PSI - Issue 28

Jan Seyda et al. / Procedia Structural Integrity 28 (2020) 1458–1466 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3. Cracks evolution observation Fig. 3 presents the fatigue life of specimens for the analyzed cases of loadings (including the data from Pejkowski and Skibicki (2019) research) and the Basquin-Manson-Coffin curve fitted for tension-compression data points. Fig. 4 shows the maximum normal and shear strain distribution in polar diagrams, for the tested loading cases. The directions of global maxima of shear and normal strain with respect to the specimen axis were also marked.

Fig. 3. Fatigue lives of PA38-T6 aluminum alloy for axial, torsional and out of-phase loadings.

Fig. 4 The values of the maximum normal ε ( φ ) end shear γ ( φ ) strain, as a function of angular position with respect to the specimen axis for different loading cases: (a) axial loading, (b) torsional loading and (c) out-of-phase loading.

Fig. 5 presents small cracks for high level of applied strain under axial loading, for which small cracks could be observed from 60% of specimen’s fatigue life, approximately. The density of small cracks was much higher than for the low strain level for which cracks could be barely seen after 90% of fatigue life (Fig. 6 ) .