Assume nothing! The first thing is to acquire as much background information as possible. This has several considerations. A few are:
- Why is this considered a problem? Presumably some expectation was not satisfied. But, what was that expectation?
- If this is a failure, is a failure analysis worth the cost? Were there significant consequences? Are there many similar units in operation that could suffer the same problem? Is this a prototype or trial unit, and many more are foreseen?
- Find out about the system that the component is a part of. If a failure, and if possible, visit the site and look at it yourself.
If a failure analysis is performed:
- Look at the failed piece without magnification.
- Then look with an optical macroscope.
- Then do "ordinary" fractography (50-10,000 X with SEM).
- TEM and replicas (10,000-300,000 X magnification) will rarely be required.
After that, you can decide where to cut samples for metallography, and chemical analysis. Chemical analysis will confirm if the material meets specification. It may also allow identification of its producer and possibly its heat identity.
Gathering history and other background of the failure is important. Operators and others present at the time should be asked to describe what they observed. Were there any unusual events prior to failure? Operational logs should be obtained. Unfortunately, people often try to protect themselves and omit or distort relevant details. Acquiring multiple accounts from multiple observers will help to discern the true facts. In the end, the material will show exactly what occurred, but much discernment may be needed to convert fractographic observations into causation.
For some types of failures, the cause (impact, tensile overload, etc.) may be found at the time of failure.For others (especially fatigue),the cause may have occurred significantly before failure was observed. Improper installation (for example, a misaligned shaft) can cause failure. Mis-application and poor design are other possible causes.
If the analysis points toward that you are not familiar with, reach out to someone who has more expertise in that area.
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Original Message:
Sent: 7/17/2023 12:00:00 PM
From: Kenneth Kirby
Subject: RE: Solving a materials problem
This really depends on the nature of the problem. A failure (fracture, wear, deformation) of a component in service requires detective work to determine if the component was abused or exposed to any unexpected conditions, and to determine if it was manufactured correctly per specifications. First, observe everything while altering as little as possible. Look at fracture surfaces for signs of fatigue, tempering oxide (which would indicate a flaw that existed during or as a result of heat treatment), etc. Chemistry should definitely be checked to make sure the part was made to specifications, but an accurate chemistry measurement is typically destructive. You can screen by XRF or other methods to non-destructively determine if the material at least has the correct alloying elements to possibly be what it is specified to be, but getting the carbon level of steel within the few hundredths of a percent of variability that is allowed in most types of steel, for example, requires destructive testing of a sampling of the material. There are texts that outline the steps of failure analysis in detail; these are just examples of the first few things.
If it is more of a design issue where an existing material is thought to be inadequate, you would still want to verify that the existing components were being made to print. Maybe the design was adequate, but a vendor has substituted materials without getting approval, or some part of the process is out of control and no one is aware. Once that is verified, I would look at what types of failures are occurring. If certain types of failures occur consistently, there is less detective work. Even if the parts are being "abused", if every user is "abusing" them, the manufacturer might need to redefine what they consider to be abusive. Either users need more guidance and warnings, or the product has to be better. Again, the failure mode is important. Brittle failures have different solutions than ductile or wear related failures.
I wouldn't really consider a completely new design to be a "problem" but you might start with a particular material based on past experience and find out it isn't adequate, which would than lead to my previous paragraph. In addition, you have to realize that lab testing might not perfectly reproduce real world conditions. You could be producing failures in the lab that would never be reproduced in actual use, and actual use might produce failures that you can't reproduce in a lab. The problem can be the tests rather than the material or design.
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Kenneth Kirby
Senior Project Engineer
Snap-on, Inc.
Kenosha WI
(262) 748-3836
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Original Message:
Sent: 07-13-2023 14:54
From: Ryan Sims
Subject: Solving a materials problem
How would you approach solving a materials problem whether that is starting with the chemical makeup, mechanical test, etc.
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Ryan Sims
Pennsylvania State University
University Park PA
(724) 831-9257
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