Issue 73

S.B. Sapozhnikov et alii, Fracture and Structural integrity, 73 (2025) 1-11; DOI: 10.3221/IGF-ESIS.73.01

With an impact with less energy (20 J), the FOS will show smaller strain along the contact line of the tab with the skin, Fig. 12. Tab. 4 shows the dependences of the maximum values of longitudinal strain in the tab material upon impact and the maximum residual values as a function of the impact energy. The stress state in the UD CFRP rib layers is shown in Fig. 13. The danger is posed by the compression stresses along the fibers of the upper layer, which are close to the strength limit, as well as the stresses across the fibers, which exceed the tensile strength of the UD CFRP (Tab. 3). Analysis of these results shows that when impact has an energy of 50 J, the upper layer of CFRP cracks along the fibers and may lose stability when compressed.

Figure 12: Strain along the contact line of the tab with the skin (20 J).

Impact energy, J

5

10

20

50

Maximum strain, %

1.35

1.67

2.05

2.57

Residual strain, %

0.57

0.83

1.28

2.07

Table 4: Strain in the impact zone.

It follows that the protective tab material should not have large transverse strain to avoid cracking of the UD CFRP along the fibers. For this purpose, it is proposed to install a thin layer (0.5 mm) of fabric AFRP under the tab, Fig. 14, and reduce the thickness of the pad from 5 to 4 mm.

Figure 13: Stress state in UD CFRP layers (50 J).

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