Photo – The delicate features on this fractured ball stud can be easily damaged by contact, or degraded by corrosion. They indicate a ductile fracture through and steel with a high manganese sulfide content, such as a free machining steel. The actual area shown in this field is approximately one thousandth of an inch square.
That component fracture that you were just called or emailed about may not seem like an asset at the moment. But if it’s important for your company to know what caused it, that fracture is one of your best allies. Depending on what an analysis determines the root cause to be, that fracture may be a key piece of evidence. Preserving it in as close to “as is” condition as possible is important.
A fracture is only the end result of a sequence of events that went wrong. There are a lot of events throughout a components life that can go wrong and end in fracture. Some of these are defective stock from a vendor, defects introduced in forming or machining, errors in heat treating or other processes, or customer abuse, to name just a few.
The root cause of many of these is apparent from analyses of aspects of the component other than the fracture. But regardless of the root cause, it’s always good to identify how the fracture finally occurred. Was it progressive over a long period of time and can other components be examined for signs of impending fracture? Can you take actions like weld repair or reinforcement and safely save the cost of replacement? Did it occur instantaneously, without warning? Instantaneous fractures are particularly dangerous.
How a fracture finally occurred is preserved in the microscopic features of the fracture surface. These features are so small that even powerful optical microscopes cannot identify them with certainty. That requires the extraordinary magnification and depth of focus that only a scanning electron microscope (SEM) can provide.
These microscopic fracture features can be extremely delicate and prone to damage. To preserve them for analysis, we suggest the following:
- Never fit the two halves of a fracture back together. Even light contact of the mating fracture surfaces can cause extensive damage microscopically.
- Protect the fracture from corrosion. It’s going to start oxidizing the moment the fracture halves separate, but any steps that can protect it from rain, snow, road salts, and other corrosion accelerators will help.
- Coating the fracture with oil or rust inhibitors can be a problem, since these typically contain additives that can mask evidence of contamination in processing or service that may have been the root cause of, or a contributing factor to, the fracture. If exposure to the atmosphere can’t be avoided, use a non-detergent motor oil to coat and protect the fracture. Use new oil. Used oil is typically contaminated with sulfur.
- Protect the fracture from high temperatures such as torch cutting or welding. These can result in the rapid conversion of the actual fracture features to a high temperature oxide.
- Never clean the fracture or remove corrosion from it for us. We use highly controlled cleaning procedures that have been developed to clean or remove rust with the absolute minimum of damage to the microscopic fracture features. We once had a helpful client sand blast a fracture to clean it up before sending it to us for analysis. That part was the subject of a lawsuit. The judge was not impressed.
We realize that the steps listed above are not always practical in “the real world”. We’ve had fractures submitted for analysis that weighed up to 8 tons and failed at the top of a South American mountain or in an Australian desert. Protecting life, limb and property is always a higher priority, but when in doubt after those priorities have been taken care of, give us a call or send an email.
We’ve learned to work around the problems that can result from damaged fracture surfaces. They’re actually the rule on the samples we receive for analysis, rather than the exception. But any of the steps listed above that you can take will help. And that will make that fracture surface a valuable ally in preventing future fractures and loss.