Abstract
Regularities of acoustic emission (AE) signals’ formation during cyclic loading of turbine blades of different Ni-based superalloys and steel specimens were considered and systematized. AE activity can be related to strain energy density, and for the beginning period of the cyclically loaded blade the value of summarized AE signals Nae recorded in a short time can be used for characterizing the critical state of blade material as blade durability Nf. The lower Nae for a considered time interval, the higher the blade durability Nf. Dependences of lgNf on lgNae were discovered in linear form with a high value of correlation factor. The similar relation between summarized AE signals and durability was demonstrated in the case of a monotonic blade bending with a stress level of 1% higher than in-service stress. For high accuracy of loading, a test-device that enables to load blades with a low velocity of stress level increasing was constructed. Well-known α-criterion appears when registered fatigue crack origination in a blade can be estimated in the number of cycles (Nf)α by the AE signals formation in a short time (Nae)t at the beginning stage of blade cyclic loading.
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