Having primed my neurons from the exercise discussed last time, I am now going to take a look at a photo of a fracture surface that I have not looked at in some time.
I see the circular end of a cylindrical object. While I know and am stating that this is a fracture surface, none of my description is going to be based on this fact. I am simply going to attempt to describe what I see. At first, I see a bright circle surrounded by a dark background. Looking more closely, the bright (interrupted) crescent that is visible above the upper edge of the circle indicates that I may be looking at a cylindrical object. There is another light-colored crescent at the upper right edge of the circular end of the cylinder. The circular end is reasonably smooth, but it seems to have some wrinkles. There are wide, horizontal bands of darker and lighter grays crossing the circular end of the cylinder.
The largest wrinkle feature is a slightly jagged line running more or less vertically. The wrinkle has a “fork” at its lower end. In addition to the wrinkle, the flatness of the circular area is interrupted by a sort of ridge that appears to protrude outward from the main plane of the circle. This ridge runs from around the 2 o’clock position to 6 o’clock. There are some very bright, irregular short arcs parallel to the center of the length of the long ridge. There is another bright arc along the edge of the circular end running from around 9 to 10 o’clock. There are some short very narrow bright concentric arc segments from 10 to 11 o’clock along the outer edge of the circle. There are multiple dark splotchy areas in the center right of this circular area. There are less-pronounced, dark, near-vertical streaks in the upper quarter of the circle. There are a few smaller bright speckles in the lower portion of the circular surface.
Now, looking more carefully within the dark and light bands, we can see some faint lines running parallel to the edges of the bands. There are two bands that are different than the others. These are near the center of the height of the circle. These bands have an interlocked “step” shape, so that the brighter, upper, wider band is even wider than the darker, lower, narrower band on the right side of the circular area than it is on the left.
What features can you see that I have not mentioned?
I challenge any readers who are not specialists in fracture analysis to read this description of the fracture to a colleague who is a specialist to find out what they say to this description. Can they sketch it from your words? Can they guess how the crack grew?
This photo is of a broken shaft that someone gave me years ago. The shaft is long gone and I don’t have any other information in my records. Next time I will report “looked for” features that I noted as a fracture analyst and also provide some comments from some colleagues.