A thorough failure analysis will provide resources to address many issues in addition to determining whether the component met the requirements of the engineering print and whether there is evidence of “abuse” of the component. A thorough failure analysis must include, but is not limited to, a determination of HOW the damage occurred. Without a detailed understanding of HOW the damage occurred, including the sequence in which it occurred, it will generally be impossible to determine when the critical event happened, why the damage occurred or how future recurrences might be prevented.
The portion of the investigation dealing with the physical damage ideally produces data that allows an understanding of the type and degree of damage present at any time between the original manufacture of the raw material used to make the component and the time the damage was detected. Obviously, this is not always possible or practical. Often, improper handling of evidence greatly complicates the task of evaluating the physical evidence.
For example, if steel parts are left outside or in a humid environment, it can be difficult to determine when the corrosion happened. In addition, the corrosion can obliterate features that might have shed light on the damage process had the part been properly protected as soon as possible after the damage event. Be sure to protect physical evidence as soon as possible. If there was loss of life or a major disaster, this becomes a secondary priority for law enforcement or emergency medical people. When the situation is more calm, make sure that evidence is protected. If you can get someone who regularly does failure analysis immediately involved to help decide how to preserve evidence, you will often “save the investigation.”
A basic analysis of the physical situation surrounding a damage event must include examination of the damaged item/assembly/structure and its associated documentation. For example, a FRACTURE analysis should generally include identification of the crack initiation site by use of the practice of macro-fractography as well as micro-fractographic and metallographic examination of that specific location. Another integral part of a fracture analysis is evaluation of the hardness, or other mechanical properties, to determine the expected strength characteristics of the component.
If you have a component that needs to be analyzed, you are not doing yourself any favors by sending “half” of the part to one party and the other “half” to someone else in an effort to get two opinions. While multiple opinions may be worthwhile, you are much better off getting a competent, trustworthy person who is experienced in the type of failure in question to perform the work. Give them a budget to do a proper job. Make sure they understand that their work will be subject to review by another failure analyst. Make sure that the analyst keeps good records of what they do.
It is not that hard these days to take photos showing how parts were sectioned, from where specimens were taken, etc. Digital cameras are inexpensive, and with a little practice and consultation of the manual, reasonably good close-up views can be captured as the investigation proceeds. Then give this (hopefully) quality document, and maybe any metallographic cross sections prepared during the investigation, to the second party. This approach will save you money and avoid a lot of potential incorrect interpretations and guesses due to only having part of the evidence. Besides, it is always fun to try to shoot holes in someone else’s procedure and data!
What is a Thorough Component Failure Analysis? (Part 1)
By Debbie Aliya
Debbie Aliya is the owner and president of Aliya Analytical, Inc. in Grand Rapids, Mich., and specializes in failure analysis and prevention. She has a BS in Metallurgy and Materials Science from Carnegie Mellon University and an MS in Materials Science and Engineering from Northwestern University. She is also an IMT associate.
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