It was late at night. An old man was fumbling around at the base of a street lamp. Another person showed up and asked the man what he was doing.
“Looking for my glasses.”
Both men proceeded to look up and down the street. No glasses to be found.
“Where, exactly, did you lose your glasses?”
“Oh. Across the street there.”
“Then why are you looking for them Here?”
“The light is better!”
In metallurgical testing, often you are constrained as to where you can measure your case depth or yield strength. But sometimes there are options.
If the engineering print does not state that there is a particular requirement, if a test is required, the cut will likely be made “where the light is better,” i.e. the easiest place to cut using the available cutting equipment.
Will the result be the same no matter where the sample is tested? Components usually have areas that are thicker and thinner. If the material is not a through-hardening grade for the size and process in question, values could be very different from one location to another.
Why leave the determination of the component characteristics to chance? Consider specifying a location that is somehow important to the function of the part. If a crack might initiate or if wear is an issue, those particular locations might be worth testing even if you have to spend a little more time preparing the specimen.
The Light is Better
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.