On the wear debris of polyetheretherketone: fractal dimensions in relation to wear mechanisms

Abstract

It has been recognized that wear debris contains extensive information about wear and friction of materials. Investigation of wear debris is important for tribological research. In order to find out an effective way that is able to diagnose and predict the wear state of polymers, the authors investigated the relationship between the wear debris morphology and the wear behaviour of the bulk material. Polyetheretherketone (PEEK) was employed as the model material. Its sliding wear and friction properties were measured by means of a pin-on-disc apparatus. At a constant sliding velocity of 1 m s −1, the specific wear rate was independent of load under lower loading conditions (1–4 MPa) but increased with a rise in load under higher loading conditions (4–8 MPa). The coefficient of friction was insensitive to the variation of contact pressure. The possible mechanisms involved were analysed on the basis of the wear debris morphology as well as the wear performance. Fractal geometry, which describes non-Euclidean objects, was applied to the quantitative analysis of the boundary texture of the wear debris due to the fact that the qualitative assessment of the wear debris morphology was not effective enough to reflect the geometrical variation of the fragmental shapes. The experimental results demonstrated that the wear debris were fractals, and could be characterized with the fractal dimensions which were determined by the slit island method. In addition, it was found that the fractal dimension of the wear debris was closely related to the wear behaviour of PEEK, and can be regarded as a measure of wear rate.