PSI - Issue 59

M. Karuskevich et al. / Procedia Structural Integrity 59 (2024) 642–649 M. Karuskevich et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The fatigue damage indicator based on surface relief was first proposed for the uniaxial loading of aircraft principle structural elements and currently for the biaxial fatigue indicator described as a concept design in this paper. 2. Surface relief as an indicator of fatigue damage under the uniaxial and biaxial loading Surface relief has been observed both on single crystals and polycrystalline metals. Surface relief on the single crystals has the regular appearance of persistent slip bands, which evolved in the process of cyclical loading (Man et al., 2009; Zasimchuk et al., 1992). Polycrystals exhibit a more complex surface structure (Karuskevich et al, 2012; Pejkowski et al., 2019) (Fig. 2).

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Fig. 2. Evolution of surface relief on D16AT clad layer at the uniaxial loading (tension-compression mode), max = 150 MPa, R = -1, N f = 181 741 cycles: (a) N = 5 000 cycles; (b) N = 10 000 cycles; (c) N = 100 000 cycles.

A strong correlation between stress amplitude and number of cycles to failure has been found for different modes of loading (tension and bending), stress level, and stress ratio. The possibility of monitoring fatigue damage under biaxial loading also was shown by experiments carried out with aluminum alloy specimens under the combined tension/torsion loading (Fig. 3, Fig. 4) (Pejkowski et al., 2019).

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Fig. 3. Evolution of surface relief on D16AT clad layer at the multiaxial loading (proportional mode), a = 106.06 MPa, a = 61.23 MPa, eq = 150 MPa: (a) N = 1 000 cycles; (b) N = 5 000 cycles; (c) N = 10 000 cycles.