While the well-established parameters CTOD and Q sets the size scale over which large stresses and strains develop, and characterise the constraint level due to geometry with no stresses present, respectively, the new R parameter provides a basis for more reliable fracture mechanics analyses in which the influence of external forces and residual stresses in front of a crack tip can be taken into account.

The difference between a solution accounting for residual stresses and the small scale yielding (SSY) field at r/(J/σ_{0}) = 2 and θ = 0 defines R:

where J stands for the so-called J-integral.

Published January 5, 2007

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