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Crack stoppers

Crack stoppers


  • How are they Saving a Pressurized Aircraft fuselage from being ripped apart by the Cyclic loads & avoiding Disasters?
Background:
  • Post investigations into 2 catastrophic airframe failures (De Havilland Comet) in the 1950s, aircraft manufacturers realized the importance of Fatigue Cracks.
  • A new design feature named "Crack stoppers" came into the fuselage that would increase the ability of the aircraft to sustain damage caused by fatigue.
  •  The skin of the fuselage, typically has a large number of high-stress locations, due to multiple Rivets & Hiloks, making these points as potential crack initiation by 'fatigue Loading'.
  •  Theoretically "Crack stoppers" are part of damage tolerant design philosophy to arrest Fatigue loads.
  •  Physically "Crack stoppers" are reinforced doublers at specific locations on the inner fuselage skin also termed 'tear strap' or 'fail-safe strap'.
  •  They are simply strips of material (Stronger material Like Titanium) attached circumferentially to the skin of the fuselage which capitalizes on the advantage of flapping.
  •  A tear strap locally reduces the hoop stress thus causing the bulge stress to become greater than the hoop stress for an axial crack length.

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