Industrial Heating Experts Speak Blog

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One of most important technical issues that a fracture analyst must deal with is evaluating whether the crack was ductile or brittle. Here we are talking about visible characteristics revealed to the human eye, and we are strictly discussing structures with features that are readily viewed with the human eye.

When I teach people how to do visual examinations as part of the original stage of a failure investigation, I remind them of a very basic group of things that are truly facts.

From last time, what is the fact there? We no longer have a simple fact that is a simple carbon content read off a simple list of elemental concentration values. We have results from a sequence of tests that were determined to be suspicious by the chemist who was performing the work.

What is a fact? Since people generally come to failure analysts when they can’t figure things out for themselves, I have come to believe that it is important to not only have reliable facts but to be able to explain to people why our facts are indeed reliable!

The indigenous inhabitants of what is now called Northern Michigan used the metallic copper they found at or near the earth’s surface for at least 6,000 years to make tools and ornaments. There was no need for what we today call mining, with its implications of underground digging, explosives and other modern technological innovations.

Now compare a different crystal of pyrite from a mine in Spain that has produced beautiful, regular, nearly perfect cubic crystals with a chunk of galena that I recently purchased.

When we are making use of a metallic object, we are not necessarily thinking about how the metal was extracted from its ore. Even if we do remember that the atoms that make up the metal object in question were once likely combined with oxygen or sulfur in a brittle (if not also hard) material, we might not take time to reflect on the beauty of the mineral forms. Yet taking the time to appreciate the natural world is beneficial to us as both simple humans and as people who work in a technology-influenced environment.

The EDS can detect nitrogen (N), present in many cleaners; as well as carbon (present in many oils); oxygen (usually not terribly informative because it is in rust, some oils and many industrial grinding media); silicon (Si); and aluminum (Al), which can be present as abrasive residue or “dirt.” EDS can’t detect hydrogen (H), helium (He) or lithium (Li).

Common substances that I find on stamped or machined parts are lubricants, cleaners and rust inhibitors. I do also sometimes find rust. But neither FTIR nor EDS can produce a firm diagnosis of “rust.” That’s because FTIR works best on carbon-based molecules, not ionic compounds (e.g., rust).

As a local heat treater told me years ago, heat treating is great, but only do it when you need to. Because heat treating does not generally make the parts prettier or straighter.