Wear processes in polymer implants - Durability and Reliability of Medical Polymers - page 145

means that H , which can be difficult to measure in some soft polymers and
elastomers, can be eliminated. For the polymers, k is usually in the range
10 -6 to 10 -3 mm 3 n -1 m -1 (hutchings, 1992). Figure 7.6 shows a UhmWpE
knee component removed after revision surgery displaying signs of both
abrasive and adhesive wear.
7.3.2 Abrasive wear
abrasion is a form of cohesive wear that can occur in two modes, viz. two-
body and three-body abrasive wear. Two-body abrasion refers to a hard
rough surface, of which the asperities 'plough' through the relatively stiffer
counterface. The surface penetrations cause localised plastic displacement
and indentations. Three-body abrasion refers to hard particles between two
sliding surfaces, ploughing through at least one of the surfaces. The two
are not mutually exclusive, as two-body abrasion can often lead to three-
body when hard wear particles are detached from a surface. abrasive wear
is dependent on the bulk properties of the materials and the geometry of
￿ ￿ ￿ ￿ ￿ ￿
7.6 A UHMWPE knee component after revision surgery, owing to
pain and instability, displaying signs of both abrasive and adhesive
wear (Gomez-Barrena et al. 2008) (reprinted by permission of Taylor
& Francis Group, http://www.informaworld.com).