Tribological contact analysis of a rigid ball sliding on a hard coated surface (original) (raw)
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Tribology International, 2005
A tribological analysis of deformations and stresses generated and their influence on crack generation and surface fracture in a coated surface loaded by a sliding sphere in dry conditions is presented. A three-dimensional finite element method (3D FEM) model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip with 200 mm radius sliding with increasing load on a 2 mm thick titanium nitride coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the surfaces. The hard coating will be stretched and accumulates high tensile stresses. At the same time, it is carrying part of the load and thus reducing the compressional stresses in the substrate under the sliding tip. The first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. The fracture toughness of the coating is calculated by identifying from a scratch test experiment the location of the first cracks and the crack density and using this as input data. q
Wear, 2010
Titanium (Ti) coatings are widely used in biomedical engineering, microelectronics and thin film industry. However, very little is known about its tribological behaviour under dynamic contact conditions. In the light of this, the present work attempts to explore the tribological properties of a micrometer thick Ti coating deposited on a D9 steel substrate. Frictional tests were carried out using a tribometer in linear reciprocating mode against steel, alumina and silicon nitride balls. Three different loads of 1, 3 and 9 N at sliding speeds of 0.1, 0.5 and 2 cm/s were used to induce different contact conditions. Wear was calculated in terms of wear rate. Resulted tribo tracks were analysed using optical microscopy, scanning electron microscopy and Raman spectroscopy. Distinct deformation behaviours were observed which led to the formation of different kind of wear debris as revealed by SEM observations. The coefficient of friction was found to decrease with increase in speed but opposite trend was observed with increase in load with all the mating partners used. Wear rates were found to increase with corresponding increase in load and speed. Highest wear rates were observed in case of alumina ball and lowest were observed in case of silicon nitride ball. These observations have significant bearing while using Ti coating for wear resistant applications.
Tribological analysis of TiN and DLC coated contacts by 3D FEM modelling and stress simulation
Wear, 2008
Surface coatings, like titanium nitride (TiN) and diamond-like carbon (DLC) coatings, offer high wear resistance and good friction performance for a wide range of applications. With novel advanced techniques like modelling and simulation, the performance of these coatings can be predicted under a wide range of loading conditions. This provides valuable information for the coating design and for the use of coatings in different applications. A previously developed three-dimensional finite element method (FEM) model was used for calculating the first principal stress distribution in a scratch test contact as a spherical diamond tip is moving with increased load on DLC and TiN coated high speed steel surfaces containing no residual stresses. The used three-dimensional model is comprehensive in the sense that it considers elastic and plastic behaviour of the contacting surfaces. The first cracks to appear on the surface are angular cracks on the edge of the scratch groove. This corresponds to the region of high two directional tensile stresses occurring in FEM stress simulations at the edge of the scratch groove. The coating/substrate stiffness ratio influences considerably on the coating behaviour. The TiN coating that had higher Young's modulus compared to the substrate material experienced high tensile stresses when loaded by the diamond stylus. The DLC coating that had lower stiffness compared to substrate material experienced comparatively low tensile stresses. The DLC coatings had maximum tensile stresses in the range of 700-900 MPa. The TiN coatings had tensile stresses in the range 2200-3000 MPa. The coating thickness had only minor effect on the maximum tensile stress level for the 1 and 2 m thick coatings. The location of the experimentally observed first crack in the surface corresponds to the location of maximum tensile stress concentrations in the stress simulations and the direction of the observed crack corresponds with the stress components in the calculated stress field. The role of residual stresses is discussed.
Friction in a coated surface deformed by a sliding sphere
Wear, 2007
Stress and strain modelling and stress field computer simulations are today an important tool for systematic approach and optimisation of tribologically stressed coated contacts. Modelling illustrates and quantifies the dominating parameters resulting in crack initiation, crack growth and failure of coated surfaces. Friction and its components, adhesive and ploughing friction, are necessary input parameters in stress modelling. In Finite Element Method (FEM) modelling the ploughing component is integrated in the model while the adhesive component needs to be determined as input value for stress simulations. This paper presents how adhesive friction is determined for the TiN (μ a = 0.066) and DLC (μ a = 0.047) coatings from experimental friction measurements. The experimental value is used as an input value in the three dimensional finite element micro-model that simulates the spherical tip sliding on a DLC coated flat substrate with increasing load similar to the conventional scratch test contact. Based on the numerical contact analysis (FEM) similar friction evolution compared to the experimental friction in scratch testing was depicted. However, the analytical approach resulted in a diverse solution.
Tribological investigations of the load, temperature, and time dependence of wear in sliding contact
PloS one, 2017
An effort was made to study and characterize the evolution of transient tribological wear in the presence of sliding contact. Sliding contact is often characterized experimentally via the standard ASTM D4172 four-ball test, and these tests were conducted for varying times ranging from 10 seconds to 1 hour, as well as at varying temperatures and loads. A numerical model was developed to simulate the evolution of wear in the elastohydrodynamic regime. This model uses the results of a Monte Carlo study to develop novel empirical equations for wear rate as a function of asperity height and lubricant thickness; these equations closely represented the experimental data and successfully modeled the sliding contact.
Coated surface design by modelling and simulation
Surface coatings, like titanium nitride (TiN) and diamond-like carbon (DLC) coatings offer high wear resistance and low friction performance for a wide range of applications. By using new techniques like modelling and simulation, the coating performance under load can be estimated and thus provide valuable information for the coating design and for the use of coatings in different applications.
Friction and wear of coated surfaces — scales, modelling and simulation of tribomechanisms
Surface and Coatings Technology, 2007
Coating a surface with a thin layer changes the surface material properties and is an important tool for controlling friction and wear. The tribological mechanisms, scale effects and parameters influencing the friction and wear of coated surfaces are discussed. The basic friction and wear mechanisms can be reduced to: friction by adhesion, ploughing and hysteresis and wear by adhesion, abrasion and fatigue combined with material fracture. The tribochemical and surface physical effects and surface fatigue taking place before material fracture are treated here as pure surface material modification mechanisms. Scale effects in a tribological contact are illustrated by explaining typical surface roughness related tribological mechanisms for diamond and DLC coated surfaces. For diamond coatings asperity interlocking effects are important for rough surfaces, graphitisation is a dominating mechanism for smooth engineering surfaces and hydrogenising of dangling bonds may be crucial for physically smooth surfaces. For DLC coated surfaces, surface graphitisation is important with rougher surfaces; building up transfer layers and graphitisation is crucial for smooth engineering surfaces and hydrogenising of dangling bonds can explain superlubricity for physically smooth surfaces. An analysis of dominating surface parameters such as elastic, plastic and fracture behaviour of the top surface, the coating, the coating/ substrate interface and the substrate in addition to the coating thickness forms the basis for surface modelling. A stress intensity factor analysis of crack growth shows the importance of considering both modes I, II and III loading, crack spacing and location of crack, while crack orientation, location in crack field as well as load biaxiality have minor influences. It is shown how surface 3D FEM modelling generates stress and strain values at the nano level, within bond layers at coating/substrate interfaces and around cracks and forms the basis for better understanding the origin of wear.
Finite element modelling of crack growth and wear particle formation in sliding contact
Wear, 2001
Two steel surfaces in sliding contact are examined analytically and experimentally. The experiments are restricted to the reciprocating sliding of a relatively hard circular cylinder on a soft plane but the analytical model developed can be applied to general two-dimensional sliding contact situations. The surfaces are nominally smooth (smooth to the touch) but microscopic roughness is modelled as surface asperities having the form of randomly spaced cylindrical corrugations, which ideally represent plane strain conditions perpendicular to the direction of sliding. Under dry sliding conditions (high friction) it is known that crack growth and particle detachment can occur below the elastic limit. By applying finite element methods to linear elastic fracture mechanics, a model is developed, which simulates crack growth and wear particle detachment from an existing surface crack. A range of mixed mode stress intensity factors for cyclic loading is evaluated and related to crack extension by a Paris type equation. The maximum tensile stress criterion is used to determine the crack-turn-angle (crack path) during crack propagation under cyclic loading. It is found that eventually the crack extends and turns toward the surface of the plane to form a single wear particle. Estimated wear volume is calculated using surface statistics and integration. The predicted particle size and the estimated wear volume are in reasonable agreement with those obtained from experiments involving hardened steel sliding on steel. Some of the tested specimens were sectioned and examined in a scanning electron microscope. Two distinct types of crack were observed. Hardness tests on the section revealed significant work hardening in the near-surface layer.
The frictional contact of coated bodies. Part I – The sliding contact
IOP Conference Series: Materials Science and Engineering, 2019
Hard coatings provide low friction, high wear resistance and corrosion protection that improve the tribological performances of the machine elements undergoing contact load. In lack of analytical solutions, a numerical study is performed in this paper for a better understanding of the engineering applications of hard coatings with consideration of friction. A previous study on the frictionless contact of bi-layered materials is extended by considering the effect of friction on the contact stress state. The assumption of a sliding contact in which the shear tractions do not affect the pressure distribution is adopted. This simplification, often present in the literature, decouples the contact problems in the normal and in the tangential direction and allows for a pressure distribution solution that is independent of the frictional regime. The shear tractions are subsequently obtained from a kinetic Coulomb-type friction law, under the assumption that the normal load is kept constant....
Comparative study on the tribological behavior of metal and ceramic model coatings
The present study concerns parametric analysis on the tribological behaviour of two model coatings, one metallic and the other ceramic, deposited onto the same carbon steel substrate by Atmospheric Plasma Spraying (APS). The metallic coating, selected as a representative of ductile mechanical behaviour, was a CuNiIn, 200 μm thick. The ceramic coating, selected as a representative of brittle mechanical behaviour, was titanium oxide (TiO2) of the same thickness. The influence of the normal load applied and of the counterbody on the evolution of the friction coefficient and the wear mechanisms was evaluated by testing the two model coatings against sliding in a ball-on-disc apparatus. The behaviour of the different tribosystems was correlated to the friction micro-mechanisms that are activated at the contact interface, during sliding.