Joachim Flöck

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.

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.

Real contact area, contact temperature rise and transfer film formation between original and worn surfaces of CF/PEEK composites sliding against steel

Abstract For composite-steel surfaces in sliding contact an anisotropic numerical contact algorithm [7] has further been developed to study the “layer type” problems and FE contact analysis was applied to evaluate the contact parameters (real contact area, contact pressure distribution and normal approach). The contact temperature rise was evaluated by using 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 m, 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 real composite-steel surfaces (based on measured surface roughness data) in sliding contact. The TFL has effect on the contact parameters especially at the higher operating temperature assumed (i.e. 150 °C), by producing a larger real 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, TFL is near to the melting state or molten at the small vicinities of the contact spots of the real contact area.