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A SEMINAR REPORT ON

FATIGUE GAILURE OF HELICAL GEARS

BY

 MR. JAMADAR IMRAN M.

ROLL NO. -102090005

UNDER THE GUIDANCE OF

 Prof. RATHOD

DEPARTMENT OF MECHANICAL ENGINEERING

2010-11

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ContentsContents

1. Introduction

2. Case study 

3.Experimental procedure

4. Results and discussion

5. Conclusion

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Introduction

Failure analysis of helical gear used in aFailure analysis of helical gear used in a bus gearbox bus gearbox

History History--Gear has been in use for 3 yearsGear has been in use for 3 years MaterialMaterial--AISI 8620 Steel AISI 8620 Steel

Evaluation methodsEvaluation methods--Visual inspection, Visual inspection,

photo documentation, chemical analysis,photo documentation, chemical analysis,micro hardness measurement,micro hardness measurement,metallographic examinationmetallographic examination

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TYPES OF GEAR FAILURESTYPES OF GEAR FAILURES

FatigueFatigue

ImpactImpact

FractureFracture  Wear Wear

Stress RuptureStress Rupture

Surface contact fatigueSurface contact fatigue-- pitting,pitting, spallingspalling

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CAUSESCAUSES

Poor design of gear setPoor design of gear set

Misalignment of gearsMisalignment of gears

OverloadsOverloads Subsurface defects in internal areasSubsurface defects in internal areas

Use of incorrect materials and heatUse of incorrect materials and heat

treatmenttreatment

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CASE STUD Y CASE STUD Y 

Bus with problem with its transmissionBus with problem with its transmissiongearboxgearbox

Gearbox running hot with excessiveGearbox running hot with excessive vibrations vibrations

Problem was with the fourth speed driveProblem was with the fourth speed drivegeargear

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General appearance of General appearance of 

failed helical gearfailed helical gear

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Parameters Value

Number of teeth

helical gear 

36

Helix angle 150

Module, normal (mm) 4

Pitch circle diameter 

(mm)

150

Outer diameter (mm) 158

Face width (mm) 42

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Spectrum analysis and microSpectrum analysis and micro

hardness measurementhardness measurement

Result revealed that material wasResult revealed that material was

 AISI8620 carburized steel AISI8620 carburized steel Core hardness =439HV Core hardness =439HV 

Surface hardness=550Hv Surface hardness=550Hv 

Case depth=0.63mmCase depth=0.63mm Microstructure consist of Microstructure consist of martensitemartensite andand

retained austeniteretained austenite

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MicrostructureMicrostructure

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 V isual inspection V isual inspection

No. of adjacent teeth failed due to fatigueNo. of adjacent teeth failed due to fatigue

 A triangular piece of the teeth had broken A triangular piece of the teeth had broken

off off  Crack initiation and bench marks can beCrack initiation and bench marks can be

seen by necked eyesseen by necked eyes

Origin of crack was at the pitch lineOrigin of crack was at the pitch line No corrosion media were found onNo corrosion media were found on

fractured surfacefractured surface

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Photograph of failed gearPhotograph of failed gear

toothtooth

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PittingPitting

Destructive pitting and spalling were alsoDestructive pitting and spalling were alsonoted on loaded side of each toothnoted on loaded side of each tooth

D

estructive pitting appears as much largerD

estructive pitting appears as much largerpits than initial pittingpits than initial pitting

In spalling pits are large in diameter andIn spalling pits are large in diameter andquite shallow quite shallow 

Spalling is caused by excessively highSpalling is caused by excessively highcontact stresscontact stress

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Photograph of Pitted gearPhotograph of Pitted gearteethteeth

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SEM and EDX ExaminationSEM and EDX Examination

SEM inspection to identify cause of fatigueSEM inspection to identify cause of fatiguecrack initiation and propagationcrack initiation and propagation

RiverRiver--like pattern could be seen inlike pattern could be seen inpropagation zonepropagation zone

EDX attached to fractured surface toEDX attached to fractured surface todetermine gear chemistry determine gear chemistry 

To verify presence of any other associatedTo verify presence of any other associatedcomponentscomponents

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Crack initiation andCrack initiation and

propagationpropagation

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ConclusionConclusion

Composition, microstructure, hardnessComposition, microstructure, hardnessand case depth found satisfactory and case depth found satisfactory 

Fractographic features indicated thatFractographic features indicated thatfatigue was the main failure causefatigue was the main failure cause

Misalignment was observed which hasMisalignment was observed which hascaused failurecaused failure

Formation of destructive pitting andFormation of destructive pitting andspalling at one end was due to loadspalling at one end was due to loadconcentration at that areaconcentration at that area

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TH ANK TH ANK 

 Y OU!

 Y OU!