A relation between the stress intensity factor K1* required for brittle crack initiation and propagation and the fractal dimension InK1* -(1/2)In (da/La) (I-D) where d is the fracture unit, Lo is the length of the straight pro-jection line of the fracture profile, Y is the real surface energy, and E1-E (plane stress) or E/(I-v2) (plane strain) The real surface energy can be calculated on the basis of the measured linear relation of In K1* vs. D The equation is not only suitable for overload fracture but also for delaycd fracturc, e.g. hydro-gen-induced cracking and stress corrosion cracking The experi-ment results showed that the hydrogen -induced delayed cracking occurred in Ti-24A1-11Nb alloy during dynamic charging, and the threshold stress intensity factor was very low, i.e. K/Kic=0.43. The experimental relation between the stress intensity factor K1* and DF was consistent with the theoretical equation.