The traditional classification of abrasive wear into two-and three-body, high and low stress, open and closed etc. does not recognise the essential importance of particle motion, which is better described as either sliding or rolling. Abrasive wear tests with free abrasives can produce either type of motion, depending on the test conditions. The widely-used dry sand rubber wheel test often produces both motions over different areas of the sample. The more recent micro-scale abrasion test tends to favour one or the other over most of the wear scar area. Analytical models can be developed which allow the dominant particle motion to be predicted, and mapped using readily accessible parameters. In erosive wear, particle motion can also be important; recent work suggests that particle rotation is imparted in some types of erosive wear test, and that it may be responsible for the differences in wear rate found in tests under nominally identical conditions with different designs of apparatus. It is suggested that in the use of laboratory abrasion and erosion tests, and in the analysis of practical instances of wear by hard particles, close attention should be paid to the nature of particle motion, since this will influence both the dominant wear mechanisms and also the wear rates.
