**3. Results**

#### *3.1. Changes in Pass Load, Corrected Load, and Weld Load*

Speed ramp up time had an influence on the pass load, corrected load and weld load of grease X and Y (see Figure 3). As shown in Figure 3A, the pass load and corrected load increased with an increase in ramp up time, they were in power-law relationship for grease X. A similar trend was observed for grease Y however the power law relationship was weaker compared to grease X (see Figure 3B). As shown in Figure 3C, the weld load for grease X was 7848 N, and the grease Y had a lower weld load of 6082 N, at the ramp up time of 0.15 s. At higher ramp up time of 0.25 s, that is a tenth of second delay in motor speed, the grease X and Y had the same weld load of 9810 N. Grease X and Y had passed maximum load of 9810 N in the four-ball tester at a speed ramp up time of 0.95 s.

**Figure 3.** Influence of speed ramp up time on corrected load, pass load and weld load for grease X and Y. A correlation between speed ramp up time and load (corrected load and pass load) for grease X (**A**) and grease Y (**B**), and the changes in weld load due to ramp up time for grease X and Y (**C**). All the measurements were in duplicate.

#### *3.2. Changes in Friction Coefficient*

Friction coefficient for the greases was in the range of 0.04 to 0.07, and it was affected by the changes in corrected load driven by changes in the speed ramp up time (see Figure 4). As shown in Figure 4A, the friction coefficient increased and then decreased before reaching a stable plateau. The average friction coefficient for grease X and Y decreased as there was an increase in corrected load, that was driven by an increase in speed ramp up time (see Figure 4B).

**Figure 4.** Influence of speed ramp up time on friction for grease X and Y. Real time changes in the friction profiles for grease X (**A**) and the relationship between average friction coefficient and corrected load due to an increase in ramp up time (**B**). All the measurements were in duplicate.
