Issue 37

H.A. Richard et alii, Frattura ed Integrità Strutturale, 37 (2016) 80-86; DOI: 10.3221/IGF-ESIS.37.11 85 steps until the threshold value is reached. A more detailed information to the experimental procedure and chosen parameters can be found in [18]. Comparison of experimental results with fatigue criterion The mixed-mode threshold values determined by the procedure described above are illustrated in Fig. 5. The threshold values of Al7075-T651 measured by Schirmeisen [13] in comparison of the criterion by Richard show for pure mode I- loading, 2D-mixed-mode-loading and for mixed-mode II + III-loading with small mode III-ratio a good congruence with the threshold value surface of the criterion by Richard. A significant variation, with around a factor of 2.2 above the hypothesis [14], depict the threshold values for pure mode III-loading. The threshold values measured by Eberlein [18] in total are closer to the threshold value surface of the hypothesis. The variation in average is around factor 1.8 above the hypothesis. In addition a comparison of other materials [19, 20] show partially similar threshold value ratios Δ K II,th /Δ K I,th and Δ K III,th /Δ K I,th (see threshold values for austenitic steel in Fig.5). Ferritic steel exhibits completely other threshold value ratios. Nevertheless, the determined mixed-mode threshold values for different materials in comparison with the criterion by Richard point out that this criterion possesses a widely validity and a generally conservative behaviour. Figure 5 : Mixed-mode threshold values in contrast to criterion by Richard R EFERENCES [1] Richard, H.A.., Sander, M., Fulland, M., Theoretical crack path prediction, FFEMS, 28 (2005) 3–12. [2] Erdogan, F., Sih, G.C., On the crack extension in plates under plane loading and transverse shear, J. Basic Eng., 85 (1963) 519-525.