Increasing Contact Load Research Articles

Tribo-corrosion-fatigue behaviors of the parallel wires of main cable in the suspension bridge

The suspension bridge in service is subjected to the coupling effects of dead load, vehicle load, wind load and corrosive environment. These factors cause the tribo-corrosion-fatigue behaviors of parallel steel wires of main cable, which seriously affect the load-bearing safety of the main cable. Therefore, it is of great significance to investigate tribo-corrosion-fatigue behaviors of steel wires and the saddle materials. The self-made test rig was developed to carry out tribo-corrosion-fatigue tests between the parallel steel wires, and between the steel wire and saddle groove. Tribo-corrosion-fatigue behaviors (friction coefficient, wear profile, failure area, wear mechanism and wear coefficient) of main cable wires was revealed by high speed digital microscope and scanning electron microscope. The results show that the friction coefficient shows a trend of rapid increase – decrease – increase – stabilization. It decreases with increasing contact load as compared to an increase with increasing fatigue load. The wear width and depth both increase nearly linearly with increasing cycles, while the failure area increases nearly parabolically. As the contact load and fatigue load increase, the wear width and depth increase, and the corrosion of wear area is more obvious. The wear coefficient decreases first and then increases with the increase of cycles. The wear mechanisms are mainly adhesive wear, abrasive wear, fatigue wear and corrosion wear. The increase of contact load and fatigue load promotes the wear deterioration behaviors of cable wires. The results have fundamental significance to ensure the load-bearing safety of the main cable and improve the service safety of the suspension bridge.

Tribological behavior of duplex CrN/DLC and nano-multilayer DLC-W coatings on valve tappet under elevated temperature and varying load

In this work, the effect of increasing contact load and elevated temperature on the friction and wear rate of duplex CrN/DLC and nano-multilayer DLC-W deposited by hybrid Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition (PVD-PECVD) on valve tappet. The tribological behavior of the coatings were studied through reciprocating dry sliding experiments at temperatures between 25 and 250 °C, with 10 N step-increment from 5 to 50 N. The results presented revealed that the coefficient of friction of the duplex CrN/DLC coating was lowest at 150 °C and 20 N, while the nano-multilayer DLC-W coating was lowest at 25 °C and 50 N. The wear rate of the duplex CrN/DLC coating and the nano-multilayer DLC-W coating were the lowest at 25 °C. The wear rates for both coatings continued to increase with increasing temperature.

Gradual Deterioration Behavior of the Load-Bearing Strength of Main Cable Wires in a Suspension Bridge

The main cable is the primary load-bearing component of a long-span multi-tower suspension bridge. The interaction between a dead load, vehicle load, wind load, and the corrosion environment leads the main cable wire to exhibit tribo-corrosion-fatigue behaviors. This behavior causes wire wear and deterioration, as well as a reduction in the effective cross-sectional area. This leads to the gradual deterioration of the wire’s load-bearing strength and seriously affects the load-bearing safety of the main cable. In order to ensure the safety of suspension bridges, it is critical to investigate the gradual deterioration behavior of the main cable wire’s load-bearing strength. A wire tribo-corrosion-fatigue test rig was established to test the wire under different friction pairs (saddle groove or parallel wires). The cross-sectional failure area of the wire with different pairs was obtained by super-depth electron microscopy and calculation. The damage degree evolution model and the deterioration model of the wire load-bearing strength were established by combining the theory of damage mechanics and the finite element method. The results show that, as contact and fatigue loads increase, so does the cross-sectional failure area of the fatigue steel wire. The fatigue wire’s damage degree has a good quadratic function relationship with fatigue cycles. The damage degree of the wire increases and the load-bearing strength decreases with increasing contact load and fatigue load. The load-bearing strength of the wire changes little at the beginning and decreases with increasing fatigue cycles. The results have fundamental significance for the life prediction of the main cable wires of suspension bridges.

Friction and Wear Behavior between Crane Wire Rope and Pulley under Different Contact Loads

Surface wear caused by contact between crane wire rope and a pulley seriously affects the mechanical properties of the wire rope. In this study, the tribological behavior of wire rope was investigated using a homemade rope–pulley sliding friction test rig. Then, the influence of different surface wear on the bending fatigue life of the rope samples was analyzed. The results show that the friction coefficient (COF) decreases with the increasing sliding distance. It reaches a minimum of approximately 0.52 when the contact load is 700 N. The surface temperature of the wire rope rises rapidly and then gradually stabilizes. The maximum temperature rise fluctuates in the range of 50 °C to 60 °C with increasing contact load. The wear scar of the wire rope is irregular, and the maximum wear width increases from approximately 1.94 mm to 2.45 mm with the contact load. Additionally, increased contact load leads to smoother wear surface of wire rope, and the wear mechanisms are mainly abrasive wear and adhesive wear. Additionally, surface wear leads to a decrease in the bending fatigue life of wire ropes, and degradation of anti-bending fatigue is more serious under a larger sliding contact load.

Ice sintering: Dependence of sintering force on temperature, load, duration, and particle size

We present experiments along with an approximate, semi-analytic, close-form solution to predict ice sintering force as a function of temperature, contact load, contact duration, and particle size during the primary stage of sintering. The ice sintering force increases nearly linear with increasing contact load but nonlinear with both contact duration and particle size in the form of a power law. The exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is also nonlinear and follows the Arrhenius equation. At temperatures closer to the melting point, a liquid bridge is observed upon the separation of the contacted ice particles. We also find that the ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is an important factor in determining the sintering force, and a value of nearly 1.1 MPa can best catch the sintering force of ice in different conditions. We find that the activation energy is around 41.4KJ/mol, which is close to the previously reported data. Also, our results suggest that smaller particles are “stickier” than larger particles. Moreover, during the formation of the ice particles, cavitation and surface cracking is observed which can be one of the sources for the variations observed in the measured ice sintering force.

Tribocorrosion Behaviour of Ti–6Al–4V Alloy in Biomedical Implants: Effects of Applied Load and Surface Roughness on Material Degradation

Tribocorrosion covers the science of surface transformations resulting from the interaction of mechanical loading and chemical reactions that occur between elements of a tribosystem exposed to corrosive environments. Implant materials are subjected to relative movements, which can cause wear damage, together with corrosive attack of the body fluids. Ti–6Al–4V alloy has been widely used for this purpose due to its superior biocompatibility and excellent corrosion resistance and good mechanical properties. The purpose of this work is to evaluate the tribocorrosion of Ti–6Al–4V alloy under different load and surface conditions. The tribocorrosion tests of Ti–6Al–4V alloy were performed using pin on disc tests at phosphate buffer saline solution (PBS), under various loading (0.5–25) N and surfaces roughness (240, 320, 400, 600) μm grits. Surface morphology, chemical composition and tribocorrosion resistance studied by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and Tafel potential polarization. The result indicate, by increasing contact load, the smoother surface (600 μm grit) give lower average tribocorrosion current density as compared with surface (320, 240, 400) μm grits suggesting that the damage is more pronounced on the smooth surface.

Fretting friction and wear of steel wires in tension-torsion and helical contact form

Fretting wear among steel wires under coupled tension-torsion force would aggravate the fatigue damage of wire rope, decrease the rope's service life, and ultimately threaten the safety of mine hoist. To explore the friction and wear behaviors of steel wires under coupled tension-torsion force and helical contact form, different fretting tests of steel wires were performed on a self-made test rig. The results show that the coefficient of friction (COF) decreases with increasing contact load and increases with the increase of sliding amplitude. When the contact load and sliding amplitude increase simultaneously, the COF is the maximum value of 0.23 for the convex contact pair, while it is 0.42 for the concave contact pair. The energy loss for the concave contact pair is faster than that for the convex contact pair. Furthermore, the wear depth and wear volume of wear scars increase with increasing contact load, sliding amplitude and their combination, respectively. The effect of the sliding amplitude on the friction and wear characteristics among steel wires is greater than that of the contact load. The common wear mechanisms of steel wires for the convex contact pair are abrasive wear and fatigue wear, while that for the concave contact pair is delamination wear. Additionally, the surfaces of wear scars for the convex contact pair are smooth, while that for the concave contact pair are rough.

Determination of maximum axial loads at the stage of operation of non-rigid pavements based on the analysis of complete deformation diagrams

The article is devoted to the development and experimental justification of the possibility of determining the axial loads of flexible pavements on the basis of full deformation diagrams recorded under shock loading. Results: The drawbacks of the existing regulatory methods for determining the axial load limit from the impact of vehicles at the operation stage are considered. It is noted that the definition of axial loads only on the strength factor, has several disadvantages associated with the need for information on the design value of the modulus of elasticity of the pavement, as well as the inconsistency of the existing regulatory framework for road design with real traffic loads. It is proposed to determine the maximum axial loads on the basis of the analysis of the complete deformation diagrams recorded at different values of the dynamic load shock load. For the first time, an approach to determining axial loads is proposed, based on the construction of a curve in the coordinates “increase of dissipated energy (ΔW) – load on the coating (F)”, and the load initiating the transition from proportional increase of the dissipated energy with increasing contact load, disproportionately. An example is given of determining the maximum axial load on the pavement cover for the exploited section of the M4 “DON” highway Conclusions: The possibility of determining the limiting axial loads on the pavement coating, based on the analysis of the complete deformation diagrams recorded during impact loading on the pavement coating, was experimentally justified. The need for further improvement and a set of a database of experimental data on changes in limiting axial loads in different periods of the year is noted.

Fretting Wear Behaviors of Aluminum Cable Steel Reinforced (ACSR) Conductors in High-Voltage Transmission Line

This work reports the fretting wear behavior of aluminum cable steel reinforced (ACSR) conductors for use in high-voltage transmission line. Fretting wear tests of Al wires were conducted on a servo-controlled fatigue testing machine with self-made assistant apparatus, and their fretting process characteristics, friction force, wear damage, and wear surface morphology were detailed analyzed. The results show that the running regime of Al wires changes from a gross slip regime to a mixed regime more quickly as increasing contact load. With increasing amplitudes, gross slip regimes are more dominant under contact loads of lower than 30 N. The maximum friction force is relatively smaller in the NaCl solution than in a dry friction environment. The primary wear mechanisms in dry friction environments are abrasive wear and adhesive wear whereas abrasive wear and fatigue damage are dominant in NaCl solution.

A study on the microstructures and three–body abrasive wear behaviors of Fe–B alloy under different Fe2B boride orientation

PurposeThe directional solidification Fe-B alloy was prepared. The microstructures and three-body abrasive wear behaviors of directional solidification alloy were investigated.Design/methodology/approachFe-B alloy was melted in medium frequency induction furnace. The hardness was measured on HRS-150 Rockwell-hardness tester and HXD-1000TMC tester. The wear characteristic of the alloy was examined with a block-on-ring geometry. The worn surface of the alloy was investigated by scanning electron microscopy and laser scanning microscopy.FindingsThe wear weight loss and worn surface roughness increase with the increasing contact load in wear tests. When the worn surface is perpendicular to the boride growth direction, the highest hardness plane of the boride can resist abrasive effectively under the surrounding and supporting of the martensite matrix.Originality/valueThe relation between boride growth direction and wear direction will cause different boride breaking tendency and wear weight loss.

Effect of Fe2B boride orientation on abrasion wear resistance of Fe-B cast alloy

The microstructures and abrasion wear resistance of directional solidification Fe-B alloy have been investigated using optical microscopy, X-ray diffraction, scanning electron microscopy and laser scanning microscopy. The results show that the microstructure of as-cast Fe-B alloy consists of ferrite, pearlite and eutectic boride. After heat treatment, the microstructure is composed of boride and martensite. The plane which is perpendicular to the boride growth direction possesses the highest hardness. In two-body abrasive wear tests, the silicon carbide abrasive can cut the boride and martensite matrix synchronously, and the wear mechanism is micro cutting mechanism. The worn surface roughness and the wear weight loss both increase with the increasing contact load. Moreover, when the boride growth direction is perpendicular to the worn surface, the highest hardness plane of the boride can effectively oppose abrasion, and the martensite matrix can surround and support borides perfectly.

A complete contact model of a fractal rough surface

This study suggested a revision to the contact model of a fractal rough surface, by extending the modified asperity contact model developed by Morag and Etsion, into a complete contact model of a fractal surface. According to the modified asperity model, the critical area of a single asperity was scale dependent and that the asperity's plastic to elastic mode transition agreed with classical contact mechanics. The total load, area and stiffness of a fractal rough surface were studied, and obtained by summing over the contact force, area and stiffness of the asperities at all length scales. The results revealed that the contact area depended linearly on the contact load and that the contact stiffness increased with increasing contact load. The share of plastic contact area decreased as the contact load increased. The impact of the fractal roughness parameter G and fractal dimension D on the contact stiffness was also discussed, and the results showed that the rougher the surface became, corresponding to a smaller value of D and a larger value of G, the smaller the contact stiffness was.

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.

Microstructural effects on the sliding-wear resistance of pressureless liquid-phase-sintered SiC under diesel fuel

Abstract The sliding wear of pressureless liquid-phase-sintered (PLPS) SiC ceramics under diesel fuel lubrication was investigated. It was found that the sliding-wear behaviour under diesel fuel is similar to what is observed under lubrication with the chemically similar paraffin oil: initial mild, plasticity-controlled wear followed by severe, fracture-controlled wear, with a well-defined wear transition. Compared to paraffin oil, however, diesel fuel lubrication decreases the extent of the mild-wear regime and results in damage that is more severe due to its lower viscosity. Also, it was found that the wear resistance under diesel fuel decreases with increasing contact load and sliding speed. Subsequent investigation of the effects of the intergranular phase content, grain size, and grain shape demonstrates nevertheless that the wear performance of PLPS SiC under diesel lubrication can be improved via microstructural control by (i) decreasing the intergranular phase content, and (ii) decreasing the SiC grain size or increasing its aspect ratio. The results of this work are likely to have relevant implications for the design of wear resistant PLPS SiC ceramic components for diesel engines.

Finite element analysis of fretting fatigue behavior of steel wires and crack initiation characteristics

The effects of fretting parameters on stress distributions of contacting wires during the initial stage of fretting–fatigue of steel wires were investigated using the finite element method. The roles of fretting parameters on crack initiation characteristics were discussed employing the multiaxial fatigue criteria of Fatemi–Socie and Smith–Watson–Topper, and three-dimensional coordinate transformation. Non-uniform stress distributions on contact surfaces and ring-shaped stress distributions near the contact zone on the symmetric plane are observed. Different fretting parameters induce distinct fretting regimes, stress distributions and abrupt changes of stress near the trailing edge. Crack initiation becomes more difficult with increasing contact load as compared to the increased possibility of crack initiation with increasing relative displacement.

Fatigue Failure of Silicon Nitride Ceramic Balls

Silicon nitride ceramic ball surface is examined after failure with scanning electron microscopy. The profile of the fatigue spalling takes the shape of an ellipse. The failure cause, fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material, and propagate, to form fatigue spalls under the action of principal tensile stresses. The contours of equal tensile stress of Oxy plane underneath surface are elliptical. Subsurface cracks are shape of ellipses and spall is also of the elliptic shape. The principal tensile stress increases with increasing contact load, causing spall formation and reduction of rolling contact life.

Influence of surface roughness and contact load on friction coefficient and scratch behavior of thermoplastic olefins

To study the effects of surface roughness and contact load on the friction behavior and scratch resistance of polymers, a set of model thermoplastic olefins (TPO) systems with various surface roughness ( R a) levels were prepared and evaluated. It is found that a higher R a corresponds to a lower surface friction coefficient ( μ s). At each level of R a, μ s gets larger as contact load increases, with a greater increase in μ s as R a level increases. It is also observed that with increasing contact load and increasing R a, the μ s tend to level off. In evaluating TPO scratch resistance, a lower μ s would delay the onset of ductile drawing-induced fish-scale surface deformation feature, thereby raising the load required to cause scratch visibility. However, as the contact load is further increased, the μ s evolves to become scratch coefficient of friction (SCOF) as significant sub-surface deformation and tip penetration occur and material displacement begins, i.e., ploughing. No dependence of R a and μ s on the critical load for the onset of ploughing is observed. In this work, the distinction between μ s and SCOF will be illustrated. Approaches for improving scratch resistance of polymers via control of R a are also discussed.

Fretting Fatigue Behavior of Cu-Al-Coated Ti-6Al-4V

Fretting fatigue of a Cu-Al coating deposited on an alumina-gritted Ti-6Al-4V substrate was investigated. Two types of tests were conducted: one series involved fretting fatigue tests at different bulk stress amplitudes under a constant contact load and the second series was run at different contact loads under a constant bulk stress amplitude. The coefficient of friction (COF) was lower on the coated substrate than on the bare substrate before fretting. However, COFs of the coated and the bare (i.e., uncoated) substrates were identical after the exposure to fretting fatigue cycles since fretting fatigue caused wear of the coating. The coating thickness as a function of fretting fatigue cycles was monitored. The coating damage increased as the applied bulk stress amplitude increased. At lower bulk stress amplitudes, the coating damage was gradual and it survived over one million cycles. However, the coating delaminated from the gritted surface and/or caused premature specimen failure at higher stress amplitudes. At the lowest contact load used in the present study, the contact condition was gross slip and the life of the coating was the shortest due to fretting wear. On the other hand, the higher contact loads induced a partial slip contact condition that caused less coating damage, and the coating life increased with increasing contact load. *The views expressed in this article are those of the authors and do not reflect the official policy or position of the United State Air Force, Department of Defense, or the U.S. government

Friction of Self-Lubricating W-S-C Sputtered Coatings Sliding Under Increasing Load

W-S-C films were deposited by non-reactive magnetron sputtering from a carbon target with several pellets of WS2 incrusted in the zone of the preferential erosion. The number of the pellets was changed to modify the carbon content in the films, which varied from 26 up to 70 at.-%. Alloying W-S films with carbon led to a substantial increase in the hardness in the range of 4–10 GPa; the maximum hardness was obtained for the coatings with carbon contents close to 40 at.-%. XRD diffraction patterns showed that there was a loss of crystallinity with the increase of the carbon content in the film. C-contents in the range (37–66 at.-%) were selected for sliding tests (pin-on-disk, 100Cr6 steel ball as a counterpart) carried out in humid air under increasing contact load. The friction coefficient was observed to decrease continuously with increasing load. The wear tracks and wear debris were also analyzed by Raman spectroscopy to understand the structural transformations induced by the increasing load. The friction results were compared with existing models for pure transition metal dichalcogenides (TMD), and it could be concluded that the friction mechanisms of W-S-C coatings fundamentally differ from those of pure TMD.

Elastic–Plastic Multi-Asperity Contact Analysis of Cylinder-on-Flat Configuration

The contact interaction between a rough cylindrical body (i.e., with asperities) and a deformable smooth flat was investigated using the finite-element analysis. Analysis included both elastic–plastic deformation and friction. Further, the effects of several parameters of rough surface on the evolution of the contact area with increasing contact load were investigated. These were radius, number, constraint, and placement of asperities. Contact area of rough surface is smaller than its counterpart of smooth surface, and this decrease depends on number, radius, constraint, and placement of asperities. The elastic material behavior results in considerably smaller contact area than that from elastic–plastic material behavior. The evolution of contact area with increasing contact load is of the complex nature with elastic–plastic material deformation since the yielded region widens and/or deepens with increasing load depending on number, radius, and constraint of asperities. The effect of constraint on the asperity depends upon its nature (i.e., from either sides or one side) and radius of the asperity. The effects of these several parameters on the contact area versus applied load relationships are expressed in the graphical form as well as in terms of equations wherever possible.