Published: May 1996
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SPECIMEN DRAWINGS THAT include machining tolerances are provided for each specimen type in all ASTM fracture test standards. All tolerances are well within what is achievable with good machine shop practice. The most important tolerance in the SE(B) specimens is the parallelism of the loading surfaces, and, in the C(T) specimen, the corresponding pinhole alignment and parallelism. Surface finishes are generally not critical, especially when side grooves are used. The initial machined notch should be perpendicular to the plane of the pinhole center lines in the C(T) and DC(T) specimens. The initial machined notch and precrack combination must lie within an envelope as shown in Fig. 22. These notches can generally be cut with slitting saws that have been ground to a tip of radius on the order of 0.1 mm. Modern wire electric discharge machining (EDM) techniques now allow initial notch openings to be as narrow as 0.2 mm, and EDM slots can be substituted for the conventionally machined notches if desired.