Qualifying an On-Line Diagnostic and Prognostic Sensor for Fixed and Rotary Wing Bearings and Gears

Karen Cassidy, PhDIEEE Aerospace ConferenceBig Sky, MT - March 2008

Abstract

A sophisticated, mature on-line sensor that provides real-time status of bearing and gear health, and monitors fault initiation, progression, and remaining useful life is qualified for field use. The technique is a continuous, full-flow measurement of metallic particles in the lubrication system using an inductive field that quantifies the time-dependent release of wear debris observed during failures. Multiple sources of data are used to support the qualification process including component rig tests, ground-based engine tests, filter debris analysis, and operational data. This paper outlines the qualification process including establishing limits for early warning of fault indication, and guidelines for in-service monitoring of aircraft engines and helicopter transmissions. The primary condition indicators are critical mass loss and rate; also particle size and count are supplemental indicators. Prognostic algorithms have been developed to set warning and alarm limits, and validated by aircraft OEMs and DOD agencies.

Outline

• Introduction• Prognostics research• Theories

- Bearing failure behavior - Prediction of remaining useful life- Alarm limits

• Test data- Component rig tests (bearing, gear)- Propulsion system tests (engine, transmission)- In-service aircraft qualification

• Summary

Introduction

• Purpose: Diagnosis and prognosis of bearing and gear failure for aircraft applications- Aircraft gas-turbine engines- Helicopter engines, transmissions and gearboxes

• Goals of condition monitoring:- Assess the current condition of machinery components- Determine severity of damage- Predict remaining useful life

Stranded SeaKing Helicopter

Can we fly home safely?

Bearing Prognostics Research

• US Air Force Research Laboratory (AFRL/PRTM, Dayton) is working on engine bearing prognostics

• GasTOPS and AFRL have collaborative R&D program for bearing prognostic methods development - Theoretical models of bearing remaining useful life- On-line oil debris monitor (ODM) sensor data - Wear debris analysis using x-ray fluorescence

• Goal: To predict the remaining life of rolling element bearings under conditions experienced by the main-shaft bearings of an advanced military gas turbine engine

Oil Debris Sensor

• On-line full-flow inductive sensor fitted in lube oil line

• Detects 100% of particles above minimum particle size

• Measures number, size, mass of ferrous & non- ferrous debris

• Detects spall initiation, progression, rate• Can be used to quantify damage severity

and remaining useful life

In-Service Aircraft ODM Applications

• F22 Raptor: F119 engine• Joint Strike Fighter: F135 engine & lift fan• Eurofighter Typhoon: EJ200 engine• SeaKing Helicopter: engine and gearbox• Pilatus PC12: PWC PT6A engine

F22 F35 Typhoon Sea King PC12

Surface Fatigue Failure

• Failure mechanism that ODM technology designed to monitor is common failure mode for bearing & gears

• Rolling contact fatigue manifested as spalling phenomena; can be initiated on surface or subsurface- Surface initiated spall from poor lubrication or pitting- Subsurface initiated spall is associated with stress

concentrations • Material surface is subjected to static and dynamic loading

- Up to a certain critical spall size, dynamic loading is stable • Spall detection and diagnosis has been studied by many

researchers; still a lack of reliable prognostic methods to predict the remaining useful life

Theory: Regions of Spall Progression

Mcrit

RUL

EndInst.

•L10 theories

•Probabilistic

•Change bearing

•Extend usability

•Slow, stable

•Load static + (stable) dynamic

•Increase mass, temp, vibration

•Duration varies

•Fast, unstable

•Vibration => end

•Critical stress, spall length, vib

•End useful life

Surface Fatigue Failure: Cause and Effect

• What factors may directly affect spall propagation rates?- Load (stress), RPM (variable, operator controlled)- Material properties, component geometry, lubrication properties

• What are direct symptoms?- Spalling: release of component wear debris into lube oil- Increase in vibration, dynamic stresses, and temperature

• What are key condition indicators?- Wear debris: mass, rate, size, count & composition- Vibration

Test Data • Bearing and Gear Component Rigs

- GasTOPS and National Research Council – small scale bearing rig- GasTOPS and Pratt & Whitney – full scale aircraft bearings- AFRL 40mm bearing rigs - test bearing materials and fluids- NASA Glenn Research Center – bearing & gear component rigs - Spur Gear component rig - truck transmission model

• Engine & Transmission Test Stands - NASA OH-58 Kiowa helicopter – main rotor transmission test stand - CAF Sea King helicopter – engine & gearbox test facilities- DTSO Bell 206 helicopter – main rotor transmission test stand- F22 Raptor - F119 engine pre-flight tests - AH-64 Apache helicopter - transmission test stand

• In-Service Aircraft Qualification- Eurofighter Typhoon / EJ200- Pilatus PC-12 / PWC PT6A Engine

Characteristic Debris Accumulation

0 20 40 60 80 100 1200

2000

4000

6000

8000

Elapsed Time [% ]

Num

ber o

f Par

ticle

s

> 500 um

> 400 um

> 350 um

> 300 um

> 250 um

> 200 um

> 700 um

*

Particle Size

Ref: JL Miller (Pratt & Whitney) and D. Kitaljevich (GasTOPS Ltd.), In-line Oil Debris Monitor for Aircraft Engine Condition Assessment, IEEE 2000

AFRL Bearing Test Program

• 40 mm bearing test facility in Dayton, OH• Bearing life and spall propagation tests on

materials, lubricants, load/stress levels• Life tests

- GasTOPS ODM used to quantify effect of variables on bearing life

• Spall propagation fests- Uses failed bearings from life test to explore

remaining useful life- Measure spall propagation rate for stress in

250-350 ksi range- Measure effect of load and stress on rate- ODM sensor characterizes damage

progression; correlated to mass loss

0

20

40

60

80

100

120

140

160

180

200

0 100 200 300 400 500 600 700 800 900 1000

Elapsed Time(mins)

Mas

s Lo

ss(m

g)

Outer race 278ksi Outer race 278ksi Inner race 364ksi Outer race 314ksiOuter race 300ksi Outer race 300ksi Outer race 250/278ksi

278 ksi278 ksi

250 ksi

300 ksi300 ksi

314 ksi

364 ksi

Data from an inductive sensor can be processed to obtain prognostic information.

Critical Mass Rate

AFRL Rig – Effects of Load on Prognostics

Critical Mass Loss

52100 steel

Ref: Forster, Thompson, Toms, Horning, ISHM 2005

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140 160Cycles (Millions)

Mas

s Lo

ss(m

g)

52100 278 ksi

52100 278 ksi

52100 250 ksi

M50 NiL 350 ksi

M50 NiL 300 ksi

52100 278 ksi

AFRL Rig with M50 NiL Propagation Rates

Affect of Stress on Rate During Operation:

250 ksi at 1820 Min. Plus 490 Min. at 278 ksi

Ref: Forster, Thompson, Toms, Horning, ISHM 2005

Reduction in Debris Generation Rate with Reduction in Stress after Damage Rate has Accelerated

0

20

40

60

80

100

120

140

160

180

0.0 10.0 20.0 30.0 40.0 50.0Cycles (Millions)

Mas

s Lo

ss(m

g)

Operator reduced stress to 250ksi

Stress 278ksi

Mass loss rate increase

Projected damage if stress remained at 278ksi Influence rate

Ref: N. Forster & K. Thompson (AFRL-PRTM); A. Toms & S. Horning (GasTOPS), Assessing the Potential of a Commercial Oil Debris Sensor as a Prognostic Device for Gas Turbine Engine Bearings, ISHM 2005

NASA Glenn Test Rigs

• Goal to quantify debris generation during bearing & gear wear• Measured debris progression, counts, mass, particle size • Test Methods: Hybrid bearing, tapered roller bearing, spur gear,

spiral bevel gear, OH-58 helicopter transmission, and others• Quantify failure effects in components and complex systems

ODM mass during spur gear failure

Ref: Dr. Paula J. Dempsey, Dr. David G. Lewicki (ARL) and Harry J. Decker (ARL), NASA Glenn Research Center, Cleveland, OH

Spur Gear Rig Test

0

10

20

30

40

50

60

70

80

90

85 90 95 100

Time on Test (hrs)

OD

M M

ass

(mg)

XRF of debris

F119 Engine / F22 Aircraft Pre-Flight Tests

• New engine run on test stand• ODM detected initial damage• Bearing replaced, no secondary

damage occurred. Found that: - Damage due to assembly error- Bearing highly over-stressed

• Debris rate returned to normal

In-Service Aircraft Qualification

• Application: Eurofighter Typhoon / EJ200

• Condition Indicators- Total Mass Accumulation Level and Rate- Large Particle Accumulation Level and Rate

• EJ200 Debris Database- 3 Bench Test Engines- 7 Flying Development Engines

• Validation- Bearing rig tests used for initial condition indicator limits- Correlated ODM mass rate to legacy debris monitor limits- Database of wear debris data (ODM, chip detector and oil filters) of

healthy and faulted engines used for ongoing limit verification

In-Service Aircraft Qualification

• Application: Pilatus PC-12 / PWC PT6A Engine

• Condition Indicators- Level 1 Threshold - total particle count threshold- Level 2 Threshold - short term particle count rate- Level 3 Threshold - medium term particle count rate

• Validation- Normal engine oil contamination rates evaluated in test cells

• Over 100 Production Engines and 50 repair/overhaul engines- Over 350 in-service aircraft

AH-64 Apache Helicopter Transmission• Application: Naval Air Station at Patuxent River

Helicopter Transmission Test Facility• Condition indicator: total mass

- Right nose gearbox sensor detected high quantity of wear debris• Damage verification

- X-ray debris analysis showed M50 in right nose gearbox, 100 x left side- Teardown showed one roller over 50% of contact surface had spall;

early signs in other rollers and race

Summary

• Bearing & gear failures complex and affected by multiple variables - Load, speed, & material properties affect the failure rate- Rate may be decreased by changing operation during failure event- Need prognostic information to aid in making operation decisions

• ODM sensor provides quantitative data to support diagnostics andprognostics for bearings and gears- 15 years of condition indicators verified by military, government & OEMs- Verification of parameters including critical mass loss & mass rate - Validated by engine tear-down and x-ray debris analysis

• US Air Force and GasTOPS collaborating on research to provide prognostics, prediction of remaining useful life on aircraft engines

Contact Information

Karen Cassidy, PhDPresident, GasTOPS Inc. Application Center, Pensacola, FLKcassidy@gastopsUSA.com, Tel: (850) 478-8512, www.gastopsUSA.com

Nelson Forster, PhDMechanical Systems Branch, AFRL Wright-Patterson AFB, Dayton, OHNelson.Forster@WPAFB.AF.MIL, Tel: (937) 255-5568

Duka KitaljevichVP Product Sales, GasTOPS Ltd., Ottawa, ONDkitaljevich@gastops.com, Tel: (800) 363-8658, www.gastops.com