As promised, here is the “quick guide to the initial visual inspection for fracture.”
1.) Look at part to see what you see.
2.) See if you can determine the primary damage category
D). Corrosion (chemical species in the environment)
E). Physical degradation due to thermal, light or nuclear energy; generally associated with microstructure deterioration
3.) Note that A-C above are mechanical (stress related), and D is chemical. E is physical, but it generally doesn’t reveal itself unless there are mechanical (stress-related) forces acting on the part/assembly.
4.) Go back and forth thinking about the first three steps several times. Maybe there are mixed modes. Realize that wear is often a combination of microscale deformation and fracture. But it could be (fretting) considered corrosion and fracture. Likewise, since most insoluble corrosion products are more voluminous than the metal they replace, you can end up getting corrosion and wear together. If the material was ductile and the circumstances allow, whenever you have fracture, you probably have at least some deformation. When you have deformation, maybe you had previously compromised the structure by corrosion or wear!
5.) If you have corrosion or wear, you now need to think about how you are going to decide which type of wear. Consult the books if needed, or characterize what is going on. In some industries, it’s very important to tie the damage to a named corrosion mechanism, but sometimes understanding what’s happening will tell you what you need to avoid the problem in the future.
We offer some sample photographs in part 3 because a picture is worth 1,000 words.