Rotation and Bending Corrections for the SE(B) Specimen

Standard tests with single-edge (bend) [SE(B)] specimens do not apply a rotation or bending correction. The load-line displacement (LLD) is generally used only for the estimation of the J integral. The compliance is preferably measured from the crack mouth opening displacement (CMOD). However, the standard equations assume that the measuring point lies at the specimen front face. With small specimens this is impractical, because the necessary cutout will decrease the effective crack length of specimen, thus reducing the constraint. If the CMOD measurement is above the front face, a special geometric rotation correction is required. Even in the case of front face measurements, a rotation correction is needed if the rotation of the specimen is large. When the LLD is used, an additional bending correction may be needed. The correction is needed because, with bending, both the effective span width, as well as the specimen cross-section dimensions will change. Bending makes the specimen appear stiffer than a straight specimen. If bend specimens are tested with the unloading compliance technique, the true crack extension will generally be underestimated, unless the measured compliance is corrected for rotation and bending. The underestimation will be a function of specimen dimensions and degree of bending, but it can, for smaller specimens, be as much as 35 %. Here new analytical rotation and bending corrections for the SE(B) specimen are proposed and validated.