Modern gas turbine engine bearings are valuable precision assets requiring significant lead time to manufacture. To adequately service variable aftermarket needs, bearing repair schemes have been developed and used for many years to safely return existing bearings to flight. Repair levels vary depending on the degree of normal service wear experienced. Successful repeated completion of repair cycles proves that the processes are robust and provides evidence of the existence of appropriate design limiting stress levels. The testing described within this report is completed as a means to scientifically evaluate repaired parts to confirm field proven expectations regarding the suitability of carefully performed aerospace bearing repairs. During the bearing life test no irregularities occurred. All test parameters (outer ring temperature, speed, load, and vibration level) did not exceed the limits valid for the acceptance test. During the red-line test also no irregularities occurred. During the oil-off test the noise of the test rig was higher than during the other tests, but no sudden or unexpected increase in noise or temperature could be detected. The tests and the investigations of the bearings S/N 0203 and S/N 3064 support the argument that the applied repair procedures do not affect the airworthiness of these bearings. Surface defects typically caused by normal engine use can be detected and removed with confidence by proper bearing refurbishment following appropriate engine bearing design and usage. Testing findings correlate with residual stress results discussed in previous FAG research. More specifically, the lack of deterioration in the finished stress curves or presence of micro-structural changes in the steel is consistent with a lack of sub-surface fatigue initiation or propagation. This finding is expected given operation beneath the FAG recommended limiting stress threshold appropriate for this product and operations conditions. More generally, the common practice of gas turbine engine repair is a means to gather useful field information regarding limiting stress values and confirm theoretical calculation and test results.
Evaluation of repaired gas turbine engine bearings demonstrates absence of subsurface fatigue propagation in appropriately designed applications
Bewertung reparierter Lager von Gasturbinenmotoren zeigen das Fehlen von Ermüdungsrissausbreitung unter der Oberfläche in geeignet ausgelegten Anwendungen
2012
13 Seiten, 12 Bilder, 7 Tabellen, 2 Quellen
Aufsatz (Konferenz)
Englisch
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