THE INFLUENCE OF COLDWORK

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THE INFLUENCE OF COLD-WORK ON THE STRESS
INTENSITY FACTOR OF CRACKED HOLES AND PIN LOADED
JOINTS
Silvestre T Pinho, Helder B M Martins, Pedro P
Camanho, Paulo M S T de Castro IDMEC - Porto,
Portugal
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summary

• analytical and semi-analytical solutions for
• residual stress distributions resulting from hole
  expansion elastic-perfectly plastic material
  using
• Tresca and von Mises criteria
• relationships
• dimension of the plastic zone vs internal
  pressure / mandrel interference,
• magnitude of residual stresses vs remote
  uniform tensile stress required to open
  symmetrical radial cracks
• reduction of K for cracked open- and
  riveted-holes as function of hole expansion,
  using numerical models elastic-perfectly plastic
  material and Al 2024-T3 Alclad

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objectives

• to develop a simplified procedure to relate
  hole expansion (internal pressure / mandrel
  interference) of an infinite isotropic plate,
  with the residual stress field and plastic zone
• to assess the reduction of K resulting from the
  cold-work process, in both open and riveted
  holes.

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semi-analytical and numerical residual stress
fields (von Mises)

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residual stresses obtained using von Mises and
Tresca yield criteria
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plate with open hole
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stress field due to cold-work and remote loading
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relationship between applied pressure and radial
interpenetration central hole in infinite plate
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plastic/elastic interface coordinate as a
function of the pressure applied von Mises yield
criterion central hole in infinite plate
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remote stress required to open two symmetrically
located cracks in a cold-worked hole
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uniaxial stress-strain relations
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K as a function of crack length and cold-working
Alclad Al 2024-T3
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regions plastically deformed for different hole
expansions
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riveted joint
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comparison between K solutions for a plate with a
riveted hole
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cosine and calculated distributions of radial
contact stress
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equivalent plastic strain due to cold-work
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?yy stress gradient cracked cold-worked pin-load
joint
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?yy stress gradient cracked cold-worked pin-load
joint detail
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K as a function of crack length and cold-work
Al 2024-T3
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conclusions I

• analytical and semi-analytical solutions are
  derived for the characterization of the residual
  stress field and plastic zone sizes of
  cold-worked holes for elastic-perfectly plastic
  materials
• the cold-working process is shown to reduce K
  for different dimensions of plastically deformed
  regions, and for different crack lengths, for
  both a remotely loaded plate containing an open
  hole, and for a riveted joint.

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conclusions II

• the reduction of stress intensity factor value
  for the cracked open hole problem was found to be
  greater than the K value reduction for the
  pin-loaded joint. This implies that claims of
  fatigue enhancement solely based upon the
  performance of open hole specimens may be
  optimistic in actual connections