As it was explained to me by a metallurgist in the engineering department.
On a fractured surface the section that looks like a fine grain is where the crack started and grew slowly
the section where it looks like a coarse grain is where the the part had been weakened to the where it grew fast and suddenly failed.
On a fractured surface the section that looks like a fine grain is where the crack started and grew slowly
the section where it looks like a coarse grain is where the the part had been weakened to the where it grew fast and suddenly failed.