Indentation Fracture and How to Apply to Thin Films Huai Huang

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

What is Indentation test Easy and cheap to perform: Properties:  Elastic properties : Modulus  Plastic properties: Hardness  Time dependent properties: Creep  Fracture properties

Hertzian Stress field For smooth sperical indenter

Hertzian cone crack However X can’t be exactly calculated

Indentation Stress field For a normal point load P the stress field can be given by Boussinesq field:

Radial-median crack Under a point load

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 Hill’s 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

Other Fracture property Inert Strength Toughness-curves Crack-velocity exponent Crack initiation Crack propagation

Hard film on a soft substrate Load vs displacement can be simulated as

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.

Indentation on Low K

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