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Keith Legg 847-680-9420
Overview of fatigue/spalling tests
HCAT Program ReviewLong Beach
April 2001
Keith Legg 847-680-9420
Findings so far
Wear - better than equal to Cr (mostly considerably better)
Fatigue - better than Cr Hydrogen embrittlement -
HVOF causes no embrittlement environmental embrittlement
under test Impact
Both Gravelometry and Whackometry show HVOF better than or equal to Cr
Rig tests F-18 pins “passed” Boeing test F-18 E/F fatigue and endurance
doing well at Messier-Dowty
Issues remaining Corrosion
C-HCAT data look good HCAT data had problems new samples being run
(Bruce Sartwell will report)
Spalling WC-Co looked good (not
perfect) WC-CoCr spalled,
especially thick coatings considerable progress
made in understanding and improving performance
Keith Legg 847-680-9420
Overview of spalling/fatigue issues
Summary of spalling issues User requirements Progress in meeting requirements - tests run Results of Tuesday evening meeting What can now be coated
Keith Legg 847-680-9420
Summary of spalling issues
C-HCAT findings WC-CoCr, 0.003” spalled above 180 ksi WC-CoCr, 0.010” spalled above 125 ksi Evidence of less severe spalling on WC-Co runouts Apparent mechanism
cracks start at surface of coating, presumably growing in tensile cycles
bifurcate or deflect at, or just above, interface when cracks join up spall occurs on compressive cycle
Data suggests WC-CoCr is generally more brittle than WC-Co, but Jerry Schell optimization suggests WC-CoCr can be made similar to WC-Co
Keith Legg 847-680-9420
Crack propagation in WC-Co (NRC/Orenda)
SurfaceSurface
InterfaceInterface BifurcationBifurcation
InitiationInitiation
Keith Legg 847-680-9420
User requirements
Commercial Typically 100 ksi, R=0.1,
thousands of cycles Maximum 170 ksi, R=0.1
Land-based military 180 ksi, R=-1, a thousand
or so cycles (Air Force) 240 ksi, R=-1, occasional
hard landings, (Air Force) Carrier-based military
Pins 235 ksi, R=-0.5, launch loads, 2,250 cycles, (OEMs)
Pistons 240 ksi, R=-1, occasional hard landings, (NAVAIR)
Yield stresses:4340M = 220 ksi 300M = 230 ksi A100 = 235 ksi
Yield stresses:4340M = 220 ksi 300M = 230 ksi A100 = 235 ksi
OEMs 0.003” typical
Airlines 0.010” or thicker for MRO
Repair Depots 0.010” or thicker for O&R
Keith Legg 847-680-9420
How many parts see maximum loads?
Thousands of landing gear cylinders, axles, pins currently chrome plated
Only a few pins see anything near yield stress, and do not see full stress reversal
loads are largely shear, not bending
Only a few inner cylinders see anything near yield stress, but do see full stress reversal
large bending loads Carrier-launched aircraft
have very small safety factor
Drag brace pins
Drag braceLaunch bar
Retract actuator pins
Keith Legg 847-680-9420
Major concerns
Depots are concerned that HVOF may be accepted by OEMs and then be required in place of Cr, but that if thick HVOF does not work, they will be in trouble must be able to use thick coatings for repair repair must meet same performance criteria as thin
OEM coatings If dispense with Cr, want to dispense with all of
it do not want a little left that requires we keep Cr tanks
running
Keith Legg 847-680-9420
0
50
100
150
200
250
300
-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1
R value
Lo
ad
(k
si)
Landing gear loads and R values
10 times
Hard carrier landinginner cylinders
Hard landinginner cylinders
1 time
Land-based military
1,000 times
2,250 times
Carrier launch drag brace pins
Normal 5,000 times
Commercial pins, cylinders, axles
Max 100 times
Keith Legg 847-680-9420
Tests run since August 2000
Additional tests and detailed materials evaluations - Orenda/NRC
Famous forty - smooth bar fatigue samples coated with WC-Co
tested at high load levels (John Sauer, Phil Bretz)
interrupted testing to track cracking and spalling
Prop hub specimens high residual stress
coatings (Engelhard), fatigue testing (Hamilton-Standard); high load testing (John Sauer)
A-10 Nose Landing Gear cylinders (Hill AFB)
using newly-optimized JP-5000 WC-Co (Jerry Schell)
bending stress spalling tests (Craig Edwards, Doug Wiser)
fatigue specimen spalling tests (Jerry Schell)
F-18 E/F Drag Brace spectrum loads, including
launch loads in-progress
HVOF WC-CoCr so far withstands spectrum loads on brace and pins
Keith Legg 847-680-9420
0
50
100
150
200
250
300
-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1
R value
Lo
ad
(k
si)
Where we are now
Com
merc
ial
(last
cen
tury
)
WC-Co 0.003”, 0.010”July 2000
WC-CoCr 0.003”September 20000.010” WC-CoCrSeptember 2000
High-resid stress 0.015”WC-Co
Jan 2001
New JP-5000WC-Co
April 2001
OEM and rebuild
Carrier-basedDrag brace pinsOEM and rebuild
OEM and rebuild
Keith Legg 847-680-9420
Summary - what now looks doable
Commercial thin and thick WC-Co or
WC-CoCr Land-based military
thin and thick WC-Co, most parts, pins, etc.
except inner cylinders prone to hard landings (A-10)
Carrier-based military thin and thick WC-Co for
most components thin and thick WC-Co on
launch train components (pins, R=-0.5)
except inner cylinders
Issues remaining Do results on small
samples equate to real parts?
Inner cylinders (R=-1) not yet demonstrated
may require coating process refinement
Optimization Are there issues with
stress corrosion cracking if we use coatings with high compressive residual stress?
Can WC-CoCr be made as good as WC-Co?