Zoltán Néder

Experimental and numerical evaluation of the mechanical properties of compacted wear debris layers formed between composite and steel surfaces in sliding contact

Abstract Microindentation experiments and non-linear FE contact analysis were used to study the hardness of a CF/PEEK (carbon fibre/polyetheretherketone) polymer composite material in the presence of a transfer film layer (TFL). The latter resulted from a sliding contact of the composite against a steel counterpart. The TFL plays an important role in the load transmission, and it therefore also affects the wear process. To study these mechanisms, requires reliable material data for the TFL. This study concentrates on TFL obtained at the beginning of a wear process on both components, i.e. the steel disk and the composite pin for two different fibre orientations relative to the sliding direction. Universal hardness values were evaluated from experimental load–depth profiles and their finite element analysis (FEA). The corresponding model contained contact elements that allowed prediction of the contact area, the contact pressure distribution, and the contact stresses and strains.

Evaluation of the real contact areas, pressure distributions and contact temperatures during sliding contact between real metal surfaces

Abstract A three-dimensional elastic contact algorithm has been developed to analyse the normal contact problems of bodies having rough surfaces. The algorithm can evaluate the real contact areas and contact pressure distributions using measured surface roughness data. Following an approximate elastic-plastic contact solution the analysis produces more realistic elastic and plastic contact areas; in addition results of contact pressure distributions can be predicted according to a given maximum plastic limit pressure. The technique can simulate (in an approximate way) the elastic-plastic sliding contact behaviour in the vicinity of asperities or concentrated contact areas by ignoring the effect of the tangential forces on the vertical displacement. Assuming a certain sliding speed and a particular coefficient of friction the local temperature distribution due to the heat generation over the real contact areas can also be calculated for ‘slow sliding’ problems. The results show the moving real contact areas and the contact temperature fields for an electric spark mechanical steel surface moving over a planed bronze surface. Changes of the rigid body displacement, as well as the average and maximum pressures are also presented during sliding. The micro-contact or asperity contact behaviour for bodies having large nominal contact area and the macro-contact behaviour for bodies being in ‘concentrated cotnact’ are also compared. In the latter case an ideal smooth steel ball was slid over the previously mentioned bronze surface.

Numerical and Finite Element Contact Temperature Analysis of Steel-Bronze Real Surfaces in Dry Sliding Contact

Numerical techniques have been developed and used to evaluate the contact temperature distribution between real surfaces in sliding contact. The contact temperature is evaluated for the entire range of Peclet numbers. In the case of “slow sliding” problems a stationary numerical technique was used, whereas for “intermediate and fast sliding” problems transient finite element (FE) solutions were preferred. At first, sliding contact of a single spherical steel asperity over a steel or bronze surface was modelled in order to study the contact temperature development on a microscopic level. Contact temperature results for real steel-bronze sliding surfaces are also presented in order to provide information about more realistic stress and wear conditions; the latter will be modelled in future works. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

Contact and thermal analysis of transfer film covered real composite-steel surfaces in sliding contact

Abstract For composite-steel surfaces in sliding contact an anisotropic numerical contact algorithm has been developed to study the ‘layer type’ problems. An FE contact analysis was applied to evaluate the contact parameters (real contact area, contact pressure distribution and normal approach). The contact temperature rise was determined by using both a numerical thermal algorithm for stationary and a FE transient thermal technique for ‘fast sliding’ problems. The effect of a continuous transfer film layer (TFL), that had built up during wear of the PEEK matrix material on the steel counterpart, was considered. Its thickness was assumed to be t=1 μm, and its material properties were that of PEEK at room temperature or, in the case of frictional heating, at a temperature of 150°C (i.e. above the glass transition temperature of the polymer matrix). Results are presented for a spherical steel asperity, with/without TFL, sliding over composite surfaces of different fibre orientation, and in addition, for real composite-steel surfaces (based on measured surface roughness data) in sliding contact. The TFL has an effect on the contact parameters especially at higher operating temperatures (i.e. 150°C); it results in the production of a larger contact area and a lower contact pressure distribution. The contact temperature rise is clearly higher if a TFL is present. Due to the low thermal conductivity of PEEK, the TFL is close to the melting state or it even gets molten within a small vicinity of the contact area.

The real contact area between composite and steel surfaces in sliding contact

An anisotropic numerical contact algorithm has been developed for real composite-steel surfaces in sliding contact. The results were based on measured surface roughness data, under conditions of different fibre orientations relative to the sliding direction. The location of the real contact area at certain positions of sliding contact could be predicted. These results can be considered as input data for contact temperature calculations and wear predictions. An experimental evaluation of the real contact area was carried out by testing a composite pin under static compressive load against a gold-covered glass surface, resulting in an asperity-type contact condition. In another experiment, the composite pin was slid over the glass surface, which resulted in the removal of the gold layer along a certain path, characterising the nature of the real contact area interaction between the two surfaces. The results showed that the densities of contact spots are similar obtained by both the contact algorithm and the experimental techniques.

FE Macro/micro Models For Contact Temperature Analysis Of A Steel Asperity Sliding Over A Normally Oriented CF/PEEK Composite Surface

FE contact and thermal macrolmicro models have been developed to study the real thermal behaviour of a fibrelmatrix micro-structure under sliding motion of a steel asperity. At first the contact parameters were evaluated using an approximate contact technique, followed by a transient thermal FE evaluation. The latter considers the heat partition between the steel asperity and the real fibrehatrix micro-environment of a normally oriented CFPEEK composite.

FE Macro/Micro Models for Contact Temperature Prediction at Steel/Composite Interfaces

Finite element (FE) contact and thermal macro/micro models have been developed to study the real thermal behavior of a fiber/matrix microstructure under sliding motion of a steel asperity. At first the contact parameters were evaluated using an approximate contact technique, followed by a transient thermal FE evaluation. The latter considers the heat partition between the steel asperity and the real fiber/matrix microenvironment of a normally oriented carbon fiber/polyether ether ketone composite. The temperature results obtained were compared with those representing a macroscopic approach.Finite element (FE) contact and thermal macro/micro models have been developed to study the real thermal behavior of a fiber/matrix microstructure under sliding motion of a steel asperity. At first the contact parameters were evaluated using an approximate contact technique, followed by a transient thermal FE evaluation. The latter considers the heat partition between the steel asperity and the real fiber/matrix microenvironment of a normally oriented carbon fiber/polyether ether ketone composite. The temperature results obtained were compared with those representing a macroscopic approach.

Contact behaviour of the original and substituted real surfaces

Abstract Several engineering components transfer load under sliding contact. Between two sliding bodies there are contacts over only small areas of the nominal contact area due to the surface roughness and surface waviness. The nominal contact pressure is therefore much smaller than the real contact pressure acting over the real contact areas inside the contour contact areas. To evaluate the contact parameters (location of the real contact area and contact pressure distribution) different numerical methods have been used in the past decades. The latest ones can consider the real surfaces based on measured surface roughness data. The present study focuses on the characteristic features of the asperities using hemispherical, ellipsoidal and parabolic surfaces as substituting surfaces. In each case the location of the real contact area and contact pressure distribution are evaluated and compared with the results representing the original measured surfaces. The best agreement was obtained if paraboloides were used for substituting asperities. This technique can provide statistical type results characterising the contact behaviour, if the substituting asperities are considered.

Contact and Thermal Analysis of the Wear Process in Linear Bearings

In linear bearings there is contact over only small areas of the nominal contact area. The real contact pressure frequently is in the range of the plastic limit pressure. Regardless of the boundary lubrication, the asperity contact is mostly Hertzian-type contact. The developed contact algorithm can approximately simulate the elastic-plastic sliding contact behavior in the vicinity of the asperities by ignoring the effect of the tangential forces on the vertical displacement. Assuming certain sliding speed and coefficient of friction, the local temperature distribution is also calculated due to the heat generation over the real contact areas for slow sliding problems. In the described method, the original surfaces, having contact with an ideal smooth surface, produce mostly plastic contact, while the worn surfaces are mostly in elastic contact, having larger real contact areas. The sliding contact analysis of the original and worn surfaces shows significant differences in contact pressure distribution and heat generation.