Fractography 

Fractography is used to determine the mode of fracture (intergranular, cleavage, or shear), the origin of fracture, and location and nature of flaws that may have initiated failure. With this information, the answer as to why a part failed can usually be determined. The major use of fractography is to reveal the relationship between physical and mechanical processes involved in the fracture mechanism. The size of fracture characteristics range from gross features, easily seen with the unaided eye, down to minute features just a few micrometers across. (reference: Dr. Zee)

Light and electron microscopy are the two more common techniques used in fractography. An important advantage of electron microscopy over conventional light microscopy is that the depth of field in the SEM is much higher; thus the SEM can focus on all areas of a three-dimensional object identifying characteristic features such as striations or inclusions.

The texture of a fracture surface, that is, the roughness and the color, gives a good indication of the interactions between the fracture path and the microstructure of the alloy. For instance, at low stress a fatigue fracture is typically silky and smooth in appearance. Stress corrosion fractures show extensive corrosion features and corrosion “beach marks.” A discontinuous ductile fracture shows some stages of crack tip blunting, crack arrest and "pop-in".