Lecture Problem 9'15

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Lecture Problem 9.15

• Jason Squiers
• 2/28/07

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Problem Statement

• A large plate is fabricated from a steel alloy
  that has a plane strain fracture toughness of
  82.4 MPa vm (75.0 ksi vin). If, during service
  use, the plate is exposed to a tensile stress of
  345 MPa (50,000 psi), determine the minimum
  length of a surface crack that will lead to
  fracture. Assume a value of 1.0 for Y.

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Fracture Mechanics
Mode I crack surface displacement (opening or
tensile mode)
Stress concentration
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Fracture Toughness

• Kc - fracture toughness
• (K - stress intensity factor)
• sc - critical stress for crack propagation
• Y - dimensionless parameter, function of
• crack length (a)
• specimen width (W)

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Y
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Plane Strain Fracture Toughness
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Conditions for Plane Strain

• In this case, we assume plane strain
• Normally, B should be checked to see if plane
  strain conditions hold
• If so, solve using KIc equation
• If not, E83-jutsu required

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Solution
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Design Applications

• 3 parameters KIc, s, a
• 2 specified, solve for third
• (material selection)
• (applied stress)
• (flaw detection)

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Final Thoughts

• KIc for Mode I surface crack displacement
• Check conditions for plane strain
• OR
• State your assumptions