Dry Contact Research Articles

Effect of Shape, Density, and an Array of Dimples on the Friction and Wear Performance of Laser Textured Bearing Steel under Dry Sliding

The present study is directed to reveal the effect of density and shape of the dimples on the friction and wear characteristics of textured bearing steel (100Cr6) under dry sliding conditions. One untextured and four laser-textured disks of 100Cr6 steel with circular and bi-triangular dimples having 7 and 20% density, respectively, in the spiral layout were tested using a pin-on-disk unidirectional tribometer against a 100Cr6 pin having a flat surface with rounded corners under flat-on-flat configuration. The tests were carried at different speeds of 0.2, 0.6, and 1 m/s at a constant load of 15 N. The results indicate that a higher density of bi-triangular dimples had less wear and a lower coefficient of friction compared to untextured disk or disk with circular dimples, particularly at a relatively higher speed. This has been attributed to a relatively higher number of dimples in the contact zone in case of a spiral array, which increases the entrapment of more wear particles leading to a reduction in wear. The friction coefficient had a relatively higher value at a relatively lower speed but decreased at the highest speed of 1.0 m/s used in the present study. The results suggest that dimples may not be too effective under dry contact because they lose their effectiveness to trap wear debris after getting filled.

Transition Between Severe and Mild Wear of 2024A-T4 Anodized Aluminum Alloy under Severe Wear Conditions

Aluminium alloys are gradually replacing grey cast iron in the automotive industry thanks to its low density. The purpose of this study is to evaluate tribological properties of 2024A anodized aluminium alloy under severe wear conditions. For this aim we are investigating the effect of the sliding speed and the anodic layer in order to improve the wear resistance and friction properties of 2024A aluminium alloy and this by using the latter with the hard metal chrome steel 100C6 in dry punctual contact. So we shall evaluate hardness, wear rate and friction properties after and before the anodizing process. The results have shown that the sliding speed affects a transition from severe wear to mild wear when u = 0.3 m/s for the alloy covered by hard anodic layer, as well as it was a significant decrease in wear rate.

Discrete and Continuous Approaches for the Failure Analysis of Masonry Structures Subjected to Settlements

Numerical modelling of masonry structures is nowadays still an active research field, given a number of open issues related to preservation and restoration of historical constructions and the availability of computational tools that have become more and more refined. This work focuses on the analysis of settlement-induced failure patterns characterizing the in plane response of two-dimensional dry-joints masonry panels, which differ in terms of texture, geometry and settlement configuration. Brick-block masonry, interpreted as a jointed assembly of prismatic particles in dry contact, can be modelled as a discrete system of rigid blocks interacting through contact surfaces with no tensile strength and finite friction, modelled as zero thickness elasto-plastic Mohr-Coulomb interfaces. Different approaches and numerical models are adopted herein: Limit Analysis (LA), a discrete model DEM and a continuous Finite Element Model (FEM). Limit Analysis is able to provide fast and reliable results in terms of collapse multiplier and relative kinematics. In this work, a standard LA procedure is coded through Linearised Mathematical Programming to take into account sliding mechanisms through dilatant joints. Discrete models are particularly suitable to study historical masonry materials, where rigid bodies interacts between contact and friction. Here, a combined Finite/Discrete Element approach (FEM/DEM) is adopted. Finally, analyses are conducted through the Finite Element approach, resorting to a continuum anisotropic elastic-perfectly plastic constitutive model. Some selected case-studies have been investigated adopting the above mentioned models and numerical results have been interpreted to highlight the capability of the approaches to predict failure patterns for various geometrical features of the structure and settlement configurations.

Tribological characterization of a bearing coated with UHMWPE/GNPs nanocomposite coating

ABSTRACT Polymer nanocomposite coatings with low friction and high wear resistance are being developed to protect aluminium surfaces against wear and tear during dry and boundary lubrication. In the present study, pure and graphene nanoplatelets (GNPs) reinforced ultra-high molecular weight polyethylene (UHMWPE) nanocomposite coatings are deposited on aluminium thrust bearings. Each bearing makes an ROD contact with a metallic disc counterface to simulate the contact configuration in an actual bearing. A set of tests involving pure and reinforced UHMWPE coatings under dry and liquid contact lubrication is conducted. The wear test results reveal that UHMWPE/1 wt-% GNPs performs better than the reference sample significantly. It reduces the friction and wear of aluminium both in the dry and boundary lubrication conditions at different conditions. The 1 wt-% GNPs reinforcement increases the load-bearing capacity of UHMWPE by 440% in the presence of base oil.

Ultrasonic Thickness Measurements Using Machine Learning

Abstract Thickness measurements using an ultrasonic contact test is a well-known nondestructive evaluation technique. However, its implementation in a robotic system with a closed-loop feedback control for artificial intelligent measurements requires precise information of positioning and force of the ultrasonic probe. In this work, we describe an ultrasonic probe developed in our lab that uses a semispherical soft membrane made from an elastomer. The aim is to develop a methodology for precise positioning and force control of a dry contact ultrasonic probe based on the ultrasonic signal information processed using sparse matrix optimization and Fourier analysis techniques. The results show that the proposed methodology makes easy to achieve a fine tuning of the probe orientation with high sensitivity to load and misalignment in order to perform accurate thickness measurements.

Large-scale tribological characterisation of eco-friendly basalt and jute fibre reinforced thermoset composites

The present research aims at understanding the tribological behaviour of advanced unsaturated polyester/vinyl ester based thermoset composites reinforced by inorganic (mineral-based) or organic (vegetal) fibres such as basalt and jute. These fibres are non-toxic and widely available in nature. Thermosets have limitations in the formation of a uniform transfer layer during sliding wear. To surpass these limitations, tribo-fillers such as polytetrafluoroethylene, polyoxymethylene or molybdenum disulphide (PTFE/POM/MoS2) are added into the contact surface. The composites developed for the current research are characterised for their friction and wear behaviour, using a large-scale (sample size typically 50 × 50 × 7 mm) linear reciprocating sliding flat-on-flat test configuration. In order to simulate real scale application, 50 mm/s sliding speed and 10 kN normal force which corresponds to 4 MPa contact pressure, are applied under dry contact conditions. In this research work 12 different tribocomposites are developed and tested against AISI 100Cr6 steel counterface. It was evidenced that composites blended with PTFE have the lowest coefficient of friction and longest service life. MoS2 filled tribocomposites have the highest coefficient of friction. The dominant wear mechanisms for the failure of all investigated composites are thermal degradation and delamination, and abrasion for the counter surface.

MEASURING OF ELASTIC MODULI BY MEANS OF SUB-SURFACE SOUNDING METHOD

The method of determination of elastic moduli for different materials by means of measuring of longitudinal and shear waves’ velocities is discussed in the paper. The velocities are measured by obtaining the time of flight between a pair of low frequency ultrasonic dry point contact transducers installed on the surface of the studied material sample. Factors defining the accuracy of such measurement are indicated which mainly consist of physical velocity frequency dispersion, fundamental although small differences between static and dynamic elastic moduli measurements, velocity dependence on temperature etc. Comparison between Young’s modulus and Poisson’s ratio, obtained experimentally and from table data, is given for various plastics and steel samples. It shows good agreement of different methods’ data and demonstrates the applicability of the suggested elastic moduli ultrasonic sub-surface measurement method.

Energy-Based Modelling of Adhesive Wear in the Mixed Lubrication Regime

Adhesive wear in dry contacts is often described using the Archard or Fleischer model. Both provide equations for the determination of a wear volume, taking the load, the sliding path and a set of material parameters into account. While the Fleischer model is based on energetic approaches, the Archard formulation uses an empirical factor—the wear coefficient—describing the intensity of wear. Today, a numerical determination of the wear coefficient is already possible and both approaches can be deduced to a local accumulation of friction energy. The aim of this work is to enhance existing energy-based wear models into the mixed lubrication regime. Therefore, the pressure distribution within the contact area will be determined numerically taking real surface topographies into account. The emerging contact area will be divided into one part of solid and a second part of elastohydrodynamically lubricated (EHL) contacts. Based on the resulting pressure and shear stress distribution, the formation of micro cracks within the loaded volume will be described. Determining a critical number of load cycles for each asperity, a locally resolved wear coefficient will be derived and the local wear depth calculated.

Effect of Intermetallic and Secondary Phases on Dry and Wet Sliding Wear Behavior of Super Duplex Stainless Steel

The purpose of this investigation was to quantify the effects of intermetallic and secondary phases on the sliding wear behavior of super duplex stainless steel 2507 against bearing steel type EN-31 under both dry and wet contact conditions. Phases were precipitated by suitable heat treatment in the range of 475–875 °C. A pin-on-disc technique was used to investigate the wear characteristics in the wet environment of 3.5% NaCl solution, 1 M HCl solution, 10−2 M sodium thiosulfate solution, and artificial ocean water. These media were chosen to closely match the actual service environment of super duplex stainless steel 2507. Pins were slid against a disc of EN-31 steel for distances of 1,000, 1,500, 2,000, 2,500, and 3,000 m. Results indicate that precipitation of the sigma phase gives the best wear resistivity, followed by precipitation of chi and R phases and then precipitation of the α′ phase. The experimental investigations reveal that hydrogen in acidic medium accelerates the reaction kinetic compared to the neutral medium because of the different cathodic reactions. Progressive wear was closely observed using the change in the sliding pin’s contact face profile and corresponding weight loss data. Scanning electron microscopy was used to study the wear mechanism.

Single-Shot Near-Field Volumetric Imaging System for Optical Ultrasound and Photoacoustics Using Capacitive Micromachined Ultrasonic Transducer Without Transmission Mode.

In this article, we present a single-shot dual-mode imaging system that uses optical ultrasound (US) as an ultrasonic pulser without a transmission circuit. The ultrasonic pulse-echo system comprises an optical US pulser generated by carbon nanotubes (CNTs), which generate a high-power photoacoustic (PA) signal and a capacitive micromachined ultrasonic transducer (CMUT) receiver. By fabricating a thin CNT-polydimethylsiloxane (PDMS) composite capable of semiabsorption of the laser, a single-shot imaging system was developed. By transmitting a semipenetration light to the object, US and PA imaging were performed in a single shot. A CNT thickness of [Formula: see text] produced a maximum pressure of 154 kPa, and US was received by CMUT with a 2-MHz center frequency in PDMS. Additionally, a low-profile and near-depth imaging system was constructed with an intermediate layer of the 6-mm PDMS for the dry contact method. We performed a single-shot dual-mode imaging experiment on point and line phantoms, as well as the particle spread in the soft tissue. Thus, we examined the feasibility of the near-depth and single-shot dual-mode (US and PA) imaging system capable of a dry contact.

Structure and Topography Modifications of Treated AISI 316LN Stainless Steel Surfaces after Friction in Dry Sliding Contact by Case Hardening Process

Austenitic stainless is having corrosion resistance property, but certain mechanical applications require improved resistance to wear, inferior cavitation, susceptibility to sensitization. These steels have numerous favourable circumstances for great cryogenic - properties, anti-corrosion, and bio-compatibility. So these steels have a broad application in low temperature innovation, saltwater applications, nourishment industry, bio-medicine, petro-chemical handling, and so forth when alloyed with nitrogen, austenitic treated steels has a progressively steady austenite structure, better mechanical properties and better wear opposition, which has animated extraordinary enthusiasm for this exploration work. Many surface hardening techniques are available, the best surface modification technique is chosen for improved service performance. Surface engineering is a technique to alter the surface of a material by mechanical or microchemical method without affecting the material properties. The alterations are done on the surfaces subjected to the liquid nitriding process to produce a hardened surface. Chosen for this research workbased on their wide application, the wear behaviour of AISI 316LN stainless steels was investigated. Of the various surface hardening techniques available, nitriding is chosen, so that these nitrogen gets penetrated into the material, in which hard iron chromium nitrides are formed at the surface level. AISI 316LN specimens were subjected to salt bath nitriding process. The specimens were nitrided to 60 minutes, 120 minutes and 180 minutes respectively. The specimens were undergone with wear tests by standardized tribiological wear machine and finally the metallographic studies were made.

Dry eye, Contact lenses and Preservatives in Glaucoma Medication

Dry eye, Contact lenses and Preservatives in Glaucoma Medication

Contact-deformation mechanism of boundary friction

Research was conducted to determine the effect of lubricants on stress and strain in the contact of metal surfaces. Experiments were carried out on the introduction of a fixed and moving indenter in contact with a dry and lubricated surface.The steel spherical specimen was pressed into a lubricated and dry metal surface. The microstructures of the structure of the surface layer are studied under various conditions of deformation. The diagrams of the relative deformation of the surface layers are constructed. The mechanism of the formation and distribution of internal stresses for dry and greased contact is described. Experimental studies of the introduction of a moving steel indenter into a lubricated surface have been carried out. The relationship of the deformation mechanisms of lubricated surfaces with their wear resistance is determined. The results obtained are recommended for predicting the durability of lubricated friction units according to the criterion of contact strength.

Numerical and experimental analysis of dry contact in pad disc brake assembly

When driving in cities, due to intensive loads, the brake disc assembly aside of mechanical and thermal stresses. Thermal stresses are the main source of risk for the braking system. In the paper, a numerical thermo-mechanical analysis was performed using ANSYS software for brake disc assembly within a hydraulic braking system. In the numerical analysis the model coupled between disc and pad was considered. In the paper were determined the total deformations, the values of Von Misses stresses and the temperature variations within a certain braking interval. In the first modelling was considered a ventilated disc made of gray cast iron and brake pads made of semi metallic material. In the second modelling was considered the same brake disc and pads made of composite material with organic fibre. The simulation models will be validated by experimental determinations on a hydraulic braking plant. Both numerical simulation and experimental determinations were performed by considering ten successive brakes. The results were used to compare the values obtained from numerical and experimental temperatures in order to validate the considered models.

Viscoelastic tribopairs in dry and lubricated sliding friction.

Soft contacts present different tribological responses compared to stiff materials, especially when soft materials exhibit viscoelastic behaviour, as viscoelastic materials have intermediate mechanical properties between viscous liquids and elastic solids. In this work, we investigated the influence of viscoelasticity of soft materials on sliding friction in dry and lubricated conditions. To achieve this, soft tribopairs with varying viscoelasticity were obtained by tuning the weight ratios of polydimethylsiloxane (PDMS) base and curing agent. The real-time friction force and preload were observed over multiple conditions, with systematic control of lubricant viscosity, preload, and sliding velocity. Tribopairs with a higher proportion of viscous character had more oscilliations in the friction force. They also presented a higher friction coefficient due to the increased contribution of viscoelastic hysteresis losses on friction. Through regression analysis, the models of the friction coefficient were found, which are in good agreement with experimental results. From the models, we found that in both dry and lubricated conditions, viscoelasticity of tribopairs, indicated as the loss modulus or loss tangent, plays a key role in determining the friction coefficient. This influence is particularly significant for dry contacts due to the direct interactions between surfaces of tribopairs. This study provides empirical proof and a focused analysis on the role of viscoelasticity in tribological contacts.

Zespół suchego oka a soczewki kontaktowe

Zespół suchego oka a soczewki kontaktowe

Numerical Study on Subsurface Stress in Hertzian Contacts under Pure Sliding Conditions

In this study, the two-dimensional numerical simulation on the subsurface stress field in Hertzian contact under the pure sliding condition for different speeds and coefficients of friction is presented. The Hertzian contacts are represented by a dry contact between a rigid flat surface and an elastic cylinder with radius R=12.5 mm. Simulation is carried out through two steps, the first one is for applying normal load and the second one is for applying angular speed for the cylinder. The results of subsurface stress filed for pure sliding are compared to non-moving Hertzian contact. The results show that pure sliding speed has a major effect on the value of maximum von Mises stress in the subsurface of contact. The effect of sliding speed is attributed to tangential forces and elastic deformation in the contact. On the other hand, the coefficient of friction has a primary effect on the position of maximum stress and the shift of the contact region. Indeed, when pure sliding motion is introduced with a low value of friction coefficient, the shift of the contact region is negligible compared to non-moving Hertzian contact. The study is extended to investigate the effect of contact geometry on subsurface stress for Hertzian contact in the cam-follower interface. The shape of the follower has a significant effect on the value and distribution of Hertzian stress, thus, the fatigue life of rubbing surfaces of the cam-follower interface.

DETERMINATION OF THE ACTUAL AREA OF DRY ACOUSTIC CONTACT IN THE SYSTEM “TRANSDUCER–PRODUCT” IN LOW-FREQUENCY DEFECTOSCOPY

The conditions for the emission of acoustic energy into the pipeline environment and the reception of reflected signals from inconsistencies in dry acoustic contact cause certain dimensions of the actual contact area between the transducers and the pipe surface. The basic approaches to the determination of the actual area of ​​dry acoustic contact between the surfaces of the piezoelectric transducer and the pipe are formulated under the influence of constant static force of pressing the surfaces in low-frequency flaw detection using ultrasonic directional waves. Expressions have been proposed to determine the area of ​​actual acoustic contact for single and numerical micro projections of the pipe surface. The principle of quality control of balancing of acoustic antenna piezoelectric transducers in modern systems of low-frequency diagnostics of the technical state of longitudinal pipelines by ultrasonic directed waves is described. It is revealed that after correct balancing of all the acoustic antenna piezoelectric transducers, the column image does not appear on the display screen and the mathematical support of the system will automatically collect the technical status of the diagnosed section of the pipeline, the results of which are displayed on the display screen. It is established that the actual area of ​​dry acoustic contact in the "piezoelectric product" system in low-frequency defectoscopy depends on the magnitude of the static force of pressing the surface of the piezoelectric transducer to the surface of the product. It is revealed that the deformation of the micro protrusions of the surface of the product under the action of static clamping force is uneven, which does not allow to fully calculate the actual area of ​​dry contact by mathematical methods. It is shown that in modern systems of low-frequency ultrasonic diagnostics of extended pipelines, directional waves control the quality of dry contact of the surface of the piezoelectric transducer with the surface of the pipe by balancing acoustic antennas with the use of special test programs.

Contact-deformation mechanics of the interaction of lubricated surfaces

The questions of the influence of the lubricant on the conditions of deformation in the contact of solids are considered. The steel spherical specimen was pressed into a greased and dry metal surface. The microstructures of the structure of the surface layer are studied under various conditions of deformation. The diagrams of the relative deformation of the surface layers are constructed. The mechanism of the formation and distribution of internal stresses for dry and greased contact is described. Experimental studies of the introduction of a moving steel indenter into a lubricated surface have been carried out. The relationship of the deformation mechanisms of lubricated surfaces with their wear resistance is determined.
 

Oxidative Damage of a Superalloy in High-Loaded Contacts

When used as a turbine material, dry contacts of nickel-based superalloy experience stresses via pressure and temperature. As a result, there is a change in material in the form of oxide layer formation and a depletion of alloying elements (e.g., Al) in the base material. The resulting layers have different material properties compared to the base material, which affect the mechanical and contact behavior. Adhesion, friction and wear are among the effects that are of interest. In addition, the operating experience has shown that the contact pressure has a yet unclarified impact on the progression rate of the damage process (oxidation). This paper deals with the development of models that contribute to the understanding of the damage scenario and its prediction. We will see that the changed material properies in the oxid layer lead to high-stress peaks at the interface between the layers. This is the expected location were the accelerated damage occures.