I recently finished teaching a fairly intense four-day seminar on Failure and Fracture Analysis for our West Michigan ASM International Chapter along with Larry Hanke, a long-time colleague from the ASM Failure Analysis committee. As I like to say, the workshop was “EYES ON – MINDS ON.” In other words, we had the participants actually performing the visual exam on my “museum of failure” and on parts others brought for the same purpose.
At one point, I looked at a complicated tubular assembly and asked the person who brought it in, “What is the damage category?” His response was torsion. "No," I responded. "That’s a loading geometry, not a damage category."
“Aha,” he responded. “Tension!”
"No," I responded again. "That’s a stress state, not a damage category!
“How about brittle?” he said.
"Nope," I replied. "That’s a material-behavior category."
The bottom line is that it can be confusing when you start doing this type of work. I asked him to try again. “Fracture,” he said.
“Bingo!” I replied. "That is a damage category. But you have three different components in this assembly. Two are fractured and one is something else.” He scrutinized the assembly more closely and said, “Deformation.”
"Yes, that’s it," I said. So now we know that we have an assembly with two fractured components and a third that was deformed. We believe that the loading geometry was torsional, and the stress state that created the cracks was tensile in nature.
I promised the group to put together a little cheat sheet as a reminder of these three separate categories of things that must be individually determined for fracture failures. We will dive into the details next time in part 2. Stay tuned.