Observation of Crack Propagation in PEEK Polymer Bearings under Water-Lubricated Conditions

Abstract

Radial ball bearings made of metal, ceramics and plastics are commonly used as important components in various types of industrial machinery. Due to the latest markets demands for elements capable of withstanding e.g. corrosive environment, metallic bearings are being gradually replaced by components produced from high performance engineering plastic polymers. In order to investigate the failure mechanism of polymer bearings and further improve their performance in practical applications in an underwater environment, in this research crack propagation in Poly-ether-ether-ketone (PEEK) was studied by rolling contact fatigue (RCF) testing under water. Crack propagation in the inner ring raceway surface and subsurface areas of PEEK bearings after testing was observed by a laser confocal microscope. Cracks and flaking failure were found on the bearing raceway surface. From the RCF tests results, it was found that the detected cracks could be divided into three groups: Main Surface Cracks, Semi-circular Cracks and Main Subsurface Cracks. It is concluded that flaking occurs on the inner ring raceway due to the fusion of semi-circular cracks and a main subsurface crack.

Flaking of PEEK under one-point rolling contact fatigue using Al2O3 ball

“…The test conditions of radial load and rotation speed were 90-360 N and 1200 rpm, respectively. They were the same as our previous works [9,14]. This is because the present tests were done in order to focus on the details of the fatigue fracture origin/propagation of the one-point RCF test.…”

“…Dearn et al reported that the location of the maximum shear stress depended on the friction condition and was related with the fracture of PEEK polymer gears [8]. Flaking was related to the internal fatigue cracks which were caused by cyclic shear stress below the contact surface [9]. Koike et al stated that in the RCF of the PEEKalumina ball bearings with an artificial pit, the subsurface fatigue crack ocuured at 100-200 um depth from the contact surface.…”

“…Koike et al stated that in the RCF of the PEEKalumina ball bearings with an artificial pit, the subsurface fatigue crack ocuured at 100-200 um depth from the contact surface. This means that the internal fatigue crack from an artificial pit was influenced by internal shear stress [9]. As Young's moduli of polymers are significantly lower than that of common metals or ceramics, internal stress and elastic deformation of friction area of polymers are greatly influenced by cyclic Hertzian contact.…”

“…Therefore, the behavior of the internal fatigue crack propagation in the machined PEEK elements is not well understood. The practical research on PEEK's tribological fatigue fracture in application of PEEK and ceramic parts is investigated in few studies [9][10][11].…”

Investigation of subsurface fatigue crack in PEEK shaft under one-point rolling contact by using 2.5D layer observation method

“…Meanwhile, the practical application research on PEEK's tribological fatigue fracture of the combination between PEEK plastic and ceramic part is only few studies [7][8][9]. In the previous study, we reported that the subsurface crack propagated along the PEEK shaft rolling direction in terms of fatigue failure mechanism when cyclic compressive stress was applied to the PEEK shaft [9].…”