Fracture initiation

Hi!

I am investigating the effect of triaxial stress state on the superelastic behavior in NiTi. In this regard I have conducted some simple tensile tests on notched specimen until fracture. The next step is to investigate the fracture surfaces in SEM to determine point of initiation and the structures. However, as my knowledge in fractography is limited at best, I am not really sure what to look for to determine eg. fracture initiation.