Abstract
Rolling contact fatigue phenomenon was investigated on unfilled PEEK and on three different PEEK composites: 10% carbon micro-fiber, graphite and PTFE filled matrix, 30% carbon micro-fiber filled matrix, 30% glass micro-fiber filled matrix. For this aim, roller-shaped specimens were machined from extruded bars of these materials and subjected to rolling contact tests at different contact pressure levels by means of a four roller machine. Contact pressure-life diagrams and wear rates were so obtained and compared, highlighting a relationship with monotonic and hardness materials properties. Microscopic observations of contact surfaces and transversal section of the specimens also allowed observing the damage mechanisms occurred in the materials tested and the effects of the filler. In particular way, deep radial cracks appeared on unfilled PEEK, while spalling and delamination phenomena where found on composites. Diffuse microcracks were found at the filler-matrix interface of the composites specimens, confirming that the fatigue life of these materials is essentially determined by the crack propagation phase, also under rolling contact loading.
Highlights
PEEK based composites are innovative materials, obtained by introducing different filler typologies in the thermoplastic resin matrix, maintaining the ease of processing and lower cost associated with thermoplastics manufacturing
Even more unknown is the behaviour of these materials when they are subjected to a rolling contact loading, some promising applications regard components where this loading condition can be present, like bearings, gears, human prostheses and implants [6, 7, 8]: while tribological behavior of polymers and in particular PEEK composites has been intensively studied [9, 10, 11, 12, 13], rolling contact fatigue has
Four materials, supplied by Ensinger Italia, were examined in this work, : unfilled grade 450G PEEK (NEAT), having glass transition temperature Tg=143 °C and melting temperature Tm=343°C; PEEK filled with 10% carbon micro-fibers, graphite and PTFE (PVX); PEEK filled with 30% carbon micro-fibers (CF30); PEEK filled with 30% glass (GF30) micro-fibers
Summary
PEEK based composites are innovative materials, obtained by introducing different filler typologies in the thermoplastic resin matrix, maintaining the ease of processing and lower cost associated with thermoplastics manufacturing. Most common filler typologies are carbon and glass short fibers, PTFE and graphite particles [1]; they allow enhancing specific properties as static and fatigue strength, resistance to creep and wear, mechanical and chemical stability, rigidity and toughness [2]. PEEK composites are suitable for several applications in different industrial sectors, like aerospace, automotive, electrical, biomedical. Despite their increasing diffusion, the mechanical behaviour of these materials has been not fully understood, especially under cyclic loading: fatigue damage evolution and fatigue strength depend strongly on microstructure and manufacturing process [3]. Even more unknown is the behaviour of these materials when they are subjected to a rolling contact loading, some promising applications regard components where this loading condition can be present, like bearings, gears, human prostheses and implants [6, 7, 8]: while tribological behavior of polymers and in particular PEEK composites has been intensively studied [9, 10, 11, 12, 13], rolling contact fatigue has
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