Issue 49

M. Bannikov et alii, Frattura ed Integrità Strutturale, 49 (2019) 383-395; DOI: 10.3221/IGF-ESIS.49.38 393 Figure 6: Wöhler curve for AlMg6 alloy. Solid line - numerical calculation, points - experimental data of the authors, squares - experiment [27] with conditions: frequency 10 kHz, R=-1. Due to the amplitudes of the applied stresses below the yield strength, the material is macroscopically in the elastic region, and the applied deformations can be considered small. Then expression (24) can be rewritten in the form: 2 ( ) p σ λ G p        (33) Since macroplastic strain is not observed, then in the very high cycle fatigue mode, the parameter p is responsible for the accumulation of damage and destruction. The growth of defects leads to a gradual change in the amplitude of the applied voltages, and consequently to a change in the amplitude of the applied displacements, since for some displacement amplitude A U in the loading machine is always assigned A σ : ( ) 2 ( ( ) ) A A A σ λε σ G ε σ p    (34) After reaching the parameter p of some critical value pc (which corresponds to 0, 4 f δ  ), an avalanche-like growth of defects occurs, leading to the destruction of the material, which in the experiment corresponds to an avalanche-like change in the amplitude of the second harmonic of displacements (Fig. 7.). Figure 7: Defect kinetics (dashed line) in the calculation and change in the amplitude of the second harmonic of displacements in the experiment (solid line) . In fig. 7 shows the normalized curves of variation of the parameter p, referred to pc and the amplitude of the second harmonic of displacements, referred to its maximum value. Figure 7 shows the experimental data corresponding to the preloaded specimen. According to the proposed model, the change in structure due to preloading is described in terms of the parameter δ. Namely, a smaller value of the initial condition δ 0 corresponds to the preloaded specimen. To obtain the dotted curve (Fig. 7), the Eqns. (24-29, 30, 32) was solved with the initial condition δ 0 = 1.02. Thus, the proposed model is able to adequately describe the behavior of the material in the modes of high- and very high cycle fatigue. Based on the results of numerical simulation, we can conclude that the change in the amplitude of the