Failure Analysis of Aircraft Turbine Blades: EAG Presents at IMECA (Independent Metallurgical & Materials Engineering Consultants of California)
Dr. Arun Kumar of EAG Laboratories will present a paper on metallurgical failure analysis to IMECA, the Independent Metallurgical & Materials Engineering Consultants of California. An investigation of an aircraft crash led to a closer look at the engine turbine blades, revealing that the failure was caused by fatigue initiated by Liquid Metal Embrittlement (LME) cracks.
The paper, entitled “Failure Analysis of Aircraft Turbine Blade due to Liquid Metal Embrittlement” will be presented at IMECA’s semi-annual meeting on April 29, 2017 in Pacific Grove, California.
An aircraft crashed shortly after take-off. Initial investigation determined that the aircraft crash occurred due to an engine failure with an accumulated 4995 hours and 4018 landing/take off cycles. Engine tear-down revealed that several turbine blades on the second stage Power Turbine (PT) had failed due to fatigue. It was initially postulated that the engine may have failed by fatigue due to its age. Metallurgical failure analysis revealed that high cycle low stress fatigue failure was caused by lead Liquid Metal Embrittlement (LME). Lead was used in the manufacturing process to encapsulate the turbine blades to form a solid block for fixture support during machining of the blades. The general operating temperature in the second stage turbine was estimated at 600-700°F while the melting point of lead is 621°F. Molten lead slowly penetrated the grain boundaries on the surface of the turbine blades during engine operation eventually leading to fatigue crack initiation sites. Fatigue striation spacing calculations estimated the crack propagation time to be only 0.34 minutes due to its high RPM, making crack discovery unlikely during maintenance inspections. The lead needed to be removed completely from the turbine blades after machining during blade manufacturing and therefore the engine manufacturer was held liable for the cause of the accident instead of the maintenance facility, pilot error, or the old age of the aircraft engine.
Dr. Kumar has many years of experience in metallurgical failure analysis and materials investigations of failures involving aircraft, helicopters, auto and motorcycles, machinery and more. As an expert witness and metallurgical consultant, he has been involved in product liability, insurance, patent infringement and other legal cases. He earned his Ph.D. in Engineering, Metallurgy and Metals Processing at the University of California, Los Angeles.