Three-body abrasion testing

The abrasion resistance of plastics can also be determined by the ASTM G 65 dry sand rubber wheel test (7), vriiich is shown schematically in Figure 2. The three-body abrasion produced by this type of test is simitar to that produced by rubbing plastic on a rigid surface with hard particles in the faying surface, but it is probably faster and easier to perform. Test times can be as short as one minute. This test can also be conduct immersed in a slurry (8) if this better simulates the system of interest. 

Somewhat similar is the abrasive tape test for plastics (9). This test rubs plaques of plastic against a contact roll covered with bonded abrasive tape. Mass loss in a prescribed amount of contact with the abrasive tape is the metric. The reference material for the test is wrought zinc. This test simulates severe abrasion. This testing standard contains a second procedure that rubs flat plastic specimens against flat plates covered wifti aluminum oxide particles. This is a three-body abrasion tribosystem as opposed to the two-body system used in the tape test These two tests and the Taber Abrasor test compete with each other and none is considered to be a reference abrasion test for plastics. 

The work of Soemantri et al. [76] is presented in Fig. 6.15. Figure 6.15a shows the results of the two-body abrasion test, whereas Fig. 6.15b pertains to three-body abrasion. This work was carried out with commercially pure Al and Cu. As can be seen from Fig. 6.15, the wear rate of Cu is independent of temperature for two-body abrasion. Similarly, the two-body abrasive wear rate of Al is also nearly constant even though an increase in wear rate is noted at 323 K. In contrast, the wear rate of Cu increases with increase of temperature during three-body abrasion. However, for Al, the three-body... 

Effect of test temperature on abrasive wear rate (a) two-body abrasion (b) three-body abrasion [76]. 

For testing dental restorative materials, many regimes exist that use similar principles to those described for assessing toothpaste abrasivity. These tests may be conducted under conditions of two-body or three-body wear [25], i.e. focussing either on attrition or abrasion. Two-body tests for restorative materials either use human enamel [26] or a hard material, such as alumina [27] or steatite [28], as the abrader. For three-body tests, an abrasive medium, such as toothpaste slurry [29, 30], or an abrasive food, such as rice or millet seeds [31,32], is typically used. These test methods are usually not truly representative of the oral environment rather, they are designed to assess the wear resistance of restorative materials under extreme conditions. 

---