Indentation Fracture and How to Apply to Thin Films

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Indentation Fracture and How to Apply to Thin
Films

• Huai Huang

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Outline

• Indentation test
• Indentation fracture mechanics
• Stress field and Crack system
• Fracture Mechanics Analysis
• Fracture toughness measurement on thin film

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What is Indentation test

• Easy and cheap to perform
• Properties
• Elastic properties Modulus
• Plastic properties Hardness
• Time dependent properties Creep
• Fracture properties

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Hertzian Stress field

• For smooth sperical indenter

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Hertzian cone crack
However X cant be exactly calculated
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Indentation Stress field
For a normal point load P the stress field can be
given by Boussinesq field
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Radial-median crack

• Under a point load

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Fracture Mechanics Analysis
System behave like a center-loaded, half-penny
crack, for which the stress intensity factor is
given by
The stress field can be expressed (by Hills
expending cavity solution) as
Combining the above two equations and assuming
the crack arrests when it grows to a length at
which the stress intensity factor is just equal
the fracture toughness
Experiment within 40 accuracy
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Other Fracture property

• Inert Strength
• Toughness-curves
• Crack-velocity exponent
• Crack initiation
• Crack propagation

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Hard film on a soft substrate

• Load vs displacement can be simulated as

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Indentation fracture for thin film

• Typical loads 1000gram and crack length 100um
  Small crack threshold need.
• Solution Change of indenter geometry.
• Vickers indenter threshold 25 grams
• Cube corner indenter 0.5 grams
• (Same theory can be apply to different indenters)
• Mechanical properties were extracted from
  hardness and modulus versus displacement profile
  minima or approximately at a depth of 10 of the
  film thickness.

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Indentation on Low K
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Summary

• Indentation test can provide fracture property
  such as fracture toughness. Indentation Fracture
  mechanics is discussed.
• Reduced crack threshold load can apply
  indentation test to very thin film.
• Further research is need to study indentation on
  thinner films