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Gears & Gear Systems: Gear Structural Design & Gear Failure Modes

- - - - Load is distributed uniformly over the full face width, F
      - Non-conservative for wide teeth or misaligned shafts
      - Radial component is negligible
      - Forces due to sliding friction are negligible
      - When load acts at tip, more than one tooth is usually in contact
      - Stress concentration at tooth fillet is negligible
      - Worst case: full load is applied to the tip of a single tooth
    - - Formula
      - With Moment of Inertia (area)
        
        Formula
      - Y = Lewis Form Factor
        
        Is a function of Tooth Shape (but not Size)
        
        It varies with number of Teeth N
        
        Table 14-2 (Shigley)
      - m = Gear module [mm]
        
        brings in the Size
      - Tooth Width F [mm]
    - - Introducing the Velocity Factor
        Kv
        
        A ‘Load Factor’ to provide for:
        
        Pitch Line Velocity
        
        Manufacturing Accuracy
        
        Formula
        
        Kv is found from Eq’s. 14-6 (Shigley)
      - Introducing the Bending Strength Geometry Factor J
        
        Substitutes
        Y to provide for:
        
        Fatigue Stress-Concentration Factor Kf
        
        Load-Sharing Ratio Mn
        
        Formula
        
        J is found from Fig. 14-6, 7 & 8 (Shigley)
        
        Graph
  - - - Modified for Surface Durability
        
        Introducing the Surface-Strength Geometry Factor I or Pitting Resistance Factor
        
        A ‘Geometry Factor’ to provide for:
        
        Pitting Resistance
        
        Gear Ratio MG
- - - - Scoring
        
        Form of adhesive wear
        
        Inadequate lubrication
      - Pitting and spalling
        
        Surface and subsurface fatigue failure
      - Abrasive wear
        
        Due to foreign particles