Issue 42

R. Pawliczek et alii, Frattura ed Integrità Strutturale, 42 (2017) 30-39; DOI: 10.3221/IGF-ESIS.42.04

It can be seen, that for curves 5 and 6 of Fig. 9 some compression stresses reordered. The same effect is visible for curves 1 and 2 on the diagram for the case of decreased mean load (Fig. 10). The aim of performed calculations is to establish a parameters of the stress history (stress amplitude σ a and mean stress σ m in this case) for each sequence of the applied block loads respecting both paths of changes of the mean load using proposed model, Garud-Mroz proposal and Chu also. Results of these investigations are presented in the Fig. 11 for increased mean load value and in the Fig. 12 for decreased mean load value.

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 a : Garud-Mroz  m : Garud-Mroz  a : Chu  m : Chu  a : proposed model m : proposed model 

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Figure 11 : Comparison of the stress history parameters calculated by proposed model and models of Garud-Mroz and Chu for increased mean load value.

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 a : Garud-Mroz  m : Garud-Mroz  a : Chu  m : Chu  a : proposed model m : proposed model 

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Figure 12 : Comparison of the stress history parameters calculated by proposed model and models of Garud-Mroz and Chu for decreased mean load value Comparing all analyzed models it can be seen, that stress amplitude are very close to each other for all cases, however for mean stress the proposed model gives results with higher values: about 40% for 7000 and 10000 cycles (second sequence in block load) and 80% for 12000 and 15000 cycles (third sequence in block load). It will generate higher level of damages – then lower, predicted fatigue life will be calculated for such load sequence. In general, such observations are indicated in the research.

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