Stress rupture ductility diagram - A diagnostic tool

The present work suggests a methodology for construction of stress rupture ductility diagram using the concept of geometrical factor k that determines the nature of creep rupture. Large volumes of stress rupture ductility data of a range of engineering materials generated experimentally in the laboratory and reported in the literature have been used to study the nature of creep rupture by superimposition of these data on the above diagram.

The rupture ductility of Ni-base superalloy, when superimposed on such diagram, indicates that the failure in this alloy could be due to limited amount of localised deformation or cavitation. In case of Zr-Nb alloy, the rupture ductility data lie in the necking regime extending from k=0.9 to 0.4. In contrast, the data on Cr-Mo steel show a wider variation extending from the regime of cavitation to extensive necking.

Reliable prediction of rupture ductility is possible within a narrow range of k in which the nature of creep rupture remains the same.