The role of crack resistance parameters in polymer wear

When polymers slide against a smooth metal counterface wear occurs via a combination of adhesive and fatigue processes. A relationship is derived to predict such wear rates from measurements of the fracture mechanics parameters characterising fatigue crack growth. The predictions are directly confirmed from wear and crack growth measurements with polymethylmethacrylate (PMMA) and polyethersulphone (PES) in different organic liquids. Supporting evidence is provided from wear and crack growth data on thermoplastics and on epoxy resins of varying cross-linking densities. In abrasive conditions against rough metal counterfaces, the most important material property controlling wear is the fracture toughness, KIc. A simple analysis suggests that the wear rate should be proportional to 1/KIc2 and this is confirmed experimentally for PMMA and PES in organic liquids and for cross-linked epoxies.