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One of the more common types of failure analysis is the investigation of something that has broken. For this column, we will be discussing a broken material, or, more commonly, a fractured or cracked material.
Fractographic analysis is sometimes perceived as a difficult analysis, given its roots in material science, but one might be surprised to learn that failure modes for this type of study are well-established and well reported and can easily be found in textbooks, reference materials, and even with a Google search! Given that, this column is not being written to teach a lesson in fractographic failure modes, but more so to provide some insight in performing the analysis yourself, or at least give you some direction to get things started.
Unlike many types of forensic analyses, a fractographic investigation most times doesn’t really need any high dollar, sophisticated instrumentation or equipment. This is true because the most pertinent information in a fracture based investigation is simply the visual examination of the fracture surface itself. Now, that can be problematic in some instances, because the fractured surface can become damaged before it is discovered. If a crack happens and is still connected on one end, it’s possible that the opposing surfaces of the fracture can make contact with each other—through movement of the specimen while still in use or even through simple vibration—potentially damaging the surface characteristics that are needed to determine the failure mode at hand. This is not overly common, but can happen, and as such it’s worth mentioning here. For this reason, one recommendation that can be made is…don’t put the pieces back together! In line with what has been mentioned just a few sentences ago, putting the fractured pieces back together can accidently damage what you’re really trying to inspect.
Editor's Note: This column originally appeared in the July 2016 issue of The PCB Magazine. This is Keith’s first in a series of columns having to do with inspection and test— from the test lab perspective.