13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 5. Setting of the ratio of Mode I to Mode II/Mode III The superposition of Mode I, Mode II and Mode III takes place by the adjustment of both angles α and γ. Thereby the load line of action always passes through the center of the specimen. Figure 6. Setting of the ratio of Mode II- or Mode III-load In this paper some experimental results on CTSR-specimen will be presented. On the one hand experiments on PMMA have been performed, in order to determine the fracture limit surface (cf. Fig. 2) for this material. On the other hand fatigue tests were performed on an EN AW-7075-T651 aluminium alloy, in order to identify the threshold value surface. The results of both experiment types are illustrated and discussed in the next chapter. 4. Results of experimental investigations Figure 7 illustrates the measured fracture toughness values for PMMA material under several Mixed-Mode-loading combinations. The fracture toughness values KIIIC for pure Mode III-loading, measured on CTSR-specimen, exhibits a significant variation in comparison with the 3D-criterion by RICHARD. The resulting values for Mode III are around factor 2.7 above the hypothesis. Similar significant variations have already been observed on other specimen, e.g. [15]. Furthermore it is noticeable, that the difference between measured KC values and the hypothesis decreases with decreasing Mode III-ratio. The
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