Multiaxial fatigue ratio

Figure 7.12 Influence of biaxiality ratio 2 on the multiaxial fatigue ratio in the case of global multiaxiality [1].

Figure 7.13 Influence of biaxiality ratio on the multiaxial fatigue ratio iu the case of locai...

Geometrical shear stress (in-plane stress condition) Multiaxial fatigue ratio ffbAyt/ffbult Non-crimp fabric... 

By definition, ESC is influenced by the level of the applied multiaxial stress, ft is expected that below an assigned value of stress in a specific medium ESC will not occur. Fatigue crack growth experiments at various constant levels of A K can be applied to study the influence of the crack-tip loading on the ESC behavior in a systematic way. As an example, cast CT specimens of PMMA (Mn = 4.6 x 105) were tested in air and IPA at different levels of AK (0.6, 0.7, 0.8, 0.9 MPa -v/m). The tests were performed as described earlier, with the application of the medium after a certain time of cyclic loading in air. From the plots of the crack length ratio vs. number of cycles, the following observations can be made (Fig. 23) ... 

Another model explicidy developed for life prediction under multiaxial loading is that by Fawaz and EUyin [76—78] the actual multiaxial loading conditions and load ratio are considered through modification of a reference fatigue curve. 

It has been shown in Sect. 6.6.1 how a multiaxial stress state can modify the ductility of a material. To this purpose the triaxiality factor (TF) was introduced with Eq. (6.41) as the ratio of the hydrostatic stress to the von Mises equivalent stress. It is quite logical to think that the TF should have an effect on fatigue... 

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