Tracking down the failure
Lufthansa Technik's central metallography laboratory
Failures and damages on aircraft components are normally diagnosed in the responsible Lufthansa Technik workshops. For very complex failure issues, however, and for cases subject to insurance claims or mandatory reporting, the specialists of the Lufthansa Technik Laboratory Services Metallography Laboratory in Hamburg are consulted. The laboratory is equipped to carry out manufacturer-standard inspections and failure analysis of all aircraft components, from undercarriage cylinders, brake discs, engine components and windows all the way to electronic components such as switches, relays and the Black Box. It doesn't matter whether the parts are made of metals such as aluminum, magnesium, steel, titanium and nickel-based alloys, plastic, or composite materials.
Every inspection is preceded by a technical material component analysis. It is rare that precise manufacturing details are available, so that the precise material basis for every component to be inspected has to be determined. In order to determine the elements making up the sample, the material specialists use, for example, spectroscopic techniques such as X-ray fluorescence spectroscopy, where the sample is subject to radiation and the resultant spectral lines reveal information about the constituent materials. After the materials have been determined, the individual failure can be analyzed. Failure analysis is strictly modelled on the VDI 3822 guidelines. This standard makes it possible to compare the results obtained at different investigative sites, fulfilling the basic prerequisites for reliable documentation.
In failure analysis, the component or a small sample from the component is initially considered macroscopically, i.e. as a whole and in parts with a stereo microscope. Parts exhibiting features of fracture origin are then inspected for fracture characteristics using a scanning electron microscope (SEM) and energy-dispersive x-ray spectroscopy (EDS). Subsequently, the samples are prepared for the various microscopic examinations. This includes subjecting the material samples to ultrasonic cleaning in a beaker with ethanol to remove grease. They are then fixed on a stub for the SEM or embedded in synthetic granules and prepared so as, for example, to make the structure of the material visible under an optical microscope. Depending on the goal of the examination, the samples may be subjected to etching in order to obtain certainty about the microstructure.
Beyond this, the metallography laboratory also conducts measurements of the hardness of the metal matrix, of the paint and surface coatings along with macro-hardness tests on larger components. Depending on the composition of the materials, various material testing equipment and systems are available to the testers and metallography experts. They make it possible to test the tension, force, and ductility of all materials. Findings, i.e. metal debris found on magnetic chip detectors, oil filters or within the hydraulic fluids during A/C operation can quickly be examined. This using scanning electron microscopy (SEM) combined with energy dispersive analysis system (EDS) to analyze them and recognize potential damages to bearings at an early stage. In the worst case, following these analytical results the engine must be replaced and repaired immediately.
Most orders for material identification and failure analysis come from Lufthansa Technik colleagues in Hamburg and Frankfurt. In some cases, though, samples are flown in from other sites and from customer airlines for rapid analysis at short notice. At other times, airline customers or authorities place direct orders with Laboratory Services Department's metallography laboratory for independent assessments or failure analysis. The laboratory's independence means that its assessments are increasingly highly regarded by external customers, and demand is rising continually. The metallography laboratory is therefore increasingly involved in joint assessment procedures with airline customers, manufacturers, and authorities.