Tribological fatigue failure of the machined PEEK shaft was investigated through the one-point type rolling contact fatigue test between a PEEK shaft and an alumina ball, in order to explore fatigue fracture mechanism of frictional parts working at high frequency in various mechanical elements. Due to Hertzian contact of cyclic compressive stress, the subsurface crack occurred within approximately 300 μm depth from thesurface and propagated along the rolling direction. After that, the subsurface crack propagation direction changed toward the surface. The flaking occurred on the raceway of the PEEK shaft when the subsurface crack reached to the PEEK shaft surface.

The growth of flaking as tribological fatigue failure in PEEK was investigated through the one-point type rolling contact fatigue test between a machined PEEK polymer shaft and an alumina bearing's ball. Due to Hertzian contact of cyclic compressive stress, the subsurface fatigue cracks in the PEEK shaft propagated in rolling and axial directions. When the rolling fatigue life of the PEEK shaft reached 106 fatigue cycles, many narrow angled cracks occurred in the near-surface of the rolling track without flaking. On the other hand, when the flaking ocuurred on the PEEK shaft before 106 fatigue cycles, semicircular surface and subsurface crack propagations were observed. From these observations, it was found that micro-flaking occurred due to the linkages between subsurface and surface cracks. Flakingdeveloped due to the accumulation of these micro-flakings.

Abstract. Subsurface fatigue cracks under rolling contact area of the PEEK shaft against an alumina bearing's ball were investigated for application of frictional part in mechanical element in special situations such as chemical environments. In order to explore the flaking process of the PEEK shaft, the rolling contact fatigue tests were carried out by using a one-point radial loading rolling contact machine. The flaking occurred on the rolling track of the PEEK shaft at approximate 4×10 5 fatigue cycles. The subsurface fatigue crack propagation was investigated by using 2.5-Dimension layer observation method. The flaking was caused by the propagations of surface cracks and subsurface shear cracks, and the flaking shape was half-ellipse. Moreover, beach marks as fatigue crack propagation in the flaking were observed.

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