In The Lord of the Rings: The Fellowship of the Ring, Boromir discovers that the pieces of the sword Narsil are being kept at Rivendell. Of course, in the first scene of the movie we see how Narsil is shattered in a battle against Sauron when Sauron steps on it.
But suppose, instead of Boromir, a forensic engineer found the Shards of Narsil. What could they learn from the pieces?
Preserving the evidence
The first thing that should be done with a fractured part is to make sure to preserve the pieces and their fracture surfaces – the areas where the pieces separated from one another. This means that as many pieces should be gathered and stored such that they cannot bump into one another and possibly destroy fragile evidence on the fracture surfaces. Our investigator must resist the temptation to put the pieces back together like a puzzle – that could damage the fracture surfaces. Instead, putting the pieces into their own individual plastic bags or wrapping them in separate pieces of cloth could help preserve them. They should also be stored in a dry area to prevent corrosion.
In the movie, the shards of Narsil appeared to have been wrapped together in one piece of cloth and stored out in the open in what may be a humid environment. This would not be the ideal way to preserve the evidence. But even if some marring of the fracture surfaces and some corrosion occurred – the pieces could still be useful forensic evidence.
Fractography is the study of fractured parts, especially their fracture surfaces, to determine where cracks started and how they grew. Fractography can provide valuable information about the material properties in a failed part, the “loading condition” or force exerted on the part to make it fail, and even the environment where the part saw service.
One of the first steps in a fractographic analysis is determining whether the failed in a brittle or a ductile manner. Signs of ductility would include macroscopic evidence of plastic deformation – i.e. the part would be permanently bent or stretched. Under a microscope, ductile fracture can be identified by microscopic features on the fracture surface. Signs of ductility tend to indicate a material with a good resistance to crack growth, but the material’s hardness and strength should be measured if possible to make sure it had adequate strength.
However, the fracture of Narsil appears to be brittle. No part of the sword appears to have bent, stretched, or demonstrated other signs of ductility. Under a microscope, we might expect to see evidence of what direction the cracks grew and where they started. A metallurgical evaluation might be needed to check and see if the metal in the sword was inherently brittle, and therefore had a low resistance to crack growth. Further laboratory characterization would also help determine if the material was induced to brittle fracture by some other factor like high strain rate, low temperature, stress corrosion cracking, hydrogen embrittlement, liquid or solid metal embrittlement, etc.
The shards of Narsil also show a very interesting trait: there are several fractures and several pieces. In this case, it suggests that the sword failed under a distributed load spread out over some area of the sword. If the sword failed in simple bending or tension, the first fracture would relieve the applied stress and we would not expect the subsequent fractures and additional pieces.
Material testing and metallurgical evaluation
Our hypothetical forensic engineer could investigate further if he could find a materials testing lab in Middle Earth. Scanning Electron Microscopy (SEM) would provide a high-resolution images of the fracture surfaces, help determine how the crack grew, and possibly find flaws that either started the crack or helped it grow. Energy Dispersive X-ray Spectroscopy (EDS) could provide an idea of what Narsil was made of and identify other particles or contaminants. Cutting or shaving away samples for ICP-OES or Spark-OES would provide a more precise measurement of the elements in Narsil, and perhaps help the investigator check whether it was made from an alloy known to become brittle under certain conditions.
Mechanical characterization – hardness testing and tensile testing – would help measure the strength of the material in Narsil and determine whether the metal itself was more prone to either ductile or brittle failure. That hardness and strength could also be used in calculations to estimate the force required to cause the sword to fracture.
Metallography – where pieces would be cross-sectioned, polished, and etched to reveal the size and shape of the grains (crystals) in the metal would tell us about how Narsil was originally made. We could learn about how it was cast, forged, heat-treated, etc. leaving different sizes of grains and different secondary phases distributed in the metal.
Did the failure shown in the movie make sense?
A lot of what is portrayed in Fellowship of the Ring makes sense. The multiple fractures in Narsil were consistent with a distributed load – as portrayed when it fractured under Sauron’s boot. On the other hand, the fractures took a rather long path, with several running diagonally across the blade. Cracks grow in a direction dictated by the applied stress and the path of least resistance through the material. We would expect the force of Sauron’s boot to load the sword in bending, and a crack that would simply take the shortest possible path across the blade. Torsion might cause an angled fracture, but it would be very difficult to induce torsion without inducing an even greater bending stress.
Then again, things like stress corrosion cracking, thermal shock, and impact loading can result in peculiar crack patterns. Who knows what unusual effects proximity to an ancient, evil magical being might have on material properties?
If you have a real-world fractured part you would like examined, an ARCCA forensic engineer can help. Call us today to talk to an expert!