NCSX

Friction Coating Peer Review

March 16, 2007

NCSX

March 16,2007 2

NCSXIntroduction

• WBS 14 will use some revision of the 0.5” McGinnis/Williamson shim (see left) between modular coils

• Friction-encouraging and insulating properties are needed in these shims

March 16,2007 3

NCSXTesting Setup

• A traditional tension/compression testing machine has been configure to pull “double shear” combinations.

• Side rams allow the application of normal (transverse) loads

March 16,2007 4

NCSXTypical Test Combination

• A 0.38” thick x 1.00” wide center element receives the application of friction-encouraging medium (if any)

• Wider (1.50”) side plates are added to each side of the center element with an axial overlap of 1.0”

• The normal/transverse load (10 kip max) is added at the center of the overlap areas (2 in**2 total area)

March 16,2007 5

NCSX2nd Design Test Combination

• The original design called for a maximum loading of 10 kip over the available area

• A choice was made to reduce the test area rather than upgrade the test rig after analysts began predicting 17 ksi loading needs.

• The lessened area results in 10 kip max applied on two series ½ in**2 areas (1 in**2 total)

March 16,2007 6

NCSXEarly Test Observations

• File 070129Summary.xls lists the outcomes of 21 trials– G-10 on SS (ambient,1trial) m=0.18– SS on SS (amb/cold, 4 trials) m=0.21-0.26– SS/diamond/SS (amb/cold, 16 trials) mavg=0.53

• Many combinations

• The fundamental failure in the diamond-assisted trials was the tearing of the seated diamonds along/through the surface of the stainless– The tear-outs look like aerial views of perfectly plowed fields– This may be the functional limit of the material

March 16,2007 7

NCSXEmergent Bad News

• The nickel-bound CT-provided diamond coating could not survive LN2 dunk testing– The coating bubbled and flaked

off

• The epoxy in the epoxy-bound diamond coating seemed to becomes a lubricant after the joints’ first “give” at ultimate slip load

March 16,2007 8

NCSXBetter Product

• Ceradyne’s EKAgrip10 was deposited onto 4 mil shim stock and tested.– CoeffFricton Mu’s of 0.576 and 0.542 were obtained at

loadings of 6 ksi and 9.5 ksi respectively.– Survived the dunk test without incident– Diamond size is small (~0.4 mil); nice for ass’y crews

March 16,2007 9

NCSXReally Better Solution

• Plasma-sprayed alumina emerged as the big winner– 1) Mu's from 0.50 to 0.71 at pressures from 6 ksi to 17 ksi– 2) Infinite electrical isolation to 45 ksi compressive

loading (at 9 volts)– 3) The ability to "give" as the test set-up (always

imperfect) aligns itself while the slip load is applied to failure

– 4) The ability to maintain its peak mu (and load) during slip to failure. The diamond solutions fall in load capacity after slipping starts.

March 16,2007 10

NCSXAlumina - Linear Relationship?

Coefficient of Friction - Alumina

0.45

0.5

0.55

0.6

0.65

0.7

0.75

5000 7000 9000 11000 13000 15000 17000 19000

Transverse/Normal Loading (PSI)

App

aren

t Mu

Alumina

w/o binderw/o binder

Nice outlier

March 16,2007 11

NCSXAlumina Images

March 16,2007 12

NCSXNext Steps

• Finish scan of alumina with & without binder

• Perform cycle testing at ZZ% (90?) of 17 ksi slip load– Need chit (# cycles, % of slip)

• Investigate/Procure on-site plasma spray rig

• Others?