Because of the need to certify a critical helicopter component, a full scale test on a titanium-composite MR(Main Rotor)/Hub was done with the failure of the component: the details and results are reported in the present paper. After the application of an amplified start-stop load spectrum a failure has occurred in the handle of the titanium hub between 59,032 and 62,305 load cycles. During the failure of the titanium part, the composite band remained undamaged and carried out the fail-safe functionality correctly. Further tests and numerical activities (not described in this article) have been done on the damaged component to check the residual strength and thus certify the damage tolerance capability too. However for what concern the test reported, a finite element model of the MR/H has been developed and the stress distribution has been estimated correctly up to the fatigue failure. A fatigue life evaluation has been done using fatigue data obtained from two different database containing both rotating bending fatigue limit and axial fatigue limit of the material. All the fatigue data processed refer to a Ti-6Al-4V forged just below Tbeta and annealed. Because of the state of stress, both monoaxial and multiaxial (Sines) fatigue criteria have been followed. The fatigue life estimation based on axial fatigue limits are in good agreement with the experimental result. Moreover the FE model shows an important stress concentration exactly in the point in which the fatigue crack nucleated. To conclude, it is possible to state that although the full scale tests remain necessary in order to asses the fatigue behaviour of complex components, numerical models can play an important role and can be used successfully also in complex life predictions like fatigue behaviour. However, the fatigue life prediction and assessment are very hard work with a lot of uncertainties. Correct simulation of the specimen and accurate characterization of the material are important issues to achieve a reliable result with a numerical model. In addiction to this a correct understanding of the relevant fatigue load spectra is an important condition to carry out correctly the experimental test. A multilevel, multidisciplinary approach is therefore necessary for the design of such a complex component.
Failure analysis of a composite main rotor helicopter hub
Fehleranalyse einer Helikopter-Hauptrotornabe aus Verbundwerkstoff
Engineering Failure Analysis ; 18 , 1 ; 97-109
2011
13 Seiten, 14 Bilder, 4 Tabellen, 18 Quellen
Article (Journal)
English
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