Using scientific methods to determine why a material or machine stopped doing its job.
Materials scientists often are called upon to determine the cause of failure of anything from bridges to machine parts. One of the first things that they attempt to determine is what the failure mode of the material was. Was there a sudden catastrophic event that caused the material to fail? Or did it fail due to fatigue?
They also try to answer the following questions.
- Was the material that failed not right for the job in the first place?
- Were there some sort of unusual or unexpected conditions that caused the material to fail?
- Did a defect produced during the manufacturing or installation of the material cause it to fail?
- Was there some flaw in the design of the system that caused the material to fail?
Sometimes materials scientists are called upon as expert witness in court cases in order to determine who was at fault when something did not do what it was intended to do.
The information gained from a successful failure analysis can be used to prevent the problem from happening again.
Some interesting failure analyses
- A K1C test performed on a piece of steel from the wreckage of the Titanic showed that it had a very low fracture toughness at low temperatures.
- The glass transition temperature of the rubber o-ring on a fuel line for the the Space Shuttle Challenger tragedy was too high. This made the ring an ineffective seal at its operating temperature because it had
become rigid at the time of the launch.
- A bridge in Australia collapsed because the welders were encouraged to finish quickly and thus they welded at a higher temperature than normal. The higher temperature welding caused water in the air to break down and allowed free hydrogen to get into the welds. This caused hydrogen embrittlement.
- The nylon removal string for a mass produced IUD
was found to form microscopic cracks along its length. These cracks allowed bacteria to enter the reproductive systems of their female users, sometimes resulting in serious infections and infertility.
- Of the nearly 2,700 liberty ships built during WW II, almost one in seven of them fell apart due to bad welds, steel that became brittle at low temperatures, and square hatches that served as stress concentrators where cracks could form.
- The term cold enough to freeze the balls off a brass monkey was used to describe the phenomenon that cannon balls would fall off of their brass tray when it got cold due to a difference in coefficient of thermal expansion.