PowerPoint Presentation: A SEMINAR REPORT ON FATIGUE GAILURE OF HELICAL GEARS DEPARTMENT OF MECHANICAL ENGINEERING 2010-11 Contents: Contents 1. Introduction 2. Case study 3. Experimental procedure 4. Results and discussion 5. Conclusion Introduction : Introduction Failure analysis of helical gear used in a bus gearbox History-Gear has been in use for 3 years Material-AISI 8620 Steel Evaluation methods-Visual inspection, photo documentation, chemical analysis, micro hardness measurement, metallographic examination TYPES OF GEAR FAILURES : TYPES OF GEAR FAILURES Fatigue Impact Fracture Wear Stress Rupture Surface contact fatigue- pitting, spalling CAUSES: CAUSES Poor design of gear set Misalignment of gears Overloads Subsurface defects in internal areas Use of incorrect materials and heat treatment CASE STUDY : CASE STUDY Bus with problem with its transmission gearbox Gearbox running hot with excessive vibrations Problem was with the fourth speed drive gear General appearance of failed helical gear: General appearance of failed helical gear PowerPoint Presentation: Parameters Value Number of teeth helical gear 36 Helix angle 15 0 Module, normal (mm) 4 Pitch circle diameter (mm) 150 Outer diameter (mm) 158 Face width (mm) 42 Spectrum analysis and micro hardness measurement: Spectrum analysis and micro hardness measurement Result revealed that material was AISI8620 carburized steel Core hardness =439HV Surface hardness=550Hv Case depth=0.63mm Microstructure consist of martensite and retained austenite Microstructure: Microstructure Visual inspection: Visual inspection No. of adjacent teeth failed due to fatigue A triangular piece of the teeth had broken off Crack initiation and bench marks can be seen by necked eyes Origin of crack was at the pitch line No corrosion media were found on fractured surface Photograph of failed gear tooth: Photograph of failed gear tooth Pitting : Pitting Destructive pitting and spalling were also noted on loaded side of each tooth Destructive pitting appears as much larger pits than initial pitting In spalling pits are large in diameter and quite shallow Spalling is caused by excessively high contact stress Photograph of Pitted gear teeth: Photograph of Pitted gear teeth SEM and EDX Examination: SEM and EDX Examination SEM inspection to identify cause of fatigue crack initiation and propagation River-like pattern could be seen in propagation zone EDX attached to fractured surface to determine gear chemistry To verify presence of any other associated components Crack initiation and propagation: Crack initiation and propagation Conclusion: Conclusion Composition, microstructure, hardness and case depth found satisfactory Fractographic features indicated that fatigue was the main failure cause Misalignment was observed which has caused failure Formation of destructive pitting and spalling at one end was due to load concentration at that area THANK YOU!: THANK YOU!