Weibull effective volumes and surfaces for cylindrical rods loaded in flexure

Formulas are given for the effective volumes and effective surfaces for cylindrical rods that have been loaded in flexure. Strength scaling for specimen size usually is dependent on whether the flaws are volume- or surface-distributed. Flexural loadings of rods of constant diameter are an exception. The ratio of three-point flexural strengths to four-point flexural strengths is independent of whether the flaws are volume- or surface-distributed. Rods that have been tested in flexure do not expose much material to the maximum stresses. Large rods produce strengths that are comparable to common standard-sized rectangular bend bars for volume flaws. For surface flaws, smaller rectangular bar specimens actually have larger effective surfaces.