Study on Crack Branching Condition for Brittle Crack Propagation in Steels

In brittle material like glass, it is observed that crack branches when the crack speed gets more than the material critical velocity. When the crack branches, the driving force at running crack tip gets lower, so it is possible to prevent the structure from serious failure. In this paper, using the devised under-matched welded joint to implement the higher crack velocity, the mechanism of crack branching and surface roughening is investigated by experiments and the dynamic Finite Element Method (FEM) analysis.In the result, crack surface roughening happens when the crack velocity is around 800m/s, contrary to the findings of the elastic dynamic fracture mechanics. FEM analysis was conducted to explain the phenomenon and it is possible that the high stress triaxiality can be the critical condition for crack branching.