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TitleS&T Campaign: Sciences for Maneuver

Energy and PropulsionDistribution and Transfer

Stephen Berkebile, Ph.D., (410) 278-9547, stephen.p.berkebile.civ@mail.mil

Brian Dykas, Ph.D., P.E. (410) 278-9545, brian.d.dykas.civ@mail.mil

SCM 006

Tribology and Lubrication Science for High-Performance Power Transmission

Research ObjectiveIncrease our understanding of the physics and chemistry of extreme lubrication conditions and limiting failure mechanisms in power transfer interfaces to enable robust vehicle drive trains with increased power density

Challenges• Innovative approaches are needed to create material

and tribological solutions for high performance and extreme lubrication conditions (starved lubrication, loss of lubrication, high contact pressures, high relative surface velocities)

• In situ measurement of lubricating fluid film and interfacial physics and chemistry remain elusive

• Modeling is multiscale and complex– High-velocity, high-pressure and high-

temperature solid-solid and solid-fluid interfaces

– Scuffing, thermal softening, wear and oxidation degradation on metallic surfaces

– Integration of chemical models

Elastohydrodynamic lubrication contacts are difficult to observe with in situ methods.

ARL Facilities and Capabilities Available to Support Collaborative Research

• High-speed ball-on-disc tribometer with a wide range of contact conditions (relative surface speeds up to >30 m/s, large range of slide-to-roll ratio, skew, load)

• High-temperature pin-on-disc and pin-on-flat tribometer• High-speed bearing rigs• High-speed gear rigs• Scanning Auger electron spectrometer• Laser scanning confocal microscope • High temperature (1000°C) hardness measurement• Ambient-sampling mass spectrometer• High Performance Computing resources• Rotorcraft Propulsion Laboratories (ARL Extended)

Complementary Expertise/Facilities/ Capabilities Sought in Collaboration

• Engineered surface structures, thin solid films, functional coatings, modified surface chemistry, nanoscale or colloidal lubricant additives, and novel lubricant chemistries with potential to increase load carrying capacity, reduce friction under high loads, or increase operation under starved lubrication conditions

• Complex models that can incorporate the large range of scales involved and relevant physics and chemistry

• Improved models of relevant portions of the tribological contact and failure modes for integration into a multiphysics model

• In situ measurement techniques to understand active chemical and physical phenomena in operating power-dense contacts

Loss-of-lubrication in steel gears leads to rapid material failure through flash heating, oxidation, and adhesive wear.

100-400 µm

High-speed tribometer can measure a wide range of tribological conditions relevant to high speed contacts. Lubricant properties can be extracted, and

starved lubrication scenarios can be explored.

0 200 400 600 800200

400

600

800

1000

1200

Tem

pera

ture

(°F)

Time (s)

Baseline Point 0.5 Point 1 Point 2 Run-in Argon purge

0 200 400 600 8001E-9

1E-8

1E-7

1E-6

Pres

sure

(Tor

r)

Time (s)

2 17 18 32 44CO2

OH

H2

H2O

O2

0 20 40 60 80 100

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Time (s)

Trac

tion

coef

ficie

nt

High Sliding(dry)Low Sliding(dry)High Sliding(oil film)Low Sliding(oil film)

Low slidingHigh sliding

Silicon nitride and steel undergo a high speed

tribochemical transition that results in low friction and wear.

After running in Superfinished (ISF)

Initial

As ground Superfinish A Superfinish B