Precracked specimens offer the opportunity to use the principles of linear elastic fracture mechanics (1)³ to evaluate resistance to stress corrosion cracking in the presence of a pre-existing crack. This type of evaluation is not included in conventional bent beam, C-ring, U-bend, and tension specimens. The precracked double beam specimen is particularly useful for evaluation of materials that display a strong dependence on grain orientation. Since the specimen dimension in the direction of applied stress is small for the precracked double beam specimen, it can be successfully used to evaluate short transverse stress corrosion cracking of wrought products, such as rolled plate or extrusions. The research applications and analysis of precracked specimens in general, and the precracked double beam specimen in particular, are discussed in Appendix X1.

The precracked double beam specimen may be stressed in either constant displacement or constant load. Constant displacement specimens stressed by loading bolts or wedges are compact and self-contained. By comparison, constant load specimens stressed with springs (for example, proof rings, discussed in Test Method G 49, 7.2.1.2) or by deadweight loading require additional fixtures that remain with the specimen during exposure.

The recommendations of this practice are based on the results of interlaboratory programs to evaluate precracked specimen test procedures (2,3) as well as considerable industrial experience with the precracked double beam specimen and other precracked specimen geometries (4-8).