PSI - Issue 28

Y. Matvienko et al. / Procedia Structural Integrity 28 (2020) 584–590 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1 ~ I K as a function of the lifetime percentage for different values of the stress ratio R .

Fig. 2. Normalized values of SIF

1 ~ I K as a function of the lifetime percentage for different values of the stress range

Fig. 3. Normalized values of SIF

3. Formulation of the problem All relationships, which are currently used for lifetime predictions of structural components operating under low- cycle fatigue conditions, employ some material constants. The most famous of them is Manson (1953)-Coffin (1954) formulation. The main specific feature of this approach resides in the fact that determination of required material constants is performed when regular coupons (specimens without stress concentrators) are subjected to cyclic loading. This means that the salient features of deformation process, connected with redistribution of plastic strains in stress concentration region, are not taken into account. This fact should be considered as the grave drawback because low cycle fatigue assumes the onset of limiting case (the disruption of material continuity) due to cyclic variation of plastic strains (Collins (1993)). Determination of the normalizing coefficient, which is essential to receive the explicit form of damage accumulation function during a study of deformation process caused by low-cycle fatigue of coupons with stress concentrator, is the main feature of the present approach. It should be also noted that Manson-Coffin approach, which