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Exhibit 18 - How Materials Break

How Materials Break - Dr Jane Blunt

Why do things fall apart?

You are probably familiar with the term ‘forensic science’ in the detection of crime, looking at items such as fingerprints, DNA evidence and footprints.

The word ‘forensic’ means ‘belonging to a court of law’, and in this exhibit you will see some of the work of physicists and engineers in examining the evidence after accidents where structures or equipment have broken.  After a catastrophe such as an aeroplane or rail crash, we always want to know whether there was a structural failure, and if so, why, so as to prevent it from happening again.

We can examine the design and decide whether the calculations were done correctly, to see whether the design was good enough.  There are International Standards that must be met for the design and construction of safety-critical items such as pressure vessels.  The item must have been built according to the specification, and we would examine the evidence to decide whether the conditions had been met.

Chemical analysis of the matter can show us whether the correct material was used in making the item.  Examination of the material under a microscope can show us whether the material was in the correct condition, or whether it had been mistreated either before manufacture or afterwards.

The broken surfaces contain a lot of clues.  We can see, often with the naked eye, in which direction the crack was running, and where it started from.  Examination under a microscope can tell us what sort of fracture it was, which further helps us to decide what went wrong.

Destructive tests, in which we break pieces of the material and measure the forces needed to break them, will give us another vital piece of information about the failure.

Finally we can put all the evidence together and decide:

  • Was the design good enough for the service?
  • Was it built correctly and from the right materials? Was it misused?

Or

  • Was there an unusual event?