Threshold angle and valid fracture of the sectored flexural specimen

The sectored flexural specimen was developed over a decade ago to measure the strength of ceramic and glass tubes and cylinders in which flaws on a tube's or cylinder's outer surface are limiters of axial tensile failure stress. Using the specimen's geometry, the associated axial tensile failure stress can be analytically calculated from the failure force measured from simple uniaxial bending, and multiple specimens (and test data) can be harvested from a single tube or cylinder. The sector angles of specimens in previous studies were somewhat arbitrarily chosen and usually produced validly occurring fractures and data; however, if the angle used was too small (relative to the tube's or cylinder's geometry), then undesirable application-irrelevant edge-located failures resulted. To avoid such failures in specimen design, a threshold sector angle was identified to guide the selection of a minimum sector angle (and consequential cross section) for any arbitrary sector flexural specimen harvested from a tube or cylinder. If the sector angle of the specimen is larger than the threshold value, then fracture will not occur at a specimen's edge and the measured axial failure stress will be limited by surface-located flaws on the tube's or cylinder's outer surface.