Effect Of Contact Load Research Articles

Hybrid finite element modeling of subsurface-originated spalling in flexible bearings with hoop stresses

The flexible bearing in a harmonic reducer undergoes structural deformation after being mounted on the cam, causing the bearing to operate under a complex stress state. A hybrid finite element model is developed to investigate crack initiation and propagation in flexible bearings with hoop stress under rolling contact fatigue loading. The model is coupled with continuum damage mechanics, and the damage evolution equation takes the maximum shear stress amplitude as the damage-causing stress since the hoop stress inevitably affects the fatigue life. The model is verified by comparison with the fatigue life of the inner ring without hoop stress. The crack initiation and spalling formation mechanisms in the inner ring assembled with the cam are analyzed in detail. Moreover, the effects of contact load and equivalent interference on the inner ring’s spalling morphology and fatigue life are studied.

Thermal contact conductance model of rough surfaces with inclination based on three-dimensional fractal theory

PurposeThe purpose of this study is to establish a thermal contact conductance model of rough surfaces with inclination based on three-dimensional fractal theory.Design/methodology/approachThe effects of contact load, inclination angle, fractal dimensional and fractal roughness on thermal contact conductance of rough surfaces were studied using numerical simulation.FindingsThe results show that the thermal contact conductance of the rough surface increases with the increase of contact load and fractal dimension and decreases with the increase of fractal roughness and inclination angle. The inclination angle of the rough surface has an important influence on the thermal contact conductance of the rough, and it is a factor that cannot be ignored in the study of the thermal contact conductance of rough surfaces.Originality/valueA thermal contact conductance model of rough surfaces with inclination based on three-dimensional fractal theory was established in this study. The achievements of this study provide some theoretical basis for the investigation of the thermal contact conductance of rough surfaces.

Fractal model of thermal contact conductance of rough surfaces based on elliptical asperity

PurposeThe purpose of this study is to present a fractal model of thermal contact conductance of rough surfaces based on elliptical asperity.Design/methodology/approachThe effects of contact load, fractal dimensional, fractal roughness and eccentricity on thermal contact conductance of rough surfaces were investigated by using numerical simulation.FindingsThe results indicate that the thermal contact conductance of rough surfaces increases with the increase of the contact load, increases with the increase of the fractal dimension and decreases with the increase of the fractal roughness. The thermal contact conductance of rough surfaces increases with the increase of eccentricity. The shape of the asperity of rough surfaces has an important influence on the thermal contact conductance of rough surfaces.Originality/valueA fractal model of thermal contact conductance of rough surfaces based on elliptical asperity was established in this study. The achievements of this study provide some theoretical basis for the investigation of thermal contact conductance of bolted joint surfaces.

Tribo-corrosion interaction of the parallel steel wires in the suspension bridges

AbstractThe effect of contact load and relative displacement on tribo-corrosion interaction of parallel steel wires of main cable in the suspension bridge was investigated in this study. A self-made tribo-corrosion test bench was employed to conduct tribo-corrosion tests of parallel steel wires in 3.5% (wt%) NaCl solution and deionized water under different contact loads and different relative displacements. The friction coefficient and wear coefficient of wires were presented. Electrochemical corrosion behavior (Tafel polarization curves, Nyquist diagram, and equivalent circuit diagram) was characterized by electrochemical analyzer. Wear morphology was observed by scanning electron microscope. Wear volume loss and corrosion-wear interaction were quantitatively demonstrated by high-precision weighing balance. The results show that the electrochemical corrosion ability of the steel wires increases with the increase of the contact load or relative displacement. The increased contact load or relative displacement increases the volume loss of corrosion-wear and pure wear, but decreases the wear coefficient. The wear mechanisms in 3.5% NaCl solution are adhesive wear, abrasive wear, and corrosive wear as compared to adhesive wear and abrasive wear in deionized water under different contact loads. The wear mechanisms of parallel steel wires are slightly different under different relative displacements. But the main wear mechanisms are similar to that under different contact loads. The interaction effects of corrosion and wear produced by the contact load and relative displacement are all the synergistic effects.

Effects of Contact Load and Torsion Angle on Crack Propagation Behaviors of Inclined Crossed Steel Wires during Tension–Torsion Fretting Fatigue in Acid Solution

The hoisting rope in the kilometer-deep coal mine exhibits the tension–torsion fretting fatigue behaviors of inclined crossed steel wires in acid solution. Distinct contact load and torsion angles of steel wires in the rope cause different crack propagation behaviors, which greatly affect the fatigue lives of steel wires. Therefore, the effects of contact load and torsion angle on the crack propagation behaviors of inclined crossed steel wires during tension–torsion fretting fatigue in acid solution were investigated in the present study. The three-dimensional X-ray tomographic micro-imaging system was used to reveal evolutions of crack profiles and crack propagation depths during the test. The evolution of friction coefficient between steel wires during the test is presented. The three-dimensional white light interference microscope, electrochemical analyzer, and scanning electron microscope were employed to investigate the wear depth profiles, Tafel polarization curves and impedance spectra, and wear scar morphologies, respectively, of steel wires. Effects of contact load and torsion angle on crack propagation behaviors of inclined crossed steel wires during the tests were explored through analyses of friction and wear mechanisms and electrochemical corrosion damage. The results show that as the contact load and torsion angle increase, the crack propagation depth and rate of steel wire both increase and the fatigue life of steel wire decreases. Those are mainly attributed to the increases in the average tangential force between steel wires, wear depth, electrochemical corrosion tendency, and surface damage of steel wire as well as the decrease in corrosion resistance.

Fractal variation of three-dimensional surface topography during sliding wear under mixed elastohydrodynamic lubrication

The surface morphology variation of the friction pair during the wear process directly affects the local lubrication effect and contact strength, and this variation is difficult to quantify in mixed lubrication. In this study, a numerical simulation and characterization model method of sliding wear surface morphology evolution based on deterministic elastohydrodynamic lubrication (EHL) model and surface three-dimensional morphology fractal method is established. The effectiveness of the lubrication model is verified by the film thickness measurement, and the actual surface wear coefficient is obtained through the wear experiment. On this basis, the variation of surface morphology and fractal parameters in the sliding wear process is investigated, and the effect of contact load and sliding speed on surface lubrication characteristics and fractal parameters is analyzed. The results show: wear will cause the higher wave peaks on the ground surface to be gradually worn away and the fine structure of the surface is reduced, and the fractal dimension of the morphology is therefore reduced. In addition, the contact area ratio and contact load ratio, as well as the coefficient of friction and surface evolution under different loads and sliding speeds are consistent.

A revised contact stiffness model of rough curved surfaces based on the length scale

Based on the continuity of length scale for asperities, a complete model of normal stiffness between curved fractal surfaces considering friction factor is proposed. Through the coupling of critical base diameter and contact area, deformation modes of all asperities are determined, and contact stiffness of the whole rough surface is derived by double integral. Accordingly, effects of contact load, surface topography, friction factor, size parameters and material properties on the contact stiffness are investigated. Results show that contact stiffness depends sensitively on the fractal dimension, and exhibits nonmonotonic characteristics as fractal roughness varies across scales. Finally, predicted values of normal stiffness are compared with existing contact models as well as experimental data.

Helium Tribology of Inconel 617 at Elevated Temperatures up to 950°C: Parametric Study

This study investigates the friction and wear behavior of Inconel 617, one of the primary candidate materials for high-temperature gas-cooled nuclear reactors. Using a custom-built, high-temperature tribometer, a helium (He)-cooled reactor environment was simulated up to 950°C. To obtain a comprehensive understanding of the Inconel 617 tribological response, the effects of contact load, temperature, air and He environments, sliding speed, and sliding distance were studied. From the conditions investigated, the coefficient of friction and wear values are the highest in a high-temperature He atmosphere. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques were used to analyze the Inconel 617 oxide layer. Analysis of the samples tested in the He atmosphere showed the presence of Cr-rich oxide with a lower presence of Co-Ni-Mo compared to the samples tested in air. Characterization also revealed the existence of a very hard protective glaze layer in air while such layer was not observed in the He environment, which was associated with higher wear/friction values.

Tribological investigation of Si3N4-hBN on HXLPE bearing couple: Effects of sliding velocity and contact load

In present study, the effects of sliding velocity and contact load on the tribological properties of silicon nitride based bearing couples were investigated via the pin-on-plate tests. Pure Si3N4 and its composite (20 vol% hBN content) pins were sliding against highly cross-linked polyethylene (HXLPE) discs under simulated body fluid lubrication. Moreover, the solid lubrication film forming mechanism was investigated via worn surface characterization.For Si3N4–20 vol% hBN/HXLPE bearing couple, friction coefficients and wear rates were decreased with increasing of the contact load or sliding velocity (p-values < 0.001). Two-way ANONA analysis show that these two factors are significantly correlated (p-value = 0.011). Abrasion of the polymer disc is the main wear mechanism. Interfacial lubrication is achieved via the formation of a solid lubrication film on the ceramic pin. It contains H3BO3, SiO2·nH2O, Mg(OH)2, and HXLPE wear debris (-CH2CH2-)n. In comparison, the effects of contact load and velocity on the tribological performance of Si3N4/HXLPE bearing couple are similar to that of Si3N4–20 vol% hBN/HXLPE bearing couple. However, poor quality solid lubrication films (e.g. discontinuity, rough, and uneven appearances) were observed, this may cause by the lack of hBN compound to promote the formation of H3BO3.

Determination of fretting parameters of hoisting rope in coalmine and fretting-fatigue behavior of steel wires

Purpose – The objective of this paper is to determine fretting parameters of hoisting rope according to the hoisting parameters in coalmine and to explore the effect of contact load on fretting-fatigue behavior of steel wires. Design/methodology/approach – Based on the mechanical model of hoisting rope in coalmine, the dynamic tension simulation of hoisting rope was performed. Static equations of hoisting rope under tension and torsion and theories of contact mechanics were applied to obtain fretting parameters. Fretting-fatigue tests of steel wires at different contact loads were conducted using a fretting-fatigue test rig. The fretting regime, normalized tangential force and fretting-fatigue life were studied. The morphologies of fretting contact scars and fracture surfaces were observed by scanning electron microscopy and optical microscopy to examine wear and failure mechanisms. Findings – Dynamic tension changes from 0 to 30,900 N. In outer strand layer, contact loads between steel wires in certain wire layers are 60.5 and 38.3 N compared with 378 and 102.7 N between wire layers; relative displacements between wires are 62.5 and 113.2 μm, respectively. Mixed fretting regimes develop in all cases. Increasing contact load decreases the stabilized relative slip and normalized tangential force, reduces the fretting fatigue life, induces accelerated adhesive wear and fatigue wear and results in rougher fracture surface topographies. In all cases, fretting zone induces crack initiation; crack propagation and rupture zones present brittle cleavage and longitudinal splitting, respectively. Practical implications – This paper presents the systemic study on determination of fretting parameters of hoisting rope according to the hoisting parameters in coalmine and the fretting-fatigue behavior of its internal steel wires. The results of fretting-fatigue tests show that the increase of contact load decreases the stabilized relative slip in mixed fretting regime and normalized tangential force, reduces the fretting fatigue life, induces accelerated adhesive wear and fatigue wear and results in rougher fracture surface topographies. Originality/value – The authors warrant that the paper is original submission and is not being submitted to any other journal. And the research does not involve confidentiality, copyright infringement, leaks and other issues, all the responsibilities that the authors will take.

Correlation between Contact Load and Surface Roughness in Plane Strain Extrusion

Effect of contact load and surface roughness on friction behavior in plane strain extrusion is one of the biggest phenomena in improving the sliding performance of cold forward extrusion. Wear resistance that commonly occurs on the plane requires an appropriate method to obtain the finest product surfaces. This paper highlighted is the correlation between contact load and surface roughness on the friction behavior and wear resistance of the sliding plane in the extrusion process. The analysis described in this paper involved the experiments to assess the contact load in the extrusion and the surface roughness. The experiments were set up by using pure aluminium A1100 as billet extruded between dies made of hot work tool steel (SKD11). Extrusion ratio of the process is three (3) and the billets were pressed by a hydraulic press machine. The contact load for each experiment was taken at a 20mm length of the extrusion, and the average surface roughness of the aluminium was plotted on a graph. Three types of lubricants were used in this study: Refined Bleached Deodorized (RBD) palm stearin and two types of paraffinic mineral oil, 95 and 460. These two types of paraffinic mineral oil differed in viscosity. These three types of lubricants were run with four different quantities: 0.1mg, 1mg, 5mg, and 20mg. The results showed that an increased amount of lubricant reduced the surface roughness. The correlation between contact load and surface roughness showed significant differences for each lubricant while at 5mg of RBD palm stearin and paraffinic mineral oil 460, the results showed the same contact load but different surface roughness.

Effect of contact load on fretting fatigue behaviour of steel wires

The tension–tension fretting fatigue tests of steel wires were performed on a self-made fretting fatigue test equipment under contact loads ranging from 40 to 70 N and a strain ratio of 0·8. The results showed that when the contact load increased, the fretting regime of steel wires transformed from gross slip regime to mixed fretting regime. The fretting fatigue life in the mixed fretting regime was significantly lower than that in the gross slip regime. The main fretting wear mechanisms in the gross slip regime, where there were serious fretting damage and a lot of wear debris, were abrasive wear and fatigue wear. Microcracks were observed in the fretting scar of the mixed fretting regime, and the main fretting wear mechanisms were adhesive and fatigue wears. The fretting wear scar was the fatigue source region, and the fatigue fracture surface could be divided into three regions.

Finite element analysis of the rolling friction of a viscous particle on a rigid plane

The rolling friction of a sphere over a rigid plane is studied by finite element method, where the material behaviour of the sphere is assumed to be viscoelastic, described by the Kelvin–Voigt model. The effects of contact load, radius and rotation speed of the sphere, as well as material properties such as Young's modulus, Poisson's ratio and viscosity coefficients, on rolling friction are analysed. The results support a theoretical model formulated based on the principles of contact mechanics.

High temperature fretting fatigue behavior of IN100

Fretting fatigue behavior of a nickel-base superalloy, IN100, was investigated at 600 °C. Fretting fatigue tests were conducted at various stress levels using cylinder-on-flat contact configuration. Effects of microstructure were also investigated by varying the gamma grain size (3 μm versus 7 μm). Additionally, effects of contact load were studied. Furthermore, plain fatigue tests of IN100 with two microstructures were also conducted. Fretting reduced the strength/life in comparison to those of the plain fatigue almost equally in both microstructures. Increase of contact load reduced the fretting fatigue strength/life. An increase of the gamma grain size decreased the fretting fatigue strength/life of IN100. Fracture surfaces of the 3 μm grain microstructure showed intergranular and tortuous crack path while the 7 μm grain microstructure had transgranular and relatively smoother crack path. Fractographic analysis indicated that the 3 μm grain microstructure had a higher resistance to the fretting fatigue crack nucleation and initiation as well as to the crack growth in comparison to the 7 μm grain microstructure, which was in agreement with the observed plain and fretting fatigue behaviors. Furthermore, plain and fretting fatigue performances improved at 600 °C in comparison to room temperature with both microstructures.

Effect of contact load and lubricant volume on the properties of tribofilms formed under boundary lubrication in a fully formulated oil under extreme load conditions

The effect of contact load and volume of lubricant in the time to tribofilm breakdown and extent of wear was examined in fully formulated oil with zinc dialkyl dithiophosphate as the main anti-wear additive. The mechanism of tribofilm formation and breakdown was followed carefully by monitoring the friction coefficient over the duration of the test. Tribological tests conducted with limited lubricant exhibited a direct relationship between the amount of lubricant and time to tribofilm breakdown with tests with smaller amounts of lubricant exhibiting shorter lifetimes. In addition the number of cycles for breakdown of the tribofilm is inversely proportional to the applied load at a fixed amount of lubricant. It is also shown that higher contact loads (405 N with maximum Hertzian contact pressure of 2.77 GPa) resulted in premature breakdown of the tribofilm while lower contact loads (297 N with maximum Hertzian contact pressure of 2.5 GPa) resulted in no failure even after 100,000 cycles and the presence of a stable tribofilm. Focused ion beam cross sections of the tribofilm reveal that at higher contact loads the tribofilm is patchy with local regions as thick as 1 μm while at lower contact loads (297 N) the tribofilms are typically 100–200 nm thick. Transmission electron microscopy analysis of the wear debris indicates a larger fraction of the crystalline particles at higher contact loads of 405 N are Fe 2O 3. This is true even though the duration of the test is quite short indicating higher friction and higher contact temperature results in rapid oxidation of the wear debris to Fe 2O 3. Fe 2O 3 is significantly more abrasive and results in rapid bread down of the tribofilm. Analyses of wear debris of tests conducted at 297 N indicate smaller number of oxide crystallites with a chemistry of Fe 3O 4 within a non-crystalline matrix. XANES analysis indicates that at loads of 405 N sulfur is present as sulfates both at the surface and interior of tribofilms while at loads of 297 N it is present as sulfates at the surface and a mixture of sulfates and sulfides in the interior. Phosphorous K-edge XANES spectra indicate phosphorous is present as a mixture of short chain Zn and Fe phosphates at both loads. Fe L-edge spectra indicates that at 405 N the Fe is present largely as FeSO 4 and FePO 4 with some oxides of Fe while at 297 N it is present as a mixture of FeS and iron phosphates together with Fe oxides. The Zn L-edge spectra indicate that it is present primarily as phosphates and not as either oxides or sulfides in the tribofilms.

A Multi-Scale System Analysis and Verification for Improved Contact Fatigue Life Cycle of a Cam-Roller System

Surface distress in the form of contact fatigue is encountered in cam-roller systems. The contact fatigue appears to be initiated at micrometer-scale subsurface region. High stress is a result of the macro-scale requirement on the cam-roller motion event that produces high contact loads due to inertia of the roller and its follower link. Sliding of the roller and its impact onto the cam surface further compounds the detrimental effect of contact load. While conventionally a Hertz contact stress analysis can be used in ascertaining contact stress and maximum subsurface von Mises stress, it generally underestimates the stress when compared to the micrometer-scale subsurface stresses due to the presence of surface roughness. Contact analyses of cam and roller with rough surfaces are performed to examine the effects of two surface treatments. These involve surface finishing process in which a surface is rendered smooth, and the addition of a coating to the roller surface. Measurements of such cam and roller surfaces are used in micro-contact analysis module of a Surface Distress Analytical Toolkit to examine the effect of surface finish and coating on maximum subsurface stress. It is found that smooth surface provides a 53% reduction in maximum subsurface stress. The analysis also shows that the addition of coating further reduces subsurface stress nearly 7%. The impact of the combined treatment of the surface is an increase in contact fatigue life of the cam-roller system by nearly two orders of magnitude. The above findings are confirmed by laboratory tests using six rollers with various degrees of finishing processes, and with and without addition of coating to the surfaces. Examination of the rollers indicates a general improvement in roller performance due to addition of coating. Most notably, the combination of finishing process and coating was found to provide the best contact fatigue life since the corresponding rollers showed no observable wear even after testing for 2161h, or the same number of cycles accumulated over about 500,000 truck miles.

Al-Si合金-グラファイト複合材料のフレッティング摩擦・摩耗特性に及ぼす荷重の影響(トライボロジー(摩擦・摩耗))

Al-Si合金-グラファイト複合材料のフレッティング摩擦・摩耗特性に及ぼす荷重の影響(トライボロジー(摩擦・摩耗))

Micro-wear properties of carbon nitride coatings

Micro-wear tests of amorphous carbon nitride (CNx) coating against a diamond pin were carried out by using a atomic force microscopy. Micro-wear properties of CNx were shown as functions of coating condition, contact load, pin radius and contact pressure. The coating condition provides about 10 times difference of specific wear amount of CNx coating. The depth of wear of CNx coating increased drastically by increasing the contact load to above a critical value. CNx was influenced pin radius. The depth of wear scar of CNx coating changed depending on the pin radius under the same contact load. Combined with the effects of contact load and pin radius, the effect of contact pressure on specific wear amount was made clear. The specific wear amount of CNx coating increased with maximum contact pressure. On the other hand, specific wear amount of DLC was shown to be independent of maximum contact pressure. At the maximum contact pressure lower than about 10 GPa, the specific wear amount of CNx coating was smaller than that of DLC. Contact pressure dependence of wear of CNx coating was introduced by nano-scale delamination of the coating.

振動環境下におけるアブレシブ摩耗特性に関する研究 Ｉ ＣＦＲＰの処女面摩擦について

In this study, an experimental apparatus designed to test abrasive wear by mean of an abrasive belt was used to rub between virgin surfaces. The effects of contact load, the rubbing direction and amplitude of vibration on wear characteristics were examined in a series of the experiments. Results obtained are as follows. (1) The wear volume of CFRP becomes larger in the order, L, T, N. (2) The wear volume in both the X- and Y-directions decreases corresponding to the amount of over lapping. (3) In the Y-direction, wear volume is influenced by the rubbing direction.