Think you need a failure analysis? Avoid some common mistakes with your broken parts
So your part broke and you’re thinking of getting a failure analysis done? Here are three rules to follow to ensure you get the most complete analysis possible, and therefore get the most for your money.
Never try to fit broken parts back together!
Mechanical damage occurs on the surface, rendering the features unidentifiable and in many cases preventing determination of fracture mode. The photos below show SEM (Scanning Electron Microscope) images of two different fracture surfaces. The fracture surface in the image on the left has lovely, clear features that help identify the fracture mode. Brittle fracture (cleavage) is indicated by the yellow arrow, and ductile fracture (MVC, Micro-Void Coalescence) is indicated by the red arrow. The fracture surface in the image on the right has extensive mechanical damage, to the extent that the fracture mode cannot be determined.
Protect the surfaces for storage and/or transport – often it works well to provide stand-off with cardboard and tape so the surface doesn’t get damaged….and always keep both halves of a fractured part—sometimes one side may be in better condition than the other.
Don’t touch OR clean the surface before sending the part for analysis!
Is the broken part dirty? Then keep your fracture surfaces dirty – as they are and without trying to clean them. Is the broken part clean? Great! Don’t touch it with your oily fingers and don’t put any grease on it. If you’re having a failure analysis done, the fracture surface is one of your best sources of information – and the engineer doing the failure analysis will clean the surface using the gentlest possible methods to preserve all those features – after deciding whether to first do any chemical composition analysis on surface deposits.
Be mindful of corrosion – touching the surface can cause rusting, due to the moisture of your fingers. Sometimes people think that packing the surface in industrial grease will help preserve it – while well intentioned, this can cause problems since grease can absorb and therefore cause exposure to moisture… besides which, even gentle cleaning methods have limits. Storage and packing are important – wrapping your fractured part in cardboard or bubble wrap are good choices to preserve the surface. If you’re storing the part for any length of time, or shipping it to a lab for analysis, also pack your specimen with a desiccant.
Send as much of the assembly as possible in with the fracture surfaces.
If you have a fractured bolt, send both halves as well as the nut and any other attached or fitted pieces that interface with the broken bolt. A good analyst will inspect for any relevant features in the vicinity of the fracture location, such as secondary cracking and plastic deformation. These are clues to the state of stress that the broken part was exposed to, and they influence the choice of samples to remove for analysis.
If you’d like more information on what failure analysis involves, or if you have experienced failures and would like an analysis performed, feel free to contact us.