Further study on the scattering of the local fracture stress and allied toughness value

Abstract

In this investigation, the values and their scatters of the local fracture stressof and the fracture load Pf and allied toughness values of base and weld metals were measured, and the main reasons for scattering were analyzed. The results showed that the scatters in σf*, in general, were the smallest. Measuring the fracture initiation sites with a scanning electron microscope and calculating the location of maximum stress and the range covered by the 95 pct maximum stress did not reveal a “characteristic distance” with a statistical feature, over which the local fracture stress must be exceeded by normal stress. Instead, a combined criterion of a critical strain for initiating a crack nucleus and a critical value and triaxiality of stress for its propagation must be satisfied. The present study discovered the phenomenon that the fracture initiation site could locate at the left side (shorter distance side) of the location of the maximum stress. The reasons for this phenomenon and for the minimum crack opening displacement (COD) value not being zero even though a characteristic distance did not exist were proposed.