Design Considerations Irwins Leak-Before-Break Criterion

1 Design Considerations (irwin s Leak-Before-Break Criterion) 

As a conceptual experiment, one might consider a wide plate, with a central, through-thickness crack of length 2a, under a uniformly apphed tensile stress a. One might further consider having both failure modes (fracture and yielding) occur at the same time. For fracture. 

The minimum fracture toughness required would depend on the yield strength of the material, and the expected crack size, which is to be set by the efficacy and fidelity of regularly scheduled nondestructive inspections. 

The effective crack length, however, is the sum of the length of the physical crack and the plastic zone correction factor. As such. 

By combining Eqns. (5.1) and (5.2) and solving for a, the physical crack size (a) at the onset of leakage/fracture becomes  

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