By means of a simplistic mechanical model a mathematical relation between the total fracture energy of an edge-cracked beam under bending and the fracture toughness was derived, Inserting the parameters of the standard Charpy specimens and accounting for the finite toot radius and the shallowness of the notch, an equation to calculate fracture toughness from the Charpy fracture energy was obtained. Unlike the commonly used empirical correlation formulas, the presented equation is applicable to any elastic-plastic material. From its theoretical basis and the underlying assumptions, it is expected to be conservative in any case. Although the derivation only holds for the upper-shelf regime. it also is applicable to the brittle-to-ductile transition regime as a lower bound, In this range, the degree of conservative can be reduced by accounting for the well-known shift of the transition temperature. Comparison with experimental data confirm theme features of the presented formula.
