## 2 Materials and Experimental Procedure
The sliding speed was set to 16 m/s, while a constant entrainment speed was chosen within \(16\pm 0.5\) m/s in order to minimize vibrations. The load was maintained at 100 N (approximately 1.3 GPa Hertzian contact stress), and oil and disk temperatures at \(125\pm 10\)\({}^{\circ}\)C. The lubricant was supplied to the contact for a running-in period of 10 min. The supply was then turned off and the experiment was continued until scuffing occurred, as indicated by a spike in COF and an observable increase in the volume of the audible sound. A set of at least five experiments was conducted for each lubricant blend. The scuffing load experiments were conducted at a constant entrainment and sliding speed with the load incrementally increased. The sliding speed was set to 16 m/s, while a constant entrainment speed was chosen within 16 \(\pm\) 0.5 m/s in order to minimize vibrations. The load was maintained for 60 s at each of 30 load stages before increasing to the next. The load stages (N) were as follows: 17.76, 28.86, 34.19, 41.51, 48.84, 58.61, 68.38, 78.14, 87.91, 100.12, 112.33, 124.54, 136.75, 151.4, 166.06, 180.71, 195.36, 212.45, 229.55, 246.64, 263.74, 285.94, 312.57, 343.66, 379.18, 419.14, 463.54, 512.38, 565.66 and 621.6. The experiment was allowed to continue until scuffing occurred, as indicated by the same criteria described previously, at which point the current load was recorded as the scuffing load. Additional details on the loss of lubrication and scuffing load procedure were reported by [PERSON], et al. [29]. One experiment was conducted for each blend. The friction mapping experiments were conducted by cycling conditions throughout a wide range of entrainment speeds from 0.35 to 16 m/s and slip from 0% to 100% at a constant load of 200 N (approximately 1.7 GPa Hertzian contact stress). During the experiment, the COF was measured while keeping slip constant and slowly ramping (gradually changing) the entrainment speed from an initial value of 16 m/s down to 0.35 m/s over a period of 90 s before ramping back up to 16 m/s over another 90 s. The slip was then stepped up to the next value of interest and the entrainment speed was ramped down and up again. The values for the slip (in %) used in this experiment were: 0.54, 1.62, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100. The final conditions witnessed by the test track were at Ue = 16 m/s and 100% slip. After completing one cycle, the process was repeated starting at Ue = 16 m/s, slip = 0.54%, until run-in of the specimen was complete. The run-in process was determined to be over when a difference in COF between subsequent cycles was less than 0.002 for each combination of entrainment speed and slip. The data in the final cycle was used to map the friction during the fully run-in state and was used to compare the various lubricant blends to the baseline oil (DoD-PRF-85734). Details on the procedure can be found in reference [30]. One experiment was conducted for each blend. A loss of lubrication condition was simulated on a pin-on-disk tribometer from Cameron-Plint. Case-carburrized AISI 9310 alloy steel was used for the tribometer specimens. As-received bulk AISI 9310 was machined to the required dimension and appropriately heat treated and case hardened to obtain a surface hardness of 60 HRC and a case depth of 0.045-0.050\".The initial contact is a line contact between a pin (6 mm diameter, 6 mm long and blended crown radius) and a disc (1 inch  
Figure 1: High speed ball-on-disk tribometer experimental setup. diameter). The specimens were reciprocated with a stroke length of 9 mm with a frequency of 6 Hz. The experiments were conducted at 100 \({}^{\circ}\)C. The first 5 min of the test was run at 20 N load as a run-in period in a fully flooded condition with a cavity filled with 1-2 mL of lubricant. The lubricant was heated to 80 \({}^{\circ}\)C and mixed prior to application. The load was then maintained at 250 N (approximately 700 MPa Hertzian contact stress) for 60 min.