PSI - Issue 38

Miloslav Kepka et al. / Procedia Structural Integrity 38 (2022) 596–603 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

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Fig. 5. Evaluation of permissible maximum stress range ∆ , of design stress spectrum. The process of determining the maximum permissible value ∆ , for safe life approach is based on the concept of linear accumulation of fatigue damage. The input data to the fatigue damage calculation are: S-N curve of the assessed structural node and stress spectrum in its critical cross-section. The stress spectrum represents a random loading process over the required service life. To apply this procedure S-N curve for welded T-joint version V1 was evaluated: log( ) = 19,09 − 5,47 ∙ log(∆ ℎ ) (3) S-N curve for welded T-joint version V7 was considered as an alternative: log( ) = 20,70 − 5,80 ∙ log(∆ ℎ ) (4) The design stress spectra were generated using the relative coordinates ∆ ℎ , / ∆ ℎ , and the equation proposed by Ruzicka et al. (1987): ℎ = ∙ ( ) ( ∆ ℎ , ∆ ℎ , ) (5) ∆ ℎ , - maximum hot-spot stress range in the spectrum; - number of cycles with ∆  max range in the spectrum; - total number of cycles in the spectrum; - shape parameter of the spectrum; ℎ - cumulative frequency of cycles with an amplitude of ∆ ℎ , .