&RQH3HQHWUDWLRQYV5KHRPHWHU3HQHWUDWLRQ1

**Figure 7.** Cone penetration vs rheometer penetration for various greases witha5N normal force.

**Figure 8.** Comparison of (**a**) yield stress and (**b**) crossover stress with rheometer penetration at a force of 5 N for various grease types.

Figure 7 shows that there is a general positive correlation between cone penetration and rheometer penetration; however, different greases show slightly different behaviors. This means that using a rheometer to assess the change to a particular grease's consistency would be a valid approach, but comparing two different greases to each other with this approach would not. Using a linear correlation between cone penetration and rheometer penetration in this case would likely lead to excessive error and it is, therefore, recommended that this approach not be taken if one is interested in comparing the consistency of different greases.

Results shown in Figure 8 are perhaps even more indicative that a correlation between rheometer penetration and the other tests that should not be used in practice since a meaningful trend cannot be established. Nevertheless, a comparison of the other tests yielded interesting results.

#### *4.4. Oscillatory Test Results*

The next results shown compare the oscillatory test results to each other and to cone penetration results.

Figure 9 shows the relationship between yield stress and crossover stress for the greases selected. As expected, based on another study [8], there is a general positive correlation between these two measurements. However, there is one particularly notable cluster of data points associated with the LiC3 grease. These points were found to completely deviate from the expected trend and indicate that there is some important discrepancy between yield stress and crossover stress.
