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Failure Analysis
Failure Analysis is the act of analyzing what went wrong and why. Engineer’s use this strategy in order to predict and prevent further damage to a piece of machinery that could cost a lost of money or cause a safety hazard. According to Machinery Failure Analysis and Troubleshooting, machinery failures reveal a reaction chain of cause and effect… usually a deficiency commonly referred to as the symptom…”. Failure Analysis can save money, life’s, and resources if done correctly and acted upon. Whether a design engineer needs to know what goes wrong, so the proper safety measures are in place, or a plant engineer and needs to know the signs of what went wrong and how to quickly resolve it, Failure Analysis is one of the answers.

Case Studies
Two Shear Key Rods failed on the Bay Bridge

People on the Case
Mr. Brahimi is an American Bridge Fluor consultant and has a Masters in materials engineering.

Mr. Aguilar is the Branch Chief for Caltrans Structural Materials Testing Branch with 30 years’ experience as an engineer.

Mr. Christensen who is a Caltrans consultant with 32 years of experience with metallurgy and failure analysis.

Steps
Visual Observation which is non-destructive examination. This revealed sign of brittleness with no permanent plastic deformation before it broke. Cracks were shown which were the final breaking point of the shear key rods. The engineers suspected hydrogen was involved in producing the cracks.

Scanning Electron Microscopy which is the scanning of the cracked surfaces under high magnification to get a better understanding of the fracture. The full fracture happened after the rod couldn’t hold under load when the crack reached a critical size.

Micro Structural Examination where cross-sections were examined to reveal more information about interworking bonds of the metal.

Hardness Testing using two strategies, the Rockwell C Hardness and the Knoop Microhardness which reveals that it was not heat treated correctly.

Tensile Test tells the engineer the yield strength, tensile strength, and elongation was sufficient to pass the requirements. Multiple pieces were taken and performed by Anamet Inc.

Charpy V-Notch Impact Test shows the toughness of the steel by taking different samples of the rod and done by Anamet Inc.

Chemical Analysis was the Final Test also done by Anamet Inc. which met the requirements for that steel.

Conclusion of the Case Study
“The rods failed from hydrogen embrittlement which was susceptible to the hydrogen from the high tensile load and the hydrogen already in the material. The rods did not fail because they did not meet the requirements for strength in these rods. While they met requirements, the structure was inhomogeneous which caused different strengths and low toughness.

This study shows a couple of the many ways Failure Analysis can be done. It always starts with a nondestructive form of observation, like a crime scene. Then pieces of the material are taken from the original piece which are used in different observations. Then destructive testing is done to find toughness and properties of the material to find exactly what went wrong.

Failure of Failure Analysis
The collapse of the Oakland Nimitz Freeway was a bridge that collapsed during an earthquake even after the program to strengthen the bridge. Different engineers were asked on their take on the situation. While some don’t blame the program or the department, like James Rogers who said that the earthquake could have “a good chance the Embarcadero would do the same thing the Nimitz did.” While some said more prevention could’ve been done. Dr. Priestly says that “neither of the department’s projects to strengthen roadways addressed the problems of weakness…” in the bridges joints. Some experts agreed that more could’ve been done to prevent this disaster. The program is under fire for making “the failure more serious”.

Failure Analysis as an Occupation
Structural Engineers and Mechanical Engineers are very common for the job. More specific majors can also get into the position such as materials engineers. Specializing in metallurgy and chemistry is always useful along with properties and strengths of materials.