Contact Pressure Conditions Research Articles

Friction-induced subsurface densification of glass at contact stress far below indentation damage threshold

It is well known that the densification of oxide glass can occur at high contact pressure (typically >5 GPa) under normal indentation conditions. This study reports that when frictional shear is involved, the subsurface densification of glass can occur under low load conditions that would involve completely elastic deformation if the load is applied along the surface normal direction without any interfacial shear. This phenomenon was observed for a borosilicate glass rubbed with a smooth stainless-steel ball in liquid water at a nominal Hertzian contact pressure of ≤0.5 GPa. Under these frictional conditions, subsurface cracking is completely suppressed, and surface wear occurs through mechanochemical reactions. Since the mechanochemical wear track was sufficiently smooth, it was possible to employ a sub-glass transition temperature (sub-Tg) annealing method to measure the volume recovery of the densified subsurface region. The friction-induced subsurface densification of the wear track was also confirmed through nanoindentation measurements and dissolution tests in pH 13 aqueous solutions. Molecular dynamics (MD) simulations with a ReaxFF reactive force also suggested that the subsurface structural change can occur readily when friction is involved at low contact pressure conditions.

Multiple point contact wear prediction and source identification scheme using a single channel blended airborne acoustic signature

Wear between sliding and rotating parts is inevitable in real world machines. Reliable predictive maintenance operations warrant accurately identifying the operating conditions causing wear. In this paper a novel study is conducted using a test rig undergoing wear at two locations with different conditions of contact pressure and lubrication between asperities. A single microphone is used for data acquisition. The blended single channel acoustic signal is first disintegrated into two separate source signals using empirical mode decomposition and principal component analysis. Statistical features of fixed segments of the two disintegrated signals are then computed. The wear volume was also measured in both wear zones, at the end of the corresponding time span. Machine learning algorithms are then trained to predict the degree and type of wear in each wear zone. A novel scheme is proposed after validation, that can be used to predict the wear conditions occurring simultaneously at multiple locations in a machine, using a single cheap acoustic sensor.

Effects of contact pressure and interface temperature on thermal contact resistance between 2Cr12NiMoWV/BH137 and γ-TiAl/2Cr12NiMoWV interfaces

Thermal contact resistance between interfaces is an important parameter in the analysis of temperature distribution for structural components. Thermal contact resistance between heat resistant steel 2Cr12NiMoWV/aluminum alloy BH137 interfaces and 2Cr12NiMoWV/titanium alloy ?-TiAl interfaces were experimentally investigated in the present paper. The effects of contact pressure and interface tem-perature were detailed. The temperature of contacting surfaces was from 80- 250?, and the contact pressure ranged from 2-17 MPa. All experiments were conducted in ambient atmosphere. Results showed that thermal contact resistance decreases with an increment of interface temperature or contact pressure. Under the same conditions of contact pressure and interface temperature, thermal contact resistance between 2Cr12NiMoWV and BH137 interfaces is lower than that between 2Cr12NiMoWV and ?-TiAl interfaces. The temperature dependence of thermal conductivity and mechanical properties was analyzed to explain the results. Furthermore, with the piston and piston pin as the research object, steady state temperature fields were simulated in cases of considering thermal contact resistance and without considering thermal contact resistance, respectively. The results showed that the maximum temperature of the piston pin will be lower when thermal contact resistance is considered.

The Tribo-Fatigue Damage Transition and Mapping for Wheel Material under Rolling-Sliding Contact Condition.

The purpose of this work is to construct a tribo-fatigue damage map of high-speed railway wheel material under different tangential forces and contact pressure conditions through JD-1 testing equipment. The results indicate that the wear rate of the wheel material varies with tangential force and contact pressure. The wear mapping of the wheel material is constructed and divided into three regions: slight wear, severe wear, and destructive wear, based on the wear rate under each test condition. With an increase in tangential force and contact pressure, the maximum crack length and average crack length of the wheel material increases. According to the surface damage morphologies and corresponding statistical results of average crack length of wheel material under each experiment condition, a tribo-fatigue damage map is constructed and divided into three regions: slight fatigue damage region, fatigue damage region, and severe fatigue damage region. Fatigue cracks initiate on the wheel specimen surface. Some cracks may propagate into material and fracture under cyclic rolling contact; some cracks may grow into inner material with a certain depth, and then turn toward the surface to form material flaking; some cracks may always propagate parallel to the wheel roller surface.

The study of hexanoate-based protic ionic liquids used as lubricants in steel-steel contact

Three novel hexanoate-based protic ionic liquids with different ammonium cations (2-hydroxyethylammonium 2-ethylhexanoate, 2-hydroxymethylammonium 2-ethylhexancate, and 2-hydroxydimethylammonium 2-ethylhexanoate) were synthesized, characterized, and studied as neat lubricants under a steel-steel sliding contact mode. The ionic liquid with the 2-hydroxyethylammonium cation presented the highest values of density, viscosity, contact angle and thermal stability. The high value of viscosity and contact angle in the 2-hydroxyethylammonium salt can be attributed to hydrogen bonding. The three protic ionic liquids, especially 2-hydroxyethylammonium 2-ethylhexanocate and 2-hydroxymethylammonium 2-ethylhexanocate, outperformed other studied lubricants showing lower and stable friction coefficient. The improved lubrication performance is attributed to the strong physical adsorption of the ionic liquids on the steel-steel surfaces to form ordered lubrication layers due to the electrostatic interaction. In addition, the formation of carbon- and oxygen-enriched layers on worn steel surfaces helped to reduce friction. The formation of this tribolayer may be due to the high contact temperature and pressure conditions that promote the reaction of the active elements of steel and functional groups ionic liquids.

Tribological Performance Improvement of Polyamide against Steel Using Polymer Coating

Polyamide (PA) is used in industrial applications such as automotive, gears, bearings, and pipeline spacers. As a bearing material, PA can support high contact pressures under low sliding speeds. To achieve high-performing and durable contacts, it is necessary to have low friction, low vibration, and low wear between PA and steel contacts at different operating temperatures. This study proposes the use of an advanced polymer coating, namely, aromatic thermosetting copolyester (ATSP), on the steel surface and investigates the friction and wear properties between PA–ATSP coating and PA–steel at environmental temperatures of 25, 50, and 80 °C. The experiments were carried out using a pin-on-disc configuration under unlubricated sliding conditions. The results showed excellent performance of the coating on reducing the coefficient of friction (COF) by 80% and PA wear by 95% compared to bare steel. The ATSP coating worked as a predeposited transfer layer and showed nonmeasurable wear under moderate to high contact pressure conditions at all temperatures. The worn surfaces and the formation of transfer layers were further examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy.

Effect of tool coatings on the interfacial heat transfer coefficient in hot stamping of aluminium alloys under variable contact pressure conditions

The interfacial heat transfer coefficient (IHTC) is an essential parameter in hot stamping for determining the optimal process parameters necessary to achieve the critical cooling rate and thus the desired post-form strength in a formed component. Aluminium chromium nitride, chromium nitride and titanium nitride are currently being widely studied in the hot stamping industry as tool coatings due to their excellent wear performance, although their effects on the IHTC have yet to be determined. In practical hot stamping processes, the contact pressure may also change over extremely short periods of time, leading to abrupt changes in the IHTC and consequently the temperature evolutions of the workpiece. These abrupt changes in contact pressure and their effects on the IHTC have yet to be studied either. In this paper, to address those challenges, the IHTCs between an AA7075 aluminium alloy and different coated tools with a 3-stage evolutionary variable contact pressure were quantitatively determined, and a mechanism-based model developed to accurately predict their values.

An improved drilling force model in friction drilling AISI 321

In this paper, the friction characteristics and the drilling force theory model have been studied in friction drilling austenitic stainless steel AISI 321 for solving the drilling difficult problem of thin sheet workpiece. Firstly, a equivalent test platform of friction drilling friction characteristics is established based on CA6140 lathe, and the friction characteristics of AISI 321 are studied under the different conditions of contact pressure and speed for revealing the effect of pressure and speed on the friction coefficient between tool and workpiece. Then, the empirical formula model of friction coefficient is established based on the experimental results. Finally, the improved drilling force theory model of friction drilling process is developed based on the unique geometrical shape of friction drilling tool and the equivalent friction model. Results show that the predicted force model is more accurate, which considered the actual friction coefficient model.

Bismuth (III) sulfide as additive: towards better lubricity without toxicity

PurposeThe purpose of this study is to design a fluid formulation with good lubricant properties by using an environmentally friendly additive for: high and low contact pressure conditions and steel/steel and polymer/steel systems.Design/methodology/approachBismuth (III) sulfide (Bi2S3, “green chemistry” synthesis) is added to a commercial vinyl-terminated silicone fluid (PDMS-Vi) to obtain different weight-per cent mixtures. Tribological performance of formulations is studied from Reichert’s tests (steel/steel system) and block on ring tests (polymer/steel). The results are compared with formulations prepared with commercial bismuth (III) sulfide (Bi2S3), molybdenum (IV) sulfide (MoS2) and graphite.FindingsAn orthorhombic crystal lattice (XRD ) and a high-purity product (XRF) are evidenced for synthesized Bi2S3. Lubricant properties increase when the weight-per cent of the synthesized Bi2S3 increases in formulations. The wear area decreases up to 90 per cent according to Reichert’s tests. The synthesized Bi2S3 shows a better tribological behavior when compared to commercial Bi2S3, MoS2 and graphite.Originality/valueReplacement of lead derivatives by an environmentally friendly lubricant in extreme pressure (EP) formulations and excellent performance compared to commercially used additives are achieved.

Shear properties under the starved condition of polyisobutylene lubricant for use in screw tightening-effect of operating condition on lubrication properties

Abstract This paper describes that shear properties of polyisobutylene (PIB) lubricant under the starved condition using in-situ observation in order to understand the lubrication mechanism in the screw tightening process. Specifically, the study focused on the effect of operating condition (sliding speed and contact pressure) on the lubrication performance. In the test at various sliding speed, the film thickness decreased with expansions in the starved area, however, the thickness was thicker than the surface roughness of the specimens even in the full starvation condition. The shear stress under fully starved condition at 15 N did not depend on shear rate and was a constant value corresponded to almost 50 MPa in all the speeds. In the test at various contact pressure conditions, the film was formed in the contact area at the full starvation condition and the value was higher than the surface roughness. It was also found that shear stress at fully starved condition increased with increases in contact pressure. These results suggest that the solidification film was formed on the contact area in the starved condition and the film formation with high limiting shear stress inhibits direct contact and wear. This lubrication performance offers a stable value of friction coefficient in the tightening process and facilitates precise control of the clamping force.

Effect of tool coating on interfacial heat transfer coefficient in hot stamping of AA7075 aluminium alloys

Chromium carbonitride coatings have been gaining importance in the hot stamping industry due to their excellent wear and corrosion resistances that extend the lifetime of tools they are applied to. However, their effect on the heat transfer between materials being formed and the tools in a hot stamping process has yet to be studied. In the present research, the interfacial heat transfer coefficient values between a hot AA7075 workpiece and cold chromium carbonitride-coated tools were experimentally determined under different contact pressure conditions. A mechanism-based interfacial heat transfer coefficient model was subsequently developed for precise finite element simulations of the temperature evolution and cooling rate of the components being formed. The model enables the selection of the tool coatings to be optimized based on the requirements of the hot stamping process, with the thermal conductivity of the coating material determining its thermal performance and effect on interfacial heat transfer coefficient.

The output characteristic of cantilever-like tactile sensor based on the inverse magnetostrictive effect

The output characteristic model of a magnetostrictive cantilever-like tactile sensor has been founded based on the inverse-magnetostrictive effect, the flexure mode, and the Jiles-Atherton model. The magnetostrictive sensor has been designed and an output voltage is analyzed under the conditions of bias magnetic field, contact pressure and deflection of cantilever beam. The experiment has been performed to determine the relation among the induced output voltage, bias magnetic field, and pressure. It is found that the peak of the induced output voltage increases with an increasing pressure under the bias magnetic field of 4.8kA/m. The experimental result agrees well with the theoretical one and it means that the model can describe the relation among the induced output voltage, bias magnetic field, and pressure. The sensor with a Galfenol sheet may hold potentials in sample characterization and deformation predication in artificial intelligence area.

An in situ synchrotron XAS methodology for surface analysis under high temperature, pressure, and shear.

The complex tribochemical nature of lubricated tribological contacts is inaccessible in real time without altering their initial state. To overcome this issue, a new design of a pin-on-disc tribological apparatus was developed and combined with synchrotron X-ray absorption spectroscopy (XAS). Using the designed apparatus, it is possible to study in situ the transient decomposition reactions of various oil additives on different surfaces under a wide range of realistic operating conditions of contact pressure (1.0-3.0 GPa), temperature (25-120 °C), and sliding speed (30-3000 rpm or 0.15-15 m/s). To test the apparatus, several tribological tests were performed at different shearing times ranging from 2.5 to 60 min. These tests were carried out under helium atmosphere at a temperature of 80 °C, contact pressure of 2.2 GPa, and sliding speed of 50 rpm. The XAS experiments indicate that the zinc dialkyldithiophosphate antiwear additive decomposes in the oil to form a tribofilm on the iron surface at different reaction kinetics from the ones of the thermal film. The tribofilm composition evolves much faster than the one of the thermal film, which confirms that the formation of the tribofilm is a thermally activated process similar to the one of the thermal film but accelerated by shear. Furthermore, the results indicate that the sulfur of the formed film, whether a tribofilm or a thermal film, appears initially in the form of sulfate, with some sulfide, which under heat or shear is reduced into mainly sulfide.

The effect of heat treatment routes on the retained austenite and Tribomechanical properties of carburized AISI 8620 steel

The objective of this study is to investigate the effect of heat treatment routes involving carburizing and quenching technique on the tribological behavior of carburized AISI 8620 steel. This particular material is commonly used in drivetrain components and undergoes sliding or rolling under high contact pressure conditions. Different levels of retained austenite (RA), hardness and residual stress were achieved by varying carbon potential (0.45% to 1.05%) during carburizing as well as by employing different end-quenching routes (from air-cooled to deep freezing). Wear tests were carried out using a ball on flat reciprocating micro-tribometer between a diamond probe and the samples under dry sliding conditions. Samples were subsequently analyzed using non-contact profilometry and field emission scanning electron microscopy to observe wear behavior and elucidate mechanisms. Hardness and RA had comparatively significant effect on wear resistance as compared to residual stress. It was observed that beyond a certain limiting Hertzian contact pressure level, higher carbon potential carburized sample resulted in increased abrasive wear resistance. This increased wear resistance is attributed to the higher hardness and conditions conducive to transformation of RA into martensite via ploughing-induced work-hardening. The findings indicate that surface treatments resulting in a combination of high hardness and moderately high RA levels result in enhanced abrasive wear resistance for AISI 8620 steel.

Influence of contact pressure, cross-shear and counterface material on the wear of PEEK and CFR-PEEK for orthopaedic applications

Total joint replacement is a successful surgical intervention for the treatment of the degeneration of many joints, particularly the hip and knee. As the demand for joint replacement grows, and the life expectancy of the population increases, the performance requirements of these implants also changes. New materials, to improve longevity and enhance performance have been explored including PEEK and CFR-PEEK.This study investigated whether CFR-PEEK and PEEK were appropriate materials for total joint replacement by examining wear performance in simple configuration studies articulating against cobalt chrome under a range of cross-shear and contact pressure conditions. Simple geometry pin on plate studies were conducted for one million cycles for each test condition, with the contact pressure and cross-shear conditions representing a range in which the material may need to operate in-vivo.The wear factor for PEEK was significantly higher than CFR-PEEK and conventional polyethylene under all test conditions. Both PEEK and CFR-PEEK wear were influenced by contact pressure, with the highest wear factors for both materials measured at the highest pressure conditions. PEEK appeared to have a cross-shear dependent wear response, but this was not observed for the CFR-PEEK material.This study has further characterised the wear performance of two materials that are gaining interest for total joint replacement. The wear performance of the PEEK material showed poorer wear performance compared to polyethylene when articulating with a metal counterface, but the performance of the CFR-PEEK material suggested it may provide a suitable alternative to polyethylene in some applications. The wear performance of CFR-PEEK was poorer than polyethylene when it was used as the plate, when there was translation of the contact zone over the surface of the CFR-PEEK plate. This has implications for applications in low conforming contacts, such as lower conformity knee replacement.

Wear resistance of a metal surface modified with minerals

The article describes the advantages of the new technology of mineral coating of metal products for the friction pair of mechanical systems. It presents the research results of the wear rate of the samples made of 12X13 steel (X12Cr13) with mineral layers, in the experiments with a piston ring sliding inside a cylinder liner with grease. The wear rate of the samples with mineral layers is lower almost by two factors than that of the samples made of grey foundry iron and untreated samples. As the result of slip/rolling abrasion tests of parts with mineral layers under conditions of high contact pressure, a suggestion was made concerning probable mechanics of surface wear.

Wear resistance of a metal surface modified with minerals

The article describes the advantages of the new technology of mineral coating of metal products for the friction pair of mechanical systems. It presents the research results of the wear rate of the samples made of 12X13 steel (X12Cr13) with mineral layers, in the experiments with a piston ring sliding inside a cylinder liner with grease. The wear rate of the samples with mineral layers is lower almost by two factors than that of the samples made of grey foundry iron and untreated samples. As the result of slip/rolling abrasion tests of parts with mineral layers under conditions of high contact pressure, a suggestion was made concerning probable mechanics of surface wear.

Crack initiation and propagation under fretting fatigue of inconel 600 alloy

The purpose of the study is to experimentally investigate the fatigue crack initiation and propagation characteristics of nuclear power plant steam generator tube materials, Inconel 600 alloy, under fretting fatigue conditions. In addition, this study aims to enhance the overall reliability of nuclear power plant equipments by developing fretting fatigue life and integrity evaluation methods. In order to achieve these purposes, a fretting fatigue experiment apparatus is developed and fatigue crack growth experiments are conducted to evaluate the characteristics of Inconel 600 alloy under various stress conditions. Finally, microstructures are observed in accordance with fretting fatigue and contact pressure conditions and fretting fatigue crack initiation mechanism is examined.

Running Torque of Slow Speed Two-Point and Four-Point Contact Bearings

A decoupled slow speed friction torque model has been developed to predict the running torque of a double-arched angular contact bearing when operating as a four-point, as well as a two-point contact bearing. The load distribution model from Amasorrain et al. (2003) and the kinematics model developed by Leblanc and Nelias (2007) have been combined after ignoring centrifugal and gyroscopic effects, a valid assumption for slow speed operation. Results from the model are compared with previous literature data, as well as with tests done on a specially-developed friction torque rig. The comparison with the literature results was done for two specific cases: (i) when only one out of the two contact lines in the four-point contact bearing is active (effectively creating a two-point contact bearing); and (ii) where both contact lines in the four-point contact bearing are active. Further, the comparison was done with a custom-built friction torque rig with FAG QJ309 bearings, again for two cases: (i) bearings mounted with a specific clearance (two-point contact); and (ii) bearings mounted with larger size balls to obtain interference (four-point contact). All tests were performed at low speeds. The sliding friction, which is an important input to the friction torque model, is carefully measured on ball-on-plate test using the same interface roughness, speed and contact pressure conditions as seen in the QJ309 friction test. The model comparison with experimental results is covered. The comparison is found to be encouraging, with the RMS difference being less than 7% between the model and experimental data for a four point contact.

626 摩耗を考慮したフレッティング疲労限の簡易予測法

Fretting fatigue process have many features such as early stage crack initiation at contact edge, very slow crack propagation and fatigue failure after very long life operation. In previous paper we present fretting fatigue model which was considering the wear process, and this model can explain these fretting fatigue features reasonably. But, the estimation of fretting wear process require a large amount of labor, so this precise wear estimation method is not suitable for actual design site. In this paper we try to present simple fretting fatigue limit estimation method considering wear. In the final stage of wear process the stress distributions near contact edges converge to a nominal contact pressures. So, we estimate the ultra high cycle fretting fatigue limit as the crack propagation threshold on this uniform contact pressure conditions. This crack propagation threshold is analyzed using fracture mechanics analysis. Finally these estimated results are of ultra high cycle fretting fatigue limit compared with the experimental results, and can confirmed the availability of this simple fretting fatigue limit estimation method.