FAILURE ANALYSIS & ROOT CAUSE DETERMINATION
Failure analysis is the method that is used to determine the root cause of failure when products, components, assets, or systems fail to meet performance expectations. The findings of a root cause failure analysis provide decision makers with the tools they need for remedial actions and preventative measures to be taken
Our Process
At Matergenics, our material, corrosion and mechanical engineers systematically perform required tests as deemed necessary based on the project at hand. Typical steps we often use in our root cause failure analysis investigations:
- Review of background information
- Visual and non-destructive examination
- Microscopic examination
- Physical measurements
- Corrosion examination
- Chemical analysis
- Metallurgical testing / metallography
- Fractography examination
- Mechanical testing
- Scanning electron microscopy (SEM)
- Elemental dispersive X-ray analysis (EDS)
- Fourier transformer infrared analysis (FTIR)
- X-ray diffraction
- Mechanical testing
- Surface analysis
- Finite elemental analysis (FEA), computational fluid dynamics (CFD) or other engineering calculations
- Determination of mode of failure and primary cause
- FEA, CFD and other detailed engineering calculations
At Matergenics, we determine if a failure is due to material selection, design, fabrication or operating conditions. Major corporations that rely on Matergentics specialists expertise include airline industry the Steel Industry, Electronics, Power Plants and many more. These investigations require not only a modern laboratory but an extensively trained professional team as well.
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TECHNICAL TEAM
Decisions must be made during any failure analysis, and the results of each step dictate the next procedure
Case History: Aircraft Component Failure Analysis
Both halves of a broken steel pin were submitted for examination. The sample was identified as Left Hand Main Landing Gear, AC 809. At a later date an unbroken pin identified as Right Hand Main Landing Gear, AC 809 was also submitted. We were asked to determine the mode, not the cause, of failure.
Visual Examination
The two as-received pins are shown above. An arrow shows the location of failure. The failure occurred in a 1.230-inch-diameter cylindrical part of the pin which was corroded on the outer surface. One side of the fracture surface is shown in the image below. Convergent chevron patterns identified the fracture initiation site on the outside surface. The fracture initiation site is marked by a red arrow in the figure below Most of the fracture surface had been darkened by corrosion. A series of coarse low cycle fatigue crack arrest marks was identified at the ends of the two discolored crack-propagation fronts. The exterior surface of the 1.230 inch diameter cylindrical part of the pin contained corrosion pits. Corrosion pitting was also visible at the fracture initiation site. The fracture surface profile is shown below.
A circumferential ridge and depression were found in the cylindrical surface. A similar ridge and depression were seen in the unbroken pin. By comparing the cylindrical parts of the two pins it was found that the fracture of the broken pin had initiated at the circumferential depression.The part of the fracture surface containing the fracture initiation site was macroetched for 30 seconds in a hot aqueous 50 percent hydrochloric acid solution to remove the corrosion products. The clean surface showed the fracture initiation site, as seen in the image below.
Metallographic Examination
A transverse cross section through the fracture initiation site was prepared for metallographic examination. The fracture surface profile is relatively flat. No crack branching was seen. The microstructure consists of dark-etching tempered martensite. No gross plastic deformation was observed at the fracture initiation site.
Conclusion
The pin failed as a result of fatigue which initiated at the outside cylindrical surface. This surface exhibited wear and corrosion pitting. The fracture initiated at a shallow circumferential groove. The corrosion of the fracture surface appears to have occurred subsequent to the fracture. No evidence of stress corrosion cracking was observed
IMPORTANT FAILURE ANALYSIS PRINCIPLES REPRESENTED IN THIS CASE HISTORY
- In this case, examination of the fracture surface and the microstructure were sufficient to reveal the mode of failure. Determination of the cause of failure would require a knowledge of the use
- Fatigue failures are sometimes quite subtle. The materials used in the parts that fail may be completely as-specified, but the service conditions exceed their long- term ability to resist the stresses applied during
“Excellent report with clear assessment of failure. Will recommend Matergenics for future work.”
Other Related projects we have completed
Although Matergenics materials testing work is vital to its clients, it is rarely seen by the public. Here are some examples of recent projects in which our experienced Matergenics engineering team provided the timely, competent, customer-oriented engineering analysis that made the difference.
- Metallurgical testing for a major commercial airline fleet that includes failure analysis investigations, corrosion investigations, and quality control testing.
- Same-day metallurgical failure analysis of the effects of a truck fire on the superstructure of a major highway bridge to determine whether or not the highway could remain open.
- Failure analysis of a gas main explosion that caused causalities.
- Failure analysis and remaining life determination of boiler components in the power industry.
- Electrochemical corrosion evaluation of implant materials such as hips, knees, stents, etc. to improve products and performance.
- Ultra-high vacuum chamber for analysis of coatings and materials surfaces.
- R&D of coatings and sensors for the construction industry.
