PSI - Issue 52

Minori Isozaki et al. / Procedia Structural Integrity 52 (2024) 176–186 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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plus shear stresses. However, unlike the compression shear test, the effect of the tensile direction, which was the same as the test direction, was significant.

Fig. 11. Stress Distribution (a) Normal Stress (b) Shear Stress (Flatwise Test, Specimen No. 5).

Table 8. Normal Stress and Shear Stress (When the load in FEM is the same as failure load of the experiment). Specimen No. Experiment FEM Normal stress ( MPa ) Shear stress ( MPa ) Normal stress ( MPa ) Shear stress ( MPa ) 5 36.5 0 50.5 24.2

4. Parabolic criterion Interfacial failure can be expressed by the parabolic criterion. Koyanagi et al. have shown that a parabolic rather than a quadratic criterion is appropriate as an interface criterion because the interfacial shear stress during interfacial detachment is greater due to compressive stress (Koyanagi et al. 2014, Koyanagi et al. 2010, Ogihara et al. 2010). In this paper, based on the experimental and finite element analysis results of compressive shear test and flatwise test, a fracture envelope of the welded interface is developed for ultrasonic welding for CFRTP. In the parabolic, the interfacial normal stress ( ) is on the horizontal axis and the interfacial shear stress ( ) is on the vertical axis, where is the interfacial normal strength and is the interfacial shear strength. and are the stresses when and are 0, respectively, and are the intercepts of the respective axes. In this study, a parabolic criterion is developed based on the following three conditions. The first is that the axis of the parabola is =0 . The second is that the parabola passes through ( , ) = (51.5, 27.9) , which is the middle value between the values of interfacial strength in the flatwise test (Table 8) and the average value of interfacial strength in the compression shear test (Table 5). Third, the following relationship between and is established as shown in equation (1) (Koyanagi et al. 2012). Based on the above conditions, a parabolic criterion was developed. The equation of the parabola is shown in Equation (2). The results were = 58 [ ] and = 82 { ] . √2= ⁄ (1) = −0.0086 2 +58 (2)