PSI - Issue 23

A.A. Shanyavskiy et al. / Procedia Structural Integrity 23 (2019) 57–62 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. Summarized AE-signals, N ae , versus the number of cycles in tests with three (“1” - “3”) stages of AE -signals formation (see comments in the text).

During stage “2” (see Fig. 2) process of AE -signals formation has stabilization for all units in tests stress levels with the different level of AE signals for each level of deformation. Average value of discussed signals has not principle change with the number of cycles increasing but on this stage, a large scatter of AE signals takes place. In spite of this scatter we used the average signals on the second stage, N̅ ae , for diagnostics of units ’ durability with description of material behavior in the next form:   ae ae f N C b N lg lg lg   (3) Based on the developed consideration tendency of AE-signal formation, all data of cyclic tests were transformed in accordance with Eq. (3) and factors C ae and b for steel were determined with a correlation factor of 0.853, 0.916 and 0.970 for a presented sequence of equation applicable to different stress levels:   ae f N MPa N for 2.318 0.912lg , lg 270 1     (4)   ae f N MPa N for 3.293 0.675lg , lg 285 2     (5)   ae f N MPa N for 3.368 0.644lg , lg 298 3     (6) The same analysis was performed for all tested specimens on all stress levels. The correlation factor of 0.955 for all stress levels characterized by the Eq. (3) with the next factors:   ae f N N specimens all for 3.420 0.648lg lg   (7) The same type of equations characterized behavior turbine blades of superalloy EI437B with a correlation factor of 0.974, 0.956 for the considered sequence of stress levels:   ae f N MPa N for 5.287 0.284lg , lg 300 1     (8)   ae f N MPa N for 4.473 0.181lg , lg 330 2     (9)

The high value of correlation factors for different stress levels and units type has a significance that considered methodology reliably described residual lifetime or durability for metallic materials. It should be pointed out that