PSI - Issue 75

Aijia Li et al. / Procedia Structural Integrity 75 (2025) 318–333 Aijia Li, Christian Garnier,, Marie-Laetitia Pastor, Xiaojing Gong, Clément Keller/ Structural Integrity Procedia (2025)

327

10

4.2. Result of the final simulation procedure

Laying on the determined shape, a plane is introduced to be in the center of the gauge region, so the variables are the external diameter of the reduced zone in gauge region’s d , plane’s diameter dp , transition’s radius R , and the shape of the reduction (see Fig. 5 and Fig. 6). When considering the first design criterion using Tsai-Hill failure criterion (Eq.1), Fig. 8 (a) and (b) summarize the influence of d and dp on the failure parameter B for the two MD composite specimens, where the quasi-isotropic specimen needs to be prioritized because the parameter B is very small close to 1 means a greater risk of failure outside the gauge region. Therefore, 20 mm and 14 mm are chosen for d and dp , respectively, since they achieve the highest failure parameter B around 1.05 for the quasi-isotropic specimen and ensure the parameter B of the cross-ply specimen is much higher than 1.0. The reason for not further extending dp is to prevent a too-small reduction feature, which would compromise the accuracy of the cutting machine (0.1 mm) in specimen manufacturing (4th criterion). Because the failure parameter B of the quasi-isotropic specimen is still very close to 1 at around 1.09, R is adjusted in the range from 13 mm to 18 mm and finally determined to be 17 mm, to increase the B of the quasi-isotropic specimen to 1.12 and maintain a high value of B at 2.09 for the cross-ply specimen, as illustrated in the comparison in Fig. 8 (c). Among the three types of reduction, linear reduction is the best option as it imposes a higher parameter B of 2.06 in the cross-ply specimen and 1.12 in the quasi-isotropic specimen, meaning that damage is more likely to take place in the gauge region. As for the second criterion, Fig. 9 shows the distribution of the stress in the fiber direction and perpendicular to the fiber direction, and the gauge region always has a uniform stress field for both cross-ply and quasi-isotropic specimens. Considering the third criterion regarding thermography, the plane in the gauge region has an area of 153.86 mm 2 , more than the target value of 100 mm 2 , allowing good thermography by most infrared cameras, as well as the displacement monitor by DIC. For the fourth criterion about manufacturing, the circular holes on the layers are adjusted to be cut every two layers, ensuring that the minimum machining size (1.5 mm) does not exceed the limitations of the cutting machine (0.1 mm). As a result, the dimension of the cruciform specimen in Fig. 5 and Fig. 6 is determined as “ d = 20 mm, dp = 14 mm, R = 17 mm, and a linear reduction of the gauge region ” .

Fig. 8. comparison of the failure parameter B in different regions: (a) gauge region; (b) plane in the gauge region; (c) transition