Increase In 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.

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 considering substrate deformation

PurposeThe purpose of this study is to propose a fractal model of thermal contact conductance (TCC) of rough surfaces considering substrate deformation. Three deformation modes of the asperity of the rough surface are considered, including elastic deformation, elastic–plastic deformation and full plastic deformation.Design/methodology/approachThe influences of contact load, fractal dimension and fractal roughness on the TCC of the rough surface were studied.FindingsThe results show that the TCC of the rough surface increases with the increase of contact load. When D > 2.5, the larger the fractal dimension, the higher the increased rate of the TCC of the rough surface with the increase of contact load. The TCC of the rough surface increases with the increase of fractal dimension and decreases with the increase of fractal roughness. The TCC of the rough surface can be achieved by selecting a contact surface with roughness.Originality/valueA fractal model of TCC of rough surfaces considering substrate deformation was established in this study. The achievements of this study provide some theoretical basis for the investigation of TCC of rough surfaces.

The Synergistic Effect of WS2 and SWNTs on Tribological Performance of Polyether MDI Polyurethane Elastomer under Dry and Wet Friction Conditions.

To adapt to the complex application of polyurethane bearings, it is feasible to improve the tribological performance of single polyurethane-based friction materials through the synergistic effect produced by multi-component-lubricating fillers. In this context, rather than using tungsten disulfide (WS2), which has demonstrated excellent self-lubricating performance as a lubricating oil additive, this paper proposes that WS2 and single-walled carbon nanotubes (SWNTs) can be designed for addition into a polyether 4,4′-diphenylmethane diisocyanate (MDI) polyurethane matrix as self-lubricating fillers so as to explore the synergistic effect of micro- and nano-lubricating fillers on the tribological performance of polyurethane matrix materials. Through a series of characterizations and tests, it was found that the dispersion of two-component-lubricating additives in a polyurethane matrix is improved when the ratio of WS2 to SWNTs is roughly 2:1. In this case, the tribological performance of polyurethane matrix composites is more satisfactory than at other ratios. In addition, compared with the blank sample, the tribological performance of the synergistically modified polyurethane composites under dry friction is more significantly improved with the increase in contact load, while there is no significant improvement under water lubrication. Aside from contributing to the idea of exploring the synergistic effect of WS2 and other micro or nanofillers, this method also opens up the possibility of practically applying WS2 in the field of friction.

Wear Experiment and Influencing Factors Analysis of 13Cr-L80 Tubing String in High-Pressure, High-Temperature and High-Yield Gas Wells

Due to wear failures caused by tubing string vibrations in high-pressure, high-temperature and high-yield (3H) gas wells, a wear experiment was performed on the 13Cr-L80 tubing string. The influence of contact load, friction frequency, and reciprocating stroke length on the wear characteristics of the tubing string were effectively analyzed using the control variable method. The results demonstrate that, the wear patterns of the tubing-casing were primarily abrasive and adhesive wears, with minimal corrosion wear. The wear amount of tubing increases linearly with the increase of contact load and reciprocating stroke, but increases nonlinearly with the increase of friction frequency, and the friction coefficient of tubing string do not change with the increase of contact load, friction frequency and reciprocating stroke. In-field operations, the service life of the tubing string in 3H gas wells can be effectively augmented by reducing the contact load and longitudinal vibration displacement of the tubing-casing, maintaining the vibration frequency of the tubing string below 1.5 Hz. These results provide useful guidance for designing and implementing approaches to improve the service life of tubing strings in high-yield gas wells.

Effect of load on tribofilms at the contact interface under dry sliding conditions at 500 °C

AbstractThis paper presents a study of the effect of load on the retention of the tribofilms formed at the interface of a dry sliding contact between exhaust valve material, Nimonic alloy (N 80A) and valve‐seat material, ductile cast iron (GGG‐40), at a temperature of 500 °C. The role of tribofilms in influencing friction and wear behaviour at elevated temperature is highlighted. Reciprocating pin‐on‐disc experiments were conducted using a hemispherical shaped pin sliding against a flat disc at 20 Hz oscillating frequency, 2 mm stroke at loads of 20 N to 50 N. Low coefficient of friction, in the range of 0.13 to 0.15, was observed at loads up to 40 N whereas at a load of 50 N, the average coefficient of friction increased to 0.29. Optical and scanning electron micrographs with energy dispersive spectroscopy analysis indicate evidence of formation and retention of well compacted and strongly adhering tribofilms at loads up to 40 N. At 50 N, even though more abrasive wear is seen, initial deterioration and subsequent reforming of the tribofilms with increasing sliding time is observed. Overall, more wear was observed for the valve‐seat material as compared to the valve material. Raman spectroscopy primarily indicates the presence of hematite on the worn surfaces at loads of 20 N to 40 N, whereas magnetite presence is strongest at the highest load of 50 N. Increase in tribofilm hardness was observed with increase in contact load whereas the thickness of the tribofilm was not significantly affected by the contact load.

A revised Majumdar and Bushan model of elastoplastic contact between rough surfaces

A revision of the elastoplastic contact model of fractal rough surfaces, initiated by Majumdar and Bushan, is further developed in this paper. According to the revised contact model, the critical contact areas of a single asperity are scale dependent. With an increase in contact load and contact area, a transition from elastic, elastoplastic to full plastic deformation takes place in this order. The relation between size distribution function for all level asperities and size distribution function for each level asperity is given. The total contact load, real contact area, contact load of each level asperity and contact area of each level asperity are obtained. The revised model shows that mechanical property of rough surface depends on asperity levels. The minimum level asperities and sequential five levels asperities are major contribution to rough surface. When asperity levels nmin and nmin+5 are less than elastic critical level nec, the rough surface appears to have elastic property under contact load. When asperity level nmin is greater than the second elastoplastic critical level npc, the rough surface appears to be carrying inelastic properties because the ratio of elastic deformation to inelastic deformation is very small.

Sliding friction and wear behavior of winding hoisting rope in ultra-deep coal mine under different conditions

Wear problems exist in multi-layer windings of ultra-deep coal mine hoisting ropes that are wound around drums. Wear decreases the life of such hoisting ropes directly, and that in turn threatens mine safety. An investigation of winding hoisting ropes was conducted using a custom test rig to study the effects of different contact loads, crossing angles and displacement amplitudes on rope friction and wear. Results show that the coefficient of friction (COF) in the steady-state period changes very little with an increase in contact load and that it stabilizes at about 0.61. Additionally, the COF slightly decreases with an increase of crossing angle. As the amplitude of sliding motion increases to 30mm and 50mm, the COF increases linearly. Using thermal imaging, the temperature rise in the steady-state period increases with the contact load and crossing angle. Moreover, the maximum wear depth increases linearly with an increase of contact load. Nevertheless, the wear depth changed very little when the amplitude is less than 30 mm, but it increases rapidly until an amplitude of 70mm. The major wear mechanisms of ropes without lubrication include adhesive wear, abrasive wear and fatigue wear.

전사공정을 위한 UV 경화성 범프형 스탬프의 점착특성 평가

Future electronics such as electronic paper and foldable cellphone are required to be flexible and transparent and should have a high performance. In order to fabricate the flexible electronics using flexibility transfer process, techniques for transferring various devices from rigid substrate onto flexible substrate by elastomeric stamp, have been developed. Adhesion between the elastomeric stamp and various devices is crucial for successful transfer process. The adhesion can be controlled by the thickness of the stamp, separation velocity, contact load, and stamp surface treatment. In this study, we fabricated the bump shape stamp consisting of a UV-curable polymer and investigated the effects of curing condition, separation velocity, and contact load on the adhesion characteristics of bumps. The bumps with hemispherical shape were fabricated using a dispensing process, which is one of the ink-jet printing techniques. Curing conditions of the bumps were controlled by the amount of UV irradiation energy. The adhesion characteristics of bumps are evaluated by adhesion test. The results show that the pull-off forces of bumps were increased and decreased as UV irradiation energy increased. For UV irradiation energies of 300 and 500 mJ/cm², the pull-off forces were increased as the separation velocity increased. The pull-off forces also increased with the increase of contact load. In the case of UV irradiation energy above 600 mJ/cm², however, the pull-off forces were not changed. Therefore, we believe that the bump shape stamp can be applied to roll-based transfer process and selective transfer process as an elastomeric stamp.

Wear of Diamond Grinding Wheel during Low Speed Dressing by Alumina

Diamond grinding wheel is used in high precision grinding process, when work piece has a very high hardness. For a specific grinding interval, the wheel must be properly dressed, in order to remove swarf, sharpen the worn diamond grits, open up new diamond protrusions, and recondition the bond material. Dressing of diamond grinding wheel by alumina dressing tool has been simulated in a pin-on-disk machine in the research. Sharpening of the wheel is indicated by the increase of its roughness value, and surface microstructure with protruding sharp diamond grits. It was found that increasing of sliding distant from 100 to 500 m will increase the roughness of the wheel. The increase of contact load from 10 to 20 N will also increase roughness of the wheel, and the severity of wheel wear, indicated by high values of friction coefficient. A proper dressing of this nickel bonded SD1200 diamond wheel is by sliding against alumina dressing tool for at least 300 m under 10 N load. Sliding velocity has minimal effect to the results. A too large sliding distant and load will cause severe damage to wheel surface, and severe wheel wear, indicated by its large mass loss.

Research on swing friction lubrication mechanisms and the fluid load support characteristics of PVA–HA composite hydrogel

Hydrogel has been extensively studied for use as articular cartilage. This study aims to investigate fluid load support mechanism of polyvinyl alcohol–hydroxyapatite composite hydrogel. Finite element method is used to study swing friction lubrication mechanism and fluid load support. The friction coefficient increases with contact load and swing angle. The fluid flow has an important effect on the fluid load support, which decreases with an increase in contact load and swing angle. The fluid load support is very high (85%), and the hydrogel has low friction coefficient. It exhibits biphasic and self-generating lubrication mechanism.

Research on the Interstitial Fluid Load Support Characteristics and Start-Up Friction Mechanisms of PVA-HA-Silk Composite Hydrogel

Hydrogel has been extensively studied as an articular cartilage repair and replacement material. PVA-HA-Silk composite hydrogel was prepared by freezing-thawing method in this paper. Mechanical properties were determined by experiments and the friction coefficient of PVA-HA-Silk composite hydrogel against steel ball was verified using micro-tribometer. Finite Element Method (FEM) was used to study the lubrication mechanism of PVA-HA-Silk composite hydrogel and the relation between the interstitial fluid load support and the start-up friction resistance. The results show that the elastic modulus and the permeability are 2.07 MPa and 10−15m4N−1s−1, respectively, and the start-up friction coefficients of PVA-HA-Silk composite hydrogel are in the range of 0.15–0.2 at different contact loads, contact time and sliding speeds. The start-up friction resistance of PVA-HA-Silk composite hydrogel increases with the contact load and contact time. With the increase in sliding speed, the start-up friction resistance of PVA-HA-Silk composite hydrogel decreases. There is an inverse relation between the start-up friction resistance and the interstitial fluid load support. The change of fluid flow with the increase in sliding displacement has an important effect on the interstitial fluid load support and friction resistance. The interstitial fluid load support decreases with the increase in contact load and contact time, while the interstitial fluid load support reinforces with the increase in sliding speed. Moreover, PVA-HA-Silk composite hydrogel has mechanical properties of recovery and self-lubricating.

Selective lateral muscle activation in moderate medial knee osteoarthritis subjects does not unload medial knee condyle

There is some debate in the literature regarding the role of quadriceps-hamstrings co-contraction in the onset and progression of knee osteoarthritis. Does co-contraction during walking increase knee contact loads, thereby causing knee osteoarthritis, or might it be a compensatory mechanism to unload the medial tibial condyle? We used a detailed musculoskeletal model of the lower limb to test the hypothesis that selective activation of lateral hamstrings and quadriceps, in conjunction with inhibited medial gastrocnemius, can actually reduce the joint contact force on the medial compartment of the knee, independent of changes in kinematics or external forces. “Baseline” joint loads were computed for eight subjects with moderate medial knee osteoarthritis (OA) during level walking, using static optimization to resolve the system of muscle forces for each subject׳s scaled model. Holding all external loads and kinematics constant, each subject׳s model was then perturbed to represent non-optimal “OA-type” activation based on mean differences detected between electromyograms (EMG) of control and osteoarthritis subjects. Knee joint contact forces were greater for the “OA-type” than the “Baseline” distribution of muscle forces, particularly during early stance. The early-stance increase in medial contact load due to the “OA-type” perturbation could implicate this selective activation strategy as a cause of knee osteoarthritis. However, the largest increase in the contact load was found at the lateral condyle, and the “OA-type” lateral activation strategy did not increase the overall (greater of the first or second) medial peak contact load. While “OA-type” selective activation of lateral muscles does not appear to reduce the medial knee contact load, it could allow subjects to increase knee joint stiffness without any further increase to the peak medial contact load.

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.

Fretting Fatigue and Wear Behaviour of Timetal 834

Abstract Fretting fatigue behaviour of solution treated and aged near a -titanium alloy Timetal 834 was investigated at a constant stress amplitude of ±800 MPa, and different contact stresses of 50, 63, and 75 MPa at cyclic frequency of 0.1 Hz, at room temperature. Also wear behaviour of the alloy was studied against EN31 steel counter body, under dry sliding condition, at different loads from 2 to 10 kg and sliding velocity of 1 ms −1 , at room temperature. The fretting fatigue life of the alloy was found to decrease drastically with increasing contact stress above 50 MPa. Wear rate of the alloy was found to increase linearly up to the entire load range investigated. Fall in fatigue life, with increase in contact load, occurs due to early crack initiation at stress concentration sites. These sites form due to combined effect of wearing in localized regions and consequent increase in absorption of oxygen in those regions because of much higher degree of plastic deformation in them.The wear behavior is discussed in terms of the nature of the debris formed.

A comparative analysis of contact algorithms in contact shape optimization problems

This paper presents a comparative analysis of contact algorithms used for solving contact shape optimization problems. Specifically, a nonlinear, feasible direction interior point method (FDIPM) for the frictional contact analysis of hyperelastic materials has been implemented in which the friction is introduced using the return mapping approach. This comparative investigation aims to find the cause of instability in sensitivity of the contact pressure nonuniformity (CPN). The results obtained by the FDIPM are found to be comparable with those by the penalty methods (PM) and the augmented Lagrange multiplier methods (ALMM); however, the FDIPM possesses advantages, including good convergence and convenience in modeling. Furthermore, the basic cause of the unstable sensitivity is revealed to be the discretization of the finite element method, which causes the discontinuous increase of contact area with respect to the continuous increase of contact load. To improve the stability of the CPN, an adaptive post-processing technique is proposed.

Some Observations on Frictional Force During Fretting Fatigue

Frictional force behavior during fretting fatigue and its interdependence on other fretting variables are investigated. Both coefficient of static friction and the normalized frictional force (i.e., the ratio of frictional force and normal contact load) increase during the earlier part of a fretting fatigue test and then both reach to a stabilized value. The variation of temperature in the contact region and normalized frictional force with increasing cycle numbers and bulk stress show similar trend implying that normalized frictional force represents the average friction in the contact region during a fretting fatigue. An increase in bulk stress, relative slip, and hardness of pad material results in an increase of the normalized frictional force, while an increase in contact load, frequency and temperature decreases the normalized frictional force. The normalized frictional force is also affected by the contact geometry. On the other hand, coefficient of static friction increases with an increase in the hardness of mating material, temperature and roughness from shot-peening treatment, but is not affected by contact geometry and displacement rate. Further, the normalized frictional force is not affected by the contact geometry, roughness and applied bulk stress level when fretting fatigue test is conducted under slip controlled mode, however it increases with increasing applied relative slip and decreasing contact load in this case.

接触転動ロールの表層変形に及ぼす潤滑と接触荷重の影響(G11-2 シール,潤滑,ポンプ,G11 機素潤滑設計部門)

In order to clarify the effect of contact load and lubrication conditions on wear amount and plastic flow in the subsurface layer of a contact rotating roll, the experiments for contact rotating of two disks were made under the lubrication condition of water and 5% solution of lubricant. As a result, it has been found that the wear amount of a roll disk decreases with the increase of contact load, and that the engineering shear strain on the surface of the roll disk under the condition of water is about one and a half times larger than that under the condition of 5% solution of lubricant in the case of 12.5kN contact load.

Characteristics of magnesium oxide single crystals polished with vibrational sliding in water

The finished surface of magnesium oxide single crystals polished with vibrational sliding in water was studied. The specimen was rubbed on a rotating disk of sintered magnesium oxide while being moved spirally and vibrated perpendicular to the sliding direction. Two distinct types of finished surface were observed: a rough surface with. R max = 1–3 μm and a smooth surface with R max = 0.01 μm. Surface characteristics were examined using optical microscopy, X-ray diffraction and ion microprobe mass analysis in order to understand the formation mechanisms of the finished surface. The rough surface was mainly formed by cleavage planes, caused by the brittle fracture which occurred irregularly around the surface. The hydration of the magnesium oxide played a dominant role in the formation of the smooth surface. The finishing of the surface on the {100} plane was markedly dependent on the mechanical contact conditions and the presence of water and independent of the main direction of sliding. A critical set of contact conditions for the formation of the smoothed surface was determined in terms of the contact load, the amplitude and frequency of vibrational sliding and the rotational speed of the disk. The volume removed was increased by vibrational sliding because of the increase in sliding distance and the equivalent increase in contact load caused by the moment of inertia of the apparatus.