Issue 41

M. Vormwald et alii, Frattura ed Integrità Strutturale, 41 (2017) 314-322; DOI: 10.3221/IGF-ESIS.41.42 318 R ESULTS AND DISCUSSION igs. (5) to (8) present results for four of the five specimens tested. The first plot (top-left) shows the evolution of the each SIF mode and the equivalent SIF ranges with crack size. The mode I and equivalent range values are identical for specimen R-028 (single axial load), mode II and III ranges being very small. For specimens R-031 (phase angle of 90°) and R-033 (phase angle of 45°), the ratios between cycle maximum values of  K II and  K I change (and grow) considerably. The influence of  K III turns out to be very important, making the equivalent 2D and 3D SIF calculated ranges differ reasonably. The second plot (bottom-left) shows the variation of the maximum I and II mode ranges with crack size. Experimentally determined crack-path tangent angle (orthogonal direction to the specimen axis) showed in the plot do not seem to be explained by the ratios between the maximum cycle values of the II and I mode SIF ranges. The third plot (top-right) shows experimentally measured (  o ) and calculated (Erdogan-Sih  o ES and Schöllmann et al.  o S3D) crack-path tangent angles for each crack length. The way the angles were calculated would impose coincidence among experimentally measured and calculated path-directions. That is seen for most cases for the determined Schöllmann et al. angles, but not seen for the Erdogan-Sih angles. The explanation comes from the fact that the 3D analyses take into consideration the large  K III values. The forth plot (bottom-right) shows the variation of mixed- mode ratios during one cycle and from cycle to cycle. While for specimens R-028 (single axial load) and R-030 (axial and torsional proportional load) the variations are shown to be small due to reasonably proportional mixed-mode I and II ratios, the same does not happen for both out-of-phase specimens, where mode-mixity variation occurs inside each cycle and gets accentuated when the crack grows with the number of cycles. Figure 5: Crack tip parameters measured and calculated for specimen R-028, single alternated tension 45kN max. force. N UMERICAL INVESTIGATIONS he first simulation is done with the specimen R-028 (single axial load). The procedure and its results have been published in ref. [14]. Summarizing, the finite-element based node-release scheme provide acceptable estimates for the effective ranges and crack growth rates could be successfully correlated with the effective cyclic  J eff -integral. 0 10 20 30 40 50 60 70 2 3 4 5 6 7 8 [MPa√m] a*[mm] ΔK vs a*. R-028 ΔKI ΔKII ΔKIII ΔK S3D ΔK ES -30 -20 -10 0 10 20 30 2 3 4 5 6 7 8 θo [deg] a*[mm] θo vs a*. R-028 θo θo S3D θo ES -45 -35 -25 -15 -5 5 15 25 35 45 0,0 0,2 0,4 0,6 0,8 1,0 2 3 4 5 6 7 8 θo[deg] ΔKi/ΔKI a*[mm] ΔKi/ΔKI vs a* R-028 ΔKII/ΔKI ΔKIII/ΔKI θo -15 5 25 45 65 -15 5 25 45 65 K II K I K I vs K II [MPa√m]. R-028 9970 10720 11220 12220 13220 14720 15720 16720 17220 F T