Reliability Assessment of a Turbogenerator Coil Retaining Ring Based on Low Cycle Fatigue Data

• Autorzy: Olmi G. , Freddi A.

Warianty tytułu

Ocena niezawodności pierścieni ustalających cewek turbogeneratora w oparciu o dane zmęczeniowe przy małej liczbie cykli

• Języki publikacji: EN

Abstrakty

EN

Turbogenerator coil retaining rings are shrunk-fitted onto the rotor over the coils, in order to restrain them against the centrifugal force. They are typically subjected to low cycle fatigue, with a cycle being completed at every machine switch-on and switch-off. The subject of this paper consists in the determination of the failure probability of a coil retaining ring. The failure mode of the ring cracking, when it swells in tension, due to the centrifugal force is here considered. The reliability assessment is preceded by the study of the input variables affecting the low-cycle fatigue load and of their stochastic distributions. This question is tackled by the experimental determination of the static, cyclic and fatigue curves of the involved material and by the application of a statistical model to compute related parameters and their standard deviations. Upon the determination of variable distributions, the probability of failure is estimated in the form of a cumulative distribution function by a computationally efficient methodology, based on the Advanced Mean Value approach. The obtained results account for the material response and the local stressstrain states at the most loaded coil retaining ring region. The determined probability at the end of the machine life, in the order of 10-12, is compatible with reference values for structures under fatigue in the mechanical and aeronautical fields.

PL

Pierścienie ustalające cewek turbogeneratora są pasowane skurczowo na wirniku wokół cerek by zabezpieczyć je przed działaniem sił odśrodkowych. W typowych warunkach, są one poddane narażeniom zmęczeniowym o malej liczbie cykli, przy czym każdy cykl rozpoczyna sie od startu maszyny, a kończy przy jej zatrzymaniu. Przedmiotem artykułu jest wyznaczenie prawdopodobieństwa awarii pierścienia ustalającego cewki. Rozważanym uszkodzeniem jest pękniecie pierścienia spowodowane puchnięciem materiału pod wpływem naprężeń wywołanych silą odśrodkową. Ocena niezawodności przeprowadzona w tej pracy wykorzystuje dane wejściowe wpływające na obciążenie zmęczeniowe przy małej liczbie cykli i ich rozkłady stochastyczne. Dla rozwiązania problemu wyznaczono eksperymentalnie charakterystyki statyczne i krzywe cykli zmęczeniowych stosowanego materiału i zastosowano model statystyczny dla wyliczenia odpowiednich parametrów i ich odchyleń standardowych. Na podstawie wyznaczonych rozkładów zmiennych estymuje się prawdopodobieństwo uszkodzenia w formie dystrybuanty rozkładu. Wykorzystany algorytm obliczeniowy o dużej skuteczności wykorzystuje metodę ”zaawansowanej średniej” (Advanced Mean Value). Uzyskane wyniki dają informacje o odpowiedzi materiału i stanie lokalnych naprężeń i odkształceń w najbardziej obciążonych obszarach pierścienia ustalającego cewki. Prawdopodobieństwo uszkodzenia, wyznaczone na koniec okresu eksploatacji maszyny, wynosi 10^-12 i jest porównywalne z wartościami referencyjnymi dla innych konstrukcji mechanicznych i lotniczych narażonych na zmęczenie.

Słowa kluczowe

EN

turbogenerator coil retaining rings; low-cycle fatigue; machine safety; probability of failure; AMV

PL

turbogenerator; niskocyklowe zmęczenie; bezpieczeństwo maszyn

• Wydawca: Komitet Budowy Maszyn PAN
• Czasopismo: Archive of Mechanical Engineering
• Rocznik: 2014
• Tom: Vol. LXI, nr 1
• Strony: 5--34
• Opis fizyczny: Bibliogr. 37 poz., rys., tab.

Twórcy

autor

Olmi G.

• Department of Industrial Engineering (DIN), University of Bologna, Bologna, Italy

autor

Freddi A.

• Department of Industrial Engineering (DIN), University of Bologna, Bologna, Italy

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