Chapter 13Fast Fracture and Toughness Key Concepts

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Chapter 13Fast Fracture and ToughnessKey
Concepts

• Assign Appendix 1--Problem 29
• A material may fail below its yield strength due
  to fast fracture
• Fast fracture condition
• The combination of stress and crack length at
  which fast fracture occurs is a material
  constant--Kc

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World War II Liberty Ship
These first all-welded ships failed
catastrophically due to fast fracture. The
problem was solved through improvements in both
ship design and steel quality.
SourceMaterials Science Gallery, Manchester
Materials Science Center, University of
Manchester, UK. http//www.umist.ac.uk/matsci/
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Fast Fracture

• A material may fail below its yield strength due
  to fast fracture
• Fracture occurs when energy released by crack
  growth gt energy consumed to extend crack

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Critical Strain Energy Release Rate--Gc

• Material Property
• Energy absorbed per unit area of crack (not per
  unit of new surface area)
• Units J/m2
• Provides a measure of toughness
• High GcMaterial very tough
• (Cu?Gc 106 J/m2)
• Low GcMaterial very brittle
• (Glass?Gc 10 J/m2)

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Fast FractureFixed Displacements
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Elastic Strain Energy
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The Final Result (Fixed Displacements)
Fast Fracture Condition
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Fast FractureFixed Loads
Same Result as Before!!
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The Fast Fracture Condition

• The combination of stress and crack length at
  which fast fracture occurs is a material
  constant.
• Fracture occurs when

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Fracture Toughness of Engineering Materials