Issue 41

V. Shlyannikov et alii, Frattura ed Integrità Strutturale, 41 (2017) 31-39; DOI: 10.3221/IGF-ESIS.41.05 37 contrast, by interpretation of the same experimental crack growth rate diagrams in terms of plastic SIF for free surface of the hollow cylindrical specimens of D16T at -60  С  +250  С temperatures a different picture is observed. It is shown that the individual test results at a fixed temperature form a common experimental curve partially overlapping crack growth rate ranges. 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 0.01 0.1 1 CMOD, mm db/dN [mm/cycle] D16T, T=+250°C B95AT, T=+250°C D16T, T=+23°C B95AT, T=+23°C D16T, T=-60°C B95AT, T=-60°C Figure 9 : Crack growth rate on the free surface of hollow specimen versus CMOD for different temperature conditions. a) b) Figure 10 : Crack growth rate as a function of (a) elastic and (b) plastic SIFs for free surface of the specimen. The same trend observed for the deepest point of the crack front (Fig. 11a, b). Moreover, compared with an elastic interpretation of the processes of fatigue failure, the interpretation of cyclic fracture diagrams in terms of the plastic SIF's has more uniform character with a small scatter band. The data presented very obvious advantages of using the plastic SIF's to characterize the material's resistance to cyclic crack growth. This conclusion is confirmed by the relative position of crack growth curves in Figs.10 and 11 for the tested aluminum alloy D16T in the terms of the elastic and the dimensionless plastic SIF K P . Fig. 12 shows the influence of material properties. On this figure the comparison of crack growth data on the free surface in terms of elastic and plastic SIF for both tested materials are presented. Experimental data interpretations in terms of plastic SIF, which take into account the influence of plastic material properties, give us two different curves for considered alloys. From Fig. 12b, the difference in the crack growth rate on the D16T and B95AT remains permanently during low temperature and gradually disappears during room temperature test condition. As presented in Fig. 12, the experimental data clearly illustrates the effect of temperature on the surface crack growth rate in aluminum alloys tested at the same loading conditions.