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Failure Mechanisms
Plasticity Effects

· In most materials some plastic deformation occurs at the propagating crack tip and plastic deformation work must be included in the overall energy.
· The plastic deformation work, P, on the region on either side of the crack surface may be included in the surface energy term in the Griffith expression: Effective Surface Energy, Ω= (S + P).
From: Barrett, Nix, and Tetelman,
"The Principles of Engineering Materials,"
Prentice Hall (1973)
· When plastic deformation work is involved in rapid fracture, a region about 10-6m thick on either side of the crack surface is plastically deformed and the plastic work is much larger than the surface energy. For this condition: Ω= (P + S) ~ P.