H. Krause

Investigation of cavitation erosion using X-ray residual stress analysis

Abstract In this paper it will be shown that by X-ray residual stress analysis it is possible to obtain information on the cavitation process after only short cavitation times. To clarify the correlation between cavitation erosion and changes in residual stress, samples of various steels were tested in a flow cavitation device. The residual stress measurements showed that cavitation leads to the development of compressive residual stresses in the surface of the samples. The rate at which these residual stresses develop depends on the intensity of cavitation. Cavitation-induced changes in residual stress may also be observed in samples with pre-existing residual stresses due to handling, e. g. mechanical working, heat treatment etc. After very short cavitation times the local variation in cavitation intensity may be very clearly seen in the residual stress distribution in the surface. After a longer period of cavitation, compressive residual stresses reach a limiting value which is not exceeded even at points of highest cavitation intensity.

Texture changes in the running surfaces of face-centred cubic metals as the result of frictional stress

Abstract Considerable plastic deformation is produced by frictional forces in the surface layers of metallic objects. This causes a preferred orientation of the crystallites in a particular direction, i.e. a texture, and therefore an alteration of the friction and wear behaviour of the system. The development of this texture has been evaluated for pairs of face-centred cubic metals after exposure to rolling under defined conditions. The development of texture in surface layers exposed to friction can be reproduced in a rolling test rig. The change in texture for an increasing distance from the surface towards the interior of the material has been studied and graphically displayed. The results are compared with results obtained with ferrous materials.

A contribution towards improving the applicability of laboratory wear tests to practice

Abstract In previous wear tests it was frequently found that there was no systematic analysis of the applicability of the results of the tests to practical systems. In the present paper an attempt was made to study the applicability of wear test results with the aid of a system analysis and similarity laws. The test conditions under which a good qualitative applicability of wear results can be expected were determined. For checking the applicability of wear test results, suitable material and surface studies were introduced. The considerations described with respect to the applicability of wear test results are summarized in a flow chart; this demonstrates how to perform the applicable wear tests.

The effect of initial orientation on the formation of tribological textures and on the wear behaviour of the region in the proximity of surface layers under continuous sliding motion in tribological systems

Abstract The formation and development of a surface crystallographic texture (“tribological texture”), characteristic of continuous sliding motion, is influenced by the initial texture of the triboelements. These changes influence the friction and wear behaviour of the system. An initial texture which promotes the rapid development of a stable final tribological texture results in less deformation of the surface zones.

Influence of non-metallic inclusions on the wear behaviour of ferrous materials in nominally dry friction systems

Abstract In non-lubricated rolling-sliding and sliding friction systems under large plastic deformation or on exceeding the deformability limit, cracks appear in the near-surface regions which can lead to very high wear rates. The cause of cracking is ascribed to non-metallic manganese sulphide inclusions but the material microstructure has an effect on the crack distribution and propagation and therefore determines the wear behaviour. To avoid the different negative effects of non-metallic inclusions on the wear behaviour, the cleanliness of the material should be generally improved.

The wear behaviour of copper alloy-steel and polyamide-steel sliding pairs for heavily loaded cardan joints

Abstract The wear behaviour of various copper alloy-steel and polyamide-steel sliding pairs for use in heavily loaded cardan joints was studied on two sliding surface test rigs that were constructed on the basis of practical considerations; the influence of numerous parameters such as surface pressure, lubrication and load oscillation was considered. For comparison with the metallic sliding pairs unfilled and filled or reinforced polyamides were used. Tests were carried out at high surface pressures under conditions of mixed friction using high additive lubricants (oils and greases) with and without contamination.

The influence of the real material and system properties on the traction-creep relationships in rolling contact

Abstract With the help of the results obtained from test rig experiments and a comparison with the original system, it is demonstrated to what extent the traction-creep relationships of wheel-rail contact are influenced by surface contamination, oxide layers, roughness, plastic deformations and the preferred crystal orientations (textures) they cause, and dynamic variations in vertical load.

Investigation of the relationship between the stresses at the rolling or the rolling-sliding contact and the texture development in the proximity of the surface of wheels and rails and their interpretation with model tests

Abstract Texture investigations have proved useful for the study of anisotropic material behaviour. The types and the strengths of textures caused by the rolling or the rolling-sliding stresses in the proximity of the surface of wheels and rails or the corresponding model rollers were determined as a function of the edge distance from the surface in order to estimate the real contact stiffness and thus the real friction behaviour between wheel and rail.

Plastische Verformungen hervorgerufen durch Wälzbeanspruchung im Kontaktflächenbereich

Zur Berechnung der ubertragbaren Tangentialkraft in Walzreibungsgetrieben wurden zwei Theorien vorgeschlagen. Bei der Haftzonentheorie /9/ wird von einer Reibungszahl ausgegangen, die unabhangig von der Gleitgeschwindigkeit ist. Es wird angenommen, das Gebiete innerhalb der Beruhrungsflache bestehen, in denen die Oberflachen sich relativ zueinander in Ruhe befinden; dort wirken kleinere als die maximal ubertragbaren Schubspannungen.

Laufflächenrauheit bei der Wälzreibung

Die tatsachliche Kontaktflache zwischen Reibungskorpern nimmt mit zunehmender Oberflachenrauheit stark ab. Je groser die Rauheit ist, umso groser ist die tatsachliche spezifische Flachenpressung.