Degradation of UHMWPE and POM due to the tribological action against stainless steel and alumina.

Author(s)

Carlos Henrique da Silva

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2003-07-01

Examining board members

Amilton Sinatora; Sebastião Vicente Canevarolo Júnior; Paulo Roberto Mei; Marcelo de Carvalho Reis; Deniol Katsuki Tanaka

• Advisor: Amilton Sinatora

Abstract

The present investigation aims to study the degradation of polymeric materials resulting from the sliding contact against rigid bodies. The effect of some tribological influences, such as the applied load, the sliding velocity, the surface roughness and the counter-face material, were investigated. Experimental sliding wear tests were performed through a pin-on-disc tribometer, with the pins of polymeric material and the discs of alumina and stainless steel. The testing conditions of the wear tests encompassed three values of load (normal pressure) and three values of sliding velocity, or PV values, and three ranges of disc surface roughness. Three tests were performed in each condition. The interface temperature between the specimens, the friction force and the vertical position of the pin were monitored along the tests. The vertical displacement of the pin, resulting from the wear, was used for the determination of the polymer wear rate. The total sliding distance was of 3,500 meters. During the tests, the relative humidity of the environment was controlled to 50 ± 5 %. Analyses on the worn surfaces of pins and discs performed through scanning electronic microscopy indicated the occurrence of three wear mechanisms: abrasion (scratches), fatigue (waves) and adhesion (transfer film). In order to analyze the wear behavior of the polymer, a parameter of global severity of the contact (PVR/DD) was proposed. This parameter comprised a mechanical factor (the PV values), a topographic factor (the disc roughness) and a thermal factor (the thermal diffusivity of the materials in contact). It was possible to verify that the polymer wear depended on the level of global severity of the contact, where the major effect was due to the counterface material. It was also observed that the vertical displacement of the pin occurred not only due to the wear phenomena, but also due to the creep and the melting of the polymer, both depending on the testing condition. The creep and the melting phenomena were considered in the polymer degradation behavior, organizing the results of polymeric pin displacement in degradation maps, showing the boundaries of each observed phenomena, in function of the contact global severity. (AU)