Abstract: The further investigation on the Necking Zone Model of ductile crack propagation suggested in 1997 by the first author is reported. The test results of double cantilever beam (DCB) specimens loaded in tensile, ModeⅠsense at crosshead velocity of up to 5m/s show again that the Necking Zone Model de-
scribes the main characteristics of ductile crack propagation.Comparing with the static test results, the necking zone width reduces and the average strain in the zone increases in dynamic case. But the productnkof the necking zone width factork1 and the strain factork2is reasonably constant and is not affected by the specimen ligament thickness and loading rate, i.e.,nkis
considered as a material constant affecting the ductile crack propagation resistance. According to the Necking Zone Model,the increase in fracture resistance with respect to loading rate is mainly attributed to the strain-rate strengthening effect of the material. The Necking Zone Model not only suggests a simple engineering approach of calculating the energy dissipated by the ductile fracture during impact case, but also suggests a simple
experimental method of measuring dynamic crack resistance using dynamic tensile test and static tensile tearing test.

Key words: ductile fracture, crack propagation, necking zone model, mild steel, double cantilever beam specimen, impact loading