Extension of the Compliance and Stress Intensity Formulas for the Single Edge Crack Round Bar in Bending

The compliance and stress intensity formulas for the solid single edge crack round bar in bending (SECRBB) specimen with a support span to diameter ratio S/D = 3.33 are extended to cover notch depth ratios 0 ≤ a/D < 0.6, an arbitrary Poisson's ratio, and a slight variation in S/D. The work is based on a precise and reliable measurement of the load point displacement on notched rock cores of Ekeberg marble. The measuring method virtually eliminates friction and twisting effects as well as nonlinear contact and crushing phenomena. It yields an accurate value of the Young's modulus. The experimental results give the extension of the formulas which are used for a thorough fracture mechanics analysis of the SECRBB specimen. The matters considered are the crack growth stability, the secant offset at 2 percent apparent crack growth, and the logarithmic derivative relating the J-integral to work done. Hence a basis is laid for correct linear and nonlinear fracture toughness measurements with the SECRBB specimen.