科研之友
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摘要
The functional use of polymers is often limited by polymer wear debris particles. This motivates research on the microscopic origin of such debris. The effects of individual hard asperities on the wear of a polymer surface can be tested in micro-scratching experiments. Based on micro-scratching with conical tips, %26quot;wall%26quot; formation and low-cycle fatigue wear at scratch intersections have been suggested to constitute a major source of debris particles. This proposition and other mechanisms of wear debris generation have been investigated in the present work on polyethylene terephthalate (PET). PET is a ductile polymer for which significant debris generation due to low-cycle fatigue may be expected. A micro-scratcher with a silicon cubic corner tip and different attack geometries were used. A variety of continuous scratching track patterns and repeated cycling of these patterns with up to 40 passes were explored to investigate effects at both, scratch intersections and end-of-track points. The micro-scratch patterns on PET were characterized with scanning electron microscopy and atomic force microscopy. Lumpy corner protuberances, known to occur in PMMA at scratch intersections, have not been observed for PET. While the formation of %26quot;walls%26quot; at intersections has been confirmed, no wear debris is generated and the %26quot;walls%26quot; appear to be diminished with increased cycling. Instead, the repeated compression and merger of end-of-track pileups at points of directional change result in long extrusions of PET debris chains. This debris generation mechanism may depend on the geometry of the tip and may be least significant with cylindrically symmetric, conical tips. Under the experimental conditions explored, the debris chain extrusions appear to be the dominant sources of wear debris particles. A sideward component of motion in the directional change at an end-of-track point favors the severing of an extrusion. The severing results in detached debris clusters that can indeed be observed for PET in the vicinity of end-of-track points. The number of merged PET particles in a debris cluster tends to be equal to the number of scratch track passes before the detachment of the extrusion.
- 出版日期2013-8
