13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- values are very close to the criterion as soon as there is no Mode III-loading. The same trend can be observed by the comparison with other criteria, mentioned in this paper. All these criteria are conservative. 40 20 20 20 KI KII KIII y x z 60 80 100 120 40 60 60 80 100 140 80 120 Mode II/III α γ = 90°; = 90° Mode I/III 0° α γ = 45°; = 9 Mode I/II/III α γ = 45°; = 45° Mode I α γ = 0°; = 0° 40 Mode I/II α γ = 45°; = 0° Mode II α γ = 90°; = 0° Mode II/III α γ = 90°; = 15° * Mode II/III α γ = 90°; = 45° Mode I/II/III α γ = 60°; = 30° experimental results of CTSR specimen experimental results of CT specimen 3D-criterion by with = 38,1 N/mm , = 1,155 and R = 1 ICHARD K IC 1 3/2 α α2 Figure 7. Comparison of experimental results with 3D-criterion by Richard Due to these results and the significant difference to the hypothesis, an approximation of the 3D-criterion by Richard on the fracture toughness values for PMMA material is proposed. In Figure 8 the approximation of the criterion by RICHARD is shown. Here the α2 parameter was changed to 0.36. This approximation is still conservative, but agrees very well with the experimental results. In addition, fatigue tests on an EN AW-7075-T651 aluminium alloy were performed. The experimentally measured threshold values for different Mixed-Mode-loading conditions are pictured in Figure 9. Compared to the threshold value surface by RICHARD the experimentally determined threshold values depict also a significant variation under pure Mode III-loading. Here the ∆KIII,th values are around factor 2.2 above the hypothesis.
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