3C2-NiCr coatings is up to three orders of magnitude lower when compared to electroless Ni-P coatings under point contact conditions and one order of magnitude lower under line contact conditions, despite all coatings offering a good corrosion resistance under high pressure CO2. The experiments performed under line contact conditions also reveal that the former coatings are also suitable for protecting components sliding against abrasive epoxy coatings. These results highlight the importance of simultaneously evaluating the wear performance of coatings in reactive environments in order to select coatings suitable for protecting sliding components in CO2 corrosive environments.

Study on friction and wear properties of cast iron material in line contact condition based on free abrasive grinding experiment

In order to study the friction and wear properties of cast iron in free grinding environment under the condition of line contact, this paper presented a new method to calculate the friction coefficient by measuring the friction torque. Through the self-developed free abrasive grinding experimental device in line contact condition, this work carried out friction and wear experiment with relative speed, load, abrasive particle diameter, and abrasive mass fraction as process parameters, and studied the evolution rules of friction coefficient and wear amount of cast iron materials under different process parameters. Based on the response surface method Box-Behnken experimental design, the significance of the experimental results was analyzed, and the prediction model of the friction coefficient and wear amount of cast iron was established. According to the significance of the prediction model, the influence degree of each process parameter on the friction coefficient and wear amount was revealed. The results showed that under the action of free abrasive, the friction coefficient of cast iron material in line contact with GCr15 was between 0.18 and 0.35. When the experimental time was 1.5 h, the removal amount of cast iron material was between 20 and 65 mg, which is significantly increased compared with that without abrasive and the wearing capacity of cast iron increased with the increase of relative speed, load, abrasive particle diameter, and abrasive mass fraction. The friction coefficient had a negative correlation with relative speed, and a positive correlation with abrasive particle diameter and abrasive mass fraction. With the increase of load, the change of friction coefficient decreased first and then increased. The influence degree of each process parameter on the friction coefficient and wear amount of cast iron material: the particle diameter and relative velocity of abrasive were relatively significant, the abrasive mass fraction was the second, and the load was the smallest. Through random experiments, the prediction model of friction coefficient and wearing capacity were verified to be highly accuracy, and could be used to predict the friction and wear performance parameters of cast iron in the process of free grinding under the condition of line contact. It provided a certain theoretical basis for the friction and wear behavior of cast iron as a grinding tool material in the grinding process.

Novel S-N curve for different hardened layers in point and line contact

Rolling contact fatigue (RCF) regularly causes mechanical components to fail under cyclic loads. Popular surface treatment processes such as case hardening (carburization), nitriding and tempered martensitic reduce the effect of RCF damage. This paper presents multi-stage S-N curve for steels with different surface treatments, under point and line contact conditions using RCF tribometers for the experiments and finite element (FEM) simulation to simulate localised stresses in the contacts. Additionally, S-N tests with 0, 5 and 11% slide to roll ratio (SRR) are presented. This work demonstrates the importance of testing key points at RCF S-N curves to optimize the hardened layers.

An effective method for calculating elasto-plastic contact pressure and contact patch size under elliptical, circular and line contact conditions

According to the Hertz's contact theory (HCT) and considering the strain hardening of materials, an effective calculation method is proposed for solving the elasto-plastic contact pressure and the contact patch size under arbitrary smooth and continuous contact conditions. Firstly, it is assumed that the outer and inner edges of the contact patch are elastic and elasto-plastic contact zones, respectively, the contact pressure in the elastic contact zone satisfies the HCT, while the contact pressure in the elasto-plastic contact zone is the superposition of a constant contact pressure and several small ellipsoidal distribution contact pressures. Then, the explicit expressions of contact patch size and contact pressure under the elasto-plastic elliptical, circular and line contact conditions are derived, respectively. Subsequently, the accuracy and applicability of the proposed method are evaluated by comparing the predicted results with the finite element simulations. Finally, the accuracy of the proposed method is further verified by comparing the predicted results with the typical results in literature. It is shown that the proposed method has high calculation accuracy, and the maximum relative errors are 9.32% for the elliptical contact, 4.61% for the circular contact and 11.84% for the line contact, respectively. Meanwhile, the proposed method can effectively predict the contact pressure distribution under the elasto-plastic elliptical, circular and line contacts, and shows a general applicability for different contact materials, contact-body's sizes and normal external loads, as well as for the elasto-plastic wheel-rail contact analysis.

Influence of surface topography on the friction and dynamic characteristics of spur gears

As an important excitation source of gear dynamic problems, the time-varying friction of tooth surface is closely related to its topography. Considering the friction characteristics of tooth surface is of great significance to improve the calculation accuracy of gear dynamic characteristics. In order to solve the problem that the variation of tooth friction coefficient was simplified too much in the previous gear dynamics research, the time-varying tooth friction coefficient is obtained by fitting the results of twin-disc test in this research. To investigate the influence of tooth surface topography on the friction and dynamic characteristics of spur gears, the relationship between surface topography and friction coefficient under line contact condition is studied using twin-disc tester and analyzed by 3D topography parameters in ISO 25178. The time-varying friction coefficients of spur gears with different tooth surface topographies during meshing are fitted with the experimental results. The influence of time-varying friction coefficient caused by the tooth surface topography on the dynamic characteristics of spur gears under different operating conditions is examined by substituting the fitting curves of time-varying friction coefficient into the multi-degree-of-freedom dynamic model of spur gears. The results show that this influence is mainly embodied in the off-line-of-action direction, which is the direction of friction force acting on the tooth surface. The dynamic characteristics of gears with different surface topography are obviously different under various working conditions. The method presents in this paper simplifies the application of tooth contact analysis in the study of time-varying tooth friction characteristics, which will provide a new way for the gear dynamics research considering the tooth surface topography.

Fretting wear of the nitrided medium carbon steel under line contact condition at an elevated temperature

PurposeFretting wear exists widely in the field of matching mechanical parts whereas previous research studies mostly focus on the point contact through a ball-plate tribometer. This paper aims to study the influence of wear debris on the fretting wear characteristics of the nitrided medium carbon steel under line contact condition at elevated temperature.Design/methodology/approachFretting wear behavior of the nitrided medium carbon steel was experimentally investigated under line contact condition at elevated temperature and different normal loads without lubrication. Wear loss, worn surface and wear debris were studied to analyze the wear mechanism of nitrided steel.FindingsThe results showed that surface hardness of the medium carbon steel was notably improved because of the generation of a 230 µm nitrided case. Wear loss increased with the normal load, which was associated with the damage of a thin solid film formed by the wear debris, consisting of iron oxides and chromium oxide rather than only iron or iron oxides. The wear debris became partially amorphous and spherical because it was trapped within the contact interface and was ground, rolled, oxidized under line contact conditions. The spherical wear debris acted as a third body and formed a lubricating film between the contact faces. This lubricating film helped to stabilize the friction coefficient and reduced the wear rate, which further caused the acceleration of wear volume to gradually decrease. The wear mechanisms of the nitrided steel were oxidation wear, abrasive wear and fatigue spalling of the oxide layer.Originality/valueThe findings are helpful to understand the fretting wear behavior of the friction pair under line contact and enrich the fretting tribology theory.

Elastic Deformation of Surface Topography under Line Contact and Sliding-rolling Conditions

Elastic Deformation of Surface Topography under Line Contact and Sliding-rolling Conditions

Modeling of Finite-Length Line Contact Problem With Consideration of Two Free-End Surfaces

Finite-length line contact conditions, existing in applications such as gears or roller bearings, lead to subsurface stress distribution influenced by the free boundaries. This paper presents a semi-analytical method (SAM) for the finite-length line contact problem, based on the overlapping concept and matrix formation, to consider the effect of two free-end surfaces. In order to obtain two free surfaces, three half-spaces with mirrored loads to be solved are overlapped to cancel out the stresses at expected surfaces. The error introduced by this method is analyzed and proven to be negligible. The conjugate gradient method (CGM) is used to solve the pressure distribution, and the fast Fourier transform (FFT) is used to speed up the elastic deformation and stress-related calculation. The model is verified by finite element method (FEM) and shows a high conformity and efficiency. Besides, the line contact situations are discussed to explore the effect of free surfaces.

Pitch cone design and tooth contact analysis of intersected beveloid gears for marine transmission

A pitch cone based geometry design method considering line contact is proposed for intersected beveloid gears. The proposed pitch cone design applies the spatial gearing model to determine working pitch cone angles and working spiral angles. For the determination of geometry design parameters, a computer program which incorporates pitch cone design and line contact condition was developed. To illustrate the meshing characteristics, example studies with three groups of geometry parameters were performed by unloaded and loaded tooth contact analysis. Through the analysis, the influences of misalignments, torque load and angle between the first principal directions of the tooth surface curvatures (FPD-angle) on the mesh were investigated. The results show that: compared with axial position errors, shaft angle errors have a more detrimental influence on both the contact path and transmission error. Both FPD-angle and torque load have an obvious effect on this type of gearing. Finally, a practical experimental setup for intersected beveloid gearing with small shaft angle was performed and loaded tooth bearing tests were conducted to demonstrate the proposed design procedure and the theoretical simulation models. The experimental results compared well with the simulation.

1304 線接触水潤滑下における各種材料の摩擦摩耗特性(トライボロジー(1))

In this paper, the relation between the friction coefficient and the specific ware ratio of stainless steel, ceramics, polymer and diamond like carbon (DLC) coated steel slid with stainless steel under line contact condition was described. The sliding tests were carried out using block on ring type friction and ware testing machine. The results of the relation between friction coefficient and specific ware ratio show the typical region of each material. The DLC coating shows the lowest friction and lowest ware. The polymer materials also show low friction and medium ware especially in ultra high molecular weight polyethylene and polyetheretherketone composite material. According to the ceramics materials, the silicon carbide (SiC) shows the high friction and ware different from the case of SiC-SiC contact.

A Simplified Thermal Analysis of Elastohydrodynamic Contacts

Under elastohydrodynamic (EHL) conditions, the temperature in the contact zone determines the load resistance of the lubricant film. Therefore, an efficient assessment of the scuffing risks requires accurate contact temperature predictions. The work presented in this paper develops a simple and prompt temperature model exploitable within any thermal EHL modeling approach. The model incorporates a multilayer lubricant film representation for the heat equation solution. The developments also include an original heat repartition factor expression and a simple formula for handling intermediate values of the Peclet number. The rolling/sliding conditions in the inlet cause temperature rises that also affect the film resistance in the contact zone; this study proposes an inlet temperature rise equation. This formula offers temperature predictions in agreement with reference values. The contact zone temperature predictions for the line of contact problem under sliding/rolling conditions agree remarkably well with published numerical results; for the evaluations presenting the higher absolute difference, the correspondence remained over 94% and 95% for the maximum and mean temperatures, respectively. Both line and elliptical contact conditions were tested and compared to experimental data available in the literature. The analysis evidenced the precision of the estimates; thus attesting to the accuracy of the model under any contact conditions. Finally, the results indicate that, depending on the pressure and speed combination, the shearing zone may occupy around 30% of the film thickness.

Friction in starved hydrodynamically lubricated line contacts

The hydrodynamic friction coefficient, which determines the friction coefficient at high Sommerfeld numbers (viscosity⁎velocity/load) has a unique solution for the fully flooded case. As such the friction coefficient can be predicted as a function of the above number. As shown by Cameron (1976) [1] the friction coefficient in the fully flooded regime increases as the square root of the Sommerfeld number. For very low Sommerfeld numbers, the asperity interaction causes the friction coefficient to increase when entering the mixed lubrication regime.Even though a unique (and low) friction coefficient exists in the fully flooded regime, the situation is more complex in the starved regime. First of all the friction coefficient is higher in the starved regime, and secondly the coefficient depends on the degree of starvation.This paper analyses the load carrying capacity, the Poiseuille flow based friction and the Couette flow based friction, as a function of the degree of starvation. It is shown that the Poiseuille friction force diminishes fastest with starvation, followed by the load carrying capacity, and finally the Couette term diminishes slowest of all three terms.As a consequence the friction coefficient for sliding starved conditions is dominated by the Couette term.The current paper analyses the friction coefficient evolution as a function of starvation for line contact conditions, using analytical and numerical tools. Finally, curve fitted equations are given for the friction as a function of the starvation level.

Micro Cavity's Tribological Property under Line Contact and Sliding-rolling Conditions

The line contact pairs widely exist in machine elements,most of them work under the elastic hydrodynamic lubrication condition.In order to study the influence of microcavities on the tribological properties of line contact friction pairs and the correlation between 3D surface characterization parameters and the tribological characteristic,the technology of laser surface texturing is introduced to control microcavity's area density,depth and distance.Four disc specimens are made,which have the same surface roughness,but the area density of microcavity are 7%,14%,21% and 28% respectively.The surface of the specimens are scanned by Talyrsurf CCI Lite and characterized by ISO25178.A series of frictional experiments under line contact with different sliding-rolling ratio,different load,different rotational speed conditions are conducted on a self-modified JPM-1 two-disc tribo-tester.The results show that the micro structure characteristics of surface topography have a significant influence on the frictional characteristic of the line contact pairs,the correlation between friction and volume parameter and feature parameter is given,and meanwhile,the micro structure characteristics of surface topography have different effects on friction under different working conditions and different sliding-rolling ratio.

DURABILITY AND TRIBOLOGICAL PROPERTIES OF THERMALLY SPRAYED WC CERMET COATING IN LUBRICATED ROLLING WITH SLIDING CONTACT

Durability and tribological properties of thermally sprayed WC-Cr-Ni cermet coating were investigated experimentally in lubricated rolling with sliding contact conditions. By means of the high energy type flame spraying (Hi-HVOF) method, the coating was formed onto the axially ground and circumferentially ground roller specimens made of a thermally refined carbon steel. In the experiments, the WC cermet coated steel roller was mated with the carburized hardened steel roller without coating in line contact condition. The coated roller was mated with the smooth non-coated roller under a contact pressure of 1.0 or 1.2 GPa, and it was mated with the rough non-coated roller under a contact pressure of 0.6 or 0.8 GPa. As a result, it was found that in general, the coating on the circumferentially ground substrate shows a lower durability compared with that on the axially ground substrate and this difference appears more distinctly for the higher contact pressure for both smooth mating surface and rough mating surface. It was also found that there are significant differences in the tribological properties of WC cermet coating depending on the contact pressure. In addition, depending on the smooth or rough mating surface, remarkable differences in the tribological properties were found.

Fretting fatigue strength of 12% Cr steel under high local contact pressure and its fracture mechanics analysis

Fretting fatigue fractures of industrial machines often occur at the point where high contact pressure occurs due to uneven contact. In this study, fretting fatigue tests were performed under high contact pressure applied in line-contact conditions using 12% Cr steel with parameters of the mean stress, contact pressure, and material strength. The fretting fatigue strength was shown to decrease as contact pressure increased, and minimized when Hertz’s average contact pressure was about 1.5 times 0.2% proof stress σ0.2, and increased again at higher contact pressure.Crack propagation behavior was examined using fracture mechanics by observing the detailed crack propagation profile of non-propagating cracks and performing finite element analysis with an inclined elliptical surface crack. Cracks were found to propagate in stage II at the angle where the maximum stress intensity factor range ΔKθmax occurred. Also, test results concerning the fretting fatigue strength could be successfully explained by the micro-crack propagation model in which a micro-crack can propagate when its stress intensity factor range ΔK is greater than the threshold value ΔKth when considering small crack effects and mean stress effects. This model also confirmed the experimental results that showed the length of non-propagating cracks decreased as the mean stress and the material strength increased.

Preliminary investigation of the effect of dimple size on friction in line contacts

The scale of surface texture is becoming an important issue of surface texture design, particularly for the condition of low speed and high load. Experiments were carried out to investigate the effect of dimple size on friction under line contact condition. The patterns of dimples distributed as square array were fabricated on the surface of brass disks. Each pattern has the same area density of 7%, the same depth over diameter ratio h/ d of 0.03, and dimple diameter d varying from 20 to 60 μm. The frictional tests of the brass disk sliding against a stationary cylindrical surface of bearing roller were conducted. It was found that the pattern with dimple diameter of 20 μm presented the effect of friction reduction. For the further understanding of the effect of dimple size under line contact condition, numerical simulations were also carried out to evaluate the hydrodynamic pressure within the contact of cylindrical and plane surfaces. The effects of dimple size and radius of the cylinder on the load carrying capacity were evaluated and discussed.

On the Dang Van fatigue limit in rolling contact fatigue

Recently, various methods have been proposed to assess the risk of rolling contact fatigue failure and in particular, the Dang Van multiaxial fatigue criterion has been suggested in a simple approximate formulation by Ekberg, Kabo and Andersson. In a recent note by Ciavarella and Maitournam, it was found that the approximation is only valid in a restricted range of cases. Here, a much larger range of conditions including elliptical contact and partial slip conditions are considered and analytical formulae are also derived. The Ekberg, Kabo and Andersson calculation is shown to be a good approximation only for nearly circular contacts, high Poisson's ratio and high Dang Van constant. The Dang Van fatigue limits are very high, particularly for line contact: however, under those conditions ratcheting deformations also are likely to occur unless perhaps for very hard materials showing cyclic yield limit much higher than fatigue limit (these materials in turn could then show very low wear and be prone to fatigue crack propagation). Classical findings about the RCF fatigue suggest nearly twice higher fatigue limit in point contact with respect to line contact conditions, and this is apparently in contradiction to the Dang Van criterion. A possible qualitative explanation is that in point contact above elastic shakedown there is a regime of cyclic plasticity, rather than the direct transition to ratcheting regime as in line contact. However, the Dang Van criterion has been found to be possibly too conservative under RCF also by other authors recently, and further investigations are required.

Fretting Fatigue Strength under High Local Contact Pressure and Its Fracture Mechanics Analysis

Fretting fatigue fractures of industrial machines often occur at the point where high contact pressure occurs due to an uneven contact. In this study, fretting fatigue tests were performed under high contact pressure applied by line-contact conditions using 12-Cr steel with parameters of the mean stress and the material strength. It was shown that the fretting fatigue strength decreased slightly with increasing the contact pressure and became minimum when Hertz's average contact pressure is about 1.5 times of 0.2% proof stress, σ0.2. I also showed that test results concerning the fretting fatigue strength and the non-propagating crack length can be successfully explained by the micro-crack propagation model in which a micro-crack can propagate when its stress intensity factor range, ΔK is greater than the threshold value, ΔKth considering small crack size effects and mean stress effects.

Effects of substrate surface finish and substrate material on durability of thermally sprayed WC cermet coating in rolling with sliding contact

In this study, using a two-roller testing machine, the authors examined the surface durability of thermally sprayed WC-Cr-Ni cermet coating in lubricated rolling with sliding contact conditions. The coating was formed onto the axially ground, blasted and circumferentially ground roller specimens made of a thermally refined carbon steel or an induction hardened carbon steel by means of the high energy type flame spraying (Hi-HVOF) method. The WC cermet coated roller finished to a mirror-like condition was mated with the carburized steel roller without coating having a surface roughness of Ry=3.0∼5.0 μm. In the experiments, a maximum Hertzian stress of P H=0.6 or 0.8 GPa was applied for the thermally refined carbon steel roller and P H=1.4 GPa was applied for the induction hardened carbon steel roller in line contact condition. As a result, it was found that in the case of induction hardened steel substrate, the coated roller generally exhibits a long life without any serious damage and the surface durability is hardly affected by the substrate surface finish, while in the case of thermally refined steel substrate, the durability of coated roller is lowered and the life to flaking is very short particularly when the substrate surface is circumferentially ground and the mating surface is rough. The surface durability of coated roller was also compared with the durability of steel roller without coating. Finally, in order to discuss the durability of coated roller, the elastic-plastic behavior of the subsurface layer under repeated rolling with sliding contact was analyzed using a finite element method (FEM).

Transversal compressive force and superconducting transition properties of Bi-2223 tapes

Abstract Transversal compressive force was applied to a face of Bi-2223 tape, and V–I characteristics and mechanical properties of the tape were measured. Contact conditions between the tape and pushing parts are two kinds (a line-contact and a face-contact). Based on measured data dependence of critical currents and n-values of the Bi-2223 tape on the transversal compressive force and deformation of the tape was experimentally studied. From the results of the line-contact condition between the tape and the pushing parts, 25 N of the force to the tape decreased the critical current and the thickness of the tape by 90% and 0.6% of the initial value, respectively. The data under the face-contact condition showed little degradation of the tape’s critical currents because of the small stress to the tape. After those experiments the tape was cut along the longitudinal direction of the tape and Bi filaments were observed microscopically in the cross-section.