Materials Technology Topic of the Month
At long last, the first article of a monthly series sponsored by Link's Materials Consulting and The Keller Group & Associates.

FAQ’s About Failure Analysis
A failure analysis investigation is a complex process involving some or all of the following in order to determine a root cause:

• Information gathering
• Visual inspection
• Non-destructive testing
• Destructive testing
• Review of data
• Documentation
• Recommendations to prevent future failures

You as the customer can help by providing as much background information as possible and protecting the fracture surface from any further damage. The information provided is used to guide the failure analyst in test selection and, ultimately, the determination of the cause of failure.

What should I submit with my fractured sample?
The following information aids the failure analyst in determining what testing to perform:

• Print (Component and Assembly)
• Material Specifications
• Service Environment
• Temperatures and Pressures
• Loading Conditions
• Time to failure
• Details relating to failure and any prior history of failures
• Testing, inspection, and maintenance information
• Unusual occurrences

If an unbroken/undamaged sample is available, this may be useful as a comparison, especially if the available component has been successful in the application.

The entire fractured component may be useful in the investigation; however, size limitations may prevent this. In this case, it is best to call ahead to discuss with the failure analyst.

How should I preserve the fracture surface?
It is extremely important to protect a fracture surface from mechanical and environmental damage that can destroy microstructural features. The condition of the surface impacts the ability to interpret a fracture. One can not prevent damage that occurs during the fracture event. However, proper handling and care of the fracture surface can minimize damage after the fracture.

Corrosion will mask critical evidence that can be obtained from the fracture surface. Moisture can be introduced even from humid air. Touching the fracture surface with your fingers introduces moisture and salts that may chemically attack the surface.

In cases where identification of foreign material is necessary, the use of a rust-preventative should be avoided.

In addition, the surfaces should be prevented from rubbing against each other or another object. Never place the mating fracture faces back together.

What types of tests will be performed?
Photo documentation is often done prior to any testing and in some cases, between steps so that the failure and location of test samples can be referred to in the final report.

In circumstances where catastrophic fracture did not result, the location of a crack or other indication is identified or confirmed by using non-destructive testing. This is crucial in order to determine where to section a component so that relevant evidence and any secondary cracking are not destroyed. Components are sectioned so that the fracture surface can be exposed and visually examined prior to any further testing.

Often, the next step is determining if the component meets specification. Techniques such as chemical analysis, mechanical testing, and metallography are employed for this task.

A scanning electron microscope is commonly utilized in conjunction with a stereo microscope to determine the failure mechanism and the initiation point(s). In cases where corrosion or some type of contamination is suspected, energy dispersive spectrometry can be used to identify elemental constituents that are present.

All of this information is then analyzed with the service conditions and history to formulate a root cause. In some circumstances, additional testing such as fatigue, hydrogen embrittlement, corrosion, or wear testing may be recommended.

How long until I get results?
Failure analysis projects require a greater length of time than routine testing. This is due to the fact that most of the testing is performed sequentially. Often, only one failed sample is available. Testing must be conducted in such a manner to not destroy evidence that may be useful further down the line. In addition, the direction of a project may change depending on the results obtained from other testing. Additional expertise and research may also be required. Depending on the size of a project, testing involved, and resources available turnaround times vary between 3 days to 2 weeks or more.

How much will this cost?
Quoting a failure analysis project, especially without seeing the sample(s) is a difficult task. Often, one does not know what testing he or she will perform until testing has begun. In many instances, the results of one test will take the failure analyst in a different direction.

The cost of a failure analysis projects usually starts at $500. Typical costs, depending on the extent of testing required, ranges from $800-$1500. If several fractures are to be analyzed or supplemental testing is required, such as fatigue or corrosion testing, additional charges will be incurred.

How long does the laboratory retain parts for a failure analysis project?
Unless otherwise directed, samples will be retained for a period of 6 months. Upon request, samples will be returned at the customer’s expense.