Papers by Author: Pieter Samyn

Abstract: Polyimide surfaces after macroscopic wear at 80 to 260°C are studied by atomic force microscopy to give additional insight in the tribophysical and -chemical processes during sliding. Three sliding regimes are distinguished with hydrolysis resulting in rough surfaces, imidisation resulting in orientation of polymer molecules and melting resulting in short-range arrangements.

Abstract: Polymer wear debris particles undergo a thermal and mechanical (shear) cycle since their generation and therefore contain information on the friction and wear processes, while it is often difficult to draw quantitative data from them relating to transitions in tribological behaviour. Results from thermal DTA/TGA analysis and morphological pattern spectra of debris are presented and related to a transition at 180°C sliding temperatures own to hydrolysis and imidisation.

Abstract: This article summarizes the efforts done for using acoustic emission as wear mechanisms monitoring technique for wear testing in a pin-on-disc setup. The basic characteristics of the mechanisms were previously determined via controlled tensile testing (fiber breakage, debonding …). The knowledge of these basic characteristics then resulted in an easier classification of wear mechanisms related to wear testing of pultruded glass fiber reinforced polyester.

Abstract: The tribological behaviour of a polymer composite is compared during small-scale and large-scale sliding tests and it is observed that test results strongly depend on the fibre orientation and test configuration. Different wear mechanisms are evaluated by optical microscopy and finite element modelling in relation to a real application of polyester/polyester discs as bearing elements.

Abstract: Pultruded glass fibre reinforced polyester where used to investigated the frictional behaviour of the 45° fibre orientation. Therefore, on a rebuild Pin-on-disc test rig, using composite discs and steel pins, the frictional behaviour of these materials is investigated. Due to the indicated fibre orientation, and a simple trigger mechanism, it was possible to distinguish the friction force for different fibre orientations. The classical know orientations, parallel and perpendicular to the direction of sliding provided expected results, for both cases. The ~45° orientation, which is extremely important regarding filament wounded bearings, behaved in both cases similar -- regarding friction force-- in an unexpected way. The friction force of the 45° orientation was higher in all cases, and the amount was similar to the difference between the parallel and perpendicular case. These findings yield the conclusion that the 45° orientations cannot be neglected in frictional studies, and the behaviour of weft-warp structures also determines performance.

Abstract: Polymer matrix composites are widely used as bearing materials for heavy load applications. Still fundamental knowledge about the wear mechanisms of these materials and the evolution in time of these mechanisms is lacking. Currently these mechanisms are only analyzed by post mortem analysis. The Laboratory Soete, based on the well-known pin-on-disc test rig, has developed a new test-setup. Instead of the standard composite specimen and steel disc, a rotating composite disc and steel pin is used to be able to have a visible composite wear track. Standard wear and friction measurements will be further combined with vibration measurements. The vibration measurements give valuable information about the pin-disc contact. The combination of all these measurements should yield valuable information on the active wear mechanisms, the occurrence of fiber and matrix fracture, fiber pull out, generated frictional heat, formation mechanisms of wear particles, and the interaction between all these effects.

Abstract: Although tribological tests on polymers are traditionally performed on small-scale pin-on-disc or bloc-on-ring configurations, present sliding tests under high load provide more accurate de-sign data. For wear tests on large samples edge effects, stress concentrations and the moveability of wear debris into the contact zone are simulated close to practice. It is illustrated that friction is gene-rally lower compared to small-scale tests, while overload and deformation occur more frequently.